ultrasound of the hindfoot and...

Ultrasound of theHindfoot and Midfoot
David P. Fessell, MDa,*, Jon A. Jacobson, MDb
KEYWORDS� Ultrasound � Hindfoot � Midfoot � Ankle � Tendons� Ligaments � Masses

Ultrasound (US) is increasingly being used toevaluate musculoskeletal disorders, includingfoot and ankle pathology.1–5 Higher frequencytransducers and technical advances in recentyears have resulted in a higher spatial resolutionfor sonography compared with MR imaging.6

Cost saving with US can also be considerable. Inmany cases the professional and technical costof an US is approximately 80% less than an MRimage of the same anatomy.7 US has the uniquecapacity to allow evaluation during dynamicmaneuvers which can reveal abnormalities thatare not apparent during static imaging. The advan-tages of an imaging modality that allows visualiza-tion during dynamic maneuvers will be highlightedthroughout this article. Additional advantages ofUS include imaging of patients who cannot un-dergo MR imaging due to pacemakers, hardware,or claustrophobia; direct and real-time evaluationof the site of pain or symptoms with additionalhistory immediately available; flexibility in thefield-of-view; ease of contralateral comparison;use of Doppler; and ease of guiding procedures.8

Disadvantages of US include the learning curveand operator dependence. These disadvantagescan be addressed by the simple application oftime and effort.

Specialties such as Physical Medicine andRehabilitation, Rheumatology, and EmergencyMedicine are increasingly using US to evaluatemusculoskeletal disorders.9–13 Radiologists, whohave years of training in anatomy, pathology, USphysics, artifacts, and technical aspects of US im-aging, are uniquely suited to apply this versatilemodality to foot and ankle pathology. If

a Department of Radiology, University of Michigan HospiTaubman Center, Room 2910Q, Ann Arbor, MI 48109-532b University of Michigan, 1500 E. Medical Center Drive,* Corresponding author.E-mail address: [email protected] (D.P. Fessell).

Radiol Clin N Am 46 (2008) 1027–1043doi:10.1016/j.rcl.2008.08.0060033-8389/08/$ – see front matter ª 2008 published by E

radiologists are not able to perform musculoskele-tal US with great expertise, this business will betaken over by other specialties. If musculoskeletalUS is lost, additional modalities such as MR imag-ing may be lost as well. It is imperative that radiol-ogists continue to be experts in all aspects ofmusculoskeletal imaging, including US.

The technique for examining the hindfoot andmidfoot with US has been described and depictedmany recent articles2,5 and will not be discussed.In this article, normal US anatomy will be shownin all cases before demonstrating the full range ofhindfoot and midfoot pathology. Color and powerDoppler can aid diagnosis by demonstratingneovascularity in cases of inflammation or fibrosisand will also be discussed.

HINDFOOTANDMIDFOOT TENDONS: GENERALCOMMENTS

Tendon pathology of the hindfoot and midfoot canbe difficult to diagnose. In the acute setting, painand swelling can limit the physical examination.In the setting of chronic injury it may not be possi-ble to differentiate tendon, ligament, or osseouspathology solely on the basis of the physical ex-amination. US is well tolerated in both the acuteand chronic settings. Real-time correlation withthe site of pain and symptoms aids diagnosisand is a strength of US. Numerous studies havedocumented the accuracy of US for detectingtendon pathology14–19 and these studies will bediscussed in each tendon section below. US isnot limited to three orthogonal planes, as is MRimaging, and is not subject to magic angle artifact,

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which can limit MR evaluation as the tendonscurve along their course. Anisotropy is one artifactwhich can be seen with US when the transducer isnot oriented parallel to the structure being evalu-ated (Fig. 1). However, this artifact is easilyavoided by rocking the transducer back and forthto alternately show a normal and anisotropic ten-don. Normal ankle tendons are round or ovoid inthe transverse plane with a speckled, hyperechoicappearance. In the longitudinal plane they demon-strate a fibrillar pattern or echogenic lines. Thisclassic tendon echo signature is seen in all ten-dons of the body.

Hindfoot and midfoot tendon pathology is mostoften due to one or more of the following entities:tenosynovitis, tendinosis, and tendon tear. Sub-luxation and tendon dislocation are also possible,most commonly with the peroneal tendons. Tendi-nosis is seen as tendon thickening and may showdiffuse or more focal regions of hypoechogenicityand loss of the normal fibrillar echotexture.1 Aswith MR imaging, with sonography it may be diffi-cult to distinguish tendinosis from low-gradepartial thickness tear in some cases. The more se-vere the tendon thickening and echogenicityalteration, the more likely partial tear is present.20

Tenosynovitis is noted as increased fluid distend-ing a tendon sheath, with or without hypervascular

Fig. 1. (A) Longitudinal US of a normal Achilles tendon (aHypoechogenicity consistent with anisotropy is noted atangulation of the transducer ‘‘fills-in’’ the hypoechoic regiothe normal Achilles tendon. (C) Transverse US of a normalappearance of the normal tendon.

synovium surrounding the tendon. In the setting ofan acute or subacute tendon tear, tenosynovitis isusually present and increases the conspicuity ofa tear. Tenosynovitis may not be present in casesof chronic tendon tears. Normal fluid, in the rangeof 1 to 3 mm, can often be seen partiallysurrounding the tibialis posterior tendon, flexordigitorum longus, and flexor hallucis longus ten-dons. Such normal fluid is usually located in thedependent portion of the tendon sheath and atthe level of the medial and lateral malleoli.21

Partial-thickness tears can be in the longitudinalplane (‘‘longitudinal-type split’’) or in the transverseplane. Longitudinal splits are the more commontype affecting the peroneal tendons and are notuncommonly seen affecting the tibialis posteriortendon as well.17,22,23 Partial-thickness tears ap-pear as a linear and in some cases globular regionof hypoechogenicity, without evidence of retrac-tion of the tendon.16,17 The transverse plane usu-ally provides the most optimal depiction ofpartial-thickness tears. Complete tendon ruptureis seen as complete fiber disruption in the longitu-dinal plane, often with retraction of the torn tendonmargins and absence of the tendon at the level ofthe defect in the transverse plane. Fluid, debris,and hematoma are often noted in the tendon gapin the setting of an acute tear, with hypoechoic

rrows) shows the fibrillar appearance of the tendon.the insertion on the calcaneus (arrowhead). (B) Slightn (arrowhead), confirming anisotropy. Arrows denote

Achilles tendon (arrows) shows the echogenic, fibrillar

Ultrasound of the Hindfoot and Midfoot 1029

granulation or scar tissue seen at this site in thesetting of more chronic tears.

ACHILLES TENDON

Though the Achilles tendon is the strongest tendonin the body, it is also one of the most frequentlyinjured. Often such injuries are sports related,a fitting irony given that the tendon’s name isderived from the great Greek warrior, Achilles.4,24

The Achilles is also unique because it issurrounded by a paratenon, a thin vascular mem-brane, rather than a synovial sheath as is seensurrounding the other ankle tendons. Thereforenormal fluid is never seen adjacent to the Achillestendon.21 A spectrum of pathology can affect theAchilles tendon, ranging from acute or chronicperitendinitis, tendinosis, partial tears, and com-plete rupture. Tears usually occur in a relativelyavascular zone located 2 to 6 cm above the calca-neal insertion, and less commonly at the insertionon the calcaneus.4

Numerous reports have used US to assess theAchilles tendon for peritendinitis, tendinosis, andtears.15,20,25 Peritendinitis is demonstrated as ill-defined tendon margins with or without associ-ated fluid and tendinosis (Fig. 2).26 Tendinosiscan be diffuse or focal and appears as hypoecho-genicity with tendon thickening, usually with a fusi-form-appearing tendon in the longitudinal plane(see Fig. 2).20,27 In the transverse plane, tendino-sis may manifest as loss of the normal anteriorconcavity. Tendon calcifications may also beseen with tendinosis, both by US and

Fig. 2. (A) Longitudinal US of the distal Achilles tendon to tis hypoechoic and enlarged (arrow) consistent with tendishows hyperemia (arrows) of the Achilles tendon (betweof the hyperemic region of tendinosis with comparison toof tendinosis (black arrows) demonstrates thickening anarrows). (D) Longitudinal US of an Achilles tendon withThe hypoechoic regions demonstrate hyperemia, consiste

radiography.4 Partial-thickness tears of the Achil-les tendon can be diagnosed by a well-defined an-echoic or hypoechoic cleft affecting less than thecomplete cross section of the tendon. As withMR imaging, US may have difficulty distinguishingtendinosis from low- or moderate-grade partialtears; however, all of these entities are usuallytreated nonoperatively.15 High-grade partial tearsinvolving more than 50% of the tendon thicknessand complete ruptures may be treated operativelyor nonoperatively depending on the surgeon andclinical circumstances. Nonoperative treatmentof complete ruptures is advocated by somesurgeons, especially when the torn tendon endsare approximated or are less than 1 cm separatedin plantar flexion (Fig. 3). Dynamic evaluation indorsiflexion and plantar flexion can be easilyperformed with US and can directly impact patientmanagement and outcome. Power Doppler evalu-ation showing hyperemia and neovascularizationhas been shown to correlate with pain severitybut not with clinical outcome.27

Acute Achilles tendon rupture may be obviousby clinical examination, however it has beenreported as missed in more than 20% of cases,likely due to pain and swelling limiting the clinicalexamination.15 The gap between the torn tendonends is often filled with hematoma and debris inthe acute setting; and scar or fibrous tissuein more chronic cases.4 An additional dynamicmaneuver, the sonographic Thompson sign, canalso be helpful. The calf is gently squeezed asthe Achilles tendon is assessed for synchronoustendon movement from proximal to distal. With

he insertion on the calcaneus (arrowhead). The tendonnosis. (B) Longitudinal US of the region of tendinosisen the arrowheads). (C) Split-screen longitudinal USthe contralateral normal Achilles tendon. The region

d hypernemia compared to the opposite side (whitehypoechogenicity (arrows) adjacent to the Achilles.

nt with peritendinitis.

Fig. 3. (A) Longitudinal US of a ruptured Achilles tendon during plantar flexion shows less than 1 cm of separationbetween the torn tendon ends. The patient was successfully treated with casting in plantar flexion. (B) Samepatient with longitudinal scanning in dorsiflexion shows increased separation and better delineation of thecomplete tendon rupture.


a complete tear, the proximal torn tendon end willretract proximally but the distal portion of the tornend will not.4 The foot may also be manuallymoved from slight dorsiflexion to plantarflexionas an alternate method to show separation oftorn tendon ends. Additional helpful signs ofa complete tear are herniation of Kager’s fat intothe site of a tear (Fig. 4), refraction artifact (poste-rior acoustic shadowing) at the site of torn tendonends (Fig. 5), and ease in visualizing the plantaristendon, which is located medially and may herni-ate into the site of the tendon tear (Fig. 6).15 Anintact plantaris tendon, in the setting of a completeAchilles rupture, should not be mistaken for intactAchilles tendon fibers. Knowledge of the normalanatomy and awareness of this potential pitfallwill prevent misdiagnosis.28 It is also important toassess and report the presence and condition ofthe plantaris tendon since it may be harvestedand used to help reinforce a surgical repair of theAchilles tendon.29

The retrocalcaneal bursa is located between thedistal Achilles tendon and posterosuperior calca-neal tuberosity. The bursa is reportedly visible in50% of normal ankles and may contain traceamounts of physiologic fluid, usually less than3 mm in anteroposterior dimension.21 This physio-logic fluid can be unilateral or asymmetric with thecontralateral ankle. Distention of the bursa is con-sistent with retrocalcaneal bursitis (Fig. 7), whichmay be isolated or seen with rheumatoid arthritis,

Reiter’s disease, or other seronegative arthritides.Retrocalcaneal bursitis can also be seen with Achil-les tendon pathology and with Haglund’s syn-drome.30 Much less commonly seen is retroAchilles or infracalcaneal bursitis which is locatedposterior to the Achilles tendon and may be seenin association with Haglund’s syndrome (Fig. 8).

PERONEALTENDONS

In experienced hands, US is highly accurate for im-aging peroneal tendon tears and can be used asthe first imaging test. A sensitivity of 100%, spec-ificity of 85%, and accuracy of 90% is reported inthe orthopedic literature, in comparison to surgicalfindings.17 Tears of the peroneal tendons areusually of the longitudinal split type, with completeruptures much less common. The peroneus brevisis more commonly affected, be it by tear, tenosyn-ovitis, or tendinosis.17,31 This is likely due to itslocation between the peroneus longus and thefibula, which allows the tendon to be pinchedbetween these two structures. Longitudinal splitsmay be acute (most frequently in young patients),or chronic (most commonly in the elderly popula-tion). Chronic splits may be asymptomatic.32 Pero-neal splits and tears are usually located at the levelof the retromalleolar groove and are morefrequently, but not exclusively, associated withinjury to the superior peroneal retinaculum.33,34

The axial plane is usually ideal for visualizing

Fig. 4. Longitudinal US ofa complete rupture of theAchilles tendon with 2.6 cm ofseparation between the torntendon ends and herniationof echogenic Kager’s fat intothe site of the tear (dottedline between the crosses).Calc, calcaneus.

Fig. 5. Longitudinal US of the Achilles tendon witha complete rupture noted between the proximal ten-don end (single arrowhead) and distal tendon end(double arrowhead). Refraction artifact is noteddeep to the torn tendon ends (arrows).

Fig.7. Longitudinal US shows an intact Achilles tendon(thin arrows) to its insertion on the calcaneus (arrow-head). The retrocalcaneal bursa is distended and con-tains debris (thick arrows).


longitudinal splits as an anechoic or hypoechoiccleft (Fig. 9). The peroneus longus tendon often in-sinuates into the split, preventing healing.4

As with MR imaging, peroneal tears are moreeasily visualized when fluid is present distendingthe tendon sheath, as is usually present in the set-ting of an acute tear.4 A potential pitfall that canmimic a peroneal split is the peroneus quartus.

Fig. 6. (A) Longitudinal US of a complete rupture ofthe Achilles tendon. The five small arrowheads de-note the proximal tendon end and the four small ar-rowheads denote debris at the site of the tendontear. The intact plantaris tendon is noted extendingthrough the site of the Achilles tear (arrows). (B)Transverse US at the site of the complete Achilles rup-ture demonstrates the plantaris tendon (arrow) anddebris at the site of the Achilles tear (arrowhead).

This accessory tendon, present in 10% to 20%of individuals, has a variable composition atits insertion, ranging from 100% tendon topredominately or completely muscle. It can be dif-ferentiated from a peroneal split by scanning to itsdistal insertion, usually onto the lateral aspect ofthe calcaneus (Fig. 10).28,34

A tear of the peroneus longus can occur in con-junction with a tear of the brevis, or in isolation.31

Tears of the peroneus longus can occur at the levelof the lateral malleolus, at the level of the os pero-neum or cuboid groove, or at the level of the mid-foot.4 The os peroneum is located within theperoneus longus tendon. When the ossicle frac-tures and significantly separates or displaces, theresult is usually equivalent to a rupture of the per-oneus longus, with retraction of the proximal por-tion of the fractured os, and often associatedperoneal tendon tears.35

While tenosynovitis and tendinosis are more com-mon than tendon tears, these entities usually do notrequire surgical treatment.4 Tenosynovitis is notedas fluid which completely surrounds the peronealtendons, while normal fluid is smaller in amount, de-pendently located, and not circumferential.21 Pero-neal tenosynovitis is more common in the athleticpopulation, in acute inversion injuries, and ankle

Fig. 8. Longitudinal US shows an intact Achilles ten-don (black arrows) to its insertion on the calcaneus(arrowheads). The retro-Achilles bursa is distendedand contains debris (region within the ellipse).

Fig. 9. (A) Transverse US shows a longitudinal split in the peroneus brevis tendon creating two separate portionsof the brevis (arrow) at the level of the lateral malleolus. (B) Transverse US from a different patient showsa longitudinal split (thick arrow) in the peroneus brevis tendon (thin arrows) at the level of the lateral malleolus(arrowhead). (C) Transverse US from a different patient shows marked enlargement and internal hypoechogenic-ity of the peroneus brevis tendon (arrow) with surrounding tenosynovitis (arrowhead). L, peroneus longustendon.


instability.4,36 If peroneal tenosynovitis is identified,special care should be taken to examine the calca-neofibular ligament, since injury to this ligamentcan permit pathologic communication of joint fluidinto the peroneal tendon sheath.4

Several factors have been reported to predis-pose to peroneal tendon pathology, including an-atomic variants such as a peroneus quartusmuscle or low-lying peroneal muscle belly.Such variants may cause crowding of the pero-neal tendons and promote subluxation. Likewisea flat or convex (rather than concave) retromal-leolar groove can also promote subluxation. Hy-pertrophy of the calcaneal peroneal tubercle orretrotrochlear eminence can abrade the peronealtendons. Acquired conditions can also predis-pose to peroneal pathology, the most commonbeing injury to the superior peroneal retinacu-lum.34 Additional factors predisposing to pero-neal pathology include tarsal coalition,hardware such as orthopedic screws impingingupon the tendons (Fig. 11), and fibular or calca-neal osseous spurs.4,37

SUBLUXATION AND DISLOCATIONOF THE PERONEALTENDONS

The peroneal tendons may partially displace (sub-luxate) or completely displace (dislocate) fromtheir normal position posterior to the fibula. Inmost cases such abnormal tendon movementoccurs intermittently and is not directly visualizedby static MR imaging. Only dynamic US candirectly visualize the tendons as they subluxateor dislocate laterally and anteriorly over the lateralmalleolus. Such subluxation or dislocation is mostoften posttraumatic, due to dorsiflexion and ever-sion injury. Typically the superior peroneal retinac-ulum is injured, allowing recurrent dislocation andleading to tendinosis and tendon tear. Dynamicevaluation of the peroneal tendons adds onlya few seconds to the standard ankle US examina-tion. The probe is placed transverse to the ten-dons, at the level of the retromalleolar grooveand the foot is dorsiflexed and everted.23 The bre-vis more commonly dislocates, although one orboth of the peroneal tendons can dislocate(Fig. 12).3,4,23

Fig.10. (A) Longitudinal US shows a peroneus quartus tendon (arrow) deep to the peroneus brevis tendon (arrow-head). Surrounding tenosynovitis is noted. (B) Longitudinal scanning more distally shows the insertion of theperoneus quartus on to the lateral aspect of the calcaneus (arrow) with the peroneus brevis noted more super-ficially (arrowhead). (C) Transverse US shows the peroneus quartus (thick arrow) deep to the brevis (arrowhead).The peroneus longus is denoted by the thin arrow. Note tenosynovitis.


The peroneal tendons can also remain behindthe fibula, in the retromalleolar groove, buttransiently ‘‘switch’’ positions during inversionand eversion (Fig. 13). This entity has been termed‘‘retromalleolar intrasheath subluxation.’’ It maybe symptomatic and surgically treated, or asymp-tomatic.23 This entity again requires a dynamic im-aging modality which, for all practical purposes, isonly possible with US.

Fig.11. (A) Lateral radiograph shows multiple screws and afibula (arrow). (B) Transverse US at the level of the lateralportions of the peroneus brevis (thin white arrows) adjacehead denotes a small amount of fluid adjacent to the per

MEDIALTENDONS

The posterior tibialis tendon (PTT) is also a com-monly injured tendon. It serves as a primary in-verter of the foot and is an important componentof the medial longitudinal arch. When the PTT isruptured or injured, flatfoot deformity can result.Rupture is, however, less common than tendinosisand partial tears. PTT pathology often begins astenosynovitis, followed by partial tear and then

fibular plate extending posterior to the cortex of thefibular plate shows a split (open arrow) creating twont to the fibular plate (thick white arrow). The arrow-oneus longus tendon.

Fig.12. (A) Transverse US shows the peroneal normal peroneal tendons (arrow) posterior to the distal fibula. As-terisk denotes the lateral aspect of the fibula. (B) Transverse US shows the peroneus longus (arrow) dislocatedlateral to the fibula (asterisk) when the ankle is dorsiflexed and everted. Note detached superior peroneal reti-naculum (arrowhead). LM, lateral malleolus.


complete rupture. Early diagnosis and treatment isthe key to preventing severe disability.38 The accu-racy of US for detecting PTT abnormalities is com-parable to MR imaging.16,18,19,39 The os tibialeexternum or os naviculare has been reported tobe associated with PTT pathology. This is likelydue to mechanical strain from altered tendonmechanics.40

As with the peroneal tendons, most pathologyinvolving the PTT is at the level of the malleolus(Fig. 14). Less commonly, pathology is at the levelof the navicular insertion since the tendon has mul-tiple strong slips that fan out and insert broadlyover the navicular and plantar aspect of the tarsalbones. Dislocation of the PTT is extremely rare.41

A unique feature of US is the ability to identify smallspurs or cortical irregularity in the medial malleolargroove (Fig. 15). Such spurs can abrade the ten-don and can be a difficult diagnosis with MR imag-ing or CT due to their small size and low signal on

Fig.13. (A) Transverse US shows the peroneal tendons in thtion. Curved arrow denotes the direction the peroneus lonof the fibular groove. (B) When the ankle is dorsiflexedadjacent to the fibular cortex (arrows). L, peroneus longu

MR imaging. With US, direct sonographic and clin-ical correlation is available for pain or symptomsrelated to a possible tendon abnormality. Normallythe axial diameter of the posterior tibial tendon isapproximately twice that of the flexor digitorumlongus (FDL) tendon.4 This ‘‘rule of thumb’’ allowsquick assessment of tendon thickening, as seenwith tendinosis, or the thinning that can be seenin some partial tears.

A potential pitfall can occur with a complete rup-ture of the PTT. In this setting the FDL may be dis-placed anteriorly and potentially be confused withan intact PTT.28 Making note that each individualtendon is located in its normal position preventsthis potential pitfall. The PTT normally has multipleslips at its navicular and plantar insertion andthese should not be mistaken for a longitudinalsplit. The tendon normally curves as it inserts,and in this region it may look artifactually hypoe-choic due to anisotropy. Again, direct correlation

eir normal location when the ankle is in neutral posi-gus will move to result in (B). Arrows denote the cortexand everted, the peroneus longus moves anteriorly,

s.

Fig.14. (A) Transverse US shows the tibialis posterior tendon (arrowhead) with a hypoechoic region extending tothe deep surface of the tendon (arrow). (B) Longitudinal US of the posterior tibial tendon (between the arrows)shows a corresponding linear region of hypoechogenicity. Findings are consistent with a longitudinal split of thetibialis posterior tendon.


with symptoms during scanning of this region aidscorrect diagnosis.4

While pathology of the FDL is extremely rare, pa-thology affecting the flexor hallucis longus (FHL)can be seen, especially in individuals involved inballet, soccer, or basketball.4 Friction injuries canaffect the FHL as it courses beneath the

Fig.15. (A) Transverse US of the tibialis posterior tendon shothe tendon (thick arrow) with a spur at the anterior aspecgitudinal US of the tibialis posterior tendon shows a corrconsistent with a longitudinal split. Arrowhead denotes thdemonstrates the osseous spur (arrow) at the anterior asp

sustentaculum tali and through the fibro osseoustarsal tunnel. Tenosynovitis, stenosing tenosynovi-tis, and tendinosis can result.4 An os trigonum andadjacent osseous spurs have been reported to bepredisposing factors for FHL pathology. The depthof the FHL can make sonographic evaluation chal-lenging; however, dynamic maneuvers such as

ws a hypoechoic region along the superficial aspect oft of the medial malleolar groove (thin arrow). (B) Lon-esponding linear region of hypoechogenicity (arrow)e medial malleolus. (C) Axial CT in soft tissue windowsect of the tibialis posterior tendon (arrowhead).


actively or passively flexing the great toe can aid inidentification and evaluation.4

ANTERIOR TENDONS

The anterior tendons are the least commonlyinvolved by pathology compared with the medial,lateral, and Achilles tendons. Of the three extensortendons, the tibialis anterior tendon (ATT) is themost commonly involved by pathology. Thoughtears of the ATT are uncommon, they classicallypresent with a history of ‘‘mass’’ and evaluation re-veals not a mass but rather a torn and retractedtendon (Fig. 16). ATT tears typically occur within3 cm of its insertion.42 Causes of ATT injury includeabrasion by impinging osteophytes from the firsttarsal metatarsal joint or talonavicular joint, orfrom impinging hardware after surgery.42,43 Im-pingement may only be noted during dynamic ma-neuvers such as plantar flexion. US is well suitedfor such dynamic evaluation. Tendon lacerationcan occur from penetrating trauma and very rarelyfrom fracture.44 Discontinuity of the tendon fibersand retraction of the torn tendon ends are notedwith US when an ATT rupture is present. A longitu-dinal ‘‘split’’ of the distal ATT has been noted onMR imaging in asymptomatic volunteers and maybe a normal variant as the tendon inserts, similarto the PPT insertion onto the navicular and plantarmidfoot.42

Tendinosis of the anterior tibial tendon is notedas thickening of the tendon less than or equal to5 mm at the level of the tarsal bones.42 Pathology

Fig.16. (A) Longitudinal split screen US of the normal rightleft (L) tibialis anterior tendon (arrow). (B) Transverse split(arrowhead) and ruptured left tibialis anterior tendon (ar

of the extensor hallucis longus and extensor digi-torum longus tendons is less common, comparedwith the ATT and has been described secondary toill-fitting shoes or impinging osteophytes. The ex-tensor digitorum longus tendon may be abradedby an osseous ridge at the dorsal aspect of thetalus.37 This can also be the site of a ganglioncyst (see Masses below).

LIGAMENTS

Injury to ankle ligaments is by far the most com-mon type of ankle pathology. A traumatic inversionforce is the typical mechanism of injury. The lateralligaments are most frequently torn; among thecomponents of the lateral collateral ligament com-plex, the anterior taloficular ligament is most com-monly torn. In most cases, ankle ligament rupturescan be diagnosed with high accuracy by physicalexamination alone.45 In acute cases with equivocaldiagnosis, or in chronic cases with persistentsymptoms, US can play a role. In some casessurgical treatment may be needed, with recon-struction of the ligaments to stabilize the ankleand restore pain-free function.4

Normal ankle ligaments have a fibrillar echotex-ture and are sharply marginated, (Fig. 17).46 An-isotropy can be seen with ankle ligaments. Aswith tendon imaging, this potential artifact isavoided by scanning with the ultrasound beamperpendicular to the ligament. Mild sprain is notedas slight thickening or loss of the normally fibrillarechotexture (Fig. 18). With partial tear there is

(R) tibialis anterior tendon (arrowhead) and rupturedscreen US of the normal right tibialis anterior tendonrow).

Fig.17. Longitudinal US of the normal anterior talofib-ular ligament (arrowhead). The normal ligament isechogenic and of uniform thickness. F, fibula. Fig. 19. Longitudinal US of an acutely ruptured ante-

rior talofibular ligament. Thick arrow denotes thesite of rupture, at the talar attachment with surround-ing hematoma. Thin arrows denote the more normalportion of the ligament at its fibular attachment.Fib, fibula.


discontinuity of the ligament but it remains tautwith dynamic maneuvers that place the ligamentunder tension. With complete tear, a hypoechoicgap is noted and the ligament fibers do notbecome taut with any maneuver (Fig. 19).47 Osse-ous avulsion at a ligament attachment site denotesa severe ligament injury.47 Chronic tears that haveundergone scarring may demonstrate thickeningof the ligament. Ossification may also be notedwithin such ligaments.4 Using a 13-MHz trans-ducer, the reported sonographic accuracy forevaluating the status of the anterior talofibular lig-ament is 90% to100%; calcaneofibular ligament,87% to 92%; and anterior tibiofibular ligament,85% when compared with MR imaging.46

When the anterior talofibular ligament is injured,the calcaneofibular ligament should be carefullyassessed since sequential injury of the lateral liga-ments, from anterior to posterior, is almost alwaysthe norm. The anterior talofibular ligament is ex-amined dynamically during plantar flexion andduring inversion stress, or using the anteriordrawer test.4 Lateral talar process fracture canalso be assessed when scanning the anterior talo-fibular ligament by sweeping the probe clockwiseto assess the lateral aspect of the talus.48 Thecalcaneofibular ligament can be examined

Fig. 18. Longitudinal US of a hypoechoic and thick-ened anterior talofibular ligament (arrows) consistentwith sprain. F, fibula; T, talus.

dynamically during dorsiflexion with inversion.The peroneal tendons are located immediately su-perficial to the calcaneofibular ligament (Fig. 20).As noted previously, fluid in the peroneal tendonsheath should prompt careful assessment of thecalcaneofibular ligament since ligament injurycan allow communication with the peroneal ten-don sheath. Visualization of the proximal attach-ment of the calcaneofibular ligament may belimited by sonography secondary to its positiondeep to the lateral malleolus.4

The anterior tibiofibular ligament is injured incases of ‘‘high ankle sprain.’’ For dynamic imag-ing, the ankle is placed in dorsiflexion and varus.4

The deltoid ligament is much less commonlyinjured but can be examined dynamically with dor-siflexion and eversion stress (Fig. 21).46 If acutedeltoid ligament injury is suspected, the lateralmalleolus should be assessed for associated frac-ture and the anterior tibiofibular ligament for asso-ciated injury.47

ANKLE JOINT PATHOLOGY

US is well suited for rapid evaluation of joint fluidand can also guide aspiration.49 It has beenreported that static US can detect as little as2 mL of ankle fluid, versus 1 mL for MR imagingof the ankle.50 Dynamic maneuvers, such as scan-ning during dorsiflexion and plantar flexion may aiddetection of smaller amounts of fluid. Simple jointfluid appears as anechoic distention of theanterior joint capsule (Fig. 22). More complex jointfluid may appear sonographically similar to synovi-tis. Dynamic maneuvers, including scanningduring dorsiflexion and plantar flexion and duringcompression of the joint capsule by the

Fig. 20. Longitudinal split screen US of a patient with a normal left calcaneofibular ligament (arrows) and a rup-tured right calcaneofibular ligament (arrows). Note the calcaneofibular ligament is located immediately deep tothe round, echogenic peroneal tendons.


transducer, can aid evaluation. With dynamic ma-neuvers, collapse of the joint capsule and visuali-zation of swirling hypoechoic fluid, and jointrecess compressibility favors complex joint fluidrather than synovitis. If the complex intra-articularregion demonstrates internal flow on Doppler eval-uation, the findings are consistent with synovitis oran intra-articular mass such as pigmented villo-nodular synovitis. Intra-articular bodies can beaccurately detected with US and appear as hyper-echoic foci, usually with surrounding fluid. Thesonographic sensitivity and specificity for detec-tion of intra-articular bodies has been reported tobe 100% and 95% respectively.51

PLANTAR FASCIITIS

While plantar fasciitis is often diagnosed clinically,US can be helpful, especially in chronic cases orthose recalcitrant to conservative therapies. Plan-tar fasciitis is the most common cause of heel painand can be found in young athletes as well asobese and elderly patients.4,52 The reported sensi-tivity and specificity of sonography is 80% and89% compared with MR imaging.53 The high prev-alence of this condition, combined with the

Fig. 21. (A) Longitudinal US of a normal deltoid ligament (adial malleolus to the talus. (B) Longitudinal US of a torn dfrom the talar insertion (arrow). M, medial malleolus; T, t

expense of MR imaging, may favor US imagingin many cases.

The normal plantar fascia appears as a fibrillarband measuring 3 to 4 mm in thickness. With plan-tar fasciitis, fascia is hypoechoic and greater than5 mm in thickness at the calcaneal attachment(Fig. 23).54,55

Rupture of the plantar fascia is much less com-mon but occurs in a similar patient population.4

Location of these entities is different, with fasciitisat the calcaneal attachment and plantar fascialruptures at the proximal or middle portion of thefascia. Acute fascial tears are noted as disruptionof the fibers with surrounding or intervening fluid.The plantar fascia can be dynamically assessedby extending the toes dorsally, potentially aidingconspicuity of fascial tears.4 The differential diag-nosis of plantar heel pain also includes a foreignbody, which is well assessed with US (see foreignbodies below).

MASSES

US can diagnostically evaluate the most commonankle masses, such as a ganglion cyst, nervesheath tumor, abscess, and aneurysm; and aid

rrows) with components noted coursing from the me-eltoid ligament with wavy, echogenic fibers retractedalus.

Fig. 22. (A) Longitudinal US of a normal anterior tibiotalar joint without detectable fluid. Arrows denote the hy-poechoic cartilage of the talus. Tal, talus; Tib, tibia. (B) Longitudinal US of a joint effusion at the anterior tibio-talar joint (arrows). Note Doppler flow in the more superficial dorsalis pedis artery.


diagnosis of other masses. Specific features whichaid diagnosis of a mass include location, relation-ship to adjacent vessels, nerves, joints and ten-dons, internal blood flow with Doppler evaluation,and compressibility.43 Dynamic evaluation duringjoint motion can also be helpful in some cases,such as differentiating joint fluid, which moveswith joint motion, from an adjacent ganglion whichdoes not.

Ganglion cysts are often multiloculated and myhave internal septations. A neck or communicationwith an adjacent tendon sheath or joint may be seenand should be searched for diligently to aid surgicalresection. Ganglia can be anechoic or, in somecases, hypoechoic and may contain internal debris(Fig. 24).56,57 They are well defined, with no internalDoppler flow.56,58 An adventitial ‘‘medial malleolarbursa’’ can be seen at the medial malleolus, mostcommonly seen in ice skaters or hockey players,and thought to be due to poorly fitting footwear.59

Infection of the soft tissues of the hindfoot andmidfoot ranges from cellulitis to abscess. Subcu-taneous edema is noted as a reticular pattern ofhypoechogenicity in the subcutaneous tissues.

Fig. 23. (A) Longitudinal US of the normal plantar fascia (plantar fascitis shows the hypoechoic and thickened plant

Clinical correlation is required to separate edemafrom cellulitis. Soft tissue gas can be seen withan infectious process, sinus tract, or secondaryto surgery or intervention. Gas is noted as a focusof hyperechogenicity which may also show comet-tail artifact.43 An abscess can appear hyperechoicor hypoechoic, often with an echogenic rim andoverlying skin thickening. An abscess may demon-strate surrounding hyperemia but does not haveinternal Doppler flow. Swirling of complex fluidmay be seen with transducer pressure. US canalso aid aspiration.49

Nerve sheath tumors appear as a well-definedfusiform mass, with hypoechoic or mixed echo-genicity. They may demonstrate internal hyper-emia. Schwannomas and neurofibromas mayexhibit a sonographic ‘‘target sign’’ with centralhypoechogenicity and peripheral hypoechogenic-ity.58 An entering or exiting nerve is a key dis-criminator and can separate a nerve sheathtumor from other more nonspecific masses.

Lipomas can have characteristic US imagingfeatures including a well-defined ovoid shapeparallel to the skin surface, relative

arrows) at the calcaneal origin (arrowhead). (B) US ofar fascia (arrows) at the calcaneal origin (arrowhead).

Fig. 24. Transverse US at the lateral ankle shows a hy-poechoic ganglion cyst between the calcaneus (calc)and talus (tal). Note the absence of internal Dopplerflow.


hyperechogenicity, and absence of internal bloodflow on Doppler evaluation.58 While the sono-graphic appearance overlaps with that of othermasses, in the context of a long-standing, stable,and pliable mass, the diagnosis can be inferredwith follow-up to assure stability. MR imaging is di-agnostic for a lipoma and can be obtained for cor-roboration as needed.

An aneurysm, while rare in the hindfoot or mid-foot, has also been described.43 Ultrasound iswell-suited to evaluate an aneurysm and can easilyand rapidly identify the mass as originating froma vessel. Doppler evaluation should be used andcan demonstrate a focal or fusiform enlargementof the vessel. Several additional uncommon anklemasses have been described by ultrasoundincluding a glomus tumor, epidermal inclusioncyst, and subcutaneous granuloma annulare.58

Like many masses which are evaluated with MRimaging, these masses have a nonspecific sono-graphic appearance.

Fig. 25. (A) Longitudinal US of a wooden foreign body (beforeign body (arrowhead) with a surrounding hypoechoic(thin arrows).

FOREIGN BODIES

Foreign bodies are relatively common in the foot.Ultrasound has shown sensitivity and specificityof 90% to100% for detection of foreign bodiesin multiple cadaveric and clinical studies.60–63

The smallest reported foreign body detected byUS is 0.5 mm.64 False negatives are unusualbut can potentially occur if the foreign body isvery small, located adjacent to a bone or liga-ment, or is obscured by soft tissue gas. Falsepositives are also rare but can potentially beseen secondary to echogenic gas bubbles, calci-fications, or echogenic scar tissue.62 Wheneverpossible, radiographs should be reviewed beforeUS to assess for associated osseous and softtissue findings. It is optimal to perform US beforesurgical exploration since soft tissue gas cancause an artifact that limits the sonographicevaluation by obscuring or simulating a foreignbody. Tissue harmonics, an optimal scanningmode used in abdominal ultrasound, may de-crease the conspicuity and shadowing of the for-eign body and should be used with caution whenassessing for a foreign body.65 In general, we donot find tissue harmonics to be of great utility inmusculoskeletal ultrasound.

All foreign bodies appear echogenic, regardlessof their composition.66 A hypoechoic surroundinghalo62 may be noted, as well as variable posteriorshadowing (Fig. 25). These features can aid detec-tion and diagnosis, especially of small foreign bod-ies. Doppler interrogation should always be usedwhen evaluating foreign bodies and can aid detec-tion of the foreign body which may be seen as anechogenic structure surrounded by hyperemia.Low-velocity Doppler settings should be used.62

Doppler evaluation can help differentiate fluid (noDoppler flow) from phlegmonous tissue (may

tween the arrows) in the foot. (B) Transverse US of thehalo (thick arrow) and posterior acoustic shadowing

Fig. 26. Longitudinal US of the plantar foot of a pa-tient who stepped on a piece of glass. The flexor hal-lucis longus tendon has been lacerated and isretracted proximally. The three arrows denote theproximal end of the ruptured tendon and the singlearrowhead the distal end of the tendon. The tendonwas surgically repaired.


demonstrate Doppler flow). The presence ofa foreign body should prompt a diligent searchfor associated complications such as tendon orneurovascular injury (Fig. 26). Associated findingssuch as tenosynovitis, joint effusion, abscess(Fig. 27), and periostitis should prompt immediatenotification of the referring clinician so that timelytreatment for infection can be instituted.

Fig. 27. (A) US performed transverse to the Achillestendon (arrowhead) shows an abscess superficial tothe Achilles with a linear echogenic foreign body(arrow, between the cursors). (B) Transverse USperformed at an adjacent level with Doppler demon-strates hyperemia surrounding the abscess (arrows).Arrowhead denotes the Achilles tendon.

SUMMARY

US offers several advantages for imaging the hindand midfoot, including its unique capacity to allowevaluation during dynamic maneuvers. This fea-ture can reveal abnormalities that are not apparentduring static imaging. US permits imaging of pa-tients who cannot undergo MR imaging and pro-vides real-time evaluation of the symptomaticsite. Additional history can be obtained from thepatient during US evaluation and the contralateralanatomy can be quickly assessed as needed. UShas demonstrated great utility and accuracy forimaging the hindfoot and midfoot, including ten-don, ligament, joint, and soft tissue pathology. Itis imperative that radiologists provide expertisein all aspects of musculoskeletal imaging, includ-ing US.

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ultrasound of the hindfoot and...

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