*2.2. Simulation of TCSR Models*

L1 burst fracture and vertebral body failure were simulated by weakening the material property of the middle 30% of the L1 vertebral body, according to the previously described method with some modifications (Figure 1) [28]. The Young's modulus of the affected cortical and cancellous bone was decreased by 90% (Table 1).

For anterior reconstruction with PMMA, the surgery model was created by replacing the weakened elements in the L1 vertebral body with PMMA modeled by solid tetrahedral elements (C3D4) (Figure 2). For reconstruction with a titanium cage, an L1 corpectomy was simulated by removing the entire L1 vertebral body and the adjacent intervertebral discs at T12-L1 and L1-L2, and a titanium cage implant was simulated (Figure 2). The three-dimensional structures of the screws, rods, and titanium cage were created in the software Patran (MSC Software). The primary dimensions (diameter, length) of the pedicle screws for the thoracic and lumbar vertebrae were 5.5 mm × 45 mm and 6.5 mm × 45 mm, respectively. The diameter of the rods was 6 mm. The outer diameter, thickness, and height of the titanium cage were 14 mm, 2 mm, and 60 mm, respectively. The pedicle screws, rods, and cage were composed of titanium. The material properties of the implants were shown in Table 1. Mesh structures were prepared using the software Hypermesh 11.0 (Altair Technologies Inc., Fremont, CA, USA) and imported into Abaqus 6.12 (Simulia Inc., Johnston, RI, USA) to solve.

**Figure 2.** Different spinal reconstruction constructs. Four spinal reconstruction constructs simulated in this study including long-segment instrumentation (U2L2), short-segment instrumentation with intermediate screw (U1L1+IS), and TCSR constructs (U1L1+PMMA and U1L1+Cage). The weakened materials were indicated in blue, and PMMA was indicated in red.

Four surgery models were simulated in the present study, including (1) posterior fixation with LSPI alone (U2L2); posterior fixation with SSPI and intermediate pedicle screw at the L1 level (U1L1+IS); (3) TCSR with PMMA and SSPI (U1L1+PMMA); (4) TCSR with a titanium cage and SSPI (U1L1+Cage) (Figure 2).
