BIOMECHANICAL PROPERTIES OF CORTICAL AUTO GRAFT HEALING FOLLOWING MEDULLARY NAILING AND REMOVAL OF MATERIAL

The aim of the study was to investigate the biomechanical properties o f segmental cortical autografts subjected to extracorporeal treatment. For this purpose, 12 beagle dogs were submitted to tibial osteotomy, when 25 mm-long diaphyseal segments of bone were removed and treated o utside the body by autoclaving or gamma radiation (Co, 5 kGy). Subsequ ently, osteosynthesis involving the use of medullary nailing was perfo rmed. After 36 weeks, the dogs were killed painlessly and, after remov ing the nails, tbe tibias were tested for the biomechanical properties . In comparison with the contralateral tibia, a mean stiffness of 47 % and 32 % was measured for tibia treated by irradiation and autoclavin g, respectively, while bending showed an increase of up to 590 %. Thes e results show the need to allow plenty of time for healing in the cas e of weightbearing transplants. When bealing is undisturbed, no biomec hanical differerences are found between proximal and distal osteotomie s, although in the X-ray image the osteotomy gap (fracture line) remai ns visible, and scintigraphic activity persists for a longer period. T his means that the radiological aspect of the former does not necessar ily reflect actual biomechanical strength.