Background Serum levels of the heterodimer S100A8/A9 have shown to correlate well with disease activity and structural abnormalities in patients across several inflammatory rheumatic diseases and seems crucially involved in cartilage destruction in osteoarthritis (OA) in murine models. Earlier we found that S100 serum levels correlate with development of human OA. However, whether there is an association between S100A8/A9 levels and clinical and structural data in patients with established OA is unknown.

Objectives To explore the association between the proinflammatory protein S100A8/A9 serum level with clinical data and structural abnormalities in patients with established knee, hip or hand OA.

Methods A cross sectional exploratory study was conducted with 162 patients fulfilling the ACR clinical criteria for knee (n=57), hip (n=47) or hand OA (n=58). Clinical data consisted of pain, stiffness, function, ESR and C-reactive protein serum levels. Pain, stiffness and function subscales were calculated and normalized using the WOMAC questionnaires for knee and hip OA and AUSCAN index for hand OA. Outcome measures for structural abnormalities included the K&Lscore (for hand OA mean score), sum score of osteophytes and joint space narrowing grades using the OARSI atlas. In case of non-normal distribution, outcome measures were dichotomized using the median split method. The association between serum levels of S100A8/A9 (independent) and clinical data (dependent) or structural abnormalities (dependent) was analyzed using linear regression or logistic regression when appropriate. For multivariate analyses, α < 0.10 was set.

Results The mean age was 56 years, 71% was female and 61% had K&L score ≥ 2. In the hand OA group, the mean age was higher and more women were included. Furthermore, hand OA patients reported the longest duration of symptoms, least pain and had the highest normalized sum score of osteophytes. The knee patients reported the highest pain score and had the least sum score of osteophytes. The serum S100A8/A9 level did not differ between knee, hip and hand OA patients. For all joints together, serum S100A8/A9 level was negatively associated with the normalized sum score of osteophytes after adjustment for sex and BMI (adjusted OR 0.99 (95% CI 0.97-1.00, p=0.06) and positively associated with ESR (adjusted OR 1.002 (95%CI 1.000-1.004 p<0.05) for each increase of S100A8/A9 with 1 ng/ml. For hand OA patients, a negative association of S100A8/A9 with sum score of joint space narrowing was found (adjusted OR 0.993 (95%CI 0.984–1.001) p < 0.10).

Conclusions Results from this cross sectional exploratory study do not support a role for serum S100A8/A9 levels as biomarker for clinical (normalized pain, stiffness and function) and structural outcome in established knee, hip and hand OA patients. The inverse relation with the sum score of osteophytes and joint space narrowing and the positive association with ESR underlines the previous finding that S100A8/A9 may reflect inflammatory synovial processes in patients with OA before structural abnormalities occur and warrant further exploration in longitudinal studies.

Disclosure of Interest None Declared