The quadriceps mechanism allows you to straighten out the knee. The patella acts like a fulcrum to increase the force of the quadriceps muscle. The underside of the patella is covered with articular cartilage , the smooth covering of joint surfaces. This slippery surface helps the patella glide in a special groove of the thigh bone, or femur. Together the patella and the groove in the femur are called the patello-femoral mechanism .
Problems commonly develop when the patella suffers wear and tear.
The underlying cartilage begins to degenerate, a condition sometimes referred to as chondromalacia patellae . Wear and tear can develop for several reasons. The patello-femoral joint is usually affected as part of osteoarthritis of the knee. One of the more common causes of knee pain is a problem in the way the patella moves through the patello-femoral groove as the knee moves. This situation can happen because of a muscle imbalance in the quadriceps muscles.