AJR 2002; 179:709-716
© American Roentgen Ray Society
Sonography of the Painful Calf: Differential Considerations
David A. Jamadar1,
Jon A. Jacobson1,
Sean E. Theisen1,
David R. Marcantonio1,2,
David P. Fessell1,
Smita V. Patel1 and
Curtis W. Hayes1
1 Department of Radiology, University of Michigan Medical Center, 1500 E.
Medical Center Dr., TC 2910, Ann Arbor, MI 48109-0326.
2 Present address: Georgia West Imaging, 605 Dixie St., Carrollton, GA
30117.
Received December 21, 2001;
accepted after revision February 28, 2002.
Address correspondence to D. A. Jamadar.
Introduction
Musculoskeletal sonography is becoming more widely available than it was
even a few years ago. With high-frequency transducers providing exquisite
anatomic detail and the ability to evaluate musculoskeletal structures
dynamically, many more applications for sonography are being discovered. The
ease of use, the relatively low cost, and the diagnostic yield make sonography
a strong contender for the first cross-sectional imaging modality to evaluate
many musculoskeletal clinical problems.
Sonography of the symptomatic calf can confirm the diagnosis of several
conditions that would otherwise be treated clinically and can exclude more
significant abnormalities. We outline common abnormal conditions detectable by
sonography and illustrate the differences among their sonographic appearances.
We describe our general approach to the evaluation of the painful calf and the
utility and applicability of sonography as a dynamic imaging modality in
directing clinical management.
Technical Considerations
Before each sonographic examination, a short focused history is obtained,
and the patient is asked to indicate the point of maximum discomfort on the
calf.
Examinations are performed with a high-frequency linear transducer (
7
MHz) for the average patient. We use a 10-12-MHz linear transducer coupled to
a dedicated musculoskeletal sonography unit (HDI 5000; ATL, Bothell, WA).
Patients are usually examined in the prone position with a small bolster
placed immediately proximal to the ankle and the foot just beyond the edge of
the table to allow manipulation of the ankle when appropriate. All structures
are scanned in longitudinal and transverse planes using dynamic imaging when
necessary. The area around the point of maximal discomfort is always
reexamined at completion of the sonographic examination.
Figure 1 illustrates the
position of the probe in relation to the underlying anatomic structures.
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Fig. 1. —Drawing of posterior calf showing position and orientation of
footprint of linear sonographic probe. A = transverse scan of Baker's cyst, B
= longitudinal scan of plantaris tendon, C = longitudinal scan of medial head
of gastrocnemius insertion, D = longitudinal scan of Achilles tendon.
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Achilles Tendon Tear
The Achilles tendon transmits the force of the gastrocnemius and soleus
muscles, which are the primary flexors of the ankle. A normal Achilles tendon
shows linear hyperechoic tendon fibers and uniform thickness in the
longitudinal plane and a flat or concave posterior margin in the transverse
plane (Fig.
2A,2B).
A tear of the Achilles tendon is a disabling injury that may require surgery.
A full-thickness tear is characterized by separation of the torn ends, a
change of contour of the tendon, acoustic shadowing at the margins of the tear
from sound beam refraction, and adjacent hypoechoic tendinosis
[1] (Figs.
3 and
4). A partial-thickness tear
will still show intact fibers, with the tendon often enlarged greater than 1
cm and containing abnormally hypoechoic or anechoic areas corresponding to the
tear and associated adjacent tendinosis. Tendinosis is characterized by
decreased echogenicity in a swollen tendon (Fig.
5A,5B)
and loss of the regular linear pattern of tendon architecture with a more
heterogeneous appearance and intrasubstance anechoic foci. Color-flow and
power Doppler sonography may be useful in defining the margins of an acute
Achilles tendon tear.
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Fig. 3. —45-year-old man with full-thickness Achilles tendon tear.
Longitudinal sonogram shows tendon ends (arrows) separated by
anechoic hematoma. Note adjacent intratendinous hypoechoic edema of
tendinosis.
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Fig. 4. —45-year-old woman with surgically proven acute complete
Achilles tendon tear. Hematoma and tendon debris (H) between tendon ends may
make visualization of margins of tear more difficult. Note change in contour
of tendon. Also, where frayed ends of ruptured tendon change direction
relative to general direction of tendon, shadowing may be produced (S). This
is more convincingly seen at distal margin (right of tear) than at proximal
margin (left of tear).
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Sonography can depict the presence of a tear and, by dynamically showing
separation of the torn tendon ends while the ankle is being dorsi-flexed,
reveal the presence of a full-thickness tear
[1] (Fig.
6A,6B).
Conservative management of an Achilles tendon tear may be contemplated. By
showing contact between the torn tendon ends when the ankle is plantar flexed,
the surgeon will be confident that by placing the plantar-flexed ankle in a
cast, the torn edges will be in apposition in the optimal position for healing
(Fig. 6B).
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Fig. 6A. —35-year-old man with acute full-thickness Achilles tendon
tear. Longitudinal sonogram shows full-thickness tear with separation of
tendon ends, better visualized with dynamic imaging (not shown) but defined by
arrows and shadowing (S).
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Tear of the Medial Head of the Gastrocnemius
Also known as tennis leg, tear of the medial head of the gastrocnemius
typically occurs when the muscle is overstretched by dorsiflexion of the ankle
with full knee extension. The patient typically points directly over the
musculotendinous junction when asked to show the point of maximal
discomfort.
Sonographically, the normal distal medial gastrocnemius muscle tapers
superficially to the soleus muscle (Fig.
7A,7B),
and, with the soleus and lateral gastrocnemius muscles, forms the Achilles
tendon. The plantaris tendon can be visualized between the medial
gastrocnemius and soleus muscles (Fig.
7A,7B).
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Fig. 7A. —53-year-old woman with normal medial head of gastrocnemius
muscle. Longitudinal sonogram shows triangular insertion of medial head of
gastrocnemius muscle (G) with regular parallel linear sonographic appearance
at insertion. Note linear hyperechoic plantaris tendon (arrow)
immediately deep in relation to gastrocnemius muscle.
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A tear of the medial gastrocnemius muscle is characterized by disruption of
the normal regular parallel linear echogenic and hypoechogenic appearance of
the tendon at its insertion, typically accompanied by indistinctness of the
tapering distal end of the tendon at its insertion
[2] (Figs.
8 and
9). Sometimes hypoechogenic
material with posterior acoustic enhancement is seen at the insertion of the
gastrocnemius tendon, compatible with a hematoma. If the injury is severe, the
fluid will accumulate across the width of the medial head of the gastrocnemius
muscle, distinct from the appearance of a plantaris tendon tear (Fig.
10A,10B).
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Fig. 8. —40-year-old woman with medial gastrocnemius muscle tear.
Longitudinal sonogram shows anechoic fluid collection (F) at distal insertion
of medial head of gastrocnemius muscle with blunting of expected triangular
configuration.
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Fig. 9. —45-year-old man with medial gastrocnemius tear. Longitudinal
sonogram shows fluid collection (F) consistent with hematoma at distal
insertion of medial head of gastrocnemius muscle, with loss of regular
fibrillar appearance (G) at insertion into triceps surae. Note intact
plantaris tendon (arrow).
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Fig. 10A. —55-year-old man with large medial gastrocnemius muscle tear.
Longitudinal scan shows extensive anechoic fluid collection (F) around distal
insertion of medial head of gastrocnemius muscle, which extends proximally
along its insertion into triceps surae.
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Fig. 10B. —55-year-old man with large medial gastrocnemius muscle tear.
Transverse scan shows fluid collection (F) extending across entire width of
medial head of gastrocnemius muscle (arrows).
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Plantaris Tendon Tear
The plantaris originates immediately proximal to the lateral femoral
condyle as a small fusiform muscle and continues as a long slender tendon that
passes between the medial head of the gastrocnemius and the soleus muscles and
then runs along the medial border of the Achilles tendon to be inserted with
it. Tears of this tendon are typically treated conservatively but may be
clinically confused with the other entities we describe.
The plantaris tendon typically tears at midcalf level, and sonographically,
discontinuity of the tendon on longitudinal scanning may be apparent
[3] (Fig.
11A,11B).
Fluid usually accumulates in a tubular configuration between the medial head
of the gastrocnemius and the soleus muscle bellies, along the course of the
plantaris tendon (Fig.
12A,12B).
The fluid collection associated with a plantaris tear is typically proximal to
a fluid collection of a medial gastrocnemius muscle tear, although both
plantaris and medial gastrocnemius muscle tears may coexist. In the latter
situation, a large collection can extend cephalad from the medial
gastrocnemius muscle tear between the soleus and medial gastrocnemius muscle
bellies.
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Fig. 11A. —58-year-old man with plantaris tendon tear. Longitudinal
sonogram shows anechoic fluid collection (F) between medial gastrocnemius (G)
and soleus muscles (S). Note torn proximal end of plantaris tendon
(arrow).
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Fig. 12A. —54-year-old man with plantaris tendon tear. G = gastrocnemius
muscle, S = soleus muscle. Longitudinal sonogram shows tubular fluid
collection (F) and nonvisualization of plantaris tendon.
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Ruptured Baker's Cyst
Distention of the semimembranosogastrocnemial bursa between the tendons of
the medial head of the gastrocnemius and the semimembranous tendons is a
"Baker's cyst" [4].
This bursa communicates with the knee joint in more than 50% of patients older
than 50 years and is typically crescent-shaped when imaged in the axial plane
[4]
(Fig. 13). Rupture of a
Baker's cyst frequently presents with the sudden onset of pain in the calf and
must be differentiated from a deep venous thrombosis or other traumatic
injuries of the calf.
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Fig. 13. —33-year-old man with Baker's cyst. Anechoic fluid distends
semimembranosogastrocnemial bursa with characteristic neck between
semimembranosus tendon (arrow) and medial gastrocnemius muscle (M)
and tendon (T).
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Acutely, a ruptured Baker's cyst will typically show abnormal and irregular
hypoechoic or anechoic areas at the distal aspect of the cyst
(Fig. 14). Larger fluid
collections can extend distally and are characteristically located superficial
to the medial gastrocnemius muscle (Fig.
15); this location is in contrast to a plantaris tendon tear, in
which fluid accumulates between the medial gastrocnemius muscle and the soleus
muscle (Fig.
12A,12B).
Residual irregularity or hyperechoic scar tissue at the distal aspect of a
Baker's cyst indicates a remote rupture.
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Fig. 14. —40-year-old man with ruptured Baker's cyst. Longitudinal
sonogram through distal aspect of Baker's cyst shows debris (D) in inferior
portion of cyst with anechoic fluid tracking distally in subcutaneous tissues
(arrow).
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Fig. 15. —83-year-old man with ruptured Baker's cyst. Sagittal sonogram
of posterior calf shows reticular pattern of anechoic subcutaneous fluid
(arrows) separating fat superficial to muscles tracking distally from
ruptured Baker's cyst.
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Intramuscular Contusion and Rupture
Unlike injuries at the musculotendinous junction, which are commonly
traction injuries, intramuscular contusion or rupture is commonly the result
of direct impact. The resultant hematoma and distortion of the normal
architecture allows identification of these injuries
[5]. Within the first 24 hr,
hematomas vary in echotexture from anechoic to hyperechoic. After 2-3 days,
the clot dissolves and the collection becomes anechoic. Subsequent
organization produces internal echoes
(Fig. 16), which later
disappear in the older hematoma.
Deep Venous Thrombosis
Duplex sonography is the imaging method of choice in depicting deep venous
thrombosis of the lower extremity. Loss of compressibility and distention of
the vein and visualization of intraluminal thrombi are characteristic of deep
venous thrombosis (Fig. 17).
Intraluminal defects or a color void on color Doppler sonography may be more
easily seen.
Calf Neoplasms
Although sonography is somewhat nonspecific in the evaluation of a
soft-tissue mass (Fig. 18), it
can be used to determine the size and consistency and to differentiate a
cystic from a solid mass. Color and power Doppler sonography may allow
visualization of tumor vascularity and may be useful in following up tumor
response to nonsurgical therapy. Soft-tissue hemorrhage and a hemorrhagic or
necrotic soft-tissue neoplasm may appear sonographically similar.
Sonographically guided biopsies of soft-tissue masses can be performed easily
and safely, with color and power Doppler sonography facilitating avoidance of
adjacent vascular structures.
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Fig. 18. —28-year-old woman with soft-tissue hemangioma. Longitudinal
sonogram of medial calf shows soleus muscle mass (cursors) with
heterogeneous echo texture and indistinct margins. g = gastrocnemius
muscle.
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Conclusion
Familiarity with the characteristic sonographic findings of these common
abnormal conditions affecting the calf will allow differentiation and an
accurate diagnosis. Besides routine sonographic evaluation for each of the
pathologic processes described previously, sonography should also focus on the
area of maximal symptoms.
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Introduction
Technical Considerations
