AJR 2000; 175:549-552
© American Roentgen Ray Society
Avulsion Fracture of the Base of the Fifth Metatarsal Not Seen on Conventional Radiography of the Foot
The Need for an Additional Projection
Duke G. Pao1,
Theodore E. Keats1 and
Robert G. Dussault1
1
All authors: Department of Radiology, University of Virginia Medical System,
Box 170, Charlottesville, VA 22908.
Received November 9, 1999;
accepted after revision January 12, 2000.
Address correspondence to D. G. Pao.
Abstract
OBJECTIVE. To our knowledge, this article is the first to describe a
series of patients with avulsion fractures of the base of the fifth metatarsal
that were not seen on conventional radiography using the standard three views
of the foot but that were seen on radiography of the ankle.
CONCLUSION. Because routine radiographs of the foot may fail to
reveal an avulsion fracture of the base of the fifth metatarsal, an additional
projection should be obtained to better assess this region in the symptomatic
patient. The additional view should be an anteroposterior radiograph of the
ankle that includes the base of the fifth metatarsal because this projection
has been shown to help in the diagnosis of this avulsion fracture.
Introduction
Fractures of the proximal fifth metatarsal are common injuries of the foot.
Based on anatomic location and clinical course, there are two distinct groups
of fractures involving the proximal portion of the fifth metatarsal
[1,2,3,4,5].
The two types are an avulsion fracture of the tuberosity and a transverse
fracture of the proximal diaphysis within 1.5 cm of the tuberosity, also known
as a Jones fracture. Tuberosity avulsion fractures heal well with nonoperative
treatment; in contrast, Jones fractures are slow to heal and often require
surgical intervention [1,
2,
3,
6]. We have observed a subset
of the first type of fracture, an avulsion fracture of the proximal tip of the
tuberosity, that is not seen on conventional radiographs of the foot but that
is revealed on the companion radiographs of the ankle. This finding is most
likely because of the different positioning of the patient and the different
location of the central ray for radiography of the ankle
[7]. In this report, we
describe the findings in a series of avulsion fractures of the base of the
fifth metatarsal.
Materials and Methods
Between June 1994 to May 1999, 443 patients of all ages from the emergency
department at our institution underwent conventional radiography of the foot
and ankle. From this group, patients with fractures of the fifth metatarsal
diagnosed on ankle radiographs for isolated ankle injuries were selected using
a computer database. During this 5-year period, 26 patients had fractures of
the proximal fifth metatarsal.
All 26 patients had tenderness at the base of the fifth metatarsal, and all
had radiographs with the standard three views (anteroposterior,
anteroposterior oblique, and lateral) of the foot obtained on the same day as
radiographs with the standard two views (anteroposterior and anteroposterior
oblique) of the ipsilateral ankle. The radiographs of the foot and ankle were
reviewed retrospectively by two musculoskeletal radiologists separately. Both
radiologists categorized fractures as present or absent and noted the location
of the fracture on each positive study. There were no disagreements between
the two reviewers.
Results
Six (23%) of the 26 patients had fractures of the proximal fifth metatarsal
not seen on foot radiographs but visualized on ankle radiographs. All six of
these fractures were tuberosity avulsion fractures located at the tip of the
tuberosity (Figs.
1A,1B,1C,1D,1E
and
2A,2B).
Four of the six fractures were seen on the anteroposterior and anteroposterior
oblique projections of the ankle (Fig.
1A,1B,1C,1D,1E).
Two of the six were seen only on the anteroposterior projection of the ankle
(Fig.
2A,2B).
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Fig. 1A. —28-year-old woman with avulsion fracture of base of fifth
metatarsal. Anteroposterior (A), anteroposterior oblique (B),
and lateral (C) digital radiographs of foot fail to reveal fracture of
base of fifth metatarsal.
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Fig. 1B. —28-year-old woman with avulsion fracture of base of fifth
metatarsal. Anteroposterior (A), anteroposterior oblique (B),
and lateral (C) digital radiographs of foot fail to reveal fracture of
base of fifth metatarsal.
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Fig. 1C. —28-year-old woman with avulsion fracture of base of fifth
metatarsal. Anteroposterior (A), anteroposterior oblique (B),
and lateral (C) digital radiographs of foot fail to reveal fracture of
base of fifth metatarsal.
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Fig. 1D. —28-year-old woman with avulsion fracture of base of fifth
metatarsal. Anteroposterior (D) and anteroposterior oblique (E)
digital radiographs of ankle show fracture of tip of tuberosity
(arrow).
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Fig. 1E. —28-year-old woman with avulsion fracture of base of fifth
metatarsal. Anteroposterior (D) and anteroposterior oblique (E)
digital radiographs of ankle show fracture of tip of tuberosity
(arrow).
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Fig. 2A. —61-year-old woman with avulsion fracture of base of fifth metatarsal
and oblique fracture of distal fibula. Avulsion fracture was not seen on foot
radiographs (not shown). Anteroposterior digital radiograph of ankle shows
fracture of tip of tuberosity (straight arrow). Oblique fracture of
distal fibula (curved arrow) is also visible.
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Fig. 2B. —61-year-old woman with avulsion fracture of base of fifth metatarsal
and oblique fracture of distal fibula. Avulsion fracture was not seen on foot
radiographs (not shown). Anteroposterior oblique digital radiograph of ankle
shows subtle radiolucency at fracture site of base of fifth metatarsal
(straight arrow), which is more conspicuous on anteroposterior
radiograph (A). Oblique fracture of distal fibula (curved
arrow) is also visible.
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Sixteen (62%) of the 26 patients had an avulsion fracture through the
expanded portion of the tuberosity revealed on both the foot and ankle
radiographs. Four (15%) of the 26 patients had a Jones fracture shown on both
the foot and ankle radiographs. There were no cases in which a fracture was
seen on the foot radiographs but was not seen on the ankle radiographs.
Discussion
Fractures of the proximal fifth metatarsal may involve the tuberosity or a
1.5-cm-long segment distal to the tuberosity. As in this study, most fractures
of the proximal fifth metatarsal are tuberosity avulsion fractures
[3,
6,
8]. The six fractures not seen
on the foot radiographs in this study were tuberosity avulsion fractures
located at the tip of the tuberosity proximal to its expanded portion.
Radiographs of the foot have been designated as the important radiographs
to obtain for the diagnosis of fractures of the proximal fifth metatarsal
[6,
8,
9]. Because of the location of
the clinical findings of pain, tenderness, and possible ecchymosis at the base
of the fifth metatarsal, referring physicians may obtain only radiographs of
the foot. However, based on the results of this study, an avulsion fracture at
the tip of the tuberosity is not revealed on radiographs of the foot. It is
important to be aware of this fact particularly because this avulsion fracture
may be clinically misdiagnosed as a "sprained ankle." If clinical
findings are suggestive a fracture at the base of the fifth metatarsal but
radiographs of the foot show normal findings, the radiologist should recommend
that an anteroposterior radiograph of the ankle that includes the proximal
fifth metatarsal be obtained to rule out this avulsion fracture. The
technologist should perform this additional examination with the film cassette
centered at the proximal fifth metatarsal instead of at the typical location
above the ankle joint.
The pathomechanics of the tuberosity avulsion fracture has been disputed in
the past. The tendon of the peroneus brevis muscle with its broad insertion to
the tuberosity (Fig. 3) was
proposed to be the structure causing the avulsion injury
[1]. In 1984, Richli and
Rosenthal [5] reported that the
lateral cord of the plantar aponeurosis with its attachment to the proximal
tip of the tuberosity (Fig. 3)
is the structure that is the basis for this avulsion injury.
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Fig. 3. —Anatomy of proximal fifth metatarsal. Drawin shows relationships
among base of fifth metatarsal, lateral cord of plantar aponeurosis
(straight arrow) and peroneus brevis tendon (curved
arrow).
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The findings in this study confirm the lateral cord of the plantar
aponeurosis as the avulsing structure. All six fractures that were seen only
on the ankle radiographs were located at the attachment site of the lateral
cord of the plantar aponeurosis. These six fractures at the tip of the
tuberosity were located proximal to most, if not all, of the broad insertion
of the peroneus brevis tendon.
It is important to distinguish between tuberosity avulsion fracture and
Jones fracture because of the differences in treatment. Patients with
tuberosity avulsion fractures are treated conservatively with weight-bearing
as tolerated and the fracture heals rapidly within 2 months
[1,
3,
6,
9].
In contrast, Jones fractures take longer to heal, almost always more than 2
months [3,
4,
6]. Clapper et al.
[3] found that in 18 (72%) of
25 patients, union with casting was achieved after an average of approximately
21 weeks; in the remaining seven patients (28%), surgery had to be performed
an average of 25 weeks after injury and union occurred an average of 12 weeks
later. The difference in healing between tuberosity avulsion fractures and
Jones fractures has been attributed to the blood supply to the base of the
fifth metatarsal [10]. The
intraosseous blood supply to the fifth metatarsal tuberosity arises from
numerous metaphyseal vessels. After a fracture of the tuberosity, both
proximal and distal fracture fragments have adequate blood supply. The blood
supply to the proximal diaphysis arises from the single nutrient artery. A
fracture of the proximal diaphysis disrupts this artery or its proximal
branch, creating a relative avascular zone.
The most likely explanation for the fracture located at the tip of the
tuberosity being seen on only the ankle radiographs, specifically on the
anteroposterior projection, is the differences in technique between obtaining
radiographs of the foot and obtaining radiographs of the ankle. There are
differences in positioning the patient and in the location of the central ray
for radiography of the foot and of the ankle
[7]. For an anteroposterior
radiograph of the foot, the patient's knee is flexed so that the entire
plantar surface of the affected foot is on the cassette. The central ray of
the beam is directed at the base of the third metatarsal. For an
anteroposterior radiograph of the ankle, the patient's knee is extended so
that the heel of the affected foot is on the cassette and the long axis of the
foot is vertical. The central ray of the beam is directed at the ankle joint
midway between the medial and lateral malleoli.
These two differences in technique between obtaining radiographs of the
foot and those of the ankle are the only two variables between these two
examinations. With the location of the six fractures at the lateral aspect of
the proximal fifth metatarsal, there are no overlapping bones that could have
masked the fractures on the foot radiographs. The difference in positioning
the foot (plantar flexion on the foot radiograph as opposed to dorsiflexion on
the ankle radiograph) and the difference in the location of the central beam
(more proximal location on the ankle radiograph) account for the findings in
this study.
Because routine foot radiographs do not show all avulsion fractures of the
proximal fifth metatarsal, the anteroposterior radiograph of the ankle allows
further evaluation of this region. Although all ankle radiographs should
include the base of the fifth metatarsal, the proximal fifth metatarsal is the
main focus of this additional examination. Therefore, the film cassette should
be centered over this region. If there is clinical suspicion of a fracture at
the base of the fifth metatarsal but the radiographs of the foot reveal normal
findings, an additional projection, the anteroposterior radiograph of the
ankle that includes the proximal fifth metatarsal, should be obtained to rule
out this avulsion fracture.
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Abstract
Introduction
