Biomechanics of the Distal Tibiofibular Syndesmosis: A Systematic Review of Cadaveric Studies

BACKGROUND: This investigation’s purpose was to perform a systematic review of the literature examining the biomechanics of the ligaments comprising the distal tibiofibular syndesmosis with specific attention to their resistance to translational and rotational forces. Although current syndesmosis repair techniques can achieve an anatomic reduction, they may not reapproximate native ankle biomechanics, resulting in loss of reduction, joint overconstraint, or lack of external rotation resistance. Armed with a contemporary understanding of individual ligament biomechanics, future operative strategies can target key stabilizing structure(s), translating to a repair better equipped to resist anatomic displacing forces. STUDY DESIGN: Systematic review. METHODS: A systematic review was conducted according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines using a PRISMA checklist. Biomechanical studies testing cadaveric lower limb specimens in the intact and injured state measuring the distal tibiofibular syndesmosis resistance to translational and rotational forces were included in this review. Only studies that included numerical data were included in this review; studies that only reported figures and graphs were excluded. RESULTS: Twelve studies met the inclusion and exclusion criteria. Two studies determined the mechanical properties of syndesmotic ligaments, finding superior strength and stiffness of the interosseous ligament (IOL), as compared to the anterior (AITFL) or posteroinferior tibiofibular ligament (PITFL). Four studies examined native ankle biomechanics establishing physiologic range of motion of the fibula relative to the tibia. Fibular range of motion was found to be up to 2.53 mm of posterior translation (Markolf et al), 1.00 mm lateral translation (Xenos et al), 3.6 degrees of external rotation (Burssens et al), and 1.4 degrees of internal rotation (Clanton et al). Four studies evaluated syndesmotic biomechanics under physiological loading and found that the AITFL, IOL, and PITFL provide the majority of resistance to external rotation, diastasis, and internal rotation, respectively. Two studies investigated the biomechanics of clinically and intraoperatively used tests for syndesmotic injuries and found increased sensitivity of sagittal plane posterior fibular translation, as opposed to coronal plane lateral fibular translation for unstable injuries. CONCLUSIONS: Study findings suggest that although the IOL is the strongest syndesmotic ligament, the AITFL has a dominant role stabilizing the distal tibiofibular syndesmosis to external rotation force. Because of these characteristics, operative repair of the AITFL along its native vector may provide a more biomechanically advantageous construct and should be investigated clinically. Additionally, evaluation of clinical stress tests revealed that the external rotation stress test is the most sensitive test to recognize an AITFL tear, and that a 3-ligament disruption is needed to cause diastasis greater than 2 mm.