- 學位論文
適用於L5-S1側路椎體融合術之可變形椎間籠設計與評估
Design and evaluation of an expandable disc cage for transverse L5-S1 interbody fusion surgery
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摘要
背景：多份臨床報告顯示傳統的側路腰椎融合手術確實能有效改善病人的症狀，術後效果良好。在術後併發症比率方面，而明顯低於其他路徑手術。此外側路腰椎融合手術尚能增加手術節的後仰程度，在矯正脊椎自然曲度方面有良好的效果。然而此路徑有一限制，即無法針對L5-S1節執行，原因是左右兩側的盆骨剛好阻礙側路手術路徑。微創手術已被證實能有效降低手術出血量與住院天數。欲打破上述限制，針對L5-S1發展一套微創側路腰椎融合手術專用的新型手術器械有其必要性。 目的：本研究擬發展一款提供外科醫生針對L5-S1進行側路腰椎融合手術之椎間籠植入器械。設計分手術器械與植入物兩部分，就器械部分必須能彎曲，以避開手術路徑上的骨盆。就植入物部分，必須具有擴張與解離的功能。為了維持椎間盤高度與穩定，此可變形椎間籠必須具備高度與水平擴張等兩項之設計。 方法：根據上述需求設計出數項機構並經臨床醫師評估建議後持續改良修正。設計成果使用有限元素法進行靜態結構分析，評估本研究之設計是否能承受脊椎的軸向力量而不受破壞。最後選定一最適設計，並加工製作原型，進行假體模型手術模擬。 結果：版本一的機械動力原理來自於滑塊機構 (Slider)，達到植入器械可彎曲角度且椎間籠可高度與水平擴張的功能，然而由於椎間籠上下端與椎骨接觸面積過小，容易造成椎間籠沉陷。版本二採用多組連桿 (Linkage) 機構，可增加椎間籠與上下椎骨的接觸面積，然而桿件連接部分的插銷直徑過小容易造成破壞，整體結構強度不足。版本三改採用頂銷撐開四周扇型塊的機構以改善強度不足的缺點，但是操縱頂銷的桿件是否能提供足夠的力量會是個問題。版本四包含一彈簧結構的植入器械，提供彎曲角度的功能，且能於非同軸間傳遞扭力。此扭力可轉動椎間籠控制螺桿並帶動前方滑塊運動，擴張耦桿 (coupler linkage) 來達到省力且提供高度及水平擴張的功能。我們使用版本四作有限元分析與原型加工，靜態結構分析結果顯示此椎間籠少許區域有應力集中的現象而無法提供足夠的結構強度。將加工完成之成品配合假體模擬手術過程中植入椎間籠的步驟，測試並驗證此椎間籠是否順利從腰椎與骨盆間空隙進入，彎曲角度並塞入L5-S1椎間盤位置，擴張後撐高椎節間高度，最後植入器械能順利解離僅留椎間籠於假體內。 結論：本研究成功設計出一款適用於L5-S1微創側路椎骨融合術並且滿足設定的手術器械，可避開兩側骨盆並且進行腰椎融合手術。本椎間籠的擴張尺寸設定合理並且可視臨床醫生需求調整幅度，維持原L5-S1椎間盤高度與脊椎自然曲度，以利追求骨融合成功率與術後立即的脊椎穩定。此設計可視為針對L5-S1腰椎融合手術的替代方案。就目前所知市面上無相似產品，並且在未來的手術應用上具有一定的潛力。
並列摘要
Background. Clinical reports to date have demonstrated the effectiveness of extreme lateral interbody fusion (XLIF) in improving patient’s symptoms with positive surgical outcome and minimal complication rates when compared to other commonly utilized paths for lumbar fusion surgery. Furthermore, XLIF has also been found to significantly increase the lordotic angle of the surgical level whilst maintaining the natural alignment of spine. Despite the demonstrated benefits of the XLIF for lumbar fusion, it remains a challenging technique to perform on patients with lower lumbar involvement due to the anatomical restriction of the pelvis. Given the likely benefit of the XLIF technique, an improved re-design of the XLIF technique that is minimally invasive in nature but with improved instrumentation flexibility in order to overcome the anatomical limitations of the lumbo-pelvic region is well warranted. Objective. To design and develop a novel surgical instrument which would allow the surgeon to perform a discectomy and fusion of the lumbar disc through the original insertion of XLIF. In order to navigate and evade around the pelvis, the novel surgical instrument must have the capacity to turn and bend along its axis as well as a mechanism to attach, expand and de-attach an expandable cage. Furthermore, in order to preserve the original disc height and stability, the expandable cage must also allow adequate expansion in terms of height as well as the base of support. Methods. Solidworks 2011 was used for the design, modification and production of a prototype of the above-described surgical instrument. Through extensive theoretical testing and discussion with surgeons, manufacturers, engineers and surgeons, a number of versions were developed. Prior to settling on a final design and sent for the production of a prototype, Finite Element Modeling were also performed to ensure the appropriate biomechanical properties are achieved with the design for clinical use and simulated with a lumbar phantom. Results. Version 1 combined four-bar linkages and a slider to meet the functional needs of the instrument; however, the contact area was deemed too small and subsidence may occur. Version 2 utilized rectangular blocks to solve the problem of small contact area; however, the connecting pin linking each of the blocks were determined to be too thin and were at risk of hardware failure. In order to overcoming the shortcomings of the previous two versions, version 3 used lifting pin to expand the structure. This appears to be able to address the functional and practical needs of the instrument, however, a direct and linear force was required to operate the expansion of the cage. Doubts were raised whether the surgeon would be able to generate enough power to perform the manual and unassisted turning of the instrument for the expansion to occur, especially when after the cage has been inserted into the intervertebral space. With the knowledge gained, version 4 of the instrument tool, incorporating a spring design, was then developed. With this design, it was possible to transfer torsion forces even when the instrument was at an angular position. Furthermore, adequate expansion of both height and contact area was still possible in this angular position. Using titanium alloy as the designated choice of manufacture material, ANSYS Workbench 14.5, estimated that some areas of version 4 design would not be able to provide enough structural strength against the axial force load from the spine, even at the L5-S1 level. After that, a prototype based on the design 4 specifications was produced and tested using a simulated phantom. The testing conducted on the simulated lumbar phantom demonstrated that the newly developed instrument was able to successfully fulfill the requirements of the original intended purpose of use with easy navigation to the desired spine level around the pelvis and successful placement and expansion of the expandable cage. Conclusion. The newly designed surgical instrument appears to fulfill its original intention in performing a Lumbar discectomy with fusion through the exploration of an alternative approach to the traditional XLIF. To the best of our knowledge, this is the first instrument of its kind and we believe it has great potential for future implications.
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