Seeing the Whole Picture: MRI and CT Together Improve Diagnosis of Equine Fetlock Pain

Combined standing low‐field magnetic resonance imaging and fan‐beam computed tomographic diagnosis of fetlock region pain in 27 sports horses

Annamaria Nagy, Sue J. Dyson

Background
There is limited information on the comparative diagnostic value of low-field magnetic resonance imaging (MRI) and fan-beam computed tomography (CT) for equine fetlock lameness, especially in live horses. Previous studies have mainly addressed imaging in cadaver limbs or with other CT modalities. This study aimed to evaluate the added diagnostic value of combining low-field MRI and fan-beam CT in sports horses with fetlock region pain and to assess the findings in both lame and nonlame limbs.

Methods
A retrospective descriptive study was conducted using clinical records of 27 sports horses (52 limbs) with fetlock region pain who underwent standing low-field MRI and fan-beam CT between 2021 and 2024. Diagnostic nerve blocks confirmed fetlock-related lameness. MRI included T1W, T2*W, STIR, and FSE sequences, and CT protocols used a 16-detector helical scanner. Imaging assessments were made subjectively by consensus, and lesions were classified by location, signal/attenuation pattern, and clinical relevance.

Results
In 16 lame limbs, the primary lesion was in the proximal phalanx, especially the sagittal groove, showing extensive STIR hyperintensity with corresponding but more localized hypoattenuation on CT. In five limbs, metacarpal condyle lesions (including incomplete fractures and resorption) were best detected via CT; some were missed on MRI. In nine limbs, lesions in multiple areas contributed to pain. In one case, a proximal sesamoid bone and palmar ligament lesion was primary. CT proved more sensitive to subchondral bone resorption, while MRI was superior for detecting bone oedema and soft tissue abnormalities. Contralateral limbs often showed milder, subclinical versions of lesions. Contrast arthrography identified cartilage defects in 7 of 13 limbs imaged with contrast.

Limitations
The study involved a small sample size with variable lesion types, and imaging of contralateral limbs was inconsistent. Lack of long-term follow-up and histopathological validation limited assessments of lesion chronicity, progression, and clinical impact. Arthrography was not universally performed, and advanced MRI techniques may have further improved sensitivity.

Conclusions
The combination of low-field MRI and fan-beam CT provided complementary diagnostic information, often revealing clinically significant lesions that would be missed using a single modality. Fan-beam CT was particularly valuable for detecting subchondral bone resorption, while MRI added critical insight into bone oedema and soft tissue integrity. The findings support integrated imaging for accurate diagnosis and prognosis of fetlock region pain in equine athletes. Further research is warranted to inform optimal imaging strategies and understand lesion evolution.

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