Foot & Ankle International - July 2018 - 855
Lawlor et al
rotation.7,9,19,20,23,26,29 While somewhat variable, one agreed
upon measurement used when evaluating these fractures is
medial clear space distance, and instability of the ankle
mortise is usually defined as greater than 4 mm and/or
greater than 1 mm compared with the superior clear
space.9,20 Controversy remains with respect to the definition
of instability, the reproducibility of gravity stress radiographs, and the possibility of stress overestimating the
degree of instability of the ankle.11,14,22,23 When gravity
stress radiographs are used to make the decision whether or
not medial injury is present, 40% to 65% of tests are positive, and surgery is indicated.7,19,26,27
In the past few years, several authors have reported the
clinical usefulness of weight-bearing radiographs with
excellent clinical outcome in patients who are selected for
nonoperative treatment based on a medial clear space measurement with this method.14,31 Weber et al31 reported the
first clinical series of 57 patients in whom the decision to
operate or not operate was made based on medial clear
space measurement on a weight-bearing radiograph. Fiftyone of the 57 patients demonstrated ankle stability with
weight bearing and were treated with variable external support, then followed clinically for an average of 62 months.
The average final American Orthopaedic Foot & Ankle
Society (AOFAS) score was 96.1 (scale 0-100, where a
higher score equates to better outcome). They concluded
that the use of weight-bearing radiographs is an easy, painfree, safe, and reliable method to exclude the need for operative treatment, with excellent clinical outcome in most
patients. Hoshino et al14 reported the results of a prospective
study with a protocol initially treating stress-positive SER
ankle fractures nonoperatively and using weight-bearing
radiographs in operative decision making. Only 3 of 36
patients had abnormal medial clear space widening on
weight-bearing films, allowing the remaining 33 patients
with an average medial clear space of 2.8 mm to be treated
without surgery. The average AOFAS score was 92 at
12-month follow-up, suggesting that a weight-bearing
radiograph could be used to assess congruency of the ankle
mortise and potentially reduce the number of surgeries performed while maintaining good to excellent clinical outcome. These and additional recent studies provide evidence
to support weight-bearing radiographs as a cost-containment strategy and to avoid the morbidity and complications
known to be associated with operative management of SER
ankle fractures.11,13,27
When weight-bearing radiographs are used to make the
decision whether or not medial injury is present, only 2% to
10% of tests are positive and surgery is indicated.14,27,31 In
all of these studies, ankle fractures with clear instability
(defined as MCS greater than 4 or 5 mm) were excluded
from the analysis and usually received operative treatment.
We are not aware of a study that has applied the diagnostic
algorithm using weight-bearing radiographs to this subset
855
of unstable SER ankle injuries. Our cadaver model created
a potentially unstable ankle, demonstrated on gravity stress
radiographs where MCS averaged 9.4 mm, and we sought
to explore the possibility that some fractures would become
anatomic under weight bearing. In fact, in our study, a group
of "stable" experimental ankles was revealed in which the
ankle mortise reduced and medial clear space was no different from the control gravity stress radiograph.
Medial clear space measurement can be a quick, easy,
and a valuable patient management tool, but it must be recognized as a uniplanar image of a complex joint. Bone overlap and variability in radiographic technique are 2 of many
factors that can make interpretation of radiographs difficult
in SER ankle fracture evaluations. CT scans are better than
radiographs for visualization of bone detail, and by review
of 2D multiplanar images as well as 3D reconstructions,
they can be very helpful for assessing the detailed configuration of fracture/dislocations in and around the joints.5,6,8,25
A new dedicated extremity CBCT scanner has been
approved by the FDA and provides the unique ability to
image subjects while weight bearing.1,2,4,12,28 We have
some early experience with the CT scanner and clinical
use on a series of patients with SER fractures of the ankle
and are investigating the diagnostic usefulness of weightbearing CT scans in this setting. We have found that, like
plain radiography, weight-bearing CT scans can indicate
stability in many SER fractures of uncertain status and
could be used to select patients for nonoperative treatment
based on medial clear space measurement.18 On the other
hand, we also noticed by examining all 3 planes of CT
images that there was rarely perfect reduction, with residual fibular shortening, fibular rotation, fracture comminution, and asymmetry of the distal tibiofibular joint present.
We are not certain of the clinical implications of these findings, and although others have shown good clinical outcome when only medial clear space is used for decision
making, the studies have been of relatively short followup.13 In the present study, we created a cadaveric model of
a grossly unstable SER fracture by severing all of the deltoid ligament as well as the anterior and posterior tibiofibular ligaments. We have demonstrated that under simulated
weight bearing, 6 of 10 ankles reduced, but the other 4
ankles remained unstable with an average medial clear
space of 11.1 mm. Possible explanations for this finding
are that the unstable ankles had ankle or foot deformity
that predisposed to instability under weight bearing. The
results of our study suggest that a weight-bearing CBCT
scan may be able to distinguish between stable and unstable SER ankle fractures.
Potential limitations of this study are a small sample size
and that testing was performed on cadaveric ankles under a
simulated weight-bearing load. We used fresh frozen cadaveric specimens for this study and recognize that temperature
and time of exposure before testing were variable. These
Table of Contents for the Digital Edition of Foot & Ankle International - July 2018
Contents
Foot & Ankle International - July 2018 - Intro
Foot & Ankle International - July 2018 - Cover1
Foot & Ankle International - July 2018 - Cover2
Foot & Ankle International - July 2018 - i
Foot & Ankle International - July 2018 - ii
Foot & Ankle International - July 2018 - Contents
Foot & Ankle International - July 2018 - iv
Foot & Ankle International - July 2018 - v
Foot & Ankle International - July 2018 - vi
Foot & Ankle International - July 2018 - vii
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Foot & Ankle International - July 2018 - 1A
Foot & Ankle International - July 2018 - 1B
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Foot & Ankle International - July 2018 - 2A
Foot & Ankle International - July 2018 - 2B
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Foot & Ankle International - July 2018 - 3B
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Foot & Ankle International - July 2018 - Cover3
Foot & Ankle International - July 2018 - Cover4
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