Sagittal instability with inversion is important to evaluate after syndesmosis injury and repair: a cadaveric robotic study

Abstract

Purpose: Disruption of the syndesmosis, the anterior-inferior tibiofibular ligament (AITFL), the posterior-inferior tibiofibular ligament (PITFL), and the interosseous membrane (IOM), leads to residual symptoms after an ankle injury. The objective of this study was to quantify tibiofibular joint motion with isolated AITFL- and complete syndesmotic injury and with syndesmotic screw vs. suture button repair compared to the intact ankle.

Methods: Nine fresh-frozen human cadaveric specimens (mean age 60 yrs.; range 38-73 yrs.) were tested using a six degree-of-freedom robotic testing system and three-dimensional tibiofibular motion was quantified using an optical tracking system. A 5 Nm inversion moment was applied to the ankle at 0°, 15°, and 30° plantarflexion, and 10° dorsiflexion. Outcome measures included fibular medial-lateral translation, anterior-posterior translation, and external rotation in each ankle state: 1) intact ankle, 2) AITFL transected (isolated AITFL injury), 3) AITFL, PITFL, and IOM transected (complete injury), 4) tricortical screw fixation, and 5) suture button repair.

Results: Both isolated AITFL and complete injury caused significant increases in fibular posterior translation at 15° and 30° plantarflexion compared to the intact ankle (p < 0.05). Tricortical screw fixation restored the intact ankle tibiofibular kinematics in all planes. Suture button repair resulted in 3.7 mm, 3.8 mm, and 2.9 mm more posterior translation of the fibula compared to the intact ankle at 30° and 15° plantarflexion and 0° flexion, respectively (p < 0.05).

Conclusion: Ankle instability is similar after both isolated AITFL and complete syndesmosis injury and persists after suture button fixation in the sagittal plane in response an inversion stress. Sagittal instability with ankle inversion should be considered when treating patients with isolated AITFL syndesmosis injuries and after suture button fixation.

Level of evidence: Controlled laboratory study, Level V.

Keywords: Ankle syndesmosis; Distal tibiofibular kinematics; Suture button; Tricortical screw.

Fig. 1

a Experimental setup with full length fibula specimen rigidly mounted to the robotic testing system through the calcaneus and a universal force-moment sensor (UFS). Optical motion capture markers are noted on the fibula and tibia. The dashed white line represent the axis of rotation of for inversion as defined by the middle of the talus and the 2nd metatarsal. b The experimental setup with the robotic testing system surrounded by six Motion Capture Cameras in a semicircular configuration

Fig. 2

Posterior translation of the fibula relative to the tibia (mean ± SD; 9 specimens) in response to a 5 Nm inversion moment at 30° and 15° plantarflexion, 0° flexion, and 10° dorsiflexion for (1) the intact ankle, (2) the AITFL transected ankle, and (3) the completely injured ankle. *p < 0.05

Fig. 3

Lateral translation of the fibula relative to the tibia (mean ± SD; 9 specimens) in response to a 5 Nm inversion moment at 30° and 15° plantarflexion, 0° flexion, and 10° dorsiflexion for (1) the intact ankle, (2) the AITFL transected ankle, and (3) the completely injured ankle. *p < 0.05

Fig. 4

Posterior translation of the fibula relative to the tibia (mean ± SD; 8 specimens) in response to a 5 Nm inversion moment at 0° flexion, 15° and 30° plantarflexion, and 10° dorsiflexion in different ankle states (intact state, complete injury, tricortical screw fixation using a 3.5 mm screw, and suture button repair). *p < 0.05