Tibial Stress Fracture: Diagnsotic Pitfall_Siriraj Med J. 9-2012
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163 S CaseReport Correspondence to: Jiraporn Sriprapaporn E-mail: [email protected] Received 7 December 2011 Revised 12 March 2012 Accepted 13 March 2012 INTRODUCTION tress fractures are divided into two types. A fatigue fracture occurs in a normal bone when the bone is overused, while an insuf fi ciency fracture occurs when a normal stress is applied over an abnormal structural bone such as an osteoporotic bone. 1 Fatigue fractures that are usually found in military and athletic populations are the most important stress fractures found in clinical practice. Diagnosis of such conditions is somewhat underestimated and sometimes may not be simple. The author reports a young man with a history of heavy running about 10 km/day for a few months, pre- senting with left shin pain. MRI findings suggested an infective or neoplastic process, which required bone biopsy, but three-phase radionuclide bone imaging implied a stress fracture, which avoided an unnecessary biopsy procedure. CASE REPORT A 19-year-old police cadet with a history of heavy running about 10 km/day for a few months presented with left shin pain especially during exercise for a few weeks. He had no other history of traumatic injury before. On physical examination, he had no fever, no bruise over the left leg, but he had a point of tenderness at the posteromedial aspect of his left leg without signs of inflammation. His first plain radiographs at a private clinic were clearly normal. He had obligatorily continued the same training program and the pain tended to be aggravated. Tibial Stress Fracture: A Diagnostic Pitfall Jiraporn Sriprapaporn, M.D. Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand. ABSTRACT The author reports a young police cadet with a history of heavy running about 10 km per day for a few months, presenting with left shin pain especially during exercise. His first plain radiograph was not helpful and his MRI findings favored an infective or neoplastic process. However, three-phase bone scintigraphy suggested a stress fracture resulting in avoidance of a dispensable biopsy procedure. Keywords: Stress fracture, bone scan, bone scintigraphy, pitfall Siriraj Med J 2012;64:ใ163-166 E-journal: http://www.sirirajmedj.com Further laboratory investigations found normal complete blood counts, normal erythrocyte sedimentation rate, suggesting so signs of infection. His magnetic resonance imaging (MRI) from another imaging center performed one month after onset of the symptom demonstrated a patchy lesion in the medulla of the mid left tibia with iso-to-low signal on T1-weighted images and high signal on T2-weighted and STIR (short tau inversion recovery) images with moderate gadolinium enhancement. There was also soft tissue edema at the posteromedial aspect of the lesion, which suggested an infective or neoplastic process. (Fig 1) He then was referred for bone scintigraphy for whole-body evaluation. A three-phase bone scintigraph of both legs was obtained using an intravenous injection of 20 mCi Tc-99m methylene diphosphonate (Tc-99m MDP). The technique included 120-second immediate vascular dynamic imaging, 5-minute static blood-pool images, and delayed 3-hour bone images. The study revealed mild hyperemia to the left leg, with focal increased uptake at the medial aspect of his left calf, and fusiform increased uptake in the cortico-medullary region at the posteromedial aspect at mid shaft of his left tibia (Fig 2). The skeleton elsewhere appeared unremarkable. These findings were compatible with grade III tibial stress fracture according to Zwas’ classification. 2 The serial plain radiograph a few days following his bone scan demonstrated a solid perios- teal reaction at his posterior cortex of the left tibia (Fig 3). Nevertheless, the patient was concerned about a bone tumor, thus a bone biopsy was then scheduled. While waiting for a bone biopsy appointment, he had been advised to discontinue running activity. After that, his pain was gradually relieved. Serial plain radiographs of the left leg one month later demonstrated progressive periosteal thickening, which favored a healing process of the stress fracture. Thus, bone biopsy was canceled and a follow-up 3-phase bone scintigraphy (Fig 4) was obtained at the three-month interval. Although he had been back
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Transcript of Tibial Stress Fracture: Diagnsotic Pitfall_Siriraj Med J. 9-2012
163
S
CaseReport
Correspondence to: Jiraporn Sriprapaporn E-mail: [email protected] 7 December 2011Revised 12 March 2012Accepted 13 March 2012
INTRODUCTION
tressfracturesaredividedintotwotypes.Afatigue fractureoccursinanormalbonewhenthebone is overused, while an insufficiency fractureoccurswhenanormalstressisappliedoveranabnormalstructuralbonesuchasanosteoporoticbone.1 Fatiguefracturesthatareusuallyfoundinmilitaryandathleticpopulationsarethemostimportantstressfracturesfoundinclinicalpractice.Diagnosisofsuchconditionsissomewhatunderestimatedandsometimesmaynotbesimple. Theauthorreportsayoungmanwithahistoryofheavyrunningabout10km/dayforafewmonths,pre-sentingwith left shinpain.MRIfindingssuggestedaninfectiveorneoplasticprocess,whichrequiredbonebiopsy,butthree-phaseradionuclideboneimagingimpliedastressfracture,whichavoidedanunnecessarybiopsyprocedure.
CASE REPORT
A19-year-oldpolicecadetwithahistoryofheavyrunningabout10km/dayforafewmonthspresentedwithleftshinpainespeciallyduringexerciseforafewweeks.Hehadnootherhistoryoftraumaticinjurybefore.Onphysicalexamination,hehadnofever,nobruiseovertheleftleg,buthehadapointoftendernessattheposteromedialaspectofhisleftlegwithoutsignsofinflammation. Hisfirstplainradiographsataprivateclinicwereclearlynormal.Hehadobligatorilycontinuedthesametrainingprogramandthepaintendedtobeaggravated.
Tibial Stress Fracture: A Diagnostic PitfallJiraporn Sriprapaporn, M.D.Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand.
ABSTRACT
Theauthorreportsayoungpolicecadetwithahistoryofheavyrunningabout10kmperdayforafewmonths,presentingwithleftshinpainespeciallyduringexercise.HisfirstplainradiographwasnothelpfulandhisMRIfindingsfavoredaninfectiveorneoplasticprocess.However,three-phasebonescintigraphysuggestedastressfractureresultinginavoidanceofadispensablebiopsyprocedure.
Keywords:Stressfracture,bonescan,bonescintigraphy,pitfall
Siriraj Med J 2012;64:ใใ163-166E-journal: http://www.sirirajmedj.com
Furtherlaboratoryinvestigationsfoundnormalcompleteblood counts, normal erythrocyte sedimentation rate,suggestingsosignsofinfection.Hismagneticresonanceimaging (MRI) fromanother imagingcenterperformedonemonthafteronsetof the symptomdemonstratedapatchylesioninthemedullaofthemidlefttibiawithiso-to-lowsignalonT1-weightedimagesandhighsignalonT2-weightedandSTIR(shorttauinversionrecovery)imageswithmoderategadoliniumenhancement.Therewasalsosofttissueedemaattheposteromedialaspectofthelesion,whichsuggestedaninfectiveorneoplasticprocess.(Fig1)Hethenwasreferredforbonescintigraphyforwhole-bodyevaluation.Athree-phasebonescintigraphofbothlegswasobtainedusinganintravenousinjectionof20mCiTc-99mmethylenediphosphonate(Tc-99mMDP).The technique included 120-second immediate vasculardynamicimaging,5-minutestaticblood-poolimages,anddelayed 3-hour bone images. The study revealedmildhyperemiatotheleftleg,withfocalincreaseduptakeatthemedialaspectofhisleftcalf,andfusiformincreaseduptakeinthecortico-medullaryregionattheposteromedialaspectatmidshaftofhislefttibia(Fig2).Theskeletonelsewhere appeared unremarkable. These findingswerecompatiblewithgradeIIItibialstressfractureaccordingtoZwas’ classification.2Theserialplainradiographafewdaysfollowinghisbonescandemonstratedasolidperios-tealreactionathisposteriorcortexofthelefttibia(Fig3).Nevertheless,thepatientwasconcernedaboutabonetumor,thusabonebiopsywasthenscheduled. Whilewaitingforabonebiopsyappointment,hehadbeenadvisedtodiscontinuerunningactivity.Afterthat,hispainwasgraduallyrelieved.Serialplainradiographsoftheleftlegonemonthlaterdemonstratedprogressiveperiostealthickening,whichfavoredahealingprocessofthestressfracture.Thus,bonebiopsywascanceledandafollow-up3-phasebonescintigraphy(Fig4)wasobtainedatthethree-monthinterval.Althoughhehadbeenback
Siriraj Med J, Volume 64, Number 5, September-October 2012 164
foranintermediatetrainingprogramrecentlypriortothesecondbonescanning,thestudyconfi rmedmuchimprove-mentwithcorrespondingsclerosisalongtheposteromedialaspectofhislefttibiaseenonSPECT/CTimages(Fig5).
DISCUSSION
Stressfracturesarecommonoveruseinjuriesamongathletesandmilitaryrecruits.Thetrueincidenceofstressfracturesishardtodetermineandtheytendtobeunder-estimatedsincemanyofthemmightbeleftunrecognized.However,itwasestimatedthatstressfracturesaccountfor0.7%-20%ofallsportsmedicine injuries.3Femalesaremoresusceptiblethanmalestodevelopstressinjuriesoftheboneespeciallyinthemilitarypopulation.4-5 Approximately75%ofstressfracturesoccurrbeforetheageof40years.6Inaddition,thetrendofsuchcondi-tioninyoungadultshasbeenincreasingduetoincreasedparticipationinsportingactivities.7Onestudyalsofoundthat9%offracturesoccurredinchildrenagedlessthan15yearsand32%inthosebetween16-19yearsofage.8The site of fractures depends on the type of activityinvolved.9-10Runninginjuriesplayanimportantrolefordevelopingstressfracturesinbothathletesandmilitarypopulations.Most stress fractures occur in the lower
extremities,especiallyinlong-distancerunners.Runningmorethan20milesaweekisatincreasedrisktodeveloplower-extremityinjuries.11Thisinjurytypicallyoccurs6to8weeksafterachangeintrainingdurationorintensity,but can occurwith repetitive stress alone.12 Themost
Fig 1.CoronalMRIimagesoflefttibiashowedpatchylesioninthemedullaofmidlefttibiawithiso-to-lowsignalonT1-weightedimages(A)andhighsignalonSTIRimages(B)withmoderate gadoliniumenhancement (C).Associated soft tissueedemaatposteromedialaspectofthelesionwasalsonoted.
Fig 2.Three-phasebonescintigraphyrevealedmildhyperremiatotheleftleg(A)withfocalincreasedblood-poolactivityatthemedialaspectofleftcalf(B).Thedelayed3-hourimagesintheanteriorandlateralprojectionsshowedfocalfusiformincreaseduptakeinthecortico-medullaryregionatposteromedialaspectatmidshaftoflefttibia.(C)Thesefi ndingsarecompatiblewithgradeIIItibialstressfracture.
Fig 3.Serialplainradiographs(AP-Lateral)oflefttibiarevealedperiostealreactionatposteriortibialcortex.
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commonsiteofstressfracturesinmostreportsisinthetibia,whichmaybeashighas72%.2,13-14 Diagnosisofstressfracturesprimarilydependsonahigh indexofsuspicionsince itmaybeproblematicbecauseseveralmusculoskeletaldisorderscancauseexer-cise-inducedlegpainsuchassofttissueinjuries,medialtibialstresssyndrome(MTSS)orshinsplints,arteryornerveentrapment,compartmentsyndrome,bonetumors,andboneinfection.15-16Theclassicclinicalfeatureofastressfractureisinsidiousonsetofactivity-relatedlocalpainwithweightbearing.Thepain is relievedbyrestandbecomesworsewhentheactivityiscontinued.Localtendernessandswellingareoftenfoundat thefracturesite.16Nevertheless,stressfracturesshouldbeconsideredinanypatientwhopresentswithlocalpainafterarecentincreaseinactivityorrepeatedactivitywithlimitedrest.9,17 Earlydefi nitediagnosisisessentialforpreventingprogressionoflesions,avoidingcomplicationsandguidingpropermanagement.Sinceclinicaldiagnosismaybein-conclusive,variousimagingtestsshouldbeperformedto
confi rmstressfractures.TheseimagingmodalitieshavetheirownadvantagesanddisadvantagesaslistedinTable1. Plainradiographyisusuallythefi rstimagingmodalityobtainedbecauseofitsavailabilityandlowcost.19Plainradiographisusuallynegativeinitially,butismorelikelytobecomepositiveovertime.21Theinitialplainradiographhasquitelowsensitivityforstressfracturesrangingbetween10%-30%,asinthiscase.2,14,18Onfollow-upexaminations,thesensitivityofradiographsishigherwithreportedvaluesrangingbetween40%to54%.2,19 Radiographicmanifestationsoftibialstressinjuriesincludedecreasedcorticaldensity,socalled“graycortex” sign,periostealreaction,endostealthickening,andacorti-calfractureline.16,20 Iftheinitialradiographisnegative,moreadvancedimagingmodalitiessuchasthree-phasebonescintigraphyandMRImay be helpful for further evaluation. Bothmodalitieshavesimilarlyhighsensitivityfordetectionofstressfractures,butMRIhasgreaterspecifi city.16Radio-nuclideboneimaginghadtraditionallybeenthestandardtooltoconfi rmstressfracturesinmoststudiespriortothedevelopmentofMRI,becauseofitshighsensitivity.14,21-22
Fig 4.Thefollow-up3-phasebonescanofthelegintheanteriorviewshowedsymmetricalbloodfl owtobothlegs(A),almostnormalblood-poolimage(B),andlessintenseuptakeatlefttibialshaft,suggestingimprovementofstressfracture.
Fig 5.SPECT/CTimagesoftheleg(acquiredwith15second/stepx60 steps, 360degreeof rotation forSPECTand130kV,50mAsforCT)demonstratedincreaseduptakealongtheposteromedialaspectoflefttibialshaftwithassociatedsclerosisobservedonthecorrespondingCTscan.
Imaging Advantages Disadvantages -PoorinitialsensitivityPlainradiography -Lowestcost -Someradiationexposure -Widelyavailable -Limiteddifferentialdetails -Limitedavailability -LimiteddifferentialdetailsBonescinitigraphy -Highercost -Someradiationexposure -Highsensitivity -Canbefalselypositiveinbonyinfectionortumor -Bestdifferentialdetails -Noradiationexposure -HighestcostMagneticresonanceimaging(MRI) -Highestdifferentialdetails -Limitedavailability -Highestspecifi city -Sometimesmaybefalselypositiveinbonyinfection -Equalorslightlybetter ortumor sensitivitythanscintigraphy
TABLE 1.Advantagesanddisadvantagesofimagingmodalitiesforstressfractures(modifi edfromPatel,etal.)16
Siriraj Med J, Volume 64, Number 5, September-October 2012 166
However, nowadays,MRI is currently considered themethodofchoiceforthispurposeduetoitshighimageresolutionofbone,bonemarrow,andsurroundingsofttissue,resultinginbetteranatomicalevaluationandhigherspecificityascomparedtobonescintigraphy.23-25 Bone scintigraphy is really sensitive andmaybepositiveasearlyas48-72hoursafterinjuries.26Inacutestressfractures,allthreephasesofthebonescanareposi-tive.Zwas,etal.,developedascintigraphicclassificationofstress fractures,whichwasdivided into fourgradesaccordingtolesiondimension,boneextension,andtraceraccumulationinthelesions.2 Three-phase bone scintigraphy is also helpful inthedifferentiationbetweenstressfracturesandMTSS.InMTSS,onlythedelayedthirdphaseispositiveandtendsto be longitudinally-oriented along the posterior cortexof the tibia. Incontrast, the increaseduptake in stressfracturestendstobemorefocal(withfusiformshapeinadvancedstages).27 Apart from planar bone imaging, SPECT (singlephoton emission tomography) acquisition, which is a3-dimentionalimagingtechnique,whichprovidesbetterdelineationofbonylesions,canbeused.CombinedSPECTandcomputedtomography(CT)imagingtogetherinthesame instrument, so called SPECT/CT scanning, addsevenmore anatomical details over the SPECT imagesalone.Todate,moreandmoreSPECTandSPECT/CTimaginghavebeenusedinthefieldofSportsMedicinetoevaluateseveralpartsofthebody,suchasthespine,hips,knees,andfeet.28-29 AlthoughMRI, isnow thegold standard for thediagnosisofstressfractures,itmightbeoflimitedavail-abilityduetoalongwaitinglist,especiallyinmostbusytertiarycenters.Furthermore,theMRIabnormalitiessuchasperiostealreactionandbonemarrowedema,ifthereisnodemonstrationofafractureline,arenonspecific.30Thus,anunawareradiologistmaybeconfusedwithotherconditionssuchasosteomyelitisorinfiltrativeneoplasms.Asinthereportedcase,MRIresultswereindicativefortumorpathology,sotheattendingclinicianhadscheduledbonebiopsyforpathologicalevidence. Prior to performing a biopsy, one should alwayskeepinmindthatthisprocedureshouldbestrenuouslyavoidedinacasewithpotentialstressfracturesincethisprocedurecandisturbbonehealingandthebiopsyspeci-menmaycontainimmaturecellsandosteoid,relatedtothehealingprocess,whichcouldbemistakenasmalignancies.Follow-up imagingstudies in thenext fewweeksmayrevealcharacteristicfindingsofstressfracturesandthusavoidanunnecessaryinvasiveprocedure.9,31
CONCLUSION
AlthoughMRIiscurrentlyacceptedastheimagingof choice for evaluationof stress fractures, it still hassomepitfalls.Three-phasebonescintigraphyontheotherhand,isgenerallylessspecific,butcarefulinterpretationalongwithpreciseclinicalcorrelationcanovercomethislimitationresultinginaccuratediagnosisforstressfractures.Therefore,three-phasebonescanningcouldbeusedsolelyorasanadjunctwhentheMRIfindingsarenon-diagnosticincasespresentingwithhighclinicalsuspicionofstressfractures.
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