Angular Limb Deformities
As we enter into foaling season we will be faced with foals with Angular limb deformities (ALD or “crooked legs”). Please use the following as a review of ALD, their causes, and potential treatments.
ALD may occur from various factors such as exercise, nutrition, infection, and abnormal weight bearing or be due to a congenital/inherited defect. The deformities develop over time from unequal growth across the growth plate (or “physis” see figure 1). There are nonsurgical and surgical options to correct these deformities.
The terms used to describe the direction of the deformity are valgus (“knock kneed”) or varus (“bow legged”). These terms refers to the angle created by the bone above and the bone below the joint in question (figure 2). The most common types of ALD are carpal varus (“knock kneed”) seen in yearlings followed by fetlock varus (“pigeon toe”) and tarsus valgus (“cow/sickle hock”) seen in weanlings. In addition to angular limb deformation, a rotational deviation of the limb can occur at the same time. A rotational deformity means that all of the angles of the bones are in lijne but the entire limb rotates inward or outward at the elbow and shoulder. It is most common to see outward rotation with valgus deformities and inward rotation with varus deformities.
Evaluation of foals born premature, dysmature, or those with ALD present at birth should be completed by your veterinarian within the first 24 hours of life. Evaluation should include both subjective visual assessment while standing and walking, and objective radiographic assessment if warranted.
Treatment options include non-surgical and surgical management. Any option has to be balanced with the age of the foal and the remaining growth potential for the affected bones. Minimal growth occurs in the growth plate of the cannon bone growth plate after 3-4 months of age. Minimal growth occurs in the growth plate of the radius (Figure 1) after 16 - 18 months. If non-surgical methods are not successful in correcting the ALD, surgical options need to be initiated while growth potential remains in the growth plate. This means that surgical options need to be started by 3 months in the fetlocks and 14 months in the knee.
- Stall Rest: Effective in newborn foals with incomplete ossification. Stall rest prevents
crushing of the carpal and tarsal bones.
- Hoof Manipulation: Frequent corrective trimming, with or without medial or lateral
extensions, can be an effective way to manage mild ALD.
Surgical correction should be used early in foals with moderate to severe conditions, or in yearlings that were treated unsuccessfully with conservative management. Surgical treatments recommended from your veterinarian are based on the type and severity of the deviation. Treatment recommendations include:
- Growth acceleration: Periosteal transection and elevation (“periosteal stripping”)
- Growth retardation: Transphyseal screw placement (single screw – Figure 3) or transphyseal bridging (“screw and wires” – Figure 4)
Overall Angular limb deformities are a serious but treatable ailment in the growing horse. Multiple treatment options exist and consultation with your veterinarian should be done early and frequently during the growth of your foal.
Reference: Auer JA: Angular Limb Deformities. In: Equine Surgery, 4th edn, Eds JA Auer and JA Stick. Saunders Elsevier, St. Louis. 2012: pp. 1207-1220.
Figure 1: The red arrow identifies the growth plate (physis). This structure is responsible for the bone growing longer.
Figure 2: The left diagram demonstrate a horse with a varus angular limb deformity (ALD) and the right demonstrates a horse with a valgus ALD.
Figure 3: Transphyseal screw placement using a single screw that crosses the growth plate to correct an ALD in the hock (left) or the fetlock (right). This procedure prevents growth on the left side of the growth while the right side grows unimpeded.
Figure 4: “Screws and wires” placed using 2 cortex screws and a steel wire. This procedure prevents growth on the left side of the growth while the right side grows unimpeded.