MRI can yield false positives for scaphoid

Magnetic resonance imaging (MRI) is often advocated as a way to evaluate patients with suspected scaphoid fractures. But according to the results of a study presented by Andele D. de Zwart, MS, a medical student at Medical Centre Haaglanden, The Hague, Netherlands, MRI should not be used as a reference standard because it is not 100 percent specific for diagnosing this injury and can yield false positives in healthy volunteers.

In their prospective study, Mr. de Zwart and his fellow researchers recruited 32 healthy volunteers and scanned both of their wrists. Researchers mixed the 64 scans of wrists lacking scaphoid fractures with 60 scans of patients who had normal scaphoid radiographs but were clinically suspected of having scaphoid fractures. The 124 MRI scans, which were blinded and randomly ordered, were independently reviewed by five radiologists using a standard protocol to determine whether a scaphoid fracture was present.

On average, the five radiologists diagnosed 2.6 fractures in healthy volunteers, indicating a specificity (proportion of healthy volunteers correctly diagnosed as having no fracture) of 96 percent (95 percent CI: 0.94–0.98). Moderate interobserver agreement was indicated statistically by the multi-rater kappa of 0.44 (p < 0.001).

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