An anatomic study of L5 pedicle classification and associated pedicle screw instrumentation

Objective:To investigate the anatomic characteristics of L5 pedicle and the optimal individualized pedicle screw placement in Chinese.Method:46 dry and intact L5 vertebrae specimens harvested from Chinese were obtained.The pedicle morphology was observed,and the anatomic parameters of the pedicle associated with pedicle screw placement were measured.Namely the pedicle isthmus were dissected along transverse section of perpendicular to the pedicle axial.Pedicle isthmus width,height,maximum diameter,minimum diameter,coronal pedicle tilt angles in the transverse section of perpendicular to pedicle axis and appropriate insertion angles in the L5 cross-section through pedicle axis were measured.In addition,the medial-lateral distance from the optimal starting point to vertex of ∧-shaped crest and isthmic crest were measured.Result:2 morphological findings were evidenced in L5 pedicles.36 vertebrae(72 pedicles) had transverse process integrated into the junction of vertebral arch and pedicle(L-type),and 10 vertebrae(20 pedicles) had transverse process integrated into vertebral body and pedicle at the posterolateral side of the vertebral body(S-type).The pedicle width,height,maximum diameter,minimum diameter,pedicle tilt angles was 18.22mm and 22.45mm,14.24mm and 14.46mm,20.62mm and 23.74mm,11.87mm and 12.83mm,35.9° and 32.3° for L and S type respectively.In the medial-lateral direction,the entrance point is 3.36mm and 5.94mm,4.66mm and 7.54mm lateral to vertex of ∧-shaped crest and the isthmic crest for L type and S type pedicle,respectively.The Optimal insertion angles was 25.4° and 27.9° for L and S type respectively.Conclusion:L5 pedicle has 2 differentiation types in the Chinese.Compared with L-type,S-type pedicle has longer diameter and more lateral entrance point to the vertex of ∧-shaped crest andisthmic crest,which optimize larger extroversion angle.