Comparison between large interbody cage versus two smaller interbody cages in unilateral biportal endoscopic transforaminal interbody fusion

Biportal endoscopic lumbar transforaminal interbody fusion (TLIF) is becoming widespread in the treatment of lumbar degenerative conditions. Ultimately, a successful fusion needs to occur. The properties and effective contact area of the interbody cage are critical for fusion success and stability. This study aimed to isolate the differential influence of cage material and the number of inserts on BELIF outcomes, while maintaining a similar total effective endplate footprint.

A retrospective cohort study of 66 consecutive patients who underwent single-segment BELIF at a single institution between January 2021 and June 2023 were studied. All patients were Class 1 using the MISDEF2 algorithm. There was a minimum 2 year follow up. Patients were divided into two groups based on the interbody cage strategy. Group A utilized two 28 × 10 mm Titanium cages (n = 34), and Group B received a single 40 × 15 mm PEEK cage (n = 32). Clinical outcomes (VAS, ODI) were collected preoperatively, at 2 weeks, and at final follow-up. Radiological outcomes were assessed using the Bridwell Interbody Fusion Grading System and the Marchi system.

Both groups were comparable in terms in demographics and perioperative recovery data. Both groups achieved significant and sustained improvement in all patient-reported outcome measures (P < 0.05), but did not differ between the groups. No major complications with neurological deficit occurred. Both groups demonstrated positive changes in alignment, with no statistically significant difference in the degree of correction between them. Lastly, there was no significant difference in the fusion results between the two groups (Bridwell Grade I or II). One asymptomatic nonunion was found in the large cage group, while none were found in the two cage group at final follow up. Subsidence did not differ between the two groups, 2 cases (5.9%) in the two cage group and 2 cases (6.3%) in the large cage group.

BELIF is an effective minimally invasive surgical technique. More importantly, our findings underscore the paramount importance of the cage footprint, demonstrating that utilizing a large interbody cage-whether a single large PEEK cage or double titanium cages-significantly mitigates the rate of cage subsidence while preserving the excellent clinical efficacy of the procedure. This evidence strongly suggests that maximizing the cage dimensions to enhance endplate contact area represents a crucial biomechanical strategy for improving postoperative stability and securing the long-term success of biportal endoscopic lumbar interbody fusion.