###### Abstract  
The aim of this study was to analyze the spinal stability and safety after posterior spinal fusion with various fixation segments and screw types in patients with an osteoporotic thoracolumbar burst fracture based on finite element analysis (FEA). To realize various osteoporotic vertebral fracture conditions on T12, seven cases of [PERSON]'s modulus, namely 0%, 1%, 5%, 10%, 25%, 50%, and 100% of the [PERSON]'s modulus, for vertebral bones under intact conditions were considered. Four types of fixation for thoracolumbar fracture on T12 (fixed with T11-L1, T10-T11-L1, T11-L1-L2, and T10-T11-L2) were applied to the thoracolumbar fusion model. The following screw types were considered: pedicle screw (PS) and cortical screw (CS). Using FEA, four motions were performed on the fixed spine, and the stress applied to the screw, peri-implant bone (PIB), and intervertebral disc (IVD) and the range of motion (ROM) were calculated. The lowest ROM calculated corresponded to the T10-T11-L1-L2 model, while the closest to the intact situation was achieved in the T11-L1-L2 fixation model using PS. The lowest stress in the screw and PB was detected in the T10-T11-L1-L2 fixation model. p 2021 2021 2021 2021 2021 2021 2021 2021 2021  
difficult to obtain human spinal specimens, and the available specimens are generally of poor bone quality, and thereby unrepresentative of the conditions of a young individual [6]. Therefore, finite element analysis (FEA) is one of the most useful methods for predicting spinal fixation failures. This is because FEA can be repeated under the same conditions and results for various surgical techniques can be derived with the same patient. Hence, a three-dimensional finite element (FE) model based on computed tomography (CT) scan has been created, and various clinical problems associated with biomechanical behavior could be predicted via FEA [7; 8]. Nonlinear FE models of the human vertebra have been validated in several studies using various methods [9; 10]. In this study, the reliability of FE models was validated via comparisons between the FE models reported in extant studies and models proposed in this paper [11; 12]. In a recent study, [PERSON] et al. investigated the physical properties of a spinal fixation rod in adjacent segments via FEA, and they found that a flexible rod or cage can alleviate the contact force of the facet joint due to spinal fixation [13]. [PERSON] et al. examined the biomechanical stress on the vertebral body after PS fixation under seven different work conditions in patients with adult degenerative scoliosis (ADS), and they demonstrated that PS fixation could reduce biomechanical stress in ADS patients [14]. Spinal fixation with a PS has been much used, but its inability to support the anterior spinal column after posterior correction and stabilization in some severe cases may lead to failure of the posterior spinal implants [1]. A cortical screw (CS), first proposed by [PERSON] in 2008 [15], was developed to enhance the stability of spinal fixation in patients with low bone density by penetrating the cortical bone, which is relatively stronger than the cancellous bone [16]. A clinical study found that a PS had better fatigue performance than a CS in the bone-degradation [17]. However, other studies reported that a CS had approximately 1.7 times higher torque than a PS and showed superior resistance to vertical and repetitive loads in normal bones [18; 19]. To date, several studies have been conducted to investigate the stability of a CS, and clinical studies have already shown that a CS had better outcomes in terms of spinal stability than a traditional PS. However, none of the studies elucidated the underlying mechanisms. Thus, it is difficult to clearly distinguish the merits of a PS and CS based solely on clinical research results alone. Specifically, previous studies compared the stability of a single segment and a long segment and determined the fixed stability of a PS or the design or material of a spinal rod.