Practice of pediatric orthopedics

466 Pages·2006·56.841 MB·English

by  Lynn T. Staheli MD

Practice
of
Pediatric
Orthopedics
Second Edition
Lynn T. Staheli, M.D.
Emeritus Professor, Department of Orthopedics
University of Washington School of Medicine
Seattle, Washington
Emeritus Editor, Journal of Pediatric Orthopaedics
Consulting Orthopedist,
Department of Orthopedics
Children’s Hospital and Regional Medical Center
Seattle, Washington
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00preface12.28.indd 1i 2/8/06 1:53:19 PM
Benjamin Alman, MD Co-Authors
Chapter 1 – Growth
The first edition of the Practice of Pediatric Orthopedics (PPO) was
Head, Division of Orthopaedic Surgery
prepared with the help 37 Consultants listed below. Each edited chapters
Hospital for Sick Children
or sections and each agreed to accept e-mail consultations.
Professor and Vice Chair Research
This second edition was prepared with the assistance of 8 Co-editors.
Department of Surgery
University of Toronto Co-editors contributed material and editing that substantially improved
Toronto, Canada their chapters. I appreciate their expertise, consultations, material, and
editing.
Consultants – First Edition
Chappie Conrad, MD James Beaty, MD Robert Hensinger, MD Ignacio Ponseti, MD
Michael Benson, FRCS Anthony Herring, MD George Rab, MD
Chapter 14 – Tumors
Jane Burns, MD John Herzenberg, MD Perry Schoenecker, MD
Director, Department of Orthopedics Jack Cheng, MD Mark Hoffer, MD David Sherry, MD
Children's Hospital and Regional Medical Chappie Conrad, MD Randy Loder, MD Kit Song, MD
Center Alvin Crawford, MD Anne Lynn, MD Carl Stanitski, MD
Professor of Orthopaedic Surgery Sharon DeMuth, DPT Dean MacEwen, MD Peter Stevens, MD
University of Washington Mohammad Diab, MD Freeman Miller, MD Michael Sussman, MD
Seattle, Washington Alain Dimeglio, Prof. Vince Mosca, MD Hugh Watts, MD
Marybeth Ezaki, MD Colin Moseley, MD John Wedge, MD
Edison Forlin, MD Carol Mowery, MD Stuart Weinstein, MD
Richard Gross, MD William Oppenheim, MD Kaye Wilkins, MD
Ham Peterson, MD
Mohammad Diab, MD Kit Song, MD
Chapter 16 – Syndromes Chapter 8 – Spine
Chief of Pediatric Orthopaedics Chapter 13 – Infections
Associate Professor of Orthopaedic Assistant Director
Surgery Department of Orthopedic Surgery
University of California at San Francisco Children's Hospital and Regional Medical
San Francisco, California Center,
Associate Professor of Orthopaedic Surgery
Department of Orthopaedics
University of Washington
Seattle, Washington
Marybeth Ezaki, MD Carl Stanitski, MD
Chapter 9 – Upper Limb Chapter 6 – Knee
Chapter 10 – Hand Chapter 12 – Sports
Chief, Hand Service Professor of Orthopaedic Surgery
Scottish Rites Hospital for Children Medical University of South Carolina
Professor Charleston, SC
Orthopaedic Surgery
UTSouthwestern School of Medicine
Dallas, Texas
Vince Mosca, MD Michael Sussman, MD
Chapter 4 – Lower Limb Chapter 15 – Neuromuscular
Chapter 5 – Foot Shriners Hospital for Children
Former Director, Clinical Professor of Orthopaedic surgery
Department of Orthopedics, Oregon Health and Science University
Children's Hospital and Regional Medical Portland, Oregon
Center
Associate Professor of Orthopaedic
Surgery
University of Washington
Seattle, Washington
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00preface12.28.indd 1ii 2/8/06 1:53:20 PM
Preface to First Edition Preface to Second Edition
The Practice of Pediatric Orthopedics (PPO) was designed to make This second edition of the Practice of Pediatric Orthopedics (PPO) was
learning childrenʼs orthopedics efficient and pleasant. This book pro- designed to build upon the strengths of the first edition. The basic objec-
vides core information, references, and e-mail access to experts. I tives are the same: to provide a guide to learning the essentials of this spe-
designed, wrote, and illustrated PPO utilizing desktop publishing tech- cialty quickly and efficiently. As with the first edition, I designed, wrote,
nology that made possible a full-color, extensively illustrated book that and illustrated PPO utilizing desktop publishing technology that made
is affordable. To insure accuracy and clarity, each section was reviewed possible a full-color, extensively illustrated book that is affordable.
by at least two consultants. Consultants are acknowledged authorities. This edition was greatly enhanced by my Co-authors. Each is an
The general features of PPO are listed below. Please read – Instructions acknowledged expert in their fields and each contributed substantially to
to Readers. 2001 improving their chapters.
Royalties for this publication will be donated to Global-HELP
General Features
Organization to make health care publications available without charge
• Designed for general orthopedists and residents for use in developing countries.
• Provides core information on pediatric orthopedics The new features and instructions for readers are detailed below:
• 37 consultants edited content and may accept e-mail consultations
New Features
• Current references are provided
• Compact, efficient design, with over 400 pages & 2500 illustrations
• Co-authors contributed information and edited content
• Practical, how to book details common problems
• Text is updated and expanded
• Management recommendations are whole child oriented
• New illustrations have been added
• Mainstream approach to management – safe and proven
• Illustrations have been updated and improved
• Management recommendations are current
• Topic discussion and procedures consolidated
• Trauma and procedures are presented in greatest detail
• Upper limb and hand chapters separated and expanded
• Flowcharts are added to guide management
• Contents presented on end sheets to simplify access
• Publication reformatted for production in Adobe InDesign
• Anticipated readership expanded to include general orthopedists,
Lynn Staheli residents, nurses, therapists and students
e-mail:
staheli@u.
Instructions for readers
washington.edu
• Citing of illustrations in the text is made by the letters in [brackets]
• Identify a specific reference by the page number followed by the letter,
such as 121C (page 121, illustration C)
• The order of citing illustrations is not always consecutive because of
page design requirements
• Information is presented with different background colors:
Tables: Light beige
Drawings: Light blue
Procedures: Light green
Flow charts: Light grey
• Syndromes are arranged alphabetically
• Errors or suggestions please contact me by e-mail :
[email protected]
In Appreciation
• Graphic assistance: Michelle Gutierrez
• Text editing: Sandra Rush
• Technical consultants: Jeff McCord and Stephen Laskevitch
• LWW team: Robert Hurley, Charlene Squibb, and Sharon Zinner
Michelle Gutierrez Noir
Design and Publication assistance More help?
Dedication.....
To Letha Staheli, my mother and inspiration who departed in 2004 at the age of 101
Lana Staheli, my wife and best friend
my children, Linda, Diane, and Todd
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Acquisitions Editor: Robert Hurley
Managing Editor: Michelle La Plante
Production Manager: Bridgett Dougherty
Senior Manufacturing Manager: Benjamin Rivera
Marketing Director: Sharon Zinner
Printer: Quebecor World
© 2006 by Staheli, Inc., 4116 48th NE, Seattle, WA 98105 USA
Lippincott Williams & Wilkins
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Philadelphia, PA 19106 USA
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All rights reserved. This book is protected by copyright. No part of this book may be reproduced in any form or by any means, including
photocopying, or utilized by any information storage and retrieval system without written permission from the copyright owner, except for
brief quotations embodied in critical articles and reviews. Materials appearing in this book prepared by individuals as part of their official
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Printed in the USA
Library of Congress Cataloging-in-Publication Data
Staheli, Lynn T.
Practice of pediatric orthopedics / Lynn T. Staheli.-- 2nd ed.
p. ; cm.
Includes bibliographical references and index.
ISBN 1-58255-818-3
1. Pediatric orthopedics. I. Title.
[DNLM: 1. Musculoskeletal Diseases--therapy. 2. Child. 3. Musculoskeletal
System--physiopathology. 4. Orthopedic Procedures. WS 270 S781p 2006]
RD732.3.C48S733 2006
618.92’7--dc22
2006002573
Care has been taken to confirm the accuracy of the information presented and to describe generally accepted practices. However, the
authors, editors, and publisher are not responsible for errors or omissions or for any consequences from application of the information
in this book and make no warranty, expressed or implied, with respect to the currency, completeness, or accuracy of the contents of the
publication. Application of this information in a particular situation remains the professional responsibility of the practitioner.
The authors, editors, and publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in
accordance with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in
government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check
the package insert for each drug for any change in indications and dosage and for added warnings and precautions. This is particularly
important when the recommended agent is a new or infrequently employed drug.
Some drugs and medical devices presented in this publication have Food and Drug Administration (FDA) clearance for limited use in
restricted research settings. It is the responsibility of the health care provider to ascertain the FDA status of each drug or device planned
for use in their clinical practice.
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Table of Contents
Growth Chapter 1 Forefoot Adductus 114 Hand Injuries 246
Normal Growth 1 Forefoot Deformities 116 Wrist Deformities 250
Abnormal Growth 12 Vertical Talus 119 Chronic Arthritis in Children 251
Abnormal Morphogenesis 12 Clubfoot 120 Hand Deformities 252
Chromosomal Abnormalities 13 Toe Walking 131 Thumb Deformities 253
Polygenic Inheritance 13 Flatfeet 132 Finger Deformities 254
Mechanism of Inheritance 14 Cavus Deformity 138
Skeletal Dysplasia 14 Other Foot Conditions 140 Trauma Chapter 11
Developmental Deformities 16
Statistics 257
Osteochondroses 16 Knee and Tibia Chapter 6 Physiology 258
Features of Immature Skeleton 18
Evaluation 144 Physeal Injuries 260
Iatrogenic Deformities 19
Knee Pain 146 Remodeling 263
Patellofemoral Disorders 150 Principles of Reduction 264
Evaluation Chapter 2 Dislocations 150 Fixation 266
Physical Examination 24 Intraarticular Disorders 152 Evaluation 268
Clinical Tests 28 Tumors of the Knee 153 Occult Injuries 270
Imaging 30 Sagittal Deformities 154 Birth and Neonatal Injuries 272
Gait Evaluation 34 Neuromuscular Disorders 155 Child Abuse 272
Laboratory Studies 35 Tibial Bowing 156 Polytrauma 273
Diagnostic Procedures 36 Pseudarthrosis of the Tibia 157 Pathologic Fractures 274
Time Line 37 Fibular Pseudarthrosis 157 Open Fractures 275
Joint Swelling 38 Complications 276
Limb Defi ciencies 40 Hip Chapter 7 Foot Injuries 278
Ankle Injuries 280
General 159
Management Chapter 3 Evaluation 161 Tibial Fractures 284
Knee Injuries 286
Managing the Family 43 Hip and Pelvic Pain 164
Knee Fractures 288
Shoes 47 Developmental Hip Dysplasia 166
Femur Shaft Fractures 290
Before Surgery 48 Legg-Calvé-Perthes Disease 182
Hip Dislocation 295
Anesthesia 50 Slipped Femoral Epiphysis 188
Fractures of Proximal Femur 296
Surgical Preparation 52 Miscellaneous Disorders 193
Pelvic Fractures 298
Operative Scars 53
Spine Injuries 300
Skin Closure 53 Spine Chapter 8 Shoulder Injuries 302
Fixation 54
Normal Development 197 Supracondylar Fractures 306
Grafts 55
Evaluation 199 Medical Epicondylar Fractures 309
Postoperative Care 56
Congenital Deformities 201 Elbow Dislocations 309
Complications 58
Back Pain 202 Lateral Condylar Fractures 310
Foreign Body Removal 62
Scoliosis 210 Radial Neck Fractures 312
Hardware Removal 63
Congenital Sciolisis 212 Olecranon Fractures 314
Amplifi ed Musculoskeletal Pain 64
Thoracic Insufficiency Syndrome 213 Monteggia Fracture Dislocation 314
Traction 65
Idiopathic Scolosis 214 Forearm Fractures 315
Casting 68
Sagittal Deformity 220 Distal Radius Fractures 319
Spica Cast Application 70
Cervical spine 222
Joint Aspiration 71
Generalized Disorders 224
Orthotics 72 Sports Chapter 12
Prosthetics 73 Introduction 323
Therapy 74 Upper Limb Chapter 9 Physiology 324
Development 227 Injury Statistics 325
Lower Limb Chapter 4 Evaluation 228 Prevention 326
Upper Limb Deficiencies 230 Special Children 327
Development 77
Torticollis 232 Injury Types 328
Limp 78
Sprengel Deformity 235 Overuse Injuries 330
Leg Aches 80
Brachial Plexus Palsy 236 Evaluation 332
Genu Varus and Genu Valgus 81
Shoulder Disorders 237 Management Principles 334
Torsion 88
Elbow Disorders 238 Sport-Specific Problems 336
Leg Length Inequality 96
Forearm Deformitis 239 Foot and Ankle Problems 339
Lower Limb Defi ciencies 101
Tibia Problems 340
Hand Chapter 10 Knee Problems 341
Foot Chapter 5 Hip and Thigh Problems 341
Development 241
Introduction 105 Pelvis Problems 342
Evaluation 241
Evaluation 106 Spine Problems 342
Management Principles 242
Foot Pain 108 Neck Problems 342
Hand Tumors 244
Toe Deformities 112 Upper Limb Problems 343
Hand Infections 245
00preface12.28.indd 0i 2/8/06 1:53:14 PM
Infection Chapter 13
Growth 1
Pathogenesis 345
Organisms 347
Evaluation 348
Management Principles 350 Evalution 2
Drainage of Septic Joint 352
Drainage of Osteomyelitis 353
Osteomyelitis 354 Management 3
Septic Arthritis 358
Pelvic Infections 360
Unusual Forms of Osteomyelitis 360 Lower Limb 4
Soft Tissue Infections 361
Tuberculosis 362
Meningococcal Infections 363
Foot 5
Tumors Chapter 14
Evaluation 365
Knee 6
Unicameral Bone Cysts 370
Operative Management of Cysts 371
Aneurysmal Bone Cysts 372
Fibrous Tumors 373 Hip 7
Benign Cartilaginous Tumors 374
Hemimelica 375
Osseous Tumors 376 Spine 8
Other Bone Tumors 377
Benign Soft Tissue Tumors 378
Malignant Soft Tissue Tumors 379 Upper Limb 9
Osteosarcoma 380
Ewing sarcoma 381
Leukemia 383
Hand 10
Metastatic Bone Tumors 383
Neuromuscular Chapter 15
Trauma 11
Development – Nervous System 385
Statistics 386
Evaluation 387
Sports 12
Management Principles 390
Cerebral Palsy 392
Myelodysplasia 404
Muscular dystrophy 408 Infections 13
Poliomyelitis 410
Arthrogryposis 410
Miscellaneous Disorders 414 Tumors 14
Syndromes Chapter 16
Introduction 418 Neuromuscular 15
Evaluation 420
Conditions in Alphabetic Order 422
Syndromes 16
Reference Chapter 17
Parents FAQ 437
What Parents Should Know 438 Reference 17
Reference Charts 442
Remodeling Examples 444
Index 18
Index 423
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1
Chapter 1 – Growth
Normal Growth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Abnormal Growth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Gamete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Classifications of Abnormal Morphogenesis. . . . . . . . . 12
Early Embryo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chromosomal Abnormalities. . . . . . . . . . . . . . . . . . . . . 13
Embryo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Polygenic Inheritance. . . . . . . . . . . . . . . . . . . . . . . . . . 13
Connective Tissue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Mechanism of Inheritance. . . . . . . . . . . . . . . . . . . . . . . 14
Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Skeletal Dysplasia . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Developmental Deformities. . . . . . . . . . . . . . . . . . . . . . 16
Growth Plate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Osteochondroses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Bone Growth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Features of Immature Skeleton . . . . . . . . . . . . . . . . . . 18
Growth and Development. . . . . . . . . . . . . . . . . . . . . . . . 8 Iatrogenic Deformities. . . . . . . . . . . . . . . . . . . . . . . . . . 19
Body Proportions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Additional Reading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Developmental Variations. . . . . . . . . . . . . . . . . . . . . . . 10
Pediatric orthopedics is a subspecialty of medi- B Femoral torsion
cine that deals with the prevention and treat- Femoral torsion is often
familial. Many common
ment of musculoskeletal disorders in children.
musculoskeletal
In 1741, Nicholas Andry, professor of medicine
problems have a
at the University of Paris, published his treatise genetic basis.
describing different methods of preventing and
correcting deformities in children [A]. He com-
bined two Greek words, orthos, or straight, and
paidios, child, into one word, “orthopedics,” which
became the name of the specialty concerned with
the preservation and restoration of the musculo-
skeletal system. Pediatric orthopedics is central to
this specialty based on Andryʼs original focus on
childhood problems, due to the large proportion of
A Andry’s Tree
orthopedic problems that originate during the early
period of growth, and finally, because pediatric
orthopedics offers a dynamic and inherently interesting subspecialty.
C Growth phase The
A knowledge of normal and abnormal growth and development is Category Period
period of growth can be
vital to an understanding of pediatric orthopedics [B]. This knowledge Early Embryo 0–2 weeks divided into six phases.
increases our comprehension of the musculoskeletal system, improves
Embryo 2–8 weeks
our understanding of the causes of disease, and makes us better able to
Fetus 8 weeks to birth
manage the varied orthopedic problems of childhood.
Dividing the period of growth into six stages provides a convenient Infant Birth to 2 years
framework to review both normal and abnormal growth and development Child 2 years to puberty
[C]. During the first stage, reproductive cells or gametes are formed.
Adolescent Transition to maturity
Normal Growth
During normal development, cells proliferate, undergo differentiation,
move and even in some cases die in order to produce a normal, mature
individual.
D Gametogenesis
Gamete X44X XX4444XX poroimcyatery The ovum and sperm
Gamete is a collective term for ovum and sperm. During gametogenesis, are formed by two
meiotic division halves the chromosome number. Genetic material, meiotic divisions that
which may include defective genes, is shuffled, and mature ova and 2X2 2X2 soeoccoyntedary halve the chromosome
number and shuffle
sperm are formed [D]. genetic material.
44 22 22 44
Early Embryo XX2X2X X2Y2XY Fertilization combines
fertilization the traits of both parents
This early embryonic phase encompasses the 2-week period from fertil-
to create a unique
ization to the implantation of the embryo. meiotic individual.
divisions 22 22 secondary
First week During the first week following fertilization, the zygote X Y spermatocyte
first
repeatedly divides as it moves through the fallopian tubes to the uterus.
second
The zygote becomes a morula, then a blastocyst. The blastocyst implants
polar 44 primary
itself on the posterior uterine wall. bodies XY spermatocyte
01gr12.28.indd 1 1/19/06 11:46:06 AM
2 Growth / Embryo
Second week During this week, the amniotic cavity and trilaminar
embryonic disc are formed [A]. The early embryo is usually aborted if a
lethal or serious genetic defect is present. During these first two weeks,
the early embryo is less susceptible to teratogens than during the follow-
A ing embryonic period.
Embryo
The embryonic period is characterized by rapid cell activity and organ
formation. Cells differentiate and mature, often through a process of
B D induction. Induction is the process by which surrounding cells act on
Neural tissue other cells to produce entirely new cells or tissue.
Mesoderm Third week This is the first week of organogenesis. During this
week, the trilaminar embryonic disc develops, somites begin to form,
Dermatome
and the neural plate closes to form a neural tube.
Myotome
Fourth week During this week, the limb buds become recognizable
Sclerotome [B]. Somites differentiate into three segments. The dermatome becomes
C
skin, the myotome becomes muscle, and the sclerotome becomes carti-
A Trilaminar Disc The neural tube closes. The mesoderm differentiates lage and bone. The apical ectodermal ridge develops in the distal end
into dermatome, myotome, and sclerotome. of each limb bud. The ridge has an inductive influence on limb mesen-
chyme, which promotes growth and development of the limb. Serious
defects in limb development may originate at this time.
AGE SIZE
Shape Form Bones Muscles Nerves
wks. mm.
Trilaminar Neural
notochord plate
Limb Neural
Sclerotomes Somites
buds tube
Hand Mesenchyme
E Premuscle
plate condenses
m
b
r
y Fusion
o 12 Digits Chondrification
myotomes
Limbs Early
17 Differentiation
rotate ossification
Fingers Definite Cord equals
23 vertebral
separate muscles
length
Sex Ossification
12 56
determined spreading
F
e
Face Joint Spontaneous
t 16 112
human cavities activity
u
s
Myelin
20 160- Body more sheath
40 350 proportional forms; cord
ends L3
B Prenatal development This chart summarizes musculoskeletal development during embryonic and C Limb rotation During the
fetal life. seventh week, the upper limb
rotates laterally. The lower limb
rotates medially to bring the great
toes to the midline.
01gr12.28.indd 2 1/19/06 11:46:12 AM
Growth / Connective Tissue 3
Fifth week The hand plate forms and mesenchymal condensations
occur in the limbs.
Sixth week The rays of the digits become evident and chondrifica-
tion of mesenchymal condensations occurs.
Seventh week The notches appear between the digit rays. This
process, responsible for joint formation, results from cell death. Failure
A Collagen helix A triple helix of peptide chains forms the basic
of the separation of rays results in syndactylism. During this week, the collagen structure.
upper and lower limbs rotate in opposite directions [C, previous page].
The lower limb rotates medially to bring the great toes to the midline,
Type Tissue involved Disorders
whereas the upper limb rotates about 90˚ laterally to position the thumb
on the lateral side of the limb. I Bone, tendon, skin Osteogenesis imperfecta
Eighth week The fingers separate completely, the embryo assumes a II Cartilage, nucleus Spondyloepiphyseal
human appearance, and the basic organ systems are completed. pulposus dysplasia
Fetus III Blood vessels Ehlers Danlos syndrome
The fetal period is characterized by rapid growth and changes in body IV Basement membranes
proportions.
V Minor component of bone
Ninth to twelfth weeks The first bone, the clavicle, ossifies by a
process of intramembranous deposition of calcium. The skeleton devel-
B Collagen types Of the numerous collagen types, five are most widely
ops in a cranial to caudad sequence, with the upper extremities develop-
distributed.
ing before the lower limbs. This results in the upper limbs becoming
proportionate compared to the rest of the body, but the lower limbs
remaining short.
C Clinical manifestations of
Thirteenth to twentieth weeks Growth continues to be rapid. The collagen types Variations of collagen
lower limbs become proportionate and most bones ossify. The fetal peri- types are common in pediatric orthopedics.
od is characterized by rapid growth and changes in body proportions This child has developmental hip dysplasia
Twentieth to fortieth weeks Growth continues and body propor- with extreme joint laxity.
tions become more infant-like.
Connective Tissue
During early fetal life, the basic structure of connective tissue is formed
largely of two families of macromolecules—collagens and proteogly-
cans
Collagen
Collagen is a family of proteins containing a triple helix of peptide chains
[A]. Although at least fifteen different types of collagen are known, five
types are most common [B].
The biosynthesis of collagen starts in the endoplasmic reticu-
lum, where the basic molecule is assembled. In the extracellular space,
procollagen is formed. It is arranged into fibrils and reinforced by
cross-linkages to become collagen. Collagen is the major component of
connective tissue.
Disorders of collagen are common They may be minor, produc-
ing only increased joint laxity [C], or severe, causing considerable dis-
ability. The major collagen disorders are classified according to the site
of the defect in the pathway of collagen biosynthesis.
Proteoglycans (mucopolysaccharides)
Proteoglycans are macromolecules that form the intracellular matrix
of hyaline cartilage and the other connective tissues. Polypeptides
or proteins attach to glycosaminoglycan to become proteoglycans
[D]. Proteoglycans attach to a hyaluronic acid by a link protein to
become an aggregate with a molecular weight in excess of one million.
Proteoglycans are highly hydrophilic, and in water they combine with
many times their weight of water to create an elastic matrix that is ideal
for joint lining. Hyaline cartilage is composed of about equal amounts of Link protein Proteoglycan aggregate
proteoglycans and collagen, and it combines with about three times its Hyaluronic acid
weight of water providing a resilient tissue with excellent shock absorb- Linkage region
Core protein
ing characteristics. Defects in the formation of these complex molecules Keratin sulfate
produce a variety of diseases. Chondroitin sulfate
Mucopolysaccharide (MPS) storage diseases result from a deficiency
of specific lysosomal enzymes necessary for the degradation of gly- D Proteoglycan aggregate These massive molecules combine with
cosaminoglycans. These diseases are caused by excessive intracellular water to form a resilient matrix such as that of hyaline cartilage.
accumulation of partially degraded molecules that result in conditions
such as avascular necrosis or spinal cord compression.
01gr12.28.indd 3 1/19/06 11:46:13 AM
4 Growth / Bone
Joints
Synovial joints develop first as a cleft in the mesenchyme, which then
chondrifies and cavitates [A]. Cavitation is completed by about the four-
teenth week, with the inner mesenchyme becoming synovium and the
outer mesenchyme becoming the joint capsule. Normal joint develop-
ment requires motion, and motion requires a functioning neuromuscular
system. Thus, defective joints are often seen in infants with neuromus-
cular disorders such as myelodysplasia or amyoplasia.
Bone
A B C
Bones are formed by osteogenesis. The mandible and clavicle are first
formed starting in the seventh gestational week by intramembranous
ossification.
Cartilage Intramembranous Ossification
Bone Osteoblasts differentiate from mesenchyme to form bone directly with-
Synovium out a cartilaginous stage. Further growth occurs by appositional bone
Mesenchyme
formation.
Sclerotome
Endochondral Ossification
During the sixth gestational week, mesenchymal cells differentiate,
D E condense, and transform into chondrocytes to form a model of the future
skeleton. The center of this model, chondrocytes hypertrophy and begin
A Syovial joint formation The synovial joints form first as condensations
to calcify. During the next week, a periosteal sleeve of bone is formed,
of mesenchyme. Cavitation, chondrification, synovial differentiation, and
finally ossification complete the basic structure. and by the eighth week, vascularization is under way [B].
During the fetal period, primary ossification centers develop in long
bones within the diaphysis [C]. Ossification first occurs under the peri-
chondrium. Within the cartilage, hypertrophied cells degenerate. Next,
vascular ingrowth occurs, and then the core of the cartilage model is
ossified to form the primary ossification center. Endochondral ossifica-
tion proceeds at the cartilage–bone interphase. Later, secondary ossifica-
tion centers develop at the ends of the bones, and the cartilage interposed
between the primary and secondary ossification centers becomes the
growth plate.
Except for the clavicle, all bones of the axial and appendicular skel-
eton are preformed in cartilage and converted to bone by enchondral
ossification. This process begins in the scapula, humerus, radius, and
ulna. Ossification continues in an orderly fashion, with centers appearing
at different ages. Ossification is earlier in girls than boys [D].
Mesenchyme
Cartilage
Bone
Blood Vessels
B Endochondral ossification A typical long bone is preformed in
mesenchyme. Chon drification precedes ossification.
Girls Boys
Humeral 0–2 mo 0–3 mo
head
Capitellum 1–6 mo 0–8 mo
Radial head 3–5 yrs 4–5 yrs
Femoral 1–6 mo 2–8 mo
head
Patella 1.5–3.5 yrs 2.5–6 yrs
Navicular 1.5–3 yrs 1.5–5.5 yrs
C Radiograph of bones
of a newborn infant This
radiograph shows primary
ossification of the skeleton.
Much of the skeleton is
cartilage at this age.
D Ossification Appearance of important ossification centers in girls and
boys.
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