Measurement of the radiological hip joint space width. An evaluation of various methods of measurement

Objective To determine the most relevant method of measurement of the radiographic hip joint space width (JSW). Design Seventy hips were examined from 36 patients of the ECHODIAH study having had one to four X-rays of the pelvis during the 3-year course of the study. Minimum interbone distance (MIDc), mean width of both the whole joint space (MJSWL) and a region of interest of the joint space (MJSWroi) were measured using computerized analysis of digitized radiographs. MID was also measured using a graduated eyepiece (MIDge). Reproducibility of the measurement was assessed by the intraclass coefficient of correlation. Sensitivity to change was evaluated by the standardized response mean. Results The intraobserver intraclass coefficient of correlation of MIDc and MJSWroi was 0.98 and 0.94, respectively. The mean value°S.D. of MJSWL, MJSWroi, MIDc and MIDge was 3.3°0.9, 2.6°0.9, 2.4°0.9 and 2.6°1.2mm, respectively. MIDge was significantly larger than MIDc (mean difference: 0.21°0.62mm, P 0.001), in both normal and osteoarthritic hips. However, the difference between MIDge and MIDc varied largely when considering topography of femoral head migration. Whatever the method was, a significant ( P 0.001) mean decrease of nearly 0.5mm was found in osteoarthritic hips over the 3 year follow-up. The standardized response mean for MJSWL, MJSWroi, MIDge and MIDc was 0.73, 0.75, 0.79 and 0.85, respectively. Superiority of MIDc, in term of sensitivity to change, was mainly seen in osteoarthritic hips showing a superomedial or a concentric migration of the femoral head. Conclusion Minimum interbone distance measured with a computer assisted method is suggested as the most suitable method for the evaluation of hip osteoarthritis (OA) progression.