Arthrosonography of the irritable hip in childhood: a review of 1 year's experience.

A retrospective study of 87 children presenting acutely with an "irritable hip" was undertaken to assess the role of arthrosonography of the hip joint. Arthrosonography detected 52 hip-joint effusions, of which 16 were aspirated and an effusion confirmed in 14 (88%). In 82 cases plain radiography was compared with arthrosonography for the detection of hip-joint effusions. Of 47 children with a positive ultrasound diagnosis, 28 (59%) showed abnormal findings on plain radiographs and, of 35 cases with negative ultrasound findings, 22 (63%) had a negative diagnosis by plain radiography. Patients with more severe clinical signs were more likely to have an ultrasonic diagnosis of an effusion (87%-100%) than those with mild clinical signs (25%). The ultrasonic measurement of the hip-joint capsule to femoral neck distance was 2.2 mm +/- 0.5 mm (mean +/- 1 SD) in normal hips and 6.3 mm +/- 1.5 mm in the joints with effusions. Our study suggests that arthrosonographically the normal capsular space is less than 3 mm and the difference between the two sides less than 2 mm. It is suggested that hip arthrosonography is a more accurate method for detecting hip-joint effusions than plain radiography; it may help select cases for hospital admission and should be performed before aspiration is attempted.