Malposition of the tibial tubercle during flexion in knees with patellofemoral arthritis

Objective. To assess the mechanisms contributing to the induction of patellofemoral arthritis (PF-OA). Design and patients. A computed tomography scan was taken at three levels of the lower extremity in full extension and at 30° of flexion. The cuts were superimposed and 12 parameters were compared in 17 PF-OA knees and 27 normal knees to assess the rotation angle of the tibial tubercle. Results. Although the tibial tubercle was in almost the same position in full extensioin in the normal and PF-OA knees, it was positioned significantly laterally at 30° of flexion in PF-OA knees. Also the articular surface of the lateral femoral condyle was significantly narrower or steeper in PF-OA knees. Conclusion. Anatomic variations and mechanical abnormalities were identified in the PF-OA knees.