Biomechanical analysis of single-level interbody fusion with different internal fixation rod materials: a finite element analysis

Abstract

Background: Lumbar spinal fusion with rigid spinal fixators as one of the high risk factors related to adjacentsegment failure. The purpose of this study is to investigate how the material properties of spinal fixation rods influence the biomechanical behavior at the instrumented and adjacent levels through the use of the finite element method. Methods: Five finite element models were constructed in our study to simulate the human spine pre-and postsurgery. For the four post-surgical models, the spines were implanted with rods made of three different materials: (i) titanium rod, (ii) PEEK rod with interbody PEEK cage, (iii) Biodegradable rod with interbody PEEK cage, and (iv) PEEK cage without pedicle screw fixation (no rods). Results: Fusion of the lumbar spine using PEEK or biodegradable rods allowed a similar ROM at both the fusion and adjacent levels under all conditions. The models with PEEK and biodegradable rods also showed a similar increase in contact forces at adjacent facet joints, but both were less than the model with a titanium rod. Conclusions: Flexible rods or cages with non-instrumented fusion can mitigate the increased contact forces on adjacent facet joints typically found following spinal fixation, and could also reduce the level of stress shielding at the bone graft.

Biomechanical Effects of Polyetheretherketone and Titanium Rods in Transforaminal Lumbar Interbody Fusion: A Finite Element Analysis

“…Similarly, Nikkhoo et al demonstrated that there was no signi cant difference in the ROM of adjacent segments between the PEEK rod models and the intact models, and PEEK rods reduced the disc height loss, uid loss, and disc stresses of adjacent segments under cyclic loading compared with those of Ti rods [30]. Additionally, during exion, the increase in disc stresses at L3/4 was highest (29.7-39.0%), and this was similar to that reported by Hsieh et al (50%) [23]. In fact, the structural stiffness provided by both rigid and semi-rigid xation systems is signi cantly greater than that of the normal spinal unit, which further changes the ROM and IDP of adjacent segments [13,41].…”

“…It is known that axial stiffness affects exion and extension, whereas lateral bending stiffness affects rotation and lateral bending [26]. Therefore, axial stiffness is mainly provided by the anterior column, while the posterior internal xation is important to bending stiffness [23,26].…”

“…However, PEEK rods simultaneously increased the risk of cage failure and endplate collapse. It is well known that cages are important than posterior xation in maintaining spinal stability because the anterior column bears approximately 75% of the load [23].…”

“…Novel polyetheretherketone (PEEK) rods, whose elastic modulus is close to that of bones, are used in clinical practice as an alternative to Ti rods in an effort to reduce the incidence of adverse events [13,15,23]. The biocompatibility, toxicity, and imaging characteristics of PEEK rods are better than those of Ti rods, which are the basis of their being potential clinical substitutes [24,25].…”

Oblique Lateral Interbody Fusion versus Transforaminal Lumbar Interbody Fusion in Degenerative Lumbar Spondylolisthesis: A Single-Center Retrospective Comparative Study

“…(2) Granular bone graft was used in both groups, and our previous study had showed that granular bone graft had a high fusion rate [ 31 ]. (3) Both groups used a posterior pedicle screw system to create a stable local mechanical environment, which was also beneficial for bone graft fusion [ 32 ].…”