Which radiographic views best reveal equine foot entheses? New guidance from cadaver studies

Radiographic imaging of the entheses of the equine thoracic foot

Donald Henre Honnas; Andrew R. Fiske-Jackson; Caroline V. Fulkerson; D. Ray Wilhite

Background

Lameness originating from the equine foot is common, and injury to tendons or ligaments frequently involves their entheses. Although advanced imaging modalities such as MRI and CT provide superior soft-tissue detail, radiography remains the most widely available first-line diagnostic tool. Radiographic identification of enthesopathies requires precise knowledge of where tendon and ligament insertions and origins are projected on standard views. Prior to this study, detailed radiographic descriptions of the entheses of major tendons and ligaments of the equine foot were lacking.

Methods

Three thoracic digits from horses euthanased for reasons unrelated to lameness were dissected to expose the entheses of five commonly injured structures: the collateral ligaments of the distal interphalangeal (DIP) joint, the collateral sesamoidean ligaments of the navicular bone, the deep digital flexor tendon, the common digital extensor tendon, and the distal sesamoidean impar ligament. Entheses were marked with surgical staples or needles and imaged using three standard radiographic projections: lateromedial (LM), dorsopalmar (DP), and 60° dorsoproximal–palmarodistal oblique (D60°PrPaDO). A total of 45 radiographic image sets were independently evaluated by a board-certified veterinary surgeon and radiologist to determine which projections best delineated each enthesis and to identify consistent radiographic landmarks.

Results

Across all structures evaluated, the D60°PrPaDO and LM projections most consistently and clearly identified the entheses. The entheses of the collateral ligaments of the DIP joint were also readily visible on the DP projection. The DP view was generally inferior for visualising insertions of the deep digital flexor tendon, common digital extensor tendon, and distal sesamoidean impar ligament due to superimposition of adjacent osseous structures. No differences were found between evaluators or among the three cadaver feet. Radiographic landmarks for each enthesis were defined and summarised to guide clinical interpretation.

Limitations

The study used a small sample size and relied on cadaver limbs with unknown lameness histories. Additionally, medial and lateral aspects of the feet could not be distinguished. However, no gross or radiographic abnormalities were identified, and the authors note that enthesis locations are consistent among horses, mitigating these limitations.

Conclusions

This study identifies the optimal standard radiographic projections for visualising the entheses of five commonly injured tendons and ligaments in the equine thoracic foot. The resulting images and described landmarks provide a practical reference for clinicians assessing radiographs for enthesopathies or avulsion injuries. While radiography has inherent limitations for detecting acute soft-tissue injury, informed interpretation of standard views can aid diagnosis and guide decisions regarding further advanced imaging.

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