In vivo precision of a depth-specific topographic mapping technique in the CT analysis of osteoarthritic and normal proximal tibial subchondral bone density

Objective To test the in vivo precision of a depth-specific topographic mapping technique (CT-TOMASD, computed tomography topographic mapping of subchondral density) for the 3D assessment of subchondral cortical and trabecular bone density in normal and osteoarthritic (OA) human tibiae. Methods Fourteen participants were recruited (3 men:11 women; mean age: 49.9, SD: 11.9 years) and categorized as normal (n = 7) or OA (n = 7). Each participant was scanned using clinical quantitative CT (QCT) three times over 2 days. We assessed average subchondral bone mineral density (BMD) across three layers (0-2.5 mm, 2.5-5 mm and 5-10 mm) measured in relation to depth from the subchondral surface. Regional analyses included: medial plateau BMD; lateral plateau BMD; anterior/central/posterior compartment BMD; medial:lateral (M:L) BMD ratio; and average BMD of a 10-mm diameter "focal spot," which searched each medial and lateral plateau for the highest focal densities present within each plateau. Precision was assessed using root mean square coefficients of variation (CV%(RMS)) and intraclass correlation coefficients (ICC). Results Average CV%(RMS) precision errors for BMD measures were 2.3%, reaching a maximum CV%(RMS) of 3.9%. ICC showed high repeatability above 0.98. Conclusions CT-TOMASD offered precise 3D measures of subchondral BMD. This method has the potential to identify and quantify changes in subchondral BMD associated with OA in vivo.