Wren T A, Yerby S A, Beaupré G S, Carter D R
Rehabilitation Research & Development Center, Veterans Affairs Health Care System, Palo Alto, California, USA.
J Bone Miner Res. 2000 Aug;15(8):1573-8. doi: 10.1359/jbmr.2000.15.8.1573.
Dual-energy X-ray absorptiometry (DXA) of the calcaneus is useful in assessing bone mass and fracture risk at other skeletal sites. However, DXA yields an areal bone mineral density (BMD) that depends on both bone apparent density and bone size, potentially complicating interpretation of the DXA results. Information that is more complete may be obtained from DXA exams by using a volumetric density in addition to BMD in clinical applications. In this paper, we develop a simple methodology for determining a volumetric bone mineral apparent density (BMAD) of the calcaneus. For the whole calcaneus, BMAD = (BMC)/ADXA3/2, where BMC and ADXA are, respectively, the bone mineral content and projected area measured by DXA. We found that ADXA3/2 was proportional to the calcaneus volume with a proportionality constant of 1.82 +/- 0.02 (mean +/- SE). Consequently, consistent with theoretical predictions, BMAD was proportional to the true volumetric apparent density (rho) of the bone according to the relationship rho = 1.82 BMAD. Also consistent with theoretical predictions, we found that BMD varied in proportion to rho V1/3, where V is the bone volume. We propose that the volumetric apparent density, estimated at the calcaneus, provides additional information that may aid in the diagnosis of osteopenia. Areal BMD or BMD2 may allow estimation of the load required to fracture a bone. Fracture risk depends on the loading applied to a bone in relation to the bone's failure load. When DXA is used to assess osteopenia and fracture risk in patients, it may be useful to recognize the separate and combined effects of applied loading, bone apparent density, and bone size.
跟骨的双能X线吸收测定法（DXA）在评估其他骨骼部位的骨量和骨折风险方面很有用。然而，DXA得出的面积骨密度（BMD）取决于骨表观密度和骨大小两者，这可能使DXA结果的解读复杂化。在临床应用中，除了BMD之外，通过使用体积密度，可能会从DXA检查中获得更完整的信息。在本文中，我们开发了一种简单的方法来确定跟骨的体积骨矿物质表观密度（BMAD）。对于整个跟骨，BMAD = （BMC）/ADXA3/2，其中BMC和ADXA分别是通过DXA测量的骨矿物质含量和投影面积。我们发现ADXA3/2与跟骨体积成比例，比例常数为1.82 +/- 0.02（平均值 +/- 标准误差）。因此，与理论预测一致，根据关系rho = 1.82 BMAD，BMAD与骨的真实体积表观密度（rho）成比例。同样与理论预测一致，我们发现BMD与rho V1/3成比例变化，其中V是骨体积。我们提出，在跟骨处估计的体积表观密度提供了可能有助于骨质疏松症诊断的额外信息。面积BMD或BMD2可能允许估计使骨骨折所需的负荷。骨折风险取决于施加于骨的负荷与骨的破坏负荷的关系。当使用DXA评估患者的骨质疏松症和骨折风险时，认识到施加的负荷、骨表观密度和骨大小的单独和联合作用可能是有用的。
