Feb 25, 2022
Patellar Luxation: Where are Your Dog’s Kneecaps?
Leah Park, DVM, practice limited to surgery, Garden State Veterinary Specialists
Patellar luxation, also known as “trick knee” or “floating kneecap,” is a common condition seen in toy and miniature breed dogs. Occasionally, large breed dogs and cats are also affected by this condition. Most cases of patellar luxation are congenital and can affect both knees up to 50 percent of the time.
Normally, the kneecap or patella is found within the patellar ligament that runs vertically over the knee joint in a v-shaped groove of the thigh bone. Patellar luxation is characterized by dislocation of the kneecap out of the v-shaped groove. The kneecap can be abnormally located to the inside or outside of the knee. Congenital patellar luxation develops secondarily to abnormal bone alignment in the hind legs. This commonly results in a v-shaped groove that is too shallow which allows the kneecap to move easily out of place, and weakened or poorly developed ligaments that usually help hold the kneecap in place. Patellar luxations can also be seen secondary to hip dysplasia or partial dislocation of the hip joint.
Clinical signs associated with patellar luxation can vary. It may be an incidental finding by your veterinarian during a routine physical examination or appear as a persistent non-weight bearing lameness. Most dogs affected with patellar luxation will suddenly hold the affected leg up for a few steps then may be seen skipping or extending the leg prior to returning to a normal gait. Severity of the luxation is graded on a scale of 1 (very mild) to 4 (severe). Grade 1 luxations are characterized when the kneecap can be manually moved, but otherwise stays within the groove during activity. Grade 4 luxations are characterized when the kneecap is found persistently out of the groove and cannot be manually replaced. As the condition progresses, the lameness may become more frequent or persistent.
Patellar luxation is not a particularly painful condition, but can be uncomfortable as the kneecap moves in and out of the v-shaped groove. This chronic movement can cause cartilage damage to the patella and femur resulting in further discomfort and development of osteoarthritis.
Treatment recommendations will vary from case to case. Patellar luxations that do not cause any clinical signs may be monitored. Surgery is considered in Grades 2 and above, depending on the degree of lameness and discomfort. Surgical repair may encompass a combination of procedures that would correct the groove and alignment of the knee to maintain the patella in its normal anatomic position. About 90 percent of dogs will have a good to excellent outcome with surgery.
Your veterinarian can generally diagnose this problem by palpating the knees and performing radiographs. Discuss with your veterinarian possible treatment options and whether referral to a specialist would be best for you and your pet.
The information contained in this article is for informational purposes only and should not be substituted for the advice of a veterinarian.
