AJR 2003; 181:1573-1581
© American Roentgen Ray Society
Sonography of Dorsal Ankle and Foot Abnormalities
David P. Fessell1,
David A. Jamadar2,
Jon A. Jacobson2,
Elaine M. Caoili2,
Qian Dong2,
Sucheta S. Pai2 and
Marnix T. van Holsbeeck3
1 Akron Radiology, 525 E Market St., Akron, OH 44304.
2 Department of Radiology, TC 2910, University of Michigan Hospitals, University
of Michigan Medical Center, 1500 E Medical Center Dr., Ann Arbor, MI
48109-0326.
3 Department of Radiology, Henry Ford Hospital, 2799 W Grand Blvd., Detroit, MI
48202.
Received February 20, 2003;
accepted after revision April 10, 2003.
Address correspondence to D. A. Jamadar.
Introduction
The dorsum of the foot is composed of a relatively thin layer of soft
tissue, traversed by tendons, nerves, and vessels, superficial to the bones
and joints of the foot (Fig.
1). Because these soft-tissue structures are all superficial,
sonographic evaluation provides excellent spatial resolution and dynamic
capability.
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Fig. 1. —Line drawing of dorsal foot and ankle shows dorsalis pedis
artery (DPA); deep peroneal nerve (DPN); and extensor digitorum longus (EDL),
extensor hallucis longus (EHL), and anterior tibial (AT) tendons.
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A strength of sonography is its ability to depict structures dynamically,
thus providing information during differential phases of movement. This
information is especially useful for evaluating tendon impingement. In
addition, tendon subluxation may occur only with the joint in specific
positions or during active movement.
Apart from pathologic processes involving tendons, a variety of other
pathologic processes may involve adjacent soft-tissue structures, such as
aneurysms and ganglionic cysts. Soft-tissue processes, such as infection, the
presence of foreign bodies, and tumors can be detected on sonography, which
can also reveal the location of the abnormality and its relationship to the
surrounding structures. Additional sonographic features such as echogenicity,
internal blood flow, and compressibility can aid diagnosis.
We present our sonographic technique, illustrate a range of abnormalities,
and describe those sonographic features that can aid in making a specific
diagnosis.
Technical Considerations
Musculoskeletal sonography is performed with a linear high-frequency
transducer (
7 MHz). We use a 10-15–MHz linear transducer (model HDI
5000, Phillips–Advanced Technology Laboratories, Bothell, WA). Patients
are positioned supine with the ankle placed beyond the edge of the examination
table to allow unimpeded active and passive movement at the ankle joint. The
examination can be tailored to assess a focal symptomatic site, and dynamic
evaluations are routinely performed. If a mass is identified, its cystic or
solid nature and its relationship to adjacent tendons, neurovascular
structures, and joints may be evaluated. Color and power Doppler imaging may
also be used to assess the vascularity of anatomic structures or suspected
masses and to determine the location of adjacent vessels.
For the sonographic examination of the ankle and foot, following an
organized checklist of anatomic structures ensures a thorough evaluation.
Structures should be examined in longitudinal and transverse planes, and if
possible, a dynamic evaluation should be performed. However, because
abnormalities may occur in any location, it is important to ask the patient to
indicate specific symptomatic areas at the time of each examination.
Sonography over these locations often reveals abnormality.
The Ankle Joint
When scanning is performed in the sagittal plane and the patient is
positioned with the tibiotalar joint in plantar flexion, the hyperechoic
anterior fat pad of the normal joint can be seen to fill the space between the
tibia and the talus anteriorly (Fig.
2A). The layer of hypoechoic hyaline cartilage should not be
mistaken for joint fluid. With a simple ankle joint effusion, anechoic fluid
fills the anterior recess over the talus, displacing the fat pad
(Fig. 2B). If present, blood
flow detected on color or power Doppler sonography can help distinguish
hypoechoic synovium (Fig. 3)
from hypoechoic complex joint fluid. Occasionally, aspiration must be
attempted to distinguish between the two. The capability of sonography to
detect other abnormalities in patients presenting with swelling and pain
around the ankle, such as aneurysm (Fig.
4), emphasizes its usefulness.
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Fig. 2A. —50-year-old woman with normal left ankle and joint effusion
in right ankle. Sagittal sonogram shows normal anterior ankle joint fat pad
(F) between tibia (Ti) and talus (t). Anechoic articular cartilage of talar
dome (arrows) should not be confused with joint fluid.
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Fig. 2B. —50-year-old woman with normal left ankle and joint effusion
in right ankle. Sagittal sonogram shows normal hyperechoic anterior fat pad
(F) is displaced anteriorly by hypoechoic ankle joint fluid (f). Ti = tibia, t
= talus.
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Fig. 4. —43-year-old man with mycotic aneurysm of dorsalis pedis
artery. Longitudinal sonogram shows dorsalis pedis artery (arrows)
and focal aneurysmal dilatation (D). Note normal fat pad (F). Ti = tibia, t =
talus.
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The Subcutaneous Tissues
Edema and soft-tissue gas have characteristic appearances. The hypoechoic
extravascular fluid and lymphatic distention of edema
(Fig. 5) separate the
subcutaneous tissues, which results in a marbled pattern on sonography. Gas in
the soft tissues is seen in patients with an infection
(Fig. 6) or in those who have
undergone an intervention and produces a highly reflective focus and shadowing
[1]. Pressure applied by the
transducer may cause gas collections to change in size and shape, which also
aids diagnosis.
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Fig. 6. —69-year-old man with soft-tissue infection. Transverse
sonogram at level of first metatarsal (M) shows sinus opening (S) at skin
surface with gas (arrows) tracking dorsally and medially in swollen
subcutaneous tissues.
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Tendinosis, Tenosynovitis, and Tendon Tears
Sonographic evaluation of the normal extensor tendons shows the linear
fibrillar nature of these tendons, which is most visible in the large anterior
tibial tendon (Fig. 7A) on
longitudinal scanning [2]. In
cross section, the oval tendons are speckled echogenic structures.
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Fig. 7A. —81-year-old man with normal right ankle and tendinosis of
left anterior tibial tendon. Longitudinal sonogram of anterior tibial tendon
(arrowheads) of asymptomatic right ankle shows linear echogenic
normal tendon.
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Tendinosis, tenosynovitis, and tendon tears are the most common entities
affecting the extensor tendons and usually result from trauma, overuse
syndromes, and infectious or inflammatory conditions. Each of the extensor
tendons may be imaged in both longitudinal and transverse planes from the
musculotendinous junction to the osseous insertion.
On sonography, tendinosis presents with swelling of the affected tendon,
usually with heterogeneous areas of decreased echogenicity
(Fig. 7B), and loss of the
normal linear parallel fibrillar pattern of the tendon infrastructure. We are
often unable to reliably differentiate tendinosis from intrasubstance or early
or mild partial-thickness tears because the spectrum of sonographic
appearances of tendinosis overlaps considerably with the those of the
tears.
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Fig. 7B. —81-year-old man with normal right ankle and tendinosis of
left anterior tibial tendon. Longitudinal sonogram (same field of view and
location as A) of anterior tibial tendon (arrows) of
symptomatic left ankle shows marked swelling of hypoechoic tendon without
disruption of tendon fibers.
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Tenosynovitis, or paratenonitis, is an inflammatory process involving the
tendon sheath. Both tendinosis and tenosynovitis are typically caused by
repetitive trauma, but tenosynovitis may also be the result of an infection
(Fig. 8A,
8B) or an inflammatory process
such as rheumatoid arthritis. On sonography, tenosynovitis presents with
anechoic or hypoechoic peritendinous fluid and, in some cases, with synovial
thickening and increased vascularity of the paratenon.
Partial tears in the ankle tendons include a longitudinal split. On
sonography, the gap in the torn tendon may be filled with anechoic fluid
(Fig. 9), but when debris
fills the gap, differentiating a torn tendon from tendinosis may be difficult.
Complete tears are accompanied by variable retraction of the tendon end that
is attached to muscle, which can aid diagnosis. The hematoma and tissue
deformity associated with retraction of a ruptured tendon may present as a
mass on the dorsum of the foot (Fig.
10) and clinically can be mistaken for a neoplasm. The absence of
internal flow in the mass on Doppler imaging and the presence of torn tendon
ends allow diagnosis. Dynamic sonographic evaluation may increase the tendon
gap and allow direct visualization. The tendon most commonly torn is the
anterior tibial tendon, and tears typically occur where it passes beneath the
extensor retinaculum to its attachment. Iatrogenic tears are rare but can
occur during arthroscopy (Fig.
11).
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Fig. 9. —48-year-old woman who presented with incomplete anterior
tibial tendon tear from laceration. Longitudinal sonogram of anterior tibial
tendon shows hypoechoic central area (L) with irregular margins and minimal
separation, consistent with incomplete tear. Adjacent tendon (T) shows
tendinosis.
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Fig. 11. —33-year-old man with partial anterior tibial tendon tear
after arthroscopy. Transverse sonogram shows anterior tibial tendon
(arrowheads) with linear cleft (c). Ti = distal tibia metaphysis.
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Orthopedic hardware may loosen or may lie in close proximity to moving
structures (Fig. 12). Tendons
may fray and become abraded by rubbing on a metallic prosthesis during
movement [3]. The dynamic
capability of sonography allows diagnosis.
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Fig. 12. —43-year-old woman with impingement of extensor hallucis
longus tendon. Longitudinal sonogram of extensor hallucis longus tendon (T)
shows impingement by head of screw (arrow). M = first metatarsal
head, P = proximal phalanx.
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Anterior Ankle Ligaments
The normal anterior tibiofibular ligament
(Fig. 13A) and normal anterior
talofibular ligament (Fig.
14A) appear as linear fibrillar structures that are hyperechogenic
and more compact than normal tendon.
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Fig. 13A. —34-year-old man with normal anterior tibiofibular ligament
and torn anterior talofibular ligament. Longitudinal sonogram shows normal
anterior tibiofibular ligament (arrows) composed of echogenic tightly
packed linear fibers and extending from fibula (F) to tibia (Ti).
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Fig. 14A. —50-year-old woman with normal anterior talofibular ligament
and abnormal anterior tibiofibular ligament. Longitudinal sonogram shows
anterior talofibular ligament (arrows) extending from talus (t) to
fibula (F).
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The anterior talofibular ligament is the weakest of the ligaments that
comprise the lateral ligamentous complex and is the most commonly injured
(Fig. 13B). Acute ligament
tears show anechoic fluid, which separates the ends of the torn ligament.
Later, hypoechoic swelling and nonvisualization of part of the ligament are
common.
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Fig. 13B. —34-year-old man with normal anterior tibiofibular ligament
and torn anterior talofibular ligament. Longitudinal sonogram of anterior
talofibular ligament shows absence of normal ligament and abnormal
hypoechogenicity. Short fragment of edematous ligament (arrows) is
attached to fibula (F). t = talus.
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The anterior tibiofibular ligament is the weakest of the distal
tibiofibular ligaments and is the first to be injured. Avulsion of its
attachment to the anterior tubercle of the tibia may also occur
(Fig. 14B). Sonographic
appearances of injury are similar to those of the anterior talofibular
ligament.
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Fig. 14B. —50-year-old woman with normal anterior talofibular ligament
and abnormal anterior tibiofibular ligament. Longitudinal sonogram of anterior
tibiofibular ligament (arrows) shows loss of normal fibrillar
appearance, swelling, and discontinuity at tibial attachment. F = fibula, Ti =
tibia.
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Masses
Sonography can reveal the location of a mass, its internal character, its
compressibility, its vascularity, and the location of adjacent vessels and
nerves and thus can facilitate sonographically guided biopsy. Neoplasms of the
dorsum of the foot occur infrequently. Giant cell tumors of tendon sheath,
synovial sarcomas, and neuromas may be encountered. Peripheral nerve sheath
tumors [4] may be markedly
hypoechoic, but may exhibit intense hyperemia. The nerve may be seen entering
the mass; this sign aids diagnosis (Fig.
15A,
15B).
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Fig. 15A. —54-year-old woman with schwannoma. Longitudinal sonogram of
lateral branch of deep peroneal nerve shows solid and relatively homogeneous
mass (M) adjacent to talus (t). Nerve (N) is seen in continuity with
tumor.
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Ganglionic cysts can be entirely cystic and multiloculated and may have a
narrow communication or neck with an adjacent joint or tendon sheath
(Fig. 16). Often anechoic or
hypoechoic, these cysts may have dependent internal echoes caused by debris.
Occasionally these cysts may be tense and may simulate a solid mass or an
underlying bone on palpation
[5].
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Fig. 16. —33-year-old woman with ganglionic cyst. Sagittal sonogram
shows anechoic incompressible ganglionic cyst (G) with through-transmission
and multiple loculations (L) deep in relation to primary cyst (G). Note
continuity with neck (arrows), which communicates with talonavicular
joint. N = navicular bone, t = talus.
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Bursae develop at friction points between bone, intervening soft tissue,
and the environment. At sonography, bursae are variable in echogenicity
depending on whether they contain blood or thickened synovium, but they
typically contain hypoechoic (Fig.
17) or anechoic fluid.
Chronic tophaceous gout may present as a focal nodule of the extensor
tendon and results in a nonspecific loss of the normal regular fibrillar
pattern with associated decreased echogenicity
(Fig. 18). Involvement of the
adjacent soft tissues can result in a palpable mass. A history of gout and
supportive biochemical evidence aid diagnosis.
Foreign Bodies
Confirmation of a nonradiopaque foreign body is often difficult. Wood,
plastic, and many other materials are poorly depicted or not visible at all on
radiography. In the extremities, sonography is effective in identifying
foreign bodies composed of nonradiopaque material (Fig.
19A,
19B).
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Fig. 19A. —43-year-old woman with retained segment of IV catheter.
Transverse sonogram of superficial vein shows superficial and deep surfaces of
catheter (arrows) at right angles to incident beam.
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Foreign bodies may create an inflammatory mass over time that is surrounded
by a characteristic hypoechoic rim, making a small hyperechoic foreign body
more conspicuous. The sonographic appearance of a foreign body depends on its
surface attributes. Smooth and flat surfaces produce reverberations, whereas
irregular surfaces with a small radius of curvature produce shadowing
[6]
(Fig. 20).
The Osseous Structures
Bone reflects sound completely, so sonography is limited in evaluating
structures that are deep in relation to the soft tissue–bone interface.
Only the overlying contour of the bone can be visualized, and care in
interpreting abnormalities should be exercised. However, fractures may be
strongly suspected (Fig. 21)
by focal cortical irregularities or step-off deformities in combination with
clinical history [7,
8]. Other structural
abnormalities such as a talar beak associated with subtalar coalition may be
identified (Fig. 22).
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Fig. 21. —33-year-old woman with calcaneocuboid ligament avulsion
fracture. Sonogram in coronal plane shows cortical fragment (arrows).
Avulsion fracture was suggested and confirmed at radiography. Arrowheads =
calcaneal cortex.
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Conclusion
Sonography is a rapid and efficient modality for the evaluation of the
extensor tendons, the anterior ligaments, and other soft tissues of the ankle.
Correlation of imaging findings for the opposite ankle and with those for the
site of focal signs or symptoms is an advantage of sonography. Sonography is
widely available and allows aspiration or biopsy to be performed immediately.
Familiarity with the range of abnormality and with imaging is essential.
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Introduction
Technical Considerations
