A luxating patella generally describes a repeatedly dislocating knee cap. The knee cap is embedded into a fibrous ligament extending from the large thigh muscle, thus moving it forward and back if the hind limb is flexed or stretched. Varous conditions may affect the knee cap and/or surrouding structures causing luxation.
There are four different degrees of severity in luxating patellas: Dogs with first degree luxating patellas are generally not impaired in their movement. However the patella can be manually luxated. Second degree luxating patellas manifest in spontaneous luxations. The dog shows signs of pain and might hop around on three legs until the kneecap returns to its normal position. It may also be manually returned by flexing the leg and pushing the patella back to a middle position. In third degree luxating patellas, the patella remains luxated most of the time, the dog tries to refrain from any movement of the affected leg or carries it in the air. The patella may be manualy returned to its normal position with a stifle joint in extension. Fourth degree luxating patellas are permanently luxated and it is not possible to manually reposition the patella. There may be a rotation of the the joint of up to 90 degrees, often the toes are rotated inwards and the dog has bow legs. Second to fourth degree luxating patellas require surgery. Constant abnormal load on the knee joints can lead to painful osteoarthritis. The longer the knee is exposed this condition the more severe the resulting damages. Therefore the dog should be immediately treated when the first symptoms show.
The patellar luxation may be passed on, be acquired in growth phase but also be developed due to injuries. It appears with dogs of all breeds, predestined are however dwarf dog breeds such as Yorkshire-Terrier or dwarf poodles, since in their case the displacement of the kneecap in direction of the inner knee side is a hereditary defect. These dogs often have O-legs. In case of other breeds frequently too fast growth is responsible for the malformation of the knee joint. The displacement to the other direction (outer knee side) is more uncommon and rather affects middle sized and larger dog breeds. These dogs often have X-legs.
The patellar luxation can quite easily be diagnosed by clinical examination. Provided the luxation is simple and no further symptoms exist, an operation is not mandatory. More severe cases require an operation since the disease equals to a disability. Unfortunately, not all changes can be remedied with a surgical intervention and often relapses occur which again require operation. The veterinarian should check after operation as often as possible the success of the operation and the dog's state of health.
Patellar luxation is not an emergency and does normally not require immediate consultation with the veterinarian. At the next opportunity, agree upon a date at the veterinarian's. If the dog hast strong pain or in case limping handicaps the dog, then the veterinarian should more urgently be consulted. If the patellar luxation is not based on a hereditary defect, measures can be taken for prevention. For that, reduced feeding for dogs of larger breeds during growth phase would be appropriate, since the increase of muscle tissue could lead to a deformation of the quite soft bones and joints of the young dog in case of excessive feeding. In light cases of patellar luxation, a diet and movement restrictions can be appropriate.