# Determinants of the Mechanical Behavior of Human Lumbar Vertebrae After Simulated Mild Fracture

 Title: Determinants of the Mechanical Behavior of Human Lumbar Vertebrae After Simulated Mild Fracture Author: Wegrzyn, Julien; Roux, Jean-Paul; Boutroy, Stéphanie; Vilayphiou, Nicolas; Guyen, Olivier; Chapurlat, Roland; Arlot, Monique E.; Delmas, Pierre D.; Bouxsein, Mary Larsen Note: Order does not necessarily reflect citation order of authors. Citation: Wegrzyn, Julien, Jean-Paul Roux, Monique E. Arlot, Stéphanie Boutroy, Nicolas Vilayphiou, Olivier Guyen, Pierre D. Delmas, Roland Chapurlat, and Mary L. Bouxsein. 2011. Determinants of the mechanical behavior of human lumbar vertebrae after simulated mild fracture. Journal of Bone and Mineral Research 26(4): 739-746. Full Text & Related Files: 3179325.pdf (1.023Mb; PDF) Abstract: The ability of a vertebra to carry load after an initial deformation and the determinants of this postfracture load-bearing capacity are critical but poorly understood. This study aimed to determine the mechanical behavior of vertebrae after simulated mild fracture and to identify the determinants of this postfracture behavior. Twenty-one human L3 vertebrae were analyzed for bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) and for microarchitecture by micro–computed tomography ($$\mu CT$$). Mechanical testing was performed in two phases: initial compression of vertebra to 25% deformity, followed, after 30 minutes of relaxation, by a similar test to failure to determine postfracture behavior. We assessed (1) initial and postfracture mechanical parameters, (2) changes in mechanical parameters, (3) postfracture elastic behavior by recovery of vertebral height after relaxation, and (4) postfracture plastic behavior by residual strength and stiffness. Postfracture failure load and stiffness were $$11\% \pm 19\%$$ and $$53\% \pm 18\%$$ lower than initial values (p = .021 and p < .0001, respectively), with 29% to 69% of the variation in the postfracture mechanical behavior explained by the initial values. Both initial and postfracture mechanical behaviors were significantly correlated with bone mass and microarchitecture. Vertebral deformation recovery averaged $$31\% \pm 7\%$$ and was associated with trabecular and cortical thickness (r = 0.47 and r = 0.64; p = .03 and p = .002, respectively). Residual strength and stiffness were independent of bone mass and initial mechanical behavior but were related to trabecular and cortical microarchitecture (|r| = 0.50 to 0.58; p = .02 to .006). In summary, we found marked variation in the postfracture load-bearing capacity following simulated mild vertebral fractures. Bone microarchitecture, but not bone mass, was associated with postfracture mechanical behavior of vertebrae. Published Version: doi:10.1002/jbmr.264 Other Sources: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3179325/pdf/ Terms of Use: This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10121018 Downloads of this work: