Screw placement of pedicle of vertebral arch—pay great attention to segmental differences of the pedicle

摘要

Objective:To investigate appropriate ways for screw placement of pedicle of vertebral arch in the horizontal plane.Methods:Fifteen prreserved thoracolunbar spine specimens(T11-L5)were used and divided into three groups at random.Firstly four anatomic parameters indicating screw positions in the horizontal plae were measured.Secondly the methods of Roy-camille,Magerl,and authors'segmental differences were used to place successively the scews of the pedicles with 5mm,6mm,and7mm 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 differemces coincided the best with the pedicle axis.The lengths of screw in the vertebra were relatively long by blth Magerl and segmental difference methods.When5mm diametral screw was used by the three methods,the rupture rate wsa very low.When 6mmand7mm 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 lunbar vertebrae when6mmor7mm diametral screws was used by any screw placement method.In contrast,the rupture was seldom seen at the lower lumbar vertebrae when 7mm diametral screws were used.Conclusions:The segmental difference methodis 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.