title: Trabecular bone modulus-density relationships depend on anatomic site.
abstract: One outstanding issue regarding the relationship between elastic modulus and density for trabecular bone is whether the relationship depends on anatomic site. To address this, on-axis elastic moduli and apparent densities were measured for 142 specimens of human trabecular bone from the vertebra (n=61), proximal tibia (n=31), femoral greater trochanter (n=23), and femoral neck (n=27). Specimens were obtained from 61 cadavers (mean+/-SD age=67+/-15 years). Experimental protocols were used that minimized end-artifact errors and controlled for specimen orientation. Tissue moduli were computed for a subset of 18 specimens using high-resolution linear finite element analyses and also using two previously developed theoretical relationships (Bone 25 (1999) 481; J. Elasticity 53 (1999) 125). Resultant power law regressions between modulus and density did depend on anatomic site, as determined via an analysis of covariance. The inter-site differences were among the leading coefficients (p<0.02), but not the exponents (p>0.08), which ranged 1.49-2.18. At a given density, specimens from the tibia had higher moduli than those from the vertebra (p=0.01) and femoral neck (p=0.002); those from the trochanter had higher moduli than the vertebra (p=0.02). These differences could be as large as almost 50%, and errors in predicted values of modulus increased by up to 65% when site-dependence was ignored. These results indicate that there is no universal modulus-density relationship for on-axis loading. Tissue moduli computed using methods that account for inter-site architectural variations did not differ across site (p>0.15), suggesting that the site-specificity in apparent modulus-density relationships may be attributed to differences in architecture.
authors.affiliation: Orthopaedic Biomechanics Laboratory, Department of Mechanical Engineering, University of California, 6175 Etcheverry Hall, Berkeley, CA 94720-1740, USA.
authors.forename: Elise F
authors.initials: EF
authors.lastname: Morgan
authors.forename: Harun H
authors.initials: HH
authors.lastname: Bayraktar
authors.forename: Tony M
authors.initials: TM
authors.lastname: Keaveny
mesh_terms: D000368:Aged; D016880:Anisotropy; D015519:Bone Density / Q000502:physiology*; D001842:Bone and Bones / Q000033:anatomy & histology* / Q000502:physiology*; D002102:Cadaver; D003198:Computer Simulation; D004548:Elasticity; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000502:physiology; D005272:Femur Neck / Q000033:anatomy & histology / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D008159:Lumbar Vertebrae / Q000033:anatomy & histology / Q000502:physiology; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D013904:Thoracic Vertebrae / Q000033:anatomy & histology / Q000502:physiology; D013977:Tibia / Q000033:anatomy & histology / Q000502:physiology