Lotz J C, Cheal E J, Hayes W C
Department of Orthopedic Surgery, Beth Israel Hospital, Boston, Massachusetts, USA.
Osteoporos Int. 1995;5(4):252-61. doi: 10.1007/BF01774015.
The rates of fracture at sites with different relative amounts of cortical and trabecular bone (hip, spine, distal radius) have been used to make inferences about the pathomechanics of bone loss and the existence of type I and type II osteoporosis. However, fracture risk is directly related to the ratio of tissue stress to tissue strength, which in turn is dependent not only on tissue composition but also tissue geometry and the direction and magnitude of loading. These three elements determine how the load is distributed within the tissue. As a result, assumptions on the relative structural importance of cortical and trabecular bone, and how these tissues are affected by bone loss, can be inaccurate if based on regional tissue composition and bone density alone. To investigate the structural significance of cortical and trabecular bone in the proximal femur, and how it is affected by bone loss, we determined the stress distributions in a normal and osteoporotic femur resulting from loadings representing: (1) gait; and (2) a fall to the side with impact onto the greater trochanter. A three-dimensional finite element model was generated based on a representative femur selected from a large database of femoral geometries. Stresses were analyzed throughout the femoral neck and intertrochanteric regions. We found that the percentage of total load supported by cortical and trabecular bone was approximately constant for all load cases but differed depending on location. Cortical bone carried 30% of the load at the subcapital region, 50% at the mid-neck, 96% at the base of the neck and 80% at the intertrochanteric region. These values differ from the widely held assumption that cortical bone carries 75% of the load in the femoral neck and 50% of the load at the intertrochanteric region. During gait, the principal stresses were concentrated within the primary compressive system of trabeculae and in the cortical bone of the intertrochanteric region. In contrast, during a fall, the trabecular stresses were concentrated within the primary tensile system of trabeculae with a peak magnitude 4.3 times that present during gait. While the distribution of stress for the osteoporotic femur was similar to the normal, the magnitude of peak stress was increased by between 33% and 45%. These data call into question several assumptions which serve as the basis for theories on the pathomechanics of osteoporosis. In addition, we expect that the insight provided by this analysis will result in the improved development and interpretation of non-invasive techniques for the quantification of in vivo hip fracture risk.
具有不同皮质骨和小梁骨相对含量的部位（髋部、脊柱、桡骨远端）的骨折发生率已被用于推断骨质流失的病理力学以及I型和II型骨质疏松症的存在。然而，骨折风险直接与组织应力与组织强度的比值相关，而这又不仅取决于组织组成，还取决于组织几何形状以及负荷的方向和大小。这三个因素决定了负荷在组织内的分布方式。因此，如果仅基于区域组织组成和骨密度，关于皮质骨和小梁骨相对结构重要性以及这些组织如何受骨质流失影响的假设可能不准确。为了研究近端股骨中皮质骨和小梁骨的结构意义以及它如何受骨质流失影响，我们确定了正常和骨质疏松股骨在代表以下两种负荷情况下产生的应力分布：(1) 步态；(2) 向一侧跌倒并撞击大转子。基于从大量股骨几何形状数据库中选取的代表性股骨生成了三维有限元模型。对整个股骨颈和转子间区域的应力进行了分析。我们发现，对于所有负荷情况，皮质骨和小梁骨所承受的总负荷百分比大致恒定，但因位置而异。皮质骨在股骨头下区域承受30%的负荷，在股骨颈中部承受50%，在股骨颈基部承受96%，在转子间区域承受80%。这些值与广泛持有的假设不同，即皮质骨在股骨颈承受75%的负荷，在转子间区域承受50%的负荷。在步态期间，主应力集中在小梁的主要压缩系统内以及转子间区域的皮质骨中。相比之下，在跌倒期间，小梁应力集中在小梁的主要拉伸系统内，峰值大小是步态期间的4.3倍。虽然骨质疏松股骨的应力分布与正常情况相似，但峰值应力大小增加了33%至45%。这些数据对作为骨质疏松症病理力学理论基础的几个假设提出了质疑。此外，我们预计该分析提供的见解将导致用于定量体内髋部骨折风险的非侵入性技术的改进开发和解释。
