[Experimental studies of the effects of prestress on intact canine bone structure]

Three types of plate made of 316L medical stainless steel were applied in the experiment. They were divided into conventional plate, concave plate, sliding plate by their different shapes and functions. They were fixed on intact canine tibias and compared with intact canine tibias that were only fixed with conventional screws. Stress values were measured with static strain instrument in different conditions and in vitro tissue that was poured with disulphine blue. CT scanning was done in different stages. The experiment results proved that different extents of intraosseous prestress were reduced by different plate fixings. The conventional plate group with high stiffness produced the greater prestress and stress shielding value and slight circulation disorder in bone tissue in early stage, but the osteoporosity of tibias bone ocurred early (1 month); conventional plate with low stiffness produced the less prestress and stress shielding value and severe circulation disorder in bone in early stage, but the osteoporosity ocurred late (3 month). We consider the cause of local osteoporosity of tibias bone after plate fixed were mainly prestress, and stress shielding is secondary in early stage (3 month). The local circulation is disorder is not important factor.