Proximal sesamoid bone fracture as a cause of nonseptic tenosynovitis of the digital flexor tendon sheath in a sport horse

Summary Nonseptic tenosynovitis (NST) of digital flexor tendon sheath (DFTS) is a common condition in horses, frequently associated with manica flexoria or deep digital flexor tendon tears. Tenosynovitis of the DFTS secondary to proximal sesamoid bones (PSBs) injury is rare. This report described a case of NST of the DFTS caused by an abaxial fracture of lateral PSB in a 7‐year‐old mare used for showjumping. The mare presented with right hindlimb (RH) lameness following a field accident. Radiographic examination of the RH fetlock revealed an abaxial fracture of the plantarolateral margin of lateral PSB. Ultrasonographic examination confirmed the presence of moderate DFTS effusion with no concurrent intrathecal pathology. Due to the lack of improvement with conservative management, the horse underwent DFTS tenoscopy. During tenoscopy, a tear of the proximolateral aspect of the sheath wall communicating with the fracture bed was found at the junction between the proximal scutum and the plantar annular ligament. The bone fragment was removed and the torn fibres debrided. After 5 months of rehabilitation, the mare returned to the previous level of activity. To the best of the authors' knowledge, this is the first report detailing the management and outcome of DFTS tenosynovitis secondary to PSB fracture.