Ankle and Foot 47 - Department of Radiology - University of ...

• Calcaneal Fractures 6,18,33
47 Ankle and Foot 2269 47
The calcaneus is the most commonly fractured tarsal bone,
with fractures typically occurring as the result of traumatic
axial loading, such as can occur with a front-end automotive
collision or falling from a height and striking the
ground feet first. Here in Wisconsin, we have hunters falling
from their tree-mounted deer stands. As a clinical aside,
patients who present to the emergency department with
bilateral calcaneal fractures should also be evaluated for
lumbar spine fractures at the time of the initial trauma
workup. The same traumatic axial loading that drives the
talus into the calcaneus also drives the lumbar vertebrae
together, and the risk of a lumbar burst fracture with fragments
retropulsed into the vertebral canal is high. An
example of the workup of such a patient with nondisplaced
lumbar fractures is outlined in Figure 47-80.
Calcaneal fractures can usually be recognized on the
lateral radiograph by the presence of lucent fracture lines
and displaced fragments (see Fig. 47-80A) or by a compression
deformity of the calcaneus with flattening of “Böhler’s*
angle” (see Fig. 47-80B). 9 When calcaneal fractures are
identified, it is important to evaluate for related injuries.
Lumbar compression fractures related to axial loading
forces are particularly associated with calcaneal fractures.
At the UW it is typical for severely traumatized patients to
receive a contrast-enhanced CT scan of the abdomen and
pelvis as part of the initial trauma workup (see Fig.
47-80C). Although this scan is designed to reconstruct the
raw data into large FOV images that are relatively thick
(5 mm) to assess for soft tissue organ injury, the same raw
data can also be reconstructed into images centered on the
spine with a smaller FOV and thinner (1 mm), overlapping
slices (see Fig. 47-80D). These thin, overlapping source
images can then be reformatted into sagittal (see Fig. 47-
80E) and other planes. Although CT images of the spine
are well suited to demonstrate the presence or absence of
cortical fragments displaced into the vertebral canal as well
as the overall alignment of the spine, MRI is used to visualize
epidural hematomas and other possible soft tissue
causes for neural compromise. T1-weighted (see Fig. 47-
80F) and proton-density–weighted (see Fig. 47-80G)
images are less sensitive to bone marrow edema than are
fat-suppressed T2-weighted (see Fig. 47-80H and I) or
inversion recovery images.
With traumatic axial loading, the wedge-shaped LPT is
driven into the calcaneus at the angle of Gissane, fracturing
and depressing the calcaneus (see Fig. 47-80J; Fig. 47-81B).
This fracture invariably involves the calcaneal articular
surface of the posterior facet of the subtalar joint (see Figs.
47-80K and 47-81C). The fracture then propagates inferiorly
and medially (see Fig. 47-81C), involving the sustentaculum
tali and the middle facet to varying degrees (see
Figs. 47-80L and 47-81D). Assessment of the integrity of the
middle facet of the subtalar joint is an important part of
preoperative surgical planning. Surgeons prefer to operate
on the calcaneus from the lateral side, meaning that they
will not directly visualize the middle facet and sustentaculum
tali. Thus, they require the preoperative CT scan to
show them these structures. For this reason, the oblique
coronal plane, angled perpendicular to the subtalar joint, is
the primary imaging plane in the assessment of calcaneal
fractures. Our CT hindfoot/midfoot reformatting protocol
(see Fig. 47-47B) also includes straight sagittal and straight
and oblique axial images to assess for extension into the
calcaneocuboid joint (see Fig. 47-81E).
One additional clinical point regarding calcaneal fractures:
they tend not to be surgical emergencies. Surgeons
typically wait for several days after the initial trauma for
the soft tissue swelling to decrease before operating. Therefore,
the preoperative CT scan of the calcaneus does not
need to be performed emergently when there may be other,
more serious injuries that need to be addressed.
• Anterior Process of the Calcaneus
The APC is the upper outer corner of the calcaneus where
it articulates with the cuboid, indicated by the orange box
on gross Figure 47-4C and the red arrow on sagittal CT
Figure 47-7A. Like LPT fractures, APC fractures can be easily
overlooked, and this structure should be carefully scrutinized
on all lateral radiographs of the ankle and foot (Fig.
47-82). APC fractures are more common in women and
are the result of an inversion injury while the foot is in
plantar flexion, such as when wearing high-heeled shoes.
Even when APC fractures are only minimally displaced
they have a tendency for nonunion despite prolonged
immobilization (Fig. 47-83). CT is useful for both detecting
these fractures and following their progress.
One potential pitfall in the diagnosis of an APC fracture
is the os calcaneus secondarius, an occasionally seen
normal variant that resides between the APC and the lateral
pole of the navicular (see Fig. 47-39). The os calcaneus
secondarius can be thought of as a forme fruste of tarsal
coalition, and it should not articulate with the cuboid as
the APC does. CT can be used to distinguish an acute
APC fracture from the normal-variant accessory ossicle
(Fig. 47-84).
• Lisfranc Dislocation
Dislocations along the tarsometatarsal joint are not uncommon.
These can be the result of severe acute trauma, but
the Lisfranc joint is also a common site for dislocation in
diabetic patients with peripheral neuropathy. As mentioned
in a footnote earlier in this chapter, Jacques Lisfranc
was a very aggressive surgeon in Napoleon’s army, and
although he did not describe the dislocation that now
*Lorenz Böhler (1885-1973) is most notable as the creator of modern accident
surgery. He was the head of the AUVA-Hospital in Vienna, Austria, that was later
named for him. This hospital was an international model during his time as the
leading surgeon there. Text continued on p. 2277
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