Examination of the Foal

It is critical to determine the extent and cause of the deformity before developing a management plan. Foals should be examined while they are standing and walking and radiographically. Occasionally foals are assessed in lateral recumbency.

Deformities can be assessed subjectively by visual examination. The foal should stand as squarely as possible, with the foot directly below the proximal part of the limb. Deviations from this stance exacerbate any deformities that truly exist. Because most foals stand still only transiently, repositioning the foal several times to evaluate each limb independently is often necessary. This allows observation of how the foal stands most frequently in a relaxed position. The clinician stands directly in front of the dorsum of the long bones for evaluation of the forelimbs, not necessarily at the front of the toe. The orientation of the toe may be affected by a concurrent rotational deformity, which confounds interpretation. Hindlimbs should be evaluated similarly but directly from behind. The forelimbs can also be evaluated by standing shoulder to shoulder with the foal, looking down the limb toward the ground.

All limbs also should be evaluated with the foal walking away from and toward the clinician. Breakover is determined for each foot, which may be helpful in deciding the most appropriate way to manage the foal. The entire assessment of a foal should be graded and recorded on video or on paper for future reference.

Radiology provides an objective assessment of angular deformity, but sequential radiographic examinatoins may be unreliable if the obliquity varies. Differences in radiographic projection can result in a misinterpretation of worsening or improvement, which is particularly true when trying to quantify small differences in the angle. Long, narrow (18 × 43 cm) cassettes should be used to measure the angle of the deformity, by evaluating the intersection of a line representing the long axis of the proximal and distal aspects of the long bones from the joint in question. This is more accurate in the carpus and fetlock than in the tarsus. Radiology is essential to identify cuboidal injury or malformation. Such a deformity dramatically worsens the foal’s prognosis. Foals with angular deformity resulting from cuboidal bone abnormalities usually have compromised range of motion, but this often is detected best with the foal in lateral recumbency.

Periarticular Laxity

Periarticular laxity is the major cause of congenital angular limb deformities and often improves dramatically within the first 4 weeks of life, without any intervention, as the periarticular tissues become less elastic. The improvement is most dramatic in a windswept foal, which has a tarsus valgus of one limb and a concurrent varus of the other. Limited exercise is all that is required for these foals to become normal.

Infrequently the deformity can be so severe, particularly in the fetlock, that the foal is unable to bear weight on the sole of its foot. Immediate treatment is required to establish normal weight bearing. Custom-made glue-on shoes are particularly useful to prevent abnormal breakover and to keep the foot flat on the ground. If the foal has excessive laxity of the lateral collateral ligaments and a tendency to break over on the lateral side of the foot, a lateral extension shoe is used to maintain appropriate alignment of the limb. The foal should initially be restricted to a stall before turnout in a small paddock or round pen with just the mare. Soft tissues become progressively stronger, and normal activity can be permitted within a relatively short time. Allowing premature excessive exercise can lead to proximal sesamoid bone fractures (see Chapter 36) and other injuries. Glue-on shoes are usually required for several weeks, but they then should be removed to prevent contracture of the foot. External coaptation also should be avoided if possible. Splints are used only to maintain joint alignment if absolutely necessary. Splints are contraindicated to try to pull or push a limb straight. Rigid support from a splint or cast usually leads to greater soft tissue laxity. Trying to support a limb results in continued laxity and soft tissue wounds from bandaging. Every foal must be managed on an individual basis with the goal of achieving normal weight bearing and function while providing the minimal amount of support necessary.

Asymmetrical Physeal Growth

Asymmetrical growth of a distal physis is a cause of angular limb deformity. Greater growth from the distal physis of the radius medially compared with growth laterally results in carpus valgus. Continued asymmetrical growth precludes the normal correction anticipated with resolution of periarticular laxity. Greater growth from the lateral aspect of the distal physes of the McIII or the MtIII results in fetlock varus. With time and limited exercise (stall or small paddock turnout, alone with the mare) substantial self-correction occurs for most foals with angular deformities. Radiology can be used to evaluate objectively the degree of deformity and the difference in physeal growth, but it is not always required.

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