The biomechanical study of different kinds of anterior internal fixation for the transverse fracture associated with Hangman′s fractures of the axis: a finite-element analysis

English Keywords:Axis  Biomechanics  Cervical fusion  Complex fractures  Finite element analysis

English Abstract:

  【Abstract】 Objectives: To explore the biomechanical stability of three kinds of anterior internal fixation for the transverse fracture associated with Hangman′s fractures of the axis by finite element(FE) analysis, and to provide theoretical reference for the clinical surgery. Methods: Thin-section spiral computed tomography(0.5mm) was performed on occiput(C0) to C3 region. A three-dimensional hexahedral FE model of upper cervical spine was established by software(Mimics 10.01, Hypermesh V 10.0 and ABAQUS 6.11), and the finite element model of intact(FE/Intact) was verified with availability. Then the weakening of the strength of grid was performed to simulate the finite element model of the transverse fracture associated with Hangman′s fractures of the axis(FE/Fracture) and was verified with availability, the three internal fixation models: anterior C2/3 discectomy+cage bone grafting+anterior cervical fusion and long plate(FE/cage+ACFLP), anterior odontoid screw fixation+C2/3 discectomy cage bone grafting+anterior cervical fusion and short plate(FE/AOSF+cage+ACFSP), anterior odontoid screw fixation+C2/3 discectomy cage bone grafting+ anterior cervical fusion and long plate(FE/AOSF+cage+ACFSP) were simulated on the FE/Fracture model. Flexion, extension, lateral bending and axial rotation were imposed on the FE/Intact, FE/Fracture and the three fixation models respectively. The ROM of different models and the displacement of fracture end were compared. Results: The model of FE/Intact was established clearly with good geometric similarity and realistic appearance, which was verified with availability. The ROM of FE/Fracture increased obviously compared with the FE/Intact under the same loading conditions, and the ROM of C2/3 in flexion-extension, lateral bending and axial rotation increased 244.7％, 203.3％, 188.9％, 200％ respectively. The ROM of C2/3 of the FE/AOSF+ cage+ACFLP in flexion-extension, lateral bending and axial rotation was 60.5％, 70％, 66.7％, 62.5％ of the FE/Intact respectively; the ROM of C2/3 of the FE/AOSF+cage+ACFSP increased 118.4％, 123.3％, 148.1％, 175％ respectively in flexion-extension, lateral bending and axial rotation compared with the FE/Intact, and the ROM of the FE/cage+ACFLP was 123.7％, 143.3％, 122.2％, 137.5％ of the FE/Intact. The FE/AOSF+ cage+ACFLP presented with highest stability and the displacement of the fracture end was the least; FE/AOSF+cage+ACFSP had least stability, especially in bending and rotation, and the displacement of fracture end was the biggest, the ROM of FE/cage+ACFLP and the displacement of fracture end was the highest in respectively flexion-extension. Conclusions: The FE/AOSF+cage+ACFLP is effective for the transverse fracture of the axis associated with Hangman′s fractures, which can ensure good stability.