A Prospective Randomized Pilot Study to Compare Open Versus Percutaneous Syndesmosis Repair of Unstable Ankle Fractures

High ankle fractures involve fracture of the fibula above the level of the syndesmosis (space between the tibia and fibula bones) that result from indirect mechanisms (e.g. pronation-external rotation (twisting) injuries. The method of injury is assumed to disrupt one or more of the syndesmotic ligaments, leading to instability of the ankle mortise . High ankle fractures comprise a significant proportion of ankle injuries (16 to 45 % of all ankle fractures patterns) . It is generally agreed that operative intervention of ankle injuries is indicated in cases of instability . However, recent advances in the understanding of the biomechanics of the ankle have given rise to particular areas of clinical uncertainty, including the treatment of unstable syndesmotic injuries and reliability of strictly radiographic assessment of ankle fractures .

The goal of operative treatment is to anatomically reduce the ankle mortise to permit syndesmosis ligament healing and restoration of the normal tibiofibular joint dynamics. Even 1 mm of displacement or lateral shift of the talus will affect ankle joint loading and lead to dysfunction and potentially degenerative joint changes. Accurate reduction of the syndesmosis and maintenance of this reduced position until the ligaments heal is crucial to ensure good outcome and to avoid long term arthritic changes in the tibiofibular joint .

If the ankle joint is unstable (too much sideways movement), the syndesmosis space between the two bones in the ankle (tibia and fibula) needs to be stabilized. One method to treat unstable syndesmosis injuries is making an incision to expose the ankle to provide direct visualization of fracture for anatomic reduction (alignment) and insertion of one or two syndesmosis screws to maintain the relationship of the fibula to the tibia. This is referred to as open reduction and internal fixation (ORIF).

Another method of repair is by closed reduction of the ankle joint and the use of one or two percutaneous syndesmosis screws only. That is, syndesmosis stabilization can be done percutaneously using intraoperative fluoroscopy to visualize the repair . Literature and standard practice support both of these methods.

The syndesmosis joint complex is composed of the anterior inferior tibiofibular ligament (AiTFL), the posterior inferior tibiofibular ligament (PiTFL) and the interosseous membrane (IOM). This complex is believed to permit ankle mortise stability and flexibility due to the elasticity of the ligaments, which allows the intermalleolar distance to change and facilitates tibial and fibular rotation. It also maintains the axis of balanced loading of the foot through the fibula. Adequate stability and anatomic restoration of the syndesmosis joint complex is vital to restoring normal tibiotalar contact forces in order to lessen the risk of posttraumatic arthritis.

Clinical studies have shown that anatomic reduction of the PiTFL provides a more accurate reduction of the ankle mortise than percutaneous reduction while ORIF fixation of the PiTFL has been shown on both biomechanical and clinical studies to provide greater stability than with syndesmotic screws alone .

However, due to the mechanism if injury, the AiTFL is the initial and may be the only lateral ligamentous stabilize structure compromised in syndesmotic injury. Kinematically, this ligament provides roughly half of the strength of the syndesmosis and acts as a vital primary restraint to excessive fibular displacement. The remainder of the stability is believed to come from bony restraints such as the posterior malleolus and the PiTFL . As such, direct reconstruction of the AiTFL component of the syndesmosis joint may accurately restore syndesmotic stability. Current syndesmosis repair techniques traverse the tibia and fibula (trans syndesmotic repair), but do not anatomically reconstruct the AiTFL.

Although it is known that an accurate reduction of the syndesmosis is essential to a good outcome, current treatments may have malreduction rates greater than 40% . In light of the existing models of syndesmosis injury, and the investigators' understanding of the importance of syndesmosis reduction, it may be that restoration of the AiTFL may potentially unlock a higher rate of anatomic reductions and positive outcomes.

Cadaveric and clinical studies have demonstrated that a flexible trans-osseous fixation technique may be viable and may improve ligamentous healing . However, current flexible techniques may not provide adequate stability and may not reduce the rate of malreduction compared to screw fixation.

The investigators recently conducted biomechanical studies in our lab using cadaveric ankles. The investigators compared whether a technique of syndesmosis repair concentrating on restoration of the AiTFL ligament (Anatomic repair technique or ART) provides a more anatomic reconstruction of the syndesmosis joint than rigid screw or posterior malleolus fixation.

The investigators' findings have demonstrated that our anatomic repair technique (ART) offers a repair which is sufficiently stable compared to screw fixation, with a lower incidence of malreduction as visualized on CT scan.

The investigator research suggests that ORIF repair of the AiTFL in addition to the stability provided by syndesmotic screw repair enhances syndesmosis stability substantially, as the AiTFL is a primary stabilizer to external rotation forces. In other words, fixing the anterior ligament may provide a better outcome and faster return to functioning.

Further in vivo testing is required to evaluate ART for repair of unstable syndesmosis injuries.