The impact of knee positioning on joint space width change: Data from the Osteoarthritis Initiative

Objective: Quantify the longitudinal effect of knee positioning on radiographic joint space width (JSW) in knee OA. Design: This longitudinal cohort study analyzed 1612 knees (806 participants) from the Osteoarthritis Initiative with baseline Kellgren-Lawrence grade = 0 and 12-month follow-up. Images obtained via a standardized fixed-flexion protocol measured minimum JSW (mJSW), fixed-location JSW (fJSW), and a variable related to knee positioning (X_rim). Generalized estimating equation (GEE) models, adjusted for age, gender, race, and BMI, examined associations between changes in ΔfJSW or ΔmJSW and ΔX_rim. A secondary case-control analysis of 69 participants KLG 1–3 over 4 years examined the effect of poor but consistent X_rim values on JSW responsiveness, using standardized response means (SRM). Results: GEE models showed a significant positive association between ΔXrim and both ΔfJSW (95% CI: 0.07–0.15) and ΔmJSW (95% CI: 0.05–0.13). The association between ΔX_rim and ΔfJSW was significantly stronger in females, with a significant ΔX_rim × gender interaction term (95% CI: 0.03–0.13), with no significant gender difference identified for the association between ΔXrim and ΔmJSW. With ΔfJSW as the outcome, estimated slope for ΔX_rim was 0.19 (95% CI, 0.15–0.22) in females and 0.11 (95% CI, 0.07–0.15) in males. No effect modification by age, race or BMI identified. Secondary analysis revealed fJSW responsiveness was unaffected by poor but consistent positioning (cases: -0.80, controls: −0.76), while mJSW was (cases: −0.81, controls: −0.58). Conclusion: Inconsistent knee positioning affects JSW measurement. Poor but consistent positioning has a minimal effect on fJSW responsiveness but a larger impact on mJSW.