Unilateral Percutaneous Transforaminal Endoscopic Approach With Bilateral Decompression for Large Central Lumbar Disc Herniation Complicated by Bilateral Neurological Symptoms: A 2-Year Retrospective Clinical Study

Introduction

Large central lumbar disc herniation (LDH) is defined as a pathological condition in which herniated disc tissue is primarily located in the central spinal canal, and the herniated mass occupies more than 50% of the canal’s cross-sectional area [1]. This condition often produces a range of clinical symptoms via compression of the cauda equina and nerve roots. The annual incidence of large central LDH represents approximately 11.54% of all LDH cases [2]. The main clinical manifestations include pain, numbness, or weakness in at least 1 lower limb; a small proportion of patients may experience urinary and fecal dysfunction, often accompanied by low back discomfort. The diagnosis of large central LDH requires a comprehensive evaluation that integrates imaging findings, clinical symptoms, and physical signs. For patients with mild symptoms, no evident cauda equina injury, and a disease duration shorter than 2 weeks, conservative treatment may be considered. In contrast, active surgical intervention is recommended for patients with cauda equina syndrome, those who show no improvement or clinical deterioration after 2 to 4 weeks of conservative treatment, those with progressive loss of lower limb muscle strength, and those with severe compression caused by a large herniated mass [3]. Both conventional open posterior lumbar surgery and minimally invasive techniques are available for the treatment of large central LDH with bilateral neurological symptoms. Conventional open posterior approaches include interlaminar discectomy and interbody fusion with internal fixation, which can achieve adequate bilateral neural decompression and yield satisfactory clinical outcomes; however, these procedures are linked to substantial challenges, including extensive tissue trauma, excessive blood loss, persistent postoperative back pain, and postoperative lumbar instability [4,5]. Minimally invasive surgery for LDH has rapidly developed in recent years; commonly used techniques include microscopic and percutaneous spinal endoscopic procedures. Nevertheless, bilateral nerve root decompression cannot be reliably achieved through a unilateral approach due to limitations inherent in microscopic interlaminar techniques and surgical instrumentation.

In recent years, given the rapid development of spinal endoscopy, percutaneous transforaminal endoscopic discectomy (PTED) has been increasingly utilized in the treatment of LDH [6]. PTED is recognized for its minimally invasive nature, efficiency, and safety, as well as rapid recovery and a low complication rate. However, in cases of large central LDH with bilateral neurological symptoms that require bilateral decompression, PTED often warrants a bilateral approach because the achievement of adequate decompression through a unilateral approach remains technically challenging. Consequently, the potential for PTED to provide safe and effective bilateral neural decompression through a unilateral approach in patients with large central LDH and concomitant bilateral neurological symptoms remains a controversial issue among spine surgeons [7–9]. Salim et al conducted a retrospective study that included 60 patients with lumbar degenerative spinal stenosis who underwent endoscopic interlaminar decompression using the Destandau technique between January 2009 and December 2013 [10]. They demonstrated that unilateral percutaneous endoscopic treatment for lumbar spinal stenosis could achieve bilateral decompression with satisfactory clinical outcomes. Despite the achievement of bilateral decompression through a unilateral approach in that study, the procedure was performed under optical endoscopy and required resection of the unilateral lamina and ligamentum flavum. Accordingly, the surgical approach and technique substantially differ from those used in the present study.

In this context, the present study investigated an improved PTED technique that facilitates access to the contralateral nerve root and enables effective removal of contralateral nucleus pulposus tissue, thereby allowing adequate contralateral neural decompression in cases of large central LDH. This modified PTED approach is intended to enhance therapeutic efficacy for large central LDH and to expand the clinical applicability of endoscopic techniques in LDH treatment, which has implications for future development of endoscopic spine surgery. The clinical efficacy and complications of this improved PTED technique were retrospectively analyzed in patients with large central LDH treated at our institution. Accordingly, this retrospective study evaluated outcomes after unilateral PTED among patients with lumbar stenosis due to a large central LDH and concomitant bilateral neurological symptoms.

Material and Methods

ETHICS STATEMENT:

The study was approved by the Ethics Committee of Honghui Hospital, Xi’an Jiaotong University (Approval No.: 202403052; March 11, 2024). Written informed consent was obtained from all participants. All procedures were conducted in accordance with the Declaration of Helsinki.

DIAGNOSTIC CRITERIA FOR LARGE CENTRAL LDH:

The diagnosis of large central LDH was based on a comprehensive assessment that integrated clinical symptoms, physical examination findings, and imaging results.

IMAGING DIAGNOSTIC CRITERIA (CORE BASIS):

Lumbar magnetic resonance imaging served as the gold standard for defining “large” and “central” characteristics. Herniated disc tissue was located in the midline of the spinal canal, compressing the dural sac and cauda equina, with possible involvement of bilateral nerve root sleeves. Imaging demonstrated that the herniated mass did not deviate toward the unilateral neural foramen but occupied the central sagittal region of the spinal canal. Reference criteria included a herniated mass measuring more than 6 mm in diameter or occupying more than 50% of the canal cross-sectional area.

CLINICAL SYMPTOM CRITERIA:

Cauda equina syndrome–related manifestations included perineal hypoesthesia or anesthesia; urinary and fecal dysfunction (eg, urinary retention and fecal incontinence); weakened or absent perianal reflex; and, in severe cases, incomplete paraplegia of both lower limbs. Bilateral nerve root symptoms included radiating pain, numbness, and weakness in both lower limbs, typically along the sciatic nerve distribution (eg, posterior thigh and lateral calf extending to the plantar region).

PHYSICAL EXAMINATION CRITERIA:

Sensory abnormalities included hypoesthesia in the bilateral calves and feet and saddle-area sensory disturbance in the perineum. Motor dysfunction included reduced muscle strength in both lower limbs, commonly involving the tibialis anterior, peroneus longus and brevis, and plantar flexors (muscle strength grade ≤4), as well as gait instability or claudication in severe cases. Reflex abnormalities included weakened or absent bilateral knee or Achilles tendon reflexes; pathological reflexes were generally negative but could be positive if the conus medullaris was involved.

INCLUSION AND EXCLUSION CRITERIA:

Study inclusion criteria were as follows: (1) preoperative imaging demonstrating single-segment large central LDH; (2) definite bilateral lower limb radicular pain; and (3) failure of formal conservative treatment for more than 3 months.

Exclusion criteria were as follows: (1) lumbar instability or spondylolisthesis; (2) a history of lumbar surgery; (3) cauda equina syndrome; and (4) spinal tumors, infectious diseases, or related conditions.

SURGICAL TECHNIQUE:

The patient was placed in the prone position on a positioning pad, with hips flexed and knees bent. The midline of the spinous processes and outline of the iliac crest on the side with more severe symptoms were marked on the skin. C-arm anteroposterior fluoroscopy was used to identify the parallel line of the affected disc and the anteroposterior puncture trajectory; lateral fluoroscopy was used to determine the safe line through the upper margin of the articular process. Based on patient body habitus, the puncture entry point was marked 10 to 15 cm from the midline of the spinous processes. After routine disinfection, local infiltration anesthesia of the skin and fascia was performed using 1% lidocaine. Additional local infiltration anesthesia with 0.5% lidocaine was administered at the apex of the superior articular process under C-arm guidance. The puncture was advanced until the target point was reached. From the anteroposterior view, the needle tip was positioned close to the midline of the spinous process; from the lateral view, it was placed near the posterior margin of the intervertebral disc. A high iliac crest represents a common anatomical challenge during puncture at the L5 to S1 level. For cases complicated by a high iliac crest, an optimized puncture localization strategy was used. Under anteroposterior fluoroscopic guidance, the iliac crest apex localization method combined with midline deviation adjustment of the spinous process was utilized. First, the positional relationship between the iliac crest apex and the L5 to S1 spinous process was determined by anteroposterior radiography. When the iliac crest obstructed the puncture trajectory, the entry point was shifted 0.5 to 1.0 cm cephalad, and the puncture angle was adjusted to 30° to 45°; the specific angle was individualized according to the degree of iliac crest prominence. Through dual-target localization that avoided iliac crest obstruction and aimed toward the base of the spinous process, accurate placement of the puncture needle into the predetermined region adjacent to the spinous process was achieved. A mixture of methylene blue and iodohexyl alcohol was injected into the intervertebral disc through the puncture needle, followed by disc staining and contrast imaging. A guidewire was then introduced through the puncture needle, which was subsequently removed, and a skin incision (length: ~1 cm) was made. A dilating sleeve was inserted; a trephine was gradually advanced to enlarge the intervertebral foramen and establish the working channel. The endoscopic system was connected, and the endoscope was introduced through the working channel. Bipolar radiofrequency was used to clear the endoscopic field, and nucleus pulposus forceps were used to remove the herniated disc tissue. Repeated exploration was performed to confirm complete removal of the protruded disc material and adequate decompression of bilateral nerve roots. Annular fibroplasty was subsequently performed using bipolar radiofrequency. Finally, the working channel was removed, and the procedure was completed.

INTRAOPERATIVE COMBINED EVALUATION:

Under direct visualization with a transforaminal endoscope, the extent of decompression was confirmed via combined lateral and anteroposterior C-arm fluoroscopy. A decompression sequence of “central first, then contralateral” was implemented to facilitate stepwise removal of herniated disc tissue and contralateral hyperplastic osteophytes.

CRITERIA FOR DETERMINING RELIEF OF NERVE COMPRESSION:

Recovery of contralateral nerve root pulsation, a negative result in the intraoperative straight leg raise test, and an endoscopically observed expansion of at least 50% in contralateral nerve root canal volume served as intraoperative indicators of adequate decompression.

VISUAL ANALOG SCALE (VAS) FOR PAIN ASSESSMENT:

A 10-cm linear VAS was used, with 0 indicating “no pain” and 10 indicating “worst imaginable pain.” Patients independently marked their current pain intensity on the scale in a quiet environment. The distance from the 0 point to the mark was measured to the nearest 0.1 cm to obtain the VAS score.

OSWESTRY DISABILITY INDEX (ODI):

The ODI was used to evaluate the impact of symptoms on daily activities. The validated Chinese version of the 10-item ODI was administered, assessing low back pain–related disability across 10 domains: pain intensity, personal care, lifting, walking, sitting, standing, sleeping, sexual activity, social life, and traveling. Each item was scored from 0 (no disability) to 5 (severe disability), yielding a total score that ranged from 0 to 50. The total score was converted to a percentage via multiplication by 2 to represent the degree of disability (0%=no disability; 100%=complete disability). Questionnaires were completed independently by patients; clarification was provided by a research nurse as needed to ensure consistent interpretation. Incomplete questionnaires were excluded, and missing items were managed by imputing the mean of completed items in accordance with ODI scoring guidelines.

MODIFIED MACNAB CRITERIA:

These criteria were used to assess overall clinical outcomes based on 4 grades: Excellent (no pain and full return to normal activities), Good (minimal pain with slight activity limitation), Fair (moderate pain with significant activity limitation), and Poor (severe pain with inability to work or perform daily activities). In this study, outcomes rated as Excellent or Good were considered satisfactory.

The automatic area calculation function of the picture archiving and communication system (miPlatform PACS, China) was used to measure dural sac area.

VAS scores, ODI scores, and dural sac area were recorded preoperatively, at 3 days postoperatively, and at the final follow-up. Satisfaction rates at the final follow-up were evaluated using modified MacNab criteria. Additionally, intraoperative blood loss, operative time, length of postoperative hospitalization, and complications were recorded.

STATISTICAL ANALYSIS:

SPSS software (version 23.0; IBM Corp., Armonk, NY, USA) was used for statistical analysis. Continuous data are presented as mean±standard deviation. Student’s t test was utilized for comparisons. The statistical significance threshold was defined as P<0.05.

Results

PATIENT CHARACTERISTICS:

In total, 34 patients (15 men and 19 women) met the inclusion criteria. Patient age ranged from 22 to 54 years (mean, 42.68±7.01 years). Disease duration ranged from 4 to 95 months (mean, 27.18±17.32 months). Lesions were located at L3/4 in 2 cases, L4/5 in 21 cases, and L5/S1 in 11 cases. Baseline demographic characteristics and clinical outcomes were recorded (Table 1).

PERIOPERATIVE INDICATORS:

All enrolled patients completed the planned surgical procedures without intraoperative complications requiring termination. The follow-up period ranged from 24 to 48 months, with a mean duration of 34.21±6.54 months. Mean intraoperative blood loss was 81.56±14.72 mL (range, 50–110), mean operative time was 85.12±13.43 min (range, 65–113), and mean length of hospitalization was 32.06±9.52 h (range, 24–72).

CLINICAL EFFICACY:

VAS and ODI scores for low back and leg pain significantly improved at all postoperative time points compared with preoperative values (P<0.05) (Table 2). According to modified MacNab criteria, the satisfaction rate (Excellent/Good) at the final follow-up was 91.2% (31/34), including 19 Excellent, 12 Good, 2 Fair, and 1 Poor outcomes. The dural sac cross-sectional area at each postoperative assessment was significantly larger than preoperative values (P<0.05) (Table 2). Representative cases are shown in Figure 1.

COMPLICATIONS:

One case of cerebrospinal fluid leakage occurred during the perioperative period. Symptom recurrence was observed in 1 patient at the 6-month follow-up; it fully resolved with conservative management. No serious adverse events, including nerve root injury, major vascular injury, or wound infection, were recorded in any patient.

Discussion

In the present study, all patients underwent complete endoscopic removal of the protruded nucleus pulposus with bilateral neural decompression. Assessment using modified MacNab criteria indicated that the satisfaction rate (Excellent/Good) reached 91.2%, consistent with previous reports [6,8,11]. All enrolled patients achieved substantial and sustained relief of low back and lower extremity pain, accompanied by significant improvement in spinal motor function throughout the follow-up period. Notably, no severe complications were observed, supporting the clinical safety and therapeutic efficacy of unilateral PTED for management of large central LDH. In recent years, several studies have utilized similar techniques for the treatment of large central LDH; most patients achieve favorable clinical outcomes and display a low incidence of complications [7–10]. In 2017, Kang et al used PTED to treat 37 patients with central LDH and reported an overall satisfaction rate of 83.5% [9]. One patient showed no postoperative improvement and subsequently underwent laminectomy with bone grafting and internal fixation, whereas 2 patients experienced recurrence that required treatment via the same procedure. In 2018, Kondo et al reported that 16 patients with central LDH underwent PTED assisted by a specially designed tunnelplasty instrument; no recurrence or segmental instability was observed during follow-up [7]. These findings suggest that PTED represents a viable alternative for the treatment of large central or paracentral LDH. In 2019, Wang et al described outcomes among 11 patients with large central LDH who underwent PTED [8]. One patient experienced an incidental dural tear at the beginning of surgery, whereas another patient displayed recurrence 5 months postoperatively and underwent contralateral endoscopic reintervention; the remaining patients achieved satisfactory results. In 2020, Salim et al reported outcomes among 60 patients with lumbar spinal stenosis who underwent bilateral decompression through a unilateral optical endoscopic interlaminar approach [10]. Their results demonstrated that this technique provided adequate bilateral spinal canal decompression, including satisfactory pain relief and functional recovery. Although the surgical techniques, instruments, and patient selection criteria in these studies differed from the approach used in the present investigation, the technical innovation of this study lies in optimization of the puncture angle in conventional PTED and refinement of the foraminoplasty procedure. These modifications facilitate access to the contralateral nerve root and enable effective bilateral neural decompression.

Conventional open surgery for LDH includes simple lumbar discectomy and interbody fusion [2,12,13]. Central LDH with bilateral neurological symptoms is characterized by herniation in the central spinal canal and compression of both nerve roots. The primary objective of surgery is to achieve adequate bilateral neural decompression and prevent residual nucleus pulposus; thus, discectomy often requires bilateral fenestration or even total laminectomy for sufficient decompression [3,4]. However, these procedures are associated with substantial risks, including extensive surgical trauma, clinically significant intraoperative blood loss, prolonged operative time, chronic postoperative low back pain, and postoperative lumbar instability. Particular attention should be given to high-risk populations, including older patients and individuals with osteoporosis, paraspinal muscle atrophy, diabetes, or long-term use of oral anticoagulants or corticosteroids – these factors increase the likelihood of complications such as excessive blood loss, persistent postoperative pain, lumbar instability, and wound infection. For patients with these risk factors, thorough preoperative evaluation and timely intervention are essential. Appropriate preoperative management can reduce the incidence of postoperative complications and improve clinical outcomes. Given the potential for serious complications, comprehensive informed consent is required before surgery. To ensure valid informed consent, physicians have a professional obligation to initiate discussion of the risks, benefits, and alternative treatment options [14]. Although lumbar interbody fusion can provide complete decompression and address postoperative instability, it is generally reserved for patients with LDH complicated by lumbar instability or cauda equina syndrome [15,16]. In cases of central LDH without instability or cauda equina syndrome, clinical management should emphasize reduction of surgical trauma and preservation of spinal stability while achieving adequate bilateral decompression.

The use of PTED for the treatment of LDH has rapidly expanded in recent years; its safety and efficacy have been widely acknowledged [17]. PTED can be performed via 2 main approaches: translaminar and transforaminal. The translaminar approach is primarily indicated for paracentral LDH [18,19]. For central LDH with bilateral nerve root compression, effective bilateral decompression through a unilateral approach is technically challenging. The risks associated with excessive intraoperative traction of the dural sac and nerve roots, as well as the need for general anesthesia, must be considered [20,21]. In contrast, the transforaminal PTED approach can be performed under local anesthesia and does not require excessive manipulation of the nerve roots or dural sac, thereby reducing the risk of neural injury [6,22].

Large disc herniations located in the central spinal canal can result in bilateral nerve root compression. Conventional unilateral transforaminal approaches, including the TESS/YESS technique, often fail to achieve adequate bilateral decompression, particularly effective relief of lateral nerve root compression [23–25]. To ensure sufficient bilateral decompression in cases of central LDH, we propose 4 key technical considerations. The first consideration is puncture angle – compared with the conventional foraminal approach, the needle entry point should be positioned more laterally, without crossing the safety line, and the abduction angle should be moderately increased. From the anteroposterior view, the needle tip and working channel should be positioned as close as possible to the midline of the spinous process after successful puncture. The second consideration is foraminoplasty – enlargement of the intervertebral foramen is performed using a visualized trephine. During this process, close attention should be directed to lower-extremity neurological symptoms to prevent nerve injury. In cases of large disc protrusion, foraminoplasty can be conducted in stages, with gradual advancement into the spinal canal to reduce the risk of neural damage. The third consideration is decompression sequence – because larger disc protrusions are associated with greater local neural compression, immediate decompression of the contralateral nerve root is not required at the initial stage. Instead, gradual removal of protruded disc tissue beneath the posterior longitudinal ligament is performed. As the dural sac and nerve roots descend, the contralateral nerve root becomes more clearly exposed, allowing safe and effective decompression. The fourth consideration is prevention of residual disc material – due to limitations in the visual field and working angle, residual nucleus pulposus may remain around the contralateral nerve root, particularly in cases of free disc fragments, which can result in incomplete decompression. Careful re-exploration of the contralateral nerve root is essential to ensure complete removal of residual disc tissue prior to completion of the procedure.

In this study, cerebrospinal fluid leakage occurred in 1 patient; no other complications, such as nerve injury or hematoma, were observed. This incidence was lower than the rate reported in previous studies [11,24–27], further supporting the safety of the improved PTED technique for treatment of large central LDH. Potential explanations for these differences include variations in surgical technique, patient selection criteria, and postoperative management. During follow-up, lower extremity neurological symptom recurrence was noted in 1 patient, a rate lower than that reported in other studies [7,9,22]. This finding may be attributable to the relatively small sample size and limited duration of follow-up.

Our study has some inherent limitations. First, it was a single-center, retrospective cohort study with a small sample size and no well-matched control group. These methodological constraints may have introduced bias into the statistical analyses, affecting internal validity and overall reliability. Future studies should include large-scale, multicenter randomized controlled trials to further evaluate the clinical efficacy and safety of unilateral PTED for large central LDH. Second, the technique has a steep learning curve, and procedures performed by surgeons with limited experience in percutaneous endoscopic surgery may be associated with a higher risk of early postoperative complications. Third, the relatively short follow-up period may have hindered assessments of long-term outcomes and delayed complications.

Conclusions

Unilateral PTED provides bilateral neural decompression with favorable safety and reliable clinical efficacy in the treatment of large central LDH with bilateral neurological symptoms, resulting in substantial relief of low back and leg pain, as well as significant improvement in lower extremity motor function. Despite the technical demands and steep learning curve, this approach yields favorable postoperative outcomes, characterized by reduced surgical trauma, decreased intraoperative blood loss, shorter hospitalization, and a low incidence of perioperative complications.