Correction of syndesmotic malreduction following fixation flexibilization.

Prior studies showed the potential of a rigid fixation, such as a trans-syndesmotic screw, to produce tibiofibular malreduction. Flexible implants, although capable of allowing forgiveness, may not provide sufficient stability for all injury patterns. To assess the malreduction forgiveness of a two-phase syndesmotic device that is designed to transition from a rigid screw construct to a flexible suture-type. Cadaveric specimens were loaded in a frame under four conditions: native (control), syndesmotic instability (injured), malreduced with engaged syndesmotic device (malreduced), and post-disengagement (disengaged). The malreduction targets were 5 mm anterior displacement, 5 mm posterior displacement, 15° of rotation, and 140 N over-compressed. Fixation was performed with a single device 20 mm proximal to the ankle, manually disengaged to allow semi-constrained motion of the syndesmosis. Weightbearing Computed Tomography (WBCT) scans were obtained, and anatomic axes of the tibia and fibula extracted to calculate tibiofibular joint position with an established orthogonal system. A total of 42 specimens were included and allocated in the four groups. Anterior and posterior malreduction demonstrated 2.50 mm (SD: ±1.37 mm) and 5.04 mm (SD: ±2.23 mm) of average malreduction. The disengaged condition resulted in average recovery of 1.79 mm (95%CI: 0.72|2.85; p = 0.0034; 72% recovery) and 1.69 mm (95%CI: 0.09|3.28; p = 0.0006; 33% recovery) toward the control position, for anterior and posterior malreduction, respectively. Rotational malreduction demonstrated 2.44° (SD: ±2.09°) of average rotational malreduction, with 1.98° (95%CI: -0.13°|4.09°; p = 0.0707; 81%) of recovery. Over-compression specimens showed average medial translation of 0.89 mm (SD: ±1.10 mm), with 0.74 mm (95%CI: 0.05|1.51; p = 0.0128; 82%) of recovery when disengaged. The two-phase syndesmotic device was able to allow partial malreduction recovery in different scenarios after transitioning to the flexible state. The use of this implant might mitigate potential surgical tibiofibular malreductions while providing the mechanical and clinical advantages of both rigid and flexible devices. Level V. Controlled laboratory study.