Zebaze Roger M D, Jones Anthony, Welsh Findlay, Knackstedt Mark, Seeman Ego
Austin Hospital, University of Melbourne, Heidelberg 3084, Melbourne, Australia.
Bone. 2005 Aug;37(2):243-52. doi: 10.1016/j.bone.2005.03.019.
The femoral neck (FN) is a cantilever with external and internal dimensions determining its size, shape, the spatial distribution of the mineralized cortical and trabecular bone tissue mass, and its strength. Geometric indices of FN strength are often derived using FN dimensions estimated in vivo from dual X-ray absorptiometry (DXA) assuming that the FN cross section approximates a circle or a square. As DXA does not measure FN depth, we examined whether circular, square, or elliptical models of FN cross sections predict FN depth, and so its external volume, shape, volumetric bone mineral density (vBMD), and geometric indices of strength. We studied paired FN specimens from 13 Caucasian female cadavers (mean age 69 years, range 29 to 85) using DXA, micro-computed tomography (mu-CT), and direct calliper measurements. DXA accurately measured FN width (supero-inferior diameter) but models assuming a circular and a square cross section overestimated FN depth (antero-posterior diameter) and volume, and so underestimated vBMD by 15.0 +/- 5.8% (circular cross section) and by 33.2 +/- 4.6% (square cross section) (both P < 0.05). As depth was less than the width, an elliptical model with a constant depth/width ratio of 0.75 reduced the accuracy error in vBMD to 14.0 +/- 8.5% (P = 0.10). However, as FN width increased, FN depth increased relatively less. An elliptical model using a quadratic equation to mimic this changing in shape with increasing size reduced the error in vBMD to 4.4 +/- 7.7% (NS). Circular cross-section models overestimated section modulus at the mid-FN by about 51%. The elliptical models reduced the error two- to three fold. Images from micro-CT scanning show that the FN cross-sectional shape resembles an ellipse with the long axis and the maximum moment of inertia (I(max)) oriented in the supero-inferior direction, and the cortical mass concentrated inferiorly. The larger the cross section, the more elliptical the shape, and the greater the I(max) supero-inferiorly, while I(min) (in the antero-posterior direction) remains relatively constant. The shape, spatial distribution of bone, and moments of inertia are likely to be adaptations to bending moments during bipedalism. Assuming the FN cross section approximates a circle or square produces errors in FN depth, volume, vBMD, and geometric indices of bone strength. Studies are needed to determine the effects of age, sex, and race on FN size and shape in health and disease.
股骨颈（FN）是一个悬臂结构，其外部和内部尺寸决定了它的大小、形状、矿化皮质骨和小梁骨组织质量的空间分布以及强度。FN强度的几何指标通常是根据双能X线吸收法（DXA）在体内估计的FN尺寸得出的，假设FN横截面近似于圆形或方形。由于DXA无法测量FN的深度，我们研究了圆形、方形或椭圆形的FN横截面模型是否能预测FN深度，进而预测其外部体积、形状、体积骨密度（vBMD）和强度几何指标。我们使用DXA、微计算机断层扫描（mu-CT）和直接卡尺测量法，对13具白种女性尸体（平均年龄69岁，范围29至85岁）的成对FN标本进行了研究。DXA准确测量了FN宽度（上下径），但假设为圆形和方形横截面的模型高估了FN深度（前后径）和体积，因此vBMD分别低估了15.0±5.8%（圆形横截面）和33.2±4.6%（方形横截面）（两者P<0.05）。由于深度小于宽度，深度/宽度比恒定为0.75的椭圆形模型将vBMD的准确性误差降低至14.0±8.5%（P = 0.10）。然而，随着FN宽度增加，FN深度增加相对较少。使用二次方程来模拟这种随尺寸增加而形状变化的椭圆形模型将vBMD的误差降低至4.4±7.7%（无显著差异）。圆形横截面模型将FN中部的截面模量高估了约51%。椭圆形模型将误差降低了两到三倍。微CT扫描图像显示，FN横截面形状类似于椭圆形，长轴和最大惯性矩（I(max)）沿上下方向，皮质质量集中在下方。横截面越大，形状越椭圆，上下方向的I(max)越大，而前后方向的I(min)保持相对恒定。骨的形状、空间分布和惯性矩可能是两足行走过程中对弯矩的适应性表现。假设FN横截面近似于圆形或方形会在FN深度、体积、vBMD和骨强度几何指标上产生误差。需要开展研究以确定年龄、性别和种族对健康和疾病状态下FN大小和形状的影响。
