Chapter 98Experiences Using a High-Speed Treadmill to Evaluate Lameness
The advent of the high-speed treadmill has led to many advances in evaluating equine poor performance in exercise physiology, gait analysis, cardiac disease, and lameness diagnosis.1-5 This chapter describes our experience using a high-speed treadmill for lameness evaluation in the performance horse.
Lameness has been implicated as a cause of poor performance in several studies involving a complete physical examination, lameness examination, and where possible a high-speed treadmill examination.1-3 In one study, 74% of horses were found to have lameness as a component of poor performance.1 In another study, in which horses with no apparent history of lameness were examined because of poor performance, clinically important lameness in 23.9% of horses precluded a high-speed treadmill investigation.2 In a third study, 4.3% of horses sound enough to undergo a high-speed treadmill examination for poor performance were clinically significantly lame after high-speed treadmill exercise.3
In our experience, convincing trainers and owners that lameness is a cause for poor performance can be difficult. Several studies using a shoe model to induce lameness to assess the metabolic cost of pain related to lameness suggested a trend that pain related to lameness may not increase the metabolic cost of exercise, but it does increase the heart rate in response to pain.6-8 However, another study suggested that a metabolic cost of pain and exercise does occur.9 Pain may alter a horse’s ability or willingness to perform up to expectations or previous performance levels.10
The most common criterion for a treadmill lameness examination is lameness that occurs at only high speeds or after an extended period of exercise. The treadmill examination is used most commonly in Standardbred (STB) racehorses or endurance horses. However, a treadmill lameness examination can be used in any breed or discipline, although a horse in which lameness is apparent only when the horse is ridden may be unsuitable.
Horses in which a complete lameness investigation, including diagnostic analgesia and appropriate imaging technologies, fails to reveal a diagnosis are potential candidates for treadmill lameness examination. Additional candidates include horses that require considerable work at low, medium, or higher speeds before the lameness becomes apparent, such as endurance horses or STB racehorses. A treadmill lameness examination also may be useful in horses that are fractious or otherwise pay little attention when jogged in hand or ridden. Horses must pay close attention when trotting on a treadmill and therefore have a more even, rhythmical, relaxed gait that is easier to evaluate.
Important historical facts need to be ascertained. Some questions are general, and some are use related. Some may need to be repeated in a different order to elicit an accurate answer. Questions may include those listed in Box 98-1.
The treadmill must have a speed of at least 7 to 10 m/sec. Most horses will not canter until the speed exceeds 7 m/sec. Lameness is usually evident at lower speeds, but occasionally it is necessary to see a horse trot at up to 7 m/sec for lameness to become manifest. In addition, for further poor performance evaluation the treadmill needs a speed of at least 14 to 15 m/sec and the capability of being elevated to at least a 6-degree slope. Ideally the treadmill should be mounted in the ground, which is safer. In our experience clients and horses easily adapt to an in-the-ground treadmill. It is easier to use video equipment with a treadmill in the ground, rather than above the ground.
At least 4 to 5 m of space in front of, behind, and on either side of the treadmill is needed to allow for equipment, cameras, and personnel and to allow room for the horse to move off the front, rear, or side. The moving treadmill surface is relatively forgiving. In one study in which a horse had a strain gauge placed on the left third metacarpal bone, bone strain was measured as the horse galloped on a dirt track, on a wood chip track, and on a treadmill. Compared with the dirt track bone strain was 75% less when the horse galloped on the wood chip track and an additional 75% less when it galloped on the treadmill.11
Kinematic analyses include high-speed cinematography, videography, electrogoniometry, or accelerometry to quantify the movements of the limbs and torso during exercise. Kinetic analyses use instrumented shoes, force plates, and pressure-sensitive mats to measure forces that affect, arrest, or modify motion. The reader is referred to Chapter 22 and other references. Many of these systems are expensive, time-consuming, and cumbersome and require considerable expertise to use. The ideal gait analysis system provides considerable data, which are obtained easily, are visually and statistically analyzed, and are not too expensive. The system must be fast enough to assess correctly diagnostic analgesic techniques in a timely fashion and simple enough to not alter the gait of the horse.12,13
Simple systems can be assembled with a digital video camera, a tripod, and a computer, using simple video editing software to review and edit the images. If a computer is not available, video editing tape decks can be used. The camera or cameras are placed perpendicular to the side and front or rear of the treadmill. Caution must be used with the rear camera. Enough light must be available for adequate video viewing (at least two 1000-W lights or equivalent).12,13
The video camera should be a digital camera (some Hi-8 cameras are still functional) with a video stabilization system and should have a shutter speed of at least 1/2000 (digital) or 1/4000 (analog).14 Most consumer-grade cameras film at 30 frames per second (fps). Therefore some video loss is apparent compared with more sophisticated (200 fps) and expensive systems. Digital and Hi-8 video create less video noise and provide a superior viewing experience. For rapid viewing the recorded tape can be placed into a digital videocassette recorder that has a jog-shuttle device for stop frame viewing or frame grabbing. Alternatively, video editing tape decks, which are more expensive than traditional videocassette recorders, can be used. Digital images also can be reviewed on a computer and thus more accurately analyzed and edited. Turnkey systems including hardware and software using universal serial bus or IEEE 1394 rapid transfer technology are available.
Using video technology allows the clinician to critically examine the baseline lameness and lameness after diagnostic analgesia, record them in real time, analyze the differences in real time slow motion, maintain a permanent record for follow-up examinations, and demonstrate to the owner or trainer the difference in gait before and after a successful block. Video analysis also can be useful in demonstrating initial footfall, footfall after trimming or shoeing, and the effects of different types and weights of shoes. The technology gives one a new appreciation for lameness, motion, conformation, and gait at a walk, trot, or higher speed. The camera is much more sensitive than the human eye and can answer many questions and create new ones.12,15,16
It is important that a horse be reasonably fit to perform an accurate treadmill lameness examination. STBs should be trained down to at least a 2-minute mile. Endurance horses, in which lameness may not occur for several miles, need to be at least fit enough to accomplish this task easily. Other horses should be in regular work. To do otherwise places the horse and examination at risk. Unfit horses run the risk of exertional myopathy, thus obfuscating the results of any lameness examination.
We prefer horses to wear shoes when being examined for lameness. Tremendous friction and therefore heat are generated by the contact of the horse’s foot and the treadmill belt. Whenever a foot contacts the belt, the foot slips and therefore causes friction. Many research horses that exercise daily on a high-speed treadmill have chronic foot problems secondary to the heat generated. This heat can be enough to melt the glue of glue-on shoes at higher speeds. If the horse is not shod, the toes of the hind feet can break off and bleed, leading to substantial lameness for several weeks. We do not place any type of tape on the horses’ shoes. We recommend using flat shoes, with no toe grabs, stickers, borium, or turndowns. This minimizes wear to the treadmill belt, which when used daily lasts 9 to 12 months before replacement is required. We recommend that shoeing changes be made 3 to 5 days before a treadmill examination, in case foot problems related to shoeing are found that may mask the horse’s actual primary lameness.
Examination for lameness on a treadmill requires at least three people. One person controls the treadmill and the horse’s head, one person stands behind the horse to keep it moving forward if necessary, and one person is the clinician. The clinician is responsible for operating the video equipment and observing the horse at a walk, trot, and any other desired gait. Occasionally, two people are required at the head for fractious horses.
Schooling of the average horse usually takes about 30 minutes to 1 hour before the horse is ready to be examined for lameness. Most (>99%) horses can be schooled and examined for lameness or poor performance in the same day. This period includes acclimating the horse to the treadmill and the fan noise, standing on the treadmill with the machine off, and moving with the treadmill at the walk, the trot, or pace at medium speed, a canter at low speed (7 m/sec) for non-STBs, and then at rest. STBs then are harnessed and moved up to a speed of about 7 m/sec for 200 to 300 m. Most horses adapt easily using this method of schooling, which is safe and successful in 99% of horses examined for lameness or poor performance. Occasionally, horses are recalcitrant or scared and need to be reschooled a day later and usually adapt well. Some horses (<1%) cannot be examined because the examination would not be safe for the horses or personnel.17
Safety of horses and personnel is paramount. Personnel must be cautioned to be alert at all times and not to stand behind the horse when the treadmill is moving. Shoes and horses can come off the treadmill without warning. Substantial injuries (e.g., tendonitis) occur in less than 1.5% of horses. Lacerations, broken-up hind feet, and myositis occur in less than 5% of horses.17 All horses wear protective boots on all limbs. All STBs are schooled first without equipment (tack), but with protective boots, and then they wear the normal equipment plus protective boots if they move at speeds greater than 7 m/sec.
To minimize the risk of injury to personnel and horses, it is important to have a trained team to examine each horse. Personnel should block any windows through which the horse can see out, eliminate as many noise distractions as possible, and ensure that no doors can be opened in front of the horse during schooling or exercise. This allows the horse to concentrate on keeping up with the treadmill and minimizes fright or distraction of the horse during the examination.
Most lameness is seen best in all breeds with a minimum of equipment in place. STBs, which usually race checked up, are examined first with a minimum of equipment (i.e., no hobbles) and not checked up. Many lameness conditions in STBs can be obfuscated, changed, or eliminated when a horse wears its equipment and in particular, when checked up. Other horses are examined wearing just a halter unless some equipment change exacerbates the lameness (rare). A riding horse may need to wear side reins. Occasionally, STBs with carpal or stifle lameness are worse when wearing hobbles.
Horses are first examined at the walk and then at the trot and are recorded on video. Recording from the side is useful to evaluate stride length and frequency. Examination from the rear is helpful in evaluating the swing of the forelimbs and hindlimbs and the footfall.
Observation of lameness using a treadmill is different from the standard lameness examination because the horse is stationary relative to the observer, allowing viewing and video recording of the horse’s gait from the side, front, and rear. The most useful gaits for observing lameness are the trot and pace. These are symmetrical gaits and allow for easier evaluation of lameness and gait rhythm.13
The horse should become comfortable at the trot, so that the lameness or gait abnormality can be established. An audible rhythmic pattern to the gait also becomes apparent. The horse is in rhythm (normal) or out of rhythm (lame). In addition to video recording for later viewing, it is important to evaluate the lameness concurrently to establish a baseline. If lameness is not readily apparent, reviewing the video immediately before performing diagnostic analgesia may be advantageous. Although detecting a difference in footfall is a standard part of any lameness examination, in our experience footfall may be exacerbated on a treadmill. Sound horses that trot have a symmetrical, diagonal, two-beat gait, and pacers have a symmetrical, lateral two-beat gait. The horse should be observed carefully for a change in how the horse swings its forelimbs or hindlimbs. In STB pacers, any change in how the horse moves from side to side at the poll or hips, when viewed from the rear after diagnostic analgesia, is important. These horses, whether pacing free-legged (no harness) or when in harness or checked up, have a tendency to swing from side to side and land more heavily or with greater excursion on the sound side. An in-depth description of these gaits is available.13
In addition to elimination of lameness, a change in stride characteristics may occur, including stride frequency, length, and swing plane. Some horses not accustomed to the treadmill, or not comfortable on the treadmill, may have an increased stride frequency and shortened stride length, which also may be seen in lame horses.13 Once accustomed to the treadmill, many sound horses exercised at medium to higher speeds on a treadmill have a longer stride and thus a lower stride frequency.18 However, lame horses may have an increased stride frequency and shortened stride length.19 This can best be demonstrated and seen using video.
Other, more subtle changes include improvement in gait fluidity, improvement in use of the head and neck and shoulder, and change of an anxious eye expression, flexion of major joints, foot flight, width and rhythm of gait, and footfall. Occasionally, horses may become stiff or anxious and lame or lamer in front or behind during or after exercise. Exercise should be discontinued. Exertional myopathy (see Chapter 83) or aortoiliac thrombosis (see Chapter 50) should be considered likely causes.20,21
It is useful to measure creatine kinase and aspartate transaminase concentrations before and after exercise to monitor horses for subclinical myopathy, overt myopathy, or previous undiagnosed myopathy.21 If aortoiliac thrombosis is suspected, a rectal examination and an ultrasonographic examination per rectum should be performed. Horses with aortoiliac thrombosis commonly become lame behind during or shortly after commencement of exercise.20 They have an anxious look and can sweat more profusely than their level of exercise would dictate.
The treadmill provides a smooth, even surface at a constant, controllable speed and a horse that is stationary relative to the observer. Some horses are lame in hand, but not on a treadmill, and some are lame on a treadmill, but not in hand. Horses that are lame only on turns are difficult to evaluate on a treadmill, which operates only in a straight line. Some horses will not tolerate working on a treadmill.22-24