A prevailing long-term outcome of surgical reconstruction of a ruptured anterior cruciate ligament (ACLR) is the development of degenerative joint diseases such as osteoarthritis. A key factor implicated in the progression of these diseases is altered contact patterns on the surface of the cartilage resulting from changes in mechanical loading and movement dynamics during repetitive cyclical tasks. Accordingly, in this project we examined the effects of graft-specific---patellar tendon (PT) or hamstring tendon (HT)---movement patterns and muscle activation strategies on the intrinsic mechanics of the knee joint during activities of daily living.;We first used experimental motion capture techniques to calculate knee joint movement and loading patterns. Our hypothesis that task complexity is the primary driver of differences in the aggregate joint mechanics between groups was supported by our results. Kinetic differences between groups were often undetectable during walking, but magnified during stair descent.;Next, we used a musculoskeletal simulation-based approach to determine how individual muscles counteract external loads, stabilize the joint, and generate movement following ACLR. Our hypothesis that graft type has a differential effect on muscle force production was supported by results showing ACLR with a PT graft has a targeted effect on the quadriceps, whereas HT graft reconstruction has a diffused effect on both the quadriceps and hamstrings.;Finally, we used a high-fidelity finite element model of the knee to examine the effects of post-surgical movement patterns and muscle activation strategies on contact stress distributions in the tibia and patella articular cartilage. We hypothesized a global effect on the tibiofemoral joint, but a differential effect on the patellofemoral joint based on graft type, which our results indicated was more affected by PT graft reconstruction. Further, variations in contact stress location as opposed to changes in magnitude appear to be the key metric in evaluating surgery-mediated changes in contact mechanics.;The results from these studies suggest a critical need to account for surgery-specific and task-specific biomechanical adaptations in an assessment of functional outcomes following ACLR. With future work, the design of surgical techniques and neuromuscular retraining protocols may improve long-term functional outcomes for individuals with ACL injury.
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