Innovative sacropelvic fixation using iliac screws and triangular titanium implants

Purpose Sacropelvic fixation is frequently used in combination with thoracolumbar instrumentation for the correction of severe spinal deformities. The purpose of this study was to explore the effects of the triangular titanium implants on the iliac screw fixation. Our hypothesis was that the use of triangular titanium implants can increase the stability of the iliac screw fixation. Methods Three T10-pelvis instrumented models were created: pedicle screws and rods in T10-S1, and bilateral iliac screws (IL); posterior fixation and bilateral iliac screws and triangular implants inserted bilaterally in a sacro-alar-iliac trajectory (IL-Tri-SAI); posterior fixation and bilateral iliac screws and two bilateral triangular titanium implants inserted in a lateral trajectory (IL-Tri-Lat). Outputs of these models, such as hardware stresses, were compared against a model with pedicle screws and rods in T10-S1 (PED). Results Sacropelvic fixation decreased the L5-S1 motion by 75–90%. The motion of the SIJ was reduced by 55–80% after iliac fixation; the addition of triangular titanium implants further reduced it. IL, IL-Tri-SAI and IL-Tri-Lat demonstrated lower S1 pedicle stresses with respect to PED. Triangular implants had a protective effect on the iliac screw stresses. Conclusion Sacropelvic fixation decreased L5-S1 range of motion suggesting increased stability of the joint. The combination of triangular titanium implants and iliac screws reduced the residual flexibility of the sacroiliac joint, and resulted in a protective effect on the S1 pedicle screws and iliac screws themselves. Clinical studies may be performed to demonstrate applicability of these FEA results to patient outcomes.

Tear-drop technique in iliac screw placement: a technical analysis

Background Instrumentation of the lumbosacral region is one of the more challenging regions due to the complex anatomical structures and biomechanical forces. Screw insertion can be done both navigated and based on X-ray verification. In this study, we demonstrate a fast and reliable open, low exposure X-ray-guided technique of iliac screw placement. Methods Between October 2016 and August 2019, 48 patients underwent sacropelvic fixation in tear-drop technique. Screw insertion was performed in open technique by using an X-ray converter angulated 25-30° in coronal and sagittal view. The anatomical insertion point was the posterior superior iliac spine. Verification of correct screw placement was done by intraoperative 3D scan. Results In total, 95 iliac screws were placed in tear-drop technique with a correct placement in 98.1%. Conclusions The tear-drop technique showed a proper screw position in the intraoperative 3D scan and therefore may be considered an alternative technique to the navigated screw placement.

The three-dimensional printed template guided technique for S2 alar iliac screw placement and a comparison with freehand technique

Purpose: Sacropelvic fixation continues to present challenges when involved in the adult spinal deformity correction. The S2 alar iliac (S2AI) fixation is commonly used in sacropelvic fixation. Several techniques, including intraoperative navigation and freehand technique, were used for S2AI screws placement. The aim of this study is to analyze the anatomic parameters for S2AI screw trajectory in Asian population and introduce a novel technique described as a three-dimensional printed template guided technique (TGT). Meanwhile, the accuracy and safety of this technique were compared with the conventional freehand technique. Methods: The S2AI trajectory parameters were measured in 100 Asian adult volunteers. Parameters were compared between different genders. Forty-eight adult patients who underwent S2AI screw placement were reviewed: 28 patients received freehand technique and 20 patients received TGT technique. Postoperative computed tomography was used to assess the accuracy of screw trajectory and cortex violation-related complications were recorded. Results: The cephalocaudal angles (CAs), maximal length of screw pathway, narrowest width of pathway within the iliar teardrop, distance from the center of teardrop to sciatic notch, and distance of the start point distal to S1 dorsal foramen showed significant gender-related difference ( p < 0.05). All 48 patients were placed S2AI screws bilaterally (40 screws in TGT vs. 56 screws in freehand). One screw penetrated iliac cortex in the TGT group but 10 screws penetrated iliac cortex in the freehand group (3% vs. 17.9%) ( p < 0.05). Conclusion: Approximately 30–35° of CA and 39° mediolateral angle are appropriate for S2AI screw placement in Asian patients. Either freehand or TGT technique is safe for S2AI screw placement. TGT technique is more accurate compared with the conventional freehand technique. Trial registration: This is a retrospective study.