Advantages of the Paraspinal Muscle Splitting Approach in Comparison With Conventional Midline Approach for S1 Pedicle Screw Placement

Study Design. A retrospective comparative study of the S1 pedicle screw (S1PS) position obtained using 2 surgical approaches. Objective. To determine whether the paraspinal approach leads to more medially oriented placement of the S1PS compared with the midline approach. Summary of Background Data. To obtain a stronger as well as safer fixation of the S1PS, medially oriented screw placement is very important. However, no study has recommended a surgical approach to achieve this object. Methods. The positions of 32 screws placed by the midline approach and 34 screws placed by the paraspinal approach were compared using postoperative computed tomography. The location of the bilateral common iliac veins (CIV) in relation to the S1PS tips was also analyzed to evaluate their safety. Results. There was no statistical difference in screw insertion point regardless of the approach employed. However, in the paraspinal group the S1PS were placed with significantly greater medial direction and with longer screws. In addition, they pierced the anterior sacral cortex closer to the midline compared with the midline approach. Four left screws in the midline approach group made contact with the left CIV, whereas no screw in the paraspinal approach group lay adjacent to the CIV. Conclusion. Our results demonstrate that the paraspinal approach for S1PS placement may be superior to the midline approach in terms of the medially oriented screw placement that is biomechanically stronger and less risky for the CIV.