BACKGROUND:It is generaly believed that the spine wil be extended, and vertebral muscle atrophy, bone loss of vertebral body, increased height and area of intervertebral disc, changes of composition of intervertebral disc wil occur in the condition of weightlessness. These are likely to be the cause of high incidence of low back pain. OBJECTIVE:To observe changes in lumbar spine bone microstructure analysis of simulated weightlessness on rhesus lumbar spine biomechanics. METHODS:Fourteen young rhesus monkeys were randomly divided into two groups: control group (n=7;free activities in the cage during the experiment), and experimental group (n=7; the use of head-down-10° on a special bed by bundle lying to simulate weightlessness). RESULTS AND CONCLUSION:(1) The results of Micro-CT examination: in the experimental group, structure model index in trabecular bone of increased. Trabecular bone changed from plate-like to the rod-like change. The intersection number of bone tissue in unit length to non-bone tissue declined. The average width of the canal between the trabecular bone increased, suggesting that there have been signs of osteoporosis in the experimental group. (2) Under an optical microscope, in the experimental group, bone hyperplasia line was disordered and irregular. Thick endplate trabecularbone became smal, shalow, and arranged substantialy perpendicular to the direction of trabecular bone and cartilage endplate. The closer the endplate surface, the smaler trabecular bone was. Compared with the control group, these smal trabecular bones were thin and curved. Bone marrow cavity was oval. The degree of the connection between the trabecular bones is poor, reflecting the structural characteristics of significant osteoporosis. (3) It is indicated that weightlessness affected the biomechanical properties of rhesus lumbar motion unit.%背景：一般认为在失重状态下，脊柱会出现异常延长、椎旁肌萎缩、椎体骨量丢失、椎间盘的高度和面积增加以及椎间盘组成成分的改变，这些都可能是导致腰痛发生率高的原因。目的：观察腰椎骨质微结构变化分析模拟失重状态对恒河猴腰椎生物力学的影响。方法：将14只青壮年恒河猴随机分为2组：对照组7只，实验期间在笼内自由活动；实验组7只，采用头低位-10°捆卧于特制的床上模拟失重。结果与结论：①Micro-CT 检查的结果：实验组中骨小梁的结构模型指数数值增加，骨小梁由板状向杆状转变，单位长度内骨组织与非骨组织交点数量下降，骨小梁之间的髓腔平均宽度增加，提示在实验组中出现了骨质疏松的征象；②光学显微镜下可见实验组骨增生线排列紊乱、不规则，终板下粗大的骨小梁浅层变细小、骨小梁的排列方向基本垂直与软骨终板，越接近终板表面，骨小梁愈变得细小，与对照组相比这些细小的小梁骨变细且弯曲，骨髓腔呈椭圆形，小梁骨之间交织连接程度差，体现出明显的骨质疏松的结构特点；③说明失重条件可对恒河猴腰椎运动单元的生物力学性能产生影响。
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