脊椎受軸向矢狀面偏心載荷時之脊骨應變與運動元全局力學反應

Abstract

摘要 設計：使用三種標準材料及豬脊椎運動元為試樣，在相同的衝擊位置之下，分別給予相等的衝擊能量，比較四種試樣的力學反應與椎骨前緣應變場的變化情形，並探討剛性材料與軟性材料的差別。 背景：由於大部分的脊椎傷害，是在過大的動態載荷下發生的，因此我們選擇豬頸椎當作研究對象，意圖模擬人體腰椎運動元在承受不同衝擊載荷時，前端應變場的分佈與其力學行為表現。 目標：觀察脊椎運動元在承受外力衝擊時，瞬間的力學反應，以及椎骨前緣的應變場變化情形。 方法：以13個豬頸椎的二節運動單元（七個C3-5、六個C6-T1）與三個工程材料（鋁、聚乙烯、優力膠）作為試樣，於試樣前緣表面黏貼一個三軸向的應變規，分別施予試樣均佈力與集中力偏心負載，並改變撞擊時的輸入能量與接觸時間，量測試樣的力學行為表現與應變場變化。 結果：當脊椎試樣承受的均佈力負載能量越高，椎骨前緣的主應變越大；當集中力偏心負載作用在試樣的前、後側時，主應變較大；主應變最小值發生在第七個撞擊點。勁度（stiffness）大的試樣（如鋁），其軸向輸出力的大小不隨撞擊位置改變而有所變化，但前後向水平輸出剪力與矢狀面輸出力矩則相反，兩者的方向與靜態時相同；勁度小的試樣（如聚乙烯、優力膠、豬頸椎），軸向反作用力的大小會隨撞擊位置而改變，其前後向水平輸出剪力與矢狀面輸出力矩也是如此，但兩者的方向與靜態時相反。

Abstract Study Design.Three standard materials and porcine cervical two-motion segments are used to investigate the mechanical reaction and strain field response to the same loading condition. The effects of material characteristics on subjects’ mechanical performance are also discussed. Background.Because spinal injuries are frequently resulted by enormous dynamic loading, we intend to simulate the strain distribution of anterior lumbar vertebral bodies and their mechanical behaviors under different impact loading. Objective.To investigate the mechanical behavior of spinal motion segments and distribution of strain field of anterior vertebral bodies while they are subjected to impact loading.

Method.13 porcine cervical two-motion segments were used. C3-5 (n=7) and C6-T1 (n=6) were dissected from them. Three standard cylinders made of AL, PE and PU, respectively, were used as reference samples. All specimens were applied with axial distributive load and point compressive load with different loading energy and contact period. Surface strains were measured with a three-axis strain gauges rosette attached to the anterior wall of the middle vertebral bodies. The mechanical behaviors of all samples were also analyzed. Result.Under distributive loading, the principle strain increases as the loading energy rises. Under point loading, the maximum principle strain occurs when the specimens are loaded at anterior and posterior points, respectively, while the strain is minimal when the specimens are loaded at the 7th point. For the specimens of larger stiffness, the axial resultant force remains constant despite the loading location changes. But the horizontal resultant force and sagittal resultant moment show opposite trend. Their directions are the same as expected. However, for the specimens of smaller stiffness, the axial resultant force, the horizontal resultant force and sagittal moment decline with the change of loading location, while the directions of the last two are different from the theoretical results.