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 radi ographic hip joint space width (JSW). Design: Seventy hips were examined from 36 patients of the ECHODIAH study h aving 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 join t 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 measur ement was assessed by the intraclass coefficient of correlation. Sensitivit y to change was evaluated by the standardized response mean. Results: The intraobserver intraclass coefficient of correlation of MIDc an d 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 .2 mm, respectively. MIDge was significantly larger than MIDc (mean differe nce: 0.21 +/-0.62 mm, P <0.001), in both normal and osteoarthritic hips. Ho wever, the difference between MIDge and MIDc Varied largely when considerin g topography of femoral head migration. Whatever the method was, a signific ant (P <0.001) mean decrease of nearly 0.5 mm was found in osteoarthritic h ips over the 3 year follow-up. The standardized response mean for MJSWL, MJ SWroi, MIDge and MIDc was 0.73, 0.75, 0.79 and 0.85, respectively. Superior ity of MIDc, in term of sensitivity to change, was mainly seen in osteoarth ritic hips showing a superomedial or a concentric migration of the femoral head. Conclusion: Minimum interbone distance measured with a computer assisted me thod is suggested as the most suitable method for the evaluation of hip ost eoarthritis (OA) progression. (C) 2001 OsteoArthritis Research Society Inte rnational.