Anatomical and Biomechanical Study of Sacral Pedicle and Lateral Mass / 医用生物力学

ABSTRACT

Objective To study the anatomical and biomechanical features of sacral pedicle and lateral mass to provide evidence for clinical sacral pedicle and lateral mass screw fixation technology. Method 60 adult patient's spiral CT images of sacrum and coccyx were selected randomly. The sacral pedicle and lateral mass screw entry point was determined, and the crew trajectory were measured using the three dimensional reconstruction. Meanwhile, the gross anatomy was done for 15 adult cadavers to determine the sacral pedicle and lateral mass screw entry point. The length, width and angle of sacral pedicle and lateral mass screw trajectory was measured. 8 of 15 cadaver specimens were selected to test for the maximal extraction force for sacral pedicle and lateral mass screws. ResultsThe diameter and length of S1～S5 sacral pedicle and lateral mass screw trajectory are significantly regular, with inclination angle is about 20°. The S1 pedicle screw entry point is located at intersection point of basal lateral part of articular process and median line of transverse process, no significant difference is found between the maximal extraction force of pedicle and lateral mass screws (P>0.05）. The entry points of S2～5 pedicle screws are located at the intersection point of the line connecting adjacent posterior sacral foramina and median line of transverse process. The lateral mass screw entry point of S2～5 is on the median side of intersection point between median line of transverse process and lateral sacral crest. The maximal extraction force of pedicle screws are significantly different from the lateral mass screws（P<0.05）. Conclusions Both the sacral pedicle and the lateral mass screw fixation technology can offer effective fixation and reconstruction for the fracture of sacrum and coccyx, but the pedicle screw fixation may be more convenient, safe and reliable than the lateral mass screw fixation technology.