2023 Volume 14 Issue 10 Pages 1298-1307
Introduction: The S1 pedicle screw (PS) is anatomically and mechanically weak and prone to looseness, which has led to the proposal of bicortical or tricortical screws that penetrate the cortical bone of the anterior aspect of the sacrum. However, percutaneous pedicle screw (PPS) placement using a guide wire carries a risk of neurovascular injury. This study retrospectively investigated the trajectory of S1 PPS and the risk of vascular injury in L5/S interbody fusion surgery.
Methods: 76 patients (49 males and 27 females, mean age 68±13 years) who underwent L5/S interbody fusion surgery including one or two vertebrae from January 2017 to December 2021 were included. A total of 152 S1 PS were placed, which were divided into three groups based on the trajectory: unicortical fixation (Uni) without anterior cortical breach, bicortical fixation (Bi) with anterior cortical breach, and modified penetrating endplate screw (mPES) group that inserted into the endplate of S1. The risk of vascular injury was evaluated based on the presence of vessels in the guide wire trajectory and the distance between the PS tip and vessels being ≤5 mm.
Results: There were 10 cases in the mPES group, 15 cases with bilateral Bi, 21 cases with unilateral Bi, and 30 cases in the Uni group, with 19 PS in the mPES group, 51 PS in the Bi group, and 82 PS in the Uni group. The risk of guide wire trajectory was significantly different among the groups, with 5.26% in the mPES group, 58.8% in the Bi group, and 30.5% in the Uni group (p<0.01). The risk of PS tip was also significantly different among the groups, with 5.26% in the mPES group, 52.9% in the Bi group, and 7.32% in the Uni group (p<0.01). The presence of vascular injury risk and the PS medial angle showed significant differences for both guide wire trajectory and PS tip risk (guide wire trajectory: 12.1±6.3° vs 18.2±6.5°, p<0.01; PS tip: 7.2±7.2° vs 17.3±0.6°, p<0.01).
Conclusions: Bicortical purchase of S1 PPS results in a smaller medial angle of the screw, which increases the risk of vascular injury. mPES is useful in S1 PPS because it keeps the PS tip within the disc space and reduces the risk of vascular injury.
