Effect of older age and/or ACL injury on the dose-response relationship between ambulatory load magnitude and immediate load-induced change in serum cartilage oligomeric matrix protein.

Purpose: This study aimed to assess the influence of older vs. younger age and previous anterior cruciate ligament (ACL) injury on resting serum cartilage oligomeric matrix protein (sCOMP[t]) concentration, on immediate load-induced sCOMP kinetics after a 30-min treadmill walking stress (∆_sCOMP[t]), and on the dose-response relationship between ambulatory load magnitude and ∆_sCOMP(t).

Methods: A total of 85 participants were recruited in 4 groups (20-30 years: 24 healthy, 23 ACL-injured; 40-60 years: 23 healthy, 15 ACL-injured). Blood samples were collected immediately before and after a walking stress at 80%, 100%, or 120% bodyweight (BW) on 3 test days and analyzed for sCOMP concentration. Linear models were used to estimate the effect of age, knee status (unilateral ACL injury, 2-10 years prior), and sex on sCOMP(t), ∆_sCOMP(t)), and the dose-response between ambulatory load magnitude and ∆_sCOMP(t).

Results: We found that sCOMP(t) was 21% higher in older than younger participants (p < 0.001) but did not differ between ACL-injured and healthy participants (p = 0.632). Also, ∆_sCOMP(t) was 19% lower in older than younger participants (p = 0.030) and increased with body mass index (p < 0.001), sCOMP(t) (p = 0.008), and with 120%BW (p < 0.001), independent of age, ACL injury, or sex.

Conclusion: Age but not prior ACL injury influences resting sCOMP and load-induced sCOMP. The dose-response relationship between ambulatory load magnitude and load-induced sCOMP changes is not affected by age, ACL injury, or sex. A better understanding of systemic sCOMP and the role of its mechanoresponse for the understanding of osteoarthritis pathophysiology and monitoring intervention efficacy may require knowledge of individual cartilage composition and tissue-level loading parameters.