Tải bản đầy đủ (.pdf) (13 trang)

Hình ảnh cộng hưởng từ của các chân và mắt cá doc

Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (1.71 MB, 13 trang )

Vol 9, No 3, May/June 2001
Magnetic resonance (MR) imaging
of the foot and ankle has lagged
behind MR imaging of other joints
in clinical acceptance and utility,
because of the complex anatomy of
the foot and ankle and the need for
small-field-of-view, high-resolution
images. Recent advances in both
hardware and software, however,
have made possible the acquisition
of high-resolution images. This
feature, combined with the degree
of soft-tissue contrast that can be
achieved with MR imaging and the
ability to obtain images in multiple
planes, has led to the increasing
importance of this modality in
imaging of the foot and ankle for
both diagnosis and surgical plan-
ning. It is important that physi-
cians understand the common clin-
ical MR imaging techniques and
their role in evaluating disorders
of the foot and ankle to most effec-
tively utilize this diagnostic mo-
Because of the complex anatomy of
the foot and ankle and the small

size of many of its structures, the
acquisition of high-resolution im-
ages is necessary. To obtain such
images, the foot and ankle should
be imaged separately by using a
surface coil. When a comparison
view of the unaffected foot is needed
to assess tendon or ligament sym-
metry, this should be accomplished
by scanning each foot separately in
a surface coil. Attempting to scan
both feet together in a body coil or a
head coil saves time but at the cost
of having to use a large field of view,
which results in low-resolution im-
ages that are often nondiagnostic.
The optimal field of view of the im-
ages should be no larger than 16
, and the matrix should range
from 192 x 256 to 256 x 512. Section
thickness depends on the pulse
sequence used but should be 3 to 4
mm when using spin-echo (SE) se-
quences and 1 to 2 mm when using
gradient-echo (GRE) sequences.
For the purpose of MR imaging,
the foot and ankle can be divided
into three zones: the ankle and

hindfoot, the midfoot, and the fore-
The midfoot is adequately
examined by imaging both the
hindfoot and the forefoot; there-
fore, examination protocols can be
further simplified into two zones:
ankle-hindfoot and forefoot.
To image the hindfoot and ankle,
the patient is placed in a supine
position with the medial malleolus
centered in the coil. The foot is
allowed to rest in a relaxed posi-
tion, generally in 10 to 20 degrees of
plantar-flexion and 10 to 30 degrees
of external rotation. The foot posi-
tion may need to be altered when
imaging specific ligaments, such as
the calcaneofibular ligament. For
forefoot examinations, the patient
can be either supine or prone with
Dr. Recht is Section Head, Outside Imaging,
Department of Diagnostic Radiology, Cleve-
land Clinic Foundation, Cleveland, Ohio. Dr.
Donley is Staff Surgeon, Department of Ortho-
paedic Surgery, Cleveland Clinic Foundation.
Reprint requests: Dr. Recht, Department of
Diagnostic Radiology, Cleveland Clinic
Foundation, A21, 9500 Euclid Avenue,

Cleveland, OH 44195.
Copyright 2001 by the American Academy of
Orthopaedic Surgeons.
Magnetic resonance (MR) imaging of the foot and ankle is playing an increas-
ingly important role in the diagnosis of a wide range of foot and ankle abnormali-
ties, as well as in planning for their surgical treatment. For an optimal MR
study of the foot and ankle, it is necessary to obtain high-resolution, small-field-
of-view images using a variety of pulse sequences. The most common indication
for MR imaging of the foot and ankle is for the evaluation of tendon and bone
abnormalities, such as osteomyelitis, occult fractures, and partial and complete
tears of the Achilles, tibialis posterior, and peroneal tendons. Magnetic reso-
nance imaging has also been shown to be helpful in the diagnosis of several soft-
tissue abnormalities that are unique to the foot and ankle, such as plantar fasci-
itis, plantar fibromatosis, interdigital neuromas, and tarsal tunnel syndrome.
J Am Acad Orthop Surg 2001;9:187-199
Magnetic Resonance Imaging of
the Foot and Ankle
Michael P. Recht, MD, and Brian G. Donley, MD
the toes centered in the coil. It is im-
portant to image in all three planes
(transaxial, sagittal, and coronal) for
all indications. However, for ten-
don and ligament disorders as well
as for soft-tissue masses, the trans-
axial plane of imaging is the most
useful; most sequences should be
acquired in this plane. For bone ab-
normalities, particularly those of the
talar dome, the sagittal and coronal

planes provide the greatest amount
of information.
A variety of pulse sequences can
be utilized in the examination of the
foot and ankle. T1-weighted (short
repetition time [TR]/short echo time
[TE]) SE images provide excellent
anatomic detail and information
about the integrity of the bone mar-
row. T2-weighted (long TR/long
TE) SE images allow detection of the
increased water content seen with
most pathologic processes as abnor-
mal high signal intensity. Fast SE
T2-weighted sequences have largely
replaced conventional SE T2-weighted
sequences because of the ability to ob-
tain images in a shorter time period
with higher resolution. Gradient-
echo sequences allow the acquisition
of thin contiguous sections that can
be reformatted in multiple planes.
These sequences have been shown
to be useful in the detection of carti-
lage abnormalities.
Short-tau inversion recovery
(STIR) imaging is a method of fat
suppression that has proved very
sensitive in detecting marrow ab-

normalities, as well as increased
water content in soft tissues.
rently, most STIR sequences also use
a variant of the fast SE technique,
which allows the images to be ac-
quired in a shorter period of time.
Another method of fat suppression is
the use of chemical-selective fat sup-
pression, which takes advantage of
the differences in resonance frequen-
cy between fat and water protons.
When evaluating a soft-tissue or
osseous mass, T1-weighted chemical-
selective fat-suppressed imaging
after injection of intravenous con-
trast material (e.g., gadolinium–
diethylenetriaminepenta-acetic acid
[DTPA]) improves the conspicuity
of the mass and facilitates the differ-
entiation of a solid soft-tissue mass
from a fluid-filled cyst.
resonance arthrography may play a
role in the detection of ligament
abnormalities and intra-articular
bodies and in the staging of osteo-
chondral defects.

The foot and ankle can be im-
aged with high-field-strength (>0.5-
T) or low-field-strength (≤0.5-T)
magnets. A high-field-strength
MR Imaging of the Foot and Ankle
Journal of the American Academy of Orthopaedic Surgeons
Definitions of Radiologic Terms
Chemical-selective The use of chemically selective radio-frequency
fat suppression pulses to eliminate fat signal by taking advantage
of the difference in resonance frequency between
fat and water protons
Echo time (TE) The time between the middle of the excitation pulse
and the middle of the spin echo
Gradient-echo (GRE) Describing a sequence in which an echo is produced
by a single radio-frequency pulse followed by a
gradient reversal
Proton-density- An image acquired with a long TR (e.g., 2,000-3,000
weighted image msec) and a short TE (e.g., 20 msec) to emphasize
differences in proton density and minimize T1 and T2
differences between tissues
Repetition time (TR) The time between successive excitations of a section
Short-tau inversion Describing a sequence that suppresses fat signal by
recovery (STIR) the use of a 180-degree inversion pulse and a short
inversion time
Spin-echo (SE) Describing a sequence in which an echo is produced
by a 90-degree radio-frequency pulse followed by
one or more 180-degree radio-frequency pulses
T1 Spin-lattice or longitudinal relaxation time. The

time constant for magnetization to return to the
longitudinal axis after application of a radio-
frequency pulse.
T1-weighted image An image acquired with a short TR (e.g., 400-600
msec) and a short TE (e.g., 10-20 msec) to emphasize
differences in T1 relaxation rates between tissues.
Fat is of high signal intensity, and fluid is of low
signal intensity on T1-weighted sequences.
T2 Spin-spin relaxation time. The time constant for loss
of phase coherence of a group of spins and the
resulting loss in the transverse magnetization signal.
T2-weighted image An image acquired with a long TR (e.g., 2,000-3,000
msec) and long TE (e.g., 80-100 msec) to emphasize
differences in T2 between tissues. Fluid is bright on
T2-weighted sequences.
magnet, with its higher signal-to-
noise ratio, allows the acquisition of
high-resolution images in a shorter
time period, thus decreasing the
potential for patient motion. In
addition, chemical-selective fat sup-
pression is not available with low-
field-strength magnets.
Ten tendons cross the ankle joint on
their path from the lower leg into
the foot (Fig. 1): the Achilles ten-
don posteriorly; the peroneus bre-
vis and longus laterally; the tibialis
posterior, flexor digitorum longus,

and flexor hallucis longus medially;
and the tibialis anterior, extensor
digitorum longus, extensor hallucis
longus, and peroneus tertius anteri-
orly. Tendons are composed primar-
ily of collagen, elastin, and reticulin
Normal tendons appear as ho-
mogeneous low signal intensity on
MR imaging because of their lack
of mobile protons.
However, on
T1-weighted and proton-density-
weighted (long TR/short TE) im-
ages, normal tendons can have inter-
mediate signal intensity because of
the “magic angle effect.”
This effect
occurs with short-TE sequences
because the signal intensity of struc-
tures with poorly hydrated protons,
such as tendons, depends in part
on the orientation of the structure
in relation to the main magnetic
field. When a structure is oriented
obliquely in relation to the main
magnetic field, its signal intensity is
increased on short-TE sequences;

this increase is greatest when the
structure is oriented at 55 degrees in
relation to the main magnetic field.
The increase in signal intensity is
not seen on long-TE (T2-weighted)
sequences. The magic-angle effect is
noted in most of the tendons of the
foot and ankle as they curve across
the ankle to pass into the foot. How-
ever, this normal increase in signal
intensity can usually be differenti-
ated from pathologic changes within
the tendon if one is aware of the
characteristic location of the magic-
angle effect, the lack of high signal
intensity on T2-weighted images,
and the normal morphology of
intact tendons.
The transaxial plane is the most
useful for evaluating the integrity of
tendons. To obtain a true transaxial
image of the tendons that traverse
the ankle to pass into the foot, it is
necessary to select a plane perpen-
dicular to the long axis of the ten-
dons as they curve about the ankle
(Fig. 2). A useful protocol for tendon
pathology includes transaxial T1-
weighted SE and STIR images or fat-
suppressed fast SE T2-weighted

images (obtained with the same sec-
tion thickness and positions to allow
comparison), coronal T1-weighted,
and sagittal fat-suppressed fast SE
T2-weighted sequences. A sagittal
T1-weighted sequence is added
when examining the Achilles tendon.
Pathologic changes that can be
seen in and about tendons on MR
imaging include tenosynovitis,
tendinopathy, and tendon tears.
Tenosynovitis is best visualized on
T2-weighted images as high-signal-
intensity fluid surrounding a normal-
appearing tendon (Fig. 3). “Ten-
dinopathy” or “tendinosis” is the
term currently favored to describe
tendons that are abnormal but not
torn. Although some authors still
use the term “tendinitis,” studies
have not shown a true inflammatory
process in tendons.
Rather, histo-
logic studies have demonstrated
hyperplasia, fibrosis, and vacuolar,
mucoid, eosinophilic, and fibrillary
degeneration. On MR imaging,
tendinopathy is characterized by
altered tendon morphology, usual-

ly thickening. There may also be
areas of mildly increased signal
intensity on short TE (T1-weighted
or proton-density-weighted) se-
quences, but this signal intensity
usually decreases on T2-weighted
images unless severe tendinopathy
is present.
Three MR patterns of tendon
rupture have been described.
Michael P. Recht, MD, and Brian G. Donley, MD
Vol 9, No 3, May/June 2001
Figure 1 Transaxial T1-weighted image
at the level of the distal tibia (T) and fibula
(F). Note the homogeneous low signal
intensity of the tendons. A = Achilles ten-
don; ED = extensor digitorum longus; EH
= extensor hallucis longus; FD = flexor dig-
itorum longus; FH = flexor hallucis longus;
PB = peroneus brevis; PL = peroneus
longus; TA = tibialis anterior; TP = tibialis

Figure 2 True transaxial images of the
peroneal tendons. The sections are graphi-
cally prescribed off a sagittal image as the
tendons curve around the ankle.
Type 1 is characterized by hypertro-
phy of the tendon with partial tears
oriented primarily longitudinally.
The tendon is enlarged (Fig. 4, A),
with foci of increased signal inten-
sity on T2-weighted and STIR images
(Fig. 4, B). Type 2 is characterized
by a partially torn atrophic tendon;
the appearance is of a small tendon
with foci of increased signal intensi-
ty on T2-weighted or STIR images
(Fig. 4, C). Type 3 tears are com-
plete tendon ruptures (Fig. 4, D).
Although all of the tendons of the
foot and ankle can be studied with
MR imaging, the tendons most
often associated with injury or dis-
ease are the Achilles, tibialis poste-
rior, and peroneal tendons.
Achilles Tendon
The Achilles tendon is the largest

and strongest tendon in the body,
ranging in length from 10 to 15 cm.
The Achilles tendon does not pos-
sess a synovial sheath but rather is
invested by loose connective tissue
(peritenon). The normal Achilles
tendon appears as homogeneously
low signal intensity on all pulse
(Fig. 5, A and B). It has
a flat or concave anterior margin on
transaxial images, giving it a cres-
centic shape. At its insertion onto
the calcaneus, the tendon becomes
more ovoid, with a flattened anterior
Acute peritendinitis is manifested
by loss of the sharp interface be-
tween the tendon and the pre-
Achilles fat, with high signal inten-
sity on T2-weighted and STIR
images about the tendon, but with
preservation of the low signal in-
tensity of the tendon itself. Chronic
Achilles tendinopathy has the
appearance of a thickened enlarged
tendon (Fig. 5, C and D). There
may be increased signal intensity
within the tendon on T1-weighted

and proton-density-weighted im-
ages, but the signal usually de-
creases in intensity on T2-weighted
and STIR images. Although mea-
surements of the thickness of the
Achilles tendon have been pub-
lished (normal, <8 mm),
assessment of the anterior margin
of the tendon on transaxial views
may be more useful. Loss of the
normal concave margin of the ante-
rior aspect of the tendon is a sign
that the tendon is thickened and
MR Imaging of the Foot and Ankle
Journal of the American Academy of Orthopaedic Surgeons
Figure 3 Tenosynovitis of the flexor hallu-
cis tendon. Note the high-signal-intensity
fluid (arrows) surrounding the normal
low-signal-intensity tendon and the metal-
lic artifact about the tibia secondary to pre-
vious hardware placement.
Figure 4 Patterns of tendon rupture. A, Type 1 tear of the tibialis posterior tendon. Transaxial T1-weighted image at the level of the
sustentaculum tali demonstrates an enlarged, irregularly shaped tibialis posterior tendon (arrow). B, Transaxial STIR image of the same
ankle demonstrates high signal intensity within the enlarged tibialis posterior tendon (arrows). C, Type 2 tear of the tibialis posterior ten-
don. Transaxial T1-weighted image demonstrates a small atrophic tibialis posterior tendon (white arrows) approximately half the diame-
ter of the flexor digitorum tendon (black arrow). D, Type 3 tear of the Achilles tendon. Sagittal T2-weighted fast SE image demonstrates

discontinuity of the Achilles tendon. There is retraction of the torn edge of the tendon (arrows) and high signal intensity in the gap
between the tendon edge and the calcaneus.
Ruptures of the Achilles tendon
most frequently occur 3 to 4 cm
above its insertion onto the calca-
The MR findings of a partial
rupture include focal areas of high
signal intensity on T2-weighted
and STIR images within the tendon
substance but with preservation of
some tendon continuity
(Fig. 5, E
and F). Acute complete ruptures
demonstrate loss of tendon conti-
nuity, with the gap in the tendon
appearing as an area of high signal
intensity on T2-weighted and STIR
images, representing blood or ede-
(Fig. 4, D). In chronic com-
plete ruptures, the gap may be
filled with low-signal-intensity
fibrotic tissue.
Tibialis Posterior Tendon
Tibialis posterior tears are most

commonly seen in middle-aged
women, who present with an ac-
quired, painful flatfoot; these are
generally chronic tears.
The tib-
ialis posterior tendon is the most
medial tendon in the posterior com-
partment at the level of the ankle.
The tendon continues into the foot,
where it inserts onto the navicular,
Michael P. Recht, MD, and Brian G. Donley, MD
Vol 9, No 3, May/June 2001
Figure 5 A and B, Normal Achilles ten-
don. A, On T1-weighted sagittal image,
the normal Achilles tendon is of homoge-
neous low signal intensity and has sharp
interfaces with the surrounding soft tissue.
B, Transaxial T1-weighted image at the
level of the distal Achilles tendon. The
concave anterior surface of the tendon
gives a crescentic shape to the distal por-
tion (arrowheads). C and D, Chronic

tendinopathy of the Achilles tendon. T2-
weighted sagittal (C) and T1-weighted
transaxial (D) images demonstrate a thick-
ened Achilles tendon (arrows), which is of
low signal intensity. Note the loss of the
normal concave anterior surface of the ten-
don on the transaxial image. E and F,
Partial tear of the distal Achilles tendon.
T1-weighted (E) and T2-weighted (F) sagit-
tal images demonstrate an enlarged, thick-
ened distal Achilles tendon. On the T2-
weighted image, there is high signal inten-
sity (arrow) within the distal Achilles ten-
don, representing a partial tear.
medial cuneiform, metatarsal bases,
and sustentaculum tali. The normal
tibialis posterior tendon has homo-
geneously low signal intensity ex-
cept for its most distal segment,
which may demonstrate intermedi-
ate signal intensity on T1-weighted
sequences. It should be twice the
diameter of the flexor digitorum
longus and flexor hallucis longus
tendons distal to the level of the
medial malleolus.
Type 1 tears of the posterior tib-
ialis tendon, which are the most
common type of tear, are manifested

by an enlarged tendon, which may
be four to five times the size of the
flexor digitorum tendon (Fig. 4, A
and B). There is increased signal
intensity within the tendon on short-
TE images, which often remains
high on T2-weighted and STIR
images. Type 2 tears present as a
smaller than normal tendon, often
the same size as or smaller than the
flexor digitorum longus (Fig. 4, C).
Type 3 tears are complete tendon
Peroneal Tendons
The peroneus longus and brevis
tendons occupy a common synovial
sheath up to the level of the calca-
neocuboid joint, beyond which the
sheath bifurcates. At the level of the
lateral malleolus, the peroneus bre-
vis tendon is anteromedial or ante-
rior to the peroneus longus tendon.
The posterior edge of the fibula is
normally concave in this region,
forming a groove within which the
tendons lie. The tendons are kept
within this groove by the superior
peroneal retinaculum.
On MR imaging, normal peroneal
tendons are of similar size and ho-

mogeneous low signal intensity.
The peroneus longus tendon is
ovoid, but the peroneus brevis ten-
don may have a flattened appear-
ance in the retromalleolar groove.
The superior peroneal retinaculum
is usually identifiable as a discrete
Although complete ruptures of
the peroneal tendons are uncom-
mon, longitudinal splits of the per-
oneus brevis tendon have been
increasingly recognized.
tudinal splits are thought to be
caused by either forced dorsiflexion
or repetitive peroneal subluxation,
which leads to compression of the
peroneal brevis against the posterior
aspect of the fibula. Interposition of
the peroneus longus between the
portions of the split peroneus brevis
tendon can occur. On MR imaging,
a split peroneus brevis appears
either as a C-shaped structure at or
below the level of the lateral malleo-
lus, which partially wraps around
the peroneus longus tendon, or as a
completely bisected tendon (Fig. 6,

A). There may or may not be in-
creased signal intensity within the
tendon. An osseous ridge at the lat-
eral margin of the fibula has been
associated with a split peroneus bre-
vis tendon, and is considered to rep-
resent changes secondary to repeti-
tive subluxation of the peroneal ten-
Other MR findings that are
associated with, and may predispose
to, splitting of the peroneus brevis
MR Imaging of the Foot and Ankle
Journal of the American Academy of Orthopaedic Surgeons
Figure 6 Lesions of the peroneal tendons. A, Transaxial T1-weighted image obtained just distal to the lateral malleolus demonstrates a
completely bisected peroneus brevis tendon (arrowheads). T1-weighted transaxial (B) and coronal (C) images show subluxation of the
peroneal tendons (arrows) so that they lie lateral to the malleolus, rather than posterior to it.
tendon include a flat or convex fibu-
lar groove, a ligamentous tear, or
the presence of a peroneus quartus
muscle or the low-lying belly of the
peroneus brevis muscle.
Traumatic peroneal subluxation
or dislocation is associated with dis-
ruption of the superior retinaculum
or stripping of the periosteum at its

attachment onto the fibula. This is
not an uncommon injury in athletes
and may be misdiagnosed as an
ankle sprain.
Traumatic dislocation
can also be seen with calcaneal frac-
tures. The abnormally positioned
peroneal tendons are easily seen on
MR images lying lateral (Fig. 6, B
and C), or in extreme cases anterior,
to the lateral malleolus.
Ankle Ligaments
Magnetic resonance imaging can
demonstrate both intact (Fig. 7) and
abnormal (Fig. 8) ankle ligaments.
However, its role in the evaluation
of ankle ligament injuries remains
uncertain, especially in cases of
acute ligament injury, which are
most often diagnosed on clinical
examination. It may play a limited
role in defining which ligaments
are injured, the extent of such in-
jury in patients with chronic ankle
instability, and the presence of os-
teochondral injuries of the talar
dome in patients with chronic ankle
pain after ligament injuries.
The ankle ligaments can be

grouped into three complexes: the
lateral complex, consisting of the
anterior talofibular, posterior talo-
fibular, and calcaneofibular liga-
ments; the deltoid ligament, which
has several components; and the
syndesmotic complex, composed of
the interosseous membrane, the
anterior and posterior tibiofibular
ligaments, and the transverse tibio-
fibular ligament. To evaluate these
ligaments with MR imaging, it is
necessary to image them in a plane
parallel to their long axes. This
plane varies for the different liga-
ments, but a cadaveric study of the
ankle ligaments demonstrated that
particular planes were optimal for
studying the various ligaments.
The transaxial plane with the foot
positioned in 10 to 20 degrees of
dorsiflexion provides the best visual-
ization of the anterior and posterior
talofibular ligaments; the anterior,
Michael P. Recht, MD, and Brian G. Donley, MD
Vol 9, No 3, May/June 2001

Figure 7 Appearance of normal ankle ligaments. A, The intact anterior talofibular liga-
ment (arrowheads) is of low signal intensity on this T1-weighted transaxial image. Note
the elliptical shape of the talus and the presence of the lateral malleolar fossa. B, Intact
anterior (arrowheads) and posterior (arrows) tibiofibular ligaments are of uniform low sig-
nal intensity. The medial border of the lateral malleolus is flattened, indicating that this is
the level of the tibiofibular ligaments. C, Intact tibiotalar component of the deltoid (arrow-
heads). Note the osteochondral defect of the lateral talar dome. D, Posterior talofibular
ligaments (arrowheads) on T1-weighted coronal image. The deltoid and posterior
talofibular ligaments have a striated appearance, rather than a homogeneous low-signal-
intensity appearance like the anterior talofibular ligament.
transverse, and posterior tibiofibu-
lar ligaments; and the various com-
ponents of the deltoid ligament.
Coronal images allow visualization
of the full length of most of the com-
ponents of the deltoid ligament. The
calcaneofibular ligament is best seen
on transaxial images with the foot in
40 to 50 degrees of plantar-flexion.
It is difficult to image the foot in
all of these positions in a reasonable
time period. Most MR examinations
of the foot and ankle are done in 10
to 20 degrees of plantar-flexion,
which is not ideal for imaging any of
the ankle ligaments. Therefore, it is
important to clearly communicate in
advance which specific ligamentous

complexes need to be imaged. The
MR sequences used to evaluate the
ankle ligaments include T1-weighted
SE, T2-weighted fast SE, and STIR
sequences. In cases of chronic ankle
instability, MR arthrography may
also be useful.
Normal ligaments are thin and of
low signal intensity on all MR pulse
sequences. Occasionally, they have
a striated appearance, especially the
deltoid and posterior talofibular
and tibiofibular ligaments.
cause of the oblique course of the
tibiofibular ligaments, the talus may
be seen on images demonstrating
their fibular attachments. This can
lead to misidentification of the
tibiofibular ligaments as the talo-
fibular ligaments. The best way to
avoid this mistake is to identify the
insertion of the ligaments. The
shape of the talus and the fibula in
the transaxial plane can also be used
to correctly identify the two sets of
At the level of the tibio-

fibular ligaments, the talus is rectan-
gular, and the medial border of the
fibula is flattened. At the level of
the talofibular ligaments, the talus is
more elongated, the sinus tarsi is
usually visible, and there is a deep
indentation along the medial border
of the lateral malleolus (the malleo-
lar fossa).
The MR findings in ligament
injuries include complete tear of the
ligament, ligament waviness or lax-
ity, thickening or irregularity of the
ligament, increased signal intensity
within the ligaments, edema and
hemorrhage about the ligament,
and abnormal increased fluid with-
in the joint and surrounding ten-
In cases of chronic insta-
bility, some of the ancillary findings
of ligament injury, such as edema
and hemorrhage and joint effusions,
may not be present.
Magnetic resonance arthrography
has been shown to be more sensitive
and more accurate than conventional
MR imaging in this situation.

is because the torn, scarred ligament
is closely applied to the bone and is
better visualized when separated
from the bone by the intra-articular
injection of contrast material (Gd-
DTPA). In addition, contrast extra-
vasation through the torn ligament
into the surrounding soft tissues
serves as convincing evidence of dis-
ruption of the ligament.
Infection of the bones of the foot
and ankle occurs most commonly in
diabetic patients, usually due to
direct extension of soft-tissue infec-
tion. Magnetic resonance images,
especially STIR and fat-suppressed
T1-weighted images acquired after
intravenous contrast administration
effectively depict the bone marrow
changes that occur with osteomye-
However, these changes are
not specific for osteomyelitis. The
differentiation of bone marrow
changes due to infection from those
due to edema or neuropathy has

proved challenging.
Although neuropathic tissue may
be visualized as low signal intensity
on all pulse sequences,
it may
have a high-signal-intensity appear-
ance on T2-weighted and STIR
Enhancement after
intravenous contrast administration
is also not specific, as it can be seen
in the presence of any process result-
ing in increased vascular permeabili-
ty. Findings useful in the diagnosis
of osteomyelitis include soft-tissue
changes that extend to the skin
surface adjacent to bone-marrow
changes, cortical disruption, and
periosteal abnormalities (Fig. 9).
Nonetheless, it is still often difficult
to reliably differentiate neuropathy
from infection on MR imaging. A
useful protocol for the evaluation of
osteomyelitis includes T1-weighted
SE, STIR, and fat-suppressed T1-
weighted SE images obtained after
contrast administration. The images

are acquired in at least two planes,
which are determined on the basis
of the site of the suspected infection.
Magnetic resonance imaging has
little role to play in the evaluation of
acute traumatic bone injuries, as
they are usually easily diagnosed on
conventional radiography. How-
ever, MR imaging may be useful in
MR Imaging of the Foot and Ankle
Journal of the American Academy of Orthopaedic Surgeons
Figure 8 Chronic tear of the anterior
talofibular ligament. This transaxial T2-
weighted image demonstrates the absence
of the anterior talofibular ligament, with
high-signal-intensity fluid (arrows) filling
the expected location of the ligament.
identifying bone contusions, occult
nondisplaced fractures, and stress
fractures and stress reactions in the
foot and ankle. Metatarsal stress
fractures can generally be diag-
nosed without MR imaging. In con-
trast, stress fractures of other tarsal
bones, such as the navicular, cunei-
forms, and calcaneus, often present
as foot pain of unknown etiology. If
conventional radiographs appear

normal, MR imaging is a valuable
modality, as it can depict pathologic
changes in both bone and soft tissue.
Stress fractures are diagnosed most
readily on STIR and T1-weighted
SE images but can also be seen on T2-
weighted images (Fig. 10). On T1-
weighted images, stress fractures
appear as a linear area of low signal
intensity compared with normal
bone marrow surrounded by a more
diffuse area of slightly higher, though
still low, signal intensity.
images, the linear component re-
mains of low signal intensity, but the
surrounding area is of high signal
intensity, consistent with bone mar-
row edema.
In addition to stress fractures, MR
imaging is also able to depict stress
responses, which represent early
changes in bone before the develop-
ment of a fracture.
Stress responses
are characterized by globular areas of
low signal intensity on T1-weighted
images, which increase in signal

intensity on STIR sequences. They
can be differentiated from fractures
by the lack of a linear component.
Stress responses appear similar to
bone bruises but can be differen-
tiated from them by the lack of an
antecedent acute traumatic event.
Osteochondral Injuries
of the Talar Dome
Osteochondral injuries of the
talar dome occur most commonly in
the second to fourth decades of life
and affect both the medial and lat-
eral aspects of the dome.
lesions are apparent on conventional
radiographs; however, MR imaging
can depict lesions too small to be
seen on plain films and may be use-
ful in evaluating the extent of the
lesion and the stability of the frag-
Increased signal intensity
separating the lesion from the un-
derlying bone on T2-weighted or
STIR images is the most frequent
MR sign of instability, but this ap-
pearance has also been reported in

stable lesions.
Other less fre-
quently seen signs of instability are
cartilage fractures, focal cartilage
defects, and underlying cysts.
Magnetic resonance arthrogra-
phy has been shown to be more
accurate in evaluating the stability
of the fragment than conventional
MR imaging in osteochondral le-
sions of the knee,
because of the
ability to see contrast material tra-
versing the overlying cartilage de-
fect and encircling the loose frag-
ment. More recently, cartilage-specific
sequences, such as fat-suppressed
T1-weighted GRE sequences, have
been used to evaluate the overlying
cartilage (Fig. 11). Although MR
imaging is highly accurate for eval-
uating the cartilage in the knee,
Michael P. Recht, MD, and Brian G. Donley, MD
Vol 9, No 3, May/June 2001

Figure 9 Osteomyelitis of the calcaneus. A, Sagittal T1-weighted image demonstrates a
soft-tissue ulcer (white arrow) on the plantar surface of the foot adjacent to the area of
abnormal low signal intensity within the calcaneus (black arrows). B, Sagittal fat-
suppressed T1-weighted image shows enhancement (arrows) of the calcaneus and adjacent
soft tissues, as well as subtle cortical disruption (lower arrow).
Figure 10 Stress fracture of the navicular.
Coronal T2-weighted image demonstrates
high signal intensity within the navicular
surrounding a thin linear area of low signal
intensity (arrowheads), which represents
the fracture line.
evaluation of talar cartilage has
been more difficult, even with both
sagittal and coronal images, because
the talar cartilage is considerably
Bone Tumors
Although MR imaging is very
sensitive in the detection of bone
tumors, it frequently lacks specific-
ity. However, MR imaging can be
useful in evaluating the extent of
the tumor and the presence of an
associated soft-tissue mass. The
imaging is done in all three planes
with a combination of T1-weighted
SE, STIR, and T2-weighted fast
SE sequences. Occasionally, a fat-
suppressed T1-weighted sequence
is used after administration of in-

travenous contrast material, as it
increases the conspicuity of the
bone and soft-tissue abnormalities
and improves the differentiation of
necrotic tissue from viable tumor.
In addition, some researchers have
suggested that dynamic contrast-
enhanced MR imaging may be use-
ful in assessing the response of
osteosarcoma and Ewing’s sarcoma
to chemotherapy.
Associated Soft-Tissue
Plantar Fasciitis
The deep plantar fascia, or plan-
tar aponeurosis, is a multilayered
fibrous structure, subcutaneous in
location, which extends as a thick,
strong, dense tissue from the calca-
neus posteriorly to the region of
the metatarsal heads and beyond.
Plantar fasciitis is one of the causes
of painful heel syndrome and may
be secondary to mechanical, degen-
erative, or systemic conditions.
The plantar fascia is best visual-
ized on sagittal and coronal images
and normally should be 3 to 4 mm

thick and of homogeneously low
signal intensity on all pulse se-
In patients with plantar
fasciitis, the plantar fascia is thick-
ened (7 to 8 mm thick) and demon-
strates areas of increased signal
intensity on T2-weighted and STIR
(Fig. 12). There fre-
quently is also abnormally increased
signal intensity in the adjacent sub-
cutaneous tissue. Increased signal
intensity may also be seen in the cal-
caneus at the insertion site of the
plantar fascia, presumably second-
ary to reactive edema.
Plantar fasciitis is a clinical diag-
nosis and rarely, if ever, warrants
MR imaging. However, in patients
with a painful heel syndrome, it can
occasionally be helpful in excluding
other etiologic possibilities, such as
calcaneal stress fractures and tarsal
tunnel masses.
Plantar Fibromatosis
Plantar fibromatosis is character-
ized by fibrous proliferation in the

plantar fascia.
An association be-
tween plantar fibromatosis and
other conditions associated with
proliferation of fibrous tissue, such
MR Imaging of the Foot and Ankle
Journal of the American Academy of Orthopaedic Surgeons
Figure 11 Osteochondral injury of the talar dome. A, T1-weighted coronal image demon-
strates deformity of the talar dome, with a focal area of low signal intensity within the
bone marrow of the talar dome (arrows). B, Fat-suppressed three-dimensional GRE coro-
nal image depicts articular cartilage as high signal intensity. There is disruption of the
articular cartilage (arrows) overlying the signal abnormality within the talar dome.
Figure 12 Plantar fasciitis. A, T1-weighted sagittal image shows thickened deep plantar
fascia at its insertion onto the calcaneus (arrow). There is also abnormal intermediate sig-
nal intensity within the deep plantar fascia. B, Sagittal STIR image demonstrates abnormal
high signal intensity about the deep plantar fascia (arrow).
as Dupuytren’s contracture and
Peyronie’s disease, has been sug-
gested but not proved.
When obtaining an MR study,
images in all three planes should be
acquired, although those in the
sagittal and coronal planes are the
most helpful. The MR appearance
of plantar fibromatosis is frequently

characteristic, presenting as single
or (less commonly) multiple nod-
ules in the subcutaneous tissues of
the plantar aspect of one or both
feet. The dorsal margin of the lesion
is usually ill defined, but the plantar
margin is well defined against the
subcutaneous fat. The nodules typi-
cally are less than 3 cm in size. On
T1-weighted images, the masses are
usually isointense to slightly hypo-
intense to skeletal muscle; they
remain of intermediate to minimally
increased signal intensity on T2-
weighted images
(Fig. 13). On
STIR imaging, the nodules can be of
increased signal intensity (hyperin-
tense to skeletal muscle). After in-
travenous contrast administration,
there is variable enhancement.
Interdigital Neuroma
Interdigital (Morton’s) neuroma
(Fig. 14) is a benign, nonneoplastic
condition consisting of perineural
fibrosis, most likely due to entrap-
The lesions most commonly

occur in the second and third inter-
metatarsal spaces at the level of the
metatarsal heads. Although the
diagnosis rarely requires MR imag-
ing, it can be useful in confirming
the presence or absence of interdigi-
tal neuromas in clinically difficult
cases, can identify multiple lesions,
and can also help localize the le-
sions. The accuracy of MR imaging
in diagnosing interdigital neuromas
has been reported to be as high as
but the diagnosis is more dif-
ficult when the lesion is smaller than
5 mm.
The coronal plane is optimal for
detecting such lesions, as it is per-
pendicular to the long axis of the
metatarsal shafts. It is important to
image from the base of the meta-
tarsals through the proximal inter-
phalangeal joints, as the lesions
may be distal or proximal to the
usual location. Lesions are best
visualized on T1-weighted images,
where they are of low signal inten-
sity and are surrounded by high-
signal-intensity subcutaneous fat.

The lesions remain of low signal
intensity on T2-weighted images,
which allows their differentiation
from true neuromas, synovial cysts,
and fluid-filled intermetatarsal bur-
sae. They frequently have increased
signal intensity on STIR images,
and there is variable enhancement
after administration of intravenous
contrast material.
Tarsal Tunnel Syndrome
Tarsal tunnel syndrome (Fig. 15)
is caused by entrapment of the pos-
terior tibial nerve and its branches
(i.e., the medial and lateral plantar
nerves) within the tarsal tunnel, a
fibro-osseous tunnel that lies be-
neath the flexor retinaculum on the
medial side of the foot. The floor of
the tarsal tunnel is osseous and is
formed by the medial surface of the
talus, the sustentaculum tali, and the
medial wall of the calcaneus. The
Michael P. Recht, MD, and Brian G. Donley, MD
Vol 9, No 3, May/June 2001
Figure 13 Plantar fibromatosis. T1-weighted (A) and T2-weighted (B) coronal images
demonstrate a mass (arrowheads) associated with the plantar fascia. The mass is isoin-
tense to skeletal muscle on the T1-weighted image and remains of low signal intensity on
the T2-weighted image. There is a marker on the plantar aspect of the foot to identify the

site of the palpable mass.
Figure 14 Interdigital neuromas of the
second and third interspaces. T1-weighted
coronal image demonstrates intermediate-
signal-intensity masses in the second and
third interspaces, which have a dumbbell
roof is formed by the flexor retinacu-
lum. Several structures lie within
the tarsal tunnel, among them the
tibialis posterior, flexor digitorum,
and flexor hallucis longus tendons;
the posterior tibial artery and vein;
and the posterior tibial nerve.
There are a variety of causes of
tarsal tunnel syndrome, including
compression of the nerve by space-
occupying lesions and conditions
that place tension across the flexor
Magnetic resonance
imaging, particularly transaxial
imaging, provides excellent visuali-
zation of the tarsal tunnel and the
structures within it and therefore
can play a valuable role in preoper-
ative assessment when tarsal tunnel
syndrome is suspected.

Magnetic resonance imaging of the
foot and ankle is playing an in-
creasingly important role in the
diagnosis of a wide range of foot
and ankle abnormalities and the
planning for their surgical treat-
ment. It is important to obtain
high-resolution images of the foot
and ankle in multiple planes with
the use of appropriate pulse se-
quences. When this is accom-
plished, disorders of tendons, liga-
ments, bone, and soft tissue can be
accurately diagnosed.
MR Imaging of the Foot and Ankle
Journal of the American Academy of Orthopaedic Surgeons
Figure 15 Space-occupying lesion of the tarsal tunnel. A, T1-weighted transaxial image
demonstrates an intermediate-signal-intensity mass (arrows) within the tarsal tunnel, rep-
resenting lymphoma. B, T2-weighted transaxial image demonstrates a multiseptate high-
signal-intensity mass (arrows) within the tarsal tunnel, representing a ganglion.
1. Mink JH: Tendons, in Deutsch AL,
Mink JH, Kerr R (eds): MRI of the Foot
and Ankle. New York: Raven Press,
1992, p 135.
2. Recht MP, Piraino DW, Paletta GA,
Schils JP, Belhobek GH: Accuracy of

fat-suppressed three-dimensional
spoiled gradient-echo FLASH MR
imaging in the detection of patello-
femoral articular cartilage abnormali-
ties. Radiology 1996;198:209-212.
3. Disler DG: Fat-suppressed three-
dimensional spoiled gradient-recalled
MR imaging: Assessment of articular
and physeal hyaline cartilage. AJR Am
J Roentgenol 1997;169:1117-1123.
4. Lucas P, Kaplan P, Dussault R, Hurwitz
S: MRI of the foot and ankle. Curr Probl
Diagn Radiol 1997;26:209-268.
5. Chandnani VP, Harper MT, Ficke JR, et
al: Chronic ankle instability: Evaluation
with MR arthrography, MR imaging,
and stress radiography. Radiology 1994;
6. Kramer J, Stiglbauer R, Engel A,
Prayer L, Imhof H: MR contrast ar-
thrography (MRA) in osteochondrosis
dissecans. J Comput Assist Tomogr
7. Resnick D, Kang HS: Ankle and foot,
in Resnick D, Kang HS (eds): Internal
Derangements of Joints: Emphasis on MR
Imaging. Philadelphia: WB Saunders,
1997, p 787.
8. Link SC, Erickson SJ, Timins ME: MR
imaging of the ankle and foot: Normal

structures and anatomic variants that
may simulate disease. AJR Am J
Roentgenol 1993;161:607-612.
9. Maffulli N, Khan KM, Puddu G:
Overuse tendon conditions: Time to
change a confusing terminology. Ar-
throscopy 1998;14:840-843.
10. Resnick D, Kang HS: Rotator cuff ten-
dinitis, tendinosis, and tendinopathy,
in Resnick D, Kang HS (eds): Internal
Derangements of Joints: Emphasis on MR
Imaging. Philadelphia: WB Saunders,
1997, p 213.
11. Rosenberg ZS, Cheung Y, Jahss MH,
Noto AM, Norman A, Leeds NE:
Rupture of posterior tibial tendon: CT
and MR imaging with surgical correla-
tion. Radiology 1988;169:229-235.
12. Khoury NJ, El-Khoury GY, Saltzman
CL, Brandser EA: MR imaging of pos-
terior tibial tendon dysfunction. AJR
Am J Roentgenol 1996;167:675-682.
13. Schweitzer ME, Eid ME, Deely D,
Wapner K, Hecht P: Using MR imag-
ing to differentiate peroneal splits
from other peroneal disorders. AJR
Am J Roentgenol 1997;168:129-133.
14. Rosenberg ZS, Beltran J, Cheung YY,
Colon E, Herraiz F: MR features of
longitudinal tears of the peroneus bre-

vis tendon. AJR Am J Roentgenol 1997;
15. Tjin A Ton ER, Schweitzer ME, Karasick
D: MR imaging of peroneal tendon dis-
orders. AJR Am J Roentgenol 1997;168:
16. Schneck CD, Mesgarzadeh M, Bonak-
darpour A, Ross GJ: MR imaging of
the most commonly injured ankle liga-
ments: Part I. Normal anatomy.
Radiology 1992;184:499-506.
17. Schneck CD, Mesgarzadeh M, Bonak-
darpour A: MR imaging of the most
commonly injured ankle ligaments:
Part II. Ligament injuries. Radiology
18. Mink JH: Ligaments of the ankle, in
Deutsch AL, Mink JH, Kerr R (eds):
MRI of the Foot and Ankle. New York:
Raven Press, 1992, p 173.
19. Morrison WB, Schweitzer ME, Wapner
KL, Hecht PJ, Gannon FH, Behm WR:
Osteomyelitis in feet of diabetics:
Clinical accuracy, surgical utility, and
cost-effectiveness of MR imaging.
Radiology 1995;196:557-564.
20. Beltran J, Campanini DS, Knight C,
McCalla M: The diabetic foot: Magnetic
resonance imaging evaluation. Skeletal
Radiol 1990;19:37-41.

21. Aerts P, Disler DG: Abnormalities of the
foot and ankle: MR imaging findings.
AJR Am J Roentgenol 1995;165:119-124.
22. Deutsch AL: Traumatic injuries of
bone and osteonecrosis, in Deutsch
AL, Mink JH, Kerr R (eds): MRI of the
Foot and Ankle. New York: Raven
Press, 1992, p 75.
23. Resnick D, Kang HS: Traumatic disor-
ders of bone, in Resnick D, Kang HS (eds):
Internal Derangements of Joints: Emphasis
on MR Imaging. Philadelphia: WB
Saunders, 1997, p 90.
24. De Smet AA, Ilahi OA, Graf BK: Re-
assessment of the MR criteria for sta-
bility of osteochondritis dissecans in
the knee and ankle. Skeletal Radiol
25. Erlemann R, Reiser MF, Peters PE, et
al: Musculoskeletal neoplasms: Static
and dynamic Gd-DTPA-enhanced MR
imaging. Radiology 1989;171:767-773.
26. Erlemann R, Sciuk J, Bosse A, et al:
Response of osteosarcoma and Ewing
sarcoma to preoperative chemothera-
py: Assessment with dynamic and sta-
tic MR imaging and skeletal scintigra-
phy. Radiology 1990;175:791-796.
27. Berkowitz JF, Kier R, Rudicel S: Plantar
fasciitis: MR imaging. Radiology 1991;

28. Morrison WB, Schweitzer ME, Wapner
KL, Lackman RD: Plantar fibromato-
sis: A benign aggressive neoplasm
with a characteristic appearance
on MR images. Radiology 1994;193:
29. Zanetti M, Ledermann T, Zollinger H,
Hodler J: Efficacy of MR imaging in
patients suspected of having Morton’s
neuroma. AJR Am J Roentgenol 1997;
Michael P. Recht, MD, and Brian G. Donley, MD
Vol 9, No 3, May/June 2001

Xem Thêm