Zebaze Roger M D, Jones Anthony, Knackstedt Mark, Maalouf Ghassan, Seeman Ego
Departments of Medicine and Endocrinology, Austin Health, University of Melbourne, Melbourne, Australia.
J Bone Miner Res. 2007 Jul;22(7):1055-61. doi: 10.1359/jbmr.070329.
Study of the design of the FN in vivo in 697 women and in vitro in 200 cross-sections of different sizes and shapes along each of 13 FN specimens revealed that strength in old age was largely achieved during growth by differences in the distribution rather than the amount of bone material in a given FN cross-section from individual to individual.
We studied the design of the femoral neck (FN) to gain insight into the structural basis of FN strength in adulthood and FN fragility in old age.
Studies in vivo were performed using densitometry in 697 women and in vitro using high-resolution microCT and direct measurements in 13 pairs of postmortem specimens.
The contradictory needs of strength for loading yet lightness for mobility were met by varying FN size, shape, spatial distribution, and proportions of its trabecular and cortical bone in a cross-section, not its mass. Wider and narrower FNs were constructed with similar amounts of bone material. Wider FNs were relatively lighter: a 1 SD higher FN volume had a 0.67 (95% CI, 0.61-0.72) SD lower volumetric BMD (vBMD). A 1 SD increment in height was achieved by increasing FN volume by 0.32 (95% CI, 0.25-0.39) SD with only 0.15 (95% CI, 0.08-0.22) SD more bone, so taller individuals had a relatively lighter FN (vBMD was 0.13 [95% CI, 0.05-0.20 SD] SD lower). Greater periosteal apposition constructing a wider FN was offset by even greater endocortical resorption so that the same net amount of bone was distributed as a thinner cortex further from the neutral axis, increasing resistance to bending and lowering vBMD. This was recapitulated at each point along the FN; varying absolute and relative degrees of periosteal apposition and endocortical resorption focally used the same amount of material to fashion an elliptical FN of mainly cortical bone near the femoral shaft to offset bending but a more circular FN of proportionally more trabecular and less cortical bone to accommodate compressive loads adjacent to the pelvis. This structural heterogeneity was largely achieved by adaptive modeling and remodeling during growth-most of the variance in FN volume, BMC, and vBMD was growth related.
Altering structural design while minimizing mass achieves FN strength and lightness. Bone fragility may be the result of failure to adapt bone's architecture to loading, not just low bone mass.
对697名女性的股骨颈进行体内研究，并对13个股骨颈标本中不同大小和形状的200个横截面进行体外研究，结果显示，老年时的强度在很大程度上是在生长过程中通过分布差异而非个体股骨颈横截面中骨材料的数量差异实现的。
我们研究了股骨颈（FN）的设计，以深入了解成年期股骨颈强度和老年期股骨颈脆性的结构基础。
对697名女性进行体内骨密度测量研究，并对13对尸检标本进行体外高分辨率显微CT和直接测量。
通过改变股骨颈的大小、形状、空间分布及其横截面中骨小梁和皮质骨的比例（而非质量），满足了承重时对强度和移动时对轻盈的相互矛盾的需求。宽度不同的股骨颈所含骨材料量相似。较宽的股骨颈相对较轻：股骨颈体积每增加1个标准差，体积骨密度（vBMD）降低0.67（95%可信区间，0.61 - 0.72）个标准差。股骨颈高度每增加1个标准差，股骨颈体积需增加0.32（95%可信区间，0.25 - 0.39）个标准差，而骨量仅增加0.15（95%可信区间，0.08 - 0.22）个标准差，因此较高个体的股骨颈相对较轻（vBMD降低0.13 [95%可信区间，0.05 - 0.20个标准差]个标准差）。构建较宽股骨颈时更大的骨膜附着被更大的皮质内吸收所抵消，以至于相同的骨净量分布在离中性轴更远的较薄皮质中，增加了抗弯能力并降低了vBMD。在股骨颈的每个点都有类似情况；沿股骨颈不同程度的绝对和相对骨膜附着及皮质内吸收，局部使用相同量的材料塑造出靠近股骨干主要为皮质骨的椭圆形股骨颈以抵消弯曲，但塑造出比例上更多骨小梁和更少皮质骨的更圆形股骨颈以适应骨盆附近的压缩载荷。这种结构异质性在很大程度上是在生长过程中通过适应性塑形和重塑实现的——股骨颈体积、骨矿含量和vBMD的大部分变异与生长有关。
在最小化质量的同时改变结构设计可实现股骨颈的强度和轻盈。骨脆性可能是未能使骨结构适应载荷的结果，而不仅仅是骨量低的结果。
