Quantitative evaluation of the influence of posterior malleolus fracture and fixation on the rotational stability of the ankle / 中华骨科杂志

ABSTRACT

Objective:To analyze the correlation between the posterior malleolus fracture and fixation and the rotational stability of the ankle and to explore the surgical indications for posterior malleolus fracture aiming to provide the theories for the diagnosis and treatment of disorder.Methods:Twenty fresh frozen cadaver specimens were selected. Further, the extent of the tibial insertion of the posterior inferior tibiofibular ligament (PITFL) and inferior transverse tibiofibular ligament (ITTFL) complex was dissected and measured. Based on the tibial insertion of the ligament complex, the model for the supination-external rotation degree 3 ankle fracture with a posterior malleolar fragment and syndesmosis diastasis was created. Moreover, the area threshold of the posterior tibial insertion of posterior malleolus fracture was biomechanically assessed. The difference of the antirotating ability of the ankle-stiffness between simple posterior malleolus fixation and simple syndesmotic fixation was analyzed statistically.Results:The PITFL and ITTFL were presented in all specimens with relatively broad in PITFL tibial insertion. The PITFL was attached to the posterolateral tibia. The distance between the highest point of the tibial insertion and the articular line was 45.2±5.6 mm, while the ITTFL was attached to the posterior distal tibia. The distance between the highest point of the tibial insertion and the articular line was 5.5±1.0 mm. The width of the tibial insertion of the PITFL and ITTFL complex decreased as the distance from the joint line increased. Biomechanical analysis showed that the threshold of posterior area of posterior malleolus fracture was 1/4S. The stiffnesses of posterior malleolus fixation and syndesmosis stabilization were 0.264±0.080 N·m/° and 0.164 ± 0.061 N·m/°, respectively. The percentage of stiffness restored by posterior ankle fixation was 60.9%±10.2%, which was greater than that by syndesmosis stabilization 37.5%±7.9% ( t=17.09, P<0.001) . Conclusion:The surgical technique for posterior malleolus fracture should consider restoration of the axial and rotational stability of the ankle simultaneously. Posterior malleolus fracture fixation is recommended when the syndesmosis is unstable with the area ratio of posterior tibial insertion of posterior malleolus fracture greater than or equal to 1/4. Syndesmotic fixation is proposed to restore and maintain the rotational stability of the ankle when the syndesmosis is unstable with the area ratio less than 1/4. Regardless of the area ratio, the surgical indications for stable syndesmosis depend on the impact of the posterior malleolus fracture on the axial stability of tibiotalar joint, on the involved articular surface area and on the displacement degree of posterior malleolus fragment.