頸椎肌肉力量模擬測試機台之設計

Abstract

摘要 前言. 肌肉組織對於脊椎穩定性有很大的影響。但由於在離體實驗中不易模擬肌肉作用，探討肌肉功能對脊椎穩定度的文獻相對有限。過去的研究亦缺乏討論頸部肌肉對於整節頸椎的影響。因此本研究的目的為：架設一肌肉模擬系統測試平台，並藉此探討頸部肌肉收縮作用對整節頸椎穩定度的影響。在實驗中所量測的參數有頸椎活動度(Range of motion, ROM) 、中性區(Neutral zone, NZ)，以及頸椎的力學行為。 材料與方法. 脊椎肌肉力量模擬測試機台，可測試單節或多節脊椎運動單元。機台可利用滾輪夾具及滑輪系統，對試樣產生不連續的純彎矩負載，以及利用氣壓缸產生拉力負載，以模擬肌肉拉力。實驗部分，我們選用七隻豬的整節頸椎試樣（C2-T1）為試樣，對試樣施予對稱的肌肉拉力，我們模擬的肌肉有胸鎖乳突肌（Sternocleidomastoid）、半棘肌（Semispinalis capitis），以及夾肌（Splenius capitis），給定肌肉力量分別為15N、5N、5N。當脊椎在屈曲姿勢和後仰姿勢下受到0.5Nm、1Nm、2 Nm的純彎矩負載時，我們分二種情況討論：Ⅰ、比較無肌肉拉力和全部肌肉同時作用的差異，以探討全部肌肉一起作用對頸椎穩定度的影響；Ⅱ、探討各別肌肉不作用時對頸椎穩定度的影響。 結果. 在不同肌肉模擬條件下，都會對C7-T1椎間盤產生軸向力，當全部肌肉同時作用產生的軸向力最大，當沒有肌作用產生的軸向力最小，而其餘肌肉作用條件下則介於兩者間。屈曲後仰方向的力矩在全部肌肉同時作用、向後拉的夾肌及半棘肌不作用三種情況下，則會對椎間盤產生屈曲方向的力矩。而當向前拉的胸鎖乳突肌不作用時，會則產生後仰方向的力矩。當我們對試樣施予屈曲方向的彎矩負載，則椎間盤量得力矩會往屈曲方向增加，而施予後仰方向的彎矩負載，則椎間盤量得力矩會往後仰方向增加；但左右方向的力量、左右側邊彎曲方向的力矩及軸向方向旋軸的力矩值不會隨肌肉拉力及純彎矩負載變化而改變。 肌肉拉力及純彎矩負載對整節頸椎試樣的運動分析，中性區、活動度會因為肌肉拉力作用而減少，但對於中性區比例（NZR）沒有明顯變化，而且在各肌肉作用條件下，中性區減少百分比會大於活動度減少百分比。 結論. 我們已初步架構一脊椎肌肉模擬測試機台，能對脊椎試樣所施予外部負載可為純彎矩負載或拉力負載，配合肌肉拉力的模擬，探討不同的外部負載及肌肉拉力作用對脊椎的力學行為，以及脊椎整體的運動分析。在實驗部分，結果發現頸部肌肉作用時，雖然造成C7-T1的椎間盤的軸向力增加，但同時亦對於整節頸椎的穩定度有正面的幫助，顯示肌肉功能的重要性。

Abstract Objective. To investigate the effect of neck muscles on the stability of cervical spines subjected to the external flexion/extension moment by evaluating neutral zone (NZ) and range of motion (ROM) of the cervical spines. Methods. Seven porcine cervical spines (C2-T1) were dissected to serve as specimens. A muscle simulation apparatus was developed to simulate the contraction force of neck muscle pairs, including sternocleidomastoid (SCM), semispinalis captis, and splenius captis. Cables representing the corresponding muscles were connected to the pneumatic cylinders, providing forces of 15N for sternocleidomastoid, and 5N for semispinalis captis and splenius captis, respectively. Neutral zone (NZ) was measured when the specimens returned steady after being slightly disturbed without external moment. Range of motion (ROM) was measured after each specimen was loaded with flexion / extension moment of 0.5Nm, 1Nm, and 2Nm sequentially. In each loading condition, the following cases were investigated: all muscle pairs contracted, only one muscle pair dysfunctioned, and all muscle pairs dysfunctioned. Results. Both of NZ and ROM decreased with the increase in the number of contracting muscle pairs. The proportion of the reduction of NZ was significantly greater that that of ROM. However, the ratio between NZ and ROM didn’t vary significantly among cases. Both NZ and ROM measured in the case that all muscle pairs contracted were significantly smaller than those measured in the case that all muscle pairs dysfunctioned. Difference in NZ wasn’t found between the case in which all muscle pairs contracted and the case in which only one muscle pair dysfunctioned. However, the same comparison for ROM revealed different results. Conclusion. The present study supports that NZ is a better index for spinal stability than ROM since it is more sensitivity to the change in muscle contraction and external loading. The present study also proves that the ventral and dorsal neck muscle pairs significantly contribute to the stability of cervical spine when it is subjected to the external load.