Sonographic diagnosis of heterotopic bone formation in spinal injury patients.

A variety of stimuli including neurological insult may provoke primitive mesenchymal cells to differentiate into bone forming cells. Such a sequel following spinal cord injury can delay rehabilitation, enhance the spasticity and reduce the range of movement in the affected joint. It is characterised by an initial inflammatory phase followed by heterotopic bone formation. The early inflammatory lesion clinically mimics deep vein thrombosis, a developing pressure sore, infection, and tumour. An early diagnosis at a time of clinical uncertainty, before the plain radiographic features develop, has distinct advantages and therapeutic implications. The unique pathological evolution and maturation of the lesion is clearly demonstrated by sequential sonographic (ultrasonic) assessment with depiction of the 'zone phenomena' seen on histology. Sonographic scans in 7 spinal injury patients proved diagnostic, before there was radiographic evidence of bone formation, and confidently excluded HBF in a further 18 patients without any false negative results.