Radiation-induced impairment of bone healing in the rat femur: effects of radiation dose, sequence and interval between surgery and irradiation

Background and purpose: Impairment of osseous healing in treatment combinin g surgery and radiotherapy is a frequent complication. Its dependence on se quence and interval was studied in a defined experimental model. Materials and methods: The effect of pre- and postoperative irradiation by single doses of X-rays on osseous closure of a 1.2 mm drill hole in the rat femur was measured 6 or 7 weeks after surgery in histological sections usi ng morphometrical methods. Results: Irradiation delivered between 1 day and 6 months before surgery re sulted in a reduction of bone healing following very similar dose response relationships; there was no evidence of any slow repair of latent radiation damage. Radiosensitivity of bone healing during the first 3 days after sur gery was not different from preoperative irradiation; however, irradiation 4 days or later after surgery failed to reduce osseous healing even after v ery high radiation doses. Conclusion: Tolerance increases enormously if radiotherapy is given later t han 4 days after surgery. This has great implications for combined radiothe rapy and surgery schedules involving bone reconstruction, but may be even m ore important for radiotherapy applied to prevent heterotopic ossification after total hip arthroplasty. Biologically, target cell regeneration alone is insufficient to account for the drastic rise in radiotolerance; it must be accompanied by an increase in cellular resistance due to differentiation . (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.