A Kettler

Universität Ulm, Ulm, Baden-Wuerttemberg, Germany

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Publications (50)97.91 Total impact

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    Annette Kettler, F Rohlmann, C Ring, C Mack, H-J Wilke
    European Spine Journal 01/2012; · 2.47 Impact Factor
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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.
    European Spine Journal 12/2010; 20(4):578-84. · 2.47 Impact Factor
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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.
    European Spine Journal 10/2010; 21 Suppl 5:S709-16. · 2.47 Impact Factor
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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.
    Der Orthopäde 06/2010; 39(6):565-72. · 0.51 Impact Factor
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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. 50.000Lastzyklen vergrößerten den Bewegungsumfang um bis zu 20%, blieb in Extension aber immer noch unter den Werten des intakten Zustands. 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. SchlüsselwörterInterspinöses Implantat-Lumbale Wirbelsäule-Biomechanik-Flexibilität-Intradiskaler Druck KeywordsInterspinous implant-Lumbar spine-Biomechanics-Flexibility-Intradiscal pressure
    Der Orthopäde 06/2010; 39(6):565-572. · 0.67 Impact Factor
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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.
    European Spine Journal 07/2008; 17(8):1049-56. · 2.47 Impact Factor
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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.
    Clinical Biomechanics 02/2008; 23(2):242-7. · 1.88 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
  • Spine 01/2008; · 2.45 Impact Factor
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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.
    European Spine Journal 01/2008; 16(12):2186-92. · 2.47 Impact Factor
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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.
    Clinical Biomechanics 12/2007; 22(9):988-98. · 1.88 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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    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.
    European Spine Journal 07/2007; 16(7):987-92. · 2.47 Impact Factor
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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.
    Spine 05/2007; 32(7):748-55. · 2.45 Impact Factor
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    ABSTRACT: Background 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.
    SAS Journal 01/2007; 1(4):125-130.
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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. · 3.03 Impact Factor
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    ABSTRACT: Vertebral compression fractures are counted among the most common complications of osteoporosis. For treatment, a new, alternative implant has been developed (BeadEx, Expandis, Hof HaCarmel, Israel). The aim of the present in vitro study was to evaluate whether this implant is able to restore the initial height and three-dimensional stability after fracture and whether it is able to maintain this height and stability during complex cyclic loading. The BeadEx implant consists of small titanium rolls, which are pressed into the vertebral body through specially designed, hollow pedicle screws. The height and the three-dimensional flexibility of 18 bisegmental spine specimens (nine T12-L2, nine L3-L5) was measured, first, before and after creating a wedge compression fracture at the middle vertebral body (L1 resp. L4), second, after treatment of the fracture, and, third, during and after complex cyclic loading. The fractures were treated either with BeadEx plus internal fixator, BeadEx plus bone cement or vertebroplasty for comparison. The height before fracture could almost be restored by BeadEx plus bone cement but not by BeadEx plus fixator and vertebroplasty. The total height loss after cyclic loading was smallest with BeadEx plus bone cement (in median -4.7mm with respect to the intact specimens) but -6.2mm with BeadEx plus fixator and -7.8mm with vertebroplasty. The three-dimensional stability of the specimens was clearly higher if treated with BeadEx plus fixator than with BeadEx plus bone cement or vertebroplasty. From a biomechanical point of view, BeadEx plus bone cement can be recommended as an alternative to vertebroplasty in the treatment of osteoporotic vertebral body fractures. BeadEx plus fixator can be recommended if additional stability is needed.
    Clinical Biomechanics 09/2006; 21(7):676-82. · 1.88 Impact Factor
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    ABSTRACT: Cages are commonly used to assist lumbar interbody fusion. They are implanted from various approaches. In many cases internal fixators are added to provide sufficient stability. However, how the rods of these fixators are loaded and whether the kind of approach affects these loads is still unknown. The aim of this in vitro study therefore was to determine the loads acting on fixator rods and cages after anterior compared to transforaminal lumbar interbody fusion. Six intact human lumbar spine specimens (L1-5) were loaded in a spine tester with pure moments (+/-7.5 N m) in the frontal, sagittal and transverse plane. Loading was repeated, first, after the segments L2-3 and L4-5 were instrumented either with an anterior or a transforaminal lumbar interbody fusion cage "stand alone" and, second, after additional stabilisation with an internal fixator. The rods of the fixator and the four "corners" of the cages were instrumented with strain gauges. The loads transmitted through the rods were highest in lateral bending. In this loading direction an axial distraction force of in median up to 140 N, an axial compression force of up to 100 N, and a resultant bending moment of up to 1.1 N m were measured in each rod. These loads tended to be lower for the anterior compared to the transforaminal approach. For comparison, the load applied was +/-7.5 N m. The axial strains recorded in the four "corners" of the cages considerably varied from one specimen to the other. Differences in cage strain between the two approaches could not be detected. The loads acting on the rods of the fixator were small compared to the load that was applied. Thus, other structures such as the cages or the facet joints still play an important role in load transfer. The type of approach (anterior or transforaminal) had only little effect on the loading of the rods. This also applies to the local loading of the cages, which probably more depends on the fit between cage and endplates and on the local stiffness properties of the adjacent vertebral bodies.
    Clinical Biomechanics 07/2006; 21(5):435-42. · 1.88 Impact Factor
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    ABSTRACT: Many different radiographic grading systems for disc degeneration are described in literature. However, only a few of them are tested for interobserver agreement and none for validity. Furthermore, most of them are based on a subjective terminology. The aim of this study, therefore, is to combine these systems to a new one in which all subjective terms are replaced by more objective ones and to test this new system for validity and interobserver agreement. Since lumbar and cervical discs need to be graded differently, this study was divided into the present Part I for the lumbar and a Part II for the cervical spine. The new radiographic grading system covers the three variables "Height Loss", "Osteophyte Formation" and "Diffuse Sclerosis". On lateral and postero-anterior radiographs, each of these three variables first has to be graded individually. Then, the "Overall Degree of Degeneration" is assigned on a four-point scale from 0 (no degeneration) to 3 (severe degeneration). For validation, the radiographic degrees of degeneration of 44 lumbar discs were compared to the respective macroscopic ones, which were defined as "real" degrees of degeneration. The agreement between observers with different levels of experience was determined using the radiographs of 84 lumbar discs. Agreement was quantified using quadratic weighted Kappa coefficients (Kappa) with 95% confidence limits (95% CL). The validation of the new radiographic grading system revealed a substantial agreement between the radiographic and the "real" macroscopic overall degree of degeneration (Kappa=0.714, 95% CL: 0.587-0.841). The radiographic grades, however, tended to be slightly lower than the "real" ones. The interobserver agreement was substantial for all the three variables and for the overall degree of degeneration (Kappa=0.787, 95% CL: 0.702-0.872). However, the inexperienced observer tended to assign slightly lower degrees of degeneration than the experienced one. In conclusion, we believe that the new radiographic grading system is an almost objective, valid and reliable tool to quantify the degree of degeneration of individual lumbar intervertebral discs. However, the user should always remember that the "real" degree of degeneration tends to be underestimated and that slight differences between the ratings of observers with different levels of experience have to be expected.
    European Spine Journal 07/2006; 15(6):720-30. · 2.47 Impact Factor
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    ABSTRACT: A new radiographic grading system for a more objective assessment of lumbar intervertebral disc degeneration has been described and tested in Part I of this study. The aim of the present Part II of the study was to adapt this system to the cervical spine, and to test it for validity and interobserver agreement. Some modifications of the grading system described in Part I were necessary to make it applicable to the cervical spine. Its basic structure, however, stayed untouched. The three variables "Height Loss", "Osteophyte Formation" and "Diffuse Sclerosis" first have to be graded individually. Then, the "Overall Degree of Degeneration" is assigned on a four-point scale from 0 (no degeneration) to 3 (severe degeneration). For validation, the radiographic degrees of degeneration of 28 cervical discs were compared to the respective macroscopic ones, which were defined as "real" degrees of degeneration. The interobserver agreement was determined between one experienced and one unexperienced observer using the radiographs of 57 cervical discs. Quadratic weighted Kappa coefficients (kappa) with 95% confidence limits (95% CL) were used for statistical evaluation. The validation of the new version of the radiographic grading system showed a moderate agreement with the "real", macroscopic overall degree of degeneration (kappa=0.599, 95% CL 0.421-0.786). In 64% of all discs the "real" overall degree of degeneration was underestimated but never overestimated. This underestimation, however, was much less pronounced and the Kappa coefficients were significantly higher for the three variables: Height Loss, Osteophyte Formation, and Diffuse Sclerosis separately. The agreement between the radiographic ratings of the experienced and the unexperienced observer was substantial for the overall degree of degeneration (kappa=0.688, 95% CL 0.580-0.796), almost perfect for the variable, Height Loss, moderate for Osteophyte Formation and fair for Diffuse Sclerosis. In conclusion, we believe that the new version of the radiographic grading system is a sufficiently valid and reliable tool to quantify the degree of degeneration of individual cervical intervertebral discs. In comparison to the version for the lumbar spine described in Part I, however, a slightly higher tendency to underestimate the "real" overall degree of degeneration and somewhat higher interobserver differences have to be expected.
    European Spine Journal 07/2006; 15(6):732-41. · 2.47 Impact Factor

Publication Stats

1k Citations
97.91 Total Impact Points

Institutions

  • 1997–2010
    • Universität Ulm
      • Institute of Orthopaedic Research and Biomechanics
      Ulm, Baden-Wuerttemberg, Germany
  • 2008
    • AO Foundation
      Давос, Grisons, Switzerland
  • 2001
    • Royal North Shore Hospital
      Sydney, New South Wales, Australia