Magnetic resonance imaging as the primary imaging modality in children presenting with acute non-traumatic hip pain.

The role of magnetic resonance imaging (MRI) in children presenting with acute non-traumatic hip pain was evaluated prospectively. Hip MRI was performed in addition to standard investigations (arthrosonography +/- hip radiographs) in 50 children presenting to the accident and emergency department of a paediatric hospital. MRI was performed on an open 0.23T system and comprised gradient echo T1 weighted coronal, fast spin echo T2 weighted coronal and inversion recovery spin echo (IRSE) axial sequences. Diagnostic quality MRI examinations were obtained in 94% of children. The IRSE sequence was the most reliable at determining underlying disorder (p<0.002). Interobserver agreement on the MRI examinations was very good with unweighted kappa value of 0.89, 95% confidence intervals 0.79, 0.99. Sensitivity of MRI was 0.79 (0.68, 0.90, specificity 1.00 (0.89, 1.00), accuracy 0.81 (0.70, 0.92), PPV 1.00 (0.89, 1), NPV 0.36 (0.25, 0.47). Sensitivity of standard imaging was 0.70 (0.54-0.86), specificity 0.57 (0.41, 0.73), accuracy 0.72 (0.56, 0.88), PPV 0.91 (0.75, 1.00), NPV 0.24 (0.08, 0.40). MRI correctly identified all seven children with serious underlying disorder whereas conventional imaging correctly diagnosed only two. Pelvic musculoskeletal infection was associated with the combination of marked alteration in signal in tissues adjacent to a symptomatic hip and an erythrocyte sedimentation rate of >20 mm 1st h (p<0.0001). In conclusion, MRI is a practical, well accepted and accurate non-invasive imaging technique in children presenting with acute non-traumatic hip pain. Combined with inflammatory markers MRI can be used to determine those children who require aggressive management. Where it is available, MRI is the imaging modality of choice in this condition.