Correlation of 2D Linear and 3D Volumetric Measurement Techniques for Subchondral Bone Sclerosis in the Equine Distal Limb Using Standing Computed Tomography.

Subchondral bone sclerosis of the distal third palmar/plantar metacarpal/metatarsal condyles is a common radiographic finding in Thoroughbred racehorses. Traditionally, assessment has relied on two-dimensional (2D) linear measurements; however, advances in imaging software now allow three-dimensional (3D) volumetric quantification of subchondral bone. This study aimed to assess the relationship and agreement between computed tomography (CT)-derived 2D linear and volumetric measurements of condylar sclerosis and computer-generated 3D volumetric measurements and determine whether 2D measurements could provide a practical alternative to 3D analysis. A total of 62 Thoroughbred racehorses (96 fetlock joints; 59 forelimbs, and 37 hindlimbs) underwent standing fan-beam CT (FBCT). Retrospective image analysis was performed using Horos for 2D measurements and Volume Graphics Studio Max for 3D volumetric quantification. Associations between 2D and 3D measurements were assessed using Pearson's correlation (r) and coefficients of determination (R2). Agreement was evaluated using Bland-Altman analysis, whereas linear mixed-effects models identified predictors of 3D sclerosis volume. Inter- and intraobserver agreements were assessed using intraclass correlation coefficients (ICC). Estimated sclerosis volume derived from 2D measurements showed a strong positive correlation with 3D sclerosis volume (r = 0.79, R2 = 0.62, 95% CI for r = 0.73-0.85). Dorsopalmar/Plantar sclerosis was strongly correlated with condylar 3D sclerosis volume (r = 0.76, R2 = 0.58, 95% CI for r = 0.69-0.81). Interobserver (ICC = 0.969) and intraobserver (ICC = 0.982) agreement was excellent. Although 2D measurements may provide a practical alternative when 3D software is unavailable, the methods are not directly interchangeable, particularly with greater sclerosis volume.