Interobserver reliability of computed tomography to diagnose scaphoid waist fracture union

To determine the interobserver agreement and diagnostic performance characteristics of computed tomography (CT) for determining union of scaphoid waist fractures. A total of 59 orthopedic and trauma surgeons rated for union a set of 30 sagittal CT scans of 30 scaphoid waist fractures. Of these fractures, 20 were treated nonoperatively, were imaged between 6 and 10 weeks after injury, and were known to have eventually achieved union. Ten were operatively confirmed to be ununited. We rated each scan as united or ununited using a Web-based rating application. We assessed interobserver reliability using Siegel's multirater Kappa. We calculated diagnostic performance characteristics using Bayesian formulas. The interobserver agreement among 59 raters was substantial. The average sensitivity, specificity, and accuracy of diagnosing union of scaphoid waist fractures on sagittal CT scans were 78%, 96%, and 84%, respectively. Assuming a 90% prevalence of fracture union of the scaphoid, the positive predictive value of a diagnosis of union on sagittal CT scan was 0.99 and the negative predictive value was 0.41. Our results suggest that CT scans are accurate and reliable for diagnosis of union but inadequate for ruling out nonunion of scaphoid waist fractures between 6 and 10 weeks after injury. Diagnostic III