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Summary
Patellar luxation is a common condition of smaller dogs. The knees, in this case, are the site of the problem. With patellar luxation, the kneecap (patella) doesn't always stay where it should. It tends to move, either occasionally or full-time, into a position outside the groove it's meant to live in (it becomes "dilocated").
Imagine if your kneecap spontaneously moved to the center or the outside of the 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 our affected pets experience.
Patellar luxation is a disease of joint structure that's passed down from affected dogs to their offspring. In some cases, the bone of the upper limb (the femur) may have a very shallow groove so that the kneecap doesn't always rest in place readily. In others, the tendon that attaches the quadriceps is misplaced so that every time this major muscle is flexed the patella moves towards the center of the body (medial patellar luxation or MPL).
This dislocation of the knee may lead to significant arthritis and, in some cases, predisposes the dog to even more severe diseases of this joint (such as cruciate ligament rupture).
In almost all cases, both limbs are affected--though one is often more significantly so.
Symptoms and Identification
Not all dogs with patellar luxation are as affected by this problems 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. Dogs may be diagnosed as early as 1-4 months of age.
Because the disease's severity is so variable, veterinarians have developed a grading system to describe the condition:
Grade I: The patella can be manually displaced but returns back to its normal position spontaneously. Affected dogs are normally quite comfortable and do not limp.
Grade II: The patella displaces all by itself with flexion and extension of the joint but it returns to its normal location spontaneously. Mild lameness may be present.
Grade III: The patella is easily displaced with flexion and extension but must be manually assisted in its return to normal position. Moderate to severe lameness is present.
Grade IV: The patella is permanently out of place and the animal is usually very lame. These dogs often shift their weight to their forelimbs by way of maintaining their balance.
Though pain is not evident in early cases, the osteoarthritis that usually results in these patients over time means that older dogs with this condition may be troubled by significant discomfort. Its severity usually depends on the dog's age, grade of luxation and weight.
X-rays are often necessary to investigate the advancement of osteoarthritis and to help determine the disease's ideal treatment in each case.
Affected Breeds
Toy and small breeds are most affected. Those with dwarfed or bowed limbs are also at risk of inheriting this structural defect.
Treatment
Treating this common disease is most often undertaken with pet-specific pain-relieving drugs once arthritis begins to cause discomfort. Nutraceuticals like glucosamine are commonly employed even before the arthritis becomes a problem. Weight management is critical for these patients. Because weight factors into the long-term wear and tear on the joint, osteoarthritis formation will be reduced by lifelong weight management.
Severely affected dogs (Grades III and IV) are best treated surgically. Nonetheless, it is widely held that less-affected dogs may benefit from surgery as well.
Veterinary Cost
The cost of surgical treatment is significant. Because board-certified veterinary surgeons are almost always in order, the expense of surgery typically ranges from $1,500 to $3,000 per affected knee.
Long-term medications for pain relief (when needed) can be expensive, too, but because these patients are usually small, their lower drug doses are considered manageable by most owners. $20-$50 per month is most typical for pets that require regular dosing with pain medications and/or nutraceuticals.
Prevention
Because patellar luxation is a genetic condition, breeders must take care to eliminate this condition from their breeding population. Responsible breeders will also ensure that any affected puppies be spayed and 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), dogs' weights must remain in the normal range. Leaner dogs tend to experience fewer complications of this disease while those already afflicted with osteoarthritis will suffer considerably less pain at lower normal weights for their breed and size.