DOI:10.2214/AJR.04.1614
AJR 2006; 186:259-264
© American Roentgen Ray Society
Posterior Subtalar Facet Coalition with Calcaneal Stress Fracture
David C. Moe1,2,
James J. Choi1 and
Kirkland W. Davis1
1 Department of Radiology, University of Wisconsin Medical School, Madison, WI
53792.
2 Present address: Hawkes Bay Hospital New Zealand, Private Bag 9014, Hastings,
New Zealand.
Received October 15, 2004;
accepted after revision December 21, 2004.
Address correspondence to D. C. Moe.
Keywords: ankle • calcaneal stress fracture • MRI • plantar fasciitis • tarsal coalition
Introduction
Tarsal coalition is an abnormal union (fibrous, cartilaginous, or osseous)
between two tarsal bones, with a reported incidence of 1-2%. Most (90%) occur
at the calcaneonavicular and talocalcaneal joints
[1]. Talocalcaneal coalition
usually involves the middle subtalar facet. It rarely occurs at the anterior
or posterior facet [2].
Diagnosis of talocalcaneal coalition can be made by radiographs, CT, or MRI.
CT classically is held as the gold standard for imaging this entity
[3]. However, MRI has been
reported to be equally efficacious and often is the choice when other
diagnoses are considerations
[3]. In this article, we
present a novel case of MRI-proven partial posterior subtalar facet coalition
with associated medial and lateral calcaneal stress fractures. To our
knowledge, this has never been reported.
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Fig. 1A —48-year-old woman presenting with worsening left heel pain.
Lateral radiograph of patient's foot shows "humpback" appearance
of osseous protuberance at superior margin of calcaneal tuberosity
(arrow). This is site of medial coalition at posterior facet of
subtalar joint.
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Case Report
A 48-year-old woman presented to the Sports Medicine Clinic with 3 months
of worsening left heel pain, without preceding accident or injury. Initially
she had tenderness at the origin of the plantar fascia. Stretching and arch
supports were prescribed for the treatment of presumed plantar fasciitis.
However, over several months she continued to suffer from chronic medial
calcaneal pain, at times severe. Initial hindfoot radiographs, consisting of
lateral and Harris (axial) views, were interpreted as normal. In retrospect,
the lateral radiograph of the foot shows a subtle osseous protuberance at the
superior margin of the calcaneal tuberosity, creating an abnormal
"humpback" appearance (Fig.
1A), which is readily apparent when compared with a lateral
radiograph of a normal foot (Fig.
1B). The Harris view of the calcaneus shows an irregular interface
at the far medial aspect of the posterior facet of the subtalar joint,
suggesting a fibrous or cartilaginous coalition. This coalition is separate
from the middle subtalar facet, which is anterior to the abnormal articulation
(Figs. 1C and
1D).
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Fig. 1C —48-year-old woman presenting with worsening left heel pain.
Harris view of patient's foot shows irregular articulation at medial aspect of
posterior facet (arrowhead). This is just posterior to normal middle
facet (arrow).
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Fig. 1E —48-year-old woman presenting with worsening left heel pain.
Sagittal T1-weighted MR image shows normal portion of posterior facet of
subtalar joint on lateral slice through calcaneus (arrow).
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Fig. 1F —48-year-old woman presenting with worsening left heel pain.
Sagittal T1-weighted MR image shows coalition at posterior facet on medial
slice through calcaneus (arrow). Note narrowed and irregular joint
space, running at more oblique angle to normal portion of posterior facet.
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The patient did not respond to conservative treatment for plantar
fasciitis, prompting further imaging with MRI to evaluate for other causes.
Coronal and axial T1 and fat-suppressed T2 images, and sagittal T1 images,
fat-suppressed T2 images, and inversion recovery sequences were performed
through the hindfoot. This evaluation revealed multiple abnormalities. The
osseous prominence giving the humpback appearance on the lateral radiograph
was confirmed at the far medial posterior aspect of the calcaneus. This
portion of the calcaneus articulated with the medial portion of the talus at
an oblique angle to the remainder of the posterior subtalar facet, which
otherwise appeared to be normal (Figs.
1E and
1F). The involved joint space
was slightly narrowed and irregular, with periarticular marrow edema and a
small amount of joint fluid, best appreciated on the axial T1- and T2-weighted
sequences (Figs. 1G and
1H). The remaining subtalar
facets were normal. The MRI features were consistent with nonosseous coalition
at the medial posterior aspect of the posterior subtalar facet.
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Fig. 1G —48-year-old woman presenting with worsening left heel pain.
Axial T1- and T2-weighted fat-saturated MR images through coalition show
narrow and irregular joint space at medial aspect of posterior facet. The T2
image reveals periarticular marrow edema and a small amount of joint fluid
(arrows).
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Fig. 1H —48-year-old woman presenting with worsening left heel pain.
Axial T1- and T2-weighted fat-saturated MR images through coalition show
narrow and irregular joint space at medial aspect of posterior facet. The T2
image reveals periarticular marrow edema and a small amount of joint fluid
(arrows).
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In addition to the coalition, there were oblique linear low T1 signal
abnormalities within the marrow space of both the medial and lateral calcaneus
extending to the cortex. These were accompanied by periosteal and marrow edema
and were consistent with stress fractures (Figs.
1I and
1J). In addition, the original
clinical diagnosis of plantar fasciitis was confirmed on the sagittal STIR
sequence, which shows abnormal thickening of the plantar fascia with
perifascial fluid and insertional marrow edema
(Fig. 1K).
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Fig. 1I —48-year-old woman presenting with worsening left heel pain.
Axial T1-weighted MR image through calcaneal tuberosity shows oblique linear
low-signal abnormalities at medial and lateral medullary space extending to
cortex, consistent with stress fractures (arrows).
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Fig. 1J —48-year-old woman presenting with worsening left heel pain.
Axial T2-weighted fat-saturated MR image through calcaneal tuberosity shows
associated periosteal and marrow edema of stress fractures
(arrows).
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Fig. 1K —48-year-old woman presenting with worsening left heel pain.
Sagittal STIR-weighted MR image shows thickened plantar fascia with
perifascial edema (arrow) and marrow edema (arrowhead) of
plantar fasciitis.
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With these MRI findings, the patient was treated as having a stress
fracture and, in order to be pain free, was instructed partially to bear
weight with crutches. Complete immobilization was not chosen, as the treating
physician believed it would aggravate the plantar fasciitis.
Discussion
Tarsal coalition is a common finding in patients of any age that present
with hindfoot and midfoot pain, frequent ankle sprains, and rigid flatfoot
[4]. Calcaneonavicular and
middle facet talocalcaneal coalition account for the large majority of tarsal
coalitions, and previously have been adequately summarized in the literature
[1] (Figs.
1L,
1M,
1N,
1O,
1P,
1Q,
1R, and
1S). Partial posterior
subtalar facet coalition is a rare entity, with only a single reported case
[5]. The specific location of
the coalition in this case has never been described. The above described
humpback appearance of the superior posterior calcaneus on the lateral view of
the foot is a novel finding and can be added to other previously described
features of tarsal coalition such as the talar beak, the C sign, the ball-
and-socket ankle, the anteater sign, and the absent middle facet
[6-10].
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Fig. 1P —48-year-old woman presenting with worsening left heel pain.
Sagittal and coronal T1-weighted images show typical location of (nonosseous)
talocalcaneal coalition at middle subtalar facet (arrows).
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Fig. 1Q —48-year-old woman presenting with worsening left heel pain.
Sagittal and coronal T1-weighted images show typical location of (nonosseous)
talocalcaneal coalition at middle subtalar facet (arrows).
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The pathophysiology of pain in talocalcaneal coalition has been well
reported. The predominant theory is that limited subtalar motion leads to
abnormal pedal biomechanics and, classically, a peroneal spastic flatfoot. Our
case has the unique addition of calcaneal stress fracture, which we postulate
is due to abnormal forces placed on the hindfoot because of the coalition. To
our knowledge, no associated stress fracture has been reported as presenting
with a tarsal coalition.
Talocalcaneal coalition may be difficult to diagnose using conventional
radiography due to the subtalar joint anatomy. Frequently, CT is used to
diagnose or confirm the radiographic suspicion of tarsal coalition. Our case
report recognizes the utility of MRI in the setting of tarsal coalition, as
both the stress fractures and plantar fasciitis most likely would have been
missed by CT evaluation. Even in cases where coalition is evident on
radiographs or previously has been confirmed by CT, MRI may be valuable in
detecting associated or unsuspected abnormalities.
Conclusion
Tarsal coalition involving the posterior facet of the subtalar joint is
highly unusual. The specific location of the coalition in this case can be
recognized on radiographs by the humpback appearance of the superior aspect of
the calcaneal tuberosity on the lateral view and the irregular articulation
extending medially from the posterior facet on the Harris view. MRI is useful
in delineating ancillary findings (calcaneal stress fracture and plantar
fasciitis in this case) that might otherwise go undiagnosed by radiographs or
CT, especially in cases where the presentation is atypical for coalition.
Moreover, unexplained edemalike bone marrow abnormality should prompt careful
evaluation for abnormalities that may lead to altered biomechanics, like the
patient's coalition in this case
[11-13].
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Introduction
Case Report
