Anatomical and biomechanical analysis of sacral pedicle and lateral mass

Abstract

【Abstract】Objective: To study the anatomical and biomechanical features of sacral pedicle and lateral mass so as to provide reference for clinical screw fixation technology of sacral pedicle and lateral mass. Methods: A total of 60 adult patients’ spiral CT images of the sacrum and coccyx were selected randomly. The entry points of sacral pedicle and lateral mass screws were determined, and the screw trajectory was measured using the three dimensional reconstruction method. Meanwhile, the gross anatomy was scrutinized in 15 adult cadaver specimens to determine the sacral pedicle and lateral mass screw entry points. The length, width and angle of sacral pedicle and lateral mass screw trajectory were measured. Eight of 15 cadaver specimens were selected to test the maximal extraction force of sacral pedicle and lateral mass screws. The clinical data of 15 cases treated by pedicle and lateral mass screw technology were collected and analyzed. Results: The diameter and length of S1-S5 sacral pedicle and lateral mass screw trajectory were regular, with about 20° inclination angle. The S1 pedicle screw entry point was located at the intersection point of the basal lateral part of articular process and median line of transverse process, and no significant difference was found for the maximal extraction force between pedicle and lateral mass screws (P>0.05). The entry points of S2-S5 pedicle screws were located at the intersection point of the line connecting adjacent posterior sacral foramina and median line of the transverse process. The lateral mass screw entry point of S2-S5 was on the median side of intersection point between median line of the transverse process and lateral sacral crest. The maximal extraction force of pedicle screws was significantly greater than that of lateral mass screws (P<0.05). Conclusion: Both the sacral pedicle and the lateral mass screw fixation techniques can offer effective fixation and reconstruction for fracture of the sacrum and coccyx, but pedicle screw fixation may be more convenient, safe and reliable than lateral mass screw fixation. Key words: Sacrum; Coccyx; Biomechanics; Anatomy; Orthopedics