The patellofemoral syndrome is a group of conditions in which the hallmark is pain beneath or surrounding the patella (kneecap). The patella is a unique bone in the leg because it is not directly weight bearing. Weight is borne through the femur through the tibia and fibula, which continue down to the ankle where they form the "dome" of the ankle joint. The patella sits in front of the knee joint and is held, as it were, on a bowstring; the patellar tendon attaches to the front of the tibia below and the quadriceps complex, four powerful thigh muscles, attach it to the hip and femur above. As the knee flexes and extends, the patella tracks along the intercondylar groove of the femur. Any factor which disrupts this normal tracking mechanism can result in inflammation or pain to the undersurface of the patella. When mild, the undersurface may simply be inflamed. When more severe, the cartilage may actually become damaged or arthritis may develop. When the tracking is poorly aligned, instability of the patella may result, with subluxation or actual dislocation. Most common in athletes, there has been too rapid an increase in training duration, intensity or other sudden changes. The term chondromalacia patella should be reserved for patients who have actually had arthroscopy, where there is a histopathological diagnosis.

There are several risk factors for developing patellofemoral syndrome. The condition is more common in women, also in people who have genu valgus (knock-knees), and has been reported to be increased in people who have pes planus (flat feet), although this has been less well proven statistically. In addition, people with excessive faxity of their joints or obesity are more predisposed.

The "malicious malalignment syndrome" is characterized by excessive internal rotation of the hips, genu valgus, pes planus, with what is known as an increased "Q" angle. The Q angle is the angle that the quadriceps makes as it encompasses the patella. IT is the angle between a line drawn through the tibia in a superior-inferior plan, and the line drawn through the anterior-superior iliac spine (ASIS) and the patella. If the Q angle is greater than 19 degrees, the patient is greatly predisposed to development of patellofemoral pain. This angle puts additional stress on the knees during the course of flexion and extension and results in increased frequency of symptoms by disrupting normal tracking mechanisms.

In its mildest state, patients report stiffness after prolonged sitting or initially in the morning. There is pain around or under the kneecap after activity, especially activities in which there is a lot of knee motion, e.g., ascending or descending steps, bicycling, and running. Symptoms are worsened by prolonged sitting with inadequate leg room, e.g., in a restaurant or a movie theater. This is referred to as a theater sign" Patients prefer to sit with their leg extended in front of them. In more serious cases, pain may become constant, there may be subtle swelling around the kneecap, or the patient may sense instability. This "pseudo-locking" is not actual instability; it is a protective mechanism. In cases of malalignment, the kneecap may actually dislocate with activities involving sudden rotation.

Treatment of patellofemoral syndromes

The hallmark of long-term treatment in patellofemoral syndromes is strengthening of the quadriceps mechanisms. This "unloads" the initial stress on the patella. This results in reduced pressure behind the patella and improved tracking. Details of quadriceps strengthening are still controversial. In most studies, simple isometric strengthening results in reduction or elimination of symptoms in 70 to 80 percent of patients. Other studies have stressed more aggressive and more physiological strengthening with a program of TKEs (terminal knee extensions). This involves isotonic strengthening up to approximately 10 percent of body weight, normally approximately 15 to 20 pounds, in the terminal 30 degrees of extension only. Initially, in very weak quadriceps, this can result in aggravation of the condition instead of improvement. In either case, it takes up to six weeks to see substantial improvement.