The patella is a kneecap and is a normal anatomical part of dog or cat’s knee. The patella is located between the femur (thigh bone) and tibia (shin bone). It sits in the femoral groove and facilitates the movement of the knee joint.
The patella is fixed in the femoral groove by multiple ligaments that originate from the quadriceps muscle on the top of the thigh bone which joins together over the knee cap and ends up as one broad ligament at the top part of the tibia (shin bone).
Patellar luxation (which means dislocation) is one of the most common knee conditions. It can dislocate to the inner side of the knee joint, which is most common, or outer. Patellar luxation can be present on one or both legs and usually occurs in small dogs. It can occur also in cats and large breeds. Patellar luxations are divided into four grades; one being the mildest and four the most severe. The grade of luxation does not mean that the dog or cat is going to have more or less problems with its knees. Surprisingly enough, many dogs that are affected with this problem may not show any signs at all. Patellar luxation is a congenital problem that has a recessive polygenic trait (many genes involved).Chihuahuas, Terriers, Pomeranians, Pekinese and Poodles are most commonly affected. It is more common in females.
How do I know that my dog has problems with knee caps?
In many cases your vet tells you on clinical examination. Some dogs show obvious pain and discomfort such as holding the leg up for a while or skipping when walking or running. Sometimes you may feel clicking in your pet’s knee when manipulated. Your vet will be able to assess your dog properly and run all tests needed. When pressure is put on a loose kneecap it usually pops out of the femoral groove and when the pressure is released, it may pop back in the groove. Some knee caps are fixed permanently out of the groove (grade four) and can’t be pushed back in the groove.
How is this problem treated?
The treatment depends on the amount of discomfort your pet is in. Grade one and occasionally grade two without any pain or symptoms may be left as they are without any intervention.
Grade two, three and four require surgical repair. The surgical procedure is successful in most of the cases and your pet is very likely to regain normal function of the knee. Before the surgery starts an x ray is taken to make sure the back legs are straight and the knee joint is thoroughly assessed. The surgery involves shifting the attachment of the patellar ligament opposite from the side to which the knee cap is dislocated. The attachment of the ligament along with the bone is pinned to its new location, and the joint capsule is tightened. Some dogs need more extensive surgery that involves deepening of the femoral groove into which kneecap slides. Your vet will be able to explain the procedure in detail so you know what is going to happen.
Your dog is sent home on antibiotics and pain relief and course of Carthophen (pentosan) injections will be commenced soon to re-establish normal function of the joint. Carthophen injections are given weekly to improve the healing of the joint and viscosity of the joint fluid.
Your pet must be on leash for four weeks and any strenuous exercise must be avoided.
Is there any alternative to surgery?
Conservative management is possible but most pets will develop arthritis. Pain relief,Carthophen injection, limited exercise and monitoring body weight will all help to a certain degree.
As a result of patellar luxation some pets may be at increased risk of cruciate ligament rupture which complicates the issue even further.
Early intervention and appropriate treatment give your pet the best chance for happy pain
If you have any questions, please contact your local Vets4Pets practice.