Magnetic resonance and radiographic diagnosis of osseous resorption of the flexor surface of the distal phalanx in the horse.

Reasons for performing study: Osseous resorption of the flexor surface of the distal phalanx of the horse has been identified previously using magnetic resonance (MR) imaging; however, little is known about the prevalence and characteristics of this lesion.

Objectives: To establish the MR prevalence of resorptive lesions in the flexor surface of the distal phalanx and identify concurrent lesions associated with this finding and associations between the MR and radiographic findings.

Methods: Horses with distal extremity MR and radiographs performed within 2 weeks of each other were included in the study. The flexor surface of the distal phalanx was graded independently on both modalities for the presence of osseous resorption. The sensitivity and specificity of radiography for identifying osseous resorption was calculated using MR as the gold standard.

Results: Eighty-two MR studies met the inclusion criteria, 8 of which included osseous resorption of the flexor surface of the distal phalanx. Concurrent injury to the deep digital flexor tendon and the navicular bone was a common finding. An association between MR and radiographic grades was identified. Radiography had a high specificity (0.96) but lower sensitivity (0.45-0.55) for detecting osseous resorption.

Conclusions: Osseous resorption of the flexor surface of the distal phalanx can be observed both on MR and radiographic examinations of horses with lameness localised to the foot. This lesion is most often associated with other pathological changes in the podotrochlear apparatus.

Potential relevance: Focal radiolucency of the flexor surface of the distal phalanx is a newly recognised radiographic sign associated with pathological changes of the podotrochlear apparatus.