Anatomical conditions of the posterior pelvic ring regarding bisegmental transverse sacroiliac screw fixation: a 3D morphometric study of 125 pelvic CT datasets

Introduction Sacroiliac (SI) screws are used for osteosynthesis in unstable posterior pelvic ring injuries. In the cases of “sacral dysplasia”, in which the elevated upper sacrum does not allow a secure SI screw insertion into the S1 level, the S2 segment must be used to achieve stable fixation. The bone quality of the S2 segment is thinner compared to that of the S1 vertebra and may cause biomechanical weakness. An additional SI screw insertion into the S3 level may improve stability. With respect to the anatomical conditions of the posterior pelvic ring, there have been no anatomical investigations to date regarding SI screw placement into the third sacral segment.