Angular Limb Deviation

What is Angular Limb Deviation?

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).

What causes ALD?

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.

How prevalent is 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.

What signs and symptoms should I look out for?

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.

What are the risk factors for ALD?

Premature or dysmature foals
Foals with angular limb deformity
Dominant foals fed in groups (crib feeding)

What are some diagnostic procedures the vet might perform?

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.

How do I know if my horse’s deviation is significant enough to request a veterinarian’s advice?

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.

What are the treatment options for my horse if they have ALD?

Non-Surgical:

Stall rest – the amount of time the horse needs to be on stall rest will vary depending on the severity of the deviation and the condition of the growth plates.
Splints and Casts – generally used when ossification is incomplete
Corrective Hoof Trimming and Glue-on Shoes – this procedure may be performed alone or in combination with the above treatments.

Surgical:

Surgery may become necessary for foals who do not respond to surgical treatment, foals that have severe deformities, or the bone is affected after the rapid growth rate is completed.
Periosteal Stripping also called “growth acceleration” – a surgery that involves stripping the periosteum (a thick fibrous membrane that covers the entire bone with exception of the joint) of the bone on the concave side thereby stimulating bone growth on that side. It is believed that this method stimulates growth by releasing tension on the growth plate on the stunted side.
Transphyseal Bridging
also called “growth retardation” – a surgical procedure that creates compression of the physis on the convex side of the deviated limb. There are four different techniques that can be utilized:

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.

Corrective Osteotomy or Ostectomy – technique utilized once the growth plates have closed or if the horse has rotational and diaphyseal deviations. There are two different techniques for this procedure:

What are some potential complications after my horse’s surgery?

Some deviations cannot be corrected.
There is a possibility of overcorrection with the transphyseal bridging technique.

What is the prognosis if my horse has ALD?

There are ranging degrees of ALD and the outcomes may vary depending on the severity of the deviation, condition of the growth plates, and age of the horse.
Mild to moderate cases of ALD with complete ossification of the cuboidal bones have a good chance of deviation correction.
Horses that show peri-articular laxity will generally correct themselves within the first few weeks of life. However, this is not always the case.
If the horse has incomplete ossification the outcome can be serious due to the possibility of developing osteoarthritis and depending on the degree of deviation.
It has generally been seen that foals with carpal deformities fare better than those with tarsal deviations.

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.