Pathological ankle fracture due to brown tumour: atypical presentation of low serum vitamin D with normal parathyroid hormone and bone profile.

Osteoclastomas or brown tumours are named as such due to increased vascularity, subsequent haemorrhage and haemosiderin deposition giving the lesion a reddish brown appearance under gross microscopic examination. It is due to an increase in parathyroid hormone activity from several causes, such as parathyroid adenomas, renal impairment and low vitamin D levels. The lesions increase the tendency of the bone to fracture.