Abstract: BACKGROUND: Cortical bone trajectory screw is a new type of spinal minimally invasive internal fixation technology. Compared with traditional pedicle screws, it has the characteristics of less trauma and strong pullout resistance, and has strong biomechanical properties for patients with osteoporosis. However, studies on the application of cortical bone trajectory screws combined with oblique lateral interbody fusion and fixation are still rare.  
OBJECTIVE: To evaluate the effect of oblique lateral interbody fusion combined with various fixation methods on stress distribution and range of motion of cage and L4-5 lower endplate by constructing three kinds of finite element models including oblique lateral interbody fusion (OLIF stand-alone) model, OLIF combined with bilateral pedicle screw (OLIF+BPS) model and OLIF combined with cortical bone trajectory screw (OLIF+CBT) model.
METHODS: The CT images of adult lumbar spine were used to establish the three kinds of OLIF finite element models: OLIF stand alone, OLIF+BPS, and OLIF+CBT. Ansys workbench was used to simulate the application of six different motion loads of human body flexion and extension, left and right bending, and left and right rotation to calculate stress distribution and the changes in the range of motion of the lumbar spine of the cage and endplate of the three lumbar spine surgery models and to compare the effects of three surgical options on the biomechanical effects of the lumbar spine.  
RESULTS AND CONCLUSION: (1) The OLIF stand-alone model, OLIF+BPS model and OLIF+CBT model were constructed successfully. (2) In terms of range of motion, OLIF+CBT model presented no obvious difference with that of OLIF stand-alone model in flexion and extension, left and right lateral bending, and left and right rotation motions. (3) In flexion, extension, and lateral bending conditions, the maximum stress of cage of OLIF+CBT model was smaller than that of OLIF stand-alone model and slightly greater than that of OLIF+BPS model. When it came to rotating condition, the maximum stress of cage in OLIF+CBT model was bigger than that of two other models. (4) The maximum stress of the lower end plate of OLIF+CBT model was smaller than that of OLIF stand-alone model but slightly greater than that of OLIF+BPS model at various conditions. (4) It is concluded that OLIF combined with CBT fixation provides a good stable support for the vertebral body of the fusion segment on the premise of ensuring the mobility of the lumbar spine, and has a relatively good biomechanical effect.

Key words: spine, intervertebral disc, oblique lateral interbody fusion, cortical bone trajectory screw, finite element