Development of a logically devised line drawing atlas for grading of knee osteoarthritis

Objectives-To (a) develop an atlas of line drawings for the assessment and grading of narrowing and osteophyte (that is, changes of osteoarthritis) on knee radiographs, and (b) compare the performance of this atlas with that of the standard Osteoarthritis Research Society (OARS) photographic atlas o f radiographs. Methods-Normal joint space widths (grade 0) for the medial and lateral tibi ofemoral and medial and lateral patellofemoral compartments were obtained f rom a previous community study. Grades 1-3 narrowing in each compartment wa s calculated separately for men and women, grade 3 being bone on bone, grad es 1 and 2 being two thirds and one third the value of grade 0. Maximum ost eophyte size (grade 3) for each of eight sites was determined from 715 bila teral knee x ray films obtained in a knee osteoarthritis (OA) hospital clin ic; grades 1-2 were calculated as two thirds and one third reductions in th e area of grade 3. Drawings for narrowing and osteophyte were presented sep arately. 50 sets of bilateral knee x ray radiographs (standing, extended an teroposterior; flexed skyline) showing a spectrum of OA grades were scored by three observers, twice using the OARS atlas and twice using the drawn at las. Results-Intraobserver and interobserver reproducibility was similar and gen erally good with both atlases, though varied according to site. All three o bservers preferred the line drawing atlas for ease and convenience of use. Higher scores for patellofemoral narrowing and lower scores for osteophyte, especially medial femoral osteophyte, were seen using the line drawing atl as, showing that the two atlases are not equivalent instruments. Conclusion-A logically derived line drawing atlas for grading of narrowing and osteophyte at the knee has been produced. The atlas showed comparable r eproducibility with the OARS atlas, but was discordant in several aspects o f grading. Such a system has several theoretical and practical advantages a nd should be considered for use in knee OA studies.