Patellar luxation occurs when the kneecap slips out of place. It can be a congenital or developmental condition, or it can occur from trauma. Pets with patellar luxations may exihibit varying degrees of lameness, and if left untreated, the condition can lead to arthritis and other orthopedic problems. Mildly affected dogs are often prescribed joint supplements and pain-relieving medications. More serious cases require surgery to remedy the condition.
Patellar luxation is a common condition of smaller dogs and, occasionally, of larger breeds. It can also occur in cats, but not as often as it does in dogs. The knees, in this case, are the site of the problem. Normally, the kneecap (or patella) sits in a groove at the bottom of the femur (the major bone of the upper leg), where the femur and the tibia (the major bone of the lower leg) meet at the knee. The patella is held in place by ligaments and muscles. Patella luxation occurs when the patella slips (luxates) out of the normal position in the groove.
Imagine if your kneecap spontaneously moved to the inside or outside of your knee (medially or laterally). What you’d inevitably feel is not so much the pain but the instability caused by the misaligned joint structure. In most cases, the abnormal positioning of the patella means your leg won’t hold you up like it should. And that’s exactly what affected pets experience.
This luxation of the kneecap may lead to significant arthritis and, in some cases, predisposes the dog to even more severe degenerative changes of this joint (such as cruciate ligament rupture or even damage to the menisci, the cartilaginous cushions inside the knee joint).
One or both hind limbs may be affected
Signs and Identification
Not all dogs with patellar luxation are as affected to the same degree as others. Some may show no outward signs, and a veterinarian must perform a physical exam to reveal the problem, while others are chronically lame and their inability to walk normally is the obvious signal that something’s wrong. Some dogs may be diagnosed as early as 1 to 4 months of age.
Because the severity of the luxation is variable, veterinarians have developed a grading system to describe it:
- Grade I: The patella can be manually displaced but returns to its normal position spontaneously. Affected dogs are normally quite comfortable but may carry the affected limb occasionally.
- Grade II: The patella displaces all by itself but doesn’t return to its normal location immediately. Mild or intermittent lameness may be present.
- Grade III: The patella is out of the normal position most of the time and must be manually assisted in its return to normal position. Moderate to severe lameness may be present.
- Grade IV: The patella is permanently out of place, and the animal is usually very lame. These dogs may carry the affected leg or shift more weight to their forelimbs in order to maintain their balance.
This grading system is designed to describe the degree of luxation of the kneecap. It does not always correspond with the pet’s degree of lameness. In any of these cases, the pet may have figured out how to change its gait so the knee is not painful, and lameness may not be obvious.
A veterinarian may be able to diagnose patellar luxation by manually manipulating the kneecap. If the dog is very painful, sedation may be recommended for a more thorough knee examination. Radiographs (X-rays) may be necessary to further evaluate the kneecap and other structures in the knee. Because a luxating patella affects the stability of the knee joint, many dogs with this problem develop arthritis over time, which may be visible on X-rays.
Toy and small breeds are most affected. Those with bowed limbs are also at risk of inheriting this structural defect. According to the Orthopedic Foundation for Animals, the top 20 affected breeds are:
- Boykin Spaniel
- Cocker Spaniel
- Yorkshire Terrier
- Chow Chow
- Bedlington Terrier
- Australian Terrier
- Japanese Chin
- Chinese Shar-Pei
- Lhasa Apso
- Tibetan Spaniel
- Tibetan Terrier
- Labrador Retriever
- Scottish Terrier
- Shiba Inu
- Norfolk Terrier
- Shetland Sheepdog
Pets that have been diagnosed with patellar luxation but do not show clinical signs, or only exhibit occasional signs, may be monitored. Maintaining an ideal body weight and following a regular veterinarian-approved exercise program may help manage the condition. Joint supplements may be recommended, as well as pain medications for occasional episodes. Unless the condition progresses, surgical correction may not be needed.
Severely affected dogs are best treated surgically. Because any instability in the knee joint may lead to arthritis, some dogs with moderate lameness may benefit from surgery as well.
Because patellar luxation may be an inherited condition, breeders must take care to eliminate this condition from their breeding population. Responsible breeders will also ensure that affected puppies be spayed or neutered as a requirement of sale.
To maximize comfort and minimize any secondary issues related to patellar luxation (such as osteoarthritis and cruciate ligament rupture), a dog’s weight must remain in the normal range. A leaner dog tends to experience fewer complications from this condition, while one already afflicted with osteoarthritis will suffer considerably less pain at a normal weight.
This article has been reviewed by a Veterinarian.
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