Biomechanical comparison of syndesmotic injury fixation methods using a cadaveric model

Abstract

Background: There is growing interest in suture-button devices for syndesmosis injury, which are intended to offer less rigid fixation than screw fixation.

Methods: The fixation strength with 2 different suture-button devices, ZipTight and TightRope, were compared using 5 cadaveric leg pairs (n = 10). In an additional 5 pairs (n = 10), ZipTight was compared to 3.5 mm quadricortical screw fixation. Ankle motion was measured intact, then following simulated syndesmosis injury and fixation. Cyclic loads (peak 750 N, 7.5 Nm) were applied. Finally, external rotation to failure was measured and failure mode was documented.

Results: Range of motion increased after simulated injury and fixation with all devices (max 14.5 degrees). In all groups, diastasis remained below 1.0 mm intact and below 2.0 mm during cyclic loading. Compared to intact, under load to failure, diastasis with ZipTight devices increased by 4.7 ± 1.3 mm and 7.6 ± 4.3 mm, with TightRope, 6.3 mm, and screw construct, 1.3 mm. ZipTight specimens rotated approximately 80 ± 22 degrees before failure, TightRope, 67 ± 13 degrees, screw constructs, 76 ± 27 degrees. Mean failure torque was between 22.2 ± 6.9 Nm and 28.1 ± 12.7 Nm for ZipTight, compared to 32.9 ± 8.0 Nm for TightRope (P = .07), and 30.1 ± 9.6 Nm for screw constructs (P = .03). The majority of suture-button constructs failed by fibular fracture (ZipTight = 6, TightRope = 4), the remaining by device pull-through (ZipTight = 3, TightRope = 1) and loosening (ZipTight = 1). Conversely, 3 of screw-fixed specimens failed by device failure, 2 from bone fracture.

Conclusion: Suture-button devices provided torsional strength below that of screw fixation. However, all devices may provide failure torques well above 20 Nm, exceeding likely torques applied in casts during healing.(1,2,4) CLINICAL RELEVANCE: Suture-button devices appear to have provided adequate fixation strength for syndesmosis injuries.

Keywords: ankle fixation; screw fixation; suture-button; syndesmosis injury.