Fractures of the distal sesamoid occur rarely. They are diagnosed in adult horses of various breeds.
Most fractures of the distal sesamoid have a traumatic origin and are the result of excessive or repetitive loading through the middle and distal phalanx and the deep digital flexor tendon. Occasionally a preexisting pathologic condition in the distal sesamoid bone (cystic lesion, see x-ray left) predisposes it to fracture.
Rarely, separate centers of ossification within the distal sesamoid bone mimic a fracture line because the two centers do not fuse to one bone. This usually occurs bilaterally.
The forelimb is more commonly involved than the hind limb.
Three different fracture types are distinguished:
Simple fractures of the body
Only the simple fractures of the body are treated with internal fixation.
The patient usually shows an acute, moderate to severe lameness accentuated during turns. The hoof and distal phalangeal region are warm to the touch, and an increased pulse can be palpated over the palmar or plantar arteries. Pressure exerted with the hoof testers might elicit a positive response.
Signs are relieved by regional anesthesia of the distal phalangeal region. In the differential diagnosis, a hoof abscess should be considered.
Radiography conﬁrms the diagnosis in most cases.
Scintigraphy, computed tomography (CT), and magnetic resonance (MR) imaging are often successful in delineating an obscure fracture. CT and MR are especially useful to assess the fractures and to identify displacement of the fragments. 3-D reconstruction of CT images provides valuable additional information on the lesion.