Approach to Diagnosis of Lameness and Stiffness in Horses

Particular attention should be directed toward palpation of the limbs. The majority of lameness will originate from the carpus distally in the front limb. Common sources of lameness in the hindlimb can be identified from the stifle distally. All palpable structures should be evaluated, including skeletal structures, synovial structures (joints, tendon sheaths, and bursa), and soft tissue structures (tendons and ligaments). This portion of the examination can be performed using different methods, either by palpating each tissue in one pass of the limb or by making multiple passes of the limb, palpating each tissue structure separately. Regardless of the preferred technique, a consistent and complete examination should be performed. Once the limbs have been palpated in the weight-bearing position, the examiner should palpate them in the non–weight-bearing position. This allows for separation of the soft tissue structures and facilitates deep palpation of the suspensory apparatus. Comparing limbs is often useful for distinguishing an abnormality from an unusual or unique conformation.

The relative size, shape, and condition of the feet (e.g., contracted heel, scuffed toe); length of heel; and pattern of shoe wear (e.g., thinner branch on the outside of the shoe than on the inside) give clinically significant but often overlooked clues to the site and cause of lameness. Evaluation of the feet with hoof testers is mandatory; most lameness arises from problems in the forefeet.

Certain signs indicating trauma (e.g., wounds, swelling, hair loss, pain) may lead to more important findings such as underlying evidence of a fracture (e.g., bony crepitus, warm or cold areas, bony protuberance). Observe from a distance—the mobile phase. Observations made from a distance while the horse is moving can be evaluated critically once clues provided by the history, as well as observations made of any postural deformities, direct the practition­er’s attention to a specific area of the horse’s body. This part of the examination is conducted while the horse is moving in at least two gaits, the walk and the trot. Sometimes it is also helpful diagnostically to observe the horse move at other gaits (e.g., canter) or while under saddle. It may also be beneficial to observe the horse on different surfaces (hard and soft) to amplify different lameness issues. If possible, the horse should be evaluated under conditions similar to those under which it performs. At a walk the horse should be observed moving toward and away from the examiner. The breakover point of the foot at the toe, the arc of the foot flight, the distance covered by the foot in the swing phase, and the placement of the foot should be evaluated for each limb and should be compared between pairs of limbs. Although many abnormalities can often be observed only during a trot, some conditions may cause a subtle alteration in gait that can be observed only at a walk (e.g., fibrotic myopathy, stringhalt).

Recognizing the asymmetric movement of the head and neck for frontlimb lameness and the asymmetric movement of the pelvis for hindlimb lameness is a common method of lameness identification. Hindlimb lameness issues often present the greatest challenge.

Sound horses at a trot show a perfect sinusoidal pattern for all midline body locations, including the head, withers, and tuber sacrale. The height of these structures falls from the beginning of the diagonal stance phase, reaching the lowest position at midstance, and then rising to the highest level at or shortly after the end of the stance phase (suspension). Correlating head and neck movement with the correct frontlimb lameness is relatively easy. It is well recognized that the head is elevated during the stance phase of the lame limb, with an increase in downward motion during the stance phase of the sound limb—“down on sound.” Lameness can also be recognized by changes in the distal limb, including changes in the motion of the MCPJ. During the stance phase, the hyperextension of the MCPJ is decreased with increasing lameness in the lame limb, whereas in the contralateral sound limb an increase is seen. With respect to stride length and foot flight, with forelimb lameness the caudal phase of both the lame and the sound limbs becomes shortened, whereas the cranial phase remains unchanged. In the hindlimbs the opposite is seen; the cranial phase is shortened and the caudal phase remains unchanged. This may be explained by the significantly decreased suspension phase following the lame diagonal. In the forelimbs the arc of the lame front foot is unchanged, but there is an increase in the arc of the sound front foot. In the hindlimbs, the arc of the foot flight in the lame hindlimb is lower than the sound limb in most cases. The change in maximal hoof height during the swing phase appears to be the result of changes in trunk height and is no indication for reduced flexion in the upper joints or an effort to reduce the pain when the hoof lands. Medial (winging) or lateral (paddling) deviation of the distal limb during the flight phase can result in interference and trauma to other limbs and potential lameness. Conformational abnormalities, most commonly toeing in or toeing out, give rise to an alteration in the point of breakover and a change in the flight of the distal limb. Poor foot balance caused either by poor conformation or by poor trimming can result in similar flight patterns.

Plaiting describes adduction of the lame limb directly in front of or lateral to the opposite limb. In the front limbs, plaiting is commonly the result of faulty conformation, but in the hindlimbs it is more commonly associated with lameness. This pattern of travel is often associated with upper limb lameness but can also be seen with distal hock or proximal metacarpal disease.

A dampening effect also appears to occur as an adaptation to lameness. This effect is more pronounced in the hindlimb than in the frontlimb. Flexion of the shoulder and hock joints actually increases during weight bearing in the lame limb. This is probably an increase in the function of the shock-absorbing mechanism. The increased flexion cannot be related to increased loadings but has to be attributed to a gentler braking of the flexion by the extensor muscles. In such a way, the loading of the lame limb with the body weight occurs more gradually, reducing the peak forces in the hoof.

The tuber coxae are typically the landmark of choice in evaluating hindlimb lamenesses. Because the tuber coxae are more laterally located, the pattern is different from that seen in the head. Also, because the hindlimbs lack closely located segments, such as the neck and head, an enhancement of the vertical movements must be found in a rotation of the back around a longitudinal axis. Such a rotation is indicated by different vertical displacements of one tuber coxae during both stance phases. The vertical movement of the tuber coxae exhibits a characteristic pattern of a double-waved, slightly asymmetric line during one stride. The lowest point of the hip is reached in the middle of the stance phase of the right contralateral limb. The highest point of the hip is reached shortly after the stance phase of the contralateral limb, just before the stance phase of the left hindlimb.

Kinematic studies have more clearly defined the notion of “hip hike” and “hip drop” and have recorded regular patterns of pelvic movement in lame horses. Consistent findings in the overall pelvic movement in the lame horse include less downward movement during the midstance phase and less upward movement at the end of and after the stance phase of the lame limb. This can give the appearance of an overall pelvic elevation during the stance phase of the lame limb as compared with pelvic height during stance of the sound limb; a similar exaggerated pattern is seen in the tuber coxae. The tuber coxae also exhibit less downward movement during the midstance phase and less upward movement at the end of the stance phase in the lame limb. More notably, there is more downward movement during midstance of the sound limb (midflight of the lame limb) and more upward movement at the end of stance of the sound limb (impact of the lame limb), giving rise to the notion of a “hip hike.” These changes result in an increase in the overall vertical movement of the tuber coxae on the lame side as compared with the sound side. Clinically, many find it easier to identify the exaggerated excursion of the tuber coxae to identify the side of the lameness.

Lateral movement or drifting of the hindend can also be seen in horses with unilateral hindlimb lameness. Horses tend to drift or move away from the side of the lameness. Subtle lameness with an absence of asymmetric pelvic movement may present with a consistent drifting to one side or the other.

Once the initial standing and mobile examinations are completed and the affected limb is identified and the lameness graded, isolating the specific region of the limb is the next goal of the lameness examination. Manipulative tests or stressing of articulations and associated soft tissue structures can provide additional information as to the location of the source of lameness. Flexion and extension tests are designed to stress selective regions of the limb and observe the effects of the manipulation on the lameness. These tests are also commonly performed on the sound horse to reveal potential areas of concern, particularly during prepurchase examinations. Flexion and extension manipulations also enable an assessment of range of motion. Interpretation of these tests should be approached with caution. They are seldom specific for one particular joint. For example, the fetlock flexion test not only stresses the fetlock joint but also places stress on the proximal and distal interphalangeal joints; the hock flexion test also flexes and stresses the stifle joint because of the presence of the stay apparatus. If a flexion test results in a positive response, the horse should be walked out of the response and observed before additional manipulations. Occasionally exacerbation of the lameness will persist for an extended period of time, which changes the baseline lameness and clouds the interpretation of additional manipulations.

It is common for horses to be presented with multiple lameness issues. Secondary lameness or compensatory lameness is the result of increased stress or overloading of the other limbs in response to the primary lameness. This most commonly occurs in the contralateral limb but can also occur between frontlimbs and hindlimbs. The secondary lameness can also be the result of shifts in body mass that produce an apparent or phantom lameness. Phantom lameness is less severe than the primary lameness. The following guidelines can be used to aid in the differentiation between a real or compensatory and an apparent or phantom lameness.