gms | German Medical Science

Objectives: Injury to the structures of the syndesmosis, the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), and interosseous membrane (IOM), has been shown to be predictive of residual symptoms after ankle injury. These injuries are typically treated surgically with cortical screw fixation or suture button fixation if the syndesmosis is unstable. Studies have shown that tibiotalar contact area decreases by 42% with even a 1 mm lateral shift of the talus. Thus, the objective of this study was to quantify tibiotalar joint motion after syndesmotic screw and suture button fixation compared to the intact ankle.

Methods: Methods: Nine fresh-frozen human cadaveric specimens (mean age 60 yrs.; range 38-73 yrs.) were tested using a six degree-of-freedom robotic testing system. The subtalar joint was fused and the tibia and calcaneus were rigidly fixed to a robotic manipulator, while complete fibular length was maintained and fibular motion was unconstrained. A 5Nm external rotation moment and 5Nm inversion moment were applied independently to the ankle at 0°, 15°, and 30° plantarflexion and 10° dorsiflexion. Talar motion with respect to the tibia was measured using the robotic testing system during each ankle condition. Outcome variables included talar medial-lateral (ML) translation, anterior-posterior (AP) translation, and internal/external rotation relative to the tibia in the following syndesmosis states:

1.

intact,

2.

AITFL transected,

3.

AITFL, PITFL, and IOM transected,

4.

3.5 mm cannulated tricortical screw fixation

5.

suture button fixation.

An ANOVA with a post-hoc Tukey analysis was performed for statistical analysis. Statistical significance was set at p < 0.05.

Results and conclusion: All significant changes were present during states with no loads applied. Significant differences in ML translation of the talus relative to the tibia existed between the tricortical screw fixation and intact ankle. The talus moved 1.1 mm less medially at 30° plantarflexion and 0.4 mm more laterally at 0° flexion with tricortical screw fixation compared to the intact ankle (p < 0.05). The total medial translation of the talus relative to the tibia during 0° flexion to 30° plantarflexion decreased from 1.1 mm to only 0.4 mm. No significant differences existed in translation or rotation of the talus between the suture button fixation and intact ankle at any ankle positions.

Suture button fixation restored tibiotalar motion in all planes, with no significant differences compared to the intact ankle. Tricortical screw fixation significantly increased lateral shift of the talus in a neutral ankle position and constrained motion during plantarflexion compared to the intact ankle, which can lead to accelerated tibiotalar arthritis. Thus, physicians should consider hardware removal after tricortical screw fixation for syndesmotic repair to avoid post-traumatic arthritis.