臨床上有多種治療腰椎退化性椎間盤疾病的手術策略。以前的研究已經運用電腦輔助工程技術開發了有限元素模型來研究各種手術策略(例如剛性和動態穩定裝置)對於脊椎生物力學的影響。然而，以前的有限元素脊椎模型大多被部分建模或將椎間盤考慮為線彈性材料，此外，穩定裝置的結構經常被簡化。因此本研究的目的是開發多節段脊椎有限元模型(T10-S1)，並將椎間盤以超彈性材料進行模擬，以研究手術策略如何影響脊椎生物力學。
在本研究中，SolidWorks 2019用於創建T10-S1多節段脊椎和腰椎植入物裝置的三維實體模型，包括剛性固定系統、DSS®動態穩定系統以及椎籠。開發了七種3D有限元素模型，一種完整模型和六種單節段(L5-S1)治療模型。對於治療模型的部分，包括經皮椎間孔鏡椎間盤切除術、顯微椎間盤切除術、剛性固定系統、DSS®動態穩定系統、經椎間孔椎間融合術、經皮內視鏡經椎間孔腰椎椎間融合術。使用ANSYS Workbench 2021 R1分析有限元素模型，並假設所有椎體元件及植入物都是線彈性及均質等向性，除了椎間盤，將其使用雙參數Mooney-Rivlin(MR)公式來定義為不可壓縮的超彈性材料。假設椎體和植入物之間的界面條件是結合的，小面關節處被設定為係數為0.385摩擦接觸。在邊界及負載條件方面，施加500 N的隨附力來代表人體上半身重量，通過在T10節段上施加位移來進行屈曲、伸展、側向彎曲和軸向旋轉的運動，而薦椎的底面被完全約束。
結果顯示，與非融合脊椎手術和椎間盤切除術相比，脊椎融合術往往會增加鄰近椎節的椎間旋轉角度以及小面關節壓力，然而其因為治療節段的剛性提升，在應力遮蔽效應作用下於大多數運動時鄰近節段椎間盤的應力較非融合脊椎手術來的低，另外，TLIF以及PE-TLIF之生物力學性能並無明顯的差異。DSS®動態穩定系統能夠提供節段穩定性，並同時保留治療節段部分活動性，可以防止因代償現象導致鄰近椎節退化以及小面關節磨損，且與剛性固定系統相比能有效降低椎弓根螺絲失效風險，然而其開槽耦合器可能因超量的運動導致結構失效。綜觀椎間盤切除術之模擬結果，其生物力學性能最接近於完整模型，然而節段的不穩定性增加可能造成椎間盤突出復發以及治療節段小面關節磨損。這項研究能夠協助臨床醫師進行術前評估，並且可被應用於幫助開發其他臨床術式以及植入物之結構設計。

There are several surgical options to treat lumbar degenerative disc disease. Previous studies have developed the finite element (FE) models to investigate the influence of various surgical strategies, such as rigid and dynamic stabilization devices, on spinal biomechanics. However, the previous FE spinal models were partially modelled or not considered the incompressible disc. In addition, the structures of stabilization devices were often simplified. Thus, the purpose of this study was to develop the multilevel FE model (T10-S1) with the incompressible disc to investigate how the surgical strategies influence spinal biomechanics.
In this study, SolidWorks 2019 was used to create the three-dimensional (3D) solid models of a T10–S1 multilevel spine and three stabilization devices, including a rigid fixation system, DSS® dynamic stabilization system, and TLIF cage. Seven types of 3D FE models, one intact model and six 1-level (L5/S1) treated models, were developed. For the treated models, the T10–S1 multilevel spine models with percutaneous transforaminal endoscopic discectomy, microdiscectomy, rigid fixation system, DSS® dynamic stabilization system, transforaminal lumbar interbody fusion, percutaneous endoscopic transforaminal lumbar interbody fusion were constructed. All the FE models were analyzed using ANSYS Workbench 2021 R1. All the components were assumed to be linear elastic isotropic material, except for the disc, that is defined as a hyperelastic material (Mooney-Rivlin). The interface between the vertebrae and the implants were assumed to be bonded. The frictional contact was considered with a coefficient of friction of 0.385 at the facet joints. In terms of the loading condition, a follower load of 500 N was applied to simulate the upper body weight. The spinal movements of flexion, extension, lateral bending, and axial rotation were performed by applying the displacement on the T10 segment. The bottom surface of the sacrum was fully constrained.
The results showed that spinal fusion tended to increase the intersegmental rotation and facet joint pressure at adjacent level as compared with non-fused spine surgery and discectomy. The DSS® dynamic stabilization system provides segmental stability while preserving partial mobility of the treated segment, preventing degeneration of adjacent vertebral segments and wear of facet joints due to compensatory phenomena. Compared with rigid fixation system, it can effectively reduce the risk of pedicle screw failure, but its slotted coupler may cause structural failure due to excessive movement. Looking at the simulated results of discectomy, its biomechanical outcomes were closest to the intact model. However, the increased instability at index level may lead to recurrence of disc herniation and wear of the facet joints of the treated segment.

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