適用於早發性脊椎側彎自我調適生長桿之風險性評估與預防

A Risk Analysis and Prevention of a Self-Adaptive Growing Rod System for Early Onset Scoliosis

林敬婷(Ching-Ting Lin)

指導教授 ： 王兆麟

國立臺灣大學/工學院/醫學工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201601968

摘要

簡介：早發性脊椎側彎(Early Onset Scoliosis)為10歲以下之孩童被診斷出其脊椎異常側向彎曲。若病症嚴重，將造成孩童胸廓變形，進而限制心臟與肺臟的發育，若無適當的治療將會使得患有早發性脊椎側彎的孩童心肺功能不佳，嚴重時甚至會導致死亡。針對早發性脊椎側彎的治療方法，有保守治療以及侵入式手術治療。若是保守治療無法有效的控制側彎角度，或是側彎角度大於50度，經過醫師評估，將會進行侵入式的手術，在脊椎上植入生長桿以矯正側彎。生長桿為一非融合式脊椎植入物，目的是為了要在矯正孩童側彎角度的同時，保有脊椎生長的能力。目前臨床使用的生長桿系統分為外力控制系統：給予側彎的脊椎一撐開的力量來達到矯正與延長脊椎的功能，但需重複性的延長手術與調整；與生長導引系統：其固定器的架構單純導引脊椎生長方向，未給予外力使其延長，或提供脊椎支撐力。兩系統各有其優缺，因此本研究將以新的概念開發一自我調適生長桿系統以解決現有生長桿的困境。

目的：針對一適用於早發性脊椎側彎自我調適生長桿系統進行風險性評估，設計一款新型自我調適生長桿以改良與預防其風險，並以動物實驗驗證之。

材料與方法：新型自我調適生長桿主要功能包含一、提供早發性脊椎側彎病患良好的脊椎矯正效果；二、避免重複的延長手術；三、風險預防與體外解離。自我調適生長桿由生長桿套筒本體、上蓋、彈簧、複合一內部磁鐵之棘爪與棘齒條所組成。生長桿套筒本體限制棘齒條只能進行一維軸向的運動，利用彈簧、棘爪、棘齒的機構特性讓生長桿能隨著脊椎生長的力量，僅能往單一方向一齒一齒的延長。棘爪與複合之內部磁鐵，可以在受到外部磁鐵吸引時，向上抵抗彈簧所給的壓力，使棘爪脫離棘齒，讓棘齒條在軸向可以自由運動。新型自我調適生長桿依所需功能設計完成後，先以有限元素軟體分析其機構強度，再加工製造出原型後進行體外及體內測試。體外測試包含拉伸測試及解離測試。下一步進行體內測試，將生長桿系統植入豬隻體內，追蹤觀察12週，並以X光影像量測生長桿延長量、脊椎生長量與Cobb Angle，以驗證其安全性及可行性。

結果：經拉伸與解離測試後，本次動物實驗將規格為拉伸力量9.2N、可解離最大距離6.5mm之自我調適生長桿植入實驗豬隻體內。比較術後一週、術後六週與術後十二週脊椎生長之狀況，單位椎節高度植入生長桿間活動節L1至L3的單位椎節高度平均增加了4.7mm，而未受生長桿拘束的T12與L6之單位椎節高度平均增加6.95mm。豬隻犧牲後將生長桿取出分析，生長桿系統僅右側尾端連接器的螺帽鬆動，無其他桿件斷裂情形。生物組織部分，左側生長桿套筒周圍組織健康，右側生長桿套筒側面發現部分組織呈現黃色纖維狀，兩側生長桿套筒開口皆有黑色金屬粒子。功能性部分，左側可距離6mm解離，右側生長桿則失效。打開生長桿套筒發現右側套筒因密封性不佳，內部磁鐵生鏽，導致無法解離，推測這也是造成外部組織泛黃的原因。

結論：本研究將新型自我調適生長桿植入實驗豬隻體內，經過十二週後並無造成傷亡。在追蹤期間，生長桿可依脊椎生長而延長、並無桿件損壞、其一生長桿可由體外解離，成功驗證其生物相容性、機械強度與磁控解離之可行性。此外，實驗發現目前的生長桿系統在密封性、有效工作長度比、以及維持脊椎矢狀面曲度上仍須進一步改良，可做為下一代生長桿改進的方向。

關鍵字

早發性脊椎側彎 ； 生長桿 ； 脊椎植入物 ； 非融合式固定器 ； 動物實驗

並列摘要

Background. Early onset scoliosis (EOS) is defined as a spinal deformity that occurs before 10 years of age. Severe EOS may be associated with an increased risk of death due to heart and lung disease. Treatments for EOS can be either conservative or invasive. Surgery with a growing rod system is generally recommended if conservative treatment fails to keep the scoliosis from progressing, or if the Cobb angle is more than 50 degrees. The growing rod system is a non-fusion spinal instrument that aims to correct the abnormal spinal curve without adversely affecting future growth. Clinically, growing rod systems can be divided into two systems: the forced growing rod system and the growth guidance system. The forced growing rod system provides a distraction force to maintain spinal posture, but requires periodical adjustment in order to realign and lengthen the rods as the child grows. The growth guidance system utilizes a gliding mechanism to guide the growing direction of the spine; however, due to the less restrictive nature of the implantation, these devices may not be able to provide sufficient spinal stability. Given the shortcomings and the disadvantages of the currently available growing rod systems, this study attempted to develop a novel self-adaptive growing rod system.

Purpose. The aim of the current study is to modify and validate the self-adaptive growing rod system in order to prevent the potential risks.

Material and Method. The design concept of the novel self-adaptive growing rod includes correcting the spinal curve, avoiding revision surgery, and preventing the potential risks. The self-adaptive growing rod consists of a connector which allows free axial expansion of the rods. The connector is comprised of springs, a ratchet, and a pawl compound with a magnet. The mechanism releases the pawl from the ratchet with the outer magnet when the growing rod is over lengthened. Finite element method was used to analyze strength and safety factors; the growing rod system was then manufactured with biocompatible materials. After obtaining the ethical approval from the Institutional Animal Care and Use Committee, the self-adaptive growing rod system was implanted into a swine by an experienced orthopedic surgeon. The swine was observed over 12 weeks in order to validate the treatment efficacy and clinical applicability of the system. In-vivo expansion of the growing rods system was determined by using x-rays taken 1, 6, and 12 weeks after the implantation to allow for comparative analysis of the elongation of the rods against the change in vertebral unit height. Further assessment of the functional integrity of the device was then conducted after the retrieval of the device post-sacrifice.

Result. The self-adaptive growing rod system, which was designed with a pullout force of 9.2 Newton, and a maximum releasing distance of 6.5 mm, was used in this animal study. The swine survived the 12 week observation period without complications. Comparing spinal growth of 1, 6, and 12 weeks after the implantation, the average vertebral unit height was increased by 4.7 mm in the implanted level and 6.95 mm in the adjacent level. Retrieval of the growing rod system revealed that the connective crosslink was slightly loosened; the integrity of the device was satisfactory without signs of implant failure. Observable metal particles were found on the opening edge of the growing rod connector. In terms of the releasing function, one of the growing rod connectors lost its efficacy due to a rusted magnet caused by inadequate water sealing, and the rusty magnet caused surrounding tissue turned to yellow. The other connector remained functional.

Conclusion. The current study demonstrated the successful implantation of a novel self-adaptive growing rod system in swine without significant lesions or complications within 12 weeks. The self-adaptive growing rod lengthened along with the natural growth of the spinal column. No rod failure was observed. Post-sacrifice, one of the connectors remained functional and could still be released from the ratchet. This study validated the system’s biocompatibility and mechanical strength, and it proved the feasibility of the magnetic release mechanism. It is acknowledged that the device in its current design may not meet the requirements of medical device regulation. Based on the results from this study, improvements can be made in future designs, particularly regarding water sealing, working length ratio, and sagittal plane alignment of the spine.

並列關鍵字

Early Onset Scoliosis (EOS) ； growing rod ； spinal implant ； non-fusion instrumentation ； in-vivo test

參考文獻

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