Luxating patella in dogs (and what "grades" mean)

April 6, 2023 - 5 min read
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Are you wondering why your dog occasionally holds up a back leg and takes a few skipping strides before everything seems to return to normal? This is the most common symptom associated with a luxating patella, a common joint condition in dogs. In this guide, we’ll take a look at what you need to know about luxating patella in dogs.

What Is Luxating Patella?

The patella (kneecap) is a bone that is embedded in a tendon that connects the upper leg bone (the femur) to a bone in the lower leg (the tibia). The patella normally lies within a groove at the end of the femur and is held in place by a dog’s normal anatomy. But when things go wrong, either due to anatomical abnormalities that are present at birth or because of an injury, the patella can move out of place (luxate) to either side of the groove.

When this happens, the leg locks up and can’t be fully straightened. Dogs may skip for a few strides or stand with a bent leg until the kneecap returns to its normal position. They may also be in pain while the patella is luxated.

Luxating patella most commonly affects small dogs. Their kneecaps tend to move to the inside of their knees, which is called medial patellar luxation (MPL). Breeds at increased risk of an MPL include:

Larger dogs can also develop a luxating patella, but their kneecaps more frequently slip to the outside of the leg, which is called lateral patellar luxation (LPL). At-risk breeds for an LPL include:

Keep in mind, however, that any dog (including mixed breeds) can develop a medial or lateral luxating patella.

Patellar luxation usually occurs because a dog’s knee did not develop correctly. In these cases, genetics often plays a role and symptoms tend to develop when dogs are young. A joint injury can also lead to a luxating patella, which can occur at any age.

How to Prevent Luxating Patella in Dogs

Since most cases of a luxating patella have a genetic origin, the best form of prevention is to not breed dogs that have the condition. The Orthopedic Foundation for Animals (OFA) maintains a database of dogs that have been screened for genetic health issues that are common for their breed. Only buy puppies from breeders who perform all the testing recommended by OFA and readily provide reports on the dogs used in their breeding program.

Trauma is a less common cause of a luxating patella in dogs, but preventing injuries (by walking dogs on leash, for example) is important for many other reasons as well. Keeping your dog at a healthy weight may also help, but if your dog has developed any signs of a luxating patella, it’s important to have them evaluated by a veterinarian.

Dog Signs of Luxating Patella

The symptoms of a luxating patella will vary based on the severity of the dog’s condition. The first sign that most pet parents see is their dog suddenly holding up a rear leg for a few strides while walking, trotting, or running. The dog may also cry out in pain, but relatively quickly, the dog often straightens out their leg and runs off as if nothing happened. Sometimes a dog will stand with one or both back legs bent.

A dog’s condition may worsen with time as the bony ridges that normally help hold the patella in place become flatter, the knee joint weakens, and arthritis sets in. When this happens, episodes of patellar luxation become more frequent, and eventually the dog may have symptoms that never go away.

To diagnose a patellar luxation, a veterinarian will first ask you some questions about your dog’s clinical signs, including when they first developed and if they've been getting worse over time. If you can, bring a video of what you have been seeing at home — some dogs are “uncooperative” and insist on looking perfectly fine when they are at the vet’s office.

Then the doctor will perform a physical exam and an orthopedic exam, including an analysis of your dog’s gait when they move. They will try to push your dog’s kneecap out of position, and if they find a patellar luxation they will give it a grade:

  • Grade 1: The kneecap can be pushed out of position but pops back into its groove on its own. Dogs with a grade 1 patellar luxation may not have any symptoms.

  • Grade 2: The kneecap can be pushed out of position and does not move back into its groove on its own. Dogs with a grade 2 patellar luxation will frequently skip and hold the affected leg up, but when the kneecap returns to its correct position, they can walk normally. The knee will often get worse with time because all the abnormal movement of the patella can further damage the knee and lead to arthritis.

  • Grade 3: The kneecap is permanently luxated but can be pushed back into its normal position. It quickly pops back out, however. Dogs with a grade 3 patellar luxation may hold up the affected leg most of the time or use it but in a bent position.

  • Grade 4: The kneecap is permanently dislocated and cannot be pushed back into its normal position. Dogs with a grade 4 patellar luxation will hold up the affected leg almost all of the time or use it but in an abnormal position.

X-rays may not always show a luxated patella since (with grade 1 and grade 2 luxations, at least) the kneecap spends most of its time where it should. But veterinarians still often want to take x-rays to look for underlying knee problems and to see if arthritis is already present.

Treating and Managing Luxating Patella

Treatment for a luxating patella will depend on the severity of a dog’s condition, age, and other factors. Veterinarians may simply recommend monitoring dogs that have a grade 1 luxating patella. It may also be beneficial to give your dog joint supplements that promote the production of healthy joint fluid and help cartilage heal and protect itself.

Grade 2 patellar luxations should be treated more aggressively. In addition to joint supplements, veterinarians often prescribe medications that reduce joint inflammation and pain. Other treatments can include weight loss, avoiding extreme activities, and physical therapy.

Surgery is necessary when a dog has a grade 3 and 4 luxating patella or a grade 2 patellar luxation that isn’t responding well to medical management. Many different surgical treatments are available that all aim to keep a dog’s kneecap from slipping out of position. The surgeon will determine which type of surgery is best based on the details of the case. Most surgeries are successful at reducing the frequency and severity of patellar luxation, and in milder cases, they may eliminate it altogether.

Costs and Insurance

Treatment for a luxating patella can get expensive, especially if surgery becomes necessary. That's why purchasing a dog insurance plan, like those offered by ManyPets, can be so valuable. Just make sure you do so when you first get your dog, before any symptoms of a luxating patella develop, so that it isn’t considered a pre-existing condition.

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Pre-existing conditions and insurance - how does it work?

ManyPets has exclusions for pre-existing conditions, but past conditions don’t always prevent future coverage. Get the details.

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Jennifer Coates, DVM
Veterinarian, Veterinary Writer, Editor, and Consultant

Dr. Jennifer Coates is a writer, editor, and consultant with experience in veterinary medicine, science, animal welfare, conservation, and communications. She has written for outlets including petMD, Chewy, and ManyPets.