Laws Cory J, Berg-Johansen Britta, Hargens Alan R, Lotz Jeffrey C
University of California, Box 0514, 513 Parnassus Avenue, Medical Sciences Bldg., San Francisco, CA, 94143-0514, USA.
UCSD Medical Center, University of California, 350 Dickinson St., Suite 121, Mail Code 8894, San Diego, CA, 92103-8894, USA.
Eur Spine J. 2016 Sep;25(9):2889-97. doi: 10.1007/s00586-015-4221-6. Epub 2015 Sep 24.
Disc herniation risk is quadrupled following spaceflight. This study tested the hypothesis that swelling-induced disc height increases (comparable to those reported in spaceflight) stiffen the spine and elevate annular strain and nuclear pressure during forward bending.
Eight human lumbar motion segments were secured to custom-designed testing jigs and subjected to baseline flexion and compression and pure moment flexibility tests. Discs were then free-swelled in saline to varying supraphysiologic heights consistent with prolonged weightlessness and re-tested to assess biomechanical changes.
Swelling-induced disc height changes correlated positively with intradiscal pressure (p < 0.01) and stiffening in flexion (p < 0.01), and negatively with flexion range of motion (p < 0.05). Swelling-induced increases in disc height also led to increased annular surface strain under combined flexion with compression. Disc wedge angle decreased with swelling (p < 0.05); this loss of wedge angle correlated with decreased flexion range of motion (R (2) = 0.94, p < 0.0001) and decreased stiffness fold change in extension (p < 0.05).
Swelling-induced increases in disc height decrease flexibility and increase annular strain and nuclear pressure during forward bending. These changes, in combination with the measured loss of lordotic curvature with disc swelling, may contribute toward increased herniation risk. This is consistent with clinical observations of increased disc herniation rates after microgravity exposure and may provide the basis for future countermeasure development.
太空飞行后椎间盘突出风险增加四倍。本研究检验了以下假设：肿胀引起的椎间盘高度增加（与太空飞行中报告的情况相当）会使脊柱变硬，并在前屈时提高纤维环应变和髓核压力。
将八个人类腰椎运动节段固定在定制设计的测试夹具上，进行基线屈曲、压缩和纯弯矩柔韧性测试。然后将椎间盘在盐水中自由膨胀至与长期失重相一致的不同超生理高度，并重新测试以评估生物力学变化。
肿胀引起的椎间盘高度变化与椎间盘内压力呈正相关（p < 0.01），与屈曲时的僵硬程度呈正相关（p < 0.01），与屈曲运动范围呈负相关（p < 0.05）。肿胀引起的椎间盘高度增加还导致在屈曲与压缩联合作用下纤维环表面应变增加。椎间盘楔角随肿胀而减小（p < 0.05）；这种楔角的丧失与屈曲运动范围减小相关（R (2) = 0.94，p < 0.0001），与伸展时刚度倍数变化减小相关（p < 0.05）。
肿胀引起的椎间盘高度增加会降低柔韧性，并在前屈时增加纤维环应变和髓核压力。这些变化，再加上测量到的椎间盘肿胀时前凸曲率的丧失，可能会增加椎间盘突出风险。这与微重力暴露后椎间盘突出率增加的临床观察结果一致，并可能为未来对策的开发提供依据。
