PROGRAM | Mechanical Engineering

By: Kelsey Neal Chair: Thomas Buchanan

ABSTRACT

Gait alterations after ACL reconstruction (ACLR) are commonly reported and have been linked to post-traumatic osteoarthritis development. It is hypothesized that these biomechanical alterations are impacting the way cartilage is stressed within the knee joint, however the acquisition of stress data is difficult/impossible from an in vivo approach limiting our understanding on this process in a clinical population. With improvements in computational abilities over the past 40 years some have begun to utilize an approach called finite element analysis to study stresses within the knee joint. The goal of this dissertation was to assess alterations in gait during the early stages of recovery after ACLR and to understand how these alterations impact the way in which cartilage is stressed between limbs and overtime using finite element models. Additionally, we sought to investigate if alterations in stress are associated with early signs of knee cartilage degeneration (assessed via advanced quantitative magnetic resonance imaging techniques).
Aim 1 of this dissertation focused on examining knee gait biomechanical variables over the entire stance phase of gait at both 3 and 6 months after ACLR and studied the progression of interlimb asymmetry between the two post-operative time points. We found that there were large asymmetries between limbs in several biomechanical variables of interest (e.g., knee flexion angles, medial compartment forces, …) and that most progressed toward a more symmetrical gait pattern by 6 months. Aim 2 focused on the development of a finite element model of the knee joint that uses subject-specific joint mechanics and loading from the gait analysis and musculoskeletal modeling performed in Aim 1. This finite element model was then used in Aim 3 to better understand the relationship between joint biomechanics and joint contact stresses after ACLR. We found interlimb asymmetries in stress magnitude within select regions of interest and observed associations between stress magnitude and knee flexion angles; indicating a coupling of early knee mechanics and the stress environment within the knee. In the fourth, exploratory aim, we examined whether or not alterations in stress early after ACLR are associated with markers for knee cartilage biochemical composition. We found that there was an association between changes in stress and changes in knee cartilage biochemistry during the 3- to 6-month time period; where those who saw increases in involved limb stress magnitude during this time period saw improvements in knee cartilage health.
This is among the first studies to explore how alterations in gait after ACLR affect how cartilage within the tibiofemoral joint is being stressed, and how these stress distributions affect cartilage at the biochemical level. This work has the potential to help link our understanding of how alterations at a macro-level are impacting the cartilage within the knee joint at a tissue level. Further investigation using the tools developed in this study could help inform clinicians on which mechanical alterations are causing the most potential damage to cartilage and may ultimately help lead to the development of rehabilitative procedures to prevent long-term disease development.

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