Non-septic tenosynovitis (NST) of digital flexor tendon sheath (DFTS) is a common condition in horses, commonly 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 five 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.

Bone oedema-like lesion is characterized by hyperintense signals in short tau inversion recovery (STIR) sequences on magnetic resonance imaging (MRI). The pattern of bone oedema-like lesions involving the enthesis of the collateral ligament (CL) of the distal interphalangeal joint (DIPJ) has not been investigated as a cause of lameness in horses. This pattern was detected in 10 forelimbs of nine horses, involving the medial collateral fossa of the distal phalanx in six feet. The STIR signal was graded as ‘severe’ in two feet, ‘moderate’ in two feet, and ‘mild’ in six feet, and involved the dorsal two-thirds of the fossa in seven feet. The bone lesion was the only lesion in six feet, while in three feet, the ipsilateral CL presented abnormalities. Follow-up MRI was available for three horses and revealed a reduction of the STIR signal. Five horses returned to a lower level of athletic activity, while four returned to the same or a higher level. Bone oedema-like lesion at the CLs enthesis is a potential cause of lameness even if the ipsilateral CL appears normal. The prognosis for return to athletic activity is good, although further studies with a larger number of horses are required.

An 8-year-old Warmblood gelding used for dressage presented with a large swelling on the craniomedial aspect of the left stifle. Conservative treatment and needle drainage had been unsuccessful. Ultrasonographic examination revealed a large anechogenic fluid filled cavity with a well-defined capsule. Standing endoscopic examination revealed separation between the deep crural fascia, the semitendinosus muscle and skin. Cytologic examination of the fluid collected revealed lymphocyte-rich transudate associated with a fibrous inflammatory reaction. Due to the poor response to conservative management and needle drainage, in-toto excision of the capsule was performed under general anaesthesia. Histopathologic examination of the resected capsule identified the presence of dense fibrovascular tissue lining a cavitated structure, with an outer thin zone of adipose connective tissue. These findings combined with the clinical presentation are consistent with Morel-Lavallee lesion (MLL). After surgery the horse underwent a period of box rest; gradual reintroduction to exercise was started 6 months after surgery. The horse returned to full work 9 months after surgery and was able to return to its former athletic function with an excellent cosmetic outcome.