Lang Thomas F, Leblanc Adrian D, Evans Harlan J, Lu Ying
Department of Radiology, University of California, San Francisco, CA 94143-0946, USA.
J Bone Miner Res. 2006 Aug;21(8):1224-30. doi: 10.1359/jbmr.060509.
We studied the effect of re-exposure to Earth's gravity on the proximal femoral BMD and structure of astronauts 1 year after missions lasting 4-6 months. We observed that the readaptation of the proximal femur to Earth's gravity entailed an increase in bone size and an incomplete recovery of volumetric BMD.
Bone loss is a well-known result of skeletal unloading in long-duration spaceflight, with the most severe losses occurring in the proximal femur. However, there is little information about the recovery of bone loss after mission completion and no information about effect of reloading on the structure of load-bearing bone. To address these questions, we carried out a study of the effect of re-exposure to Earth's gravity on the BMD and structure of the proximal femur 1 year after missions lasting 4-6 months.
In 16 crew members of the International Space Station (ISS) making flights of 4.5-6 months, we used QCT imaging to measure the total, trabecular, and cortical volumetric BMD (vBMD) of the proximal femur. In addition to vBMD, we also quantified BMC, bone volume, femoral neck cross-sectional area (CSA), and femoral neck indices of compressive and bending strength at three time-points: preflight, postflight, and 1 year after mission.
Proximal femoral bone mass was substantially recovered in the year after spaceflight, but measures of vBMD and estimated bone strength showed only partial recovery. The recovery of BMC, in the absence of a comparable increase in vBMD, was explained by increases in bone volume and CSA during the year after spaceflight.
Adaptation of the proximal femur to reloading entailed an increase in bone size and an incomplete recovery of vBMD. The data indicate that recovery of skeletal density after long-duration space missions may exceed 1 year and supports the evidence in the aging literature for periosteal apposition as a compensatory response for bone loss. The extent to which this compensatory effect protects against fracture remains to be seen.
我们研究了在持续4 - 6个月的任务结束1年后，再次暴露于地球重力对宇航员股骨近端骨密度（BMD）和结构的影响。我们观察到，股骨近端重新适应地球重力会导致骨尺寸增加以及体积骨密度的不完全恢复。
骨质流失是长期太空飞行中骨骼卸载的一个众所周知的结果，最严重的骨质流失发生在股骨近端。然而，关于任务完成后骨质流失的恢复情况几乎没有相关信息，并且也没有关于重新加载对承重骨结构影响的信息。为了解决这些问题，我们开展了一项研究，以探究在持续4 - 6个月的任务结束1年后，再次暴露于地球重力对股骨近端骨密度和结构的影响。
在16名执行4.5 - 6个月飞行任务的国际空间站（ISS）机组人员中，我们使用定量计算机断层扫描（QCT）成像技术测量股骨近端的总体积骨密度、小梁体积骨密度和皮质体积骨密度（vBMD）。除了vBMD，我们还在三个时间点对骨矿物质含量（BMC）、骨体积、股骨颈横截面积（CSA）以及股骨颈抗压和抗弯强度指数进行了量化：飞行前、飞行后以及任务结束后1年。
太空飞行后的一年内，股骨近端骨量有显著恢复，但vBMD测量值和估计的骨强度仅显示部分恢复。在vBMD没有相应增加的情况下，BMC的恢复是由于太空飞行后一年内骨体积和CSA的增加。
股骨近端对重新加载的适应导致骨尺寸增加以及vBMD的不完全恢复。数据表明，长期太空任务后骨骼密度的恢复可能超过1年，并且支持衰老文献中关于骨膜附着作为骨质流失补偿反应的证据。这种补偿作用在多大程度上能预防骨折仍有待观察。
