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

  • International Journal of Spine Surgery
  • October 2025,
  • 19
  • (5)
  • 611-624;
  • DOI: https://doi.org/10.14444/8788

Abstract

Background 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.

Methods 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.

Results 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%, P = 0.629), but grade I was more prevalent with 3D-printed titanium than with PEEK (75.0% vs 53.2%, P = 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.

Conclusions 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.

Clinical Relevance The use of double 3D-printed titanium cages is recommended in BETLIF.

Level of Evidence 3.

Introduction

Endoscopic spine surgery techniques for discectomy have been used for decades;1–3 however, lumbar fusion using these techniques gained wider recognition in 1996.4 Endoscopic lumbar interbody fusion (ELIF) is a minimally invasive approach for treating degenerative lumbar conditions that require stabilization. Compared with conventional open operations, minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) using a muscle-sparing tubular retractor leads to better outcomes and reduced hospital stays, surgical morbidity, and approach-related complications.5,6 However, MIS-TLIF remains challenging for surgeons in performing neural decompression, disc removal, and endplate preparation owing to limited anatomic visualization and decreased haptic feedback.7 Endoscopic spine surgery offers a smaller surgical footprint than MIS, minimizing tissue disruption, intraoperative blood loss, and hospital stays.8–12 Furthermore, endoscopic procedures can be performed under conscious sedation, which has enhanced patient satisfaction.13,14

The unilateral biportal endoscopic TLIF (BETLIF) is a leading alternative to ELIF.15 This method improves ergonomics and is comparable to the full-endoscopic uniportal approach by isolating the working portal from the endoscope. Unlike uniportal operations, BETLIF does not require specialized tools, as the working and viewing portals can be interchanged as necessary. Moreover, BETLIF does not require tubular retractors and is performed through 2 separate portals with continuous saline irrigation, which helps control bleeding and remove debris and bone fragments. The 4-mm diameter of the endoscope allows it to reach deep structures such as the neural foramen and contralateral lateral recess, providing a bright, clear, and enlarged operative field that enhances the surgeon’s ability to perform delicate procedures with a reduced risk of neural damage.

Recent studies have explored biportal endoscopy in lumbar interbody fusion surgery.16–21 However, most studies have used polyetheretherketone (PEEK) cages for interbody fusion, with limited reports on fusion rates assessed through computed tomography (CT).16–21 Heo and Park21 reported a 78.3% successful fusion rate based on serial radiography, whereas Kang et al17 reported 87.7% at 1 year postoperatively based on CT. Recently, a double cage combining a PEEK cage with another PEEK cage covered with titanium plates achieved a successful fusion rate of 93.3%.18

Additionally, cage subsidence should be carefully evaluated because endplate preservation is crucial for BETLIF. Various cages are currently used for endoscopic fusion, and efforts to increase fusion rates and prevent subsidence are ongoing. However, no research has been conducted on double cages with 3-dimensional (3D)-printed titanium. Therefore, this study aimed to introduce an optimized double cage strategy using a 3D-printed titanium cage for BETLIF and to compare its fusion stability and subsidence risk with those of conventional PEEK cages.

Methods

Participants

Patients from 5 neurosurgical spine specialties participated in an Institutional Review Board–approved retrospective assessment of a prospectively gathered database at a spine facility. Data from 89 consecutive patients who underwent BETLIF between the L2 and S1 levels between January 2020 and May 2023 were included.

Demographic variables were collected from a retrospective medical record review and included age, sex, body mass index (BMI), American Society of Anesthesiologists (ASA) classification, bone mineral density (BMD), and the presence of comorbidities (history of tobacco smoking, diabetes mellitus (DM), and osteoporosis or osteopenia). These patients had been followed up for more than 1 year, and data on perioperative, clinical, and radiological conditions were collected. Forty-six patients underwent BETLIF with a 3D-printed titanium cage (Lumbar 3D Cage, Genoss, Suwon, Kyunggi-do, Korea), and 43 underwent BETLIF with a PEEK cage (IVA posterior lumbar interbody fusion cage, Huvexel, Seongnam-si, Kyunggi-do, Korea). Despite receiving conservative therapy for 3 months, all patients continued to experience radiating pain in the lower limbs and back. These patients had spondylolisthesis, instability, recurrent herniated discs, and spinal stenosis (central or foraminal). However, anti-osteoporotic medications with anabolic effects, such as teriparatide and romosozumab, were not administered. The appropriate Institutional Review Board approved this study (No. 2024-W03) and waived the requirement for informed consent as it involved the use of anonymous secondary data published for research purposes.

Preparation of 3D-Printed Titanium Cage

We used a 3D-printed titanium cage (Lumbar 3D Cage, Genoss, Suwon, Kyunggi-do, Korea) based on the size of the patient’s disc (Figure 1). The metal powder bed fusion technology used to create this 3D model is often referred to as the Selective Laser Melting 3D printer (EOSINT-M280, EOS GmbH, Munich, Germany).22 This cage has a mean pore size of 1100 μm and a mean porosity of 70%. A straight bullet type was used for the PEEK and the 3D-printed titanium cages. Patients’ anatomical features were considered while measuring and applying the height and length of the cages.

Interbody cages. (A) A polyetheretherketone cage (IVA posterior lumbar interbody fusion cage, Huvexel, Seongnam-si, Kyunggi-do, Korea) and (B) a 3-dimensional (3D)–printed titanium cage (Lumbar 3D Cage, Genoss, Suwon, Kyunggi-do, Korea) (B). The 3D-printed cage has an internal lattice-like structure.
Figure 1

Interbody cages. (A) A polyetheretherketone cage (IVA posterior lumbar interbody fusion cage, Huvexel, Seongnam-si, Kyunggi-do, Korea) and (B) a 3-dimensional (3D)–printed titanium cage (Lumbar 3D Cage, Genoss, Suwon, Kyunggi-do, Korea) (B). The 3D-printed cage has an internal lattice-like structure.

Evaluation of Radiological and Clinical Results

The patients’ records were assessed. Dynamic plain lateral radiographs and CT scans were performed 6 months and 1 year postoperatively, respectively (Figure 2). The Bridwell fusion grading system was applied to the CT scans to evaluate bone fusion at these intervals.23 The grades were defined as follows: grade I, fusion with trabecular bone formation; grade II, graft intactness without complete remodeling or lucency; grade III, graft intactness with lucency above and below; and grade IV, no fusion with graft collapse or resorption (Figure 3). The fusion rate was calculated based on the total number of grades I and II. The CT data at the 1-year mark were examined to confirm the subsidence grade. Dual-energy x-ray absorptiometry results were also collected for analysis. The width and length of the cage were obtained from the intraoperative implant log. For bone graft materials, we used a total of 5 mL of demineralized bone matrix (DBM) putty (Grafton, Medtronic, Memphis, TN, USA) inside the cages and a mixture of DBM putty and local autografts outside the cages for each level. We defined “subsidence” as a segmental vertebral endplate decrease of 2 mm or more, depending on the depth of cage migration into the endplate on coronal or sagittal CT images. Significant subsidence ≥2 mm was considered clinically relevant.24

Fusion evaluation was used to assess a successful fusion with dynamic plain radiography and computed tomography (CT) at 6 mo and 1 y postoperatively. (A and B) Flexion-extension plain x-ray images at 6 mo postoperatively. (C) CT scan at 6 mo postoperatively.
Figure 2

Fusion evaluation was used to assess a successful fusion with dynamic plain radiography and computed tomography (CT) at 6 mo and 1 y postoperatively. (A and B) Flexion-extension plain x-ray images at 6 mo postoperatively. (C) CT scan at 6 mo postoperatively.

The Bridwell grading system is used to evaluate fusion grade. The bottom row is a PEEK cage, while the top row is a 3-dimensional–printed titanium cage. The grades are (A) grade I, (B) grade II, and (C) grade III. Fusion is ranked from I to IV: I represents fusion with remodeling and trabeculae; II represents graft intactness, not entirely remodeled and integrated, but without lucency; III represents graft intactness, with possible lucency at the top and bottom of the graft; and IV represents fusion absence with graft collapse or resorption. Solid fusion is classified as grade I and II in the Bridwell grading system based on radiological results. The present study did not have any grade IV data.
Figure 3

The Bridwell grading system is used to evaluate fusion grade. The bottom row is a PEEK cage, while the top row is a 3-dimensional–printed titanium cage. The grades are (A) grade I, (B) grade II, and (C) grade III. Fusion is ranked from I to IV: I represents fusion with remodeling and trabeculae; II represents graft intactness, not entirely remodeled and integrated, but without lucency; III represents graft intactness, with possible lucency at the top and bottom of the graft; and IV represents fusion absence with graft collapse or resorption. Solid fusion is classified as grade I and II in the Bridwell grading system based on radiological results. The present study did not have any grade IV data.

Surgical Technique of Biportal Endoscopic TLIF Using a Double Cage

The BETLIF technique uses a double cage. The patient’s disc height at the surgical level guided the selection of cage height. Two ports were created around the operative level to accommodate BETLIF. An endoscopic visualization portal was created near the lateral boundary of the pedicle, and a functional gateway was created at the lateral boundary of the pedicle (Figure 4A). The skin incision length of the endoscopic viewing portal was 5 mm. However, the working portal length was approximately 20 mm (Figure 4A). A working sheath was often introduced to facilitate the smooth insertion of spinal devices and ensure effective drainage of saline irrigation (Figure 4B). The right lamina and facet joint were dissected and made visible if a right-sided BETLIF of L4 to L5 was performed. A unilateral laminotomy for bilateral decompression from L4 to L5, along with a right L4 to L5 facetectomy, was also performed. The bilateral ligamentum flavum was resected to decompress the central canal and treat the lateral recess stenosis (Figure 5). A complete discectomy was performed using various shavers and pituitary forceps, along with dissectors and curettes to separate the cartilaginous endplate from the osseous endplates (Figure 5D). Endplate preparation was completed using an enlarged endoscopic view, and subsequent procedures were guided by C-arm imaging.

Biportal endoscopic transforaminal lumbar interbody fusion skin incision sites. (A) The skin incision location for the endoscopic viewing portal is shown by the black line, while the skin incision point for the working portal is indicated by the white line. Using 2 portals and a C-arm fluoroscopic radiography picture (B), a working sheath is inserted into the working portal.
Figure 4

Biportal endoscopic transforaminal lumbar interbody fusion skin incision sites. (A) The skin incision location for the endoscopic viewing portal is shown by the black line, while the skin incision point for the working portal is indicated by the white line. Using 2 portals and a C-arm fluoroscopic radiography picture (B), a working sheath is inserted into the working portal.

Intraoperative endoscopic images of biportal endoscopic transforaminal lumbar interbody fusion. Fully decompressive status of the right ipsilateral traversing nerve root (A), contralateral traversing nerve root (B), central canal (C), and endoscopic endplate preparation image (D). The cartilaginous endplate is separated from the osseous endplate using a dissector.
Figure 5

Intraoperative endoscopic images of biportal endoscopic transforaminal lumbar interbody fusion. Fully decompressive status of the right ipsilateral traversing nerve root (A), contralateral traversing nerve root (B), central canal (C), and endoscopic endplate preparation image (D). The cartilaginous endplate is separated from the osseous endplate using a dissector.

The dura and traversing nerve root were medially retracted using a probe to protect the exiting nerve root using a scope cannula self-retractor. For each single-level fusion, a total of 5 mL of DBM was used. DBM was packed primarily into the cage cavities, and any remaining DBM was mixed with local autograft bone harvested from the decompressed lamina or facet. This mixture was placed into the residual disc space and used to seal the rims around the cages.

The initial cage serves as a spacer to maintain the disc space, allowing bone grafts to be placed in the remaining disc area. The first cage was obliquely inserted deep into the midline and contralateral sides (Figure 6A) and repositioned longitudinally on the contralateral side (Figure 6B) using cage impactors. The trial cage was inserted contralaterally to advance the first cage. A funnel was used to impact bone transplants into the disc space (Figure 6C). The second cage was inserted vertically while protecting the ipsilateral nerve roots (Figure 6D). The cage was positioned on both peripheries, including the anterior endplate ring apophysis. A Hemovac drainage catheter was inserted, and percutaneous pedicle screws were placed under C-arm fluoroscopic guidance. Dorsal compression was applied before the final tightening of the set caps to optimize lordosis.

Surgical steps of 2-cage insertion during biportal endoscopic transforaminal lumbar interbody fusion. (A) The first cage is obliquely inserted deeply into the contralateral disc space. (B) The cage is repositioned under endoscopic view. (C) A funnel may be used to impact bone transplants into the disc space. (D) The second cage is inserted vertically while protecting the nerve roots in the ipsilateral direction.
Figure 6

Surgical steps of 2-cage insertion during biportal endoscopic transforaminal lumbar interbody fusion. (A) The first cage is obliquely inserted deeply into the contralateral disc space. (B) The cage is repositioned under endoscopic view. (C) A funnel may be used to impact bone transplants into the disc space. (D) The second cage is inserted vertically while protecting the nerve roots in the ipsilateral direction.

Statistical Analysis

Data were analyzed using IBM SPSS Statistics version 25 (IBM Corp, Armonk, NY, USA). Subsidence was compared at 6 and 12 months postoperatively. Univariate analyses assessed the relationship between subsidence outcomes and the cage type, smoking status, patient age, BMI, ASA classification, DM, osteopenia, and osteoporosis. Comparisons among the factors were made using the χ 2 test and the Wilcoxon rank-sum test.

Binarized subsidence outcomes were analyzed using multivariate logistic regression, incorporating covariates such as cage material, osteoporosis, cage length, and patient age. Wald tests assessed the significance of odds ratio parameter estimates, with statistical significance set at P < 0.05 and no multiplicity adjustments.

Results

This study included 89 patients (26 men and 63 women). The initial therapy and demographic information are presented in Table 1. The mean patient age at the time of surgery was 66.0 years. Each level was treated with 2 cages for 1- or 2-level fusion in each patient. The groups receiving 3D-printed titanium and PEEK implants were closely matched, with 48 and 47 individuals, respectively, resulting in a total of 95 fusions. Notably, 7.9% were smokers, 69.5% had osteopenia or osteoporosis, 29.2% had DM, and 18.9% had a prior diagnosis of osteoporosis. Table 2 provides the baseline demographic and treatment group comparisons.

View this table:
Table 1

Summary of demographic and treatment data of study participants.

View this table:
Table 2

Group comparisons of demographic and clinical data of study participants.

The groups were well-matched regarding follow-up duration, sex, age, ASA classification, DM, tobacco use, cage length, and group size, with no significant differences. The PEEK group had a slightly higher incidence of osteopenia or osteoporosis than the 3D-printed titanium group, but the difference was not statistically significant (P = 0.718). The mean follow-up period was 66.3 weeks. The BMD, BMI, DM, and clinical outcomes (Oswestry Disability Index [ODI] and visual analog scale [VAS] score) did not vary significantly (Table 2).

Bridwell fusion grade was used to assess successful fusion using dynamic plain x-ray and CT. At the 1-year follow-up, successful fusion was observed in 46 (95.8%) 3D-printed titanium levels and 44 (93.6%) PEEK levels. The differences were not statistically significant at 6 months and 1 year postoperatively (87.5% vs 83.0%, P = 0.534; 95.8 % vs 93.6%, P = 0.629, respectively). However, the precise fusion grades varied. At the 6-month follow-up, grades I, II, and III were 25.0%, 62.5%, and 12.5%, respectively, in the 3D-printed titanium cage, which changed to 75.0%, 20.8%, and 4.2%, respectively, at 1 year. For the PEEK cage, grades I, II, and III were 17.0%, 66.0%, and 17.0%, respectively, at 6 months and 53.2%, 40.4%, and 6.4%, respectively, at 1 year. No grade IV fusions were observed in either group (Table 3). At 1-year follow-up, grade I for the 3D-printed titanium cage was significantly higher than that for the PEEK cage (75.0% vs 53.2%, P = 0.027), whereas grade II was significantly lower (20.8% vs 40.4%, P = 0.038; Table 3).

View this table:
Table 3

Radiological parameters of study participants.

Subsidence occurred in 12 levels (25.0%) of the 3D-printed titanium cage and 10 levels (21.3%) of the PEEK cage. Although the titanium cage showed a substantially higher subsidence rate at 1-year follow-up, this difference was not statistically significant (25.0% vs 21.3%, P = 0.667). In the univariate analysis of BETLIF, poorer BMD (T score ≤ −1.0, P = 0.050) was borderline significant, whereas poorer BMD (T score ≤ −2.5, P = 0.017) and older age at surgery (P = 0.010) were significantly associated with higher subsidence at 1 year. No greater subsidence was observed compared with that in patients with smoking history, BMI, ASA class, DM, and cage length.

Age was the only variable significantly associated with binarized subsidence in multivariate analysis (Table 4), indicating an increased probability of subsidence by a factor of 1.08 for each yearly increase in age over the 12-month period.

View this table:
Table 4

Multivariate analysis of subsidence at 12 mo.

No difference was observed in the subsidence rate among 4 of the 5 surgeons. However, for one surgeon who performed 5 BETLIF surgeries, the 1-year subsidence rate was 60% (3/5; P = 0.045).

No statistically significant difference was observed in clinical results (VAS or ODI) between the 3D-printed titanium cage group and the PEEK cage group at the 1-year follow-up (Table 2). The improvement in the VAS score between the subsidence group and the nonsubsidence group was not significantly different at the 1-year follow-up (Table 5). The improvement in the ODI scores was not significantly different between the 2 groups.

View this table:
Table 5

VAS and ODI Scores of subsidence and non-subsidence groups.

Complications included epidural hematoma in 3 cases (3.4%), dural tear in 4 cases (4.5%), and pedicle screw malposition in 1 case (1.1%). One patient was converted to open microscopic surgery for dural repair. One patient underwent surgical revision for hematoma evacuation and adjustment of a pedicle screw. No posterior cage migration or pedicle screw loosening was observed.

Discussion

In the early 2000s, a trend emerged favoring spinal implants with a lower modulus of elasticity to align the stiffness of the implant with the bone. During this period, PEEK use increased. The final rigidity of any biomaterial used in spinal implants varies based on production processes; however, Heary et al determined the elastic moduli of titanium and pure PEEK using load-displacement curves at 50.20 and 3.84 gigapascals, respectively.25 A significant mismatch between the implant and the bone may cause stress shielding and prompt bone remodeling, potentially accelerating implant subsidence.26,27

Despite their benefits, PEEK implants have limitations. A PEEK halo effect, attributed to a biofilm layer and poor osseointegration at the closest vertebral endplate, has been reported.28 According to an assessment of dental implants, PEEK is inferior to titanium in terms of implant osteoconductivity and bioactivity.29 Basic science reports have shown that titanium surfaces are superior to PEEK in achieving osseointegration, particularly when the right surface topography is present.30,31

Solid titanium cages have a higher fusion rate than PEEK interbody cages32 but are limited by their high elastic modulus and subsidence rate,33–35 prompting a shift toward PEEK. Titanium-coated PEEK implants aim to combine the advantages of both materials; however, compared with titanium implants, these hybrid devices do not offer an advantage in reducing subsidence32,36 and are associated with a surface coating delamination risk after implantation.37

Authors note that amorphous or modified titanium surfaces promote the production of osteogenic and cell-matrix adhesion proteins, which are crucial for bone remodeling and fusion. Studies suggest that these surfaces facilitate early bone formation, resulting in improved clinical outcomes.38,39 Consequently, a 3D-printed titanium cage was created to preserve the biocompatibility of solid titanium and solve the elastic modulus issue.40–42

A comparative study43 showed that fusion grades in 3D-printed titanium cages surpass those in PEEK. Therefore, advancements in 3D printing technology may help to overcome the shortcomings of earlier spinal implants. 3D-printed porous titanium cages perform better in subsidence testing than standard PEEK cages.44,45 They offer superior fusion outcomes and lower subsidence rates owing to their structure and material properties, promoting better bone ingrowth and stability.34,46 These results may be attributed to the titanium cage’s porous structure, derived from 3D printing technology, which resembles physiological cancellous tissue.47 These features promote osseous integration and demonstrate high biocompatibility.48,49

Biportal endoscopy has recently emerged as a prominent minimally invasive technique. It has been used in various MIS spinal decompression procedures, such as laminotomy for lumbar discectomy, bilateral-contralateral decompression, unilateral laminotomy for bilateral decompression, and unilateral foraminotomy for foraminal decompression, all of which exhibit high clinical effectiveness.50–54 This technique is now expanding to the thoracic and cervical regions.55,56

Furthermore, biportal endoscopic procedures may be used for ELIF.57 The uniportal endoscopic technique is technically more challenging than the biportal method, as the surgical instruments are restricted to a rigid working channel, with the surgeon’s hands, instruments, and endoscopic vision aligned on the same axis. In contrast, the biportal approach allows the surgeon to handle the endoscope and surgical tools separately, allowing for a magnified, bloodless surgical field that facilitates efficient disc removal without the need for precise instrument control.

BETLIF utilizes biportal endoscopy to perform facetectomy and cage insertions along the same corridor as the MIS-TLIF.17,21 Therefore, both BETLIF and MIS-TLIF demonstrate similar fusion rates and favorable clinical outcomes. However, BETLIF is associated with reduced early postoperative back pain compared with MI-TLIF, potentially enabling earlier ambulation and a shorter hospitalization period.17,58–60 This advantage may be attributed to the small intraoperative incision and limited soft tissue damage associated with the BETLIF technique. However, the removal of the graft material due to constant irrigation throughout the operation remains a concern. A study by Park et al61 revealed decreased instances of definite fusion and increased instances of uncertain fusion after BETLIF. Therefore, the BETLIF technology has been applied in several pioneering studies to increase the fusion rate and reduce subsidence. A large cage footprint lowers the risk of cage subsidence, as it improves segmental stability,19,62 and efforts are ongoing to increase fusion rates. Notably, BETLIF has been attempted using large cages; however, inserting a large-sized cage in the upper lumbar spine is limited and carries the risk of nerve damage.16 Our double cage insertion method mitigates the risk of neurological damage and postoperative complications associated with overretraction during large cage insertion. The 2-cage technology enables the use of a large cage floor area while mitigating the risk of neurological problems associated with excessive retraction. Its design effectively doubles the cage footprint, distributing the load across the endplate.18,63,64

An issue that may hinder the effectiveness of interbody fusion is the quantity of bone grafts in the disc space.65 Typically, a limited bone graft within the cages prevents it from dislodging while tapping the cage into the disc area. This underscores the significance of bone grafting outside the cage. However, only a small amount of bone graft remains in the disc space because the outer cage bone grafts are often placed in the collapsed disc area before inserting the cage. In our investigation, the use of more bone grafts might have affected the disc space because of the sequential insertion of the double cages. Before installing the second cage, the surgeon may place an extra bone graft in the vacant disc space because of the placement of the first cage as the disc spacer.

Therefore, a significant volume of the bone graft facilitates bone fusion by increasing the contact between the exposed bony endplates and the bone graft. Additionally, successful fusion offers strong anterior support.66,67

The most typical postoperative issue is cage subsidence. Depending on the types of cages used, the surgical methods, the length of follow-up, and the imaging assessment tools, the incidence may vary from 12.1% to 70%.68 Mild cage subsidence is a typical spinal fusion condition that has no bearing on the course of treatment.69 However, recent research indicates that postoperative disc height collapse and loss of lumbar lordosis are associated with considerable cage subsidence (≥2 mm), resulting in recurring complaints and unfavorable outcomes.43 One essential risk factor for cage subsidence is endplate damage.70,71 Furthermore, the importance of endplate preparation quality in preventing pseudoarthrosis and boosting the fusion rate has been observed in earlier research.72 The key to accelerating fusion and avoiding cage subsidence is appropriately removing the disc material and cartilaginous endplate to reveal the bleeding endplate.73 However, few studies provide applicable methods for avoiding this issue during endplate preparation.

In BETLIF, most endplate preparations use a freer elevator to gently separate the disc from the bony endplate, as traditional serial disc shavers and curettes may be too forceful and risk damaging the endplate. By viewing the endoscope inside the disc space during preparation, surgeons can ensure complete disc removal while preserving the bony endplate. Careful endoscopic observation helps prevent endplate damage, which is a key advantage of biportal endoscopic fusion techniques. BETLIF is particularly encouraging because preserving the endplate is crucial in preventing cage subsidence. Endplate damage is more likely to occur in patients with osteoporosis,74 and BETLIF has the potential to minimize this risk.

The most reliable imaging technique for assessing fusion status is a CT scan.75,76 However, few studies have used CT to assess BETLIF fusion rates.17,19 To the best of the authors’ knowledge, this is the first study to radiologically compare the fusion rate and subsidence between double-cage BETLIF using PEEK cages and 3D-printed titanium cages. We used two 3D-printed titanium cages for BETLIF to determine the best outcome based on previous studies. In our series, the fusion rate reached 95.8% when using the 3D-printed titanium double-cage BETLIF. The high fusion rate was achieved through disc removal, the use of twin cages to extend the cage footprint, and the insertion of a large amount of bone graft into the disc space.

Therapy outcomes indicated significant improvements in VAS scores and ODI. The relationship between cage subsidence and patient-reported outcomes is contentious, with most research indicating that subsidence does not correlate with these results.77,78 The disparity in outcome score improvement may be attributed to its association with reduced disc height in patients who experienced cage subsidence. Reduced disc height may lead to decreased segmental and lumbar lordosis, which may correlate with unfavorable patient-reported outcomes. In the future, the correlation between cage subsidence and lumbar sagittal alignment changes needs further investigation.

Our results also showed no difference in VAS and ODI between the subsidence and the nonsubsidence groups at the 12-month follow-up after surgery. However, in one patient with subsidence of 4 mm or more owing to cage impaction during surgery, low recovery back VAS and ODI were observed at the 6-month follow-up. In BETLIF, the incidence of dural tears may be higher due to the more extensive dural handling required compared with simple decompression or discectomy. Dural tears that occur during endoscopic surgery can be managed by applying a layered fibrin sealant patch, such as Tachosil (Baxter, Deerfield, IL, USA).79 For dural tears smaller than 1.2 cm, covering them with Tachosil alone or with surgical clips is generally sufficient. For most cases involving minimal dural tears, using a layered fibrin patch alone is sufficient.80,81 However, in this study, a dural tear larger than 2 cm occurred in one case owing to the use of a punch during the removal of adhesion flavum. We deemed the use of endoscopic dural suturing to be unstable and switched the procedure to microscopic surgery for dural repair. No specific complications occurred.

The results of the surgery may vary depending on the experience of the surgeon. In our study, 5 surgeons who have performed more than 500 biportal endoscopic surgeries and with at least 6 years of experience in microscopic fusion surgery performed the BETLIF. Less experienced surgeons who performed 5 BETLIFs had a subsidence rate of over 60% (3/5; P = 0.045). These findings highlight the importance of both adequate surgical experience and careful technique to achieve stable outcomes in biportal endoscopic fusion. When inserting the cage, fluoroscopy should be used throughout the insertion process to continuously monitor cage advancement. This approach helps prevent excessive cage impaction into the vertebral body and ensures proper anterior positioning for lumbar lordosis recovery. It also prevents the risk of iatrogenic injury to retroperitoneal organs such as the aorta and inferior vena cava, thus preserving the benefits of endoscopic fusion.

Radiological results demonstrated a minimal incidence of cage subsidence and a good fusion rate. This study demonstrates that using double 3D-printed porous titanium cages in BETLIF can enhance early fusion quality while minimizing subsidence risk, supporting optimal material selection.

This study had some limitations. First, the BETLIF procedure involves a complex set of tasks throughout the operational phase, and no clinical trials have consistently mapped this process. Factors such as patient comorbidities, surgeon expertise, equipment availability, bone graft volume, and case complexity influence the surgical procedure.57,82,83

Second, although numerous factors68,84 influence fusion rate and subsidence, our research did not incorporate other parameters, such as cage location, the extent of disc space distraction, scoliosis, and lordosis correction. The 2 cages were positioned on both peripheries, including the anterior endplate ring apophysis, although the extent of variation was not examined. An oversized cage may increase axial tension at the cage-endplate contact, resulting in more cage subsidence.84 Future studies will aim to quantify side-specific cage positions, the extent of disc space distraction, and their influence on fusion rate and subsidence. Moreover, although the amount of DBM was standardized to 5 mL per level, the volume of autograft bone could vary depending on the anatomical condition and decompression extent of each patient. Therefore, this variability should be considered when interpreting the fusion outcomes.

In the multivariate analysis, only age emerged as a strong predictor to yield a statistically significant outcome. The sample size was inadequate to identify significant differences for this specific variable. A binary subsidence endpoint was used, indicating that the study likely lacked the statistical power to extrapolate these findings to multivariate analysis due to the insufficient sample size.

Conclusion

In conclusion, the overall fusion rate for BETLIF showed no notable differences between 3D-printed titanium and PEEK cages. Although extended clinical follow-up is necessary to identify variations in long-term fusion quality, the fusion grade of 3D-printed titanium cages was superior to that of PEEK cages at the 1-year follow-up. BETLIF using double 3D-printed titanium cages showed similar subsidence results to those using PEEK cages. Age was the strongest indicator of subsidence in BETLIF. Therefore, any research that assesses the effect of PEEK or 3D-printed titanium cages on subsidence must also consider other critical factors. Subsidence in BETLIF should be regarded as a multivariate process rather than a simple outcome of cage selection, involving patient factors and surgeon experience with biportal endoscopic fusion.

Footnotes

  • Funding The authors received no financial support for the research, authorship, and/or publication of this article.

  • Declaration of Conflicting Interests The authors report no conflicts of interest in this work.

  • Institutional Review Board approval The Institutional Review Wiltse Memorial Hospital Board approved this study (No. 2024-W03) and waived the requirement for informed consent as it involved the use of anonymous secondary data published for research purposes.

References

  1. 1.
    ↵
    Kambin P , Sampson S . Posterolateral percutaneous suction-excision of herniated lumbar intervertebral discs. report of interim results [Report of interim results. Clin Orthop Relat Res]. Clin Orthop Relat Res. 1986;207(207):37–43. 10.1097/00003086-198606000-00008
    Google ScholarCrossRefPubMed
  2. 2.
    ↵
    Hijikata S . Percutaneous nucleotomy. a new concept technique and 12 years’ experience. Clin Orthop Relat Res. 1989;(238):9–23. 10.1097/00003086-198901000-00003
    Google ScholarCrossRef
  3. 3.
    ↵
    Mayer HM , Brock M . Percutaneous endoscopic lumbar discectomy (PELD). Neurosurg Rev. 1993;16(2):115–120. 10.1007/BF00258242
    Google ScholarCrossRefPubMed
  4. 4.
    ↵
    Leu HF , Hauser RK . Percutaneous endoscopic lumbar spine fusion. Neurosurg Clin N Am. 1996;7(1):107–117. 10.1016/S1042-3680(18)30410-8
    Google ScholarCrossRefPubMed
  5. 5.
    ↵
    Wu K , Yun Z , Suvithayasiri S , et al . Evolving paradigms in spinal surgery: a systematic review of the learning curves in minimally invasive spine techniques. Neurospine. 2024;21(4):1251–1275. 10.14245/ns.2448838.419
    Google ScholarCrossRef
  6. 6.
    ↵
    Kim CH , Easley K , Lee J-S , et al . Comparison of minimally invasive versus open transforaminal interbody lumbar fusion. Global Spine J. 2020;10(2):143S–150S. 10.1177/2192568219882344
    Google ScholarCrossRef
  7. 7.
    ↵
    Wanderman NR , Francois EL , Nassr A , Sebastian AS . Is minimally invasive transforaminal interbody fusion superior to traditional open technique? Clin Spine Surg. 2018;31(4):139–142. 10.1097/BSD.0000000000000596
    Google ScholarCrossRef
  8. 8.
    ↵
    Kim HS , Wu PH , Jang IT . Current and future of endoscopic spine surgery: what are the common procedures we have now and what lies ahead? World Neurosurg. 2020;140:642–653. 10.1016/j.wneu.2020.03.111
    Google ScholarCrossRef
  9. 9.
    ↵
    Ju CI , Kim P , Seo JH . Full-endoscopic j-shaped transforaminal L5 nerve decompression in bertolotti syndrome. Neurospine. 2024;21(4):1131–1136. 10.14245/ns.2449112.556
    Google ScholarCrossRef
  10. 10.
    ↵
    Lim KT , Nam HGW , Kim SB , Kim HS , Park JS , Park C-K . Therapeutic feasibility of full endoscopic decompression in one- to three-level lumbar canal stenosis via a single skin port using a new endoscopic system, percutaneous stenoscopic lumbar decompression. Asian Spine J. 2019;13(2):272–282. 10.31616/asj.2018.0228
    Google ScholarCrossRef
  11. 11.
    ↵
    Choi G , Pophale CS , Patel B , Uniyal P . Endoscopic spine surgery. J Korean Neurosurg Soc. 2017;60(5):485–497. 10.3340/jkns.2017.0203.004
    Google ScholarCrossRef
  12. 12.
    ↵
    Liawrungrueang W , Cholamjiak W , Sarasombath P , et al . Endoscopic spine surgery for obesity-related surgical challenges: a systematic review and meta-analysis of current evidence. Asian Spine J. 2025;19(2):292–310. 10.31616/asj.2024.0376
    Google ScholarCrossRef
  13. 13.
    ↵
    Butler AJ , Brusko GD , Wang MY . Awake endoscopic transforaminal lumbar interbody fusion: a technical note. HSS J. 2020;16(2):200–204. 10.1007/s11420-020-09748-6
    Google ScholarCrossRef
  14. 14.
    ↵
    Yeung A , Gore S . Endoscopic foraminal decompression for failed back surgery syndrome under local anesthesia. Int J Spine Surg. 2014;8:22. 10.14444/1022
    Google ScholarCrossRefAbstract/Full Text
  15. 15.
    ↵
    Heo DH , Son SK , Eum JH , Park CK . Fully endoscopic lumbar interbody fusion using a percutaneous unilateral biportal endoscopic technique: technical note and preliminary clinical results. Neurosurg Focus. 2017;43(2):E8. 10.3171/2017.5.FOCUS17146
    Google ScholarCrossRef
  16. 16.
    ↵
    Heo DH , Jang JW , Park CK . Enhanced recovery after surgery pathway with modified biportal endoscopic transforaminal lumbar interbody fusion using a large cage. comparative study with minimally invasive microscopic transforaminal lumbar interbody fusion. Eur Spine J. 2023;32(8):2853–2862. 10.1007/s00586-023-07747-9
    Google ScholarCrossRef
  17. 17.
    ↵
    Kang M-S , You K-H , Choi J-Y , Heo D-H , Chung H-J , Park H-J . Minimally invasive transforaminal lumbar interbody fusion using the biportal endoscopic techniques versus microscopic tubular technique. Spine J. 2021;21(12):2066–2077. 10.1016/j.spinee.2021.06.013
    Google ScholarCrossRef
  18. 18.
    ↵
    Pao JL . Biportal endoscopic transforaminal lumbar interbody fusion using double cages: surgical techniques and treatment outcomes. Neurospine. 2023;20(1):80–91. 10.14245/ns.2346036.018
    Google ScholarCrossRef
  19. 19.
    ↵
    Kim J-E , Kim H , Park EJ , Park DK . A comparison of 2 cage sizes in biportal endoscopic transforaminal lumbar interbody fusion. Clin Spine Surg. 2024;37(10):E464–E471. 10.1097/BSD.0000000000001633
    Google ScholarCrossRef
  20. 20.
    ↵
    Park S-M , Park H-J , You K-H , Kim H-J , Yeom JS . Biportal endoscopic lumbar interbody fusion using a large polyetheretherketone cage: preliminary results. Asian Spine J. 2025;19(2):252–258. 10.31616/asj.2025.0010
    Google ScholarCrossRef
  21. 21.
    ↵
    Heo DH , Park CK . Clinical results of percutaneous biportal endoscopic lumbar interbody fusion with application of enhanced recovery after surgery. Neurosurg Focus. 2019;46(4):2019.1.FOCUS18695. 10.3171/2019.1.FOCUS18695
    Google ScholarCrossRef
  22. 22.
    ↵
    Ran Q , Yang W , Hu Y , et al . Osteogenesis of 3D printed porous ti6al4v implants with different pore sizes. J Mech Behav Biomed Mater. 2018;84:1–11. 10.1016/j.jmbbm.2018.04.010
    Google ScholarCrossRef
  23. 23.
    ↵
    Bridwell KH , Lenke LG , McEnery KW , Baldus C , Blanke K . Anterior fresh frozen structural allografts in the thoracic and lumbar spine. do they work if combined with posterior fusion and instrumentation in adult patients with kyphosis or anterior column defects? Spine (Phila Pa 1976). 1995;20(12):1410–1418. 10.1097/00007632-199506020-00014
    Google ScholarCrossRef
  24. 24.
    ↵
    Lin G-X , Quillo-Olvera J , Jo H-J , et al . Minimally invasive transforaminal lumbar interbody fusion: a comparison study based on end plate subsidence and cystic change in individuals older and younger than 65 years. World Neurosurg. 2017;106:174–184. 10.1016/j.wneu.2017.06.136
    Google ScholarCrossRef
  25. 25.
    ↵
    Heary RF , Parvathreddy N , Sampath S , Agarwal N . Elastic modulus in the selection of interbody implants. J Spine Surg. 2017;3(2):163–167. 10.21037/jss.2017.05.01
    Google ScholarCrossRef
  26. 26.
    ↵
    Niu C-C , Liao J-C , Chen W-J , Chen L-H . Outcomes of interbody fusion cages used in 1 and 2-levels anterior cervical discectomy and fusion: titanium cages versus polyetheretherketone (PEEK) cages. J Spinal Disord Tech. 2010;23(5):310–316. 10.1097/BSD.0b013e3181af3a84
    Google ScholarCrossRefPubMed
  27. 27.
    ↵
    Peitgen DS , Innmann MM , Merle C , Gotterbarm T , Moradi B , Streit MR . Periprosthetic bone mineral density around uncemented titanium stems in the second and third decade after total hip arthroplasty: a DXA study after 12, 17 and 21 years. Calcif Tissue Int. 2018;103(4):372–379. 10.1007/s00223-018-0438-9
    Google ScholarCrossRef
  28. 28.
    ↵
    Phan K , Hogan JA , Assem Y , Mobbs RJ . PEEK-halo effect in interbody fusion. J Clin Neurosci. 2016;24:138–140. 10.1016/j.jocn.2015.07.017
    Google ScholarCrossRef
  29. 29.
    ↵
    Najeeb S , Bds ZK , Bds SZ , Bds MSZ . Bioactivity and osseointegration of PEEK are inferior to those of titanium: a systematic review. J Oral Implantol. 2016;42(6):512–516. 10.1563/aaid-joi-D-16-00072
    Google ScholarCrossRef
  30. 30.
    ↵
    Olivares-Navarrete R , Hyzy SL , Gittens RA , et al . Rough titanium alloys regulate osteoblast production of angiogenic factors. Spine J. 2013;13(11):1563–1570. 10.1016/j.spinee.2013.03.047
    Google ScholarCrossRefPubMed
  31. 31.
    ↵
    Rao PJ , Pelletier MH , Walsh WR , Mobbs RJ . Spine interbody implants: material selection and modification, functionalization and bioactivation of surfaces to improve osseointegration. Orthop Surg. 2014;6(2):81–89. 10.1111/os.12098
    Google ScholarCrossRefPubMed
  32. 32.
    ↵
    Massaad E , Fatima N , Kiapour A , Hadzipasic M , Shankar GM , Shin JH . Polyetheretherketone versus titanium cages for posterior lumbar interbody fusion: meta-analysis and review of the literature. Neurospine. 2020;17(1):125–135. 10.14245/ns.2040058.029
    Google ScholarCrossRef
  33. 33.
    ↵
    Chen Y , Wang X , Lu X , et al . Comparison of titanium and polyetheretherketone (PEEK) cages in the surgical treatment of multilevel cervical spondylotic myelopathy: a prospective, randomized, control study with over 7-year follow-up. Eur Spine J. 2013;22(7):1539–1546. 10.1007/s00586-013-2772-y
    Google ScholarCrossRef
  34. 34.
    ↵
    Patel NA , O’Bryant S , Rogers CD , et al . Three-dimensional-printed titanium versus polyetheretherketone cages for lumbar interbody fusion: a systematic review of comparative in vitro, animal, and human studies. Neurospine. 2023;20(2):451–463. 10.14245/ns.2346244.122
    Google ScholarCrossRef
  35. 35.
    ↵
    Tan J-H , Cheong CK , Hey HWD . Titanium (ti) cages may be superior to polyetheretherketone (PEEK) cages in lumbar interbody fusion: a systematic review and meta-analysis of clinical and radiological outcomes of spinal interbody fusions using ti versus PEEK cages. Eur Spine J. 2021;30(5):1285–1295. 10.1007/s00586-021-06748-w
    Google ScholarCrossRef
  36. 36.
    ↵
    Torstrick FB , Klosterhoff BS , Westerlund LE , et al . Impaction durability of porous polyether-ether-ketone (PEEK) and titanium-coated PEEK interbody fusion devices. Spine J. 2018;18(5):857–865. 10.1016/j.spinee.2018.01.003
    Google ScholarCrossRef
  37. 37.
    ↵
    Kienle A , Graf N , Wilke H-J . Does impaction of titanium-coated interbody fusion cages into the disc space cause wear debris or delamination? Spine J. 2016;16(2):235–242. 10.1016/j.spinee.2015.09.038
    Google ScholarCrossRef
  38. 38.
    ↵
    Arts M , Torensma B , Wolfs J . Porous titanium cervical interbody fusion device in the treatment of degenerative cervical radiculopathy; 1-year results of a prospective controlled trial. Spine J. 2020;20(7):1065–1072. 10.1016/j.spinee.2020.03.008
    Google ScholarCrossRef
  39. 39.
    ↵
    Silva‐Bermudez P , Almaguer‐Flores A , Garcia VI , Olivares‐Navarrete R , Rodil SE . Enhancing the osteoblastic differentiation through nanoscale surface modifications. J Biomedical Materials Res. 2017;105(2):498–509. 10.1002/jbm.a.35926
    Google ScholarCrossRef
  40. 40.
    ↵
    Fiani B , Newhouse A , Cathel A , Sarhadi K , Soula M . Implications of 3-dimensional printed spinal implants on the outcomes in spine surgery. J Korean Neurosurg Soc. 2021;64(4):495–504. 10.3340/jkns.2020.0272
    Google ScholarCrossRef
  41. 41.
    ↵
    McGilvray KC , Easley J , Seim HB , et al . Bony ingrowth potential of 3D-printed porous titanium alloy: a direct comparison of interbody cage materials in an in vivo ovine lumbar fusion model. Spine J. 2018;18(7):1250–1260. 10.1016/j.spinee.2018.02.018
    Google ScholarCrossRef
  42. 42.
    ↵
    Sheha ED , Gandhi SD , Colman MW . 3D printing in spine surgery. Ann Transl Med. 2019;7(Suppl 5):S164. 10.21037/atm.2019.08.88
    Google ScholarCrossRef
  43. 43.
    ↵
    Kim D-Y , Kwon O-H , Park J-Y . Comparison between 3-dimensional-printed titanium and polyetheretherketone cages: 1-year outcome after minimally invasive transforaminal interbody fusion. Neurospine. 2022;19(3):524–532. 10.14245/ns.2244140.070
    Google ScholarCrossRef
  44. 44.
    ↵
    Adl Amini D , Okano I , Oezel L , et al . Evaluation of cage subsidence in standalone lateral lumbar interbody fusion: novel 3D-printed titanium versus polyetheretherketone (PEEK) cage. Eur Spine J. 2021;30(8):2377–2384. 10.1007/s00586-021-06912-2
    Google ScholarCrossRef
  45. 45.
    ↵
    Moolman F , kat C-J , Du Plessis A , Khodja M . Comparative analysis of the subsidence of solid polyetheretherketone (PEEK) and 3D printed lattice titanium interbody fusion cages. MATEC Web Conf. 2023;388:01001. 10.1051/matecconf/202338801001
    Google ScholarCrossRef
  46. 46.
    ↵
    Toop N , Dhaliwal J , Grossbach A , et al . Subsidence rates associated with porous 3D-printed versus solid titanium cages in transforaminal lumbar interbody fusion. Global Spine J. 2024;14(7):1889–1898. 10.1177/21925682231157762
    Google ScholarCrossRef
  47. 47.
    ↵
    Wang H , Wan Y , Li Q , et al . Porous fusion cage design via integrated global-local topology optimization and biomechanical analysis of performance. J Mech Behav Biomed Mater. 2020;112:103982. 10.1016/j.jmbbm.2020.103982
    Google ScholarCrossRef
  48. 48.
    ↵
    Li P , Jiang W , Yan J , et al . A novel 3D printed cage with microporous structure and in vivo fusion function. J Biomedical Materials Res. 2019;107(7):1386–1392. 10.1002/jbm.a.36652
    Google ScholarCrossRef
  49. 49.
    ↵
    Lewandrowski KU , Vira S , Elfar JC , Lorio MP . Advancements in custom 3D-printed titanium interbody spinal fusion cages and their relevance in personalized spine care. J Pers Med. 2024;14(8):809. 10.3390/jpm14080809
    Google ScholarCrossRef
  50. 50.
    ↵
    Lee MH , Jang HJ , Moon BJ , et al . Comparative outcomes of biportal endoscopic decompression, conventional subtotal laminectomy, and minimally invasive transforaminal lumbar interbody fusion for lumbar central stenosis. Neurospine. 2024;21(4):1178–1189. 10.14245/ns.2448830.415
    Google ScholarCrossRef
  51. 51.
    ↵
    Lee DH , Lee D-G , Park CK , et al . Saving stabilizing structure treatment with bilateral-contralateral decompression for spinal stenosis in degenerative spondylolisthesis using unilateral biportal endoscopy. Neurospine. 2023;20(3):931–939. 10.14245/ns.2346504.252
    Google ScholarCrossRef
  52. 52.
    ↵
    Lee DH , Park CK , Jang J-W , Lee D-G . Safety and utility of bilateral-contralateral decompression for adjacent segment stenosis after lumbar interbody fusion using unilateral biportal endoscopy. Clin Spine Surg. 2025. 10.1097/BSD.0000000000001777
    Google ScholarCrossRef
  53. 53.
    ↵
    Lee DH , Park CK , Kim J-S , et al . O-arm navigation-based transforaminal unilateral biportal endoscopic discectomy for upper lumbar disc herniation: an innovative preliminary study. Asian Spine J. 2025;19(2):194–204. 10.31616/asj.2025.0072
    Google ScholarCrossRef
  54. 54.
    ↵
    Ham D-W , Lee J , Kwon B-T , Yoo Y , Park S-M , Song K-S . Comparison of postoperative epidural hematoma formation between biportal endoscopic spine surgery and conventional microscopic surgery: a randomized controlled trial. Int J Spine Surg. 2024;18(5):533–539. 10.14444/8578
    Google ScholarCrossRefAbstract/Full TextPubMed
  55. 55.
    ↵
    Akbari KK , Terry THL , Kanade U , Choi J . Clinical outcomes following treatment of cervical spondylotic radiculopathy with cervical posterior decompression using unilateral biportal endoscopic technique: a single center retrospective series of 20 patients. Int J Spine Surg. 2025;19(1):19–26. 10.14444/8690
    Google ScholarCrossRefAbstract/Full TextPubMed
  56. 56.
    ↵
    Jang J-W , Lee D-G , Park C-K . Rationale and advantages of endoscopic spine surgery. Int J Spine Surg. 2021;15(suppl 3):S11–S20. 10.14444/8160
    Google ScholarCrossRefAbstract/Full TextPubMed
  57. 57.
    ↵
    Park H-J , Shin JI , You K-H , et al . Biportal endoscopic transforaminal lumbar interbody fusion: how to improve fusion rate? Int J Spine Surg. 2024;18(5):582–588. 10.14444/8648
    Google ScholarCrossRefAbstract/Full TextPubMed
  58. 58.
    ↵
    Gatam AR , Gatam L , Mahadhipta H , Ajiantoro A , Luthfi O , Aprilya D . Unilateral biportal endoscopic lumbar interbody fusion: a technical note and an outcome comparison with the conventional minimally invasive fusion. Orthop Res Rev. 2021;13:229–239. 10.2147/ORR.S336479
    Google ScholarCrossRef
  59. 59.
    ↵
    Yu Q , Hu X , Pan X , et al . Early efficacy and safety of unilateral biportal endoscopic lumbar interbody fusion versus minimal invasive in the treatment of lumbar degenerative diseases. Clin Spine Surg. 2023;36(8):E390–E396. 10.1097/BSD.0000000000001470
    Google ScholarCrossRef
  60. 60.
    ↵
    Kim J-E , Yoo H-S , Choi D-J , Park EJ , Jee S-M . Comparison of minimal invasive versus biportal endoscopic transforaminal lumbar interbody fusion for single-level lumbar disease. Clin Spine Surg. 2021;34(2):E64–E71. 10.1097/BSD.0000000000001024
    Google ScholarCrossRef
  61. 61.
    ↵
    Park M-K , Park S-A , Son S-K , Park W-W , Choi S-H . Clinical and radiological outcomes of unilateral biportal endoscopic lumbar interbody fusion (ULIF) compared with conventional posterior lumbar interbody fusion (PLIF): 1-year follow-up. Neurosurg Rev. 2019;42(3):753–761. 10.1007/s10143-019-01114-3
    Google ScholarCrossRef
  62. 62.
    ↵
    Yuan W , Kaliya-Perumal AK , Chou SM , Oh JYL . Does lumbar interbody cage size influence subsidence? a biomechanical study. Spine (Phila Pa 1976). 2020;45(2):88–95. 10.1097/BRS.0000000000003194
    Google ScholarCrossRef
  63. 63.
    ↵
    Han Z , Ma C , Li B , et al . Biomechanical studies of different numbers and positions of cage implantation on minimally invasive transforaminal interbody fusion: a finite element analysis. Front Surg. 2022;9:1011808. 10.3389/fsurg.2022.1011808
    Google ScholarCrossRef
  64. 64.
    ↵
    Suvithayasiri S , Kim Y-J , Liu Y , Lee C , Vasant Khandge A , Kim J-S . Placement of 2 cages using navigation-guided biportal endoscopic transforaminal lumbar interbody fusion: illustrative case. J Neurosurg Case Lessons. 2024;8(8):CASE23512. 10.3171/CASE23512
    Google ScholarCrossRef
  65. 65.
    ↵
    Yoo J-S , Min S-H , Yoon S-H . Fusion rate according to mixture ratio and volumes of bone graft in minimally invasive transforaminal lumbar interbody fusion: minimum 2-year follow-up. Eur J Orthop Surg Traumatol. 2015;25 Suppl 1(suppl 1):S183–9. 10.1007/s00590-014-1529-6
    Google ScholarCrossRef
  66. 66.
    ↵
    Lee J , Lee D-H , Jung C-W , Song K-S . The significance of extra-cage bridging bone via radiographic lumbar interbody fusion criterion. Global Spine J. 2023;13(1):113–121. 10.1177/2192568221993097
    Google ScholarCrossRef
  67. 67.
    ↵
    Lee DH , Lee D-G , Hwang JS , Jang J-W , Maeng DH , Park CK . Clinical and radiological results of indirect decompression after anterior lumbar interbody fusion in central spinal canal stenosis. J Neurosurg Spine. 2021;34(4):564–572. 10.3171/2020.7.SPINE191335
    Google ScholarCrossRef
  68. 68.
    ↵
    Yao Y-C , Chou P-H , Lin H-H , Wang S-T , Liu C-L , Chang M-C . Risk factors of cage subsidence in patients received minimally invasive transforaminal lumbar interbody fusion. Spine (Phila Pa 1976). 2020;45(19):E1279–E1285. 10.1097/BRS.0000000000003557
    Google ScholarCrossRef
  69. 69.
    ↵
    Tempel ZJ , Gandhoke GS , Okonkwo DO , Kanter AS . Impaired bone mineral density as a predictor of graft subsidence following minimally invasive transpsoas lateral lumbar interbody fusion. Eur Spine J. 2015;24 Suppl 3(suppl 3):414–419. 10.1007/s00586-015-3844-y
    Google ScholarCrossRef
  70. 70.
    ↵
    Singhatanadgige W , Sukthuayat A , Tanaviriyachai T , et al . Risk factors for polyetheretherketone cage subsidence following minimally invasive transforaminal lumbar interbody fusion. Acta Neurochir (Wien). 2021;163(9):2557–2565. 10.1007/s00701-021-04923-y
    Google ScholarCrossRef
  71. 71.
    ↵
    Zhou Z-J , Xia P , Zhao F-D , Fang X-Q , Fan S-W , Zhang J-F . Endplate injury as a risk factor for cage retropulsion following transforaminal lumbar interbody fusion: an analysis of 1052 cases. Medicine (Baltimore). 2021;100(5):e24005. 10.1097/MD.0000000000024005
    Google ScholarCrossRef
  72. 72.
    ↵
    Rihn JA , Gandhi SD , Sheehan P , et al . Disc space preparation in transforaminal lumbar interbody fusion: a comparison of minimally invasive and open approaches. Clin Orthop Relat Res. 2014;472(6):1800–1805. 10.1007/s11999-014-3479-z
    Google ScholarCrossRef
  73. 73.
    ↵
    Li H , Zou X , Laursen M , Egund N , Lind M , Bünger C . The influence of intervertebral disc tissue on anterior spinal interbody fusion: an experimental study on pigs. Eur Spine J. 2002;11(5):476–481. 10.1007/s00586-002-0455-1
    Google ScholarCrossRefPubMed
  74. 74.
    ↵
    Park M-K , Kim K-T , Bang W-S , et al . Risk factors for cage migration and cage retropulsion following transforaminal lumbar interbody fusion. Spine J. 2019;19(3):437–447. 10.1016/j.spinee.2018.08.007
    Google ScholarCrossRef
  75. 75.
    ↵
    Carreon LY , Djurasovic M , Glassman SD , Sailer P . Diagnostic accuracy and reliability of fine-cut CT scans with reconstructions to determine the status of an instrumented posterolateral fusion with surgical exploration as reference standard. Spine (Phila Pa 1976). 2007;32(8):892–895. 10.1097/01.brs.0000259808.47104.dd
    Google ScholarCrossRef
  76. 76.
    ↵
    Selby MD , Clark SR , Hall DJ , Freeman BJC . Radiologic assessment of spinal fusion. J Am Acad Orthop Surg. 2012;20(11):694–703. 10.5435/JAAOS-20-11-694
    Google ScholarCrossRefPubMed
  77. 77.
    ↵
    Zhou Q-S , Chen X , Xu L , et al . Does vertebral end plate morphology affect cage subsidence after transforaminal lumbar interbody fusion? World Neurosurg. 2019;130:e694–e701. 10.1016/j.wneu.2019.06.195
    Google ScholarCrossRef
  78. 78.
    ↵
    Oh KW , Lee JH , Lee JH , Lee DY , Shim HJ . The correlation between cage subsidence, bone mineral density, and clinical results in posterior lumbar interbody fusion. Clin Spine Surg. 2017;30(6):E683–E689. 10.1097/BSD.0000000000000315
    Google ScholarCrossRef
  79. 79.
    ↵
    Nam HGW , Kim HS , Park JS , Lee DK , Park C-K , Lim KT . Double-layer tachosil packing for management of incidental durotomy during percutaneous stenoscopic lumbar decompression. World Neurosurg. 2018;120:448–456. 10.1016/j.wneu.2018.09.040
    Google ScholarCrossRef
  80. 80.
    ↵
    Ju CI , Lee SM . Complications and management of endoscopic spinal surgery. Neurospine. 2023;20(1):56–77. 10.14245/ns.2346226.113
    Google ScholarCrossRef
  81. 81.
    ↵
    Park H-J , Kim S-K , Lee S-C , Kim W , Han S , Kang S-S . Dural tears in percutaneous biportal endoscopic spine surgery: anatomical location and management. World Neurosurg. 2020;136:e578–e585. 10.1016/j.wneu.2020.01.080
    Google ScholarCrossRef
  82. 82.
    ↵
    Chung RD , Hunter-Smith DJ , Spychal RT , Ramakrishnan VV , Rozen WM . A systematic review of intraoperative process mapping in surgery. Gland Surg. 2017;6(6):715–725. 10.21037/gs.2017.11.02
    Google ScholarCrossRef
  83. 83.
    ↵
    Lewandrowski K-U , Lorio MP , Burkhardt BW , Vaccaro AR . High-value procedures in endoscopic spine surgery: an analysis of clinical outcomes based on surgeon experience, skill, and training. Int J Spine Surg. 8705. 10.14444/8705
    Google ScholarCrossRef
  84. 84.
    ↵
    Pisano AJ , Steelman T , Wagner S , Helgeson MD , Kang DG . Achieving lumbar interbody fusion: 196. preoperative disc height predicts TLIF cage subsidence. Spine J. 2018;18(8):S96–S97. 10.1016/j.spinee.2018.06.461
    Google ScholarCrossRef
View Abstract
Loading
Loading
PDF
Back to top
In this Issue
International Journal of Spine Surgery

Vol. 19, Issue 5

1 Oct 2025

Table of Contents Index by author

Jump to Section

Keywords

biportal endoscopy, spinal fusion, 3D printing, titanium, osteoporosis, minimally invasive surgery, double cages, upper lumbar