Identifying and Targeting Modifiable Risk Factors Linked with Knee Joint Health after Anterior Cruciate Ligament Reconstruction

Abstract

High body mass index (BMI) is consistently, and independently, linked with elevated OA risk in uninjured and anterior cruciate ligament reconstruction (ACLR) populations. High BMI is a national health concern and nearly 40% of patients with ACLR are categorized as overweight or obese. Nonetheless, a lack of data has directly assessed the potential mechanisms driving elevated risks of post-traumatic osteoarthritis (OA) in high BMI patients with ACLR and it is plausible these patients experience differential recovery trajectories – necessitating unique rehabilitation strategies. Altered walking patterns are ubiquitous following ACLR which if left unresolved, may perpetuate cartilage degradation and influence OA onset. Unfortunately, typical rehabilitation lacks gait-specific rehabilitation tools to adequately restore walking patterns. Identifying clinically feasible strategies to facilitate gait recovery is essential to improving patient function and minimizing post-traumatic OA risk. Therefore, the overarching aims of this dissertation represents a series of cross-sectional investigations aimed at 1) assessing modifiable risk factors (i.e., high BMI and walking biomechanics) linked with post-traumatic OA following ACLR and 2) examining gait retraining strategies and monitoring strategies to improve and better detect biomechanical risk factors for post-traumatic OA. Aim one of this dissertation explored the effects of BMI on ultrasound-based measures of trochlear cartilage thickness and gait biomechanics after ACLR. We found high BMI uniquely influenced cartilage thickness differences and moderated the relationship between walking mechanics and trochlear cartilage thickness. Aim two further explored the impact of high BMI on joint health after ACLR by evaluating surrogate measures of cartilage mechanical integrity. We found those with high BMI after ACLR exhibited greater cartilage strain, larger echo-intensity (EI) changes post-exercise and larger between-limb differences in cartilage outcomes compared to normal BMI counterparts with ACLR. Further, individuals who habitually walked with greater knee loads, and joint range of motions exhibited lesser strains and EI changes. For aim three, we assessed the feasibility of manipulating walking cadence to improve knee motions and load outcomes using auditory biofeedback. We found cueing individuals with ACLR to walk at slower cadences acutely facilitated sagittal knee motions and moments. Modifying cadence is highly translatable to the clinic given the need for minimal equipment, but future longitudinal investigations are needed to confirm the long-term efficacy of this biofeedback approach. Lastly, aim four investigated how acutely manipulating walking speeds altered interlimb symmetry in gait mechanics between ACLR individuals and uninjured controls. We observed those with ACLR experienced differential responses to speed manipulations compared to uninjured individuals where gait asymmetries became magnified at fast speeds and reduced at slow speeds, but only in ACLR patients. The use of fast walking speeds could be advantageous when assessing gait function clinically as it may aid in characterizing an individual’s functional competence. Further, increasing speed could be used as a gait retraining strategy to increase knee loads and motions after ACLR. Overall, data from this dissertation suggests that those with high BMI after ACLR may present with earlier OA-related disease features and may require more aggressive rehabilitation and implementation of disease-modifying treatments. Further, we provide initial evidence that cadence manipulation could be an avenue for future gait intervention programs while manipulating walking speeds may be a useful task-specific constraint that can increase (or decrease) musculoskeletal demands – such knowledge may be of use when designing or modifying intervention approaches or when assessing gait recovery throughout post-operative rehabilitation.