Use of magnetic resonance imaging to diagnose distal sesamoid bone injury in a horse.
METHODS
A 5-year-old Appaloosa mare was examined for severe left forelimb lameness of 4 months' duration.


RESULTS
Lameness was evident at the walk and trot and was exacerbated when the horse circled to the left. Signs of pain were elicited in response to hoof testers placed over the frog of the left front hoof, and a palmar digital nerve block eliminated the lameness. Radiographs revealed no abnormalities, but magnetic resonance imaging (MRI) revealed increased bone density in the medullary cavity of the distal sesamoid (navicular) bone in the proton density and T2-weighted images and a defect in the fibrocartilage and subchondral bone of the flexor cortex.


RESULTS
Because of the absence of improvement after 4 months and the poor prognosis for return to soundness, the mare was euthanatized. An adhesion between the deep digital flexor tendon and the flexor cortex defect on the navicular bone was grossly evident, and histologic evaluation revealed diffuse replacement of marrow trabecular bone with compact lamellar bone. Changes were consistent with blunt traumatic injury to the navicular bone that resulted in bone proliferation in the medullary cavity.


CONCLUSIONS
Use of MRI enabled detection of changes that were not radiographically evident and enabled accurate diagnosis of the cause of lameness. Navicular bone injury may occur without fracture and should be considered as a differential diagnosis in horses with an acute onset of severe unilateral forelimb lameness originating from the heel portion of the foot.
Barber
Matthew J
MJ
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, 99164, USA.
Sampson
Sarah N
SN
Schneider
Robert K
RK
Baszler
Timothy
T
Tucker
Russell L
RL
D000818:Animals; D003937:Diagnosis, Differential; D017809:Fatal Outcome; D005260:Female; D005552:Forelimb / Q000293:injuries; D006736:Horses / Q000293:injuries*; D007794:Lameness, Animal / Q000175:diagnosis* / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods / Q000662:veterinary*; D011379:Prognosis; D012716:Sesamoid Bones / Q000293:injuries* / Q000473:pathology; D012720:Severity of Illness Index