In efforts to study the pathoetiology of post-traumatic osteoarthritis (PTOA), we propose a collaborative, prospective cohort study of 38 patients undergoing primary anterior cruciate ligament (ACL) reconstruction after ACL rupture. We will assess the longitudinal progression of patient-reported outcomes, knee laxity, MRI-based articular cartilage morphology and composition, and serum-borne biomarkers of cartilage degeneration up to 1 year of follow-up. Furthermore, stem cell mobilization, chemokine and pro-inflammatory cytokine concentrations, and inflammatory cell recruitment into synovial tissue will be measured from intraoperatively-collected samples. We will perform mixed multivariate linear regression modeling to elucidate potentially novel relationships between patient demographics, anatomy, biological factors, and downstream alterations in articular cartilage morphology and composition.