Sagittal Alignment and Clinical Outcomes After Biportal Endoscopic Transforaminal Lumbar Interbody Fusion Using a Single Expandable Cage: One Year Follow-up.

Abstract

Advancements in expandable cage technology may overcome limitations, such as narrow working corridor, continuous irrigation, and endplate injury risk in biportal endoscopic transforaminal lumbar interbody fusion (BE-TLIF). We evaluate sagittal realignment, fusion rates, and clinical outcomes over 1 year using a single bullet-type expandable cage. This retrospective study included 29 patients (38 levels) who underwent BE-TLIF with a single expandable cage and were followed for at least 12 months. Radiological assessments included disc height (DH), segmental lordosis (SL), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), PI-LL mismatch, and cage subsidence. Clinical outcomes were evaluated using back and leg Visual Analog Scale (VAS), Oswestry Disability Index (ODI), 36-Item Short Form Survey (SF-36), and EuroQol-5 Dimension (EQ-5D). Fusion was evaluated using CT based Bridwell classification at 6 and 12 months. At 12 months, the fusion rate was 92.1%, with significant subsidence (≥2 mm) in 3 levels. Anterior and posterior DH increased by 3.97 and 4.22 mm, while SL and LL improved by 3.01° and 5.00°, respectively. Back and leg VAS and ODI decreased by 3.0, 5.0, and 12.76 points, while EQ-5D increased by 5.81 points. Greater PI-LL correction correlated with higher fusion rates and better functional recovery. Patients with preoperative sagittal malalignment showed significant improvements. Cage size and type had limited effect on outcomes. BE-TLIF using a single bullet-type expandable cage achieved favorable outcomes at 1 year, with meaningful sagittal correction and fusion rates, supporting the non-inferiority of this construct in short-segment lumbar fusion.