Paper 93: Biomechanical Comparison of Tibiotalar Contact Pressures After Syndesmosis Injury With or Without Deltoid Ligament Repair

Abstract

Objectives:Recent studies have stressed the important role of the deltoid ligament in maintaining global ankle stability. However, controversy remains around whether deltoid ligament repair is necessary in addition to syndesmotic repair when addressing injuries that disrupt both the syndesmosis and deltoid ligament. The purpose of this study was to measure differences in tibiotalar joint contact pressures and tibio-talar torsional stability in the presence of deltoid ligament injury, syndesmotic injury, and after their respective repairs using a cadaveric model. Our hypotheseis were 1) injury to the syndesmoosis and deltoid would increase contact pressures and decrease torsional stability, 2) repaired injuries would restore biomechanics to near native state, and 3)that there would be similar tibiotalar contact pressures and torsional stability with syndesmosis repair alone compared to syndesmosis and deltoid ligament repair.Methods:Twelve fresh-frozen human cadaveric lower extremity specimens with intact ankle joints were randomized and tested under a series of conditions: 1) intact syndesmosis and deltoid, 2) sectioning of syndesmosis or deltoid, 3) sectioning of both the syndesmosis and deltoid, 4) repair of syndesmosis or deltoid, 5) repair of both the syndesmosis and deltoid. In one group, the syndesmosis was sectioned and repaired first and in the other the deltoid was sectioned and repaired first. The syndesmosis was repaired with a single high-tensile strength suture mechanism (TightRope, Arthrex), and deltoid ligament repairs were performed with a single suture anchor (FiberTak, Arthrex). Specimens were tested under each condition with 800 N axial compression load, followed by cyclic torsional preconditioning of 5 Nm internal tibial torque (i.e., external foot rotation) at a rate of 2.5 Nm/s, and then a single rotation test of 7.5 Nm internal tibial torque at 1 Nm/s under 800 N axial compression load on a servohydraulic mechanical testing system. Contact pressures within the tibiotalar joint were measured with a digitized pressure sensor film (Tekscan, Boston MA), and coronal plane motion about the tibia was measured in angular displacement.Results:There was no significant difference in peak contact pressures between conditions except when the comparing an isolated deltoid ligament injury to a combined deltoid and syndesmosis injury (4.43±1.33MPa vs 2.67±0.45MPa, p=0.038). Total contact area was less following syndesmosis repair in isolation (609.55±312.37mm2) and combined syndesmosis and deltoid repair (598.28±181.47mm2) compared to all other conditions (p<0.001). There was also a decrease in total contact area compared to native state when the deltoid was repaired in isolation (951.51±72.79mm2 vs 888.72±105.74mm2, p=0.027). The mean external rotation angle was greater when the syndesmosis (15.67±5.39°), deltoid (13.21±3.28°), and both injuries combined (16.59±4.01°) compared to native state (8.55±2.02°), however these values did not achieve statistical significance. Additionally, There was no statistically significant difference in external rotation angle between isolated syndesmosis, isolated deltoid, or combined repairs.Conclusions:These findings demonstrate that ankle contact pressures and torsional stability do not differ significantly when a deltoid ligament repair is performed in conjunction with a syndesmosis repair for a purely ligamentous injury. However, the change in contact area following syndesmosis repair may play a role in the development of post-traumatic arthritis. This finding reinforces the importance of striving for an anatomic syndesmotic reduction, and care should be taken not to over-reduce the syndesmosis during repair.