Heterotopic bone formation: clinical, laboratory, and imaging correlation.

The clinical findings, laboratory data, radiographs, and radionuclide studies of 50 patients referred for evaluation of possible heterotopic bone formation (HBF) were reviewed. HBF begins approximately 17 days following injury or neurologic insult, heralded by an acute rise in serum alkaline phosphatase (SAP), and increased vascularity on three-phase radionuclide bone imaging (RNBI). RNBI soft-tissue uptake is evident at 24 days and radiographic calcification is visible 1 wk later. Clinical signs and symptoms occur relatively late in the course of disease. HBF mimics thrombophlebitis and should be considered in all patients referred for venography if the clinical situation is appropriate. Serial SAP measurements and three-phase RNBI should allow early diagnosis in virtually all cases.