A luxating patella occurs when the kneecap moves out of its natural position. The patella (knee cap) lies in a cartilaginous groove at the end of the femur at the stifle. The patella in dogs is shaped like an almond and its purpose is to assist in knee extension. The patella resides in the tendon of the quadriceps muscle group which attaches to the tibia. When this muscle group contracts, it pulls on the tendon and the kneecap, thereby extending the stifle. If the patella is pulled out of its normal groove with knee extension, this is called a luxating patella. The causes of this condition can be congenital, genetic and/or traumatic. When the kneecap is dislocated from the groove of the thigh bone, it can only be returned to its normal position once the quadriceps
muscles in the hind legs of the animal relax and lengthen. The initial symptoms include occasional limping, an intermittent skip in the gait, sudden loss of support on the limb, abnormal sitting posture with the knee placed outward; all of which are usually intermittent.

Apart from breed predisposition, if a dog has poor conformation, such as no angulation in the hock, then this can also cause luxating patella. This condition is usually diagnosed early on. A luxating patella is usually diagnosed by feel and is assigned a grade based on the severity of the condition. Grade 1 is the least severe and the knee cap easily slips back into place on its own where a Grade 4 means the kneecap is actually stuck and fixed outside its normal resting position in the groove of the femur. Sometimes, chronic cases can lead to erosion of the cartilage on the femur from the constant friction, and eventually lead to osteoarthritis. In this case, pain is usually involved and lameness is more constant and severe. Occasionally, a luxating
patella can lead to a ruptured cranial cruciate ligament. Female dogs are 1 1/2 times more likely to acquire the condition. At least 15% to 20% of dogs with patella luxation will eventually rupture their cranial cruciate ligament.

Medical treatment for kneecap dislocation has very little effectiveness; surgery is the
preferred treatment of choice for severe cases. Surgery can correct both the affected structures and the movement of the kneecap itself, and in 90 percent of cases, frees the dog from lameness and dysfunction. Testing for Luxating Patella is readily available by a veterinarian on a physical examination of the stifle.