Blake G M, Griffith J F, Yeung D K W, Leung P C, Fogelman I
Osteoporosis Scanning and Research Unit, King's College London School of Medicine, London, UK.
Bone. 2009 Mar;44(3):495-501. doi: 10.1016/j.bone.2008.11.003. Epub 2008 Nov 19.
Quantitative examination of iliac crest bone biopsies shows that as subjects become older bone and functional marrow are replaced by adipose tissue. Studies of vertebral marrow fat using nuclear magnetic resonance spectroscopy ((1)H-MRS) show that subjects with lower spine T-scores have significantly higher marrow fat content. These findings suggest that the ability of DXA scans to determine fracture risk may be partly explained by the effect of increased marrow fat on BMD. However, a proper evaluation of the relationship between WHO spine T-score status and marrow fat content requires that the BMD data are first corrected for the bias caused by a selection effect in which subjects with higher marrow fat are more likely to be identified as having osteoporosis. In this study we have therefore reanalysed previously published data for 185 elderly Hong Kong Chinese subjects (103 women, mean age 73 y; 82 men, mean age 73 y) who had spine DXA scans and (1)H-MRS measurements of L3 marrow fat. The effect of varying marrow fat on BMD was modelled using vertebral body thicknesses measured in 50 men and women. Spine T-scores in each individual were adjusted for the measured marrow fat. Subjects were assigned to WHO categories based on their corrected T-scores, and the relationship between marrow fat and T-score status evaluated using regression analysis and analysis of variance. The average change in percent marrow fat per T-score unit was used to infer the fraction of the spine BMD fracture discrimination explained by marrow composition. The mean (SD) of the L1-L4 vertebral body thickness was 30.2 (2.1) mm for Hong Kong women and 33.4 (2.5) mm for men. A change in marrow fat content from 0 to 100% was estimated to produce a BMD decrease of 0.14 g/cm(2) (1.3 T-score units) in women and 0.16 g/cm(2) (1.3 T-score units) in men. Although adjusting spine BMD for marrow fat reduced the significance of the correlation, there was still a trend for marrow fat to increase with decreasing T-score with a slope of -1.2+/-0.7% per T-score unit (p=0.078) for women and -1.4+/-0.6% per T-score unit (p=0.023) for men. When the effect of marrow composition on fracture discrimination was evaluated the results showed that the higher vertebral marrow fat content found in osteoporotic subjects made a negligible contribution to the ability of spine BMD measurements to predict fracture risk.
对髂嵴骨活检的定量检查表明，随着受试者年龄增长，骨组织和功能性骨髓会被脂肪组织取代。使用核磁共振波谱法（¹H-MRS）对椎体骨髓脂肪进行的研究显示，脊柱T值较低的受试者骨髓脂肪含量显著更高。这些发现表明，双能X线吸收法（DXA）扫描确定骨折风险的能力，可能部分是由于骨髓脂肪增加对骨密度（BMD）的影响所致。然而，要正确评估世界卫生组织（WHO）脊柱T值状况与骨髓脂肪含量之间的关系，首先需要对BMD数据进行校正，以消除因选择效应导致的偏差，即骨髓脂肪含量较高的受试者更有可能被认定为患有骨质疏松症。因此，在本研究中，我们重新分析了之前发表的185名香港老年华人受试者（103名女性，平均年龄73岁；82名男性，平均年龄73岁）的数据，这些受试者均接受了脊柱DXA扫描以及L3骨髓脂肪的¹H-MRS测量。使用在50名男性和女性中测量的椎体厚度，对不同骨髓脂肪对BMD的影响进行建模。对每个个体的脊柱T值进行校正，以考虑测量到的骨髓脂肪。根据校正后的T值将受试者分为WHO类别，并使用回归分析和方差分析评估骨髓脂肪与T值状况之间的关系。每个T值单位骨髓脂肪百分比的平均变化，用于推断骨髓成分对脊柱BMD骨折判别能力的解释比例。香港女性L1-L4椎体厚度的平均值（标准差）为30.2（2.1）mm，男性为33.4（2.5）mm。估计骨髓脂肪含量从0%增加到100%，会使女性的BMD降低0.14 g/cm²（1.3个T值单位），男性降低0.16 g/cm²（1.3个T值单位）。尽管对脊柱BMD进行骨髓脂肪校正降低了相关性的显著性，但骨髓脂肪仍有随T值降低而增加的趋势，女性为每T值单位-1.2±0.7%（p=0.078），男性为每T值单位-1.4±0.6%（p=0.023）。在评估骨髓成分对骨折判别能力的影响时，结果显示，骨质疏松症受试者中较高的椎体骨髓脂肪含量，对脊柱BMD测量预测骨折风险的能力贡献可忽略不计。
