A 5 year-old Chilean pure breed rodeo gelding was evaluated for lameness in the right forelimb and effusion of the common carpal sheath of the digital flexor tendons. Radiographs revealed exostosis with rounded margins arising from the palmar cortex of the distal metaphysis of the radius. Ultrasonographic examination revealed a thickened and proliferative synovium, excessive anechoic fluid and a hiperechogenic mass protruding from the cortical bone. Tenoscopic exploration confirmed the presence of the mass, and removal was successfully performed through thecotomy. At 4 months postoperatively, the horsed was successfully competing although present mild right forelimb lameness and improving.