Patella Luxation

The patella, or the knee cap, is a small bone that sits in the tendon of the hind leg, running from the thigh muscles (quadriceps) to the lower leg.

The patella normally slides in a groove on the knee, and helps pull the leg forward.

What is Patella Luxation?

Patellar luxation is a disease where the knee cap jumps outside the femoral groove, causing discomfort and affecting leg movement. The patella can jump towards the inside of the knee (medial) or outside of the knee (lateral).

Patella luxation is one of the most common orthopaedic conditions in dogs, affecting up to 7% of all puppies. It is seen most commonly in small dogs, especially breeds such as Yorkshire Terriers, Miniature Poodles, Chihuahuas, Pomeranians and Boston Terriers. Patella luxation is usually a condition that dogs are born with, and often affects both knees.

Symptoms of Patella Luxation.

The symptoms of patella luxation vary greatly depending on how badly the knee is affected. Most commonly, affected dogs will suddenly carry the limb for a few steps (intermittent lameness or skipping), and may appear to shake or stretch the leg prior to regaining its normal activity. More severe symptoms include bunny hopping (hopping on the back legs), arched back and a ‘bow-legged’ appearance. In mild cases, a luxating patella may not show any outward signs, but can still be detected by your veterinarian on a health check.

Causes of Patella Luxation.

Patella luxation is usually due to the underlying genetics of a dog and the way their bones develop. A number of skeletal issues can predispose a dog to patella luxation, including:

• A very narrow or shallow knee groove, preventing the patella (kneecap) sitting normally in the knee
• Incorrect alignment or formation of the thigh bone and/ or the shin bone
• Tightness or atrophy of the quadriceps muscles
• Overly long or loose patella ligament
• Abnormal conformation of the hip joint

The diagram above shows the hindlimbs of an affected dog. The left hind leg is normal and has no patella luxation. The right hindleg has a shallow knee groove (shown by the blue arrow) and the ligament attachment on the lower leg (shown by the red arrow) is rotated to the side, resulting in the kneecap being pulled out (patella luxation).

Treatment of Patella Luxation.

A dog with signs of patellar luxation should be examined by your veterinarian. A surgery is often performed to achieve a proper alignment of the affected legs. The surgery generally involves reconstructing the knee to deepen the knee groove, tighten the ligaments and adjust the attachment point of the tendon. Although care is always needed, the surgery is usually very successful and will fix the problem in most cases. Dogs that do not show any symptoms should be monitored but do not typically warrant surgical correction.

This x-ray shows a recently repaired knee, with the kneecap (orange arrow) sitting in the centre of the knee, and a small meal implant (green arrow) attaching the tendon in a more appropriate position.