Operative treatment of AO Weber B fibular fractures with additional posterior malleolar fragment: reduction and functional outcome after prolonged follow up

Ankle fractures are frequently (incidence 2 in 1000 people per year) seen in
the emergency department of hospitals. In most cases (67%) there is a fracture
of the lateral or medial malleolus (unimalleolar), in a quarter of the cases of
a bimalleolar fracture and in the remaining 7% of the ankle fractures there is
also a fracture at the posterior side of the distal tibia (tertius fragment), a
trimalleolar fracture.

Despite the prominent place that ankle fractures occupy within (orthopedic)
trauma surgery, relatively little is known about the long-term prognosis of
these injuries. Trimalleolar fractures may have a worse prognosis for function
and pain than uni- / bimalleolar fractures, with an important predictive role
for the tertius fragment. There is still no consensus about the influence of
the size of the fragment, the degree of dislocation and the best treatment.

Theories about the influence of tertius fragments on the clinical prognosis
come from, among other things, biomechanical studies. The central idea here is
that long-term development of osteoarthritis is dependent on the size of the
contact surface in the tibiotal joint. Macko investigated the influence of the
size of the tertius fragment on the contact surface in 1991 by means of a
cadaver study with 8 ankles. He described that a larger tertius fragment
resulted in a smaller contact surface. Hartford also confirmed this in a study
of 16 cadavers. Macko assumes a relevant reduced contact surface for a tertius
fragment larger than 25% of the tibiotalar joint surface, while Hartford shows
that this is only the case at a size of 33%. On the basis of these studies,
they argue that obtaining the largest possible contact surface in the tibiotal
joint reduces the risk of osteoarthritis. That is why they advise striving for
the largest possible contact surface and thus the best possible anatomical
position.

Recent studies indicate that a postoperative step-off is a superior predictor
of functional outcome and the development of osteoarthritis. Therefore,
fixation via a direct exposure of the posterior tibia via a posterolateral
approach in the prone position, followed by open reduction and fixation with
screws in the posterior-anterior direction or antiglide plate has gained
popularity. It is unclear whether this approach leads to less development of
osteoarthritis and a better functional outcome.

The multicentre POSTFIX study (RCT) has been set up at the HMC to answer this
question (intended end date summer 2021). This is a continuation of that study.

To asses if there is a difference in functional outcome between open reduction
and fixation of the posterior fragment in trimalleolar AO-Weber B fractures
with additional medium-sized posterior fragment (5-25% of the involved
articular surface, AO type 44-B3) and no fixation of the posterior malleolar
fragment assessed by the AOFAS-score after 4-7 years.

Retrospective cohort study.

Participants of this study will not benefit directly by participating, other
than the opportunity to receive extra information if they experience any
problems or have any questions regarding their operated ankles during the visit
to the outpatient clinic. The extra radiation exposure of the X-rays is about
1/100th of the background radiation and does not outweigh the benefits of this
study.