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

Overview

• This study investigated how well traditional two-dimensional (2D) linear measurements of subchondral bone sclerosis in horse fetlock joints correlate with advanced three-dimensional (3D) volumetric measurements obtained via standing computed tomography (CT).
• The goal was to determine if simpler 2D measurements could serve as a practical substitute for more complex 3D analysis in assessing bone sclerosis in Thoroughbred racehorses.

Background

• Subchondral bone sclerosis refers to the abnormal hardening or increased bone density beneath joint cartilage.
• In Thoroughbred racehorses, sclerosis often occurs in the distal third palmar/plantar metacarpal/metatarsal condyles (lower part of the fetlock joint), commonly detectable by radiographs.
• Traditionally, assessment of sclerosis severity used two-dimensional (2D) linear measurements from radiographs or CT images.
• Recent imaging advances enable three-dimensional (3D) volumetric evaluation of sclerosis, which could offer more precise quantification.
• However, 3D volumetric analysis requires specialized software and expertise, which may limit its routine use.

Study Design and Methods

• Subjects: 62 Thoroughbred racehorses, covering 96 fetlock joints (59 forelimbs and 37 hindlimbs).
• Imaging: Standing fan-beam computed tomography (FBCT) scans were performed on the fetlock joints to obtain detailed images.
• 2D Measurements: Retrospective image analysis utilized Horos software to perform linear 2D measurements of sclerosis on CT images.
• 3D Measurements: Volume Graphics Studio Max software was used to generate computer-aided 3D volumetric quantifications of sclerosis from the same CT data.
• Statistical Analysis:
  • Pearson’s correlation coefficient (r) and coefficient of determination (R) were calculated to assess the strength and proportion of variance explained between 2D and 3D measurements.
  • Bland-Altman analysis evaluated the agreement and potential bias between the two measurement methods.
  • Linear mixed-effects models identified predictors influencing 3D sclerosis volume based on 2D metrics.
  • Inter- and intraobserver reliability of measurements was assessed using intraclass correlation coefficients (ICC) to check consistency across and within evaluators.

Key Findings

• There was a strong positive correlation between 2D estimated sclerosis volume and the 3D volumetric measurements (r = 0.79, R = 0.62), indicating that 2D measurements reasonably reflect actual 3D sclerosis volume.
• Specifically, dorsopalmar/plantar sclerosis measurements from 2D images correlated well with 3D volumetric sclerosis (r = 0.76, R = 0.58).
• Interobserver and intraobserver repeatability for the 2D measurements were excellent, with ICC values of 0.969 and 0.982 respectively, demonstrating high reliability of the 2D measurement technique.
• Bland-Altman analysis revealed that while 2D and 3D methods correlate, they are not directly interchangeable, especially at higher sclerosis volumes where differences become more pronounced.
• The 2D measurements may underestimate or overestimate actual sclerosis volume compared to the 3D standard when sclerosis is more extensive.

Conclusions and Implications

• 2D linear measurements provide a practical and reliable alternative for assessing subchondral bone sclerosis in situations where 3D volumetric software or expertise is unavailable.
• Despite strong correlation, 2D and 3D measurements should not be considered directly interchangeable; caution is advised particularly when evaluating larger volumes of sclerosis.
• This research supports the continued use of traditional 2D methods for routine clinical assessments but highlights the enhanced precision 3D volumetric techniques offer for detailed research or diagnostic purposes.
• The findings may help veterinarians and researchers choose appropriate imaging analysis methods based on resources, clinical needs, and the severity of bone changes.