Background Rheumatoid arthritis (RA) and osteoarthritis (OA) are two major types of arthritic disease. Although the features of both diseases are similar at the end stage, which is characterised by severe cartilage destruction, the progression of joint destruction may have radiographic differences. To clarify precisely the differences in radiographic images, we have developed a novel computer program, KOACAD (knee OA computer aided diagnosis) system, which automatically and quantitatively measure radiographic parameters of knee joint, such as space area (JSA), the minimum joint space width (mJSW) at both medial and lateral sides, osteophyte area (OPA), and tibiofemoral angle (TFA) on the plain antero-posterior radiographs.
Objectives To quantitatively elucidate the radiographic features of knee joint RA and OA by using the KOACAD system.
Methods We enrolled 99 patients (49 with RA and 50 with OA) who underwent total knee arthroplasty. This study was approved by the institutional review board of The University of Tokyo. Data obtained from pre-operative radiographic examinations of both knees in the antero-posterior view with weight bearing were retrospectively analysed by using the KOACAD system. Patient characteristics and radiographic parameters were compared statistically between RA and OA groups. We investigated the association of knee radiographic features of RA by logistic regression analysis. Multivariable models were used to adjust for age, sex, BMI (body mass index) and radiographic parameters.
Results In the investigation and comparison of the demographic and background characteristics between the RA and OA patients, mean age and BMI were significantly lower in the RA patients than in the OA patients (mean age: 64±9.2 years vs 76±7.4 years, p<0.001; BMI: 24±4.2 kg/m2 vs 26±4.0 kg/m2, p<0.05). Regarding the morphological differences between RA and OA by using the KOACAD system, the lateral JSA, lateral mJSW, TFA, and OPA were significantly lower in the RA patients than in the OA patients (lateral JSA: 52±5 mm2 vs 130±70 mm2, p<0.0001; lateral mJSW: 1.8±2.0 mm vs 4.5±2.4 mm, p<0.0001; OPA: 5.0±8.0 mm2 vs 13±17 mm2, p<0.01; TFA: 177±12° vs 186±11°, p<0.001). The multivariate logistic regression model used in the examination of the correlation of morphological features of RA after adjusting for age, sex, and BMI revealed that the lateral mJSW was associated with the morphological feature (odds ratio, 1.4; 95% confidence interval, 1.1–1.9).
Conclusions The differences in the radiographic features of the knee joints between RA and OA were analysed quantitatively by using the KOACAD system. We found that the lateral knee joint space narrowing suggested to be joint destruction of RA rather than OA.
Disclosure of Interest None declared