Low-field magnetic resonance imaging of sagittal groove disease of the proximal phalanx in non-racing sport horses.
Authors: Faulkner Josephine E, Joostens Zoë, Broeckx Bart J G, Hauspie Stijn, Mariën Tom, Vanderperren Katrien
Journal: Equine veterinary journal
Summary
# Sagittal Groove Disease in Sport Horses: MRI Findings Challenge Clinical Assessment Sagittal groove disease (SGD) of the proximal phalanx represents a significant concern in sport horses, particularly eventers and showjumpers, where chronic bone stress overload drives the pathological process; this study examined low-field MRI scans from 132 limbs across 111 horses to characterise the full spectrum of SGD abnormalities and develop a classification system reflecting progressive injury severity. Using a novel six-point grading scheme, researchers found that most horses (72 limbs) presented with classification 4 (bone oedema-like signal within subchondral and trabecular bone, with or without microfissures or demineralisation), whilst 23 limbs showed incomplete fractures; notably, hindlimbs demonstrated distinctly different lesion patterns, with demineralisation and macrofissures occurring almost exclusively in the plantar third of the P1 sagittal groove. A striking finding challenged conventional clinical thinking: there was no significant difference in either SGD classification or extent of bone oedema between lame and non-lame limbs, suggesting that MRI appearance does not reliably predict clinical presentation. Additionally, periosteal new bone formation and oedema-like signal were identified at the dorsoproximal P1 in 25–39% of cases, representing a previously undescribed feature that further supports the bone stress injury model. For practitioners, these results underscore that clinical lameness is an unreliable indicator of SGD severity or prognosis, whilst the expanded understanding of pathological patterns—particularly the previously unrecognised periosteal involvement—may refine both diagnostic interpretation and expectations for return to work following injury.
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Practical Takeaways
- •Absence of lameness does not exclude significant sagittal groove disease; low-field MRI is essential for accurate diagnosis in sport horses with suspect P1 pathology regardless of clinical signs.
- •The novel periosteal findings support SGD as a bone stress injury rather than simple degenerative change, suggesting training load management and careful rehabilitation protocols are critical for affected athletes.
- •Classification of SGD severity on MRI should inform prognosis and return-to-work timelines more reliably than lameness assessment alone, particularly in valuable competition horses.
Key Findings
- •A novel 6-point MRI classification system identified SGD severity ranging from small subchondral defects (class 1) to complete fractures, with class 4 (bone oedema-like signal) being most common (n=72/132 limbs).
- •Lameness was not a reliable indicator of SGD severity; no significant difference in classification or bone oedema extent between lame (n=116) and non-lame limbs (p>0.05).
- •Periosteal oedema-like signal and new bone were identified in 39% and 25% of limbs respectively at the dorsoproximal P1, a finding not previously described in SGD MRI studies.
- •Plantar third hindlimb involvement (demineralisation and incomplete fractures) was more common in hindlimbs compared to forelimbs, suggesting anatomical variation in stress pathways.