Comparison of the biomechanical effects of posterior and anterior spine-stabilizing implants

Rohlmann, A.; Zander, Thomas; Bergmann, G.

doi:10.1007/s00586-004-0784-3

Cited by 47 publications

(37 citation statements)

References 20 publications

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“…A fractured endplate would reduce intradiscal pressure and lead to different stress distribution in the vertebral endplate. For the intact model, the loading case standing was supposed to be characterized by a fixed orientation of the L1 vertebra, and only a change of the shape within the lumbar spine was allowed [19,21,32]. This assumption has not been proven, but small deviations of this orientation have only a minor effect on spinal loads.…”

Section: Discussionmentioning

confidence: 99%

Spinal loads after osteoporotic vertebral fractures treated by vertebroplasty or kyphoplasty

Rohlmann¹,

Zander²,

Bergmann³

2005

Eur Spine J

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111

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Vertebroplasty and kyphoplasty are routine treatments for compression fractures of vertebral bodies. A wedge-shaped compression fracture shifts the centre of gravity of the upper body anteriorly and generally, this shift can be compensated in the spine and in the hips. However, it is still unclear how a wedge-shaped compression fracture of a vertebra increases forces in the trunk muscle and the intradiscal pressure in the adjacent discs. A nonlinear finite element model of the lumbar spine was used to estimate the force in the trunk muscle, the intradiscal pressure and the stresses in the endplates in the intact spine, and after vertebroplasty and kyphoplasty treatment. In this study, kyphoplasty represents a treatment with nearly full fracture reduction and vertebroplasty one without restoration of kyphotic angle although in reality kyphoplasty does not guarantee fracture reduction. If no compensation of upper body shift is assumed, the force in the erector spine increases by about 200% for the vertebroplasty but by only 55% for the kyphoplasty compared to the intact spine. Intradiscal pressure increases by about 60 and 20% for the vertebroplasty and kyphoplasty, respectively. In contrast, with shift compensation of the upper body, the increase in muscle force is much lower and increase in intradiscal pressure is only about 20 and 7.5% for the vertebroplasty and kyphoplasty, respectively. Augmentation of the vertebral body with bone cement has a much smaller effect on intradiscal pressure. The increase in that case is only about 2.4% for the intact as well as for the fractured vertebra. Moreover, the effect of upper body shift after a wedge-shaped vertebral body fracture on intradiscal pressure and thus on spinal load is much more pronounced than that of stiffness increase due to cement infiltration. Maximum von Mises stress in the endplates of all lumbar vertebrae is also higher after kyphoplasty and vertebroplasty. Cement augmentation has only a minor effect on endplate stresses in the unfractured vertebrae. The advantages of kyphoplasty found in this study will be apparent only if nearly full fracture reduction is achieved. Otherwise, differences between kyphoplasty and vertebroplasty become small or vanish. Our results suggest that vertebral body fractures in the adjacent vertebrae after vertebroplasty or kyphoplasty are not induced by the elevated stiffness of the treated vertebra, but instead the anterior shift of the upper body is the dominating factor.

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Section: Discussionmentioning

confidence: 99%

Spinal loads after osteoporotic vertebral fractures treated by vertebroplasty or kyphoplasty

Rohlmann¹,

Zander²,

Bergmann³

2005

Eur Spine J

Self Cite

111

View full text Add to dashboard Cite

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“…Experimental data performed by Rohlmann et al [44] and Baroud and Bohner [45] suggested that altered biomechanical properties of disk-somatic complex is associated with increased intradiscal pressure after PVP, producing increased mechanical stress to the endplates of adjacent vertebral bodies. Other authors have suggested that the presence of new vertebral fracture is not a complication of PVP [27,46,47].…”

Section: Sandwich Vertebra and Prophylactic Pvpmentioning

confidence: 99%

Is 3T-MR Spectroscopy a Predictable Selection Tool in Prophylactic Vertebroplasty?

Masala

Massari

Assako

et al. 2010

Cardiovasc Intervent Radiol

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This study was designed to confirm relationships between decrease of bone mineral density and increase of marrow fat and to delineate, through MR spectroscopy, vertebral body at high risk for compression fracture onset to justify prophylactic vertebroplasty. We enrolled 127 women: 48 osteoporotic, 36 osteopenic, and 43 normal subjects, who underwent DXA and MR examination of spine. Then, we selected 48 patients with at least two acute osteoporotic vertebral fractures with interposed normal ''sandwich'' vertebrae; all patients underwent MR examination of spine. Significant statistical differences were found among ''Fat Fraction'' (FF) values in normal, osteopenic, and osteoporotic subjects: 59.8 ± 5.1%; 64.8 ± 4.4%; and 67.1 ± 3.3%. A mild, significant, negative correlation was observed between T-score and vertebral fat content (r = -0.585; P = 0.0000). In the second part of the study, 9 new vertebral fractures were observed in 48 patients (19%): 6 were ''sandwich'' vertebrae (12.5%), and 3 were located in distant vertebral body. The mean FF in sandwich fractured vertebrae was 72.75 ± 1.95 compared with the FF of the nonfractured sandwich, and distant control vertebrae were 61.83 ± 3.42 and 61.42 ± 3.64. We found a significant statistical difference between fractured and nonfractured vertebrae (P \ 0.001). The results of this study suggest that MR spectroscopy could be a reliable index to predict the risk of new compression vertebral fracture and could be used for vertebroplasty planning contributing to clarify the possibility to add prophylactic PVP to standard treatment.

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“…In this study, the vertebrae were assumed to be rigid in order to reduce computer time. The material properties of the different soft tissues were taken from the literature (Table 1) [5,13,19,21,23,27] and are specified in detail elsewhere [18,19,21,27].…”

Section: Fe Model Of Intact Lumbar Spinementioning

confidence: 99%

Effect of an artificial disc on lumbar spine biomechanics: a probabilistic finite element study

et al. 2008

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The effects of different parameters on the mechanical behaviour of the lumbar spine were in most cases determined deterministically with only one uncertain parameter varied at a time while the others were kept fixed. Thus most parameter combinations were disregarded. The aim of the study was to determine in a probabilistic finite element study how intervertebral rotation, intradiscal pressure, and contact force in the facet joints are affected by the input parameters implant position, implant ball radius, presence of scar tissue, and gap size in the facet joints. An osseoligamentous finite element model of the lumbar spine ranging from L3 vertebra to L5/S1 intervertebral disc was used. An artificial disc with a fixed center of rotation was inserted at level L4/L5. The model was loaded with pure moments of 7.5 Nm to simulate flexion, extension, lateral bending, and axial torsion. In a probabilistic study the implant position in anterior-posterior (ap) and in lateral direction, the radius of the implant ball, and the gap size of the facet joint were varied. After implanting an artificial disc, scar tissue may develop, replacing the anterior longitudinal ligament. Thus presence and absence of scar tissue were also simulated. For each loading case studied, intervertebral rotations, intradiscal pressures and contact forces in the facet joints were calculated for 1,000 randomized input parameter combinations in order to determine the probable range of these output parameters. Intervertebral rotation at implant level varies strongly for different combinations of the input parameters. It is mainly affected by gap size, ap-position and implant ball radius for flexion, by scar tissue and implant ball radius for extension and lateral bending, and by gap size and implant ball radius for axial torsion. For extension, intervertebral rotation at implant level varied between 1.4°and 7.5°. Intradiscal pressure in the adjacent discs is only slightly affected by all input parameters. Contact forces in the facet joints at implant level vary strongly for the different combinations of the input parameters. For flexion, forces are 0 in 63% of the cases, but for small gap sizes and large implant ball radii they reach values of up to 533 N. Similar results are found for extension with a maximum predicted force of 560 N. Here the forces are mainly influenced by gap size, implant ball radius and scar tissue. The forces vary between 0 and 300 N for lateral bending and between 0 and 200 N for axial torsion. The parameters that have the greatest effect in both loading cases are the same as those for extension. Intervertebral rotation and contact force in the facet joints depend strongly on the input parameters studied. The probabilistic study shows a large variation of the results and likelihood of certain values. Clinical studies will be required to show whether or not there is a strong correlation of parameter combinations that cause high facet joint forces and low back pain after total disc replacement.

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Comparison of the biomechanical effects of posterior and anterior spine-stabilizing implants

Cited by 47 publications

References 20 publications

Spinal loads after osteoporotic vertebral fractures treated by vertebroplasty or kyphoplasty

Spinal loads after osteoporotic vertebral fractures treated by vertebroplasty or kyphoplasty

Is 3T-MR Spectroscopy a Predictable Selection Tool in Prophylactic Vertebroplasty?

Effect of an artificial disc on lumbar spine biomechanics: a probabilistic finite element study

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