Annette Kettler

Universität Ulm, Ulm, Baden-Wuerttemberg, Germany

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Publications (60)117.4 Total impact

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    Annette Kettler · F Rohlmann · C Ring · C Mack · H-J Wilke

    Preview · Article · Jan 2012 · European Spine Journal
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    Annette Kettler · F Rohlmann · C Ring · C Mack · H-J Wilke
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    ABSTRACT: Early stages of intervertebral disc degeneration are postulated to cause instability. In the literature, however, some authors report the opposite. These contradictory positions are probably supported by the mostly small number of segments which are investigated. The aim of this project therefore was to investigate the influence of intervertebral disc degeneration on lumbar spine rotational stability using a large data set. The flexibility data from all spine specimens tested in our institute so far were collected in a large in vitro database. From this database, all lumbar spine specimens were selected, which had been tested for flexibility under pure moment loads of ±7.5 N m and for which radiographs were accessible. 203 segments met these criteria. Their radiographic degree of disc degeneration was determined on a scale from 0 (no degeneration) to 3 (severe degeneration) and their influence on the respective range of motion and neutral zone was examined. The different lumbar levels differ in flexibility, which increases the variability of the data if pooled together. To minimise this effect a statistical model was fitted. The model-based mean estimates showed a decrease of the range of motion from grade 0 to 3 in flexion/extension (by 3.1°, p < 0.05) and lateral bending (by 3.4°, p < 0.05). In contrast, in axial rotation the range of motion tended to increase; however, not only from grade 0 to 1 but also towards grade 3 (by 0.2°) (p > 0.05). The neutral zone was affected in a similar way but to a smaller degree (p > 0.05). In conclusion, the results indicated that early stages of intervertebral disc degeneration do not necessarily cause rotational instability. In contrast, stability increased in flexion/extension and lateral bending. Only in axial rotation stability tended to decrease.
    Preview · Article · Dec 2010 · European Spine Journal
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    Annette Kettler · Michael Bushelow · Hans-Joachim Wilke
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    ABSTRACT: Pre-clinical wear testing of intervertebral disc prostheses is commonly carried out according to ISO 18192-1. Ten million multiaxial loading cycles are applied at a frequency of 1 Hz. At this frequency, testing takes about 4 months. Testing at higher frequencies would therefore be desirable. ISO 18192-1 also offers testing at 2 Hz; however, it says the impact on the implant material behaviour as well as on the accuracy of the test machine shall be investigated by the user. Since such data are not available so far, the aim of this study was to carry out comparative wear tests at 1 and 2 Hz. Seven Prodisc-L lumbar disc prostheses were tested. After a pre-soak period, the implants were placed in specimen cups filled with calf serum, mounted to a Spine Wear Simulator and loaded according to ISO 18192-1. Testing was carried out at a temperature of 37 ± 2 °C. Four million loading cycles were applied at 1 Hz and eight million at 2 Hz in an alternating sequence. Each time after 12 days of testing the implants were removed to measure the weight and the height of the polyethylene cores. Then, the test serum was exchanged and the implants were remounted to the testing machine. The mean wear rate was 5.6 ± 2.3 mg per million cycles at 1 Hz and 7.7 ± 1.6 mg per million cycles at 2 Hz during the first six million loading cycles (p < 0.05) and 2.0 ± 0.6 and 4.1 ± 0.7 mg per million cycles during the second six million cycles (p < 0.05). Similarly, the mean heightloss was also smaller at 1 Hz than at 2 Hz (p < 0.05) with -0.02 ± 0.02 mm versus -0.04 ± 0.02 mm per million cycles during the first half of testing and -0.01 ± 0.01 versus -0.02 ± 0.01 mm per million cycles during the second half. The accuracy of the test machine was within the limits described by ISO 18192-1 at both frequencies. The results showed that the wear rate was higher at the beginning than at the end of testing. Also, the results indicated that testing at 2 Hz increases the wear rate compared with 1 Hz in case of a polyethylene-on-metal implant design. In the absence of retrieval studies it is difficult to decide which rate results in a more physiological wear pattern. However, a loading frequency of 1 Hz is probably closer to physiology than 2 Hz since the loading amplitudes prescribed by ISO 18192-1 are high. They rather represent movements like tying shoes or standing up from a chair than walking or sitting. The authors therefore suggest testing at 1 Hz.
    Preview · Article · Oct 2010 · European Spine Journal
  • H-J Wilke · J Drumm · K Häussler · C Mack · A Kettler
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    ABSTRACT: Interspinous spacers are commonly used to treat lumbar spinal stenosis or facet joint arthritis. The aims of implanting interspinous devices are to unload the facet joints, restore foraminal height, and provide stability especially in extension but still allow motion. This paper summarizes several in vitro studies, which compared four different interspinous implants - Coflex, Wallis, DIAM, and X-STOP - in terms of their three-dimensional primary stability, the intradiscal pressure, and stability after cyclic loading. 24 human lumbar spine specimens were divided into four equal groups and tested with pure moments in flexion/extension, lateral bending, and axial rotation: intact, after decompression with hemifacetectomy, and after implantation. Implantation had similar biomechanical effects with all four implants. In extension, they overcompensated the instability caused by the defect and restricted extension to about 50% compared to the intact state. In contrast, in flexion, lateral bending, and axial rotation the values of the range of motion stayed similar compared to the defective state. Intradiscal pressure after implantation was similar to that of the intact specimens in flexion, lateral bending, and axial rotation but much smaller during extension; 50,000 load cycles increased the range of motion in all motion planes by no more than 20%, but in extension motion this was still less than in the intact state.
    No preview · Article · Jun 2010 · Der Orthopäde
  • H.-J Wilke · J. Drumm · K. Häussler · C. Mack · A. Kettler
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    ABSTRACT: Interspinöse Platzhalter werden häufig implantiert, um eine lumbale Spinalkanalstenose oder eine Gelenkfacettenarthrose zu behandeln. Ziel ist es; mit deren Hilfe die Extension in den betroffenen Segmenten einzuschränken, die Gelenkfacetten zu entlasten, die Höhe des Foramens wiederherzustellen, gleichzeitig aber die Bewegung im physiologischen Bereich zu erhalten. In dieser Arbeit werden mehrere In-vitro-Studien zusammengefasst, in denen die vier verschiedenen interspinösen Implantate – Coflex™, DIAM™, Wallis und X-STOP – bezüglich der Primärstabilität, des Bandscheibendrucks und der Stabilität nach zyklischer Belastung untersucht wurden. 24 humane lumbale Wirbelsäulensegmente wurden in vier gleiche Gruppen eingeteilt und in Flexion/Extension, Seitneigung und axialer Rotation getestet: jeweils intakt, nach Dekompression mit einer Hemifacettektomie und mit Implantat. Die Implantation hatte bei allen vier Typen ähnliche biomechanische Effekte. In Extension konnten die Implantate die Instabilität aufgrund des Defekts überkompensieren und reduzierten den Bewegungsumfang auf ca. 50% des intakten. Im Vergleich dazu blieb der Bewegungsumfang in Flexion, Seitneigung und axialer Rotation bei Werten des Defektzustands nahezu unverändert. Die Charakteristik des Bandscheibendruckes scheint für alle Implantate vergleichbar. In Flexion, Seitneigung und axialer Rotation erlaubt die Behandlung einen annähernd physiologischen Druck, während in Extension die Bandscheibe deutlich entlastet wird. 50.000 Lastzyklen vergrößerten den Bewegungsumfang um bis zu 20%, blieb in Extension aber immer noch unter den Werten des intakten Zustands.
    No preview · Article · Jun 2010 · Der Orthopäde

  • No preview · Article · Aug 2008 · Spine

  • No preview · Article · Jul 2008
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    ABSTRACT: Interspinous implants are used to treat lumbar spinal stenosis or facet joint arthritis. The aims of implanting interspinous devices are to unload the facet joints, restore foraminal height and provide stability especially in extension but still allow motion. The aim of this in vitro study was to compare four different interspinous implants--Colfex, Wallis, Diam and X-Stop--in terms of their three-dimensional flexibility and the intradiscal pressure. Twenty-four human lumbar spine specimens were divided into four equal groups and tested with pure moments in flexion/extension, lateral bending and axial rotation: (1) intact, (2) defect, (3) after implantation. Range of motion and the intradiscal pressure were determined. In each implant-group the defect caused an increase in range of motion by about 8% in lateral bending to 18% in axial rotation. Implantation had similar effects with all four implants. In extension, Coflex, Wallis, Diam, and X-Stop all overcompensated the instability caused by the defect and allowed about 50% of the range of motion of the intact state. In contrast, in flexion, lateral bending and axial rotation the values of the range of motion stayed about the values of the defect state. Similarly the intradiscal pressure after implantation was similar to that of the intact specimens in flexion, lateral bending and axial rotation but much smaller during extension. All tested interspinous implants had a similar effect on the flexibility: they strongly stabilized and reduced the intradiscal pressure in extension, but had almost no effect in flexion, lateral bending and axial rotation.
    Preview · Article · Jul 2008 · European Spine Journal
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    ABSTRACT: ContentsThis review will present a characterization of basic molecular processes in the mammalian oviduct. Oviducts of the cow (Bos taurus) were examined during the various cycle stages using a combination of cell biology- and molecular-biology techniques [reverse transcriptase polymerase chain reaction (RT-PCR), RNase protection assay (RPA), immunohistology, radio-immunoassay (RIA), receptor-assay, cell culture]. In detail the oviductal expression of the following components was analysed: fibroblast (FGF) and vascular-endothelial (VEGF) growth factor systems; extracellular matrix (ECM) enzymes such as plasminogenactivator (PA) and matrixmetalloproteases (MMP), adrenergic receptors (α2 and β2 AdR) and an anti-oxidative protein (glutathionperoxidase = GPx). A specific cycle-dependant and local regulation of the expression could be demonstrated, not only for growth factors such as FGF1 and VEGF but also for ECM components. Remarkable progesterone-dependent increases of the β2 adrenoceptor concentrations were found in the oviductal epithelium. New observations showed the presence of antioxidative enzymes (GPx) in the bovine oviduct possibly interacting with the gametes. Obviously, a network of local factors seems to influence the function of the oviduct, controlled by peripheral hormones. Cycle–dependent interactions between the growth factor, ECM and adrenergic systems will create the optimal environment for fertilization and early embryo development in the mammalian oviduct.
    No preview · Article · Jun 2008 · Reproduction in Domestic Animals
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    ABSTRACT: Intervertebral disc (IVD) degeneration is an often investigated pathophysiological condition because of its implication in causing low back pain. As human material for such studies is difficult to obtain because of ethical and government regulatory restriction, animal tissue, organs and in vivo models have often been used for this purpose. However, there are many differences in cell population, tissue composition, disc and spine anatomy, development, physiology and mechanical properties, between animal species and human. Both naturally occurring and induced degenerative changes may differ significantly from those seen in humans. This paper reviews the many animal models developed for the study of IVD degeneration aetiopathogenesis and treatments thereof. In particular, the limitations and relevance of these models to the human condition are examined, and some general consensus guidelines are presented. Although animal models are invaluable to increase our understanding of disc biology, because of the differences between species, care must be taken when used to study human disc degeneration and much more effort is needed to facilitate research on human disc material.
    Full-text · Article · Feb 2008 · European Spine Journal
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    A Kettler · J Drumm · F Heuer · K Haeussler · C Mack · L Claes · H-J Wilke
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    ABSTRACT: Interspinous spacers are mainly used to treat lumbar spinal stenosis and facet arthrosis. Biomechanically, they stabilise in extension but do not compensate instability in axial rotation and lateral bending. It would therefore be desirable to have an interspinous spacer available, which provides for more stability also in these two planes. At the same time, the intervertebral disc should not completely be unloaded to keep it viable. To meet these requirements, a new version of the Coflex interspinous implant was developed, called "Coflex rivet", which can be more rigidly attached to the spinous processes. The aim was to investigate whether this new implant compensates instability but still allows some load to be transferred through the disc. Twelve human lumbar spine segments were equally divided into two groups, one for Coflex rivet and one for the original Coflex implant. The specimens were tested for flexibility under pure moment loads in the three main planes. These tests were carried out in the intact condition, after creation of a destabilising defect and after insertion of either of the two implants. Before implantation, the interspinous spacers were equipped with strain gauges to measure the load transfer. Compared to the defect condition, both implants had a strong stabilising effect in extension (P<0.05). Coflex rivet also strongly stabilised in flexion and to a smaller degree in lateral bending and axial rotation (P<0.05). In contrast, in these three loading directions, the original Coflex implant could not compensate the destabilising effect of the defect (P>0.05). The bending moments transferred through the implants were highest in extension and flexion. Yet, they were no more than 1.2 Nm in median. The new Coflex rivet seems be a suitable option to compensate instability. Its biomechanical characteristics might even make it suitable as an adjunct to fusion, which would be a new indication for this type of implant.
    Preview · Article · Feb 2008 · Clinical Biomechanics
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    A Kettler · L Liakos · B Haegele · H-J Wilke
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    ABSTRACT: Pre-clinical in vitro tests are needed to evaluate the biomechanical performance of new spinal implants. For such experiments large animal models are frequently used. Whether these models allow any conclusions concerning the implant's performance in humans is difficult to answer. The aim of the present study was to investigate whether calf, pig or sheep spine specimens may be used to replace human specimens in in vitro flexibility and cyclic loading tests with two different implant types. First, a dynamic and a rigid fixator were tested using six human, six calf, six pig and six sheep thoracolumbar spine specimens. Standard flexibility tests were carried out in a spine tester in flexion/extension, lateral bending and axial rotation in the intact state, after nucleotomy and after implantation. Then, the Coflex interspinous implant was tested for flexibility and intradiscal pressure using another six human and six calf lumbar spine segments. Loading was carried out as described above in the intact condition, after creation of a defect and after implantation. The fixators were most easily implantable into the calf. Qualitatively, they had similar effects on ROM in all species, however, the degree of stability achieved differed. Especially in axial rotation, the ROM of sheep, pig and calf was partially less than half the human ROM. Similarly, implantation of the Coflex interspinous implant caused the ROM to either increase in both species or to decrease in both of them, however, quantitatively, differences were observed. This was also the case for the intradiscal pressure. In conclusion, animal species, especially the calf, may be used to get a first idea of how a new pedicle screw system or an interspinous implant behaves in in vitro flexibility tests. However, the effects on ROM and intradiscal pressure have to be expected to differ in magnitude between animal and human. Therefore, the last step in pre-clinical implant testing should always be an experiment with human specimens.
    Preview · Article · Jan 2008 · European Spine Journal
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    ABSTRACT: Disc prolapses can result from various complex load situations and degenerative changes in the intervertebral disc. The aim of this finite element study was to find load combinations that would lead to the highest internal stresses in a healthy and in degenerated discs. A three-dimensional finite element model of a lumbar spinal segment L4-L5 in different grades of disc degeneration (healthy, mild, moderate, and severe) were generated, in which the disc height reduction, the formation of osteophytes and the increasing of nucleus' compressibility were considered. The intradiscal pressure in the nucleus, the fiber strains, and the shear strains between the annulus and the adjacent endplates under pure and complex loads were investigated. In all grades of disc degeneration the intradiscal pressure was found to be highest in flexion. The shear and fiber strains predicted a strong increase under lateral bending+flexion for the healthy disc and under axial rotation and lateral bending+axial rotation for all degenerated discs, mostly located in the postero-lateral annulus. Compared to the healthy disc, the mildly degenerated disc indicated an increase of the intradiscal pressure and of the fiber strains, both of 25% in axial rotation. The shear strains showed an increase of 27% in axial rotation+flexion. As from the moderately degenerated disc all measurement parameters strongly decreased. The results support how specifically changes associated with disc degeneration might contribute to risk of prolapse. Thus, the highest risk of prolapses can be found for healthy and mildly degenerated discs.
    No preview · Article · Dec 2007 · Clinical Biomechanics
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    ABSTRACT: One of the greatest challenges in the development of a nucleus prosthesis is to minimize the risk of implant expulsion. At the same time, the physiological flexibility, compressive behavior, and height of the disc should be restored. In this biomechanical in vitro study we investigated the ability of a new nucleus prosthesis made of knitted titanium filaments to meet these challenges. Flexibility, axial deformation, and height of six bovine lumbar spine segments were measured in the intact condition, after implantation of the new prosthesis, and during and after complex cyclic loading (100,000 cycles). For this purpose, six new prostheses preformed according to the shape of the bovine nucleus pulposus were manufactured. Flexibility was tested in the three main planes under pure moment loads of 7.5 Nm. Axial deformation was measured under application of an axial force of 1000 N. Radiographs taken before and after cyclic testing were used to assess implant migration and expulsion. In lateral bending, the intact range of motion (RoM) could almost be restored after implantation. However, in axial rotation, the RoM increased slightly with the implant. This was also the case in extension, with an increase from -2.9° to -6.4°, whereas in flexion, RoM decreased from 4.3° to 3.2°. In all loading planes, cyclic loading caused the RoM to increase asymptotically by 0.1° to 1.8°. The axial deformation of the specimens was nearly equivalent in all tested states, as was their height. Cyclic loading did not cause implant expulsion. In this feasibility study, the new knitted nucleus prosthesis showed promising results in segmental flexibility, axial deformability, height, and implant expulsion. However, further study is needed for other factors, such as wear and fatigue behavior.
    Preview · Article · Dec 2007 · SAS Journal
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    ABSTRACT: There is a gap between in vitro and clinical studies concerning performance of spinal disc prosthesis. Retrieval studies may help to bridge this gap by providing more detailed information about motion characteristics, wear properties and osseous integration. Here, we report on the radiographic, mechanical, histological properties of a cervical spine segment treated with a cervical spine disc prosthesis (Prodisc C, Synthes Spine, Paoli, USA) for 3 months. A 48-year-old male received the device due to symptomatic degenerative disc disease within C5-C6. The patient recovered completely from his symptoms. Twelve weeks later, he died from a subarachnoid hemorrhage. During routine autopsy, C3-T1 was removed with all attached muscles and ligaments and subjected to plain X-rays and computed tomography, three dimensional flexibility tests, shear test as well as histological and electronic microscopic investigations. We detected radiolucencies mainly at the cranial interface between bone and implant. The flexibility of the segment under pure bending moments of +/-2.5 Nm applied in flexion/extension, axial rotation and lateral bending was preserved, with, however, reduced lateral bending and enlarged neutral zone compared to the adjacent segments C4-C5, and C6-C7. Stepwise increase of loading in flexion/extension up to +/-9.5 Nm did not result in segmental destruction. A postero-anterior force of 146 N was necessary to detach the lower half of the prosthesis from the vertebra. At the polyethylene (PE) core, signs of wear were observed compared to an unused core using electronic microscopy. Metal and PE debris without signs of severe inflammatory reaction was found within the surrounding soft tissue shell of the segment. A thin layer of soft connective tissue covered the major part of the implant endplate. Despite the limits of such a case report, the results show: that such implants are able to preserve at least a certain degree of segmental flexibility, that direct bone implant contact is probably rare, and that debris may be found after 12 weeks.
    Preview · Article · Aug 2007 · European Spine Journal
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    A Kettler · K Werner · H-J Wilke
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    ABSTRACT: To better understand the role of facet joint degeneration in chronic neck and back pain epidemiological and morphological data are needed. For the cervical spine, however, such data are rare. Therefore, the aim of this study was to determine the degree of cartilage degeneration of cervical facet joints with respect to spinal level and age, to investigate whether any region of the joint surface is more often affected by degeneration and to determine the localisation of osteophytes. A total of 128 left-sided facet surfaces from 15 fresh frozen cervical spine specimens (59-92 years) including in maximum C2-C7 were inspected in a way to ensure a direct comparability to data reported for the lumbar spine. First, the macroscopic degree of cartilage degeneration was determined and correlated to spinal level and age. Then, each facet surface was divided into five regions (anterior, posterior, lateral, medial and central) to check whether cartilage degeneration occurs more often in any of these regions. Finally, the localisation of osteophytes was determined. The results showed that the mean degree of cartilage degeneration was 2.8 (+/-0.6) on a scale from Grade 1 (no degeneration) to 4 (severe degeneration). None of all 128 facet surfaces was classified as Grade 1. All spinal levels had about the same degree of degeneration (in mean 2.5-3.0). The youngest age group (<70 years) had a somewhat lower degree of degeneration (2.6) than the oldest (> or = 90 years) (3.1). Cartilage defects were found all over the joint surfaces, none of the five regions was more often affected than the others. Least osteophytes were found on the medial border of the facet joints. In conclusion, the prevalence of cervical facet joint degeneration is probably very high in individuals aged 50 years and more, with a tendency to increase in severity with age. All levels of the middle and lower cervical spine were affected to almost the same degree, whereas in the lumbar spine an increase in degeneration towards the lower levels was reported. Also, in the cervical spine in most cases the cartilage was evenly degenerated all over the joint surface while in the lumbar spine certain regions were reported to be affected predominantly.
    Preview · Article · Jul 2007 · European Spine Journal
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    ABSTRACT: Finite element study. To investigate intradiscal pressure, shear strain between anulus and adjacent endplates, and fiber strain in the anulus under pure and combined moments. Concerning anulus failures such as fissures and disc prolapses, the mechanical response of the intervertebral disc during combined load situations is still not well understood. A 3-dimensional, nonlinear finite element model of a lumbar spinal segment L4-L5 was used. Pure unconstraint moments of 7.5 Nm in all anatomic planes with and without an axial preload of 500 N were applied to the upper vertebral body. The load direction was incrementally changed with an angle of 15 degrees between the 3 anatomic planes to realize not only moments in the principle motion planes but also moment combinations. Intradiscal pressure was highest in flexion and lowest in lateral bending. Load combinations did not increase the pressure. A combination of lateral bending plus flexion or lateral bending plus extension strongly increased the maximum shear strains. Lateral bending plus axial rotation yielded the highest increase in fiber strains, followed by axial rotation plus flexion or axial rotation plus extension. The highest shear and fiber strains were both located posterolaterally. An additional axial preload tended to increase the pressure, the shear, and fiber strains essentially for all load scenarios. Combined moments seem to lead to higher stresses in the disc, especially posterolaterally. This region might be more susceptible to disc failure and prolapses. These results may help clinicians better understand the mechanical causes of disc prolapses and may also be valuable in developing preventive clinical strategies and postoperative treatments.
    Full-text · Article · May 2007 · Spine
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    ABSTRACT: The aim of this project is to simulate the effect of external pertubations on the body to the spine, for e.g. comfort studies and reconstruction of accidents. Furthermore, with this model it is possible to study fatigue effects of the spine stabilizing muscles on internal stresses and strains in either the vertrebral bodies ort he intervertebral disc. The spine is modelled from os sacrum to C1 with spine segments, soft tissues, ligaments and the respective muscle tendon complexes as rigid bodies. The X-modell [12,13] is used as movement control algorithm, a model of the equilibrium point hypothesis group [2]. The resultant contact and tensile forces of the rigid body spine model calculation are transferred to a more detailed finite element model of the L4-5 spine segment in order to calculate internal stresses and strains of either the intervertebal disc or the vertebral body itself. The finite element model consists of two vertebral bodies, the intervertebral disc and ligamentary strucures. spine, rigid body simulation, finite element analysis, movement control, stress-strain analysis.
    No preview · Article · Jan 2007 · VDI-Berichte

  • No preview · Article · Dec 2006 · Journal of Biomechanics
  • A. Kettler · W. Schmoelz · E. Kast · M. Gottwald · L. Claes · H. J. Wilke

    No preview · Article · Dec 2006 · Journal of Biomechanics

Publication Stats

2k Citations
117.40 Total Impact Points

Institutions

  • 1997-2010
    • Universität Ulm
      • Institute of Orthopaedic Research and Biomechanics
      Ulm, Baden-Wuerttemberg, Germany
  • 2000-2008
    • Technische Universität München
      • Chair of Nutrition Physiology
      München, Bavaria, Germany