A Study of Unilateral Biportal Endoscopic Discectomy and Transforaminal Endoscopic Discectomy for Single-level Calcified Lumbar Disc Herniation

Summary

This study evaluates the therapeutic outcomes between unilateral biportal endoscopic (UBE) discectomy and percutaneous endoscopic transforaminal discectomy (PETD) for single-level calcified lumbar disc herniation.

Abstract

Calcified lumbar disc herniation (CLDH) presents unique surgical challenges due to its hard texture and frequent adhesion to neural structures. This study compares the efficacy and safety of unilateral biportal endoscopic discectomy (UBE) and percutaneous endoscopic transforaminal discectomy (PETD) in treating single-level CLDH. An analysis was conducted on 107 patients, with 45 undergoing UBE and 62 PETD. Both techniques significantly improved postoperative visual analogue scale (VAS) and Oswestry Disability Index (ODI) scores. PETD demonstrated advantages in operative time, blood loss, incision length, and hospital stay, but required more intraoperative fluoroscopy. UBE was associated with higher early postoperative low back pain VAS scores and a higher incidence of dural tears (2 cases), whereas PETD resulted in one case of transient nerve root symptoms.

While both methods effectively decompress neural elements, PETD offers less invasiveness and faster recovery, particularly beneficial for continuous central calcifications, though it demands specialized instruments and greater radiation exposure. UBE provides a broader operative field and familiar instrumentation but involves more tissue dissection. The findings support the use of either technique for CLDH, with selection influenced by lesion characteristics, surgical expertise, and resource availability. Future efforts should focus on standardizing training and indications to expand access to these minimally invasive options, especially in settings where traditional open surgery remains prevalent.

Introduction

Calcified lumbar disc herniation (CLDH) is a degenerative disease of lumbar disc herniation caused by precipitation or conversion of substances in the body into calcium carbonate or other insoluble calcium salt complexes. It often occurs in patients with long-term conservative treatment of lumbar disc herniation, but the specific cause of the formation is not clear^1,2. The calcified protruding disc can occupy the space of the spinal canal and lateral recess, resulting in or aggravating lumbar pain and neurological symptoms of the lower extremities. Due to the hard texture of calcification and poor elasticity, it often produces persistent neurological symptoms after compressing the nerve root, which usually requires surgical treatment.

In the past, it was considered that it was difficult to deal with CLDH under endoscope and remove it completely, so open surgery was often used to remove it completely under direct vision³. However, the traditional posterior lumbar interbody fusion not only causes great muscle injury and bleeding, but also affects the stability and range of motion of the spine. With the development of spinal endoscopy technology and tools, CLDH is no longer a relative taboo in minimally invasive surgery^4,5.

Percutaneous endoscopic transforaminal discectomy (PETD) is the direct percutaneous discectomy of herniated intervertebral disc tissue through the intervertebral foramen under uniaxial endoscope to complete nerve decompression. With the application of endoscopic grinding drill, it is also gradually used in CLDH^6,7,8 . However, the learning curve of PETD is steep, and the operating space is narrow, which may lead to nerve root injury and dural tear, which is challenging for surgeon⁷.

Unilateral biportal endoscopic (UBE) discectomy has been especially popular in Asia recently because of its convenient access to instruments and simple operation⁹ . It shows a good curative effect in the aspects of lumbar disc herniation, lumbar spinal stenosis, and so on^10,11. However, there are a few reports about the application of UBE discectomy in the treatment of CLDH, and few studies have compared the difference of CLDH between PETD and UBE discectomy¹², so this study compared the efficacy and safety of PETD and UBE discectomy in the treatment of single-level CLDH.

Protocol

This study was approved by the Ethics Committee of the Third Hospital of Hebei Medical University (K-2024-014-1). All patients' data collection was informed in advance, and informed consent was obtained from all subjects.

Study population

Patients with single-level CLDH were included based on the following criteria: 1) diagnosis confirmed by lumbar intervertebral disc CT; 2) presentation of typical symptoms, including low back pain with lower limb radicular pain, numbness, or muscle weakness; 3) failure to improve after a minimum of 3 months of regular conservative therapy. Exclusion criteria were defined as: 1) a follow-up duration of less than 12 months; 2) incomplete follow-up data; 3) a history of prior lumbar spine surgery; 4) presence of segmental instability; 5) diagnosis of spinal tumor, infection, or fracture. All surgical procedures were performed by two senior attending surgeons.

Clinical data and efficacy evaluation

Medical records were reviewed to collect demographic and perioperative data, including age, sex, body mass index (BMI), operative segment, operative time, length of hospital stay, estimated blood loss, incision length, and intraoperative fluoroscopy frequency. Preoperative imaging (X-ray, CT, MRI) and postoperative X-rays were reviewed. Based on preoperative disc CT, patients were classified into three morphological subtypes of CLDH: solitary type (calcification < 3 mm), semilunar type (calcification 3-10 mm), and continuous type (calcification > 10 mm)⁴. Clinical efficacy was assessed using the visual analogue scale (VAS) for low back and leg pain and the Oswestry Disability Index (ODI). These scores, along with records of complications, were collected preoperatively and at 1 day, 3 months, 6 months, and 12 months postoperatively. Modified MacNab criteria at the last follow-up were compared between the two groups.

Unilateral Biportal Endoscopic Discectomy

Anesthesia and patient positioning

General anesthesia with endotracheal intubation was administered. After successful anesthesia induction, the patient was placed in a prone position. Soft pillows were placed under the chest and bilateral iliac spines to ensure the abdomen was free, reducing intra-abdominal pressure and epidural venous bleeding during surgery. The operating table was adjusted to slightly flex the lumbar spine, helping to open the interlaminar space.

Preoperative localization and marking

The lamina on the side of the approach was located with a Kirschner needle (Figure 1A). Syringe needles were used to simulate the positions of the working channel and the observation channel, and the directions of the channels were observed under X-ray fluoroscopy ( Figure 1B,C). Two longitudinal incisions, approximately 1.5 cm each, were marked approximately 1.5-2.0 cm lateral to the midline (on the symptomatic side) at the level of the target disc space.

Establishing operational portals

The skin and superficial fascia were incised sequentially with a No. 11 scalpel. Subcutaneous tissue and the thoracolumbar fascia were bluntly dissected using haemostatic forceps. A series of muscle dilators were used to bluntly separate the paraspinal muscles along the direction of the interlaminar space until the lower edge of the lamina and the medial margin of the facet joint were exposed. The working cannula was inserted, and its position was secured.

Endoscopic procedure

A 30° or 0° arthroscope was introduced through the viewing portal cannula. Continuous saline irrigation was maintained for clear visualization and haemostasis. A radiofrequency probe was introduced through the working channel to clear soft tissue over the lamina and ligamentum flavum, exposing the surgical field. A high-speed drill or Kerrison rongeurs was used to perform a partial laminectomy and medial partial facetectomy of the responsible segment for decompression. The thickened ligamentum flavum was removed using punch or Kerrison rongeurs to expose the thecal sac and traversing nerve root. The nerve root was carefully identified and protected, and was gently retracted medially using a nerve retractor. The herniated calcified disc material was explored and exposed (Figure 1D). The posterior longitudinal ligament and annulus fibrosus were circumferentially incised. Disc forceps, pituitary rongeurs, or curettes were used to remove the calcified nucleus pulposus in pieces. For large or severely adherent calcifications, a micro-drill bit was used to break them down before removal. The ventral side, shoulder, and axilla of the nerve root were carefully explored to ensure no residual fragments were causing compression and that the nerve root was well relaxed and pulsating. Haemostasis was achieved thoroughly using the radiofrequency probe.

Wound closure

The endoscope and instruments were withdrawn. A negative pressure drain was placed through the working channel. The deep fascia was sutured with absorbable suture, and the skin incision was closed with suture and covered with a sterile dressing.

Percutaneous endoscopic transforaminal discectomy

Anesthesia and patient positioning

Local infiltration anesthesia (1% lidocaine) supplemented with sedation and analgesia was typically used. The patient was placed in a prone or lateral decubitus position (symptomatic side up). In the lateral position, the hips and knees were flexed, and a pillow was placed under the waist to increase the foraminal volume.

Puncture and localization

The surface projection of the target intervertebral space was marked under AP and lateral C-arm fluoroscopy. The skin entry point was calculated based on the "Yeung's safety triangle" principle, typically 8-14 cm lateral to the midline and at a 15-30° angle to the sagittal plane. After local anesthesia, an 18 G puncture needle was inserted. Under lateral fluoroscopy, the needle tip was ultimately located in the posterior third of the target disc space; under AP fluoroscopy, it was on the mid-pedicular line.

Foraminoplasty and cannula placement

Once the needle was correctly positioned, a guidewire was inserted, and the needle was withdrawn. A series of dilating tubes were sequentially rotated over the guidewire. If the patient had a narrow foramen or a large calcification, foraminoplasty was required. A smaller diameter protective cannula was placed near the foramen. Using a trephine, drill, or endoscopic forceps through the protective cannula, part of the ventral aspect of the superior articular process was removed to enlarge the foramen. After foraminoplasty, the final working cannula was placed (Figure 2A,B).

Endoscopic decompression

An endoscope system was introduced through the working cannula (Figure 2C). The annulus fibrosus was incised using a scalpel. Hard calcifications were broken down using an endoscopic drill. The herniated nucleus pulposus was gradually removed using Disc forceps, pituitary rongeurs, or curettes. The key step was adequate decompression of the nerve root. The endoscope angle was adjusted to carefully explore the shoulder, axilla, and ventral side of the nerve root, ensuring all compressive material was removed and the nerve was completely released (Figure 2D). Haemostasis was achieved with radiofrequency.

Completion of surgery

The endoscope was slowly withdrawn, checking for any active bleeding. The incision usually required only a single suture or was directly covered with a sterile adhesive bandage.

Postoperative

After the operation, patients were given mannitol and dexamethasone to relieve neuroedema. Ground movement was encouraged on the first day after the operation in the PETD group, and on the second day after the drainage tube was removed in the UBE group.

Data analysis

Statistical analyses were performed using SPSS software (version 26.0). Continuous data were compared between the two groups using independent t-tests or Mann-Whitney U tests. Categorical data are presented as numbers (percentages) and were compared using the chi-square test or Fisher's exact test. VAS scores and ODI scores were compared between the two groups using repeated-measures analysis of variance (ANOVA). All pairwise comparisons were adjusted using the Sidak method. The modified MacNab criteria were compared using the Mann-Whitney U test. A two-sided P value < 0.05 was considered statistically significant.

Results

Apart from three cases of loss to follow-up, a total of 107 patients were enrolled in the study, including 45 patients with UBE and 62 patients with PETD. Table 1 shows that there is no significant difference in general information between the two groups, including sex, age, BMI, surgical segment, type of calcification, and so on (P ＞ 0.05). Table 2 shows that the amount of intraoperative blood loss, operation time, length of hospital stay, and surgical incision length in the PETD group ...

Discussion

In our study, the quality of life outcomes of patients showed that both UBE and PETD groups had a significant decrease in ODI and VAS scores after operation, which could improve the symptoms of CLDH patients. Compared with the UBE group, the PETD group showed less bleeding, shorter operation time, smaller incision, and shorter hospital stay, but more fluoroscopy times were needed during the operation. No obvious lumbar instability was observed in both groups one year after the operation.

CLDH ...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
4-0 or 5-0 Polydioxanone	Shandong Weigao Group Medical Polymer Co. , Ltd.	9270504	Their PDS sutures are typically used for soft tissue approximation and ligation.
Electric grinder	Guizhou Zirui Technology Co. , Ltd.	04-14-08	Grinding removes lamina bone and exposes ligamentum flavum tissue
Endoscope	UninTech	UNTV-076.30.171	WL 171 mm/OD 7.6 mm/30°/ WChD 4.7 mm/2 x IC 1.5 mm
Kerrison Rongeur Forceps	Xi'an Surgical Medical Science and Technology Co. , Ltd.	38049	Used for biting dead bones or repairing bone stumps.
Minimally invasive spinal surgery channel expansion tube	Xi'an Surgical Medical Science and Technology Co. , Ltd.	04-17-13	Used to expand the surgical field of view.
Nerve stripping ion	Xi'an Surgical Medical Science and Technology Co. , Ltd.	04-18-01	Used for stripping or separating nerve root tissue
Periosteal stripping ion	Xi'an Surgical Medical Science and Technology Co. , Ltd.	04-18-01	Used to peel off or separate the periosteum and soft tissue attached to the bone surface.
Plasma Surgical Blade (RF electrode/ablation electrode)	Xi'an Surgical Medical Science and Technology Co. , Ltd.	1798824	Used to ablate soft tissue such as muscle and fascia, or to clot the surface of muscle and nerve tissue
Radiofrequency coagulator	Kai Zhuo	RFS-4000KD	None
Spinal surgery using nerve hooks	Xi'an Surgical Medical Science and Technology Co. , Ltd.	38078	Used in orthopedic surgery to expose the surgical field of view, or to peel, stretch, or occlude nerve roots during orthopedic surgery.
SPSS Statistics for Windows	IBM Corp	version 26.0	None
T-head cannula	UninTech	UNT-II-167989T	7.9 mm × OD 8.9 mm × L168 mm
Trephine	UninTech	UNT-III-177888	7.8 mm × OD 8.8mm × L 171 mm
U-head cannula	UninTech	UNT-II-159010U	9.0 mm × OD 10.2 mm × L151 mm