Determination of trunk muscle forces for flexion and extension by using a validated finite element model of the lumbar spine and measured in vivo data

Charité Universitätsmedizin Berlin, Berlín, Berlin, Germany
Journal of Biomechanics (Impact Factor: 2.75). 02/2006; 39(6):981-9. DOI: 10.1016/j.jbiomech.2005.02.019
Source: PubMed


Muscle forces stabilize the spine and have a great influence on spinal loads. But little is known about their magnitude. In a former in vitro experiment, a good agreement with intradiscal pressure and fixator loads measured in vivo could be achieved for standing and extension of the lumbar spine. However, for flexion the agreement between in vitro and in vivo measurements was insufficient. In order to improve the determination of trunk muscle forces, a three-dimensional nonlinear finite element model of the lumbar spine with an internal fixation device was created and the same loads were applied as in a previous in vitro experiment. An extensive adaptation process of the model was performed for flexion and extension angles up to 20 degrees and -15 degrees, respectively. With this validated computer model intra-abdominal pressure, preload in the fixators, and a combination of hip- and lumbar flexion angle were varied until a good agreement between analytical and in vivo results was reached for both, intradiscal pressure and bending moments in the fixators. Finally, the fixators were removed and the muscle forces for the intact lumbar spine calculated. A good agreement with the in vivo results could only be achieved at a combination of hip- and lumbar flexion. For the intact spine, forces of 170, 100 and 600 N are predicted in the m. erector spinae for standing, 5 degrees extension and 30 degrees flexion, respectively. The force in the m. rectus abdominus for these body positions is less than 25 N. For more than 10 degrees extension the m. erector spinae is unloaded. The finite element method together with in vivo data allows the estimation of trunk muscle forces for different upper body positions in the sagittal plane. In our patients, flexion of the upper body was most likely a combination of hip- and lumbar spine bending.

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    • "A validated FE model of the intact lumbosacral spine L1-S1 with all major ligaments was employed (Fig. 1). The model and its validation for intervertebral rotations and p intr using published in vitro data [9] [10] [11] have been described in detail elsewhere [12] [13]. The intervertebral disc takes into account an incompressible nucleus pulposus, an annulus fibrosis (fibre-reinforced hyperelastic composite) and cartilaginous endplates (hyperelastic composite). "
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    ABSTRACT: Knowledge about in vivo spinal compressive forces is a basic requirement for spinal biomechanics. Their direct measurement is not yet possible. Therefore, compressive forces are estimated from in vivo measured intradiscal pressure values. However, it is still not evident how precise these estimations are. A finite element model of the spine was employed to simulate elementary body positions and the compressive force at level L4-5 was calculated. This value was compared with different estimations calculated by multiplying the intradiscal pressure with the disc's cross-sectional area and with a correction factor. A model specific and different previously employed correction factors were used. Separately, in vivo forces were estimated from previously measured pressure values. A model specific correction factor leads for all body positions to a good estimation (error <4%) of the force except for extension (error >27%). Non-model specific correction factors lead to estimation errors of up to 44%. When accounting for these limitations, in vivo forces were estimated e.g. for standing between 430N and 600N. Compressive forces can be estimated for non-extended body positions when the individual correction factor is known. In vivo forces can be estimated from intradiscal pressure values within a certain range.
    Medical Engineering & Physics 04/2013; 35(9). DOI:10.1016/j.medengphy.2013.03.007 · 1.83 Impact Factor
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    • "In addition to the experimental observations, such as the effect of chair design on spinal forces [50], or changes in spinal fixator forces after a staged anterior interbody fusion [51], these data have been used to validate computational models [52], as well as to inform on developing more realistic in vitro models for spine testing [53]. "
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    Arthritis research & therapy 01/2013; 15(1):203. DOI:10.1186/ar4138 · 3.75 Impact Factor
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    • "A part of an existing osseoligamentous finite element model of the lumbosacral spine ranging from L3 vertebra to the sacrum was used (Fig. 1). The complete model was extensively validated using experimentally determined data (Rohlmann et al., 2006a; Zander et al., 2001; Zander et al., 2009). Solid hexahedral elements represented the vertebrae, the sacrum and the ground substance of the intervertebral discs. "
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    ABSTRACT: Up to now, plain radiographs are not well suited to assess spinal fusion. Radiostereometric analysis performed for two postures may deliver more reliable results. However, it is unknown, which postures are most suitable for this procedure. In a finite element study, spinal fusion at the level L4-5 was simulated assuming a posterior approach and the implantation of two cages and a spinal fixation device. The change of the distance between markers in vertebrae adjacent to the cages was calculated for moving from one of the following postures standing, flexion, extension, axial rotation, lying, and extension in a lying position to another. The changes of marker distances were calculated for the intact model, as well as for the situations: directly after surgery before fusion started, in the early-fusion-phase and in the late-fusion-phase. Differences in the marker motion between two postoperative situations were also calculated. The most anteriorly placed markers showed the greatest motion between two postures. The greatest differences in marker motions between the two situations before-fusion and early-fusion-phase (0.54 mm) as well as between early-fusion-phase and late-fusion-phase (0.34 mm) were found for the two postures flexion while standing and extension in a lying position. Pairs of X-rays taken while standing with maximum flexed upper body and while lying with maximum extended trunk are most suited for the assessment of spinal fusion when using radiostereometric analysis.
    Clinical biomechanics (Bristol, Avon) 09/2011; 27(2):111-6. DOI:10.1016/j.clinbiomech.2011.08.012 · 1.97 Impact Factor
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