The Effects of Ligamentous Incompetence on Sagittal Tibiofibular Overlap When Assessing Syndesmotic Reduction

Research Type: Level 5 - Case report, Expert opinion, Personal observation Introduction/Purpose: Sagittal plane alignment has become increasingly important for evaluating syndesmotic reduction in ankle fractures. Traditional parameters including tibiofibular overlap/clear space have limitations. Intraoperative CT or arthroscopy are not universally accessible. Consequently, reliance often remains on lateral fluoroscopic imaging. There is an increasing reliance as previous investigations confirm that sagittal tibiofibular alignment can reliably assess syndesmotic reduction. However, ankle fractures are often associated with concomitant medial and/or lateral ligamentous injuries which may alter talar positioning and affect measurements, even if the syndesmosis is intact and may result in apparent syndesmotic malalignment. This study used a cadaveric model to determine the impact of sequentially sectioning these ligaments on sagittal tibiofibular alignment and hypothesized that progressive ligament destabilization would change the apparent radiographic syndesmotic alignment. Methods: Twelve knee disarticulated cadaveric lower leg specimens, each with an intact syndesmosis, were mounted in neutral position. Lateral ankle fluoroscopic images were obtained with a C-arm ensuring a true lateral view by confirming talar dome superimposition. Baseline tibiofibular alignment measurements—specifically, the fibula-tibial interval ratio, anterior-posterior fibular translation, and fibular plafond coverage—were recorded. Then sequential ligament sectioning followed this order: (1) superficial deltoid ligament, (2) deep deltoid ligament, and (3) anterior talofibular ligament (ATFL). After each cut, the specimen was repositioned to recapture a true lateral radiograph and the tibiofibular alignment measurements were repeated. Results: In the intact condition, the mean PTFI/(PTFI+FW) ratio was 0.245, which rose to 0.323 following deltoid ligament sectioning. After subsequent ATFL sectioning, the ratio was 0.292, demonstrating that most of the increase in tibiofibular overlap occurred after medial-sided (deltoid) disruption. Additional sectioning of the ATFL had only a minimal effect on sagittal tibiofibular measurements. Neither anterior-posterior fibular translation (AD measure) nor fibular plafond coverage showed statistically significant differences across the three conditions. These data suggest that the deltoid ligament incompetence can create the impression of syndesmotic malalignment even when the syndesmosis remains anatomically intact. Ongoing analysis will further clarify the influence of isolated lateral ligament disruption, though early results indicate its overall impact is significantly smaller than that of deltoid insufficiency. Conclusion: While there is an increased reliance on sagittal plane alignment to assess syndesmotic malreduction, the effects of ligament disruption are unknown. Sequential sectioning of medial and lateral ligaments altered tibiofibular alignment on sagittal radiographs in cadaveric models resulting in apparent syndesmotic malalignment despite intact syndesmotic ligaments. Notably, deltoid ligament disruption produced the greatest change, indicating that medial-sided ligamentous incompetence alone can alter lateral radiographic assessments of syndesmotic reduction. Surgeons should remain cognizant that an intact syndesmosis may appear malaligned on lateral imaging when deltoid integrity is compromised.