Function Of Anterior Inferior Tibiofibular Ligament And The Strategy Of Repair

Syndesmosis injury is quite common in clinical practice.It can be isolated but more likely accompanied with ankle fracture.The instability of syndesmosis may course pain in anterior-lateral part of ankle,dysfunction of the involved joint,and even finally become traumatic arthritis.The anterior inferior tibiofibular ligament(AITFL),a complex structure with multiple bands,is one of the most essential components of syndesmosis.It is proved that,AITFL provide 35%of the syndesmosis stability.Clinically,however,surgeons showed little interest on this ligament and its repair.Actually,more and more fundamental research evidences have indicate that AITFL is not only of great importance,but also not so easy to recover spontaneously after injury.First of all,histological studies prove that AITFL is comprised of densely packed parallel fiber,which infer that this ligament is consistently bearing a large stress.Secondly,kinematical researches show that when an ankle joint move from the extreme plantar flexion position to the extreme dorsal extension position,the movement of distal fibula is displaced laterally,posteriorly,and rotated external,all of which can be controlled effectively by AITFL.Last but not least,in the majority population(63%)AITFL is exclusively supplied by the anterior branch of the peroneal artery.The peroneal artery perforates the interosseous membrane at an average of 3 cm above the plafond,where is nearly of no chance to maintain intact when the interosseous membrane ruptured in an ankle fracture.As a result,AITFL rupture is very likely recovered in a deficient blood supply environment,which may lead a poor repair quality.On the other hand,syndesmosis screw,the most common treatment of tibiofibular instability,is being rethought more and more profoundly.In recent years,doctors take more and more attention on the too-high rate of malreduction;show more and more strong aspiration to save the physiological movement function of distal tibiofibular joint;and make more and more efforts to avoid the secondary surgery of removing the screw.Anatomic fixation is an encouraging alternative method.One old theory holds that the system remains stable when there is only one fault in a stable ring.However,the theory can only be applied to the rigid structure,while in the flexible ring connected by a plurality of ligaments;even only one site of rupture may still cause instability of the whole system.Obviously,syndesmosis is one kind of the "flexible ring".Thus,the repair of injured AITFL should no longer be ignored.In this study,we made detailed measurements of anatomic parameters of AITFL in Chinese population.Through the finite element analysis we proved that AITFL played an important role in maintaining the stability of syndesmosis,especially for resisting external rotation stress.Then a motion capture study was performed in cadaver specimens which strengthened and confirmed the fact that AITFL is an essential component of syndesmosis.Following the basic researches above,we evaluated a novel method,cartoonish tap test for intraoperative diagnosis of syndesmosis instability.It was proved that the cartoonish tap test has excellent specificity and greatly improved sensitivity compared with external rotation stress test and hock test.And then,a lateral scoop-shaped incision of the ankle joint was developed to ensure satisfying exposure of posterior mortise fragment,fibular fracture and AITFL and open reduction of syndesmosis at the same time.During the clinical appliance of the modified incision,we observed and classified the injury pattern of AITFL.It was divided into 3 types.Type I:large avulsion fracture in tibial side(Chaput tubercle)or fibular side;type II:ligament stripped from the bone surface(probably with very small unfixable avulsion fragment);type III:ligament body rupture.We developed the treatment strategy according to the classification.Type 1:2.5mm cannulated compression screw fixation;type II:suture repair with anchors;type III:end to end suture repair.The outcome was satisfying.In addition,a randomized comparative study was designed,and we demonstrate that the reconstruction of stability of AITFL achieved similar outcome compared with syndesmosis screw,but with siganificantly lower rate of malreduction and fewer secondary surgeries.