Construction of a Statistical Cervical Vertebrae Geometric Model for Children 3–10 Years Old

Finite Element Analysis and Comparative Study of 4 Kinds of Internal Fixation Systems for Anterior Cervical Discectomy and Fusion in Children

Background

Spinal injury in children usually occurs in the cervical spine region. Anterior fixation of the lower cervical spine has been applied in treating pediatric cervical spine injury and disease due to its stable and firm mechanical properties. This study performed finite element analysis and comparison of four different anterior cervical internal fixation systems for children to explore more standard methods of anterior cervical internal fixation in children and seek more effective and safe treatment for children's cervical spine diseases.

Methods

A finite element model of 6-year-old children with lower cervical spine C4/5 discectomy was established, and the self-designed lower cervical spine anterior locking internal fixation system ACBLP and the children's anterior cervical internal fixation system ACOP, ACVLP, and ACSLP plate screws were fixed and loaded on the model. 27.42 N·m torque load was applied to each internal fixation model under six working conditions of anteflexion, backward flexion, left flexion, right flexion, left rotation, and right rotation, to simulate the movement of the cervical spine. The activity and stress distribution cloud diagram of each finite element model was obtained to explore the optimal method of anterior cervical fixation in children.

Results

In the four internal fixation models of ACOP, ACVLP, ACSLP, and ACBLP, the mobility of the C4/5 segment showed a decreasing relationship, and the mobility of adjacent segments increased significantly. In the Mises stress cloud diagram of the cervical spine of the four models, the vertebral body and accessories of the ACBLP model born the least stress, followed by ACSLP. The steel plate and screws in the ACVLP internal fixation model were the most stressed. The stress of the internal fixation system (plate/screw) in all models increased in the order of ACBLP, ACSLP, ACVLP, and ACOP.

Conclusions

ACBLP internal fixation system had obvious advantages in anterior internal fixation of the lower cervical spine in children, C4/5 had the smallest degree of movement, relative displacement was minimal, and the stress on the centrum and pedicle was the least, while the stress on the plate screw was relatively the smallest.

Quantification and statistical analysis on the cranial vault morphology for Chinese children 3-10 years old

BACKGROUND AND OBJECTIVE

Head injury is the leading cause of fatalities and disabilities in children. Characterizing the variation in cranial size/shape and thickness during growth is important for developing finite element models of child heads and evaluating head injury risk at different ages. However, the quantitative morphological features of the cranial vault (size/shape and non-uniform thickness distribution) have not been accounted for in children aged between 3 and 10 years old (YO).

METHODS

Geometrically equivalent discrete points were identified on 42 head CT scans of 3-10 YO children by separation, curve dividing, and point fitting. Based on discrete points, the principal component analysis and regression (PCA&R) method was used to develop a statistical model of the cranial vault as a function of age and head circumference.

RESULTS

The ontogeny of three-dimensional cranial morphology and non-uniform thickness from 3 to 10 years of age was quantified and cranial vault morphologies for 3-10 YO children were generated in 1 year intervals.

CONCLUSIONS

The automatic method, the procedure of identifying discrete points from CT scans, and the developed quantitative cranial vault model are reliable and accurate.

Estimation of a statistical geometric model for the cervical vertebrae of children aged 10-18 years

Child neck injuries in motor vehicle crashes (MVCs) result in high morbidity and mortality rates. Estimating a statistical cervical vertebrae geometric model and quantifying the variations of the size and shape with age are very important for investigating the dynamic response and injury risk to a child's cervical spine, as well as for providing a geometric basis for developing child anthropomorphic test devices (ATDs) and finite element models (FEMs) of different ages. In this study, spatial geometric points were automatically extracted from the cervical vertebrae computed tomography (CT) scans of 30 children aged 10 to 18 years old (YO), and a statistical geometric model was estimated for the cervical vertebrae as a function of age and neck circumference/neck length according to the method of principal component analysis and regression (PCA&R). Based on this statistical model, geometric point sets representing cervical vertebrae geometries at different ages and percentiles were generated and formed to envelope surfaces. Meanwhile, the size changes of the cervical vertebrae with child growth from 10 to 18 YO were quantified. In general, the anteroposterior length (APL), transverse process width (TPW), vertebral body height (VBH), and vertebral body depth (VBD) of the cervical vertebrae increase with age; the VBH and VBD increase faster than the APL and TPW. Compared with other vertebrae, the APL of C7 is larger, and the rate of increase of C1 with age is evidently slower. The TPWs of C1 and C7 are greater than those of C2 to C6. C7 has higher average values for the VBH and VBD than C3 to C6.

Combining statistical shape modeling, CFD, and meta-modeling to approximate the patient-specific pressure-drop across the aortic valve in real-time

BACKGROUND

Advances in medical imaging, segmentation techniques, and high performance computing have stimulated the use of complex, patient-specific, three-dimensional Computational Fluid Dynamics (CFD) simulations. Patient-specific, CFD-compatible geometries of the aortic valve are readily obtained. CFD can then be used to obtain the patient-specific pressure-flow relationship of the aortic valve. However, such CFD simulations are computationally expensive, and real-time alternatives are desired.

AIM

The aim of this work is to evaluate the performance of a meta-model with respect to high-fidelity, three-dimensional CFD simulations of the aortic valve.

METHODS

Principal component analysis was used to build a statistical shape model (SSM) from a population of 74 iso-topological meshes of the aortic valve. Synthetic meshes were created with the SSM, and steady-state CFD simulations at flow-rates between 50 and 650 mL/s were performed to build a meta-model. The meta-model related the statistical shape variance, and flow-rate to the pressure-drop.

RESULTS

Even though the first three shape modes account for only 46% of shape variance, the features relevant for the pressure-drop seem to be captured. The three-mode shape-model approximates the pressure-drop with an average error of 8.8% to 10.6% for aortic valves with a geometric orifice area below 150 mm² . The proposed methodology was least accurate for aortic valve areas above 150 mm² . Further reduction to a meta-model introduces an additional 3% error.

CONCLUSIONS

Statistical shape modeling can be used to capture shape variation of the aortic valve. Meta-models trained by SSM-based CFD simulations can provide an estimate of the pressure-flow relationship in real-time.

Development, validation, and application of ligamentous cervical spinal segment C6-C7 of a six-year-old child and an adult

BACKGROUND AND OBJECTIVE

The cervical spine is one of the primary regions that is easily injured in traffic accidents. Although adult cervical spine finite element models have been widely adopted to investigate the cervical injury, few efforts have been made with respect to the development and application of FE models of the pediatric cervical spine, especially that of a six-year-old child. The objective of this study is to develop and validate high quality cervical spinal segment C6-C7 FE models of a six-year-old child and an adult, and to further investigate the differences of C6-C7 between the child and adult under different loading conditions.

METHODS

The cervical spinal segment C6-C7 FE models were developed by a structured multiblock method, and were verified under flexion, extension, axial rotation, and lateral bending conditions. The validated models were used to investigate the differences of C6-C7 between the child and adult under different loading conditions.

RESULTS

The global angular displacement of C6-C7, the ligament elongation ratio, and the maximum effective strain of annulus fibrosus of the child were obviously larger than those of the adult under the same loading conditions. Regarding the loading forms, the flexion angular displacement of C6-C7 of the child was obviously larger than those of the extension and lateral bending, while for the adult cervical segment C6-C7, no obvious differences existed. The elongation ratio of different ligaments was highly dependent on the types of loadings. The maximum effective strain of annulus fibrosus under flexion, extension and lateral bending loads occurred at the compressive region of the front, rear, and one compressive lateral side, in which the annulus fibrosus was more susceptible to injury under the lateral bending condition, compared with those of the flexion and extension conditions.

CONCLUSIONS

Both the developed child and adult cervical spinal segment C6-C7 FE models exhibited high biofidelity. The responses (angular displacement, the ligament elongation ratio, and the maximum effective strain of annulus fibrosus) of the child and adult are dependent on the loading types, and the responses of the child were obviously larger than those of the adult under the same loading conditions.