ObjectiveTo evaluate the biomechanical characteristics and effectiveness of repairing anteroinferior tibiofibular ligament and fixing the posterior malleolar fracture in reconstructing syndesmotic stability after ankle fracture of pronation-external rotation type (PER) stage IV. MethodsTwenty-four normal lower extremity cadaver specimens were collected and made into intact ankle specimens. A MTS Bionix 858 test system was used to measure the maximum rotation of the foot under a static axial load of 150 N, internal rotation torque to the tibia at a rate of 1°/second and 4 N·m torque. Then a fracture of PER stage IV model was established in each specimen. Internal fixation of lower tibiofibular ligament union was performed by screws in group A, fixation of posterior malleolar fractures in group B, fixing posterior malleolar fracture combined with repairing anteroinferior tibiofibular ligament in group C (8 specimens each group). Then the maximum rotation of the foot was measured under the same condition, and the syndesmotic stability was calculated. Between July 2009 and September 2012, 32 patients with ankle fracture of PER stage IV were treated. There were 19 males and 13 females with an average age of 35 years (range, 20-63 years). The locations were the left ankle in 14 cases and the right ankle in 18 cases. The time from injury to admission was 3.5 hours on average (range, 1-72 hours). Open reduction and plate compression internal fixation were performed in fibula, and medial malleolus was fixed by conpression screws, then anteroinferior tibiofibular ligament was mended and posterior malleolar fracture was fixed by screws. ResultsThe preservation rates of syndesmotic stability after repair were 46.2%±12.3%, 62.6%±10.7%,and 66.5%±12.6% in groups A, B,and C, respectively; groups B and C were significantly superior to group A (P<0.05),but no significant difference was found between groups B and C (P>0.05). All patients achieved wound healing by first intention, and were followed up 12-24 months (mean,15 months). All fractures healed,with an average healing time of 11.2 weeks (range, 10-14 weeks) on the X-ray films. No seperation of inferior tibiofibular syndesmosis was observed during the follow-up period. American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score was 88.4 on average (range, 61-98) at last follow-up; the results were excellent in 13 cases,good in 15 cases, and fair in 4 cases, with an excellent and good rate of 87.5%. ConclusionIn patients with ankle fracture of PER stage IV, a combination of fixing the posterior malleolar fracture and repairing anteroinferior tibiofibular ligament can reconstruct syndesmotic stability effectively.