A Study of the Variability of the Parameters of Sacroiliac Joint Screw Path and Related Factors through S_2 Pedicle

Objective: To provide the anatomic basis for sacroiliac screw fixation through S2 pedicle . and study the variability of the parameters. Method: 100 pelvic of the healthy adaults were scaned by spiral CT to measure the broad and height of the pediele of S2;the distance from the optimal entry point to contrary anterior cortex of S2. The distance from the optimal entry point to the posterior infe- rior iliac spine, to the greater sciatic notch. The direction of the centre axis of the pedicle of S2,the gender ,age ,height and weight were recorded at the same time. Results: The broad and height of the pediele of S2 was 16.6±3.8mm and 12.8±4.5mm,The distance from enty point to contrary anterior cortex of S2 vertebral body was74.8±2.9mm, The direction of serew was 14.5±2.4°to the coro- nal plane and 8.9±1.9° to the horizontal plane. The optimal entry point on posterolateral iliac ala for screw fixation was fund to exist 24.7±3.5mm anterior to posterior inferior iliac spine and 19.3±4.6mm superior to the greater sciatic notch. Bsides the direction of the centre axis , pararneter of screw fixation showed a wide range value and quantity .No inter-gender difference existed between man and woman after effects of height and weight was removed.Both height and weight showed significant positive correlation with the screw path length and transverse diameter of pedicle ,but no correlation with the direction of the centre axis. Conclusion: The parameters of the screw path varied in different subjects.the height and weight are two important factors to influence the parameters.