[Suppression of heterotopic ossification: single-dose versus fractionated irradiation--animal study]

Periarticular ossification is one of the main problems of total hip replacement. Irradiation with megavolt photons is known to be a well recognized means of prevention of heterotopic ossification. So far only little scientific basis exists about the most favourable way of radiotherapy for prevention of ectopic ossification. In this study two theoretically equivalent doses are compared. Allogeneic bone matrix was implanted into both thighs of 50 adult male Wistar rats for experimental induction of heterotopic ossification. Immediately after operation the thigh implants were irradiated with a single dose of 7 Gy or a total dose of 10 Gy given in 5 fractions of 2 Gy each. In the model of matrix-induced osteogenesis in rats fractionated irradiation by 5 x 2 Gy leaded to a highly-significant (p = 0.001) better suppression of ectopic ossification compared to irradiation by 1 x 7 Gy. Once-only irradiation with 1 x 7 Gy leads to a reduction of the calcium contents by 27.5%, split irradiation by 5 x 2 Gy obtained a reduction by 66.9% compared to the calcium contents of thigh implants not exposed to radiation. In view of experimentally proven better effects, fractionated irradiation has to be preferred to single dose radiation also considering less side effects in split radiation.