Patellofemoral Pain Syndrome

Patellofemoral pain syndrome (PFPS) is anterior knee pain caused by abnormal patellar tracking and increased contact pressure between the patella and femoral groove — and USMLE Step 1 tests it as a recognition-and-management vignette. Students who assume 'knee pain = rest and immobilize' will pick the wrong answer: first-line treatment is quadriceps strengthening (specifically the VMO) and activity modification, not bracing or strict rest. The theater sign — aching anterior knee pain after prolonged knee flexion in a seat — is the detail most commonly missed. PFPS is common in runners and young active patients and is sometimes called chondromalacia patellae when cartilage softening on the posterior patella is confirmed.

The exam tests two things: identifying the presentation by its aggravating factors, and knowing that treatment is active rehabilitation, not rest. The classic vignette gives you a young runner or athlete with anterior knee pain that worsens with stairs, squatting, or sitting in a movie theater for a long time. That last one — the 'theater sign,' where prolonged knee flexion in a seat causes aching — is the detail students most commonly miss. The mechanism is straightforward: sustained or repeated knee flexion increases patellofemoral contact pressure, which irritates the joint.

What makes this tricky is that students conflate 'knee pain' with 'rest and immobilize.' That reflex is wrong here. USMLE Step 1 will likely give you a scenario asking what to recommend next, and the right answer is quadriceps strengthening (specifically the VMO — vastus medialis oblique) plus activity modification, not casting, bracing, or strict rest. The logic is that a stronger quad improves patellar tracking, reducing the abnormal contact pressure that causes the pain.