Macdonald Heather, Kontulainen Saija, Petit Moira, Janssen Patricia, McKay Heather
School of Human Kinetics, University of British Columbia, Vancouver, Canada.
Bone. 2006 Sep;39(3):598-608. doi: 10.1016/j.bone.2006.02.057. Epub 2006 Apr 4.
Higher fracture rates in women than men may be related to a sex difference in bone strength that is thought to emerge during growth. However, sexual dimorphism in bone strength and the determinants of bone strength in boys and girls are not well understood. Thus, our objectives were to (1) compare tibial bone strength and its components (geometry and density) between pre- and early pubertal boys and girls and (2) identify the contribution of muscle cross-sectional area and other modulating factors to bone outcomes. We used pQCT to assess the distal tibia (8%) and tibial midshaft (50%) in 424 Asian and Caucasian pre- and early pubertal boys and girls. Our primary outcomes were bone strength index (BSI, mg2/mm(4)) at the distal tibia and strength strain index (SSI, mm3) at the midshaft. We also assessed components of bone strength including bone geometry [total (ToA) and cortical (CoA) cross-sectional areas, mm2] and total (ToD, mg/cm3) and cortical (CoD, mg/cm3) density. We used ANCOVA to compare bone outcomes between boys and girls in each maturity group (PRE or EARLY pubertal by Tanner stage) and multiple regression to evaluate the contribution of muscle cross-sectional area (MCSA, mm2 by pQCT), maturity, ethnicity, physical activity, dietary calcium, and vertical jump height to bone outcomes. After adjusting for tibial length and MCSA, bone strength indices were 6-15% (P < 0.05) greater in PRE and EARLY boys compared with PRE and EARLY girls. The sex difference in bone strength was due largely to greater bone areas (4-6%) in boys. At the distal tibia ToD was significantly greater in PRE boys (6%, P < 0.001) compared with PRE girls and at the midshaft CoD was slightly greater in both PRE and EARLY girls (1%, P = 0.01). After adjusting for tibial length, MCSA was the primary explanatory variable of tibial bone geometry and strength in both sexes accounting for 10-16% of the variance. The influence of maturity, ethnicity, physical activity, and dietary calcium on pQCT bone outcomes was small and was both site- and sex-specific. Sexual dimorphism in tibial bone strength is evident in prepuberty. Our results are consistent with a functional model of bone development in which bone adapts its geometry and strength to withstand challenges from muscle forces during growth.
女性骨折率高于男性，这可能与生长过程中出现的骨强度性别差异有关。然而，骨强度的性别二态性以及男孩和女孩骨强度的决定因素尚未得到充分了解。因此，我们的目标是：（1）比较青春期前和青春期早期男孩与女孩的胫骨骨强度及其组成部分（几何形状和密度）；（2）确定肌肉横截面积和其他调节因素对骨结果的影响。我们使用外周定量计算机断层扫描（pQCT）评估了424名亚洲和高加索青春期前及青春期早期男孩和女孩的胫骨远端（8%）和胫骨骨干中部（50%）。我们的主要结果是胫骨远端的骨强度指数（BSI，mg2/mm(4)）和骨干中部的强度应变指数（SSI，mm3）。我们还评估了骨强度的组成部分，包括骨几何形状[总（ToA）和皮质（CoA）横截面积，mm2]以及总（ToD，mg/cm3）和皮质（CoD，mg/cm3）密度。我们使用协方差分析（ANCOVA）比较每个成熟组（根据坦纳分期为青春期前或青春期早期）中男孩和女孩的骨结果，并使用多元回归评估肌肉横截面积（MCSA，通过pQCT测量，mm2）、成熟度、种族、身体活动、饮食钙摄入量和垂直跳跃高度对骨结果的影响。在调整胫骨长度和MCSA后，青春期前和青春期早期男孩的骨强度指数比青春期前和青春期早期女孩高6 - 15%（P < 0.05）。骨强度的性别差异主要是由于男孩的骨面积更大（4 - 6%）。在胫骨远端，青春期前男孩的ToD显著高于青春期前女孩（6%，P < 0.001），在骨干中部，青春期前和青春期早期女孩的CoD均略高（1%，P = 0.01）。在调整胫骨长度后，MCSA是两性胫骨骨几何形状和强度的主要解释变量，占方差的10 - 16%。成熟度、种族、身体活动和饮食钙对pQCT骨结果的影响较小，且具有部位和性别特异性。胫骨骨强度的性别二态性在青春期前就很明显。我们的结果与骨发育的功能模型一致，即骨在生长过程中调整其几何形状和强度以承受肌肉力量的挑战。
