Arthrocentesis of suspected septic sternoclavicular arthritis: microbial yield and predictors of culture positivity.

Objective: Evaluate the microbial yield and factors predicting culture positivity for image-guided arthrocentesis of suspected septic sternoclavicular (SC) arthritis.

Materials and methods: An electronic health record search identified image-guided SC joint aspirations for suspected septic arthritis. Data was extracted by retrospective chart review including patient demographics, procedure characteristics, pre-procedure lab testing, joint culture results, final SC joint diagnoses and any effect of positive synovial cultures on subsequent antibiotic therapy. Factors associated with positive joint fluid cultures were assessed using a Chi-squared test for categorical predictors and logistic regression for continuous predictors.

Results: A total of 31 SC arthrocenteses met inclusion criteria with most (81%) performed using ultrasound guidance. Synovial fluid was successfully aspirated in 19/31 (61%) of cases, and in all other cases lavage fluid was successfully obtained. Synovial cultures were positive in 9/31 (29%) of cases. A final diagnosis of septic arthritis was assigned to 20/31 cases (65%) in which 9/20 (45%) had positive synovial cultures. There was no statistically significant association between synovial culture positivity and risk factors for septic arthritis, positive blood cultures, pre-aspiration antibiotics and whether synovial fluid or lavage fluid was cultured. Serum white blood cell count (WBC) and erythrocyte sedimentation rate (ESR) demonstrated statistically significant positive correlation with positive synovial cultures.

Conclusion: Arthrocentesis is effective for microbial speciation in SC septic arthritis, and diagnostic yield may be increased with lavage when encountering a dry tap. Normal serum WBC and ESR values indicate an extremely low likelihood of positive synovial cultures.