Deep Learning-Based Comparison of Knee Minimum Joint Space Width in Patients With Rheumatoid Arthritis and...

Although both osteoarthritis (OA) and rheumatoid arthritis (RA) can necessitate total knee arthroplasty (TKA), their mechanisms and radiographic patterns of joint space narrowing (JSN) differ. Deep learning (DL) enables compartment-specific measurement of minimum joint space width (mJSW). This study compared JSN patterns between patients with RA and OA undergoing TKA and evaluated the associations between mJSW and RA disease activity.

In this retrospective study, 409 patients with RA undergoing TKA (2000-2021) were age- and sex-matched with OA patients. A validated DL model quantified medial and lateral mJSW from anteroposterior knee radiographs at 2 timepoints: early (> 2 years before TKA) and late (≤ 2 years before TKA). The rate of JSN was calculated in 302 patients with paired radiographs. Mixed-effects models adjusted for BMI and alignment. RA disease activity, serology, and medications were recorded.

RA demonstrated narrower lateral mJSW than OA at the late timepoint (5.6 vs 7.0 mm; P < 0.001), with comparable medial values. RA exhibited uniform bicompartmental JSN, whereas OA showed medial narrowing. RA had a faster mean lateral ΔmJSW (0.11 mm/year; P = 0.01), whereas OA had a faster mean medial ΔmJSW (0.21 mm/year; P < 0.001). Longer RA duration and higher inflammatory markers were negatively associated with lateral mJSW. Seronegative patients showed faster lateral ΔmJSW in the surgical knee than seropositive patients (0.12 vs 0.06 mm/year; P = 0.03).

Patients with RA demonstrated diffuse, symmetric cartilage loss that contrasted with medial-predominant narrowing in patients with OA. Automated DL-based measurement enables scalable, compartment-specific assessment of joint degeneration patterns.