兩種新型前位椎間融合器的生物力學特徵比較之有限元素模擬分析

Abstract

椎間盤退化和其所引發的各種併發症是目前國人時常遭遇的脊椎病變之一，其治療方式分為物理、藥物與手術治療，其中，脊椎融合術是用來治療嚴重退化的手術治療方式，其方法在於利用補骨或椎間融合器植入退化椎節，取代椎間盤以達到提供穩定脊椎、避免神經壓迫所造成的疼痛與不適等治療效果。椎間融合器是專門用於脊椎融合術的醫療器材，由人體前方植入的椎間融合器就稱為ALIF（anterior lumbar interbody fusion）融合器。目前研究指出，單獨使用傳統ALIF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。但植入後位內固定器需增開後方傷口，可能導致肌肉血管組織甚至是脊神經的傷害，增加術後感染的機率以及減緩病患恢復速度等不良影響。因此，能夠提供充份穩定性的新型stand-alone ALIF融合器被設計發展出來，期望透過特殊的幾何設計，使脊椎退化患者接受融合手術時無需搭配後位內固定器就能擁有正常穩定的融合效果。 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）的情形下，進行兩種新型stand-alone ALIF融合器與傳統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、環帶所受應力、小面關節受力以及植入物所受之應力，來探討新型stand-alone ALIF融合器對植入腰椎的影響。 本研究結果發現，新型stand-alone ALIF融合器SynFix-LR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SynFix-LR融合器，就可提供腰椎足夠的穩定性與適合融合的環境；而Stabilis融合器的表面螺紋雖然能夠在前彎與扭轉動作下穩定腰椎，卻無法避免腰椎在後彎與側彎動作時的不穩， 因此不建議使用為治療病患的選項之一。

Vertebral disc degeneration and resulting complications were commonly seen in recent years. The treatments for the degeneration included physical therapy, medicine, and surgery. “Fusion” was one of the surgical techniques for severe degeneration, using autograft or fusion cages implanting into the degenerative level to provide stability, and relief the pain resulting from the compression of nerve roots. “Fusion cage” was the device designed for fusion surgery, and the type of cages which were implanted via anterior approach was called ALIF (anterior lumbar interbody fusion) cages. In present studies, the clinical use of traditional stand-alone ALIF cages could not provide lumbar spine with sufficient stability in extension unless supplemented with posterior fixation. However, the extra approach for supplemented fixation increased operative morbidity and complications. Therefore, the new stand-alone ALIF cages were developed, expecting with special geometry designs to provide sufficient stability for lumbar spine without the use of posterior fixation. The purpose of this study was to use the validated finite element model of L1-L5 with follower load to mimic the muscle traction, to investigate the biomechanical differences of the newly designed stand-alone ALIF cages (SynFix-LR and Stabilis) versus the traditional ALIF cage supplemented with posterior fixation. Based on the parametric measurements such as stability, facet contact force, and stresses on the annulus and implants, the influences of new stand-alone ALIF cages on implanted lumbar spine were assessed. The results revealed that the stability of SynFix-LR cage was similar to that of the established fixation, and for reducing the risk of extra approach for supplemented fixation, SynFix-LR cage was recommended to be used in clinical treatment. However, Stabilis cage was not favored for its insufficient stabilization in extension and lateral bending.