Clinical and radiologic predictive factors of septic hip arthritis

The purpose of our study was to identify the clinical and radiologic factors associated with a positive culture during image-guided hip joint aspiration.

We performed a retrospective analysis of 167 consecutive hip aspirations for septic arthritis at a large tertiary medical center. Chart review was performed on the following clinical factors: serum WBC count≥11×10(3)/μL, serum erythrocyte sedimentation rate (ESR)≥20 mm/h, C-reactive protein (CRP)≥100 mg/L, synovial fluid WBC count, synovial fluid polymorphonuclear (PMN) leukocytes≥90%, fever, immunosuppression, antibiotic use, diabetes, presence of a prosthesis, and IV drug use (IVDU). Radiologic studies were reviewed for the following imaging and technical factors: presence of a sinus tract, fluid turbidity, volume of fluid (mL) aspirated, and whether the fluid analyzed was primarily aspirated or reaspirated after lavage. Logistic regression was used to calculate odds ratio (OR) and 95% CI.

Of the 167 aspirations, 29 (17.4%) had positive cultures; 6 of 29 (20.7%) positive cultures occurred in reaspirated lavage fluid. On multivariate analysis using logistic regression with stepwise backward elimination, the significant clinical and radiologic predictors were elevated WBC (OR, 4.4; 95% CI, 1.1-17.3), high percentage of synovial fluid PMN leukocytes (OR, 10.6; 95% CI, 2.9-39.8), IVDU (OR, 9.0; 95% CI, 1.3-64.7), and fluid turbidity (OR, 20.5; 95% CI, 6.9-61.4).

Positive hip cultures are associated with elevated serum WBC, IVDU, high percentage of synovial fluid PMN leukocytes, and fluid aspirate turbidity. Reaspiration of lavage fluid with either nonbacteriostatic saline or contrast material can yield positive cultures.