STABILITY: Physical Activity Intervention at 7 Years Post-Anterior Cruciate Ligament Reconstruction

ACL injuries are extremely common knee injuries sustained by athletes participating in sports involving sudden changes of direction like jumping, cutting and pivoting. Every year, approximately 1 in 3500 individuals injure their ACL. ACL reconstruction surgery is a popular treatment option for young athletes that aims to re-establish knee stability and restore function, enabling high rates of return to sport. Unfortunately, despite reconstruction surgery's short-term benefits, it does not significantly alter the course of post-traumatic osteoarthritis (PTOA) that often develops after sustaining a severe knee injury. In fact, over half of ACL patients present radiographic signs of OA by 20 years post-reconstruction surgery. Individuals with OA often have significantly impaired mobility, functionality, and quality of life, so appropriate rehabilitation protocols and conservative joint management strategies are necessary to improve knee health outcomes post-reconstruction and keep these patients healthy and active for as long as possible.

Physical activity has widely known preventive and therapeutic effects across many chronic diseases such as diabetes, hypertension, heart disease, and obesity. Similarly, there is widespread evidence of high physical activity levels reducing pain and increasing function and health-related quality of life in individuals with knee and hip osteoarthritis, indicating its efficacy as a conservative measure for improving joint health. In contrast, sedentary behaviour increases the risk of OA development and other comorbidities by increasing body mass index (BMI), causing poorer cartilage health, reducing muscle quality, and increasing systemic inflammation. Following ACL reconstruction, individuals are susceptible to adopting more sedentary lifestyles due to a fear of re-injury through movement, evidenced by relatively lower self-reported physical activity levels compared to before injury. While ACL injuries may initiate OA pathogenesis, sedentary behaviour is a modifiable risk factor that can further facilitate disease progression. Since physical activity prescription effectively increases physical activity levels, it offers potential utility for improving knee joint health post-reconstruction surgery and preventing or delaying the onset of PTOA.

Objectives:

1. To examine the effects of physical activity prescription on patient-reported outcomes (KOOS and IKDC scores)

2. To examine the effects of physical activity prescription on femoral trochlear cartilage thickness and echo intensity based on ultrasound imaging over 1 year.

3. To analyze the impact of patients' gait biomechanics on changes in patient-reported outcomes and femoral trochlear cartilage health outcomes due to the physical activity intervention.

Hypotheses:

1. Those assigned to the physical activity prescription group will have higher KOOS and IKDC scores than those in the control group following 1 year.

2. Physical activity prescription will lead to less reductions in echo intensity and heterogeneity of the femoral trochlear cartilage over 1 year.

3. Poorer femoral trochlear cartilage health imaging outcomes (greater reductions in echo intensity and heterogeneity) and lower KOOS and IKDC scores at 1 year will be associated with larger vertical ground reaction forces, smaller knee flexion angles, greater knee adduction moments, smaller knee extensor moments, and larger vertical loading rates of the involved limb.