Sonography of bone and bone-related diseases of the extremities

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Sonography of bone and bone-related diseases of the extremities
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  Pictorial Essay Sonography of Bone and Bone-RelatedDiseases of the Extremities Kil-Ho Cho, MD, 1  Young-Hwan Lee, MD, 2 Sung-Moon Lee, MD, 3 Muhammad Usman Shahid, MD, 1 Kyung Jin Suh, MD, 4 Joon Hyuk Choi, MD 5 1 Department of Diagnostic Radiology, College of Medicine, Yeungnam University, 317-1, Daemyung-Dong,Nam-Ku, Daegu, 705-717, Korea  2 Department of Diagnostic Radiology, College of Medicine, Daegu Catholic University, Daegu, Korea  3 Department of Diagnostic Radiology, College of Medicine, Keimyung University, Daegu, Korea  4 Soo & Joo MR Clinic, Daegu, Korea  5 Department of Anatomical Pathology, College of Medicine, Yeungnam University, Daegu, Korea   Received 23 May 2003; accepted 29 July 2004 R adiography is the baseline modality in theevaluation of bone diseases, commonly fol-lowed by radioisotope scanning, CT, or MRI. Accelerated development of MRI and the initiallylow-resolution imaging capability of sonographymay have resulted in the underutilization of sonog-raphy for bone diseases. 1 However, MRI itself does not have the fine resolution of plain radiog-raphy or CT to define cortical abnormalities of bone. The use of sonography for evaluation of theskeletal system has been hampered by the mis-conception that the lack of propagation of ultra-sound through the bone and small field-of-viewimages are insurmountable obstacles to evaluatethe skeletal system, resulting in reduced use and a lack of literature on musculoskeletal sonography(MSUS). Nevertheless, the high reflectivity of sound at the bone–soft tissue interface and tomo-graphicnatureofsonographymake it idealforeval-uation of bone contours. 2 High-resolution sonog-raphy can reveal subtle changes of the bone surfacenot detected on plain radiographs, such as tinyperiosteal reactions and subperiosteal fluid collec-tions, and can differentiate soft tissue lesions frombone lesions (Figure 1).Using the extended-field-of-view function of MSUS, a large lesion can now be displayed on a single sonogram, 3–5 and the relationship of thelesion to adjacent anatomic structures can bedepicted with osseous and articular landmarks, asis possible on radiographs. Recent technologic im-provements in ultrasound scanning and increasedawareness of the advantages of sonography overother imaging modalities have led to a resurgencein interest. 6 Correlative imaging, however, remainsmandatory to avoid errors in interpretation. TECHNICAL CONSIDERATIONS The operator must have sufficient knowledge of regional bone and soft tissue anatomy, including normal anatomic variants, and be familiar withspecific sonography-related artifacts. In additionto MSUS findings, results from other imaging studies and laboratory tests should be consideredin making the diagnosis. Crucial information canbe obtained by history taking from the patients ortheir guardians, and by continued sonographic andphysical examination.In general, high-frequency (10–15-MHz) linear-array transducers are the most appropriate choicesfor MSUS allowing detailed depiction of pertinentanatomic structures. Using a stand off pad or thickapplicationofacousticcouplinggelontheskinishelp-ful for evaluating very superficial bones. Low-fre-quency (3–5-MHz) curved-array transducers havean advantage when the lesion is deep-seated in largeormuscularpatients,buttheresolutionisinferiortothatofhigh-frequencytransducers,andtheoperatorshouldidentifytheartifactualhypoechoicappearanceofthebonesurfaceoneachsideofthesectorimage. Correspondence to:  K.-H. Cho Grant Sponsor:  Yeungnam University Academic Fund  J Clin Ultrasound 32: 511–521, 2004; Published online in WileyInterScience(www.interscience.wiley.com).DOI:10.1002/jcu.20066   2004 Wiley Periodicals, Inc. VOL. 32, NO. 9, NOVEMBER/DECEMBER 2004  511  Scanning methods for bone are similar to theaccepted protocol for MSUS. 5–9 Examiners surveythesymptomaticareafirst,andthencompareitwiththe contralateral and usually asymptomatic side,helpingdifferentiateabnormalfromnormalfindings,avoiding diagnosis of normal variants as pathologicand occasionally revealing unsuspected abnormal-itiescrucialfordiagnosis(Figure2).ColorandpowerDoppler sonography show the vascularity associatedwith pathologic conditions and the relationshipbetweenlesionsandadjacentneurovascularbundles. NORMAL BONE The normal periosteum, a dense, fibrous connectivetissue,isadherenttothesurfaceofthebone,attachedby Sharpey’s fiber, and currently cannot be recog-nized as a separate structure sonographically. Thus,the term ‘‘bone surface’’ is applied to describe theregular hyperechoic line at the interface betweentheboneandsofttissues,producedbyastrongreflec-tionofsoundduetothemarkeddifferenceinacousticimpedance of the soft tissues and bone. The acousticshadow deep to the hyperechoic bone surface repre-sentsthenormalappearanceofthebone.Reverbera-tion artifacts projecting in the shadow beyond thebonecanbeseenonbothlongitudinalandtransversescans. 1,2,7–9 Therearesomepitfallsintheinterpretationofthesonographic appearance of the normal bone surface(Table 1). The growth plate in the immature skele-ton, the canals for perforating vessels or grooves fornutrient arteries, and accessory ossicles may appearasinterruptionsalongthecontinuityofthebonesur-face, mimicking fractures (Figure 3). The fascialthickening of the normal myelotendinous attach-mentsitesontothebonemayalsoresultinirregular-ityofthebonesurface. 2 Right-leftsidecomparisonof paired structures and supplementary dynamic eval-uation are very helpful MSUS maneuvers wheneverthere is doubt regarding the normal appearance. PATHOLOGIC CONDITIONS OF THE BONE Diseasedbonemaypresent,soonerorlater,asabonealteration, a consequential soft tissue change, orboth. MSUS can diagnose lesions directly by depict-ingbonesurfacechanges,whethercausedbyboneorperiosseous soft tissue disease, and indirectly bydemonstrating soft tissue changes in the case of  FIGURE 1.  Myositis ossificans in a 37-year-old woman after traumaabout 1 month previously.  (A)  Longitudinal sonogram of the anterioraspect of the proximal thigh shows the irregular hyperechoic line(arrows), with posterior acoustic shadowing in the muscle juxta-cortically. On dynamic examination, the calcific shadow could be dif-ferentiated from the cortical surface (arrowheads) of the femur, whichis visible deep to the calcific shadow.  (B)  Lateral radiograph of the rightthigh obtained 1 day before the sonographic examination shows noabnormality.  (C)  Lateral radiograph obtained 10 days later shows themultipennate calcific density (arrows) in the soft tissues. CHO ET AL 512  JOURNAL OF CLINICAL ULTRASOUND  bonediseasesthathaveaneffectontheadjacentsofttissues. 6–10 Bonesurfacechangescanbecategorizedsonogra-phically as follows: thinning or thickening of thehyperechoic line; interruption of the bone continu-ity, including a step-off deformity, expansion, orexcavation; periosteal reactions; and cortical dis-ruption, with visualization of intraosseous compo-nents. It is important to interpret sonographicallydocumented abnormalities of the bone surface inthe context of findings on plain radiographs. Cur-rently, sonography is unable to depict intraosseouschanges unless the cortex is sufficiently thinned ordestroyed. FIGURE2. A 64-year-old womanwith pain inthe lefthip for2weeks.Anteroposterior radiographs ofthe right  (A)  and left (B)  hipsshowthetransversesclerosis(arrow,B)attheleftfemoralneck.Anteriorlongitudinalsonogramsoftheright (C) andleft (D) hipsshowtheabruptinterruption(whitearrow,D) of the cortical continuity at the upper portion of the left femoral neck. The contralateral image (C) shows the normal bone surface, with continuity. (E)  Fat-suppressed T2-weighted coronal MR image shows the hypointense transverse fracture line (arrow) and bone marrow edema. SONOGRAPHY OF EXTREMITY BONES VOL. 32, NO. 9, NOVEMBER/DECEMBER 2004  513  Traumatic Lesions MSUS is not the first-line imaging modality whenbonetraumaissuspected.However,itisworthwhilefor detecting occult fractures that are not shownon radiographs, 11–18 as it may avoid more costlyMRI. 6,11 MSUS can detect rib fractures in 6 timesas many patients as radiography and will detect 10times more fractures overall. 13 It can uncover frac-tures coincidentally, while being used to examinesoft tissue, 14 and can be useful in further assessing fractures after initial radiography 19 (Figure 4).Sonographically guided monitoring during closedreduction of fractures has reportedly yielded resultscomparable to those obtained using a conventionalradiographic technique. 20,21  A fracture may be demonstrated sonograph-ically as an abrupt discontinuity of the bone sur-face, with or without a step-off deformity, anangular or buckle deformity of the cortex at thefracture site, hypoechoic subperiosteal blood col-lection, and overlying soft tissue edema, with orwithout a soft tissue injury (Figure 2 and 3). Whenpain,withorwithoutswelling,ispresentinnewbornsandchildrenaftersuspectedbonetrauma around a joint, findings on physical examinationareusually nonspecific and radiographs are commonlynondiagnosticbecausethenonossifiedepiphysesarenot visualized. 6,17,18,22–24 In this situation, MSUSmaybecome areliable substituteforthe plain radio-graphs in selected cases, 17,22 not only by visualizing the unossified cartilaginous bone, but also by corre-lating the symptoms and physical signs with sono-graphic findings (Figure 5). Tenderness or painelicited from a suspected lesion as the transducerpasses over it is known as positive ‘‘sonographicpalpation.’’Rotator cuff tears, arthritis, and rarely calcifictendinitis may cause periarticular bone erosion,which may reflect repetitive pressure, stress, ortraction force on the insertion site of tendons orlocal hyperemia due to inflammation. 25–27 Thesebone changes sometimes may have an MSUSappearance similar to that of fractures. Becausea stress fracture may be chronic, a focally thickhyperechoic callus commonly overlies the corticalinterruption at the fracture site, a finding thatmay contribute to diagnosis in conjunction withthe findings on radiographs.MSUScanbeusedtoassessfracturehealinginitsearlyphasebecauseradiographicfindingsareinsuf-ficient. The initial hypoechoic appearance of thefracture is replaced by the image of a hyperechoiccallus bridging the fracture gap; this hyperechoicregion progressively increases in volume as the cal-lus matures and casts a greater posterior shadow.Serial correlation of histologic findings with FIGURE 3.  Stress fracture in a 22-year-old man suffering from heel pain for 20 days.  (A)  T2-weighted sagittal MR image of the ankle shows thevertical fracture line (arrow) in the calcaneus. Longitudinal sonograms of the lateral aspect of the calcaneus show various features:  (B)  the step-off deformity (arrow) of the bone surface;  (C)  anteroinferior to the step-off deformity, another cortical disruption (arrowhead) is seen, whichcorresponds the canal (arrow) for a perforating vessel on color Doppler sonography  (D) . TABLE 1Common Pitfalls in Bone Sonography Pitfall Cause TechnicalartifactIncorrect position of transducerHeterogeneity by geometric relationshipMechanicalartifactAnisotropyAcoustic shadowing from fibrous septa or calcificationAnatomicfactorsPerforating canal or nutrient grooveFascial thickening at the attachment to the boneDiscontinuity at the growth plateSesamoidPatientfactorsObesity or large physiqueDeep-seated tumorLimited motion and improper posture CHO ET AL 514  JOURNAL OF CLINICAL ULTRASOUND  sonographic appearance in a healing fracture inhumanshasnotbeenpossiblebecauseitwouldbeun-ethical to biopsy the fracture site in patients who donothaveanycomplication. 28 Incanines,thepresenceofahyperechoicappearanceatafracturesitereport-edly represents neo-osteogenesis histologically. 29 OnserialMSUSexaminations,thenormalhealing processofafracturegoesthrough5stages:(1)initialsonolucency at the fracture gap; (2) progressiveincrease of dot-like hyperechoic foci at the fracturesite;(3)formationofapoorlydefinedechogenicbridgeacrossthefracturesite(probableprimarycallus);(4)prominence of a thin hyperechoic line at the super-ficialaspectoftheprimarycallusalongthelongaxisof thebone;and(5)developmentofathickhyperechoicregularlinecontinuouswiththeadjacentnormalcor-tex(probablesecondarycallus).ColorDopplersonog-raphy may demonstrate progressive formation of new vessels at the site of the developing callus untilabout 100 days after surgery, from which time flowsignals decrease and bone remodeling continues. 2,30 The resistance index tends to decrease in the earlyweeksaftersurgeryandthenincreaseslightlyastibialfractures heal. In contrast, a lack of development of flowsignalsandpersistenceofahighresistanceindexisobservedwhenfracturehealingisdelayed.Osteochondral injury can be evaluated sonogra-phically by assessing the subchondral bone andoverlying cartilage simultaneously. 31 However, theintra-articular deep portion is difficult to examine. MSUS in Patients with Orthopedic MetallicImplants/Hardware MSUS has potential value stemming from itsabilitytodemonstratenewboneformationandmeasurethedistraction gap in patients who undergo Ilizarovlimb-lengthening procedures. MSUS can demon- FIGURE 4.  A 40-year-old man complaining of ankle pain for 6 monthsafter treatment of multiple fractures of the tibia and foot. Radio-graphs of the ankle obtained over the previous 6 months (not shown)were unremarkable.  (A)  Coronal T2-weighted MR image shows asmall amount of low-signal material (arrow) between the lateralmalleolus (L)and lateralaspect of the talus (T).  (B)  Sonogram obtainedalong the intact anterior talofibular ligament (small arrows) showsthe curved echogenic line (thick arrow) with posterior shadowing.This line was surgically confirmed to correspond to a bone fragment.After surgical removal of the fragment, the ankle pain was relieved. FIGURE 5.  A 2-year-old girl refusing to use her right arm.  (A)  Obliqueradiograph of the right elbow shows the equivocal curvilinear densearea (arrow) in the lateral condyle of the distal humerus.  (B)  Laterallongitudinal sonogram of the right elbow shows the focal corticaldisruption (small arrow) at the distal end of the metaphysis, periostealelevation (arrowhead), and separation (large arrow) of the meta-epiphyseal junction.  (C)  Contralateral asymptomatic left elbow showsintact bone surface and the junction between the metaphysis (M) andepiphysis (E) of the distal humerus. SONOGRAPHY OF EXTREMITY BONES VOL. 32, NO. 9, NOVEMBER/DECEMBER 2004  515
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