A biomechanical finite element analysis of two varieties of axial screw fixation techniques

Abstract

Abstract Background To compare the biomechanical properties of C2 pedicle and translaminar screws by establishing an atlantoaxial vertebral model using three-dimensional finite element analysis. Methods A finite element model of the atlantoaxial vertebra model was developed. C2 pedicle and translaminar screws were implanted in the model. The screw load-displacement ratios were analysed and compared between the two types of screws under the up/down and left/right load conditions; the vertebrae load-displacement ratios under the anterior flexion/posterior extension (FLX/EXT), left /right lateral bending (LLB/RLB), and left/right rotation (LAR/RAR) load conditions; bone-nail interface stress values and screw load-displacement ratios under the physiological load conditions; and structural stress values of the nail-rod structure under the front/back and left/right load conditions. Results The C2 pedicle screw group (C2PG) exhibited significantly higher load-displacement ratios than the C2 translaminar screw group (C2TG) in all directions: up/down and left/right. The vertebral load-displacement ratios in FLX/EXT, LLB/RLB, and LAR/RAR were significantly higher in C2PG compared to C2TG. Under physiological loading, the maximum stress of cortical bone in C2TG exceeded threshold significantly, and the anteriormost part of the vertebrae had much more displacement in C2TG than in C2PG. In nail-rod stability studies, C2TG had higher peak screw-rod structure stress under anterior-posterior loading. Conclusions The present finite element model suggested that the C2 translaminar screw provide lower biomechanical stability compared to the C2 pedicle screw.