Rotational stability of thoracolumbar junction fixation systems

Abstract

Objective To compare the rotational stability of fusion constructs using bisegmental fixation of Th12-L2 vertebrae with anterior stabilization or pedicle screw fixation.Material and Methods The strength, rigidity and limit of elasticity in the “injured vertebral motion segments (VMS) – bisegmental anterior stabilization” system under dislocating rotational loads were estimated. The data obtained were compared with the similar characteristics of the “injured VMS – bisegmental 4-screw transpedicular metal construction” system and intact spine segments.Results Under rotational loads the limits of elasticity of injured spine segments of Th12-L2 with anterior stabilization and transpedicular screw fixation (TSF) is 45.5 and 41.7%, respectively, and the general strength is 66.4% and 80%, respectively, as compared with those intact VMS. Rigidity parameters of anterior-stabilized and pedicle screw fixated VMS with unstable damage of L1 are 60.2 and 93.9%, accordingly, in comparison with those intact VMS.Conclusion No significant differences were observed between bisegmental anterior stabilization and bisegmental pedicle screw fixation of thoracolumbar junction in terms of the key mechanical properties. When treating patients with unstable thoracolumbar spine injuries using bisegmental anterior stabilization or transpedicular fixation with 4-screw spinal system possible rotation motion amplitude of operated segments must not exceed 50% of maximum physiological limits.