Luxating Patellae

A luxating patella is the medical/veterinary terminology used for a dislocating kneecap. This condition is particularly common in small breed dogs (especially toy and miniature breeds). In these dogs there is often a congenital deformity that enables the kneecap to move in and out of its normal position. The kneecap can also be dislocated traumatically... we refer to this as acquired patellar luxation.

Animals with this condition are often seen to skip while running. Often no pain is evident, however, occasionally animals will cry out especially if the kneecap remains dislocated rather than popping back into its normal position. Some animals are affected bilaterally both kneecaps may pop in and out.

If we believe that your pet has a luxating patella we will attempt to dislocate the kneecap. This will indicate to us how easy it is for the kneecap to be moved from its proper position. We use a grading system to determine whether your pet requires corrective surgery.

Grade 1 the kneecap can be dislocated only if the knee is extended and digital pressure applied. Once pressure is released the kneecap returns to its normal position.
Grade 2 the kneecap is in its normal position but can be dislocated when the leg is straightened. Once the pressure is released the kneecap remains dislocated.
Grade 3 the kneecap is dislocated most of the time but can be put back in its normal position.
Grade 4 the kneecap is always dislocated and cannot be placed in its normal position.

Animals whose kneecaps fall into the grade one range do not require surgery. It is important however that the veterinarian reassess the animal annually as there is always the potential that the condition could worsen. Also in 25% of these cases the inflammation sets up the conditions that cause cranial cruciate ligament rupture later in life.

Surgery is indicated for the other three grades. Surgery involves deepening the groove the kneecap normally sits in and also straightening the alignment of the knee. The latter is done by relocating the tibial crest and pinning it into a position that will encourage stability.

Post surgery we encourage at least four weeks of strict rest, followed by a gradual increase in exercise starting with short leash walks. During this recovery period we provide your pet with anti inflammatories to help with the postoperative discomfort. In addition, we recommend that at the time of suture removal your animal receive a drug called Pentosan. This drug inhibits the inflammatory mediators that are detrimental to the joint and encourages healthy cartilage formation. This drug is given as a weekly injection for four weeks.

The prognosis for animals post surgery depends to a large extent on the preoperative grade. Patients with kneecaps that fall into the grade two to four categories, if left untreated, will develop arthritis. Early surgical correction will avoid serious and permanent damage to the joint.

On a final note we discourage owners to breed from animals that have congenital luxating patellae as there is a hereditary component to this condition and the offspring may inherit the trait.

Dr Lucy Micklethwaite