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(A) Real-time MR images of the patellofemoral (PF) joint of a pain-free control subject during upright, weight-bearing knee extension. (B) Real-time MR images of the PF joint of a subject with pain during upright, weight-bearing knee extension. Notice the lateral position and rotation of the patella relative to the femur as the pain subject nears full extension. These are oblique-axial views through the knee corresponding to four knee flexion angles between 0 and 60°.
