Ultrasound assessment of an increased capsular width as a predictor of temporomandibular joint effusion

The aim of this study was to evaluate whether an increased capsular
width evidenced by ultrasound (US) could be an indirect marker of
temporomandibular joint (TMJ) effusion. METHODS: 138 TMJs were evaluated by US
and magnetic resonance imaging (MRI) by two blinded calibrated investigators. US
measures of capsular width (in mm) and MRI diagnosis of TMJ effusion
(presence/absence) were used to perform a receiver operating characteristic (ROC)
curve analysis in order to assess the most accurate cut-off value of capsular
width that was able to discriminate between joints with and without MRI effusion.
RESULTS: Diagnostic accuracy of US to detect MRI-depicted TMJ effusion was good
(area under the ROC curve=0.817). US sensitivity was high for values below the
cut-off value of 1.950 mm (true positive rate (TPR)=83.9%; false positive rate
(FPR)=26.3%), while specificity was high for values above the cut-off value of
2.150 mm (TPR=71.0%; FPR=11.8%). CONCLUSIONS: Analysis of ROC curve appears to
reveal that the critical area is around the 2 mm value for TMJ capsular width.
These findings need to be refined by further studies assessing the smallest
detectable difference in capsular width, with attention to reliability of
interobserver observations.