LectureBiomechanical evaluation of anterior lumbar interbody fusion with various fixation options: Finite element analysis of static and vibration conditions
Introduction
Anterior lumbar interbody fusion (ALIF) is commonly used as a surgical treatment of low back pain caused by degenerative disc disease (Phan et al., 2018). Compared with transforaminal lumbar interbody fusion (TLIF), ALIF provides larger surface area for fusion, better graft loading performance (Phillips et al., 2004), and shows a higher segmental stability (Niemeyer et al., 2006). To further increase stability and fusion rates, pedicle screw fixation is commonly used in conjunction with ALIF procedure (Yeager et al., 2015). Recently, various fixation options, such as the anterior lumbar plate (ALP) (Snyder et al., 2016) and part of the interspinous process devices (IPD) (Godzik et al., 2016; Techy et al., 2013), have been introduced as alternatives to the traditional pedicle screw system.
Currently, scholars have evaluated the biomechanical performance of different fixation options for ALIF. An in vitro study launched by Gerber et al. (2006) compared segmental flexibility between bilateral pedicle screw fixation (BPSF) and ALP for ALIF. Results showed that compared with ALIF alone, BPSF reduced the range of motion (ROM) of surgical segment by 61%, while the ROM was reduced by 41% in ALP group. A similar trend was also reported in Choi et al.'s finite element (FE) study (Choi et al., 2013). Lo et al. (2011) investigated the biomechanics of a U-shaped IPD (Coflex-F device) combined with ALIF and TLIF respectively. It was reported that Coflex-F has higher stability when applied after ALIF rather than TLIF. However, few studies have investigated the influence of fixation variation on facet joint force (FJF) and cage subsidence. Moreover, most of the previous biomechanical studies were performed under static loads, leaving the dynamic responses of lumbar spine after ALIF with various fixations during whole body vibration (WBV) unclear. In daily life, patients may be inevitably exposed to WBV caused by vehicles, which is more dangerous than static loading conditions (Amiri et al., 2019; Fan et al., 2019).
Therefore, this FE study was aimed at investigating the biomechanical performance of ALIF with various fixation options under both static and vertical vibration loading conditions. The stability and subsidence at surgical segment were the main foci as well as stress responses at adjacent segments.
Section snippets
FE models of the lumbar spine
In this study, a previously developed and validated anatomic FE model of the intact L1ā5 lumbar spine was employed (Fig. 1A). The model included cortical bone, cancellous bone, posterior elements, intervertebral discs, and 7 types of ligaments. Detailed modeling procedures and validation results were described elsewhere (Shen et al., 2019). To simulate the ALIF procedure, with the patient in the supine position, the L3ā4 segment of the lumbar spine underwent partial discectomy and total
ROM
The predicted ROM at surgical segment under static loading conditions was displayed in Fig. 2. The ROM data were normalized to the intact case. After ALIF procedure, the ROM decreased significantly in all motion modes. Compared with intact case, ROM of ALIF alone decreased by 88.32%, 76.56%, 83.96% and 93.72% in flexion, extension, lateral bending and axial rotation, respectively; ROM of ALP decreased by 94.29%, 90.05%, 89.42% and 96.01%; ROM of CF decreased by 94.32%, 93.55%, 87.64% and
Discussion
Supplementary fixation favorably influenced the healing of lumbar fusion (Fogel et al., 2014). Traditional BPSF could provide multiplanar stability of spinal segments (Ambati et al., 2015), compared to which, ALP may decrease the incidence of complications attributed to the addition of posterior approach (Choi et al., 2013). IPD was a flexible system that could preserve movement and improve load transmission between spinal segments (Guo and Yin, 2019). Previous biomechanical studies reported
Conclusion
In conclusion, supplementary fixation significantly influenced the biomechanics of lumbar spine after ALIF under both static and vibration loading conditions, among which BPSF provided the highest stability at surgical level. After ALIF, the application of supplementary fixation decreased the dynamic responses of lumbar spine. Compared with ALP and CF, BPSF reduced the stress responses of the endplates and cage under both static and vibration conditions, but increased the FJF at adjacent
Declaration of Competing Interest
The authors declared that they have no conflict of interest.
Acknowledgements
This study was supported by the National Key Research and Development Plan (2016YFC1102002) and the Application Demonstration Project of Shenzhen (KJYY20170405161248988).
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