Comparative analysis of single vs. double cage insertion in unilateral biportal endoscopic lumbar interbody fusion: clinical and radiological outcomes

Objective To compare clinical and radiological outcomes of single vs. double cage insertion in unilateral biportal endoscopic lumbar interbody fusion (UBE-LIF) for lumbar degenerative diseases (LDD). Methods This retrospective study analyzed 103 LDD patients undergoing UBE-LIF from June 2021 to June 2023, with 1:3 matching for age, sex, and operative level, forming unilateral cage (Group S, n = 51) and bilateral cage (Group D, n = 17) groups. Outcomes included fusion rates (assessed by lumbar CT at 1 and 2 years), perioperative metrics (surgical time, estimated blood loss [EBL], hospital stay), postoperative cage subsidence, complications, and patient-reported outcomes (VAS back/leg, ODI, SF-12 PCS). Statistical analyses used Student's t-tests and Fisher's exact tests ( p < 0.05). Results Groups were similar in age, sex, BMI, smoking status, diabetes, and fusion level, except Group D had lower BMD (−1.7 ± 0.3 vs. −1.3 ± 0.5, p = 0.005). Group D had longer surgical time (204.1 ± 36.1 vs. 157.6 ± 16.2 min, p < 0.001) and higher EBL (150.0 ± 76.8 vs. 106.8 ± 26.8 mL, p = 0.001). Postoperative cage subsidence was significantly more frequent in the single-cage group (17/51, 33.3%) than in the double-cage group (1/17, 5.9%; p = 0.029). Fusion rates were comparable at 1 year (94.1% vs. 88.2%, p = 0.675) and 2 years (100% vs. 98.0%, p = 1.000), with Group D showing a numerically higher 1-year rate. Group D had lower VAS back scores at 6 months (1.8 ± 0.9 vs. 2.4 ± 1.0, p = 0.041). Complication rates and hospital stay were similar. Conclusion Single-cage UBE-LIF offers comparable fusion rates and clinical outcomes with reduced surgical time and blood loss, despite a higher incidence of cage subsidence. Double-cage insertion may provide advantages in early stability and lower subsidence risk, making it preferable in select patients with lower BMD. Both techniques yield favorable long-term results in UBE-LIF for lumbar degenerative diseases.