Description

Physitis is a condition that causes deformities in the legs of young foals, mostly weanlings and yearlings, that are growing rapidly and that have a diet that is out of balance in certain minerals. The condition can develop at any time while the growth plates in the limbs are still open.

Physitis involves swelling around the growth plates of certain long bones in young horses causing angular limb deformity. It can be a component of osteochondrosis which is a condition related to the process by which cartilage is converted to bone.

The changes seen in physitis also occur in clinically normal horses; the condition is seen frequently in well-grown, fast-growing, heavy-topped foals during the summer when the ground is dry and hard, and on stud farms where the calcium to phosphorus ratio in the diet is unbalanced.

The condition can result in an angular limb deformity in a foal can take the form of a lateral or medial deviation of the limb. In some cases there will be a rotational deformity present in conjunction with the angular deformity.

Sometime, factors related to physitis are present at birth, but foals that are normal at birth and develop an angular limb deformity are more likely to suffer from one or more developmental factors related to growth of bones in their legs.

Symptoms

• Lameness
• Stiff gait
• Reluctance to move
• Pain on deep palpation
• Heat in affected area
• Enlargement of the distal radius, tibia, and cannon bones
• Hourglass appearance of the knee, hock, and fetlock joints

Causes

Suggested causes of physitis include malnutrition, conformational defects, faulty hoof growth, compression of the growth plate, and toxicosis. The most acceptable hypothesis at this time appears to be the compression theory.

Prevention

Since the condition affects foals with pre-existing angular limb deformities and weanlings or yearlings with straight legs, attention needs to be given to proper diet, proper exercise, and careful hoof trimming based on a veterinarian's advice.

As a preventive measure, the older foal or yearling that is fat or heavy-topped should be watched carefully for clinical signs, especially when the ground is hard and dry. When these conditions prevail, feed rations and exercise should be restricted.

Treatment

Conservative treatment includes corrective hoof trimming and shoeing. Corrective trimming should be performed on all foals that are confined in order to accentuate the benefit of stall rest. If the feet are trimmed properly, the weight distribution across the physis changes and it will adapt it's growth in order to straighten the leg.

Treatment consists of reducing food intake to reduce body weight or at least growth rate, confining exercise to a yard or a large, well-ventilated loose box with a soft surface, ensuring that the feet are carefully and frequently trimmed, and correcting the diet if necessary. Vitamin D supplements are indicated, but the dosage must be monitored closely to avoid hypervitaminosis D.

Anti-inflammatories and other treatments may be recommended by a veterinarian to provide pain relief and enable the foal to engage in proper exercise.

Veterinarians sometimes suggest surgical options. Surgery becomes necessary in some cases if the best possible outcome is desired. There are different surgical options, some depending on the severity of the angulation, and others on the surgeon's preference.

Periosteal stripping is performed on the concave surface of the limb, just proximal to the affected growth plate. Periosteal stripping is only beneficial in cases where the angular deformity is coming from an active growth plate.

Periosteal stripping can be performed at any time and is beneficial up to the time that the growth plates close, but is most effective prior to 4 weeks in the distal metacarpus/metatarsus, and 4 months in the distal radius/tibia.

The drawbacks of periosteal stripping is that it is unlikely to provide enough straightening with legs that are deviated more than 15 degrees, and stripping alone is unlikely to improve any type of rotational deviation.

Transphyseal bridging should be used in any case in which the deformity is 15 degrees or greater, or after 4 weeks in the distal metacarpus/metatarsus, and 4 months in the distal radius/tibia. There are different techniques used to bridge the physis.

The basic premise is to retard the growth of the convex surface of the limb by bridging the physis with some type of mechanical device such as bone screws and wires, staples, or bone screws and small bone plates. All of the techniques have positive aspects and drawbacks. The veterinary surgeon's preference usually dictates the method chosen.