[Influence of stress-relaxation plate on bone geometrics and mechanical property: an experimental study]

In order to maintain the effective fixation effect of rigid bone plate in the early stage of fracture and to prevent osteoporosis induced by stress shielding effect of rigid plate in later stage of fixation, a washer made of viscoelastic material was placed between the screw and the screw hole of plate to form a stress-relaxation plate system. Both in vitro and in vivo experiments demonstrated that there was no statistical difference between the stress shielding effect of padded and unpadded plate groups. The washer showed significant deformation and damaged 8 weeks after implantation, and 10 weeks after implantation the stress shielding rate of the padded plate group was significantly lower than that of the unpadded group (P < 0.05). As a consequence, the degree of osteoporosis of the tibia in the padded group was significantly milder than the unpadded group, and 20 weeks after implantation, the diameter of the tibia medullary cavity of the padded group was significantly smaller than that of the unpadded group. The thickness of cortical bone and the bending strength of the tibia of padded group were significantly larger than those of the unpadded group (P < 0.05-0.01). These results showed that the stress-relaxation plate system can effectively maintain the stability of fracture fixation at the similar level of rigid plate during the early stage of fracture and can gradually lower down the stress shielding rate so as to prevent severe osteoporosis and reduction of bone mechanical property in the later stage of fixation.