title: Feasibility and trajectory study of anterior transarticular crossing screw placement for atlantoaxial joint instability: a cadaveric study and description of a novel technique.
abstract: OBJECTIVE
  In unique clinical situations where C1-C2 anterior transarticular screw (ATS) fixation is not available or has failed, an anterior transarticular crossing screw (ATCS) with transcorporal pathway of the screws inside the contralateral promontory of C2 may enhance the stabilization and achieve atlantoaxial arthrodesis. The present study was to describe a novel technique of ATCS fixation for atlantoaxial joint instability and its applied anatomy, and compared it with ATS fixation method.
  
  
  METHODS
  Direct measurements using digital calipers and a goniometer were conducted on 30 pairs of dried human C1 and C2 vertebrae. The ATS and ATCS with screws (Φ 4.0 mm) were performed on 11 fresh cervical spine specimens. The screw lengths in the C1 and C2, and screw entry angles of the ATS and ATCS were measured, respectively. Cadaver specimens were dissected to observe the incidence of violation to the important structures surrounding the ATS and ATCS fixation technique.
  
  
  RESULTS
  There was enough osseous space for ATCS placement. The lateral and incline angle of the ATCS was 36.2° and 28.7°, respectively. Screw purchase in C2 of the ATCS (25.6 mm) was greater than that of the ATS (11.4 mm). The ATCS C1 purchase (14.8 mm) was similar to the ATS C1 purchase (14.9 mm). No violation to the vertebral artery groove, the spinal canal or the atlanto-occipital joint was observed after the ATCS placement.
  
  
  CONCLUSIONS
  Anterior transarticular crossing screw is a feasible and viable option for atlantoaxial fixation in selected cases. This technique achieved remarkable longer screw purchase and could enhance the atlantoaxial stability.
authors.affiliation: Department of Spinal Surgery, Nanfang Hospital, Southern Medical University, 1838 North Guangzhou Avenue, Guangzhou, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Ji
authors.affiliation: Department of Spinal Surgery, Nanfang Hospital, Southern Medical University, 1838 North Guangzhou Avenue, Guangzhou, China.
authors.forename: Minghui
authors.initials: M
authors.lastname: Zheng
authors.affiliation: Department of Spinal Surgery, The First People's Hospital of Chenzhou, Chenzhou, Hunan, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Tong
authors.affiliation: Department of Spinal Surgery, Nanfang Hospital, Southern Medical University, 1838 North Guangzhou Avenue, Guangzhou, China.
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Huang
authors.affiliation: Department of Spinal Surgery, Nanfang Hospital, Southern Medical University, 1838 North Guangzhou Avenue, Guangzhou, China.
authors.forename: Jianting
authors.initials: J
authors.lastname: Chen
authors.affiliation: Department of Spinal Surgery, Nanfang Hospital, Southern Medical University, 1838 North Guangzhou Avenue, Guangzhou, China.
authors.forename: Dongbin
authors.initials: D
authors.lastname: Qu
authors.affiliation: Department of Spinal Surgery, Nanfang Hospital, Southern Medical University, 1838 North Guangzhou Avenue, Guangzhou, China. qinganzhu@gmail.com.
authors.forename: Qingan
authors.initials: Q
authors.lastname: Zhu
mesh_terms: D001268:Atlanto-Axial Joint / Q000601:surgery*; D001863:Bone Screws; D002102:Cadaver; D005240:Feasibility Studies; D006801:Humans; D007593:Joint Instability / Q000601:surgery*; D011474:Prosthesis Design
keywords: Anterior approach; Atlas; Axial; Crossing screw; Transarticular screw