Multiplanar Stability After Syndesmotic Screw Fixation vs Deltoid Ligament Repair in a Cadaveric Weber B/SER4b Ankle Fracture Model With Fibular Plate Fixation

Weber B / Lauge-Hansen supination-external rotation 4b (SER4b) ankle fractures are unstable injuries characterized by complete deltoid ligament ruptures. Biomechanical studies suggest that fibular plate fixation alone is insufficient for SER4b fractures. Concurrent deltoid ligament repair seems necessary. This study explores how syndesmotic fixation, which is a simpler surgical approach, restores stability compared to deltoid repair or combined. Eight fresh frozen human cadaveric ankle specimens were tested sequentially by a robot in all 5 states: native, SER4b injury model with anatomic fibular plate fixation only, or reinforced with a syndesmotic screw and/or deltoid ligament repair. Stability was measured in lateral translation (talar shift), valgus, and internal and external rotation during a constant 45-N axial load. The primary outcome was talar shift on fluoroscopic images. The minimal clinically important difference (MCID) was predefined as 1.0&#x2009;mm. Combined plate and syndesmotic screw fixation restored lateral translation stability. The mean difference in talar shift was -0.2&#x2009;mm compared with native (95% CI -0.8 to 0.5,&#x2009;=&#x2009;.57). However, talar valgus tilt increased by 18.1&#xb0; (95% CI 16.1-20.0,&#x2009;<&#x2009;.001) and external rotation by 15.9&#xb0; (95% CI 12.6-19.2,&#x2009;<&#x2009;.001). For combined plate fixation and deltoid ligament repair vs native, the mean difference in talar shift was 0.3&#x2009;mm (95% CI -0.4 to 1.0),&#x2009;=&#x2009;.37), also below the pre-defined MCID. Mean valgus and external rotation deviated less from native but were still significantly different, the respective mean differences were 2.7&#xb0; (95% CI 0.8-4.7,&#x2009;=&#x2009;.006) and 5.2&#xb0; (95% CI 1.9-8.5,&#x2009;=&#x2009;.002). In this cadaveric SER4b injury model, both syndesmotic screw fixation and deltoid ligament repair restore lateral translational stability, when combined with fibular plate fixation. However, only deltoid ligament repair-addressing both the deep posterior and anterior deltoid components-substantially restored rotational and valgus stability, suggesting it provides more comprehensive joint stabilization than syndesmotic screw fixation alone. Syndesmotic screw fixation restores lateral translational stability as well as deltoid ligament repair when both are combined with lateral plate fixation. Complete deltoid ligament repair is superior to the syndesmotic screw in restoring overall stability in cadaveric SER4b ankle fracture models. Given their potential clinical relevance, these findings may be considered in future clinical studies and choice of treatment.