Assessment of primary hip osteoarthritis: comparison of radiographic methods using colon radiographs comparison of radiographic methods using colon radiographs

Objective—To compare the reliability of quantitative measurement of minimum hip joint space with a qualitative global assessment of radiological features for estimating the prevalence of primary osteoarthritis (OA) of the hip in colon radiographs. Methods—All colon radiographs from patients aged 35 or older, taken at three diVerent radiographic departments in Iceland during the years 1990–96, were examined. A total of 3002 hips in 638 men and 863 women were analysed. Intraobserver and interobserver reliability was assessed by measuring 147 randomly selected radiographs (294 hips) twice by the same observer, and 87 and 98 randomly selected radiographs (174 and 196 hips) by two additional independent observers. Minimum hip joint space was measured with a millimetre ruler, and global assessment of radiological features by a published atlas. Results—With a minimum joint space of 2.5 mm or less as definition for OA, 212 hips were defined as having OA. When the global Kellgren and Lawrence assessment with grade 2 (definite narrowing in the presence of definite osteophytes) or higher as definition for OA was used, 202 hips showed OA. However, only 166 hips were diagnosed as OA with both systems. With 2.0 or 3.0 mm minimum joint space as cut oV point, the diVerence between the two methods increased. Both intrarater and interrater reliability was significantly higher with joint space measurement than with global assessment. Conclusions—Overall prevalence of radiological OA was similar with the two methods. However, the quantitative measurement of minimum hip joint space had a better within-observer and betweenobserver reliability than qualitative global assessment of radiographic features of hip OA. It is thus suggested that minimum joint space measurement is a preferable method in epidemiological studies of radiological hip OA. (Ann Rheum Dis 2000;59:650–653) Most population studies of osteoarthritis (OA) prevalence have used the radiographic classification developed by Kellgren and Lawrence. The system is based on qualitative assessment and grading of joint space narrowing and osteophytes, generating a composite global score. This scoring system has, however, shown a low interrater reliability. Further, the emphasis on osteophytes as the initial defining feature of hip OA has been questioned. Other investigators have used assessment of individual radiological joint features—that is, minimum joint space, to define OA. 5–7 We have previously estimated the prevalence of primary OA of the hip in Iceland, using colon radiographs and a cut oV point of 2.5 mm or less of minimum hip joint space as the definition of hip OA. The purpose of the present investigation was to compare the Kellgren and Lawrence system and the minimum joint space classification systems for the assessment of primary hip OA. Material and methods