THE INFLUENCE OF WEIGHT-BEARING AND FLEXION ON 3D JOINT SPACE WIDTH IN KNEE OSTEOARTHRITIS

In knee OA, radiographic JSW is used as a surrogate for MRI-measured cartilage thickness, though they often do not correlate well. Variations in positioning between radiography (weight-bearing semi-flexion) and MRI (non-weight-bearing extension) may contribute to discrepancies. This study aimed to evaluate differences in 3D JSW and cartilage thickness distribution between these positions in knee OA patients. 21 symptomatic knee OA patients (KLG 2/3) were included. Exclusion criteria included prior knee surgery, MRI ineligibility, inability to stand unassisted for 15 minutes, or knee width > 15 cm (knee coil limit). A knee MRI protocol was performed using a 0.25T weight-bearing MRI system (G-scan Brio, Esaote). A coronal 3D dual-echo SSFP sequence (SHARC) was acquired to obtain images with an isotropic resolution of 0.66mm in both extended and flexed knee positions under weight-bearing conditions by rotating the system to 81°. Both scans were repeated under non-weight-bearing conditions by rotating the system to a horizontal position (0°). Knee flexion angles were measured, and the femur and tibia bones were segmented in 3D Slicer. 3D models were exported to Stradview to measure the tibia-femur distance at each vertex as a measure of JSW. The models and data were registered to canonical surfaces in wxRegSurf and further analyzed in MATLAB using the Surfstat package for statistical parametric mapping to derive p-values corrected for multiple vertex-wise comparisons. The average knee angles of the 21 patients were 7.4±3.7° (extended) and 19.1±5.5° (flexed). The average JSW ranged from 3.1 mm to 14.7 mm across patients (Figure 1). A significantly smaller JSW for weight-bearing vs non-weight-bearing conditions, particularly in the outer medial and posterior lateral tibia for extended positions, and in the posterior medial tibia for flexed positions, was seen (Figure 2). Flexion increased the JSW in the anterior tibia and decreased it in the posterior tibia, particularly laterally in weight-bearing positions. JSW distribution in knee OA patients varies significantly depending on both weight-bearing and knee flexion angle, and radiographic JSW measurements may not accurately reflect the joint space in non-weight-bearing positions, such as those used in MRI, especially in the lateral compartment. Currently ongoing cartilage analyses will indicate to which extent these JSW variations are attributable to changes in cartilage thickness or meniscal positioning.