Heterotopic ossification following hip replacement or spinal cord injury. Two clinical studies with EHDP

We report two double-blind, placebo-controlled studies of the effects of disodium etidronate (EHDP) on the incidence and severity of heterotopic ossification following total hip arthroplasty or spinal cord injury. The large placebo groups in these studies allowed the estimation of the incidence of heterotopic ossification in these patient populations. Heterotopic ossification occurred in 65% of patients after hip replacement and in the majority of these within 15 weeks. Clinically significant ossification occurred in 19% of affected patients. The incidence of heterotopic calcification after spinal cord injury was less (35%) but followed a similar natural history. Treatment with EHDP reduced the incidence and severity of lesions both at the time of stopping EHDP and up to 9 months after treatment.