[Biomechanical properties of heat and irradiation treated spongiosa]

Cylindrical specimens of trabecular pig bone were tested to uniaxial compressive strain levels of 30% to study the influence of various sterilization techniques and methods of HIV-inactivation on the mechanical properties characterized by compressive modulus, yield point, energy absorption and maximum stress. Heat inactivation at 60 degrees C (Lactated Ringer, 1 h) showed no effect; 80 degrees C (Lactated Ringer, 1 h) resulted in a diminution of the yield point and the maximum stress (p less than 0.005), while energy absorption and compressive modulus were not affected. No reduction in the stability was seen when ethanol was used instead of Lactated Ringer. At a temperature of 100 degrees C, all measured parameters were reduced to approximately 60% compared with the control group. A decrease to 13% to 25% was seen after autoclavation (120 degrees C, 2 bar, 20 min and 134 degrees C, 3 bar, 12 min). Irradiation (60Co) with 3 respectively 10kGy did not impair the stability, whereas a dose of 25 kGy led to a reduction to 61% to 69%. No additional effect was seen when irradiation was followed by storage at -80 degrees C for one week. These effects on bone stability should be considered when choosing a method of bone preparation to obtain HIV-inactivated bone grafts. Autoclavation should be used with caution when stability of the bone graft is essential. In this case, irradiation seems to be a safe method of sterilizing bone grafts ensuring both a high degree of safety and stability.