Application of a new calibration method for a three-dimensional finite element model of a human lumbar annulus fibrosus.
BACKGROUND
Major deficits of many finite element models of the lumbar spine are the oversimplification, assumed constellation of the material properties or the insufficiently performed calibration using experimental in vitro data. The aim of this study was, to develop a method for calibrating the two-composite structure of the annulus fibrosus, the ground substance and collagen fibers.


METHODS
For that purpose, a three-dimensional, non-linear finite element model of a denucleated intervertebral disc with the adjacent vertebral bodies (L4-L5) was created. Previously performed in vitro experiments provided experimental data for the range of motion in each load direction, needed for calibration. A method was developed to determine the individual contribution of the fibers and the ground substance for bending moments with four different magnitudes (2.5, 5.0, 7.5 and 10 Nm). For each bending moment, the stiffness of fibers was varied to approximate the Young's modulus of the ground substance in order to fulfil the required range of motion obtained from in vitro results within an accuracy of 99%.


RESULTS
Infinite material parameter combinations of collagen fibers and ground substance led to the same range of motion, which were different for each bending moment. However, there was only one combination, which was valid for all applied bending moments; and in all load direction.


CONCLUSIONS
This calibration method was performed on range of motion data; however, the procedure could also be applied to other loading scenarios and measurement parameters like disc bulge, translation and intradiscal pressure.
Schmidt
Hendrik
H
Institute of Orthopaedic Research and Biomechanics, University of Ulm, Germany.
Heuer
Frank
F
Simon
Ulrich
U
Kettler
Annette
A
Rohlmann
Antonius
A
Claes
Lutz
L
Wilke
Hans-Joachim
HJ
D002138:Calibration; D003094:Collagen / Q000378:metabolism*; D019245:Compressive Strength; D003198:Computer Simulation; D004548:Elasticity; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D007403:Intervertebral Disc / Q000503:physiopathology*; D007405:Intervertebral Disc Displacement / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000503:physiopathology*; D008954:Models, Biological; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical
D003094:Collagen