Equine Diagnostic Imaging: Anatomy, Modalities, and Lameness
Core concepts
Equine imaging emphasizes anatomy-driven interpretation and modality selection. Know the radiographic anatomy of the distal limb (P1, P2, P3, navicular bone, distal sesamoidean ligaments) and standard views: lateral, dorsopalmar/dorsoplantar, and oblique projections. Understand the navicular bone skyline and flexor surface evaluation for navicular syndrome.
Modalities
- Radiography: first line for distal limb and joint disease; know osteophyte, enthesophyte, subchondral bone changes.
- Ultrasound: tendons and ligaments (superficial/deep digital flexor, suspensory ligament); anisotropy and technique.
- Nuclear scintigraphy: sensitive for early bone turnover; poor specificity.
- CT/MRI: advanced cross-sectional detail; MRI excels for soft tissue and bone marrow.
Traps
- Confusing summation artifacts with true lesions in the equine tarsus/carpus.
- Misinterpreting growth plates in young horses as fractures.
- Assuming scintigraphy localizes a specific lesion-it indicates regions of increased turnover.
- Overlooking contralateral comparison views when subtle.
Worked rule of thumb
For a horse with forelimb lameness and a positive flexion test, start with radiographs of the distal limb plus ultrasound of the flexor tendons/suspensory. If radiographs are normal but lameness is localized, consider MRI or scintigraphy for early or soft-tissue disease. Remember: "localize first (blocks), then image."
Thoracic and abdominal imaging
Know thoracic radiography for pneumonia/pleural disease and the limits of equine abdominal radiography; ultrasound is preferred for abdominal organ evaluation.