Lordotic restoration: A comparison of transforaminal lumbar interbody fusion expandable and static cages at the lumbosacral junction

Background: L5-S1 is a challenging level for achieving fusion, where traditional transforaminal lumbar interbody fusion (TLIF) techniques may fail to maintain disc height and lordosis. Expandable cages, offering in situ expansion, may improve radiographic outcomes. Their use specifically at L5-S1 has not been previously studied. Methods: We retrospectively reviewed patients ≥18 years who underwent TLIF at L5-S1 between January 2015 and September 2023. Patients were grouped by cage type (expandable vs. static). Radiographic data included anterior and posterior disc heights, disc angle, L5-S1, L4-S1, and L1-S1 sagittal lordotic angles, and lumbar distribution index. Measurements were recorded preoperatively and at two postoperative intervals. Results: A total of 43 patients were analyzed (15 expandable, 28 static). At baseline, the expandable group had greater posterior disc height (5.03 mm vs. 3.06 mm, P < 0.001). At first follow-up, expandable cages showed higher anterior disc height (18.86 mm vs. 11.80 mm, P < 0.001), posterior disc height (7.80 mm vs. 5.30 mm, P < 0.001), and disc angle (16.27° vs. 11.82°, P = 0.040). From preoperative to final follow-up, expandable cages had greater gains in anterior disc height (9.22 mm vs. 3.27 mm, P < 0.001), disc angle (7.84° vs. 0.24°, P = 0.002), and L5-S1 lordosis (7.03° vs. 0.81°, P = 0.012). Conclusions: Expandable TLIF cages at L5-S1 offer significantly improved radiographic correction over static cages, addressing key limitations of traditional posterior approaches.