The L4-L5 segment was selected to simulate oblique lumbar interbody fusion (OLIF) with ALSR screw fixation, and we performed surgical simulation according to a literature review and our surgical experience (Guo et al., 2020 (link); Xi et al., 2020 (link)). In this process, lateral parts of the annulus, all of the nucleus, and CEPs were removed, and a polyether-ether-ketone (PEEK) OLIF cage (18 mm width and 50 mm length) filled with grafted bone was inserted into the interbody space. The lordotic angle and disc height of the postoperative models were identical to those of the intact model to eliminate the mechanical effects of these parameters (Kim et al., 2012 (link); Wang et al., 2019 (link); Guo et al., 2020 (link)).
Three different grades of contact sufficiency between the BEP and GB (including ideal, acceptable, and poor) were simulated by changing the GBOR in the coronal plane. The ideal contact was defined completely match between BEP and GB, GBOR in acceptable and poor contact models were defined as 80 and 60%, respectively. Based on the review of radiographic data, the mismatch on the superior side was mainly in the central region, while that on the inferior side was in the peripheral region. By combining different contact sufficiency grades between the GB and superior and inferior BEPs, five different OLIF models were constructed (Table 1 ; Figures 1 , 5 ).
During the simulation of ALSR screw fixation, two titanium alloy (TI) screws were inserted into the L4-L5 vertebral bodies and penetrated the contralateral cortex. The axes of the screws in the transverse plane were parallel to the OLIF cage, whereas those in the coronal plane were parallel to the BEPs (Guo et al., 2020 (link); Xie et al., 2020 (link)). Screw threads were preserved, and the screw compaction effect was simulated by adjusting the material property of cancellous around the thread (Hsu et al., 2005 (link); Matsukawa et al., 2016 (link)). The connection between the screw tulip, the nut, and the spacer was simplified to increase the computational efficiency.
Three different grades of contact sufficiency between the BEP and GB (including ideal, acceptable, and poor) were simulated by changing the GBOR in the coronal plane. The ideal contact was defined completely match between BEP and GB, GBOR in acceptable and poor contact models were defined as 80 and 60%, respectively. Based on the review of radiographic data, the mismatch on the superior side was mainly in the central region, while that on the inferior side was in the peripheral region. By combining different contact sufficiency grades between the GB and superior and inferior BEPs, five different OLIF models were constructed (
During the simulation of ALSR screw fixation, two titanium alloy (TI) screws were inserted into the L4-L5 vertebral bodies and penetrated the contralateral cortex. The axes of the screws in the transverse plane were parallel to the OLIF cage, whereas those in the coronal plane were parallel to the BEPs (Guo et al., 2020 (link); Xie et al., 2020 (link)). Screw threads were preserved, and the screw compaction effect was simulated by adjusting the material property of cancellous around the thread (Hsu et al., 2005 (link); Matsukawa et al., 2016 (link)). The connection between the screw tulip, the nut, and the spacer was simplified to increase the computational efficiency.
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