Angular Limb Deviation, also known as ALD, is defined as the shift of a limb from the normal axis in the frontal plane. ALD is most common among young foals due to their constant development.
There are two types of deviation, valgus and varus. Valgus deviation refers to lateral deviation of the limb distal to, or below, the point of deformity. A limb with valgus deviation would bend outward (away from the mid-line of the body). Varus deviation is the second type and describes a limb with medial deviation distal to the point of deformity. A varus deviation would bend inward (toward the mid-line of the body).
Many factors can contribute to the development and severity of ALD. The perinatal factors include premature birth, twin pregnancy, placentitis, perinatal soft tissue trauma, and flaccidity of the soft tissue structures surrounding the joints. These factors can be responsible for the improper development of the small, cuboidal bones in the knee or hocks and/or the elasticity of the joints. Commonly, this condition usually corrects itself as the horse ages and becomes stronger through exercise. However, if the cuboidal bones do not ossify fully, they can be crushed by exercise. The result is abnormally shaped cuboidal bones, which then cause ALD once the ossification does occur.
Developmental factors can also contribute to ALD development and include unbalanced nutrition, excessive exercise, and/or trauma. When horses are involved in group feeding, or “crib feeding,” the most dominant horses are at risk for developing ALD. These dominant horses will generally get the most food and can then over-indulge. When horses over-indulge they have too many carbohydrates and proteins in their diet. The result is disproportionate growth across the growth plate, which ultimately leads to deviation. Alternatively, excessive exercise is not ideal for a developing horse because it can cause micro fractures and crushing of the growth plate. Once again, this situation leads to deviation in the growth plate that usually results in ALD.
Angular Limb Deviation can affect horses of any breed. Studies have shown that thoroughbreds are particularly at risk with an incidence of approximately 11% of foals affected.
In order to diagnose ALD, a licensed veterinarian should always examine the horse and perform the proper diagnostic tests. Some steps to take in order to preliminarily screen a horse for ALD would be to make sure the horse is on a flat, level, hard surface and view each extremity from the front, side, and rear. Deviation from the mid-line can be an indication of a problem.
Additionally, swelling of the joints, palpable swelling (medial or lateral) at the level of the growth plate, wearing of the inside or outside of the hoof, and lameness should not be ignored. If any of these symptoms are present, a licensed veterinarian should be consulted immediately.
The vet will usually observe and examine the horse for an initial diagnosis. They may also do some limb manipulation to rule in or out ALD. Radiographs may be taken in order to determine the location of the “pivot point,” degree of deviation, shape of cuboidal bones, and appearance of the growth plates. If radiographs are taken initially, they help the vet to have a base-line for comparison of future radiographs which allow them to evaluate how well the treatment is working.
It is always appropriate to seek a veterinarian’s opinion. In the case of ALD timing is extremely important and cannot be stressed enough. If caught in time (before the growth plate stops growing or before the cuboidal bones ossify) conservative treatment and stall rest may be all that is needed to treat the horse. Generally, the longer the condition goes untreated, the more invasive the treatment and the greater the chances that it may not be successful.
· Screws with cerclage wires in a figure eight pattern
· Screws with 2.7mm bone plate
· Single screw inserted across the growth plate
Transphyseal bridging is generally used for young foals (less than 3 months old) with severe ALD or foals with major ALD after completion of the rapid growth rate.
Lopez, V.M.D., Jose Garcia. "Angular Limb Deviation." American College of Veterinary Surgeons. ACVS, 17Jun2008. Web. 11 Nov 2011. <http://www.acvs.org/AnimalOwners/HealthConditions/LargeAnimalEquineTopics/Angular LimbDeviationinHorses/>.
*This article has been adapted from the ACVS website. To view the original article by Dr. Jose Garcia Lopez, please refer to the above link.