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Finite element analysis of infant brain expansion and muscle activation shows the importance of cranial sutures for healthy skull growth

Authors:
Finite element analysis of infant brain expansion and muscle
activation shows the importance of cranial sutures for healthy skull growth
Louisa Hulls1, Mehran Moazen2, Alana C Sharp3
1 Human Anatomy Resource centre, University of Liverpool, Liverpool, UK; 2UCL Mechanical Engineering,
University College London, UK; 3Institute of Life course and Medical Sciences, University of Liverpool, UK
Craniofacial sutures are unique joints consisting of soft connective tissues between the skull
bones. They are important sites for bone growth during development, and for absorption of
mechanical stress, but their mechanical function is not well understood.
Craniosynostosis is a congenital condition causing premature fusion of one or more cranial
sutures (Figure 1), which can lead to head malformations and brain damage.
Corrective surgery, including cranial vault remodelling, fronto-orbital advancement or spring-
mediated cranioplasty, aims to separate the fused cranial bones, restore head shape, and
allow for normal cranial development.
It is therefore important to understand the role sutures play in skull function and growth.
Material and Methods
Conclusions and Future Research
Computational modeling can reveal important biomechanical relationships between craniofacial sutures and mechanical strain.
FE stimulations show that sutures are important sites for cranial strain during brain expansion and masticatory muscle activation in infants.
Higher strain in the patent sutures reduced strain in the surrounding bone.
The frontal suture is particularly important as a strain sink during jaw muscle activation.
Further research is needed to enhance our understanding of individual suture synostosis to explore patient-specific craniosynostosis.
Our findings suggest FE analysis has the potential to improve our understanding of the biomechanical environment of the infant skull during
growth and could be used as a clinical tool for planning appropriate treatment strategy and optimising recovery for patients with
craniosynostosis.
Figure 1
We applied finite element (FE) analysis to an infant skull model
developed by Libby et al. (2017). The specimen used to create the
FE model was obtained from the archaeological collection at the
University of Dundee.
The 3D FE model contained bone, suture and intracranial volume
(ICV) as separate materials (Figure 2).
ICV expansion (modelled as thermal expansion) and jaw muscle
activation were simulated in Abaqus CAE 6.14 (SIMULA TM) FE
software.
We simulated “fused” sutures by applying the material properties
of bone to the suture areas.
We then compared the model with fused and non-fused cranial
sutures to explore the biomechanical effect.
Figure 2. (a) CT sagittal section of an infant skull; (b) 3D FE model with bone (green), cranial
sutures (red) and internal ICV (unseen) materials. Mechanical loads for the temporalis and
masseter are shown as arrows.
(a) (b)
Results
There was significantly higher strain in surrounding bone in the
fused model compared to the unfused model (Figure 3) suggesting
fusion of sutures causes bone deformation due to the loss of
compliant soft tissue sutures.
During bilateral temporalis and
masseter muscles activation,
tensile strain was significantly
higher at the frontal suture in the
unfused model compared to the
fused model.
Figure 4 (left). Tensile strain distribution during
bilateral muscle activation for fused (a) and
unfused (b) suture models.
0.05ε 0.08ε 0.15ε 0.25ε
(b)
Figure 3. Tensile strain distribution during ICV expansion for fused (a) and unfused (b) suture
models. Blue shows areas of low strain, red shows high strain at respective limits and grey
represents strain above this upper limit show under each model.
(a)
References
Libby J. et al. (2017) Modelling human skull growth: a validated computational model: Journal of the royal society interface; Cohen M, & MacLean R. (2000) Craniosynostosis: Diagnosis, Evaluation, and
Management. Journal of Medical Genetics, 37:727; Malde, O. et al. (2019) An Overview of Modelling Craniosynostosis Using the Finite Element Method. Molecular Sindonology, 10:74-82.
(a)
(b)
Lateral Anterior
1. Design
FE skull model with fused
(craniosynostosis) sutures and
non-fused (normal) sutures.
2. Simulate
Forces experienced during
brain growth and activation
of masticatory muscles.
3. Compare
Tensile strain distribution
between these two scenarios in
our model with and without
patent sutures
Dolichocephaly
Plagiocephaly
Trigonocephaly
Brachycephaly
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Article
Full-text available
During the first year of life, the brain grows rapidly and the neurocranium increases to about 65% of its adult size. Our understanding of the relationship between the biomechanical forces, especially from the growing brain, the craniofacial soft tissue structures and the individual bone plates of the skull vault is still limited. This basic knowledge could help in the future planning of craniofacial surgical operations. The aim of this study was to develop a validated computational model of skull growth, based on the finite-element (FE) method, to help understand the biomechanics of skull growth. To do this, a two-step validation study was carried out. First, an in vitro physical three-dimensional printed model and an in silico FE model were created from the same micro-CT scan of an infant skull and loaded with forces from the growing brain from zero to two months of age. The results from the in vitro model validated the FE model before it was further developed to expand from 0 to 12 months of age. This second FE model was compared directly with in vivo clinical CT scans of infants without craniofacial conditions (n = 56). The various models were compared in terms of predicted skull width, length and circumference, while the overall shape was quantified using three-dimensional distance plots. Statistical analysis yielded no significant differences between the male skull models. All size measurements from the FE model versus the in vitro physical model were within 5%, with one exception showing a 7.6% difference. The FE model and in vivo data also correlated well, with the largest percentage difference in size being 8.3%. Overall, the FE model results matched well with both the in vitro and in vivo data. With further development and model refinement, this modelling method could be used to assist in preoperative planning of craniofacial surgery procedures and could help to reduce reoperation rates.
Article
Craniosynostosis is a medical condition caused by the early fusion of the cranial joint. The finite element method (FEM) is a computational technique that can answer a variety of “what if” questions in relation to the biomechanics of this condition. The aim of this study was to review the current literature that has used FEM to investigate the biomechanics of any aspect of craniosynostosis, being its development or its reconstruction. This review highlights that a relatively small number of studies (n = 10) has used FEM to investigate the biomechanics of craniosynostosis. Current studies set a good foundation for the future to take advantage of this method and optimize reconstruction of various forms of craniosynostosis.