Lumbar degenerative diseases (LDD) represent a leading cause of chronic low back pain and neurological dysfunction. The incidence of LDD has risen significantly with global population aging, leading to a notable decline in quality of life (1, 2). Lumbar discectomy and lumbar interbody fusion (LIF) have traditionally been the primary surgical interventions for LDD when conservative management fails (3). LIF is essential for achieving sufficient neural decompression and restoring spinal function. It is primarily indicated for lumbar spinal stenosis (LSS), lumbar spondylolisthesis (LS), disc herniation, and scoliosis. Clinically, LIF has been widely adopted for its ability to alleviate pain, decompress nerve roots, correct sagittal imbalance, and treat spinal deformities. Posterior lumbar interbody fusion (PLIF) is a well-established technique with proven efficacy in managing LDD. However, traditional PLIF requires extensive resection of the lamina, spinous processes, ligamentum flavum, facet joints, and interspinous structures. This disruption compromises the posterior ligamentous complex, reduces spinal stability, and raises the risk of adjacent segment degeneration (ASD) (4). Preserving the posterior ligamentous complex is crucial for maintaining spinal stability and flexibility. It also supports normal biomechanics and helps prevent ASD after PLIF (5). To reduce iatrogenic injury, minimally invasive techniques have gained increasing attention. MIS-TLIF, one such technique, minimizes the surgical corridor using tubular retractors. However, limited visualization and traction-induced ischemia of paraspinal muscles may still affect outcomes (6, 7). Recent advancements in endoscopy have facilitated further progress in minimally invasive spinal surgery. Endo-PLIF enables precise, full-visualization procedures that reduce disruption to posterior structures. This technique provides effective neural decompression and promotes faster postoperative recovery (8, 9). Alternatively, ULIF employs separate endoscopic and working channels. This design expands the surgical field while preserving traditional instrument flexibility, offering a viable option for complex cases (10, 11). Despite their increasing adoption, no comprehensive studies have compared the clinical outcomes of Endo-PLIF, ULIF, and conventional PLIF in managing LDD. This study aims to compare the clinical efficacy of these three techniques. A comparative analysis of clinical data was conducted to provide robust evidence for guiding surgical decision-making. The results may help spine surgeons select the most appropriate approach based on individual patient characteristics, thus improving outcomes and reducing complications.

A total of 193 patients with lumbar degenerative disease (LDD) were retrospectively enrolled between January 2020 and July 2023 based on predefined inclusion criteria. Of these, 73 underwent full-endoscopic posterior lumbar interbody fusion (Endo-PLIF group), 63 received biportal endoscopic lumbar interbody fusion (ULIF group), and 57 underwent conventional posterior lumbar interbody fusion (PLIF group). Informed consent was obtained from all patients through an electronic consent form. Demographic and intraoperative data were collected, including age, sex, weight, height, body mass index (BMI), operative duration, disease stage, and incision length. Preoperative and postoperative heights of intervertebral discs and intervertebral spaces were measured. Clinical outcomes were assessed by comparing visual analog scale (VAS) scores for back and leg pain and Oswestry Disability Index (ODI) scores before and after surgery. All perioperative complications were recorded. At the final follow-up, patient satisfaction was evaluated using the modified MacNab criteria. All patients underwent CT evaluation, and fusion status was independently assessed by two radiologists using the Bridwell grading system, with Grades I and II considered indicative of successful fusion. All surgeries were performed by a single senior spine surgeon with substantial experience in lumbar fusion. The study was approved by the Institutional Review Board of Qinghai Red Cross Hospital and conducted in accordance with the Declaration of Helsinki. Inclusion criteria included: (1) age between 40 and 80 years; (2) low back pain or sciatica unresponsive to ≥6 months of conservative treatment; and (3) imaging-confirmed single-segment lumbar degeneration or isthmic spondylolisthesis (Meyerding≤ grade II), spinal stenosis with instability or spondylolisthesis, or disc herniation with canal stenosis. Exclusion criteria were: (1) spondylolisthesis > Meyerding grade II; (2) history of revision surgery at the affected segment; (3) other spinal conditions (e.g., severe osteoporosis, ankylosing spondylitis, tumors, fractures, or tuberculosis); (4) incomplete follow-up; (5) psychiatric or neurological illness; and (6) other contraindications as determined by the surgeon (see Figure 1).

Descriptive statistics were employed to summarize the baseline characteristics of the patients. The Shapiro–Wilk test was applied to assess the normality of continuous variables, and Levene's test was utilized to evaluate the homogeneity of variances between groups. One-way analysis of variance (ANOVA) was conducted for variables with a normal distribution. Non-normally distributed data were analyzed using the Kruskal–Wallis test. Categorical variables were reported as frequencies and percentages. Intergroup comparisons were performed using Pearson's chi-square test or Fisher's exact test, based on the data characteristics. Multiple comparisons were carried out for Visual Analog Scale (VAS) and Oswestry Disability Index (ODI) scores, along with changes in disc and foraminal height. Clinical outcomes were evaluated using the modified MacNab criteria. Longitudinal data were analyzed using a mixed-effects model to account for repeated measurements and estimate group differences. In the model, follow-up time was considered as a categorical variable, with the interaction between time and treatment method included, along with patient ID as a covariate. Given that VAS scores reflected repeated measurements over time, a generalized linear mixed model (GLMM) was used to examine the independent effects of the surgical method. The model considered VAS scores as the dependent variable, with fixed effects including gender, age, BMI, surgical level, and operative time. Potential interactions between confounding factors and their influence on the primary outcome were also examined. In the GLMM, fixed effects comprised the surgical method, age, gender, BMI, surgical level, and operative time. The interaction between time and treatment method was tested in the model and excluded if not significant. The model fit was assessed using the Akaike Information Criterion (AIC) and likelihood ratio tests to ensure the robustness of the final model. Normally distributed data were presented as means ± standard deviation (SD), while non-normally distributed data were reported as medians with interquartile ranges (IQR). A two-tailed P-value of <0.05 was considered statistically significant. All analyses were conducted using SPSS software (version 27.0; IBM Corporation, Armonk, NY, USA).

Research has shown that the posterior spinal column is essential for maintaining spinal stability, and its structural integrity significantly influences postoperative outcomes (12). The posterior column includes the interspinous ligaments, facet joints, and joint capsules. Conventional lumbar fusion surgery often requires extensive dissection and prolonged retraction of the paraspinal muscles, leading to iatrogenic injury that may delay postoperative recovery. Therefore, minimizing injury to the paraspinal muscles and posterior column structures is essential for promoting optimal recovery (13, 14). Minimally invasive spinal surgery has gained popularity in recent years due to its advantages over conventional fusion techniques. These advantages include preservation of anatomical structures, less surgical trauma, shorter operative time, and quicker recovery (15, 16). However, conventional minimally invasive techniques have inherent limitations. Notably, the single-channel design limits visualization and increases procedural complexity. In addition, limited workspace and reliance on specialized instruments may compromise disc preparation and increase the risk of equipment fatigue. To address these limitations, Endo-PLIF and ULIF have emerged as promising alternatives. In this study, all three surgical techniques showed satisfactory clinical outcomes at 12-month follow-up. Based on the modified MacNab criteria, excellent and good outcome rates were 96.8% in the ULIF group, 95.9% in the Endo-PLIF group, and 91.2% in the PLIF group. Both minimally invasive techniques achieved decompression effects comparable to those of conventional open surgery. These findings are consistent with prior reports of patient satisfaction using other minimally invasive fusion techniques, such as endoscopic transforaminal lumbar interbody fusion (Endo-TLIF) (17, 18) and minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) (19), further supporting the effectiveness and clinical feasibility of Endo-PLIF and ULIF for managing lumbar degenerative disease. Prior studies have reported fusion rates of 95.4% for MIS-TLIF, 94.7% for BE-LIF (20), and 93.3% for PE-PLIF (21). In the present study, the fusion rates of Endo-PLIF and ULIF were comparable to those of other minimally invasive techniques and conventional PLIF.

In our study, All three surgical techniques in this study demonstrated significant effectiveness in relieving both low back and lower limb pain. On postoperative day 3, the ULIF group showed greater improvement in back pain VAS scores. This advantage may be related to the dual-channel endoscopic design, which offers a wider surgical field, clearer visualization, and more flexible instrument handling. These features enable more precise neural decompression and intervertebral space preparation, while reducing paraspinal muscle injury. As a result, early postoperative recovery is facilitated. However, no significant differences were observed among the groups after three months. These results suggest that the three techniques yield comparable long-term outcomes in the management of lumbar spondylolisthesis. This finding aligns with those of Kim et al. (22), who reported similar improvements in VAS scores after MIS-TLIF and Endo-TLIF at 2 weeks and 2 months, with no significant differences at later follow-up points. For lower limb pain, the ULIF group exhibited superior early improvement at both day 3 and 3 months postoperatively. This may be attributed to the enhanced visualization, wider range of instrument motion, and direct access via the working channel afforded by ULIF. The separation of working and viewing portals allows for greater instrument flexibility, enabling precise decompression in an expanded, well-lit surgical field. This configuration facilitates effective intervertebral space preparation and sufficient harvesting of autologous bone (23). Moreover, the wide visual field allows comprehensive decompression with minimal obstruction. However, the differences in leg pain relief among the groups diminished over time, indicating similar long-term pain control across all techniques. Regarding functional recovery, the ULIF group demonstrated more substantial improvement at day 3 and 3 months, likely due to minimal muscle disruption and refined surgical manipulation, which contribute to faster rehabilitation. Nevertheless, both the Endo-PLIF and PLIF groups also showed significant functional gains throughout follow-up, yielding generally favorable clinical outcomes. The PLIF group had a markedly shorter operative time compared to the Endo-PLIF and ULIF groups. As a conventional open posterior approach, PLIF offers a larger incision, direct exposure, and simpler operative steps. The wide surgical field allows efficient disc removal, decompression, and fixation. However, extensive muscle dissection and prolonged retraction may cause muscle atrophy and denervation, potentially delaying recovery. Furthermore, the limited field of view and anatomical constraints may restrict complete decompression, particularly in deep or complex lesions. In addition, the preservation of certain bone structures for stability may prevent full removal of compressive tissues such as osteophytes or hypertrophic ligaments, limiting the overall decompression effect. Despite these limitations, PLIF was found to significantly improve postoperative disc and foraminal heights. This effect may be attributed to its broader surgical field and direct visualization, which permit the placement of larger interbody cages and enable more effective distraction of the intervertebral space. The structural advantages of PLIF also support segmental correction and the restoration of stability, leading to superior improvement in disc height compared with minimally invasive techniques. Among the two, ULIF achieved greater disc and foraminal height restoration than Endo-PLIF. The latter, performed through a single interlaminar approach, is constrained by the narrow anatomy of the intervertebral foramen, limiting maneuverability and field of view. However, its minimal muscle and bone disruption, comparable fusion rates and long-term outcomes to ULIF, absence of postoperative drainage, and faster wound healing render it a widely accepted minimally invasive technique. This study has several limitations that should be considered. First, the relatively small sample size may have limited the statistical power and generalizability of the results. Although 193 patients were included, the small sample size may have hindered the detection of subtle differences between the surgical groups. Furthermore, all surgeries were performed by a single senior surgeon, which may impact the external validity of the results. Variations in surgeon experience, skill, and technique may affect surgical outcomes, limiting the generalizability of the results to other healthcare institutions. Second, the retrospective design of this study may have introduced selection bias in patient selection. The selection of patients for surgery was non-random, and both preoperative and postoperative data may have been influenced by recording bias. This design may have resulted in incomplete control of some confounding factors, potentially affecting the interpretation of the results. Despite efforts to adjust for these factors, the influence of selection bias could not be entirely excluded. Additionally, the study did not formally evaluate the impact of the learning curve. Although all surgeries were conducted by an experienced surgeon, the mastery and proficiency of new techniques may evolve over time. The learning curve may influence postoperative outcomes, particularly in the early stages when surgical skills are not fully refined. Therefore, future studies should account for the learning curve and include inter-surgeon comparisons to enhance the generalizability of the results. The recurrence and reoperation rates were not assessed in this study. Although no major complications were observed during the study period, postoperative recurrence or the need for reoperation may occur with longer follow-up, which is critical for evaluating overall patient prognosis. Therefore, future studies should incorporate these factors to further validate the long-term outcomes of various surgical approaches. Finally, while this study provides valuable clinical data, its retrospective design and single-center nature limit the generalizability of the findings. To improve the reliability and external validity of the results, future research should involve large-scale, prospective, multi-center studies that assess the long-term effects, recurrence rates, reoperation rates, and other complications of different surgical techniques.

This study provides important insights into the clinical efficacy of ULIF, Endo-PLIF, and PLIF in the treatment of lumbar degenerative diseases. Although ULIF demonstrates superior outcomes in terms of early postoperative pain control and functional recovery, the long-term results are similar across the three techniques. Spine surgeons can make individualized decisions regarding the choice of surgical approach based on specific patient factors, such as disease severity, comorbidities, and recovery goals.