前方腰椎骨融合術（Anterior Lumbar Interbody Fusion, ALIF）已廣泛使用於治療腰椎椎間盤病變，為了增加骨融合成功率，提升手術後脊椎的穩定度是首要課題，能夠提供術後穩定度的參數也一直被專家學者們研究著。本研究主要目的為使用有限元素法，分析在前方腰椎骨融合術配合後方椎弓根固定器時，椎籠擺放位置對於穩定度的影響，並利用田口方法探討椎籠擺放的最佳參數組合。
本研究使用之模型為腰椎第4-5節（L4-L5），依照田口方法將椎籠擺放位置設定為控制因子，包含1.前後(AP)；2.寬度(ML)；3.角度(CD)，鬆質骨強度設定為誤差因子，包含1. 40MPa；2. 100MPa，由L9直交表配置不同因子擺放水準，以軸向壓力及四種力矩（屈曲、伸展、側彎、扭轉）分別施加於L4上方，並將L5底部完全拘束，執行直交表實驗，所得數據使用田口方法進行解析。
經過有限元素分析，結果顯示，即使已經使用椎弓根固定器，椎籠擺放位置還是對脊椎的穩定度有影響，在屈曲以及伸展負載時，擺放前方則位移量愈少；側彎、扭轉及軸向壓力時，擺放寬度愈寬則位移量愈少；擺放角度雖然沒有非常顯著的效果，但是前窄後寬的角度表現較佳，綜合以上結果，得出最佳化組合。經過田口方法驗證，本研究之最佳擺放位置明顯增加手術環節穩定度，因此建議前方骨融合術於椎籠植入時，椎籠位置應靠近前方、靠近外側及使用前窄後寬的角度，並配合椎弓根固定器使用，如此可增強脊椎整體穩定度以及有利於術後骨融合。

Anterior lumbar interbody fusion (ALIF) with cages has been widely used to treat internal disc degeneration. However, different cage positions and their orientations may affect the initial stability leading to different fusion results. The aim of the present study was to evaluate the optimum cage position and orientation for ALIF with block cages and supplemental pedicle screw fixation using finite element analysis and Taguchi method.
The three-dimensional finite element model were used to simulate the stability of the L4/L5 fusion segment under five different loading conditions (axial compression, flexion, extension, lateral bending, and axial rotation). The Taguchi method was used to determine the optimized placement of the cages. Three control factors (the anterior-posterior position, medial-lateral position, and convergent-divergent angle between the two cages) and one noise factor (the strength of cancellous bone, 40MPa and 100MPa) were indemnified in the parameter design. Each control factor had three levels. Therefore, the L9 orthogonal array was used to set different factor levels.
From the results of FEA and the Taguchi method showed that cage position affected the spinal stability even when the pedicle screw fixation was used. In flexion and extension, the rotation displacement was decreased when the cages were placed at anterior position. The widely bilateral placement of the cages showed more stability than central regions. The convergent-divergent angle between the two cages had slight effect on the segmental stability, but divergent angle had good performance in the clinical outcome to avoid the subsidence and increase the fusion rate. Therefore, we suggested that the optimal cage position has an anterior and widely bilateral placement and a diverging angle between the two cages on ALIF with pedicle screw fixation.

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