MicroCT characterization of subchondral bone lesions in 5 isolated equine proximal phalanges

Subchondral bone (SCB) lesions in the proximal phalanx (P1) are a common cause of lameness in horses. This study aims to assess the micro-computed tomography (µCT) appearance of the SCB in isolated P1 specimen with Magnetic Resonance Imaging (MRI) changes.
Five P1 proximal epiphyses, with MRI evidence of SCB thickening and/or resorption, were scanned using µCT. µCT changes and objective trabecular bone analysis parameters were assessed in the glenoid and sagittal groove, including degree of anisotropy, trabecular thickness and spacing, and bone volume fraction (BV/TV). These findings were compared between different anatomical locations (medial glenoid, lateral glenoid, sagittal groove), and between areas with and without MRI changes.
µCT revealed loss of SCB plate integrity, coalescing microcracks, collapse of the chondro-osseous interface and articular cartilage defects in areas of resorption identified on MRI. Areas of µCT hypoattenuation were also observed in regions where MRI showed only SCB thickening. Mean values for the degree of anisotropy, trabecular thickness and BV/TV were highest in the medial glenoid and lowest in the sagittal groove. Trabecular spacing was greatest in the sagittal groove. The degree of anisotropy was significantly higher adjacent to SCB abnormalities (p<0.05) compared to normal SCB plate.
Early signs of resorption were detected on µCT in SCB plates with only thickening at MRI, and the highest degree of anisotropy was found medially and adjacent to SCB changes. These results suggest that SCB lesions could develop secondary to repetitive biomechanical stimulation in horses, supporting the hypothesis of overload arthropathy.