Biomechanical evaluation of various cage implantation angles and screw constructs in L4-5 PLIF surgery: a finite element study

Abstract

Abstract Background This study investigates the biomechanical impact of different pedicle screw constructs and cage implantation angles on the L4-L5 segment. The aim is to optimize spinal stability and mobility in Posterior Lumbar Interbody Fusion (PLIF) surgery. Methods Three cadaveric specimens with osteoporotic bone density were used to construct finite element models of the L1-S1 segment. The L4-L5 segment underwent posterior lumbar interbody fusion (PLIF) surgery with three screw constructs: traditional pedicle screws (TT-TT), cortical bone trajectory screws (CBT-CBT), and modified cortical bone trajectory screws (MCBT-MCBT), with cage implantation angles of 30°, 45°, 60°, and 90°. Biomechanical analysis was performed under various loading conditions using ANSYS Workbench 19.1. Parameters such as range of motion, intervertebral disc stress, and pedicle screw stress were calculated to assess the effects of different fixation techniques and angles. Results The finite element analysis validated the impact of different screw types and cage angles on L4-L5 biomechanics. At 45°, all screw types showed the highest range of motion (ROM) in most directions. CBT screws resulted in higher intervertebral disc stress, particularly at 45° and 60°. Pedicle screw stress remained stable across angles, with MCBT exhibiting higher stress in lateral bending. Rod stress increased markedly at 60° and 90° for CBT, while MCBT showed higher stress during rotation. The results highlight the biomechanical effects of screw constructs and implantation angles on spinal stability. Conclusion CBT screws achieved the highest ROM at 45° but with elevated disc stress. MCBT screws showed lower disc stress and moderate ROM. No single construct or angle was uniformly favorable across all parameters in this finite element model.