Serum Urate Levels Predict Joint Space Narrowing in Non-Gout Patients With Medial Knee Osteoarthritis.

OBJECTIVE: The pathogenesis of osteoarthritis (OA) includes both mechanical and inflammatory features. Studies have implicated synovial fluid uric acid (UA) as a potential OA biomarker, possibly reflecting chondrocyte damage. Whether serum UA levels reflect/contribute to OA is unknown. We investigated whether serum UA levels predict OA progression in a non-gout knee OA population.

METHODS: Eighty-eight patients with medial knee OA (body mass index [BMI] <33 kg/m2 ) but without gout were studied. Baseline serum UA levels were measured in previously banked serum samples. At 0 and 24 months, patients underwent standardized weight-bearing fixed-flexion posteroanterior knee radiography to determine joint space width (JSW) and Kellgren/Lawrence grades. Joint space narrowing (JSN) was calculated as the change in JSW from 0 to 24 months. Twenty-seven patients underwent baseline contrast-enhanced 3T knee magnetic resonance imaging for assessment of synovial volume.

RESULTS: Serum UA levels correlated with JSN values in both univariate (r = 0.40, P < 0.01) and multivariate (r = 0.28, P = 0.01) analyses. There was a significant difference in mean JSN after dichotomization at a serum UA cut point of 6.8 mg/dl, the solubility point for serum urate, even after adjustment (JSN of 0.90 mm for a serum UA ≥6.8 mg/dl and 0.31 mm for a serum UA <6.8 mg/dl; P < 0.01). Baseline serum UA levels distinguished progressors (JSN >0.2 mm) and fast progressors (JSN >0.5 mm) from nonprogressors (JSN ≤0.0 mm) in multivariate analyses (area under the receiver operating characteristic curve 0.63 [P = 0.03] and 0.62 [P = 0.05], respectively). Serum UA levels correlated with the synovial volume (r = 0.44, P < 0.01), a possible marker of JSN, although this correlation did not persist after controlling for age, sex, and BMI (r = 0.13, P = 0.56).

CONCLUSION: In non-gout patients with knee OA, the serum UA level predicted future JSN and may serve as a biomarker for OA progression.