Computed tomography topographic mapping of subchondral density (CT-TOMASD) in osteoarthritic and normal knees: methodological development and preliminary findings.

Objectives: To develop a precise imaging tool which measures three-dimensional (3D) subchondral bone mineral density (BMD), and investigate its ability to distinguish subchondral bone properties in osteoarthritic and normal cadaveric tibiae.

Methods: We developed a novel imaging tool [Computed tomography topographic mapping of subchondral density (CT-TOMASD)], which employs a surface projection image processing technique to map 3D subchondral BMD measured in relation to depth from the joint surface. Sixteen intact cadaver knees from 10 donors (8M:2F; age: 77.8+/-7.4) were scanned using quantitative computed tomography (QCT). Projections of average BMD to normalized depths of 2.5mm and 5.0mm were acquired, with regional analyses including: (1) medial and lateral BMD, (2) anterior/central/posterior compartmental BMD, (3) max BMD contained within a 10mm diameter 'core', and (4) medial:lateral BMD ratio. Precision was assessed using coefficients of variation (CV%). Osteoarthritis (OA) severity was assessed by examination of computed tomography (CT) and fluoroscopic radiographic images, and categorized using modified Kellgren-Lawrence (mKL) scoring.

Results: Precision errors for CT-TOMASD BMD measures were focused around 1.5%, reaching a maximum CV% of 3.5%. OA was identified in eight compartments of six knees. Substantial qualitative and quantitative differences were observed between the OA and normal knees, with the medial:lateral BMD ratio and peak core regional analyses demonstrating differences greater than 4.7 standard deviations (SDs) when compared with normals. Preliminary results revealed effect sizes ranging from 1.6 to 4.3 between OA and normal knees.

Conclusions: CT-TOMASD offers precise 3D measures of subchondral BMD. Preliminary results demonstrate large qualitative and quantitative differences and large effect sizes between OA and normal knees. This method has the potential to identify and quantify changes in subchondral BMD associated with OA disease progression.