Longitudinal Analysis of Serum Biochemical Changes following Anterior Cruciate Ligament Injury and Reconstruction: A Matched Comparison-Control Analysis

Objectives: Individuals with an anterior cruciate ligament (ACL) injury are at high risk of developing posttraumatic osteoarthritis (PTOA). A comprehensive study is needed to determine the time course of joint tissue metabolic changes occurring following ACL injury and reconstruction (ACLR). The purpose of this longitudinal nested comparison-control study was to simultaneously evaluate serum biomarkers of inflammation and cartilage matrix damage in ACL injured patients prior to ACLR and 6 and 12 months post-ACLR, as well as in matched uninjured controls. Methods: Serum was collected from 34 ACL injured individuals (53% female, 20.7±2.4 years old, 24.2±4.1 body mass index [BMI]) within 14 days of primary ACL injury (baseline), as well as at 6 and 12 months following bone-patellar-tendon-bone autograft ACLR. Serum was also collected from 34 uninjured matched controls (53% Female, 20.5±2.4 years old, 24.1±3.5 BMI) at a single timepoint. Blood was collected from the antecubital fossa, centrifuged and stored at -80°C prior to batch analysis. Commercial enzyme-linked immunosorbent assays were used to evaluate concentrations of: 1) a pro-inflammatory cytokine [Monocyte Chemoattractant Protein; MCP-1]; 2) a matrix degrading enzyme [matrix metalloproteinase-3; MMP-3]; 3) a cartilage breakdown biomarker [cartilage oligomeric matrix protein; COMP]; and type-II collagen turnover [type-II collagen cleavage: synthesis; C2C:CPII]. Separate Bonferroni-corrected independent t-tests were used to determine differences between the ACL injured group at each timepoint and uninjured controls for each biomarker (P ≤ 0.015). Similarly, separate Bonferroni-corrected dependent t-tests were used to determine differences in biomarker concentrations over time for the ACLR group. Results: Serum concentrations of MCP-1 and COMP were greater in the ACL injured individuals at all timepoints compared to the controls (P ≤ 0.015, Table 1), yet no differences were found over time in the ACL injured group. MMP-3 concentrations increased between baseline and 6 months post-ACLR (P ≤ 0.015, see Table), yet no differences were found between 6 and 12 months post-ACLR, between baseline and 12 months, or between ACLR and controls at any of the time points. C2C:CPII was not different between ACL injured individuals and controls at baseline or 6 months post-ACLR. C2C:CPII was significantly increased between 6 and 12 months-post ACLR, and was found to be greater than baseline and greater than controls at 12 months post-ACLR (P ≤ 0.015, see Table). Conclusion: Our study is critical in demonstrating the time course of multiple joint tissue metabolic changes following ACL injury and ACLR. Elevated serum MCP-1 and COMP concentrations, linked to early deleterious metabolic processes associated with PTOA development, are evident soon after ACL injury and persist at 12 months post-ACLR. Serum MMP-3 concentrations were elevated 6 months post-ACLR compared to the baseline measurements, suggesting factors occurring after ACLR initiate upregulation of matrix degrading enzymes. Furthermore, elevated C2C:CPII occurs within the first 12 months post ACLR but not until after the 6-month post-ACLR timepoint. Further studies are needed to determine how long these joint tissue metabolic changes persist after ACL injury and ACLR, as well as how joint tissue metabolism is affected by the type and timing of different surgical and nonsurgical treatments.