Chronic low back pain is a significant public health problem in industrialized society. The intact spine carries the upper body and external loads, allows motion in a physiological range and protects the spinal cord. These different demands necessitate a high degree of complexity with various sources for disorders and pain. The Julius Wolff Institute conducts research in order to counter pain causes and to further optimize the pain treatment.
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Finite Element Models
Finite element models used for the mechanical analysis of biological structures have the advantage of being bloodless and not being dependent on preparations. Their results are reproducible and parameter variations can be performed by keeping all but one parameter constant. Here different finite element models are described that were developed in our laboratory. Although the main interest is in the lumbar region, the thoracic and sacral parts being adjacent to the lumbar one cannot be neglected when dealing with questions related to pelvis and spine altogether.
Model of the Lumbar Spine
The current model of the lumbar spine contains five lumbar vertebrae, four lumbar intervertebral discs, and the lumbosacral disc. All ligaments and facet joints were modelled. The model was developed to simulate static body postures. All in all the model contains about 60,000 elements with about 200,000 nodal points. It is nonlinear in all three points of view due to large possible deformations, due to mostly progressive material behaviour, and due to possible contact in the facet joints.
Model of the Thoracic Spine
Although the focus of spinal research is the lumbar region, it is also necessary to consider the adjacent thoracic region that loads the lumbar one. The model of the thoracic spine consists of twelve vertebrae modelled as rigid bodies and their intervertebral discs whose material behaviour was modelled transverse isotropic to mimic the rotational stiffness with and without rib cage measured in experiments. Ribs and sternum were modelled as one dimensional beam elements. The ribcage is elastically connected to the vertebrae by the costotransverse and costovertebral ligaments. The facet joints are simulated kinematically.
Entire Model of Thoracic and Lumbar Spine with Pelvis
The complete model consists of the models of the thoracic and the lumbar spine, also incorporating sacrum and pelvis which provide insertion points of the muscular system. The modelled muscle fibres enable to load the model physiologically. The complete model allows to study multisegmental implants.