Discrepancies in anthropometric parameters between different models affect intervertebral rotations when loading finite element models with muscle forces from inverse static analyses

Abstract

In only a few published finite element (FE) simulations have muscle forces been applied to the spine. Recently, muscle forces determined using an inverse static (IS) model of the spine were transferred to a spinal FE model, and the effect of methodical parameters was investigated. However, the sensitivity of anthropometric differences between FE and IS models, such as body height and spinal orientation, was not considered. The aim of this sensitivity study was to determine the influence of those differences on the intervertebral rotations (IVRs) following the transfer of muscle forces from an IS model to a FE model. Muscle forces were estimated for 20° flexion and 10° extension of the upper body using an inverse static musculoskeletal model. These forces were subsequently transferred to a nonlinear FE model of the spino-pelvic complex, which includes 243 muscle fascicles. Deviations of body height (±10 cm), spinal orientation in the sagittal plane (±10°), and body weight (±10 kg) between both models were intentionally generated, and their influences on IVRs were determined. The changes in each factor relative to their corresponding reference value of the IS model were calculated. Deviations in body height, spinal orientation, and body weight resulted in maximum changes in the IVR of 19.2%, 26% and 4.2%, respectively, relative to T12-S1 IVR. When transferring muscle forces from an IS to a FE model, it is crucial that both models have the same spinal orientation and height. Additionally, the body weight should be equal in both models.

The Effect of Muscle Direction on the Predictions of Finite Element Model of Human Lumbar Spine

“…However, it was difficult to share the above-mentioned muscle forces for other researchers due to their private optimization techniques. We have previously carried out sensitivity studies when transferring muscle forces from a shared inverse static model to load an FE model [ 16 , 17 ]. The findings showed that many parameters have to be considered when combining two biomechanical models and artificial errors may be induced in the model which may have a significant impact on the outcome.…”