Investigating the mechanical response of paediatric bone under bending and torsion using finite element analysis

Abstract

Fractures of bone account 25% of all paediatric injuries (Cooper et al. in J Bone Miner Res 19:1976-1981, 2004. https://doi.org/10.1359/JBMR.040902 ). These can be broadly categorised into accidental or inflicted injuries. The current clinical approach to distinguish between these two is based on the clinician's judgment, which can be subjective. Furthermore, there is a lack of studies on paediatric bone to provide evidence-based information on bone strength, mainly due to the difficulties of obtaining paediatric bone samples. There is a need to investigate the behaviour of children's bones under external loading. Such data will critically enhance our understanding of injury tolerance of paediatric bones under various loading conditions, related to injuries, such as bending and torsional loads. The aim of this study is therefore to investigate the response of paediatric femora under two types of loading conditions, bending and torsion, using a CT-based finite element approach, and to determine a relationship between bone strength and age/body mass of the child. Thirty post-mortem CT scans of children aged between 0 and 3 years old were used in this study. Two different boundary conditions were defined to represent four-point bending and pure torsional loads. The principal strain criterion was used to estimate the failure moment for both loading conditions. The results showed that failure moment of the bone increases with the age and mass of the child. The predicted failure moment for bending, external and internal torsions were 0.8-27.9, 1.0-31.4 and 1.0-30.7 Nm, respectively. To the authors' knowledge, this is the first report on infant bone strength in relation to age/mass using models developed from modern medical images. This technology may in future help advance the design of child, car restrain system, and more accurate computer models of children.

Investigating rolling as mechanism for humeral fractures in non-ambulant infants: a preliminary finite element study

“…Jenny, 4 however, claimed that it is difficult to draw a clear conclusion on the likelihood of self-inflicted humeral fracture caused by rolling because the range of bone strength of healthy infants is yet unknown. Since that paper, data have been published on the injury tolerance of infant bones, 8,9 which coupled with the present findings supports Rosado's opinion that the mechanism is unlikely to cause humeral fractures.…”

“…The maximum modulus of elasticity was estimated from the measured Hounsfield units of the CT scans. 8,9 M, male; F, female; E x , modulus of elasticity of the linear elastic model; SIDS, sudden infant death syndrome; SUDI, sudden unexpected death in infancy.…”

“…Therefore, the conventional principal strain threshold was used. 8,9 A further limitation is that bone biopsy was not performed, and underlying bone disease could not be completely excluded; however, at the authors' institution, routine post-mortem investigation of all infants dying suddenly and unexpectedly, consists of a full skeletal survey or anteroposterior and lateral "babygrams" (depending on size) and conventional autopsy. The radiographs of the three infants recruited to this study were reported as normal by experienced consultant radiologists as part of their routine clinical work.…”

“…13e15 This procedure has previously been used for paediatric bone, details were described in Li et al (2015) and Altai et al (2018). 8,9 Mesh convergence analysis was conducted and an anatomical reference system was defined following the same procedure used in Altai et al (2018). 9…”

Finite element modelling of the developing infant femur using paired CT and MRI scans

“…In contrast, magnetic resonance imaging (MRI) shows cartilage more clearly, providing anatomical information for soft tissues, while avoiding exposure to radiation [15–18]. Although finite element (FE) models available in the literature are not fully representative of the complete age range of younger children, they already provide preliminary quantitative information to differentiate accidental from inflicted injury [19–22]. However, none of these models include geometric detail of the ossifying regions of the long bone.…”