To prospectively monitor levels of proinflammatory cytokines and aggrecan ARGS neoepitope in synovial fluid and serum as well as levels of C-terminal crosslinking telopeptide of type II collagen (CTX-II) and N-terminal crosslinking telopeptide of type I collagen (NTX-I) in urine after acute anterior cruciate ligament (ACL) rupture.
Synovial fluid, serum, and urine were collected from 121 adults on 6 occasions over 5 years after acute ACL injury. Reference samples were obtained from subjects without knee injury. Concentrations of interleukin-6 (IL-6), IL-8, IL-10, interferon-γ (IFNγ), tumor necrosis factor (TNF), aggrecan ARGS neoepitope, CTX-II, and NTX-I were measured by enzyme-linked immunosorbent assay.
Shortly after ACL injury, cytokine concentrations in synovial fluid were elevated 6-fold (TNF) to 1,050-fold (IL-6) compared to reference levels, while concentrations of aggrecan ARGS neoepitope in synovial fluid and serum and CTX-II in urine were elevated 1.4-fold to 8-fold. Thereafter, concentrations of cytokines and aggrecan ARGS neoepitope in synovial fluid decreased with different half-lives (in years: IL-6 0.9, IL-8 2.2, IL-10 2.3, IFNγ 3.1, TNF 3.6, aggrecan ARGS neoepitope 4.0). After 5 years, the TNF concentration in synovial fluid remained higher than the reference level. There was a correlation between the concentrations of aggrecan ARGS neoepitope in synovial fluid and serum (rs  = 0.36). Concentrations of aggrecan ARGS neoepitope in synovial fluid and of CTX-II and NTX-I in urine were correlated with concentrations of cytokines in synovial fluid (rs  = 0.41-0.49 and rs  = 0.21-0.31, respectively).
Acute ACL injury induced highly increased levels of inflammatory cytokines in the joint, and these were associated with proteolysis of aggrecan and type II collagen. Cytokine levels remained increased up to 5 years after injury, indicative of extended local inflammation in the joint.