ASSESSMENT OF JOINT SPACE WIDTH IN PATIENTS WITH OSTEOARTHRITIS OF THE KNEE - A COMPARISON OF 4 MEASURING-INSTRUMENTS

Objective. To evaluate the intra and interobserver reproducibility of 4 measuring instruments for assessing joint space width in knee osteoa rthritis (OA) and to estimate the effects of patient, instrument, sess ion order, and reader variation. Methods. We studied 30 patients with unilateral tibiofemoral OA selected to represent a broad range of radi ographic changes. Joint space width (JSW) was measured on plain antero posterior weight bearing radiographs. Using an experimental design, 3 readers assessed JSW 3 times with 4 measuring instruments (ruler, cali per, graduated magnifying glass, digitized assessment). Results. Intra and interobserver reproducibility was high with all measuring instrum ents (intraclass correlation coefficients from 0.95 to 0.98 and from 0 .91 to 0.97, respectively). Analysis of variance (ANOVA) showed a pati ent effect (p < 10(-6)), a reader effect (p = 0.0001), an instrument e ffect (p = 0.0001), and a session order effect (p = 0.04). The varianc e component estimates were patients 55%, readers 34%, session order 2% , instruments 8%. ANOVA performed separately for each instrument showe d that session order differences always represented less than 1% of th e total variance. The reader component accounted for 0% of the total v ariance for the ruler, 2% for the digitized method, 16% for the calipe r, and 18% for the graduated magnifying glass. Conclusion. Ruler and d igitized assessment have better reliability than caliper and graduated magnifying glass.