Congenital Limb Deformities in Horses

By Sara Mastellar

This article discusses congenital deformities in horses. Before we begin, let’s define a few terms. “Congenital” refers to a condition that is present from birth. “Deformity” refers to the state of being malformed or misshapen. This discussion will focus on conformation, health, and well-being aspects affected by congenital deformities in horses. There are many congenital deformities, but we will focus on contracted flexor tendons and angular limb deformities.

Figure 1. Contracted Flexor tendon. Image courtesy of InfoVets.

The flexor tendons are located behind the cannon bone (the large bone between the horse’s knee and fetlock). The deep digital flexor tendon attaches to the bone inside the horse’s hoof, known as the coffin bone. If the flexor tendons were to be contracted or shortened, it would cause the horse’s leg to curl up beneath itself. Contracted flexor tendons are usually associated with postural and foot changes; there may be signs of lameness and a lack of strength and energy needed for a newborn foal to thrive. Contracted flexor tendons are common in foals, and is a problem that most equine practitioners handle routinely. This disorder may be present at birth or acquired during the growth process.

Potential causes
Possible causes include malpositioning of the foal in the uterus, exposing the mare to toxic substances, or the parents passing genetic defects onto the foal. In cases where the horse acquires the disorder, it could be caused by lack of strength because of long-term pain. The pain may arise from different reasons, such as physitis, osteochondritis dissecans, osteoarthritis, soft tissue wounds, or even infections. The horse may try to relieve the pain by withdrawing the limb, walking on its toes or even walk on the front of the fetlocks, depending on the amount and source of the pain the foal is experiencing. Also, nutritional imbalances can cause problems with bone growth, which can cause the foal to acquire contracted tendons while growing.

Signs/Symptoms
The foal may have a contracted flexor tendon if it cannot stand, attempts to walk on the upper part of its fetlocks, or it may stand knuckled over the fetlocks or carpi (knees). They may walk on their toes or even with their heels off the ground and may move slower and produce a “boxy” hoof with an elongated heel and toe that curves up. Horses that are 1-2 years of age usually knuckle over at the fetlock joints, resulting in the swelling of the joint and surrounding tissue. The horses are usually upright and straight-legged in both forelimbs and hind limbs. Yearlings are usually more difficult to treat than younger horses.

Treatment
Identifying this condition early will result in the best outcome for your young horse. The veterinarian must do a complete examination to determine which specific tendons are affected and if the cause was a nutritional or congenital factor. Treatment will vary on a case by case basis. Common treatments include splints, casts, changes in nutrition, and corrective hoof care. For foals less than 1 year of age the pain can usually be subsiding with nutritional correction, proper hoof trimming and treatment of underlying pain. Surgery and stretching exercises may also be indicated. The outlook and recovery for this condition is fair to good if the horses are diagnosed early and managed properly, even if surgery is required. This means many will go on to have successful performance careers.

Angular Limb Deformities
Young foals are commonly known to have crooked legs (either front, hind or both), which is also known as an angular limb deformity. Some congenital deformities can affect the horse’s conformation or even its ability to perform, depending on the severity of the deformity. Angular limb deformities are defects in the musculoskeletal system. Foals with angular limb deformities have legs that deviate from straight when looked at from the front or rear.

Potential causes
Potential causes include how the foal is positioned in the womb, a thyroid deficiency, trauma, a poorly formed or loosely jointed limb, or even under-development of the carpal (knee) or tarsal (hock) joints and long bones. Depending on the case and the foal, one to all four of the limbs may be affected. The joint that is affected most often is the carpus (knee), but on some occasions the tarsus (hock) and fetlocks are involved.

Signs/symptoms
Signs, other than deviation of the limb, are not visible in foals, but lameness and soft-tissue swelling that can accompany severe deformities. Foals with poorly conformed carpal (knee), outermost tarsal (hock) bones, or excessively loose joints often become lame as the deformity worsens. One way this deformity is diagnosed is through a veterinarian taking radiographs of the limb. Treatment varies depending on the severity of the condition and the tissue affected.