The patella, or kneecap, is a small round bone at the front of the knee. It is embedded in a major ligament that attaches the huge quadriceps muscle group of the upper hind leg to the tibia, or shin bone. The patella may seem like a small, cute and innocent little bone, but it can be a trouble-maker if it doesn’t do what it’s supposed to! You see, the patella’s rightful place is the trochlear groove at the front of the femur bone. Its position is very important to the mechanics of the knee joint, and it should track nicely in the trochlear groove when the knee flexes and extends. In some dogs and cats, the patella does not sit properly in the groove, and pops in and out of it sideways as the knee moves. This condition is called ‘patellar luxation’ and is most common in toy breed dogs and miniature breed dogs.