Patella Luxation (Knee Cap Dislocation) in Pets

INTRODUCTION

Patella Luxation is when the patella (knee cap) luxates (dislocates) out of its normal position in a groove in the femur (upper leg). It is a common cause for limb lameness in dogs. The stifle (knee) is essentially a hinge joint, allowing the major muscles of the upper leg to cause the normal swinging movement of the lower leg with walking or running. The patella (knee cap) is a small bone in the patellar tendon of the quadriceps muscle that rides in a groove in the femur (upper leg) at the stifle joint, stabilizing the stifle. The patellar tendon attaches to the tibial crest below the stifle. These structures make up the quadriceps mechanism.

Occasionally the quadriceps mechanism is not well aligned during development, generally due to bowing of the femurs. The end result is that the bones and stifle joint do not develop properly allowing the patella to luxate or dislocate, flipping in and out of the groove. The result is excessive wear on the cartilage, which may lead to osteoarthrosis (degenerative arthritic changes). Dislocation of the kneecap also causes the shin bone to turn inward which may cause the cranial cruciate ligament (CCL) to tear. In fact, about 20 to 25% of the dogs that have a patellar luxation sustain an injury to this main stabilizing ligament of the knee.

Luxations occur most commonly in small breed dogs, although cats and larger dogs can also be affected. In mild cases, the abnormality may have gone unnoticed until the pet is much older. In moderate to severe cases the diagnosis can be made as early as 3 months of age. In these cases, the earlier that corrective surgery can be performed, the less likely future problems will develop or that future surgeries will be necessary.

SIGNS AND DIAGNOSIS

Signs of a dislocating kneecap include lameness, intermittent skipping gait, intermittent crying out or unwillingness to jump on elevated surfaces. The diagnosis is made on physical examination, in which the surgeon can feel the kneecap dislocate out of place. X-rays of the knee and thigh bone will be made to evaluate for twisting of the femur bone.

Whenever your pet is showing signs of a health issue your first step is to contact your primary care veterinarian. If it is indicated that your pet may suffer from patella luxation or another serious condition, a veterinary specialist is available at an ExpertVet certified hospital.