Comparison of clinical efficacy and minimal invasiveness between unilateral biportal endoscopic and percutaneous endoscopic lumbar discectomy in the treatment of calcified lumbar disc herniation: a retrospective analysis

Abstract

Background

This study aimed to compare the clinical efficacy and minimal invasiveness of percutaneous endoscopic lumbar discectomy (PELD) and unilateral biportal endoscopic (UBE) in the treatment of calcified lumbar disc herniation (CLDH), to provide evidence for spinal surgeons to select the most appropriate surgical method for individual patients.

Methods

A retrospective analysis was conducted on the data of 49 CLDH patients who underwent PELD or UBE in our hospital from January 2016 to August 2024, including 20 who underwent PELD and 29 who underwent UBE. The demographic, clinical, and perioperative data of the two groups of patients were collected and analyzed.

Results

All surgeries were completed successfully, with significant improvement in clinical symptoms observed in both groups postoperatively. The mean fluoroscopy frequency was 5.52 times higher in the PELD group than in the UBE group. The average operative time in the PELD group was 9.21 min shorter than in the UBE group. The mean preoperative-to-postoperative difference in hemoglobin level was 3.65 g/L lower in the PELD group than in the UBE group. The mean preservation rate of the lumbar facet joints was 9.10% higher in the PELD group than in the UBE group. These differences were statistically significant (P < 0.05). The excellent-to-good rate was 90.00% in the PELD group and 93.10% in the UBE group. Additionally, two patients in the PELD group experienced complications, and two patients had recurrence at 12 months postoperatively, with no severe outcomes. No complications or postoperative recurrences were observed in the UBE group.

Conclusions

PELD and UBE are both effective minimally invasive procedures for the treatment of CLDH. The short-term clinical efficacy of the two methods is similar; PELD is characterized by shorter operative time, less intraoperative blood loss, and less damage to facet joints. The advantages of UBE are more sufficient surgical field exposure and more flexible operation, though it may require a wider range of facet joint resection. Clinical decision-making should be based on the patient’s clinical symptoms, imaging features, and the surgeon’s procedural expertise to formulate an individualized surgical plan.

Introduction

Calcified lumbar disc herniation (CLDH), a subtype of lumbar disc herniation (LDH), is a more complex condition characterized by concurrent disc herniation and calcification [1]. It has been reported in the literature that the incidence ranges from 4.7% to 15.9% [2–3]. The main clinical manifestations of CLDH include lower limb pain, numbness, weakness, and bladder dysfunction [4]. During the calcification process, the herniated intervertebral disc may adhere to adjacent nerves and the dural sac, which increases the risk of dural tear, cerebrospinal fluid leakage, and nerve injury [5]. Therefore, the treatment of CLDH differs from that of LDH. When conservative treatment fails to provide relief for a period of time or symptoms severely affect patients’ quality of life, surgical treatment should be sought [6]. Open surgery remains the standard treatment for CLDH [7], but it is associated with significant invasiveness, slow postoperative recovery, and even an increased risk of muscle atrophy [8]. Thus, minimally invasive alternatives have been developed to replace traditional open surgery [9]. Percutaneous endoscopic lumbar discectomy (PELD) is a minimally invasive surgical technique for the management of LDH, which is characterized by less intraoperative blood loss, shorter hospital, and even ambulatory procedures. Consequently, PELD has been increasingly widely used in the surgical treatment of LDH [10]. Recently, PELD has also been reported for the treatment of CLDH, with satisfactory outcomes [11–12]. However, due to a single observation and working channel, the flexibility of PELD is greatly limited. Moreover, CLDH is often associated with adhesion to adjacent nerves and the dural sac, which is prone to complications such as nerve root injury and dural tear [13]. We reviewed relevant reports showing that the incidence of complications associated with PELD for CLDH ranges from 2.0% to 12.9% [12, 14–18], which requires surgeons to have extensive experience to avoid neurological complications [19]. Unilateral biportal endoscopic (UBE) discectomy is a novel surgical technique, and its separate observation and working channels largely compensate for the limitations of PELD [20]. Recent studies have reported that UBE has achieved satisfactory outcomes in the treatment of various types of LDH [21, 22]. At present, no systematic studies have been reported on the clinical efficacy and minimal invasiveness of PELD versus UBE in the treatment of CLDH. The purpose of this study is to compare the clinical efficacy and minimal invasiveness of PELD and UBE in the treatment of CLDH, analyze the relevant imaging and perioperative data, and provide a new reference for spine surgeons managing CLDH.

Materials and methods

This study was a single-center, non-randomized, retrospective case-control study. The data of 49 CLDH patients who underwent PELD or UBE in Jiangxi Provincial Hospital of Integrated Traditional Chinese and Western Medicine from January 2016 to August 2024 were collected and analyzed. They were divided into the PELD group (n = 20) and UBE group (n = 29). The demographic characteristics, perioperative parameters, and clinical outcomes were collected.

After a comprehensive evaluation of the patients’ clinical symptoms, imaging characteristics and anatomical characteristics, the spinal surgeons fully informed the patients of the technical characteristics, clinical advantages and scope of application of the two surgical methods, and jointly determined the final surgical plan on the basis of fully soliciting the patients’ informed wishes.

The imaging diagnostic criteria for CLDH are [23]: meeting the typical manifestations of lumbar disc herniation on magnetic resonance imaging (MRI) (e.g., intervertebral disc tissue extending beyond the vertebral body margin, compression of nerve roots or the dural sac, etc.), and clear identification of intradiscal calcification on computed tomography (CT).

Inclusion criteria

(1) Patients with MRI-confirmed LDH with or without lumbar spinal stenosis (LSS) who met the imaging diagnostic criteria for CLDH; (2) Patients with lower limb pain and numbness who exhibited no improvement after standardized conservative treatment for 6 months; (3) Patients with single-segment CLDH who agreed to undergo PELD or UBE; (4) Patients with complete clinical data; (5) Patients who completed a follow-up period of more than 12 months.

Exclusion criteria

(1) Patients with other types of LDH without calcification or with calcification involving multiple segments; (2) Patients with lumbar spondylolisthesis, scoliosis, spinal tumors, spinal infections, or ankylosing spondylitis; (3) Patients with lumbar instability (defined as > 3 mm of translation or > 5° of angular motion); (4) Patients with severe underlying diseases who could not tolerate anesthesia; (5) Patients with a follow-up period of less than 12 months.

Ethical approval

This study was approved by the Ethics Committee of Jiangxi Provincial Hospital of Integrated Traditional Chinese and Western Medicine (Ethical Approval No.: 2025002) and complied with the ethical standards outlined in the Declaration of Helsinki. All patients who underwent surgery provided written informed consent for participation in this study.

Demographic data, surgical parameters, and clinical outcomes were collected. Demographic characteristics included age (years), gender (male/female), body mass index (BMI, kg/m²), and follow-up duration (months). Surgery-related parameters included length of hospital stay (days), surgical segment, fluoroscopy frequency (times), operative time (minutes), preoperative-to-postoperative hemoglobin difference (g/L), and facet joint preservation rate (%). Clinical outcomes included visual analog scale (VAS) scores [24] for low back pain and leg pain preoperatively, at 1 day, 1 month, 6 months, and 12 months postoperatively; Oswestry Disability Index (ODI) [25] scores preoperatively and at 12 months postoperatively; modified MacNab scores [26] at final follow-up; surgical complications; and recurrence at 1 year postoperatively.

Fluoroscopy frequency was defined as the total number of fluoroscopic images obtained per surgical procedure, with the radiation dose being consistent for each fluoroscopy.

Lumbar CT scans were obtained on postoperative day 3. The facet joint preservation rate at the surgical segment was calculated using axial CT images. Taking the L5/S1 segment as an example, the calculation was performed according to a previous study [27]: we measured the preoperative axial length of the midportion of the surgical-side facet joint (A) and the postoperative axial length of the same facet joint at the same level (B), with the facet joint preservation rate calculated as B/A (Fig. 1).

Fig. 1.

A: Preoperative axial length of the middle part of the surgical-side facet joint; B: Postoperative axial length measured at the same position of the identical surgical-side facet joint; The facet joint preservation rate was calculated as B/A

The modified MacNab criteria were as follows: Excellent (100% resolution of symptoms at 1 year after surgery); Good (50–99% resolution of symptoms at 1 year after surgery); Fair (1–49% resolution of symptoms at 1 year after surgery); Poor (0% resolution or worsening of symptoms at 1 year after surgery).

In this study, all imaging measurements were performed by two independent physicians with experience in interpreting spinal imaging studies. The measurers were completely blinded to the patients’ specific surgical method (PELD/UBE) and grouping information when measuring preoperative and postoperative CT images. If discrepancies exist between the measurement results of the two physicians, a third senior physician will conduct a review and make the final determination of the measurement.

In this study, postoperative recurrence was defined as follows [28]: radiologically confirmed recurrence of intervertebral disc herniation at the original surgical level following lumbar disc herniation (LDH) surgery, after an asymptomatic interval.

Surgery

UBE

All surgeries were performed by a spine surgeon with experience in more than 500 UBE. The patients were placed in the prone position. After successful induction of general anesthesia, the target intervertebral space and working channel were localized under C-arm fluoroscopy. The working channel was established approximately 1 cm lateral to the junction of the spinous process and lamina, and the viewing channel was established 3 cm cranially or caudally to the working channel. Two skin incisions (each 0.8–1.5 cm in length) were made at the sites of the working and viewing channels. Soft tissues were gradually dilated using dilators, followed by the insertion of surgical instruments and the endoscope. Radiofrequency ablation was used to coagulate soft tissues and establish a working space. A high-speed burr, osteotome, and rongeur were employed to resect parts of the lamina and superior/inferior articular processes, ensuring adequate exposure of the cephalad and caudal ligamentum flavum. The ligamentum flavum was selectively managed according to whether the patient had concomitant LSS. For patients with LSS, the ligamentum flavum was excised as extensively as possible to fully expose the dural sac. Subsequently, the traversing nerve root and exiting nerve root of the target segment were exposed and dissected. Under endoscopic visualization, a nerve stripper was first used to explore the calcified lesion to clarify its relationship with the surrounding nerve tissue. If adhesions were present, they were carefully released. After confirming that the calcified lesion was completely mobilized, the herniated calcified nucleus pulposus was removed; finally, the annulus fibrosus was sutured to prevent postoperative recurrence of disc herniation. Intraoperative dural sac injuries were managed as follows: minor injuries required no special treatment, but revision surgery was performed if persistent cerebrospinal fluid leakage occurred postoperatively; for major injuries, an open surgical repair of the dura was performed directly. Finally, the incisions were closed to complete the procedure (Fig. 2).

Fig. 2.

An adult patient presented with low back pain accompanied by radiating pain in the left lower extremity for 3 months, which had worsened over the past 3 days. The left straight leg raising test was positive, and muscle strength of both lower limbs was normal. MRI revealed a left-sided L5-S1 intervertebral disc herniation with nerve root compression; lumbar CT demonstrated disc calcification. The patient underwent UBE, and the left lower extremity symptoms resolved completely postoperatively, with significant relief of low back pain

PELD

All PELD procedures were performed by the same spine surgeon with experience in at least PELD cases. Thirty minutes before surgery, patients received 8 mg lornoxicam for injection (a non-steroidal anti-inflammatory drug) for pain relief. The transforaminal approach was adopted: the patients were placed in the lateral decubitus position, and the surgical site was localized under C-arm fluoroscopy. The surgeon administered local infiltration anesthesia with an 18G needle and an appropriate volume of 1% lidocaine, and the patients remained awake throughout the entire procedure. A single skin incision (0.8–1.5 cm in length) was made, and soft tissues were gradually dilated with dilators prior to the insertion of the endoscope and surgical instruments. If the intervertebral foramen was found to be too narrow intraoperatively, a rongeur was used to resect part of the bone to ensure the smooth progression of the procedure. Then the nerve root was decompressed. During the resection of the calcified intervertebral disc, the relationship between the calcified intervertebral disc and the surrounding soft tissues as well as neural structures was explored using a nerve stripper. If adhesions were present, they were carefully dissected, and the calcified herniated disc was carefully removed. Our principles for managing the ligamentum flavum and the protocol for intraoperative dural sac injury were consistent with those employed in UBE. After completion of decompression, the incision was closed to complete the procedure (Fig. 3).

Fig. 3.

A young adult patient presented with low back pain with radiating pain in the right lower extremity for 1 year, which worsened over the past 10 days. The right straight leg raise test was positive, and the muscle strength of both lower limbs was normal. MRI revealed a right-sided L5-S1 intervertebral disc herniation with nerve root compression; lumbar CT demonstrated disc calcification; The patient underwent PELD, and the right lower extremity symptoms resolved completely postoperatively, with significant relief of low back pain

Perioperative management

Postoperatively, patients received routine symptomatic treatment including analgesia. They were instructed to perform in-bed muscle contraction exercises to prevent complications such as deep vein thrombosis (DVT) of the lower extremities. Based on individual patient conditions, early ambulation with a customized lumbar brace was encouraged, typically starting on postoperative day 2. On postoperative day 3, patients underwent lumbar X‑ray, CT, and MRI. If the postoperative re‑examination results were satisfactory, patients were generally discharged on postoperative day 4.

Statistical analysis

Data were processed using SPSS 26.0 statistical software. Normality tests were first performed for continuous data. For data meeting the normal distribution criteria, an analysis was performed using the independent samples t-test, with results expressed as mean ± standard deviation (mean ± SD). For data not meeting the normal distribution criteria, the Mann–Whitney U test was applied; categorical data were analyzed using the chi-square test or Fisher’s exact test. A p-value < 0.05 was considered statistically significant.

Results

Demographic and surgical outcomes

In total, 55 patients with calcified disc herniation underwent PELD or UBE. Among them, 3 patients were lost to follow-up, and 3 patients lacked complete imaging data. Ultimately, 49 patients were included in this study: 20 patients were in the PELD group, and 29 patients were in the UBE group. There were no significant differences between the two groups in age, gender, BMI, or follow-up duration (p > 0.05) (Table 1). Hospital stay and surgical segment showed no significant differences between groups (p > 0.05). Significant differences were observed in fluoroscopy frequency, operative time, preoperative-to-postoperative hemoglobin difference, and facet joint preservation rate (p < 0.05). The mean fluoroscopy frequency was 8.80 ± 1.20 shots in the PELD group and 3.28 ± 1.03 shots in the UBE group, with the PELD group having an average of 5.52 more fluoroscopy shots than the UBE group. The mean operative time was 69.65 ± 7.83 min in the PELD group and 78.86 ± 10.21 min in the UBE group, with the PELD group operative time being 9.21 min shorter than that in the UBE group. The mean preoperative-to-postoperative hemoglobin difference was 7.90 ± 2.57 g/L in the PELD group and 11.55 ± 3.31 g/L in the UBE group, which was 3.65 g/L lower in the PELD group than in the UBE group. The mean facet joint preservation rate was 85.16% ± 5.15% in the PELD group and 76.06% ± 4.53% in the UBE group, which was 9.10% higher in the PELD group than in the UBE group (Table 1; Fig. 4).

Table 1.

Comparison of baseline characteristics and surgical parameters between the two groups

	PELD(N = 20 )	UBE(N = 29 )	P-value
Age (years)	47.35 ± 15.13	50.52 ± 16.27	0.494
Gender (male/female)			0.884
Male	8	11
Female	12	18
BMI (kg/m²)	24.78 ± 2.78	23.91 ± 2.27	0.235
Follow-up duration (months)	15.05 ± 1.82	15.03 ± 1.61	0.975
Hospital Stay (days)	4.40 ± 1.39	4.28 ± 0.59	0.670
Surgical segment			0.720
L1/L2	1	2
L2/L3	0	1
L3/L4	2	1
L4/L5	5	10
L5/S1	12	15
Fluoroscopy frequency (times)	8.80 ± 1.20	3.28 ± 1.03	< 0.001
Duration of operation (min)	69.65 ± 7.83	78.86 ± 10.21	< 0.001
HGB Reduction (g/L)	7.90 ± 2.57	11.55 ± 3.31	< 0.001
Facet joint preservation rate (%)	85.16% ± 5.15%	76.06% ± 4.53%	< 0.001

Results are expressed as mean ± SD, number, and P < 0.05 represents statistical difference

Fig. 4.

Comparison of fluoroscopy frequency, operative time, HGB Reduction, and facet joint preservation rate between the two groups. Error bars represent standard deviation (SD)

Clinical outcomes

Postoperative low back and leg pain symptoms showed significant improvement in both groups compared with preoperative levels. The mean VAS scores for low back pain and leg pain in the PELD group were 5.75 and 7.40 preoperatively, decreasing to 2.50 and 1.95 on the first postoperative day. The preoperative mean VAS scores for low back pain and leg pain in the UBE group were 5.66 and 7.31, respectively, decreasing to 2.90 and 2.10 on the first postoperative day. Both groups demonstrated continuous improvement in VAS scores for low back pain and leg pain at all postoperative time points, with no significant differences between groups (P > 0.05). Preoperative mean ODI scores in the PELD and UBE groups were 57.70 and 56.62, respectively, decreasing to 9.15 and 8.72 at 1 year postoperatively. These findings indicate that the two surgical methods are equivalent in terms of pain relief and functional recovery. At 1 year postoperatively, patients were evaluated using the modified MacNab criteria. The excellent and good rate was 90.00% in the PELD group and 93.10% in the UBE group, with no statistically significant difference between the two groups (P > 0.05) (Table 2; Fig. 5).

Table 2.

Preoperative and postoperative VAS, ODI, and modified MacNab outcomes at 12 months

	PELD(N = 20 )	UBE(N = 29 )	P-value
LBP VAS score
Preoperative	5.75 ± 1.59	5.66 ± 1.54	0.835
Post-1 day	2.50 ± 1.15	2.90 ± 1.26	0.260
Post-1 month	1.60 ± 1.05	2.00 ± 1.28	0.254
Post-6 months	1.45 ± 1.10	1.76 ± 1.35	0.403
Post-12 months	1.30 ± 1.13	1.48 ± 1.02	0.558
LP VAS score
Preoperative	7.40 ± 1.10	7.31 ± 1.14	0.784
Post-1 day	1.95 ± 1.05	2.10 ± 1.01	0.613
Post-1 month	1.50 ± 1.05	1.62 ± 1.08	0.700
Post-6 months	1.30 ± 0.92	1.34 ± 0.97	0.872
Post-12 months	1.10 ± 1.17	1.21 ± 0.77	0.701
Pre ODI	57.70 ± 13.71	56.62 ± 12.62	0.757
Post-1 year ODI	9.15 ± 4.72	8.72 ± 3.93	0.733
Post-1 year MacNab			0.831
Excellent	7	14
good	11	13
fair	1	1
poor	1	1

Results are expressed as mean ± SD, number, and P < 0.05 represents statistical difference

Fig. 5.

Comparison of LBP and LP VAS scores between the two groups. Error bars represent standard deviation (SD)

Complications and recurrence

There were 2 cases of complications in the PELD group, with an incidence rate of 10.0% (2/20). One patient had a minor dural tear during the operation. Due to the small scope of injury, conservative treatment was administered without additional surgical intervention; the other patient had postoperative lower limb paresthesia. After 5 days of clinical observation and routine postoperative symptomatic treatment, the symptoms resolved spontaneously. No related discomfort was reported in either patient during the follow-up period. At the 12-month follow-up after surgery, two patients (10.0%, 2/20) in the PELD group experienced recurrent symptoms such as lower limb numbness. Imaging examination confirmed recurrent disc herniation at the original surgical level. For these two patients, clinical symptoms were resolved following 2–4 weeks of short-term bed rest and administration of non-steroidal anti-inflammatory drugs (NSAIDs), and no subsequent revision surgery was required (Table 3).

Table 3.

Complications and recurrence of UBE and PELD

	PELD(N = 20 )	UBE(N = 29 )	P-value
Complications	2 (10.0)	0 (0.0)	0.082
Dural tear	1	0
Sensory impairment	1	0
Recurrence	2	0	0.082

Results are expressed as mean ± SD, number, and P < 0.05 represents statistical difference

Discussion

CLDH is a distinct subtype of lumbar disc herniation [16]. Recent studies have identified its associations with infection, persistent microtrauma, metabolic factors, local tissue ischemia, and a lumbar disc herniation disease course exceeding 6 months [12, 29]. Literature reports indicate that patients with CLDH experience more severe chronic low back pain and lower limb radicular pain compared with those with LDH. Conservative treatment yields poor outcomes and a high recurrence rate, which are unsatisfactory for most patients and often necessitate surgical intervention [30]. Traditional open surgery has long been the standard approach for CLDH. However, it is associated with multiple postoperative complications. Relevant studies have further demonstrated that traditional open surgery may increase the risk of postoperative LSS and spondylolisthesis [31–32]. In contrast, UBE is an emerging technique for degenerative lumbar diseases. Since its first description by Kambin et al. in 1996 [33], it has been applied to various complex degenerative lumbar conditions, such as severe LSS, spondylolisthesis, far-lateral disc herniation, and highly downward-migrated LDH, demonstrating excellent clinical efficacy [34–37]. The purpose of this study was to analyze and compare the clinical efficacy of PELD and UBE in the treatment of CLDH, as well as to evaluate the minimally invasive characteristics of the two surgical methods.

Our study revealed that both groups exhibited significant improvements in VAS pain scores and ODI functional status on postoperative day 1, as well as at 1 month, 6 months, and 1 year postoperatively. Additionally, the excellent and good rates based on the modified MacNab criteria at 1 year postoperatively were 90.0% and 93.1% for the PELD and UBE groups, respectively. These findings confirm that both surgical methods are effective for CLDH. However, the PELD group had a smaller incision, shorter operative time, and less hemoglobin reduction, which indicates that PELD was less invasive than UBE.

Notably, local anesthesia was used in the PELD group and general anesthesia in the UBE group. General anesthesia requires induction and emergence, which may prolong non-surgical operative time. In addition, mean arterial pressure under general anesthesia is usually maintained at a relatively low level, which may help reduce intraoperative blood loss. However, the influence of general anesthetics on vascular tone may introduce additional uncertainty. In contrast, patients undergoing PELD under local anesthesia are awake and may exhibit greater blood pressure fluctuations, but general anesthesia-related circulatory depression is avoided. Given that differences in anesthetic methods may confound perioperative outcomes, we will design future studies to compare different surgical techniques under uniform anesthesia to obtain more reliable conclusions.

From the perspective of biomechanics, facet joints play a key role in maintaining spinal stability. The degeneration of facet joints is closely related to chronic low back pain [38]. Therefore, in lumbar decompression surgery, spine surgeons should preserve as much of the lumbar facet joints as possible to prevent postoperative spinal instability [39]. Previous studies have reported that the average facet joint preservation rate for UBE ranges from 80.0% to 95.6% [35, 40–41]. In our study, the facet joint preservation rate for UBE was 76.06%, slightly lower than values reported in previous research. However, we consider this difference reasonable. In clinical practice, calcified intervertebral discs are more difficult to remove than non-calcified ones [4]; thus, a larger working space is required to maximize calcified tissue resection [42] and adequately decompress the nerve root. The volume and morphology of calcified lesions are also important factors affecting the facet joint preservation rate. Some studies have noted that the volume of calcified lumbar discs is positively correlated with the severity of adhesion to surrounding tissues. The larger calcified foci, the more severe the adhesion to adjacent structures such as the dural sac and nerve root [42]. The location of calcification (e.g., central, paracentral, foraminal) may also increase the difficulty of surgical dissection. Intraoperatively, larger calcified foci often require a larger surgical working space for complete resection. Compared with small-volume calcified foci, they result in more severe facet joint injury. Disc calcification is frequently accompanied by LSS [42]. In this study, some patients presented with LSS, which posed additional surgical challenges. The narrowed spinal canal was often accompanied by ligamentum flavum hypertrophy and dural sac adhesion, further increasing surgical complexity [43–44]. To achieve adequate decompression of the dural sac and nerve root, the extent of facet bone resection may be correspondingly increased, which will have a certain impact on the facet joint preservation rate. In this study, the facet joint preservation rate in the PELD group was 85.16%, which was significantly higher than 76.06% in the UBE group. There was no significant difference in the improvement of clinical symptoms at the 1-year short-term follow-up after surgery. Previous studies have shown that the biomechanical characteristics of the lumbar spine are not significantly altered when the facet joint preservation rate exceeds 50% [45–46], which is consistent with our results. Therefore, whether PELD, with its better facet joint preservation rate, can translate into the potential advantage of long-term lumbar stability remains an important issue worthy of in-depth discussion.

Two complications occurred in the PELD group: one patient sustained a minor dural tear intraoperatively but no special treatment was administered, and no severe postoperative sequelae were observed; the other developed postoperative lower extremity paresthesia and symptoms improved after conservative observation, and the patient was discharged. This may be attributed to the narrow working channel in PELD, which makes it technically challenging to dissect calcified intervertebral discs and nerve roots; and during the operation, instruments or radiofrequency ablation may lead to dural injury, adhesion of soft tissues in the spinal canal, migration of large disc fragments and dural laxity, which are the risk factors for the occurrence of dural tears [47]. According to a study by Zhang et al. [42], PELD is not suitable for severe disc calcification as it increases the risk of surgical complications. The development of UBE has provided a solution to this clinical dilemma. UBE possesses independent working and observation channels, which provide greater surgical flexibility and a broad field of view [20], and the angulation of the instruments does not interfere with the independent operation of the working channel [48], which may render UBE advantageous in managing more complex calcified disc herniation, especially when the operation is performed by a surgeon with extensive experience in biportal endoscopy. However, the sample size of this study is relatively limited. Although no statistically significant differences in complications and recurrence were observed between the two groups, there remains a high risk of type II error, which makes it difficult to accurately identify the potential true differences between the two groups. Our findings still need to be further validated by large‑sample, multicenter studies. In future studies, we will collaborate with multiple centers to further compare the complications and safety between UBE and PELD in the treatment of CLDH.

This study has certain limitations. (1) The follow-up time was short, and the impact of the two groups of surgical procedures on the long-term spinal stability could not be evaluated. In the future, we will extend the follow-up time of patients; (2) Some patients included in this study had LSS, which may have a certain impact on the facet joint preservation rate; (3) Due to the small sample size of the study, although the complications, recurrence and other results of the two groups did not show statistical differences, there was a high risk of type II error, and it was difficult to accurately detect the potential true differences between the two groups. In addition, limited by the small sample size, multivariate analysis or propensity score matching was not performed in this study, which made it impossible to fully adjust for the confounding bias. Therefore, our findings need to be further validated in large-sample and multi-center studies. (4) This study did not measure the size, shape, and density of the calcified protrusions, making it impossible to clarify differences in the facet joint preservation rate between the two surgical procedures across different calcification grades. Future follow-up studies can further perform subgroup analyses of calcification grades. (5) This study is a single-center retrospective study, which inevitably has selection bias and may affect the generalizability of the results. Although surgical procedures were selected based on the patients’ clinical symptoms, imaging findings, anatomical characteristics and patient preferences, this may lead to potential confounding factors, and thus affect the objectivity and comparability of the results. (6) In the measurement of facet joint preservation rate, relying solely on preoperative and postoperative measurements of the axial length of the mid-facet joint on the surgical side may not comprehensively reflect the actual extent of facet joint resection. In future follow-up studies, we will further investigate this issue and explore more accurate quantitative evaluation methods. (7) Differences between the two anesthesia methods may have some impact on the operative time, intraoperative blood loss, and postoperative recovery.

Conclusion

PELD and UBE are both effective minimally invasive procedures for the treatment of CLDH. PELD is characterized by shorter operative time, less intraoperative blood loss, and less damage to facet joints. The advantages of UBE are more sufficient surgical field exposure and more flexible operation, though it may require a wider range of facet joint resection. In terms of short-term efficacy, there is no significant difference between the two methods. Therefore, clinical decision-making should follow the principle of individualization and comprehensively consider the patient’s clinical symptoms, imaging characteristics, and the surgeon’s procedural expertise, so as to formulate the optimal operation plan.

Authors’ contributions

Footnote. Zhifeng Cheng and Lei Sun contributed equally to this work. BH , ZFC, LS and TT made substantial contributions to the conception and design of the work; QW, LS and LKL made substantial contributions to the analysis and interpretation of data; ZFC, HNL and HX drafted the work; All authors revised it critically for important intellectual content; All authors approved the version to be published; All authors agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Funding

Our study on biomedicine has no financial support.

Data availability

The data of this article can be obtained from the corresponding author.

Declarations

Ethics approval and consent to participate

This study was approved by the Ethics Committee of Jiangxi Province Hospital of Integrated Chinese and Western Medicine (Ethical Approval No.: 2025002) and complied with the ethical standards outlined in the Declaration of Helsinki. All participating patients signed informed consent forms before surgery.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.