Chapter 1: Head impact – Introduction
1.1
Definition of the problem
Will define terms such as Traumatic Brain Injury (TBI), and give statistics on head injury
prevalence and causes. Differentiation between penetrating and blunt impact.
Already written most of this subsection. Need a few more details from Emma’s referenced
papers regarding statistics.
It is difficult to estimate the prevalence of head injury incidences: the degree of trauma can
vary so greatly that complications arise defining what is and is not classified as a 'head injury'.
Although injury to the head is technically a very broad category, the term 'head injury' is often
assigned a more specific meaning, namely damage to the brain - this is sometimes also referred
to as 'traumatic brain injury' (TBI). There are many sets of figures, but as a general overview:
1.7 million people in the US sustain TBI per year, and of these 52,000 die. Of those that
survive a head injury, many continue to suffer and require care. Research conducted in the UK
found that slightly less than 50% of subjects studied after having sustained severe concussion
had persistent problems, or had become unemployable. Direct medical and indirect loss of
productivity costs from TBI was estimated at $60 billion in the US in 2000. (Hardy, Khalil, &
King, 1994; US Centre for Disease Control and Prevention, 2010) These social and economic
ramifications act as strong divers for head injury research.
Impact injuries to the human body occur when biological tissues are deformed beyond their
recoverable limit. As a result, anatomical structures may be damaged or their function
impaired. With regards to impact head injury a variety of different mechanisms have been
postulated for the resulting trauma: while the significant level of research in this area has
provided numerous advances in the understanding of these mechanisms, the head's complex
anatomy means impact head injury remains poorly understood. (Viano, King, Melvin, &
Weber, 1989) Furthermore, in comparison, the location and mechanism of brain trauma
resulting from penetrating impact (i.e. where the skull does not remain intact) are often more
obvious than those resulting from blunt (non-penetrating) impact.
pg. 1
More info on statistics where head injury comes from etc.?
Goldsmith 1972: more indepth comparison between penetrating and blunt impact:
In many respects, the cause of the injury may initially appear to be irrelevant as it is clear
that the issue is of serious matter but it is important to note that the type of injury sustained,
is dependent upon its cause. A penetrative injury, such as that caused by bullets or debris,
will inevitably result in skull fracture often accompanied by bone fragmentation and tissue
perforation. Although clearly a severe type of injury, tissue damage may be limited to the
localised area according to the size of the penetrating object. A blow to the head without
penetration, can result in damage to a large area of the brain due to dissemination of the
impact energy underneath the skull. Although skull fracture may not occur, bruising or
even laceration of the neural tissue may result in long term damage. Brain damage can even
occur without object collision for example through the rapid acceleration or deceleration of
the head. Typical symptoms include contusions, lacerations, nerve degeneration, edema and
haematoma (Goldsmith, 1972).
Stålhammar, (1986) defined three different categories of injury mechanism, as impact,
impulsive and compressive, which vary according to load application and time history.
Impact loading, the mechanism of interest in the current study, is.....
Investigation of the methods through which trauma is sustained from blunt impact offer
greater opportunities for mitigation, and was the purpose of this study. (no refs)
The aim of this report is to provide a literature survey outlining the development and current
status of numerical models used in non-penetrating (blunt) head injury research; with particular
focus on the finite element method. First, relevant background information on the topic is
presented, followed by a literature review. Finally the current key issues and advancements in
this field are summarised, and recommendations for future work provided. It is hoped that this
survey will act as an overview of the numerical techniques used in the field of head impact
modelling, and aide further development of these methods.
pg. 2
1.2 Anatomy and properties of the head
1.2.1 The skull
Figures, description, literature review on material properties. Explanation of large degree of
anatomical variation between individuals.
Have a very brief description of anatomy for my literature review.
1.2.2 The brain and other structures within the cranial vault
As previous: Figures, description, literature review on material properties. Explanation of large
degree of anatomical variation between individuals.
As above, brief description in literature review.
1.3 Head impact modelling
Why model the head? What are the alternatives? Mention Nahum et al and other cadaveric
impact benchmarks which may compare results to for validation. Pros and cons. This will be
main literature review section.
Good version of all these sections, except more detail needed on Emma’s work and on the
finite element models, in literature review & in research proposal.
1.3.1 Analytical modelling
Early math models.
1.3.2 Physical modelling
Including short description of Emma Johnson’s work.
pg. 3
1.3.3 Numerical modelling
1.3.3.1 Finite element method
Have good FE descriptions, look through 4th year papers, and also literature review: include
“Simplifications” section. Good descriptions of current models in literature review and
research proposals as well.
Brief explanation/background of finite element method. Discuss progression of model
complexity and talk about some of the most advanced FE head models being used at the
moment.
1.3.3.2 Image based meshing
Discuss background of image based meshing, its pros and cons, and some of the advanced
imaged based models available today.
Good background and description in literature review and research proposal.
1.4 Impact injury mechanisms
1.4.1 Impact mechanics
Description of exactly what an impact is and how it happens (ref. PGY’s Cambridge impact
mechanics book).
1.4.2 Impact conditions and injury mechanisms
Blunt vs. penetration. Direct vs. oblique. Rotational vs. linear acceleration.
Explanation, and conditions which may cause, contusion, diffuse axonal injury (DAI) etc.
Define terms: pole, anti-pole, coup, contre-coup.
pg. 4
1.4.3 Severity coefficients and the head injury criterion (HIC)
1.4.4 Role of intracranial pressure
Why pressure peaks in the brain are important. What injuries could be expected from these
peaks? Explain cavitation hypothesis (and include information on the current state of research
into identifying a cavitation threshold – difficulties in this research: in vivo study not possible
because dangerous etc.). Explain “contre-coup phenomenon” (ricochet theory) post mortem
finds trauma at opposite point to impact. Yuelin Zhang research.
Explain quasi-static response, and using examples, explain its prevalence in head impact
literature. Why is it that only QS response observed?
1.5 Related research (unsure for title of this section)
Previous research on the dynamic pressure magnification effect.
Subsections detailing Young and Morfey FE impact research, the analytical model, Emma
Johnson’s work (and James Price’s work?). Explain dynamic pressure magnification effect, how
it can be predicted using Tomega.
Define the limited of this research: going to be looking at blunt, direct, low energy impact.
Many good, but too short, descriptions of PGY’s and Emma’s previous research in CMBBE
manuscript, literature review, and first year report.
1.6 Hypothesis
Done in research proposal (re-examine the grades, comments I got for this coursework, for
tips.)
The hypothesis underlying this proposed research is: if the “intracranial pressure
magnification” effect is not an artefact of simplified head models, then a link between
intracranial pressure and impact duration should also be observed in a highly accurate model.
In order to test this hypothesis the following research questions will be answered:
pg. 5
1. Once modified, has the new Simpleware head model become an accurate
representation of the human head suitable for validating this effect?
2. In this model does the brain exhibit the same, or similar, impact response behaviour as
impact duration is reduced as identified in Young and Morfey’s analysis? (Young &
Morfey, 1998)
1.7 Aims
What exactly are Aims? Check Emma’s thesis and the Research Methodology handouts.
1.8 Objectives
Done in research proposal.
Objectives and hypothesis stated in past, future, or present 3rd person?
The measurable objectives required in order to answer the research questions stated above:
To answer research question 1.
Objective 1: Modify the Simpleware head model such
that it contains all structures and material properties relevant to study the brain
response. This objective will be evaluated by comparison of the modified model with
the latest findings in the literature regarding features which are important.
To answer research question 1.
Objective 2: Validate the accuracy of this model by
simulated recreation of a set of well established cadaveric experiments, and comparison
of results. (Several benchmark cadaveric experiments exist in the literature which are
often used to validate models.)
Once the model has been modified and found to be accurate, the objectives now deal with
validation of Young and Morfey’s observed “pressure magnification effect”:
To answer research question 2.
Objective 3: Investigate the effect of varying impact
duration on the location of pressure maxima in the brain. The results will be compared
to Young and Morfey’s analysis.
pg. 6
To answer research question 2.
Objective 4: Investigate the effect of varying impact
duration on the magnitude of pressure maxima in the brain. The results will be
compared to Young and Morfey’s analysis.
To answer research question 2.
Objective 5: Investigate at what critical value of impact
duration the brain response changes from standard “quasi-static” response to dynamic
“pressure magnification” response. The results will be compared to Young and
Morfey’s analysis. (Young & Morfey, 1998)
Hardy, W., Khalil, T. B., & King, A. I. (1994). Literature review of head injury biomechanics.
International Journal of Impact Engineering, 561-586. Retrieved January 11, 2011, from
http://linkinghub.elsevier.com/retrieve/pii/0734743X94800347.
US Centre for Disease Control and Prevention. (2010). Get the stats on traumatic brain injury in the
United States. http://www.cdc.gov/traumaticbraininjury/pdf/BlueBook_factsheet-a.pdf (updated 17th
March 2010) (p. 2).
Viano, D. C., King, A. I., Melvin, J. W., & Weber, K. (1989). Injury biomechanics research: an
essential element in the prevention of trauma. Journal of biomechanics, 22(5), 403-17.
Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/2674145.
Young, P. G., & Morfey, C. L. (1998). Intracranial pressure transients caused by head impacts.
Proceedings of the International IRCOBI, Conference on Biomechanics of Impact (pp. 391-403).
pg. 7