AJR 2000; 175:1313-1321
© American Roentgen Ray Society
An Illustrated Tutorial of Musculoskeletal Sonography
Part 3, Lower Extremity
John Lin1,
David P. Fessell,
Jon A. Jacobson,
William J. Weadock and
Curtis W. Hayes
1
All authors: Department of Radiology, The University of Michigan Medical
Center, 1500 E. Medical Center Dr., TC 2910, Ann Arbor, MI 48109-0326.
Received December 8, 1999;
accepted after revision February 10, 2000.
Address correspondence to J. Lin.
Introduction
Sonography is ideal for the evaluation of a broad range of pathologic
conditions affecting the foot and ankle. The higher spatial resolution of
sonography is a major advantage over MR imaging when dealing with small
lesions. Because of the accuracy and effectiveness of MR imaging, there are
fewer routine clinical indications for sonography of the adult hip and knee.
However, certain specific indications can be evaluated principally with
sonography in an efficient and cost-effective manner.
Foot and Ankle
Joint effusions are easily identified as anechoic or hypoechoic fluid
collections, typically with well-defined margins. An ankle effusion is best
visualized at the anterior tibiotalar articulation
[1]. Metatarsal-phalangeal and
interphalangeal joint effusions are usually identified dorsally
(Fig. 1). When a joint effusion
is present, diagnostic aspiration of the fluid can be performed using
sonographic guidance.
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Fig. 1. —34-year-old man with metatarsal-phalangeal joint effusion.
Longitudinal sonogram of first-digit metatarsal-phalangeal joint from dorsal
approach reveals teardrop-shaped joint effusion (arrows). Fluid was
aspirated under sonographic guidance to exclude infection. Note first
metatarsal head (MT) and base of proximal phalynx (PP).
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The Achilles tendon, posterior tibial tendon, and peroneal tendons are the
most frequently injured tendons. Tendinosis manifests as heterogeneity and
thickening of the tendon without discrete defects
(Fig. 2). Longitudinal splits
are particularly common in the peroneal and posterior tibial tendons,
involving a variable length of tendon usually at or near the malleolus
(Fig. 3). Subluxation of the
peroneal tendons can occur after lateral ankle trauma and rupture of the
superior peroneal retinaculum. This finding may be present only transiently,
emphasizing the advantage of real-time dynamic imaging with direct
visualization. Dynamic sonography can reveal whether the retracted ends of a
torn Achilles tendon can be approximated with plantar flexion, which is
important when deciding between conservative casting and surgical treatment
[1] (Fig.
4A,4B).
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Fig. 2. —48-year-old woman with Achilles tendinopathy. Extended
field-of-view longitudinal sonogram shows diffuse fusiform thickening of
Achilles tendon, representing tendinosis (arrowheads). No discrete
tear was identified. Note posterior calcaneal cortex (arrows) at
Achilles insertion. p = proximal, d = distal.
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Fig. 3. —64-year-old woman with posterior tibial tendon tear.
Longitudinal sonogram shows longitudinally oriented central hypoechoic defect
(arrowheads) extending through posterior tibial tendon
(arrows) near level of medial malleolus, consistent with longitudinal
split tear. More proximal and distal portions of posterior tibial tendon (not
shown) were not torn. p = proximal, d = distal.
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Fig. 4A. —37-year-old man with Achilles tendon tear. p = proximal, d =
distal. Dynamic sonogram of Achilles tendon obtained at dorsiflexion shows
complete tear with retraction of tendon ends (double arrow).
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Fig. 4B. —37-year-old man with Achilles tendon tear. p = proximal, d =
distal. Dynamic sonogram obtained at plantar flexion reveals close
approximation of torn tendon ends (open arrows) with obliteration of
defect gap. Note proximal tendon end (solid arrows) and distal tendon
end (arrowheads).
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Achilles tendon xanthomas are considered pathognomonic for heterozygous
familial hypercholesterolemia and can be accurately diagnosed using sonography
[2]. Disease is typically
bilateral, with thickened tendons and hypoechoic xanthomatous plaques (Fig.
5A,5B).
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Fig. 5A. —31-year-old woman with familial hypercholesterolemia and
Achilles tendon xanthomas. Longitudinal (A) and transverse (B)
sonograms of Achilles tendon reveal diffuse thickening and numerous discrete
hypoechoic plaques, representing xanthomas (black arrows). Note
posterior calcaneal cortex (white arrows, A). In A, p
indicates proximal, and d indicates distal.
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Fig. 5B. —31-year-old woman with familial hypercholesterolemia and
Achilles tendon xanthomas. Longitudinal (A) and transverse (B)
sonograms of Achilles tendon reveal diffuse thickening and numerous discrete
hypoechoic plaques, representing xanthomas (black arrows). Note
posterior calcaneal cortex (white arrows, A). In A, p
indicates proximal, and d indicates distal.
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Normal variants such as a secondary ossification center and bipartite
sesamoid bones should be recognized and not mistaken for fractures. However,
some normal variants may be symptomatic such as type II accessory navicular
bones (Fig.
6A,6B,6C).
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Fig. 6A. —14-year-old girl with medial foot pain. Longitudinal
split-screen sonogram reveals type II accessory navicular bone (AN),
congenital variant, as additional curvilinear echogenic foci with distal
shadowing similar to other osseous structures. Intact posterior tibial tendon
(TP and arrows) inserts on accessory navicular bone. Note navicular
bone (NAV) and medial cuneiform bone (CUN).
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Fig. 6B. —14-year-old girl with medial foot pain. Anteroposterior
(B) and oblique (C) radiographs of right foot confirm presence
of type II accessory navicular bone (arrows), which was
symptomatic.
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Fig. 6C. —14-year-old girl with medial foot pain. Anteroposterior
(B) and oblique (C) radiographs of right foot confirm presence
of type II accessory navicular bone (arrows), which was
symptomatic.
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Ankle sprains are one of the most common injuries. Radiographs frequently
show only soft-tissue swelling even when significant ligamentous derangement,
resulting in ankle instability, is present. Disruption of the normal fibrillar
pattern with ill-defined hypoechoic edema indicates ligamentous injury. The
status of the anterior talofibular ligament (the most commonly injured) (Fig.
7A,7B)
and the tibiofibular ligaments (important for ankle mortise stability) can be
assessed with sonography
[3].
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Fig. 7A. —Tear and normal anatomy of anterior talofibular ligament. F =
distal fibula, T = talus. Longitudinal sonogram of 40-year-old woman with
ankle sprain reveals disruption of anterior talofibular ligament resulting in
residual lax ligament fiber (arrows).
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Fig. 7B. —Tear and normal anatomy of anterior talofibular ligament. F =
distal fibula, T = talus. Longitudinal sonogram of healthy 32-year-old man
shows normal anterior talofibular ligament (arrows).
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Plantar fasciitis is a frequent cause of heel pain, especially in the
athletic population. When the clinical diagnosis is unclear, sonography can be
used to determine whether the plantar fascia is abnormal. The plantar fascia
normally appears as a fibrillar echotecture and measures less than 4 mm in
thickness. Plantar fasciitis manifests as thickening and hypoechogenicity with
surrounding edema [4]
(Fig. 8).
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Fig. 8. —65-year-old man with plantar fasciitis. Longitudinal
split-screen image compares painful right heel (left image) with asymptomatic
left heel (right image). Plantar fascia is markedly thickened and slightly
hypoechoeic in right foot (x, left image), consistent with plantar
fasciitis, and of normal caliber in left foot (+, right image). C =
calcaneus.
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Perineural fibrosis of a plantar digital nerve (Morton's neuroma) can be a
cause of pain and paresthesias in the forefoot. Sonography can be an effective
means of diagnosis in cases of suspected Morton's neuroma
[5] (Fig.
9A,9B).
This neuroma appears as a hypoechoic lesion within the plantar aspect of the
web space. The digital nerve may be identified extending to the lesion.
Dorsally, the adjacent intermetatarsal bursa may be distended indicating
associated bursitis.
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Fig. 9A. —35-year-old woman with Morton's neuroma. Transverse
(A) and longitudinal (B) sonograms of distal metatarsal region
from plantar approach show discrete hypoechoic lesion (solid arrows)
located in second web space between second (2, A) and third (3,
A) distal metatarsals; arrowheads mark cortices. Plantar digital nerve
(open arrows, B) was noted adjacent to hypoechoic lesion
representing Morton's neuroma, which was surgically proven.
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Fig. 9B. —35-year-old woman with Morton's neuroma. Transverse
(A) and longitudinal (B) sonograms of distal metatarsal region
from plantar approach show discrete hypoechoic lesion (solid arrows)
located in second web space between second (2, A) and third (3,
A) distal metatarsals; arrowheads mark cortices. Plantar digital nerve
(open arrows, B) was noted adjacent to hypoechoic lesion
representing Morton's neuroma, which was surgically proven.
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Knee
A joint effusion is easily confirmed on sonography, which typically reveals
anechoic to hypoechoic fluid in the suprapatellar bursa deep in relation to
the quadriceps insertion onto the patella
(Fig. 10). Fluid can also be
identified in the medial and lateral recesses. This finding is nonspecific and
may indicate a variety of conditions including posttraumatic injury, an
inflammatory process, osteonecrosis, or osteoarthritis. In most patients,
loose bodies are readily identifiable in the presence of a joint effusion and
usually appear as echogenic foci.
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Fig. 10. —39-year-old man with knee joint effusion. Longitudinal
sonogram of knee shows anechoic distention of suprapatellar bursa (solid
white arrows) representing joint effusion. Note echogenic cortex of
patella (open arrows), distal femur (arrowheads), and
quadriceps tendon (black arrows).
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A common indication for sonography of the knee is to diagnose a Baker's
cyst. The patient usually presents with a palpable posteromedial mass and
occasional posterior knee pain. An uncomplicated Baker's cyst has a
characteristic sonographic appearance—namely, a variably sized,
well-defined anechoic structure communicating with the joint space by way of a
neck insinuating between the semimembranous tendon and the medial head of the
gastrocnemius muscle [5]
(Fig. 11). Thin septations and
a multilobulated configuration may be present. Complications include
hemorrhage, dissection, rupture, and loose bodies.
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Fig. 11. —67-year-old woman with Baker's cyst. Transverse sonogram of
popliteal fossa from posteromedial approach shows large cystic lesion (BC)
with a couple of thin septations. Fluid communication with joint is present
via neck (double arrow) interposed between semimembranosis tendon
(arrowheads) and medial head of gastrocnemius muscle (MG) and
tendinous (single arrows) junction, which is diagnostic for Baker's
cyst.
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Meniscal cysts are another cause of periarticular cystic masses. These
cysts are typically identified along the joint line adjacent to the meniscus,
more common laterally. An underlying meniscal tear can be identified in some
patients as a hypoechoic defect within the echogenic meniscus, communicating
with the meniscal cyst [5]
(Fig. 12). The accuracy of
sonographic evaluation for diagnosing meniscal tears
(Fig. 13) remains to be
proven.
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Fig. 12. —33-year-old woman with meniscal cyst. Longitudinal sonogram
of medial knee reveals large cystic lesion at medial joint line just
superficial to meniscus (arrows) and deep in relation to medial
collateral ligament (arrowheads). Meniscus appears heterogeneous with
possible hypoechoic defects. Large meniscal cyst (MC) with associated meniscal
tear was confirmed on MR imaging. Note medial femoral condyle (F) and medial
tibial plateau (T).
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Fig. 13. —57-year-old woman with medial knee pain. Longitudinal
sonogram of medial knee shows heterogeneity of posterior horn of medial
meniscus (white arrows) with hypoechoic defects (black
arrows), suggestive of meniscal tear. Findings were confirmed using MR
imaging. Note medial femoral condyle (F) and medial tibial plateau (T).
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Quadriceps and patellar tendon injuries can be quickly and easily diagnosed
[5,
6]. Focal hypoechogenicity of
the proximal patellar tendon with variable increased flow on power Doppler
sonography is known as patellar tendinosis or jumper's knee
[7] (Fig.
14A,14B).
Minimally displaced patella fractures can be identified on sonography; they
manifest as discrete cortical surface disruption
[8]. Only the anterior surface
of the patella is evaluated because of shadowing of the remainder of the
structure. Prepatellar and superficial infrapatellar bursitis are other causes
of anterior knee pain, which can be evaluated using sonography. Characteristic
findings include fluid distention of the corresponding bursa, tenderness with
transducer compression, and possible increased flow on power Doppler
sonography.
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Fig. 14B. —18-year-old woman with patellar tendinosis. Longitudinal
power Doppler sonogram shows increased flow in abnormal proximal patellar
tendon. Findings are consistent with patellar tendinosis, or jumper's
knee.
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Medial collateral ligament integrity can be assessed using sonography
[9]. The criteria are the same
as those for other ligamentous pathology. Disruption of the uniform compact
fibrillar pattern indicates injury, from strain to complete tear (Fig.
15A,15B).
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Fig. 15A. —Partial tear and normal anatomy of medial collateral
ligament. F = femur, T = tibia. Longitudinal sonogram of 41-year-old man
reveals disruption of fibrillar pattern representing partial tear
(arrowheads) that involves deep fibers of medial collateral ligament
(solid black arrows). Note femoral cortex (open arrows) and
tibial cortex (solid white arrows).
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Fig. 15B. —Partial tear and normal anatomy of medial collateral
ligament. F = femur, T = tibia. Longitudinal sonogram of healthy 17-year-old
girl shows normal medial collateral ligament (arrows).
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Other structures that can be assessed are the iliotibial band; plantaris
tendon [10] (Fig.
16A,16B);
additional bursae, including the pes anserinus bursa; and the popliteal
vessels. Consistent evaluation of deeper components, such as the menisci and
cruciate ligaments, is more difficult, and global assessment of these
structures should be completed using MR imaging.
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Fig. 16A. —61-year-old man with plantaris tendon tear. Longitudinal
(A) and transverse (B) sonograms of calf show large hypoechoic
lesion (arrows) interposed between medial gastrocnemius (MG,
A; MED GASTROC, B) and soleus (S, A; SOLEUS, B)
muscle groups representing large hematoma from plantaris tendon tear.
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Fig. 16B. —61-year-old man with plantaris tendon tear. Longitudinal
(A) and transverse (B) sonograms of calf show large hypoechoic
lesion (arrows) interposed between medial gastrocnemius (MG,
A; MED GASTROC, B) and soleus (S, A; SOLEUS, B)
muscle groups representing large hematoma from plantaris tendon tear.
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Hip
Bursitis is most common in either the greater trochanteric bursa or the
iliopsoas bursa, although bursitis may develop in numerous other locations.
Localized tenderness is often present during the sonographic examination when
the probe compresses the distended hypoechoic or anechoic bursa
(Fig. 17).
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Fig. 17. —55-year-old man with iliopsoas bursitis. Longitudinal
extended field-of-view sonogram of anterior hip reveals large ovoid cystic
collection (asterisk) consistent with fluid distention of iliopsoas
bursa (single arrows). This collection connects (double
arrow) with multilobulated hypoechoic lesion distally
(arrowheads), anterior to femur, representing dissection of iliopsoas
bursa and echogenic debris. Note femoral head (F).
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Joint effusions manifest as anechoic or hypoechoic fluid distention of the
joint capsule, best visualized anteriorly, along the femoral neck region (Fig.
18A,18B,18C).
Sonography can be useful to evaluate for periarticular abscesses, which may
not be continuous with the joint space
[11]. If no intraarticular
connection exists, these lesions will not be identified on hip arthrography
(Fig.
19A,19B,19C).
Sonographically directed needle aspiration of joint and soft-tissue fluid
collections can be efficiently performed immediately after the diagnostic
examination.
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Fig. 18A. —17-year-old boy with hip joint effusion. Arrows indicate
anterior femoral cortex. Longitudinal sonogram of anterior hip revealed tear
drop-shaped fluid collection (+ and x) consistent with hip joint
effusion.
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Fig. 18B. —17-year-old boy with hip joint effusion. Arrows indicate
anterior femoral cortex. Longitudinal sonogram of anterior hip obtained with
needle (arrowheads) placed into joint effusion during sonographically
guided aspiration.
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Fig. 18C. —17-year-old boy with hip joint effusion. Arrows indicate
anterior femoral cortex. Longitudinal sonogram of hip in same location as
A shows diminished amount of joint effusion (+ and x) after
aspiration.
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Fig. 19B. —65-year-old man with extraarticular thigh abscess.
Longitudinal power Doppler sonogram of anteromedial proximal thigh reveals
large ill-defined hypoechoic region (black arrows) in soft tissues
extending to femoral cortex (white arrows). Sonographically guided
aspiration revealed infection. Artifact from overwriting of power Doppler
signal shows needle tract (arrowheads) after needle was withdrawn. FH
= femoral head.
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Fig. 19C. —65-year-old man with extraarticular thigh abscess. Axial CT
image obtained with IV contrast material shows large abscess (arrows)
in anteromedial thigh. Drain was subsequently placed under CT guidance.
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Top
Introduction
Foot and Ankle
