H J Wilke

Universität Ulm, Ulm, Baden-Wuerttemberg, Germany

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Publications (112)172.77 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Finite element (FE) model studies have made important contributions to our understanding of functional biomechanics of the lumbar spine. However, if a model is used to answer clinical and biomechanical questions over a certain population, their inherently large inter-subject variability has to be considered. Current FE model studies, however, generally account only for a single distinct spinal geometry with one set of material properties. This raises questions concerning their predictive power, their range of results and on their agreement with in vitro and in vivo values. Eight well-established FE models of the lumbar spine (L1-5) of different research centers around the globe were subjected to pure and combined loading modes and compared to in vitro and in vivo measurements for intervertebral rotations, disc pressures and facet joint forces. Under pure moment loading, the predicted L1-5 rotations of almost all models fell within the reported in vitro ranges, and their median values differed on average by only 2° for flexion-extension, 1° for lateral bending and 5° for axial rotation. Predicted median facet joint forces and disc pressures were also in good agreement with published median in vitro values. However, the ranges of predictions were larger and exceeded those reported in vitro, especially for the facet joint forces. For all combined loading modes, except for flexion, predicted median segmental intervertebral rotations and disc pressures were in good agreement with measured in vivo values. In light of high inter-subject variability, the generalization of results of a single model to a population remains a concern. This study demonstrated that the pooled median of individual model results, similar to a probabilistic approach, can be used as an improved predictive tool in order to estimate the response of the lumbar spine.
    Journal of biomechanics 04/2014; · 2.66 Impact Factor
  • Journal of Biomechanics 07/2012; 45:S51-S51. · 2.72 Impact Factor
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    ABSTRACT: Hydrogels offer unique opportunities for regenerative strategies of the intervertebral disc. A nucleotomy necessary for the implantation of hydrogels, however, disrupts the annulus integrity and destroys natural interfaces in the disc. To clarify whether hydrogels can restore the mechanical competence of the disc an experimental testwas used. Intradiscal pressure(IDP) in an ovine disc was measured in vivo for 24 h and adapted to an axial compressive test consisting of three cycles 15-min diurnal and 30-min night load. To study the fluid mechanics, 30 motion segments in different defect conditions were used: (i) INTACT; (ii) DEFANN: isolated annulus defect; (iii) DEF-NUC: re-implanted nucleus; (iv) DDAHA and (v) iGG-MA: two hydrogels. DEF-ANN showed no significant difference in disc height loss or IDP compared to INTACT, while DEF-NUC reduced the IDP by ~30%(p = 0.03) and tended to increase the height loss(p = 0.2). Both DDAHA and iGG-MA better reflected the height loss of INTACT, but caused an even stronger loss in IDP than DEF-NUC(~34%). Neither the hydrogels nor the re-implanted nucleus, assumed to be the ideal implant, could restore the mechanical functionality of the disc. Hydrogels designed to mimic the mechanical behavior of the native nucleus may fail in restoring IDP due to the destruction of natural interfaces and an inappropriate annulus closure. To regain a biomechanical equivalent of the natural nucleus, more attention needs to be paid to the anchoring of the substitute inside the disc.
    Journal of Tissue Engineering and Regenerative Medicine 01/2012; 6:43-43. · 4.43 Impact Factor
  • H. Schmidt, H. J. Wilke
    Economic ENGINEERING. 01/2011; 2:36-41.
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    ABSTRACT: A new carrier material for the autologous discderived chondrocyte transplantation (ADCT) was developed. The material is based on an albumin hyaluronic acid gel which can be injected in a degenerated intervertebral disc and subsequently polymerizes in situ. In order to evaluate the biomechanical behavior after injection and to evaluate the extrusion risk a biomechanical in-vitro study was performed using 6 bovine lumbar functional spinal units. The specimens were subjected to a complex multi-axial loading condition in order to simulate worst-case conditions. In between the segmental height was measured repeatedly. Also a possible gel extrusion was observed permanently. After injection and polymerization of the gel the median increase of height was 0.3 mm for all 6 specimens. During cyclic loading a gradual decrease of height could be detected. However, this was considered to be the result of visco-elastic creep and liquid extrusion. No gel extrusion could be observed for all specimens within the whole test procedure. Finally, macroscopic sections exhibited an accumulation of the polymerized gel in the center of the nucleus. The results demonstrated that injection of the new polymerizing gel has the potential to anchor injected autologous discderived chondrocytes as a source for regenerative cell populations in the damaged nucleus pulposus.
    01/2010: pages 42-45;
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    U Wolfram, H -J Wilke, P K Zysset
    Journal of Mechanics in Medicine and Biology 01/2010; 10(1):139 - 150. · 0.76 Impact Factor
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    ABSTRACT: With regard to the literature, several factors are considered to have an impact on postoperative mobility after lumbar total disc replacement (TDR). As TDR results in a distraction of the ligamentous structures, theoretically the postoperatively disc height and ligamentous integrity have also an influence on biomechanics of a treated segment. The purpose of the study was to evaluate the influence of posterior longitudinal ligament (PLL) resection and segmental distraction on range of motion (ROM). Six human, lumbar spines (L2-L3) were tested with pure moments of ±7.5 Nm in a spine loading apparatus. The ROM was determined in all three motion planes. Testing sequences included: (1) intact state, (2) 10 mm prosthesis (PLL intact), (3) 10 mm prosthesis (PLL resected), (4) 12 mm prosthesis (PLL resected). The prosthesis used was a prototype with a constrained design using the ball-and-socket principle. The implantation of the 10 mm prosthesis already increased the disc height significantly (intact: 9.9 mm; 10 mm prosthesis: 10.6 mm; 12 mm prosthesis: 12.7 mm). Compared to the intact status, the implantation of the 10 mm prosthesis resulted in an increase of ROM for flexion/extension (8.6° vs 10.8°; P = 0.245) and axial rotation (2.9° vs 4.5°; P = 0.028), whereas lateral bending decreased (9.0° vs 7.6°; P = 0.445). The resection of the PLL for the 10 mm prosthesis resulted in an increase of ROM in all motion planes compared to the 10 mm prosthesis with intact PLL (flexion/extension: 11.4°, P = 0.046; axial rotation: 5.1°, P = 0.046; lateral bending: 8.6°, P = 0.028). The subsequent implantation of a 12 mm prosthesis, with resected PLL, resulted in a significant decrease of ROM in all motion planes compared to the 10 mm prosthesis with intact PLL (flexion/extension: 8.4°, P = 0.028; axial rotation: 3.3°, P = 0.028; lateral bending: 5.1°, P = 0.028). Compared to the intact status, the 12 mm prosthesis with resected PLL only decreased lateral bending significantly while the 10 mm prosthesis with intact PLL increased axial rotation significantly. The resection of the PLL during TDR results in a significant increase of ROM in all three principle motion planes. But it still remains unclear if this increase which is in median not more than 1° may alter the clinical results. Moreover, the destabilizing effect of PLL resection can be reversed using a higher implant. The prosthesis height seems more crucial than PLL preservation to maintain the primary stability after TDR.
    European Spine Journal 10/2009; 21 Suppl 5:S592-8. · 2.47 Impact Factor
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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.
    European Spine Journal 02/2008; 17(1):2-19. · 2.47 Impact Factor
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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.
    European Spine Journal 08/2007; 16(7):1015-20. · 2.47 Impact Factor
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    ABSTRACT: To study the biomechanical behavior of lumbar interbody instrumentation techniques using titanium cages as either transforaminal lumbar interbody fusion (TLIF) or anterior lumbar interbody fusion (ALIF), with and without posterior pedicle fixation. Six fresh-frozen lumbar spines (L1-L5) were loaded with pure moments of +/-7.5 Nm in unconstrained flexion-extension, lateral bending, and axial rotation. Specimen were tested intact, after implantation of an ALIF or TLIF cage "stand-alone" in L2-L3 or L3-L4, and after additional posterior pedicle screw fixation. In all loading directions, the range of motion (ROM) of the segments instrumented with cage and pedicle screw fixation was below the ROM of the intact lumbar specimen for both instrumentation techniques. A significant difference was found between the TLIF cage and the ALIF cage with posterior pedicle screw fixation for the ROM in flexion-extension and axial rotation (P < 0.05). Without pedicle screw fixation, the TLIF cage showed a significantly increased ROM and neutral zone compared with an ALIF cage "stand-alone" in two of the three loading directions (P < 0.05). With pedicle screw fixation, the ALIF cage provides a higher segmental stability than the TLIF cage in flexion-extension and axial rotation, but the absolute biomechanical differences are minor. The different cage design and approach show only minor differences of segmental stability when combined with posterior pedicle screw fixation.
    Neurosurgery 12/2006; 59(6):1271-6; discussion 1276-7. · 2.53 Impact Factor
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    ABSTRACT: In recent years, non-fusion implants to stabilise the lumbar spine have become more and more popular. However, little is known on the load bearing of such dynamic stabilisation systems. In order to investigate the load bearing of discs bridged with rigid and dynamic stabilisation systems, six lumbar cadaver spines were mounted in a spine tester and loaded with pure moments in the three main motion planes. Four different states of the specimens were studied: intact, destabilised, stabilisation with a Dynesys and stabilisation with an internal fixator. Intradiscal pressure (IDP) measurements were used to assess the load bearing of the bridged disc. In the neutral unloaded position, there were small but not significant differences in disc pressure for the four states of the treated disc (P>0.05). Concerning the disc pressure during the course of loading, both the Dynesys and internal fixator did significantly reduce the pressure change from neutral to extension in comparison to the intact state (-0.05, -0.04 and +0.24 MPa, respectively) (P<0.05). Compared to the intact state, there was no significant pressure change from neutral to flexion (0.14, 0.15 and 0.18 MPa, respectively) (P>0.05). The devices apparently eliminated the pressure change from neutral to lateral bending (Dynesys 0.01 MPa, Fixator 0.01 MPa and intact 0.24 MPa), but due to large variations in the intact and defect states the differences were not significant (P>0.05). In axial rotation, the pressure change for the internal fixator was reduced compared to the intact state; however, the change was only significant in left axial rotation (P<0.05). The Dynesys showed no significant differences (P>0.05) in axial rotation. No changes in IDP were seen in the adjacent discs for either the Dynesys or the internal fixator. Our results showed that the IDPs for both devices were similar, but altered compared to the intact disc.
    European Spine Journal 09/2006; 15(8):1276-85. · 2.47 Impact Factor
  • Journal of Biomechanics - J BIOMECH. 01/2006; 39.
  • Journal of Biomechanics - J BIOMECH. 01/2006; 39.
  • Journal of Biomechanics 01/2006; 39. · 2.72 Impact Factor
  • Journal of Biomechanics 01/2006; 39. · 2.72 Impact Factor
  • Journal of Biomechanics - J BIOMECH. 01/2006; 39.
  • H.-J. Wilke, A. Kettler, L. Claes
    Journal of Biomechanics - J BIOMECH. 01/2006; 39.
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    ABSTRACT: Purpose of this study was to determine the spinal shrinkage in several activities of daily life and to assess a relationship with intradiscal pressure during these activities. Low back pain is thought to be related to spinal load. In a clinical evaluation of low back pain as provoked by everyday activities, we found a relationship between the amount of complaints during static activities and intradiscal pressure. However, because invasive intradiscal pressure measurements during dynamic activities like walking and cycling are complicated and hardly done before, an analogue relationship between low back complaints and dynamic activities is lacking. Therefore spinal load was ascertained by stadiometric measurement of the decrease in standing height, so-called "spinal shrinkage", quantified by the exposure of a 1-h adopted posture or activity. Ten subjects performed five daily life activities: standing, sitting, walking, cycling and lying down. By doing different activities during 1 h, immediate after getting up in the morning, following average values for shrinkage were measured: standing -7.4 mm (SD 0.5); sitting -5.0 mm (SD 0.6); walking -7.9 mm (SD 0.5); cycling -3.7 mm (SD 0.4) and lying down +0.4 mm (SD 0.5). Overall, good correlation was found between spinal shrinkage and intradiscal pressure. The use of spinal shrinkage measurement seems a good alternative for intradiscal pressure measurement in static situations, but is still questionable in dynamic situations.
    Clinical Biomechanics 07/2005; 20(5):547-50. · 1.87 Impact Factor
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    ABSTRACT: The finite helical-axes method can be used to describe the three-dimensional in vitro kinematics of the spine. However, this method still suffers from large stochastic calculation errors and poorly conceived visualisation techniques. The aim of the present study, therefore, was to improve the currently used finite helical axes description, by use of a less error-prone calculation algorithm and a new visualisation technique, and to apply this improved method to the study of the three-dimensional in vitro kinematics of the spine. Three-dimensional, continuous motion data of spinal motion segments were used to calculate the position and orientation of the finite helical axes (FHAs). The axes were then projected on plane antero-posterior, lateral and axial radiographs in order to depict the relation to the anatomy of each individual specimen. A hinge joint was used to estimate the measurement error of data collection and axes calculation. In an exemplary in vitro experiment, this method was used to demonstrate the ability of a prosthetic disc nucleus to restore the three-dimensional motion pattern of lumbar motion segments. In the validation experiment with the hinge joint, the calculated FHAs were lying within +/-2.5 mm of the actual joint axis and were inclined relative to this axis at up to +/-1.5 degrees . In the exemplary in vitro experiment, the position and orientation of the FHAs of the intact specimens were subject to large inter-individual differences in all loading directions. Nucleotomy of the lumbar segments caused the axes to spread out, indicating complex coupled motions. The implantation of the prosthetic disc nucleus, for the most part, more than reversed this effect: the axes became oriented almost parallel to each other. The experiments showed that the present improved description of finite helical axes is a valid and useful tool to characterise the three-dimensional in vitro kinematics of the intact, injured and stabilised spine. The main advantage of this new method is the comprehensive visualisation of joint function with respect to the individual anatomy.
    European Spine Journal 11/2004; 13(6):553-9. · 2.47 Impact Factor
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    W Schmoelz, J F Huber, T Nydegger, Dipl-Ing, L Claes, H J Wilke
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    ABSTRACT: In recent years, nonfusion stabilization of the lumbar spine has gained more and more popularity. These nonfusion systems intend to maintain or restore the intersegmental motions to magnitudes of the intact spine and have no negative effects on the segments adjacent to the stabilized one. This study investigated the DYNESYS, a dynamic nonfusion system, which is designed to stabilize the bridged segments while maintaining the disc and the facet joints. To determine the magnitude of stabilization and the effect of the stabilization on the adjacent segment, six lumbar cadaver spines were fixed in a spine tester and loaded with pure moments in the three main motion planes. For each spine, four different stages were tested: intact, defect of the middle segment, fixation with the DYNESYS, and fixation with the internal fixator. Intersegmental motions were measured at all levels. For the bridged segment, the DYNESYS stabilized the spine and was more flexible than the internal fixator. This difference between the internal fixator and the DYNESYS was most pronounced in extension (P < 0.05), with the DYNESYS restoring the motion back to the level of the intact spine. The motion in the adjacent segments was not influenced by either stabilization method. Our results suggest that the DYNESYS provides substantial stability in case of degenerative spinal pathologies and can therefore be considered as an alternative method to fusion surgery in these indications while the motion segment is preserved.
    Journal of Spinal Disorders & Techniques 08/2003; 16(4):418-23. · 1.77 Impact Factor

Publication Stats

3k Citations
172.77 Total Impact Points

Institutions

  • 1991–2010
    • Universität Ulm
      • • Institute of Orthopaedic Research and Biomechanics
      • • Clinic of Trauma, Hand, Plastic and Reconstructive Surgery
      Ulm, Baden-Wuerttemberg, Germany
  • 2008
    • AO Foundation
      Давос, Grisons, Switzerland
  • 2006
    • Universitätsklinikum Tübingen
      • Department of Orthopaedic Surgery
      Tübingen, Baden-Württemberg, Germany
  • 2005
    • Erasmus Universiteit Rotterdam
      • Department of Biomedical Physics and Technology
      Rotterdam, South Holland, Netherlands
  • 2002
    • Technische Universität München
      München, Bavaria, Germany
  • 2001
    • Royal North Shore Hospital
      Sydney, New South Wales, Australia
    • Freie Universität Berlin
      Berlín, Berlin, Germany
  • 1998–1999
    • University of Duisburg-Essen
      Essen, North Rhine-Westphalia, Germany