Patients and methods
This prospective study included all adult patients with suspected SA seen in the emergency department or rheumatology department at the University Hospital, Clermont-Ferrand, France, over a period of 18 months.
In total, 105 patients with suspected SA were included, 38 (36%) presenting with SA (29 [28%] with bacteriologically documented SA). In the univariate analysis, chills (p=0.015), gradual onset (p=0.04), local redness (p=0.01), as well as an entry site for infection (p=0.01) were most often identified in SA. A history of crystal-induced arthritis (p=0.004) was more frequent in non-SA cases. An erythrocyte sedimentation rate (ESR)>50 mm (p=0.005), a C-reactive protein (CRP) level >100 mg/L (p=0.019), and radiological signs suggestive of SA (p=0.001) were more frequent in the SA cases. Synovial fluid appearance: purulent (p<0.001) and clear (p=0.007), synovial white blood cell (WBC) count >50,000/μL (p < 0.001), differentiated between SA and non-SA.
In multivariate analysis, only chills (odds ration [OR]=4.7, 95% confidence interval [CI] 1.3–17.1), a history of crystal-induced arthritis (OR=0.09, 95% CI 0.01–0.9), purulent appearance of the joint fluid (OR=8.4, 95% CI 2.4–28.5), synovial WBC count >50,000/mm3 (OR=6.8, 95% CI 1.3–36), and radiological findings (OR=7.1, 95% CI 13–37.9) remained significant.
No clinical sign or laboratory test (excluding bacteriological test), taken alone, is conclusive for the differentiation between SA and non-SA, but the association of several signs, notably chills, history of crystal-induced arthritis, radiological findings, and the appearance and cellularity of joint fluid may be suggestive.