Initial appearance and temporal distribution of pedicle screw loosening after single-level lumbar interbody fusion.

Pedicle screw (PS) loosening is a recognized complication after lumbar interbody fusion, but the timing of its initial appearance and its temporal distribution remain insufficiently defined. This retrospective study evaluated 212 patients who underwent single-level lumbar interbody fusion with PS fixation to clarify when PS loosening first appears, how it changes over time, and which clinical factors are associated with its development. The median follow-up duration was 502 days [364.5-731.75]. PS loosening was identified on postoperative computed tomography in 18.9% of patients. Approximately half of the cases were observed within 90 days, and nearly two-thirds within 180 days. Most cases occurred during the early postoperative period, but a smaller number continued to emerge up to one year. Occurrences beyond one year were rare. Older age and lower lumbar levels, particularly L4/5 and L5/S1, demonstrated significant associations with PS loosening. These findings provide a clearer understanding of the temporal characteristics of PS loosening and emphasize the importance of postoperative CT for detecting early changes. They also highlight the need for appropriate follow-up strategies to identify delayed cases that may otherwise be overlooked.