What are the symptoms?
A luxating patella can affect both cats and dogs of any breed, but is most common in small or miniature dogs and is rarer in cats. Luxating patella in cats is most commonly found in domestic short-haired cats. Most animals start showing signs as puppies or young adults, although mature dogs can also suffer from patellar luxation.
Although the signs of patellar luxation can vary, you might notice your pet ‘skipping’ as they walk, with their hind leg carried for a few steps before quickly returning to normal. This happens when the patella slips out of the groove and stops when it goes back in again. Some animals will limp continuously, or – if both knees are affected – they may have difficulty walking, or move with a stiff gait.
Patella luxation grading system
Grade 1: the patella can be pushed out of the groove but spends most of time in the groove
Grade 2: the patella approximately half the time in the groove and half the time out of the groove. It can easily be manipulated in or out but has no tendency to stay in either position.
Grade 3: the patella spends almost all the time outside the groove and with pressure can be pushed back into the groove.
Grade 4: the patella spends all the time outside the groove and even with pressure the patella cannot be pushed back into the groove.
When the patella is out of the groove, the groove becomes shallower, or the ridge may be worn away, making the problem worse. Abnormal loading of the joint can, in time, lead to cranial cruciate ligament injury.
Causes of medial patella luxation are not fully understood but include genetic factors, trauma when growing or ligament problems. Many dogs may have a combination of several causes. The luxating patella rubs on the edge of the ridge or the rough bone to the side of the ridge. This wears away the cartilage, eventually causing pain and arthritis.