Comparison of Extragraft Bone Formation after Anterior Cervical Discectomy and Fusion Using Simultaneous and Sequential Algorithms

Abstract

Extragraft bone formation is crucial for obtaining a successful outcome after spinal fusion surgery. However, the cause of bone formation is not well investigated. In this study, it was hypothesised that extragraft bone formation is generated by mechanical stimuli. A preoperative plan for anterior cervical discectomy and fusion was applied to the finite element model of the C5–C6 motion segment. Extragraft bone formations posterior to the interbody cage were simulated using simultaneous and sequential algorithms. While the simultaneous algorithm predicted the formation of extragraft bone bridging under flexion and extension, the bridge was generated only under extension with the sequential algorithm. This was caused by an ill-defined design space in cases where the simultaneous algorithm was used. Our results using the sequential algorithm show how the progress of extragraft bone formation affects spine mechanics, and our results support the hypothesis that a mechanical stimulus is a major factor influencing extragraft bone formation.

Biomechanical Evaluation of Intervertebral Fusion Process After Anterior Cervical Discectomy and Fusion: A Finite Element Study

“…They found that the average change in interbody force magnitude from full extension to full flexion decreased significantly during fusion. Furthermore, Park and Jin (2019 ) and Jin and Park (2021 ) simulated extragraft bone formation at the C5–C6 motion segment after ACDF using a developed finite element model and a sequential bone-remodeling algorithm in flexion and extension. The results suggested that both the stress and strain energy density slightly changed in flexion while a significantly stepwise decrease was predicted in extension until the fusion was terminated ( Park and Jin, 2019 ).…”

“…Finite element (FE) analysis is an effective method to evaluate the spinal biomechanics after surgery or during bone remodeling process ( Palissery et al, 2009 ; Ganbat et al, 2016 ; Jin and Park, 2021 ). Several previous finite element studies have investigated the biomechanical effect of ACDF.…”

Recent advancement in finite element analysis of spinal interbody cages: A review

“…In both the simultaneous and sequential algorithms, the bone formation and resorption were calculated based on the mechanical stimulation of the strain energy density (SED, U) predicted in the FEA. The density of the bone, ρ, was calculated using an equation as follows (Park and Jin, 2019;Jin and Park, 2021):…”

“…After that, the bone formation and resorption were calculated again as the second step of simulation. This procedure was repeated until no new bone formation occurred ( Jin and Park, 2021 ). The simultaneous algorithm is easier to compute, whereas the sequential algorithm is more consistent with the actual physiological situation.…”

“…In both the simultaneous and sequential algorithms, the bone formation and resorption were calculated based on the mechanical stimulation of the strain energy density (SED, ) predicted in the FEA. The density of the bone, , was calculated using an equation as follows ( Park and Jin, 2019 ; Jin and Park, 2021 ): where , , , and are the units of time, remodeling rate coefficient, homeostatic equilibrium SED, and threshold range of the lazy zone, respectively. The SED per unit mass, , is calculated as .…”