Segmental Normalisation of Lumbar Lordosis Following Transforaminal Lumbar Interbody Fusion for Low-Grade Isthmic Spondylolisthesis

Background Isthmic spondylolisthesis is commonly associated with back pain and neurological symptoms. The primary localised kyphotic deformity at the level of the spondylolisthesis is counterbalanced by increased lordosis across the lumbar spine. Spondylolisthesis reduction and fusion corrects the initial deformity and may also restore lumbar lordosis and sacral slope. In this study, we aimed to investigate how lumbar lordosis normalises following short-segment transforaminal lumbar interbody fusion (TLIF) for isthmic spondylolisthesis. Methodology In total, 54 consecutive patients from a single surgeon series of isthmic spondylolisthesis undergoing reduction and TLIF performed between 2013 and 2023 underwent retrospective radiological analysis by two independent observers. Measurements of the lumbar lordosis, sagittal cobb angle across the lumbar spine as a whole, and individual motion segments were taken using pre and postoperative standing radiographs. Results A total of 39 fusions were performed at L5/S1, 12 at L4/5, two on both levels L5/S1 and L4/5, and one at L3/4. Normalisation of lordosis was noted at all spinal levels, including those distant from the surgical site. Global lumbar lordosis decreased from a median of 66° to 50° (p < 0.001). All segmental levels showed significant reductions in lordotic angle (p < 0.05), with the greatest proportional change at L1/2 and the largest angular correction at L5/S1. Conclusions This study is the first to demonstrate that surgical reduction of isthmic spondylolisthesis can restore global sagittal harmony by correcting the compensatory hyperlordosis across all lumbar segments.