Biomechanical Study Of The Relationship Between The Inferior Tibiofibular Syndesmosis Ligaments’ Injury And The Ankle Position

Objective To explore which position the tibiofibular syndesmosis ligament’s changeof length and strain before and after the force are the most largest when the ankle are inneutral position, dorsiflexion and plantarflexion, varus, valgus, internal rotation,external rotation.we infer that which position is the most easily damage by abiomechanical study of the anterior tibiofibular syndesmosis ligament, the interosseousligament, the posterior tibiofibular syndesmosis ligament(including the deep transverseligament).Methods8(left4, right4) fresh adult leg specimens which have no skeletal systemdiseases and anatomical variation by visual observation were stored at-20℃. Allspecimens which are maintained a certain humidity and covered with saline gauze arenaturally thawed at room temperature12hours before the experiment. We remove skin,fascia, muscle of all specimens to reveal completely the inferior tibiofibularsyndesmosis and try to reserve the tissue which is not influence ligament’s exposition.All specimens are cut horizontally at20cm above the ankle. The top of them areembedded with the poly methyl methacrylate also known as denture powder simulatingthe upper tibiofibular joint. They are cut in front of calcaneus by keeping away fromsubtalar, talonavicular, calcaneocuboid joints. The bottom of specimens are embeddedwith denture powder by paralleling to the foot plate too. Then two miniature screws(there is groove in the middle of the tail for measuring easily) are placed on middle of each tibiofibular syndesmosis ligament’s beginning and ending’s place attaching tibiaand fibula paralleling each ligament. Each samples’ ankle joint is placed in neutralposition, dorsiflexion (15°), plantar flexion (20°), varus (15°), valgus (20°), internalrotation (10°), external rotation (5°) seven positions by BOSE Eletroc Force3510biological material experimental system. We measure the long changes of two miniaturescrews tag of each tibiofibular syndesmosis ligament with sub-metric and electronicvernier caliper after loading slowly the axial500N force (normal ankle can bear thehighest pressure up to4~5times weight of the people, but we gradually give axial500N force in this experiment in order to avoid irreversible damage because of repeatedstress loading. At the beginning, we give pre-load to eliminate the error due to ligamentcreep)and external rotation torque (5N·m) relative to the neutral position which is notgiven force and external rotation torque. We completely release the force and torque, do2times again in the above method to find three time’s length change average of the eachtibiofibular syndesmosis ligament as a final result. To explore which position theinferior tibiofibular syndesmosis ligament’s final long change and strain are the mostlargest before and after the force when the ankle is in different positions by comparisonand statistical analysis to infer which position is the most easily damaged.Results The long change of the anterior ligament is respectively the largest, thesecond largest when the ankle is in varus, plantarflexion, is respectively (1.73±0.04)mm,(1.54±0.02) mm,the strain is respectively (0.1294±0.0030),(0.1150±0.0018).The long change of the interosseous ligament is respectively the largest, the secondlargest when the ankle is in varus, plantarflexion, is respectively（1.16±0.03）mm,（0.99±0.05）mm,the strain is respectively（0.1331±0.0030）,（0.1138±0.0053）.The long change of the posterior ligament(including the deep transverse ligament) is thelargest, the second largest when the ankle is in varus, plantarflexion, is respectively（0.66±0.02）mm,（0.44±0.02）mm,the strain is respectively（0.0427±0.0016）,（0.0285±0.0015）, there is a significant difference by statistical analysis (P <0.05). Conclusion The strain of the anterior ligament is respectively the largest, the secondlargest when the ankle is in varus, plantarflexion.We infer that the force of ankle joint isthe most largest when it is in varus or supination and the anterior ligament is the mosteasily damaged when the ankle joint is varus or supination.So the interosseous ligamentand the posterior ligament (including the deep transverse ligament) are the most easilydamaged when the ankle joint is in varus or supination too.