Hybrid手术对颈椎力传导方式的影响

目的研究人工椎间盘置换(total disc replacement,TDR)合并融合的Hybrid手术后颈椎的力传导模式,从生物力学角度加深对Hybrid手术的认识。方法建立正常颈椎有限元模型(INTACT模型),模拟C4~6节段退变的3种手术方案:上置换+下融合(TDR45模型)、上融合+下置换(TDR56模型)、双节段融合(Fusion456模型)。结果所有手术模型中,融合节段的活动能力完全丧失,置换节段的活动能力有所增加。在160 N轴向力作用下,INTACT模型整个节段后伸4°,而TDR45与TDR56模型的颈椎节段分别后伸8.2°与8.9°。在TDR56模型中,经过C5椎体的力减少20%,经过置换节段小关节的力增加3.8倍。在TDR45模型中,经过置换节段小关节的力增加50%。INTACT模型的最大关节应力为0.8 MPa,而TDR45与TDR56模型置换节段的小关节应力均高达正常颈椎的2倍。结论由于置换节段活动范围的增加,Hybrid术后颈椎曲度在轴向力作用下发生较大改变(后伸)。这种改变将导致经过置换节段椎体的力有所减少,而经过小关节的力有所增加,从而增加置换节段小关节的应力。

Effects of Hybrid surgery on load transfer pattern of cervical spine

Objective To investigate the pattern of load transfer in cervical spine treated with Hybrid surgery using total disc replacement (TDR) and spinal fusion, so as to deepen the understanding of Hybrid surgery from the biomechanical view. Methods A finite element model of cervical spine C3-7 (INTACT model) was built to simulate three types of fusion surgeries at C4-6 degenerative segments: upper TDR combined with lower bone graft fusion (TDR45 model), upper fusion combined with lower TDR (TDR56 model), two-level fusion (Fusion456 model). Results In all surgical models, mobility of the fused levels was almost lost, while mobility of the TDR levels increased. Under the axial load of 160 N, the entire cervical motion was less than 4° in the INTACT model, while the motion in the TDR45 model and TDR56 model increased to 8.2° and 8.9°, respectively. In the TDR56 model, the force transferred through the C5 vertebra decreased by 20%, while the force transferred through the facet joint force was 3.8 times larger than that of the INTACT model. The facet contact force in the TDR45 model increased by 50%. The maximal stress in the INTACT model was 0.8 MPa, while the facet contact force in the TDR45 model and TDR56 model were almost 2 times as that in the INTACT model. Conclusions Due to the increased mobility at the TDR levels, the cervical curvature after Hybrid surgery changes greatly under the axial load. The alteration of spinal alignment will result in a decrease in anterior vertebral section force at the operative level, as well as an increase in facet joint force and facet cartilage stress.