Article Preview
TopIntroduction
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.