Spontaneous Osteonecrosis in a Thoroughbred Racehorse

Introduction: Spontaneous osteonecrosis is a progressive, painful condition recognized in people due to an underlying subchondral insufficiency fracture. The diagnosis is best made using magnetic resonance imaging in people with joint arthroplasty usually performed. Similar conditions occur in dogs such as avascular necrosis of the femoral head or necrosis of the distal femur in foals secondary to osteochondrosis or sepsis. To our knowledge spontaneous osteonecrosis as described in human literature has not been reported in the horse. We aim to describe the clinical findings of spontaneous osteonecrosis in the phalanges of a horse and the imaging features with nuclear scintigraphy, radiography, computed tomography and magnetic resonance imaging.

Materials and Methods: A 3-year old Thoroughbred filly presented for nuclear scintigraphy with grade 4 of 5 lameness after a breeze with no previous history of performance limiting lameness.

Results: Nuclear scintigraphy and MRI were the only two modalities that showed severe abnormalities of the proximal, middle, and distal phalanges, which was confirmed as osteonecrosis on histopathology. The filly was humanely euthanatized due to laminitis in the affected limb following attempts at medical and surgical management.

Discussion/Conclusion: Spontaneous osteonecrosis has been associated with mechanical, biochemical and traumatic origins in people that leads to loss of blood supply to the bone. We suspect that one of these mechanisms was responsible for the findings in this horse and may require a combination of nuclear scintigraphy and MRI to make a diagnosis.

Acknowledgement: There were no proprietary interest or funding provided for this project.

No conflict of interest has been declared by the author(s).