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each trial to keep this effect to a minimum. Similar to the
current study, Burns et al3 reported a significant reduction in
contact area with complete syndesmotic and deltoid disruption. A measured reduction in contact area with syndesmotic
disruption suggests that the tibiotalar joint does not fully
autocentralize into normal articular congruity with a simple
axial loading protocol in an unconstrained hindfoot.
Despite reduction using 3 different techniques, no technique was able to restore normal contact area or total plafond joint force. Using a clamp or a suture button to reduce
the injury caused a significant reduction in contact area and
a reduction in joint force, which imply that the syndesmosis
may have been overreduced with these techniques and
structures other than the tibial plafond were carrying more
loads (eg, medial and lateral gutters). The fact that contact
area was reduced with a complete injury and with a clamp
or a suture-button construct, but to a lesser degree with the
thumb technique, suggests that contact mechanics was very
sensitive to small perturbations in tibiofibular relationships.
These differences were significant, despite the syndesmotic
screw pilot hole being drilled in the reduced condition prior
to testing. Additionally, the relationship between the ankle
ligaments, bones, and interosseous membrane may be critical in influencing tibial plafond contact mechanics.15
Our results demonstrate that native syndesmotic ligaments are necessary to maintain the ankle mortise, thus
facilitating appropriate ankle congruity and loading
mechanics. Syndesmotic reduction under ideal conditions
did not restore native ankle loading mechanics.25,31
However, despite reducing the syndesmosis with conventional intraoperative techniques, the fact that contact area
remained significantly decreased suggests that other soft
tissues play critical roles in establishing normal ankle contact mechanics.5,6,15 Liu et al15 developed a finite element
model to assess the pressure distribution around the ankle
with a syndesmotic injury and with screw fixation. Their
model showed that with a syndesmotic injury, ankle ligaments experience different loads than in the intact situation.
In particular, with loads commensurate with standing, the
anterior talofibular ligament experienced less loads, and the
medial posterior tibiotalar band experienced greater loads.
This has been supported with a cadaveric study demonstrating that with syndesmotic disruption, the deltoid ligament
experiences greater strain than with an intact lateral syndesmosis.3 This suggests that collateral ligaments, the deltoid
in particular, may play a key role in ankle contact mechanics. In keeping with this, 2 studies have reported decreased
ankle contact area between 20% to 43% with deltoid sectioning.5,6 The current model had a complete deltoid injury,
and this could explain why ankle contact area remained
lower in the reduced and repaired situations.
Treatment of the deltoid remains a controversial issue as
well. Many authors will not repair the deltoid after a

Foot & Ankle International 38(6)
syndesmotic injury. Instead, syndesmotic fixation is used to
obtain an anatomic ankle mortise, and the deltoid is left to
heal without operative intervention. While deltoid instability may be infrequently encountered after a syndesmotic
injury, the current study does have several implications with
regard to deltoid repair. Clinically, if early weightbearing is
allowed after isolated syndesmotic fixation regardless of
the reduction technique, the contact mechanics of the joint
is abnormal. This may predispose the ankle joint to early
wear. If early weightbearing is desired, it may be advantageous to address the soft tissues acutely to minimize abnormal contact stress. Specifically, acute repair of the deltoid
may be beneficial to patients in whom early weightbearing
is desired. Clearly, future biomechanical and clinical studies will be needed to further investigate this.
The current study used 3 reduction techniques. Recent
data suggest that syndesmotic malreduction is common8
and that syndesmotic malreduction may portend a worse
patient outcome.26,34 Performing reduction with a clamp
may malreduce the syndemosis.18 A suture-button construct
may be used to reduce the syndesmosis.22 Based on the
rationale that clamps may malreduce the syndesmosis, the
current study also used a technique in which the syndesmosis was palpated with a thumb, and when the anterior distal
tibiofibular incisura was congruent and lacking any steps or
gaps, the syndesmosis was secured with a screw. Although
this technique performed better than the other reduction
techniques, the differences were small, and no technique
was able to return contact area or total joint force back to
the intact situation. This could be due to the concomitant
deltoid injury or the presence of the fixation itself. Placing
a rigid screw across the syndesmosis altered the pressure
distribution of tissues around the ankle in a finite element
model.15 However, this is less likely to be the cause in the
current study as there were no differences in contact
mechanics between the rigid screw and the flexible suturebutton construct.
The current study has several limitations. Although the
sensor was designed specifically for use in ankles and is very
thin (0.1 mm),2 the sensor itself may have altered the articular cartilage contact mechanics.35 While these pressure-sensitive sensors do deteriorate following multiple loading
cycles, previous work demonstrated no change in measurements when loaded regularly over 8 hours.18 The sensor was
also limited in that it was not designed to simultaneously
measure gutter and plafond contact mechanics. Hence, tissues experiencing loads other than the tibial plafond were
not directly measured. The loading protocol used was a simple axial load with an Achilles load. This loading protocol
was not able to demonstrate dynamic instability of the ankle,
which may significantly alter contact mechanics.31 Since the
primary outcome of the study was global contact mechanics,
the sensor was moved to ensure capture of the entire contact

Table of Contents for the Digital Edition of Foot & Ankle International - June 2017