What is patellar luxation? Simply put, patellar luxation in the dog (and occasionally, the cat) is where the patella (knee cap) does not stay in place on the femur and causes the pet to occasionally hop & skip in the rear leg while running. This is because the pet has learned that if it straightens its leg, the patella will often move back into a normal position. Of course, in severe cases where the patella is always out of place, the pet often walks in a bowlegged and crouched position. Patellae can luxate either medially or laterally, but medially is more common.
What happens if your pet has a luxating patella? Unfortunately, even an occasional luxation can cause damage to the smooth cartilage surface of the posterior patella, and sometimes to the cartilage of the femoral joint surface. In addition, when the patella luxates, it puts additional stresses on the stifle joint and can sometimes cause rupture of the anterior cruciate ligament (ACL). That is why we generally recommend surgery to repair a luxating patella.
What is a repair for patellar luxation? The repair is always specific to the individual pet depending on the cause of the luxation in the animal, and often the causes are multiple and complex.
As seen in the diagram, progablems can begin in the hip joint, mal-positioning of the thigh muscles, twisting or bowing of the femur, mal-position of the tibial crest, a shallow femoral groove, and excessive medial tibial roation. One or more of these causes can be present in one animal, thus the repair has to be specific for that particular animal.
In repair, we must fix the alignment of the entire limb. Depending on the cause, we must release the medial retinaculum, move the tibial crest (figure C), straighten and/or rotate the distal femur. In addition, we usually have to deepen the groove in the distal femur (figure B) and sometimes use an implant to prevent excessive medial tibial rotation.
As stated, patellar luxation is the result of a complex series of structural problems resulting in poor alignment of the rear limb, thus the repair is often complicated and complex but well worth doing to help prevent rupture of the ACL and to discourage formation of early osteoarthritis of the stifle joint.
Medial Patellar Luxation (MLP) repair: limb straightening