Stability and Instrumentation Stresses Among Sacropelvic Fixation Techniques With Novel Porous Fusion/Fixation Implants: A Finite Element Study

Background: Sacropelvic fixation is frequently combined with thoracolumbar instrumentation for correcting spinal deformities. This study aimed to characterize sacropelvic fixation techniques using novel porous fusion/fixation implants (PFFI).Methods: Three T10-pelvis finite element models were created: (1) pedicle screws and rods in T10 -S1, PFFI bilaterally in S2 alar- iliac (S2AI) trajectory; (2) fixation in T10 -S1, PFFI bilaterally in S2AI trajectory, triangular implants bilaterally above the PFFI in a sacro alar- iliac trajectory (PFFI-IFSAI); and (3) fixation in T10 -S1, PFFI bilaterally in S2AI trajectory, PFFI in sacro- alar- iliac trajectory stacked cephalad to those in S2AI position (2-PFFI). Models were loaded with pure moments of 7.5 Nm in flexion-extension, lateral bending, and axial rotation. Outputs were compared against 2 baseline models: (1) pedicle screws and rods in T10 -S1 (PED), and (2) pedicle screws and rods in T10 -S1, and S2AI screws.Results: PFFI and S2AI resulted in similar L5 -S1 motion; adding another PFFI per side (2- PFFI) further reduced this motion. Sacroiliac joint (SIJ) motion was also similar between PFFI and S2AI; PFFI- IFSAI and 2- PFFI demonstrated a further reduction in SIJ motion. Additionally, PFFI reduced max stresses on S1 pedicle screws and on implants in the S2AI position.Conclusion: The study shows that supplementing a long construct with PFFI increases the stability of the L5 -S1 and SIJ and reduces stresses on the S1 pedicle screws and implants in the S2AI position. Clinical Relevance: The findings suggest a reduced risk of pseudarthrosis at L5 -S1 and screw breakage. Clinical studies may be performed to demonstrate applicability to patient outcomes.Level of Evidence: Not applicable (basic science study).