Cement distribution, volume, and compliance in vertebroplasty: some answers from an anatomy-based nonlinear finite element study.
METHODS
The biomechanics of vertebral bodies augmented with real distributions of cement were investigated using nonlinear finite element (FE) analysis.


OBJECTIVE
To compare stiffness, strength, and stress transfer of augmented versus nonaugmented osteoporotic vertebral bodies under compressive loading. Specifically, to examine how cement distribution, volume, and compliance affect these biomechanical variables.


BACKGROUND
Previous FE studies suggested that vertebroplasty might alter vertebral stress transfer, leading to adjacent vertebral failure. However, no FE study so far accounted for real cement distributions and bone damage accumulation.


METHODS
Twelve vertebral bodies scanned with high-resolution pQCT and tested in compression were augmented with various volumes of cements and scanned again. Nonaugmented and augmented pQCT datasets were converted to FE models, with bone properties modeled with an elastic, plastic and damage constitutive law that was previously calibrated for the nonaugmented models. The cement-bone composite was modeled with a rule of mixture. The nonaugmented and augmented FE models were subjected to compression and their stiffness, strength, and stress map calculated for different cement compliances.


RESULTS
Cement distribution dominated the stiffening and strengthening effects of augmentation. Models with cement connecting either the superior or inferior endplate (S/I fillings) were only up to 2 times stiffer than the nonaugmented models with minimal strengthening, whereas those with cement connecting both endplates (S + I fillings) were 1 to 8 times stiffer and 1 to 12 times stronger. Stress increases above and below the cement, which was higher for the S + I cases and was significantly reduced by increasing cement compliance.


CONCLUSIONS
The developed FE approach, which accounts for real cement distributions and bone damage accumulation, provides a refined insight into the mechanics of augmented vertebral bodies. In particular, augmentation with compliant cement bridging both endplates would reduce stress transfer while providing sufficient strengthening.
Chevalier
Yan
Y
Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Vienna, Austria. yan@ilsb.tuwien.ac.at
Pahr
Dieter
D
Charlebois
Mathieu
M
Heini
Paul
P
Schneider
Erich
E
Zysset
Philippe
P
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D019245:Compressive Strength / Q000187:drug effects / Q000502:physiology; D020342:Finite Element Analysis; D006801:Humans; D008159:Lumbar Vertebrae / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D008875:Middle Aged; D017711:Nonlinear Dynamics; D013314:Stress, Mechanical; D054854:Vertebroplasty / Q000379:methods