The patella—also called the kneecap—is a small, flat triangular bone that is located on the front of the knee. It is only 2 to 3 inches wide, yet it is a critical part of the extensor mechanism, the group of muscles, tendons, and ligaments that work together to make it possible to straighten the leg and perform such essential activities as standing and walking. Because the patella is such an integral part of the extensor mechanism, we often use the broader label of extensor mechanism discomfort to describe patella-related problems.

The extensor mechanism consists of the quadriceps muscles, the quadriceps tendon, the patella, the patellar tendon, the tibial tubercle, and the lateral and medial retiniculum.

From the top of the knee, the quadriceps muscles hold the patella against the femur, or thigh bone. From the side, the patella is held in place by fibrous bands called retinicula. From the bottom of the knee, the patella is connected to the tibia via the patellar tendon. The back of the patella is covered with the thickest layer of articular cartilage of any joint in the body, which gives the patella special properties.

The patella moves as the leg moves—it glides up and down, and rotates on the femur until it’s in its track, the trochlea. The patella helps to keep the knee joint properly aligned, and it is also important for muscle strength by giving the quadriceps the extra leverage they need to cope with the enormous force that runs through the knee with each step or run. In fact, if the patella is removed, the force of extension is reduced by about 30 percent, which severely hampers the efficiency of the quadriceps and increases the force exerted through the joint. The patella also cushions and protects the other bones of the joint. For example, in the case of a fall or blow to the knee, the patella may prevent the condyles (bony knobs) of the tibia or femur from being injured.

Nonspecific knee pain or extensor mechanism pain is one of the most common complaints among patients. (Your doctor may refer to it as anterior knee pain or extensor mechanism discomfort.) It is characterized by a dull ache while walking up stairs or squatting, or the knee may suddenly give way or may catch when flexing. Very often, patients complain of grating and creaking when they extend or flex their knee or discomfort after sitting in one spot for a long time, such as when watching a movie.

At one time, kneecap pain was routinely diagnosed as chondromalacia, which is really a pathological condition characterized by the softening and progressive breakdown of articular cartilage. However, autopsy studies and surgery of patients without knee pain have shown that chondromalacia is very common, particularly among older people and, in most cases, does not cause problems. Therefore, we now use the broader term of anterior knee pain to describe patellar discomfort. What precisely does cause patellar pain? There are several potential culprits.

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