Finite element analysis on anterior and posterior internal fixation for treating type ⅡHangman’s fracture / 医用生物力学

ABSTRACT

Objective To evaluate biomechanical differences between anterior titanium plate internal fixation and posterior pedicle screw internal fixation for treating type Ⅱ unstable Hangman’s fracture by finite element analysis. Methods An intact finite element model of the upper cervical spine (C0-3) was established and validated, and an unstable model was also established. Two different internal fixation models, i.e. anterior titanium plate+Cage with bone graft (Plate+Cage) and C2 pedicle screws+C3 lateral mass screws (C2PS+C3LMS) were established, respectively, based on the unstable model. The vertical load of 40 N was applied on the occiput to simulate head weight and 1.5 N•m torque was applied on the occiput to simulate loading conditions of flexion, extension, lateral bending and rotation. Range of motion (ROM) of C2-3, force pathway and strain at the fractured line were calculated and analyzed. ResultsCompared with the unstable model, the Plate+Cage model could decrease the ROM by 92.4%, 97.1%, 96.5% and 90.0%, while the C2PS+C3LMS model could decrease the ROM by 88.6%, 90.2%, 95.7% and 90.3%, in flexion, extension, lateral bending and axial rotation, respectively. The maximum stress of the Plate+Cage model was smaller than that of the C2PS+C3LMS model under 4 loading conditions. Conclusions The anterior Plate+Cage fixation possesses better stability than the posterior C2PS+C3LMS fixation in flexion and extension, while both fixation methods show similar stability in lateral bending and axial rotation. The anterior Plate+Cage fixation is more reasonable in structure and stress distributions, and can achieve reduction, decompression, fixation and fusion in one step, thus it is an effective operative procedure for treating typeⅡ Hangman’s fracture.