Biomechanical study of two different pedicle screws combining "Ω" transverse connection in the treatment of type Ⅱ Hangman fracture

English Keywords:Hangman fracture  C2 pedicle screws  "Ω" transverse connection  Three-dimensional finite element  Biomechanics

English Abstract:

  【Abstract】 Objectives: To investigate the biomechanical characteristics of two different C2 pedicle screws (common and new) combining "Ω" transverse connection for type Ⅱ Hangman fractures. Methods: C0-3 vertebrae of a healthy male adult were scaned by CT, and the original data of CT images were obtained. The finite element model(including intervertebral disc, ligament and other tissues) of normal C0-3 was established by Mimics10.01 et al, and the validity of the model was verified. On the basis of the verified finite element model, the following models were established: Hangman fracture model, Hangman fracture + common C2 pedicle screws + "Ω" transverse model, Hangman fracture + new C2 pedicle screws + "Ω" transverse model. Range of motion(ROM) and implant stress of each model in different working conditions were compared. Results: Under physiological load, the ROM of Hangman fracture model in flexion, extension, lateral flexion and torsion was significantly higher than that of normal cervical spine model, mainly in C2-3, which increased by 3.89°, 5.65° and 2.10°, and the ROM of C2-3 of two internal fixation models was significantly lower than that of fracture model. The ROM between two internal fixation models was similar. The stress of screws in two internal fixation models reached the largest when they extended back, which was 403.3MPa and 370.4MPa respectively, and the stress mainly concentrated in the part of the screws passing through the fracture line. The maximum stress of the new C2 pedicle screws was lower than that of the common C2 pedicle screws in all working conditions. Conclusions: Two different C2 pedicle screws (common and new) combining "Ω" transverse connection can effectively restore the stability of cervical vertebra while retaining the physiological activity of cervical vertebra. The new C2 pedicle screws had better anti-fatigue effect than the common C2 pedicle screws.