Baseline 3D joint space width on weight-bearing CT in comparison with 2D JSWx on radiographs for predicting 24-month worsening of knee structure in the multicenter osteoarthritis study

This study evaluated the predictive validity of baseline 3D joint space width (3D-JSW) measured using weight-bearing computed tomography (WBCT) versus 2D-JSW on radiographs for predicting knee structural worsening over 24 months, assessed by radiographs and MRI. A prospective observational study using data from the Multicenter Osteoarthritis Study (MOST) included 425 knees. Baseline 3D-JSW was assessed using WBCT acquired in a standing fixed-flexion position, and 2D-JSW was assessed from standing fixed-flexion posteroanterior radiographs. Outcomes included 24-month changes in tibiofemoral Osteoarthritis Research Society International (OARSI) joint space narrowing (JSN) grade and MRI Osteoarthritis Knee Score Cartilage Morphology (MOAKS-CM). Predictive validity was evaluated using logistic regression and comparison of areas under ROC curves. The study population (N=302) had a mean age of 63.2 years (standard deviation 8.9) and BMI of 28.2 kg/m² (standard deviation 4.8), with radiographic OA observed in 45.9 %. For medial JSN worsening, 2D-JSW (AUC=0.711) showed significantly better predictive validity than the basic demographic model (AUC=0.626, p=0.032), while 3D-JSW (AUC=0.681) did not outperform 2D-JSW (p=0.184). For lateral JSN worsening, 3D-JSW (AUC=0.900) and 2D-JSW (AUC=0.893) were similar (p=0.814). For medial MOAKS-CM worsening, 3D-JSW (AUC=0.729) and 2D-JSW (AUC=0.742) were similar (p=0.579), as were 3D-JSW (AUC=0.699) and 2D-JSW (AUC=0.692) for lateral worsening (p=0.779). 3D-JSW did not show superior predictive validity over 2D-JSW in predicting knee structural worsening over 24 months in a cohort predominatly without radiographic knee OA. WBCT remains a promising imaging modality for osteoarthritis assessment. Further studies are needed to determine its role as a diagnostic tool.