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

2264 VII Imaging of the Musculoskeletal System
Figure 47-73. Anderson stage IV osteochondral
lesion of the talus—displaced fragment. A, Mortise
radiograph; B, mortise coronal CT scan; C, mortise
coronal T1-weighted MRI; D, mortise coronal T2-
weighted fat-suppressed MRI. All images show the
displaced fragment (arrowheads) as well as the talar
donor site (short arrows). Long arrows point to marrow
edema at the donor site. (Courtesy of Richard
Kijowski, MD.)
A
B
C
D
by joint fluid. In the partially attached fragments, the
interface line was more irregular and not as bright as fluid,
and at surgery this was found to represent loose granulation
tissue. The stable lesions did not have increased T2
signal at their interface (Fig. 47-74). De Smet also found
several patients with “focal oval or spherical lesions
resembling cysts,” similar to the Anderson stage IIA lesions.
These were all at the bases of unstable lesions, although
at surgery these were found to be filled with loose granulation
tissue rather than fluid. De Smet speculated that
“these defects were traumatic cysts that were filled by the
reactive tissue forming at the unstable interface.” De Smet
also noted that the signal within the fragment, whether
high, normal, or low on T2-weighted images, was not
useful in distinguishing stable from unstable lesions (Fig.
47-75).
These seminal works by Anderson and De Smet and
colleagues point out the need for close communication
between radiologists and orthopedic surgeons with regard
to imaging and managing patients with OLT.
Once the diagnosis of OLT has been established, the
decision as to whether to treat the patient conservatively
or surgically often comes down to determining whether the
fracture is stable and has a potential for continued healing,
or unstable and at risk of dislocating.
• Lateral Process of Talus
The lateral process of the talus (LPT) is the pointed anterolateral
corner of the posterior facet of the subtalar joint,
indicated by the brown arrow on gross Figure 47-4C and
on sagittal CT Figure 47-7A. LPT fractures are the result of
trauma, often athletic trauma. Snowboarding, in particular,
is so often cited that fractures of the LPT are also referred
to as snowboarder’s ankle. 48 The LPT fracture lines tend to be
transversely oriented (Fig. 47-76), although vertically oriented
LPT fractures can occur (Fig. 47-77). LPT fractures
are often difficult to see radiographically (Fig. 47-78A) and
are best imaged with CT. Because LPT fractures are typically
transversely oriented in the axial plane, they are best visualized
in the sagittal (Fig. 47-78B) and oblique coronal
planes (Fig. 47-78C) to appreciate the size of the fracture
fragment as well as the extension of the fracture line into
the subtalar joint. Like OLT, LPT fractures are often diagnosed
months after injury, and reports in the orthopedic
literature state that “40% are missed at initial presentation.”
It is incumbent on anyone who looks at radiographs
of the ankle to scrutinize the LPT on all views because these
fractures can be subtle and sometimes are seen only on
frontal views (Fig. 47-79).
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