適用於脊椎壓迫性骨折椎體撐開器之開發

Abstract

人類到達一定年齡後，骨密度的下降被視為老化正常現象，骨質密度低於正常年輕女性平均兩個標準差以下，則被判患有骨質疏鬆症。當骨密度下降、骨骼間的孔隙變大，導致骨頭變得脆弱易斷，骨折的風險也隨之增加。在因骨質疏鬆造成的骨折中，接近一半比例發生在脊椎骨；當骨折發生於脊柱的前側即稱為壓迫性骨折。儘管壓迫性骨折不一定伴隨著骨頭斷裂，但椎體變形易造成脊柱曲度改變，甚至壓迫到神經引起下背痛。目前常見的壓迫性骨折治療方式可分為保守性及手術治療，保守性治療通常採取藥物搭配背架或物理治療等方式，但此方法僅對症狀輕微的患者有效，症狀嚴重者仍須採用手術治療。 主要手術治療方式為椎體成形術與椎體後凸成形術。椎體成形術是將骨水泥注入骨折處以增強支撐力，但此種作法僅能增加脊椎穩定性，無法恢復失去的高度；椎體後凸成形術則是先植入一氣球，將氣球擴張撐開椎體後再抽除，並將骨水泥注入空腔中，但氣球的方向較難控制且此方法仍存在骨水泥溢流的風險，因此市面上開始出現先植入具有擴張功能的撐開器，將椎體撐開後直接以骨水泥固定，並在術後將植入物留在椎骨中的治療方式。 目前市面上已有許多治療壓迫性骨折相關的植入物產品，其中效果反應最好的為SpineJack®千斤頂，但因其只具有垂直方向的擴張功能，且價格昂貴病患通常只植入一個植入物，使椎體撐開的效果受限，因此本研究期望可以設計出一同時具有水平及垂直擴張功能的椎體撐開器，以改良目前市面產品的問題。 本研究選用鈦合金作為植入物材料，透過軟體進行設計及有線元素分析法模擬撐開形狀，並依據模擬結果重複修改設計，將設計優化後再進行實品打樣及測試。目前研究的設計可分為八種版本，並成功打樣出其中五種版本，進行擴張測試。 在模擬結果中，版本2-2及版本3具有對稱的擴張形狀和良好的擴張幅度；但在進行實體樣品測試時卻無法達到相同效果，甚至發生在測試時樣品尚未觀察到撐開現象即直接斷裂的情況。推測原因為設計結構過強、加工誤差及實驗方法不妥，未來將嘗試更換加工方式及藉由調整桿件厚度和初始傾斜角度以降低設計結構的強度。

Osteoporosis is a bone disease which leads the bones to become porous and brittle. It is defined by the bone mineral density being two standard deviations below the average of young adults. After humans reach certain age, bone loss becomes a normal phenomenon. However, following the problem of population ageing, osteoporosis has become a common problem. Due to osteoporosis, the bones become fragile and easily damaged. Among the fractures caused by osteoporosis, almost half of them occurs in the vertebrae, and the vertebral compression fracture is the most common one. Vertebral compression fracture may change the spine curvature and leads to chronic pain and limited mobility. The treatments of compression fracture can be divided into conservative treatment and surgical treatment. The conservative one is only adequate for patients with mild symptoms. Surgical treatment is needed in severe situations. In vertebroplasty, bone cement is injected to the vertebral body to increase the stabilization, but this treatment cannot recover the reduced height. In kyphoplasty, a balloon is placed and inflated in the vertebral body to restore the height and create a void. After the balloon being removed, bone cement is injected into the void. Although the height can be restored in this method, the position of balloon is hard to control and the risk of bone cement leakage still exists. Consequently, expandable intravertebral implants have been developed to replace the function of balloon. The implants are left in the vertebral body after surgery to provide better effect on height restoration. There have been several products on the market. However, most of the products are expensive and cannot provide enough supporting area. As a result, this study aims to develop an expandable vertebral implant with the function of both horizontal and vertical expansion. Titanium alloy is used as the material for the implant in this study. The implants was designed with drafting software, and deformation was simulated by finite element analysis method. After going through several times of modulation, implant samples were manufactured. Eight versions of implants have been developed in this study, and five of them were manufactured. Deformation was imposed on the samples with surgical instrument, mechanical testing machine, or self-made system. Among the eight versions, version 2-2 and 3 showed great potential in the result of FEA results. Nevertheless, the testing results of the samples were not as fine as expected. This could be referring to the manufacturing errors, testing method, and the over-designed structure. The modulation of the design of the implant is needed lower the structure stiffness, and different manufacturing method should be considered in the future.