Practical management of patellofemoral pain.

Abstract

Patellofemoral pain (PFP) is one of the most common disorders of the knee, accounting for 25% of all knees injuries seen in a sports medicine clinic. The cause of PFP, however, is not clearly understood and may consist of multiple origins. The most commonly accepted hypothesis is related to increased patellofemoral joint stress (force per unit area) and subsequent articular cartilage wear. Athletes typically note the insidious onset of an illdefined ache localized to the anterior knee, behind the patella. Occasionally the pain may be centered along the medial or lateral patellofemoral joint and retinaculum. Typically, pain is aggravated with functions that increase patellofemoral compressive forces, such as ascending and descending hills or stairs, squatting, and prolonged sitting with the knee in a flexed position. While clinical studies have not been able to consistently demonstrate biomechanical or alignment differences between patients with patellofemoral pain and healthy individuals, a systematic exam may highlight predisposing factors. The location of symptoms may indicate the specific structures involved and may give direction with respect to making a differential diagnosis: lateral pain—small nerve injury of the lateral retinaculum, or iliotibial band friction syndrome; medial pain—recurrent stretching of the medial retinaculum or symptomatic medial plica; retropatellar pain—articular cartilage damage or stress on the subchondral bone; superior pain—quadriceps tendinitis; inferior pain—patellar tendinitis or fat pad irritation. When making a diagnosis of PFP, it is important to rule out other disorders. For example, joint line tenderness may be indicative of meniscal injury or femorotibial arthritis, and more vague pain patterns may indicate referred pain from the hip or the L2–L4 nerve roots. Magnetic resonance imaging (MRI) is particularly helpful at assessing degenerative joint changes such as cartilage fissuring or thinning, subchondral bone marrow edema, subchondral cysts, synovial plica, and patellar tendinitis. If more definitive information is required regarding patellar tracking, kinematic studies can be obtained with MRI or computed tomography (CT). To more accurately define patellar tracking abnormalities at our institution, we are now using an MR unit in which the patient can stand upright in a weight-bearing position while performing continuous flexion and extension movements (Figure 1).