Using an instrumented cadaver lower extremity, the forces in the
quadriceps, patella, and tibia during flexed-knee stance were measured and
the calculated and experimental data were found to correlate with an
average discrepancy of 6 per cent. The quadriceps force required to
stabilize the knee was 75 per cent of the load on the femoral head at 15
degrees of knee flexion, 210 per cent at 30 degrees, and 410 per cent at 60
degrees. Stresses at the tibiofemoral and patellofemoral joint surfaces
increased in similar fashion. The quadriceps force was equivalent to 20 per
cent of average maximum quadriceps strength at 15 degrees and to 50 per
cent at 30 degrees, as determined from torque tests on five normal
subjects.