Patellar Luxation and Dislocation of the Kneecap

Patellar luxation refers to the condition where the patella (kneecap) dislocates out of its normal position. The luxation may be to the indies of the leg (medial) or to the outside of the leg (lateral). The patella normally glides back and forth in a groove in the femur. When this groove is too shallow or there is an abnormal angulation to the limb, the knee cap is displaced out of the groove causing lameness. Patellar luxation is graded from 1(mild) to 4 (severe). Surgery is usually indicated when the degree of luxation reaches a 2 or a 3 and the pet starts to develop consistent lameness. Signs commonly seen with this disorder include intermittent limping or skipping for a few steps and then walking normally again. Dogs may also appear “bowlegged”.

Patellar luxation is most common in Yorkies, Chihuahuas, Pomeranians, miniatures Poodles, but has also been reported in large breed dogs as well. Patellar luxation is most often inherited and affects both knees. A small percentage of cases are traumatic in origin.

Surgery has two goals: to deepen the groove and to realign abnormal tissue tension. The groove is deepened through a process called trochleoplasty. This allows the groove to “capture” the kneecap and hold it throughout the complete range of motion of the knee.

Tissues are realigned by loosening the over tightened tissues (release) and tightening the lax tissues (imbrication). A final step involves moving the small area of bone where the patellar tendon is anchored. This allows the entire apparatus to be realigned down the center of the limb, thus reinforcing the new position of the kneecap within the trochlear groove. The bone is held in place with 2 small pins while it heals. In some case, the pins are removed after healing has completed (in about 8 to 12 weeks).

The overall prognosis with surgery is excellent. Approximately 90% of owners are very happy with the results after surgery.