The patellofemoral joint occupies its greatest contact area with the femur at which knee flexion range?

• A. 90-135 degrees
• B. 20-60 degrees
• C. 0-20 degrees
• D. 60-90 degrees

Answer: (D)

The amount of contact between the patella and the femur is greatest when the knee is in midflexion, about 60 to 90 degrees. In this range, the patella sits securely in the central part of the trochlear groove and the broad articulating surfaces of the patella and femoral groove engage each other over a larger area, spreading the load across both medial and lateral facets. When the knee is near full extension (0–20 degrees), the patella sits higher and engages less of the groove, so the contact area is smaller. In deeper flexion (beyond about 90 degrees), the contact pattern shifts toward the odd facet and becomes more localized, so the maximal area is not maintained as in midrange.