Role of Trabecular Microarchitecture in Whole-Vertebral Body Biomechanical Behavior

Abstract

The role of trabecular microarchitecture in whole-vertebral biomechanical behavior remains unclear, and its influence may be obscured by such factors as overall bone mass, bone geometry, and the presence of the cortical shell. To address this issue, 22 human T 9 vertebral bodies (11 female; 11 male; age range: 53-97 yr, 81.5 ± 9.6 yr) were scanned with mCT and analyzed for measures of trabecular microarchitecture, BMC, cross-sectional area, and cortical thickness. Sixteen of the vertebrae were biomechanically tested to measure compressive strength. To estimate vertebral compressive stiffness with and without the cortical shell for all 22 vertebrae, two high-resolution finite element models per specimen-one intact model and one with the shell removed-were created from the mCT scans and virtually compressed. Results indicated that BMC and the structural model index (SMI) were the individual parameters most highly associated with strength (R 2 = 0.57 each). Adding microarchitecture variables to BMC in a stepwise multiple regression model improved this association (R 2 = 0.85). However, the microarchitecture variables in that regression model (degree of anisotropy, bone volume fraction) differed from those when BMC was not included in the model (SMI, mean trabecular thickness), and the association was slightly weaker for the latter (R 2 = 0.76). The finite element results indicated that the physical presence of the cortical shell did not alter the relationships between microarchitecture and vertebral stiffness. We conclude that trabecular microarchitecture is associated with whole-vertebral biomechanical behavior and that the role of microarchitecture is mediated by BMC but not by the cortical shell.

Cross-sectional analysis of the association between fragility fractures and bone microarchitecture in older men: The STRAMBO study

“…Bone strength depends on microarchitecture of cortical and trabecular bone. (12) In women with vertebral fractures, trabecular parameters were impaired in those with normal cortical bone, whereas cortex was thinner in those with normal trabecular bone. (13) Women with vertebral fractures had thinner cortex and poor trabecular connectivity, as assessed by histomorphome-ORIGINAL ARTICLE J JBMR try.…”

Lumbar Vertebral Body Bone Microstructural Scaling in Small to Medium‐Sized Strepsirhines

“…Experimental and computational studies using human vertebrae (Rockoff et al, 1969;McBroom et al, 1985;Yoganandan et al, 1988;Silva et al, 1997;Eswaran et al, 2006) have investigated the relative contributions of these two tissues to lumbar vertebral body strength in axial compression and found that the cortical shell carries up to 45% of compressive loads depending on the region (maximum load at middle third of craniocaudal length), indicating that the role of trabecular bone in vertebral body strength is primary (Silva et al, 1997;Eswaran et al, 2006;Fields et al, 2009). However, the cortical shell's contribution to strength may be greater if the associated trabecular bone is poorly organized (low anisotropy) (Silva et al, 1997) or if bending is the primary mode of loading (Fields et al, 2009). Although axial compression is likely to be the major mode of lumbar vertebral body loading across most species (Smit, 2002), bending loads will also occur.…”

“…Although axial compression is likely to be the major mode of lumbar vertebral body loading across most species (Smit, 2002), bending loads will also occur. In humans, it is in this latter condition that the cortical shell's contribution to load bearing (e.g., Fields et al, 2009) may increase. The variety of positional behaviors among strepsirhines and other primates provides an opportunity to better understand the integrated function and mechanics of trabecular and cortical bone in lumbar vertebral bodies.…”

“…In the lumbar vertebral body, adaptations to body mass could lead to several changes, including increased endplate cross-sectional area and/or changes in the trabecular or cortical bone relative volume, micro-architecture, or tissue density. For example, since trabecular bone may carry more of the load in lumbar vertebral body compressive loading, an increase in the vertebral body trabecular bone apparent density or bone volume fraction and the cross-sectional area would increase its compressive strength (Silva et al, 1997;Fields et al, 2009). Evidence indicates that vertebral body cross-sectional area scales isometrically (Shapiro and Simons, 2002) but no data exist regarding the scaling of strepsirhine trabecular bone volume fraction or any other architectural parameters.…”

Whole Bone Mechanics and Bone Quality

“…In human vertebrae, for example, alignment of the trabeculae along the axis of the spine makes the bone nearly twice as strong when loaded along the superior-inferior axis as when loaded in either the AP or left-right direction [45,91]. Combined imaging and computational modeling advances allow cancellous bone architecture to be captured (see articles by Donnelly [35] and Burghardt et al [18] in this issue) and input into mechanics-based models that can be used to understand the effect of architecture on stiffness of whole bones such as the vertebral body, distal radius, or proximal femur [42,57,98,126]. These computational modeling approaches will be essential to identify trabecular failure mechanisms in whole bones [41], especially at clinically important sites.…”