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 i 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 ii 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 iii 00preface12.28.indd 1iii 2/8/06 1:53:22 PM 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 530 Walnut Street Philadelphia, PA 19106 USA LWW.com 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 duties as U.S. government employees are not covered by the above-mentioned copyright. 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. To purchase additional copies of this book, call our customer service department at (800) 638 -3030 or fax orders to (301) 223-2320. International customers should call (301) 223-2300. Visit Lippincott Williams & Wilkins on the Internet: at LWW.com. Lippincott Williams & Wilkins customer service representatives are available from 8:30 am to 6pm, EST. 10 9 8 7 6 5 4 3 2 1 iv 00preface12.28.indd 1iv 2/8/06 1:53:23 PM 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 00preface12.28.indd 0ii 2/8/06 1:53:19 PM 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. 01gr12.28.indd 4 1/19/06 11:46:14 AM