What is patellar luxation?

The knee cap (patella) normally fits into a groove in the thigh bone (femur). The patella slides up and down in this groove as the leg bends and straightens. Patellar luxation means that the knee cap has slipped out of the groove. There are several reasons why this happens, including malformation of the groove. Luxation may happen only occasionally, or may happen continuously. The knee cap may pop back into the groove on its own, or your veterinarian may need to push it back into place. Your dog will be lame when the patella is out of place. Over time your dog may develop other degenerative joint changes, such as osteoarthritis.

How is patellar luxation inherited?

The mode of inheritance is not yet known. Some researchers think that this disease may be polygenic.

What breeds are affected by patellar luxation?

This disease is inherited in the following breeds: miniature and toy poodle, Yorkshire terrier, pomeranian, Pekingese, chihuahua, Boston terrier, basset hound, shih tzu, silky terrier, and lhasa apso.  (Patellar luxation may also occur in any breed as a reult of trauma.)

For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive. We have listed breeds for which there is a consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.

What does patellar luxation mean to your dog & you?

When present, the condition is usually evident in young dogs by around 6 months of age, but if mild it may go unnoticed until the dog is older. When the knee cap is out of place, your dog will be lame and may refuse to bear weight, or his/her knee may be "locked". The severity of the condition varies widely. In mild cases, the knee cap may only slip out of place occasionally, causing your dog to "hop" for a few steps, and then it may slide back into the groove on its own. In severe cases, the knee cap slips out of place more often, or is never in a normal position. It may not go back into the groove on its own and your veterinarian may need to push it back into place.

As a result of patellar luxation, your dog may develop other degenerative joint changes, such as osteoarthritis. If your dog has a mild case of this disease, you may not notice the actual luxation, but your dog may eventually develop pain due to osteoarthritis.

How is patellar luxation diagnosed?

Your veterinarian will diagnose this disease based on physical examination and palpation. He/she may take radiographs to see if your dog has other problems (such as osteoarthritis) as a result of this disease.

How is patellar luxation treated?

The treatment and long term outcome (prognosis) depend on the severity of disease (how often the knee cap slips out of place, and how easily it slips back into the normal position), and whether there are other problems such as osteoarthritis. Moderate or severe cases often require surgery to make sure that the knee cap stays in the groove in the femur, and to prevent painful osteoarthritis. Exercise restriction is important for a period after surgery, and the results are usually very good.

For the veterinarian:

Patellar luxation may be classified in four grades, with grade I being the most mild. Mild patellar luxation may be discovered as an incidental finding. Severe cases in growing dogs may result in limb deformity. Surgery is usually recommended in moderate or severe cases to stabilize the patella and correct the underlying anatomic deformity. Surgical correction may or may not stop the progression of degenerative joint disease, and reluxation is a possible complication of surgery.

Breeding advice

Affected dogs, as well as their parents, their litter-mates, and any dog which has had surgery for patellar luxation, should not be bred. The Orthopedic Foundation of America - www.offa.org - and Institute for Genetic Disease Control in Animals -  www.vetmed.ucdavis.edu/gdc/gdc.html - have registries for this condition.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources

Martinez SA. 1997. Congenital conditions that lead to osteoarthritis in the dog. Veterinary Clinics of North America Small Animal Practice. pp. 261-290.

Schrader SC . 1995. Differential diagnosis of nontraumatic causes of lameness in young growing dogs. In JD Bonagura and RW Kirk(eds.) Kirk's Current Veterinary Therapy XII Small Animal Practice p. 1171-1180. WB Saunders Co., Toronto.

Copyright 1998 Canine Inherited Disorders Database. All rights reserved.
Revised: April 23, 2002.

This database is a joint initiative of the Sir James Dunn Animal Welfare Centre at the Atlantic Veterinary College, University of Prince Edward Island, and the Canadian Veterinary Medical Association.