Applied anatomy of the lower cervical pedicle screw insertion.

Objective: To ascertain an accurate approach to inserting the pedicle screw into C3-C7 segments of the cervical vertebra.

Methods: Anatomic morphology of lateral mass and pedicle, and their anatomic relationship with the adjacent tissue were observed on C3-C7 segments of 25 adult embalmed cadavers (50 sides).

Results: 1) The inferior edge of the base of the posterior tubercle of the transverse process and the inferior edge of the pedicle were connected with each other on 25 adult embalmed cadavers (50 sides). The transverse section which passed through the median point between the superior edge and the inferior edge of the base of the posterior tubercle of the transverse process, and the transverse section which passed through the central axis between the superior edge and the inferior edge of the pedicle, were in the same horizontal plane. The superior and inferior position of placing the pedicle screw was determined by this transverse section, which passed through the median point between the superior and the inferior edge of the base of the posterior tubercle of the transverse process. 2) There was a directed internal-downwards "triangular sulcule" between the base of the posterior tubercle of the transverse process and the anterolateral edge of the inferior articular process. The anterior wall of the triangular sulcule was the base of the posterior tubercle of the transverse process, the posterior wall was the anterolateral edge of the inferior articular process, and the bottom of the sulcule was connected with the interior edge of the pedicle. The vertical length between the top of triangle and the planes of inferior edge of the pedicle was (2.78+/-1.71) mm. The inferior edge of the cervical pedicle could be detected using a blunt probe along the "triangular sulcule" between the base of the posterior tubercle of the transverse process and the anterolateral edge of the inferior articular process in surgical operation. 3) The lateral fovea of the articular process was observed on all lateral masses (50 sides). The internal and external position of the entrance point could depend on anatomic landmarks: the lateral edge of the lateral fovea of the articular process. The horizontal length between the lateral fovea of the articular process and the entrance point was (3.14+/-1.45) mm. 4) The diameter of pedicle screw, about (2.78+/-1.71) mm, was the transverse diameter of the cancellous bone of the greatest narrow part of the cervical pedicle.

Conclusions: The median point between the superior edge and the inferior edge of the base of the posterior tubercle of the transverse process, the lateral fovea of the articular process, and the triangular sulcule between the base of the posterior tubercle of the transverse process and the anterolateral edge of inferior articular process, are easy to be exposed and identified in surgical operation. The pedicle screw can be precisely inserted through this method.