新型腰椎獨立式融合器的生物力學分析

Abstract

腰椎間盤退化和其所引發的各種併發症是目前世界常遭遇的脊椎病變之一，其治療方式分為保守與手術治療，其中，腰椎間融合術是手術治療方式之一，其方法是清除發生病變的腰椎間盤，再將自體或異體骨植入，且合併使用椎間融合器，以達到去除病源、提供穩定脊椎、避免神經壓迫等治療效果。研究指出，在前腰椎融合術(Anterior lumbar interbody fusion, ALIF)單獨使用融合器，無法提供脊椎在後彎動作下足夠的穩定性，必須搭配後位內固定器才能有良好穩性效果，達成椎間融合的目的。但植入後位內固定器需增開後方傷口，會損壞肌肉血管組織甚至傷及脊神經。因此，一種具備自我穩定能力的獨立椎間融合器(Self-stabilizing stand-alone fusion cage)設計發展出來，期望透過特殊的幾何設計，在融合手術時無需搭配後位內固定器就能達成椎間融合的融合效果。 本研究利用一個經過驗證的五節腰椎有限元素模型，在施加伴隨負荷（Follower load）的情形進行分析，共分為兩個部分，第一部分進行三款Self-stabilizing stand-alone cage：新型 Latero 融合器，與兩種舊有的ALIF融合器(SynFix，Stabilis)，對比傳統ALIF融合器搭配後位內固定器的穩定效果比較，並藉由多種生物評估參數包括：穩定性、環帶應力、小面關節受力以及植入物應力，來探討三款Stand-alone 融合器的椎間穩定度與此三種融合器對於腰椎界面造成的影響。第二部分則對Latero融合器提出後續設計建議並加以分析。 本研究第一部分結果發現，新型Stand-alone 融合器Latero的穩定效果相似於和傳統ALIF融合器搭配後位內固定器，若在考量避免增開後方傷口對病患造成影響的情形下，建議使用Latero融合器，就可提供腰椎間足夠的穩定性與適合融合的環境。第二部分結果則提出針對Latero融合器的後續設計建議。

For anterior lumbar interbody fusion (ALIF), stand-alone cages can be supplemented with vertebral plate, locking screws, or threaded cylinder to avoid the use of posterior fixation. Intuitively, the plate, screw, and cylinder aim to be embedded into the vertebral bodies to effectively immobilize the cage itself. The kinematic and mechanical effects of these integrated components on the lumbar construct have not been extensively studied. In the part-1 of this study, a nonlinearly lumbar finite-element model was developed and validated to investigate the biomechanical differences between three stand-alone (Latero, SynFix, and Stabilis) and SynCage-Open plus transpedicular fixation. All four cages were instrumented at the L3-4 level. In the part-2 of this study, the Latero was analyzed for different design parameters. The lumbar models were subject to the follower load along the lumbar column and the moment at the lumbar top to produce flexion (FL), extension (EX), left/right lateral bending (LLB, RLB), and left/right axial rotation (LAR, RAR). A 10 Nm moment was applied to obtain the six physiological motions in all models. The comparison indices included disc ROM, facet contact force, and stresses of the annulus and implants. At the surgical level, the SynCage-open model supplemented with transpedicular fixation decreased ROM (>76%) greatly; while the SynFix model decreased ROM 56-72%, the Latero model decreased ROM 36-91%, in all motions as compared with the INT model. However, the iii Stabilis model decreased ROM slightly in extension (11%), lateral bending (21%), and axial rotation (34%). At the adjacent levels, there were no obvious differences in ROM and annulus stress among all instrumented models. ALIF instrumentation with the Latero or SynFix cage provides an acceptable stability for clinical use without the requirement of additional posterior fixation. However, the Stabilis cage is not favored in extension and lateral bending because of insufficient stabilization.