[Biomechanics of healing of cortical autotransplants after intramedullary nailing and device removal].

The aim of the study was to investigate the biomechanical properties of 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 outside the body by autoclaving or gamma radiation (Co, 5 kGy). Subsequently, osteosynthesis involving the use of medullary nailing was performed. After 36 weeks, the dogs were killed painlessly and, after removing the nails, the 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 autoclaving, respectively, while bending showed an increase of up to 590%. These results show the need to allow plenty of time for healing in the case of weightbearing transplants. When bealing is undisturbed, no biomechanical differences are found between proximal and distal osteotomies, although in the X-ray image the osteotomy gap (fracture line) remains visible, and scintigraphic activity persists for a longer period. This means that the radiological aspect of the former does not necessarily reflect actual biomechanical strength.