Introduction
With the global aging population, the treatment of lumbar degenerative disease (LDD) is becoming an increasingly common and costly challenge for spine surgeons and healthcare systems worldwide [1]. Lumbar interbody fusion surgery is a standard treatment for LDD; however, the conventional open approach is associated with a relatively long recovery period [2].
In 1968, Wiltse et al. [3], first described a transforaminal lumbar interbody fusion (W-TLIF) approach through the natural cleavage plane between the multifidus and longissimus muscles, preserving the integrity of posterior osseous structures and reducing paraspinal muscle injury and postoperative chronic low back pain [4]. More recently, unilateral biportal endoscopic transforaminal lumbar interbody fusion (UBE-TLIF) has emerged as a novel minimally invasive technique [5]. The UBE approach has been successfully applied in a substantial number of patients with LDD, with studies reporting reduced paravertebral muscle injury compared with conventional open lumbar decompression or discectomy [6,7].
Regardless of the type of surgery, LDD can contribute to the degeneration of the paravertebral muscles. This may occur through direct surgical injury, disuse atrophy after long-term fixation and fusion, or age-related increase in intramuscular fat infiltration and atrophy [8–11]. However, few studies have focused on the long-term progression of paravertebral muscle atrophy after W-TLIF and UBE-TLIF. Therefore, the present study aimed to compare postoperative paravertebral muscle atrophy, fat infiltration, and clinical outcomes between UBE-TLIF and W-TLIF in patients with single- and two-segment LDD.
Materials and Methods
Ethics statement
This retrospective cohort study compared the efficacy of UBE-TLIF and W-TLIF using data from the Guangdong Provincial People’s Hospital. The study protocol was approved by the Ethics Committee of Guangdong Provincial People’s Hospital (KY2025-131-01). Owing to the retrospective design, the requirement for informed consent from individual patients was waived.
Study design and participants
This retrospective observational study included 1,819 patients who underwent single- or two-segment TLIF at our institution between January 2020 and February 2022. The inclusion criteria were as follows: (1) single- or two-segment lumbar spinal stenosis, degenerative or spondylolytic lumbar spondylolisthesis (degree I–II), or lumbar disc herniation, consistent with imaging findings and symptoms; (2) neurological compression symptoms unresponsive to strict conservative treatment for ≥3 months; (3) treatment with either UBE-TLIF or W-TLIF; (4) minimum follow-up of 2 years; (5) and availability of complete imaging data.
The exclusion criteria were as follows: (1) age <18 years or >75 years; (2) presence of spinal infection or tumor; (3) previous surgical history involving the index lumbar vertebrae; and (4) severe cardiopulmonary or coagulation dysfunction. The patient screening process is illustrated in Fig. 1.
Surgical procedure
Patients were positioned prone under general anesthesia, and a C-arm fluoroscope was used to identify the target intervertebral space and pedicles. UBE-TLIF was performed via a transforaminal approach under endoscopic guidance. Two 1.5 cm incisions were made on the symptomatic side: one for the endoscope (30° arthroscope) and the other for instruments. The working portal was established between the multifidus and longissimus muscles, avoiding muscle dissection. Decompression, discectomy, and cage insertion were performed under continuous saline irrigation. In contrast, the Wiltse approach was used for W-TLIF, involving bilateral fascial incisions and intermuscular separation between the multifidus and longissimus, with muscle retraction required for pedicle screw placement (Fig. 2).
On the side with more severe symptoms, the bone structures were exposed, followed by a facetectomy and laminotomy to enlarge the lateral recess and nerve root canal. The resected bone was preserved for further analysis. The ligamentum flavum was excised to achieve decompression. The intervertebral disc was then removed, the endplates were prepared, and an appropriately sized bone graft fusion cage was inserted. Pedicle screws and a titanium rod were implanted, and their placement was confirmed using C-arm fluoroscopy. After confirming hemostasis, a drainage catheter was placed, and the incision was closed in layers.
Perioperative data collection
All patients received routine antibiotic prophylaxis for 2 days after surgery, and the drainage tube was removed once the 24-hour drainage volume was <50 mL. Recorded perioperative outcomes included operative duration, intraoperative blood loss, postoperative drainage, length of hospital stays, time to postoperative mobilization, fusion rate, and complications. Serum creatine kinase levels were measured preoperatively and on the first postoperative day to assess muscle injury.
Follow-up
Patients underwent scheduled reexaminations, including lumbar anteroposterior and lateral radiographs, computed tomography, and magnetic resonance imaging (MRI) at 3, 6, 12, and 24 months postoperatively. The Oswestry Disability Index (ODI) was assessed at 3, 6, 12, and 24 months. The Japanese Orthopaedic Association (JOA) scores and Visual Analog Scale (VAS) scores were recorded preoperatively and at 1 day, 3, 6, 12, and 24 months postoperatively. Clinical outcomes were further evaluated using the Macnab criteria at 24 months.
Outcome measures
Axial T2-weighted MRI (1.5T; Siemens, Erlangen, Germany) was performed from L1 to S1 in all patients. The central axial slice was imported into ImageJ software ver. 1.54f (National Institutes of Health, Bethesda, MD, USA) for image processing. Cross-sectional areas (CSA) of the multifidus, erector spinae, and psoas muscles were measured. Two blinded spine surgeons independently outlined regions of interest, and excellent inter-rater reliability was confirmed (intraclass correlation coefficient [ICC] >0.90). Muscle atrophy and fat infiltration rates were calculated by comparing pre- and postoperative CSA values of the psoas major, longissimus, and multifidus muscles. To account for anatomical variability, CSA values were normalized to the corresponding intervertebral disc area. All measurements were independently completed by two blinded spine surgeons within one week, and the mean of both observers’ values was used for analysis to minimize inter-observer variability. However, the potential influence of the surgical learning curve was not quantitatively assessed in this study.
To reduce metal artifact interference from internal fixation, imaging was performed with a 1.5T MRI system to limit field strength. Artifact reduction was further optimized by increasing receiver bandwidth, enhancing image resolution, and adjusting frequency and phase encoding directions (Fig. 3).
Statistical analysis
Categorical variables were compared using the chi-square test or Fisher’s exact test, as appropriate. Continuous variables were assessed for normality before analysis and are presented as mean±standard deviation. Between-group comparisons were performed using an independent-sample t-test for normally distributed variables and the Wilcoxon rank sum test for ordinal data. To adjust for potential confounders such as age, body mass index (BMI), and other baseline variables, multivariable logistic regression was applied for categorical outcomes and multivariable linear regression for continuous outcomes. Statistical analyses were conducted using IBM SPSS software ver. 27.0.1 (IBM Corp., Armonk, NY, USA). All p-values <0.05 were considered indicative of statistical significance. GraphPad Prism ver. 9.1.0 (GraphPad, San Diego, CA, USA) was used to plot the temporal changes in paravertebral muscle atrophy and fat infiltration.
Results
All enrolled patients successfully completed the surgical procedure. Compared with the W-TLIF group, the UBE-TLIF group had significantly less intraoperative blood loss, shorter operative time, and reduced postoperative drainage volumes (including on postoperative days 1, 2, and 3, as well as total drainage volume) (p<0.05). Patients in the UBE-TLIF group also demonstrated faster postoperative recovery and shorter hospital stays (p<0.05). In addition, serum creatine kinase levels on the first postoperative day were significantly lower in the UBE-TLIF group than in the W-TLIF group (p<0.05) (Table 1).
The VAS scores for both leg pain and low back pain, as well as the JOA and ODI scores, improved significantly in both groups at all postoperative time points compared with preoperative levels (p<0.05). The W-TLIF group had higher VAS scores for low back pain at 1 day, 1 year, and 2 years postoperatively, and higher VAS scores for leg pain at 1 day and 2 years postoperatively, relative to the UBE-TLIF group (p<0.05). The UBE-TLIF group also showed significantly lower ODI scores at 1 and 2 years postoperatively (p<0.05). Importantly, VAS and ODI scores in the UBE-TLIF group met the minimal clinically important difference (MCID) thresholds at both 1 and 2 years. Although JOA scores were consistently higher in the UBE-TLIF group across all postoperative time points, the between-group differences did not reach statistical significance (p>0.05) (Table 2).
At 6 months, 1 year, and 2 years postoperatively, the W-TLIF group showed significantly higher rates of atrophy of multifidus and erector spinae muscles compared with the UBE-TLIF group (p<0.05). The psoas major muscle also exhibited a higher atrophy rate in the W-TLIF group at 3 months, 6 months, 1 year, and 2 years (p<0.05). The UBE-TLIF group demonstrated significantly lower fatty infiltration rates in the multifidus, psoas major, and erector spinae muscles at 1 year and 2 years postoperatively (p<0.05) (Table 3, Fig. 4).
At the 2-year follow-up, excellent or good outcomes according to the modified Macnab criteria were achieved in 88% of patients in the UBE-TILF group and 86% in the W-TLIF group. The fusion rate was 94% in the UBE-TLIF group and 92% in the W-TLIF group. These differences were not statistically significant (p>0.05) (Table 4).
In multivariable logistic and linear regression analyses, BMI was associated with postoperative drainage, while age and sex were associated with muscle fat infiltration. Fat infiltration of the erector spinae was also associated with surgical level and the presence of diabetes.
The incidence of surgical complications was 6% (3/50) in the UBE-TLIF group and 10% (5/50) in the W-TLIF group. In the UBE-TLIF group, one patient sustained an intraoperative dural tear and two developed transient L5 nerve root paralysis postoperatively. In the W-TLIF group, there were three cases of dural tears and two of transient L5 nerve root paralysis. The UBE-TLIF group had a lower overall incidence of surgical complications. All complications were managed conservatively, and none of the patients in either group required revision surgery.
Discussion
Lumbar interbody fusion is a widely used treatment for LDD. However, traditional open approaches are associated with extensive paravertebral muscle injury, prolonged recovery, and an increased risk of chronic low back pain [2]. To address these drawbacks, minimally invasive techniques such as W-TLIF and UBE-TLIF have been developed. W-TLIF, first described by Wiltse et al. [3] in 1968, utilizes the natural intermuscular plane to preserve posterior osseous structures and minimize muscle damage. UBE-TLIF, a more recent advancement, has shown lighter paravertebral muscle injury compared to conventional open decompression or discectomy [5–7].
In this study, both UBE-TLIF and W-TLIF achieved satisfactory clinical outcomes, with no significant differences in fusion rates or modified Macnab criteria, indicating that both techniques are effective in treating LDD. However, the UBE-TLIF group was associated with less intraoperative blood loss, shorter operative times, reduced postoperative drainage volumes, faster recovery, and shorter hospital stays [5,6]. These findings highlight the minimally invasive nature of UBE-TLIF and are consistent with previous studies. Tian and Liu [12] demonstrated that MIS-TLIF offered reduced blood loss, shorter operative duration, and smaller incisions compared with W-TLIF. More recently, Luan et al. [13] found UBE-TLIF to be superior to MIS-TLIF in terms of hospital stay, intraoperative blood loss, early functional recovery, and postoperative drainage. The benefits of UBE-TILF likely stem from its smaller incisions, minimal muscle dissection, and endoscopic visualization, which allows for precise surgical maneuvers and reduced tissue trauma. Consequently, UBE-TILF may lower complication rates and accelerate postoperative recovery, as supported by our results [14]. Collectively, these findings suggest that UBE-TLIF may represent a preferable option for patients with LDD, particularly when minimizing paravertebral muscle damage and recovery time is prioritized.
Postoperative atrophy and fatty infiltration of the paravertebral muscles are common sequelae of lumbar fusion surgery, affecting long-term outcomes [15–17]. W-TLIF, despite its minimally invasive approach, can still cause muscle damage due to the need for muscle retraction and dissection [4]. In contrast, UBE-TLIF employs a unilateral approach with minimal muscle dissection and has been reported to reduce muscle trauma [6,7]. In our study, the UBE-TLIF group exhibited significantly lower creatine kinase levels on the first postoperative day, accompanied by lower VAS scores for low back pain. Since creatine kinase is a biomarker of muscle injury [18], which is influenced by the extent of muscle compression and surgical duration [19], these findings suggest that the UBE-TLIF minimizes muscle injury. Furthermore, UBE-TLIF was associated with lower rates of atrophy and fatty infiltration in the erector spinae, psoas major, and multifidus muscles at 1 year and 2 years postoperatively [5,20].
The differences in muscle handling between the two techniques likely account for these findings. Even when correctly performed, W-TLIF may cause paravertebral muscle injury due to the need for retraction and dissection, especially during contralateral screw placement [4]. In contrast, UBE-TLIF employs a unilateral approach with minimal muscle dissection, reducing the risk of iatrogenic muscle damage. The use of peelers for initial muscle separation and radiofrequency plasma ablation to displace muscles further minimizes damage, and the single-sided approach for decompression and fusion avoids unnecessary exposure of contralateral muscles [14].
Long-term follow-up studies have shown that muscle atrophy and fatty infiltration can occur after lumbar fusion surgery, affecting spinal stability and function [16]. These changes can lead to increased postoperative pain and reduced functional outcomes. In the present study, the UBE-TLIF group demonstrated lower paraspinal muscle atrophy and fatty infiltration at 3 months, 6 months, 1 year, and 2 years postoperatively, particularly in the psoas major muscle. The psoas major muscle is a crucial component of the spine-pelvis-hip complex, playing an essential role in maintaining trunk and core stability [21]. The lower atrophy and fatty infiltration rates in the UBE-TLIF group suggest that this technique better preserves muscle function and helps maintain the integrity of the spinal-pelvic-hip complex, which is essential for overall spinal health and function [7,22,23]. These findings differ from those of Ahn et al. [24], who reported minimal change in the multifidus muscle at 4 weeks following UBE decompression. This discrepancy may reflect differences in follow-up duration and surgical approach. Unlike Ahn et al. [24], who evaluated decompression alone over a short-term period, our study examined outcomes after both decompression and fusion with a 2-year follow-up. Another methodological difference is that Ahn et al. [24] measured only the CSA of the multifidus muscle, whereas we normalized muscle measurements to the corresponding intervertebral disc areas. This ratio-based method reduces interindividual variability and may provide a more reliable assessment of long-term muscle changes.
Postoperative pain relief and functional improvement are key indicators of surgical success. Previous studies have shown that minimally invasive techniques can lead to better pain control and faster functional recovery [6,7,13]. In the present study, both groups demonstrated significant improvements in JOA scores, VAS scores for leg pain and back pain, and ODI scores at all postoperative time points. However, the UBE-TLIF group achieved lower VAS and ODI scores at 1 and 2 years postoperatively, with differences reaching the MCID threshold. These superior outcomes may be explained by reduced muscle damage and stimulation associated with the UBE-TLIF procedure, reflected in lower postoperative creatine kinase levels and a lower incidence of complications. Collectively, these findings support the concept that preservation of muscle function and minimization of tissue trauma contribute to improved long-term pain control and functional recovery, consistent with previous research [13,17].
Surgical complications are important determinants of recovery and long-term outcomes. Consistent with prior reports, the most common complications observed with UBE-TLIF and W-TLIF were dural tears and nerve root injuries [25,26]. In our study, the UBE-TLIF group had a lower complication rate, with fewer cases of dural lacerations and transient L5 nerve root paralysis, most of which occurred during the early learning phase of the procedure [27]. The lower complication rate in the UBE-TLIF group is likely attributed to the minimally invasive nature of the technique, which limits tissue disruption and facilitates safer manipulation. Endoscopic visualization and precise surgical control further enhance safety. These findings are consistent with previous studies reporting the safety and efficacy of UBE-TLIF [13,14,28–30].
Some limitations of our study should be acknowledged. First, its retrospective design and lack of randomization may have introduced selection bias, despite propensity score matching. Second, long-term functional outcomes beyond 2 years were not evaluated. Third, although MRI measurements were standardized, they may have been affected by postoperative artifacts. Finally, the potential impact of the surgical learning curve for UBE-TLIF was not assessed. Future prospective multicenter studies with larger cohorts and longer follow-up are required to validate our findings and further clarify the long-term effects of these surgical techniques.
Conclusions
Both UBE-TLIF and W-TLIF offer satisfactory fusion rates and clinical outcomes in the treatment of LDD. However, UBE-TLIF offers distinct advantages, including reduced intraoperative blood loss, shorter operative time, faster recovery, and fewer complications. Over the long-term, UBE-TLIF is associated with less paravertebral muscle atrophy and fat infiltration, as well as superior VAS and ODI scores, highlighting better muscle protection and pain management. These results suggest that UBE-TLIF may represent a preferable option for patients with LDD, although confirmation in larger, prospective studies is warranted.
Key Points
Better muscle preservation: unilateral biportal endoscopic transforaminal lumbar interbody fusion (UBE-TLIF) resulted in less paravertebral muscle atrophy and fat infiltration than Wiltse approach transforaminal lumbar interbody fusion.
Lower postoperative pain: Visual Analog Scale scores were consistently lower in the UBE-TLIF group.
Shorter operative time: UBE-TILF required shorter surgical duration.
Comparable fusion outcomes: Fusion rates and modified Macnab outcomes were similar between groups.
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