Follow-Up Magnetic Resonance Imaging of Sagittal Groove Disease of the Equine Proximal Phalanx Using a Classification System in 29 Non-Racing Sports Horses

Simple Summary Sagittal groove disease (SGD) of the equine proximal phalanx is considered to be a chronic bone stress injury and reported to have variable evolution. The aim of this study was to describe SGD on sequential low-field magnetic resonance imaging (MRI) examinations using a classification system. The 29 horses included were predominantly warmbloods used for show jumping and had repeat MRI examinations ranging from 1 month to 3.2 years from initial examination. During the initial rehabilitation period, evolution of SGD MRI classification varied among horses. Importantly, two limbs with a subchondral microfissure and one with subchondral demineralisation progressed to incomplete macrofissure/fracture, indicating that these classifications should be considered a potential prodromal sign of macrofissure formation and horses with these findings should be carefully managed to minimise the risk of catastrophic fracture propagation. In this study, successful return to full training and competition was achieved in 86% of horses with SGD; however, 20% of horses re-presented for MRI with recurrent lameness after varying time periods. Further research is needed into patterns of progression of SGD on a larger scale with the objectives of improving risk assessments, prognostication and treatment plans.Abstract Evolution of magnetic resonance imaging (MRI) findings in horses with sagittal groove disease (SGD) of the proximal phalanx is relatively sparsely described. This retrospective, descriptive, longitudinal study describes the findings of sequential low-field MRI fetlock examinations in horses with SGD of the proximal phalanx using a classification system. Twenty-nine horses were included, predominantly warmbloods used for show jumping (79%). For 29 limbs re-examined during the initial rehabilitation period, classification remained constant (n = 18), increased (n = 2), decreased (n = 7), and fluctuated (n = 2). Notably, two limbs with initial classification 4b (bone oedema-like signal with subchondral microfissure) and one with 4c (bone oedema-like signal with subchondral demineralisation) progressed to classification 5 (incomplete macrofissure/fracture), highlighting their potential as prodromal or imminent fissure pathology. Following conservative (n = 28) and surgical (n = 1) treatment, 86% of the horses re-entered full training and competition with a mean +/- sd recovery time of 9.4 +/- 4.4 months. In total, 20% of horses in the study subsequently presented for repeat MRI due to recurrent lameness after resuming full work, with classification that was the same (n = 2), increased (n = 2), or decreased (n = 2) compared with the last scan. This study underscores the variability in progression of SGD MRI findings, emphasising the need for further larger-scale research into patterns of progression.