The Role of the Lateral Ankle Joint Ligaments on the Stability of the Syndesmosis
Authors: Rojas Edward O. , Figueroa Ana , Sailer Wyatt , Goetz Jessica , Netto Cesar de Cesar 
Published: December 2024

Category: Ankle; Basic Sciences/Biologics Introduction/Purpose: The tibiofibular syndesmosis is a fibrous joint essential for ankle stability. Injury to the syndesmotic ligaments in high-ankle sprains are destabilizing and cause considerable time lost to injury and long-term disability. Stability imparted by the lateral ankle ligaments in the setting of a high ankle sprain and their interplay has not previously been elucidated in the literature. Sequelae of ligamentous injuries include multidirectional instability and posttraumatic arthritis, likely from altered joint mechanics, impingement, and changes in ligamentous strain. This study aimed to determine the role of individual lateral and syndesmotic ankle ligaments on ankle tissue mechanics and joint stability. We hypothesized that ligament strain and relative bony ankle motion would increase with sequential ligamentous injury. Methods: 22 through-knee lower extremity specimens underwent mechanical testing with an axially loaded external rotation (ER) stress. Specimens were randomized into either a high sprain (sequence 1, n=11, AITFL, IOL, PITFL, ATFL, CFL) or low sprain (n=11, ATFL, CFL, AITFL, IOL, PITFL) ligament transection sequence. Specimens were mounted on an MTS load frame (MTS Inc. Eden Prairie, MN), axially loaded to 750 N, and 5Nm of ER torque stress was applied. Degrees to target ER torque were compared between sequences using linear regression modeling. AITFL and ATFL strain was measured throughout load application using an optical digital image correlation system (ARAMIS, GOM, Braunschweig, Germany). Mean strain was measured for loading tests after each sequential ligament transection. Signed rank tests were utilized to compare the mean strain in the AITFL or ATFL referencing the intact specimen. Results: Upon application of 5 Nm of torque in intact specimens, mean ATFL strain was consistently higher vs AITFL strain. In the high sprain group, ATFL strain gradually decreased after each syndesmotic ligament transection. No statistical differences were identified in this trend vs intact specimens (p=0.69,p=0.44, p=0.69, for AITFL, IOL, PITFL transection). Torsional angle increased with each ligament transection within the high sprain group. In contrast, AITFL strain and torsional angle remained constant after each lateral ligament transection in low ankle sprains. No significant difference in strain on the AITFL in the (p=0.69 and p=0.94) for ATFL and CFL transection, respectively. For both groups, there was no statistically significant difference in rotation angle resulting from 5 Nm of applied ER force after any individual ligament transection. Conclusion: This study used a novel strain tracking approach to quantify the ligament strain in high and low ankle sprains. Contrary to the initial hypothesis, it was found that ATFL strain decreased, and ankle rotation increased with increasing severity of high sprain. AITFL strain and ankle rotation angles remained consistent through increasing severity of low sprains. While the differences in rotation and strain were not statistically significant, greater ankle rotation could amplify the trends identified in ligament strain behavior. It is expected the reduction in strain results from bony impingement under greater rotation in the ligament deficient ankles.