The patella is commonly referred to as the kneecap. It is a sesamoid bone that sits within the tendon of the quadriceps muscle group and is an integral part of the stifle (knee) joint functioning to modify the direction of pull of the quadriceps and increase the efficiency of the stifle’s extension.
Luxation occurs when this bone moves out of the groove, situated at the anterior distal end of the femur (large leg bone), designed to allow the patella to glide up and down when the knee joint is bent back and forth. This luxation can either be to the inside (medial) of the knee or to the outside (lateral) of the knee.
This condition is often a congenital problem in toy and miniature breeds i.e. Poodles, Yorkshire Terriers, Pomeranians, Pekingese, Chihuahuas and Boston Terriers. It can also effect large breed dogs and especially predisposed are Labrador retrievers, although it can occur in any breed or size following a traumatic event that disrupts the supporting structures of the stifle joint.
Malformation of the patella or the groove can also occur whilst the dog is growing. Generally there are four grades of luxation that can occur ranging from mild; where the patella, if pushed out of the groove, easily relocates itself back to; severe where the patella is permanently out of its groove and cannont be relocated. The most common grade tends to be the 2nd one where the patella is within the groove most of the time but periodically will move out and the dogs action of kicking out its hind leg ‘pops’ it back in.
