[Biomechanical study of screw implant angle in reconstruction of tibiofibular syndesmosis injury].

Objective: To investigate ideal screw implant angle in reconstruction of tibiofibular syndesmosis injury by using a biomechanical test.

Methods: A total of 24 ankle specimens from adult cadavers were used as the tibiofibular syndesmosis injury model. According to the angle of screw placement, the tibiofibular syndesmosis injury models were randomly divided into groups A (0°), B (10°-15°), C (20°-25°), and D (30°-35°), and the screws were placed at a level 2 cm proximal to the ankle joint. The displacement of fibula was measured by biomechanical testing machine at neutral, dorsiflexion (10°), plantar flexion (15°), varus (10°), and valgus (15°) positions, with axial load of 0-700 N (pressure separation test). The displacement of fibula was also measured at neutral position by applying 0-5 N·m torque load during internal and external rotation (torsional separation test).

Results: In the pressure separation test, group C exhibited the smallest displacement under different positions and load conditions. At neutral position, significant differences were observed ( P<0.05) between group A and group C under load of 300-700 N, as well as between group B and group C under all load conditions. At dorsiflexion position, significant differences were observed ( P<0.05) between group A and group C under load of 500-700 N, as well as between groups B, D and group C under all load conditions, and the displacements under all load conditions were significantly smaller in group A than in group B ( P<0.05). At plantar flexion position, significant differences were observed ( P<0.05) between group D and group C under all load conditions. At valgus position, significant differences were observed ( P<0.05) between group A and group C under load of 400-700 N, as well as between groups B, D and group C under all load conditions. In the torsional separation test, group C exhibited the smallest displacement and group B had the largest displacement under different load conditions. During internal rotation, significant differences were observed ( P<0.05) between group B and group C under all load conditions, as well as between group D and group C at load of 3-5 N·m. During external rotation, significant differences were observed between groups B, D and group C under all load conditions ( P<0.05). No significant difference was detected between groups at the remaining load conditions ( P>0.05).

Conclusion: The ideal screw implant angle in reconstruction of tibiofibular syndesmosis injury was 20°-25°, which has a small displacement of fibula.