Digital Analysis on the Impact of Sacral Morphological Changes on the Third Sacral Safe Zone

Zhang Yueteng; Zhang Yuanzhi

Abstract：Objective We have quantified the skeletal anatomy of the sacrum with congenital curvature and analyzed its normal and malformed conditions using digital analysis and measurement of the transverse bony foramina in the third sacral vertebrae of adult humans.Methods Data was collected from 910 healthy adult volunteers at the First Affiliated Hospital of Inner Mongolia Medical University between December 2018 and December 2023.The participants included 399 males and 511 females aged 18～80 years,with an average age of(40.80±13.89)years.All individuals underwent pelvic X-rays and CT scans and were categorized into normal pelvis and abnormal pelvis groups based on their pelvic anatomy.Additionally,measurements of the transverse width,coronal width,and sagittal safety zone area in the CT scan were taken for the sacroiliac joint screw channel.Results Among the 910 volunteers,389 cases were identified as having a deformed sacrum,leading to a deformation rate of 42.75％.Moreover,in the abnormal group,the width at the level of the third sacrum was(10.35±1.92)millimeters on average,significantly higher than the normal group's average of(7.06±1.02)millimeters.The average cross-sectional width in the longitudinal section for the abnormal group was(8.17±1.74)millimeters,while the normal group's average was(5.57±0.82)millimeters.Additionally,the average area of the safety zone for the abnormal group was(129.68±7.46)square millimeters,larger than the normal group's average of(91.17±4.17)square millimeters.Conclusion A lateral bony corridor is present in S3,which has a smaller safe zone compared to S1 and S2.In contrast to a normal sacrum,a deformed sacrum provides a higher probability and a larger area for passage,enabling a safer insertion of lateral screws into the sacroiliac joint.