Luxating Patella
Symptoms, Causes, Treatment and Prevention

"Veterinarians rank patellar luxations according to their severity
based on physical examination."

Luxating patella or "patellar luxation" describe a relatively common condition wherein a dog's kneecap, or "patella," slips out its normal position within the knee joint. While the patella is dislocated, the dog cannot straighten out its leg and will stand with its leg bent or "skip" for a few strides until the kneecap slides back into its normal position.

Luxating Patella - Overview/Snapshot of the Disease

Small breeds like the Pomeranian, Chihuahua, Yorkshire Terrier, Pekingese, Maltese, Miniature Pinscher, Papillion, Poodle, Pug, and Shih Tzu are most commonly affected by luxating patellas. Their kneecaps tend to move to the inside of their knees, which is called a medial patellar luxation (MPL).

Large breed dogs like the Great Dane, Irish Wolfhound and Saint Bernard can also develop the disorder, but their kneecaps more frequently slip to the outside of the leg, which is called a lateral patellar luxation (LPL). In some cases, only one leg will be affected, but about half of the time both legs develop symptoms of the disorder.

Luxating Patella Symptoms

The symptoms of patellar luxation vary depending on the severity of a dog's condition. Most commonly, an owner will notice that while his or her dog is walking, trotting or running it will suddenly hold up a rear leg for a few strides and may cry out in pain. Eventually, the dog straightens out its leg and runs off as if nothing happened.

Veterinarians rank patellar luxations according to their severity based on physical examination. Exam findings include:

• Grade 1: The kneecap can be pushed out of position but pops back into its groove on its own.
• Grade 2: The kneecap can be pushed out of position and does not move back into its groove on its own.
• Grade 3: The kneecap is permanently dislocated, can be pushed back into its normal position but quickly pops back out.
• Grade 4: The kneecap is permanently dislocated and cannot be pushed back into its normal position.

Causes

Patellar luxations develop either because the knee did not develop correctly, in which case genetics may play a role, or because of injury to the joint. The kneecap normally rests in and slides up and down a groove at the end of the femur.

The groove is supposed to be deep enough to prevent the kneecap from spontaneously popping out to one side or the other. But if the groove is abnormally shallow or if an injury has damaged the joint, the patella can move out of the groove causing the leg to "lock up" until the kneecap returns to its normal position.

Luxating Patella Treatment

Treatment for patellar luxations depend on the severity of the condition.

• Grade 1: No surgery. Your veterinarian may prescribe medications that decrease inflammation and pain, promote the production of joint fluid and help cartilage heal and protect itself. Closely monitor your dog to make sure his condition does not worsen.
• Grade 2: Surgery may or may not be recommended. Medical treatment and monitoring as is described for Grade 1 should begin.
• Grade 3 and 4: Surgery.

Several different surgical treatments are available. A veterinary surgeon will determine which is best depending on the severity and exact details of a particular dog's condition. In all cases, the goal of surgery is to keep the patella from popping out of its normal position.

Prevention of Luxating Patella

It is not possible to prevent cases of patellar luxation that originate because of abnormal development of the knee. If you are picking out a puppy from an at-risk breed, it does not hurt to ask if any of the puppy's relatives have symptoms of patellar luxation.

Otherwise, make sure your dog does not become overweight as this increases stress on his knees. At the first sign of any problems, have him evaluated by a veterinarian.

Consulting Veterinarian: Jennifer Coates, DVM

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