Foot and Ankle International - 2026-06-10 - Journal Article
Multiplanar Stability After Syndesmotic Screw Fixation vs Deltoid Ligament Repair in a Cadaveric Weber B/SER4b Ankle Fracture Model With Fibular Plate Fixation.
Haanæs EKØ, Dalen AF, Gregersen MG, Skrede A, Molund M
Topics
Key Takeaway
In cadaveric SER4b ankle fractures with fibular plate fixation, syndesmotic screw fixation restored lateral talar shift to within 0.2 mm of native but left valgus tilt 18.1° and external rotation 15.9° above native, whereas deltoid ligament repair reduced those deficits to 2.7° and 5.2° respectively.
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Summary
This study compared multiplanar stability of four fixation states—fibular plate alone, plate plus syndesmotic screw, plate plus deltoid repair, and combined—in a robotically loaded cadaveric SER4b model. Syndesmotic screw fixation matched deltoid repair for lateral talar translation (mean difference vs native: -0.2 mm vs 0.3 mm, both below the 1.0 mm MCID) but failed to control valgus (18.1° excess) and external rotation (15.9° excess). Deltoid ligament repair addressing both deep posterior and anterior components substantially restored rotational and valgus stability, with residual deviations of only 2.7° valgus and 5.2° external rotation.
Key Limitation
The small sample of eight specimens provides insufficient statistical power to detect differences between fixation constructs in rotational and valgus outcomes, and sequential testing on the same specimen precludes independent group comparisons.
Original Abstract
BACKGROUND
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.
METHODS
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 mm.
RESULTS
Combined plate and syndesmotic screw fixation restored lateral translation stability. The mean difference in talar shift was -0.2 mm compared with native (95% CI -0.8 to 0.5, P = .57). However, talar valgus tilt increased by 18.1° (95% CI 16.1-20.0, P < .001) and external rotation by 15.9° (95% CI 12.6-19.2, P < .001). For combined plate fixation and deltoid ligament repair vs native, the mean difference in talar shift was 0.3 mm (95% CI -0.4 to 1.0), P = .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° (95% CI 0.8-4.7, P = .006) and 5.2° (95% CI 1.9-8.5, P = .002).
CONCLUSION
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.
CLINICAL RELEVANCE
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.