title: The V(2) segment of the vertebral artery: anatomical considerations and surgical implications.
abstract: OBJECTIVE
  Iatrogenic injury of the V(2) segment of the vertebral artery (VA) is a rare but serious complication and can be catastrophic. The purpose of this study was to characterize the relationship of the V(2) segment of the VA to the surrounding anatomical structures and to highlight the potential site and mechanisms of injury that can occur during common neurosurgical procedures involving the subaxial cervical spine.
  
  
  METHODS
  Ten adult cadaveric specimens (20 sides) were included in this study. Quantitative anatomical measurements between selected landmarks and the VA were obtained. In addition, lateral mass screws were placed bilaterally, from C-3 to C-7, reproducing either the Magerl technique or a modified technique. The safety angle, defined as the axial deviation from the screw trajectory needed to injure the VA, and the distance from the entry point to the VA were measured at each level for both techniques.
  
  
  RESULTS
  The VA coursed closer to the midline at C3-4 and C4-5 (mean distance [SD] 14.9 ± 1.1 mm) than at C2-3 or C5-6. Within the intertransverse space it coursed closer to the uncinate processes of the vertebral bodies (1.8 ± 1.1 mm) than to the anterior tubercle of the transverse processes (3.4 ± 1.6 mm). The distance between the VA and the uncinate process was less at C3-6 (1.3 ± 0.7 mm) than at C2-3 (3.3 ± 0.8 mm). The VA coursed on average at a distance of 11.9 ± 1.7 mm from the anterior and 4.2 ± 2.6 mm from the posterior aspect of the intervertebral disc space. Lateral mass screw angles were 25° lateral and 39.1° cranial for the Magerl technique, and 36.6° lateral and 46.1° cranial for the modified technique. The safety angle was greater and screw length longer when using this modified technique.
  
  
  CONCLUSIONS
  The relation of the V(2) segment of the VA to anterior procedures and lateral mass instrumentation at the subaxial cervical spine was reviewed in this study. A detailed anatomical knowledge of the V(2) segment of the VA combined with careful preoperative imaging is mandatory for safe cervical spine surgery.
authors: Department of Neurosurgery, Louisiana State University, New Orleans, Louisiana, USA. vichanit@yahoo.it
authors: Vittorio M
authors: VM
authors: Russo
authors: Francesca
authors: F
authors: Graziano
authors: Maria
authors: M
authors: Peris-Celda
authors: Antonino
authors: A
authors: Russo
authors: Arthur J
authors: AJ
authors: Ulm
mesh_terms: D000328:Adult; D059925:Anatomic Landmarks / Q000033:anatomy & histology / Q000601:surgery; D001863:Bone Screws / Q000009:adverse effects; D002102:Cadaver; D002574:Cervical Vertebrae / Q000098:blood supply / Q000601:surgery*; D004210:Dissection / Q000379:methods; D006801:Humans; D007049:Iatrogenic Disease / Q000517:prevention & control*; D007431:Intraoperative Complications / Q000517:prevention & control*; D010781:Photography; D012828:Silicones; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation; D014711:Vertebral Artery / Q000033:anatomy & histology / Q000293:injuries / Q000601:surgery
chemical_list: D012828:Silicones