The knee is the largest joint in the body and consists of the femur (thigh bone), patella (knee cap) and tibia (shin bone). The surface of each bone is covered in cartilage, a smooth and slippery material that helps bones glide and move without pain. When the knee bends and straightens (flexes and extends), the patella glides up and down within a groove on the femur, called the trochlea. The patella normally stays within this groove because it is shaped in a way to slide smoothly in middle. In some people there are variations in the shape and contour of the trochlea that can predispose the patella to subluxation or dislocation.
Patella instability can be the result of an acute event (sudden injury) or due to the shape of the groove. If the groove is too shallow, the patella could “slide off” one side of the femur. Alternatively, an injury such as a fall or a twisting mechanism could result in an injury to the stabilizing ligaments and cause the knee cap to slide out of place, called a dislocation. If the injury is not treated properly or does not fully heal, you may be at risk for recurrent dislocations or chronic knee pain. Symptoms of patella instability include pain, buckling/catching, pain when sitting, stiffness, or the knee cap slipping off to the side during activity.
Surgical treatment for patella instability involves stabilizing the ligaments opposite the side of instability. Most commonly, the patella slips laterally (away from the body). Thus, treatment may involve a repair and sometimes replacement of the medial stabilizing structures, a release of the lateral displacing structures, or both. The purpose of treatment is to align the patella in the center of the trochlea (groove in the femur) allowing for a smooth motion throughout a full arc of knee flexion and extension. Each individual is unique and you should speak with your surgeon about his or her particular treatment recommendations.
Your physician will recommend a specific rehabilitation protocol to enhance your recovery to activities. This will consist of exercises for improving strength, maintaining motion, and re-training your muscles and balance. Specifically, the exercises may be designed to strengthen particular muscles that become secondary stabilizers to the patella. Often cycling is recommended to increase strength, and a stabilizing brace may be provided as well. Exercises should be performed in a supervised setting, as well as at home on your own time. Your commitment to rehabilitation is key to a successful outcome.