Foot & Ankle International - July 2018 - 852

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Foot & Ankle International 39(7)

Figure 2. (A) An ankle specimen in the cone-beam computed tomography (CBCT) scanner positioned for a gravity stress scan. (B) A
piezoelectric sensor verifying that a stack of weights applies a 50-lb load to simulate weight bearing. The screws on the threaded rods
lock the top plate in place to maintain the load during imaging. (C) An ankle specimen in the CBCT scanner positioned for a weightbearing scan.

tibial attachment perpendicular to its fibers. To ensure complete transection, the AITFL cut was continued distally to
include the anterolateral capsule until a small portion of the
anterolateral talar dome was visualized. Next, an oblique
osteotomy of the fibula was made with an osteotome at the
level of the talar dome in an anterior-distal-medial to posterior-proximal-lateral direction. The posterior inferior tibiofibular ligament (PITFL) was then isolated and identified
running from the posterior tubercle of the tibia in a distallateral direction to insert on the fibula. The PITFL was transected at its tibial attachment perpendicular to its fibers.
Next, a curvilinear skin incision was made at the anteromedial aspect of the ankle joint. The superficial deltoid ligament was identified and transected, taking care to avoid the
tibialis posterior tendon. Finally, to gain access to the deep
deltoid ligament, a 1-cm length of the anteromedial joint
capsule was opened, and the deep deltoid ligament was then
transected by placing a scalpel into the medial tibiotalar
joint space and cutting from inside-out while moving in a
posterior direction. For each specimen, this last step produced visual and palpable gross ankle instability. Once the
fracture model was created, we repeated the same sequence
of imaging as described above for the control images.
For every condition, the width of the medial clear space
was measured as the distance between the lateral border of
the medial malleolus and the medial border of the talus at
the level of the talar dome.7,10,15 The ankle medial clear
space was measured for all samples using the digital line
tool of a PACS viewing system. After imaging was complete, we noticed 2 distinct groups within our data set,
which we separated into stable (n = 6) and unstable (n = 4)
specimens. Stable specimens were those with medial clear
space less than 5 mm (range, 1.2-1.9 mm), and unstable
specimens were those with medial clear space greater than
or equal to 5 mm (range, 6.2-16.8 mm). Figures 3 and 4
show a representative example of a series of images from a
specimen in each of these groups.

Statistical Analysis
Paired t tests were used to compare the control and experimental conditions for medial clear space measured on gravity stress radiographs, gravity stress CBCT scans, and
weight-bearing CBCT scans. Measures obtained from gravity stress radiographs from the controls served as the referent group for all analyses, and analyses were performed for
both stable and unstable ankle cadavers, separately.
Unpaired Student t tests were used to compare stable versus
unstable ankles with respect to medial clear space measured
on gravity stress radiographs, gravity stress CBCT scans,
and weight-bearing CBCT scans for both the control and
experimental conditions. Means ± standard deviation are
reported, and SAS 9.4 (SAS Institute, Cary, NC) was used
for statistical analysis.

Results
The results are shown in Table 1 and summarized here:

Experimental Versus Control Group
Compared with controls assessed by gravity stress radiographs (1.8 ± 0.6 mm), the medial clear space was significantly greater for the experimental condition when assessed
by gravity stress radiograph (9.3 ± 3.5 mm, P = .002) and
gravity stress CBCT scan (7.0 ± 2.3 mm, P = .003) within
the group of stable ankles. There was no difference between
controls assessed by gravity stress radiographs (1.8 ± 0.6
mm) or gravity stress CBCT scan (1.5 ± 0.5, P = .18) and
the weight-bearing CBCT experimental condition scan (1.5
± 0.3, P = .10). Compared with controls assessed by gravity
stress radiographs (1.0 ± 0.4 mm), the medial clear space
was significantly greater for the experimental condition
when assessed by gravity stress radiograph (9.5 ± 0.5 mm,
P < .0001), gravity stress CBCT scan (8.3 ± 1.2, P = .001),

Table of Contents for the Digital Edition of Foot & Ankle International - July 2018