Foot and Ankle Radiology

578 Pages·2003·57.97 MB·English

by  Robert A. Christman, DPM (Auth.)

../J)
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FOOTANDANKLERADIOLOGY
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NOTICE
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LibraryofCongressCataloging-in-PublicationData
Christman,RobertA.
Footandankleradiology/ RobertA.Christman.
p.;em.
Includesbibliographicalreferencesandindex.
ISBN-I3: 978-0-443-08782-0 ISBN-lO: 0-443-08782-2
1.Foot--Radiography.2.Ankle--Radiography.3.Foot--Diseases--Diagnosis.4.
Ankle--Diseases--Diagnosis.1.Title.
[DNLM:1.Foot--radiography.2.Ankle--radiography.3.FootDiseases--radiography.
WE880V555f2003]
RC951.C4772003
f,17.5'8507572--dc21
2002034871
ISBN-13: 978-0-443-08782-0
ISBN-IO: 0-443-08782-2
ManagingEditor:ChristieM.Hart
ProjectManager:JoyMoore
De.•igner:JuliaDummitt
C01JerArt: SheilahBarrett
RDC·MY
PrintedintheUnitedStatesofAmerica
Lastdigitistheprintnumber: 9 8 7 6 5
Tomywife,Irene.forherloveandsupport.
Tomydaughter,Jessica,forprovidingoccasional(andnecessary) distraction.
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TotheLordGod,forallHisprovisionsandblessings.
CONTRIBUTORS
RobertL.Baron,DPM, FACPR, FACFAOM LawrenceS.Osher,DPM, BS
Professorand Chair, Departmentof Radiology Directorof Radiology
WilliamM.SchollCollegeofPodiatric Medicine Full Professor
Finch UniversityofHealth Sciences/The Chicago Ohio College ofPodiatric Medicine
Medical School Cleveland,OH
PrivatePractice University HospitalsEast
Chicago,IL St. VincentCharityHospital
Fellow,American CollegeofPodiatric Radiology Cleveland,OH
FellowinPrimaryPodiatric Medicine,ABPOPPM
Robin C.Ross,DPM, FACFAS, FACFAOM
Fellowin Podiatric Orthopedics,ABPOPPM
Diplomate,American Board ofPodiatric Surgery
PhilipJ. Bresnahan,DPM, DABPS,FACFAS
Diplomate,American Board ofPodiatric Orthopedics and
PastAssistantProfessor,DepartmentofOrthopedics PrimaryPodiatric Medicine
Temple University SchoolofPodiatric Medicine Private Practice
Philadelphia,PA Southold and Shelter Island,NewYork
PastPresident,American College ofFoot and Ankle
WilliamH. Sanner,DPM
Pediatrics
Diplomate, American Board ofPodiatric Surgery Chairman
Fellow,American CollegeofFoot and Ankle Surgeons PodiatryDepartment
PrivatePractice,Souderton,PA OchsnerClinicFoundation
Baton Rouge,LA
RandyE.Cohen,DPM, FACFR
JeffreyE.Shook,DPM
Professorand Chairman, Radiology Department
NewYorkCollege ofPodiatric Medicine, NewYork Director ResidencyTraining
Diplomate ofAmerican Board ofPodiatric Orthopedics Huntington Podiatric SurgicalResidency
PrivatePractice St.Mary's Hospital
Staten Island, NY Huntington,WV
Scott OrthopedicsCenter,Inc.
YouseffKabbani,DPM
Huntington,WV
Northeastern Hospital
FrankSpinosa,DPM, FACFAS, FACFAOM,
Philadelphia, PA
FACPR,FAAHP, FASPM
BambinoMartins,PhD
Diplomate,American Board ofPodiatric Surgery
Westville,N]
Diplomate,American Board ofPodiatric Orthopedicsand
DavidMayer,MD,MS,FACR PrimaryPodiatricMedicine
Diplomate,American Board ofPodiatric Public Health
Chairman,Departmentof Radiology
Diplomate,American Board ofQualityAssuranceand
Mercy Health System
Utilization ReviewPhysicians
Darby,PA
Former Associate Professor
MaryC.Oehler, RT
Departmentof Radiology
RadiologySupervisor NewYorkCollege ofPodiatric Medicine
RadiologyDepartment PastPresident,NewYorkStatePodiatricMedicalAssociation
Temple University SchoolofPodiatric Medicine Private Practice
Philadelphia, PA Shelter Island,NY
vii
viii Contributors
CasimirF.Strugielski,RT(R),ASRT DavidE.Williamson
Instructorand Supervisor Sr.Technical Representative
DepartmentofRadiology PlanningandTechnicalManager
Dr.William M. SchollCollegeofPodiatric Medicine DistrictManager
FinchUniversity ofHealth Sciences/The Chicago Photo Products Department
Medical School Medical Products Division
Chicago,IL E.1.DuPontde Nemours & Company,Inc.
American RegistryofRadiologicTechnologists Wilmington, DE
American Societyof RadiologicTechnologists
MarieL.Williams,DPM
DirectorofPodiatric SurgicalResidencyParkway Regional
Medical Center
DiplomateAmericanBoard ofPodiatric Surgery
Adjunct ProfessorBarryUniversitySchoolofPodiatric
Medicine
PrivatePractice
North Miami Beach,FL
FOREWORD
Dr. Robert Christmanhasprovided us,inhisunique text,insights intohispersonal approach to
evaluating radiographsofthe foot. How to logicallyanalyze the cardinalradiographicfindings
seen in a radiograph and its most appropriate list of differential diagnoses is made easy.In his
chapter dealing with joint disease,thereader isled step bystep into constructing practicaland
concise differential diagnoses.Thisapproach is rare in most texts dealing with this important
subject.Dr.Christman'semphasisonradiographicanatomyandvariantsaretrulyappreciated.In
mosttextsthissectionisonlyskimmed.Also,sectionsdealingwith radiographic biomechanical
analysis correlating radiographic positional finding to foot structure and function as well as
fractureanddislocation classificationsusingactualradiographs areincluded.An entiresectionis
alsodedicated todealingwith the radiologicsciences.Dr.Christmanhassucceededinincluding
everything necessaryfor a podiatric student to learn aswell aspracticepodiatric radiologyand
radiologicinterpretation.
The bookshould serveasareferencefor allpodiatrists,students,andpodiatricassistants.
Harvey Lemont,DPM
ix
PREFACE
Thepurpose ofFootandAnkleRadiology isthreefold: to introduce the podiatric medicalstudent
to the scope of diagnostic radiology applicable to podiatric medicine, to prepare the podiatric
medical student to apply podiatric radiography and radiographic interpretation in practice,and
to providethe podiatric practitionerwith acomprehensive baseofknowledge to makeinformed
decisions.
Radiology is an important diagnostic tool useful for the evaluation of foot and ankle
pathology. However, because of the potential risks associated with ionizing radiation, those
involved in its production must have knowledge ofthe radiologic sciencesin order to provide
protection and safety to all involved.The Doctor of Podiatric Medicine is responsible for the
practice of proper radiography in the office setting, whether by himself or herself or by an
appropriate assistant/technologist. The doctor must also be familiar with all special imaging
studies applicabletoimaging ofthe foot and anklesothat they areordered aswarranted.
The podiatric physicianencounters numerous pathologic conditions radiographically that are
either intrinsic to the foot orrepresent manifestations ofextrinsicdisease.Thereforethe student
must not only learn specific radiologic pathology of the foot and ankle, but must acquire an
understanding of general diagnostic radiology and pathologic correlation. Furthermore the
student must learnhowto analyzearadiograph systematicallyand acquireabasicknowledgeof
bone radiology tointerpretradiographs and establish differential diagnoses.
To these ends, this text includes sections on plain film radiography (radiologic science,
radiation protection and safety, principles of radiography, and foot and ankle radiography);
radiographic anatomy (normal and variant presentations of the adult and developing foot and
ankle);systematicapproach tobone andjointabnormalities (howtoselectappropriate viewsand
a using a fundamental process to analyze the radiographic study); radiographic biomechanical
analysis (correlating the clinical and radiographic presentations of both the adult and child);
specialimaging procedures(emphasizingindications and cross-sectional imaging);andboneand
joint disorders (including systematic approaches to interpreting skeletal pathology rather than
simplydescription bydisease).
Podiatric radiology textbooks havecome and gone overthe years;at this writing, not one is
in print. A scattering of foot and ankle radiology texts written byradiologist or orthopedist is
presentlyavailable; however,they aregeared to the practicing physician and not the student. As
aresult,theyaredevoidofsectionspertinentto the podiatristintraining, in particular radiologic
scienceand systematic assessment of skeletal abnormalities. Furthermore this textbook devotes
serious attention to plain film radiographic anatomy and radiographic biomechanical analysis.
An entire chapter isdevoted to fracture and dislocation classification systems,classicallyfound
not in radiology textbooks but orthopedic texts.Also unique to this text is the inclusion of a
chapter on podiatric radiography equipment.
Foot andAnkle Radiology will also serve as a valuable reference source to the podiatric
assistant,radiologictechnologist, andlimitedlicenseextremitytechnologist.Also,the radiologist
and orthopedistmayfind this text to beavaluableaddition to their library.
Thistextwaswrittenwith the followinggoalsinmind. Specifically,that the podiatric student
and practitionerbeableto:
• Describe the principlesofradiationphysicsand biology.
• Practice appropriate radiation protection and safety.
xi
xii Preface
• Describe lowerextremity radiography equipment and accessories.
• Discussthe formation ofthe radiographic image.
• Assessfilmquality.
• Perform radiologicpositioningtechniquesof the foot and ankle.
• Applythe principles offilm interpretation to anygivenradiograph.
• Identify normal and variant radiographicanatomyofthe foot and ankle.
• Identify normal andvariant developmentofthe foot and ankle.
• Systematicallyassessbone andjointabnormalities inaradiograph.
• Identify and describe the radiologicfeaturesofpertinentpathology,including the following:
o Positional abnormalities
o Congenitalanomalies
o Skeletaldysplasias
o Fractures and related disorders
o Arthritis
o Infection
o Tumors,tumor-like processes,and soft tissueabnormalities
o Metabolic, endocrine, circulatory,and nutritional disorders
o Soft tissueabnormalities
• Discussspecialimaging techniques applicable to foot and ankle imaging.
• Discussindications and alternatives forprescribing specialimaging procedures.
• ACKNOWLEDGMENTS
Stephen D. Weissman, DPM, for providing the opportunityto pursue a personalized two-year
podiatric radiologyfellowshipprogram. Harvey Lemont,DPM,forhisprofessionalandpersonal
mentorshipasmychairand friend. Carol Romano,forassistingwhenever needed and forwords
of comfort.Jean Martino, for invaluable last-minute assistance.Temple University School of
PodiatricMedicine, for appreciating mytalentsand gifts.
CHAPTER 1
Radiation Physics, Biology, and Safety
BAMBINO MARTINS
• THE PHYSICS OF DIAGNOSTIC ionization. In the electromagnetic spectrum, this
IMAGING includes radiations with energy exceeding that ofUV
light (i.e., x rays and gamma rays). In Sweden, the
Animagemaybedefined asalikenessofanobjectproduced dividing line between ionizing and nonionizing
on photographic material. A diagnosticimage is one that electromagnetic radiations isset at 12.4 eV.Particulate
contains information that may be useful in medical diag radiations such as alpha rays and beta rays, neutrons,
nosis. Although many modern diagnostic imaging proce and heavyionsarealsoionizing radiations. Nonionizing
dures may involve neither x rays nor photographic film, radiations include ultraviolet,visible,and infrared light,
most diagnostic imaging ofthe foot and ankle isdone with microwaves, television and radio waves, and low
x rays and photographic film. This section describes the frequencyelectricand magneticfields,aswellasacoustic
nature ofradiationand matter, howxraysareproduced,and and ultrasound waves. Ionizing radiation may be
howthey interactwith matter. Other aspectsofthe physics directlyionizingorindirectlyionizing. Directlyionizing
of diagnostic radiology, such as characteristics of photo radiation includes charged particles such as electrons
graphic filmand image quality,arediscussedin Chapter5. and alpha particles,whichhavesufficientkinetic energy
to cause ionization by collision. Indirectly ionizing
radiation includes uncharged particles such as x rays,
Radiationand Matter gamma rays, and neutrons, which release directly
ionizingparticles or initiate nuclear transformation.
Radiation isdefined as,~nergyin motion. Radiation maybe
classifiedasfollows: The Structure of MaUer
1. Particulate/nonparticulate. When radiation (e.g., When a philosopher was asked what mind is, she said,
electrons and protons) acts primarily as a particle or "Doesn'tmatter"andwhen askedwhatmatteris,shereplied,
corpuscle, it is considered particulate radiation; if the "Never mind." Fortunately, physicists havecome along way
radiation (e.g.,xrays)interacts primarilyasawave,then intheir understandingofmatter.Allmatterismadeofatoms.
it isnonparticulate. An atom is the smallest part into which matter can be
2. Charged/uncharged When radiation carries a positive dividedwhile stillretaining the properties ofthat material.
(+) charge (e.g., alpha particles) or negative (-) charge
The Structure of an Atom
(e.g., electrons), then it is charged radiation, if it is
neutral (e.g.,photons) then it isuncharged radiation. In its simplest form, an atom may be visualized as a solar
3. Ionizing/nonionizing. Ionization is the formation of system, with the nucleus being the sun and the electrons
positivelyor negativelycharged particles or ions.Ifthe representing the orbiting planets (Figure 1-1).The primary
radiation hasenough energyto causeionization,then it subatomicparticles constitutingthe nucleusarethe neutron,
is considered to be ionizing radiation; otherwise, it is which has no electricalcharge, and the proton,which has a
nonionizing radiation. Only those radiations having positive charge. The nucleus, as a whole, has a positive
energy exceedingthe ionization potential,whichvaries charge,which inaneutralornonionizedatom isbalancedby
from 4.3 eV (electron volt) to 17.4 eV (averageabout the negative charge on the orbitingelectrons.The electrons
13eV) for biologically significant atoms, can cause arein specificorbits, the innermostorbitbeing the K-shell;
3
4 SECTION I Plain Film Radiography
the subsequent shells are L, M, N, and O. The maximum protons), Z is the atomic number, which is the number of
numberofelectronsineachshellisgovernedbyspecificlaws protons(and alsothe numberoforbitalelectronsinaneutral
and the innershellsarefilledin before electrons enterouter atom), and X is the chemical symbol for the atom. For
shells. Electrons in each shell have a specific energy level, example 1H represents tritium,an atom ofhydrogen with a
and whenan electron from aninnershellisknocked out, its mass of3, and 2~~pU isthe atom ofplutonium,with amass
place is taken up by an electron from an outer shell with of235.
release of electromagnetic radiation. An atom is about
10-10m in size,whereas the nucleus isonly 10-15m. Dual Nature of Matter
An atom is symbolized by AzX, where A is the mass Physicists recognize that matter and energy are inmteer ,
number, which is the number of nucleons (neutrons + changeable, asgivenbyEinstein'sfamous equation: E =
where E = energy injoules (J), m = mass in kilograms (kg),
and c= velocityoflight,which is3x108meters per second
(rn/s). Matter also has a dual nature, particulate and
wavelike,aspostulatedbyde Broglie.
X rays are a form of electromagnetic radiation. Electro
magnetic radiation is characterized by the simultaneous
transferofenergy throughbothelectric and magneticfields.
Helium Lithium Carbon
It coversthe spectrum from low-frequencyelectromagnetic
8, fields through visible light to cosmic rays (Table 1-1).
Electromagnetic radiation often propagates like waves in
water. The velocity ofpropagation, in a vacuum, is always
the same and is equal to 3 X 108 m/s. The wavelength and
Hydrogen
frequency ofpropagationarerelated byc='Av,where cisthe
velocityin meters per second, 'Aisthe wavelengthin meters,
and visthe frequency in Hertz. From this relationship,it is
obvious that the longer the wavelength, the lower is the
frequency.Electromagneticradiationalsobehavesasthough
itwere made ofdiscrete particles orbundlesofenergycalled
photons or quanta. The energy carried by a photon isgiven
Neon Sodium Phosphorus byE = hv,where E is the energy inJoules, h isthe Planck
Figure1-1 Schematicdiagram showingelectrons inorbit aroundthe constant(=6.63X 10-34J-s), andvisthe frequencyinHertz.
Combining the two relationships, it can be shown that E
nucleiofhydrogen,IH;helium, 2He;lithium,3Li;carbon, 6C;neon,lONe;
sodium,11Na;andphosphorous,lSp. (in kiloelectronvolts, keY) = 12.4/'A(in angstrom units, A,
TABLE 1-1
The Electromagnetic Spectrum
RadiationType Frequency(Hz) Wavelength (m) Photon Energy(eV)
Low-frequency electromagneticfields <105 >3x 103 <4.1 x 10-10
Radiowaves 105to 3X 1010 3x103 4.1 X 10-10
10-2 1.24 X10-4
Infrared 3x1012to 3x1014 10-4 1.24 X10-2
10-6 1.24
Visible 3x1014 to 7.5 x1014 10-6 1.24
4X 10-7 3.1
Ultraviolet 3 X 1015 10-7 12.4
Xrays 3x1016to 3x 1023 10-8 124
10-15 1.24 x 109
Gamma rays 3x 1018to 3x 1021 10-10 1.24 xl04
10-1> 1.24 x 107
Cosmic rays 3x 1021 to 3x 1022 10-1> 107
10-14 108
Note that inSweden,radiationswithenergyabove12.4eVareconsideredionizing andradiationsbelow 12.4eVareconsiderednonionizing.Adaptedfrom
ShleienB:Thehealth physicsandradiologicalhealth handbook, SilverSpring,Md., 1992, Scinta.
CHAPTER 1 Radiation Physics, Biology, and Safety 5
which equals 10-10m). Thus we see that high-energy Bremsstrahlung
radiations, such asx rays,have a high frequency and short Bremsstrahlung is a German word meaning "braking
wavelength, whereas long-wavelength radiations, such as radiation."When the negatively charged electrons approach
television and radio waves, have low energy and a short the vicinity ofapositivelycharged nucleus,the electron may
frequency (seeTable 1-1). be deflected from its path.This sudden change in velocity
causes the electron to lose part ofits energy asx rays.The
efficiency ofbremsstrahlung production increases with the
Production ofX Rays
square ofthe atomic number. Bremsstrahlungradiation has
The productionofxraysisan example ofthe conversionof abroadrange ofenergies upto apeakenergydeterminedby
oneform ofenergyinto another. In anx-ray tube,whenfast the kVp.
moving electrons produced by heating a tungsten filament
Characteristic X Rays
strike a tungsten target, a very small fraction of energy
is converted into x rays. The filament is the cathode An electron may also interact with an orbiting electron,
(- terminal), and the target is the anode (+ terminal). The ejecting it from the atom. The vacancycreated in thatorbit
cathode and anode are enclosed in an evacuated glass bulb is filled up by an electron from a higher orbit. In this
(Figure 1-2). process, electromagneticradiationisreleased.Theenergy of
The numberofelectrons passingfrom the cathodeto the the radiation is characteristic ofthe target material and is
anode in 1secondisameasure ofthe x-ray tube currentand sharply definedinenergy.Forhigh-Ztargets andinnershell
is usually expressed in milliamperes (mA). The voltage, transitions,the escaping radiationhasenergyinthe range of
usually expressed in kilovolts (kV), is the potential the x-ray spectrum.
difference acrossthe anode and the cathode.
Quality of X Rays
There are several types of x-ray generators, and
dependingon the circuitryproducingthe highvoltage,these Whereas characteristic x rays have discrete energies,
may be classified as single-phase, three-phase, or constant bremsstrahlungradiation has abroad range ofenergies,and
potential. The maximum or peak potential difference therefore the photons produced by an x-ray generator are
applied acrossthe cathode and anode is the kVp.The kVp heterogeneous in energy. Because of the heterogeneous
determinesthe qualityofthexrays,and the mAisameasure nature ofthe photons produced by an x-ray machine, one
ofthe quantityofxraysproduced. needs aquantityto characterize aphoton beam.
When electrons from the cathode hit the anode, most Severalfactors,such askVp,averagekeY,halfvaluelayer
(99%) of the energy is converted into heat and only about (HVL), and equivalent keV,are used for this purpose; but
1% goes into the production ofx rays. The efficiency of each has its limitations. The kVp is a measure of the
x-ray production is the ratio ofthe energy put out asx rays maximumenergyinkeVofthexraysproduced.Theaverage
to the energy deposited onto the anode by the electrons. It keVisabout one third ofthe maximum keV and isabetter
isgivenbyE = 9 X 10-10Zv, where E isthe efficiency,Z is measure ofx-ray quality. The HVL is the thickness of a
the atomic numberofthe target, and Visthe tube voltagein givenmaterial(usuallyaluminumorcopper) thatwillreduce
volts. the intensityofthe photonbeam to half Unfortunately, the
There aretwo processesbywhichenergy ofthe electrons HVLforaheterogeneousbeam isnot constantbutincreases
isconverted into xrays:bremsstrahlung and characteristicx with each succeeding HVL because of the preferential
rays. absorptionoflow-energyxraysbythe initial HVLsand the
consequent hardening ofthe beam. To account for this, a
homogeneitycoefficient hasbeen defined asthe ratio ofthe
Tungstentarget second HVLto the firstHVL.Thehigherthe homogeneity
coefficient, the more homogeneous is the beam. The
equivalent keY isthe keY ofahomogeneous beam that has
the same HVL asthe given heterogeneous beam.
Note that low-energy photons do not contribute to a
Anode
diagnostic image, because these photons do not reach the
film but are absorbed by the patient, unnecessarily
/ Tungstenfilament increasingpatientdose. Even though some verylow-energy
xraysareabsorbed bythe tube housing(inherentfiltration),
the National Council on Radiation Protection and Mea
Evacuatedbulb
surements (NCRP) recommends and state regulations
Figure1-2 Schematicdiagramofanx-raytube. require the use ofadded filters (usually made ofaluminum)