Biomechanical study of rod stress after pedicle subtraction osteotomy versus anterior column reconstruction: A finite element study.

Abstract

Background:In an effort to minimize rod fractures and nonunion in pedicle subtraction osteotomy (PSO) constructs, surgeons have adopted multirod constructs and interbody cages. Anterior column realignment (ACR) with posterior column osteotomies is a minimally invasive alternative to PSO in sagittal balance correction, however, there is a paucity of evidence with respect to rod survival.Methods:Three-dimensional (3D) finite-element-model of a T12-sacrum spine segment was used to compare a 25° PSO at L3 and an ACR with a posterior column osteotomy and 30° hyperlordotic interbody cage at L3–4. The amount of overall T12–S1 lordosis correction was the same for each condition. Each simulation included cobalt chromium alloy primary rods with: (1) PSO; (2) PSO with an interbody cage (IB) at L2–3 (PSO+IB); (3) PSO with accessory (A) rods and IB at L2–3 (PSO+IB+A); (4) PSO with satellite (S) rods and IB at L2–3 (PSO+IB+2S); (5) ACR; 6) ACR with satellite rods (ACR + 2S). A 400 N follower preload was simulated for each condition.Results:PSO condition had the largest rod stress of 286 MPa in flexion. Adding interbody support reduced the rod stress by 15%. The 4-rod constructs further reduced rod stress, with the satellite rod condition facilitating the largest reduction. The rod stress in the ACR+2S was equivalent to the PSO+2S, with 50% reduction in rod stress.Conclusion:The rod stress with an ACR was comparable to a PSO coupled with interbody support. These results suggest an ACR is a viable MIS alternative to a PSO without the need for a large posterior osteotomy.