Exostosis of the sustentaculum tali causing tibiotarsal joint pathology in a Standardbred racehorse trotter.

an ultrasound-guided extra-articular surgical approach. Postoperative management included a structured rehabilitation program, resulting in a return to full-speed training by Day 76 with no recurrence of lameness. Follow-up evaluations demonstrated improved performance and complete resolution of TTJ effusion and associated swelling. This case highlighted the importance of multimodal imaging in identifying extra-synovial lesions of the ST and supported ultrasound-guided extra-articular removal as an effective surgical option for ST exostosis. Although the underlying cause of the lesion was uncertain, subclinical trauma was considered a likely contributing factor. Key clinical message: The ST is a horizontal bony projection on the plantaromedial aspect of the calcaneus. Due to its minimal soft-tissue coverage, it is particularly vulnerable to external trauma and subsequent osseous proliferation. Exostosis of the ST may result in impingement of the plantaromedial pouch of the tarsocrural (tibiotarsal) joint, contributing to joint irritation and secondary pathology. Accurate diagnosis and effective case management rely on the combined use of radiography and ultrasonography, which together enable detailed assessment of both osseous changes and associated soft-tissue structures.