Effect of Cage Material and Size on Fusion Rate and Subsidence Following Biportal Endoscopic Transforaminal Lumbar Interbody Fusion

Objective: Biportal endoscopic transforaminal lumbar interbody fusion (BE-TLIF) is an emerging, minimally invasive technique performed under biportal endoscopic guidance. However, concerns regarding cage subsidence and sufficient fusion during BE-TLIF necessitate careful selection of an appropriate interbody cage to improve surgical outcomes. This study compared the fusion rate, subsidence, and other radiographic parameters according to the material and size of the cages used in BE-TLIF.

Methods: In this retrospective cohort study, patients who underwent single-segment BE-TLIF between April 2019 and February 2023 were divided into 3 groups: group A, regular-sized three-dimensionally (3D)-printed titanium cages; group B, regular-sized polyetheretherketone cages; and group C, large-sized 3D-printed titanium cages. Radiographic parameters, including lumbar lordosis, segmental lordosis, anterior and posterior disc heights, disc angle, and foraminal height, were measured before and after surgery. The fusion rate and severity of cage subsidence were compared between the groups.

Results: No significant differences were noted in the demographic data or radiographic parameters between the groups. The fusion rate on 1-year postoperative computed tomography was comparable between the groups. The cage subsidence rate was significantly lower in group C than in group A (41.9% vs. 16.7%, p=0.044). The severity of cage subsidence was significantly lower in group C (0.93±0.83) than in groups A (2.20±1.84, p=0.004) and B (1.79±1.47, p=0.048).

Conclusion: Cage materials did not affect the 1-year postoperative outcomes of BE-TLIF; however, subsidence was markedly reduced in large cages. Larger cages may provide more stable postoperative segments.