The kneecap anatomically called the patella is the small bone embedded in a tendon in the front of the knee. The patellofemoral joint is where the kneecap and thigh bone meet. Below the kneecap there is a large tendon (patellar tendon), which attaches to the front of the tibia or shine bone. This mechanism allows the quadriceps, the large muscles of the front of the knee to extend the knee joint with a very slight rotation.
From a flexed position of around 135 degrees the knee extends or straightens to 0 degrees. Fluid-filled sacs called bursae serve as gliding surfaces for the tendons to reduce the force of friction as tendons move. Each meniscus, that is, the cartilage serves to evenly load the surface during weight-bearing, which also adds to the reduction of friction by disbursing joint fluid for joint lubrication. Having strong thigh muscles is important in reducing patellofemoral stresses during activity.
Until recently there has been disagreement in the literature as to which exercises and ranges of motion best accomplish the goal of low patellofemoral stress. It has been found that performing knee extension from 90° to 45° has significantly lower stress then isokinetic knee extensions and squatting movements. This is confirmed in the May 2014, Journal of Orthopaedic & Sports Physical Therapy. Therefore when prescribing exercise, non-weight-bearing quadriceps exercises are extremely important in managing joint stress especially in persons with knee pain.
Pendulum Leg Extension Starting from 90 degrees
Pendulum Leg Extension to 45 degrees
Training between 90° and 45° causes the least amount of patellofemoral stress and often allows pain free training enabling an athlete to re-strengthen the quadricep. Once knee pain dissipates and knee strength is normalized or increased the athlete can resume full range exercise.
Full range Pendulum Leg Extensions