適用於前側路腰椎融合術之可變形椎間籠設計與功能性分析

Abstract

背景介紹：腰椎融合術是脊柱外科常見且能有效治療腰椎疾病的方法，前側路腰椎融合術在臨床上為一效果良好且新穎的手術路徑。此路徑從身體前側方進入，為閃避人體之肌肉、血管、骨盆等結構，椎間籠擺放方向常無法平行於身體冠狀面，導致椎間籠於椎體間相對不穩定。為破除前側路腰椎融合術之限制，同時因應微創手術需求，針對前側路腰椎融合手術開發一款新型微創手術器械有其必要性。 研究目的：本研究針對前側路手術路徑設計一新型可變形椎間籠與植入器械，其同時具備水平、垂直擴張以及植入後轉向之功能。 材料與方法：新型可變形椎間籠透過鎖緊驅動軸與對側零件，來將圍繞於外側之耦桿及滑塊向外推擠，達到水平、垂直擴張的效果；透過將驅動軸連接於側邊耦桿上，使椎間籠在擴張的同時達到轉向目的。本研究對新型椎間籠進行運動學分析、動力學分析、以及臨床應用分析以驗證椎間籠之功能。在運動學分析上，透過計算椎間籠垂直擴張量隨手工具轉動角度的變化，可得知手工具轉動角度與椎間籠實際擴張高度之對應關係。在動力學分析上進行椎間籠垂直擴張力測試，找到使用者施予手工具之扭矩與椎間籠最終擴張力大小之關係。在臨床應用上，透過模擬臨床手術流程，將椎間籠植入六節人體腰椎屍骨試樣，並於過程中對試樣拍攝X光輔助量測脊椎前凸角度、椎間盤高度、椎間籠轉向角度以及椎間籠寬度，用以驗證其擴張、轉向等功能，同時確保椎間籠在過程中能與手術器械順利進行解離或重組。 結果：在分析椎間籠垂直方向運動狀態後可推估：傳動軸每轉動一圈，椎間籠將擴張0.18 mm之高度。椎間籠垂直擴張力測試中，平均最大擴張力為131 (23) N，平均施予之扭矩為0.64 (0.11) N·m。進行人體屍骨試樣功能性驗證的六節椎間盤試樣當中，有三節成功完成椎間籠的植入及部分擴張，三節椎間盤在進行椎間盤切除後無法置入椎間籠。成功植入椎間籠的試樣，其椎間籠在進行擴張的同時能達到轉向的效果，使椎間籠往平行椎體冠狀面的方向逆時針旋轉，而椎間籠的擴張也增加了椎間盤高度。 討論：椎間籠動力學分析結果提供手工具之刻度設計一可靠的換算依據。而椎間籠將驅動扭矩轉換為垂直擴張力的轉換效率甚高，一般人能在手部產生的扭矩極限內給定椎間籠足夠扭矩，以提供椎間籠抵抗兩相鄰椎體向其擠壓的軸向力並進行擴張。新型椎間籠植入椎間盤位置後能達到水平、垂直擴張及椎間籠轉向之功能，符合臨床需求。然而與市售椎間籠相比，本研究之新型椎間籠尺寸偏大，導致椎間籠無法植入部分試樣，至於機構設計之微調，如：增加驅動零件之厚度、降低椎間籠高度等，皆可做為椎間籠未來的改良方向。 關鍵字：可變形椎間籠、前側路腰椎融合手術、微創手術、薦椎

Background Oblique lumbar interbody fusion (OLIF) is an innovative selection of surgery path for clinical surgeons. The benefit of OLIF surgery is its surgery trajectory which avoids vital organs such as veins, nerves and pelvis. However, this procedure remains a challenge; the implantation direction is not parallel to the frontal line of spinal column, the flawed alignment of the implant may make the disc cage unstable. In order to overcome this restrictions, developing a minimally invasive surgical device with better maneuver function for OLIF surgery is in need. Objective The objective of this study is to develop a surgical device for OLIF surgery. The new device features the function of expansion and the ability of controlling the implant direction after implantation. Method The new disc cage consisted of eight linkages which made the cage expand vertically, a slider which made the cage expand vertically, and a cage head connected with driving nut. In order to control the direction of the cage, the driving system was connected to the linkage on the side instead of the cage head in the middle line. A kinematics test was conducted to describe the vertical expansion of the cage with respect to the angle change of the auxiliary instrument. A kinetics test was conducted to describe the cage’s vertical expansion force with respect to the screw driver’s driving torque given by the user. Through in vitro testing, the disc cage was implanted into the cadaver by following the OLIF surgery procedure. The lordotic angle, disc height, cage vector, and cage width were measured through radiography images of the specimens to verify the cage’s function. Result The height of the cage increased 0.18 mm for each turn of the screw driver. For the expansion force test, the mean maximum expansion force was 131 (23) N at a mean torque of 0.64 (0.11) Nm. For the in vitro test, three specimens successfully finished the cage implantation and expanded partially; while the other three specimens failed to finish the cage implantation. In the case of the successfully implantation, the cage rotated counterclockwise to approach the direction parallel to the coronal plane of the vertebral body, reaching the objective of controlling the cage direction. Conclusion The kinematics analysis offers a reliable basis to the scale design of the auxiliary instrument which displays the cage expansion during the operation in real time. The conversion efficiency between input torque and output vertical expansion force is good. Under the limitation of hand’s motion and kinematics, people can afford an enough torque, which will be effectively converted to the cage expansion force to withstand the compressive load from the adjacent vertebral body. However, the driving shaft, one component of the cage, cannot afford the input torque due to the thickness of the hexagon socket head, resulting in the expansion failure. The new disc cage reaches the criterion of vertical expansion, horizontal expansion, and controlling direction. However, the size of disc cage is slightly larger than the commercial disc cage. The larger dimension gives the reason why some specimens failed to implant the new disc cage in this study. Based on the result of this study, improvement can be made in future designs, particularly regarding cage vertical dimension and driving shaft thickness. Keywords: Expandable cage, OLIF, Minimally invasive surgery