Mann’s surgery of the foot and ankle V.1 P. 1

698 Pages·186.6 MB·English

by  Coughlin M., Saltzman C., Anderson R.

MANN’S SURGERY OF
THE FOOT AND ANKLE
Volume 1
MANN’S SURGERY
OF THE FOOT
AND ANKLE
NINTH EDITION
Michael J. Coughlin, MD
Director, Saint Alphonsus Foot and Ankle Clinic, Boise, Idaho
Clinical Professor, Department of Orthopaedic Surgery
University of California, San Francisco, San Francisco, California
Past-president, American Orthopedic, Foot and Ankle Society
Past-president, International Federation of Foot and Ankle Societies
Charles L. Saltzman, MD
Chairman, Department of Orthopaedics
Louis S. Peery MD Endowed Presidential Professor, University of Utah
University Orthopaedic Center, Salt Lake City, Utah
Past-president, American Orthopaedic Foot and Ankle Society
Vice President, International Federation of Foot and Ankle Societies
Robert B. Anderson, MD
Chief, Foot and Ankle Service
Vice-chair, Department of Orthopaedic Surgery, Carolinas Medical Center
OrthoCarolina Foot and Ankle Institute, Charlotte, North Carolina
Past-president, American Orthopaedic Foot and Ankle Society
1600 John F. Kennedy Blvd.
Ste 1800
Philadelphia, PA 19103-2899
MANN’S SURGERY OF THE FOOT AND ANKLE ISBN: 978-0-323-07242-7
Volume 1 Part Number: 9996074684
Volume 2 Part Number: 9996074749
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Library of Congress Cataloging-in-Publication Data
Mann’s surgery of the foot and ankle / [edited by] Michael J. Coughlin, Charles Saltzman, Robert B.
Anderson.—Ninth edition.
p. ; cm.
Surgery of the foot and ankle
Preceded by Surgery of the foot and ankle / edited by Michael J. Coughlin, Roger A. Mann, Charles
L. Salzmann. 8th ed. c2007.
Includes bibliographical references and index.
ISBN 978-0-323-07242-7 (set : hardcover : alk. paper)
I. Coughlin, Michael J., editor of compilation. II. Saltzman, Charles L., editor of compila-
tion. III. Anderson, Robert B. (Robert Bentley), 1957- editor of compilation. IV. Title: Surgery of
the foot and ankle.
[DNLM: 1. Ankle—surgery. 2. Foot—surgery. 3. Ankle Injuries—surgery. 4. Foot Diseases—
surgery. WE 880]
RD563
617.5’85059—dc23
2013017557
Executive Content Strategist: Dolores Meloni
Content Development Manager: Lucia Gunzel
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Project Manager: Cindy Thoms
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Printed in China
Last digit is the print number: 9 8 7 6 5 4 3 2 1
Preface
In 1959, Henri L. DuVries, MD, published the first edition believe that the principles initially espoused by Drs.
of Surgery of the Foot. This text summarized his 30-year Inman and DuVries and expanded on by Dr. Mann have
personal experience in diagnosing and treating disorders, given me a unique perspective.
deformities, and injuries of the foot and ankle. His book In 1993, Dr. Mann and I collaborated on the sixth
became a classic, but it was also significant because it was edition, which was expanded to a comprehensive two-
written by a physician who originally had obtained his volume text. In 1999, this was revised by us as the seventh
training as a podiatrist and then subsequently became a edition and, in 2005, it was published as a colorized
doctor of medicine. eighth edition, in which we were joined by, Dr. Charles
In 1965, Dr. DuVries expanded the book to include L. Saltzman, as a co-editor.
several other contributors, taking a form that is a model This is a living text and has continued to evolve from
even for the current textbook. Included in this second the initial work of Henri L. DuVries. Much of our ortho-
edition were Verne T. Inman, MD, chairman of the paedic careers have been devoted to working with this
Department of Orthopaedic Surgery at the University of text; Dr. Mann has contributed to or edited all but one
California, San Francisco, and Roger A. Mann, MD, a of the first eight editions, and I have contributed to or
senior resident in orthopaedic surgery. Eight years later, in edited half of the editions. However, change and growth
1973, Dr. Inman succeeded Dr. DuVries as the editor of are important! As of this edition, Dr. Mann has become
the third edition of Surgery of the Foot. Again, with this text, an editor emeritus but has continued to give us his
an expanded objective included discussion of the ankle input and valued advice. To recognize and honor his
joint as well as an in-depth analysis of the biomechanics invaluable contributions to the textbook, we have named
of the foot and ankle. Five years later, in 1978, Dr. Mann this ninth edition Mann’s Surgery of the Foot and Ankle.
became the editor of the fourth edition. Dr. Mann, having Most important, Robert B. Anderson, MD, a past fellow
been a resident under Dr. Inman and having served a fel- of John Gould, MD, joins Dr. Saltzman and me as an
lowship under Dr. DuVries, was presented with a unique editor of this text. Dr. Anderson brings a wealth of clini-
opportunity to blend the special interests of these two cal knowledge and a sports medicine background to
unique clinicians—Dr. Inman’s basic biomechanical this association. Just as Dr. DuVries complemented his
research and Dr. DuVries’ wealth of clinical knowledge. In text by adding Dr. Inman, and Dr. Inman introduced
1986, Dr. Mann edited a revised fifth edition. Dr. Mann, we feel strongly that Dr. Anderson’s addition
In 1978, as Dr. Mann’s first foot and ankle fellow, I will make this a stronger and more well-rounded work.
had the opportunity to be exposed to both his philosophy The ninth edition is also enhanced by the work of many
of patient care and the creativity with which he addressed of our excellent fellows and colleagues from around the
the evaluation and treatment of his patients. His meticu- world who have made substantial sacrifices to contribute
lous surgical technique and comprehensive postoperative to this textbook. In this edition, 25 authors continue
program were coupled with an introspective method of to contribute, but 42 new authors have been added.
assessing the results of specific procedures to delineate the These contributing authors are at the forefront of their
preferred treatment regimen. Dr. Mann’s 45 years in specific area of foot and ankle surgery. Each contributing
private practice, stimulated by more than 75 foot and author has covered a specific topic in a comprehensive
ankle fellows, have complemented my interaction with fashion, which we believe will leave the reader with a
him. In 1999, I initiated my own fellowship program and clear, concise appreciation of the subject. Although this
have learned a great deal from the 15 fellows who I have book is not meant to be encyclopedic in nature, our
trained. I also have frequently reviewed the surgical pro- goal has always been to provide the reader with a method
cedures used in my everyday practice, with the common of evaluating and treating a particular problem. More
goal of defining the strengths of individual procedures as than 40% of the ninth edition has been completely
well as their weaknesses. From the 34 years that I have rewritten by both new and returning contributors, and
been in private practice in Boise, Idaho, I have come to the remaining chapters have been updated.
xiii
Preface
In 1990, Dr. Mann and I published the Video Textbook plantar plate tears and treatment of this complex
of Foot and Ankle Surgery, the second volume of which problem. The chapters on sesamoids, keratotic disorders,
appeared in 1995. This enabled foot and ankle surgeons and toenail abnormalities have all been updated as well.
to view a surgical procedure while simultaneously reading Part III, Nerve Disorders, and Part IV, Miscellaneous,
about the operative technique. Encouraged by the success have been completely updated to cover both acquired and
of this endeavor, the eighth edition of Surgery of the Foot static neurologic disorders; the material about heel pain
and Ankle incorporated, for the first time, 60 edited videos has been rewritten and updated by new authors.
on two DVDs. This unique addition has now become an Part V, Soft Tissue Disorders of the Foot and Ankle,
industry standard. To enhance the current edition, we includes revised chapters on infection, dermatology, and
have retained 45 classic videos narrated by Dr. Mann and soft tissue reconstruction and a completely new chapter
added 75 new videos contributed by us as well as many on tumors of the foot and ankle.
other colleagues. Furthermore, advances in Internet and Part VI, Arthritis, Postural Disorders, and Tendon Dis-
online learning have enhanced the electronic version of orders, has been completely revamped, updating our
the ninth edition textbook and video compilation to current knowledge and treatment of systemic inflamma-
allow viewing on smartphone and tablet devices before tory arthritis, traumatic arthritis, and osteoarthritis. The
performing surgical procedures, affecting both learning chapter on total ankle arthroplasty presents substantial
and improving patient care. changes because of the dramatic developments that have
This new edition has been divided into 10 sections that occurred over the past decade in ankle joint replacement.
have been subdivided into chapters. Specific surgical tech- Revisions of the chapters on pes planus and pes cavus are
niques within the chapters are described and illustrated included. The chapter on arthrodesis of the foot has been
in detail to afford the reader an understanding of the replaced by one on arthritis of the hindfoot and midfoot,
indications for each procedure and insight into the per- containing both assessment and surgical treatment of
formance of the technique. Although many different conditions in this region. The chapter on tendon abnor-
treatment regimens are presented, our goal is to recom- malities has been extensively rewritten to reflect signifi-
mend a specific treatment plan for each pathologic entity. cant technical advances in this area.
Furthermore, some topics are presented in more than one A separate section, Part VII, Diabetes, contains three
section, enabling the reader to appreciate the varying completely updated chapters on diabetes, amputations,
points of view presented by individual contributors. It is and prostheses of the foot and ankle.
our goal to provide the reader with an accurate assess- Part VIII, Sports Medicine, includes a comprehensive
ment of both the attributes and the deficiencies of specific chapter on athletic soft tissue injuries as well as specific
orthopaedic foot and ankle procedures, new and old. In chapters regarding stress fractures and arthroscopy; all
this edition, we present our most up-to-date thinking three chapters have been revised and updated to familiar-
regarding the diagnosis, treatment, and specific surgical ize the reader with this exciting and evolving area of
care of foot and ankle problems. orthopaedic technology.
In Part I, General Considerations, the biomechanics, Pediatrics is covered in Part IX with two chapters: a
examination, and conservative treatment of foot and general pediatric chapter and a separate chapter on con-
ankle problems are addressed. In large part, the initial genital and acquired neurologic disorders, where new
principles advocated by Dr. DuVries, Dr. Inman, and Dr. authors have added significant new information.
Mann, as presented in their early editions, are included Finally, Part X, Trauma, includes six chapters. These
in this portion of the text but have been updated. Anes- chapters, which have been updated and revised, include
thetic techniques have been completely rewritten and discussion of fractures of the distal tibia; ankle; disloca-
have been updated to include popliteal blocks and tions of the foot and ankle; and calcaneus talus, midfoot,
indwelling catheters. Discussions of imaging methods, and forefoot fractures, which are covered in a comprehen-
an integral part of the evaluation process for foot and sive fashion.
ankle disorders, have also been completely rewritten and As Roger Mann stated in the preface of the fifth edition,
include in-depth coverage of magnetic resonance imaging “As medicine continues to progress, the information of
and computed tomography. this textbook will again need to be upgraded. The prin-
In Part II, Forefoot, an extensive analysis of deformi- ciples presented, however, are basic in their approach and
ties of the great toe, along with complications associated will not change significantly over the years.” We believe
with individual hallux valgus procedures, has been com- that the ninth edition of Mann’s Surgery of the Foot and
pletely revised to make the reader aware of primary sur- Ankle will strongly enhance this dynamic and exciting
gical techniques as well as salvage techniques used for field of orthopaedics and will complement the learning
postsurgical complications. Inclusion of newer, popular experience of the resident and fellow-in-training as well
surgical techniques has been added. The chapter on lesser as the practicing surgeon.
toes has been completely rewritten and updated because Michael J. Coughlin, MD
of the vast number of advances made in the area of
xiv
We are proud to dedicate the ninth edition of Surgery of the Foot and Ankle to Roger A.
Mann, MD, and have changed the official name to Mann’s Surgery of the Foot and Ankle.
Dr. Mann served as a mentor and teacher at a time when there were few foot and ankle
fellowships or fellows. He guided the American Orthopaedic Foot and Ankle Society in its
early years and promoted education of residents and surgeons in active practice through
programs at the American Academy of Orthopedic Surgeons and the American Orthopaedic
Foot and Ankle Society meetings. Prolific in his studies and publications, he has introduced
more than 75 fellows to his methods of investigation and surgery, thus truly changing
surgery in America during his time. He took the rather small primer entitled Surgery of
the Foot and changed it to a two-volume color textbook—Surgery of the Foot and Ankle,
with a video supplement—that has become the definitive textbook for foot and ankle
surgery in the world.
His vision and action are proof that one man can truly make a difference, and he has
done that.
xvii
1
Chapter
Biomechanics of the Foot
and Ankle
Andrew Haskell, Roger A. Mann
Hindfoot Alignment 29
CHAPTER CONTENTS
Midfoot Alignment 30
Forefoot Principles 31
GAIT CYCLE 4
Tendon Transfers 31
Walking Cycle 4
Ligaments of the Ankle Joint 31
First Interval 4
Second Interval 5
Third Interval 6
Running Cycle 7 The human foot is an intricate mechanism that functions
KINEMATICS OF HUMAN LOCOMOTION 7 interdependently with other components of the locomo­
Vertical Body Displacements 8 tor system. Failure of the functioning of a single part,
Lateral Body Displacements 9 whether by disease, external forces, or surgical manipula­
Horizontal Limb Rotation 9 tion, will alter the functions of the remaining parts. To
KINETICS OF HUMAN LOCOMOTION 10 further complicate things, wide variations occur in the
Measuring Whole Body Kinetics and normal component parts of the foot and ankle, and these
Plantar Pressure 10 variations affect the degree of contribution of each part
Types of Studies 11 to the function of the entire foot. Depending on the
Data Representations 13 contributions of an individual component, the loss or
Measurement Variability 14 functional modification of that component by surgical
Kinetics of Walking 15 intervention may result in minor or major alterations in
Whole Body Kinetics 16 the function of adjacent components. This variation helps
Plantar Pressure Kinetics 17 to explain why the same procedure performed on the foot
Kinetics of Running 18 of one person produces a satisfactory result, whereas in
BIOMECHANICS OF THE COMPONENT OF THE another person the result is unsatisfactory.
LOCOMOTOR SYSTEM 19 Yet the surgeon is called on constantly to change the
Heel Strike to Foot Flat: Supple for anatomic and structural components of the foot. When
Impact Absorption 19 so doing, awareness of the consequences of these changes
Ankle Joint 19 is fundamental to achieving desired results. Put another
Subtalar Joint 20 way, an understanding of interrelationships between
Transverse Tarsal Joint Complex 22 foot and ankle components and how they interact with
Foot Flat to Toe-Off: Progression to the greater locomotor system is critical to achieving
a Rigid Platform 23 predictable outcomes when altering these components
Ankle Joint 24 surgically.
Subtalar Joint 25 Understanding the biomechanics of the foot and ankle
Transverse Tarsal Articulation 25 also contributes to sound surgical decision making and
Plantar Aponeurosis 25 adds to the success of postoperative treatment. Appre­
Metatarsophalangeal Break 26 ciating the mechanical behavior of the foot allows the
Talonavicular Joint 27 physician to differentiate foot disabilities that may be
Swing Phase 27 successfully treated by nonsurgical procedures rather than
Component Mechanics of Running 28 approached surgically. Furthermore, some operative pro­
SURGICAL IMPLICATIONS OF BIOMECHANICS cedures that fail to completely achieve the desired result
OF THE FOOT AND ANKLE 28 can be improved by minor alterations in the behavior of
Biomechanical Considerations in adjacent components through shoe modification or the
Ankle Arthrodesis 29 use of orthotic inserts or braces.
3
Part I ■ General Considerations
With increased attention being given to athletics, the Heel Foot Heel Heel
physician must have a basic knowledge of the mechanics Strike Flat Rise Toe-off Strike
that occur during running. Many of the same basic mech­
anisms that will be described for the biomechanics of the
Opposite Opposite
foot and ankle are not significantly altered during running. Toe-off Heel Strike
The same stabilization mechanism within the foot occurs
Stance phase Swing phase
during running as during walking. The major differences
observed during running are that the gait cycle is altered
considerably, the amount of force generated (as measured Double Single Double
Limb Limb Limb
by force plate data) is markedly increased, the range of Support Support Support
motion of the joints of the lower extremities is increased,
and the phasic activity of the muscles of the lower extrem­
ities is altered. Differences between walking and running
will be highlighted in the following sections. 0 7 12 34 50 62 100
Starting this textbook with a chapter focused on foot
Percent of gait cycle
and ankle biomechanics is meant to provide a foundation
Figure 1-1 Phases of the walking cycle. Stance phase
for the reader upon which the remaining chapters are
constitutes approximately 62%, and swing phase 38% of
built. It has been assumed that the orthopaedic surgeon
cycle. During stance phase of walking, there are two periods
possesses an accurate knowledge of the anatomy of the
of double limb support and one period of single limb
foot and ankle. If this knowledge is lacking, textbooks of support. Stance phase is further divided into three intervals:
anatomy are available that depict in detail the precise from heel strike to foot flat at approximately 7% of the gait
anatomic structures constituting this part of the human cycle, foot flat to heel rise at approximately 34% of the gait
body.46,49 In this chapter, the gait cycle is reviewed, kine­ cycle, and heel rise to toe-off at approximately 62% of the
gait cycle.
matic and kinetic aspects of gait are explored, and specific
anatomic interrelationships of the foot and ankle are
emphasized. Throughout this discussion, mechanics that 34% as the contralateral leg swings through and passes
differentiate running from walking are described. Finally, the stance foot. Finally, contralateral heel strike occurs at
clinical examples are explored, and methods for func­ 50% of the gait cycle.
tional evaluation of the foot are presented as practical In a patient with spasticity, the initial heel strike may
demonstrations of the concepts within. be toe contact, and foot flat may not occur by 7% of the
cycle. Heel rise may be premature if spasticity or an
equinus contracture is present or delayed in the case of
GAIT CYCLE weakness of the gastrocnemius–soleus muscle group.
Weakness of anterior compartment leg musculature
Walking Cycle
resulting in a footdrop may lead to accentuated hip and
Human gait is a rhythmic, cyclic forward progression knee flexion during swing­through and alteration in
involving motion of all body segments. A single cycle is attaining a foot­flat position.
often defined as the motion between the heel strike of The walking cycle being one of continuous motion is
one step and the heel strike of the same foot on the sub­ difficult to appreciate in its entirety because so many
sequent step. Gait parameters, such as stride length, veloc­ events occur simultaneously. To help appreciate the dif­
ity, and cadence, are easy to measure based on this ferent activities and functions of the components of the
definition. foot and ankle during gait, the stance phase can be
A single cycle can be divided further. The walking cycle divided into three intervals: the first interval, extending
for one limb is broken into a stance phase and a swing from initial heel strike to the foot laying flat on the floor;
phase. The stance phase typically constitutes 62% of the the second interval, occurring during the period of foot
cycle and the swing phase 38%. The stance phase is flat as the body passes over the foot; and the third inter­
further divided into a period of double limb support val, extending from the beginning of ankle joint plantar
(from 0% to 12%), in which both feet are on the ground, flexion as the heel rises from the floor to when the toes
followed by a period of single limb support (from 12% lift from the floor.
to 50%) and a second period of double limb support
(from 50% to 62%), after which the swing phase begins First Interval
(Fig. 1­1). The first interval occurs during approximately the first
The opposite leg also goes through a predictable 15% of the walking cycle and is defined from the moment
sequence during a gait cycle. The position and activities of initial heel strike to when the foot becomes flat on the
of this contralateral leg can be seen at predictable times. floor. Typically, the opposite heel has lifted from the floor,
For instance, contralateral toe­off is typically at 12% of but weight remains on the forefoot. During the first inter­
the gait cycle, occurring after the ipsilateral foot has val, the foot helps to absorb and dissipate the forces
reached a foot­flat position. Ipsilateral heel rise begins at generated by the foot striking the ground.
4
Biomechanics of the Foot and Ankle ■ Chapter 1
appears to play a role in restricting this motion at initial
ground contact.
The subtalar joint links rotation of the hindfoot to
First interval rotation of the leg. During the first interval, eversion of
the calcaneus is translated by the subtalar joint into
inward rotation that is transmitted proximally across the
ankle joint into the lower extremity (Fig. 1­2E). Distally,
Body weight
125% this hindfoot eversion unlocks the transverse tarsal joint
Percentage 100%
(Fig. 1­2D), allowing the midfoot joints to become
of
50%
A body weight supple. This allows the flattening of the longitudinal arch
that contributes to energy dissipation during this phase.
20˚ Ankle rotation At heel strike, the center of gravity of the body is decel­
Dorsiflexion 10˚ erated by ground contact, then immediately accelerated
Neutral standing position
upward to carry it over the extending lower extremity. The
heel’s impact and body’s center of gravity shift accounts
Plantar
10˚
B flexion for a vertical floor reaction that exceeds body weight by
20˚ 15% to 25% (Fig. 1­2A).
EMG activity Eccentric contraction of the anterior compartment leg
Intrinsic muscles of foot muscles slows the rapid ankle plantar flexion during this
phase from heel strike until a foot­flat position is reached.
Posterior tibial muscles
The posterior calf muscles all are electrically quiet, as are
Anterior tibial muscles
C the intrinsic muscles in the sole of the foot (Fig. 1­2C).
There is no muscular response in those muscles usually
20˚ Subtalar rotation considered important in supporting the longitudinal arch
10˚ of the foot. Weakness of the anterior compartment
Supination Neutral standing position
muscles leads to a loss of this deceleration and a charac­
teristic slap foot gait.
Pronation 10˚
D
20˚
20˚ Horizontal rotation Second Interval
Internal of tibia The second interval extends from 15% to 40% of the
rotation 10˚
walking cycle. During this interval, the body’s center of
gravity passes from behind to in front of the weight­
Neutral standing position
External 10˚ bearing leg. It reaches a maximum height as it passes over
E rotation
20˚ the leg at about 35% of the cycle, after which it com­
0% 15% mences to fall. During this interval, the foot transitions
Percentage of from a flexible, energy­absorbing structure to a more rigid
walking cycle
one, capable of bearing the body’s weight.
Figure 1-2 Composite of events of first interval of walking, The ankle joint undergoes progressive dorsiflexion
or period that extends from heel strike to foot flat. EMG,
during the second interval, reaching its peak at 40% of
electromyograph.
the walking cycle. This is when the force across the ankle
joint has reached a maximum of 4.5 times body weight.
Heel rise begins at 34% of the cycle as the contralateral
The ankle joint undergoes rapid plantar flexion from leg passes by the stance foot and precedes the onset of
heel strike until foot flat is achieved. At approximately 7% plantar flexion, which begins at 40% (Fig. 1­3B).
of the walking cycle, dorsiflexion begins (Fig. 1­2B). During the second interval, the subtalar joint progres­
As the foot is loaded with the weight of the body sively inverts. This starts at about 30% of the cycle in a
during the first interval, the calcaneus rapidly everts and normal foot and at about 15% of the cycle in a flatfoot
the longitudinal arch flattens. This flattening of the arch (Fig. 1­3D). Multiple factors contribute to this inversion,
originates in the subtalar joint and reaches a maximum but precisely which plays the greatest role is unclear.
during this interval (Fig. 1­2D). The hindfoot is often Above the subtalar joint, the swinging contralateral limb
mildly supinated at initial ground contact associated with externally rotates the stance limb. This external rotation
ankle dorsiflexion during swing­through. The hindfoot torque is translated by the subtalar joint into hindfoot
moving from supination to pronation during the first inversion. The oblique nature of the ankle joint axis, the
interval is a passive mechanism, and the amount of oblique setting of the metatarsal break, and the function
motion appears to depend entirely on the configuration of the plantar aponeurosis also contribute to hindfoot
of the articulating surfaces, their capsular attachments, inversion. Inversion of the subtalar joint is passed distally
and ligamentous support. No significant muscle function into the midfoot, increasing the stability of the transverse
5
Part I ■ General Considerations
Second
interval
Third interval
Body weight
Percentage 125%
100%
of body
weight 50% 125% Body weight
A Percentage 100%
20˚ Ankle rotation of 50%
A body weight
Dorsiflexion 10˚
20˚ Ankle rotation
Plantar Neutral standing position
10˚
flexion Dorsiflexion 10˚
B 20˚
EMG activity Neutral standing position
Intrinsic Plantar
10˚
muscles of foot B flexion
Posterior 20˚
tibial muscles EMG activity
Anterior tibial
C muscles Intrinsic muscles of foot
20˚ Subtalar rotation Posterior tibial muscles
Supination 10˚ Anterior tibial muscles
C
Pronation 10˚ Neutral standing position 20˚ Subtalar rotation
D 20˚ 10˚
Supination
20˚ Horizontal rotation of tibia
Internal 10˚ Neutral standing position
rotation Pronation 10˚
D
External 10˚ Neutral standing position 20˚
rotation
E 20˚ 20˚ Horizontal rotation
15% 30% 40% Internal of tibia
Percentage of walking cycle rotation 10˚
Neutral standing position
Figure 1-3 Composite of events of second interval of
walking, or period of foot flat. EMG, electromyograph. External 10˚
E rotation
20˚
40% 65%
tarsal articulation and transforming the flexible midfoot Percentage of
into a rigid structure. walking cycle
During this interval, full body weight is not borne on Figure 1-4 Composite of all events of third interval of
the foot, smoothing the transition to single limb support. walking, or period extending from foot flat to toe-off. EMG,
Force plate recordings show that the load on the foot electromyograph.
may be as low as 70% to 80% of actual body weight
(Fig. 1­3A).
During the second interval, important functional Third Interval
changes occur in both the foot and leg, which are the The third interval constitutes the last of the stance phase
result of muscular action. The posterior and lateral com­ and extends from 40% to 62% of the walking cycle.
partment leg muscles (triceps surae, peroneals, tibialis The ankle joint demonstrates rapid plantar flexion
posterior, long toe flexors) and intrinsic muscles in the during this interval as the foot essentially extends the
sole of the foot demonstrate electrical activity (Fig. 1­3C). stance, effective length. The subtalar joint continues to
Intrinsic muscle activity of the normal foot begins at 30% invert during this interval, reaching its maximum at
of the cycle, whereas in flatfoot, activity begins at 15% of toe­off (Fig. 1­4D). This completes the conversion of the
the cycle. The posterior calf musculature slows the forward forefoot from the flexible structure observed in the first
movement of the tibia over the fixed foot, which permits interval at the time of weight acceptance to a rigid struc­
the contralateral limb to increase its step length. Weak­ ture at the end of the third interval in preparation for
ness of the posterior compartment muscles may lead toe­off. The inversion is a continuation of the processes
to premature contralateral heel strike and shortened that began in the second interval. These include external
stride length. rotation of limb above the foot passing across the ankle
6