Tibiofemoral contact pressures and osteochondral microtrauma during anterior cruciate ligament rupture due to excessive compressive loading and internal torque of the human knee.

Background: The knee is one of the most frequently injured joints, including 80 000 anterior cruciate ligament (ACL) tears in the United States each year. Bone bruises are seen in over 80% of patients with ACL injuries, and have been associated with an overt loss of cartilage overlying those regions within 6 months of injury.

Hypothesis: The level of contact pressure developed in the human knee joint and the extent of articular cartilage and underlying subchondral bone injuries will depend on the mechanism of applied loads/moments during rupture of the ACL.

Study Design: Controlled laboratory study.

Methods: Seven knee pairs, flexed to 30 degrees , were loaded in compression or internal torsion until injury. Pressure-sensitive film recorded the magnitude and location of contact. Histologic analysis and magnetic resonance imaging were used to document microtrauma to the tibial plateau cartilage and subchondral bone.

Results: All specimens suffered ACL injury, either in the form of a midsubstance rupture or avulsion fracture. The contact area and pressures were higher for compression than torsion experiments. After being loaded, the articular cartilage in the central and posterior regions of the medial tibial plateau showed increased magnetic resonance imaging signal intensity, corresponding to an increased susceptibility to absorb water. Histologically, there were more microcracks in the subchondral bone and more articular cartilage damage in the compression than torsion experiments.

Conclusion: Significant damage occurs to the articular cartilage and underlying subchondral bone during rupture of the ACL. The types and extent of these tissue injuries are a function of the mechanism of ACL rupture.

Clinical Relevance: Patients suffering an ACL injury may be at risk of osteochondral damage, especially if the mechanism of injury involves a high compressive loading component, such as during a jump landing.