| Objective To design a new titanium alloy expansile lumbar fusion cage(EFC) then perform in vitro biomechanical test for the new cage and two different surgical approaches.Background From the early nineties, many kinds of interbody fusion cages, such as BAK, Ray TFC, have been used in clinic widely. This kind of spinal implants can provide an acute postoperative stability, along with eliminating the associated donor sit morbidity. The satisfying biomechanical properties and clinical outcomes obtained much concerns to cages. Followed with the popularization in clinic and progress in theory, there have been some new problems about cages. First, the poor restoration of postoperative lumbar sagittal alignment. Second, theoretically, the bigger cage can provide more stability to spine segment involved. But inserting bigger cage need to excise more facet joint, so the postoperative stability is diminished. So there is aninconsistency in the two attempts. Third, some research scientists indicated that one-diagonal-cage-insert approach had better postoperative stability than the traditional two-cage-insert approach.Methods 1. Design titanium alloy expansile interbody fusion cage(EFC) according to the problems mentioned above and the special requirement of endoscopic surgery. 2. Carry out biomechanical tests to evaluate EFC's and the two different surgical approaches' biomechanical characters. 21 calf lumbar function spinal units(FSU) were used in all. 12 FSUs were used in stiffness tests, 6 in EFC group, 6 in BAK group. Stiffness tests were conducted on the intact FSUs in the WE-lOA MTS (made in china). Then insert cages in each group by two surgical approaches: two-cage insert and one diagonal cage insert. They were all performed from posterior approach. After inserting, conducted stiffness tests again. The stiffness tests included axial compression, flex, extension, lateral bending, and torsion control. 9 FSUs were used in pull-out testing and were separated into 3 groups randomly. EFC, BAK, and iliac crest bone were inserted into them respectively from anterior approach. The pull-out tests were conducted in WE-lOA MTS, too. Record the maximum pull-out force and displacement. At last, carried out the EFC mechanical hardness tests.Results The stiffness of EFC groups were lower than BAK groups, while there were no statistical differences except in torsion tests(p>0.05). The stiffness were significantly greater for two-cage groups as compared to one diagonal cage groups in axial compression and extension (p<0.05). While in torsion the stiffness of one diagonal cage group was significantly greater (P<0.05). In flex and lateral bending tests two-cage groups' stiffness were greater than one diagonal cage groups', but no statistical differences(p>0.05). The anti-pullout load of EFC was lower than BAK (P<0.05), and greater than iliac crest bone (P <0.05). EFC can provide 3° Lumbar lordosis for it's wedge shape. EFC's mechanical hardness is sufficient for daily life.Conclusion. 1. EFC meets the expectations theoretically and the mechanical hardness of EFC meets the criteria for clinical using; 2.EFC's biomechanical properties are almost as good as BAK's, the expansile structure contributes a lot to EFC's stability; 3. Compared with inserting one diagonal fusion cage from posterior approach, inserting two-cage can provide better stiffness in all modes except in torsion;...
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