Comparison of index-level reoperation-free survival and complication rates between endoscopic and conventional transforaminal lumbar interbody fusion: a retrospective comparative study in Korea
Article information
Abstract
Study Design
Retrospective comparative study.
Purpose
To compare index-level reoperation-free survival and implant-related complication rates between patients undergoing endoscopic transforaminal lumbar interbody fusion (ETLIF) and conventional open transforaminal lumbar interbody fusion (TLIF) for degenerative lumbar spine disorders.
Overview of Literature
ETLIF is a popular minimally invasive alternative to conventional TLIF for degenerative lumbar spine disorders; however, there are concerns regarding its long-term durability and the risk of reoperation compared with the established open TLIF.
Methods
We retrospectively analyzed clinicodemographic characteristics (including bone mineral density), operative parameters, and implant-related complications of 199 patients who underwent lumbar interbody fusion at two spine centers (ETLIF: n=97; TLIF: n=102). Kaplan-Meier survival analysis and Cox proportional hazards modeling were used to evaluate index-level reoperation rates. Statistical significance was set at p<0.05.
Results
The ETLIF group had a significantly higher rate of index-level reoperation (7.2% vs. 1.0%, p=0.017), longer operative time (182 minutes vs. 162 minutes, p=0.014), and shorter follow-up duration (23.5 months vs. 37.2 months, p=0.001) than the open TLIF group. Kaplan-Meier analysis demonstrated a progressive decline in reoperation-free survival in the ETLIF group, whereas the TLIF group maintained 98.9% survival at 24 months. Cox regression revealed a hazard ratio of 8.34 (95% confidence interval, 1.36–22.20) for ETLIF. Although the ETLIF group showed slightly higher rates of screw loosening, infection, and implant breakage, between-group differences were not statistically significant.
Conclusions
ETLIF was associated with a higher incidence and risk of early index-level reoperation compared to open TLIF, highlighting the need for careful monitoring of initial construct stability in endoscopic fusion. Further studies are required to verify these observations and their clinical implications.
Introduction
Transforaminal lumbar interbody fusion (TLIF) is a widely performed surgical procedure for treating degenerative lumbar spine conditions, including lumbar disc herniation, spinal stenosis, and spondylolisthesis [1–3]. However, in recent years, minimally invasive surgical approaches have gained popularity owing to their potential to reduce postoperative pain, minimize tissue damage, and facilitate quicker recovery. Among these, endoscopic TLIF (ETLIF) represents one of the most advanced techniques; employing full-endoscopic or uniportal/biportal approaches, it allows access to the disc space to perform fusion under direct endoscopic visualization [4–6].
Despite these advantages, there are concerns regarding the long-term durability of ETLIF, particularly related to the risk of surgical complications, mechanical failure, and the need for revision surgery [7–9]. In contrast, conventional open TLIF, though more invasive, has established efficacy with lower rates of mechanical failure [7–9].
Therefore, this study aimed to compare ETLIF versus open TLIF in terms of index-level reoperation-free survival rates. Additionally, we evaluated other clinicodemographic characteristics (including bone mineral density [BMD]), as well as implant-related complications, to provide a comprehensive assessment of both techniques.
Materials and Methods
Study design and patient population
In this retrospective comparative study, we included patients who underwent lumbar interbody fusion for degenerative spinal disorders between January 2019 and May 2024. A total of 199 patients were enrolled, of which 97 underwent ETLIF at a secondary care hospital, and 102 underwent conventional open TLIF at a tertiary academic spine center.
Patients aged ≥50 years, having a confirmed diagnosis of lumbar spinal stenosis, spondylolisthesis, or degenerative disc disease requiring interbody fusion, a minimum follow-up duration of 12 months, and with complete medical records were considered for inclusion. Those with a history of prior lumbar fusion surgery, spinal tumors, infections, trauma, or systemic inflammatory diseases, such as ankylosing spondylitis or rheumatoid arthritis, were excluded.
Surgical techniques
All procedures were performed by experienced spine surgeons. Surgical techniques were standardized within each group and are described as follows:
ETLIF
For ETLIF, a uniportal full-endoscopic interlaminar approach was used under general anesthesia. Patients were positioned prone on a radiolucent table. A single small incision (approximately 1.5 cm) was made lateral to the midline, and a working cannula was inserted under fluoroscopic guidance. After soft tissue dissection, a full-endoscopic system was introduced. First, resection of the inferior articular process and partial laminectomy were performed; subsequently, ligamentum flavum was removed bilaterally to achieve thorough bilateral neural decompression via the unilateral interlaminar route. To access the disc space, the ipsilateral superior articular process (SAP) was resected, creating a transforaminal window. Following discectomy and meticulous endplate preparation, an interbody cage, typically polyetheretherketone or titanium, filled with allogenic and/or local bone graft, was inserted under endoscopic and fluoroscopic visualization. After achieving interbody fusion, percutaneous pedicle screws were inserted bilaterally under fluoroscopic guidance; rods were placed subcutaneously and connected to the screws, and final screw tightening was performed percutaneously.
Conventional TLIF
In the open TLIF group, a standard posterior midline approach was used. A midline skin incision was made, and subperiosteal dissection was carried out to expose the laminae, facet joints, and transverse processes. A bilateral facetectomy, including SAP resection and laminotomy, was performed to access the disc space. Following discectomy and endplate preparation, an interbody cage filled with demineralized bone matrix and/or local bone graft was inserted into the space. Pedicle screws were placed using the freehand technique under direct visualization, and rods were connected bilaterally. All instrumentation was confirmed under intraoperative fluoroscopy. Hemostasis was achieved, and the surgical wound was closed in layers over a subfascial drain.
Postoperative management
Postoperative rehabilitation protocols were similar in both groups, including mobilization on postoperative day one and radiographic follow-up at regular intervals.
Data collection and outcome measures
Patient data regarding demographic variables (age, sex), BMD measured by dual-energy X-ray absorptiometry, levels operated, operation time, and the presence of systemic comorbidities were recorded. Postoperative complications, including surgical site infection, screw loosening, instrument breakage, cage migration, and the need for index-level reoperation, were documented. Reoperation was defined as any subsequent surgery performed at the same level due to nonunion, cage displacement, hardware failure, infection, or recurrent symptoms. Surgeries performed for adjacent segment pathology were explicitly excluded from the analysis.
Statistical analysis
The primary study outcome was time to index-level reoperation, which was analyzed using Kaplan-Meier survival curves, with intergroup comparisons performed using the log-rank test. Hazard ratio (HR) and corresponding 95% confidence interval (CI) were estimated using a Cox proportional hazards regression model. Secondary outcomes included comparisons of age, sex, BMD, and complication rates between the two groups. Continuous variables were analyzed using Welch’s t-test to account for variance inequality; categorical variables were compared using the chi-square or Fisher’s exact test, as appropriate. All statistical analyses were conducted using R ver. 4.3.1 (R Foundation for Statistical Computing, Vienna, Austria). A p-value of <0.05 was considered statistically significant.
Ethics statement
This study was approved by the Institutional Review Board of Pusan National University Hospital (approval no., 1909-001-082) and retrospectively registered as a clinical trial (registration no., NCT04867148). The requirement for informed consent from individual participants was waived owing to the retrospective design of this study.
Results
Patients in the ETLIF group were slightly younger (mean age, 66.8 years) than the open TLIF group (mean age=69.6 years) (Table 1); however, the sex distribution was comparable between the two groups, with females comprising about 65% of the ETLIF group and 59% of the open TLIF group. The two groups showed a statistically significant difference in terms of mean BMD (ETLIF: 0.820 g/cm2; TLIF: 0.848 g/cm2); however, this difference was clinically modest. The mean number of levels operated was 1.2±0.5 in the ETLIF group and 1.6±0.9 in the TLIF group, demonstrating a statistically significant between-group difference (p=0.01). The average operative time was 182±60 minutes in the ETLIF group and 162±40 minutes in the TLIF group; this difference was statistically significant (p=0.014). Regarding follow-up, the ETLIF group had a mean follow-up duration of 23.5±10.3 months, whereas patients in the TLIF group were followed up for a significantly longer duration (mean duration, 37.2±13.0 months; p=0.001).
Details of the patients
Seven patients in the ETLIF group and one patient in the open TLIF group underwent index-level reoperation during the follow-up period. A detailed breakdown of cases with index-level reoperation is summarized in Table 2. In the ETLIF group, complications requiring reoperation occurred relatively early. Specifically, two cases required revision within a month due to acute screw loosening and deep surgical site infection, respectively; the other two cases underwent revision at 2 months due to cage migration with nonunion; and the remaining three cases required revision at seven, 13, and 14 months postoperatively due to nonunion accompanied by screw loosening or instrument breakage. In contrast, the single case of reoperation in the open TLIF group occurred at 24 months postoperatively and involved instrument breakage (rod fracture) secondary to nonunion. The Kaplan-Meier survival analysis showed a progressive decline in survival for the ETLIF group, with 97.9% survival proportions at 1 month, 95.9% at 2 months, and 92.3% at 14 months (Fig. 1). Conversely, the open TLIF group maintained a reoperation-free survival of 98.9% at 24 months.
Detailed characteristics of patients requiring index-level reoperation
Kaplan-Meier survival curves showing the probability of remaining free from index site reoperation after endoscopic transforaminal lumbar interbody fusion (ETLIF) and open transforaminal lumbar interbody fusion (TLIF). The ETLIF group (blue line) exhibited a lower reoperation-free survival rate compared to the TLIF group (brown dashed line).
The log-rank test demonstrated a statistically significant difference in reoperation-free survival rates between the two groups (p=0.017). Cox regression analysis revealed an HR of 8.34 (95% CI, 1.36–22.20), meaning that patients who underwent ETLIF were more than 8 times more likely to require index-level reoperation compared to those treated with open TLIF.
Finally, in terms of implant-related complications, the ETLIF group had slightly higher rates compared to the open TLIF group across all categories: postoperative infection (3.1% vs. 2.0%), screw loosening (6.2% vs. 3.9%), instrument breakage (2.1% vs. 1.0%), and cage migration (2.1% vs. 2.0%) (Table 3). Nevertheless, none of the differences reached statistical significance, suggesting that both approaches offered similar mechanical safety profiles.
Implant-related complications
Discussion
The present study provides a direct comparison of the mechanical safety and durability of ETLIF versus conventional open TLIF in terms of reoperation-free survival and peri-implant complication rates. Our findings revealed a significantly higher risk of index-level reoperation in the ETLIF group compared to the open TLIF group (HR, 8.34; p=0.017), suggesting that patients undergoing ETLIF may be at a higher risk of requiring revision surgery at the operated segment than those treated with the conventional open approach.
The Kaplan-Meier survival curves showed a progressive decline in the ETLIF group’s reoperation-free survival, beginning as early as the first postoperative month and reaching 92.3% by 14 months. In contrast, the open TLIF group exhibited a stable survival curve, with only one reoperation observed during the entire 24-month follow-up, and maintained a high survival rate of 98.9%. These findings suggest that patients undergoing ETLIF may require more attention in the initial postoperative phase to ensure mechanical stability.
We further compared implant-related complication rates between the two groups. Although statistically nonsignificant, the ETLIF group demonstrated slightly higher incidences of screw loosening (6.2% vs. 3.9%), postoperative infection (3.1% vs. 2.0%), and instrument breakage (2.1% vs. 1.0%) compared to the open TLIF group. These results may be attributed to the technical demands of the endoscopic approach, where limited visualization and working space can hinder optimal screw trajectory and cage positioning, potentially increasing the risk of biomechanical instability [10–12].
Interestingly, patients in the ETLIF group were younger (mean age, 66.8 years vs. 69.6 years) and had slightly lower bone mineral density (0.820 g/cm2 vs. 0.848 g/cm2) than the open TLIF group. Although younger age generally supports better healing and fusion outcomes, the lower BMD may have contributed to increased implant micromotion or delayed union, potentially leading to higher complication and reoperation rates. This is particularly relevant for a technique like ETLIF that relies heavily on precise instrument placement within narrow anatomical corridors.
Taken together, these results highlight the importance of balancing surgical invasiveness and initial mechanical stability. While the preservation of posterior soft tissues in ETLIF facilitates rapid recovery, it may paradoxically increase the mechanical burden on the spinal construct immediately after surgery. Unlike open dissection, which temporarily relaxes paraspinal muscles, the intact musculature in ETLIF exerts continuous, high-tension axial compression; when these high forces are concentrated on a smaller endoscopic cage, the resulting stress on the endplates increases significantly. This phenomenon mirrors the biomechanical challenges observed in oblique or lateral lumbar interbody fusion, where the tension of the preserved anterior longitudinal ligament has been identified as a significant factor contributing to endplate failure and cage subsidence [13–15]. This biomechanical setting likely explains why minor screw loosening or cage migration occurred early in our ETLIF cohort, particularly in patients with suboptimal bone density. Therefore, despite the substantial biological advantages of the endoscopic approach, open TLIF may provide a relatively stable mechanical environment in the initial postoperative phase for patients with poor bone quality or complex pathologies. Future prospective, randomized trials with larger sample sizes and long-term follow-up are needed to validate these observations and refine the clinical criteria for selecting endoscopic versus open approaches.
This study has several limitations inherent to its retrospective, two-center design. First, the heterogeneity between the two cohorts is a major consideration. The procedures were performed by different surgeons at different institutions using different bone graft materials (allograft for ETLIF versus DBM for TLIF) and cages. Although both surgeons were experts in their field, with over 15 years of experience, these variations, along with the difference in preoperative diagnoses (spondylolisthesis versus foraminal stenosis), may have introduced confounding variables that were not fully adjusted for. Therefore, the observed differences should be interpreted as reflecting real-world variations in clinical practice rather than purely technique-driven outcomes. Second, the number of reoperation events was small (n=8); consequently, the HR in the Cox regression yielded a wide CI. We acknowledge that this statistical fragility limits the precision of our risk estimate. Hence, the results should be viewed as exploratory trends signaling potential safety concerns rather than definitive causal evidence. Third, the follow-up period was significantly shorter in the ETLIF group (23.5 months vs. 37.2 months); considering that reoperation rates typically increase with time, the higher failure rate in the ETLIF group suggests that our findings might actually underestimate the true risk difference. Finally, radiographic evidence of fusion was not systematically assessed using computed tomography (CT), and we relied on reoperation as a definitive clinical endpoint. Future prospective studies with standardized protocols, matched cohorts, and CT-based fusion assessment are necessary to validate these preliminary findings.
Conclusions
While ETLIF offers the benefits of a minimally invasive approach and comparable implant-related complication rates, it is associated with a higher risk and incidence of early index-level reoperation compared to open TLIF. This observation implies that the endoscopic technique may possess different initial mechanical characteristics compared to the open approach. Given the limitations of using a retrospective study design, definitive conclusions regarding specific risk factors should be avoided. However, our results highlight the importance of considering biomechanical characteristics distinct to the endoscopic approach and recommend further research to clarify the optimal conditions for applying the ETLIF approach.
Key Points
In this retrospective study, endoscopic transforaminal lumbar interbody fusion was associated with a higher rate of early index-level reoperation compared to open transforaminal lumbar interbody fusion.
Despite the difference in reoperation rates, implant-related complication rates were comparable between the two techniques.
The endoscopic approach may present different initial mechanical characteristics, warranting careful consideration in patient selection.
Further research is necessary to better understand the biomechanical properties and optimal indications for endoscopic fusion.
Notes
Conflict of Interest
No potential conflict of interest relevant to this article was reported.
Acknowledgments
This work was supported by clinical research grant from Pusan National University Hospital in 2023.
Author Contributions
Conceptualization: MSY, YJC. Data curation: MSY, YJC. Formal analysis: MSY. Funding acquisition: JSL. Methodology: MSY, YJC. Project administration: JSL. Resources: JSL. Validation: TSG. Visualization: YJC. Writing–original draft: MSY. Writing–review & editing: YJC, TSG, JSL. Supervision: TSG, JSL. Final approval of the manuscript: all authors.