Modeling Dynamic ACL Loading During Running in Post-ACL Reconstruction Individuals: Implications for Regenerative Engineering

Purpose Neuromuscular deficits in post-anterior cruciate ligament reconstruction (ACLR) individuals result in the adoption of compensatory movement strategies that alter how the knee and ACL are loaded. While it is understood that post-ACLR individuals load the knee and ACL differently than healthy controls, the challenge is quantifying the loading in the ACL as it can provide insight regarding secondary ACL tears. Computational modeling is advantageous because it provides a way to compute the forces in the ACL in individuals during dynamic tasks. Thus, this study sought to employ computational modeling to investigate differences in how the ACL is loaded during running in healthy controls and post-ACLR individuals. Methods Sixteen post-ACLR individuals and twelve healthy controls performed a running protocol where they were instructed to run at a self-selected speed. Subject-specific computational models were generated for each participant, and joint kinematics, joint kinetics, and muscle and ACL forces were extracted from the simulations. Results Despite the post-ACLR individuals exhibiting significantly lower peak knee flexion angles and peak knee extensor moments than the controls, the peak ACL forces were marginally higher in post-ACLR individuals than in healthy controls (p = 0.33). Conclusion These findings suggest that secondary ACL tears may be more of a reflection of the challenges faced in mimicking the structural and functional roles of the ACL with transplanted tissues rather than the effects of elevated ligament loading. The knowledge gained from this study will have significant implications for regenerative engineering and the design of more robust tissues. Lay Summary Individuals after an anterior cruciate ligament reconstruction (ACLR) suffer from diminished muscle function that causes them to adopt new movement patterns. A consequence of these new movement patterns is a change in the forces that are placed on the newly transplanted ACL. This study used computational modeling to compare the forces experienced by the ACL in healthy controls and post-ACLR individuals during running. No differences in ACL forces were measured between the two groups, suggesting that secondary ACL tears may be due to the altered structural integrity of the newly transplanted grafts.