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

2254 VII Imaging of the Musculoskeletal System
surgical emergencies. The patients with significantly displaced
fractures may go to the operating room the day of
the injury for traction reduction and external fixation to
restore relative alignment to the mortise, and then wait
several days for the swelling of the surrounding soft tissues
to reduce before returning to the operating room for the
more anatomic ORIF of the pilon fracture. This means that
these patients typically receive their CT scans during this
interim period, after the external fixator is in place. However,
as illustrated in Figure 47-62, such external fixation hardware
is no impediment to obtaining the CT images the
surgeon requires. To maintain alignment between the hindfoot
and leg, the surgeon will percutaneously drill thick
metal pins through the calcaneus (white arrows in Fig. 47-
62A, B, and D) and through the tibia proximal to the fracture
(this pin is not seen in Fig. 47-62). These pins are
rigidly attached by metal clamps (white arrowheads in Fig.
47-62A and B) to nonmetallic connecting bars (gray arrows
in Fig. 47-62A to C). It is these nonmetallic bars that span
the length of the fracture and maintain the tibia length.
Because these nonmetallic bars are made of materials
(usually carbon fiber) that block very few x-rays from reaching
the detectors, they are nearly radiolucent and cause no
CT streak artifacts (see Fig. 47-62C). The metal pin-bar
clamps block many x-rays from reaching detectors and thus
will cause some CT streak artifacts. However, because the
clamps are always placed proximal and distal to the pilon
fracture, they never cause any CT streak artifacts across the
reformatted fracture margins (see Fig. 47-62B and D). Using
our standard bone CT scanning protocol of thin/overlapping
slices, metallic streak artifacts are often not appreciable.
Notice the good visualization of the calcaneus cortex
in Figure 47-62B and D, which is only minimally affected
by streaking caused by the metal pin-bar clamps.
Juvenile Tillaux Fracture
Juvenile Tillaux fractures are Salter-Harris type 3 fractures.*
These fractures have a characteristic appearance, particularly
on CT. The fracture is the result of an external rotation
force pulling on the anterior tibiofibular ligament, causing
avulsion of the anterolateral corner of the distal tibial
epiphysis (Fig. 47-63A). These fractures always occur laterally
because the distal tibial physis fuses from medial to
lateral as a child matures (Fig. 47-63B). As such, juvenile
Tillaux fractures occur exclusively in adolescents in whom
the lateral growth plates have not yet fused, usually between
the ages of 12 and 15 years. Coronal and sagittal images
are useful to demonstrate the degree of displacement particularly
at the articular surface (Fig. 47-63B and C, white
arrow). While minimally displaced juvenile Tillaux fractures
are usually treated nonoperatively, fractures displaced
more than 2 mm should have orthopedic consultation and
surgery to restore the congruity of the joint surface.
Triplane Fracture
Triplane fractures are Salter-Harris type 4 fractures. Like the
juvenile Tillaux fracture, triplane fractures occur in adolescents
in whom the lateral growth plates have not yet fused.
When minimally displaced, triplane fractures can be difficult
to see radiographically, and frontal and lateral views are
needed to appreciate their multiplanar nature (Fig. 47-64A
to C): the epiphysis fracture running vertically in a sagittal
orientation (plane 1), the physeal fracture running horizontally
in the axial plane (plane 2), and the metaphyseal fracture
running obliquely vertically in a coronal orientation
(plane 3). Multiplanar CT scans are ideally suited to visualize
these fractures in all planes (Fig. 47-64D to F) and often
reveal more deformity of the articular surface than would
be anticipated from radiographs alone.
• Talar Fractures 3,47
Talar fractures can be thought of as either traumatic or
insidious. Traumatic fractures are considered surgical emergencies
because of the high risk of avascular necrosis, and
patients usually go straight from the emergency department
to the operating room without stopping at CT (although
CT scans of displaced fractures of the body of the talus can
be dramatic; Fig. 47-65). Even with anatomic internal fixation,
avascular necrosis sometimes occurs, and CT can be
useful to confirm the presence of abnormal medullary sclerosis
suspected radiographically (Fig. 47-66).
• Osteochondral Lesions of the Talus
Fractures of the talar dome are insidious. They typically
occur at the medial edge or posterolateral corners of the
talar dome and are thought to be the result of an impaction
of the talar dome on the tibial plafond during an inversion
or eversion twisting injury. Refer to the illustrations of
Weber injuries (see Fig. 47-60). Because they involve the
cortical bone and the overlying articular hyaline cartilage,
they are referred to as osteochondral fractures. A gross example
is indicated by the green arrow in Figure 47-2. Osteochondral
fractures notoriously occur on convex articular surfaces,
including the femoral condyles of the knee and
capitellum of the elbow. Generically, these fractures have
been referred to by many names, including osteochondral
defect, osteochondral lesion, and osteochondritis dissecans. The
last term is the oldest and perhaps the most misleading,
for although the suffix “itis” by definition implies inflammation,
histologically these lesions have not been shown
to be inflammatory. We prefer the term osteochondral lesions
of the talus, to distinguish them from osteochondral lesions
at other sites.
*The Salter-Harris system is applied to fractures that involve the growth plate
(physis) at the ends of skeletally immature bones. Type 1 refers to simple transverse
fractures that involve the physis only. Type 2, the most common, refers to
fractures that involve the physis and the adjacent metaphysis. Type 3 fractures
extend from the physis through the epiphysis at the end of the bone, typically disrupting
the articular surface at a joint. Type 4 fractures involve the epiphysis, the
physis, and the metaphysis. Type 5 fractures are rare and are crush injuries to the
growth plate. Text continued on p. 2260
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