頸部肌肉功能缺損對頸椎穩定度之影響

Abstract

背景：根據脊椎穩定度的研究，肌肉力量有助於增加脊椎穩定度，但以往的研究缺乏肌肉功能缺損後，肌力調整對脊椎穩定度之影響。 目的：探討頸椎肌肉功能缺損對頸椎穩定度的影響，並觀察特定肌肉功能缺損後，肌力調整的模式與椎體穩定度的關係。 材料與方法：採用8副豬頸椎(C2-T1)做為試樣，以尼龍繩模擬胸鎖乳突肌（Sternocleidomastoid，SCM）、夾肌（Splenius capitis，SPL），與半棘肌（Semispinalis capitis，SSC）等三組肌肉走向，並在末端架設砝碼以模擬肌肉力量。實驗中模擬的肌肉狀況分別為：無肌肉力量、正常肌肉力量、右側SCM肌肉功能缺損。在右側SCM功能缺損的部分，除了模擬周圍肌群無補償行為外，還採用兩種最佳化條件對周圍肌群進行肌力調整，分別為「能量消耗最小值」，以及「椎間盤受力最小值」。以實驗室自製的穩定度測試機台對各種肌肉條件之試樣施予0~2Nm的外部負載，觀察頸椎活動度的變化。量測參數包含活動度(ROM)、中性區(NZ)、初始位置變化量(δIP)，以及C7-T1節椎間盤所受軸向力(Fz)。 結果：相較於正常肌肉力量，在肌肉功能缺損的狀況下，若周邊肌肉力量未調整，試樣會有較大的初始位置變化量(4.1±1.2°)。而當周邊肌肉力量調整後，試樣的初始位置變化量與正常肌肉力量相比，並無顯著性差異，但試樣的活動度與中性區有顯著性的增加。此外，若僅比較兩種調整機制對頸椎力學性質的影響，頸椎在能量消耗最小的調整機制下，有較小的活動度與中性區(ROM：14.6±1.7°、NZ：4.7±1.1°)，但椎間盤所受力較大(42.9±0.7N)。 結論：肌肉功能缺損時，周圍肌群肌力的調整有助於椎體姿勢的恢復，但穩定度的恢復卻有限。此外，對於兩種調整機制而言，雖然能量消耗最小的調整機制雖會對椎間盤造成較大的軸向力，但卻較能提供椎體的穩定度。

Background. Spinal stability is thought to increase by muscle forces. However, the relationship between spinal stability and muscle dysfunction with respect to different compensatory strategies are unknown. Object. To investigate the stability of the cervical spine with an damaged muscle, specifically to evaluate the compensation provided by the surrounding muscles. Methods. Eight porcine cervical spines (C2-T1) were acquired. Neck muscles pairs were simulated by cables attached to the specimen, including： sternocleidomastoid (SCM), semispinalis captis (SSC), and splenius captis (SPL). A fixed weight was suspended at the end of each cable to simulate the muscle force. Each group was tested ： normal muscle forces, zero muscle force, and right side SCM dysfunction with three compensation strategies minimization of the summation of the squared 1) muscle forces, 2) axial forces, 3) no compensation. The normal muscle force group served as the control condition. The samples were tested in flexion/extension using pure moments (0~2Nm), without axial preload. In the present study, the parameters measured include the range of motion (ROM), neutral zone (NZ), deviation of initial position (δIP), and axial load (Fz) at the C7-T1 disc.

Result. The maximum δIP, from the normal muscle force condition, was the group with right side SCM dysfunction without compensation. Compensation of the right side SCM dysfunction by surrounding muscles did not significantly increase δIP, when compared to the normal condition. Compared to the normal condition, the ROM and NZ was significantly increased for the right side SCM dysfunction group compensated either by minimizing muscle force or by minimizing axial forces. The ROM and NZ in the compensation strategy which minimized muscle forces was smaller than the strategy which minimized axial forces. Fz in the compensation strategy which minimized muscle forces was larger than the compensation strategy which minimized axial force. Conclusion. The compensation strategy which minimized the muscle forces provided better spinal stability than the strategy using minimized axial forces. In conclusion, the muscles surrounding an impaired muscle were unable to stabilize the cervical spine, when compared to the normal muscle condition.