In dogs, the growth plates are responsible for longitudinal bone growth, which takes place primarily during the fourth to eighth months after birth. On an X-ray, growth plates appear as a black lines at the ends of the bones. By one year of age, most growth plates have disappeared and growth, for the most part, ceases. The growth plate is the softest part of the bone; therefore, it is prone to injury. If an injury to the growth plate has occurred during the period of rapid growth, the bone may not grow to a normal length, or it may become twisted.
Cause of angular limb deformity of the forelimb
The forelimb has two bones between the carpus (wrist) and the elbow joint, the radius and ulna. The growth plate of the ulna, located near the carpus, is particularly susceptible to becoming injured, as it is shaped like a cone (indicated by the white arrow). This V-shaped (conical) growth plate of the ulna is responsible for about 90% of the bone’s longitudinal growth. Therefore, following damage to this growth plate, the ulna will be shorter than normal. The result is a “bow-string” effect in which the radius becomes bowed. This causes the limb to become twisted and bowed near the carpus. In addition, the elbow joint may become pulled out of alignment due to the shortened ulna.
Signs and diagnosis
Angular limb deformities may affect both large and small breed dogs, and signs are typically seen when the dog is less than one year of age. Lameness and twisting of the limb are the cardinal signs of an angular limb deformity. In some dogs, the elbow joint may be pulled out of alignment, thus causing swelling and pain in this joint. Bowing of the limb to the side may cause pain in the carpus joint due to excessive stresses put on the ligaments (medial collateral ligaments). The diagnosis of an angular limb deformity is based on physical examination findings and X-rays of the affected forelimb. The surgeon likely will take X-rays of the affected and normal limbs, with your pet under sedation, in order to develop a precise surgical plan to correct the deformities.
If the patient is still growing, and the angular limb deformity is not severe, a simple surgery involving partial removal of the ulna will allow the limb to straighten out within a few months.
If the patient is eight months of age or older, or if the deformity is severe, the limb must be surgically straightened. The ulna and radius bones are cut near the carpus, where the bones are twisted. The limb is then realigned to correct the deformity. The bones are held in place by means of an external skeletal fixator or a bone plate and screws.
The external skeletal fixator involves placement of pins through the skin and bone. These pins are fastened to external bars with a series of clamps (see photo on next page). The advantage of the external fixator over plate/screws is that the surgeon can readjust the bones after surgery to fine tune the alignment of the limb.
The second method to secure the bones in place is with a bone plate and screws. This method of bone fixation has the advantage that less patient care is required in the post-op period.
If the elbow joint has been pulled out of alignment by the shortened ulna, an additional cut is made in the ulna bone, just below the elbow, to allow the bones (ulna/radius) to spring back into position.
Surgically correcting an angular limb deformity has the advantage of relieving carpus and elbow pain and preventing arthritis from developing within the joints over time. Uncommon complications following surgery include infection, non-healing of the cut bones, breakage of the implants (metal plate, screws or pins), bone cancer (from leaving implants in place), cold sensitivity and fracture of the bone. In general, about 90 to 95% of the patients that have surgery will heal uneventfully.
For more information on this subject, speak to the veterinarian who is treating your pet.