Introduction
As the population ages, lumbar degenerative disease (LDD) increases in prevalence and becomes a major global cause of disability [1,2]. Over 90% of adults over the age of 60 years exhibit radiographic signs of LDD [3]. Clinically, LDD can present as symptomatic lumbar disc herniation (LDH), lumbar spinal stenosis (LSS), or disc and facet joint degeneration. When conservative treatments fail to alleviate symptoms, surgical decompression methods, such as discectomy, laminectomy, and fusion, are often indicated [4,5]. In recent years, the development of minimally invasive spine surgery (MISS) techniques has played a major role in the evolution of the surgical management of LDD [6]. These minimally invasive approaches, such as spine endoscopy, minimize soft tissue damage, preserve the integrity of the paraspinal musculature, decrease blood loss and postoperative pain and infection rates, and accelerate overall postoperative recovery [7–9]. Although MISS techniques have significant clinical advances, their benefits must be weighed against potential limitations, including higher costs, increased radiation exposure, reduced tactile feedback, limited ability to address certain intraoperative complications, and the technical learning curve required for surgeons [10–13].
The latest development in MISS is biportal endoscopy, which has gained significant attention for its manageable learning curve, enhanced endoscopic visualization, and improved instrument maneuverability, which help achieve effective spinal canal decompression while minimizing complications [14–16]. This technique uses two separate portals; one is dedicated to the endoscope for visualization (observation portal) and the other is for surgical instruments (operation portal) [17,18]. By combining the advantages of uniportal endoscopy and traditional open surgery, biportal endoscopy is expected to be a more versatile and highly effective approach than the other MISS techniques [19].
Despite the rapid advances and expected benefits of minimally invasive lumbar spine surgery, there is no global consensus on how newer endoscopic approaches, such as biportal endoscopy, compare with traditional open spine surgery. Therefore, this systematic review and meta-analysis aimed to elucidate the differences between conventional open and biportal endoscopic approaches for treating LDD.
Methods
Search strategy
Systematic searches were conducted using PubMed (MEDLINE), Embase, and Scopus databases, with adherence to the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and the Cochrane Review recommendations [20]. The search aimed to identify all relevant articles published up to October 7, 2024. A combination of keywords, synonyms, and variations was used, including the terms “biportal,” “open,” “conventional,” “endoscopic spine surgery,” “lumbar,” “discectomy,” “laminectomy,” “laminotomy,” and “fusion.” These terms were combined using Boolean operators to optimize the search strategy. To ensure comprehensive coverage, the reference lists of all included articles were reviewed to identify any additional relevant studies. The complete search string is provided in the Supplementary Materials.
Selection criteria
This systematic review and meta-analysis included comparative studies that compared single-level biportal endoscopic spine surgery (BESS) and single-level open spine surgery for treating LDD. Studies were included if they reported at least one of the following outcomes: Visual Analog Scale (VAS) scores for back or leg pain, Oswestry Disability Index (ODI), complication rates, operative duration, and hospital length of stay (LOS). Studies involving patients with fractures, tumors, infections, or scoliosis were excluded. In addition, noncomparative studies; case reports; reviews; conference abstracts; letters; and studies lacking essential outcome data, such as mean and standard deviation (SD) values, were excluded. Only peer-reviewed articles written in English were considered eligible.
Study screening and data extraction
The identified studies were screened by two independent reviewers based on the titles, abstracts, and full texts, according to the inclusion and exclusion criteria. Any conflicting decision between the two reviewers was resolved by discussion with a third reviewer. The reasons for ineligibility or exclusion of studies were documented. Inclusion of studies was confirmed by the senior author (S.K.C.).
Data were collected independently by the reviewers using standardized data extraction forms. The collected data included the general study characteristics, such as authors, year of publication, study design, sample size, age, and sex ratio, and outcomes, such as VAS score for back and leg pain, ODI, operation time, hospital LOS, and complication rate.
Risk of bias assessment
The Newcastle-Ottawa Scale (NOS) was used by two independent reviewers to assess the methodological quality of nonrandomized studies [21]. This scale comprised three sections: selection, comparability, and outcome. The highest possible score for each study was nine. Studies that scored between 5 and 9 were considered to have a lower risk of bias, whereas those that scored below 5 were deemed to have a higher risk of bias. Any disagreement between the two reviewers was resolved by a third reviewer.
Statistical analysis
Clinical outcomes, including operative time, LOS, VAS, and ODI, were compared between the open spine surgery and BESS cohorts. Subgroup analysis was performed on patients who underwent decompression (e.g., discectomy and laminectomy) and interbody fusion. The mean values for each subgroup and all patients were calculated by combining the mean and SD of each study, as outlined in Cochrane’s handbook for systematic reviews of interventions. p-values for differences between the open spine surgery and BESS cohorts were calculated using the effect size measure Cohen’s d in a random effects model, which was used to account for variations in factors, such as patient population and surgical technique, and to strengthen the generalizability of our results. The control group comprised patients who underwent open spine surgery, whereas the treatment group comprised those who underwent biportal surgery. To be consistent with previous literature and minimize variations due to time period, clinical outcomes were grouped into the immediate (≤1 week) and long-term (1 year) postoperative categories. Therefore, effect size was determined as the difference in SDs between BESS and open spine surgery. Heterogeneity was assessed using Cochran’s Q-test and I2 statistics. Statistical significance was defined as a p-value of <0.05. All statistical analyses were performed using IBM SPSS ver. 29.0 (IBM Corp., Armonk, NY, USA).
Results
Search results
The initial database search yielded 634 studies after removing duplicates. Following title and abstract screening, 357 studies were excluded. After assessment of the remaining 277 full-text reports, eight studies were considered suitable for inclusion in the final analysis. Of these, six studies were retrospective and two were prospective. A PRISMA flowchart detailing the screening process and literature search outcomes is shown in Fig. 1.
Eight studies comparing open and biportal endoscopic lumbar spine surgery from 2018 to 2024 were analyzed. All patients underwent single-level surgery. The open surgery cohort (n=414) had a mean age of 61.0±13.7 years and comprised 174 (42.0%) men. The BESS cohort (n=383) had a mean age of 59.8±12.2 years and comprised 179 (46.7%) men. The baseline characteristics and risk of bias assessment of the included studies are presented in Table 1 [22–29].
Overall outcomes
Compared with the open surgery cohort, the BESS cohort had significantly longer mean operative time (134.57±80.75 minutes vs. 101.34±41.91 minutes; d, 2.19; 95% confidence interval [CI], 0.75 to 3.64; p=0.003) (Fig. 2) [22–29]; significantly shorter mean hospital LOS (5.18±2.46 days vs. 7.84±2.94 days; d, −1.34; 95% CI, −2.07 to −0.62; p<0.001) (Fig. 3) [22–28]; and similar complication rates, VAS for back and leg pain, and ODI at any of the time points. The mean values of the clinical outcomes and p-values from Cohen’s d effect size measure for all eight studies are summarized in Table 2. Heterogeneity analysis demonstrated significant variations between studies for operative time (I2=0.99, Q=260.74, p<0.001); LOS (I2=0.94, Q=96.27, p<0.001); preoperative ODI (I2=0.62, Q=16.83, p=0.01); VAS for back pain at 1 week postoperatively (I2=0.97, Q=166.21, p<0.001); and ODI at 1 week postoperatively (I2=0.76, Q=8.95, p=0.01). There was no significant heterogeneity in the remaining variables among the studies.
Biportal versus open decompression
Subgroup analysis was performed for three studies on decompression. Patients who underwent open decompression (n=169) had a mean age of 61.0±17.4 years and comprised 74 (43.8%) men. Those who underwent biportal endoscopic decompression (n=155) had a mean age of 57.9±15.2 years and comprised 87 (56.1%) men. Hospital LOS was significantly shorter in the BESS cohort than in the open cohort (d, −1.78; 95% CI, −2.90 to −0.66; p=0.002) (Fig. 3). The complication rate, operative time, VAS for leg pain, VAS for back pain, and ODI at any time point were not significantly different between the two subgroups. The clinical outcomes of the decompression subgroup analysis are summarized in Table 2. Heterogeneity analysis demonstrated significant variations among the studies for operative time (I2=0.99, Q=99.81, p<0.001); LOS (I2=0.94, Q=33.69, p<0.001); VAS back pain at 1 week postoperatively (I2=0.97, Q=67.31, p<0.001); and ODI at 1 week postoperatively (I2=0.89, Q=8.78, p<0.001).
Biportal versus open interbody fusion
Subgroup analysis was performed for five studies on interbody fusion. Patients who underwent open interbody fusion (n=245) had a mean age of 61.1±10.4 years and comprised 100 (40.8%) men. Those who underwent biportal endoscopic interbody fusion (n=228) had a mean age of 61.2±9.6 years and comprised 92 (40.4%) men. Compared with the open interbody fusion cohort, the BESS interbody fusion cohort had significantly lower VAS for back pain at ≤1 week postoperatively (3.50±1.03 vs. 4.57±1.23; d, −0.35; 95% CI, −0.63 to −0.07; p=0.02) (Fig. 4) [22–25,27,29]; significantly longer mean operative time (186.69±63.83 minutes vs. 129.25±24.87 minutes; d, 2.57; 95% CI, 0.61 to 4.52; p=0.01) (Fig. 2); significantly shorter mean hospital LOS (6.10±2.15 days vs. 8.69±3.28 days; d, −1.01; 95% CI, −1.95 to −0.07; p=0.035) (Fig. 3); and similar complication rates, VAS for back and leg pain, and ODI at the remaining time points. Heterogeneity analysis demonstrated significant variations among studies for operative time (I2=0.98, Q=142.80, p<0.001); LOS (I2=0.93, Q=45.25, p<0.001); preoperative ODI (I2=0.75, Q=6.85, p=0.03); and VAS leg pain at 1 week (I2=0.97, Q=67.31, p<0.001). The clinical outcomes for the interbody fusion subgroup analysis are summarized in Table 2.
Discussion
Endoscopic spine surgery, which is performed through a uniportal or biportal approach, is central to the recent advancements in LDD treatment [19,30,31]. This minimally invasive procedure offers several potential advantages, including less paraspinal soft tissue and muscle dissection, increased spinal stability, reduced scarring, and diminished perioperative blood loss [30,31]. The biportal approach comprises two independent portals, which provide a wide range of views and improved maneuverability [32]. Despite these technical advances, a comprehensive comparison between the biportal approach and conventional open surgery for LDD remains lacking. This systematic review and meta-analysis aimed to compare the biportal and open approaches for lumbar decompression and interbody fusion, focusing on perioperative characteristics and postoperative outcomes.
The analysis included eight studies with 414 and 383 patients who underwent open and biportal approaches, respectively. The average age was approximately 60 years, with a balanced sex distribution. Of these studies, three focused on decompression and five on interbody fusion. Biportal procedures were associated with significantly longer operative time but shorter hospital stay. There were no significant differences in complication rates, VAS scores for back or leg pain, and ODI scores in the preoperative and immediate and long-term postoperative periods. Subgroup analysis showed improved VAS for back pain in the immediate postoperative period after biportal fusion.
Although the minimally invasive nature of BESS offers theoretical advantages, our results indicated minimal differences in postoperative outcomes compared with conventional open surgery. Moreover, the postoperative outcomes were consistent among the groups, with no significant differences in complications, ODI, and VAS leg pain scores in the immediate and long-term postoperative periods, regardless of whether decompression or fusion was performed. Given the critical importance of long-term pain reduction in LDD treatment, further studies are needed to optimize the endoscopic approach and enhance patient care.
Our findings of comparable patient-reported outcomes between the two approaches were consistent with those of previous studies. For instance, You et al. [33] found no significant differences in ODI and VAS scores for back or leg pain at 1 month, 6 months, and 1 year between biportal endoscopic transforaminal and open posterior lumbar interbody fusion. Similarly, Yu et al. [34] reported no differences in ODI and VAS scores at 6 months between the unilateral biportal endoscopic and open techniques for LDH. These results reinforce the need for further investigation to fully maximize the benefits of endoscopic approaches for LDD treatment.
Our results revealed a significantly longer operative time with the BESS approach than with the open approach, with a mean difference of 33 minutes in the overall cohort and 57 minutes in the interbody fusion subgroup. This discrepancy can be attributed to the intrinsic technical complexity and learning curve of the biportal approach.
In the biportal technique, the need to establish two distinct working portals, one for visualization and another for instrumentation, adds to the operative time [35,36]. In contrast, the open technique involves direct visualization by tissue retraction, allowing more immediate access to the surgical site. The additional time required for portal placement and orientation, along with maintenance of continuous visualization and irrigation, in the biportal approach likely explains the observed difference in operative time [37,38]. Our findings were consistent with those of previously published studies. A retrospective analysis by Kim et al. [39] reported longer operative time for BESS than for traditional open techniques in lumbar procedures. In addition, in an article highlighting the technical considerations for BESS, Park et al. [40] noted the time-intensive nature of guaranteeing adequate portal triangulation and subsequent intraoperative adjustments.
The longer operative time with the biportal approach can also be attributed to the learning curve associated with mastering this technique. The biportal endoscopic technique introduces unique challenges for surgeons because of its dual surgical channel setup, continuous saline irrigation, and the need to maintain pressure throughout the procedure. These factors contribute to the steep learning curve. Research indicated that surgeons must gain proficiency by performing at least 89 procedures to move beyond the initial learning phase and consistently achieve successful outcomes [41]. Studies from Korea, where BESS is commonly practiced, have suggested that the learning curve to achieve proficiency in biportal endoscopic procedures extends to over 30–50 cases [42,43]. In addition, Chen and Pei [44] found that the learning curve for BESS required approximately 41–45 cases for surgeons with prior endoscopic experience. However, one study has shown that the learning curve of BESS was reproducible, based on the findings of markedly increased efficiency with experience [45]. Comparatively, open surgical techniques have a shorter learning curve because of their relatively straightforward approach and more established surgical steps; in fact, most studies stated that surgeons reach proficiency after approximately 10 procedures [46,47]. Comparison of the learning trajectories between the two approaches highlighted the importance of surgeon experience in minimizing the operative time for biportal procedures. Our findings supported these insights, particularly in the fusion cohort, in which the impact of a steep learning curve appeared more pronounced.
The hospital LOS was significantly shorter in the biportal group than in the open group; it was approximately 2.5 days in the overall cohort and 3.5 days in the discectomy cohort. This outcome was consistent with the minimally invasive nature of the biportal approach, which often results in reduced tissue disruption and muscle injury and faster postoperative recovery [48,49]. The shorter LOS in this study was supported by findings in previous research. Heo et al. [50] showed reduced hospitalization times in patients who underwent biportal endoscopic procedures than in those who underwent open surgery. Reduced LOS has significant clinical and economic implications. Shorter hospital stays can translate to decreased exposure to nosocomial infections, improved satisfaction, reduced economic burden, and increased efficiency in resource utilization [51–53].
The relatively long LOS in this meta-analysis can be partially attributed to the predominance of studies from Asia. Healthcare systems in this region often prioritize prolonged inpatient care, compared with practices in the United States [54]. Cultural traditions, healthcare policies, and postoperative management in Asia likely contributed to extended hospital stay [55,56]. Although such practices offer valuable perspectives on extended recovery and monitoring, they may not align with the growing trend in the United States toward ambulatory procedures and same-day discharge [57]. Further research on biportal endoscopy in the United States is necessary to clarify these LOS findings.
In the interbody fusion cohort, the VAS scores for back pain were significantly higher in the biportal group than in the open group in the immediate postoperative period. Although the difference was statistically significant, the clinical relevance was less apparent. Among the included studies, the mean difference in VAS for back pain in the immediate postoperative period was only one point. This improvement may not meet the threshold for clinical significance, given that a study by Parker et al. [58] cited 2.2 points as the minimum clinically important difference for VAS for back pain among patients undergoing neural decompression and fusion for recurrent lumbar stenosis. Although the difference in VAS for back pain in the immediate postoperative period was statistically significant, the mean difference of only one point may lack clinical significance. This difference emphasizes the need for cautious analysis of early postoperative pain outcomes.
Our findings showed no significant difference in complication rates between open spine surgery and BESS. A prior study on lumbar interbody fusion reported a tendency for lower postoperative complications in the BESS group than in the conventional open group (5.67% vs. 14.29%) [48]. A systematic review of 3,673 cases of BESS identified durotomy (2.23%), inadequate decompression (1.29%), and epidural hematoma (3.79%) as notable complications [59]. Similarly, a meta-analysis of BESS for LSS reported an overall complication rate of 5%, with dural tears (2%) and epidural hematomas (1%) being the most common [60]. These findings suggested that BESS has a lower overall complication rate than open spine surgery, although specific risks, such as dural tears and epidural hematomas, remain.
This meta-analysis had certain limitations, which are mostly due to the quality of the included studies. Most studies were retrospective, and there were no randomized controlled trials, which can reflect the current body of available research and impact the strength of the conclusions. Furthermore, the inconsistent definitions and techniques used for open and biportal endoscopic surgery, as well as variations in follow-up protocols, may have affected the comparability of the findings. Surgeon experience and surgical approach (e.g., transforaminal or interlaminar and posterior) likely influenced outcomes, such as blood loss and operative time; these factors were not stratified in the analysis. Moreover, the relationship between outcomes and severity of disc herniation or stenosis was not examined, because not all studies included detailed information on these parameters. Finally, exclusion of non-English studies may have omitted relevant studies published in other languages.
Heterogeneity was anticipated due to variations in study design, surgical technique, and patient characteristics among the included studies. Although some level of heterogeneity is inherent in meta-analyses involving nonrandomized studies, this was quantitatively confirmed in this analysis using Cochran’s Q-test and I2 statistics. The substantial heterogeneity (I2>90%) in several outcomes, such as operative time and LOS, likely reflected clinical and methodological variability among institutions and surgical teams. Importantly, all included studies were comparative in design and evaluated both biportal and open surgical approaches using their own patient cohorts. This within-study comparison reduced the risk of intrastudy confounding, because baseline characteristics, such as age, sex distribution, and disease severity, were likely matched or statistically controlled. However, interstudy differences in demographics and surgical practices likely contributed to the observed heterogeneity in the pooled results. Given this context, the use of a random effects model was both appropriate and necessary. Unlike fixed effects models, the random effects approach accounts for both within-study sampling error and between-study variation, thereby, improving generalizability of the findings.
Despite these limitations, this study had notable strengths. Although randomized controlled trials were unavailable, the results were consistent and supported by high NOS scores. The rigorous inclusion and exclusion criteria, extensive literature search, and independent data collection helped minimize potential biases. In addition, the fact that all surgical procedures included in this meta-analysis were performed at a single spinal level enhanced data uniformity. Importantly, to the best of our knowledge, this systematic review was the first to provide a comprehensive meta-analysis comparing conventional open and biportal decompression and fusion. Future multicenter randomized controlled trials are needed to validate these findings and offer stronger recommendations for clinical practice.
Conclusions
In conclusion, biportal endoscopy had comparable immediate and long-term postoperative outcomes with conventional open spine surgery for LDD. The biportal approach offers several potential advantages, including shorter hospital stay and statistically improved short-term VAS scores for back pain after interbody fusion, although these benefits may not always be clinically significant. The relatively long operative time and steep learning curve are challenges in the widespread adoption of the biportal approach. Further research is needed to optimize the biportal endoscopic technique, address its limitations, and maximize its minimally invasive benefits to enhance patient outcomes after LDD treatment.
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