Comparison of surgical outcomes between unilateral biportal endoscopic technique and open microdiscectomy in patients with single-level lumbar disc herniation: a single-center retrospective study in China

Study cohort

This retrospective study was approved by the ethics committee of Liupanshui Hospital (approval no., 52020-2023-0-1-54). We retrospectively included all patients with single-level LDH who underwent surgical treatment at our clinic between January 2020 and December 2022. The inclusion criteria were as follows: (1) presence of back pain or radiating pain associated with LDH; (2) persistent symptoms for more than 4 weeks; (3) magnetic resonance imaging (MRI) findings correlating with symptoms and confirming the presence of the hernia; and (4) follow-up at 3 and 12 months after surgery. The exclusion criteria were as follows: (1) foraminal or extraforaminal disc involvement; (2) recurrent LDH; (3) spondylolisthesis exceeding Meyerding grade II; (4) presence of cauda equina syndrome; and (5) coexisting tumorous or infectious pathology. All patients in our study provided written informed consent.

Criteria for the surgical method

Patients were counseled in detail about both surgical options, including potential benefits, risks, and recovery expectations. The decision-making process was collaborative, involving both the patient and the surgeon, to ensure that the chosen surgical approach was consistent with the patient’s health status, lifestyle, and personal preferences. Specific anatomical considerations, such as the size and location of the herniated disc, significant spinal canal stenosis, and any previous spinal surgery were taken into account. The surgeon’s judgment also took into account the complexity of the herniation and the likelihood of achieving optimal results with each technique.

Data collection and radiographic measurements

Demographic information, including age, sex, and body mass index (BMI), was obtained from the patient records. Data were collected from the preoperative period through 12 months postoperatively.

Using the preoperative standing sagittal and coronal radiographs of the lumbar spine, the sagittal disc angle (DA) at the surgical level was measured as the angle between the inferior endplate of the superior vertebra and the superior endplate of the inferior vertebral body. Disc height (DH) at each level was measured using the modified Farfan method (Fig. 1). Preoperative and 12 months postoperative DH and DA were measured to evaluate disc degeneration [10]. Standard clinical T2-weighted MRIs of the lumbar spine were obtained, and disc degeneration was also assessed preoperatively using the modified Pfirrmann grading system. All measurements were performed using the picture archiving and communication system.

Fig. 1

The disc height (DH) at each level was measured using the modified Farfan method.

Outcome measures

Pain intensity, patient satisfaction, and quality of life were assessed using the Visual Analog Scale (VAS) and the Oswestry Disability Index (ODI) at 1 week, 3 months, and 12 months postoperatively. Clinical outcomes were assessed using the back and leg pain VAS scores (ranging from 0 to 10) and the ODI (scaled from 0% to 100%). Perioperative data, including operative time, estimated blood loss, and complications, were evaluated using video recordings of endoscopic and microscopic procedures and clinical records. Radiological outcomes were assessed using both preoperative and postoperative radiographs. To accurately assess the volume of blood loss during UBE, we calculated the difference between the total volume of irrigation fluid used and the volume of fluid collected in the suction canister. This difference provided an estimate of the fluid retained in the surgical field, which was subtracted from the total volume collected to approximate blood loss. Additionally, the hemoglobin concentration in the collected aspirate fluid was measured and compared with the patient’s baseline hemoglobin level, providing a further estimate of the blood loss during the procedure.

Surgical techniques

UBE

The UBE surgery was performed by Deputy Chief Physician Dr. Tianyao Ke, who has over 15 years of experience in spinal surgery, ensuring consistency in surgical expertise. The procedure was performed under epidural anesthesia (general anesthesia) with the patient in the prone position on a fluoroscopy-capable operating table. The table allowed for anteroposterior and lateral views using a C-arm. The surgical instruments used included a 0° or 30° rigid arthroscope (Hopkins Arthroscope; KARL STORZ Endoscopy-America Inc., El Segundo, CA, USA), a 3.5 mm spherical drill (Dyonics Drill; Smith & Nephew Inc., Andover, MA, USA), a 3.5 mm radiofrequency ablation probe (RF Ablation System; Stryker Corp., Kalamazoo, MI, USA), and standard open laminectomy instruments, such as 3 mm laminar forceps and nucleotomy forceps (Fig. 2). The surgical procedure consists of the following steps:

Fig. 2

Unilateral biportal endoscopic incision. The length of the surgical incision is 2 cm.

Localization

Using C-arm fluoroscopy, the target segment is identified and the optimal entry points for the two channels on the skin and the optimal trajectory are determined.

Channel establishment

Skin incisions of 0.8 cm and 1.5 cm are made 1–1.5 cm lateral to the spinous process of the target segment. Sequential expansion sleeves are inserted to establish subcutaneous and muscular dissection to create an endoscopic observation channel and an instrumentation operation channel. The endoscopic channel is continuously irrigated for visualization, while the operation channel is used for instrument manipulation and disc removal.

Exposure and discectomy

First, hemostasis is achieved and the bone membrane on the lamina is removed using a radiofrequency ablation probe through the instrument operating channel, exposing the lamina and its space. Next, the lamina is either drilled with an automated burr or the lower portion of the lamina, and the partial inferior articular process to the origin of the ligamentum flavum is removed with laminar bone-biting forceps. The ligamentum flavum is then carefully dissected using a nerve-detaching probe or nerve hook, followed by its removal to expose the dural sac and nerve roots. The spinal canal is probed to identify the protruding disc. The fibrous ring is then incised with a blade, and the protruding disc material is removed with nucleotomy forceps, resulting in the removal of the herniated disc. Finally, a neurological assessment is performed with a nerve hook to confirm adequate decompression of the nerve roots. The muscle and skin layers are then closed with sutures.

Open microdiscectomy

The open microdiscectomy procedures were conducted by Dr. Jiaxue Zeng, who also has over 15 years of experience in spinal surgery. This ensured that the comparison between the UBE and open microdiscectomy techniques was not confounded by differences in surgical skills. The anesthetic approach and patient positioning for the subsequent surgical procedure were similar to those used for UBE surgery. Using standard open laminectomy instruments, including 3 mm laminar bone-biting forceps and core forceps, as shown in Fig. 3, the surgical steps are outlined as follows:

Fig. 3

Open microdiscectomy incision. The length of the surgical incision is 6 cm.

Localization

The target segment is confirmed using C-arm fluoroscopy.

Channel establishment

At the target segment, a 3–4 cm skin incision is made 2 cm lateral to the center of the spine. The skin, subcutaneous tissue, and deep fascia are sequentially incised, followed by blunt dissection to separate the paraspinal muscles from the lamina. The canal is then positioned at the lamina of the target segment. C-arm fluoroscopy is used for confirmation to ensure accurate placement.

Exposure and discectomy

Under microscopic visualization, an electric scalpel is first used to achieve hemostasis and expose the lamina and its interspace. Next, an automatic burr is used to grind the lamina, or laminar bone-biting forceps are used to remove the inferior edge of the lamina of the target segment and the superior edge of the lamina of the next segment. The inner wall of the lamina is then grounded intracavitarily to expose the spinal canal. Nerve-detaching probes or nerve hooks are used to carefully separate and expose the dural sac and nerve roots. The nerve roots are gently pulled toward the midline, creating tension on the dura mater and nerve roots. The protruding disc is identified and the fibrous ring is incised with a blade. The protruding nucleus pulposus is extracted with nucleus forceps, resulting in the removal of the herniated disc. Finally, decompression of the spinal canal and nerve roots is thoroughly evaluated under neuroendoscopic observation. Stratified closure of skin and muscle tissue is then performed.

Statistical analysis

The baseline characteristics were described using descriptive statistics. Continuous variables were presented as mean±standard deviation and between-group differences were assessed using the independent two-sample t-test. Categorical variables were presented as frequency (percentage) and analyzed using the chi-square test and Fisher’s exact test. Statistical analyses were performed with IBM SPSS Statistics ver. 20.0 (IBM Corp., Armonk, NY, USA). The significance level for all statistical tests was set a priori at p<0.05.

Demographic and preoperative characteristics

A total of 46 patients were included in the study: 22 underwent UBE surgery and 24 underwent open microdiscectomy. There were no significant between-group differences in terms of age (50.5±9.9 years versus 52.5±12.0 years, p=0.227), sex distribution (p=0.232), BMI (23.7±1.8 kg/m² versus 23.8±1.9 kg/m², p=0.787), symptom duration (6.5±2.0 versus 6.1±1.7, p=0.431), or symptom distribution (p=0.632). Similarly, there were no significant differences in terms of disc location (p=0.613), disc level (p=0.372), or Pfirrmann grade (p=0.379) between the UBE and open microdiscectomy groups (Table 1).

Table 1

Patients’ demographic data

Operative characteristics

The UBE technique was associated with significantly longer operative time (86.1±11.4 minutes versus 72.3±8.0 minutes, p=0.032), lower estimated blood loss (54.1±13.7 mL versus 92.5±11.6 mL, p=0.001) and shorter hospital stay (3.7±1.2 days versus 6.6±1.4 days, p=0.001) compared with open microdiscectomy (Table 2).

Table 2

Comparison of clinical outcomes of UBE and open microdiscectomy for lumbar disc herniation

Postoperative clinical outcomes

Postoperative changes in DH and DA were not significantly different between the two groups (p=0.079, p=0.143, and p=0.558, respectively). While preoperative VAS scores for back and leg pain were similar in both groups, the UBE group showed superior improvement in VAS back scores at 1 week (3.59±0.72 versus 1.88±0.60, p=0.004). Pre- and postoperative ODI scores were not significantly different between the UBE and open microdiscectomy groups (75.7±7.7 versus 81.5±6.0, p=0.415 and 22.0±5.1 versus 23.8±7.8, p=0.213, respectively). The incidence rates of neurological complications (9.1% versus 8.3%, p=0.543) and recurrent disc herniation (18.2% versus 16.7%, p=0.653) were comparable between the two techniques (Table 2).

Operative characteristics

The longer duration of the UBE procedure is attributed to the technical demands of endoscopic methods, specifically the precise placement of portals and the use of endoscopic techniques [11]. However, the prolonged operative time does not necessarily translate into a clinically significant disadvantage.

The technical complexity of UBE, which involves two portal placements and intricate maneuvers with specialized endoscopic instruments, inherently leads to longer operative times. However, as surgeons gain more experience and expertise in UBE, they can reduce operative times [12,13].

The longer operative time for UBE surgery is attributed to the meticulousness required in endoscopic maneuvers and portal placement, highlighting a nuanced balance between technical precision and procedural efficiency [11–14]. The benefits of UBE include potentially faster recovery and reduced postoperative morbidity, such as infection, significant blood loss requiring transfusion, prolonged pain, decreased mobility, and delayed wound healing. Notably, this aspect of UBE underscores a potential learning curve wherein operative times tend to decrease as surgeons gain proficiency, consistent with the broader surgical literature advocating for the adaptability and skill refinement inherent in endoscopic procedures [15].

In summary, the extended operative time of the UBE procedure is a dynamic parameter influenced by surgeon experience, learning curve dynamics, and technical intricacies inherent to endoscopic approaches. While it raises considerations, the potential for reduced operative time with increasing surgeon expertise, combined with the benefits of reduced blood loss and shorter hospital stay, makes UBE a viable and advantageous surgical option for single-level LDH.

Postoperative clinical outcomes

Both UBE and open microdiscectomy showed similar efficacy in addressing LDH. Both techniques effectively restored spinal alignment and relieved neural compression. The equivalence in clinical outcomes between the two groups was also reflected in patient-reported measures. Specifically, the VAS scores for back and leg pain and ODI scores showed no significant between-group difference. These findings are consistent with previous studies [16–18]. For instance, Park et al. [19] found that biportal endoscopic discectomy yielded comparable outcomes to microscopic discectomy over a 12-month period, with the added benefit of reduced muscle damage. However, they also highlighted the need for careful consideration of surgical site pain, emphasizing a balanced approach to evaluating surgical options. These findings underline the utility of UBE as a viable alternative to open microdiscectomy.

The comparable complication rates between UBE and open microdiscectomy suggest similar levels of safety and postoperative morbidity. This is consistent with existing literature on the overall safety of surgical interventions for LDH [20,21]. The lack of significant differences in complication rates is a critical consideration for clinicians and patients when evaluating the risk-benefit profiles of these surgical approaches.

Clinical implications

Our findings support UBE’s perioperative benefits, including lower blood loss and shorter stays, without compromising long-term outcomes. These results align with studies showing minimally invasive techniques can achieve outcomes comparable to traditional open procedures [22]. Comparable outcomes and complication rates make UBE and open microdiscectomy viable options for single-level LDH. Clinicians should consider patient-specific factors, surgeon expertise, and perioperative advantages when choosing between UBE and open microdiscectomy.

UBE and open microdiscectomy are comparable options for single-level LDH treatment, allowing clinicians to tailor their approach to individual patient needs. UBE’s benefits, including reduced blood loss and early postoperative pain relief, may be particularly relevant for certain patient populations. Future research should focus on long-term outcomes and potential late complications beyond 12 months. Larger multicenter studies can improve the generalizability of the findings. Two notable challenges with UBE are achieving effective hemostasis and managing dural tears. Continuous irrigation required during UBE can obscure the surgeon’s view of bleeding sources. Additionally, the endoscopic approach can make direct suturing of dura tears difficult, necessitating alternative dural repair strategies and potentially increasing the risk of postoperative cerebrospinal fluid leak.

This study highlights UBE’s advantages in early recovery and encourages consideration regarding the relative positioning of these two surgical approaches in patient selection. As patients increasingly opt for minimally invasive surgery, UBE may meet this demand, particularly among younger and more active patient populations. Our research suggests that UBE’s early recovery benefits could be a key factor in decision-making, emphasizing the importance of considering individual patient needs and expectations. Advances in UBE techniques and training may broaden its clinical application. While further research is needed to assess the long-term outcomes of UBE, it holds promise for specific patient groups. Future studies should focus on refining UBE techniques, improving surgical proficiency, and establishing standardized assessment metrics to personalize patient care.

Limitations

Some limitations of this study should be acknowledged. The retrospective study design may have introduced an element of selection bias. In addition, the short duration of follow-up limits our ability to assess the long-term outcomes. Longer postoperative follow-up is required to assess the durability of efficacy and identify any delayed complications. Additionally, variations in surgical techniques, surgeon expertise, and patient demographics introduce confounding variables. Future prospective randomized controlled trials comparing UBE and open microdiscectomy are required to address these limitations.