豬腰椎受衝擊載荷時之減震性分析

椎間盤的退化常被認為是脊椎的過度受力所造成的。脊椎在生物力學上最重要的功能之一在於緩衝身體所受到的衝擊能量。臨床上對於椎間盤的退化情形，除了給予藥物上治療外，也會考慮以使用人工椎間盤作置換。然而，在高速動態載荷狀態下，椎間盤分攤載荷能量的實際情況並無法得知，迄今也鮮少文獻探討之。因此本研究的目的在於探討當脊椎受到衝擊時椎間盤對衝擊能量分佈影響以及脊椎的吸收衝擊現象。實驗中以12個新鮮豬腰椎的三節運動元(L1~L4)作為試樣，所有周邊軟組織以及韌帶皆已被移除，而椎間盤以及關節囊等皆須完整保存。四個雙軸向加速規被安置在椎體上。測試是在以自由落體方式提供衝擊能量的儀器下進行的，此測試平台稱為連續試衝擊測試平台(CITA)。透過程式控制系統的觸發，重錘由設定高度降落，而衝擊的能量則由衝擊承受器傳遞到試樣，而試樣的頂部以及底部皆被牢固地固定在測試平台上，且頂部以及底部分別有單軸測力元以及六維測力元記錄試樣在實驗時的受力情形。這次的實驗是以改變三種衝擊能量以及兩種不同接觸時間的緩衝件的參數下進行。試樣在受到衝擊的過程中會量測到向下壓迫的加速度(gd)，隨著卸載的發生會產生向上回彈的加速度(gu)，將這兩種加速度的絕對值加在一起，為整個試樣受到振動時的整體加速度(gt)。從加速度變動的趨勢來看，當脊椎受壓卸載後，向上回彈的加速度大於向下壓縮的加速度，且加速度的量值是隨著能量的增加而增加。再來，則是整個試樣的整體加速度衰減值部分，整體的衰減趨勢是會隨著位置越遠離受衝擊端而有明顯增加。也就是說，越遠離衝擊端的椎間盤，必須要提供越多的吸收衝擊能力來衰減受衝擊時的加速度以維持脊椎的穩定。在脊椎體所量測到的加速度分佈來看，在試樣未受破壞的前提下，椎體在受壓縮時會受到限制，而向上回彈的過程中，在回復原先的變形後，若還有剩餘的動能，則衝擊承受器則會拉著試樣頂部繼續向上運動，造成軟組織的拉扯，而此情況也在實驗完成後可觀察到小面關節囊有因拉扯破壞的情形。這樣的情況也可以在衰減值的趨勢上做觀察，在原先的變形量中，壓縮與回彈時候的衰減值應相同，當試樣在過度拉扯的情況開始進行時，由於軟組織的介入，使得回彈部分的衰減值也隨之受影響而增加。

關鍵字

脊椎生物力學；椎間盤；衝擊載荷；衝擊吸收

並列摘要

The degeneration of intervertebral discs is usually a result of abnormal load on the spine. One of the important biomechanical function of the spine is to absorb the impact energy during daily activities. Clinically, in the case of disc degeneration, besides using drugs, therapists may suggest performing disc prosthesis replacements for severely degenerated discs. However, the real condition of the impact energy shared by discs during high speed loading is still not well understood, and it is discussed in few reports. Therefore, the purpose of this study is to explore how intervertebral discs affect the distribution of impact energy and the shock absorbing phenomenon of the spine during impact loading. Twelve fresh-frozen porcine lumbar three-motion segments (L1~L4) were used in the experiment. All passive elements including muscles and ligaments were removed. However discs, capsules, and intra-capsular structures were preserved intact. Four dual axial accelerometers were mounted on the left lateral side of each L1~L4 vertebral bodies. A “drop-tower type” impact testing apparatus was used for the testing. This testing apparatus is called the “Continuous Impact Testing Apparatus”, CITA. Triggered by a systematic program control system, the impactor drops from the set height, and the energy is transmitted to the specimen through the impounder. The top and bottom part of the specimen were firmly fixed on the CITA. There were uniaxial loadcells and six-dimensional loadcell recording the top and bottom force during impact. The parameters of the experiment were three magnitudes of impact energy and two different contact times. The downward compressing acceleration (gd) is measured on the specimen in the process of being impacted, while an upward rebounding acceleration (gu) with the occurrence of stress-relaxation is produced. When we add both absolute values of gd and gu together, the result is the total acceleration (gt) on which the whole specimen is impacted. Judging by the varying trend of gt, the absolute value of gd in each corresponding point is smaller than that of gu. That is, the upward rebounding acceleration gu is greater than the downward compressing acceleration gd after the spine is compressed and then stress-relaxed. Moreover, the value of gt will increase according to the increase of energy. Then, as to the attenuate value of gt of the whole specimen, the whole attenuating trend is able to increase distinctly when the location is much further from the side of impact. Therefore, in order to maintain the stability of the spine, more shock-absorbing ability must be provided to attenuate the impact energy when the intervertebral disc is much further from the side of impact. From the gt distribution measured on the intervertebral bodies, the range of compression will be limited by the prerequisite that the specimen is not destroyed. In the process of upward rebounding, if energy still remains after recovering from the previous deformation, the impounder will drag the top of the specimen and continue to move upwardly, producing a rending of soft tissue (intervertebral disc, facet joint capsule). Furthermore, we can observe that the facet joint capsule may be destroyed due to rending, after the experiment is completed. This condition can also be verified by observing the trend of attenuate value. In the original deformation, the attenuate value of compressing should be equal to that of rebounding. When the specimen enters a condition of excessive rending, the attenuate value of rebounding is partly increased on account of the intervention of the soft tissue.

並列關鍵字

Spinal Biomechanics ； Intervertebral Disc ； Impact Loading ； Shock Absorption

參考文獻

2.Keith L. Moore, Arthur F. Dalley, Clinical oriented Anatomy, Fourth Edition, 1999

3.Margareta Nordin, Victor H. Frankel, Basic Biomechanics of the Musculoskeletal System, Third edition; 2001

4.A.Voloshin, L. Wosk. An in vivo study of low back pain and shock absorption in the human locomotor system, Journal of Biomechanics 1982; 15(1), pp 21-27

5.A.D. Holmes and D.W.L. Hukins, Analysis of load-relaxation in compressed segments of lumbar spine. Medical Engineer &Physics 1996；18(2) : pp 99-104

7.Mark D. Brown, Measurement of Cadaver Lumbar Spine Motion Segment Stiffness, Spine 2002 ; 27(9): pp 918-922

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豬腰椎受衝擊載荷時之減震性分析

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