Patellar luxation is dislocation of the kneecap. It is positioned between the quadriceps muscle and a tendon that attaches to the shin bone (tibia). The patella glides in a groove at the end of the thigh bone (femur) as the knee flexes and extends. It only takes a small change to make it slip sideways. This is called luxation, or dislocation, of the patella.
Patellar luxation can affect dogs and cats.
There are four grades of patella luxation.
Grade 1: These kneecaps can be manually pushed out of position but return to the normal position by themselves.
Grade 2: These kneecaps sit in the normal position most of the time, but when they move out, may stay out for some time before returning.
Grade 3: These kneecaps permanently sit in the incorrect position, out of the groove. They can be moved back into the normal position but often return to the incorrect position.
Grade 4: These kneecaps are permanently in the wrong position and are difficult to get back into the correct position.
Trochlea (groove) deepening surgery
In dogs and cats with patellar luxation the groove (trochlea) at the end of the thigh bone is often shallow. In these cases it may be necessary to deepen the groove by removing a block or wedge of bone and cartilage from the groove, deepening the base, and replacing the block or wedge.