Ebook Basic musculoskeletal imaging: Part 1

(BQ) Part 1 book Basic musculoskeletal imaging presents the following contents: Imaging modalities used in musculoskeletal radiology, axial skeletal trauma, pediatric skeletal trauma, arthritis and infection, metabolic bone diseases, bone infarct and osteochondrosis,...

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BASIC MUSCULOSKELETAL

IMAGING

Editor Jamshid Tehranzadeh, MD

Director of Musculoskeletal Imaging Chief of Radiology and Nuclear Medicine Imaging/Radiation Therapy

Veterans Affairs Long Beach Healthcare System

Long Beach, California Emeritus Professor and Vice Chair of Radiology

University of California, Irvine Irvine, California

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NoticeMedicine is an ever-changing science As new research and clinical experience broaden our knowledge, changes in treatment and drug therapy are required The authors and the publisher of this work have checked with sources believed to be reliable in their efforts to provide information that is complete and generally in accord with the standards accepted at the time of publication However, in view of the possibility of human error or changes in medical sciences, neither the authors nor the publisher nor any other party who has been involved in the preparation or publication of this work warrants that the information contained herein is in every respect accurate or complete, and they disclaim all responsibility for any errors or omissions or for the results obtained from use of the information contained in this work Readers are encouraged to confirm the information contained herein with other sources For example and in particular, readers are advised to check the product information sheet included in the package of each drug they plan to administer to be certain that the information contained in this work is accurate and that changes have not been made in the recommended dose or in the contraindications for administration This recommendation is

of particular importance in connection with new or infrequently used drugs

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who is my role model and a great source of inspiration for thousands of

radiologists in the world.

2 Skeletal Trauma: Upper Extremity 15

Cornelia Wenokor and Marcia F Blacksin

3 Skeletal Trauma: Lower Extremity 29

Cornelia Wenokor and Marcia F Blacksin

Marcia F Blacksin and Cornelia Wenokor

Marcia F Blacksin and Cornelia Wenokor

Michael E Cody and Jamshid Tehranzadeh

Aydin Soheili, Maryam Golshan Momeni,

and Jamshid Tehranzadeh

Quazi Al-Tariq, Benjamin D Levine, Kambiz Motamedi,

and Leanne L Seeger

9 Bone Infarct and Osteochondrosis 193

David T Nakamura and

Jamshid Tehranzadeh

10 Orthopedic Hardware and Complications 211

Reza Dehdari and Minal Tapadia

11 Signs in Musculoskeletal Radiology 233

Amilcare Gentili and Shazia Ashfaq

Quazi Al-Tariq, MD

Radiology Resident, Department of Radiological Sciences,

David Geffen School of Medicine at University of

California, Los Angeles, Los Angeles, California

Shazia Ashfaq, MD

Research Fellow, University of California, San Diego,

La Jolla, California

Marcia F Blacksin, MD

Professor of Radiology, Department of Radiology, University

of Medicine & Dentistry – New Jersey Medical School,

University Hospital, Newark, New Jersey

Sabrina Véras Britto, MD

Service de Radiologie et Imagerie Musculosquelettique,

Centre de Consultation et d’Imagerie de l’Appareil

Locomoteur, CHRU de Lille, Lille, France, Serviço de

Radiologia Músculo Esquelética, Santa Casa de

Misericórdia de São Paulo, São Paulo, Brasil

Joseph E Burns, MD, PhD

Associate Clinical Professor, Department of Radiological

Sciences, University of California, Irvine School of

Medicine, Orange, California

Juan Manuel Cepparo, MD

Service de Radiologie et Imagerie Musculosquelettique,

Centre de Consultation et d’Imagerie de l’Appareil

Locomoteur, CHRU de Lille, Lille, France

Mark Chambers, DVM, PhD, MD

Health Sciences Assistant Professor of Radiology, University

of California Irvine, Radiology/Nuclear Medicine

Imaging Service, Veterans Affairs Long Beach Healthcare

System, Long Beach, California

Michael E Cody, MD

Radiology Resident, University of California, Irvine Medical

Center, Orange, California

Anne Cotten, MD, PhD

Professor of Radiology and Head of the Department of

Musculoskeletal Radiology, Service de Radiologie et

Imagerie Musculosquelettique, Centre de Consultation et

d’Imagerie de l’Appareil Locomoteur, CHRU de Lille,

Ramon Gheno, MD

Service de Radiologie et Imagerie Musculosquelettique, Centre de Consultation et d’Imagerie de l’Appareil Locomoteur, CHRU de Lille, Lille, France

Monica-Shahla Modarresi, MD

Health Sciences Associate Clinical Professor, David Geffen School of Medicine at University of California, Los Angeles, West Los Angeles VA Medical Center, Los Angeles, California

Maryam Golshan Momeni, MD

Clinical Instructor/Musculoskeletal Fellow, University of California, Irvine, Orange, California

David T Nakamura, MD

Radiology Resident, University of California, Irvine, Orange,

California

Ben Plotkin, MD

Assistant Professor of Radiological Sciences at University of

California, Los Angeles, Harbor-UCLA Medical Center,

Professor and Chief Musculoskeletal Imaging, Department

of Radiological Sciences, David Geffen School of

Medicine at University of California, Los Angeles,

Los Angeles, California

Alya Sheikh, MD

Assistant Professor of Radiological Sciences at University of

California, Los Angeles, Body Imaging at Harbor-UCLA

Medical Center, Torrance, California

Jader José da Silva, MD

Serviço de Radiologia Músculo Esquelética do Hospital do

Coração, São Paulo, Brasil

Arash David Tehranzadeh, MD

Attending Radiologist, Kerlan-Jobe Integrated Facility/Centinela Radiology Medical Group, Los Angeles, California

Jamshid Tehranzadeh, MD

Director of Musculoskeletal Imaging, Chief of Radiology and Nuclear Medicine Imaging/Radiation Therapy at VA Long Beach Healthcare System, Long Beach, California, Emeritus Professor and Vice Chair of Radiology at University of California, Irvine

Laurent Vandenbusche, MD

Service de Radiologie et Imagerie Musculosquelettique, Centre de Consultation et d’Imagerie de l’Appareil Locomoteur, CHRU de Lille, Lille, France

Rajeev K Varma, MD

Associate Professor of Radiological Sciences at University of California, Los Angeles, Section Chief, Musculoskeletal Imaging at Harbor-UCLA Medical Center, Torrance, California

Cornelia Wenokor, MD

Assistant Professor of Radiology, Department of Radiology, University of Medicine & Dentistry – New Jersey Medical School, University Hospital, Newark, New Jersey

Hiroshi Yoshioka, MD, PhD

Professor of Radiology, Musculoskeletal Section Chief, University of California, Irvine, Orange, California

My own desire to become a radiologist took shape during my time as a medical student years ago, when I first began reading some of the basic texts in radiology My decision to specialize in bone imaging occurred during my radiology residency, once again based in part on reading some of the classic texts in musculoskeletal radiology So I know firsthand the importance of books to many medical students and radiology residents as they try to find the specialty or subspecialty that is right for them Because of this, I am excited to write a foreword for a book that, I believe, will fill a void in the literature and is long overdue

Jamshid (Jim) Tehranzadeh has edited a masterpiece, Basic Musculoskeletal Imaging, that is filled with useful information, pearls,

and pitfalls and is ideally suited to medical students and residents in many different fields who want to learn more about this subspecialty He and his contributors are to be congratulated for recognizing the need for such a publication and for filling this void

All the necessary information is here Chapters are written by both internationally recognized experts in the field and young enthusiastic “bone-lovers,” and these chapters cover a wide range of subjects The reader can find material dealing with the axial and appendicular skeleton and the ways in which it reacts to trauma, tumor, ischemia, infection, surgical intervention, and other processes This skeletal reaction is displayed vividly with a variety of imaging techniques that include conventional radiography,

CT scanning, ultrasonography, and MR imaging Indeed, separate chapters summarize the role of MR imaging in the ment of disorders of the shoulder, elbow, wrist, hip, knee, ankle, and spine Each chapter is focused and concise, emphasizing information that is critical to accurate diagnosis, containing pearls of wisdom and employing highly appropriate illustrations

assess-In addition, the material is easy to read and to digest, with “take-home” messages in every chapter This is a book that is ing as well as informative, and it is one that, once opened, will be hard to put down

stimulat-I want to personally congratulate Jim and the contributors for taking on this task They and the publisher correctly saw the need for a text dedicated to medical students and residents (in radiology, orthopedic surgery, and other fields) that would serve

as an easy-to-read source for information related to musculoskeletal imaging As an author myself, I fully recognize that erable thought and effort went into this project to ensure that the book contained information that is highly organized and es-sential to such imaging Yes, a void has been filled with the publication of this work Now, as was the case early in my medical education, there exists a text that will stimulate many medical students and residents and, for some, may prove influential in the choice of a specific career A job well done and one for which I am indeed honored to write this foreword

consid-Donald Resnick, MD

Professor of RadiologyChief, Musculoskeletal ImagingUniversity of California, San Diego School of Medicine

San Diego, CaliforniaSeptember 2013

ix

The title of this book being Basic Musculoskeletal Imaging may sound ironic to some It was customary to name a book “Basic” in

radiology when only plain radiographs were discussed, but times have changed Cross-sectional imaging such as CT and MRI, and even ultrasound and scintigraphy, once considered advanced imaging proved to be basic and are now mainstays in radiology.Michael Weitz, Executive Editor in the medical publishing division of McGraw-Hill, and I saw a void for an easy-to-read teaching textbook that is primarily targeted to medical students and residents in radiology, orthopedics, and physical therapy and rehabilitation and that addresses the basic aspects of not only general diagnostic but also advanced imaging of musculo-skeletal (MSK) radiology

My and all contributors’ efforts have been to create an MSK book that presents the materials in a simple and fluent text with superb example figures and illustrations that assist in a better understanding and learning of the subject Each chapter has one

or more lists of “Pearls,” which summarize the highlights and take-home messages of that section or chapter

The senior authors and contributors of this book are all experts in their subject matter and are presenting the latest tion in the literature Chapter 1 introduces the reader to the concepts of using different modalities in MSK imaging The next four chapters superbly discuss and illustrate MSK trauma in the upper and lower extremities, axial skeleton, and pediatrics Chapter 6 provides analysis with arthritis and infection in detail Chapter 7 covers the essentials of common bone and soft tissue neoplasms The basics of metabolic bone diseases are elegantly discussed and superbly illustrated in Chapter 8 The causes of bone infarct and types of osteochondroses are discussed in Chapter 9 The reader will find information on how to evaluate or-thopedic hardware and its complications in Chapter 10 The signs in MSK imaging are an interesting addition to this book in Chapter 11 Chapters 12 through 18 are dedicated to the basics of MSK MRI of different joints in the upper and lower extremi-ties and axial skeleton Our international experts from France and Brazil dedicated a great introduction to MSK ultrasound that appears in Chapter 19 Finally, the current advances in MSK scintigraphy is the topic of the last chapter

informa-I would like to thank all the authors and contributors of this book for their hard work and their fine products and timely contributions I am highly indebted to the great contributions of John Lotfi, JD, for his help in researching, editing, and proof-reading of the text and illustrations of this book, and obtaining necessary permissions I also thank Arash David Tehranzadeh for his contribution and line drawings for this book I am highly grateful to Robert Pancotti, Senior Project Development Editor

in the medical publishing division of McGraw-Hill, for his great assistance and kindness I also thank Michael Weitz for giving

me the opportunity to put this book together Last but not least, I thank Dr Donald Resnick for his gracious foreword to this book

Jamshid Tehranzadeh, MD

x

Imaging Modalities Used in

Musculoskeletal Radiology

Joseph E Burns, MD, PhD

INTRODUCTION

No single modality is all-encompassing for musculoskeletal

diagnosis Rather, each modality is like a tool in a toolbox,

used to perform specific functions and solve specific

diagnos-tic problems For instance, while radiographs (“X-ray films”)

are useful as screening tools for appendicular (extremity)

fractures, magnetic resonance imaging (MRI) is a more

use-ful tool for diagnosing meniscal tears in the knee Used in

varying combinations, the different modalities can diagnose

and characterize a wide range of musculoskeletal pathology

Herein, we describe the various common modalities in

clini-cal application and some examples of their usages

RADIOGRAPHS

Radiographs are the predominant modality of

musculoskel-etal imaging (at the very least in terms of numbers of

stud-ies) In their current form, X-ray machines and scanners use

electronic devices to produce and detect X-rays The device

used to detect the X-rays may in some sense be said to be

similar to the detector in your digital camera, except that

these detector plates are designed to detect photons from the

X-ray region of the spectrum rather than photons of optical

(light) wavelengths Once formed at the detector plate, X-ray

images are stored electronically on computers in a manner

similar to how images are stored on your digital camera (albeit with specialized formatting) These X-ray images are then viewed with image storage, display, and editing soft-ware libraries called picture archiving and communication systems (PACS)

There is, of course, a more fundamental difference tween image formation in digital photography and digital (or computed) radiography In digital photography, optical photons emanate from the flash element of the camera, are reflected from the object being photographed, and are picked up by the detector in your camera, creating an image

be-of the subject’s “surface.” Remember that X-rays have a shorter wavelength and higher energy than visible light, and

more easily pass through tissue X-rays thus pass through the

patient to the detector plate, being only partially stopped (generally, scattered or absorbed) in the process The resul-tant image is a cumulative superposition of multiple over-lapping structures the X-ray photons encountered along their pathway through the patient How does this occur? The internal anatomic structures of the patient are of varying densities, with structures of higher density (such as bones) preferentially attenuating the beam, and organs of lower density (such as the lung) allowing more photons to pass through A transmission, or “shadow” image of the internal structure of the patient is so created by the X-ray photons passing through the patient

Magnetic Resonance Imaging Molecular Imaging (Nuclear Medicine) Bone Scan

Five fundamental tissue densities are defined in the

human body, forming a method of scaling the brightness

of the resulting images and so identifying anatomic

struc-tures At the lowest end of the density spectrum is air,

which appears on X-ray images as black or extreme dark

gray regions Next is fat tissue, also low density, showing

itself as dark gray Fluid is higher in density, and not

usu-ally seen in isolation, being paired with other soft tissue

such as fat or muscle Muscle density is still higher, usually

appearing as a medium to light gray Finally, at the

(usu-ally) highest naturally occurring density in the body is

bone or calcification, appearing as light gray to white

Metal structures such as orthopedic fixation hardware for

fractures and joint prostheses appear white.What is seen

mainly in the final image are “edges” of objects, due to

den-sity differences between organs and other internal

struc-tures If there is no significant density difference, adjacent

structures or pathologies appear invisible or near invisible

on plain radiograph as they cannot be individually

distin-guished with confidence and may require other modalities

for visualization (Figure 1-1)

Additionally, remember that the X-ray photon will pass

through many structures in the patient on its way to the

de-tector, and so many structures will be superimposed on the

resulting images as a result of three-dimensional data

pro-jection into two-dimensional format The resultant

individ-ual radiographic images are incomplete data sets (somewhat

like having two equations with three unknowns), but a

num-ber of inferences and conclusions can be drawn from them

The amount of information about a particular structure

(say, a joint) can be increased by taking multiple images

from different perspectives Typically, perpendicular views

(frontal and lateral views) as well as an obliquely oriented

view (for joints) are taken as part of a study “series.” These

differing view perspectives allow objects of interest in the

series to be more completely localized in space inside the

patient (Figure 1-2)

Radiographs are commonly used as screening

examina-tions for fractures and joint dislocaexamina-tions, postsurgical

follow-up of bone fixation procedures, and arthritis assessment

Drawbacks include radiation exposure for the patient,

rela-tive low sensitivity for certain types of subtle fractures such as

nondisplaced intra-articular fractures, and low soft tissue

contrast.1–4

COMPUTED TOMOGRAPHY

Computed tomography (CT) scanning is a sophisticated

method for obtaining X-ray images of the body As described

in the radiograph section, the electronic X-ray source creates

X-ray beams that penetrate and pass through multiple layers

of body structure to a detector In this case, however, the X-ray

source and detectors are rotated about the patient following a

cylindrical surface geometry The beam is oriented toward the

central axis of the cylinder, where the patient has been placed, while a source-detection apparatus rotates along a helical arc Thus, the beam passes through the patient projecting from all directions (like a flashlight placed on the edge of a carousel, with the beam pointed toward the center of the carousel) A computer analyzes the degree of X-ray beam penetration through the patient at each point, and then uses sophisticated techniques to reconstruct data from these exposures and sepa-rate the objects along the beam path as it passes through the patient The resulting volume data set is then reformatted into body “sections”—images that have the appearance of the body cut into cross sections and photographed, with each cross section viewed as an image The computer thus creates a three-dimensional image data set from a three-dimensional structure

Modern CT scanners can create high spatial resolution cross sections in any arbitrary plane, but typically axial, coro-nal, and sagittal planes (relative to the body axis in anatomic positioning) are chosen By convention, the right side of the patient is on the left side of the computer screen while facing the screen For axial images, it is as if you are standing at the patient’s feet looking cranially, and for coronal images, it is as

if the patient is facing you

As with radiographs, X-ray CT images represent “maps”

of body organ density These images are displayed on the PACS system in gray scale, typically with the highest den-sity structures such as bone scaled at the bright or white end of the gray scale, and low-density material such as air

at the dark or black end of the gray scale Density units within the body as determined by the CT scanner are so scaled into units called Hounsfield units (HU) (just as units of length may be scaled as centimeters or inches) In

HU, air has an approximate density of –1000 HU, fat of –100 HU, water of 0 HU, muscle of 40 HU, and bone of

1000 HU Now, each pixel on a computer is capable of playing a large number of intensities, or shades of gray, de-pending on the bit depth For instance, 256 shades of gray are possible for 8 bits per pixel (bit depth of 8), 1024 shades

dis-at 10 bits per pixel, 4096 dis-at 12 bits, and 65,536 dis-at 16 bits Most diagnostic systems are 10 or 12 bit depth However, the human eye can only differentiate between approxi-mately 30 shades of gray (somewhat more with training)

So, only limited ranges on the gray scale (or HU scale) may thus be perceived at any time, and to appreciate this grada-tion, ranges of density (window width) centered about usual densities of interest (window center levels) such as bone are used to isolate and amplify anatomic details in the structures of interest

Intravenous (IV) contrast may be used in musculoskeletal imaging studies to increase density differences between body tissues and separate adjacent structures, as well as to demon-strate physiologic processes Except in unusual circum-stances, CT examinations use iodine-based IV contrast materials due to iodine’s ability to absorb X-rays Examples

B

Figure 1-1 Utility of multiple imaging modalities (A,B) Frontal and frog-leg lateral view radiographs of the right

hip (C,D) T1 and T2 fat saturation coronal MRI of pelvis demonstrating large right acetabular chondrosarcoma The

chondrosarcoma, which is easily and distinctly apparent on MRI, is more subtle on radiographs of 1A and 1B, which shows secondary bone remodeling and somewhat vague soft tissue irregularity

of contrast usage include delineation of the neurovascular

bundles in extremities, evaluation of hyperemia in

inflam-matory and infectious processes, and diagnosis of

hypervas-cular tumors While expanding the potential usages of CT,

contrast administration carries its own risks Approximately

2% of the general population will experience a mild reaction

to low-osmolar iodine contrast agents, which may include

hives Severe reactions to iodine contrast agents are seen in

approximately 0.1% of the population and may include

ana-phylactic reactions A summary of current symptoms,

previ-ous medical history, and medications should be obtained

from the patient, with an assessment of vital signs Treatment

of milder allergic reactions (e.g., urticaria) includes

observa-tion, with possible administration of diphenhydramine In

more severe reactions, the patient should be stabilized, with

monitoring of vital signs, IV fluid, epinephrine

administra-tion, and establishment of an airway, depending on clinical

symptomatology Vasovagal reactions may be treated with

elevation of the patient’s legs, oxygen, IV fluid, and in more severe cases with IV atropine Other reactions include contrast-induced nephropathy, with risk factors of contrast-induced nephropathy including elevated creatinine (>1.5 mg/dL), multiple myeloma, diabetes, and dehydration

CT scans are commonly used for evaluating complex tures (such as comminuted intra-articular fractures) and oc-cult fractures (such as non- or mildly displaced intra-articular and spinal fractures), where osseous structures and fractures may be vague or obscured on radiographs (Figure 1-3) CT visualization may also be used in bone or soft tissue tumor assessment, as well as for arthrograms in cases where MRI examination is contraindicated for a particular patient As in the case of radiographs, drawbacks again include radiation exposure (higher than a radiograph, however, progress is being made toward lower radiation doses), as well as artifact from very dense objects within (hardware) or around (exter-nal fixators, monitoring devices) the patient.4,5

Figure 1-2 Utility of multiple image projections Frontal (A) and lateral (B) radiograph series of the right tibia and

fibula Subtle nondisplaced comminuted fracture of the distal tibial diaphysis is apparent (white arrows) There are also

multiple metallic fragments, including a bullet (black arrows) Using the frontal view (A) in isolation, it is not possible to

localize the bullet any more than along an anterior-to-posterior line projection, such that the bullet may lie partially within the cortex of the tibia or fibula, or within the interosseous membrane With the addition of the lateral projec-tional view, it is now possible to more completely localize the bullet location in space, projecting within the posterior soft tissues of the leg

C

B

Figure 1-3 Utility of radiograph and CT (A,B) Frontal

and lateral radiographs of the right knee There is a small cortical avulsion fracture of the medial condyle of the femur (arrow), and vaguely apparent fracturing of the fibular head (arrow) On the lateral view, joint fluid can be

seen in suprapatellar bursa (continued)

Ultrasound examinations make use of the fact that sound

trav-els with different speeds in different materials Sound is

re-flected from the boundaries between anatomic structures with

different compositions (which yields different internal sound

speeds) Clinical ultrasound uses high-frequency sounds waves

of 1–20 MHz (1 MHz is 1 million cycles per second),

com-pared with the range of human hearing of 20 HZ-20 kHz

(1 kHz is 1000 cycles per second) A probe with sound

con-ducting material (gel) at the tip is put into contact with the

body surface The ultrasound gel is used to conduct the signal

into the body tissue more efficiently, as air is a relatively poor

conductor of sound waves compared with, say, water The

ul-trasound probe then emits high-frequency sound waves that

penetrate into the body tissues and are reflected back to the

probe tip where they are detected Using the return time and

amplitude of the reflected waves, the scanner then reconstructs

an image of the structures the sound waves encountered within

the body Each image typically provides a small “view portal”

into the body, which sometimes gives the feeling of looking

into through a tube at objects Ultrasound is also capable of

real-time visualization of the movement of structures, and so it

can be used to create “cine sequences” of tendon movement, for instance Finally, you may remember the principle of the Doppler effect from physics: sound from a source moving to-ward you will appear to be a higher frequency than that sound from that same source as it moves away from you Using this principle, ultrasound may be used to measure the velocity of movement within the tissue of interest, and so it may detect and measure the velocity and direction vascular flow

Ultrasound is a targeted modality, most commonly used

in the diagnosis of pathologies in musculoskeletal structures such as tendons (rotator cuff tears and Achilles tendonitis) and for real-time guidance of musculoskeletal procedures

On the positive side, ultrasound does not involve exposing the patient to radiation, can visualize dynamic processes, and

is portable Drawbacks include relative low image resolution

in many cases, limited bone penetration, and image quality dependence on the operator performing the examination.6

MAGNETIC RESONANCE IMAGING

MRI uses the magnetic properties of body tissues (in lar, the fact that different body tissues have differing magnetic

Figure 1-3 (Continued) (C–E) Coronal and sagittal CT images of the right knee CT examination of bone shows fibular

fracturing in more detail (arrows), as well as corner fractures of the medial and lateral tibial plateaus (arrows), and fracturing of the patella (arrow)

properties) to create cross-sectional images of the body

re-gion of interest Examples of body areas imaged include the

knee, shoulder wrist, ankle, and hip, as well as other

nonmus-culoskeletal regions such as the brain The images created are

actually “maps” of the magnetic properties of the varying

tis-sues in the body These maps are based on nuclear magnetic

resonance (NMR) spectral principles you may remember

from your college organic chemistry laboratory, applied to a

spatially distributed “sample,” mapping the signal at each

point in space

A simple model for the basis of MRI is that of a bar

magnet, or ferromagnet, which has magnetic properties

in-corporating north and south poles like the earth The

mag-netic poles “come out of ” one side and “go into” the

opposite side (by convention, north pole and south pole,

respectively) This configuration is then called a magnetic

dipole So, we now know the direction of the field (out of

the north pole of the magnet and back in at the south

pole) If we also know how strong the field is, we can put

these two quantities together to form a quantity called the

magnetic moment, which then tells us the orientation and

strength of the dipole An example of a dipole you may

al-ready be familiar with is the compass, which is basically a

small bar magnet (magnetic dipole) If you then put the

compass into the magnetic field of the earth (another

di-pole), the two dipoles line up in the direction of opposite

polarity (one dipole lines up in the direction of the field

created by the other)

Let’s go down to the microscopic level now The

neu-trons and protons that make up the nucleus of the

constit-uent atoms and molecules of the body also have a magnetic

moment A conceptual way to think about them, then, is as

miniature bar magnets in space A simple atom that has the

largest magnetic moment, and is in great abundance in the

body, is hydrogen Hydrogen is a constituent atom of a

great number of molecules in the body including water

(H2O), fat, and other tissues The nucleus in hydrogen

con-sists of a proton (like a small bar magnet) When placed in

a magnetic field, the proton in hydrogen will tend to line

up with it (like a compass in the earth’s magnetic field) If

you were to try to turn the compass needle in the opposite

direction, it would resist, and try to turn back Therefore,

you must exert energy (give energy to the compass needle)

to turn the compass needle (or dipole) into the direction

aligned opposite the magnetic field, which is a higher

en-ergy state

Now, when energy is applied to the body part in the

scanner in the form of an external electromagnetic field

(radio wave), energy is absorbed in the tissue, putting the

dipoles into a higher energy state (rotating them into the

opposite direction of the field) When this external energy is

removed, the dipoles relax to their lower energy state

(giv-ing off energy), but at different rates depend(giv-ing on the local

environment (tissue type) The different relaxation rates of

the dipoles in different tissues are then used to create an image

The basic method of visualizing body tissues with MRI is

to place the patient into the center of a large ring-shaped magnet, and then turn on the magnet, alternating the polar-ity of the magnet at various frequencies (similar to the chem-ical in the test tube you put into the magnet in your organic chemistry laboratory) MRI of the patient is obtained in this manner, and in the form of “sequences,” which are ways of varying MR scanner settings or parameters to emphasize dif-ferent physical characteristics of tissues While there are cur-rently a multitude of different sequences available to scan for specific pathologies, there are a basic set of sequences seen ubiquitously in musculoskeletal (as well as other subfields of) radiology: T1, T2, and PD (proton density) Additionally, each of these sequences may be modified with a variation called “fat saturation.”

The T1 sequence is good for anatomical assessment, with

a higher level of anatomic detail than seen on T2 On dard T1, fat is bright (or high signal), and generally, fluid is intermediate to dark (or low signal) However, variations do occur, with notable examples including proteinaceous fluid, which can be bright on T1 (as in the example of blood in the Met-Hb stage where it is paramagnetic), and gadolinium contrast (also a “fluid”), which is also bright on T1 With “fat saturation” (fat sat) on a T1 sequence, the fat is turned dark—now whole image appears in shades of dark gray to black (recall that fluid in generally dark on T1) Why is this important? If IV (gadolinium) contrast is given, any struc-ture that enhances (tumor, infection, etc.) can show up as bright (light gray to white) in a background of dark gray to black (Figure 1-4)

stan-The T2 sequence is useful for fluid assessment, in lar with “fat saturation” (“T2 FS”) Normally, on T2 se-quences, both fat and fluid are “bright.” With “fat sat,” a signal

particu-is sent into the scanner turning fat signal intensity dark while leaving the fluid signal intensity intact (fluid stays bright) This allows better visualization of fluid in tissues Why is this important? Fluid distinction allows for better visualization of

a number of normal anatomic structures, particularly the ternal structure of the joints, and edema often occurs in con-junction with tissue pathology Pathology is usually associated with responsive edema, which helps to highlight ligament and tendon injuries, tumors, osteomyelitis, phlegmon, and abscesses, as well as acute fractures T1 and T2 sequences may

in-be differentiated by looking for fluid—in a joint, a cyst, or the bladder If the fluid is bright, it is a T2 (rather than T1) se-quence (Figure 1-5)

The proton density (PD) sequence is intermediate tween T1 and T2 On PD sequences, fluid is relatively bright and fat is bright The PD sequence demonstrates better ana-tomic detail than the T2 sequence, but worse than that seen

be-on T1 Thus, it is somewhat of a hybrid sequence between T1 and T2 So why is it of interest? Fluid is relatively bright on

A B

D C

Figure 1-4 Utility of MRI for assessment of contrast enhancement Patient with osteosarcoma of the left tibia

(A) T1 image without fat saturation Fatty tissues appear as high signal, while muscle and fluid demonstrate ate signal intensity (B) T1 image with fat saturation Figures (A) and (B) were both obtained prior to intravenous con- trast administration Note predominant low-signal intensity on (B) (C) T1 image with fat saturation, after intravenous

intermedi-contrast administration Note enhancement of the tumor in the tibia and surrounding soft tissue enhancement, as well

as increased signal of lower extremity vasculature (D) T2 fat saturation image obtained prior to intravenous contrast

administration There is increased T2 signal component within the tumor, and peritumoral edema

PD, and thus PD is good for fluid assessment, in particular

with “fat saturation.” So, now we have a fluid-sensitive

se-quence, like T2, but with a higher level of anatomic detail

available PD is good for assessment of cartilage, among other

joint structures, particularly with fat saturation (Figure 1-6)

Further extension of the above three sequences’ ability to

evaluate pathology may be obtained through the

administra-tion of contrast (either IV or intra-articular, depending on the

relevant pathology) In parallel to iodine-based CT contrast

described above, which interacts with X-rays, contrast for

MRI scans is accomplished via materials with magnetic

prop-erties The most commonly used agents are gadolinium

che-lates, which are paramagnetic materials that produce magnetic

moments when placed in an external magnetic foil material

As noted above, an enhancing tumor on a T1 sequence with

fat saturation would show up as a region of light gray to white

Allergy to gadolinium is rare, but gadolinium should be used

with caution in patients with renal failure due to the risk of

nephrogenic systemic fibrosis (NSF), with the connection

be-tween the two coming to light in approximately 2006

As in the case of CT, cross-sectional planes again onstrate the internal anatomy of the body structure of in-terest MRI is optimal for visualizing soft tissue structures

dem-of the body due to higher sdem-oft tissue contrast than CT or ultrasound, and is particularly useful for evaluating liga-ments or tendons for pathology, in assessing bone infection, internal derangement of the joints, and musculoskeletal tumor evaluation MRI does not expose the patient to ion-izing radiation A disadvantage of MRI relative to CT is the scanning time A CT scan may now be performed in a mat-ter of seconds, whereas for each MRI “sequence” the patient will likely have to lie motionless for 3–6 minutes This has traditionally limited the usage of MRI for visualizing mov-ing structures (such as bowel and heart); however, adaptive sequences have been created Additional disadvantages of MRI include limitations of usage due to patient claustro-phobia, requiring sedation or specialized visualization equipment, as well as contraindications for MR scanning such as pacemakers, neurostimulators, or cerebral aneu-rysm clips.4,7

A B

Figure 1-5 Utility of MRI for soft tissue tumor-fluid assessment Coronal MR images of an intramuscular myxoma

of the right thigh, with and without contrast (A) T1 image without fat saturation Subcutaneous, intermuscular, and other fatty tissues appear as high signal, with intermediate signal in muscle and fluid (B) T1 image with fat saturation Figures (A) and (B) were both obtained prior to intravenous contrast administration Most structures on the fat satura- tion image are now low signal intensity, including subcutaneous and intermuscular fat (C) T1 image with fat saturation,

after intravenous contrast administration Note enhancement of the vascularized tumor nidus, adjacent hyperemic

tis-sue, and lower extremity vasculature (D) T2 fat saturation image obtained prior to intravenous contrast administration

Fluid signal structures show high signal intensity on this T2 image, including fluid-like intensity with the tumor and adjacent reactive edema Note tumor nidus is now of intermediate signal intensity

MOLECULAR IMAGING (NUCLEAR MEDICINE)

In molecular imaging, molecules that preferentially localize

to specific organs and regions of abnormal physiology are

attached to “radiotracer” molecules These radiotracers are

usually mild- and short-lived photon or particle emitting

ra-dioisotopes, which decay and are generally excreted from the

body For instance, the half-life of the commonly used

radio-nuclide technetium-99m (99mTc) is 6 hours; so 24 hours

after the patient is injected, 6.25% of the original activity will

be left Photons emitted by the radiotracers are then absorbed

by specially designed detectors, producing images either in a

plane or three-dimensional cross section Examples of

detec-tors include gamma cameras (which detect gamma rays) and

positron emission tomography (PET) scanners Generally,

gamma ray photon emitters are used as radiotracers due to

the ability of gamma rays to pass through and escape body

tissues, to be picked up by detectors outside the patient’s

body The detectors then create an image of the distribution

of radiotracer within the patient’s body, and of particular

in-terest, any focal abnormal radiotracer accumulation that

could indicate pathology

Thus, a benefit of molecular imaging is the integration

of physiologic and anatomic information obtained from

the scans One drawback of molecular imaging scans is a spatial resolution of the resultant images, which is lower than radiographs, CT, or MRI Other drawbacks include a requirement for specialized radiotracers and ionizing ra-diation exposure for patients To overcome the spatial reso-lution limitation, a number of combined modality scans are now being performed, including PET/CT and single photon emission computed tomography (SPECT/CT) scans In these cases, physiologic information from the mo-lecular imaging scan is combined with and superimposed

on high anatomic resolution CT scan (Figure 1-7) In culoskeletal imaging, the main molecular imaging scans performed are the conventional bone scan, a three- dimensional version of bone scan called the SPECT scan, and the PET scan

mus-BONE SCAN

In the molecular imaging bone scan, the molecule lene diphosphonate (MDP) is attached to the radioactive tag 99mTc before injection into the patient, forming the 99mTc MDP, or “radiolabeled” MDP The physiologic mechanism

methy-of action for this imaging agent is the binding methy-of the MDP to

Figure 1-6 Sagittal MR images of the knee showing meniscal tear (A) Sagittal PD without fat saturation

(B) Sagittal PD with fat saturation Note the conspicuously bright knee joint effusion and excellent visualization of

cartilage Partially visualized linear bright signal in the meniscus reaching the articular surface of the knee representing

a tear of the posterior horn of the medial meniscus (arrows)

hydroxyapatite crystals within the body after injection This

occurs as osteoblasts lay down (organic phase) bone matrix

Bone matrix initially consists of unmineralized osteoid with

type 1 collagen and matrix proteins Mineral deposition

(in-organic phase) then occurs, with the resultant in(in-organic

portion linked to hydroxyapatite Accumulation of 99mTc

MDP within the body is thus linked to bone turnover with

associated osteoblastic activity

So, the physiologic mechanism of action for 99mTc MDP

is osteoblastic activity, which in many pathologic

circum-stances corresponds to focally increased bony turnover and

results in focally increased 99mTc MDP accumulation A

confounding factor in this increased uptake of radiotracer to

keep in mind is that uptake is also linked to increased blood

flow as a mechanism of transport, and in the extreme case, no

blood flow corresponds to no radiotracer uptake Generally,

however, increased uptake of 99mTc MDP is linked to

creased bone turnover to a much greater extent than to

in-creased blood flow, facilitating its usefulness for imaging

Pathologic processes can also result in focal regions of no

ra-diotracer uptake, due to purely lytic processes (no

osteoblas-tic activity), with examples of lyosteoblas-tic tumors including thyroid

and renal cell carcinoma metastasis

There are two main geometries of “Bone Scan” imaging

acquisition The first is spot or planar imaging, which is the

traditional method in which a bone scan is obtained

(some-what similar to a digital camera picture) with low anatomic

resolution The second is called SPECT This is the cross-

sectional version of a bone scan, similar in image geometry to

a CT scan In SPECT scanning, the three-dimensional

distri-bution of radiotracer is imaged in a fashion somewhat

analo-gous to the CT scan, resulting in a higher spatial resolution than the standard bone scan, but much lower resolution than

a CT scan As a side note, combined CT/SPECT is now able, where scans are performed at the same imaging session, and the computer then co-registers and superimposes SPECT images (showing regions of abnormal metabolic activity) onto CT images (for anatomy)

avail-Increased 99mTc MDP uptake and focal accumulation in body tissues is seen in bone fracture and repair in the osteo-blastic reparative process, as well as in active epiphyseal growth plates, where uptake is again related to osteoblastic activity Increased uptake and accumulation of 99mTc MDP

is also seen in conjunction with reparative processes ing bone destruction due to tumors and infection Two vari-ants of the planar molecular imaging bone scan are commonly ordered Whole body bone scans are usually obtained as single-phase screening scans to look at large areas of the skeleton for entities such as bone metastases (Figure 1-8) A more sophisticated study called a three-phase bone scan may

follow-be performed to rule out a bone infection, or osteomyelitis, and separate this pathology from a simple infection of the adjacent soft tissue In the three-phase bone scan, images are obtained immediately after injection (dynamic flow phase), a few minutes after injection (blood pool phase), and 2–6 hours after injection (the static phase scan) The dynamic flow phase scan is an essential molecular imaging angiogram, showing increased or decreased blood flow to the region of interest The blood pool phase shows soft tissue activity such

as third spacing or leaky capillaries The static phase scan is obtained to demonstrate bone involvement through osteo-blastic activity, which separates sole involvement of soft

Figure 1-7 FDG PET/CT showing soft tissue mass FDG PET/CT scan in a patient with a soft tissue tumor of the right

thigh (A) Axial CT image of the right mid-thigh A heterogeneous soft tissue density mass is seen within the muscles of the thigh (B) Axial co-registered (fused) image of PET/CT, same right mid-thigh region A soft tissue density mass

within the muscles of the thigh demonstrates heterogeneous increased signal intensity, corresponding to increased radiotracer uptake in regions with increased glycolysis

Figure 1-8 Bone scan showing bone metastases

Whole-body MDP bone scan in a patient with skeletal

metastases from prostate cancer Anterior (left) and

posterior (right) images of the patient’s entire body Note

regions of expected radiotracer uptake, forming anatomic

map of bones Additionally, concentrated radiotracer in

the process of excretion is noted within the bladder

There are multifocal regions of bright increased uptake

corresponding to foci of bone metastasis

18F is the radiotracer in this case, emitting positrons that are annihilated as they come into contact with nearby electrons, producing two gamma rays for each collision that are then detected

After injection, 18F-FDG becomes trapped within tumor cells There are various theories for tumor uptake of FDG, including overexpression of glucose membrane trans-porter proteins in neoplastic cells and tumor hypoxia in high-grade malignancy resulting in higher rate of glycolysis Ultimately, there is increased activity of glycolytic enzymes and glycolysis by tumor cells, which increases glucose up-take in tumor cells relative to normal cells, leading to focal increased activity on the PET scan The FDG PET scan di-rectly detects tumor cells, unlike the bone scan, which de-tects reparative activity due to tumor destruction (Figure 1-7) Uses include early lesion detection before bone scan, prediction of tumor grade in primary bone tumors, and distinguishing benign and malignant spinal compression fractures

An alternative imaging agent for PET is fluorine-18 dium fluoride (18F-NaF) Like the bone scan, uptake is re-lated to osteoblastic activity (bone repair), and is taken up when fluoride ions are exchanged with hydroxyapatite crys-tals 18F-NaF is reported as highly sensitive for the detection

so-of sclerotic bone metastases (in prostate and breast cancer), among other uses8,9 (Figure 1-9)

tissues in the infection process (cellulitis) from combined

soft tissue and underlying bone infection (cellulitis with

os-teomyelitis) The single-phase bone scan is performed in

static phase only

PET SCAN

The most commonly used radiotracer for PET scanning is

fluorine-18-fluorodeoxyglucose (18F-FDG), a glucose analog

PEARLS

Radiographs are transmission images of the patient, generated via X-rays, which use tissue density differ-ences to generate an anatomic map

CT scans also use X-rays and generate tissue density maps of the body, but resolve individual anatomic structures by generating body cross sections

MRI generates anatomic maps of the magnetic ties of the body, and is generally superior to CT for soft tissue contrast

proper-Ultrasound imaging utilizes sound speed propagation differences of body tissues and reflections from struc-ture interfaces to generate both anatomic maps and velocity profiles

 Molecular imaging uses mildly radioactive tags tached to physiologic molecules to generate anatomic maps of abnormal tissue physiology to de-tect pathology While spatial resolution of molecular imaging studies is low, hybrid methods such as SPECT/CT and PET/CT may be used to combine the physiologic information of the molecular scan with the high-resolution anatomic information of the CT scan

at-A C

B

Figure 1-9 NaF PET/CT scan showing bone metastases NaF PET/CT scan in a patient with skeletal metastasis from

prostate cancer (A) Three-dimensional PET signal reconstruction of the lower extremities demonstrating regions of

expected uptake, forming visualized anatomic map of bones Note multifocal superimposed regions of dark gray to

black signal, corresponding to regions of increased uptake, and bone metastases (B,C) Axial CT images of the pelvis

and femur, respectively, with heterogeneous marrow density within the lower pelvis (prostate cancer metastases

typi-cally show as sclerotic or high density, on CT) (D,E) Same section co-registered (fused) axial PET/CT images of the pelvis

and femur Note high-signal foci in the lower pelvis image and left mid-femur corresponding to bone metastases

1 Bushberg JT, Seibert JA, Leidholdt EM Jr, Boone JM The Essential

Physics of Medical Imaging 2nd ed Baltimore, MD: Lippincott

Williams & Wilkins; 2006:97-144, chap 5

2 Bushberg JT, Seibert JA, Leidholdt EM Jr, Boone JM The Essential

Physics of Medical Imaging 2nd ed Baltimore, MD: Lippincott

Williams & Wilkins; 2006:145-174, chap 6

3 Bushberg JT, Seibert JA, Leidholdt EM Jr, Boone JM The Essential

Physics of Medical Imaging 2nd ed Baltimore, MD: Lippincott

Williams & Wilkins; 2006:293-316, chap 11

4 Brant WE, Helms CA Fundamentals of Diagnostic Radiology 2nd

ed Baltimore, MD: Lippincott Williams & Wilkins; 1999:3-24,

chap 1

5 Bushberg JT, Seibert JA, Leidholdt EM Jr, Boone JM The Essential

Physics of Medical Imaging 2nd ed Baltimore, MD: Lippincott

Williams & Wilkins; 2006:327-372, chap 13

6 Bushberg JT, Seibert JA, Leidholdt EM Jr, Boone JM The Essential

Physics of Medical Imaging 2nd ed Baltimore, MD: Lippincott

Williams & Wilkins; 2006:469-554, chap 16

7 Helms CA, Major NM, Anderson MW, Kaplan P Musculoskeletal

MRI 2nd ed Philadelphia, PA: Saunders/Elsevier; 2008:1-19,

chap 1

8 Mettler FA, Guiberteau MJ Essentials of Nuclear Medicine

Imag-ing 5th ed Philadelphia, PA: Saunders/Elsevier; 2006:243-292,

chap 9

9 Mettler FA, Guiberteau MJ Essentials of Nuclear Medicine Imaging

5th ed Philadelphia, PA: Saunders/Elsevier; 2006:359-424, chap 13

Skeletal Trauma:

Upper Extremity

Cornelia Wenokor, MD Marcia F Blacksin, MD

SHOULDER

The shoulder girdle consists of the clavicle, scapula, and

hu-merus It connects the upper extremity to the axial skeleton

with only one true joint, the sternoclavicular joint Between

the scapula and the thorax, there is a muscular connection,

allowing for extended mobility, compared to the limited

mobility of the pelvic girdle The joints of the shoulder

gir-dle are the glenohumeral or shoulder joint, the

acromiocla-vicular (AC) joint, and the sternoclaacromiocla-vicular joint The

scapula is a complex bone and serves as a muscle attachment

site Seventeen muscles surround the scapula, supporting

movement and stabilizing the shoulder The scapula extends

from the second to the seventh rib and has 30° anterior tilt

Scapular fractures (Figure 2-1) are relatively uncommon

They require high-energy and associated injuries, such as

other fractures, pulmonary contusions, pneumothorax,

neurovascular injuries, and spine injuries, which occur in

35–98% of patients.1,2

Scapulothoracic dissociation (Figure 2-2) is a rare entity

that consists of disruption of the scapulothoracic

articula-tion It is in essence an internal forequarter amputaarticula-tion

Vas-cular disruption (Figure 2-3) and brachial plexus injuries are

usually present Clinically, patients have massive soft tissue

swelling, a pulseless upper extremity, and complete or partial

neurologic deficits Radiographically, there is lateral

displace-ment of the scapula, AC separation, displaced clavicle

frac-ture, or sternoclavicular disruption These devastating

injuries require violent traction and rotation, usually seen in motorcycle or motor vehicle accidents.3 There is a high mor-tality rate Survivors with complete brachial plexus injuries suffer from flail upper extremity

The clavicle serves as a rigid support from which the ula and arm are suspended It keeps the upper limb away from the thorax so that the arm has maximum range of movement and transmits physical impacts from the upper limb to the axial skeleton It also protects the neurovascular bundle and lung apices Clavicle fractures are usually caused

scap-by a fall onto the affected shoulder Eighty percent of tures occur in the midshaft region (Figure 2-4) and only about 2% in the medial clavicle.4 The remainder occurs in the distal third, where the coracoclavicular ligaments may be in-jured Clavicle fractures can be associated with other frac-tures, most commonly rib fractures, brachial plexus injuries, and pneumo-/hemothorax.5

frac-The AC joint is the articulation between the acromion process of the scapula and the distal end of the clavicle It is a diarthrodial and synovial joint The acromion of the scapula rotates on the distal end of the clavicle The most common mechanism of injury in AC joint separation is direct trauma

to the proximal shoulder, such as in contact sports Stability

of the AC joint is maintained by the AC ligaments in the axial plane Craniocaudal stability is achieved by the coracoclavic-ular ligaments AC joint injuries (Figure 2-5) are classified into six groups, ranging from minor sprains only detectable

Wrist Hand

2

Shoulder

Elbow

Figure 2-2 Scapulothoracic dissociation The medial

scapula border is laterally displaced with respect to the

rib cage (arrowheads) The acromioclavicular joint is

disrupted (double-headed arrow)

with a comparison stress view to gross deformities of the AC joint with AC ligament and coracoclavicular ligament dis-ruption The average coracoclavicular distance is 1.1–1.3 cm Detailed classification can be found in any standard radiol-ogy textbook

The shoulder joint is a ball and socket joint Its stability is provided by the bony anatomy of the glenoid fossa, the cora-coid, and acromion processes The rotator cuff muscles and long head biceps muscles provide muscular restraints, whereas the glenohumeral ligaments, glenoid labra, and joint capsule also contribute to stability Nonetheless, the shoulder joint is the most commonly dislocated major joint

in the body About 95% of shoulder dislocations are anterior dislocations (Figure 2-6) The humeral head is displaced an-teriorly and inferiorly to the glenoid, in subcoracoid posi-tion There may be a resultant impaction fracture at the posterior, superior, and lateral aspect of the humeral head, a so-called Hill–Sachs lesion (Figure 2-7) At the anterior– inferior aspect of the glenoid, a fracture may be seen on radiograph, a so-called “bony Bankart” lesion Both lesions are best seen on postreduction films Non-bony Bankart le-sions are best evaluated with MR arthrography An engaging Hill–Sachs lesion is defined as a defect in the humeral head large enough that the edge drops over the glenoid rim when

Figure 2-1 Scapular neck fracture There is a

minimally displaced fracture of the scapular neck (arrow),

with hairline extension into the scapular body No

exten-sion to the glenoid surface is seen Note that this patient

is skeletally immature; the proximal humeral physis is

patent

Figure 2-4 Midshaft clavicle

fracture The oblique fracture (arrows)

is distracted and the distal fracture

fragment is inferiorly displaced by

about one shaft’s width

Figure 2-5 Acromioclavicular joint

separation There is malalignment

between the distal end of the clavicle

and the acromion process (arrowheads)

Note also the increased distance

between the clavicle and the coracoid

process

Figure 2-6 Anterior shoulder dislocation The

humeral head (white star) is displaced inferiorly and

medially to the glenoid (black star) and sits inferior

to the coracoid process

Figure 2-8 Posterior shoulder dislocation The

humeral head is locked in internal rotation, but typically

at the same level as the glenoid (arrowheads), which makes the dislocation difficult to recognize A trough sign

is seen (arrows), representing an impaction fracture of the humeral head, also called a reverse Hill–Sachs lesion

Figure 2-9 Inferior shoulder dislocation The

humeral head (star) is wedged against the inferior glenoid (arrow) There is an associated displaced greater tuberosity fracture (arrowhead)

the arm is externally rotated.6 This represents an indication

for surgery, as are lesions representing more than 30% of the

articular surface (determined on pre-op CT) The most

common complication after anterior shoulder dislocation is

a recurrent dislocation, due to damage of the stabilizing

structures

Posterior shoulder dislocations (Figure 2-8) represent

about 4% of shoulder dislocations Frequently, they are

un-recognized by primary care or emergency room physicians,

but are also missed radiographically in more than 50% of

cases.7 Trauma or convulsive seizures can result in posterior

dislocations The average age of patients with traumatic

pos-terior dislocation is 50 years Patients present with history of

trauma, pain, and inability to externally rotate the arm

Com-plications include associated fractures (glenoid rim and

proximal humerus) and injury to the neurovascular bundle,

especially the axillary nerve

An inferior dislocation of the shoulder (Figure 2-9) is also

called “luxatio erecta,” as the arm is locked in a forwardly

el-evated position This is caused by a severe hyperabduction

injury, where the humeral neck impinges against the

acro-mion, which levers the humeral head inferiorly There is a

high rate of associated neurovascular injuries, involving the

brachial plexus and axillary artery.8

Figure 2-7 Anterior shoulder dislocation This axillary

view demonstrates the humeral head (white star) being

displaced anteriorly and medially to the glenoid (black star)

The Hill–Sachs impaction fracture is marked with an arrow

Radial head (Figure 2-10) or neck fractures (Figure 2-11)

often occur as the result of a fall on an outstretched arm with

the distal forearm angled laterally, valgus stress on the elbow,

or from a direct blow to the elbow, such as with a motor

ve-hicle accident The elbow is a complex joint due to its

intri-cate functional anatomy The ulna, radius, and humerus form

Figure 2-10 Radial head fracture There is a

nondisplaced, minimally comminuted fracture through

the radial head (arrow), without gapping or step-off at

the articular surface

A

Figure 2-11 Radial neck fracture (A,B) There is a

slightly impacted fracture through the radial neck ( arrows), resulting in a sclerotic line across the radial neck There is a sharp angle at the radial head/neck junction, which is not seen in a normal neck (compare

with Figure 2-10) (continued)

four distinctive joints, which are stabilized by the ulnar lateral ligament complex, the lateral collateral ligament com-plex, and the joint capsule Motion is facilitated by four muscle groups: the elbow flexors, the elbow extensors, the flexor–pronator group, and the extensor–supinator group The most commonly used classification system for both treatment and prognosis assessing radial head or neck fractures is the Mason classification (Table 2-1)

col-A B

Figure 2-12 Galeazzi fracture-dislocation (A) The forearm film demonstrates an oblique fracture through the distal

radial shaft (arrow) There also is a torus fracture of the distal ulnar shaft (arrowhead) (B) The wrist film demonstrates

marked ulnar angulation of the distal radial shaft fracture (arrow) The ulnar head is dislocated from the distal nar joint (arrowhead) and there is a mildly displaced fracture of the ulnar styloid

Type III: Comminuted fractures of the whole radial headType IV: A comminuted fracture, with an associated dislocation, ligament injury, coronoid fracture, or Monteggia lesion

WRIST

The Galeazzi fracture–dislocation (Figure 2-12) is a radial shaft fracture with associated dislocation of the distal radio-ulnar joint (DRUJ) There may be associated compartment syndrome Anterior interosseous nerve (AIN) palsy may also occur, but it is easy to overlook, as the AIN is a pure motor nerve, and therefore there is no sensory deficits Injury to the

Figure 2-13 Colles fracture There is an impacted

fracture through the distal radial metaphysis (arrows)

There is a neutral ulnar variance; the radial and ulnar

articular surface are at the same level

Figure 2-14 Scaphoid fracture There is a

nondis-placed fracture through the waist of the scaphoid bone (arrow)

AIN can cause paralysis of the flexor pollicis longus and

flexor digitorum profundus muscles to the index finger,

re-sulting in loss of the pinch mechanism between the thumb

and the index finger Galeazzi fractures are sometimes

associ-ated with wrist drop due to injury to radial nerve, extensor

tendons, or muscles They are the most likely fractures to

re-sult in malunion

The term Colles fracture (Figure 2-13) is used for any

fracture of the distal radius, with or without involvement of

the ulna that has dorsal displacement of the fracture

frag-ments It typically occurs in the metaphysis The mechanism

of injury is falling on an outstretched arm with the wrist

dor-siflexed, resulting in a characteristic “dinner fork” or

“bayo-net” like deformity Colles fractures are commonly seen in

osteoporotic patients It is important to assess ulnar variance

on radiographs, as there can be significant foreshortening of

the radius, resulting in the ulna impinging upon the lunate

bone

A scaphoid fracture (Figure 2-14) is the most common type of carpal bone fracture Scaphoid fractures usually cause pain at the base of the thumb and sensitivity to palpation in the anatomic snuffbox Scaphoid bone fractures can be subtle and may not be apparent initially Therefore, people with ten-derness over the scaphoid are often casted for 7–10 days at which point a second set of radiographs are taken, and may show a more conspicuous fracture line Alternatively, a CT scan can be used to evaluate the scaphoid Complications include delayed union, nonunion, and osteonecrosis ( Figure 2-15) The scaphoid receives its blood supply primar-ily from lateral and distal branches of the radial artery Blood flows from the distal end of the bone to the proximal pole; if this blood flow is disrupted by a fracture, the bone may not heal and may necrose

Carpal dislocation patterns include the perilunate cation, lunate dislocation, and midcarpal dislocation The injuries are secondary to hyperdorsiflexion Perilunate dislo-cation (Figure 2-16) is initially missed in 25% of cases.9 A severe ligament injury is necessary to tear the distal carpal row from the lunate to result in a perilunate dislocation This

dislo-injury usually begins at the radial side, with the energy

ex-tending through the body of the scaphoid, resulting in a

scaphoid fracture The scaphoid bridges the proximal and

distal carpal rows With dislocation between these rows, the

scaphoid must either rotate or fracture, which produces a

perilunate dislocation If there is an associated scaphoid

frac-ture, the injury is called a transscaphoid perilunate

disloca-tion (Figure 2-17)

Intercarpal ligamentous injury may lead to the

scapholu-nate dissociation, producing a gap between the scaphoid and

the lunate, so-called “Terry Thomas” sign, named after the

British comedian’s gap-toothed smile, also known as the

“David Letterman” sign (Figure 2-18) The normal distance

between the scaphoid and the lunate is 1–2 mm A distance of

3 mm or more indicates scapholunate dissociation The

con-comitant volar rotation of scaphoid bone is best depicted on

a lateral wrist radiograph

The lunate dislocation (Figure 2-19) is the most severe

of the carpal instabilities The lunate rotates volarly with

respect to the radial articular surface The volar rotation

measures approximately 90°, so that the concave distal

sur-face sur-faces anteriorly and the convex proximal sursur-face is

dor-sally directed The remaining carpal bones are dorsal to the

lunate and the capitate drops into the space vacated by the

Figure 2-16 Perilunate dislocation The lunate bone

(black star) maintains its articulation with the radius, but the capitate (white star) is dorsally dislocated from its lunate articulation

Figure 2-15 MRI of scaphoid fracture T1-weighted

image The fracture is marked with white arrows There is

decreased signal in the proximal pole of the scaphoid,

consistent with avascular necrosis (white star)

lunate This injury results in tearing of most major carpal ligaments

Carpometacarpal (CMC) dislocations (Figure 2-20) occur infrequently, as these joints are supported by the strength and complexity of the CMC and intermetacarpal ligaments The fourth and fifth CMC joints are the most common to be individually dislocated because they are more mobile than the third and the second The oblique view of the hand is most useful in demonstrating this type of injury.10

B

Figure 2-17 Transscaphoid perilunate

dislocation (A,B) PA and lateral views of the

wrist, respectively, show the lunate well aligned

with the distal radius However, the remainder of

the carpal bones are posteriorly dislocated

(peri-lunate dislocation) This is associated with a

frac-ture of the scaphoid waist (transscaphoid),

so-called transscaphoid perilunate dislocation

Figure 2-18 Scapholunate dissociation

Rotary subluxation of the scaphoid Note the

wide gap between the scaphoid and the

lu-nate bones (double-headed arrow)

A B

Figure 2-19 Lunate dislocation (A) PA wrist film demonstrating a triangular appearance of the L, with the apex of

the L pointing distally The L is partially superimposed on the distal radius (B) Lateral wrist film demonstrates the L to

be completely dislocated from its normal position and approximately 90° rotated The capitate (white arrowhead) is dorsal to the L and occupies the space vacated by the L The distance to the radial articular surface (black arrowhead) is decreased L, lunate; S, scaphoid; T, triquetrum

HAND

The Bennett fracture (Figure 2-21) is a fracture of the base

of the first metacarpal bone that extends into the CMC joint

This intra-articular fracture is the most common type of

frac-ture of the thumb and is nearly always accompanied by some

degree of subluxation or frank dislocation of the CMC joint

Pull of the abductor pollicis longus (APL) and adductor

pol-licis (ADP) muscles results in displacement of the metacarpal

base Failure to properly recognize and treat the Bennett

fracture will not only result in an unstable, painful, arthritic CMC joint with diminished range of motion but will also re-sult in a hand with greatly diminished overall function.11

A boxer fracture (Figure 2-22) involves a break in the neck

of the metacarpal It was originally described as a fracture of the fifth metacarpal bone because this is the most common one to break when punching a stationary object Indications for surgery include more than 40° angulation and 10° of mal-rotation

A B

Figure 2-20 Fourth and fifth carpometacarpal dislocation (A) There is overlap of the fourth and fifth metacarpal

bases with respect to the hamate bone (arrowhead), resulting in joint space loss Joint spaces at the second and third metacarpophalangeal joints are well preserved (arrows) Note foreshortening of the fourth and fifth metacarpal bones

(follow the arc formed by the metacarpal heads) (B) The fourth and fifth metacarpal bases are dorsally displaced

(curved arrow) A small avulsion fracture from the hamate is also seen (arrowhead)

Figure 2-21 Bennett fracture There is an intra-

articular fracture through the base of the first metacarpal

bone The first carpometacarpal joint is disrupted and the

metacarpal bone (arrow) is pulled proximally by the

abductor pollicis longus muscle A small bone fragment

(arrowhead) remains in anatomic position

Mallet finger, also called baseball finger, is an injury of the

extensor digitorum tendon of the fingers at the distal

inter-phalangeal joint (DIP) It results from hyperflexion of the

extensor digitorum tendon, and usually occurs when a ball

hits an outstretched finger and jams it, creating a ruptured or

stretched extensor digitorum tendon The extensor

digito-rum tendon can avulse a bone fragment (Figure 2-23)

Indi-cations for surgery are if the bony mallet involves more than

30% of the articular surface or there is an open injury

Figure 2-22 Boxer fracture There is a dorsally

angulated fracture at the fifth metacarpal neck (arrow)

Figure 2-23 Mallet finger There is an avulsion

fracture at the dorsal base of the distal phalanx of the fourth digit (arrow)

Anterior Shoulder Dislocation

A Bankart lesion is a tear to the anterior–inferior brum that occurs after an anterior shoulder dislocation and leads to shoulder instability

la-The axillary and musculocutaneous nerve may be jured

in-The most common complication after initial dislocation

is recurrent dislocation, due to injury of the shoulder stabilizers (ligaments, joint capsule, and labra)

Posterior Shoulder Dislocation

The humeral head is locked in internal rotation in a posterior shoulder dislocation and typically at the same level as the glenoid

The trough sign is seen in about 75% of cases.7

Persistent pain with limitation of motion may clinically mimic adhesive capsulitis.12

the tubercle of the trapezium bone of the CMC joint This ensures that the proximal fragment remains in its correct anatomical position.

Tension from the APL and ADP will result in fracture displacement over time, therefore requiring surgical fixation

A comminuted fracture at the first metacarpal base is called a Rolando fracture

Thumb function constitutes about 50% of overall hand function

Inferior Shoulder Dislocation

 The patient presents in a “salute” position

 The axillary nerve is the most commonly injured nerve

 Axillary artery injury is rare, but can be a devastating

complication If there is persistent excessive swelling

after reduction or vascular compromise, an

arterio-gram or CT-A should be performed

Elbow Injury

 Occult fractures of the radial head or neck are

sug-gested by the presence of an elbow joint effusion

( anterior sail sign and/or posterior fat pad sign) in the

setting of acute trauma

 Complications include elbow contracture, chronic wrist

pain due to unrecognized injuries to the interosseous

membrane or DRUJ, and complex regional pain

syn-drome, formerly named reflex sympathetic dystrophy

Galeazzi Fracture

 In children, a Galeazzi fracture is treated with closed

reduction, but surgical fixation is necessary in adults to

prevent recurrent dislocations of the DRUJ.13 Therefore,

it is also called a “fracture of necessity.”

Colles Fracture

 When evaluating distal radius fractures, remember the

11–22–11 rule: radial height (mm), radial inclination

(degrees), and palmar tilt (mm)

 In the elderly, because of the weaker cortex, the

frac-ture is more often extra-articular Younger individuals

tend to require a higher energy and tend to have more

complex intra-articular fractures

 Acute carpal tunnel syndrome is frequently seen with

Colles fractures and may require surgical intervention

sooner rather than later.14

Lunate Dislocation

 Lateral radiographs of the wrist are key to the

diagno-sis of carpal dislocation patterns

Carpometacarpal

 The fifth CMC is the most frequently injured

 The extensor carpi ulnaris tendon pulls the metacarpal

bone proximally

 Fifth CMC fracture dislocation is also termed a “reverse

Bennett fracture.”

Metacarpal Bone Fracture

 The proximal metacarpal fragment remains attached

to the anterior oblique ligament, which is attached to

REFERENCES

1 Ideberg R, Grevsten S, Larsson S Epidemiology of scapular

frac-tures Incidence and classification of 338 fracfrac-tures Acta Orthop

Scand 1995;66(5):395-397.

2 Ada JR, Miller ME Scapular fractures: analysis of 113 cases Clin

Orthop Relat Res 1991;Aug(269):174-180.

3 Ebraheim NA, An HS, Jachson T, et al Scapulothoracic

dissocia-tion J Bone Joint Surg Am 1988;70:428-432.

4 Postacchini F, Gumina S, De Santis P, Albo F Epidemiology of

clavicle fractures J Shoulder Elbow Surg 2002;11(5):452-456.

5 McGahan JP, Rab GT, Dublin A Fractures of the scapula

J Trauma 1980;20(10):880-883.

6 Burkhart SS, De Beer JFB Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: significance of the inverted-pear glenoid and the humeral engag-

ing Hill-Sachs lesion Arthroscopy 2000;16:677-694.

7 Cisternino SJ, Rogers LF, Stufflebam BC, Kruglik GD The trough

line: a radiographic sign of posterior shoulder dislocation Am J

multicenter study J Hand Surg Am 1993;18(5):768-779.

10 Harris J, Harris W, Novelline R The Radiology of Emergency

Medicine 3rd ed Baltimore, MD: Lippincott Williams & Wilkins;

1993:452

11 Kjær-Petersen K, Langhoff O, Andersen K Bennett’s fracture

J Hand Surg Br 1990;15(1):58-61.

12 Hill NA, McLaughlin HL Locked posterior dislocation

simulat-ing a frozen shoulder J Trauma 1963;3:225-234.

13 Atesok KI, Jupiter JB, Weiss AP Galeazzi fracture J Am Acad

Or-thop Surg 2011;19(10):623-633.

14 Lynch AC, Lipscomb PR The carpal tunnel syndrome and

Col-les’ fractures JAMA 1963;185(5):363-366.

Skeletal Trauma:

Lower Extremity

Cornelia Wenokor, MD Marcia F Blacksin, MD

PELVIS

The pelvis is formed by the ischium, the pubic bones, and

ilium, which through the sacroiliac joints (SI joints) connect

to the sacrum This forms a ring structure The pubic bones

are joined anteriorly by the pubic symphysis and form the

anterior ring The posterior ring is formed by the sacrum, the

SI joints, and iliac bones To disrupt this ring usually requires

significant force, which can occur in motor vehicle accidents

or similar high-energy trauma A ring structure usually breaks

in more than one place, so it is important to carefully examine

the entire ring for a second injury once a fracture is

encoun-tered The second injury does not need to be a fracture; it can

be disruption of the SI joints or pubic symphysis (Figure 3-1)

For diagnosing acetabular fractures (Figure 3-2), it is

im-portant to differentiate between the acetabular wall, column,

or a combination of wall and column fractures In short, the

anterior column extends from the iliac crest to the symphysis

pubis and includes the anterior wall The posterior column

extends from the superior gluteal notch to the ischial

tuber-osity and includes the posterior wall The acetabular roof is

the superior weight-bearing portion of the acetabulum and

contributes to the anterior and posterior column.1–3 For

ad-equate radiographic assessment, bilaterally angled oblique

views, so-called “Judet views,” are obtained in addition to the

standard AP radiograph because the anterior and posterior

columns are better visualized on the Judet views All

Knee Ankle Foot

Figure 3-1 Open book injury There is marked

wid-ening of the right SI joint (curved large white arrow) and disruption of the pubic symphysis (curved small black arrow) The right hemipelvis is inferiorly displaced The left SI joint is disrupted (curved small white arrow) There

is a comminuted fracture of the right iliac wing (gray arrow), and there are fractures of both pubic rami (white arrows), as the obturator ring in itself comprises a ring structure