Modified paravertebral foramen screw trajectory for posterior cervical spine fixation: feasibility of computed tomographic evaluation.

Abstract

Retrospective cohort study. This study aimed to investigate bone quality and the trajectories of modified paravertebral foramen screw (mPVFS) on computed tomography (CT) images compared with those of PVFS and lateral mass screw (LMS). With increasing demand for cervical posterior fusion in aging populations, achieving optimal fixation remains challenging. The PVFS offers biomechanical stability with a safer trajectory than traditional pedicle screw and LMS. However, its efficacy in elderly patients with poor bone quality is a concern. We analyzed the cervical CT images of 40 patients (10 patients per group), stratified by age and sex. Bone mineral density was assessed using CT attenuation values of the C5 vertebral body and lateral mass. We compared screw length, insertion area, and CT attenuation values along the screw trajectory across techniques. Bone quality decreased significantly with age, particularly in women. The mPVFS had a significantly longer trajectory than that of the PVFS (2.5-3.0 mm longer) and the LMS (1 mm longer) and a larger screw-bone contact area (1.2× that of PVFS, 1.4× that of LMS). CT attenuation values were higher along the mPVFS trajectory than along the PVFS and LMS trajectories. The differences were not consistently significant. mPVFS provides a biomechanical advantage by increasing screw length and contact area while targeting dense cancellous bone. mPVFS could safely accommodate screws that are 2.5-3.0 mm longer than conventional PVFS, irrespective of patient age or sex, which may be a potential clinical advantage. To validate its efficacy and long-term stability, further biomechanical and clinical studies are required.