Department of Industrial Chemistry and Materials Engineering, University of Messina, Salita Sperone 31, 98166 Sant'Agata (ME), Messina, Italy.
Med Eng Phys. 2010 Oct;32(8):889-97. doi: 10.1016/j.medengphy.2010.06.005. Epub 2010 Jul 23.
The present study addresses the question of evaluating, by combining both experimental and numerical methods, the stress/strain distribution within a standardized composite femur implanted with an anterograde intramedullary nail. A transverse diaphyseal fracture has been introduced in order to evaluate the implant response in the early postoperative clinical stage. By comparing these experimental data with those obtained in the fully healed stage, in which the bone continuity had been recovered, it was possible to get information on load sharing between the bone and the intramedullary nail, location of high strain concentrations, bone relative motion at the fracture site, and stiffness reduction caused by bone discontinuity. Experimental data were correlated with those predicted by a validated 3D finite element model of the complete implant/femur assembly to investigate the full field stress distribution either in the cortical bone, in the nail or in the locking screws. The obtained results suggest that full weight bearing in the immediate post-operating stage should not be allowed since high stress levels are generated in the outer shell of the cortical bone either around the proximal screw hole or the upper locking screw hole. Long-term implant reliability should be guaranteed instead, since after fracture consolidation equivalent von Mises stresses never exceed critical levels neither in the bone nor in the implant.
本研究通过实验和数值方法相结合，评估了标准化复合股骨中植入顺行髓内钉后的应力/应变分布。引入横向骨干骨折是为了评估早期术后临床阶段植入物的反应。通过将这些实验数据与完全愈合阶段（骨连续性已恢复）获得的数据进行比较，可以了解骨和髓内钉之间的负荷分担、高应变集中的位置、骨折部位的骨相对运动以及骨不连续性引起的刚度降低。实验数据与完整植入物/股骨组件的经过验证的三维有限元模型的预测数据相关联，以研究皮质骨、钉或锁定螺钉中的全场应力分布。研究结果表明，在术后早期不应允许完全负重，因为在外层皮质骨中，无论是在近侧螺钉孔周围还是在上部锁定螺钉孔周围，都会产生高应力水平。相反，应该保证长期植入物的可靠性，因为在骨折愈合后，无论是在骨还是植入物中，等效 von Mises 应力都不会超过临界水平。
