Computed Tomography of Stress Fractures

Journal of Computer Assisted Tomography 10(1):92-95,January/February @ 1986Raven Press. New York

Computed Tomographyof StressFractures

D. Yousem,D. Magid, E. K. Fishman,F. Kuhajda,and S. S. Siegelman

Abstract: Three cases of stress fractures of the lower extremities ate pfe- sentedwith correspondingCT. Findings of increasedmedullary cavity density, endostealsclerosis, callus formation, and soft tissue swelling are demonstrated even though they are thought to be nonspecificin differentiating stressfracture from infectious or neoplastic processes. Only when actual failure lines are demonstratedby CT can stress-relatedinjury be specifically suggested.Index Terms: Bones, fractures- Legs, wounds and injuries-Computed tomog- rapby.

Although stress fractures of the extremities have Computed tomography of the right femur revealed cir- becomeincreasingly well recognized,the patient cumferential cortical thickening with moderate increased with periostitis,an abnormalbone scan,and only a density of the medullary cavity. In addition, lucent frac- posteromedial cortex vague history of skeletal trauma may still present a ture lines of the anteromedial and (Figs. lb and c). With CT follow-up exami- of the right femur were defined diagnostic dilemma. Subsequent fracture the most likely diagnosis, the cli- painful ex- making stress nations often reveal the etiology of the nicians elected conservative managementrather than tremity but may subject the patient to weeks of un- open biopsy. Follow-up films showedresolution and con- certainty and inadequate treatment. In addition, solidation of the periosteal reaction compatible with a stressfractures may progressto complete fractures healing stress fracture. if appropriate casting, fixation, or limb rest are not provided (1,2). Recently the value of CT for as- Case 2 sistingin the diagnosisof stressfractures has been demonstrated(3). We report three casesof occult An 8-year-old girl presented with a history of several fracturesof the lower extremities.In two casesCT weeks of left shin pain and a warm, tender, swollen left aided in establishingthe diagnosis,and in one case midleg after taking up "break-dancing." Roentgenog- fibula showed significant focal scle- CT was unable to distinguishbetween stressfrac- raphy of the tibia and rosis of the midtibial region with periosteal reaction fo- ture and malignancy. cally around an area of permeated lucent cortex. A radionuclide bone scan displayed a focal, sharply CASE REPORTS marginated area of increased activity of unknown etiology in the left leg. SubsequentCT revealedincreased Case 1 density within the medullarycavity, endostealsclerosis, and areas of cortical rarefaction in the left midtibia (Figs. A 7-year-old boy was referred because of a 4 week 2aand b). Becauseno distinct fracture line was defined, history of right thigh pain. Roentgenographyrevealed CT could not distinguish with certainty between stress middiaphysealperiosteal reaction of the right femur (Fig. fracture and neoplasm. Continued clinical suspicion of a la), and a gallium scan demonstrated increased tracer neoplasmled to an open biopsy of the lesion.Pathologic in this region. A radionuclide bone scan also uptake specimensdisclosed fragments of bonewith reactivenew showed increased ee'Tc-pyrophosphateaccumulation at bone formation, loose fibrous tissue, chronic inflamma- the samelocation. Although there was a history of minor tion, and perivascularedema of the periosteum(Fig. 2c). trauma, the patient's weight loss and anorexia thigh Pathologicinterpretation was that ofa healing stressfrac- raised the clinical suspicion of an early Ewing sarcoma ture. The periosteal reaction and biopsy site healed un- of the right femur. eventfully on follow-up radiography and the patient's symptomsabated over severalweeks.

From the Russell H. Morgan Department of Radiology (D. Yousem,D. Magid, E. K. Fishman,and S. S. Siegelman),and Case 3 the Department of Pathology(F. Kuhajda), Johns Hopkins Hos- pital, Baltimore, MD 21205,U.S.A. Address correspondence A 55-year-oldwoman, recently treated for deepvenous and reprint requeststo Dr. E. K. Fishman. thrombosis, had undertaken a vigorous walking program

92 SZRESSFRACTURES: CT FINDINGS 93

FlG. 1. Case 7. A 7-year-oldboy with a 4 week historyof right thigh pain.a: Plainfilm of right femur demonstrates periostealreaction without evidence of a fractureline. b: CT scan through midfemurdemonstrates evidence of a fracture line with adjacent periosteal reaction (arrow). The image is at 'l window width 2,500and center ,400. c: lmage at soft tissuewindows dem- onstratesincreased medullary density of right femur when comparedwith the left femoral medullarycavity.

and presented with diffuse left calf pain and swelling. continuum of changeswith subtle early, blurring of Plain roentgenographyshowed diffuse periostealreac- trabecularmargins, followed by small specklesof tion, cortical thickening, and an area of radiolucency in new bone formation, fluffy clusters of new bone, the left tibia (Fig. 3a). Because of the focality of the leg scleroticbands along fracture sites, and, finally, pain, a bone scan was obtained and demonstrateddiffuse callus formation with periosteal reaction would be tracer uptake along the lateral tibial cortex of both legs seen with sequential examinations (4). with no focal accumulation.This was felt to be secondary Unfortu- to stress-relatedchange or venoocclusivedisease, with nately, positive plain radiography at acute presen- no evidence of stress fracture. SubsequeritCT revealed tation was found in only 22-40Vo of three major endostealthickening, increaseddensity of the marrow series(5-7). Even severalweeks after the clinical cavity, as well as a focal area of irregularity of the inner and scintigraphic confirmation of stress fractures, cortical margin suggestiveof an incompletefracture (Figs. the estimatedfrequency of continued negativeplain 3b and c). Follow-up plain radiography showedresolution radiographyis 20-50% (2,4,6,8,9).Because of this of these changesafter nonweight bearing treatment. well-recognizedinsensitivity, plain roentgenog- raphy alone may provide inadequateevaluation of DISCUSSION stress-relatedtrauma. Radionuclidebone scanninghas becomethe sine Plain radiography is notoriously insensitive in the qua non of stress-relatedinjuries. Most radiologists initial evaluation of stress-related injury. Ideally, a have adoptedthe Wilcox conviction that a normal

FlG.2. Case2. An 8-year-oldgirl with a historyof several weeks with a painful,swollen left midleg.a: CT scan at soft tissuewindow settingsdemonstrates in- creasein medullarydensity of cortex of left tibia. b: CT scan at bone setting demonstratesirregularity of cortex with diffuse lucencyseen within cortex.The patternsuggests a permeatedlesion. No fracturewas seen.c: Reactive bone formationat fracturesite. Note the irregularspicules of woven bone with associatedosteoblast activity (arrows). Hema- toxylin/eosinstain. x 115.

J ComputAssist Tomogr, Vol. 10, No, 1, 1986 94 D. YOUSEM ET AL,

FlG. 3. Case 3. A S5-year-oldwoman with diffuse left calf pain and swelling. a: Film of left tibia demonstratescor- tical buttressingand periostealreaction with apparent lucent lesion within cortex noted (arrow). b: CT scan through the lesion demonstratesin- crepsein medullarydensity when comparedwith the right tibia.c: Evidenceof irregularityin inner cortexof tibia noted (arrowhead).

bone scan excludesthe diagnosisof stressfracture Recently,Somer and Meurman in a survey of 12 (10).In Matin's study of scintigramsfollowing acute patients demonstratedthe successfuluse of CT in fractures, 80Vowere positive within 24 h after in- diagnosingstress fractures (3). They found endos- jury, and 95Vopositive within 72 h (ll). With stress teal as well as periosteal callus formation, increased fractures there generally is a later clinical presen- density of the bone marrow cavity, and soft tissue tation (average15.4 days), by which time the bone edema at the site of the stress fractures in the ma- scanis routinely positive (5). Roub et al. described jority of their cases(3). The bony callus formation a progressionof injury on bone scintigraphyfrom occurred at the sites described earlier as'rnost a nondescript, poorly defined area of slightly in- common for stressfractures: however, a visible frac- creaseduptake to a sharply marginated fusiform ture line was seenin only one of their 12 cases(3). area of activity in casesproceeding from "injury" Murcia et al. reporteda singlecase of a tibial stress to actualstress "fracture," with reversalof this pat- fracture in which multiple linear infractions were tern after proper treatment (8). Unfortunately sim- seen within the tibial cortex at CT, although plain ilar bone scan findings may be seen with focal me- films were negative(15). tastases,early osteomyelitis,periostitis, osteoid os- Somerand Meurman's finding of increasedbone teomas, bone infarcts, primary bone tumors, and marrow densitywith stressfractures has been dem- dysplasiasof bones (1,4,8).Even with a history of onstratedin casesof osteomyelitis,fibrous dys- trauma, soft tissue injury with hemorrhage,liga- plasia,Gaucher disease, Ewing sarcoma,osteosar- mentousinjury, bone abrasions,and acute fracture coma, and other neoplasms(3,16- 19).The findings may produce abnormalbone scans,as can trau- of localizedhomogeneous endosteal and periosteal matic myositis ossificans and rhabdomyolysis callus formation may be seen with osteoid os- (10,12),Nearly all of the authors reporting ab- teomas,osteomyelitis, as well as with stressfrac- normal bone scansin stressfractures describe their tur€, but demonstrationof a nidus and the clinical findings as areas of increased uptake but report no history may separatethe three (16,20).Demonstra- specificdiagnostic features (1,4-6,9,13,14). Be- tion of thin linear infractionsin the bony cortex in causeof this, all of the authorsemphasize the need the absenceof other "malignant" findings seems for roentgenographic correlation and heed Roub's most specific for stressfractures althoughthe po- admonition"to rememberthat diagnosesother than tential for misdiagnosingpathologic fractures of bone stressmust also be consideredwith this ra- bone remains (3,15). Although fracture lines have dionuclideappearance" (8). However, sinceconfir- been reported to be better seen on plain radiog- matory roentgenogramsare seenin less than 50% raphy than on CT, obscuration on plain films by of cases of abnormal bone scans, the differential periostealbone and callus formation may permit CT diagnosismust still include diseasessuch as early demonstrationof otherwiseoccult stressfractures. osteomyelitis,subtle osteoid osteomas,Ewing sar- Thus CT, althoughoften nonspecificfor stressfrac- coma, as well as the nonfracture traumatic entities tures, may occasionallyassist as a third line mo- discussedabove. dality for the differentiation of stress fracture from

J ComputAssist Tomogr, Vol. 10, No. 1, 1986 STRESSFRACTURES: CT FINDINGS 95

neoplasm.We confirmed Somer and Meurman's 5. GeslienGE, Thrall JH, EspinosaJL, Older RA. Early de- findings of increasedbone marrow tection of stressfractures using 99m Tc-polyphosphate.Ra- density,endos- -7 teal and periosteal new diology 1976;121 :683 . bone formation, and soft 6. Prather JL, Nusynowitz ML, Snowdy HA, Hughes AD, tissueedema, all nonspecificfindings, in our three McCartney WH, Bagg RJ. Scintigraphic findings in stress casesof stressfractures. In addition. fracture lines fractures. J Bone Joint Surg lAml 1977;59:869-74. were visualizedin two of the three cases,thereby 7. Giladi M, Nili E, Ziv Y, Danon YL, Aharonson Z. Compar- supportingthe diagnosisof stressfracture. In the ison between radiography, bone scan and ultrasound in the diagnosisof stress fractures. Milit Med 1984;149:459-61. third case the CT findings were nonspecific and an 8. Roub LW, Gumerman LW, Hanley EN, Clark MW, open biopsy was required to rule out a neoplasm. Goodman M, Herbert DL. Bone stress: a radionuclide im- Finally in one case a bone scan failed to demon- aging perspective.Radiology 1979;132:431 -8. strate a localized focus of activity within a 9. Meurman KOA, Elfving S. Stressfracture in soldiers:a mul- back- -7 ground of diffuse uptake, although tifocal bone disorder. Radiology 1980;134:483 . CT revealed a 10. Wilcox JR, Moniot AL, Green JP.Bone scanningin the eval- subtle inner cortical fracture. uation of exercise-relatedstress injuries. Radiology In conclusion,in those caseswhere a distinct 1977:'123:699-703. fracture can be demonstrated, CT may be able to I l. Matin P. The appearanceof bone scansfollowing fractures, make the definitive diagnosisof stressfracture including immediate and long term studies. J Nucl Med 1979:.20:1227-31. when neither plain film nor radionuclide bone scan 12. Collier BD, JohnsonRR Carrera GF, Akhtar K, Isitman AI. is sufficiently specific.It is important to note, how- Scintigraphic diagnosis of stress-inducedincomplete frac- ever, that in many instances,CT will demonstrate tures of the proximal tibia. J Trauma 1984;24:156-60. only the nonspecificfindings associatedwith stress 13. Kaltsas DS. Stress fractures of the femoral neck in young fractures, and that in such adults.J Bone Joint Surg[Brl 198l;63:33-7. casesthe differential di- 14. SaundersAJS, El SayedTF, Hilson AJW, MaiseyMN, Gra- agnosiswill continue to include neoplasmsand in- hame R. Stresslesions of the lower leg and foot. Clin Radiol fectiousprocesses. 1979;30:649-51. 15. Murcia M, Brennan RE, Edeiken J. Computed tomography Acknowledgment:Our appreciationto NancyLaw- of stress fracture. Skeletal Radiol 1982;8:193-5. b rencefor preparationof manuscript. 16. Berger PE, Kuhn JP. Computed tomography of tumors of the musculoskeletal system in children. Radiology REFERENCES 1978;127:l7l-5. /:l 17. deSantosLA, Goldstein HM, Murray JA, Wallace S. Com- L Norfray JF, Schlachter L, Kernahan WT, et al. Early con- puted tomography in the evaluation of musculoskeletalneo- firmation of stress fractures in joggers. JAMA plasms. Radiology 1978;128:89-94. 1980;243:1647-9. 18. deSantos LA, Bernardino ME, Murray JA. Computed to- 2. DevereauxMD, Parr GR, Lachmann SM, Page-ThomasP, mography in the evaluation of osteosarcoma:experience Hazleman BL. The diagnosisof stressfractures in athletes. with 25 cases.AJR 1979;132:535-40. JAMA 1984;252:531-3. 19. VanelD, ContessoG, CouanetD, PiekarskiJD, SarrazinD, 3. Somer K, Meurman KOA. Computed tomography of stress Masselot J. Computed tomo$aphy in the evaluation of 41 fractures.J Comput AssistTomogr 1982;6:109-15. casesof Ewing's sarcoma.Skeletal Radiol 1982;9:8-13. 4. Greaney RB, Gerber FH, Laughlin RL, et al. Distribution 20. Hermann G, Rose JS. Computed tomography in bone and and natural history of stress fractures in U.S. marine re- soft tissue pathology of the extremities. J Comput Assist cruits. Radiology 1983;146:339 -46. Tomogr 1979;3:58-66.

J Comput Assist Tomogr, Vol. 10, No. 1, 1986