Abstract
BACKGROUND: Single-level posterior lumbar interbody fusion (PLIF) or transforaminal lumbar interbody fusion (TLIF) is a commonly performed surgical procedure for L4-5 isthmic spondylolisthesis. Postoperative L5 pedicle fracture with rapidly progressive spondylolisthesis at L5-S1 segment after L4-5 PLIF/TLIF is quite rare, and the etiology remains unclear. This report describes this rare complication and proposes a possible etiology focusing on the lumbosacral sagittal imbalance characterized by an anteriorly shifted lumbar loading axis. OBSERVATIONS: The authors report a case complicated by L5 bilateral pedicle fractures and rapidly progressive spondylolisthesis at the L5-S1 segment very early after a single-level PLIF for L4-5 isthmic spondylolisthesis. Meyerding grade III anterolisthesis was observed at L5-S1 segment by 3 months after the initial surgery. Additional surgery was performed, and the fixation was extended to L4-ilium. Fracture healing was observed at 6 months postoperatively. LESSONS: This complication may have been caused by abnormal local shear forces on the posterior neural arch of L5 vertebra and L5-S1 intervertebral disc, which were triggered by the fusion surgery for L4 shear-type spondylolisthesis. L4 sagittal vertical axis is considered a reasonable parameter representing lumbosacral sagittal imbalance with an anteriorly shifted loading axis and may be a candidate for the predictive parameters of this rare complication.