A probabilistic finite element analysis of the stresses in the augmented vertebral body after vertebroplasty

If conservative treatment of osteoporotic vertebral compression fractures fails, vertebro- or kyphoplasty is indicated. Usually, polymethylmethacrylate cement (PMMA) is applied coming along with many disadvantageous features. Aluminum-free glass-polyalkenoate cement (GPC) appears to be a benefit alternative material. This study aimed at comparing the mean stress values in human vertebrae after kyphoplasty with PMMA and GPC (IlluminOss™) at hand of a finite element analysis. Three models were created performing kyphoplasty using PMMA or IlluminOss™, respectively, at two native, human lumbar vertebrae (L4) while one remains intact. Finite element analysis was performed using CT-scans of every vertebra. Moreover the PMMA-treated vertebra was used as a model as analyses were executed using material data of PMMA and of GPC. The unimpaired, spongious bone showed potentials of 0.25 MPa maximally. After augmentation stress levels showed fivefold increase, rising from externally to internally, revealing stress peaks at the ventral border of the spinal canal. At central areas of cement 1 MPa is measured in both types of cement. Around these central areas the von Mises stress decreased about 25-50% (0.5-0.75 MPa). If workload of 500 N was applied, the stress appeared to be more centralized at the IlluminOss™-model, similar to the unimpaired. Considering the endplates the GPC model also closely resembles the unimpaired. Comparing the PMMA-treated vertebral body and the GPC-simulation, there is an obvious difference. While the PMMA-treated model showed a central stress peak of 5 MPa, the GPC-simulation of the same vertebral body presents lower stress of 1.2-2.5 MPa. Finite element analysis showed that IlluminOss™ (GPC), used in kyphoplasty of vertebral bodies, creates lower level stress and strain compared to standardly used PMMA, leading to lower stress concentrations on the cranial and caudal vertebral surface especially. GPC appears to own advantageous biological and clinical relevant features.

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FINITE ELEMENT ANALYSIS OF THE SPACE CREATED BY SPLIT SPINOUS PROCESSES IN DOUBLE-DOOR LAMINOPLASTY TO OPTIMIZE SHAPE OF AN ARTIFICIAL SPACER

Journal of Musculoskeletal Research ◽

10.1142/s0218957700000070 ◽

2000 ◽

Vol 04 (01) ◽

pp. 47-54 ◽

Cited By ~ 4

Author(s):

Shigeru Hirabayashi ◽

Kiyoshi Kumano

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Vertebral Body ◽

Clinical Case ◽

Spinous Process ◽

Lateral Deviation ◽

Element Analysis ◽

Spinous Processes ◽

Inner Surface ◽

The Difference

In double-door laminoplasty, several types of artificial spinous process spacers have been used instead of grafted bone from the iliac crest. However, inadequate contact between the spacer and the spinous process has recently been reported. From the observation during operation, we suspect that the main cause of the inadequate contact is the difference in shape between the spacer and the widened space created by the split spinous processes. The purpose of this study was to investigate the shape of the widened space by means of a finite element analysis in order to confirm our observation objectively and to provide a shape design of a spacer adapting to the space. Half-sectioned finite element models of the second cervical (C2) vertebra and the C6 vertebra were made from both the computed tomography (CT) of a clinical case and a plastic model of a cervical spine. The finite element model was designed to have almost the same size and shape as those of the genuine vertebra in the clinical case. Since cancellous bone and soft tissues were thought not to meaningfully influence the rigidity of the model, the model was made of only cortical bone with a thickness of 1.5 mm. The x-axis was defined as the lateral direction of the vertebral body, the y-axis as the anteroposterior direction of the vertebral body and the z-axis as the craniocaudal direction along the posterior margin of the vertebral body. The boundary conditions were fixed at the inner surface of the half-sectioned vertebral body. A force of 100 N was applied to the inner surface of the half-sectioned spinous process (to the cranial side and the caudal side, 50 N each) in the direction of the x-axis. The lateral deviation of each split spinous process was defined as the degree of deviation in the x-axis direction. The degree of lateral deviation of each split spinous process was analyzed in two types of models with and without making a lateral gutter 4 mm wide along the z-axis direction. The lateral deviation at the cranial side was larger than that at the caudal side in both the C2 and C6 vertebrae. The difference between the lateral deviation at the cranial side and the caudal side of each vertebra was larger in the type of model with the lateral gutter than in the type of model without it. It was confirmed that the shape of the widened space is trapezoidal in not only the axial but also frontal sections. In conclusion, the optimal shape of a spacer adapting to the widened space in double-door laminoplasty is trapezoidal in not only the axial but also frontal sections.

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Experimental Validation of Finite Element Analysis of Human Vertebral Collapse Under Large Compressive Strains

Journal of Biomechanical Engineering ◽

10.1115/1.4026409 ◽

2014 ◽

Vol 136 (4) ◽

Cited By ~ 17

Author(s):

Hadi S. Hosseini ◽

Allison L. Clouthier ◽

Philippe K. Zysset

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Trabecular Bone ◽

Axial Compression ◽

Vertebral Body ◽

Computer Tomography ◽

Strain Localization ◽

Vertebral Collapse ◽

Element Analysis ◽

Custom Made

Osteoporosis-related vertebral fractures represent a major health problem in elderly populations. Such fractures can often only be diagnosed after a substantial deformation history of the vertebral body. Therefore, it remains a challenge for clinicians to distinguish between stable and progressive potentially harmful fractures. Accordingly, novel criteria for selection of the appropriate conservative or surgical treatment are urgently needed. Computer tomography-based finite element analysis is an increasingly accepted method to predict the quasi-static vertebral strength and to follow up this small strain property longitudinally in time. A recent development in constitutive modeling allows us to simulate strain localization and densification in trabecular bone under large compressive strains without mesh dependence. The aim of this work was to validate this recently developed constitutive model of trabecular bone for the prediction of strain localization and densification in the human vertebral body subjected to large compressive deformation. A custom-made stepwise loading device mounted in a high resolution peripheral computer tomography system was used to describe the progressive collapse of 13 human vertebrae under axial compression. Continuum finite element analyses of the 13 compression tests were realized and the zones of high volumetric strain were compared with the experiments. A fair qualitative correspondence of the strain localization zone between the experiment and finite element analysis was achieved in 9 out of 13 tests and significant correlations of the volumetric strains were obtained throughout the range of applied axial compression. Interestingly, the stepwise propagating localization zones in trabecular bone converged to the buckling locations in the cortical shell. While the adopted continuum finite element approach still suffers from several limitations, these encouraging preliminary results towardsthe prediction of extended vertebral collapse may help in assessing fracture stability in future work.

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