Reliability of radiological measurements in the assessment of hip dysplasia in adults

Radiographic measurements are commonly used to quantify the treatment results of hip dysplasia and assess further need of operative treatment. We investigated the interobserver and intraobserver reliability of the commonest radiographic techniques in the assessment of hip dysplasia in skeletally mature adults. Three observers independently analysed 100 hip radiographs of patients with hip dysplasia aged between 16 and 32 years. We measured centre-edge angle of Wiberg, acetabular angle of Sharp, acetabular index of the weightbearing zone, acetabular index, of depth to width, ACM-angle, MZ-distance, acetabular head index, lateral subluxation and neck-shaft angle. In addition, the radiographs were reviewed a second time 3 months apart by two of the observers to assess intraobserver reliability. We found a high correlation (intraclass correlation coefficient) for interobserver reliability (0.76-0.87) and intraobserver reliability (0.70-0.92) for all radiographic measurements except acetabular index of depth to width, ACM-angle and MZ-distance. Depending on the clinical question we therefore recommend the use of one of the reliable measurements to assess the radiograph of a dysplastic hip.