The Lameness Examination: Which Gait Is Best?

The trot is the most useful gait to determine the location of the lame limb or limbs. Forelimb lameness in particular is difficult to observe at the pace, especially in horses that are led in hand. Lame trotters may pace, supporting the supposition that the pace is an easier gait in a lame STB. I have seen horses with severe forelimb lameness at the trot that looked barely lame when pacing.

Comparing Lameness Seen at the Walk and Trot

Although lameness score should be determined when trotting a horse (see later), it is useful to compare gait deficits at the walk and trot. In horses with forelimb lameness, an exaggerated head and neck nod may be observed while walking horses with upper limb lameness (genuine shoulder region pain, for instance), and, in fact, head and neck excursion may be more pronounced than that seen while the horse is trotting. Some horses may exhibit odd gait deficits while walking, but deficits may abate at the trot. Horses with rare upper forelimb pain from rib fractures or anomalies may manifest abduction of the forelimb during protraction at the walk but not the trot. The stance phase of the stride is relatively longer at the walk than at the trot. The deep digital flexor tendon and the collateral ligaments of the distal interphalangeal joint are stressed maximally with extension of the distal interphalangeal joint. Thus with severe injuries of either structure lameness may be more severe at the walk than at the trot because of greater extension of the distal interphalangeal joint associated with the relatively long stance duration.⁵ Horses with hindlimb lameness characterized by a shortened caudal phase of the stride at the walk but shortened cranial phase at the trot often have upper limb lameness, such as that caused by pelvic fractures or osteoarthritis of the coxofemoral joint or from severe pain originating from the foot. In general, horses that have limb flight characteristics that differ between walk and trot should be evaluated carefully because in my experience they often have bona fide pain originating from the upper limb or are affected with an unusual mechanical or neuromuscular deficit.

Relevance of Lameness at a Trot in Hand

Is lameness seen at a trot in hand the same lameness that compromises performance at speed? Is the lameness seen at a trot in hand in a jumping horse the same problem that causes the horse to refuse fences? The answer is usually, but not invariably, yes. For instance, I have seen many STBs show subtle unilateral hindlimb lameness at a trot in hand, but when the horse was later examined at the track and hooked to a cart, pronounced contralateral hindlimb lameness was noted. Differences include the track surface, the act of pulling a cart, the additional weight of the driver, and a faster gait. Lameness often is evaluated on a smooth hard surface useful in exacerbating even subtle problems, but most horses perform on softer surfaces, when other problems may be apparent. More than one lameness problem may exist—one evident at a trot in hand and another while the horse is ridden or driven. Horses can show lameness from one problem when trotted in a straight line but lameness from an entirely different problem while being trotted in a circle. The answer to the first question is complex because performance itself entails the inextricably intertwined relationship between horse and rider or driver and the possible presence of compensatory and coexistent pain. Ideally, to evaluate the role of lameness on poor performance, horses would be evaluated at the speed, at the gait, and in the manner in which they perform, conditions that usually are not always possible to reproduce.

Horse Temperament and Lameness Examination

Safety of the handler, observers, and the horse must always be considered throughout a lameness examination, and with a difficult horse the examination may need to be modified, especially on cold, windy days. In some female horses and geldings, judicious use of the tranquilizer acetylpromazine (0.02 to 0.04 mg/kg intravenously [IV]) permits continuation of the examination. I avoid use of this tranquilizer in stallions, although the possibility of paraphimosis is remote. Low doses of sedatives such as xylazine can be used (0.15 to 0.30 mg/kg IV) in stallions or other horses but can produce mild ataxia. Detomidine may be a better choice than xylazine because the drug lasts longer, thus allowing diagnostic analgesic procedures to be performed.⁵

I try to avoid using tranquilization and sedation, although some clinicians use them frequently and report that lameness in most horses may be more pronounced and easier to observe. Mild muscle relaxation may reduce the tendency of the horse to guard the lame leg. Mild analgesic effects of sedatives may mask mild pain, and in racehorses care must be taken to avoid use of drugs that may cause a positive result in a drug screen. In big moving, exuberant Warmblood horses, especially dressage horses (particularly stallions), sedation may be essential to accurately assess lameness.⁵

Leading the Horse during Lameness Examination

The horse must be led with a loose lead shank so that it can move the head and neck freely. It is impossible to see a head nod in a fractious or excited horse that is held tightly. Use of a chain lead shank over the nose facilitates control but is resented by some horses, and use of a bridle with a lunge line attached may be preferable.⁵

Horses should move at a consistent speed, not too fast and not too slow. A lazy horse may need encouragement with a whip. Constantly changing speed can make assessment of lameness difficult, but occasionally, assessing a horse during deceleration may reveal useful information about the existence of subtle lameness.⁵ A horse may have to be trotted up and down many times. It is sometimes useful for the examiner to lead the horse to assess subtle forelimb lameness, because gait abnormalities may become more obvious.

Surface Characteristics and Lameness Examination

The horse should be examined on a smooth, flat surface. I prefer a hard surface, such as pavement or concrete that creates maximal concussion and may exacerbate subtle lameness. However, the clinical relevance of mild lameness seen on hard surfaces, especially on turns, should not be overinterpreted. Many horses that are actively competing successfully show mild lameness on hard surfaces; it is important to understand that the horse does not perform on a surface of pavement, and foot strike patterns and gait could be much improved if the horse performs on firm but forgiving surfaces. Crushed rock, cobblestone, deep sand, or undulating grassy areas and potentially dangerous slippery surfaces should be avoided.

It is important that the surface be nonslip because some horses appear to lack confidence while moving on hard surfaces and alter the gait. In these situations, horses may shorten the stride for protection rather than from lameness.⁵ Horses with studs or caulks on the shoes may develop induced lameness unrelated to the baseline lameness when trotting on hard surfaces.⁵

Ideally the gait on hard and soft surfaces should be compared, to help differentiate soft tissue from bony problems. Horses with foot pain usually perform worse on a hard surface. Lameness from soft tissue injuries, such as suspensory desmitis or tendonitis, tends to be worse on soft or deep ground. To evaluate lameness during transition from a hard to a soft surface and vice versa, a horse can be examined while circling on a lunge line in an area where both surfaces coexist side by side.⁵ Care must be taken to prevent the horse from slipping during this examination.

Compensatory Lameness

Compensatory (secondary or complementary) lameness results from overloading of the other limbs as a result of a primary lameness. It must be differentiated from the stride-to-stride compensation by a horse to avoid interference injury because of a gait deficit, or lameness, or to shift weight (load) during examination. A compensatory problem develops as the result of predictable compensation a horse may make over time for a primary lameness in a single limb. However, a horse may compensate for lameness in one limb by shortening the stride in another, a stride-to-stride change in gait that is not the result of lameness. For instance, in some trotters with severe LF lameness, reluctance to extend the LF may induce a compensatory shortening of the cranial phase of the stride in the LH limb, creating what appears to be a hike in the LH. If the veterinarian looks only at the hindlimbs, LH lameness may be diagnosed. A trotter performing at speed with LF lameness is likely to develop compensatory lameness in the RF or RH but not in the LH. However, the horse may appear to be hiking (lame) in the LH to avoid interfering with the LF. Elimination of obvious unilateral forelimb lameness usually resolves an ipsilateral pelvic hike. Most horses with pronounced forelimb lameness examined at a trot in hand will have a concomitant shortening of the cranial phase of the stride in the contralateral hindlimb, giving the false impression of coexistent lameness in this limb and vice versa. Experimental results appear to support this clinical impression. In 6 of 10 horses with stance phase forelimb lameness, compensatory movements of horses created a false lameness in the contralateral hindlimb (see following text).⁸ Once forelimb lameness is abolished using diagnostic analgesia, the shortened cranial phase of the stride in the contralateral hindlimb will abate.

It is often difficult to know which lameness came first, but it is important to understand how horses compensate for lameness and which limbs are at risk to develop compensatory problems. Compensatory problems range from obvious lameness to only mild palpable abnormalities that may still compromise performance. Several predictable patterns of compensatory lameness are possible; the most common is bilateral forelimb or hindlimb lameness. Horses with a specific lameness in one forelimb are at risk to develop the same condition in the opposite forelimb. This tendency may not always be compensation for the primary lameness but may reflect simultaneous injury or degeneration of bone or soft tissue of both limbs. Abnormal loading of forelimbs or hindlimbs, faulty bilateral conformation, and the same shoeing or foot conditions all likely contribute to bilateral, simultaneous lameness. In horses with bilateral lameness, eliminating lameness in one limb usually results in pronounced contralateral limb lameness. Bilateral lameness may affect both limbs equally, resulting in a short, choppy gait. The horse may be lame in one limb while being circled in one direction and lame in the contralateral limb in the opposite direction.

Racehorses that gallop are most likely to develop compensatory lameness on the contralateral limb or the ipsilateral forelimb or hindlimb. A TB racehorse with a left metatarsophalangeal joint lameness is most likely to develop a similar problem in the RH but may also develop LF lameness. In a trotter the contralateral limb is most at risk, followed by the diagonal forelimb or hindlimb. If a trotter has a right carpal lameness, the left carpus should be examined carefully; compensatory lameness also may occur in the diagonal LH limb. In a pacer the ipsilateral forelimb or hindlimb should be considered after the contralateral limb. In a pacer with LH lameness the RH and LF are at risk.

The most common compensatory lameness is the same problem in the contralateral limb. However, suspensory desmitis is a common compensatory problem in both the contralateral and other limbs. In a TB racehorse or a jumper with LF lameness, RF suspensory desmitis is common. Primary RH lameness may result in suspensory desmitis in the RF. It is logical that soft tissue structures are particularly vulnerable to the effects of overload. Superficial digital flexor tendonitis may develop secondary to a primary problem in the contralateral limb. In trotters a common pattern is primary carpal lameness and compensatory osteoarthritis of the medial femorotibial joint in the diagonal hindlimb, or vice versa.

Compensatory lameness also can develop in the same limb. In horses with front foot lameness the suspensory ligament (SL) often is sore, and some horses have suspensory desmitis. In horses with lameness abolished by palmar digital analgesia, most with navicular syndrome, scintigraphic examination revealed increased radiopharmaceutical uptake (IRU) in the proximal palmar aspect of the McIII in 30% of horses, indicating possible abnormal loading of the proximal aspect of the SL (Figure 7-1).⁹ Complete resolution of lameness may not be achieved until high palmar analgesia is performed.

Fig. 7-1 A, Lateral delayed-phase scintigraphic view showing focal, mild increased radiopharmaceutical uptake (IRU) of the navicular bone (bottom arrow) and proximal aspect of the third metacarpal bone (McIII; top arrow). Normal modeling is seen in the dorsal aspect of the proximal phalanx. B, Dorsal delayed-phase scintigraphic image, and C, dorsomedial-palmarolateral oblique xeroradiographic image of a dressage horse with lameness abolished by palmar digital analgesia. IRU of the medial aspect of the distal phalanx (bottom arrow) corresponds to the area of subchondral radiolucency seen in the xeroradiographic image (C, arrowhead). Note the focal area of mild IRU involving the proximal aspect of the McIII (top arrow, A and B). Abnormal loading of the suspensory ligament may occur as a compensatory problem in some horses with navicular syndrome or other sources of palmar foot pain.

Horses with primary metatarsophalangeal joint lameness often have associated ipsilateral stifle pain, or vice versa.¹⁰ Determination of the primary site of lameness may be difficult without use of diagnostic analgesia and observing that blocking one site abolishes the majority of lameness. This phenomenon may be most common in STBs, but I have recognized it in all types of sport horses and in TB racehorses.

Supporting, Swinging, and Mixed Lameness

Lameness has classically been divided into three categories in an attempt to characterize the motion associated with the lame leg and to assign a cause to the lameness condition. These categories are described and discussed, but I firmly believe that adequate characterization of most lameness conditions is impossible and may be unnecessary.

Supporting limb lameness describes a lameness that results in pain during the weight-bearing phase of the stride. Most lameness conditions are of this type. Supporting limb lameness also has been referred to as stance phase lameness, but this term is inappropriate because the swing phase of the stride is also altered.

Swinging limb lameness describes lameness that primarily affects the way the horse carries the lame limb. However, most horses with painful lameness conditions alter the swing phase of the stride in a typical and repeatable fashion, and it is difficult to make a clear separation between supporting and swinging limb lameness. Swinging limb lameness should be a term reserved for mechanical defects of gait, such as fibrotic myopathy, upward fixation of the patella, stringhalt, or other lameness conditions causing a mechanical restriction of gait. In these horses, lameness is manifested in the swing phase of the stride with no apparent pain. Unfortunately, the term swinging limb lameness often is used inappropriately to describe the gait deficit in horses with painful, supporting limb lameness. Lameness associated with osteochondrosis of the scapulohumeral joint is often described as a swinging limb lameness because of a markedly shortened cranial phase of the stride. Dramatic improvement in the shortened cranial phase of the stride can be achieved by diagnostic analgesia, eliminating pain associated with lameness. Thus the gait deficit is the direct result of pain, and no clear differentiation between supporting and swinging limb lameness can be made. Horses with painful forelimb lameness almost always shorten the cranial phase of the stride, although perhaps not to the extreme as in a horse with authentic scapulohumeral joint lameness. Horses with any painful hindlimb lameness consistently shorten the cranial phase of the stride, a reliable clinical indicator of which limb is affected, and when pain is abolished, the cranial phase (swing phase) of the stride improves (lengthens). Because the terminology is confusing and often erroneous, I prefer to avoid use of these terms and simply describe lameness as accurately as possible. For instance, describing a horse as grade 2 of 5 LF lame, with a marked shortening of the cranial phase of the stride reminiscent of other horses I have seen with shoulder region lameness, gives the most accurate and useful information.

There is an erroneous tendency to equate a swinging limb lameness with one that is more evident when the lame limb is on the outside of a circle. Upper limb lameness is often presumed yet not confirmed by diagnostic analgesia. It is logical that if a horse is reluctant to swing a limb forward, the lameness may be most prominent when the lame limb is on the outside of a circle. However, many horses with painful weight-bearing lameness show more pronounced lameness with the limb on the outside of a circle, a finding that neither suggests that lameness originates from the upper limb nor indicates the presence of swinging limb lameness (see following text). The outer limbs must stretch further and cover a larger circumference circle than the inside limbs. Slight temporal differences in the stance and swing phases of the inside and outside limbs are necessary to maintain gait symmetry.⁵ Therefore the stance phase of the stride may be relatively longer for the inside hindlimb, resulting in extension of the fetlock for a longer time and stress on the suspensory apparatus, whereas for the outside hindlimb covering a longer distance in the same time, there may be greater extension of the fetlock for a relatively short time, but still with stress on the suspensory apparatus. Thus pain associated with hindlimb proximal suspensory desmitis is worse in some horses with the lame or lamer limb on the inside of the circle, whereas with others lameness is accentuated with the lame limb on the outside of a circle.

The results of cinematographic analysis of gait in lame horses seem to support reservation of the term swinging limb lameness for horses with authentic mechanical gait deficits, rather than those induced by painful lameness. In a horse with a supraglenoid tubercle fracture examined at a trot in hand, a marked decrease in the cranial phase of the stride (protraction) was observed, along with a marked head and neck nod. A markedly shortened stride could be equated with swinging leg lameness, but high-speed cinematography showed that the cranial and stance phases of the stride were shorter than in the sound limb.¹¹ A horse with unilateral semitendinosus fibrotic myopathy had a shortened stride length and a shortened cranial phase of the stride, but the stance phase did not differ from that of the unaffected contralateral limb.¹²

In my experience, most lameness conditions can be considered mixed lameness, with changes in gait during weight bearing or the stance phase and during the swing phase of the stride. With the exception of mechanical defects in gait, I have not been able to categorize the clinical characteristics of most lameness conditions into swinging or supporting limb types. However, it has been suggested that swinging limb lameness is caused by muscle injury; supporting limb lameness is caused by bone, tendon, and ligament injury; and mixed lameness is caused by joint, tendon sheath, and periosteal injury.¹³ A shortened cranial phase of the stride is a common characteristic in forelimb and hindlimb lameness and should not be considered pathognomonic for the location or type of lameness.

Recognition of Forelimb Lameness

Forelimb lameness often is easier to recognize than hindlimb lameness. Understanding the concept of the head nod is vital to the correct interpretation of equine lameness. The head and neck elevate or rise when the lame forelimb is bearing weight or hits the ground and nod down or fall when the sound forelimb hits the ground. “When the [forelimb] is the lame one, the movements of the foot and head occur somewhat in unison. When the lame foot is raised, the head is elevated, but only to fall when the sound leg is brought to a rest.”¹ Some clinicians find it easier to appreciate the head nod down, whereas others find it easier to recognize elevation of the head.

When slow-motion videotape of lame horses is evaluated, it is immediately obvious that the elevation of the head and neck is much easier to see than the head nod down. In slow motion the horse appears to be elevating the head and neck just before the lame limb hits the ground, and then, during the later portion of the support or stance phase, the head and neck nod down. In fact, in slow motion it is head and neck elevation from a baseline level and later settling of the head and neck (nod downward) that are seen. The head returns or settles to baseline, giving the distinct impression that the horse is unloading the lame limb rather than loading the sound limb. The head and neck nod occurs as the contralateral limb begins the support or stance phase. Both head elevation and falling are present, but head elevation is much easier to detect when it occurs in unison with the lame limb hitting the ground. It is likely that a combination of visual clues allows the clinician to decide the primary forelimb lameness. Quantification of lameness and description of the actions of the lame and compensatory limbs have been attempted using gait analysis systems. In horses with amphotericin-induced carpal lameness, head movements were the most consistent indicator of lameness, followed by sinusoidal motion, or a rising and falling action, of the head and withers.¹⁴ The motion of the lame limb was assessed, and a falling of the head and withers during the support phase of the lame limb was noted, contrary to clinical perception and evaluation of slow-motion videotape of lame horses. It was suggested that an uncoupling of the weight from the lame forelimb and a “free fall–like” phenomenon occurred during weight bearing.¹⁴ The problem with this description is that it considers only the lame limb and is confusing. When evaluating a lame horse, the observer sees both forelimbs. During the later portion of the support phase of the lame limb, the sound limb is in the later portion of the swing phase and beginning the support or stance phase. Thus the head and withers drop described experimentally appears to occur concomitantly with the sound limb hitting the ground. The observer perceives the early portion of the stance or support phase.

In general, a good correlation between clinical evaluation of forelimb lameness and that described using motion analysis has been observed. There was complete agreement between clinical determination of location of forelimb lameness and that detected by motion analysis using a computerized three-dimensional motion measurement system. However, the degree of lameness differed in 6 of 29 horses.¹⁵ In a more recent study subjective forelimb lameness grades were significantly associated with kinetic parameters, and vertical force peak and impulse had the lowest coefficients of variations and highest correlations with subjective lameness score.¹⁶ In fact, kinetic parameters using GRFs measured by force plate analysis detected subclinical lameness not seen by a trained observer, a finding that may indicate that quantitative lameness analysis may be useful in horses with subtle lameness.¹⁶ The maximal vertical acceleration of the head was the best indicator of forelimb lameness.¹⁷ Although horses with forelimb lameness shifted weight in a caudal direction to the diagonal hindlimb, the amount of withers motion was minimal. The authors reasoned that the tremendous mobility of the head and neck, allowing the horse to asymmetrically elevate the neck and thus load the nonlame forelimb, accounted for the lack of withers movement and the horse’s adaptation to forelimb lameness.¹⁷ A similar compensatory ability is not present in the hindlimb. Vertical displacement of the tuber coxae and forward motion or translation of the pelvis occur in horses with hindlimb lameness, because a mechanism such as head and neck movement does not exist.¹⁷ In a computer-generated model of a trotting horse the dynamic effects of head and neck movement accounted for the majority of load shift to the contralateral forelimb and diagonal hindlimb in horses with unilateral forelimb lameness.¹⁸ Load shift and compensation by the diagonal hindlimb in horses with unilateral forelimb lameness lend support to the clinical findings of compensatory lameness in the diagonal limbs in trotters.

Instrumented shoes have been used experimentally to study motion in horses by quantifying GRF but have had limited clinical use.^19,20 Lack of correlation between an in-shoe system and force plate analysis was disappointing, and neither research nor clinical application of the system was recommended.²¹ Although these systems are not currently widely available, in the future these or similar systems may be useful to objectively assess lameness and the response to diagnostic analgesic techniques in clinical patients. A remote monitored sensor-based accelerometer-gyroscopic (A-G) system showed good correlation in horses with either forelimb or hindlimb lameness when compared with a video-based motion analysis system used in horses moving on a treadmill.²² Hindlimb lameness was consistently higher (in grade) using the A-G system, but the system yielded false-positive results in horses with concurrent forelimb lameness.²² However, for a skilled observer, direct observation of the horse may be more accurate than kinetic or kinematic analysis of gait when a horse is lame in more than one limb.⁵

Recognition of Hindlimb Lameness

Historically descriptions of hindlimb lameness have been confusing. An important principle in the recognition of hindlimb lameness is the concept of the pelvic hike or asymmetrical movement of the pelvis. This has also been termed hip hike, but I prefer the term pelvic hike because it accurately describes how the pelvis moves in a horse with unilateral hindlimb lameness. The entire pelvis, not just the lame side of the pelvis, appears to undergo elevation. Because the horse has two “hips” and only one pelvis, the term pelvic hike seems preferable. Pelvic hike is the vertical elevation of the pelvis when the lame limb is weight bearing. In other words, the pelvis “hikes” upward when the lame limb hits the ground and moves downward when the sound limb hits the ground. The “haunch settles downward when the sound leg touches the ground.…”¹ Some clinicians find it easier to see the downward movement of the pelvis, on the side of the lame limb, rather than the pelvic hike.⁵ It may be simpler to determine which side has the most movement, rather than looking for either a hike or a drop.⁵ The clinician must keep in mind that the pelvic hike is the clinical impression of the change in height of the pelvis, not the absolute or measured height. It is the shifting of weight or load that occurs as the horse tries to reduce weight bearing (unload) in the lame limb and transfer weight (load) to the sound limb. The ease with which this can be seen depends on the horse’s tail carriage; in a horse with a tail set on high and that is also carried high, this may completely obscure movements of the pelvis.

Another explanation for asymmetrical movement of the pelvis involves one of the protective or compensatory mechanisms used by the horse to assist in breakover and minimize load on the lame limb. Many horses with hindlimb lameness drift away from the lame limb toward the sound limb. Drifting may decrease the magnitude of the observed pelvic hike, but more important, it makes the lame side look lower than the sound side. This is why it is important to watch the entire pelvis as a unit rather than the individual sides of the “hips.”

In most horses with hindlimb lameness, particularly those without a substantial tendency to drift away from the lame limb, the elevation of the pelvis (pelvic hike up) when the lame limb hits the ground surpasses that when the sound limb is weight bearing. This elevation can be seen readily in slow-motion videotape analysis, but it may not be as obvious during clinical examination. Observing horses with hindlimb lameness from the front as the horse trots toward you may be useful. This approach allows the pelvic hike to be seen clearly using the horse’s top line as a frame of reference. Subtle pelvic elevation is best seen from this perspective. The use of markers on a fixed part of the pelvis can help to identify asymmetry. Stride length characteristics, height of foot flight, sound, and fetlock drop are also helpful (see following text).

Horses with bilateral hindlimb lameness may have a short, choppy gait that lacks impulsion, but they may have no pelvic hike. Other methods to exacerbate the baseline lameness should be performed, such as circling the horse at a trot in hand or while on a lunge line. Lameness may be accentuated when the lame or lamer limb is on the inside or outside of the circle (see following discussion).

Hindlimb Lameness Confused with Forelimb Lameness

It is important to understand how a horse with unilateral hindlimb lameness modifies its gait so that hindlimb lameness can mimic forelimb lameness at the trot. When the lame hindlimb hits the ground, the horse shifts its weight cranially to transfer load away from the lame limb. This causes the head and neck to shift forward and nod down at the same time. The contralateral forelimb bears weight simultaneously with the lame hindlimb and the head nod coincides, thus mimicking lameness in the forelimb ipsilateral to the lame hindlimb. I find it difficult to distinguish clinical characteristics of a head and neck nod caused by forelimb lameness from that caused by ipsilateral hindlimb lameness. Some clinicians have suggested that the head and neck nod caused by ipsilateral hindlimb lameness is less vertical in nature and more forward and downward. Head and neck movement in horses with hindlimb lameness is not always observed. Horses generally must have prominent (>3 out of 5, see later grading discussion) hindlimb lameness before compensatory head and neck movement develops. However, two horses with very similar severity of hindlimb lameness may have different characteristics of movement, which will result in an associated head nod in one, but not in the other. At the pace, a lateral gait, LH lameness mimics RF lameness and RH lameness mimics LF lameness. Evaluation of the horse moving in circles may help to determine if a head nod is related to primary forelimb or hindlimb lameness. If a head nod is exacerbated but a hindlimb lameness is less obvious, then there is probably coexistent forelimb and hindlimb lameness. However if the head nod and hindlimb lameness remain similar or both appear worse, it is more likely that the head nod reflects a primary hindlimb lameness.

Horses can have a head and neck nod at the trot caused by singular forelimb lameness, singular ipsilateral hindlimb lameness, or concurrent forelimb and ipsilateral hindlimb lameness. A prominent head nod is seen in horses with simultaneous LF and LH lameness. The examiner first must determine whether both limbs are affected. Problems arise because occasionally a horse with only LF lameness may shorten the LH stride at the trot, leading the veterinarian to question whether LH lameness also exists. More commonly, however, horses with only lameness in a single forelimb shorten the cranial phase of the stride of the contralateral hindlimb. Horses with only LH lameness can have a rather pronounced head nod, and thus the veterinarian may question the existence of LF lameness. Although a horse with LF lameness may have a compensatory shortened stride of the LH, in the absence of lameness a marked pelvic hike should not be present. A head nod consistent with LF lameness may be inappropriately severe to be caused by mild LH lameness. If a horse has simultaneous LF and LH lameness, it is essential to perform diagnostic analgesia in the hindlimb first, because moderate-to-severe hindlimb lameness produces head and neck nod that is not abolished unless the hindlimb lameness is resolved. Resolution of the pelvic hike and reduction in the head nod should be expected with resolution of the hindlimb lameness.

Simultaneous lameness of a diagonal pair of limbs is less common than simultaneous ipsilateral lameness, except in trotters, because many horses perform at gaits that appear to induce compensatory lameness in the ipsilateral limbs. With simultaneous LH and RF lameness the head nod reflects the forelimb component, a mandatory clinical sign for perception of RF lameness. The horse may drift away from the LH with shortening of the cranial phase of the stride. The horse may have a short, choppy stride in the forelimbs and hindlimbs. The horse may have a rocking gait. It cannot shift weight or compensate from stride to stride in the usual manner and thus tends to rock back and forth from the hindlimbs to the forelimbs.

Reasonable agreement generally exists between clinical recognition of hindlimb lameness and that found experimentally. The use of markers placed on each tuber coxae of 13 horses with unilateral hindlimb lameness showed a consistent increase in vertical displacement of the pelvis during early weight bearing of the lame limb.²³ Although the rise and fall of the pelvis was readily apparent and occurred consistently with weight bearing of the lame and sound limbs, respectively, the absolute height of the pelvis on the lame side did not rise above that of the sound limb.²³ These findings are consistent with my clinical impressions. A head nod down when the diagonal forelimb was bearing weight further confirmed clinical observations that hindlimb lameness can mimic lameness of the ipsilateral forelimb.²³ In a kinematic study using a three-dimensional optoelectronic locomotion system, hip acceleration quotient increased in horses with hindlimb lameness.²⁴ Vertical displacement corresponded to the pelvic hike up on the lame limb, with a simultaneous forward movement of the head and neck during the stance phase of the lame limb.²⁴ Pelvic height differed significantly between sound and lame limbs in an experimental study using a custom-made heart-bar shoe to induce transient hindlimb lameness.²⁵ Pelvic height was reaffirmed as an important indicator of hindlimb lameness, but exaggerated pelvic hike seen on the lame side was proposed to be caused by push-off from the sound limb and occurred immediately before weight bearing of the lame limb.²⁵ The importance of weight support and asymmetrical dorsoventral hindlimb movement (pelvic hike) was reaffirmed in a study using continuous three-dimensional kinematic monitoring of movement of the tubera coxae.²⁶ The hip (pelvic) hike seen on the lame side was found to be a rapid upward movement that led to an increased dorsoventral displacement.²⁶

GRF has been measured in normal horses and those with forelimb and hindlimb lameness.^27-30 GRF is reduced in the lame forelimb or hindlimb with compensation by the other limbs. In horses with unilateral forelimb lameness, decreased horizontal GRF in the lame limb is compensated for by increased GRF in the contralateral forelimb and ipsilateral hindlimb.³¹ Decreased vertical GRF in the lame limb is compensated for by increased vertical GRF in the contralateral forelimb during the swing phase of the lame limb, and increased vertical GRF in both the ipsilateral and contralateral hindlimbs during the stance phase of the lame limb.³¹ During unilateral hindlimb lameness the decreased GRF in the lame limb is compensated for by increased GRF in the contralateral hindlimb and the contralateral and ipsilateral forelimbs.³¹ These experimental data support the clinical impression that a lame horse adapts by shifting load to the contralateral limb or by shifting load in a caudal direction for forelimb lameness and in a cranial direction for hindlimb lameness. Kinetic gait analysis in horses with hindlimb lameness or spinal ataxia was recently studied using a force plate mounted in an examination aisle, a setup that may prove useful for clinical use during lameness examination.³² Horses with hindlimb lameness had significant differences from normal and ataxic horses and their own contralateral hindlimbs in vertical peak force, vertical force impulse, and coefficient of variance of vertical force peaks.³² Uniquely, investigators examined ataxic horses at the trot and found significant differences in lateral force peaks (lateral hindlimb movements) between normal horses and those affected with spinal ataxia.³²

Bilaterally Symmetrical Forelimb or Hindlimb Lameness

Bilateral lameness is a common cause of poor performance and may go unrecognized without additional movement, such as circling, lunging, or riding. Horses with bilaterally symmetrical forelimb lameness may have a short, choppy gait when trotted in straight lines. Horses with hindlimb lameness may lack lift to the stride, have a subtle change of balance, or have reduced hindlimb impulsion.⁵ If bilaterally symmetrical lameness is suspected, the veterinarian should select one limb and begin diagnostic analgesia. Horses often show pronounced lameness in the contralateral limb when the source of pain is eliminated.

Fetlock Drop

Assessment of fetlock drop, or extension of the metacarpophalangeal and metatarsophalangeal joints, may be helpful in recognition of the lame limb. In general, the fetlock joint of the sound limb drops farther when this limb is weight bearing than does the fetlock joint of the lame limb, because the horse is attempting to spare the lame limb by increasing load in the sound limb. This may be easier to detect by video analysis than in a clinical situation and may be more recognizable at the walk than at a trot. However, in some horses with moderate or severe unilateral suspensory desmitis or tendonitis, the fetlock drops markedly on the lame limb when the horse is walking, but at a trot fetlock drop usually is more pronounced in the sound limb. With bilateral suspensory desmitis or severe tendonitis the fetlock may drop further in the lamer limb. In horses with chronic hindlimb suspensory desmitis excessive fetlock excursion on the affected side may falsely reduce pelvic excursion (hike) and make hindlimb lameness less obvious and more difficult to detect.

Use of Sound

Sound can be useful in lameness evaluation. A lame horse usually lands harder on the sound limb, resulting in a louder noise. For this sound to be appreciated, the horse must be trotted on a firm or hard surface such as pavement or concrete. However, the sound a horse makes while landing depends greatly on symmetry of the front or hind feet, and the loss of one shoe, different shoe types, or disparity in foot size confounds interpretation. Listening for regularity of rhythm and sound of footfall are important, especially when evaluating the response of lame horses to diagnostic analgesia, particularly in horses with subtle lameness.⁵

Drifting

Horses with hindlimb lameness generally drift away from the lame limb. Drifting is one of the earliest adaptive responses of a horse with unilateral hindlimb lameness, allowing the horse to break over more easily or to reduce load bearing. Drifting may alleviate the need for extensive pelvic excursion (hike). It may make pelvic drop on the lame side more obvious. The horse may mask the lameness by reducing pelvic excursion. In some horses a pelvic hike is undetectable or subtle, but consistent drifting away from the lame side indicates the presence of hindlimb lameness. Many driven STBs with hindlimb lameness drift away from the lame limb or are “on the shaft.” Horses with LH lameness have a tendency to be on the right shaft and vice versa. Drifting away from the lame limb may be most evident when horses have pain from the tarsus distally, although some clinicians have different experiences.⁵ Drifting may result in the horse moving on three tracks.

Horses with severe forelimb lameness also tend to drift away from the lame limb, but this tendency usually is less obvious than in horses with hindlimb lameness. Drifting is most common with carpal lameness when the horse tends to abduct the limb during the swing phase of the stride and appears to push off with the limb, forcing the horse away from the lame side. Abduction seen in horses with carpal lameness should not be confused with swinging the limb or a swinging limb lameness. During protraction abduction seen in horses with carpal region pain appears to involve the horse carrying and placing the limb lateral to the expected site of limb placement. Racehorses with either forelimb or hindlimb lameness tend to drift away from the lame limb while training or racing at speed. This finding is an important piece of the lameness anamnesis.

Drifting toward the lame hindlimb is an unusual but important clinical sign. In horses that drift toward the lame limb, I suspect weakness and lameness exist simultaneously, suggesting a neurological component to the gait abnormality. However, a jumping horse at takeoff may push off more strongly with the nonlame hindlimb and drift across the fence toward the lame limb.⁵

Cranial and Caudal Phases of the Stride

Changes in limb flight in the cranial and caudal phases of the stride can be seen only when the horse is evaluated from the side. In a normal horse the length of the stride of the paired forelimbs and hindlimbs, measured from hoof imprint to hoof imprint, is nearly identical from side to side. Extension and flexion of the limbs is also similar. From a clinical perspective the length of the stride of the affected limb cranial to the stance position of the contralateral limb is called the cranial phase of the stride, and the length of the stride caudal to the stance position of the contralateral limb is called the caudal phase of the stride. Obviously in a normal horse these individual parts of the stride are symmetrical. In a lame horse the overall stride length does not appear to change. If stride length changed, the horse could not trot in a straight line. Drifting is associated with lameness and could be explained by a change in stride length, but shorter stride length would be expected in the lame limb, causing the horse to drift toward the lame side, in contrast to the usual observation, drifting away from the lame limb. In racehorses, some of the tendency to drift away or toward the inside of the track could be easily explained by mild differences in stride length or strength (power). However, with the horse at a trot in hand we can assume that total stride length does not change.

In most lame horses the cranial phase of the stride of the affected limb is shortened. The caudal phase is lengthened to maintain a near equal overall stride length side to side. Shortening of the cranial phase of the stride appears to be a learned response of the horse to reduce the time spent during the stance phase and to help during breakover. Loss of propulsion, or an unwillingness to push off with the lame limb, could also explain reduction in the cranial phase of the stride. Because most lame horses have a shortened cranial phase of the stride, this finding, although quite useful in determining in which limb the horse is lame, is not particularly useful in localizing or classifying lameness and is not synonymous with swinging limb lameness. It is also important to recognize that pain causing lameness results in altered proprioceptive responses, to protect the painful area, and these responses may persist for some time after pain has resolved.⁵ A classic example of attenuation of the cranial phase of the stride in the hindlimbs occurs mechanically in horses with fibrotic myopathy. This authentic swinging limb lameness causes a marked abrupt change in the later portion of the protraction phase of the affected hindlimb, shortening the cranial phase and causing a sudden downward and backward action of the limb.

The caudal phase of the stride is lengthened in most lame horses because for overall equal stride length to be maintained, this portion of the stride must compensate. I generally have not found evaluation of the caudal phase of the stride at the trot in hand clinically useful, but it is sometimes a useful observation in horses at a walk (see following text). Some horses with severe palmar foot pain have a shortened caudal phase of the stride at both walk and trot.⁵

Contrast of the cranial and caudal phases of the stride in the lame limb at a walk and a trot is useful. In most horses with forelimb lameness the cranial phase of the stride is slightly shortened at a walk but markedly shortened at a trot. Obviously, in horses with subtle lameness, this clinical sign is absent at the walk and only mildly apparent at the trot. Horses with pain in the dorsal aspect of the foot, such as hoof abscessation or laminitis, may have a shortened caudal phase of the stride at a walk. This response is an attempt to protect the painful area and to shorten during breakover. These horses walk with a marked camped-out appearance in the forelimbs. At the trot, however, the cranial phase of the stride is likely to be shortened, a clinical contrast useful in localizing lameness to the dorsal aspect of the hoof.

Most horses with hindlimb lameness have a reduction in the cranial phase of the stride at the walk and the trot. Horses with pelvic fractures involving the acetabulum prefer to keep the lame limb ahead of the contralateral limb at the walk and have marked shortening of the caudal phase of the stride, but at the trot the horse has a shortened cranial phase of the stride. Horses with hoof abscessation, most commonly of the dorsal aspect of the hoof, walk similarly, only to trot with a pronounced shortening of the cranial phase of the stride. An explanation for disparity at walk and trot in the phases of the stride in horses with pain at either end of the hindlimb is not readily apparent, but recognition of this phenomena has been quite useful, and consistent. Unilateral or bilateral laminitis and other severe causes of pain in the digit are rare in the hindlimbs and can cause similar clinical signs.

Shortening of the cranial phase of the stride does not always indicate that lameness is present in that limb. At speed a trotter with forelimb lameness shortens the cranial phase of the stride in the ipsilateral hindlimb to avoid interference with the lame limb. This observation sometimes is also made in horses being trotted in hand. This compensatory movement gives the impression that the horse may be lame in the ipsilateral hindlimb, with a subtle pelvic hike. Lameness of the foot and carpus in trotters most often causes this compensatory ipsilateral hindlimb pelvic hike. Once lameness has been abolished in the ipsilateral forelimb, the subtle pelvic hike and shortened cranial phase of the stride in the hindlimb abate. In trotters a shortened cranial phase of the stride and a pelvic hike may be related to faulty weight distribution and interference problems and not to lameness at all.

Front Foot Interference

Hind Foot Interference

Interference as a result of a hind foot hitting the foot of the ipsilateral forelimb (forging) is common and usually does not result in injury. Many horses forge at a trot in hand or while being ridden. In horses with shoes the sound is unavoidable but may not be a sign of a pathological condition. Forging is most common in horses that are trotted in deep footing. Forging may reflect imbalance, lack of strength, incoordination, or poor foot trimming.⁵

Forelimb: Common Abnormalities of Limb Flight

Hindlimb: Common Abnormalities of Limb Flight

Mechanical Lameness of the Hindlimb and Limb Flight

Mechanical conditions of the hindlimb can cause profound abnormalities of limb flight (see Chapter 48). These are termed lameness conditions because of the gait abnormality exhibited, although in many horses pain is not characteristic.

Hard and Soft Surfaces

Comparison of movement on hard and soft surfaces is valuable. Foot lameness usually is worse when the horse is trotted on hard surfaces and better on a soft surface, such as grass or sand. Horses with suspensory desmitis or digital flexor tendonitis are more likely to show lameness on a soft surface. Deep sand may accentuate some lameness conditions, but an extended lameness examination under these conditions could cause proximal suspensory desmitis.⁵ A slight downward incline or an uneven, rough surface may make subtle lameness more apparent.⁵

Circling

Lameness often is much more pronounced when a horse is circled. Horses should be circled in both directions: to the left (counterclockwise, LF and LH on the inside) and to the right (clockwise, RF and RH on the inside). Lameness may be more pronounced when circling at either the walk or the trot. In some horses with incomplete fractures, baseline lameness at a trot in straight lines in hand may be subtle or absent. Lameness may be readily apparent during circling, even at the walk. The additional forces of torsion and bending during circling are added to those of compression and tension. In horses with incomplete fractures, such as those involving the proximal or distal phalanges, torsion or bending forces during circling likely cause mild separation of the fracture fragments and exacerbate lameness. In horses with other lameness conditions, exacerbation of lameness may be caused by a change of load on the affected soft tissue structure or bone, redistribution of the forces of compression and tension in a medial-to-lateral direction, or additional forces of bending and torsion.

From a clinical perspective the force of compression may be dominant to other forces in determining a horse’s response to circling, but it is not the only factor. Extension of the limb is also influential.⁵ When the lesion is in the outside limb while the horse is circling and undergoing compression, exacerbation of the lameness occurs. For instance, lameness in horses with medially located lesions of the distal phalanx or of the third carpal bone is worse when the limb is on the outside of the circle and the lesion is being compressed. For some soft tissue injuries, tension forces may be more important. Lameness in horses with proximal suspensory desmitis often is worse with the limb on the outside of the circle, suggesting that tension is important in the expression of lameness. The same observation is not seen in horses with more distally located suspensory desmitis.

Is the lameness seen in a horse that is moving in a circle the same lameness that is seen while the horse is walking or trotting in straight lines? In most instances, circling exacerbates the primary lameness seen in straight lines. If lameness is subtle or nonexistent when the horse is evaluated in a straight line, the lameness seen during circling becomes the baseline lameness. The clinician must recreate the same conditions of circling when evaluating the results of diagnostic analgesic techniques. There is always the possibility that lameness seen during circling may be different from the baseline lameness seen in straight lines. For example, a horse has grade 1 RF baseline lameness when it moves in a straight line that increases to grade 3 when trotted in a circle to the left, but still has grade 1 lameness when trotted to the right. Lameness in a straight line and when trotting to the right is absent after palmar digital analgesia but still is rated grade 3 when the limb is on the outside of the circle. This horse has two problems in the RF: palmar foot pain and an additional carpal lameness that becomes evident when the horse is trotted to the left (RF on the outside of the circle). With bilateral forelimb or hindlimb lameness, primary lameness often is seen in a single limb in straight lines, but during circling the lameness is seen in whichever limb is on the inside (or outside) of the circle. Circling is useful in exacerbating the primary lameness problem and identifying an additional cause of lameness not previously noted. This additional lameness must be recognized and treated separately from the baseline lameness.

Good correlation usually exists between the cause of lameness seen on the straight and that seen while circling the horse; thus it is helpful to circle the horse to try to exacerbate lameness. Circling can be done at the walk and trot in hand and while lunging or riding the horse. Horses often move more freely and naturally when lunged than when being led.⁵ However, lunging is not possible in some horses, particularly racehorses, and circling while being led is better than no circling. The surface should be nonslip because horses may be hesitant to move freely on slippery surfaces and shorten or alter the stride even when lameness is not present.⁵ Soft footing is best when the horse is first being lunged, because the horse can buck and play without risk of injury. Hard or firm surfaces are best to exacerbate many lameness conditions, but the surface must be nonslip to avoid possible injury.

That lameness of the upper forelimb or hindlimb is worse when the limb is on the outside of the circle is a common misconception. This is true in some horses, but a generalization cannot be made (see following text). Shortening of the cranial phase of the stride may appear more obvious with the limb on the outside of the circle, but exacerbation of lameness judged by the degree of head nod may not be observed. Another misconception is that horses with lameness of the foot are lamest when the limb is on the inside of the circle. Although a majority (65%) of those with lameness localized to the foot are lamest when the limb is on the inside of a circle, lameness can be worst with the lame limb on the outside of a circle. This depends in part on the location of pain within the foot.

Observation during Riding

Lameness may not be apparent when the horse is evaluated in hand in straight lines and circles but is obvious when the horse is ridden. This lameness becomes the baseline lameness for further investigation. The additional weight of a rider can exacerbate both forelimb and hindlimb lameness. Gait abnormalities and performance in horses with primary back pain or those with substantial muscle pain secondary to hindlimb lameness usually are worse when they are ridden. Hindlimb gait restriction can occur in horses with back pain but may be apparent only when a horse is ridden.⁵ Problems related to an ill-fitting saddle or girth, behavioral problems, head shaking, abnormal posture or carriage of the head and neck, and refusal to take a lead or bend in certain directions may be evident only when a horse is ridden.

A horse may be easier to control when ridden than when in hand or on the lunge. Performance of specific maneuvers by the horse may accentuate lameness. A collected trot that forces more weight onto the hindlimbs may exacerbate hindlimb lameness. An extended trot may reveal the horse’s inability to extend one limb compared with another and reveal lameness that was completely imperceptible under all other circumstances. The primary complaint, such as poor-quality flying changes of lead at canter, may require a riding assessment regardless of whether baseline lameness is evident under other circumstances.

However, it is important for the veterinarian to separate his or her observations from those perceived by the rider. Identification of the lame limb may be difficult for a rider, although he or she may have a very strong opinion. If the veterinarian’s observations differ, the rider may be difficult to convince. It is also essential to recognize that bad riding can actually induce a false lameness that is completely unapparent if the horse is ridden well. Nonetheless, an experienced rider, trainer, or driver can be quite helpful in assessing the horse’s response to diagnostic analgesia or therapy, particularly in horses with thoracolumbar pain, subtle hindlimb lameness manifested only when ridden, and poor performance related to a musculoskeletal problem. Working regularly with a skilled, experienced, and reliable rider can be very helpful.

Subtle differences in weight distribution of the rider may exacerbate or mask the presence of forelimb and especially hindlimb lameness. When the horse is performing the posting (rising) trot, lameness may be more or less prominent depending on which diagonal the rider is using. In the rising trot the rider sits on either the left or right diagonal. On the left diagonal the rider is sitting when the LF and RH are bearing weight and rising during the swing phase of these limbs. On the right diagonal the rider is sitting when the RF and LH are bearing weight. The correct diagonal is the outside diagonal (i.e., left diagonal on the right [clockwise] rein). Hindlimb lameness often is worse when the rider sits on the diagonal of the lame limb.⁵ Therefore if the horse is lame in the RH, the lameness appears and feels worse when the rider sits on the left diagonal. Horses with hindlimb lameness may try to force or throw the rider to sit on the more comfortable (for both horse and rider) diagonal.⁵ A horse with bilateral hindlimb lameness may appear lame in the RH when the rider sits on the left diagonal and lame in the LH when the rider sits on the right diagonal.⁵ Forelimb lameness is influenced less by the diagonal on which the rider sits, but a similar pattern exists. RF lameness is worse with the rider sitting on the right diagonal.⁵ This difference in lameness expression may be perceptible only by an experienced rider. Mild hindlimb lameness may become most obvious when a horse is ridden in small figure eights (two 10-m–diameter circles linked), especially when the horse changes direction from left to right or from right to left.

Observation of Inclines

Walking or trotting a horse uphill or downhill may exacerbate lameness or identify previously unapparent lameness. Lameness in horses with suspensory desmitis may be worse when they walk uphill or downhill. Lameness associated with palmar foot pain may be worse when the horse walks downhill, and the horse may show a tendency to stumble. Horses that tend to stumble or knuckle behind while walking downhill may have loose stifles (inability to maintain the position of the patella, usually caused by lack of muscle tone). Horses with neurological disease usually show more pronounced clinical signs when walking uphill or downhill.

A superficially flat, hard surface may actually slope; this can influence lameness because the horse’s feet will be tilted with one side lower than the other. Thus the horse may appear different when trotting away from the observer than when returning.