Abstract
Background Unilateral laminectomy bilateral decompression with unilateral biportal endoscopy (UBE-ULBD) is widely used for lumbar spinal stenosis (LSS). This study introduces a modified UBE-ULBD technique, the “look-back” technique, aiming to reduce postoperative complications.
Methods This retrospective study enrolled 88 lumbar spinal stenosis patients, with 45 undergoing conventional UBE-ULBD surgery and 43 undergoing the look-back technique. Baseline characteristics, surgical level distribution, operative time, hemoglobin level, hematocrit level, blood loss, hospital stay, complications, visual analog scale (VAS) for back and leg pain, the Oswestry Disability Index, and modified MacNab criteria were assessed.
Results Demographics, comorbidities, and American Society of Anesthesiologists classifications showed no significant differences between the groups. The calculated blood loss in the look-back group was significantly less than that in the UBE-ULBD group (302 mL [Q1, Q3 166, 424 mL] vs 384 mL [Q1, Q3 267.5, 524 mL], P < 0.05). The VAS for leg pain at 1 day after surgery in look-back group was significantly lower than that in UBE-ULBD group (1.72 ± 0.96/2 [1, 2] vs 2.27 ± 1.25/2 [2, 3], P < 0.05). No significant difference was observed in surgical level distribution, surgical time, preoperative/postoperative hemoglobin or hematocrit level, complications, hospital stay, VAS back pain score at 1 day after surgery, VAS low back/leg pain scores at 1 month and 6 months, Oswestry Disability Index scores at 1 month and 6 months, or MacNab outcome at 6 months.
Conclusions The look-back technique significantly reduces intraoperative blood loss and early leg pain after UBE-ULBD, although it does not significantly lower the overall complication rate.
Level of Evidence 3.
- unilateral biportal endoscopy
- unilateral laminectomy bilateral decompression
- lumbar spinal stenosis
- surgical complications
- epidural hematoma
Background
Unilateral biportal endoscopy (UBE) technique is a minimally invasive approach for treatment of spinal disorders with 2 separate observation and operation windows. Since the first report in 1996, UBE has undergone the establishment of theoretical frameworks, innovations in surgical instruments, and the expansion of indications.1–3 Recently, it has become a powerful tool in the treatment of spinal diseases due to the minimally invasive injury, optimal visualization, direct decompression, and quick recovery. Currently, UBE technology finds its most extensive application in lumbar spine disorders, including lumbar spinal stenosis (LSS), lumbar disc herniation, and lumbar spondylolisthesis, among others.
However, while UBE offers minimally invasive advantages, it also presents postoperative complications with expanding surgical cases, unstandardized indication criteria, and operator learning curve disparities. According to literature reports, the overall complication rate of UBE surgery ranges from 6.27% to 8.1%, with the most common complications including dural tear, epidural hematoma, transient paralysis, inadequate decompression, and nerve root injury.4–6 These complications have led to diminished patient satisfaction, prolonged hospital stays, increased medical costs, and erosion of patient trust. Minimizing postoperative complications in UBE technique is crucial in improving patient outcomes.
In recent years, unilateral laminectomy bilateral decompression with unilateral biportal endoscopy (UBE-ULBD) surgery has gained increasing popularity as an alternative surgical modality for LSS. Concurrently, technical refinements and improved outcomes continue to dominate scholarly discourse in minimally invasive spine surgery. In the present article, we proposed the “look-back” technique to refine UBE-ULBD surgery with the aim of comparatively evaluating whether this novel technique yields superior clinical outcomes in patients with LSS.
Methods
Patient Selection
In this retrospective study, we enrolled 88 consecutive patients with the diagnosis of LSS who underwent UBE surgery between January 2023 and December 2024. Among them, 45 underwent conventional UBE-ULBD surgery (UBE-ULBD group) and 43 underwent modified UBE-ULBD surgery referred to as the look-back technique (look-back group). The inclusion criteria were as follows: (1) the patients have typical symptoms such as low back pain, limb neurological impairment, and intermittent claudication for more than 6 months with failure of conservative treatment; (2) bilateral lumbar stenosis on preoperative magnetic resonance imaging (MRI) with Schizas grade B to C (grade A, cerebrospinal fluid is clearly visible inside the dural sac with inhomogeneous rootlets distribution; grade B, rootlets occupy the whole dural sac but can still be individualized; grade C, rootlets cannot be recognized with posterior epidural fat and invisible cerebrospinal fluid; grade D, rootlets cannot be recognized with no posterior epidural fat);7 (3) the image characteristics were in accordance with the symptoms and physical examination; (4) patients underwent single level lumbar surgery with a minimum follow-up of 6 months. Exclusion criteria were spinal deformity, spondylolisthesis, infection, tumor, or previous lumbar operation at the same level. All surgeries were performed by a single experienced spinal surgeon. This study was approved by the Ethics Committee of the Third Affiliated Hospital of Naval Medical University, and written informed consent was obtained from all patients.
Surgical Techniques
UBE Technique
The conventional UBE-ULBD techniques (UBE-ULBD group) was followed, as outlined by others8–10 and futher described here. The patient is placed in a prone position with the abdomen suspended after satisfactory general anesthesia. The operating table is adjusted to keep the target disc level perpendicular to the ground and mild lumbar flexion so that the operating intervertebral space is stretched. Then anteroposterior x-ray imge of the lumbar spine is obtained under “C”-arm fluoroscopy with a grid-shaped metal plate on surgical site (Figure 1A). At the target disc level, midline of the spinous process, pedicles, the inferior endplate line of the cephalad vertebra, and the line connecting the medial borders of ipsilateral pedicles of 2 adjacent lumbar vertebrae are drawn. The 2 longitudinal incisions as endoscopic and instrumental portals are set at 1 to 1.5 cm cephalad and caudad from the intersection point of the latter 2 lines according to the individualized characteristics10 (Figure 1B). Anteroposterior (if necessary) and lateral fluoroscopy is again required to confirm the exact surgical level with Kirschner pins on surgical site (Figure 1C–D). After disinfection and draping, the skin, subcutaneous tissue, and deep fascia are sequentially incised, and then graduated tubular dilators are inserted to establish a triangular operative space. Then intraoperative fluoroscopy is again performed to confirm the exact surgical level (Figure 1E–F). The UBE endoscope with isotonic saline under gravity-based hydrostatic perfusion is inserted into the observation channel to ensure a clear field of vision. Key procedural steps of the ULBD are schematically presented in Figure 2. In the operating channel, the plasma radiofrequency device is used to achieve hemostasis of soft tissues. Partial laminotomy for bilateral spinal stenosis is performed to remove the lower part of the cephalad vertebra lamina and the upper part of the caudad lamina using a high-speed microdrill and Kerrison punches.11 Next, contralateral and dorsal parts of the ligamentum flavum were dissected and removed by a nerve dissector and Kerrison punches. Hemostasis or coagulation pretreatment of diffuse epidural vessels by radiofrequency devices is necessary when handling the exposure and separation of the adhesion between the disc and the dural sac (nerve root) by a nerve hook. The contralateral nerve root canal entrance and lateral recess were carefully expanded to achieve decompression by the osteotome or Kerrison punches. The identical technique was performed to remove the ipsilateral ligamentum flavum and decompress the ipsilateral nerve root canal. Gentle retraction of the dural sac and nerve root with a nerve retractor enables clear visualization of the herniated disc, allowing subsequent removal of the herniated nucleus pulposus using nucleus pulposus forceps. Following confirmation of adequate dural sac and nerve root decompression and definitive hemostasis, a drain is inserted, and the surgical incision is closed.
Fluoroscopic localization steps for targeting surgical level. (A) Anteroposterior (AP) radiograph of the lumbar spine obtained with a grid-shaped metal plate positioned over the surgical site. (B) Markers drawn on the patient’s back according to the radiograph from panel A. (C) The AP view with K-wires for identifying spinal markers projection. (D) The lateral view for confirming the target disc level. (E and F) AP/lateral views with graduated tubular dilators for confirming the target level.
Key procedural steps of the unilateral laminectomy bilateral decompression (ULBD). (A) Partial laminectomy for ipsilateral spinal stenosis. (B) Partial laminectomy for contralateral spinal stenosis. (C) Contralateral and dorsal parts of the ligamentum flavum resection. (D) Decompression of the contralateral nerve root canal. (E) Contralateral nerve root exploration. (F) Ipsilateral part of the ligamentum flavum resection. (G) Decompression of the ipsilateral nerve root canal. (H) Discectomy with ventral dural decompression. (I) ULBD endpoint verification.
Look-Back Technique
The look-back technique remains identical to conventional UBE-ULBD techniques in surgical preparation, fluoroscopic localization, surgical approach, partial laminotomy, the ligamentum flavum dissection, the nerve root canal decompression, and nucleus pulposus removal. Key procedural steps of the look-back technique are illustrated in Figure 3 and recorded in Video 1. Before drain placement, we withdraw the endoscope and surgical instruments from the 2 channels and wait for 5 minutes and 30 seconds (average time) according to the standardized normal Ivy bleeding time.12 Next, the endoscope is again inserted into the observation channel to inspect the dural sac and nerve root. As expected, a massive blood clot covers the dural sac and nerve root. Specifically, we gently remove the blood clots by nerve hook and nucleus pulposus forceps via the operating channel (Figure 4). The purpose of this procedure is that evacuation of the epidural hematoma could reduce inflammatory and compressive irritation of the hematoma on the nerve roots, which may cause potential sensorimotor deficits in the early postoperative stage. Following secondary radiofrequency hemostasis beside the dural sac and nerve root, the surgery concludes with drain placement and wound closure.
Key procedural steps of look-back technique. (A) Unilateral laminectomy bilateral decompression (ULBD) endpoint verification. (B) Massive blood clot covers the dural sac and nerve root after 5 min and 30 s undisturbed period following ULBD. (C) Removal of ipsilateral blood clots by a nerve hook. (D) Removal of ipsilateral blood clots by nucleus pulposus forceps. (E) Radiofrequency hemostasis beside ipsilateral dural sac and nerve root. (F) Removal of contralateral blood clots by a nerve hook. (G) Removal of contralateral blood clots by nucleus pulposus forceps. (H) Radiofrequency hemostasis beside contralateral dural sac and nerve root. (I) Look-back technique endpoint verification.
Epidural hematoma evacuation by look-back technique. (A) Intraoperative view of ipsilateral dural sac and nerve roots after unilateral laminectomy bilateral decompression (ULBD). (B) Clot mass covering the dural sac and nerve root after 5 min and 30 s undisturbed period following ULBD. (C) Intraoperative view of ipsilateral dural sac and nerve roots when removing epidural hematoma by look-back technique. (D) Intraoperative view of ipsilateral dural sac and nerve roots after evacuation of epidural clot mass by Look-back technique. (E) Retrieved hematoma clots on sterile gauze.
Perioperative Management
No anticoagulant or antifibrinolytic agents (including tranexamic acid) were used during the perioperative period in any patient for both groups. Intraoperative blood pressure management was standardized for all cases. We maintained systolic blood pressure at approximately 100 mmHg (within a range of 90–110 mmHg) throughout the procedure to minimize bleeding and ensure a clear surgical field. All patients were routinely treated with analgesic and neurotrophic drugs and performed ankle pump exercises to keep blood circulating and prevent deep vein thrombosis. Functional exercises such as straight leg raising on postoperative day 1 (POD1) are also encouraged for the purpose of preventing nerve root adhesion. Based on low drain output (<50 mL) and complication-free status, the drainage catheter is electively removed in the morning of POD1. Early mobilization and ambulation independence with a lumbar brace are encouraged in patients without postoperative complications following drain removal.
Data Collection and Assessment
Baseline characteristics including age, gender, height, weight, body mass index, hypertension, diabetes, cardiocerebrovascular disease, and American Society of Anesthesiologists classification were recorded.
Perioperative information, including target disc level, surgical time, hemoglobin, hematocrit, total blood loss, complications (dural tear, epidural hematoma, transient paralysis, and nerve root injury), and hospital stay, was collected and evaluated. Given the challenge in quantifying intraoperative blood loss due to continuous saline irrigation during endoscopic surgery, patient blood volume (PBV) was calculated based on the formula proposed by Nadler et al,13 as follows:
PBV = k1 × height (m)3 + k2 × weight (kg)2 + k3
k1 = 0.3669, k2 = 0.03219, and k3 = 0.6041 for males; k1 = 0.3561, k2 = 0.03308, and k3 = 0.1833 for females.
TBL was calculated according to the formula proposed by Gross,14 as follows:
TBL = PBV × (HCTpre − HCTpost)/HCTave
HCTpre is the preoperative hematocrit, HCTpost is the hematocrit on POD1, and HCTave is the average of the pre- and postoperative hematocrits.
Clinical outcomes were assessed by visual analog scale (VAS) for back and leg pain, Oswestry Disability Index (ODI) at 1 day, 1 month, and 6 months after surgery. The patient satisfaction rate of clinical outcomes was evaluated at 6 months after surgery by modified MacNab criteria with four grades: excellent, good, fair, and poor. Excellent and good grades were classified as satisfactory efficacy. Blinding of outcome assessors to surgical techniques is implemented during pain and functional assessment to reduce observer bias.
Statistical Analysis
GraphPad PRISM version 9 (GraphPad Software Inc., CA, USA) was used to analyze the data. Continuous variables were expressed as mean (SD) or median (Q1 and Q3) and compared using t test or Wilcoxon rank sum test conditionally on the distribution of the variables. Categorical variables were depicted as count and compared using the χ2 test or Fisher exact test. The level of statistical significance was set at P value < 0.05.
Results
Baseline characteristics
A total of 88 patients (45 and 43 cases in the UBE-ULBD and look-back groups, respectively) met the inclusion criteria and were enrolled in the study. The patients’ baseline characteristics are shown in Table 1. Demographic data, such as age, gender, height, weight, body mass index, comorbidity (hypertension, diabetes, or cerebrovascular disease), and American Society of Anesthesiologists classifications showed no significant differences between the groups.
Baseline characteristics.
Perioperative Information
Perioperative information was depicted in Table 2. Surgical levels were similarly distributed between the UBE-ULBD and look-back groups (3 vs 2 at L3/L4; 29 vs 25 at L4/L5; 13 vs 16 at L5/S1; P = 0.68). There was no significant difference in surgical time between the 2 groups (130.0 minutes [Q1, Q3 112.5, 139.0 minutes] vs 133.0 minutes [Q1, Q3 118.0, 146.0 minutes], P = 0.12). No significant differences were observed in pre- and postoperative hemoglobin or hematocrit levels. The TBL in the look-back group was significantly less than that in the UBE-ULBD group (302 mL [Q1, Q3 166, 424 mL] vs 384 mL [Q1, Q3 267.5, 524 mL], P < 0.05). Complications occurred in 3/45 (6.67%) patients in the UBE-ULBD group and 1/43 (2.33%) patients in the look-back group (P = 0.62). In the UBE-ULBD group, complications included 1 case of dura tear and 2 cases of acute neurological symptoms, while for the look-back, 1 case of dura tear developed. For all patients who developed complications, symptoms resolved with conservative treatment, and no secondary surgical intervention was required. Patients in the UBE-ULBD group had a longer length of hospital stay than those in the look-back group (5 days [Q1, Q3 4, 6 days] vs 6 days [Q1, Q3 4.5, 6 days], P = 0.11).
Perioperative information.
Surgical Outcomes
All the surgical outcome assessments are shown in Table 3. There were no significant differences in VAS scores for low back and leg pain and ODI preoperatively between the 2 groups (P > 0.05). The VAS leg pain score at 1 day after surgery in the look-back group was significantly lower than that in the UBE-ULBD group (1.72 ± 0.96/2 [1, 2] vs 2.27 ± 1.25/2 [2, 3], P < 0.05), but this difference was not found in the VAS back pain score at 1 day after surgery. No significant differences existed in VAS or ODI scores between the 2 groups at 1 month or 6 months after surgery (P > 0.05). There was no significant difference in MacNab outcome assessment at 6 months after surgery between the 2 groups (P = 0.85), with no intergroup difference in satisfactory efficacy rates (P = 0.42).
Surgical outcomes.
Discussion
The UBE-ULBD technique represents an advanced minimally invasive spine technique in the past decade. It enables surgical intervention through 2 minimally invasive portals on a single side and achieves ipsilateral stenosis decompression and contralateral indirect decompression.15 Compared with conventional ULBD surgery, UBE-ULBD technique demonstrates superior spinal stability preservation, reduced perioperative blood loss, shorter hospitalization, and enhanced long-term functional outcomes.11,16 However, patients complained of symptoms such as acute back pain, sensory abnormalities, radicular pain, or motor weakness in lower extremities during early postoperative stages. Evidence indicates that specific postoperative complications contribute to early sensorimotor deficits following UBE surgery.4–6,17–19
To improve early perioperative outcomes, we implemented “Look-back” technical modifications to allow intrinsic coagulation mechanisms to achieve stable clot formation and then remove the compressive hematomas adherent to the dura and nerve root by secondary surgical exploration. Reradiofrequency hemostasis with the natural coagulation process helps mitigate postoperative hematoma formation. Although this technique increased operation time at the personalized level, results demonstrated significant reductions in blood loss and VAS score of leg pain at the early postoperative stage. In this research, our modified ULBD technique refinements yielded 21.35% hemorrhage reduction and 0.55-point VAS improvement within the first day after the operation. Although no statistically significant differences were observed in length of hospital stay, complication rates, or 6-month follow-up satisfaction between the 2 groups, the modified technique did yield significant reductions in intraoperative blood loss and early postoperative leg pain, which are clinically relevant perioperative benefits.
With regard to early postoperative complications, postoperative spinal epidural hematomas (PSEH) represent a highly concerning and frequently reported factor. Compared with lumbar discectomy, LSS surgery often requires extensive laminectomy and ligamentum flavum resection, leaving bare cancellous bone surface damaged epidural vessels, which consequently contribute to greater blood loss and a higher risk of PSEH. In UBE-ULBD surgery, continuous saline irrigation maintains a clear surgical field for effective radiofrequency hemostasis, paradoxically masking bleeding when high-pressure irrigation exceeds average venous pressure (40 mmHg) and suppresses normal hemorrhagic responses.20 Hemorrhagic recurrence following irrigation discontinuation at the surgical site may lead to unnoticed hematoma formation, posing a significant risk for symptomatic PSEH.16 PSEH must be suspected when new-onset neurological deterioration develops or aggravated symptoms compared with the preoperative state in the early postoperative period, including severe pain from the surgical site, radicular pain or paresthesia in the lower extremities, and decreased muscle strength.20,21 In our study, although the look-back group showed lower blood loss and less early leg pain, the incidence of suspected PSEH did not differ significantly between the 2 groups, suggesting that the observed pain improvement may be related to other mechanisms such as local decompression of adherent clots rather than a reduction in the overall PSEH rate. Objectively, it is undeniable that the causes contributing to acute neurological symptoms also include traction or adhesiolysis on the nerve root, thermal injury from radiofrequency, incomplete decompression, and improper positioning of the drainage.5,17,18
Limitations
Several limitations should be noted in our study. First, the significant improvement in leg pain VAS on POD1 in the look-back group might be associated with the clearance of blood clots adhering to the nerve root, thereby reducing local inflammatory irritation and space-occupying pressure. However, this finding should be interpreted with caution. Multiple potential sources of bias, such as subjective pain perception, perioperative analgesic use, nerve root manipulation, irrigation pressure, or subtle differences in decompression extent, may have influenced early VAS scores. Second, our findings suggest that the look-back technique may help reduce calculated TBL. While soft tissue bleeding is typically manageable, persistent oozing from the cancellous bone surface exposed during laminectomy remains a significant challenge in UBE-ULBD. By re-evaluating the surgical field with the look-back technique, we identified that in certain cases active bleeding directly from the bone surface often persisted, necessitating additional targeted hemostasis. It must be noted, however, that TBL calculated via formulas is a theoretical estimate and may be influenced by surgical technique, surgeon preference, extent of decompression, coagulation function, intraoperative blood pressure management, individual patient variations, etc. Despite these variables, the look-back technique provides a structured intraoperative option for definitive hemostasis, which is particularly beneficial as a reference for surgeons in their learning curve. Third, when assessing surgical outcomes, we adopted suspected PSEH symptoms rather than MRI scanning to determine the likelihood of PSEH. Routine MRI screening for mild symptomatic PSEH was clinically impractical, as it would incur unnecessary healthcare expenditures. Evidence indicates that mild PSEH symptoms without neurological aggravation usually disappear within 3 weeks postoperatively, with corresponding radiological regression occurring spontaneously within 3 months.22 Of course, postoperative neurological recovery itself constitutes a critical factor in surgical outcome assessment. Finally, we must acknowledge the limitations of this retrospective analysis. The potential for overattribution of clinical improvements to the look-back technique exists due to inherent biases in pain assessment and blood loss calculation. Future research should focus on randomized controlled trials to better define the causal relationships suggested here.
Conclusions
The look-back technique, as a strategic enhancement of UBE-ULBD, shows considerable promise in improving perioperative outcomes in LSS. Our findings confirm its capacity for decreasing blood loss and leg pain severity (VAS) at the early postoperative stage. However, its effect on direct complications requires further investigation.
Supplementary material
online supplementary video 1.
Footnotes
Funding This work was supported by Science and Technology Innovation Action Plan from the Science and Technology Commission of Shanghai Municipality (23Y11903100), Naval Equipment Integrated Research Program (ZB2025B11), Tengfei Project of Third Affiliated Hospital of Naval Medical University (to Lin Han), National Natural Science Foundation of China (82502953), and Naval Medical University Qihang Programme (to WenBo Lin).
Declaration of Conflicting Interests None declared.
Disclosures None declared.
Ethics Approval and Informed Consent Approval was obtained from the Ethics Committee of Third Affiliated Hospital of Naval Medical University. The procedures used in this study adhere to the tenets of the Declaration of Helsinki. Written form of consent was obtained from each participant.
Disclosures None declared.
- This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2026 ISASS. To see more or order reprints or permissions, see http://ijssurgery.com.
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