S1 Pedicle Screw Loosening: A Systematic Review and Meta-Analysis of Risk Factors and Outcomes.

Background: Despite advancements in fixation techniques, S1 pedicle screw loosening remains a common complication of lumbosacral fusion surgeries for degenerative lumbar conditions, with reported rates ranging from 15.6% to 41.9%. This complication can compromise fusion success, leading to nonunion, adjacent segment disease, and revision surgeries. Compared with other surgical challenges, less is known about the incidence and predictors of S1 pedicle screw loosening. Given the high prevalence of S1 screw loosening and its associated complications, this systematic review and meta-analysis aim to report the incidence and risk factors contributing to S1 pedicle screw loosening in sacral fixation for degenerative lumbar conditions.

Methods: The literature search was conducted across 2 databases: PubMed and OVID. Study inclusion criteria were adults (age >18 years) undergoing lumbar fusion with S1 sacral fixation for degenerative lumbar conditions, with a minimum follow-up of 12 months and radiographic confirmation of screw loosening. Eligible studies included cohort or case-control designs that reported screw loosening rates. Extracted data included patient demographics (age, gender, body mass index, and bone mineral density [BMD]), surgical factors (screw type, length, and number of fusion levels), and complication rates.

Results: Of 174 studies queried, 21 met inclusion criteria, comprising 2598 patients who underwent lumbar fusion with sacral fixation with S1 pedicle screws (mean age 62 ± 7.2 years). The overall screw loosening rate in patients was 23.8% (696/2924) but varied from 3.0% to 55.0%. The pooled proportion of S1 pedicle screw loosening in patients after lumbosacral fixation was 27% (relative risk = 0.27, 95% CI 0.22-0.34, P < 0.0001). When assessed per screw, the screw-specific loosening rate was 8.7%. The pooled proportion of individual S1 pedicle screws loosening after lumbosacral fixation is 10% (relative risks = 0.10, 95% CI 0.06-0.17, P < 0.0001). Among included patients, the mean BMD was -0.63 ± 1.5, and the mean vertebral bone quality score was 3.3 ± 0.02.

Conclusion: The aggregate rate of S1 pedicle screw loosening after sacral fixation is 23.8%, highlighting a significant complication rate that may compromise surgical success. This complication is associated with adverse outcomes, pseudarthrosis, and adjacent segment disease, which can significantly impact patient quality of life. The high failure rate emphasizes the need for careful surgical planning, including patient-specific considerations such as BMD and vertebral bone quality, as well as the selection of optimal fixation techniques in lumbosacral fusion surgeries.

Clinical relevance: While advancements in surgical techniques and hardware design have reduced failure rates, the persistent variability across studies underscores the need for further research.

Level of evidence: 1: