The Manufacture And Animal Tests Research Of Posterior Minimallyinvasive Lumbar Interbody Fusion Cage

Objective To manufacture a new type of minimally invasive lumbar interbody fusion device which is deformable and can achieve the manipulation under microendoscopy and to comprehend the mechanical behavior of it also the biomechanical behavior by comparing with the general lumbar interbody fusion device through animal tests. Methods With the suing of Niti shape memorying alloy we can manufacture a new type of lumbar interbody fusion device with a placket on one side and test the mechanical behavior of it simultaneously. 12 sheep lumbar functional spinal units (L2-3,L4-5) were randomly distributed into 4 groups in the animal tests. One acted as controls(n=3); the other three were treated either with autogenous iliac crest bone dowel graft(n=3);a threaded cylindrical titanium interbody fusion device(TFC,Sofamor)(n=3) or a new type of interbody fusion device made of NiTi shape-memorying alloy containing autogenous iliac crest graft respectively(n=3);Nondestructive mechanical tests were performed in pure compression, extension, lateral bending and torsion and the biomechanical behavior of the new type of interbody fusion device were tested simultaneously. All the datas were statistically analyzed. Results The maximal destructive load of the NiTi-TFC was 11200N and the safety coefficient was above 1.2 and was in coincident with the demand of safety. The strength of segments demonstrated both in NiTi-TFC and Sofamor group were closer and greater than in the control group, but there were no significant statistical difference between the front two groups (P> 0.05). The change of stiffness of them were similar. The difference of strength and stiffness between NiTi-TFC and Sofamor group were 7.6% and 5.6% respectively and there were no statistical difference between them (P> 0.05). The strength of the segments of the autogenous iliac crest bone dowel graft group were significantly different from the NiTi-TFC and Sofamor group, 22% and 28% respectively(P<0.05). The stiffness of the autogenous iliac crest bone dowel graft group were significantly different from the NiTi-TFC and Sofamor group too, 15% and 10% respectively(P<0.05).To compare the torsion mechanical behavior of the operational groups, their change of torque and torsion stiffness were similar to the change of strength and stiffness. Conclusion The mechanical behavior of the new type of lumbar interbody fusion device is superior and is safe and reliable. The most important is that we can perform the minimally invasive lumbar interbody fusion in the procession of the removal of nucleus under endoscopy simultaneously. With special matched instruments we will build a satisfactory background to spread this new technique.