Search

This paper details the quantitative three-dimensional anatomy of cervical, thoracic and lumbar vertebrae (C3–T12) of Chinese Singaporean subjects based on 220 vertebrae from 10 cadavers. The purpose of the study was to measure the linear dimensions, angulations and areas of individual vertebra, and to compare the data with similar studies performed on Caucasian specimens. Measurements were taken with the aid of a three-dimensional digitiser. The means and standard errors for linear, angular and area dimensions of the vertebral body, spinal canal, pedicle, and spinous and transverse processes were obtained for each vertebra. Compared to the Caucasian data, all the dimensions were found to be smaller. Of significance were the spinal canal area, and pedicle width and length, which were smaller by 31.7%, 25.7% and 22.1% on average, respectively. A slight divergence, instead of convergence, was found from T8 to T12. According to the findings, the use of a transpedicle screw may not be feasible. The results can also provide more accurate modelling for analysis and design of spinal implants and instrumentations, and also allow more precise clinical diagnosis and management of the spine in Chinese Singaporeans.

This paper details the quantitative three-dimensional anatomy of lumbar vertebrae L1–L5 from Asian (Singaporean) subjects based on 60 lumbar vertebrae from 12 cadavers. The purpose of the study was to measure the dimensions of the various parameters of the lumbar vertebrae and thereafter to compare the data with a study performed on Caucasian specimens. Measurements were taken with the aid of a three-dimensional digitiser. The means and standard errors for linear, angular and area dimensions of the vertebral body, spinal canal, pedicle, and spinous and transverse processes were obtained for each lumbar vertebra. From this comparison, it was found that the dimensions of the vertebral body of the Asian subjects are slightly larger, with a maximum average difference of 8% for the posterior vertebral body height. The dimensions of the spinal canal, pedicle, and spinous and transverse processes of Asian subjects are smaller. The greatest difference can be found in the spinal canal area and pedicle width, which are smaller by an average of 30% and 20%, respectively. With the exception of the spinal canal depth, spinal canal area and pedicle width, all other parameters compared show a similar trend. The findings can provide more accurate modelling for analysis and spinal implant design and also allow more precise clinical diagnosis in sub-Asian groups.

An anatomically realistic three-dimensional (3D) finite element (FE) model of L4–L5 motion segment was created. The intact model was further modified to simulate two different disc degeneration grades, slight and moderate, at the L4–L5 segment. The implanted models were accordingly developed by incorporating a pair of 6mm diameter straight longitudinal rods position bilaterally into the degenerated models. In order to study the effect of implant stiffness on disc loading under compression, the stiffness of the longitudinal rod was varied between 1 and 83,000 N/mm in discrete steps. The intact, degenerated and implanted models were then exercised by applying 3,000N compressive force on the superior surface of L4 vertebra to investigate the load transmission characteristics of different implants. The results showed that the side effect of a degenerated disc is obvious for the lumbar segment load bearing capacity. The stiffness of the segment was increased due to the stiffer disc, which is caused by the severity of disc degeneration. The implant stiffness of lower than 2,000N/m has greater effect on disc loading and segment behavior. For an implanted model, the predicted annulus stress is close to the intact model when the implant stiffness is around 2000N/m. In addition, the effect of stiffness became less significant beyond this value. For dynamic stabilization purpose, the stiffness implant is suggested to be lower than 2000N/m

A comprehensive, geometrically accurate, nonlinear FE model of thoracolumbar spine multisegment (T12-L5) was developed to simulate the response of thoracolumbar spine under the mine blast condition with two initial postures. The vertical accelerations along the Y-axis of the T12-L5 FE model were applied on the inferior surface of L5 based on the simulated sitting postures. For both postures, the L5 inferior surface was constrained to move only in vertical direction. The predicted responses of each motion segment during the first 100ms were computed and compared under the two conditions. The results showed that the motion segments oscillate during and after the sudden impact. The maximum compressive deformation of the discs and segmental rotations occurred at around 36ms which also corresponds to the ending of the impact force. After that, the discs expand in the opposite direction. During the expansion phase, the disc heights exceeded their original position. The predicted frequency of the vibration of the motion segments was around 15Hz, which implied that a number of oscillations occur in less than one second before dying out (with the larger amplitudes of these oscillations occurring during the first hundredths of a second). Compared against sitting posture, although the resultant magnitude of disc deformations and segmental rotations were higher due to the relative anterior position of the mass point for the napping posture, the basic trends of segmental motions and predicted injury location were similar. Under such a rapid high axial impact (up to nearly 30G within 30ms), a slight difference between the position of centre of body gravity will not produce any differences in response of the thoracolumber spine.

Objective A three-dimensional poroelastic finite element (FE) L2-L3 model was developed to study lumbar spinal instability and intrinsic parameters in the intervertebral disc (IVD). Methods The FE model took into consideration poroelasticity of the IVD and viscoelasticity of the annulus fibers and ligaments to predict the time-dependent behavior. To simulate a holding task, the motion segment was subjected to a combined loading of constant compressive load (1600 N) and anterior shear (200 N) for 2 hours, and the role of facet joints and ligaments in the biomechanical response was investigated by removal of unilateral/bilateral facets, posterior ligaments (supraspinous and interspinous), and facets and ligaments. Results The results show the stabilizing role of the facets and ligaments in resisting anterior shear and sagittal rotation under combined loading over time. The main pathway of fluid movement was found to permeate through the central region of the endplate, and the fluid diffusion occurred earlier at the posterior nucleus than the anterior nucleus. The fluid loss from the nucleus dictated the time-dependent motion under the sustained loading, whereas the intrinsic properties of ligaments/annulus fibers played a role only in the early stage of the loading. Conclusion The predicted results using poroelastic elements provide new insight into the IVD in providing the spinal stiffness under combined loading.

In human, the cervical spine region is very susceptible to impact injury. The complex structures of C1 and C2 serve to transmit the weight of the cranium to the greatly similar structural cervical spine from C3 caudally. Application of sudden disruption forces will detach the junction of the cervico-cranium with the pars interarticularis of the neural arch of C2 from the lower cervical spine by fracturing, as in a "hangman's fracture". Severe falls or blows to the head from heavy objects will cause the fracture of the odontoid process of C2. Many biomechanical studies were conducted based on full restraint of the inferior aspects of isolated C2 to produce odontoid fracture. In this study, two different restraining conditions of C2 were adopted experimentally to determine the absolute fracture load and the corresponding fracture patterns that are common to C2.Nine C2 vertebrae obtained from cadaver spines, ranging from 51 to 80 years, were used. Two specified restraint conditions were employed: (1) fully constrain the posterior element postero-anteriorly up to one-quarter of the inferior facet; and (2) fixing of C2 by a specially-designed rig whereby the body of C2 embedded in the pivoted cup and its inferior facets positioned on top of two lateral plates. Antero-posterior shear force was applied on the anterior articulating facet of the dens until failure.These specified restraint conditions had resulted in specific fracture of C2. Antero-posterior shear force ranges from 840 to 1220 N was required to cause fracture across the pars interarticularis under restraint condition 1. Failure load of between 900 and 1500 N was found to cause odontoid fracture under restraint condition 2. These values are in agreement with published data.The biomechanical response of C2 was specific to the mode of restraint conditions of C2. In reality, depending on the force vector applied to the head, precise posture at the time of trauma, spinal geometry, and physical properties, different types of C2 fracture patterns may happen. These findings are of potentials for the biomechanical correlation and validation study of C2 vertebra using analytical approaches, and in the surgical anterior screw fixation of odontoid fracture.

Fracture of the atlas was first described by Jefferson (1920). He theorised a bursting mechanism of fracture as the occipital condyles were driven into the atlas. Experimental studies by Hays and Alker (1988) and Panjabi et al (1991) were also conducted to explain the injury mechanisms. Injury mechanisms and fracture patterns are important in the clinical evaluation of spinal injuries. Recognition and interpretation of the fracture patterns help to determine the spinal instability and consequently the choice of treatment. Although the fracture mechanics of the atlas have received much attention, it has not been investigated using theoretical modelling.A high-definition digitiser was used to obtain the geometrical data for the finite element mesh generation. Contrary to the widely used method, such as computed tomography scan for geometric extraction, the direct digitising process of the dried specimen reliably preserves the accurate topography of up to 0.1-mm interval of the original structure. The finite element model was exercised under an axial compressive mode of pressure loading to investigate the sites of failure reported in vivo and in vitro.Using material properties from literature, the predicted results from the 7808-finite element model demonstrate high concentration of localised stress at the anterior and posterior arch of the atlas, which agrees well with those reported in the literature. Furthermore, our results are also in good agreement with the findings reported by Panjabi et al (1991), which show that the groove of the posterior arch is subjected to enormous bending moment under simulated hyperextension conditions.The close agreement of the failure location provided confidence to perform further analysis and in vitro experiments. The predicted results from finite element analysis may be potentially used to supplement experimental research in understanding the clinical biomechanics of the C1.