Reliability of radiographic parameters in adults with hip dysplasia

To assess the reliability of radiographic measurements in adults previously treated for developmental dysplasia of the hip (DDH) and to clarify whether these parameters differ according to position of the patient (supine versus standing).

Fifty-one patients (41 females and 10 males) with 63 affected hips were included in the study. The mean follow-up period was 45 (44-49) years in the patients who had not undergone total hip replacement (THR). Anteroposterior radiographs of the pelvis were taken with the patient in the supine and in the standing position. Measurements used for residual hip dysplasia were center-edge (CE) angle and migration percentage (MP). The joint space width (JSW) was measured at three or four locations of the upper, weight-bearing part of the joint, and the shortest distance was termed the minimum joint space width (minJSW). One radiologist and one orthopaedic surgeon, each with more than 30 years of experience, independently measured the radiographic parameters.

The limits of agreement (LOA) of the CE angle (mean interobserver difference ± 2SD) were within the range -8 to 7°. The LOA of the MP were in the range -8 to 8% and of the minJSW -0.6 to 1.1 mm. The mean differences in CE angle between supine and standing radiographs (supine - standing) ranged from -1.1 to 0.0° and the mean differences in MP between supine and standing positions were below 1%. The mean positional differences in minJSW were below 0.1 mm and were not statistically significant.

The interobserver variations with regard to CE angle, MP, and minJSW were moderate, indicating that these are reliable measurements in clinical practice. Femoral head coverage and JSW did not significantly differ between supine and weight-bearing positions.