The Pocket Podiatry Guide: Functional Anatomy

326 Pages·2009·32.135 MB·Paperback, 336\326

by  James Watkins, Series Editor and Ian Mathieson (Auth.)

First published 2009 © Elsevier Limited. All rights reserved.
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ISBN 978 0 7020 3032 1
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Foreword
I Itt ggiivveess mmee ggrreeaatt pplleeaassuurree ttoo iinnttrroodduuccee yyoouu ttoo FFuunnccttiioonnaall AAnnaattoommyy , the
fi rst book in the Pocket Podiatry sseerriieess.. TThhee vviissiioonn ooff RRoobbeerrtt EEddwwaarrddss,,
the then Commissioning Editor for Podiatry at Elsevier, the series will see
volumes published over the next 5 years or so. These will build into a
highly informative and clinically-oriented reference library for both under-
and post-graduate podiatrists alike, as well as those from other disci-
plines who are involved in the management of foot, ankle and lower limb
disorders. Other titles in the series include G ait, The Ageing Foot, The
Paediatric Foot, Examination and Diagnosis, Pharmacology, Footwear
and Orthoses , and Podiatric Surgery . It is perhaps indicative of the
progress, and current status, of Podiatry that a series providing such
breadth of information can be presented as refl ecting the true scope of
clinical practice, and as representing vital knowledge for contemporary
clinical practise.
T his fi rst volume, concerned with Functional Anatomy , is an entirely
appropriate ‘series opener’: podiatrists are only too aware of the impor-
tance of the weight bearing function of the foot, and its functional com-
plexity. This volume reviews the nature of the stresses applied to the foot,
their impact on various tissues, how they are managed, and how pathol-
ogy can result from functional impairment. The author, James Watkins, is
Professor of Biomechanics at Swansea University, but has a long history
of involvement with Podiatry through a previous post in Glasgow which
saw him teach the principles of mechanics to undergraduate Podiatrists
for many years. This places him in a unique position to reconcile the sci-
ence of biomechanics with the demands of clinical practice, and the lucid
way in which this is achieved makes this volume an exciting and welcome
addition to the Podiatric literature.
Professor Watkins is one of a team of writers recruited to the project
who rank as some of the brightest talents working within, or with, the
Podiatry profession. Each has substantial experience and a passion for
their subject that is conveyed in their writing, and it is an enviable position
I fi nd myself in, being involved in the development of the manuscripts.
I hope that, as more volumes are published, you judge the series to be
the valuable companion to clinical podiatry it is designed to be and that
your patients benefi t.
Ian Mathieson
Preface
H Huummaann mmoovveemmeenntt iiss bbrroouugghhtt aabboouutt bbyy tthhee mmuussccuulloosskkeelleettaall ssyysstteemm
(bones, joints, skeletal muscles) under the control of the nervous sys-
tem. The bones of the skeleton are linked together at joints in a way that
allows them to move relative to each other. The skeletal muscles pull on
the bones in order to control the movements of the joints and, in doing
so, control the movement of the body as a whole. By coordinated activ-
ity of the various muscle groups, forces generated by the muscles are
transmitted by the bones and joints to enable the individual to maintain
an upright or partially upright posture, move from one place to another
and manipulate objects.
T he open-chain arrangement of the bones of the skeleton maximizes
the range of possible body postures. However, this movement capability
is only possible at the expense of low mechanical advantage of skeletal
muscles, which results in relatively high forces in all components of the
musculoskeletal system in most postures and movements. In response to
the forces exerted on them, the musculoskeletal components experience
strain (deformation). Under normal circumstances, the musculoskeletal
components adapt their size, shape and structure to readily withstand the
strain of everyday physical activity. This process is referred to as struc-
tural adaptation and is continuous throughout life. In the absence of dis-
ease, structural adaptation tends to maintain normal function. However,
the capacity of the musculoskeletal components, especially bone, to
undergo structural adaptation decreases with age. Consequently, strain
that would normally result in structural adaptation in a young person may
result in tissue degeneration and dysfunction in an older person.
In weightbearing activities, the function of the musculoskeletal system
is to transmit the weight of the body to the ground by creating ground
reaction forces at the feet to maintain upright posture and move the
body in the intended direction. In walking, and other forms of locomotion
such as running, hopping and jumping, the feet act alternately as shock
absorbers, to cushion the impact of the foot with the ground, and pro-
pulsion mechanisms, to propel the body in the desired direction. These
distinct functions are refl ected in the fl exible arched structure of the foot,
which is indicative of the essence of functional anatomy, i.e. the intimate
relationship between the structure and function of the musculoskeletal
system. Accurate diagnosis and appropriate treatment of disorders of
the musculoskeletal system depends largely on the clinician’s knowledge
and understanding of this relationship.
The purpose of this book is to develop knowledge and understanding
of functional anatomy with particular reference to the foot. The book is
primarily designed as a course text for undergraduate students of podia-
try, but it also has a great deal to offer the practising podiatrist and other
healthcare professionals, in particular, physiotherapists and occupational
therapists, who deal with the acute and chronic effects of lower limb
musculoskeletal pathology.
The book has seven chapters. Chapter 1 describes the elementary
mechanical concepts and principles that underlie human movement,
which are referred to throughout the book. Chapter 2 describes the
basic structure of the body in relation to tissues, organs and systems.
Chapter 3 describes the bones of the skeleton and, in particular, the fea-
tures of the bones associated with force transmission and relative motion
between bones. Chapter 4 describes the structure and functions of the
various connective tissues, with particular reference to structural adapta-
tion in bone. Chapter 5 describes the structure and function of the vari-
ous types of joint. Chapter 6 describes the structure and function of the
neuromuscular system. Chapter 7 describes the structure of the foot
and, in particular, the function of the foot in walking.
No previous knowledge of functional anatomy is assumed. To aid
learning, the book features a content overview at the start of each chap-
ter, key concepts highlighted within the text, extensive use of illustrations,
review questions, references to guide further reading, and an extensive
glossary and index.
James Watkins
Acknowledgements
Thank you to the series editor Dr Ian Mathieson and all of the staff at
Elsevier who contributed to the commissioning and production of the
book. Thanks also to my academic colleagues and the large number of
students who have helped me, directly and indirectly, over many years,
to develop and organize the content of the book.
1
C H A P T E R
chapter contents
Force 2
Elementary
Mechanics and
biomechanics 3
biomechanics
Forms of motion 6
Units of measurement 7
Newton’s laws of motion 9
Newton’s law of
gravitation 12 A ll movements and changes in movement are
Centre of gravity 13 brought about by the action of forces. In human
Stability 14 movements, we interact with the environment
Load, strain and stress 18 largely through pulling forces (e.g. opening a
Friction 23 fridge door, closing a car door from the inside),
Musculoskeletal system
pushing forces (e.g. closing a fridge door,
function 30
climbing a fl ight of stairs), pressing forces (e.g.
Centre of pressure 33
ringing a door-bell, pressing a key on a key-
Vector and scalar
board) or combinations of pressing forces (e.g.
quantities 33
Moment of a force 40 gripping a pen or the handle of a cup). Human
Achilles tendon force and ankle movement is brought about by the neuromus-
joint reaction force in upright culoskeletal system, i.e. the musculoskeletal
standing 46 system (bones, joints, skeletal muscles) under
Levers 48 the control of the nervous system. The bones
Load on the musculoskeletal of the skeleton are linked together in a way
system 51
that allows them to move relative to each other.
Review questions 52
The skeletal muscles pull on the bones in order
References 52
to control the movements of the joints and, in
doing so, control the movement of the body as
a whole. By coordinated activity between the
various muscle groups, forces generated by
the muscles are transmitted by the bones and
joints to enable us to maintain an upright or
partially upright posture (e.g. standing, sitting),
move from one place to another (e.g. crawl-
ing, walking, running, swimming) and manipu-
late objects (e.g. carrying a bag, lifting a box,
pushing a wheelbarrow, driving a car, threading
a needle).
The open-chain arrangement of the bones
of the skeleton maximizes the range of pos-
sible body postures. However, this movement
1
 elementary biomechanics
capability is only possible at the expense of low mechanical advantage of
skeletal muscles, which results in relatively high forces in all components
of the musculoskeletal system in most postures and movements. Under
normal circumstances the musculoskeletal components adapt their size,
shape and structure to more readily withstand the time-averaged forces
exerted on them, i.e. there is an intimate relationship between the struc-
ture and function of the musculoskeletal system. To understand this rela-
tionship, it is necessary to understand elementary biomechanics. The
purpose of this chapter is to develop knowledge and understanding of
elementary biomechanical concepts and principles.
Force
All bodies, animate and inanimate, are continuously acted upon by forces.
A force can be defined as that which alters or tends to alter a body’s
state of rest or type of movement. For example, in a stationary sitting
position, body weight exerts a constant downward force acting on the
body is counteracted by upward forces exerted on the body by the seat,
the floor beneath the feet and, perhaps, arm rests supporting the arms. In
a standing position, the body is prevented from collapsing by the forces
in the skeletal muscles that stabilize the joints. In order to start walk-
ing forward from a stationary standing position, it is necessary to push
backwards against the ground; the more forcibly we push backward
against the ground, the faster we move forward. Climbing stairs involves
a succession of downward pushes against the stairs.
The forces that act on a body arise from interaction of the body with
its environment. There are two types of interaction: contact interaction,
which produces contact forces, and attraction interaction, which pro-
duces attraction forces (Watkins 2007). Contact interaction refers to
physical contact between the body and its environment, such as the
contact forces between our feet and the floor when standing, walking,
running and jumping. Attraction interaction refers to naturally occurring
forces of attraction between certain bodies that tend to make the bod-
ies move towards each other and to maintain contact with each other
after contact is made. For example, a magnetized piece of iron attracts
other pieces of iron to it by the attraction force of magnetism. The human
body is constantly subjected to a very considerable force of attraction,
i.e. body weight, the force due to the gravitational pull of the earth. It is
body weight that keeps us in contact with the ground and which brings
us back to the ground should we leave it, e.g. following a jump into
the air.
Mechanics and biomechanics 
Key Concepts
All bodies, animate and inanimate, are continuously acted upon by
forces which arise from interaction of the body with its environment.
The environment exerts two kinds of forces, contact forces and
attraction forces
mechanics and biomechanics
Forces tend to affect bodies in two ways (Watkins 2007):
l They tend to deform bodies, i.e. change the shape of the bodies by
stretching, squashing, bending or twisting. For example, squeezing a
tube of toothpaste changes the shape of the tube.
l They determine the movement of bodies, i.e. the forces acting on a
body determine whether it moves or remains at rest and determine its
speed and direction of movement if it does move.
Mechanics is the study of the forces that act on bodies and the effects
of the forces on the size, shape, structure and movement of the bodies.
The actual effect that a force or a combination of forces has on a body,
i.e. the amount of deformation and change of movement that occurs,
depends upon the size of the force in relation to the mass of the body
and the mechanical properties of the body.
The mass of a body is the product of its volume and its density. The
volume of a body is the amount of space that the mass occupies and its
density is the concentration of matter (atoms and molecules) in the mass,
i.e. the amount of mass per unit volume. The greater the concentration
of mass, the larger the density. For example, the density of iron is greater
than that of wood and the density of wood is greater than that of poly-
styrene. Similarly, with regard to the structure of the human body, bone is
more dense than muscle and muscle is more dense than fat.
The mass of a body is a measure of its inertia, i.e. its reluctance to
start moving if it is at rest and its reluctance to change its speed and/or
direction if it is already moving. The larger the mass, the greater the iner-
tia and, consequently, the larger the force that will be needed to move
the mass or change the way it is moving. For example, the inertia of a
stationary football (a small mass) is small in comparison to that of a heavy
barbell (a large mass), i.e. much more force will be required to move the
barbell than to move the ball.
Whereas the effect of a force on the movement of a body is largely
determined by its mass, the amount of deformation that occurs is largely
1
 elementary biomechanics
determined by its mechanical properties, in particular, its stiffness (the
resistance of the body to deformation) and strength (the amount of force
required to break the body). For a given amount of force, the higher the
stiffness and the greater the strength of a body, the smaller the deform-
ation that will occur.
Biomechanics is the study of the forces that act on and within living
organisms and the effect of the forces on the size, shape, structure and
movement of the organisms (Watkins 2007). In relation to humans, bio-
mechanics is the study of the relationship between the external forces
(due to body weight and physical contact with the environment) and
internal forces (active forces generated by muscles and passive forces
exerted on connective tissues) that act on the body and the effect of
these forces on the size, shape, structure and movement of the body.
Key Concepts
Mechanics is the study of the forces that act on bodies and the
effects of the forces on the size, shape, structure and movement of
the bodies
Sub-disciplines of mechanics
The different types and effects of forces are reflected in four overlapping
sub-disciplines of mechanics: mechanics of materials, fluid mechanics,
statics and dynamics. Mechanics of materials is the study of the mechan-
ical properties (strength, stiffness, resilience, toughness) of materials.
Mechanics of materials includes, for example, the study of materials used
to make shoes, materials used to make orthoses to be worn in shoes to
treat certain foot disorders, and the effects of ageing on bone, muscle and
connective tissues. Fluid mechanics is the study of: (1) the forces that affect
the movement of liquids and gases, such as the flow of water in a pipe or
blood flow in the cardiovascular system; and (2) the effect of liquids and
gases on the movement of solids, such as the movement of the human
body through water and air. Statics is the study of bodies under the action
of balanced forces, i.e. study of the forces acting on bodies that are at rest
or moving with constant speed in a particular direction. In these situations,
the resultant force (the net effect of all the forces) acting on the body is zero.
Figure 1.1A shows a man standing upright. Since the man is at rest, there are
only two forces acting on him, the weight of his body W acting downward
and the upward reaction force R exerted by the ground. The magnitude of
1
W and R is the same, but they act in opposite directions and, therefore,
1
cancel out, such that the resultant force acting on the man is zero.
Mechanics and biomechanics 
A B
W W
R R
1 2
Figure 1.1 (A) The forces acting on a man standing upright and (B) just after starting to walk.
W  body weight, R and R  ground reaction forces.
1 2
Dynamics is the study of bodies under the action of unbalanced forces,
i.e. bodies moving with non-constant speed. In this situation, the result-
ant force acting on the body will be greater than zero, i.e. the body will
be accelerating (speed increasing) or decelerating (speed decreasing) in
the direction of the resultant force. For example, as the man in Figure 1.1A
is at rest, the resultant force acting on him will be zero. As he starts to
walk (Figure 1.1B), he will be accelerated forward under the action of the
resultant force acting on his body, i.e. the resultant of his body weight W
and the force acting on his right foot R .
2
Kinematics is the branch of dynamics that describes the movement
of bodies in relation to space and time (Gk. kinema, movement). A kin-
ematic analysis describes the movement of a body in terms of distance
(change in position), speed (rate of change of position) and acceler-
ation (rate of change of speed). Kinetics is the branch of dynamics that
describes the forces acting on bodies, i.e. the cause of the observed
kinematics (Gk. kinein, to move).
Key Concepts
There are four overlapping sub-disciplines of mechanics: mechanics
of materials, fluid mechanics, statics and dynamics