title: Four lateral mass screw fixation techniques in lower cervical spine following laminectomy: a finite element analysis study of stress distribution.
abstract: BACKGROUND
  Lateral mass screw fixation (LSF) techniques have been widely used for reconstructing and stabilizing the cervical spine; however, complications may result depending on the choice of surgeon. There are only a few reports related to LSF applications, even though fracture fixation has become a severe complication. This study establishes the three-dimensional finite element model of the lower cervical spine, and compares the stress distribution of the four LSF techniques (Magerl, Roy-Camille, Anderson, and An), following laminectomy -- to explore the risks of rupture after fixation.
  
  
  METHODS
  CT scans were performed on a healthy adult female volunteer, and Digital imaging and communication in medicine (Dicom) data was obtained. Mimics 10.01, Geomagic Studio 12.0, Solidworks 2012, HyperMesh 10.1 and Abaqus 6.12 software programs were used to establish the intact model of the lower cervical spines (C3-C7), a postoperative model after laminectomy, and a reconstructive model after applying the LSF techniques. A compressive preload of 74 N combined with a pure moment of 1.8 Nm was applied to the intact and reconstructive model, simulating normal flexion, extension, lateral bending, and axial rotation. The stress distribution of the four LSF techniques was compared by analyzing the maximum von Mises stress.
  
  
  RESULTS
  The three-dimensional finite element model of the intact C3-C7 vertebrae was successfully established. This model consists of 503,911 elements and 93,390 nodes. During flexion, extension, lateral bending, and axial rotation modes, the intact model's angular intersegmental range of motion was in good agreement with the results reported from the literature. The postoperative model after the three-segment laminectomy and the reconstructive model after applying the four LSF techniques were established based on the validated intact model. The stress distribution for the Magerl and Roy-Camille groups were more dispersive, and the maximum von Mises stress levels were lower than the other two groups in various conditions.
  
  
  CONCLUSIONS
  The LSF techniques of Magerl and Roy-Camille are safer methods for stabilizing the lower cervical spine. Therefore, these methods potentially have a lower risk of fixation fracture.
authors.forename: Mingzhi
authors.initials: M
authors.lastname: Song
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhang
authors.forename: Ming
authors.initials: M
authors.lastname: Lu
authors.forename: Junwei
authors.initials: J
authors.lastname: Zong
authors.forename: Chao
authors.initials: C
authors.lastname: Dong
authors.affiliation: Department of Orthopedics, The First Affiliated Hospital of Dalian Medical University, 222 Zhongshan Road, Dalian 116011, P,R, China. dmu_makai@sina.com.
authors.forename: Kai
authors.initials: K
authors.lastname: Ma
authors.forename: Shouyu
authors.initials: S
authors.lastname: Wang
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D007796:Laminectomy; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed
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