Biomedical subjects

Ee-Chon Teo

Publications and source records attributed to Ee-Chon Teo.

13 recordsLinked to original sources

PubMed2006

Effect of bilateral facetectomy of thoracolumbar spine T11-L1 on spinal stability.

Spinal stenosis can be found in any part of the spine, though it is most commonly located on the lumbar and cervical areas. It has been documented in the literature that bilateral facetectomy in a lumbar motion segment to increase the space induces an increase in flexibility at the level at which the surgery was performed. However, the result of bilateral facetectomy on the stability of the thoracolumbar spine has not been studied. A nonlinear three-dimensional finite element (FE) model of thoracolumbar T11-L1 was built to explore the influence of bilateral facetectomy. The FE model of T11-L1 was validated against published experimental results under various physiological loadings. The FE model with bilateral facetectomy was evaluated under flexion, extension, lateral bending and axial rotation to determine alterations in kinematics. Results show that bilateral facetectomy causes increase in motion, considerable increase in axial rotation and least increase in lateral bending. Removal of facets did not result in significant change in the sagittal motion in flexion and extension.

Biomechanical Phenomena↗

PubMed2006

Influence prediction of injury and vibration on adjacent components of spine using finite element methods.

OBJECTIVES: A three-dimensional finite element (FE) model of the lumbar spine L3-L5 segment, the ligaments of which were assumed to be nonlinear materials, was established based on the actual vertebra geometry to investigate the influence of the injury lumbar spine on its adjacent components on the condition of whole-body vibration. Several injury conditions of the spine components were assumed, such as facetectomy, nucleotomy, and removal of bony posterior elements. METHODS: The dynamic FE analyses were carried out for those FE conditions under cyclic compression loads at the frequencies of 5 and 10 Hz. Then a comparison between the dynamic results and the static results was conducted to analyze the influence of both the nucleus injury and the facet joint injury on the adjacent intervertebral discs. RESULTS AND CONCLUSIONS: The results indicate that the lumbar spine exhibits not only vertical vibration but also the flexion--extension motion during vibration. The denucleation will cause high stress and large disc bulge on the disc annulus under vibration. The facet joints of lumbar spine can limit the motion amplitude of flexion-extension and protect both the posterior regions and the posterolateral regions of disc annulus from large strain and stress during vibration. The facet joint removal will increase the stress of disc annulus by around 15% at the posterior region for the conditions of nucleotomy or no vibration. The stress of annulus circumference is higher at the posterolateral region than that of other regions of annulus circumference, and the facet joint removal may exacerbate the intervertebral disc degeneration on the condition of whole-body vibration.

Compressive Strength↗

PubMed2006

Comparison of kinematics between thoracolumbar T11-t12 and T12-L1 functional spinal units.

The purpose of this study was to compare the kinematics in terms of the locations and loci of instantaneous axes of rotation (IARs) at levels T11-T12 and T12-L1 of thoracolumbar junction (TLJ). The LAR is one of the kinematics characteristics of a functional spinal unit (FSU) in a plane under load. There is little information about loci of IARs in the TLJ. Validated finite element (FE) models of T11-T12 and T12-L1 FSUs were used to determine the locations and loci of IARs in three anatomical planes. In the sagittal plane, the locations and loci of the IARs were located below the intervertebral disc for T11-T12, and situated in the intervertebral disc for T12-L1. In the frontal plane, they were all located around the mid-sagittal plane for T11-T12 and T12-L1. In the transverse plane, they fell in the medio-anterior region of the movable vertebra T11 for T11-T12, and located near the cortical shell of the upper vertebra T12 for T12-L1. These findings may offer an insight to better understanding the kinematics of the human thoracolumbar spine and provide clinically relevant information for the evaluation of spinal stability and functionality of implant devices.

Biomechanical Phenomena↗

PubMed2005

Investigation of thoracolumbar T12-L1 burst fracture mechanism using finite element method.

A finite element model of the T12-L1 motion segment was subjected to dynamic vertical impact to investigate vertebral burst fracture mechanism at the thoracolumbar junction. A rigid ball was directed vertically towards a rigid plate fixed on top of the T12 vertebral body to simulate the axial impact. The results show that upon impact, the T12 vertebra exhibited a vibratory motion. At its maximum compression, the endplates bulged towards their vertebral bodies. The central parts of the endplates adjacent to the nucleus experienced the highest effective stress, and localized stress concentration developed correspondingly within the central parts of the cancellous bone adjacent to the endplates. This appears to confirm the hypothesis that nucleus material is forced to enter the vertebral body, pressurizing it further and squeezing the fat and marrow contents out of the cancellous bone. When the nucleus material enters the vertebral body faster than fat and marrow being expulsed, the vertebral body could burst through the anterior and posterior cortical shell. Upon sudden posterior cortex fracture, the transient fragment encroachment could be further into the spinal canal than the final observed locations, as the fragments are retropulsed to the vertebral body during the bursting process.

Biomechanical Phenomena↗

PubMed2005

Vibration characteristics of the human spine under axial cyclic loads: effect of frequency and damping.

STUDY DESIGN: A nonlinear finite element model of lumbar spine segment L3-L5 was developed. The effects of upper body mass, nucleus injury, damping, and different vibration frequency loads were analyzed for the whole body vibration. OBJECTIVES: To analyze the influence of whole body vibration on facets of lumbar spine and to analyze the influence of nucleus injury, upper body mass, and damping on the dynamic characteristics of lumbar spine. SUMMARY OF BACKGROUND DATA: Many studies have investigated whole body vibration for lumbar spine. However, very few investigations analyzed the influence of whole body vibration on facets and vibration characteristics of the injured spine. METHODS: The nonlinear finite element model of the L3-L5 segment was constructed based on the embalmed vertebra geometry and validated. Besides static and modal analyses, transient dynamic analyses were also conducted on the model with an upper body mass under damping and different frequency cyclic loads. RESULTS: In the period of human spine vibration, the vibration effects of different regions of the lumbar spine are not the same. Anterior regions of the L3-L5 segment show small vibration amplitudes, but posterior regions show large amplitudes. The vibration amplitude of facet contact force is more than 2.0-fold as large as that of displacement and stress on vertebrae or discs. To decrease the weight of the upper body will increase the resonant frequency. To remove the nucleus will decrease the resonant frequencies. The vibration displacement, stress, and facet contact force will reduce generally by 50% using damping ratio 0.08. CONCLUSIONS: The posterior regions of intervertebral discs of the lumbar spine are easy to injure during long-term whole body vibration compared to anterior regions. The vibration of human spine is more dangerous to facets, especially during whole body vibration approximating a sympathetic vibration, which may lead to abnormal remodeling and disorder of the lumbar spine.

Cadaver↗

PubMed2005

Influence of preload magnitudes and orientation angles on the cervical biomechanics: a finite element study.

OBJECTIVE: Although a number of in vivo, in vitro, and finite element studies have attempted to delineate the natural biomechanics, injury mechanisms, and surgical techniques of the cervical spine, none has explored the influence of various preload magnitudes and orientations on the biomechanical responses. METHODS: A nonlinear three-dimensional finite element model of the lower cervical spine (C5-C6) was used for this study. The model was tested under four preload magnitudes and three orientations. For every preload, magnitude, and orientation, pure moments of 1.8 Nm were applied to the superior surface of the moving vertebra (C5) in flexion, extension, lateral bending, and torsion. The resulting rotational motions were obtained and compared against literature data. RESULTS: The predicted biomechanical responses under the same loading directions varied, depending on the preload magnitudes and orientations. With flexion and extension, increasing the preload magnitudes and varying the C5-C6 orientation in the sagittal plane changed the rotational motions by 1% and 18%, respectively. Under normal orientation and with increasing preload magnitudes, flexion and extension increased, whereas lateral bending and torsion decreased. These changes were found to be influenced by several spinal components: posterior facets, passive ligaments, and stiffening of the intervertebral disc. The predicted responses under the direction of loading varied significantly, depending on the preload magnitudes and orientations. Under fixed preload magnitudes and varying the three types of orientations, rotational motions were not affected under flexion but changed under extension, lateral bending, and axial rotations. Under normal orientation and increasing preload magnitudes, biomechanical responses under flexion and extension increased, whereas lateral bending and torsion decreased. Changes in the predicted responses were found to be influenced by several spinal components: posterior facets, passive ligaments, and stiffening of the intervertebral disc. CONCLUSION: The findings of the current study were important for the further understanding of the cervical biomechanics during in vitro testing.

Biomechanical Phenomena↗

PubMed2005

Influence of cervical disc degeneration after posterior surgical techniques in combined flexion-extension--a nonlinear analytical study.

Laminectomy and facetectomy are surgical techniques used for decompression of the cervical spinal stenosis. Recent in vitro and finite element studies have shown significant cervical spinal instability after performing these surgical techniques. However, the influence of degenerated cervical disk on the biomechanical responses of the cervical spine after these surgical techniques remains unknown. Therefore, a three-dimensional nonlinear finite element model of the human cervical spine (C2-C7) was created. Two types of disk degeneration grades were simulated. For each grade of disk degeneration, the intact as well as the two surgically altered models simulating C5 laminectomy with or without C5-C6 total facetectomies were exercised under flexion and extension. Intersegmental rotational motions, internal disk annulus, cancellous and cortical bone stresses were obtained and compared to the normal intact model. Results showed that the cervical rotational motion decreases with progressive disk degeneration. Decreases in the rotational motion due to disk degeneration were accompanied by higher cancellous and cortical bone stress. The surgically altered model showed significant increases in the rotational motions after laminectomies and facetectomies when compared to the intact model. However, the percentage increases in the rotational motions after various surgical techniques were reduced with progressive disk degeneration.

Biomechanical Phenomena↗

PubMed2005

Prediction of the modal characteristics of the human spine at resonant frequency using finite element models.

To understand the dynamic characteristics of the human spine, a detailed three-dimensional finite element model of the lower thorax to pelvis segment, T12-pelvis, was developed based on actual vertebral geometry. After modal analysis, the resonant frequencies of different spinal segments were obtained. The vibration mode of T12-pelvis shows that the human upper body mainly performs the vertical motion during whole-body vibration and the lumbar spine segment conducts translation and rotation in the sagittal plane. The lower segments of the lumbar spine move in flexion and the upper lumbar segments move in extension. This investigation may be helpful in understanding further the biomechanical behaviour of the human spine under the condition of whole-body vibration and to offer potential references for spinal disease treatments and product design in industry.

Computer Simulation↗

PubMed2004

Kinematics of the thoracic T10-T11 motion segment: locus of instantaneous axes of rotation in flexion and extension.

The purpose of this study was to determine the locations and loci of instantaneous axes of rotation (IARs) of the T10-T11 motion segment in flexion and extension. An anatomically accurate three-dimensional model of thoracic T10-T11 functional spinal unit (FSU) was developed and validated against published experimental data under flexion, extension, lateral bending, and axial rotation loading configurations. The validated model was exercised under six load configurations that produced motions only in the sagittal plane to characterize the loci of IARs for flexion and extension. The IARs for both flexion and extension under these six load types were directly below the geometric center of the moving vertebra, and all the loci of IARs were tracked superoanteriorly for flexion and inferoposteriorly for extension with rotation. These findings may offer an insight to better understanding of the kinematics of the human thoracic spine and provide clinically relevant information for the evaluation of spinal stability and implant device functionality.

Biomechanical Phenomena↗

PubMed2004

Effects of cervical cages on load distribution of cancellous core: a finite element analysis.

METHODS: The study was designed to analyze the load distribution of the cancellous core after implantation of vertical ring cages made of titanium, cortical bone, and tantalum using the finite element (FE) method. The intact FE model of C5-C6 motion segment was validated with experimental results. RESULTS: The percentage of load distribution in cancellous core dropped by about one-third of the level for the intact model after the cage implantation. The difference among cages made of different materials (or different stiffnesses) was not very obvious. CONCLUSIONS: These results implied that the influence of the cage on the load transfer in the cancellous core is greatly related to the cage's dimensions and position within the intervertebral space. The dimension and position of the cage that least disturb the load distribution in cancellous core could be criteria in cage development.

Cadaver↗

PubMed2004

Prediction of inter-segment stability and osteophyte formation on the multi-segment C2-C7 after unilateral and bilateral facetectomy.

The objective of this study was to determine the intersegment stability, disc degeneration, and osteophytes formation on the multisegment cervical spine (C2-C7) after unilateral and bilateral facetectomy. A geometrically accurate non-linear three-dimensional model of the intact human cervical spine was created from the digitized coordinates of the dry vertebrae. The intact model was validated against the published results under physiological loading conditions. Eight surgically altered models were created from the intact model. The intact and surgical altered models were subjected to physiological loading. The inclusion of five levels in the present model allowed accurate determination of the intersegment responses and internal cortical bone and disc annulus stress in the adjacent spinal components. Results indicated that facetectomy performed on C5-C6 significantly affects the corresponding stress and intersegment motions at the corresponding C5-C6 levels. The maximum increases were 18 per cent for bilateral facetectomy and 7 per cent for unilateral facetectomy under lateral bending. Combined flexion-extension and axial rotation caused an approximately similar amount of increases after total facetectomy. In addition, adjacent segments (C4-C5 and C6-7) also experience a slight increase in the intersegment responses and internal stress after facetectomy. It has been shown that facetectomy of greater than 50 per cent resulted in segment hypermobility and substantial increase in the disc annulus and cortical bone stress. Increase in the stress may lead to osteophytes formation. This study revealed important information that will help clinicians identify the critical intersegment stability and to decide on the amount of facets resection.

Cervical Vertebrae↗

PubMed2003

Validation of T10-T11 finite element model and determination of instantaneous axes of rotations in three anatomical planes.

STUDY DESIGN: A finite element (FE) model of thoracic spine (T10-T11) was constructed and used to determine instantaneous axes of rotation (IARs). OBJECTIVES: To characterize the locations and loci of IARs in three anatomic planes. SUMMARY OF BACKGROUND DATA: The center of rotation is a part of a precise method of documenting the kinematics of a spinal segment for spinal stability and deformity assessments and for implant devices study. There is little information about loci of IARs in thoracic spine. METHODS: A FE model of thoracic spine (T10-T11) was developed and validated against published data. The validated model was then used to determine the locations and loci of IARs in three anatomic planes. RESULTS: Within the validated range, The IARs locations and loci were found to vary with the applied pure moments. Under flexion and extension pure moments, the loci of IARs were tracked anterosuperiorly for flexion and posteroinferiorly for extension with rotation between the superior endplate and the geometrical center of the inferior vertebra T11. Under left and right lateral bending pure moments, the loci were detected to diverge latero-inferiorly from the mid-height of the intervertebral disc, then converge medio-inferiorly toward the geometrical center of the inferior vertebra T11. For axial rotation, the IARs were located between anterior nucleus and anulus and found to diverge in opposite direction latero-posteriorly with increasing left and right axial torque. CONCLUSIONS: The results of IARs would provide further understanding to the kinematics and biomechanical responses of the human thoracic spine, which is important for the diagnosis of disc degeneration and implant study.

Biomechanical Phenomena↗

PubMed2003

Finite element analysis of cervical spinal instability under physiologic loading.

The definition of cervical spinal instability has been a subject of considerable debate and has not been clearly established. Stability of the motion segment is provided by ligaments, facet joints, and disc, which restrict range of movement. Moreover, permanent damage to one of the stabilizing structures alters the roles of the other two. Although many studies have been conducted to investigate cervical injuries, to date there are only limited finite element investigations reported in the literature on the biomechanical response of the cervical spine in these respects. A comprehensive, geometric, nonlinear finite element model of the lower cervical spine has been successfully developed and validated under compression, anterior-posterior shear, and sagittal moments. Injury studies were done by varying each spinal component independently from the validated model. Seven analyses were conducted for each injury simulation (model without ligaments, model without facets, model without facets and ligaments, and model without disc nucleus). Results indicate that the role of the ligaments in resisting anterior and posterior shear and flexion and axial rotation moments is important. Under other physiologic loading (anterior-posterior shear, flexion-extension, lateral bending, and axial rotation), the disc nucleus is responsible for the initial stiffness of the cervical spine. The results also highlight the importance of facets in resisting compression at higher loads, anterior shear, extension, lateral bending, and torsion. The results provide new insight through injury simulation into the role of the various spinal components in providing cervical spinal stability. These findings seem to correlate well with experimental results as well as with common clinical experience.

Cervical Vertebrae↗