Trauma Biomechanics An Introduction to Injury

Biomechanics - 5th Edition

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Preface

Understanding how humans are injured through interactions with their environment
is a fundamental societal need as it is a prerequisite to designing a safe environment.
Unfortunately, although most basic principles of injury prevention are straightfor-
ward, the complexity of the human body and the environments in which we operate
make the reduction of traumatic injuries a difficult task. Underpinning all of this is
the multidisciplinary field of Injury Biomechanics, founded on Newtonian
mechanics and applied to the prevention of injuries. It is the science that allows us
to move from purely empirical approaches to an evidence-based discipline for
injury prevention with diverse applications from transport to sport to military
protection. The application of Injury Biomechanics is a clear case of “the devil is in
the detail”, but it has yielded rich dividends since the middle of the twentieth
century in reducing the burden of injuries in many countries.
Injury Biomechanics is also a young science and is in need of seminal textbooks
which help to define the discipline. However, there are only a handful of textbooks
directly addressing our field. In that context, this book is a singular achievement,
being succinct and yet broad in its scope and it has become the de facto reference
text. It is an excellent first port of call on most aspects of Injury Biomechanics.
I regularly refer students and others to this book, and I frequently have cause to
search in it myself, for example when I need details of injury criteria for specific
body regions or a description of available injury databases or regulatory tests. It is a
testament to its popularity that it is now in its fifth edition, and the scope and author
list are again expanded. This edition now includes a chapter which directly
addresses the cellular response to injury, thereby strengthening the link between
injury and mechanics.
The clear benefit of several authors is to extend the available expertise. Some-
times this can come at the expense of cohesion. However, that is not the case here
as there is a clear cohesiveness underpinning the various chapters, perhaps aided by
the extraordinary organizational skills of the lead author, in addition to his scientific
and educational activities. Kai-Uwe Schmitt, Duane Cronin, Felix Walz and Bar-
clay Morrison are all past or present Board members of the International Research
Council on the Biomechanics of Injuries (IRCOBI), where a significant part of the
science in this book was first presented at one of the annual IRCOBI conferences,
and readers might note that all IRCOBI papers are freely available for download.

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vi Preface

Markus Muser is a “lifetime participant” in IRCOBI activities and an expert in

accident reconstruction and collision analysis. Peter Niederer performed seminal
work on pedestrian impact modelling and also has a special interest in collaborative
learning across the engineering and medical professions, which is also the aim of
this book.
Trauma Biomechanics is essential reading for anyone starting to work or con-
tinuing to practise in the field of Injury Biomechanics.

Dublin, Ireland Ciaran Simms

Associate Professor of Biomechanics
Trinity College Dublin
President of the International Research Council
on the Biomechanics of Injury
Preface to the Fourth Edition

Injury is arguably one of the most under-recognized health problems facing society
today. Potential injury hazards exist everywhere in our daily environments
including the workplace, home, transportation, and sports and recreational settings.
From traffic-related injuries alone, the World Health Organization estimates that
1.2 million people die each year worldwide and as many as 50 million are injured or
disabled. The associated expenditures, lost productivity, legal and medical costs
resulting from these injuries and fatalities are staggering. More importantly, the
personal losses resulting from serious injury and death are incalculable. While this
trauma often results from catastrophic events that are deemed accidents, the
mechanisms of these injuries are both understandable and preventable. Trauma
biomechanics uses engineering principles to explore the physical response of the
human body to applied forces that produce failure of the tissues. With a firm
understanding of trauma biomechanics, researchers and designers are able to apply
existing knowledge and to generate new data for the development of improved
injury prevention strategies.
The book, Trauma Biomechanics, provides a comprehensive overview and
introduction to the subject for these researchers and designers. While countless
examples of protective equipment such as seat belts, airbags and helmets have been
designed using the principles of trauma biomechanics, the prevalence and severity
of the injuries necessitate that we continue to educate and train the next generation
of engineers, scientists and medical professionals.
I have taught injury biomechanics for more than two decades, and this book on
trauma biomechanics has become a mainstay as a supplemental text in my graduate
engineering courses. The book deftly and succinctly covers the background, tools,
methods and resources of trauma biomechanics before delving into a systematic
review of the anatomy, injury classification, injury mechanisms and injury criteria
of each body region. Each chapter includes summaries of the most relevant sci-
entific literature and biomechanical research that provide background and context
for the interpretation of the graphical and tabular information. The book concludes
with a chapter on injury prevention that combines both collision avoidance and
passive injury countermeasures. While the intended audience of the book is pri-
marily scientists and clinicians working in the area of trauma, the straightforward

vii
viii Preface to the Fourth Edition

writing style and graphical depictions make even the most technical engineering
and medical concepts approachable for a broad array of injury prevention profes-
sionals including epidemiologists, social scientists and policymakers.

Charlottesville, USA Jeff Crandall

Nancy and Neal Wade
Professor of Engineering and Applied Sciences
Director, Center for Applied Biomechanics
University of Virginia
Preface to the Third Edition

Injury is a leading cause of death, hospitalization and disability worldwide. The

World Health Organization predicts that unintentional injuries arising from road
traffic incidents will rise to take third place in the rank order of international disease
burden by the year 2030. Although these statistics and the associated economic
costs are staggering, the effect of unintentional injury and death from trauma is
more apparent, and more disturbing, when seen personally. By a young age, nearly
everyone in the world, regardless of region, wealth or education, has had a relative
or someone that they know killed or disabled in an “accident”. The quality of life
and financial effects on the injured person and their families and friends are plainly
evident and clearly devastating. Many unintentional injuries are in reality not
accidents; they could be prevented with changes in policy, education, or through
improved safety devices. Arrayed against these preventable injuries, a diverse group
of injury prevention researchers and practitioners work to decrease the incidence of
unintentional injury.
In trauma biomechanics, the principles of mechanics are used to understand how
injuries happen at the level of the bones, joints, organs and tissues of the body. This
knowledge is central in the development, characterization and improvement of
safety devices such as helmets and seat belts and in the safe design of vehicles and
equipment used for transportation, occupation and recreation. The field of trauma
biomechanics is highly interdisciplinary, with engineers and physicists being cen-
trally involved with medical practitioners and many other experts. This book,
Trauma Biomechanics, is organized as a short primer of this subject, and it provides
a logical overview of the field. It is written to be accessible to a range of students or
practitioners, while still providing considerable detail in each section. Each chapter
contains plentiful and up-to-date references to guide readers who require more
information on a particular topic.
In contrast to the relative abundance of texts that describe basic biomechanics,
sports biomechanics, gait analysis and orthopaedic biomechanics, this is one of only
two or three texts focused on trauma biomechanics that I am aware of. I have used a
previous version of the book as a required text for a combined senior undergrad-
uate- and graduate-level Mechanical Engineering class called the “Fundamentals of
Injury Biomechanics” at the University of British Columbia. The students com-
mented positively on the layout and accessibility of the book, and they used it as a

ix
x Preface to the Third Edition

key reference in the assigned problems and project work in the class. I think the
short primer structure of the book helped to make it accessible to the students. It is
possible to start reading at the beginning of any chapter and quickly come up to
speed with the most important basic knowledge about the anatomy, tolerance and
injury prevention techniques for that region of the body. This is of great utility for
students but also for people working in injury research contexts where they can be
asked to rapidly switch their focus from injury in one area of the body or from one
mechanism to another. This can occur not only while studying in university but also
in many industrial and academic research contexts. For example, this is frequently
required of people working on government-sponsored injury reconstruction teams
or who are engaged in reconstructing injuries in the litigation context.
I recommend this book as a key basic resource for anyone interested in injury
prevention. Everyone, from graduate students working in an academic injury
biomechanics setting to engineers, physicists, clinicians, surgeons, kinesiologists,
biologists, statisticians and social scientists working in the broad field of injury
prevention, frequently has questions about how injuries happen in various parts
of the body. This book is an essential and accessible resource to anyone with these
questions.

Vancouver, Canada Peter A. Cripton

Associate Professor of Mechanical Engineering
and Associate Faculty Member of the Department of
Orthopaedics
The University of British Columbia
Preface to the Second Edition

Everyday, more than 140,000 people are injured, 3000 killed and 15,000 disabled
for life every day on the world’s roads. Likewise, sport-related injuries are
numerous and have a significant socio-economic impact. The field of trauma
biomechanics, or injury biomechanics, uses the principles of mechanics to study the
response and tolerance level of biological tissues under extreme loading conditions.
Through an understanding of mechanical factors that influence the function and
structure of human tissues, countermeasures can be developed to alleviate or even
eliminate such injuries.
This book, Trauma Biomechanics, surveys a wide variety of topics in injury
biomechanics including anatomy, injury classification, injury mechanism and injury
criteria. It is the first collection I am aware of that lists regional injury reference
values, or injury criterion, either currently in use or proposed by both US and
European communities. Although the book is meant to be an introduction for
medical doctors and engineers who are beginners in the field of injury biome-
chanics, sufficient references are provided for those who wish to conduct further
research, and even established researchers will find it useful as a reference for
finding the biomechanical background of each proposed injury mechanism and
injury criterion. As more people become aware of and understand this subject, it
will someday lead to better mitigation and prevention of automotive and
sport-related injuries. I like this book very much and believe that you will find the
same.

Detroit, USA King H. Yang

Professor of Biomedical Engineering
and Mechanical Engineering
Director of Bioengineering Center
Wayne State University

xi
Acknowledgements

This new edition sees again an expansion of the scope of the book. Aspects of
cellular injury biomechanics were added to introduce a basic understanding of how
cells (particularly in the nervous system) respond to mechanical force. While many
questions in trauma biomechanics are still unanswered, we believe that tissue-level
aspects will increasingly be addressed in future work and thus it is relevant to
introduce the corresponding basic principles.
Although the expansion brings in new aspects of trauma biomechanics, the
general intention of the book remains unchanged. It is a short primer for everyone
interested in the basics of trauma biomechanics and injury prevention. We thank all
readers for support and feedback and hope you will also appreciate this latest
edition. I am also greatly indebted to my co-authors and everyone who contributed
to making a further edition possible.

Prof. Dr. Kai-Uwe Schmitt

xiii
Contents

1 Introduction . . . . . . . . . . . . . . . ...... . . . . . . . . . . . . . . . . . . . . . 1
1.1 About the Contents of This Book . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Historical Remarks . . . . . . ...... . . . . . . . . . . . . . . . . . . . . . 8
References . . . . . . . . . . . . . . . . . ...... . . . . . . . . . . . . . . . . . . . . . 13
2 Methods in Trauma Biomechanics . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1 Statistics, Field Studies, Databases . . . . . . . . . . . . . . . . . . . . . . 15
2.2 Basic Concepts of Biomechanics . . . . . . . . . . . . . . . . . . . . . . . 18
2.3 Injury Criteria, Injury Scales and Injury Risk . . . . . . . . . . . . . . 23
2.4 Accident Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5 Experimental Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.6 Standardised Impact Test Procedures . . . . . . . . . . . . . . . . . . . . 34
2.6.1 Anthropomorphic Test Devices . . . . . . . . . . . . . . . . . . 40
2.7 Numerical Methods, Including Human Body Modelling . . . . . . 46
2.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
2.9 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3 Cellular Injury Biomechanics of Central Nervous System
Trauma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... 63
3.1 Introduction to Cellular Biomechanics in Central Nervous
System Trauma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
3.1.1 Cellular Physiology . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.1.2 Anatomy of Neuronal Cells . . . . . . . . . . . . . . . . . . . . 67
3.2 Mechanoporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.2.1 Calcium and Sodium Influx and Potassium Efflux . . . . 70
3.3 Energy Depletion and Excitotoxicity . . . . . . . . . . . . . . . . . . . . 71
3.3.1 Mitochondrial Disruption . . . . . . . . . . . . . . . . . . . . . . 73
3.4 Reactive Oxygen and Nitrogen Species Production . . . . . . . . . . 75
3.5 Calpain Mediated Proteolysis . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.6 Blood Brain Barrier Breakdown . . . . . . . . . . . . . . . . . . . . . . . . 77
3.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

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3.8 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4 Head Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.1 Anatomy of the Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.2 Injuries and Injury Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . 89
4.3 Mechanical Response of the Head . . . . . . . . . . . . . . . . . . . . . . 94
4.4 Injury Criteria for Head Injuries . . . . . . . . . . . . . . . . . . . . . . . . 97
4.4.1 Head Injury Criterion (HIC) . . . . . . . . . . . . . . . . . . . . 98
4.4.2 Head Performance Criterion (HPC) . . . . . . . . . . . . . . . 99
4.4.3 The 3 ms Criterion (A3ms) . . . . . . . . . . . . . . . . . . . . . 100
4.4.4 Generalized Acceleration Model for Brain Injury
Threshold (GAMBIT) . . . . . . . . . . . . . . . . . . . . . . . . . 100
4.4.5 Brain Injury Criterion (BrIC) . . . . . . . . . . . . . . . . . . . 101
4.5 Head Injuries in Sports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
4.6 Head Injury Prevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
4.6.1 Head Injury Prevention in Pedestrians . . . . . . . . . . . . . 108
4.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.8 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5 Spinal Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
5.1 Anatomy of the Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
5.2 Injury Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
5.2.1 Biomechanical Response and Tolerances . . . . . . . . . . . 128
5.3 Injury Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
5.3.1 Neck Injury Criterion NIC . . . . . . . . . . . . . . . . . . . . . 134
5.3.2 Nij Neck Injury Criterion . . . . . . . . . . . . . . . . . . . . . . 134
5.3.3 Neck Protection Criterion Nkm . . . . . . . . . . . . . . . . . . 135
5.3.4 Neck Injury Criteria in UNECE and FMVSS . . . . . . . . 138
5.3.5 Further Neck Injury Criteria . . . . . . . . . . . . . . . . . . . . 138
5.3.6 Correlating Neck Injury Criteria to the Injury Risk . . . . 141
5.3.7 Spinal Injuries in Sports . . . . . . . . . . . . . . . . . . . . . . . 142
5.4 Prevention of Soft Tissue Neck Injury . . . . . . . . . . . . . . . . . . . 144
5.4.1 Head Restraint Geometry and Padding Material . . . . . . 145
5.4.2 Controlling Head Restraint Position . . . . . . . . . . . . . . . 146
5.4.3 Controlling Seat-Back Motion . . . . . . . . . . . . . . . . . . . 147
5.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
5.6 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
6 Thoracic Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
6.1 Anatomy of the Thorax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
6.2 Injury Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Contents xvii

6.2.1 Rib Fractures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

6.2.2 Lung Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
6.2.3 Injuries to Other Thoracic Organs . . . . . . . . . . . . . . . . 162
6.3 Biomechanical Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
6.3.1 Frontal Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
6.3.2 Lateral Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
6.4 Injury Tolerances and Criteria . . . . . . . . . . . . . . . . . . . . . . . . . 172
6.4.1 Acceleration and Force . . . . . . . . . . . . . . . . . . . . . . . . 172
6.4.2 Thoracic Trauma Index (TTI) . . . . . . . . . . . . . . . . . . . 172
6.4.3 Compression Criterion (C) . . . . . . . . . . . . . . . . . . . . . 173
6.4.4 Viscous Criterion (VC) . . . . . . . . . . . . . . . . . . . . . . . . 173
6.4.5 Combined Thoracic Index (CTI) . . . . . . . . . . . . . . . . . 174
6.4.6 Other Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
6.5 Thoracic Injuries in Sports . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
6.7 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
7 Abdominal Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
7.1 Anatomy of the Abdomen . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
7.2 Injury Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
7.3 Testing the Biomechanical Response . . . . . . . . . . . . . . . . . . . . 185
7.4 Injury Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
7.4.1 Injury Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
7.5 Influence of Seat-Belt Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
7.6 Abdominal Injuries in Sports . . . . . . . . . . . . . . . . . . . . . . . . . . 189
7.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
7.8 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
8 Injuries of the Pelvis and the Lower Extremities . . . . . . . . . . . . . . 193
8.1 Anatomy of the Lower Limbs . . . . . . . . . . . . . . . . . . . . . . . . . 193
8.2 Injury Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
8.2.1 Injuries of the Pelvis and the Proximal Femur . . . . . . . 198
8.2.2 Leg, Knee and Foot Injury . . . . . . . . . . . . . . . . . . . . . 200
8.3 Impact Tolerance of the Pelvis and the Lower Extremities . . . . 202
8.4 Injury Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
8.4.1 Compression Force . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
8.4.2 Femur Force Criterion (FFC) . . . . . . . . . . . . . . . . . . . 207
8.4.3 Tibia Index (TI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
8.4.4 Other Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
8.5 Pelvic and Lower Extremity Injuries in Sports . . . . . . . . . . . . . 208
8.6 Prevention of Lower Extremity Injuries . . . . . . . . . . . . . . . . . . 212
8.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
xviii Contents

8.8 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
9 Injuries of the Upper Extremities . . . . . . . . . . . . . . . . . . . . . . . . . . 221
9.1 Anatomy of the Upper Limbs . . . . . . . . . . . . . . . . . . . . . . . . . 221
9.2 Injury Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
9.3 Impact Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
9.4 Injury Criteria and Evaluation of Injury Risk from Airbags . . . . 226
9.5 Upper Extremity Injuries in Sports . . . . . . . . . . . . . . . . . . . . . . 227
9.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
9.7 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
10 Impairment and Injuries Resulting from Chronic Exposure
to Unfavourable Mechanical Loads . . . . . . . . . . . . . . . . . . . . . . . . . 235
10.1 Occupational Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
10.2 Sports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
10.2.1 Non-contact Sports . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
10.2.2 Contact Sports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
10.3 Household Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
10.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
11 Ballistic and Blast Trauma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
11.1 Ballistic Injury and Protection . . . . . . . . . . . . . . . . . . . . . . . . . 248
11.1.1 Wound Ballistics and Penetrating Ballistic Injuries . . . . 250
11.1.2 Personal Protective Equipment . . . . . . . . . . . . . . . . . . 253
11.1.3 Armour Performance and Testing . . . . . . . . . . . . . . . . 256
11.1.4 Behind Armour Blunt Trauma (BABT) . . . . . . . . . . . . 258
11.2 Blast Injury and Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
11.2.1 Explosives and Detonation . . . . . . . . . . . . . . . . . . . . . 261
11.2.2 Waves and Impedance . . . . . . . . . . . . . . . . . . . . . . . . 263
11.2.3 Blast in Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
11.2.4 Blast Injury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
11.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
11.4 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
12 Solutions to Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
Introduction
1

The human body is exposed to mechanical loads throughout its life. Aside from
forces deriving from ubiquitous and penetrating fields, such as gravity, or forces
due to electromagnetic fields that are non-contact in nature and as such effective
over distances, there is a great variety of forces acting on the human body from
contact with the surrounding environment. In addition, numerous forces are gen-
erated in the course of physiological processes inside the body, in the different
organs and tissues. Throughout evolution, all forms of life, including plants, ani-
mals and humans, adapted their physiology to mechanical interactions; some of
them to the extent that proper function requires the influence of forces, for example
bone remodelling. Mechanical forces are known to modulate cell development even
in utero (Knothe Tate et al. 2008).
The science of biomechanics is devoted to the analysis, measurement and
modelling of the effects that are observed under the various mechanical loading
situations, primarily in humans, but also in animals and plants. As this definition
suggests, a quantitative approach is therefore the predominant one. The range of
forces that may be of interest is thereby enormous: internal forces may originate
from the action of molecules, contractile fibres on a cellular level or muscles on a
macroscopic scale, moreover, pressures and shear stresses may be generated by
biological fluid flows or active biological transport processes, including osmosis.
External forces, in turn, occurring in everyday life can also span a virtually
unlimited range. Accordingly, the forces of interest in biomechanics typically cover
a range from pN to MN (lower or higher forces, respectively, are barely considered
because of lack of biological effect on the lower side or complete devastation on the
upper), and they may vary in time from picoseconds to years.
An inevitable consequence of forces acting inside or outside the human body is
the possibility that they may cause injury. Such adverse consequences are usually
associated with the action of excessive external forces being brought to bear during
unfavourable life events, particularly accidents. In fact, accidents of all kinds rep-
resent a leading cause of death, particularly among young people (see Table 1.1 for

© Springer Nature Switzerland AG 2019 1

K.-U. Schmitt et al., Trauma Biomechanics,
https://doi.org/10.1007/978-3-030-11659-0_1
2 1 Introduction

Table 1.1 Reported number of deaths and percentage of total deaths for the 10 leading causes of
death for those aged 24–35 years, United States, 2016
Cause of death Rank Deaths (%)
All causes 77,792 100.0
Accidents (unintentional injuries) 1 20,975 27.0
Malignant neoplasms 2 10,903 14.0
Diseases of the heart 3 10,477 13.5
Intentional self-harm (suicide) 4 7,030 9.0
Assault (homicide) 5 3,369 4.3
Chronic liver disease and cirrhosis 6 2,851 3.7
Diabetes mellitus 7 2,049 2.6
Cardiovascular diseases 8 1,854 2.4
Human immunodeficiency virus (HIV) 9 971 1.2
Septicaemia 10 897 1.2
Adapted from the National Vital Statistics Report, Vol. 67, No. 6

US figures). By contrast, internal forces are mostly thought to be governed by

anatomical or physiological constraints that prevent the occurrence of injury.
However, broken ribs due to intense coughing, rupture of muscle fibres due to
tetanic contraction or endocardial bleeding in cases of hypovolemic shock are
injuries resulting from forces produced by the body itself.
The special discipline of biomechanics, which is concerned with injury caused
by mechanical interaction, is denoted as biomechanics of injuries or trauma
biomechanics and is the subject of this book. Since there are a great many types of
injuries, injury mechanisms and injury-causing activities, biomechanics must con-
sider a large variety of human activities and situations where excessive loads may
occur. When performing a thorough analysis of such circumstances, it becomes
evident eo ipso that trauma biomechanics is a highly interdisciplinary science. As
with the field of biomechanics in general, trauma biomechanics must take into
account a wide range of disciplines, e.g. when performing macroscopic motion
analysis in sports or modelling molecular transmembrane transport. Many basic
biological aspects are thereby involved, for we are dealing with living matter
associated with intrinsic active processes, such as muscle contraction or electro-
chemical activities. Clinical medicine is ultimately of importance, e.g. with respect
to the severity of injuries.
The widespread knowledge obtained during recent decades in the different fields
covering mechanics and biology in general has contributed greatly to trauma
biomechanics, in that for an in-depth understanding of injury processes all aspects,
from the macroscopic scale to the sub-cellular level, may have to be taken into
account. Therefore, many subjects of importance for trauma biomechanics, relating
to mechanics, anatomy, physiology and medicine, must be covered to enable a
systematic approach across the entire field. However, while this broad diversity is
essential, ultimately a selection has to be made, which means a level of complete
comprehensiveness cannot be reached.
1.1 About the Contents of This Book 3

1.1 About the Contents of This Book

A number of preliminary remarks will be useful in order to delineate the extent and
limitations of the subjects treated in this book.

1. A distinction has to be made between injury resulting from unexpected, sudden

and singular events, i.e. accidents in a strict sense, and injury caused by chronic
exposure to unfavourable loads over extended periods of time. A head injury of
a pedestrian that is sustained from an impact on the hood of an automobile
during a collision, or the gradual destruction of hair cells in the inner ear as the
result of a chronic exposure to loud music—both examples are associated with
injury, yet the type of injury, the injury mechanisms, tolerance levels, injury
criteria, reconstruction and analysis methods as well as protection measures
differ fundamentally. In addition, with respect to insurance and liability issues,
procedures also vary greatly.
2. The injury-causing period in the course of a traffic accident has a duration of
100–200 ms typically, with the early part of this period often proving decisive.
In many cases the person involved is not aware of the event and does not
(cannot) react prematurely to the imminent danger. Accordingly, muscular
reactions that set in with a time delay of 60–80 ms typically are often of
secondary importance only, and can therefore be disregarded. This situation is
fundamentally different in cases of chronic overloading, where physiological
and also psychological reactions are always of primary importance.
3. A further important aspect is related to age. The mechanical properties of human
tissue, organs and body as a whole change during aging, in particular with respect
to injury tolerance, moving decisively towards unfavourable levels. There are a
number of reasons for this, among them a reduction of tissue compliance due to a
decrease of body water content along with a stiffening of soft tissue and a gradual
demineralisation of bone at ages above 30–40 years. As a result, the potential for
and occurrence of injury, primarily bone fractures, increases dramatically with
age. This includes the incidence of spontaneous fractures occurring under normal
physiological loads. In view of the aging population in the industrialised coun-
tries of the world, this aspect demands particular attention.
4. Adolescence, at the other end of the age scale, likewise poses important problems
for trauma biomechanics in that mechanical and biological properties undergo
dramatic changes from birth to adult age. Experiments with children are hardly
conceivable, and similarly work with adolescent cadavers is not common or
straightforward. Downscaling from adult characteristics to children requires a
careful analysis (“children are not small adults”). The development of child
dummies (see Chap. 2, Sect. 2.6.1), is therefore not a straightforward and simple
matter. Due to the lack of experimental approaches, statistics represent the main
method for the analysis of child injury. A significant contribution in this area is
being made by The Center for Injury Research and Prevention at The Children’s
Hospital of Philadelphia, USA (http://injury.research.chop.edu/).