This study investigated the effects of flexion angle and anterior-posterior (AP) joint constraint on the nature and severity of knee injury during tibial-femoral (TF) compression loading via axial loads in the tibia. The effect of flexion angle was examined using 10 unconstrained human knees from 5 cadavers aged 73.2 +/- 9.4 years. The TF joint was loaded in compression as a result of axial loading along the tibia using a servo-hydraulic testing machine until gross failure with the knee flexed 60 degrees or 120 degrees. Both 60 degree and 120 degree flexed preparations failed by rupture of the anterior cruciate ligament (ACL) at 4.6 +/- 1.2 kN, and the internal joint loads were significantly higher on the medial versus the lateral aspect of the tibial plateau. The effect of AP constraint of the femur along the longitudinal axis of the femur was investigated in a second series of tests using the same TF joint loading protocol on 6 pairs of human joints (74.3 +/- 10.5 years) flexed at 90 degrees. The primary failure mode for the AP constrained joints was bone fracture via the femoral condyle at a maximum load of 9.2 +/- 2.6 kN. The failure mode for unconstrained joints was primarily due to rupture of the ACL at a maximum load of 5.8 +/- 2.9 kN. Again, the pressure sensitive film indicated an unequal internal TF load distribution for the unconstrained knee (medial versus lateral plateau). However, there was a more equal distribution of internal loads between the medial and lateral aspects of the tibial plateau in the constrained joints. The study showed that the mechanism of TF knee joint injury and internal TF joint load distribution depends on the degree of AP constraint offered by the test apparatus. The study findings may be useful in understanding the complex failure mechanisms for an unconstrained knee under axial compression loads in the tibia during automobile crashes. For the covering abstract of the conference see ITRD E206605.
Abstract