*Orthopaedic and Developmental Biomechanics Laboratory, Department of Mechanical Engineering; Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA.
Integr Comp Biol. 2009 Jul;49(1):59-68. doi: 10.1093/icb/icp024. Epub 2009 May 15.
The mechanical properties of a healing bone fracture depend not only on the geometry of the fracture callus but also on the material properties of the callus tissues. Despite the biomechanical importance of callus tissues in restoring mechanical integrity to the injured bone, little is known about the material properties of these tissues and whether these properties can be estimated non-invasively. This study used nanoindentation to quantify the spatial variations in indentation modulus throughout the fracture callus and correlated the measurements of modulus with measurements of tissue mineral density (TMD) obtained from images from micro-computed tomography (µCT). Fracture calluses were harvested from rats 24 days following creation of a full-thickness, transverse osteotomy in the femoral mid-diaphysis. Calluses were imaged using µCT, and the average TMD and the median grayvalue (X-ray attenuation) of five, pre-defined volumes of interest (VOIs) in each callus were computed. Nanoindentation was then performed at multiple, regularly spaced locations across 150 µm-thick, sagittal sections of the calluses. The indentation modulus ranged from 0.51 to 1680 MPa throughout the callus, with the highest moduli in the center of the fracture gap and the lowest in the periphery of the gap (P < 0.05). TMD was also highest in the center of the gap (P < 0.05). An increasing trend in both modulus and TMD was observed in the regions of the callus adjacent to the periosteal surfaces of the cortex. While no correlation was found between the average indentation modulus in a given VOI and the median grayvalue of that VOI, the average indentation modulus and the average TMD were positively correlated (R = 0.70, P < 0.05). Together, these findings establish the spatial heterogeneity in the mechanical behavior of tissues in fracture calluses and indicate that the indentation modulus of these tissues can be estimated by non-invasive measurements of tissue mineralization.
愈合骨骨折的力学性能不仅取决于骨折痂的几何形状，还取决于痂组织的材料特性。尽管痂组织在恢复受伤骨骼的机械完整性方面具有生物力学重要性，但人们对这些组织的材料特性知之甚少，也不知道这些特性是否可以非侵入性地估计。本研究使用纳米压痕技术来量化整个骨折痂中压痕模量的空间变化，并将测量结果与从微计算机断层扫描 (µCT) 图像获得的组织矿物质密度 (TMD) 测量结果进行相关。在股骨干中横断全层骨切开术后 24 天，从大鼠中收获骨折痂。使用 µCT 对痂进行成像，并计算每个痂中五个预先定义的感兴趣体积 (VOI) 的平均 TMD 和中位数灰度值 (X 射线衰减)。然后，在痂的 150 µm 厚的矢状切片的多个规则间隔位置进行纳米压痕。压痕模量在整个痂中从 0.51 到 1680 MPa 不等，在骨折间隙的中心最高，在间隙的外围最低（P < 0.05）。TMD 也在间隙中心最高（P < 0.05）。在靠近皮质骨外表面的痂的区域中观察到模量和 TMD 均呈增加趋势。虽然在给定 VOI 中的平均压痕模量与该 VOI 的中位数灰度值之间未发现相关性，但平均压痕模量与平均 TMD 呈正相关（R = 0.70，P < 0.05）。这些发现共同确定了骨折痂中组织力学行为的空间异质性，并表明可以通过对组织矿化的非侵入性测量来估计这些组织的压痕模量。
