Heterotopic ossification in the residual lower limb in an adult nontraumatic amputee patient.Heterotopic ossification usually occurs in association with various neurologic injuries, trauma, and burns. There have been few reports in the literature of heterotopic bone formation at the distal residual limb in the adult amputee population. All previous cases with a documented cause have involved traumatic amputations. An adult diabetic patient who underwent left below-the-knee amputation for progressive Charcot foot is presented. The patient began to experience residual limb pain and decline in functional mobility 4-5 mos after surgery. Radiographs demonstrated heterotopic bone around the distal tibial and fibular remnant with extension into adjacent soft tissue. Triple-phase bone scan testing and tissue biopsy verified active heterotopic ossification. The patient was treated with etidronate and eventually was able to ambulate with a prosthesis on a regular basis. This case demonstrates that heterotopic ossification may occur and be a source of residual limb pain in the adult nontraumatic amputee population.