Anterior Cruciate Ligament Failure and Cartilage Damage During Knee Joint Compression: A Preliminary Study Based on the Porcine Model

¹ Department of Orthopaedic Surgery, National University of Singapore
² Biomechanics Lab, Defence Medical and Environmental Research Institute, Singapore
³ Division of Bioengineering, National University of Singapore, Singapore
⁴ Division of Bioengineering, National University of Singapore, and Biomechanics Lab, Defence Medical and Environmental Research Institute, Singapore
⁵ Department of Orthopaedic Surgery, National University of Singapore, and Division of Bioengineering, National University of Singapore

^* To whom correspondence should be addressed. E-mail: dosgohj{at}nus.edu.sg.

	Abstract

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 explants were extracted from the meniscus-covered sites (anterior, exterior, and posterior) and exposed (interior) sites on both tibial compartments. The explants 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.