[ANATOMIC STUDY ON ENTRY POINT AND IMPLANT TECHNIQUE FOR C2 PEDICLE SCREW FIXATION].

OBJECTIVE: To determine the entry point and screw implant technique in posterior pedicle screw fixation by anatomical measurement of adult dry samples of the axis so as to provide a accurate anatomic foundation for clinical application. METHODS: A total of 60 dry adult axis specimens were selected for pedicle screws fixation. The entry point was 1-2 mm lateral to the crossing point of two lines: a vertical line through the midpoint of distance from the junction of pedicle medial and lateral border to lateral mass, and a horizontal line through the junction between the lateral border of inferior articular process and the posterior branch of transverse process. The pedicle screw was inserted at the entry point. The measurement of the anatomic parameters included the height and width of pedicle, the maximum length of the screw path, the minimum distance from screw path to spinal canal and transverse foramen, and the angle of pedicle screw. The data above were provided to determine the surgical feasibility and screw safety. RESULTS: The width of upper, middle, and lower parts of the pedicle was (7.35 ± 0.89), (5.50 ± 1.48), and (3.97 ± 1.01) mm respectively. The pedicle height was (9.94 ± 1.16) mm and maximum length of the screw path was (25.91 ± 1.15) mm. The angle between pedicle screw and coronal plane was (26.95 ± 1.88) degrees and the angle between pedicle screw and transverse plane was (22.81 ± 1.61) degrees. The minimum distance from screw path to spinal canal and transverse foramen was (2.72 ± 0.83) mm and (1.98 ± 0.26) mm respectively. CONCLUSION: According to the anatomic research, a safe entry point for C2 pedicle screw fixation is determined according to the midpoint of distance from the junction of pedicle medial and lateral border to lateral mass, as well as the junction between the lateral border of inferior articular process and the posterior branch of transverse process, which is confirmed to be effectively and safely performed using the entry point and screw angle of the present study.