Role of Syndesmotic Ligaments in Lateral Ankle Instability

CATEGORY: Ankle; Sports; Trauma INTRODUCTION/PURPOSE: Despite the success of surgical intervention, about 13-35% of patients continue to have ankle symptoms after surgery for lateral ankle instability which could be due to presence of undetected and thus untreated injury to other ankle ligaments.Concomitant lateral ankle ligament and syndesmotic ligamentous injuries are common. It is unknown, however, whether syndesmotic ligaments directly contribute to lateral ankle stability. Therefore, the aim of this study was to fluoroscopically evaluate whether the syndesmotic ligaments contributes to lateral ankle stability. METHODS: Twenty-four above-knee cadaveric specimens were divided into three groups that underwent fluoroscopic evaluation for lateral ankle stability. In all the groups, the assessment was first done with all syndesmotic and ankle ligaments intact. Thereafter, Group 1 underwent sequential transection of the lateral ankle ligaments: (1) anterior talofibular ligament (ATFL), (2)calcaneofibular ligament(CFL), and (3)posterior talofibular ligament (PTFL). Group 2 underwent sequential transection of the lateral ankle ligaments followed by the syndesmotic ligaments: (1) ATFL, (2) CFL, (3) PTFL, (4) anterior inferior tibiofibular ligament(AITFL), (5)interosseous ligament(IOL), and (6)posterior inferior tibiofibular ligament (PITFL). Group 3 alternating and sequential transection of the syndesmotic and lateral ankle ligaments: (1) AITFL, (2) ATFL, (3) CFL, (4) IOL, (5) PTFL, and (6) PITFL. In all scenarios, three loading conditions were considered:(1)An anterior drawer test at 50N and 80N of direct force, (2) talar tilt under 1.7Nm torque, and (2) lateral clear space (LCS) under 1.7Nm torque. Wilcoxon rank-sum test was used to compare the findings of each ligamentous transection state to the intact state. RESULTS: The lateral ankle remained stable after transection of all syndesmotic ligaments (AITFL, IOL, PITFL). However, after additional transection of the ATFL, the lateral ankle became unstable in varus and anterior drawer testing conditions (p-values ranging from 0.036-0.012). Lateral ankle instability was also observed after transection of the ATFL and AITFL (p-values ranging from 0.036-0.012). Subsequent transection of the CFL worsened the lateral ankle instability. CONCLUSION: Our findings suggest that syndesmotic injuries can destabilize otherwise stable lateral ankle sprains. When treating lateral ankle instability, clinician should maintain a lower threshold for operative intervention for syndesmotic stabilization if there are any residual symptoms over the AITFL.