title: Screw placement of pedicle of vertebral arch--pay great attention to segmental differences of the pedicle.
abstract: OBJECTIVE
  To investigate appropriate ways for screw placement of pedicle of vertebral arch in the horizontal plane.
  
  
  METHODS
  Fifteen preserved thoracolumbar spine specimens (T(11)-L(5)) were used and divided into three groups at random. Firstly four anatomic parameters indicating screw positions in the horizontal plane were measured. Secondly the methods of Roy-camille, Magerl, and authors' segmental differences were used to place successively the screws of the pedicles with 5 mm, 6 mm, and 7 mm in diameter. Coincidences between the drilling point, drilling direction and pedicle axis, and ruptures of the pedicle as well as the length of the screw in the vertebral body were observed.
  
  
  RESULTS
  Four anatomic parameters at various segments showed significant differences (P<0.05). The drilling point by the Roy-camille's method deviated medial to pedicle axis in most segments, and its drilling direction did not coincide well with most E-angles of the pedicles. The drilling point by Magerl's method coincided relatively well with pedicle axis in lumbar vertebrae, but there were still some differences between its drilling direction and E-angles of the pedicles. The method of segmental differences coincided the best with the pedicle axis. The lengths of screw in the vertebra were relatively long by both Magerl and segmental difference methods. When 5 mm diametral screw was used by the three methods, the rupture rate was very low. When 6 mm and 7 mm diametral screws were placed, the rupture rate was accordingly increased. Of the three methods, Roy-camille's method showed a relatively high rupture rate, while the method of segmental differences a comparatively low rupture rate. Various degrees of rupture of the pedicle of vertebral arch were found at the juncture of the thoracic and lumbar vertebrae when 6 mm or 7 mm diametral screws was used by any screw placement method. In contrast, the rupture was seldom seen at the lower lumbar vertebrae when 7 mm diametral screws were used.
  
  
  CONCLUSIONS
  The segmental difference method is proved to have the anatomic safety and screw biomechanical stability. It is appropriate to choose different diametral screws, different drilling points and directions according to different segments of the vertebra.
authors.affiliation: Second Affiliated Hospital, Suzhou University, Suzhou 215004, China. yinqudong@sina.com
authors.forename: Qudong
authors.initials: Q
authors.lastname: Yin
authors.forename: Zugen
authors.initials: Z
authors.lastname: Zheng
authors.forename: Qirong
authors.initials: Q
authors.lastname: Dong
authors.forename: Ping
authors.initials: P
authors.lastname: Tang
mesh_terms: D000328:Adult; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000293:injuries*; D006801:Humans; D008159:Lumbar Vertebrae / Q000293:injuries*; D013124:Spinal Injuries / Q000601:surgery