Angular limb deformities are common and treatable

By Annette McCoy, DVM
Colorado State University

It's a common scenario---you've been waiting the better part of a year for your mare to foal, and now the day has come. You watch in eager anticipation as the new arrival struggles to stand for the first time, but excitement turns to concern as you realize that the baby's legs are clearly crooked.

Not to worry. It's likely that your foal has an angular limb deformity, which is both common and often treatable. Here are some basics you should know about this condition.

Angular limb deformity, also called ALD, is part of the constellation of developmental orthopedic diseases that can affect young foals. Deformities can be either valgus, with the lower leg pointing away from the middle of the body, or varus, with the lower leg pointing towards the center of the body. The most commonly affected joints are the knee, called carpus; fetlock, or ankle; and hock. More than one joint is commonly affected in the same animal.

There are a variety of different factors that can lead to ALD. These include inadequate maturation of the small bones of the carpus or hock, called incomplete ossification; weakness or laxity of soft tissue structures surrounding the joints; unbalanced nutrition; excessive exercise; and trauma.

Evaluation of ALD should include both a physical exam and radiographs. When looking at the leg, the deformity should be evaluated by lining up perpendicular to the bone below the affected joint. This is important because these foals often have rotational deformities such as toed-in or toed-out conformation in addition to their angular deformities, and that rotation can make the angle look more or less severe when looking straight-on at the leg.

Radiographs can be useful both to determine the severity of the ALD and to determine its origin - the growth plate or the joint itself. In general, deformities originating from the growth plate are more amenable to surgical correction than those originating within the joint. Serial exams done at regular intervals are useful to determine if the ALD is getting worse or better. For example, digital photographs taken weekly from the same distance and at the same angle provide a good objective measure for progression of the condition.

Management of ALD may include conservative or surgical treatment. When deciding which route to pursue, the age of the foal, the affected joints, and the direction--varus or valgus--and severity of the deformity should be taken into account.

Conservative management may consist of stall rest, splints or casts, and corrective hoof trimming. Foals with incomplete ossification must be stall rested and are often placed in splints to support their joints while the bones mature. Stall rest for foals with moderate to severe deformities should not be maintained for longer than four to six weeks; if there is no improvement by that time, surgical correction is recommended.

Corrective trimming, with or without application of special shoes, is best for young foals and those with mild deformities, but is not appropriate as the sole treatment for foals with significant deformities. It is often used successfully in combination with surgical therapy.

Surgical treatment is aimed either at accelerating the growth on the "short" side of the affected growth plate--a procedure called periosteal stripping--or decreasing the growth on the "long" side of the affected growth plate by placement of a screw or screws and wire across the growth plate. These different techniques may be combined on opposite sides of the same growth plate. In very rare cases, a section of bone may need to be removed to straighten the leg.

The outcome for foals treated appropriately for angular limb deformities is very good. Studies have reported that 60 to 80 percent of surgically treated foals have gone on to have athletic careers. However, early, appropriate intervention is crucial for a good outcome. If you suspect that your foal has an angular limb deformity, call your veterinarian, and together the two of you can develop a treatment plan that will give you the best possible result.

Dr. Annette McCoy is a resident veterinarian at the Colorado State University James L. Voss Veterinary Teaching Hospital. She is a member of the surgery and lameness service, serving patients with various performance-, lameness- and surgery-related problems alongside the hospital's faculty veterinarians. Appointments at 297-4471.