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n radiologic case study
Enhance your diagnostic skills with
this “test yourself” monthly column,
which features a radiograph and
challenges you to make a diagnosis.
The case:
A
35-year-old male athlete presented with acute pain plantar to the hallux
metatarsophalangeal joint following jumping to catch a basketball.
Figure: Coned-down internal oblique radiograph of the hallux metatarsophalangeal joint.
Your diagnosis?
650
For answer see page 706
ORTHOPEDICS | Healio.com/Orthopedics
n radiologic case study
Diagnosis:
Acute Fibular Sesamoid Fracture: One Part of
the Spectrum of Sesamoid Pathologies
Tejas Patel, MD; Albert J. Song, MD; Laurie M. Lomasney, MD; Terrence C. Demos, MD; Sarah Dickey, DPM
Answer to Radiologic Case Study
Case facts appear on page 650
T
he internal oblique radiograph of the left foot (Figure 1) shows a complete transverse cleft through the fibular
sesamoid of the first metatarsal
head with open-ended trabeculae and sharp margination, indicating an acute fracture. There
is minimal distraction of the
fracture fragments. Soft tissue
swelling is difficult to appreciate, given the natural fullness
of the ball of the foot, although
clinical examination verified
this finding. Acute fracture is
only one of the many pathologies that can affect the hallucal
sesamoids, and imaging plays a
major role in diagnosis prior to
treatment that can be conservative or surgical.
Anatomy and Function
The sesamoid bones are integral for stability of the first
metatarsophalangeal joint with
weight bearing. The proximal
phalanx has a small articular
facet that does not provide sufficient stability during weight
bearing. Contrarily, the hallucal sesamoid complex allows
the metatarsophalangeal joint
to bear 40% to 60% of body
weight during walking. During strenuous activity, it can
even bear multiple times the
body weight.1
Two sesamoid bones are
located at the plantar aspect
of the first metatarsophalangeal joint. The tibial sesamoid
is usually larger and bears
The authors are from the Department of Radiology (TP, AJS, LML, TCD)
and the Department of Orthopaedics (SD), Loyola University Medical Center, Maywood, Illinois.
The authors have no relevant financial relationships to disclose.
Correspondence should be addressed to: Laurie M. Lomasney, MD, Department of Radiology, Loyola University Medical Center, 2160 S First Ave,
Maywood, IL 60153 ([email protected]).
doi: 10.3928/01477447-20140924-01
706
greater weight than the fibular counterpart, accounting
for the greater incidence of
injury.2 The sesamoid bones
ossify between ages 7 and
10 years. The sesamoids often have multiple ossification
centers that may not fuse, resulting in bipartite or tripartite
sesamoids. The sesamoids are
multipartite in up to one-third
of the general population, usually involving both sesamoids.
If only one is involved, it is
usually the tibial sesamoid.2,3
Each sesamoid has limited arterial supply. The first
plantar metatarsal artery is the
main resource for the tibial
and fibular sesamoid bones,
an artery derived from the medial plantar artery, the plantar
arch, or more commonly, a
combination of the two. The
medial branch of the first plantar metatarsal artery supplies
the tibial sesamoid bone. The
fibular sesamoid is supplied
by the main branch of the first
plantar metatarsal artery that
continues distally along the
lateral side of the bone. The
arteries penetrate the sesamoid bones on their proximal,
Figure 1: Acute fracture of the fibular
sesamoid in a young athlete. Coneddown internal oblique radiograph of
the hallux metatarsophalangeal joint
showing well-defined transverse lucency of the fibular sesamoid fracture.
plantar, and distal sides. Capsular vessels do not provide
significant blood supply to the
sesamoids. This limited arterial supply may account for the
high rate of delayed union and
nonunion of fractures.3
The medial (tibial) and
lateral (fibular) sesamoids lie
within the medial and lateral
ORTHOPEDICS | Healio.com/Orthopedics
n radiologic case study
heads of the flexor hallucis
brevis tendon. The medial
abductor and lateral adductor
hallucis tendons also attach
to the tibial and fibular sesamoids, respectively. The sesamoids articulate with the medial and lateral first metatarsal
facets that are separated by a
ridge called the crista. The
transverse sesamoid (intersesamoidal) ligament is a
thickened band of the central plantar plate that extends
between and connects the 2
sesamoids and is an integral
part of the plate.3 There are
also medial and lateral sesamoid ligaments that originate
from the medial and lateral
first metatarsal and attach to
the outermost tibial and fibular
sesamoids. These attachments
form the medial and lateral
margins of the plantar plate
and are thicker than the central
plate. The flexor hallucis longus tendon courses plantar to
the plate between the 2 sesamoids (Figure 2). Functionally, the sesamoids provide
leverage for the flexor hallucis
brevis tendon in dorsiflexion,
while giving a mechanical
advantage to the flexor hallucis longus to act as a hallux
stabilizer against ground reactive force. The sesamoids also
absorb shock during forefoot
load, distributing the ground
reactive forces and thus protecting the metatarsal head.2
Overview of Sesamoid
Abnormalities
There are numerous causes
of sesamoid pain, including
acute and chronic trauma, inflammation, infection, and
osteonecrosis. The differen-
tial diagnosis of regional pain
includes nerve impingement,
bursal pathology, and arthritides. Differentiating first
metatarsophalangeal pain due
to sesamoid pathology from
these other disorders can be
difficult because signs and
symptoms may be similar.
Signs and symptoms most
often include swelling and pain,
specifically at the ball of the
foot underlying the first metatarsophalangeal joint. Although
the various pathologies may
have a similar clinical presentation, the initial history, including onset and duration, can be
used to differentiate traumatic
and atraumatic etiologies. The
results of physical examination
are also similar in several entities, consisting of tenderness to
palpation and loss or decrease
of active dorsiflexion or plantar
flexion at the metatarsophalangeal joint.2
The hallux sesamoids have
been reported to be involved in
9% of foot injuries. One study
reported the incidence of specific sesamoid abnormalities:
stress fracture, 40%; sesamoiditis, 30%; acute fracture,
10%; osteochondritis, 10%;
osteoarthritis, 5%; and bursitis, 5%.3
Imaging of symptomatic patients begins with weight-bearing anteroposterior, oblique,
and lateral views of the foot
with additional axial sesamoid
radiographs. In the early stages
of nontraumatic pathologies,
the radiographs may yield
normal findings. Computed
tomography (CT) provides enhanced bone detail and visualization of peri-articular calcifications. However, magnetic
A
B
Figure 2: Sesamoid anatomy. Osseus (A) and soft tissue (B) components of
the hallucal sesamoid complex. Medial (tibial) and lateral (fibular) sesamoids
(S) lie within corresponding slips of flexor hallucis brevis (FHB) tendons
that insert at the plantar base of the proximal phalanx (PP). Adductor hallucis (ADH) and abductor hallucis (ABH) muscles insert on medial and lateral
sesamoids, respectively. Ligaments include a thickened transverse band of the
plantar plate (intersesamoidal ligament [ISL]), medial (not shown), and lateral
sesamoidal (LSL) attaching to the metatarsal (MT) head. Abbreviation: LCL,
lateral collateral ligament of the metatarsophalangeal joint.
resonance imaging (MRI) is
more sensitive for bone pathology and has the advantage of
providing detailed demonstration of affected bone, ligaments, nerves, and soft tissue.
Bone scan is also sensitive for
bone pathology, but nonspecific with poor anatomy depiction. Sonography can demonstrate soft tissue injuries of the
hallucal sesamoid complex, but
is user-dependent.
Sesamoiditis
Sesamoiditis is a generic term applied for acute or
chronic sesamoid pain when
alternative diagnoses have
been excluded. By definition,
the etiology is unknown but
is generally considered to be
mechanical due to repetitive
axial loading. Postulated risk
factors include excessive dorsiflexion, repetitive axial loading (especially in athletes), and
increased forefoot pressure
caused by wearing high heel
shoes.4 Pain exacerbated with
weight bearing is common. On
physical examination, there
may be redness, swelling, and
pain with direct palpation or
with passive dorsiflexion of
the first metatarsophalangeal
joint.3
Initial radiographs yield
normal findings in sesamoiditis, even on axial sesamoid
views.5 Magnetic resonance
imaging is much more sensitive, with increased bone marrow signal indicating fluid in
the affected sesamoid bone.5
Computed tomography images
are not useful for diagnosing
sesamoiditis, but can demon-
OCTOBER 2014 | Volume 37 • Number 10707
n radiologic case study
A
C
A
B
Figure 3: Sesamoiditis in a young
woman with subacute nontraumatic
medial forefoot pain. Axial (A) and
dorsal-plantar (B) radiographs of
the right hallux metatarsophalangeal
showing uniform sclerosis of the tibial
sesamoid (S) without fracture. 99mTcmethylene diphosphonate nuclear
scintigraphy focused at the right foot
(C) showing focal intense tracer deposition (red arrow) at the tibial sesamoid.
B
Figure 4: Evolution of an acute fibular sesamoid fracture in a young athlete.
Dorsal-plantar coned-down radiograph of the hallux metatarsophalangeal joint
showing an acute nondisplaced fracture (blue arrow) of the fibular sesamoid
(S) (A). Repeat radiograph 6 weeks later showing increased distraction (red
arrow) and nonunion (B).
strate sclerosis due to other
pathologies such as stress fractures or osteonecrosis.6 Finally, 99mTc-methylene diphosphonate (Tc-99m-MDP) bone
scan will show focal increased
radiotracer uptake localized to
the region of the plantar hallux
sesamoid (Figure 3).7 Single
photon emission computed tomography (SPECT), with improved spatial resolution compared with planar imaging,
shows mildly increased uptake
708
of the affected sesamoid with
sesamoiditis.8
Treatment options are generally conservative, including
rest, nonsteroidal anti-inflammatory medications, spica taping of the hallux, and custom
orthotics. Specific orthotic
modifications include a reverse
Morton’s extension, dancer’s
pad, or carbon fiber plate for
short durations of immobilization. Also, pneumatic cam
walker boots have been used
for immobilization of sesamoid
complex after conservative
treatment options have failed.
Injectable steroids remain
controversial in acute fracture,
but can be used for treatment
of sesamoiditis. A newly reported trend in sports medicine involves hyaluronic acid
injections, commonly used for
osteoarthritis of the knee, for
chronic sesamoid pain. This is
controversial, and these injections are not Food and Drug
Administration approved for
use in the first metatarsophalangeal joint. However, hyaluronic acid injected around the
affected sesamoid(s) has been
shown anecdotally to reduce
pain and restore function to
the sesamoid complex.9,10 Surgical excision of the affected
sesamoid bone is reserved for
patients who do not respond
after 6 months of conservative
treatment.3,11
Traumatic Injuries
Acute. Traumatic injuries of
the hallux sesamoids include
acute fracture, dislocation, and
stress fracture.12 Acute fractures of the hallux sesamoids
are due to trauma to the first
metatarsophalangeal joint, often hyper-dorsiflexion of the
joint or an abrupt axial load to
the forefoot. The tibial sesamoid is fractured much more
often than the fibular sesamoid
because it bears the majority of
axial loading. Also, the fibular
sesamoid can slip into the joint
on metatarsophalangeal dorsiflexion and thus avoid direct
contact with the plantar surface
of the metatarsal head.3 Acute
pain after trauma is the primary
symptom. Physical examina-
tion findings include pain with
palpation, while swelling is
less frequent.13
Initial radiographs should include anteroposterior, oblique,
lateral, and axial sesamoid
views. The majority of fractures are simple transverse
fracture planes with minimal
or mild distraction due to the
multiple regional stabilizers.
Broad distraction is indicative
of destabilization of the plantar
metatarsophalangeal (Figure
4). Radiographs often present a
diagnostic dilemma because bipartite sesamoids may resemble
acute fractures. Both bipartite
and multipartite sesamoid fragments have smooth, narrow,
sclerotic margins, while an
acutely fractured sesamoid has
a nonsclerotic, irregular margin.
In addition, a multipartite sesamoid is larger than a unipartite
sesamoid, including sesamoid
fracture fragments.13 Computed
tomography may better show
the normal corticated, smoothly
marginated multipartite sesamoids vs the noncorticated,
irregular margins of an acute
fracture.14 Associated soft tissue injuries such as transverse
sesamoid ligament tears, tears
of the medial or lateral sesamoid ligaments, and plantar
plate ruptures not shown by CT
can be demonstrated by highresolution MRI. A bone scan
can help diagnose a fracture, as
it will show increased radiotracer uptake by fracture fragments
but not by multipartite sesamoid
fragments.15 Callus formation is
visible on radiographs and CT
after 2 to 3 weeks. Full healing
takes approximately 6 weeks.
Sesamoid fractures are difficult to treat due to the poor
ORTHOPEDICS | Healio.com/Orthopedics
n radiologic case study
blood supply and the location
within the foot. If early diagnosis is made, 6 to 8 weeks of
immobilization in a tall pneumatic cam boot or short leg cast
with crutches can effectively
allow for healing. It is largely
presumed that the sesamoid
fractures do not heal by osseous union but rather by fibrous
bridging that may be asymptomatic. However, in many cases, fractures go on to delayed
union, nonunion, malunion, or
intra-articular arthritis. Because
sesamoid fractures are known
to have poor healing potential, it
is common practice to prescribe
a bone stimulator in conjunction with immobilization.
If there is a delay in fracture
diagnosis, conservative efforts
may be futile and more invasive treatment required. Partial
or complete surgical excision
of the injured sesamoid is well
discussed in the literature and
can serve as a viable treatment
option if conservative measures have failed. Anecdotal
concerns have been raised regarding the development of
subsequent deformities after
removal of a sesamoid bone:
loss of hallux purchase, hallux
malleus, hallux varus, and hallux valgus deformity. Because
of the bone’s small size and location and the general success
with excisional procedures,
open reduction with internal fixation of acute fractures
has not been commonly employed. Platelet-rich plasma,
bone marrow aspiration injections, and autogenous bone
grafting have been advocated
as adjunctive measures during
surgical interventions for nonunion.9,10
Chronic. Chronic stress
can also affect the sesamoids.
The mechanism is repetitive
hyper-dorsiflexion injuries associated with activity over a
prolonged period. The symptoms and signs are similar to
those of the patients who have
acute fractures, but the symptoms are chronic and there is
no history of an acute injury.
As with an acute fracture, a
stress fracture is usually a simple transverse fracture. Differentiation of subacute/chronic
fractures from bipartite sesamoids can be difficult on the
basis of radiographs and CT.
Because early fracture plane
definition may be subtle, other
imaging modalities are more
sensitive for showing fractures
but may yield similar results
for both acute and chronic
stress fractures.15 A nondisplaced fracture plane may
be sclerotic on CT but nonsclerotic when fragments are
distracted. Bridging callus
formation and periosteal new
bone indicate healing. Magnetic resonance imaging has the
advantage of demonstrating
both bone marrow and periosteal edema. The appearance is
different for undisplaced and
displaced fractures. The undisplaced fracture plane has globally hypointense signal on all
sequences if there is bridging
callus or fibrous tissue (Figure
5). There is hyperintense signal (granulation tissue or fluid)
in the cleft on fluid-sensitive
sequences if distraction or displacement is present.
Initial treatment of chronic
fractures is conservative; immobilization and non-weight
bearing for at least 6 weeks
A
B
Figure 5: Chronic tibial sesamoid fracture in a middle-aged adult. Tibial sesamoid (S) is sclerotic on dorsal-plantar radiograph (A). Sagittal T2-weighted
magnetic resonance imaging with fat saturation confirming low signal at the
chronic transverse fracture (red arrow) and diffuse high-signal bone marrow
edema (blue arrow) (B). Overlying superficial high T2 signal soft tissue edema
(white arrow) is also present.
are the first steps. The cast
should include the entire hallux to prevent continued metatarsophalangeal dorsiflexion.15
Orthotics such as steel shank
and rocker sole boots help to
reduce stress at the metatarsophalangeal joint.13 Stress
fractures may take months to
heal. Rates of delayed union,
nonunion, and fracture recurrence are high.15
If healing is not evident
after 6 weeks of conservative treatment, surgery is a
consideration. Older surgical
recommendations for resection of both sesamoids have
been discarded due to longterm malalignment including
cock-up deformity with persistent metatarsophalangeal
joint extension. The current
standard of care is excision of
only the fractured sesamoid,
but this surgery is avoided in
high-end athletes. Removal of
only the tibial sesamoid can
lead to hallux valgus, while
removal of only the fibular
sesamoid has resulted in hallux varus deformity.13 Therefore, bone grafting or partial
excision is recommended for
athletes.3
Osteochondritis and
Osteonecrosis
When referring to the sesamoids, osteochondritis and
osteonecrosis are used interchangeably to indicate an ischemic vascular injury leading
to necrosis. This is thought
to be a sequela of chronic
stress, fracture, or infection.14
Osteochondritis typically affects young women who have
gradual onset of pain at the
metatarsophalangeal joint with
physical examination signs
similar to sesamoiditis. In fact,
osteochondritis or osteonecrosis is often initially misdiagnosed as sesamoiditis.14
Specific radiographic signs
of osteochondritis such as
fragmentation, cyst formation,
sclerosis, and collapse may not
be evident for 9 to 12 months
after initial presentation. Bone
scan is helpful and may show
increased radiotracer uptake
early on. However, increased
uptake is nonspecific and can
be found in other sesamoid
OCTOBER 2014 | Volume 37 • Number 10709
n radiologic case study
A
B
Figure 6: Tibial sesamoid osteonecrosis in a middle-aged woman. Axial sesamoid radiograph (A) showing heterogeneous trabecular architecture (white
arrow) plantar tibial sesamoid. Short axis T2-weighted magnetic resonance
image (B) confirming plantar sesamoid subcortical high T2 cystic change
(red arrow) and corresponding ill-defined bone marrow edema of the metatarsal head (blue arrow). There is attenuation of the medial sesamoid ligament
(MSL) and lateral sesamoid subluxation, but an intact intersesamoidal ligament (green arrow). Abbreviations: C, crista; FHL, flexor hallucis longus; LSL,
lateral sesamoidal ligament.
A
C
B
Figure 7: Fibular sesamoid osteomyelitis
in a middle-aged diabetic patient. Axial
sesamoid radiograph showing sclerosis
of the fibular sesamoid (S) (A). Sagittal
T1-weighted (B) and T2-weighted (C)
magnetic resonance imaging showing
abnormally low T1 signal and high T2
signal of the fibular sesamoid deep to the
excavating ulcer (asterisk). Joint effusion
(red arrow) is likely reactive, with a normal bone marrow signal of the proximal
phalanx and metatarsal.
Figure 8: Crystalline arthropathy
(gout) tibial sesamoid in a 56-year-old
man. Lateral coned-down radiograph
of the great toe showing erosion and
fragmentation (red arrow) of the tibial
sesamoid with punctate soft tissue
calcification.
pathologies. In later stages of
osteonecrosis, bone scan will
show a “cold” defect with pau-
710
city of tracer deposition in the
affected sesamoid, a more specific finding.14 On MRI, a bone
marrow edema pattern will be
evident in early osteonecrosis
(Figure 6), while late-stage
findings will include decreased
signal on all sequences secondary to lack of viable cells
that corresponds to sclerosis
on CT and radiographs.6
Initial treatment is conservative, including orthoses and
nonsteroidal anti-inflammatory
medications. Joint injection
with corticosteroids is controversial because it may delay or
prevent diagnosis.16 Surgical
removal is considered after failure of conservative treatment.
Osteomyelitis
Osteomyelitis of the sesamoid bones is uncommon,
mostly seen in diabetic and/
or neuropathic patients due
to direct extension from a
soft tissue infection or ulceration.3,6 Sesamoid osteomyelitis has also been reported
following a puncture wound,
in which pseudomonas was
a frequent causative organism.17 Common signs and
symptoms include pain, fever, redness, and swelling at
the site. Patients may also
have increased white blood
cell count and elevated erythrocyte sedimentation rate or
C-reactive protein.14
Early radiographs show
no abnormalities, as is the
case for acute osteomyelitis
at other sites. Late findings
include cortical erosion, periosteal reaction, and fragmentation.14 Magnetic resonance
imaging is the preferred imaging modality for diagnos-
ing osteomyelitis. Findings
include low bone marrow
signal on T1-weighted and
high bone marrow signal on
T2-weighted sequences, usually with periosseus soft tissue inflammatory changes
(Figure 7). In addition, there
is often avid enhancement of
the bone marrow after intravenous gadolinium administration. An adjacent soft tissue
ulcer, fistulous tract, soft tissue fluid collection, or abscess
may also be encountered. A
soft tissue abscess will have
low T1- and high T2-weighted
signal centrally with peripheral rim enhancement.6
Treatment includes intravenous antibiotics and resection of the involved sesamoid.3
As with sesamoidectomy for
other etiologies, there is an increased risk of secondary metatarsophalangeal malalignment
when sesamoids are resected.
Depositional Disease
Similar to other synovial
joints, the hallux-sesamoid articulations can also be affected by the crystal deposition
diseases. In particular, gouty
arthropathy has been reported,18-20 including tophaceous
gout.21 Gout may be primary
or secondary, with precipitation of monosodium uric acid
crystals in the synovial compartment inciting an inflammatory response. The acute
precipitous manifestation includes intense pain, redness,
and warmth. Fever, leukocytosis, and elevated inflammatory
markers are other signs. The
first metatarsophalangeal joint
is most often involved, but no
joint is exempt.
ORTHOPEDICS | Healio.com/Orthopedics
n radiologic case study
Radiographic changes occur only after several years
of clinical gouty arthropathy,
with initial soft tissue tophus
(with or without dystrophic
calcification) adjacent to the
affected bone or joint followed by well-demarcated
pressure erosions of the subjacent bone (Figure 8). The
scalloping effect results in
the prototypic overhanging
margin.22 Magnetic resonance
imaging findings are not specific. The affected joint may
show intermediate signal on
T1-weighted and high signal
on T2-weighted sequences
due to inflammation and effusion. Calcified tophi may
have complex signal characteristics or have low signal
on all sequences, but they
generally enhance with gadolinium.23 Visualization of
joint aspirate under polarized
light microscopy will show
strong negative birefringence.22 Treatment of the
acute pain syndrome is
symptomatic, usually involving nonsteroidal antiinflammatory drugs and corticosteroids. Long-term management is directed at systemic therapies to reduce uric
acid.24
Conclusion
The anatomy of the first
metatarsophalangeal joint is
complex, and the tibial and
fibular sesamoids of the first
metatarsal head are crucial
for maintaining stability and
function of the joint with
weight bearing. Multiple pathologies can affect the sesamoids, typically with overlapping signs, symptoms, and
findings on physical examination. Imaging is fundamental
for diagnosing these entities
and determining the extent
of disease. With appropriate
diagnosis, conservative or
surgical management can be
tailored to achieve a successful outcome.
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