Cavitation

As discussed earlier, adjustive thrusts are frequently associated with a cracking sound. Typically, this occurs at the end range of passive joint motion when a quick thrust overcomes the remaining joint fluid tension. However, any procedure that produces joint separation has the potential to cause the cracking sound. The separation of the joint is theorized to produce a cavity within the joint, the induction of joint cavitation, and an associated cracking sound.

Cavitation is the “formation of vapor and gas bubbles within fluid through the local reduction of pressure” and is a well-established physical phenomenon. Evidence strongly suggests that it also occurs during the application of spinal adjustive therapy, although this premise has not been proven conclusively.^23,272,273

It has long been known that a liquid confined in a container with rigid walls can be stretched. If stretched sufficiently, cavitation occurs. The pressure inside the liquid drops below the vapor pressure, bubble formation and collapse occur, and a cracking sound is heard.²⁷⁴ The case for synovial joint cavitation and cracking is supported by experimental evidence conducted on metacarpophalangeal (MP) joints, the cervical spine, and the thoracic spine.^23,275 276 277 278 279 280 281 282 Experiments conducted on MP joints indicate that there is a linear relationship between an applied load and joint separation up to the point of joint cavitation.^276,278 At the point of joint cavitation, there is a sudden increase in joint separation without a proportional increase in the applied load (Figure 4-10). When the joint is reloaded after cavitation, there is no second cavitation, and the joint separates to the same degree with a much more linear relationship between the applied load and the degree of joint separation (Figure 4-11). The inability of the joint to undergo a second cavitation persists for approximately 20 minutes, and has been labeled the refractory period. The bubbles formed within the MP joint cavitation consist of water vapor and blood gases and have been measured at 80% carbon dioxide. The bubbles persist for approximately 30 minutes before the gas is absorbed back into solution.276 277 278 279 280

Figure 4-10 Force displacement curve representing the effects of joint separation and cavitation: As the joint tension increases with joint surface separation, a quick and dramatic separation occurs, and a cracking noise is produced.

Figure 4-11 Force displacement curve illustrating that immediate reloading of the joint after cavitation is not associated with a second cavitation, and the joint separates to the same degree with a much more linear relationship between the applied load and the degree of joint separation.

In manipulative experiments conducted on the thoracic spine, joint cavitation typically occurred just before the peak adjustive force. In a few cases, the cavitation occurred just after the delivery of the peak force.²⁸¹ In the experiment conducted on the MP joints, a small percentage of the manipulated joints did not produce an audible crack. It is postulated that the joint capsule in these individuals was very tight, not allowing for sufficient joint separation to produce cavitation²² (Figure 4-12). This observation might offer an explanation for the clinical occurrence in which some individuals need several adjustive treatments before joint cavitation is produced. Over time, treatments might produce enough flexibility in the joint capsule to permit joint cavitation.

Figure 4-12 Force displacement curve in joints in which no audible release could be generated. In these individuals, it is postulated that the joint capsule is very tight, not allowing for sufficient joint separation to produce cavitation.

Several mechanisms have been proposed for how joint cavitation produces the audible crack. Speculation centers on the formation and collapse of gas bubbles or a rapid stretch of the capsular ligament. Unsworth, Dowson, and Wright²⁷⁸ suggested that cracking is not the result of bubble formation but the result of the rapid collapse of bubbles caused by fluid flow. The crack is viewed as a postcavitation phenomenon generated by the collapse of bubbles as the newly formed bubbles rush from the higher-pressure periphery to the relative low-pressure pocket generated in the center of the distracted joint. Meal and Scott²⁷⁹ have more recently shown that the crack produced in the MP joint and in the cervical spine are actually double cracks separated by several hundredths of a second. The significance of two separate recorded cracks is a matter of speculation. The two sounds may be a direct consequence of cavitation, the first crack being the product of gas bubble formation and the second crack associated with the rapid collapse of gas bubbles. Other possibilities include cavitation plus soft tissue vibrations, stretching, or artifacts to account for the second sound.

Brodeur²⁷² has presented a slightly different model of joint cavitation and cracking based on a mechanism described by Chen and Israelachvili.²⁸³ Within this model, the capsular ligament plays a primary role in the production of joint cavitation and cracking. During the first phase of joint manipulation, as the joint is being loaded and the joint surfaces are being distracted, the joint and the capsular ligament are seen as invaginating (drawing inward) to maintain a constant fluid volume within the joint space. As distractive pressure is increased, the capsular ligament reaches its elastic limits and snaps away from the synovial fluid, producing cavitation at the capsular-synovial interface. A rapid increase in joint volume follows, and the gas bubbles formed at the periphery rush to form a single coalesced bubble in the center of the joint space (Figure 4-13). Brodeur²⁷² speculates that the “snap-back” of the capsular ligament is the event responsible for the audible crack. He also proposes that this mechanism offers an explanation for why some individuals with very tight or loose joint capsules do not crack. “For loose joints, the volume of the articular capsule is larger and traction of the joint does not cause a sufficient tension across the ligament to initiate the snap-back of the joint capsule. Similarly, an overly tight joint reaches the limits of its anatomic integrity before the joint capsule can begin to invaginate.”²⁷²

Figure 4-13 Model of the changes in the periarticular structures during a manipulation. A, The joint in its resting position. B, Long-axis distractive load applied to the joint. C, Once the tension exceeds a certain threshold, the energy stored in the capsular ligament initiates an elastic recoil that causes the capsule to snap back from the synovial fluid. Cavitation occurs at the capsular ligament–synovial fluid interface. D, The sudden increase in joint volume temporarily decreases tension on the capsular ligaments. E, The distractive forces continue to traction the joint, stimulating high-threshold receptors. F, The joint volume is increased, gases have coalesced into the central area, and the joint is significantly distracted relative to its resting position.

Besides the cracking itself, cavitation is considered to be associated with several postadjustive phenomena: a transitory increase in passive ROM, a temporarily increased joint space, an approximate 20-minute refractory period during which no further joint cracking can be produced, and increased joint separation. Sandoz²⁴ has labeled the postadjustment increase in joint range of movement paraphysiologic movement because it represents motion induced only after cavitation (see Figure 3-23).

The postcavitation refractory period, discussed previously, and associated phenomena may be explained by microscopic bubbles of carbon dioxide remaining in solution for approximately 30 minutes. During this period, the bubbles will expand with any subsequent joint separation, maintaining the pressure within the joint. The postcavitation expanded joint space appears as a radiolucency on a radiograph of the distracted joint. The postcavitation increase in joint space appears to be temporary and corresponds to the refractory period. Because the pressure within the joint cannot drop until the gas bubbles are reabsorbed, no further cavitation can occur during this time.²⁷⁸ Furthermore, the force contributed by the stretching of fluid will be absent, causing a decrease in force holding the joint surfaces together and thus resulting in the increased passive ROM noted by Sandoz^23,277 and Mireau and colleagues.²⁸⁴

As noted earlier, the crack associated with joint cavitation may not be the product of the formation of gas bubbles, but rather a rapid collapse of gas bubbles. In this model, the temporary increased joint space cannot be explained by the persistence of gas bubbles. An alternate explanation postulates that the increased joint space persists from the excess synovial fluid that rushes to the decompressed center of the joint. The joint does not immediately return to its precavitation resting space because synovial fluid is viscoelastic and slow-moving. The flow of excess synovial fluid between the joint surfaces takes time to reestablish equilibrium and allow the joint to return to its precavitation resting position.²⁷⁸

A study conducted by Mireau and colleagues²⁸⁴ brings into question whether the temporary increase in joint space after manipulation is a product of gas bubble formation. They compared the resting joint spaces of subjects who did and did not have an audible crack with manipulation of the MP joints. Only 68% of the 62 subjects manipulated experienced an audible crack, yet the resting joint space increased for both groups, with no statistical difference noted between the groups. If the inaudible-crack group was able to achieve a post-treatment increase in joint space, it suggests that joint cavitation may have occurred, but without the intensity necessary to record an audible release, or that some other unknown phenomenon is at work for both groups.

Mireau and colleagues²⁸⁴ also studied the postmanipulation joint mobility of the subjects who recorded an audible release and those who did not. Both groups had 6 lbs of long-axis distraction applied after treatment. In the audible-crack cohort, an increase in joint space of 0.88 mm was noted, and an increase in joint space of 0.45 mm was recorded for the group without an audible crack. These findings suggest that there is some different physical effect between those who experience an audible release and those who do not. Perhaps a more profound separation of joint surfaces and stretching of periarticular tissues is associated with joint cracking. This supposition is further reinforced by the noted difference the researchers reported between those individuals receiving a third MP mobilization versus manipulation. The groups receiving joint manipulation had a significantly larger post-treatment ROM.

Although articular cracking (cavitation) is commonly used by chiropractors as evidence of a successfully delivered adjustment,²⁷² the process of cavitation is not assumed to be therapeutic in and of itself. Rather, it represents a physical event that signifies joint separation, stretching of periarticular tissue, and stimulation of joint mechanoreceptors and nociceptors. These events, in turn, are theoretically responsible for alleviating or reducing pain, muscle spasm, joint hypomobility, and articular soft tissue inflexibility.^236,272 Whether cavitation represents movement that is necessary to produce a better outcome as compared with patients who do not cavitate is largely unanswered. One study has compared the outcome of patients who did and did not cavitate with manipulation. The population was a cohort of 71 LBP patients who received a single sacroiliac manipulation. Subjects were reassessed 48 hours after the manipulation for changes in ROM, numeric pain rating scale, and modified Oswestry Disability Questionnaire. Both groups improved (21 noncavitators) and there were no clinically significant differences between groups. This study was limited to one area of the spine, evaluated only one adjustive method, and the application of only one manipulation. These factors limit the study’s generalizability and clinical implications.

The presence or absence of cavitation (an audible crack) is also commonly presented as a means for distinguishing mobilization and thrust manipulation (adjustment).²⁷² Manipulation purportedly produces a cavitation, and mobilization does not. Thrust manipulation is much more frequently associated with joint cracking than mobilization. However, deep mobilization may also be associated with cavitation. The original studies conducted on cavitation in the MP joints were the product of joint mobilizations.²⁷⁶ If manipulation and mobilization were differentiated by the presence or absence of cavitation, a thrust manipulation, not associated with an audible release, would have to be reclassified as a mobilization. Any therapy that induces enough joint separation to overcome the fluid tension between synovial joint surfaces can produce joint cavitation. Therefore, manipulation and mobilization should be distinguished by the velocity of their application, not by the presence or absence of an associated joint cavitation.

Whether repetitive joint cavitation is associated with any negative side effects is a matter of debate. Brodeur²⁷² reviewed the literature and concluded that the investigations were very limited and inconclusive. It appears that habitual joint cracking is not associated with an increase in cartilage damage or osteoarthritic changes, although one study did note an increase in joint swelling and loss of grip strength in habitual joint crackers.

There are other potential causes of noises associated with various forms of manual therapy that are not a product of cavitation. With the development of cross-linkages in traumatized soft tissues, a manual procedure can break them apart, theoretically producing an audible tearing sound. With some mobilizing or manipulating procedures, the necessary movements of the parts can cause muscle tendons to move over bony protuberances, producing an audible snapping sound. Bony outgrowths can produce impingement that, with movements of the involved parts, can produce an audible clunking sound. Degenerative joint disease can produce crepitus on joint movement, producing an audible crackling sound.

Interarticular Adhesions

Interarticular adhesions refer to the hypothesis that joint fixation or hypomobility may be a product of adhesions that have developed between the articular surfaces of the Z joints.²⁸⁵ This process is speculated to result from joint injury, inflammation, or immobilization.^{241,247,249,254,}286 287 288 289 Joint injury or irritation leading to chronic inflammation and joint effusion may induce synovial tissue hyperplasia, invasion of fibrous connective tissue, and consequent interarticular adhesions.^56,57,247 In addition, Gillet²⁸⁹ has suggested that prolonged joint immobilization secondary to periarticular ligamentous shortening may eventually lead to fibrous adhesion formation between joint surfaces. Adjustive therapy is postulated to induce gaping of the involved joints breaking the adhesions between joint surfaces and improving or restoring joint mobility.

Interarticular Block

The term interarticular block refers to a reduction (blockage) of joint movement that is a product of some derangement within the synovial joint, internal to the joint capsule. Entrapment of the interapophysary meniscus within the posterior spinal joints has been hypothesized as a cause of episodic acute back pain and joint locking.^10,290 291 292 293 294 295 The menisci are purportedly drawn into a position between the joint margins during poorly coordinated spinal movements or by sustained stressful postures (Figure 4-14, A). With resumption of normal postures, pain results from impaction of the menisci or traction of the articular capsule, inducing reactive muscle spasm and joint locking. The development of a painful myofascial cycle is initiated as prolonged muscle contraction leads to muscle fatigue, ischemia, and more pain. If spasm and locking persist, the articular cartilage may mold around the capsular meniscus, causing it to become more rigidly incarcerated within the joint (see Figure 4-14, B and C).294 295 296

Figure 4-14 Position and postulated incarceration of synovial joint meniscoids. A, Diagram of the structural components of a meniscoid in a lumbar facet joint. B, Meniscoid entrapment in cervical facet joints restricting extension and flexion movements. C, Entrapment of meniscoids is postulated to produce deformation of the articular cartilage surface; after reduction and over time the articular cartilage will remodel.

(A modified from Dupuis,¹⁸⁶. C modified from Lewit⁹⁸.)

To interrupt the cycle of pain, muscle cramping, and joint locking, distractive adjustments have been presented as a viable therapy capable of inducing joint separation, cavitation, and liberation of the entrapped meniscoid (Figure 4-15).

Figure 4-15 Techniques producing joint distraction have the potential to produce cavitation and reduce entrapment or extrapment of meniscoids. A, Technique applied to induce flexion, lateral flexion, and rotation in the left lumbar facets. B, Separation and expulsion of entrapped meniscoid.

Bogduk and Engel²⁹⁷ question the plausibility of meniscus entrapment as a source of acute joint locking and make a compelling case for meniscoid extrapment. They contend that meniscoid entrapment would require the meniscus to have a firm apex strongly bound to the capsule by connective tissue. Their morphologic studies did not confirm such an anatomic entity. They did imply, however, that a piece of meniscus torn and dislodged from its base could form a loose body in the joint, capable of acting as a source of back pain amenable to manipulation.

Bogduk and Jull²⁹⁸ favor instead the theory that the meniscoids become extrapped rather than entrapped. In their model of dysfunction, as the joint goes into flexion, the meniscoid is drawn out of the joint, and on return into extension, the meniscoid fails to properly reenter the joint cavity. Instead it lodges against the edge of the articular cartilage, where it buckles, serving as a space-occupying lesion that causes pain by distending the joint capsule (Figure 4-16).²⁹⁷ Manipulation that produces passive flexion should reduce the impaction, and rotation should gap the joint, encouraging the meniscoid to reenter the joint cavity.²⁹⁸

Figure 4-16 Theory of meniscoid extrapment. A, On flexion, the inferior articular process of a zygapophyseal joint moves upward, taking a meniscoid with it. B, On attempted extension, the inferior articular process returns toward its neutral position, but the meniscoid, instead of reentering the joint cavity, buckles against the edge of the articular cartilage, forming a space-occupying lesion under the capsule. C, Manipulation gaps the joint, allowing the meniscoid to return to its neutral resting position (D).

Other theories of interarticular soft tissue entrapment suggest that impingement of synovial folds or hyperplastic synovial tissue are additional sources of acute back pain and locking.299 300 301 302

Bony locking of the posterior joints at the end-range of spinal motion have also been proposed. It is suggested that the developmental incongruencies and ridges in joint surface anatomy, combined with the complex coupled movements of the spine, may lead to excessive joint gapping at the extremes of movement, which may in turn lead to bony locking as the surfaces reapproximate.³⁰⁰ In both circumstances, distractive adjustive therapy has the potential to reduce the locking.

Interdiscal Block

Interdiscal block refers to internal derangement of the disc that leads to alterations or reductions in normal motion of the spinal motion segments. The mechanical derangements of the IVD that may lead to joint dysfunction are postulated to result from pathophysiologic changes associated with aging, degenerative disc disease, and trauma. Farfan³⁰³ has proposed a model of progressive disc derangement based on repetitive rotational stress to the motion segment. He postulates that repetitive torsional loads of sufficient number and duration may, over time, lead to a fatigue injury in the outer annular fibers. The process begins with circumferential distortion and separation in the outer annular fibers, followed by progression to radial fissuring and outward migration of nuclear material. The rate of fatigue and injury depends on the duration and magnitude of the force applied. In the individual with disrupted segmental biomechanics, the process is potentially accelerated as an altered axis of movement leads to increased rotational strain on the IVD.

As presented earlier, the significance of torsional stress on the IVD, especially without coupled flexion, has been questioned. The sagittal orientation of the lumbar facets and the protective rotational barrier they provide bring into question the susceptibility of the lumbar discs to rotational torsion.^{165,169,170,303,304} Regardless of the mechanism or process, there is little doubt that internal disc derangement can lead to episodic or prolonged painful alterations or reductions in spinal movement.

Further complicating discal injury and internal disc disruption are the likely inflammatory and potential autoimmune reactions triggered by cellular disruption. Naylor³⁰⁵ has suggested that a discal injury with its associated connective tissue repair and vascularization is sufficient to create an antibody-antigen inflammatory reaction by exposing proteins of the nuclear matrix. The net effect is diminished protein polysaccharide content of the nucleus pulposus, loss of fluid content, and progression and acceleration of nuclear degeneration. As the nucleus atrophies, the disc becomes more susceptible to loading, and additional tractional forces may be transferred to the annulus, inducing mechanically based pain as the intact outer fibers are excessively stretched.¹⁴⁰

Interwoven into the natural history of degenerative disc disease may be episodes of acute mechanical back pain and joint locking. Others^24,29,12,305 306 307 308 309 have postulated that incidents of blockage may occur during movements of trunk flexion as nuclear fragments become displaced and lodged along incomplete radial fissures in the outer fibers of the posterior annulus (interdiscal block) (Figure 4-17). Consequently, when extension is attempted, the displaced fragment cannot return to its central position and becomes compressed. The compressed fragment produces radial tension on the posterior annulus, causing pain and potential local muscle guarding and joint locking. Cyriax³⁰⁸ proposes that these lesions may induce tension on the dura mater, inducing low back pain (LBP) and muscle splinting. Once local pain and muscle spasm are initiated, a self-perpetuating cycle of pain, cramping, and joint locking may result. Adjustive therapy has been proposed as a viable treatment for interrupting this cycle of acute back pain and joint locking. In addition to the distractive effect on the posterior joints, adjustive therapy is thought to have a potential direct effect on the IVD, either by directing the fragmented nuclear material back toward a more central position or by forcing the nuclear fragment toward a less mechanically and neurologically insulting position between the lamellae of the annulus.³⁰⁹

Figure 4-17 Fragments of nuclear material migrate in annular defects, creating an interdiscal block.

Two separate mechanical concepts have been proposed as models for how this might occur. The Gonstead adjustive technique has presented a model using adjustments to close down the side of nuclear migration (slippage) and force the material back toward the center (Figure 4-18).³¹⁰ The second concept, presented by Sandoz,²⁴ proposes a model in which distractive side posture adjustments combine disc distraction with rotation to induce helicoid traction and draw the herniated nuclear material back toward the center (Figure 4-19).

Figure 4-18 Techniques designed to close the side of nuclear migration (open wedge) are performed to force nuclear material toward the center of the disc.

Figure 4-19 Techniques using distraction combined with rotation induce a helicoid traction that is intended to draw nuclear material toward the center of the disc.

Internal derangement of the disc without associated NR dysfunction is difficult to conclusively differentiate from other mechanical disorders of the motion segment. Repetitive end-range loading and centralization of the patient’s symptoms, especially in the presence of leg pain, has demonstrated value in helping clinically diagnoses this condition,³¹¹ but consensus has not been reached on the clinical criteria and standard of care for definitively establishing this disorder. Consequently, clinical research evaluating the effects of chiropractic HVLA adjustive treatment on IVD syndromes has focused primarily on biomechanical studies investigating chiropractic management of disc protrusion or herniation confirmed by imaging.

Levernieux³¹² noted reduction in disc herniation with axial traction, and Matthews and Yates³¹³ reported epidurographic reductions in disc herniations with manipulation. In contrast, Christman, Mittnacht, and Snook³¹⁴ reported a notable improvement in 51% of their patients treated with manipulation, but they reported no change in disc hernia as measured with myelography. Sandoz²⁴ concluded that the contradictory findings between these two studies can be accounted for by the fact that epidurography may measure smaller derangements of the disc, whereas myelography reveals only larger protrusions that are less amenable to manipulative care. It is doubtful that manipulation can reduce an external protrusion, but Sandoz²⁴ has suggested that manipulation may have a role to play in shifting the herniation away from the NR, minimizing the mechanical conflict and associated inflammation. In such circumstances, treatment is expected to be more protracted.²⁴

Well-designed and well-conducted clinical trials on HVLA adjustive therapy for disc herniation and associated radiculopathy (sciatica) are very limited. Clinical trials, uncontrolled descriptive studies, and case reports on the manipulative treatment of lumbar disc herniations are few, but they do indicate that this patient population may benefit from chiropractic manual therapy.^24,304,314 315 316 317 318 319 320 321 322 323 324

The incidence of complications arising from the manipulative treatment of disc herniation patients is extremely low. However, this procedure may carry some very minimal risk. Accordingly, modifications of side posture manipulative techniques have been suggested in the treatment of patients with marked disc herniations. To minimize the risk of further annular injury, side posture adjusting or mobilization postures, which minimize excessive lumbar flexion and compression, have been proposed.³⁰⁴ Procedures and positions that increase the patient’s leg pain are assumed to be more stressful to the annular fibers and are to be avoided. Those that reduce or centralize back pain while decreasing the patient’s leg pain are presented as potentially the safest and most effective. Disc herniation patients suffering progressive neurologic deficits or midline herniations with an associated CES should not be considered for manipulation.325 326 327 328

Periarticular Fibrosis and Adhesions

As mentioned previously, acute or repetitive trauma may lead to articular soft tissue injury. In the process of fibrotic repair, adhesions and contractures may develop, resulting in joint hypomobility. Distractive adjustments are advanced as procedures capable of effectively treating these derangements by stretching the affected tissue, breaking adhesions, restoring mobility, and normalizing mechanoreceptive and proprioceptive input. ^30,237 238 239

It is further postulated that manipulation may sever the adhesive bonds, stretch tissue, and promote mobility without triggering an inflammatory reaction and recurrence of fibrosis. However, when articular or nonarticular soft tissue contractures are encountered, incorporation of procedures that minimize inflammation and maintain mobility should be considered. Viscoelastic structures are more amenable to elongation and deformation if they are first warmed and then stretched for sustained periods.³²⁹ Therefore, the application of moist heat, ultrasound, and other warming therapies might be considered before applying sustained manual traction or home-care stretching exercises.

Joint Instability

Although emphasis has been placed on the adjustive treatment of mechanical disorders resulting from joint hypomobility, manipulative therapy also may have a role in the treatment of clinical joint instability. Clinical joint instability can be defined as a painful disorder of the spine resulting from poor segmental motor control or a loss of stiffness in the controlling soft tissues that leads to a loss of motion segment equilibrium and an increase in abnormal translational or angular movements. ^330,331 Common proposed causes of joint instability include acute trauma, repetitive-use injuries, compensation for adjacent motion segment hypomobility,³³² ineffective neural control, degenerative disc disease, and muscle weakness or poor endurance.³³³ Clinical joint instability is not to be confused with gross orthopedic instability resulting from marked degeneration, traumatic fracture, or dislocation.

Joint instability may predispose the patient to recurring episodes of acute joint locking and may be seen more frequently in individuals who have some degree of hypermobility that is a result of advanced training in athletics such as gymnastics or ballet dancing.³³² Adjustive therapy applied in this condition is not intended to restore lost movement but rather to reduce the episodic pain, temporary joint locking, joint subluxation, and muscle spasm that are commonly encountered in patients with unstable spinal joints. Adjustive therapy delivered in these circumstances is considered to be palliative. It should not be applied during an extended period, and it should be incorporated with stabilization therapy, appropriate exercise, and lifestyle modification. ^332,333

Analgesic Hypothesis

The reduction of pain and disability from spinal manipulation is well recognized and clinically documented. ^147,194,199,334 335 336 337 338 339 340 “Numerous studies suggest that SM alters central processing of noxious stimuli because pain tolerance or pain threshold levels can increase after manipulation.”²⁶¹ The mechanisms by which manipulation inhibits pain, however, are matters of speculation and still under investigation. Proposed hypotheses have suggested that manipulation has the potential to remove the source of mechanical pain and inflammation or induce stimulus-produced analgesia.

The case for decreasing pain by removing its mechanical source is empiric and deductive. The pain associated with mechanical disorders of the musculoskeletal system is a product of physical deformation, inflammation, or both.³⁴¹ It is reasoned that manual therapy effective at reversing or mitigating underlying structural and functional derangements will remove the source of pain and the associated pain-producing agents as structures are returned to normal function.

The argument for stimulus-produced analgesia is bolstered by experimental evidence that suggests that chiropractic adjustments induce sufficient force to simultaneously activate both superficial and deep somatic mechanoreceptors, proprioceptors, and nociceptors. The effect of this stimulation is a strong afferent segmental barrage of spinal cord sensory neurons, capable of altering the pattern of afferent input to the central nervous system and inhibiting the central transmission of pain (Figure 4-20).341 342 343 344 345

Figure 4-20 Diagram suggesting the mechanism by which a high-velocity chiropractic adjustment inhibits the central transmission of pain through activation of mechanoreceptors and nociceptors.

(Modified from Gillette, Cassidy JD, Lopes AA, Yong-Hing K: The immediate effect of manipulation versus mobilization on pain and range of motion in the cervical spine: A randomized controlled trial, J Manipulative Physiol Ther 15:570, 1992.)

Gillette³⁴² suggests that spinal adjustments may initiate both a short-lived phasic response triggered by stimulation of superficial and deep mechanoreceptors, and a longer-lived tonic response triggered by noxious-level stimulation of nociceptive receptors. The phasic response is hypothesized to initiate a local gating effect, but pain inhibition terminates with cessation of therapy. The tonic response initiated by noxious levels of mechanical stimulation is more powerful and capable of outlasting the duration of applied therapy.³⁴⁴

Adjustments that induce joint cavitation and capsular distraction may be a source of nociceptive stimulation capable of initiating relatively long-lasting pain inhibition. This concept supports the premise that the slight discomfort that may be associated with adjustments is causally associated with a positive therapeutic effect.³³⁴

The potential for spinal adjustments to act directly on the pain system opens up the possibility that manipulation may have the ability to diminish persistent pain that is neuropathic in origin.³⁴⁵ Chronic neuropathic pain may result from plastic changes and central sensitization of the nervous system. Central sensitization refers to plastic changes in the nervous system that result from persistent amplification of nociceptive synaptic transmission. This can result in the persistence of pain states even after the offending peripenial pathologic injury and inflammation have resolved.³⁴⁴

The short-term bursts of proprioceptive and nociceptive input associated with adjustments, much like transcutaneous electrical nerve stimulation and acupuncture, have also been theorized to increase the levels of neurochemical pain inhibitors.³³⁷ Both a local release of enkephalins, initiated by stimulation of the neurons of substantia gelatinosa, and a systemic increase in plasma and cerebrospinal fluid endorphin levels, initiated by simulation of the hypothalamic pituitary axis, have been proposed. Both substances act as endogenous opioid pain inhibitors and may play a role in the analgesic effects of adjustments.

Doctor reassurance and the laying-on of hands may also impart a direct analgesic effect, which must be factored into the equation when calculating the effects of adjustments and manual therapy. The contact established during a skilled evaluation of the soft tissues indicates the doctor’s sense of concern and skill. Paris³³¹ states that with the addition of a skilled evaluation involving palpation for soft tissue changes and altered joint mechanics, the patient becomes convinced of the clinician’s interest, concern, and manual skills. If the examination is followed by treatment and an adjustive cavitation (crack), further positive placebo effects may be registered. The astute clinician accepts and reinforces this phenomenon if it influences the patient’s recovery. This does not excuse misrepresentation or irresponsible exaggeration of the therapeutic effect.

Muscle Spasm (Hypertonicity)

Numerous authors have presented the potential causative role of hypertonic muscles in the development of joint dysfunction and spinal pain.^{24,238,289,292,}346 347 348 349 The concept that restricted joint movement may result in increased segmental muscle tone or spasm is supported by the knowledge that muscles not only impart movement but also impede movement. Joint movement depends on a balance between its agonist and antagonists. If this balance is lost and antagonistic muscles are unable to elongate because of involuntary hypertonicity, the joint may be restricted in its range or quality of movement.

Increased resting muscle tone or spasm may be initiated by direct provocation or injury to myofascial structures or indirectly by stimulation or injury to associated articular structures. Direct overstretching and tearing of muscle lead to stimulation of myofascial nociceptors and protective muscle splinting. The intersegmental muscles of the spine may be especially vulnerable to incidents of minor mechanical stress and overstretching. They are not under voluntary control. They act primarily to stabilize and integrate segmental movements in response to global movements of the trunk. As a result, they may be especially vulnerable to unguarded movements and the induction of reactive splinting.

Korr³⁴⁶ suggests that unguarded and uncoordinated movements may approximate the short segmental muscles of the back and reduce annulospiral receptor activity in the muscle spindle complex and produce muscle spasm. Maigne²⁹¹ envisions a similar lesion (articular strain), but speculates that it results from abnormal sustained postures or poorly judged movements that induce minor intersegmental muscle overstretching and cramping. Both speculate that segmental muscle spasm, once initiated in the back, may be hard to arrest. Contracted segmental muscles of the back, unlike the voluntary appendicular muscles, are not easily stretched by the contraction of antagonistic muscle groups. As a result, this condition may not be inhibited by active stretching and therefore may be less likely to be self-limiting.²⁹¹ Research published in 2000 demonstrated that muscle spasm reduced the ability of paraspinal muscle stimulation to evoke cerebral potentials.³⁵⁰ “Spinal manipulation reversed these effects, reducing muscle spasm and restoring the magnitude of the evoked cerebral potentials.”²⁶¹

Myofascial Cycle

A central complicating feature of many of the internal and external derangements of the motion segment is the induction of a self-perpetuating myofascial cycle of pain and muscle spasm. The articular soft tissues are richly innervated with mechanoreceptors and nociceptors, and traction or injury to these structures may lead to the initiation of local muscle splinting. With time, the continued muscle contraction may lead to further muscle fatigue, ischemia, pain, and maintenance of muscle spasm and joint locking (Figure 4-21).

Figure 4-21 The self-perpetuating cycle of myofascial pain and muscle spasm.

High-velocity adjustments are suggested as treatments that may be effective in interrupting this cycle. Several theories exist as to the mechanism by which adjustments relieve muscle spasm. Both are speculated to induce a reflex response in muscle—one through direct action on muscle and the other reflexly through joint distraction (cavitation). The direct muscle model³⁴⁶ speculates that quick traction and excitation of the Golgi tendon organ (GTO), located in the muscle tendon junction, act as brakes to limit excessive joint movement and possible injury by inhibiting motor activity. The concept is that adjustments induce a strong stretch on the muscle tendon complex, activate the GTO, and induce reflex muscle relaxation (autogenic inhibition). Although this model seems reasonable, evidence suggests that the GTO has a less profound effect than initially envisioned. Watts and associates³⁴⁹ found that stimulation of the GTO produces a very meager inhibitory effect on motor neuron activity. This information implies that the GTO plays a more minor role in the inhibition of muscle spasm than initially proposed and brings into question its relationship to postadjustment muscle relaxation.

In contrast, stimulation of articular low- and high-threshold mechanoreceptors and nociceptors has demonstrated a notable inhibitory effect on segmental motor activity.³⁴² Mechanoreceptors and nociceptors are also widely embedded in articular soft tissues, muscle, and skin. High-velocity adjustments induce enough force to stimulate these structures and induce a burst of somatic afferent receptor activity.^281,342 Based on this information, it seems reasonable to assume that joint and soft tissue mechanoreceptors and nociceptors have the potential to play a material role in the inhibition of muscle spasm and the interruption of painful myofascial cycles and joint locking.

Clinical investigations on the effects of spinal manipulation on muscle activity are very limited. Investigations have centered on the effects of manipulation during and after the application of manipulation. Using surface electromyograph (EMG), Herzog and others351 352 353 investigated the immediate effects of thoracic SMT on paraspinal muscle activity. They applied prone unilateral quick (HVLA) and slow (3- to 4-second) “manipulations” to the thoracic transverse processes. Both procedures consistently induced momentary increased muscle activity during their application. The high-velocity manipulations were associated with a fast, burstlike EMG signal, and the slow manipulation with a gradual increase in EMG activity. Cavitations induced during the application of the slowly applied manipulation were not associated with increased EMG activity, leading the researchers to speculate that cavitation alone is not sufficient to induce a reflex muscular response. The myoelectric response recorded during thoracic adjustments did conflict with the application of the adjustive forces. In contrast, Triano and Schultz¹⁶¹ were unable to record any significant myoelectric activity or muscular responses with the application of HVLA SP lumbar-adjusting procedures.

Investigations into more prolonged effects on resisting muscle activity, although very limited, have shown reductions in paraspinal muscle activity and imbalance with full-spine adjusting procedures.^352,353

Nerve Root Compression

Chiropractic, osteopathy, and manual medicine has envisioned manual therapy affecting not only somatic disorders, but also visceral disorders through neurologic means.¹⁷ The early paradigm presented in chiropractic stressed a model of altered NR function as the basis for secondary somatic or visceral dysfunction. It was theorized that subluxations induce structural alteration of the intervertebral foramina, leading to compression of the contained neurovascular structures and altered function of the NR as electrical transmission or axoplasmic flow is impaired. The postulated net result of this process (nerve interference) was dysfunction or disease in the somatic and visceral structures supplied by the affected NR^17,354 355 356 357 358 359 The subluxation-induced narrowed intervertebral foramen (IVF) was hypothesized to induce NR dysfunction through direct bony compression (pinched-hose model) or indirectly by increasing pressure around the NR and its vascular structures.

In 1973, Crelin³⁶⁰ challenged the anatomic plausibility of subluxated motion segments producing NR compression. His anatomic dissections and measurements, made at the lateral borders of the IVF, demonstrated a minimum of 4 mm of space around the NR. He concluded that the space was more than adequate and that the NR was not anatomically vulnerable to compression. More recently in 1994, Giles³⁶¹ revisited the issue of NR vulnerability but at a different anatomic site. His measurements were taken at the interpedicular zone and demonstrated an average of only 0.4 to 0.8 mm of space around the NR and the NR ganglion. He concluded that the NR was anatomically vulnerable, but at the interpedicular zone, not at the lateral borders of the IVF. Furthermore, “dorsal roots and dorsal root ganglia [DRG] are more susceptible to the effects of mechanical compression than are axons of peripheral nerves because impaired or altered function is produced at substantially lower pressures.”³⁶¹

A potential site of anatomic vulnerability does not, by any means, validate chiropractic models of subluxation-induced NR dysfunction. The plausibility of uncomplicated subluxations commonly inducing NR compression still seems unlikely.355 356 357 358 359 360 It does, however, raise an interesting issue about the potential for spinal motion segment dysfunction to contribute to NR compression when it is associated with other compromising joint pathologies.^300,361,362 Disc herniation and exposure of the NR to discal material increase spontaneous nerve activity and the mechanical sensitivity of the NR and possible mechanical hyperalgesia. Spinal NRs already compromised by disc herniation, degenerative joint and disc disease, or central or lateral stenosis and the associated inflammation may become more serious when associated with dysfunction that fixes the joint in a more compressive and compromising position. In such circumstances, adjustive therapy that reduces a position of fixed subluxation and root irritation may have an effect on reducing NR traction, compression, or inflammation.

Reflex Dysfunction

Beginning with the work of Homewood,³⁵⁸ the profession has gradually moved away from reliance on NR compression and toward a more dynamic model of subluxation-induced neurodysfunction. As presented in Chapter 3, the reflex paradigm presents a model in which somatic dysfunction or joint dysfunction induces persistent nociceptive and altered proprioceptive input. This persistent afferent input triggers a segmental cord response, which in turn induces the development of pathologic somatosomatic or somatovisceral disease reflexes357 358 359 363 364 365 366 367 368 (Figure 4-22). If these reflexes persist, they are hypothesized to induce altered function in segmentally supplied somatic or visceral structures.

Figure 4-22 Afferent and efferent pathways from and to the viscera and somatic structures that can produce (1) somatosomatic, (2) somatovisceral, (3) viscerosomatic, and (4) viscerovisceral reflex phenomena.

(Modified from Schmidt,¹⁸⁸.)

Chiropractic adjustive therapy has the potential for arresting both the local and the distant somatic and visceral effects by normalizing joint mechanics and terminating the altered neurogenic reflexes associated with joint dysfunction. For example, a patient with a strained posterior joint capsule accompanied by reflex muscle spasm may have nociceptive bombardment of the spinal cord. If the nociceptive bombardment is of sufficient strength and duration, it may cause segmental facilitation. The spinal adjustment may reduce the strain on the joint capsule and reduce muscle spasm that stops nociception from these tissues into the spinal cord. At the same time, adjustments stimulate many different types of mechanoreceptors. The result is a reduction of a harmful somatosomatic and potential somatoautonomic reflex. This model has become the focus of more attention and investigation as chiropractors search for an explanation to the physiologic effects that they have clinically observed to be associated with spinal adjustive therapy. This relationship is not consistent, and the frequency of response is undetermined, but the anecdotal and empiric experiences of the profession are significant enough to warrant serious further investigation.

An additional model of subluxation-induced neurodysfunction focuses attention on the potential direct mechanical irritation of the autonomic nervous system. The paradigm for irritation of sympathetic structures is based on the anatomic proximity and vulnerability of the posterior chain ganglion, between T1 and L2, to the soma of the posterior chest wall and costovertebral joints. Altered spinal and costovertebral mechanics are hypothesized to mechanically irritate the sympathetic ganglia and to induce segmental sympathetic hypertonia.³⁶⁸ The target organs within the segmental distribution then theoretically become susceptible to altered autonomic regulation and function as a result of altered sympathetic function.

In contrast to the sympathetic chain, the parasympathetic system, with its origins in the brain, brainstem, and sacral segments of the spinal cord, does not have anatomic proximity to the spinal joints. Models of mechanically induced dysfunction of the parasympathetic system propose dysfunction in cranial, cervical, and pelvic mechanics as potential sources of entrapment or tethering of the parasympathetic fibers. Altered cervical, cranial, or craniosacral mechanics are theorized to induce traction of dural attachments and the cranial nerves as they exit through the dura and skull foramina. The treatment goal in mechanically induced autonomic dysfunction is to identify the sites of joint dysfunction and implement appropriate manual therapy to balance membranous tension.³⁶⁹

From the discussion of spinal dysfunction and its potential neurobiologic effects on health, it must be remembered that spinal dysfunction and pain may be the product of, not the cause of, somatic or visceral dysfunction or disease.³⁷⁰ Spinal pain and dysfunction may be secondary to a disorder that needs direct treatment. Manual therapy may be a fitting component of appropriate care, but would be inadequate as the singular treatment. The patient with caffeine-induced gastritis who develops secondary midback pain and dysfunction (viscerosomatic) should not receive manual therapy without also being counseled to discontinue ingestion of caffeinated beverages. The spine is a common site of referred pain, and when a patient with a suspected mechanical or traumatic disorder does not respond as anticipated, the possibility of other somatic or visceral disease should be considered.

Neuroimmunology

An interaction exists between the function of the central nervous system and the body’s immunity that lends support to the chiropractic hypothesis that neural dysfunction is stressful to the body locally and globally. Moreover, with the resultant lowered tissue resistance, modifications to the nonspecific and specific immune responses occur, as well as altered trophic function of the involved nerves. This relationship has been termed the neurodystrophic hypothesis.

Selye371 372 373 demonstrated neuroendocrine-immune connections in animal experiments and clinical investigations. Physiologic, psychologic, psychosomatic, and sociologic components compose the stress response. From studies of overstressed animals, Selye observed nonspecific changes that he labeled the general adaptive syndrome. He also observed very specific responses that depended on the stressor and on the part of the animal involved, which he termed local adaptive syndrome. Furthermore, he established a stress index comprising major pathologic results of overstress, including enlargement of the adrenal cortex, atrophy of lymphatic tissues, and bleeding ulcers. Selye also felt that long-term stress would lead to diseases of adaptation, including cardiovascular disease, high blood pressure, connective tissue disease, stomach ulcers, and headaches.

Stressors can produce profound health consequences.³⁷⁴ Theorists propose that stressful events trigger cognitive and affective responses that, in turn, induce sympathetic nervous system and endocrine changes, and these ultimately impair immune function.375 376 377 378 379 Stressful events cannot influence immune function directly. Instead, stress is thought to affect immune function through central nervous system control of the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic-adrenal-medullary axis.^377,380 381 382 383 Stressors produce reliable immune changes.³⁷⁴ Segerstrom and Miller³⁸⁴ analyzed different types of stressors separately and found that the immunologic effect of stressors depends on their duration.

However, because all individuals do not develop the same syndrome with the same stressor, Mason³⁸⁵ suggested that emotional stimuli under the influence of internal (genetics, past experiences, age, and sex) or external (drugs, diet, and hormone use) conditioning are reflected in the responses of the endocrine, autonomic, and musculoskeletal systems³⁸⁵ (Figure 4-23).

Figure 4-23 Internal and external conditioning can affect emotional stimuli, resulting in autonomic, endocrine, or musculoskeletal changes.

Stein, Schiavi, and Camerino³⁸⁶ convincingly demonstrated psychosocial and neural influences on the immune system. They showed that the hypothalamus has a direct effect on the humeral immune response, explaining how psychosocial factors can modify host resistance to infection. Moreover, Hess³⁸⁷ produced sympathetic and parasympathetic responses by stimulating different parts of the hypothalamus. The sympathetic response (ergotropic response) is characteristic of the fight-or-flight mechanism, whereas the parasympathetic response (trophotropic response) produces relaxation that promotes a restorative process. Table 4-2 lists the characteristics and physiologic responses of the ergotropic and trophotropic states.

TABLE 4-2 Characteristics of the Ergotropic and Trophotropic Responses

The three classically separated areas of neuroscience, endocrinology, and immunology, with their various organs—the brain; the glands; and the spleen, bone marrow, and lymph nodes, respectively—are actually joined to one other in a multidirectional network of communication, linked by information carriers known as neuropeptides. The field of study is called psychoneuroimmunology (PNI). PNI is a scientifically solid field of study, grounded in well-designed experiments and in the resolute tenets of behaviorism.³⁸⁸ The first components of the process of linking the systems of the body together, and ultimately the body and mind, are the receptors found on the surface of the cells in the body and brain. Almost every peptide receptor, not just opiate receptors, could be found in this spinal cord site that filters all incoming bodily sensations. It has also been found that in virtually all locations at which information from any of the five senses enters the nervous system there is a high concentration of neuropeptide receptors. These regions are called nodal points.³⁸⁸

Today’s health care provider should recognize the interconnectedness of all aspects of human emotion and physiology. The skin, the spinal cord, and the organs are all nodal points of entry into the psychosomatic network. Health care providers that incorporate touching and movement in their treatment of patients affect them all.

Leach³⁸⁹ points out that there is a paucity of studies that directly link vertebral lesions with immunologic competence, although his review of the literature suggests that such a connection is possible. Fidelibus,³⁹⁰ after conducting a recent review of the literature, concluded that the concepts of neuroimmunomodulation, somatosympathetic reflex, and spinal fixation provide a theoretic basis for using spinal manipulation in the management of certain disorders involving the immune system, including asthma, allergic rhinitis, and the common cold. He further postulates that musculoskeletal dysfunction can result in immune dysfunction and that, by removing the musculoskeletal dysfunction, spinal manipulation can affect the immune dysfunction. As mentioned previously, chiropractic manipulation did not have a positive outcome in treating childhood asthma in a population of children who were less than optimally responsive to medication.²¹⁶

Two studies on infantile colic^233,391 indicate that chiropractic treatment results in a reduction of the daily length and number of colic periods. Klougart and associates²³⁴ found that 94% of the infants studied were helped by chiropractic treatment within 14 days from the start of treatment. Wiberg, Nordsteen, and Nilsson³⁹¹ compared spinal manipulation with dimethicone medication. The infants in the chiropractic group exhibited a 67% reduction of daily hours of colic, whereas the dimethicone group had a 38% reduction. However, a 2001 randomized placebo controlled study that blinded the parents from the therapy found no difference between placebo and spinal manipulation in the treatment of infantile colic.²³⁵

Vernon and colleagues³³⁷ reported a slight, but statistically significant, increase in B-endorphin levels in asymptomatic males after cervical manipulation, whereas Sanders et al³⁹² and Christian, Stanton, and Sissons³⁹³ found no change in B-endorphin levels in either symptomatic or asymptomatic male study participants after chiropractic manipulation.

Whelan and associates³⁹⁴ examined 30 asymptomatic male chiropractic students in a randomized clinical trial to determine the effect of HVLA cervical manipulation on salivary cortisol secretion. They found no effect of chiropractic manipulation on salivary cortisol and concluded that in asymptomatic subjects familiar with chiropractic manipulation, neither the sham nor cervical manipulation induces a state of anxiety sufficient to disrupt the homeostatic mechanisms and activate the HPA axis.

Teodorczyk-Injeyan, Injeyan, and Ruegg³⁹⁵ report that SMT in asymptomatic subjects down-regulates production of the inflammatory cytokines tumor necrosis factor–α and interleukin 1β (IL-1β). They also determined that this change in cytokine production was unrelated to serum substance P levels.

The work of Brennan and others396 397 398 399 400 401 402 403 remains the only extended line of investigation into the effect of chiropractic SM and immune function. They reported that a single manipulation in the thoracic or lumbar spine produced a short-term priming of the polymorphonuclear cell response to an in vitro particulate challenge. They observed an enhanced chemiluminescent respiratory burst in both asymptomatic and symptomatic study participants. ^396,398,403 This enhanced polymorphonuclear cell activity was associated with slight, but statistically significant, rise in plasma substance P. Further investigation suggested that this systemic effect depends on both the applied force and vertebral level.^398,403 In follow-up, Kokjohn and co-workers⁴⁰⁴ hypothesized that the force applied to the thoracic spine by manipulation is sufficient to result in increased plasma levels of substance P, which may prime circulating phagocytic cells for enhanced respiratory burst. However, whether the effect is significant in fighting infection has not been determined, and the exact mechanism whereby manipulation affects phagocytic cells remains speculative, because significant levels of plasma substance P were not determined.

The available studies suggest mechanisms by which spinal influences may mediate a clinically significant effect on immune function, but few studies have directly examined those mechanisms, and the evidence to date is conflicting. Consequently, there are clearly both plausible mechanisms to explore and clinical practice–driven justification for additional basic science studies in this area.²⁶¹

Physiologic and Unphysiologic Movement

Knowledge of the physiologic movements (normal coupled movements) of the spine and extremities is important in the process of determining how to localize and apply adjustive therapy. Localization of adjustive forces depends on an understanding of the normal ranges of joint movement and how combinations of movement affect ease and range of joint movement. Each spinal region and extremity joint has its own unique range and patterns of movement. Knowing the ranges and patterns of movement allows the doctor to know what combination of movements is necessary to produce the greatest range of movement and what combination is necessary to limit movement.

The spine can flex, extend, laterally flex, and rotate, but in combination, these movements can act to either limit or increase movement. Performance of movement in one plane limits movement in another plane; flexion of the spine limits the amount of lumbar rotation, and lumbar rotation limits the amount of flexion. An additional coupling of motion in a third plane can combine to further restrict or enhance the ROM. For example, the greatest range of combined lumbar rotation and lateral flexion is achieved if rotation and lateral flexion are executed in opposite directions and coupled with extension instead of flexion.

Combined movements that allow for the greatest total combined range are referred to as physiologic movements, and combined movements that lead to limited movement are referred to as unphysiologic movements. Right lateral flexion combined with left rotation and extension is an example of physiologic movement in the lumbar spine. Right lateral flexion combined with right rotation or flexion is an example of unphysiologic movement.

Unphysiologic movements bring the joints to positions of tension earlier in their ROM, limiting their overall ROM. Positioning sections of the spine in unphysiologic postures during the application of adjustive therapy is a strategy referred to as joint locking.⁴⁰⁹ Application of this procedure helps focus the adjustive forces to the affected region or joint and minimizes mobility at adjacent joints. When adjacent spinal regions are placed in unphysiologic positions, a block of resistance may be created superior or inferior to the joint to be adjusted, establishing earlier preadjustive tension. Joints placed in their unphysiologic positions have greater impact between joint surfaces, which may decrease the likelihood of paraphysiologic joint movement and gapping at those joints.

The region and motion segment to be adjusted is placed in the transition area between unphysiologic motion and physiologic motion or between sections placed in unphysiologic locking (Figure 4-28). The joints to be adjusted must have sufficient slack remaining so that the adjustive thrust may induce gapping or gliding within the joint’s physiologic range. If an adjustive thrust is delivered against a joint placed in its close-packed position, there is a greater risk of inducing joint injury. Placing joints in unphysiologic positions may be especially valuable in circumstances in which clinical joint instability is suspect at adjacent levels.

Figure 4-28 The joints above the level to be adjusted (L3 and L4) are placed in unphysiologic position (flexion, left rotation, and right lateral flexion) to develop locking of the joints above the level to be adjusted.

Reduction of Articular Slack

Articular slack refers to the joint play (JP) present in all synovial joints and their periarticular soft tissues. Although it is a normal component of joint function, available slack should be reduced during or before delivery of an adjustive thrust to improve the likelihood of inducing joint cavitation. Reducing articular slack helps isolate tension to the specific periarticular soft tissues that may be limiting JP and impeding joint motion. The removal of articular slack and the development of preadjustive tension also help focus the adjustive thrust to the desired spinal level or extremity joint. The energy and force generated by adjustive thrusts may be dissipated into superficial soft tissue and adjacent articular soft tissue if preadjustive tension is not first established.^410,411

The doctor may reduce articular slack by passively distracting the involved spinal region or joint or by altering patient positions to move the joints from their neutral position toward their elastic barrier. Joint distraction induced by the doctor may be developed by the gradual transfer of body weight through the adjustive contacts or by directing tractional forces through the adjustive contacts. The degree of preadjustive tension is gauged by the doctor’s sense of joint tension and by the patient’s response to pressure. Excessive traction or compression of joints during the application of adjustive procedures can lead to jamming of joints, uncomfortable contacts, and patient splinting. It is common for chiropractic students to overdo articular slack reduction and preadjustive tension when first learning adjustive techniques.

Lighter contacts and less preadjustive tension are necessary when patient discomfort and splinting are encountered. Joints with limited mobility need less movement to reduce articular slack and are often adjusted closer to their neutral positions. Joints with greater flexibility usually necessitate patient positions that move the joint from neutral positions toward the elastic barrier.

Patient Positioning

Preadjustive joint tension and localization are significantly affected by patient placement and leverage. Localization of adjustive forces may be enhanced by using patient placement to position a joint at a point of distractive vulnerability. Locking adjacent joints and positioning the joint to be adjusted at the apex of curves established during PP enhance this process (Figure 4-29). Joint localization and joint distraction may be further enhanced if forces are used to either help (assist) or oppose (resist) the adjustive thrust. Assisted and resisted patient positions refer to principles involved during the adjustive setup and development of preadjustive tension.

Figure 4-29 Proper patient positioning is necessary to develop appropriate preadjustive joint tension. A, Sagittal plane movement (flexion) and separation of the posterior element of the joint. B, Coronal plane movement (lateral flexion) and separation of the joint away from the table (left facet joints and disc). C, Transverse plane movement and development of counter-rotational tension and gapping of the left facet joints.

Assisted and Resisted Positioning

The notion of applying assisted and opposing forces during the performance of manipulation was first described relative to thoracic manipulation by the French orthopedist Robert Maigne.⁴¹² In the chiropractic profession, Sandoz²⁴ was the first to describe similar terms. Sandoz proposed using the terms assisted and resisted to describe patient positions that either assist or resist side posture (SP) lumbar adjustive thrust.²⁴ Both methods are used to improve the localization of preadjustive tension. Their application is based on the mechanical principle that the region of maximal tension will be developed at the point of opposing counter-rotation.⁴¹³

Assisted and resisted patient positions are distinguished from each other by the positioning of vertebral segments relative to the adjustive thrust. In both circumstances, the trunk and vertebral segments superior to the adjustive contacts are prestressed in the direction of desired joint movement. In the assisted method, the contacts are established on the superior vertebral segments, and movement of the trunk and the thrust are in the same direction (Figure 4-30, B). Resisted procedures use patient positions in which the segments superior to the adjustive contact are prestressed in a direction opposing the adjustive thrust. In the resisted method, the contacts are established on the lower vertebral segments, and the direction of adjustive thrust is applied opposite the direction of trunk movement (see Figure 4-30, A).

Figure 4-30 A, Resisted patient positioning with mammillary contact established on the inferior vertebra. B, Assisted patient positioning with spinous contact established on the superior vertebra. Both procedures are applied to produce left rotation.

Sandoz²⁴ has suggested that resisted positions bring maximal tension to the articulations superior to the established contact (e.g., contact at the L3 mammillary inducing tension at the L2-3 motion segment and above) and assisted positions bring maximal tension to the articulation inferior to the established contact (e.g., L2 spinous contact inducing tension at the L2-3 motion segment and below). In the assisted method, the area of countertension is inferior to the point of contact because the inferior segments are stabilized or rotated in a direction opposite the adjustive thrust (see Figure 4-30). In the resisted approach, the site of countertension is superior to the point of contact because the segments above the point of contact are rotated in a direction opposite the adjustive thrust (see Figure 4-30). Research by Cramer and co-workers²⁶⁵ has demonstrated that side posture-resisted lumbar mammillary push adjustments induce positional and postadjustment gapping in the articulations superior to the level of contact. In principle, either method can be used to induce the same joint motion within the same articulations. With assisted patient positions, the thrust is oriented in the direction of joint restriction; with resisted patient positions, the thrust is directed against the direction of joint restriction.

Assisted and resisted patient positions have been most frequently discussed relative to the development of rotational tension of the spine. In theory, the same methods and principles may be applied to treat dysfunction in lateral flexion or flexion and extension. To treat a loss of right lateral bending in the lumbar spine using the assisted method, the patient is placed on the right side with a roll placed under the lumbar spine to induce right lateral flexion. A contact is then established over the left mammillary of the superior vertebra, with an adjustive vector directed anteriorly and superiorly (Figure 4-31). To treat the same restriction with a resisted method, the same patient postioning should be maintained, but the left mammillary process of the inferior vertebra is contacted with a thrust delivered anteriorly and inferiorly (see Figure 4-31). Although both techniques are directed at distracting the left facet joints, one is assisting and the other is resisting the direction of bending.

Figure 4-31 Adjustment for loss of right lateral flexion. With a resisted method, the contact is established on the left mammillary process of the inferior vertebra. The assisted method incorporates a contact established on the left mammillary process of the superior vertebra.

To treat a loss of lumbar flexion with a side posture-assisted method, the patient should be placed on either side and segmental flexion induced, the superior vertebrae of the involved motion segment should be contacted, and the thrust should be anterior and superior. Conversely, without changing PP, the same restriction could be treated with a resisted method by simply contacting the lower vertebrae and thrusting anteriorly and inferiorly (Figure 4-32). The same principles described for flexion can easily be applied to treat an extension restriction, the only difference being the prestressing of the patient into segmental extension.

Figure 4-32 Adjustment for loss of flexion using resisted (inferior vertebra) or assisted (superior vertebra) methods.

When applying side posture adjustive thrusts in the treatment of lateral flexion, flexion, or extension, it is typically less stressful to the doctor’s wrist and shoulder to couple P-A thrusts with an I-S vector, as opposed to a coupled superior-to-inferior vector. The superior-to-inferior vector induces a posture of wrist extension and internal shoulder rotation that is uncomfortable and possibly injurious. Therefore, lateral flexion and flexion adjustments may be more safely and comfortably delivered with assisted patient positions and extension adjustments delivered with resisted patient positions.

The principles presented for assisted and resisted lateral flexion and flexion-extension side posture adjustments are potentially limited by the same biomechanical issues discussed previously relative to prone thoracic adjustments. Biomechanical research indicates that it is very unlikely adjustive contacts can establish effective tension with underlying bone, fascia, or muscle.²⁶⁹ In this context it seems unlikely that adjustive vectors directed superiorly or inferiorly will generate forces helpful in assisting in the production of lateral flexion or flexion-extension movements. It seems more plausible that attention to PP and factors that assist in deforming the spine in lateral flexion or flexion-extension would be potentially most effective.

Although the classification scheme of assisted and resisted patient positions is useful for contrasting different methods, it does create a possible void for those procedures in which both hands establish adjustive contacts and both deliver opposing adjustive thrusts. Counterthrust procedures, commonly applied during rotational spinal adjustments, do not conform to the strict definitions of assisted or resisted PP because these terms are defined relative to the delivery of one thrust, not two. In methods applying counterthrust techniques, both arms thrust; one arm establishes an assisted position and thrust as the other develops a resisted position and thrust. Based on the previous guidelines, they do not fit either category. To distinguish them from single-thrust patient positions, we suggest referring to them as counterthrust procedures (Figure 4-33).

Figure 4-33 A counterthrust procedure applied to treat a lumbar right rotation restriction.

Neutral Positioning

Neutral patient positions refer to circumstances in which the patient and articulations are left in a relatively neutral position during the delivery of an adjustive thrust. Any preadjustive reduction of articular slack is established through the doctor’s contacts without significant alterations in PP (Figure 4-34). Neutral positioning may be practical in some procedures such as prone spinal adjustive positions but impractical in others such as side posture rotational adjustments in which rotational leverage works to the doctor’s advantage.

Figure 4-34 Prone thoracic bilateral thenar transverse adjustment applied to induce segmental extension with neutral patient positioning.

Principles of Patient Positioning

To take advantage of the potential increased specificity and efficiency that modifications in PP offer, the doctor must be aware of the various options available and the principles that underlie them. Although one approach is not necessarily superior to the other, each method has unique attributes that may make it more appropriate in certain circumstances. To make the appropriate distinction and effectively deliver adjustments, the doctor needs a clear understanding of each method’s unique mechanical characteristics and differences. For example, a thrust delivered against the left L3 mammillary of a patient lying on the right side with shoulders in neutral may not have the same mechanical effect as in the patient whose shoulders are rotated toward the table into left rotation.

With the patient in the neutral position, the thrust against the left L3 mammillary is typically and traditionally applied to induce right rotation of L3 relative to L4 and the segments below (Figure 4-35). If the same thrust is delivered with the patient’s shoulders rotated into left rotation (resisted position), maximal tension and cavitation may be induced in left rotation at the ipsilateral articulations above (L2-3 and superior). If the doctor wishes to induce right rotation at the L3-4 motion segment with an adjustive technique that involves shoulder counter-rotation and a mammillary contact, the patient should be placed on the opposite side (left) with a mammillary contact established at L4 instead of L3 (Figure 4-36).

Figure 4-35 Assisted adjustment applied to induce right rotation of the L3-4 joint using an L3 mammillary contact and neutral patient position.

Figure 4-36 Resisted method applied to induce right rotation of the L3-4 joint. In this method, a contact is established on the right mammillary of L4, with the patient lying on the left side and the patient’s shoulders rotated posteriorly to induce right rotation.

Adjustive Specificity

Adjustive specificity describes the degree to which an adjustment is localized to a specific spinal region or joint. Historically the chiropractic profession has emphasized the value and application of methods believed to focus maximal effect in one joint. Application of the principles of PP and joint localization maximizes the potential for specific effects, but does not ensure that adjustive set-ups and thrusts will produce movement only at the desired level. The spine is a closed kinetic chain, making it highly unlikely that spinal movements can be induced at one joint at a time.^264,269 Any adjustive thrust will have some effect on the other components of the three-joint complex and the joints superior to and inferior to the contacted vertebrae.²⁶⁴

The adjustive objective is not to eliminate all adjacent movement but to stress the skills that increase the probability of producing regional and focused joint cavitation while minimizing movement and tension at unwanted spinal regions and adjacent joints.

Ross, Bereznick, and McGill²⁶⁹ conducted some groundbreaking work evaluating the level of applied adjustment and the level of induced joint cavitation. They were able to localize the level of thoracic and lumbar joint cavitations by fixing accelerometers to the skin over the spinal column and measuring the relative time it took for cavitation-induced vibrations to reach each accelerometer. Lumbar adjustments produced multiple levels of cavitation in most cases (2 to 6). The average cavitation site was 5.29 cm off the target level (at least one vertebra away) with a range of 0 to 14 cm. In the thoracic spine, the average cavitation site was 3.5 cm off the target site, with a range of 0 to 0.95. Their research indicates that the tested procedures did not produce the frequency of targeted joint-level joint cavitations desired. Lumbar SMT was accurate approximately half the time. However, because lumbar adjustments were associated with multiple cavitations, at least one cavitation also typically emanated from the targeted joint. In the thoracic spine, SMT appears to the more accurate. Other studies evaluating cervical rotational adjustments and side posture lumbar and SI adjustments also indicate less precision in producing cavitations to side or level to targeted joint.^267,268

Research evaluating HVLA adjustive specificity depends on the chiropractor’s initial judgment of which joint is being targeted. This depends on the accuracy of the segmental contacts, the methods the chiropractor applies, and the biomechanical assumptions he or she has about the applied adjustment. The chiropractic profession has a history of assuming that adjustive contacts can be focused to one vertebra. It is also common to assume that the joint below the level of vertebral contact is the joint being targeted for treatment (adjusted). There are some presumptions in this model that seem improbable. First, it is unlikely that surface adjustive contacts can be precise enough to contact just one vertebra. In addition, surface contacts do not appear capable of hooking or binding to underline vertebra and individual vertebra.³⁵ As mentioned previously, individual vertebra are part of a closed kinetic chain, making it highly improbable that chiropractic adjustments can induce movement of a single vertebra.^264,269

It is also unlikely that all adjustive methods are uniform in their biomechanical effects and equal in their ability to focus adjustive forces. It is possible that some methods are more likely to affect joints above the level of contact or equally affect joints on either side of the contact level. For example, side posture-resisted mammillary lumbar and SI adjustments have demonstrated cavitations commonly occurring at levels above the contacted level.^268,269 If chiropractors were to apply selected side posture lumbar methods with the intent of targeting joints above the level of adjustive contact, the specificity outcomes might be different. As our understanding of adjustive biomechanics deepens, our assumptions may evolve and our concepts regarding adjustive specificity may change. It seems likely that HVLA adjustments will be viewed more in the context of being region-specific (several joints) rather that single-level–specific.

The emerging biomechanical information concerning the characteristics of HVLA adjustments raises the important clinical question of whether single-level localization of adjustive forces or cavitation is materially associated with clinical outcomes. What we say we do and what we really do may be two very different things. Although this information should initiate reevaluation of our clinical assumptions and possibly change our clinical approach, it must also be emphasized that it is biomechanical research and not clinical research. Clinical research is necessary to answer questions of clinical effectiveness. Basic science research cannot answer the question of which adjustive procedures are the most effective. They can guide the research, but answers to the questions of clinical effectiveness must be addressed with patient-centered clinical research. The likelihood that adjustments have a regional rather than a precise single-level effect does not diminish the demonstrated clinical effectiveness of chiropractic adjustive therapy. It is possible that the principles we apply to achieve joint specificity have a clinical effect and advantage not related to level of precise joint cavitation. Furthermore, much of the research on adjusting specificity is based on measuring the sites of joint cavitation, and it is possible that the sites of cavitation do not always correlate to the site of the focused adjustive force. It is possible that adjustive forces are relatively focused and yet induce cavitation at multiple sites or adjacent sites because the targeted joint is more fixed than adjacent joints. Adjustive therapy rarely reaches maximal clinical effect with several adjustments and, over time, the applied adjustments may start to induce cavitation at the targeted joint as it becomes more mobile and capable of cavitating. Clinical research comparing different adjustive approaches is necessary to determine if there are clinical differences or advantages to one approach versus another.

Research evaluating the premise that “specific” HVLA adjustments produce better outcomes has not been conducted. This research question cannot be clinically addressed until biomechanical evidence exists demonstrating that there are adjustments capable of producing a specific targeted effect. Up to this point, the overwhelming majority of clinical outcomes research on chiropractic adjustive treatment of mechanical spine pain has been conducted using standard approaches and methods that assume specificity does matter. The adjustments and vectors selected were applied with this principle in mind. Although the elements associated with different adjustive methods and vectors may produce better results, it is uncertain if this is a product of a localized specific effect. The outcome may have nothing to do with how a joint is moved or the precision of the level of effect. There are a number of possible clinical effects, and some may be sensitive to the direction adjustive forces generated and not germane to how the spine deforms and moves.

Patient Positioning

PP denotes the placement of the patient before and during the delivery of an adjustment. It is an essential component of effective adjustive treatment. It is a learned skill, which is often overlooked during the instruction and learning of adjustive technique. Proper attention to PP is critical to patient comfort and protection. Patients placed in awkward positions are apprehensive and unlikely to relax. Improper selection can leave the doctor at a mechanical disadvantage and in a position of increased risk of injury. The doctor is also vulnerable to injury as he or she assists patients in their positioning.

Whenever possible, the doctor should allow the patient to position himself or herself. The patient should be instructed on how to comfortably assume or modify his or her position on an adjustive bench. If it is necessary to assist a patient, the doctor should ensure that his or her back is in a stable position and that the patient is close to his or her center of gravity. Whenever possible, the doctor should use the power available in his or her legs to assist with lifting, pushing, or pulling movements.

As previously described, PP is critical to the development of joint preadjustive tension, adjustive localization, and efficiency. Adjustive localization and efficiency are products of adjustive leverage, preadjustive tissue resistance, and joint locking. All these factors in turn depend on PP. Increased tissue resistance and locking of adjacent joints are developed by inducing opposing forces through non-neutral PP. By positioning the joint to be distracted at the apex of secondarily established curves, joint distraction is increased, and the dysfunctional joint and spinal section is established as the area to receive the most distractive forces (see Figure 4-29).

There is a variety of postures available, each offering its own advantages and disadvantages. The selection of a specific position is governed by the specific mechanical features of each patient position, the clinical condition being treated, and the specific preferences of the doctor and patient. The standard PP options include prone, supine, standing, sitting, knee-chest, and side posture position. Within each adjustive description presented in Chapters 5 and 6, the PP section describes and illustrates the mechanics of PP, the type of adjusting table used, the position of the table’s sectional pieces, and the appropriate use of any additional pillows or rolls. When indicated, the positioning of the extremities is described to ensure proper segmental tension.

Equipment Varieties and Management

The development of the equipment used by chiropractors and other practitioners of manipulation has taken place over time. Almost all procedures make use of a table or bench of some sort. The first chiropractic table had a flat, wooden surface atop ornate turned legs. It had no padding and no face opening, providing little comfort to the patient. It was not until 1943 that the first pad was designed for the adjusting table surface.⁴¹⁴ As new tables were developed, attention was paid to PP and the location of the clinician, providing for increased leverage and an advantageous adjacent stance.⁴¹⁵

A wide range of specialized adjusting tables and equipment is now available to enhance patient comfort and adjustive efficiency (Figure 4-37). Table options include flat benches, articulated tables, elevation tables, high-low (tilting) tables, knee-chest tables, manual and automatic distraction tables, and drop-piece tables. Some equipment is designed for the application of specific techniques, but most tables may be used with any of the common adjustive methods.

Figure 4-37 Specialized tables and equipment are used to enhance patient comfort and adjusting efficiency. A, Headrest pillow. B, Pelvic or Dutchman’s roll. C, Dorsal or pediatric block. D, Pelvic block. E, Sternal roll.

Regardless of the equipment used, some general habits should be developed. A doctor should select a table height advantageous to his or her physical attributes, use clean face paper on the head-piece of the adjusting table, and regularly apply a disinfectant to the table. The appropriate table height varies depending on the patient’s size, the doctor’s specific physical attributes, and the body area being adjusted. The average table height for pelvic, lumbar, and thoracic adjusting is the distance from the floor to the middle or superior aspect of the doctor’s knee. For supine cervical adjusting, a higher table may be selected to minimize stress on the doctor’s back.

Adjusting Bench

An adjusting bench (Figure 4-38) is a padded, nonarticulated, flat table with a face slot. It typically has a brachial cut out to allow comfortable placement of the patient’s shoulders in prone positions. A pelvic bench is very similar to the standard adjusting bench. It is usually wider than the articulated adjusting tables and lacks the brachial cut out commonly featured on other adjusting benches (see Figure 4-38). The pelvic bench is useful for side posture or supine adjustive methods, but is uncomfortable on patients’ shoulders in the prone position. The lack of articulated sections limits the ability of adjusting benches to modify patient positions and spinal postures. However, the use of wedges or cylindrical cushions are effective ways to achieve similar modifications in side posture or prone PP (Figure 4-39).

Figure 4-38 A, Typical adjusting bench with brachial cut out. B, Pelvic bench.

(Courtesy Lloyd Table Company, Lisbon, Iowa.)

Figure 4-39 Use of rolls and wedges to modify preadjustive patient positioning. A, Use of a cylindrical roll to induce lateral flexion toward the table (right lateral flexion). B, Use of a wedge to induce lateral flexion away from the table (left lateral flexion).

Articulated and Hydraulic Tables

An articulated table has movable head, thoracic, pelvic, and foot pieces to properly accommodate the patient in both the prone, side posture, and supine positions (Figure 4-40, A). High-low tables tilt from a vertical to a horizontal position, making it easier for a patient to get on and off the table (see Figure 4-40, B). Elevation tables have the ability to adjust to variable heights for different procedures as well as for different-sized doctors (see Figure 4-40, C).

Figure 4-40 Articulated and hydraulic tables. A, Stationary: (1) footrest, (2) pelvic section, (3) thoracic section, and (4) headrest. B, High-low with vertical to horizontal tilt. C, Elevation table to variable heights.

(Courtesy Lloyd Table Company, Lisbon, Iowa.)

When the patient is in the supine position on an articulating table, the headrest should be closed and elevated, and all other sections should be lowered to a level position. When performing cervical or upper thoracic adjusting, the headpiece may be slightly lowered. For prone positioning, to achieve a relaxed neutral posture, the footrest, pelvic, and thoracic sections should be elevated slightly, and the headrest should be lowered slightly.

Knee-Chest Table

The knee-chest table (Figure 4-41) gets its name from the position the patient assumes when on the table. The patient’s chest and face are supported by a head and chest piece and the patient’s knees rest on the padded base of the table. The chest piece should be situated so that the patient’s spine remains parallel to the floor.⁴¹⁶ The lower thoracic and lumbar spine are left in an unsupported and unrestricted position. It is this feature that provides the table’s most unique and potentially effective attribute. In this position the doctor has the mechanical advantage to easily develop full adjustive pretension, especially into extension. Consequently, this table may be most effective when applied in the treatment of lower thoracic and lumbar extension restrictions. It has also been suggested for those patients with large abdomens for whom the prone position is uncomfortable. Patients beyond the first trimester of pregnancy may be more comfortable and have less anxiety in the knee-chest position than prone when having P-A thrusts applied to the lower back.

Figure 4-41 Knee-chest table.

The attributes of the knee-chest table are also the features that contribute to its greatest inherent risk for hyperextension injuries. The risk of injury can be minimized by gently developing pretension and delivering shallow and nonrecoiling adjustive thrusts.

Although cervical, thoracic, and lumbar techniques can be performed in the knee-chest position, lower thoracic and lumbar dysfunctions are the areas more commonly adjusted in this position.

In a predicament, the knee-chest position can be approximated by having the patient kneel on a pillow at the head end of the traditional table with the face on the headrest and forearms on the armrests. The kneeling modification cannot duplicate the comfort and modifications available in a knee-chest table and should be used only in unusual circumstances.

Some doctors and patients are quite apprehensive about knee-chest positioning. In such circumstances, an articulated table may be used to achieve a similar position. This may be accomplished by slightly raising the pelvic piece and allowing the thoracic piece to drop away.

Drop Tables

Mechanical drop pieces are available on any or all of the sections of an articulated table (Figure 4-42). Drop mechanisms allow for the elevation of sectional pieces and the subsequent free fall of those sections when sufficient adjustive force is applied against the patient. The drop sections elevate a fixed amount (approximately 1/2 inch), but the degree of resistive tension varies. The amount of tension varies depending on the size of the patient, the extent of established preadjustive tension, and the force of the adjustive thrust. The degree of tension established in the drop mechanism should not be ascertained by thrusting against the patient. Tension should be determined by placing the patient on the table and thrusting against the table, not the patient.

Figure 4-42 Mechanical drop pieces on stationary articulated table: (1) pelvic section cocking lever, (2) lumbar section cocking lever, (3) thoracic section cocking lever, (4) cervical section cocking lever.

(Courtesy Lloyd Table Company, Lisbon, Iowa.)

Although no supporting clinical data exist, drop-piece mechanisms have been promoted as a technology for increasing adjustive efficiency. One position suggests that the degree of adjustive effort and force may be reduced because the drop of the table decreases the counter-resistance of the table and the patient. The other assertion is that the force of the adjustive thrust is enhanced by the counter-reactive force generated across the joint when adjustive thrusts are maintained through the impact of the drop piece.

Proponents of the first approach set low resistive tension on the drop mechanism and apply multiple light shallow recoil thrusts. The thrust is typically terminated before the drop mechanism has completely terminated its drop. In the second approach, resistive tension of the drop mechanism is increased to the point at which it can withstand the patient’s weight and additional loading applied from the doctor as he or she establishes pretension. The thrust is nonrecoil and maintained until the drop mechanism has terminated its drop. One of the potential disadvantages of the drop mechanism is the noise generated during the dropping action, which makes it difficult to perceive specific joint movement with the thrust.

Distraction Tables

The distraction table (Figure 4-43) offers a form of mechanical assistance for the application of manual therapy by having a fully movable pelvic section. The mobile pelvic piece provides a long-lever action that allows the lumbar spine to be positioned in or mobilized in flexion, extension, lateral flexion, or rotation, as well as the combined movement of circumduction.

Figure 4-43 Flexion distraction table.

(Courtesy Lloyd Table Company, Lisbon, Iowa.)

Technique procedures applied to mechanical distraction tables commonly use a manual vertebral contact and either a manual or motorized mobile pelvic section to create distraction. Distraction tables can be used to evaluate spinal mobility, mobilize spinal articulations, or assist the doctor in the application of thrust techniques. Most chiropractic table manufacturers (e.g., Leader, Lloyd, Zenith Cox, Chattanooga and Hill) make a table that provides continuous passive spinal distraction. This motion is produced as the motorized pelvic section of the table rhythmically depresses toward the floor and back to a neutral position. Additional tension in rotation and lateral flexion can be added by prepositioning the table into the desired direction of rotation or lateral flexion. Some tables also provide the added feature of linear axial distraction, focusing on the long axis of the body (Figure 4-44).

Figure 4-44 A, Flexion-distraction of L3–L4 motion segment. Patient is prone, with ankles strapped (optional). Clinician stands adjacent, in a lunge position (fencer stance), with the treating hand over the L3 spinous process and other hand on the handle of the pelvic section. Clinician depresses the pelvic section in a pumping action four to fire times while maintaining cephalic pressure on the spine, than repeats the four to fire pumps for one to two additional cycles, with a 30-second rest between. B, Diagrammatic representation of contact over the L3 spinous process, with the distractive vector shown.

When applying motion-assisted procedures for spinal joint dysfunction, the patient is typically positioned on the table so that the pelvis is on the pelvic section. All recumbent positions (prone, supine, and side posture) can be used. Because the use of linear distraction is considered an enhancement to the clinician’s physical application, virtually all recumbent techniques can be performed. There are, of course, specific considerations for each joint to be adjusted, such as the segmental contact point (SCP), vector of thrust, and clinician position. Doctors should take caution not to use excessive flexion with segmental distraction; excessive flexion has the potential to overstretch the posterior joints and posterior portion of the IVD.

Cervical Chair

The cervical chair (Figure 4-45) is a padded chair with a movable backrest. The backrest is adjusted so that the patient’s spine remains straight and the area to be adjusted lies just below the doctor’s forearm when the elbow is flexed to 90 degrees. The patient should sit with legs comfortably straightened and hands relaxed on the thighs. The cervical chair is used exclusively for adjustments applied to the cervical spine and upper thoracic spine.

Figure 4-45 Cervical chair.

Doctor Positioning

Chiropractic is a physically demanding profession associated with significant risk of occupational injury. Providing adjustive treatments subjects the doctor’s spine and upper extremities to numerous stressful postures and repetitive movements involving pushing, pulling, twisting, bending, and lifting. A study was undertaken to determine the prevalence and types of work-related injuries among a random sample of chiropractors and to identify factors associated with these injuries.⁴¹⁷ Many chiropractors (40.1%) reported experiencing injuries while working. Most of those injuries were classified as soft tissue injuries and occurred while either performing (66.7%) or positioning (11.1%) a patient for manipulation. The clinician’s body parts most commonly injured were the wrist, hand, and fingers (42.9%); shoulder (25.8%); and low back (24.6%). These injuries were most often related to side posture manipulation to the lumbar spine.⁴¹⁷ To avoid fatigue and injury, it is critical that DP involve sound body mechanics.

Good body mechanics start by selecting an appropriate table height to maintain a balanced and relaxed stance. If the table is too high, the doctor is at a mechanical disadvantage, unable to use the strength and leverage of his or her lower torso and legs. Instead, the doctor must rely on the strength of his or her upper body. Excessive dependence on the upper body can lead to underpowered adjustments and repetitive stress injuries to the upper extremities. If the table is too low, unnecessary stress may be applied to the doctor’s back as he or she attempts to accommodate the height of the table. Accommodations to lower tables should be made by bending at the knees and hips and abducting the thighs, not by slouching with the trunk (Figure 4-46).

Figure 4-46 A, Illustration of sound body mechanics and doctor accommodating the table by bending hips and widening his stance and maintaining neutral spinal posture. B, Example of poor body mechanics illustrating the doctor excessively flexing his spine and slouching over the patient.

Whenever possible, the doctor should establish postures that maintain symmetric and neutral joint positioning. Delivering thrusts through articulations positioned at end range or in close-packed positions places additional tension on the joint capsule and surrounding soft tissues. To perform safe and effective adjustments, the doctor needs to establish a stable kinetic chain through the spine and extremities. Core spinal stability and muscular bracing of the involved extremity joints are essential to the application of manual therapy and adjustments in particular. Common hazardous postures include excessive flexion and twisting of the trunk, excessive internal rotation and abduction of the shoulder, and unsupported extension of wrists.

Proper attention to DP applies equally to the cervical spine. Unfortunately, this region is frequently overlooked during discussion and presentations of adjustive technique. The doctor should maintain a stable neck position and avoid excessive cervical flexion to observe segmental contacts. Flexion of the neck encourages slouching of the upper back and excessive stress on the posterior soft tissues, and it weakens the stability of the neck and upper back (Figures 4-46 and 4-47).

Figure 4-47 A, Illustration of poor side-posture doctor positioning. The doctor has dropped his head and upper back into excessive flexion and has positioned his torso and center of gravity to superior and anterior to his contact point. This results in ineffective use of body weight and a stressful position on the doctor’s shoulder. B, Illustration of sound side-posture doctor positioning. The doctor’s center of gravity and body weight are effectively positioned to reinforce the thrusting vector and establish a neutral and stable position for his shoulder.

Another critical element in the efficient and effective use of DP is the orientation of the doctor’s center of gravity relative to the level of his or her adjustive contacts. The doctor’s center of gravity should be placed as close as possible to the SCP and positioned so that his or her body weight can effectively be used to establish preadjustive joint tension (see Figure 4-47). The effective use of body weight (mass) can minimize the effort expended in developing preadjustive tension and in delivering an adjustive thrust. If the mass of the adjustive thrust is increased, force can be increased during the adjustment without increasing the velocity.^{410,411,418,419} Placing his or her center of gravity behind the line of drive (LOD) allows the doctor to transfer appropriate body weight into the adjustive set-up and thrust. Using body weight and leg strength saves energy for the adjustive thrust and minimizes the workload on the upper extremities. This helps minimize muscular effort and fatigue. As much as possible, the doctor’s legs should bear the workload, thereby protecting his or her own back.

There are a number of named doctor stances used to describe the doctor’s position during the delivery of adjustments. They commonly denote the position of the doctor’s lower extremities and trunk in relation to the adjusting table and patient. Figure 4-48 illustrates two of the common stances; other modifications are discussed and illustrated in the regional sections on adjusting.

Figure 4-48 Two common doctor positions. A, Square stance: feet are parallel and aligned in the coronal plan. When accommodating a lower table, the doctor attempts to maintain a neutral spinal posture by widening the stance and bending at the knees and hips. B, Fencer’s stance (lunge position): legs are separated at shoulder width or greater and angled to the torso. The knees are bent, and the doctor’s back heel is off the floor. This position allows the doctor to efficiently transfer weight forward and inferior toward his front foot.

Contact Point

The CP designates which hand is the thrusting hand and the specific area of the hand that develops the focus of the adjusting contact. Attention to localizing a portion of the hand as the CP helps focus the adjustive force.^258,260 However, it is also possible for adjustive contacts to be established too firmly on or near a bony prominence (e.g., pisiform). Excessively bony or penetrating contacts can prevent an adjustment from succeeding by generating unnecessary splinting and resistance from the patient. Uncomfortable contacts in the thoracic and lumbar spine may be associated with postures involving excessive extension of the wrist or arching of the hand. Uncomfortable contacts in the neck are often encountered when the lateral and bony edge of the index finger, rather than the more padded palmar lateral surface of the finger, is used as the contact. The CP may be described anatomically or by a numbering convention developed to represent the common CPs (Figure 4-49). This text describes the contacts anatomically.

Figure 4-49 Contact points on the hand: (1) pisiform; (2) hypothenar; (3) metacarpal or knife-edge; (4) digital, used typically with the index and middle fingers; (5) distal interphalangeal; (6) proximal interphalangeal; (7) metacarpophalangeal or index; (8) web; (9) thumb; (10) thenar; (11) calcaneal; and (12) palmar.

Indifferent Hand

The indifferent hand (IH) specifies which hand is used to stabilize the patient, fixate adjacent joints, or reinforce the contact hand. The points of patient contact and forces necessary to maintain positioning and stabilization are also presented within this category. The IH is not always passive during the delivery of an adjustment. There are circumstances in which the IH moves from the realm of stabilization into either an assisting or counter-resisting thrust. In such circumstances, both extremities deliver an adjustive thrust. In the illustrations throughout the text, when thrusting forces are delineated from stabilization forces, an arrow is used to demonstrate adjustive vectors, and a triangle is used to demonstrate stabilization points (Figure 4-50).

Figure 4-50 Arrows indicate adjustive vectors; triangle indicates stabilization.

Segmental Contact Point

The SCP specifies anatomically where the adjustive contact or contacts are to be established on the patient. The SCPs are listed and described specifically in this chapter and in Chapters 5 and 6. When possible, they are illustrated in photographs or drawings. The SCPs are typically referenced as bony landmarks. This is intended to be illustrative and clarify the underlying focal point of the adjustive force (Figure 4-51).

Figure 4-51 Segmental contact points are bony landmarks located close to the joint(s) to be adjusted. In this illustration, segmental contacts are illustrated for a spinous push-pull adjustment. Bony landmarks are illustrative and clarify the focal area of contact. They are not meant to imply that contact points are limted to bony structures. Overlying and adjacent soft tissue strucures are obviously also contacted

Segmental contacts focused at specific bony landmarks cannot be established without contacting overlying or adjacent soft tissues. Adjustive contacts established at or near the level of the dysfunctional joint are referred to as short-lever (direct) adjustments. Adjustive contacts established at some distance from the level of the dysfunctional joint are referred to as long-lever (indirect) adjustments, and adjustments that combine short- and long-lever contacts are referred to as semidirect adjustments.

In spinal adjusting, a single thrusting contact is conventionally taken on the superior vertebrae of the dysfunctional motion segment. Methods that incorporate thrusting contacts on the lower vertebra or both vertebrae of the involved motion segment are also effective and in common use. Contacts established on the lower vertebra of the dysfunctional motion segment establish a resisted method; contacts on the superior vertebra establish an assisted method; and contacts established on adjacent vertebrae establish a counter-resisted method (see Figure 4-51). Assisted and resisted methods are summarized in Table 4-3.

TABLE 4-3 Comparison of Assisted, Resisted, and Counter-Resisted Spinal Adjustive Methods*

Hand contacts established near the level of desired adjustment are assumed to improve the specificity of the adjustment, and research indicates chiropractors are capable of developing an area of focused force within the broader area of their contact.^260,261 Whether specific short-lever contacts are universally associated with more specific successful joint cavitations is in doubt. It appears that short-lever prone thoracic adjustments do induce relatively specific effects as compared with side posture lumbar adjustments.²⁶⁹ However, research indicates that employing a short-lever contact and thrust in side posture lumbar adjustments works against the doctor’s ability to induce joint cavitation.⁴²⁰ The authors conclude that “successful generation of cavitation during side posture lumbar manipulation requires emphasizing forces to areas on a patient remote from the spine such as the pelvis and/or lateral thigh.”⁴²⁰ Although focused short-lever contacts may produce a more local force in the spine, it is apparent that additional added points of leverage are necessary to induce sufficient lumbar axial rotation and cavitation.

If a local focused force is desired, then errors in the placement of adjustive contacts may lead to the localization of adjustive forces at undesired segmental levels. However, this does not imply that it is always desirable or possible to establish a segmental contact over a single vertebra. What is important is the ability to locate contacts in a manner that focuses the adjustive forces and desired movements in the joints or region to be adjusted.

A number of the adjusting methods used by chiropractors involve close physical contact between the patient and the doctor. The nature of this contact, if not properly explained, can lead to misunderstandings and complaints of inappropriate touching. It is paramount that doctors explain the procedures they are going to use and receive permission to proceed before applying treatment. Explanation of procedures is essential, followed by the questions “Do you understand?” and “Is it okay?” These give the patient an opportunity to question or refuse treatment.

The chiropractic educational process demands the development of highly perfected manual palpation and therapy skills. Students learn these skills by voluntarily practicing on each other. In the process there tends to be a desensitization to touch, disrobing, examination, and treatment procedures through familiarity. However, naïve patients will not feel that familiarity. Therefore, it is important to be attentive to procedures that chiropractors may take for granted but that patients may look on in an entirely different manner. Casual and unconscious contact with sensitive body parts may go unnoticed by the practitioner but not by the patient. Doctors must be mindful and aware of the potential to inadvertently touch sensitive areas during the application of adjustive procedures.

Methods to be especially conscious of include supine thoracic adjustments and side posture lumbar or pelvic adjustments. During supine adjustments, unwanted contact between the doctor and the breasts of the female patient or between the breasts of the female doctor and the patient can become an issue. This can be minimized by placing a small pillow or roll between the patient’s breasts and arms or between the doctor and the patient’s arms (Figure 4-52). In side posture adjustments, inadvertent contact between the doctor’s genitals and the patient’s thigh can occur. This can easily be avoided if the doctor is simply aware of this potential and positions himself or herself accordingly.

Figure 4-52 A, Supine thoracic adjustment in the midthoracic spine illustrating the use of a small roll to pad the patient’s anterior chest. B, Use of a rectangular pillow to minimize contact between the doctor’s anterior chest and patient.

Any examination or treatment procedure performed on a member of the opposite sex that involves exposure or contact with the genitals or rectal region should be performed only when an assistant is in the room. The internal mobilization or manipulation of the coccyx is an example of a procedure for which this is warranted.

Tissue Pull

Superficial tissue traction (pull) is typically applied during the establishment of an adjustive contact. Proper tissue pulls are necessary to ensure that a firm contact is established before a thrust is delivered. If this is not taken into consideration, the CP may slip during the thrust and dissipate the adjustive force into superficial soft tissues and decrease the doctor’s ability to impart a force to the spine. The IH may be used to draw the tissue slack as the CP is established. Tissue pulls are commonly initiated in the direction of the adjustive thrust and, as such, will not be listed separately. Prone patient P-A thrusts are a common exception. In this circumstance the direction of tissue pull is often irrelevant. Tissue pulls up or down the spine are appropriate and are applied to prevent the doctor’s contacts from sliding. The direction of tissue pull is based on the region of the spine and the doctor’s preference.

Vector (Line of Drive)

The vector, or LOD, indicates the direction of the adjustive force (thrust). Historically, the profession has described the direction of adjustive thrusts in anatomic terms. For example, an adjustive vector delivered with a patient in the prone position with a ventral and cephalic orientation is described as a P-A vector and an I-S vector. This text adheres to this standard and illustrates the direction of adjustive vectors in drawings and pictures with the aid of solid arrows (see Figure 4-50).

Attention to alignment is necessary to ensure anatomically sound, specific, and efficient adjustments. To produce joint distraction and movement without producing injury, the doctor must have knowledge of the functional anatomy and kinematics and match the adjustive vector accordingly. Misguided Vs may lead to unwanted joint compression, joint tension, ineffective dissipation of forces, or joint cavitation at undesired levels. A single adjustive thrust and cavitation may not free multiple directions of joint restriction.⁴²¹ Therefore, at times, a single articulation may be adjusted in multiple directions, with different adjustive Vs applied for each adjustive thrust.

Thrust

The adjustive thrust can be defined as the application of a controlled directional force, the delivery of which effects an adjustment. The adjustive vector describes the direction of applied force; the adjustive thrust refers to the production and implementation of that force.

The adjustive force is typically generated through a combination of the practitioner’s muscular effort and body weight transfer. The chiropractic adjustive thrust is a ballistic HVLA force designed to induce joint distraction and cavitation without exceeding the limits of anatomic joint motion.

The thrust is the adjustive component, which, if delivered incorrectly, carries the greatest risk of patient injury. Adjustive thrusts performed with too much force, depth, or pretension carry the risk of exceeding the limits of physiologic joint movement. It takes extensive training and time to perfect adjustive skills and the ability to sense and control the appropriate depth and force of an adjustive thrust. This skill cannot be effectively learned over the course of a few months or by attending weekend courses. Chiropractors have devoted years of training to refine their manipulative skills, and in the hands of skilled practitioners, manipulation carries a very low rate of complication.

There is a critical adjustive force that must be supplied by the doctor to bring a synovial joint to cavitation and influence its structural and functional relationships. The development of this force depends on a multitude of factors, including stiffness and elasticity of the joint and patient, the proportion of impacting energy entering the joint and patient, and the amount of joint distraction at which cavitation takes place. These parameters are governed by numerous properties of the patient, the doctor, the joint, and the adjustive process.³³⁵

The average adjustive force produced by spinal manipulation can be expressed in terms of the impact kinetic energy (mass and velocity) of the clinician and the combined mechanical resistance to deformation (stiffness and elasticity) of both clinician and patient.³⁴³ This necessitates acquiring reflex contractile speed and stabilizing contractions of specific muscles (frequently the triceps and pectorals), as well as having enough applied leverage and body mass. It is thought that mechanical assistance can be used to augment these physical attributes.

The advantage of leverage and use of the doctor’s body mass to induce lumbar joint cavitation is illustrated by recent research that demonstrates that dropping the doctor’s body weight through CPs established on the patient’s posterior pelvis or lateral thigh is necessary to induce lumbar cavitation.⁴²⁰ The authors concluded that “successful generation of cavitation during side posture lumbar manipulation requires emphasizing forces to areas on a patient remote from the spine such as the pelvis and/or lateral thigh.”⁴²⁰

The use of preadjustive tension can limit the dissipation of thrust energy that occurs because of damping forces. Preloading the joint limits further motion during the thrust so that force and energy are not lost to other areas.⁴¹⁰ Use of preliminary distraction means that the thrust has to supply only the remainder of the force necessary for joint cavitation, diminishing the physical requirements of the clinician. Therefore, the resulting enhanced efficiency facilitates a more gentle adjustment⁴¹⁹ with less exertion by the clinician.

If preadjustive tension or countertension can be produced through a mechanical device (adjusting table), theoretically even less force, speed, and energy will be required from the clinician. There are manual and motorized mechanical assistance components to adjusting tables. One such modification is the drop-section mechanism, representing a form of manual mechanical assistance. Another modification is a moving table section, representing a form of motorized mechanical assistance.

Adjustive thrusts may be delivered in a variety of ways. Some of the common distinguishing attributes include the physical means the doctor uses to deliver the thrust (e.g., arm-centered thrust vs. body-centered thrust) (Figure 4-53), the positioning of the joint when the thrust is delivered (e.g., in a neutral position compared with a point near the joint’s end ROM), and whether the adjustment is delivered with or without an active recoil⁴²² or whether the thrust is delivered with a postpretension pause or nonpause.

Figure 4-53 A, Illustration of recoil thrust. The body is held in stationary position, and thrust is generated by rapid acceleration at the elbows. The thrust is very shallow, with a quick termination, followed by an elastic recoil as full elbow extension is reached. B, Illustration of shoulder-drop thrust. The body is held in a stationary position, and the thrust is generated through a quick depression (elongation) at the doctor’s shoulder. The doctor maintains a light contact after terminating the thrust to dampen reverberations generated by the shoulder thrust. C, Illustration of body-drop thrust. The thrust is generated by acceleration of the doctor’s body weight through the adjustive contact. Transfer of body weight is generated by transferring weight from the doctor’s heels toward the front of his feet. This is usually accomplished by inducing slight ankle dorsiflexion, knee flexion, and flexion of the trunk. Body-drop thrusts are often combined with shoulder-drop thrusts to produce a more rapid and rigid thrust and kinetic chain.

Adjustive thrusts are not always manually delivered. A number of mechanical thrust devices have been developed. Some are designed for hand-held application (Figure 4-54), and others are simply positioned by the doctor and do not require the doctor to hold the instrument during the application of the thrust. Whether these devices produce the same physical and therapeutic effects as manual thrust techniques remains untested.

Figure 4-54 Prone manually assisted instrument (activator) adjustment illustrating sacroiliac (SI) joint application.

Impulse Thrust (Dynamic Thrust)

Impulse thrusts also use an HVLA force but are performed in a manner to minimize the normal elastic recoil that occurs after the quick cessation of an adjustive thrust. This is accomplished by maintaining mild pressure and contact with the surface for a short time after the termination of the adjustive thrust. The adjustive velocity may be varied, with either a slow or fast termination.

Impulse thrusts are most commonly delivered with the affected joint prestressed to reduce articular slack, but they should not be delivered with the joint stressed beyond its elastic limits. Impulse thrusts may be primarily arm centered or body centered, or their forces may be combined through the doctor’s arms and body.

All adjustive thrusts involve relatively high-velocity forces, but vary in the degree of associated body weight coupled with the adjustment. When less mass and total force are desired, the thrust is typically delivered only through the upper extremities. This is commonly the case in the adjustive treatment of the cervical spine and small extremity joints and in the treatment of pediatric, geriatric, or frail patients.

During the delivery of arm-centered thrusts, the doctor’s torso is stationary. The adjustive force is produced by the initiation of pushing, pulling, or rotation forces generated through the doctor’s forearms, elbows, and shoulders (see Figure 4-53). Arm-centered thrusts may be delivered through one arm or both arms. When one arm is the focus of the adjustive force, the other arm (the IH) either reinforces the contact or stabilizes the patient at another site. When used for stabilization, the IH maintains the patient in a neutral position or induces positions or forces that assist or resist the adjustive force (Figure 4-55).

Figure 4-55 A, Prone unilateral hypothenar transverse push adjustment delivered to induce right rotation. B, Prone crossed bilateral hypothenar transverse counterthrust adjustment delivered to induce right rotation.

When more total force is desired, the doctor transfers additional weight from the trunk or pelvis into the adjustive thrust. In body-centered (body-drop) thrusts, the majority of the adjustive force is generated by propelling the weight of the doctor’s trunk through the adjustive contacts (see Figure 4-53). This is accomplished with a quick and shallow flexion of the doctor’s trunk and lower extremities, along with a simultaneous contraction of the abdominal muscles and diaphragm. Schafer and Faye⁴²¹ have described the abdominal and diaphragmatic contractions as a process similar to the event that occurs during sneezing.

During the delivery of body-drop thrust, it is critical that the upper extremities remain rigid. If the joints of the upper extremity give way during the delivery of an adjustive thrust, the adjustive force is dissipated. Rigidity is ensured by locking the upper extremity joints and by combining the trunk acceleration with a simultaneous shallow thrust through the upper extremities.

Adjustments delivered with prone patient position may be delivered as pure body-drop procedures, pure arm-centered thrusts, or combined body drop–arm thrusts. Lumbar and pelvic side posture adjustments, which commonly demand more total force, invariably involve the transfer of trunk and pelvic weight along with a simultaneous arm thrust. To transfer the additional body mass to the patient, the doctor typically establishes additional contacts along the lateral hip or pelvis of the patient (Figure 4-56, A).

Figure 4-56 A, Side-posture resisted mammillary push adjustment with a thigh-to-thigh contact delivered to induce left rotation. B, Side-posture resisted spinous pull adjustment with a shin-to-knee contact delivered to induce right rotation.

A common technique variation in side posture lumbar adjusting couples a segmental contact with a reinforcing thrust through the doctor’s leg. Instead of the doctor’s weight resting against the patient’s upper thigh and hip, a contact on the patient’s knee is established. The impulse is then delivered by combining a pulling impulse through the arm with a quick extension of the doctor’s knee (see Figure 4-56, B). In this method, the leg provides the additional leverage and force instead of the doctor’s body weight.

Assisted, Resisted, and Counter-Resisted (Thrust) Methods

Assisted methods incorporate contacts established on and above the superior vertebrae of the dysfunctional motion segment. They are applied to focus the adjustive force in the joints inferior to the level of segmental contacts. Assisted patient positions are incorporated if modifications in neutral PP are used. The adjustive Vs are directed to produce movement of the superior vertebra relative to the inferior vertebrae in the direction of joint restriction (direction opposite malposition).

The adjustive thrust may be focused through a single segmental contact or incorporate additional contacts and reinforcing thrusts applied at levels superior to the segmental contact. Figure 4-57 illustrates the application of a short-lever method incorporating a single level of focused thrust. Figure 4-58 illustrates a method incorporating a segmental contact coupled with a superior hand contact established on the patient’s ipsilateral forearm. In this example additional leverage is provided through the superior contact, and both arms thrust to induce movement in the direction of joint restriction.

Figure 4-57 Prone unilateral hypothenar transverse push applied to treat a right rotation restriction at T5-6. Segmental contact is established over the left T5 transverse process.

Figure 4-58 An example of an assisted sitting thoracic adjustment applied in the treatment of a left rotation restriction at T5-6. This technique incorporates a segmental contact on the transverse process of the superior vertebrae of the dysfunction motion segment with an assisting hand and thrusting contact established on the patient’s ipsilateral forearm.

Resisted methods incorporate segmental contacts established on and below the inferior vertebrae of the dysfunctional motion segment. They are applied to focus the adjustive effect in the joints superior to the level of segmental contacts. Resisted patient positions are incorporated if modifications in neutral PP are used. The adjustive Vs are directed to produce movement of the joint in the direction of restriction (direction opposite malposition). This is accomplished by moving motion segments inferior to the dysfunctional joint in the direction opposite the joint restriction. Research by Cramer and colleagues²⁶⁶ has demonstrated that side posture-resisted lumbar mammillary push adjustments induce positional and postadjusting gapping in the articulations superior to the level of contact.

The adjustive thrust may be focused through a single segmental contact, but commonly incorporates additional contacts and reinforcing thrusts applied at levels inferior to the segmental contact. Figure 4-59 illustrates the application of a short-lever method incorporating a single level of focused thrust (very uncommon). Figure 4-60 illustrates a method incorporating a segmental contact coupled with a distal contact established inferior to the level of segmental contact. The vertebral segments superior to the contact are rotated in the direction of restriction, opposite the direction of the thrust, and preadjustive tension is localized to the articulations superior to the contact. Additional leverage is provided through the inferior contact established on the patient’s leg. At tension, a thrust is delivered through both contacts to induce cavitation and movement in the direction of restriction.

Figure 4-59 Prone thoracic resisted unilateral hypothenar transverse push adjustment applied to induce right rotation at the T4-5 joint. Adjustment is applied in the treatment of a right rotation restriction or a left rotation malposition at T4-5. Segmental contact is established over the right T5 transverse process.

Figure 4-60 An example of a resisted side-posture adjustment applied in the treatment of a right rotation restriction at L4-5. This technique incorporates a segmental contact on the spinous process of the inferior vertebrae of the dysfunction motion segment with a resisted leg contact on the patient’s leg.

Counter-resisted methods incorporate segmental contacts established on both sides of the joint or region to be adjusted. Pretension and the adjustive thrusts are directed in opposing directions to maximize distraction across a given area and joint. The adjustive thrust may be focused through segmental contacts or may incorporate additional contacts and reinforcing thrusts applied at levels superior to and inferior to the segmental contacts. In the spine this procedure is most commonly applied in the treatment of rotational dysfunction. Figure 4-61 illustrates the application of a short-lever method incorporating a neutral patient position. Figure 4-62 illustrates a method incorporating a segmental contact established on adjacent spinous processes, coupled with additional points of leverage. The adjustive thrust is applied in opposing directions through the segmental contacts and contacts established on the patient’s forearm and lateral pelvis.

Figure 4-61 Prone thoracic crossed bilateral hypothenar transverse counterthrust technique applied to induce left rotation at T6-7. Adjustment is applied in the treatment of a left rotation restriction or a right rotation malposition at T6-7. Segmental contacts are established over the right T6 transverse process and the left T7 transverse process.

Figure 4-62 Side-posture lumbar spinous push-pull applied to induce right rotation at the L3-4 articulation. Adjustment is applied in the treatment of a right rotation restriction or a left rotation malposition at L3-L4.

Although for didactic purposes it is useful to separate the adjustive thrust into its component parts, it can be misleading and distracting to the student who is trying to perfect the art of adjusting. Instead of focusing on the act as a singular event, the novice often tries to develop a thrust by mentally producing each event separately, resulting in an unfocused, uncoordinated thrust. The thrust, developed through repetitive practice, is a fluid, habitual procedure, not a series of segmented and separated steps. Box 4-16 lists some basic rules and principles for the effective and safe use of chiropractic adjustive technique.

BOX 4-16 Basic Rules for Effective Adjustive Technique

1. Select the most efficient and specific technique for the primary problem.

2. Position the patient in a balanced, relaxed, and mechanically efficient position.

3. The doctor should be relaxed and balanced with his or her center of gravity as close to the contact points as possible.

4. The contacts should be taken correctly and specifically.

5. Articular and soft tissue slack should be removed before thrusting.

6. Any minor alterations in position or tension should be made before thrusting.

7. Visualize the structures contacted and the direction of your adjustive vector.

8. Guard against the loss of established preadjustive joint tension. Do not noticeably back off before thrusting.

9. The thrust must be delivered with optimum velocity and appropriate depth.

10. Maintain stability and rigidity through the upper extremities during the delivery of the adjustive thrust.

11. During the thrust, use additional body weight if appropriate (body-drop). This is especially important in side-posture pelvic and lumbar adjusting, in which most of the adjustive force is derived from a body-drop thrust.

12. It is just as important to know when not to adjust as to know when and where to adjust.

13. Primo est non nocere—First, do no harm.

Drop-Section Mechanical Assistance

The first drop headpiece was introduced in chiropractic in 1952; B.J. Palmer stated that the principle behind the drop head piece constituted one of the greatest advancements in chiropractic.⁴²² Dr. J. Clay Thompson developed adjusting tables with cervical, thoracolumbar, and pelvic drop-piece sections in 1957, with the stated intention of providing a mechanical advantage for producing an HVLA adjustment with minimal discomfort for the patient.

Dr. Thompson believed drop-table procedures used Newton’s laws of motion to develop a certain amount of kinetic energy not seen in other forms of chiropractic technique. He theorized that the mechanical drop mechanism reduced the muscular effort needed by the clinician to produce the adjustive thrust. Therefore, the muscular strength of the clinician is not a limitation in providing manipulative therapy. Moreover, it is thought that when the drop piece releases, the amount of force exerted on the joints is minimal and therefore more comfortable for the patient. Finally, because the patient cannot resist the effects of the drop sections, it is reasoned that joint movements are more easily achieved.

Another theory proposes that the mechanical advantage gained by drop pieces is the shear reactive force that is generated at the termination of the drop. In this model the doctor sets more resistance in the drop mechanism and maintains adjustive force through the termination of the drop. There are, however, no studies to support either of these contentions.⁴²³

The Thompson table, and all drop tables, feature mechanical drop sections that drop a small distance on the delivery of a chiropractic thrust. The amount of resistance to pressure can be independently adjusted in each drop section. The patient is positioned on the table with the segment to be adjusted on a drop section with the tension properly set so that the patient’s body weight will not cause the section to drop (Box 4-17). When additional force is applied and the resistance of the drop section is overcome, the section drops and terminates its fall at a preset short distance.

Tables equipped with drop-section mechanisms have levers used to set each drop section in a “cocked-up” position. Some tables use a pneumatic cocking mechanism that is operated by a foot pedal, freeing the clinician’s hands from having to locate the levers. There are, of course, specific considerations for each joint to be adjusted, such as the SCP, vector of thrust, and clinician position. Specific procedures for each joint are described and demonstrated in detail in other works.⁴²⁴

Motorized Mechanical Assistance (Motion-Assisted Adjusting)

Motorized mechanical traction is provided by adjusting tables that provide continuous, rhythmic mechanical movement and distraction of the articulations to be mobilized or adjusted. Assisted mechanical distraction of spinal joints began with manually operated tables (McManis table)⁴²⁵ and progressed to include tables that provide motorized movement and distraction (Cox, Leander, and Hill). The fundamental principle and potential advantage of motion-assisted adjusting is the delivery of an adjustive thrust across a joint that has been mechanically distracted. The preadjustive tension established at the involved joints is established through the movements of the motorized table, freeing the doctor to conserve energy and focus on his or her adjustive contacts, sense of joint tension, and adjustive thrust.

In addition, traction tables are assumed to induce some additional long-axis distraction in the joint to which it is applied. The movement of long-axis distraction (y-axis translation) in spinal segments is not specifically addressed with many manipulative approaches. In the extremity joints, considerable attention and significance are placed on the evaluation and manual treatment for loss of long-axis distraction and its role in producing joint dysfunction.^42,426

Using a motorized distraction table may increase the element of long-axis distraction during manipulative treatments. Because motion-assisted palpation and treatment may also be performed with the patient recumbent, many different patient presentations (e.g., acute, chronic, aged, and obese) may be accommodated by this technique.

Most mobilization and adjustive techniques are applicable to motorized distraction tables. Mechanized distraction tables simply provide additional preadjustive tension and joint distraction. This has the potential to decrease the amount of muscular effort and force the doctor must generate to preload a joint before delivering an adjustive thrust. When adjustive procedures are applied, segmental contacts and tissue pulls are established in the same fashion as they would be for an adjustment delivered on any adjusting table. The adjustive thrust is typically delivered at full excursion of the mechanized table as the doctor senses maximal distraction of the joint.

The fundamental components of motion-assisted adjusting can be illustrated with prone thoracic or lumbar adjustments. In the prone positioning, the adjustive thrust is delivered as the caudal section stretches. The intermittent distraction opens the involved motion segment, facilitating the adjustment and reducing the required force needed for the thrust. In this tractive state the thrust can also be delivered repeatedly with less force being produced by the clinician. The table is in motion, creating distraction of the patient with the force of the treating hands directed primarily headward. A pull-push effect is thus created along the long axis (y-axis) of the body, facilitating the mobilization of the joint and the restoration of long-axis distraction movement (Figure 4-63). In addition, lateral flexion can be induced using a roll for producing prestress and a pulling vector while the table creates long axis distraction (y-axis) movement (Figure 4-63).

Figure 4-63 A, Diagrammatic representation of the contact point for a left lateral flexion restriction, right lateral flexion malposition, L4-L5. B, Motion-assisted thrust technique for intersegmental lateral flexion dysfunction (left lateral flexion restriction, right lateral flexion malposition, L4-L5).

The science of chiropractic has made significant strides in the investigation of the art of chiropractic. The profession now has a body of credible research to document some of what it claims. Advocates of manipulative therapy in the healing arts of chiropractic, medicine, osteopathy, and physical therapy have independently concluded that the HVLA thrust is an important clinical intervention for the treatment of dysfunctional conditions associated with the NMS system. The acceptance of spinal manipulation by other health care professions, industries, and the general population continues to grow despite controversies that still exist in clinical practice. The controlled delivery of the adjustive thrust demands much discipline and skill. An adjustive thrust delivered incorrectly carries the risk of patient injury. It takes extensive training and time to perfect adjustive skills and the ability to sense and control the appropriate depth and force of an adjustive thrust. This skill cannot be effectively learned over the course of a few months or by attending weekend courses. The authors hope that this chapter helps advance the development and perfection of adjustive psychomotor knowledge and skills necessary for the delivery of safe and effective chiropractic adjustments.