Radiographic S1 Pedicle Screw Loosening After Lumbosacral Fusion for Degenerative Disease: A Single-Institution Cohort Study

BACKGROUND: S1 pedicle screw loosening remains a recognized complication after lumbosacral fusion, but its incidence in shorter-segment constructs for degenerative lumbar disease remains incompletely defined. METHODS: Adults who underwent lumbosacral fusion, including S1 pedicle fixation, for degenerative lumbar pathology between 2021 and 2024 were retrospectively reviewed. Included patients had at least 12 months of radiographic follow-up. Screw loosening was defined as a radiolucent zone of at least 1 mm around the S1 screw and graded using a modified Shimizu-Lenke scheme (grades 0, 1, 2A, 2B, and 3). RESULTS: A total of 68 patients met inclusion criteria, with a mean age of 58.6 ± 14.4 years. The overall incidence of S1 screw loosening was 4.4% (3/68), with a mean time to screw loosening of 43.0 ± 9.2 weeks postoperatively. Interbody devices were placed at L5 to S1 in 66/68 (97.1%), most commonly via transforaminal lumbar interbody fusion approach (48/68, 70.6%), followed by anterior lumbar interbody fusion (13/68, 19.1%) and oblique lateral interbody fusion (5/68, 7.4%). Most constructs were short-segment fusions, and most patients received interbody support. Because loosening events were uncommon, analyses of potential associations with bone quality, construct characteristics, and alignment parameters should be interpreted as exploratory. CONCLUSION: In this single-institution cohort, S1 pedicle screw loosening after degenerative short-segment lumbosacral fusion was uncommon. The findings support the need for larger studies with longer follow-up to clarify the contributions of bone quality, alignment, and fixation strategy to loosening risk. CLINICAL RELEVANCE: Variability of clinical presentation of S1 screw loosening highlight the need for further investigation into the relationship between S1 screw loosening and clinical outcomes.