Risk factors for screw loosening in patients with lumbar degenerative spondylolisthesis treated with Dynesys dynamic stabilization.

Background: Posterior decompression with Dynesys dynamic stabilization (DDS) is an effective treatment option for degenerative spondylolisthesis. However, postoperative pedicle screw loosening (PSL) often results in poor outcomes. Determining possible risk factors may aid in making informed decisions. This study aimed to evaluate the incidence and risk factors for PSL in patients who underwent elective DDS.

Methods: We conducted a retrospective analysis of 94 patients with L4-L5 grade I degenerative spondylolisthesis who underwent DSS at a single academic institution between May 2008 and February 2015. Screw loosening was defined as a halo or double halo sign on plain radiography.

Results: The screw loosening rate was 4.8% among screws and 11.7% among patients. Multivariate analysis revealed that age >65 years, smoking, segmental ROM >13°, and L1 vertebral body (VB) Hounsfield unit (HU) <110 were risk factors for PSL after DDS. Five reoperations were performed; however, no screw breakage was observed. The Oswestry Disability Index and visual analog scale scores did not differ significantly at the final follow-up between the screw loosening and no screw loosening groups.

Conclusion: Our study suggests that patients with age >65 years, smoking, segmental ROM >13°, and L1 VB HU <110 had a higher risk of PSL after DDS.