WHAT IS THE CAUSE?
There are two causes: congenital and traumatic.
In the normal knee, the quadriceps muscle group (large muscles on the front of the thigh) is attached to the top of the kneecap. A ligament attaches the lower part of the kneecap to the tibial tuberosity (the bony prominence on the shinbone just below the knee). The kneecap itself slides in the trochlear groove, a depression in the thighbone.
In congenital cases, early abnormalities in the development of the hip joint promote a complex series of events which results in an inward tension on the kneecap and eventual breakdown of the ligament allowing the kneecap to dislocate. Often, the trochlear groove is abnormally shallow.
Trauma can also cause tearing of the ligament.

HOW IS THE PROBLEM TREATED?
If the cause is trauma, the usual treatment is surgical repair of the ligament.
In congenital cases, the type of treatment is usually determined by the severity of symptoms. Generally, pets with no lameness are not treated. Occasional mild lameness may be treated medically but recurring or persistent lameness is usually treated surgically.

WHAT HAPPENS IF THE PROBLEM IS NOT TREATED?
Chronic patellar luxation can predispose the patient to degenerative joint disease and chronic pain. Dislocated kneecaps cause decreased joint stability and contribute to other ligament injury, such as, tearing of the anterior cruciate ligament.

WHAT IS DONE DURING SURGERY?
Basically, the anatomy of the joint is corrected. In trauma cases, the ligament is surgically reconstructed. In congenital cases, the trochlear groove is deepened (if necessary), the tibial tuberosity is cut off and reattached in an anatomically correct position, and the damaged ligament is reconstructed.

WHAT KIND OF CARE IS REQUIRED AFTER SURGERY?
The recovery period is usually very uneventful. Restricted exercise (no running or jumping) for the first 30 days is very important. It is usually 2-3 weeks before they begin to bear weight and 8-12 weeks before normal activity is resumed.

WHAT IS THE PROGNOSIS?
The outcome varies with the severity of the problem, but most surgery patients are able to resume a normal, active, pain free life.