Percutaneous unilateral biportal endoscopy versus uniportal endoscopy for lumbar spinal stenosis: a single-centre, prospective, non-randomised cohort trial protocol

Abstract

Introduction

Unilateral biportal endoscopic (UBE) technique and uniportal endoscopic (UE) technique have both been used to treat lumbar spinal stenosis (LSS) with satisfactory outcomes. Although previous studies have reported no difference in clinical outcomes between UBE and UE techniques, the evidence was weak due to the lack of a prospective design. Therefore, the present prospective study aimed to compare the efficacy and safety of UBE and UE for treating patients with LSS.

Methods and analysis

This single-centre, prospective, non-randomised cohort trial is designed to compare the efficacy and safety of UBE and UE in treating patients with LSS. We will include 120 participants (60 per group) with single-level or double-level LSS. The primary outcome will be determined using the Oswestry Disability Index at the 12-month postoperative follow-up between the two groups. Secondary outcomes will include the following: visual analogue scale scores for lower back and leg pain, Japanese Orthopaedic Association score, modified MacNab criteria, Medical Outcomes Study 36-Item Short Form Health Survey, operation time, blood loss and duration of postoperative hospital stay. Radiographic outcomes will include the enlargement ratio of the dural sac, bony decompression range and preservation rate of the facet joint measured on postoperative radiological data. Laboratory outcomes will include postoperative creatine kinase level and erythrocyte sedimentation rate. Adverse events will be recorded to assess safety. Participants will be assessed by a blinded assessor preoperatively and postoperatively at 3 days, 2 weeks, 1, 3, 6 and 12 months.

Ethics and dissemination

This study received approval from the Institutional Review Board of Beijing Friendship Hospital, Capital Medical University (2022-P2-336-02). All participants will provide informed consent prior to enrolment, and the study will be conducted in strict accordance with the Declaration of Helsinki. Study results will be disseminated via peer-reviewed publications and presentations at academic conferences.

Trial registration number

ClinicalTrials.gov (NCT06365229) and Chinese Clinical Trial Registry (ChiCTR2200066192).

STRENGTHS AND LIMITATIONS OF THIS STUDY.

• This study employs a prospective controlled cohort design.

• Clinical and radiological outcomes are comprehensively assessed.

• The limitations include single-centre design and non-double-blind methodology.

Introduction

Lumbar spinal stenosis (LSS) is a common degenerative disease in the elderly that usually causes low back pain, leg pain and neurogenic claudication.¹ A decompressive laminectomy is an effective option for patients whose chief complaints do not improve with standard conservative treatment.^{2 3} Recently, percutaneous endoscopic techniques, especially the unilateral biportal endoscopic (UBE) technique and the uniportal endoscopic (UE) technique, have been widely used in spinal degenerative diseases such as lumbar disc herniation, cervical spondylopathy and thoracic ossified ligamentum flavum.4,8 Similarly, unilateral or bilateral decompression performed using UBE or UE showed good clinical and radiological outcomes in patients with LSS.^{9 10} Furthermore, endoscopic decompression provides the advantages of minimally invasive surgery, such as reduced injury to the paraspinal musculoligamentous structures and enhanced recovery after surgery, compared with conventional decompression surgery.^{11 12}

There have been several studies comparing the efficacy and safety of UBE and UE techniques for treating patients with LSS. The results showed similar outcomes of these two techniques with slight differences in surgical duration or intraoperative complication rate.13,16 However, all these studies had retrospective designs; thus, the evidence suggesting the advantages of decompression using either the UBE or UE technique for LSS was weak. Therefore, a prospective cohort study is warranted to provide higher-level evidence on this topic. The present single-centre, prospective, non-randomised cohort trial aims to compare the clinical and radiological outcomes between UBE and UE techniques in order to provide a higher level of evidence, which will be helpful for spine surgeons to make better decisions in clinical practice.

Materials and analysis

Trial design

The present study presents the protocol of a single-centre, prospective, non-randomised cohort trial that proposes to compare the efficacy and safety of percutaneous UBE and UE decompressions for the treatment of LSS. The study will enrol 120 patients (60 in the UBE group and 60 in the UE group) from 1 January 2023 to 31 December 2023. Each patient will be postoperatively followed up at 3 days, 2 weeks, 1, 3, 6 and 12 months. The study is due to be completed on 31 December 2024. The flow chart of this study is shown in figure 1.

Figure 1. Flow chart of the study.

Participants

Enrolment eligibility will be determined based on the following inclusion and exclusion criteria:

Inclusion criteria

1. Age range: 50–80 years.

2. Diagnosed with LSS of 1–2 response levels.

3. The predominant manifestation is neurogenic intermittent claudication, and conservative treatment has been ineffective for at least 3 months.

4. Degenerative lumbar spondylolisthesis of Grade I or without spine instability.

5. Patients agree to participate in the study and are willing to complete the follow-up.

Exclusion criteria

1. Isthmic lumbar spondylolisthesis or degenerative lumbar spondylolisthesis of greater than Grade I.

2. Instability at the response level.

3. Prior surgical history at the response level.

4. Scoliosis with Cobb angle >20 degrees.

5. Other conditions affecting the lumbar spine (infection, tumour, fracture, neurological diseases and others).

6. Patients with medical disorders who are unable to tolerate surgery.

Recruitment

Patients with LSS undergoing UBE or UE decompression performed by two experienced spine surgeons at the same hospital will be recruited for the study. The assignment to either the UBE or UE group will be determined after thorough discussion between the operating surgeon and the patient regarding their condition and the advantages/disadvantages of both endoscopic techniques, with full respect for the patient’s autonomous decision. After providing written consent, all participants will receive a baseline test and an outcome assessment. For all participants, demographic variables, including age, sex, body mass index (BMI), medical comorbidities, smoking or alcohol status, symptom duration, physical examination findings, previous spinal surgery and affected level and stenosis grade, will be collected. No harmful or adverse events (AEs) are anticipated, as the outcome data will only be obtained using preoperative and postoperative questionnaires and clinical and radiological assessments. Therefore, no incentives will be provided to the study participants.

Blinding

This is a single (assessor) blinded trial comparing UBE and UE techniques. Only the assessor will be blinded because the participants and surgeons will have knowledge about the surgical procedure they have undergone or performed, respectively. All clinical and radiological information will be collected by the blinded assessor. The assessor will provide a detailed justification of the event if unblinding becomes necessary.

Treatment

UBE group

All procedures will be performed under general anaesthesia in the prone position with mild spine flexion. After confirming the surgical level under fluoroscopic guidance, the lumbosacral area will be prepared and sterilised. Subsequently, two transverse incisions, each 1 cm in length, will be made approximately 1.5 cm above and below the target position, the intersection site of the lower margin of the upper vertebral lamina and the middle line of the inferior articular process in the lower vertebra. The cranial portal will be used for a 0 degree endoscope with a continuous irrigation system, and the caudal portal will be used for decompressive operations. The positions of the working portals will be confirmed using fluoroscopy. Subsequently, the muscles will be divided using a blunt separator and an electrical coagulator. Unilateral or bilateral decompression will be determined based on clinical symptoms and radiological images. Bony decompression will be performed using an arthroscopic emery burr 4 mm in diameter and a Kerrison rongeur until the cranial, caudal and bilateral endpoints of the ligamentum flavum are exposed. This will be followed by partial laminotomy and facetectomy. The ligamentum flavum will then be removed using a Kerrison rongeur or pituitary forceps after confirming complete detachment from both the dura and lamina. Decompression of the lateral recess will be considered complete after normal respiration-induced pulsatility of the dura and nerve roots is observed (figure 2).

Figure 2. Radiological images of unilateral biportal endoscopy (UBE) and uniportal endoscopy (UE) technique for lumbar spinal stenosis. (A) UBE decompression procedure. (B) Preoperative CT scan of the lumbar spine showed stenosis at the L4/5 level. (C) Postoperative CT scan showed sufficient decompression after the UBE procedure. (D) UE decompression procedure. (E) Preoperative CT scan showed stenosis at the L3/4 level. (F) Postoperative CT scan showed sufficient decompression after UE procedure.

UE group

All procedures will be performed with the patient in the prone position. Intravenous Sufentanil (5 µg) and local anaesthesia (1% ropivacaine, 10 mL; 2% lidocaine, 15 mL; 0.9% normal saline, 20 mL) will be administered. Under fluoroscopic guidance, an 18-gauge spinal needle will be advanced into the posterior ligamentum flavum, confirming placement at the interlaminar space midpoint. Sequentially, the guidewire, obturator, working cannula, endoscopic trephine and endoscope system will be introduced. Bony decompression will proceed endoscopically using trephines or Kerrison punches in the following sequence: ipsilateral lower lamina, upper spinous process, contralateral lower lamina, ipsilateral lateral recess, lower spinous process and contralateral lateral recess. The ligamentum flavum will be detached from its insertion site and removed en bloc. The decision for unilateral or bilateral decompression will be based on preoperative clinical symptoms and radiological findings. Decompression will be deemed complete when direct endoscopic visualisation confirms: relief of dural and neural compression, and free mobilisation of bilateral nerve roots using a flexible probe (figure 2).¹⁷

Follow-up

Patients will be followed up postoperatively at 3 days, 2 weeks, 1, 3, 6 and 12 months at an outpatient clinic. Clinical and radiological evaluations will be performed as described in table 1.

Table 1. Evaluation schedule.

Variables	Preoperative	Postoperative	Follow-up
		Immediately/0 day	1–3 days	2 weeks	1 month	3 months	6 months	12 months
Demographic variables
Age	√
Gender	√
BMI	√
Medical comorbidity	√
Smoking status	√
Alcohol status	√
Symptoms duration	√
Physical examination finding
Previous spinal surgery	√
Affected level	√
Stenosis grade	√
Surgical information
Operation time		√
Blood loss		√
Postoperative hospital stays			√
Primary outcomes
ODI	√				√	√	√	√
Secondary outcomes
VAS for leg/back pain	√	√	√	√	√	√	√	√
JOA	√				√	√	√	√
Modified MacNab criteria				√		√		√
SF-36	√			√	√	√	√	√
Surgical complication		√	√	√	√	√	√	√
CT				√
MRI				√
CK	√	√	√	√
ESR	√	√	√	√

BMI, body mass index; CK, creatine kinase; ESR, erythrocyte sedimentation rate; JOA, Japanese Orthopaedic Association; ODI, Oswestry Disability Index; SF-36, Medical Outcomes Study 36-Item Short Form Health Survey; VAS, visual analogue scale.

Outcome measures

Primary outcome

The primary outcome will be the efficacy of UBE and UE in treating patients with LSS. Efficacy will be determined using the Oswestry Disability Index (ODI) at the 12-month postoperative follow-up between the two groups. The simplified Chinese version of the ODI comprises 10 questions with a score range of 0–5 points for each question. The ODI score is the summed score divided by the total score and is expressed as a percentage.¹⁸

Secondary outcome

The secondary outcomes include clinical, radiographic, laboratory outcomes and AEs. Clinical outcomes include (1) Lower back pain and leg pain, measured based on the visual analogue scale (VAS), which ranges from 0–10, (2) Japanese Orthopaedic Association (JOA) score; the simplified Chinese version of the JOA score includes five aspects: lower back pain, lumbar function, walking ability, social life function, mental health and the recovery rate is calculated based on the JOA score before and after surgery¹⁹, (3) Modified MacNab criteria, which is used to assess the overall effectiveness of the surgery; it includes four grades: excellent, good, fair and poor, (4) Medical Outcomes Study 36-Item Short Form Health Survey (SF-36), which ranges from 0–100, with higher scores indicating better health-related quality of life and (5) Surgical information, such as operation time (minutes), blood loss (mL) and postoperative hospital stay (days). The radiographic outcomes include the (1) Enlargement ratio of the dural sac ((postoperative dural sac cross-sectional area/preoperative dural sac cross-sectional area −1)×100%), (2) Bony decompression range (coronal projection area of the resected lamina and facet joint complex) and (3) Preservation rate of the facet joint (postoperative facet joint width/preoperative facet joint width×100%) measured on postoperative MRI or CT scans.^{20 21} The laboratory outcomes include postoperative creatine kinase (CK) levels and erythrocyte sedimentation rate (ESR). AEs during the period from enrolment to the end of the study will be monitored and recorded to assess the safety of decompression using UBE or UE for LSS.

Data collection and management

The electronic Case Report Form (eCRF) will be designed according to the study protocol. Trained researchers will collect and enter all data, with subsequent independent verification by a second trained researcher. A specialised data management partner will maintain the database, leveraging their expertise in eCRF systems. To ensure data quality and trial integrity, an independent clinical research associate will conduct regular audits of the research data.²²

Quality control

All participating researchers will receive standardised training in protocol implementation, data collection, eCRF completion, clinical evaluation and radiological assessment. Radiological data will undergo dual independent measurements, with final results averaged. Major discrepancies will trigger third-party verification and documented analysis. Post-study, all data will undergo three-tier quality checks before database locking. Original records will be securely stored in both electronic and physical formats according to the corresponding regulations.

Sample size consideration

This trial will recruit 120 participants (60 participants per group) to compare the primary outcome (ODI score) between UBE and UE decompression for LSS. The sample size calculation was based on the ODI score at 12-month follow-up. According to previous literature reported, the minimal clinically important ODI score difference was 12.8,²³ and the SD of the ODI score 12 months after endoscopic decompression was 19.6.²⁴ A sample size of 60 patients per group was determined based on the following values and parameters: alpha 0.05, power 0.90, two-sided CI 95% and 10% loss to follow-up. Power Analysis and Sample Size software V.15 (NCSS, Kaysville, UT, USA) was used for calculating the sample size.

Statistical analyses

Participants failing to complete the 12-month postoperative follow-up will be excluded from the primary analysis. To mitigate potential bias from missing data and maintain study validity, we aim for a minimum follow-up rate of >80%. Data distribution will be assessed using the Shapiro-Wilk test. Continuous variables will be expressed as mean±SD (normally distributed) or median and IQR (non-normally distributed). Categorical variables will be reported as frequencies and percentages. Data will be compared between the two groups using independent sample t-tests for continuous variables, including the ODI, VAS, JOA, SF-36, operation time, blood loss, postoperative hospital stay, enlargement ratio of the dural sac, bony decompression range, preservation rate of the facet joint, CK and ESR levels. The χ² tests will be used for modified MacNab criteria, surgical complications and AEs. Non-parametric alternatives (Mann-Whitney U test) will be employed if normality assumptions are violated. Statistical significance was set at p<0.05. All data analyses will be performed using the SPSS V.25.0 software (IBM, Armonk, NY, USA).

Safety reporting

All AEs occurring from enrolment through study completion will be actively monitored and documented. Documentation will include: AE terminology, start/end dates, time of reporting, severity grade, relationship to study procedures, whether it led to participant withdrawal and outcome. Any unexpected AEs must be reported immediately to the Institutional Review Board, Principal Investigator and Sponsor. Participants experiencing AEs requiring medical attention will receive timely intervention. All AEs will be followed until resolution or stabilisation.²⁵

Patient and public involvement

Patients or the public were not involved in the design, or conduct, or reporting or dissemination plans of our research.

Ethics and dissemination

This study has been registered in the ClinicalTrials.gov (NCT06365229) and the Chinese Clinical Trial Registry (ChiCTR2200066192). This study received approval from the Institutional Review Board of Beijing Friendship Hospital, Capital Medical University (2022-P2-336-02). All participants will provide informed consent (online supplemental file Participant Consent Form) prior to enrolment, and the study will be conducted in strict accordance with the Declaration of Helsinki and the Standard Protocol Items: recommendations for Interventional Trials statement.²⁶ Study results will be disseminated via peer-reviewed publications and presentations at academic conferences.²⁵

Discussion

Endoscopic lumbar decompression, including UBE and UE techniques, has been widely used to treat patients with LSS.27,33 These results showed that both techniques provide similar clinical outcomes compared with traditional microsurgical procedures. In a prospective randomised controlled study, which included 32 patients per group, Park et al²⁷ compared the clinical outcomes between UBE decompression and mini-open microscopic laminectomy in the treatment of LSS. The results showed the UBE technique achieved more rapid pain recovery, less fentanyl usage and shorter hospital stay compared to the mini-open microscopic technique. Heo et al²⁸ carried out a prospective case-control study to evaluate whether sufficient lumbar decompression can be achieved by using the UBE technique. A total of 88 patients were involved in the study, including 46 patients in the UBE group and 42 in the microscope group. With a mean follow-up period of 14.5±2.3 months, the results showed both techniques could achieve significant dura sac enlargement compared with the preoperative area. There was no difference in both radiological and clinical outcomes in terms of dura expansion, VAS for back and leg pain and ODI between the two groups.

UE decompression has also been used to treat patients with LSS and shown comparable clinical outcomes with conventional microsurgical techniques.^{13 30 34 35} Süner et al³⁰ compared the long-term results of patients with LSS, who received the uniportal and tubular endoscopic procedures and the long-term results were similar between these two techniques, of which the PE group had an advantage in less blood loss during operation. Komp et al^{31 32} reported two prospective results of UE decompression for patients with LSS, indicating that the decompression results were equal to those of conventional procedures; however, the UE technique brought advantages in complications, traumatisation and rehabilitation. In a recent study, Kesornsak et al³³ reported long-term clinical outcomes of UE interlaminar approach for lateral recess stenosis. At 10 years of follow-up, 69.35% of the patients were satisfied with surgical results, and the reoperation rate was 8.06%. A relatively steep learning curve associated with UE was one concern for this technique in patients with LSS and around 35 cases would be needed for the early period of the learning curve.^{36 37} While the learning curve analysis of the UBE technique also demonstrated that a substantial learning period of more than 50 surgical cases may be needed before gaining adequate expertise in performing UBE decompression.^{38 39}

The UBE technique, characterised by its dual-port design featuring independent viewing and working channels, offers an expanded endoscopic visual field and more flexible intracorporeal manipulation.¹³ Additionally, UBE presents a relatively gentler learning curve compared to UE, as its operative workflow more closely resembles conventional open procedures.³⁸ However, UBE’s limitations include slightly greater surgical trauma associated with dual-portal establishment (typically 7–8 mm each) and the routine requirement for general anaesthesia. Conversely, UE technique employs a single working channel (usually 6–8 mm), resulting in minimised soft tissue disruption and consequently faster postoperative recovery.³² Its compatibility with conscious sedation makes it particularly suitable for elderly patients with multiple comorbidities who are poor candidates for general anaesthesia.¹⁷ The transforaminal approach provides optimal access for foraminal stenosis decompression, demonstrating unique technical superiority in such scenarios.⁴⁰ Nevertheless, UE’s relatively constrained visual field and restricted instrument working space may present a little challenge for surgeons to master it.

Evidence comparing the efficacy of UBE and UE in treating patients with LSS is limited. Heo et al¹³ compared the clinical and radiological outcomes of three types of minimally invasive decompressive surgeries for treating LSS—microsurgery, UBE and UE—and found that the UBE group had better radiological outcomes than the UE group. Hua et al¹⁴ performed a pair-matched case-control study and reported little difference in the clinical outcomes of UBE and UE in the treatment of LSS, except for surgical duration. Another cohort study based on a prospective registry indicated that UBE and UE had identical efficacy in the treatment of LSS; however, the UBE technique had potentially lower risks of intraoperative complications, inadequate decompression and conversion to open surgery during the early period of the learning curve.¹⁵ One recent meta-analysis of the above studies showed no significant differences in most clinical outcomes between the uniportal and biportal surgeries, although UBE might have a better ODI score at the end of follow-up than UE.¹⁶ However, most of these studies had a retrospective design, meaning that only preliminary results with a low level of evidence were available. Only one prospective randomised controlled trial (RCT) from Wei et al⁴¹ reported no difference in ODI, VAS, EQ-5D and JOA scores between the Delta large-channel endoscopy and UBE for treating LSS at 3-month follow-up. However, this study had limitations, especially in short follow-up and the absence of radiological evaluation.

To the best of our knowledge, this is one of the few single-center, prospective, non-randomised cohort trials to compare the efficacy and safety of UBE and UE decompression in patients with LSS. The clinical and radiological results will be evaluated comprehensively and in detail during the prospective follow-up up to 1 year after surgery, which is also a favourable supplement to the existing studies in terms of study design and content. We expect similar outcomes between the two groups.

However, this study protocol has some limitations. First, this was not a double-blind RCT. Second, all participants in this study were enrolled from only one spine the centre, and there may be a selection bias. Despite these limitations, this trial will provide a high level of evidence for the efficacy and safety of UBE and UE in patients with LSS and will facilitate the development of clinical practice guidelines on the UBE technique for spine surgery.

Trial status

The protocol was the second (V.2, 2022/10/17). The protocol status was in follow-up status and had not been completed.