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.