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首页> 外文期刊>Spine >A comparison of fatigue failure responses of old versus middle-aged lumbar motion segments in simulated flexed lifting.
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A comparison of fatigue failure responses of old versus middle-aged lumbar motion segments in simulated flexed lifting.

机译：模拟屈曲抬起中老年和中年腰椎运动段的疲劳失效响应比较。

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STUDY DESIGN: Survival analysis techniques were used to compare the fatigue failure responses of elderly motion segments to a middle-aged sample. OBJECTIVES: To compare fatigue life of a middle-aged sample of lumbosacral motion segments to a previously tested elderly cohort. An additional objective was to evaluate the influence of bone mineral content on cycles to failure. SUMMARY OF BACKGROUND DATA: A previous investigation evaluated fatigue failure responses of 36 elderly lumbosacral motion segments (average age, 81 +/- 8 years) subjected to spinal loads estimated when lifting a 9-kg load in 3 torso flexion angles (0 degrees, 22.5 degrees, and 45 degrees). Results demonstrated rapid fatigue failure with increased torso flexion; however, a key limitation of this study was the old age of the specimens. METHODS: Each lumbosacral spine was dissected into 3 motion segments (L1-L2, L3-L4, and L5-S1). Motion segments within each spine were randomly assigned to a spinal loading condition corresponding to lifting 9 kg in 3 torso flexion angles (0 degrees, 22.5 degrees, or 45 degrees). Motion segments were statically loaded and allowed to creep for 15 minutes, then cyclically loaded at 0.33 Hz. Fatigue life was taken as the number of cycles to failure (10 mm displacement after creep loading). RESULTS: Compared with the older sample of spines, the middle-aged sample exhibited increased fatigue life (cycles to failure) in all the torso flexion conditions. Increased fatigue life of the middle-aged specimens was associated with the increased bone mineral content (BMC) in younger motion segments (mean +/- SD, 30.7 +/- 11.1 g per motion segment vs. 27.8 +/- 9.4 g). Increasing bone mineral content had a protective influence with each additional gram increasing survival times by approximately 12%. CONCLUSION: Younger motion segments survive considerably longer when exposed to similar spine loading conditions that simulate repetitive lifting in neutral and flexed torso postures, primarily associated with the increased bone mineral content possessed by younger motion segments. Cycles to failure of young specimens at 22.5 degrees flexion were similar to that of older specimens at 0 degrees flexion, and survivorship of young specimens at 45 degrees flexion was similar to the older cohort at 22.5 degrees.
机译：研究设计：生存分析技术用于比较老年人运动节段对中年样本的疲劳失效响应。目的：比较腰s运动节段的中年样本与先前测试的老年队列的疲劳寿命。另一个目标是评估骨矿物质含量对衰竭周期的影响。背景资料摘要：先前的一项研究评估了36个老年腰s运动节段（平均年龄，81 +/- 8岁）在承受3个躯干屈曲角度（0度， 22.5度和45度）。结果显示快速疲劳衰竭，躯干屈曲增加;但是，这项研究的关键局限性在于标本的年龄。方法：将每个腰s部脊椎解剖成3个运动段（L1-L2，L3-L4和L5-S1）。将每个脊柱内的运动段随机分配给脊柱负荷条件，该条件对应于在3个躯干屈曲角度（0度，22.5度或45度）下举9公斤。对运动段进行静态加载并使其蠕变15分钟，然后以0.33 Hz的频率进行周期性加载。疲劳寿命取为失效的循环数（蠕变载荷后位移10 mm）。结果：与较老的脊柱样本相比，中年样本在所有躯干屈曲情况下均表现出更长的疲劳寿命（衰竭循环）。中年样本的疲劳寿命增加与年轻运动节段中骨矿物质含量（BMC）的增加有关（平均+/- SD，每个运动节段30.7 +/- 11.1 g，而27.8 +/- 9.4 g）。增加骨矿物质含量具有保护作用，每增加一克，生存时间就会增加约12％。结论：年轻的运动节段在相似的脊柱负荷条件下（在中性和弯曲的躯干姿势下反复举起）的存活时间更长，这主要与年轻的运动节段所具有的骨矿物质含量增加有关。弯曲22.5度的年轻标本的失效周期与弯曲0度的旧标本相似，而弯曲45度的年轻标本的存活率与22.5度的旧样本相似。

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