Usefulness of Dynamic Contrast-Enhanced MRI in Differentiating Between Septic Arthritis and Transient Synovitis in the Hip Joint

The purpose of this study was to show the usefulness of dynamic contrast-enhanced MRI (DCE-MRI) and to determine the optimal time window in MRI for differentiating between septic arthritis and transient synovitis in painful hip joints.Eighteen patients who underwent DCE-MRI were enrolled, and the final diagnoses were septic arthritis (n = 7) and transient synovitis (n = 11). The enhancement patterns of DCE-MRI were dichotomized according to the shape of the time-signal intensity curves. The time at the maximal difference in the signal intensity between two time-signal intensity curves of both femoral heads was recorded. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were calculated. Receiver operating characteristic curves were calculated.Six of seven patients with septic arthritis in the hip joint had decreased enhancement during the early phase of DCE-MRI. The enhancement difference between the two patient groups was statistically significant (p = 0.0498). The time at the maximal difference in the signal intensity between two time-signal intensity curves of both femoral heads was approximately 3.5 minutes. The area under the receiver operating characteristic curve for predicting septic arthritis was 0.792.DCE-MRI is useful in differentiating between septic hip arthritis and transient synovitis. If static contrast-enhanced coronal MRI is used, the optimal time for the acquisition of contrast-enhanced coronal MRI is approximately 3.5 minutes.