Tibiofemoral and patellofemoral mechanics are altered at small knee flexion angles in people with patellofemoral pain

ObjectivesTo test the hypothesis that, at 0° and 20° of knee flexion, patellofemoral contact area would be lower, while tibiofemoral rotation and patellofemoral malalignment would be higher in participants with patellofemoral pain (PFP) compared to pain-free participants. We hypothesized that no differences would be detected at 40° due to increasing patellar stability.DesignCross-sectional, descriptive study.MethodsTwenty-seven people with PFP and 29 pain-free people participated. Participants underwent magnetic resonance imaging at 0°, 20°, and 40° knee flexion with the limb in a simulated weight-bearing position. Patellofemoral contact area, tibiofemoral rotation angle, patellofemoral alignment (bisect offset index and patellar tilt angle) were quantified and compared between groups at each angle using Student's t-tests. An a-posteriori comparison was made between the pain-free group and a subgroup of 15 participants with patellofemoral pain who demonstrated a faulty lower limb movement pattern (“medial collapse”).ResultsIn the patellofemoral pain group, contact area was lower at 0° (203.8 ± 45.5 mm2 vs. 224.1 ± 46.6 mm2, p = 0.05) and 20° (276.8 ± 56.2 mm2 vs. 316.7 ± 82.8 mm2, p = 0.02), bisect offset index (BOS) and patellar tilt angle (PTA) were higher at 0° (bisect offset index: 0.69 ± 0.13 vs. 0.64 ± 0.09, p = 0.04; patellar tilt angle: 12.5 ± 7.6° vs. 9.2 ± 5.8°, p = 0.04). In the patellofemoral pain subgroup, tibiofemoral rotation was higher at 0° compared to pain-free participants (6.4 ± 5.9° vs. 4.0 ± 4.6°, p = 0.07).ConclusionsWhile contact area and patellofemoral alignment were altered in people with patellofemoral pain, tibiofemoral rotation was altered in a subgroup of people who demonstrated medial collapse. Subgroup classification may help identify mechanisms of pain and assist in developing targeted interventions.