Use of Double Cages for Biportal Endoscopic Transforaminal Lumbar Interbody Fusion: A Comparison of 3-Dimensional-Printed Titanium and Polyetheretherketone Cages

<h3>Background</h3> This study aimed to compare a 3-dimensional (3D)–printed titanium cage with a polyetheretherketone (PEEK) cage in biportal endoscopic transforaminal lumbar interbody fusion (BETLIF) using a double cage construct, evaluate differences in fusion stability and subsidence between the 2 cage types, and analyze factors influencing subsidence. <h3>Methods</h3> We retrospectively examined 89 patients who underwent BETLIF using a double cage (3D-printed titanium, 48 levels; PEEK, 46 levels). Fusion status and subsidence were assessed using dynamic plain lateral lumbar spine radiographs and computed tomography images at 6 months and 1 year postoperatively. Fusion was graded according to the Bridwell system, and significant subsidence was defined as ≥2 mm endplate depression on computed tomography. Demographic and clinical variables, including age, sex, body mass index, American Society of Anesthesiologists classification, history of tobacco smoking, diabetes mellitus, bone mineral density measured using dual-energy x-ray absorptiometry, cage length, and cage material, were collected and analyzed as potential risk factors. <h3>Results</h3> At 1-year follow-up, fusion grades were I (75.0%, 36 levels), II (20.8%, 10 levels), and III (4.2%, 2 levels) for 3D-printed titanium and I (53.2%, 25 levels), II (40.4%, 19 levels), and III (6.4%, 3 levels) for PEEK. The overall fusion rate (grades I and II) was similar for both cages (95.8% vs 93.6%, <i>P</i> = 0.629), but grade I was more prevalent with 3D-printed titanium than with PEEK (75.0% vs 53.2%, <i>P</i> = 0.027). No significant differences were observed in subsidence or complications between the 2 cages. Multivariate analysis revealed age as the only variable significantly associated with subsidence in BETLIF. <h3>Conclusions</h3> Both double 3D-printed titanium and PEEK cages demonstrated high fusion rates with no significant differences in overall success. However, double 3D-printed titanium cages showed better early fusion grades and comparable subsidence to that of PEEK cages. Although long-term follow-up is necessary to ascertain efficacy, these findings suggest that 3D-printed titanium cages offer advantages in early fusion quality in BETLIF. Further research is needed to optimize cage arrangement, cage design, and surgical techniques to improve outcomes. <h3>Clinical Relevance</h3> The use of double 3D-printed titanium cages is recommended in BETLIF. <h3>Level of Evidence</h3> 3.