Bilateral avulsion fracture of the medial proximal tubercle of the tibiotarsal bone

A 5-year old swiss wormblood gelding was admitted to the Veterinary Surgery Clinic of the University of Zurich with a history of lameness in both hind limbs. The site of the lameness was located by intraarticular anesthesia a t the tibiotarsal joints. Radiographically two small fragments where diagno sed at the dorsal aspect of the intermediate sagittal ridge of the distal t ibia and bony proliferations at the medial proximal tubercle on both tibiot arsal bones. Furthermore the horse showed signs of bone spavin at the dista l intertarsal joints of both limbs. The conservative treatment consisting o f an intra articular injection of a hyaluronan and a steroidal antiinflamma tory drug was not successful in abolishing the lameness. Because of the gua rded prognosis and other reasons, the owner; decided to put the horse down. The post mortem examination showed targe bony fragments with on irregular surface at the proximal end of the medial trochlear ridge of the right and the left talus. On both sides the medial proximal tubercle of the tibiotars al bone was too smalt compared to a normal tarsal bone. These bony fragments showed signs, which con be found in osteochondrosis, i n separate ossification, in cases of direct trauma and avulsion fractures. Combining the findings of the anamnesis, the clinical, radiographic and pos t mortem examination, an avulsion fracture of the medial proximal tubercle of the tibiotarsal bone in both rear limbs was diagnosed.