Patello-femoral contact area and compressive force after anteromedial displacement of tibial tuberosity in amputated knees

Contact force and contact area in the patello-femoral joint was biomechanically analyzed using seven amputated legs. The knees were fixed firmly to the experimental apparatus and 300 N of tension was applied to the quadriceps tendon. Total contact force was measured using pressure-sensitive film, and the ratio of the contact area to the patellar joint surface (%) was measured using hydrophilic vinyl polysiloxane impression material. At a Q-angle of 0° with no advancement, 10 mm and 20 mm advancement of the tibial tuberosity, the total contact force on the patello-femoral joint at a knee flexion of 45° was 266±55 N, 191±58 N and 146±58 N, respectively. The total contact force became smaller as the advancement of the tibial tuberosity changed to 5, 10, 15 and 20 mm. Especially, the total contact force with Q-angle of 0° and anterior advancement of 15 and 20 mm was significantly smaller than that with no advancement. With a Q-angle of 0°, the contact area of the patello-femoral joint at 10 mm advancement was the greatest, occupying 30.1±9.9% of the whole patellar joint surface. The mean contact pressure with Q-angle of 0° and anterior advancement of 10 mm was smaller than that with all other positions, but there was no significant difference. In this experiment, combined anterior and medial displacement of the tibial tuberosity reduced the contact force in the patello-femoral joint of the amputated legs, and an advancement of 10 mm achieved optimal reduction of force and the greatest contact area.