Suture-Button versus Screw Fixation in a Syndesmosis Rupture Model: A Biomechanical Comparison

Abstract

Flexible suture-button devices are used to stabilize the distal tibiofibular joint after syndesmotic rupture, but little is known about how they affect fibular motion during cyclic physiological loading. This study examined how much fibular motion occurs during cyclic loading of ankles repaired with suture-buttons or screws relative to one with intact ligaments. Ten pairs of cadaveric legs with intact ligaments were tested in axial compression (750 N), external rotational torque (7.5 Nm), and a combination thereof. Fibular rotation and translation in the sagittal and frontal planes were measured with linear variable displacement transducers. Then we sectioned the anterior tibiofibular, posterior tibiofibular, deltoid, and interosseous ligaments. Ankles were repaired with suture-buttons or a 3.5-mm screw through four-cortices. The ankles were tested for 10,000 cycles using the same loading protocol. Surviving ankles were brought to failure by increasing external rotation (1 degree/sec). Data from the linear variable differential transducers were used to calculate fibular motion at 100, 1,000, 5,000, and 10,000 cycles. There was no significant difference in the effect of the suture-button or screw for translation in the sagittal or coronal plane or for rotation about the fibular axis. The screw repair had a significantly greater (p = 0.02) failure torque (median, 26.5 Nm; inner quartile range, 25.7 to 35.2 Nm) than did the suture-button repair (median, 23.6 Nm; inner quartile range, 16.5 to 25.6 Nm). The fibular motion that occurs during cyclic loading appears to be similar for the suture-button and syndesmotic screw. Motion in both constructs was similar, but neither restored native ankle motion. It appears the suture-button behaves similarly to the syndesmotic screw in the syndesmotic rupture injury model tested. Clinical trials are needed to determine how the device performs in vivo.