Effect of Fatigue and Rest on the Rheological Properties of Intact Intervertebral Disc

目的：探討疲勞負載次數與休息對椎間盤流變性質的影響。景：疲勞負載是引發下背痛的主要因子之一，並且影響椎間盤水分的含量及黏彈性行為的表現。文獻上指出，長期的疲勞負載會造成椎間盤力學性質改變，推測是椎間盤微結構破壞而改變椎間盤水分進出情形。然而，實際機制仍有待詳盡地探討，因此探討疲勞負載與休息對椎間盤流變性質的影響，有助於了解因疲勞負載所引起的脊椎病變機制。料與方法：使用六個月大的豬隻腰椎運動單元作為試樣(L1-L2，L3-L4，共十副)，每副試樣在疲勞負載前先經過一次潛變測試，於食鹽水中休息24小時後，依序進行「疲勞負載-休息-潛變測試-休息」的實驗流程，五次循環後即完成一組實驗。潛變測試時間為1小時，負載力量為420N；疲勞負載的大小為190至590N (平均為420N)，頻率為5Hz。五次疲勞負載時間依序為0.5、1、2、3、4小時(次數：9,000、18,000、36,000、54,000、72,000次)；休息時，將試樣浸泡於生理食鹽水溶液中24小時。以線性位移計量測計錄試樣於潛變測試中的高度改變，擷取頻率為2Hz，並使用雙相(固液相)線性模型對椎間盤於潛變期間的高度變化量進行聚合模數(HA，類似材料之楊氏係數)、滲透性(k)的擬合。實驗結束後，將椎間盤沿著中央冠狀面及矢狀面切半觀察內部結構改變。果：椎間盤高度在承受0.5小時(9000次)的疲勞負載後所下降的高度並無法藉由浸泡24小時食鹽水溶液完全回復，且隨著疲勞負載時間的增加，無法回復的高度量愈多。椎間盤在承受10.5小時的疲勞負載後，聚合模數並無顯著性的改變，滲透性則會隨著疲勞負載時間增加而明顯地下降，直到疲勞負載時間達到3小時以上才不再降低。實驗後從椎間盤的橫剖面可發現靠近椎間核內側的椎間環有明顯的扭曲變形現象，有些甚致產生斷裂。論：椎間盤因為疲勞負載所流失的水分無法藉由浸泡生理24小時食鹽水的過程中完全回復。隨著疲勞負載時間的增加，椎間盤的滲透性會明顯地下降，聚合模數則無顯著性改變。椎間盤受到10.5小時的疲勞負載後，內側椎間環產生扭曲或斷裂，但外側椎間環並沒有出現肉眼可觀察到的損傷。Objective: To evaluate the effect of the duration of fatigue loading and the rest on the rheological properties of healthy porcine intervertebral disc.ummary of Background Data: Fatigue loading can induce the low back pain by altering the water content and viscoelastic behaviors of the intervertebral disc. Long term fatigue loading was suspected to result in changes of material properties due to the irreversible failure. However, the mechanical properties of disc fluid flow (i.e., the rheology) within the disc have not been fully discussed yet. The understanding of effect of fatigue loading and rest on the disc rheological properties can be beneficial to delineate the mechanism of fatigue loading induced spinal disorders.ethods: Ten porcine lumbar motion segments (L1-L2，L3-L4) without posterior elements were applied with fatigue loading (190~590N) at 5 Hz for 0.5, 1, 2, 3, and 4 hours (9,000, 18,000, 36,000, 54,000, 72,000 cycles), respectively. A creep test using 420 N was applied after a 24 hours saline immersion post fatigue loading. The axial deformation during creep phase was curve-fitted with linear biphasic model to obtain the aggregate modulus (HA) and permeability coefficient (k). After the fatigue loading, the disc was sectioned along sagittal and coronal plane to find the structure changes of anulus fibrosus and nucleus pulposus. The paired-t test was performed to evaluate the change of disc height, HA, and k after a series of fatigue loading and 24 hours rest. esults: The height of intervertebral disc was not recovered by a 24 hours rest after fatigue loading. The permeability decreased significantly with the duration of fatigue loading, while the aggregate modulus remained the same. The ruptured inner fibrosus were found after fatigue loading. onclusion: A 24 hours rest is not able to fully restore the fluid loss during fatigue loading. The increase of duration of the fatigue loading reduces the disc permeability and damages the structure of inner anular fibrosus.論文口試委員審定書 i謝 ii文摘要 iii文摘要 v一章 前言 1-1 脊椎的基本構造 1-2 脊椎盤的基本構造及功能 1-3 椎間盤水分對其生物力學影響之分析 3-4 椎間盤之潛變生物力學測試 5-5 疲勞負載與休息對椎間盤性能影響 6-6 實驗目的與假設 9二章 實驗設備 11-1 連續式衝擊測試平台(Continuous Impact Testing Apparatus) 11-2 衝擊錘(Impactor) 12-3 撞擊承受器(Impounder) 12-4 往復式衝擊模組(Cyclic Loading) 13-5 線性位移計(Linear variable differential transformer) 14-6 一維測力元(1-D Load Cell ) 14-7 訊號量測及控制系統 15三章 材料與方法 18-1 試樣準備 18-2 實驗方法 19-2-1 實驗流程 19-2-2 載荷狀況 21-3 數學模型及統計分析 21四章 結果 24-1 椎間盤高度變化及參數定義 24-2 椎間盤初始高度(H0)與疲勞負載後之高度(H1) 26-3 預壓負載下降高度(hpre) 26-4 瞬時負載下降高度(hins)及瞬時剛性係數(Sins) 27-5 潛變測試下高度下降(hcreep)及其應變(strain) 29-6 聚合模數(Aggregate Modulus, HA)與滲透係數(Permeability, k) 31-7 椎間盤切面觀察 32五章 討論 34-1 椎間盤內含水量之討論 34-2 潛變測試之材料參數討論 35-3 疲勞負載對椎間環破壞 36-4 實驗限制 37六章 結論與未來展望 39-1 結論 39-2 未來展望 39獻參考 4