Patellofemoral pain syndrome

American Family Physician,  Nov 15, 1993  by Kent Davidson

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Patellofemoral pain syndrome is a problem commonly encountered by physicians who provide medical care for competitive or recreational athletes. Other names for this entity are retropatellar pain syndrome,(1) patellofemoral arthralgia,(2) extensor mechanism disorder,(3) lateral patellar compression syndrome,(4) patellalgia(5) and patellofemoral dysfunction.(6)

Chondromalacia patellae,(7) which involves degeneration of the cartilage on the articular surface of the patella, has been inappropriately included with the patellofemoral disorders. No damage to the articular cartilage occurs in most patellofemoral disorders.(8)(9) Furthermore, there is little epidemiologic evidence that patellofemoral pain syndrome, if untreated, leads to chondromalacia.(10)

This article focuses on a relatively common problem involving the patellofemoral articulation or the peripatellar soft tissurs. This problem may develop if mild malalignment of the extensor mechanism is present or through overuse when anatomy and alignment are normal.

Anatomy

The patella is a sesamoid bone that is situated within the quadriceps tendon proximally and within the patellar tendon distally (Figure 1). The patella acts as a guide for the quadriceps mechanism, sliding between the femoral condyles, which hold it in place. It also increases the efficiency of the quadriceps muscles in extending the knee.

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Proper tracking of the patella during flexion and extension of the knee is influenced by a number of factors. The height of the femoral condyles and, consequently, the depth of the sulcus between the condyles are important in keeping the patella "seated" and tracking properly (Figure 2). The shape of the facets on the undersurface of the patella help determine the "fit" between the patella and the femoral groove. The medial and lateral retinacula keep the patella "centered" between the femoral condyles during patellar movement. Two additional factors involved in tracking are the relative strength of the individual muscles composing the quadriceps group and the composite angle of pull of the quadriceps group, referred to as the Q angle (Figure 3).

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Etiology and Pathology

Patellofemoral pain syndrome seems to develop under one of two circumstances: anatomic abnormalities or repetitive microtrauma (overuse). Repetitive microtrauma most commonly occurs in overzealous recreational athletes and adolescents.(11)

Anatomic abnormalities can lead to abnormal tracking of the patella during knee movement. The abnormalities usually involve a shallow intercondylar sulcus, deformed patellar facets, weakness of the vastus medialis oblique muscle or tightness of the medial or lateral retinaculum. Any of these abnormalities can cause excessive pressure between the patella and the femoral condyles during flexion and extension.

Two major explanations for the source of the pain experienced in patellofemoral pain syndrome have been proposed. When the pain occurs at the patellofemoral articulation, the most likely explanation is that it originates from the richly innervated subchondral bone of the patella, since cartilage has no pain fibers.(12) Fulkerson(8)(13) reported that peripatellar soft tissues may be the source of the pain, especially in young active patients with mild malalignment. In these cases, strain on a laterally contracted retinaculum can produce inflammation and pain. Occasionally, neuromatous degeneration, analogous to the development of an interdigital (Morton's) neuroma in the foot, can occur within the contracted retinaculum.

Epidemiology

Patellofemoral pain syndrome is most common in adolescents and young adult.(2)(7) In one British sports injury clinic,(2) 5.4 percent of the total injuries seen and 25 percent of all knee problems treated over a five-year period were attributed to this entity. In 32 percent of these cases, running was felt to be the major cause. Females appear to be affected more often than males,(2)(8)(14) possibly because the increased width of the gynecoid pelvis results in an exaggerated Q angle.

Clinical Presentation

Patients with patellofemoral pain syndrome usually present with retropatellar or peripatellar knee pain. The pain is usually of a dull, aching nature, occasionally becoming sharp during activities that increase pressure over the knee cap. These activities include climbing or descending stairs, squatting or performing deep knee bends. Patients may report pain after sitting with flexed knees for a prolonged period--the so-called "theater" sign.

Crepitus during knee flexion and extension, an extremely common finding in young patients, generally does not always imply pathology of the patellofemoral articulation.(15) "Giving way," or the sensation of instability associated with patellofemoral dysfunction, is uncommon and usually indicates a more severe form of malalignment that results in subluxation or dislocation.(2)

Physical Examination