Biomechanical Study of Lumbar Spine (L2-L4) Using Hybrid Stabilization Device - A Finite Element Analysis

Biomechanical Study of Lumbar Spine (L2-L4) Using Hybrid Stabilization Device - A Finite Element Analysis

Pushpdant Jain (National Institute of Technology Rourkela, Rourkela, India) and Mohammed Rajik Khan (National Institute of Technology Rourkela, Rourkela, India)
DOI: 10.4018/IJMMME.2020010102

Abstract

Spinal instrumentations have been designed to alleviate lower back pain and stabilize the spinal segments. The present work aims to evaluate the biomechanical effect of the proposed Hybrid Stabilization Device (HSD). Non-linear finite element model of lumbar segment L2-L4 were developed to compare the intact spine (IS) with rigid implant (RI) and hybrid stabilization device. To restrict all directional motion vertebra L4 bottom surface were kept fixed and axial compressive force of 500N with a moment of 10Nm were applied to the top surface of L2 vertebrae. The results of range of motion (ROM), intervertebral disc (IVD) pressure and strains for IVD-23 and IVD-34 were determined for flexion, extension, lateral bending and axial twist. Results demonstrated that ROM of HSD model is higher than RI and lower as compared to IS model. The predicted biomechanical parameters of the present work may be considered before clinical implementations of any implants.
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Introduction

Spinal arthrodesis with rigid posterior fixation has been the gold standard procedure to treat the lower back pain and degenerative lumbar diseases (Bono & Lee, 2004; Chen, Huang, & Shih, 2015). In spite of higher fusion rate and satisfactory clinical results, spinal fusion results in pain, loss in functionality and re-surgery of the affected part (Lee, 1988; Park, Garton, Gala, Hoff, & McGillicuddy, 2004). To alleviate the lower back pain and spinal disorders, methods like facet joints arthroplasty, disc replacement and dynamic stabilization have been adopted by the practitioners (Mas et al., 2017). The pedicle based posterior dynamic stabilization is proposed as an alternative to fusion which results in better flexibility and induces more load transfer to adjacent segments as compared to fused fixation (Mulholland & Sengupta, 2002a; Mulholland & Sengupta, 2002b; Sengupta, 2004). As a result, various dynamic stabilization systems have been developed with the advancement in the technologies (Chen et al., 2015; Erbulut, Kiapour, Oktenoglu, Ozer, & Goel, 2014; Jahng, Kim, & Moon, 2013; Ledoux, Ramos, & Mesnard, 2017).

Biswas et al. (2018) conducted a finite element (FE) study on two level (L3-L5) lumbar model, implanted with various rod materials and concluded that poly ether ether ketone (PEEK) rod might be a better option for implant design to get an optimum range of motion. Similar FE study was performed by Kang et al. (2017) using single level (L3-L4) and two levels (L3-L5) fixation systems with Titanium, PEEK and carbon fiber reinforced (CFR) PEEK rod materials. Their findings suggest that CFR-PEEK is a better rod material for fusion and also reduces the chances of pedicle screw breakage / failure. Dmitriev et al. (2008) have performed experimental trials on ten human lumbar (L3-L5) cadaver spines to compare the biomechanical effect of total disc replacement (TDR) and anterior interbody cages with pedicle screws. It was suggested to use two-level arthroplasty (TDR) which provides favorable biomechanical environment to the adjacent segments as compared to conventional pedicle fixation system. The study of Ciplak et al. (2017) shows clinical follow-up of on 103 patients implanted with a two-level dynamic stabilization system. It was reported that the use of dynamic stabilization device resulted in a higher rate of screw loosening and adjacent segment disease as compared to the fused systems. However, it is important to consider the significance of design factors associated with pedicle screw to achieve spinal stability by reducing its chances of loosening or breakage (Biswas et al., 2019). Moreover, it is also advised to consider the bone conditions to select the optimum pedicle screw diameter to avoid failures at bone screw interface. To obtain spinal stability according to injury / disease, predictive models and multi-level fixation design is still a challenge to the researchers and practitioners.

The hypothesis of the present work is that the proposed hybrid stabilization device can be used as a stand-alone device in case of total disc replacement and minor degeneracy, where limited vertebral motion is required after surgery. (See Table 1) The present study aims to assess a novel hybrid stabilization device having characteristics of the rigid and dynamic stabilization system. An FE study considering three-dimensional two-level spinal (L2-L4) models instrumented with the rigid and hybrid stabilization was designed to evaluate biomechanical parameters. Results in terms of ROM, intervertebral disc pressure and strain were calculated for flexion (FLX), extension (EXT), lateral bending (BEND) and twist (TWST) using FE analysis. A detailed comparison of obtained results has been performed between intact spine model and instrumented models.

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