This article reviews the use of magnetic resonance imaging (MRI) in the evaluation of the foot, including a discussion of bone and cartilage abnormalities, sinus tarsi pathology, and the evaluation of the foot in hindfoot, midfoot, and forefoot subsections. Compared with computed tomography, MRI offers superior contrast resolution and exquisite detail of soft tissue structures.
are Fellows in Musculoskeletal Radiology, RadNet Management, Los
is the Medical Director of RadNet Management, and a Volunteer
Clinical Professor of Medicine, University of California-San
Diego School of Medicine, San Diego, CA.
In an article published in the August 2006 issue of this
journal, the authors reviewed magnetic resonance imaging (MRI) of
the ankle. This article will present a review of the use of MRI in
the evaluation of the foot, detailing bone and cartilage
abnormalities as well as sinus tarsi pathology. The discussion will
address the evaluation of the foot in hindfoot, midfoot, and
Foot MRI technique
Depending on the clinical question, MRI of the foot should be
tailored to a hindfoot, midfoot, or forefoot examination. For hind-
and mid-foot, a 12- to 14-cm field of view is applied. For the
forefoot, a 10- to 12-cm field of view is used to image the smaller
peripheral joints in detail.
Similar to the ankle, the foot is placed in a neutral position
for high-field-strength scanners and in approximately 30˚plantar
flexion for extremity scanners.
The pulse sequences for the mid- and forefoot are T1-weighted
(T1W) in the coronal and axial planes, short tau inversion recovery
(STIR) in the coronal and sagittal or axial planes, and T2-weighted
(T2W) in the coronal plane.
For the evaluation of a mass or the diabetic foot, we add T1W
sequences before and after intravenous (IV) contrast (gadolinium
chelate) administration. On low-field-strength scanners, these are
performed without fat saturation; on high-field-strength scanners,
fat saturation is applied. Precontrast fat-suppressed images are
essential to avoid the pitfall of pseudoenhancement of a mass on
fat-saturated postcontrast images when compared with the non-
fat-suppressed precontrast images. This is because of a narrow
dynamic range of the contrast display on the fat-saturated images
when compared with those without fat saturation.
Bone and cartilage abnormalities
The talus is a relatively common site for osteochondral injury
(Figure 1). The middle third (in the sagittal plane) of the lateral
border and the posterior third of the medial border of the talar
dome are the common locations.
In our anecdotal experience, the middle third of the medial talar
margin is a more common site than the posterior third. The MRI
classification of osteochondral injuries was presented by Hepple et
and stages the talar injuries according to the severity of the
injury and the degree of the osteochondral fragment instability.
Fluid between the osteochondral fragment and the underlying bone,
displacement of the fragment, and a fragment size >1 cm are
signs of an unstable osteochondral fragment. Unstable or necrotic
osteochondral fragments are treated surgically with drilling and
curettage. Conservative treatment is preferred when the overlying
cartilage is intact and the fragment is stable.
Talar neck fractures can lead to avascular necrosis (AVN) of the
proximal fragment. Stress fractures can occur in the talus but are
less common than calcaneal stress injuries.
Calcaneus stress fractures can have a diffuse or ill-defined
geographic marrow edema pattern (Figure 2). A low-signal fracture
line, usually in a vertical orientation, may be visible. Complex
calcaneal fractures secondary to a vertical fall mechanism are best
evaluated with computed tomography (CT).
Coalition of the middle talocalcaneal joint is second only to
calcaneonavicular coalition. Osseous, fibro-osseous, fibrous, and
fibrocartilaginous forms have been described. MRI findings include
a direct bony connection or (in the case of nonosseous coalition)
irregularity and eburnation of the articulating surfaces and
visualization of low-signal fibrous bridging. Medial downsloping of
the sustentaculum tali articulating surface (Figure 3) instead of
the normal lateral slope and presence of a dorsal talar spur (not
to be confused with the physiologic, more proximal dorsal spur at
the capsular insertion) are useful ancillary findings.
Calcaneonavicular coalition (Figure 4) is the most common of the
As with other sites, it can be osseous or nonosseous. An elongated
anterior process of the calcaneus (anteater nose sign) may be
Some of the more common masses in the calcaneus include lipomas,
solitary bone cysts, and chondroblastomas. Lipomas have
characteristic fat signal. They can have central calcification or
cystic focus that appears as signal void or fluid signal,
respectively (Figure 5). Bone cysts in calcaneus are more common in
the older age group (>20 years). They have fluid signal and are
located in the calcaneus body more inferiorly as compared with the
chondroblastomas. Chondroblastomas are more common in men in their
second or third decade. They occur in a subarticular location and
have high signal on T2W images and low signal on T1W images because
of their cartilaginous nature. Low-signal foci of chondroid
calcifications and linear low- signal septations may be
Navicular osteochondrosis (Köhler's disease) is seen in younger
patients (3 to 7 years of age). Fragmentation and low signal on T1W
and T2W images are seen.
It must not be confused with the fragmented appearance of nonunited
ossification centers. In adults, AVN secondary to trauma can occur
There is collapse and low signal of the bone on all pulse
sequences. Bony changes seen with subtalar instability and
inflammatory arthropathies are discussed with sinus tarsi
Sinus tarsi pathology
The sinus tarsi contain 3 ligaments extending from the talus to
the calcaneus. The lateral-most is the continuation of the inferior
extensor retinaculum. The cervical ligament has a striated
appearance. It extends from the talar neck to the body of the
calcaneus in an oblique anteroposterior direction, providing
stability to the subtalar joint. The interosseous ligament is the
most medial of the 3. It extends from the talus to the calcaneus in
an oblique mediolateral direction (Figure 6). The ligaments limit
the inversion of the hindfoot and play an important role in
maintaining the stability of the subtalar joint. The sinus tarsi is
predominantly filled with fat and also contains blood vessels and
The ligaments can be torn secondary to acute trauma or more
commonly by chronic recurrent microtrauma. This can lead to
subtalar instability with resulting degenerative changes in the
joint. Articular surface irregularity and subchondral sclerosis
with or without subchondral edema can be seen. Posterior
talocalcaneal facet is involved to a greater degree. Normal fat
signal in the sinus tarsi is replaced with edema or fluid signal.
There is associated nonvisualization of the torn sinus tarsi
ligaments (Figure 7).
Ankle, subtalar, and tarsal joints can be affected by
inflammatory arthropathies (Figure 7), such as Reiter's disease, or
crystal deposition disease, such as gout. MRI can reveal inflamed
synovium in addition to the bony erosions and edema. Masses, such
as ganglion cysts and lipomas, can occur and lead to pain from
compression of nerve endings.
Plantar fasciitis is most pronounced within 2 to 3 cm of the
calcaneal attachment. It manifests as a smooth thickening (>4
mm) of the plantar fascia, with adjacent subcutaneous edema. Edema
may also be seen in the calcaneus at the insertion site of the
plantar fascia (Figure 8). It is associated with a plantar
calcaneal spur in approximately 50% of cases.
Tears of the plantar fascia occur most commonly in the
midportion of the fascia. This is more distal to the typical
location of plantar fasciitis (Figure 9). They can be partial or
complete. Trauma is the usual etiology. Discontinuity and waviness
of the fascial cords with adjacent soft tissue edema are seen on
Plantar fibromatosis is nodular fibrous proliferation of the
plantar fascia. The appearance can vary from a well-circumscribed
low-signal lesion on all pulse sequences to a locally invasive
lesion with ill-defined borders and intermediate signal (Figure
10). This is a difficult lesion to treat because of its tendency to
recur following local resection.
Differential diagnoses include soft tissue masses (such as giant
cell tumor) and sarcomatous neoplasm (such as synovial sarcoma and
fibrosarcoma). A well-circumscribed appearance and homogenous
low-signal characteristics suggest fibromatosis.
Osseous abnormalities of the hindfoot were discussed
A traumatic tear of the Lisfranc ligament (a short bandlike
ligament that extends from the plantar anterolateral corner of the
medial cuneiform to the plantar posteromedial corner of the base of
the second metatarsal) is an important injury (Figure 11).
It can lead to instability and progressive disorganization of the
Lisfranc joint. Additionally, there can be loss of the medial
longitudinal arch. The rupture of the ligament fibers is more
common than is the avulsion fracture at the bony attachments.
It is an important diagnosis, since early internal fixation may
give the ligament a chance to heal and can help to avoid the need
for future arthrodesis. Even with early intervention, the success
rate is <50%.
The tarsal bones are a common site of trabecular stress injury.
Marrow edema with a lack of a clear fracture line is present.
The flexor hallucis longus (FHL) tendon is prone to tendinosis
and tears at the knot of Henry. The mechanism is chronic repetitive
friction with the flexor digitorum longus (FDL) tendon from
activities like jogging.
This is analogous to the intersection syndrome between the first
and second extensor compartment tendons in the wrist. The medial
plantar nerve branches can get entrapped between the knot of Henry
and the abductor hallucis muscle, leading to first and second toe
Synovial sarcoma is a malignant neoplasm with predilection for
the foot. It is predominantly seen in patients between the ages of
15 and 40 years. It is an aggressive neoplasm with a posttreatment
5-year survival rate of approximately 55%.
Local recurrence and pulmonary and bone metastasis are common. On
MRI, it appears as a well-defined mass with a heterogeneous low
signal on T1W images. On T2W images, it has a heterogeneous high
signal (Figure 12). Cystic areas are common. Fluid-fluid levels can
be present in close to 20% of cases. Foci of calcifications can
lead to areas of low signal on T2W images. Heterogeneous
enhancement is seen with IV contrast ad-ministration. It usually
displaces the adjacent structures rather than invading them.
Sometimes a small size, slow growth, and well-circumscribed
appearance can lead to an erroneous diagnosis of a benign mass.
Other soft tissue neoplasm, benign and malignant primary bony
neoplasm, and, less commonly, metastasis can all involve the
The Lisfranc and Chopart (intertarsal) joints are commonly
disrupted in neuropathic arthropathy (Charcot joint). Rapid
destruction of the joints and bones is the rule if protective
measures are not taken early in the process. Therefore, early
detection of neuropathic changes is very important. Signs on MRI
include tear of the Lisfranc ligament and edema in the tarsal and
metatarsal bones adjacent to the joints. Loss of normal bony
relationship and articular and osseous destruction are advanced
findings (Figure 13).
A common clinical question is the differentiation between
osteomyelitis and a neuropathic joint. Certain findings (such as
the presence of more focal involvement of the bones, skin ulcers,
sinus tracts, and abscess) are more suggestive of infection (Figure
14). In early neuropathic joint, the signal abnormalities are
centered on the joint. However, a clear distinction between
infection and neuropathic changes is not always possible with
The midfoot is often involved in arthropathies such as gout and
rheumatoid arthritis. The findings on MRI include erosions, bone
marrow edema, and synovitis. In the absence of a correlative
history, these can be confused with osteomyelitis. Degenerative
changes in the midfoot can be seen with altered mechanics or can be
"Turf toe" refers to a capsuloligamentous injury of the
metatarsophalangeal (MTP) joint of the first toe. The mechanism of
injury includes anterior thrust of the metatarsal head in a
hyperextended joint with a relatively fixed great toe. This is
common in sports played on synthetic turf, like football, hence the
There is stretching and tearing of the plantar capsule and tearing
of the plantar plate. The plantar plate is a fibrocartilaginous
structure that extends from the metatarsal neck to the base of the
proximal phalanx. It reinforces the plantar capsule and also
attaches the hallux sesamoid bones to the base of the proximal
phalanx (Figure 15). Discontinuity of the plantar plate and focal
edema and fluid is seen. Associated proximal displacement of the
hallux sesamoids may be seen.
Collateral ligament tears are also more common in the great toe.
Varus or valgus force is the usual etiology. Edema and
discontinuity of the medial or lateral collateral ligaments is
present (Figure 16). The MTP collateral ligament tear is more
common than that of the interphalangeal joints.
Hallux sesamoids can be involved with fractures, AVN, and
sesamoiditis secondary to inflammatory arthropathies or
osteomyelitis. The medial sesamoid is more commonly involved with
trauma, and lateral sesamoid tends to get AVN. Replacement of the
normal marrow fat signal with edema signal can be seen. Freiberg's
infraction of the metatarsal heads is characterized by fissuring,
osteonecrosis, and eventual collapse of the subchondral bone
(Figure 17). The second and third metatarsal heads are most
Repetitive microtrauma and vascular compromise are the most popular
theories of the etiology. It is more common in young women and may
be secondary to the wearing of high heels. In its acute stage,
there is a marrow edema pattern. In its chronic phase, there is
deformity of the metatarsal head and associated degenerative
"March fracture" is a stress fracture of the metatarsal neck.
The name comes from its common occurrence in military recruits. It
is predominantly seen with activities that place excessive stress
on the metatarsals, such as ballet dancing and gymnastics. Marrow
edema and adjacent soft tissue edema are seen in early stages.
Periosteal thickening is present in the subacute stage as a healing
Pressure lesions are fibrofatty lesions that occur in the
subcutaneous fat. These typically develop at the load-bearing bony
prominences, including the plantar aspects of the first and fifth
metatarsal heads or below the calcaneal tuberosity. These lesions
are of low signal on T1W images and of variable signal
(intermediate-to-high signal) on T2W images. They can have fat in
the interstices. Sometimes they can develop central cystic changes.
They generally lack the well-defined morphology of a mass, and
their appearance is that of an ill-defined fibrotic tissue (Figure
18). The characteristic location and interspersed fat in the lesion
favor the diagnosis and help differentiate it from a neoplasm.
Morton neuroma is a focal perineural fibrosis of the plantar
interdigital nerves. It is not a true neuroma. The most common
location is the third and fourth web spaces between the plantar
aspects of the metatarsal heads.
It is more common in women, and, once again, the wearing of high
heels is implicated as a causative factor. Other etiologic
possibilities include the compression of the nerves by the
intermetatarsal ligament or a distended intermetatarsal bursa. Pain
in the web space with or without radiation to the toes is the usual
presenting symptom. These are small lesions that are nearly
isointense to the muscles on T1W images, are intermediate to high
in signal on T2W images, and can be isointense to fat (Figure 19).
Fat-suppressed IV contrast-enhanced T1W images give the highest
lesion conspicuity because of intense lesion enhancement. It can be
a mobile lesion and can change positions in the intermetatarsal
A giant cell tumor of the tendon sheath is a relatively common
benign lesion. It is a focal form of extra-articular pigmented
villonodular synovitis. It is low in signal on T1W images and is
low-to-intermediate signal on T2W images (Figure 20).
Other masses, such as foreign body granulomas, ganglion cysts,
and malignant neoplasms (like synovial sarcomas or metastasis) can
all occur in the forefoot location.
The MTP joint of the great toe is the characteristic location
for gout. Monoarticular involvement is common but not the rule.
Gouty tophi cause characteristic erosions with punched-out,
overhanging edges of the periarticular bones. They also occur at
extra-articular locations with associated osseous erosions. Tophi
have low signal intensity on T1W images and low-to-intermediate
signal intensity on T2W images (Figure 21).
Variable enhancement is seen with IV contrast administration.
Septic arthritis should always be considered in the differential
diagnosis of monoarthritis. Rheumatoid arthritis and Reiter's
disease are other common arthropathies in the forefoot.
Osteoarthritis commonly involves the first MTP joint as well.
MRI is the imaging modality of choice for evaluation of
musculoskeletal pathology, including the soft tissue and osseous
trauma, neoplasms, and inflammatory pathology. Compared with CT, MR
provides a superior contrast resolution and exquisite detail of
soft tissue structures. It also surpasses CT in the evaluation of
trabecular bone injury. The strengths of MRI in evaluating various
foot pathologies have been briefly reviewed in this article.