Metaphyeal and Diaphyseal Dysplasia of the Third Cervical Vertebra Secondary to Physeal Necrosis in a Quarter Horse Foal.

Ischaemia-induced physeal injury has not been described previously in the horse. A 1-month-old Quarter horse foal was submitted for necropsy examination due to an acute onset of ataxia followed by a 4-week history of progressive decline. Focal narrowing of the spinal canal due to ventral compression by the rotation of the cranial aspect of the third cervical vertebra (C3) was observed. The metaphysis and diaphysis of C3 were markedly shortened and white-tan in colour. Microscopically, there was complete loss of the dorsal compact bone of C3 and replacement of 80% of the physis that runs parallel to the vertebral canal with fibrous tissue and thickened viable trabecular bone. Both cranial and caudal physes of C3 showed widespread bands of coagulative necrosis of the hypertrophic and calcifying zones. Marked bone marrow hypoplasia with slight fibrosis was observed in the metaphyses and diaphysis. There was no evidence of fracture or inflammation. The epiphyses were microscopically unremarkable. It was hypothesized that a regional transient incomplete and possibly multiphasic ischaemia involving the nutrient artery caused necrosis of the physes, resulting in dysplasia of the bone. Ischaemic injury to the physis should be considered in the pathogenesis of focal bone dysplasia in horses.