Elevated C-reactive protein levels in osteoarthritis are associated with local joint inflammation

Purpose

Previous studies have demonstrated an association between osteoarthritis (OA) progression and inflammation as measured by systemic C-reactive protein (CRP) levels. We hypothesized that CRP levels in patients with OA are pathogenically linked to synovial membrane inflammation. This study investigated the relationship between CRP and local synovial appearance, synovial histology, and synovial fluid IL-6 levels.

Methods

Patients with idiopathic OA undergoing either total hip or knee arthroplasty or knee arthroscopic debridement were identified. Synovial membrane inflammation was graded intraoperatively and by histologic examination of samples obtained from standardized locations. Synovial fluid IL-6 levels and plasma CRP levels were measured using a high-sensitivity ELISA.

Results

Twelve patients with early OA and 37 patients with end-stage OA were identified. These OA patients were dichotomized into two groups: high CRP (CRP level > 3 μg/ml) and low CRP (CRP < 3 μg/ml). The high CRP group demonstrated elevated synovial fluid IL-6 levels (P < 0.001) as well as increased intraoperative and histologic synovitis scores (P = 0.045 and P = 0.03, respectively) compared with the low CRP group. There was a highly statistically significant correlation between synovial fluid IL-6 levels and systemic CRP levels (rho = 0.66, P < 0.001).

Conclusions

We have demonstrated an association between a marker of systemic inflammation and local synovial inflammation in patients with OA. The more aggressive disease seen in OA patients with elevated CRP levels may be mechanistically linked to a more inflammatory synovial response in the diseased joint.