以腰椎椎弓固定系統作為剛性支架之不同薦椎骨折的有限元素分析

Finite Element Analysis of Different Sacral Fractures Base on Rigid Supporter of Lumbar Pedicle Fixation System

黃金福(Jin-Fu Huang)

指導教授 ： 劉保興

義守大學/醫學科技學院/生物醫學工程學系/碩士(2022年)

摘要

隨著成像技術的進步，因高能量創傷或骨質疏鬆所導致的薦骨骨折越來越容易被診斷出來。骶髂骨釘是最常見的治療方式但是因為固定效果不佳，復位後的骨頭容易發生再次錯位的情況。然而為了有更良好的固定效果，後來就研究出三角固定和S2-翼-髂骨釘，但是目前臨床上常用的固定方式都無法提供骨折範圍較大的類型足夠的穩定度。所以為了讓大範圍骨折類型有較佳的穩定度，本研究嘗試將腰椎椎弓固定系統向下延伸到薦骨，使得腰椎椎弓固定系統中的金屬桿，可以做為薦骨骨釘的支撐點並且將該新型固定方式應用於薦骨骨折手術中。但是此固定方式的生物力學影響仍未清楚所以使用五種不同的薦骨骨折模型進行有限元素分析，以便了解不同骨釘數量、不同骨折癒合程度、有無橫桿等分析參數搭配四種運動後的影響。本研究透過逆向工程獲得腰薦髖骨三維影像模型後，匯入Geomagic Essential重建軟體中進行皮質骨與海綿骨的表面修飾及沿著椎體結構來設定表面曲線分布，再使用電腦輔助設計軟體將腰薦髖骨模型與椎弓固定器械組配起來後，根據下列五個分析參數，(一)五種骨折類型；(二)三種骨釘數量；(三)椎弓固定系統中無橫桿和有橫桿；(四)三種骨折癒合程度；(五)四種不同的運動，來進行有限元素分析。
分析完的結果表示，在屈曲運動中五種薦椎骨折的應力數值比其他運動大。四種運動中S1的應力分布會隨著運動方向改變，屈曲運動分布正面比較多、伸展運動背面應力分布比較多、側向彎曲運動應力分布偏右邊、軸向旋轉運動應力分布偏左邊。骨釘數量越多應力數值就會越小。椎弓固定器械組別中五種骨折的最大應力數值發生在U型骨折，最小應力數值發生在T型骨折。在椎弓固定器械中加入橫桿會使薦椎應力值下降，但是要在S12應力數值才會下降比較多。骨折癒合程度越好應力值就越大，應力分布範圍越大且骨折線會逐漸消失。在後期固定階段時五種薦骨骨折的應力值會大於正常薦骨的應力值。
屈曲運動對五種薦骨骨折類型薦骨上的應力數值和分布影響最大。使用越多的骨釘來固定，整體的穩定度會越佳且也較不易造成骨釘晃動，但是若想要有較好的腰薦活動度，又不想固定效果變差，可以只在S1與S2打入薦骨骨釘並使用橫桿將左右兩側的骨釘連接在一起來增強穩定度。若是因為高能量創傷導致骨折的年輕病患，建議骨折完全癒合後將固定器械移除，避免應力遮蔽發生對釘孔周圍的骨質造成不良的影響。

關鍵字

薦骨骨折 ； 生物力學 ； 腰椎椎弓固定系統 ； 有限元素分析

並列摘要

With advances in imaging technology, sacral fractures due to high-energy trauma or osteoporosis are more and more easily diagnosed. Sacroiliac screw is the most common treatment selection, but poor fixation is caused after surgery and the sacrum reduction is easily dislocation again. However, triangular fixation and S2-ala-iliac screws were developed in order to have a better fixation effect, but the current fixations cannot provide sufficient stability in types of large fractures. Therefore, in order to provide better stability for a wide range of fracture types, this study attempts to extend the lumbar pedicle fixation system down to the sacrum, so that the rod in the lumbar pedicle fixation system can be used as a connected supporter for locating the sacral screws and apply this innovation fixation in sacral fracture surgery. However, the biomechanical effect of this fracture fixation is still unclear, hence, this study selected five different sacral fractures to perform biomechanical evaluation of finite element analysis to understand fixation effects of numbers of screws, different degrees of bone healing, and usage of cross-link. In this study, the 3D solid model of the lumbar vertebra, sacrum, hip was obtained through reverse engineering. The scanning file was transferred into Geomagic Essential software to modify the surface, reconstructed cortical and spongy bone, and set the surface curve distribution along the vertebral structure. The lumbosacral part was obtained, and then the hip and the lumbar pedicle fixation system are further assembled according to surgery protocol. The five parameters of this finite element analysis included five types of fractures, three numbers of bone screws, usage of cross-link, three degrees of bone healing, and four spinal movements.
The results showed that the max von Mises stresses for the five sacral fractures were greater in flexion than in the other movements. In the four spinal motions, the stress distribution of S1 will change with the motion direction. The location of the maximum von Mises stress in flexion is significant in the anterior region, in extension is significant in the posterior region, in lateral bending is significant in the right side, and in axial rotational is significant in the left side. The increase numbers of fixation screws were significantly decreased in the stress value. The maximum stress values of the five fractures in the pedicle fixation device group occurred in U-typed fractures, and the smallest stress values occurred in T-typed fractures. Adding a cross-link to the lumbar pedicle fixation device will reduce the stress value of the sacrum, but the stress value will significantly decrease at the S12. The bone healing is more increase to accompany with the higher stress in the sacrum. The greater stress distribution could induce gradual disappearance of the fracture line. The stress values of the five sacral fractures were bigger than that of the normal sacral bone in the final fixation stage.
The Flexion was detected the greatest effect on the magnitude and distribution of the maximum von Mises stress on the sacrum for the five sacral fracture types. The increase fixed screws could enhance overall stability of the sacral fixation, and reduce bone screws loosening. However, surgeon can only select the S1 and S2 sacral screws insertion and to add the cross-link for connecting the two rods to enhance stability, if patient want to have a better range of motion in the lumbosacral bones and do not want the worse fixation effect. For young patients with fractures caused by high-energy trauma, it is recommended that the lumbar pedicle fixation device should be remove after the fracture fully healing, which avoid adverse effects on the bone surrounding the screw hole due to stress shielding.

並列關鍵字

sacral fracture ； biomechanics ； lumbar pedicle fixation system ； finite element analysis

參考文獻

[1] Kuklo, T. R., Potter, B. K., Ludwig, S. C., Anderson, P. A., Lindsey, R. W., Vaccaro, A. R. (2006). Radiographic measurement techniques for sacral fractures consensus statement of the Spine Trauma Study Group. Spine, 31(9), 1047-1055.

[2] Bydon, M., De la Garza-Ramos, R., Macki, M., Desai, A., Gokaslan, A. K., Bydon, A. (2014). Incidence of sacral fractures and in-hospital postoperative complications in the United States: an analysis of 2002–2011 data. Spine, 39(18), E1103-E1109.

[3] Kannus, P., Palvanen, M., Niemi, S., Parkkari, J., Järvinen, M. (2000). Epidemiology of osteoporotic pelvic fractures in elderly people in Finland: sharp increase in 1970–1997 and alarming projections for the new millennium. Osteoporosis international, 11(5), 443-448.

[4] Bellabarba, C., Stewart, J. D., Ricci, W. M., DiPasquale, T. G., Bolhofner, B. R. (2003). Midline sagittal sacral fractures in anterior—posterior compression pelvic ring injuries. Journal of orthopaedic trauma, 17(1), 32-37.

[5] DonTigny, R. L. (2011). Sacroiliac 101; Form and Function; A biomechanical study. Journal of Prolotherapy, 3(1), 561-567.