Combined standing low-field magnetic resonance imaging and fan-beam computed tomographic diagnosis of fetlock region pain in 27 sports horses.
Authors: Nagy Annamaria, Dyson Sue J
Journal: Equine veterinary journal
Summary
# Editorial Summary When evaluating fetlock lameness in sports horses, neither magnetic resonance imaging nor computed tomography alone tells the complete story. Nagy and Dyson's 2025 retrospective analysis of 52 limbs (31 lame, 21 non-lame) from 27 horses demonstrates that low-field MRI and fan-beam CT provide complementary diagnostic information, with each modality detecting significant pathology missed by the other. MRI proved superior for characterising bone marrow oedema in the proximal phalanx—particularly in the sagittal groove and medial fovea, where hyperintense STIR signals extended beyond CT-visible changes in 16 lame limbs—whilst CT was essential for identifying metacarpal condyle fractures and resorptive lesions that were radiographically occult on MRI in five limbs, including an incomplete fracture and four resorptive lesions. The practical implication for practitioners is clear: combined imaging protocols should be considered the gold standard when initial diagnostic imaging fails to correlate with clinical findings, especially given that resorptive subchondral bone lesions can be present without MRI signal abnormalities, and that multi-location pathology contributing to fetlock pain may only become apparent through dual-modality assessment.
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Practical Takeaways
- •Use both MRI and CT imaging together when investigating fetlock lameness in sports horses, as each modality reveals different pathology—MRI excels at soft tissue and bone marrow edema, while CT is superior for detecting cortical bone resorption and fractures.
- •Do not rely on MRI alone for fetlock diagnosis; resorptive lesions of the metacarpal condyles and some proximal phalanx abnormalities may be missed, potentially leading to incomplete treatment planning.
- •Expect MRI STIR signal abnormalities to be more extensive than CT findings in proximal phalanx lesions; this does not indicate imaging error but reflects different tissue sensitivity.
Key Findings
- •In 16 lame limbs, subchondral/trabecular bone lesions of the proximal phalanx showed hyperintense STIR signal on MRI that was more extensive than CT abnormalities, with CT providing useful complementary information in all cases.
- •In 5 lame limbs with metacarpal condyle lesions (1 incomplete fracture, 4 resorptive lesions), 3 lesions were not detected on MRI but were identified on CT.
- •Fan-beam CT and low-field MRI provided complementary diagnostic information that could not have been achieved using either modality alone in some horses.
- •Resorptive subchondral bone lesions in the fetlock may be present without associated low-field MRI abnormalities.