The patella, or the knee cap, is a small bone that sits in the tendon at the front of the leg that runs 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. 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).
What is Patella Luxation?
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
- malformation 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 (grey arrow) sitting in the centre of the knee, and a small meal implant (green arrow) attaching the tendon in a more appropriate position.
Care after Surgery.
Patella repair operations are generally very successful. After surgery and healing, a dog should be able to walk, play and exercise and play as normal, and people are generally very happy with the outcome of the operation. The surgery is generally more successful if performed before there is a large amount of wear and damage to the joint. More severely affected dogs can be more difficult to completely repair, but there is generally still a significant improvement in use and function of the leg. Complications are rare, but as with any surgery there is a small risk of infection or poor healing.
If you suspect your dog suffers from luxating patellas, or you would like to find out more about our surgical options, please call us on 2915 3999 to make an appointment.
Written by Dr Joanna Lee
Head of Surgery, East Island Animal Hospital and Creature Comforts Group.