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

2284 VII Imaging of the Musculoskeletal System
Figure 47-90. Subtle Lisfranc dislocation in a 56-
year-old, nondiabetic patient who mis-stepped from
a high curb and landed awkwardly, injuring the foot.
A, Initial radiograph shows the fracture off the base of
the second metatarsal (arrow). The alignment of the
Lisfranc joint is relatively maintained. Because of the
degree of soft tissue swelling, the patient was initially
treated with a boot. B, Axial CT scan obtained 5 days
later showed the second metatarsal fracture to be
essentially nondisplaced and the first and second
tarsometatarsal joints to be in anatomic alignment.
When the soft tissue swelling subsided 4 days later,
the boot was exchanged for a cast. C, Postcasting
anteroposterior radiograph reveals that there is lateral
displacement of the first (white arrow) and second
(black arrow) metatarsals. Because this demonstrated
that the Lisfranc joint was not stable, 3 days later the
patient was taken to the operating room for open
reduction and internal fixation (D).
A
B
C
D
subcortical sclerosis, and subcortical round lucencies called
geodes—are typically well seen radiographically. But some
joints, such as the ankle and subtalar joints, can be difficult
to profile radiographically, and in such cases CT should be
well able to demonstrate all these osteoarthritic changes
(Fig. 47-91).
• Rheumatoid Arthritis
For rheumatoid arthritis, we prefer MRI to CT when crosssectional
imaging is required. MRI after the administration
of intravenous contrast well demonstrates abnormally vas-
cularized synovium and thickened pannus (see Fig. 47-55)
as well as small cortical erosions before they become radiographically
apparent.
• Gout
Gout is uric acid crystal deposition arthropathy with a
predilection for the foot, particularly the first metatarsophalangeal
joint. The cortical erosions caused by gout form
slowly and can take as long as a decade to be manifest
radiographically. These erosions are classically described as
being well circumscribed with sharp overhanging edges.
The diagnosis of gout is confirmed when an aspirate of
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