Association Between Biochemical Joint Tissue Response To Loading And Femoral Cartilage Composition After Knee Surgery

Abstract

Serum cartilage oligomeric matrix protein (sCOMP) is used to measure acute biochemical joint tissue response to loading. Greater delayed sCOMP post-loading is linked to femoral cartilage thinning over 5 years. It remains unclear if sCOMP response to loading is associated with early femoral cartilage compositional changes linked to osteoarthritis development. PURPOSE: The purpose of this cross-sectional study was to estimate the associations between changes in sCOMP after a standardized walking protocol and femoral cartilage composition in individuals with anterior cruciate ligament reconstruction (ACLR). METHODS: Serum was collected before, immediately after, and 3.5 hours after a standardized 3,000 step walking protocol conducted at each participant’s self-selected speed (speed = 1.2 ± 0.1 m/s). sCOMP changes were calculated as the difference in concentrations from before to immediately and 3.5 hours after walking. Enzyme-linked immunosorbent assays were used to assess sCOMP (mean intra-assay variability = 15%). T1ρ relaxations times were collected bilaterally using magnetic resonance imaging and weightbearing portions of the cartilage were segmented into medial (MFC) and lateral (LFC) femoral condylar regions. Regional interlimb ratios were calculated by dividing mean T1ρ relaxation times in the ACLR limb by the non-injured limb. Greater T1ρ interlimb ratios were interpreted as lower proteoglycan density (worse cartilage composition) in the ACLR relative to the non-injured limb. Linear regressions were used to determine the association between change in sCOMP and T1ρ relaxation times after controlling for sex and months since surgery. RESULTS: 19 participants (9 male/10 female, 20.5 ± 4.1 years old, 24.8 ± 3.1 kg/m2 BMI, 7.3 ± 1.5 months since surgery) completed the study. Greater LFC T1ρ interlimb ratios were associated with greater increases in COMP at 3.5 hours (∆R2 = 0.28, p = 0.03), but not immediately (∆R2 = 0.08, p = 0.32) after walking. Associations between MFC T1ρ interlimb ratios and changes in sCOMP after walking were not statistically significant (p = 0.57-0.82). CONCLUSIONS: Delayed increases in sCOMP concentrations after walking may be more closely linked to deleterious cartilage metabolism and may be a better marker of early degenerative changes in knee joint health than acute changes.