Anterior Cruciate Ligament Failure and Cartilage Damage during Knee Joint Compression

Background Anterior cruciate ligament (ACL) injury incurred from high-impact activities leads to an increased risk of osteoarthritis. Hypothesis Impact forces that cause ACL failure can also inflict cartilage damage, whereby its extent and distribution may be influenced by the ligament failure mechanism. Study Design Descriptive laboratory study. Methods Six porcine knee specimens were mounted to a material testing system at 70° of flexion. During compression, rotational and translational data of the specimens were recorded with a motion-capture system. Compression was successively repeated with increasing actuator displacement until a significant drop in compressive force response was observed; ligament failure was assessed by dissection. Osteocartilage expiants were extracted from the meniscus-covered sites (anterior, exterior, and posterior) and exposed (interior) sites on both tibial compartments. The expiants were sectioned, stained, and histologically scored using the modified Mankin grading system. Results Five of the 6 specimens incurred ACL failure. On failure, a significant compressive force drop (1812.5–2659.3 N) was observed together with considerable posterior femoral translation; 2 specimens underwent external rotation, while 2 had internal rotation and 1 had no substantial rotation. Generally, the meniscus-covered sites displayed significant surface fraying and occasional deep clefts; the exposed site did not present substantial surface irregularities but indicated more tidemark disruption. Higher Mankin scores observed at certain sites illustrated a localized presence of contact and shear forces, which may be caused by pivoting and sliding of the femoral condyles during rotation. Conclusion The porcine model can be a tenable preliminary option for assessing the role of the human ACL during joint compression. Impact loads that result in ligament failure can potentially inflict considerable cartilage damage; the damage profile may be affected by the type of failure mechanism. Clinical Relevance Cartilage injury arising at the time of ACL injury may lead to an accelerated risk of joint degeneration.