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Tails of Seattle: A pets blog

Your local source for news and tips about dogs, cats and other critters, featuring fun videos, reader photos, Q&As and more.

June 22, 2011 at 6:00 AM

Veterinary Q&A: Knee problems in dogs

Posted by Neena Pellegrini

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1. Patella; 2. Femur; 3. Patellar ligament; 4. Tibial tubersity; 5. Medial luxation of patella; 6. Lateral luxation of patella

Courtesy of Animal Specialty Group, in Los Angeles

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Dr. Byron Misseghers, a veterinary surgeon at Puget Sound Animal Hospital for Surgery in Kirkland, answer's this week's questions.

Question: My dog has been diagnosed with luxating patellas. What does that mean in layman terms?

Answer: The knee cap (or patella) is a small, rounded bone associated with the knee joint (called a stifle joint in dogs). Its function is to increase the power that the quadriceps muscle can generate to extend the knee. In layman's terms a "luxating patella" is a knee cap that dislocates to either side of its normal central position over the knee. Medial patella luxation dislocates to the inside region of the knee, and lateral patella luxation dislocates in the opposite direction.

Question: What are symptoms of luxating patellas?

Answer: The most common symptom of a patella luxation is intermittent, non-weight-bearing lameness (limping) where the dog will intermittently carry the affected leg for two to three steps, then walk on it almost normally, then intermittently carry it again. This symptom reflects the intermittent nature of the patella luxation and then resuming its normal position (reduction).

Other symptoms may include weakness in the back legs, making the dog reluctant to jump or climb stairs, or constant ongoing lameness. In severe cases of patella luxation there may be obvious deformity of the hind leg causing severe disability.

Question: Is the problem graded by severity? Can you explain?

Answer: Patella luxation varies from very mild, with the dog showing very little or no symptoms (grade 1), to severe (grade 4). In general, symptoms become more severe and persistent as the grade gets higher. High-grade luxations are more difficult to fix and unfortunately even low-grade luxations (grade 1's and 2's) can progressively worsen to become higher-grade luxations (3's and 4's) over time.

Question: Is it an inherited problem or can it develop in once-healthy knees?

Answer: Medial patella luxation in toy and small-breed dogs is considered a heritable trait that can be passed on from parent to offspring, although the exact mode of inheritance is not fully known (it is polygenic, i.e. multiple genes are involved). As such, it now is recommended that dogs with medial patella luxation should not be used for breeding.

Lateral patella luxation and medial patella luxation in large dogs are also strongly suspected to be a heritable condition according to the Orthopedic Foundation for Animals (OFA).

That being said, patella luxation certainly can occur in a previously healthy knee as a result of injury or trauma, but this only occurs in a small minority of identified cases and is usuallyaccompanied by a clear history of severe trauma.

Question: What kinds of activities aggravate the problem and potentially make the problem worse? Should a dog with luxating patellas limit activity?

Answer: For lower-grade luxations that are actively luxating and reducing spontaneously, activities that cause a lot of twisting of the knee (ball chasing, Frisbee catching, running with quick turns, etc.) can aggravate the problem. For higher-grade luxations the same concern holds true, but they may also exhibit signs ofweakness to the back legs that will make jumping or climbing stairs more difficult.

For both groups, however, it is still important to encourage regular controlled leash walk activity to keep the muscles as strong as possible and also to try to prevent weight gain, which will also aggravate the symptoms of patella luxation.

Question: Is it more common in big dogs or small dogs? Specific breeds?

Answer: Patella luxation can occur in any size and breed of dog (and cats), but, by far, patella luxation is most common in toy and small breed dogs. Most of these are termed medial patella luxations based on the direction of the luxation. Breeds that are commonly affected include, but are not limited to, small/toy terrier breeds (i.e., Yorkshire terriers), Chihuahuas, pomeranians, toy and mini-poodles, Cavalier King Charles spaniels, etc.

In affected dogs, more than half greater than 50% will have patella luxation in both knees.

Question: What are my treatment options: drugs, surgery, etc? Do the grades correspond with treatment?

Answer: For dogs with documented low-grade (grade 1) patella luxation but no appreciable or significant symptoms, a conservative "wait and see" approach is often appropriate. As previously stated, many low-grade luxations will, over time, worsen to a higher grade, so re-evaluation with your veterinarian is important.

Surgical correction should be considered in young dogs with grade 2 to 4 luxations, if possible, as this will slow the progression of arthritis and generally resolve or significantly improve the amount of lameness and give them better overall quality-of-life.

With older dogs, a decision as to whether or not to proceed with surgery may depend on how severe or how frequent the lameness is and how well they respond to medical treatment (non-steroidal anti-inflammatory analgesics, glucosamine, chondroitin sulfate, etc.).

Question: Assuming surgery is the last resort, what can I do to best avoid surgery?

Answer: If surgery is either not recommended by your veterinarian, or not possible for other reasons, the single best thing you can do is to work toward a lean body weight and better muscle conditioning. Overweight pets typically suffer more, and have more disability as a result of orthopedic abnormalities, and medial patella luxation is no exception.

In addition to helping with weight loss, regular, controlled leash walks will also help maintain better muscle tone and strength. Ongoing use of a chondroprotectant medication (glucosamine, chondroitin sulfate, MSM, etc) is also advised, and as a final step, use of a non-steroidal anti-inflammatory analgesic may be helpful, used under the supervision of a veterinarian and on a "lowest effective dose and frequency" protocol.
It should be noted that dogs which are treated conservatively for medial patella luxation appear to have an increased risk of cranial cruciate ligament rupture (a knee injury).

Question: What does the surgery entail? Recovery? Cost?

Answer: The details of surgery are beyond the scope of this blog, but surgery usually involves correcting several anatomical problems, including deepening the groove over the knee where the patella glides, tightening the soft tissues on either side of the patella and moving the bony attachment of the knee cap tendon below the knee to re-align the knee cap.

If both knees are affected and require surgery, the procedure can often be performed on both knees during the same surgery, but generally only in small and toy breeds. For large breed dogs knees are operated one at a time, 2-3 months apart.

Full recovery generally takes eight weeks, but most dogs already are walking well on the leg by three to four weeks following surgery.

The cost of having a patella luxation fixed will vary depending on the severity of the luxation, whether one or both knees are affected, and the size of the dog, but the cost ranges from $2,400 to $3,200.

Dr. Byron Misseghers
Misseghers graduated from the Western College of Veterinary Medicine in 1995. He completed his surgical residency and doctorate program at the University of Guelph near Toronto and is board-certified in small-animal surgery. He has practiced in the Seattle-area for 12 years and practices in Kirkland at Puget Sound Animal Hospital for Surgery.

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Next week's topic: Water safety

Read our past Q&As:

Veterinary Q&A: Flea-control treatment
Veterinary Q&A: Bearded dragon lizards
Veterinary Q&A: Vaccinations for indoor cats
Veterinary Q&A: Lumps and bumps
Veterinary Q&A: More on aging dogs and arthritis
Veterinary Q&A: Puppy and geriatric exams
Veterinary QA: What dogs can safely chew
Veterinary QA: Why does it cost so much to clean a dog's teeth?
Veterinary QA follow-up: More on cleaning a dog's teeth

Veterinary QA: When to spay or neuter

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Do you have a question about pet health? Ask now! We'll pose some of your questions to a local vet in an upcoming post.

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