Comparison of Ultrasound and Magnetic Resonance Imaging for Identifying Soft Tissue Abnormalities in the Palmar Aspect of the Equine Digit.
Authors: Barrett Myra F, Goorchenko Georgette E, Frisbie David D
Journal: Animals : an open access journal from MDPI
Summary
Soft tissue injuries within the equine digit represent a significant cause of lameness, yet diagnostic imaging choice often hinges on cost and availability rather than diagnostic capability. Barrett and colleagues compared ultrasound's diagnostic accuracy against MRI for identifying common digit pathology—specifically deep digital flexor tendon (DDFT) tearing, collateral sesamoidean ligament (CSL) enlargement, and navicular bursa changes—in 70 examinations across 45 horses, with blinded ultrasound operators and subsequent MRI confirmation. Ultrasound demonstrated good sensitivity (85%) and reasonable accuracy (70%) for detecting dorsal DDFT tears proximal to the navicular bone, but performed considerably less well for navicular bursa effusion (67% accuracy), bursal proliferation (61%), and CSL enlargement (61%), with modest specificity of only 60%. Critically, MRI identified DDFT tearing distal to the navicular bone in 27 limbs, yet ultrasound prospectively detected proximal damage in only 20 of these cases, indicating that concurrent injuries in the distal hoof capsule were frequently missed on ultrasound alone. Whilst ultrasound remains a valuable first-line screening tool for proximal DDFT pathology in cost-conscious practice, practitioners should recognise its substantial limitations for diagnosing bursal and ligamentous changes, and should advocate for MRI when clinical signs persist despite normal ultrasound findings or when distal hoof pathology is suspected.
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Practical Takeaways
- •Ultrasound remains a valuable first-line screening tool for proximal DDFT injuries but should not be considered definitive; normal ultrasound does not exclude significant pathology
- •MRI is necessary to fully characterize digit pathology when lameness persists or ultrasound findings are ambiguous, particularly for navicular region and distal soft tissue structures
- •When planning treatment, assume that distal DDFT tearing and concurrent hoof capsule pathology may be present even if ultrasound appears negative—consider MRI before committing to conservative management alone
Key Findings
- •Ultrasound achieved 85% sensitivity and 70% accuracy for dorsal DDFT tearing proximal to the navicular bone
- •Ultrasound accuracy was substantially lower for navicular bursa effusion (67%), proliferation (61%), and CSL enlargement (61%)
- •Of 27 limbs with MRI-identified distal DDFT tearing, only 20 had concurrent proximal dorsal damage detected by ultrasound
- •Concurrent distal DDFT and osseous/soft tissue pathology in the hoof capsule is unlikely to be identified without MRI