title: The utility of ultrasound for diagnosing purulent infections of the upper extremity.
abstract: BACKGROUND
  The purpose of this study was to determine the test characteristics of formal ultrasound when used to diagnose upper extremity soft tissue abscess in the setting of suspected infection.
  
  
  METHODS
  We completed a retrospective chart review of all patients who had formal ultrasounds at our institution for the indication of diagnosing upper extremity abscess between July 2010 and July 2013. Using presence of purulence as the gold standard for diagnosis of abscess, we calculated the test characteristics of ultrasound. We then performed a series of logistic regression models with ultrasound being the independent variable of interest.
  
  
  RESULTS
  Using search criteria consistent with upper extremity abscess, we identified 512 patients who underwent ultrasound examinations during our study period. Of these, 178 met the enrollment criteria. Ultrasound reports revealed 110 negative findings, 37 definitively positive findings, and 31 ambiguous findings. Forty-four patients had a final diagnosis of abscess, and 15 of these patients had negative or ambiguous ultrasounds. The sensitivity of definitively positive ultrasound was 65.9 %. The specificity was 94.0 %. Positive predictive value (PPV) of a definitively positive ultrasound result was 78.4 %, and negative predictive value (NPV) of a definitively negative result was 90 %. Logistic regression demonstrated a statistically significant association between definitively positive ultrasound and abscess, but no association between ambiguous ultrasound and abscess after adjustment for significant covariates.
  
  
  CONCLUSIONS
  Ultrasound is not a sensitive method to detect the presence of abscess in the setting of upper extremity infection. However, in this population of patients with suspected abscess, the negative predictive value was high with and without the inclusion of ambiguous results, suggesting reasonable utility of ultrasound as a rule-out test.
  
  
  METHODS
  Diagnostic study, Level II.
authors.affiliation: Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, 800 Howard Avenue, New Haven, CT 06510 USA.
authors.forename: Andrea
authors.initials: A
authors.lastname: Halim
authors.affiliation: Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510 USA.
authors.forename: Yushane
authors.initials: Y
authors.lastname: Shih
authors.affiliation: Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, 800 Howard Avenue, New Haven, CT 06510 USA.
authors.forename: Seth D
authors.initials: SD
authors.lastname: Dodds
keywords: Soft tissue infection; Ultrasound; Upper extremity abscess