Percutaneous endoscopic transforaminal vs. interlaminar discectomy for L5–S1 lumbar disc herniation: a retrospective propensity score matching study

Lumbar disc herniation (LDH) is a common and prevalent spinal disease with an increasing incidence, affecting 1–5% of the global population annually [1]. Approximately 80% of Americans have been reported to experience at least one episode of LDH and subsequent low back pain in their lifetime [2]. Conservative treatment is the first-choice approach for patients with LDH, but some patients need surgical intervention after conservative treatment to alleviate pain [3]. With the popularization of the minimally invasive concept and the innovation in the design of surgical instruments, minimally invasive spine endoscopy has become the mainstream surgical technique for treating LDH due to its advantages, such as minimal trauma, rapid recovery, and shorter hospitalization [4, 5]. Currently, percutaneous endoscopic lumbar discectomy (PELD) is widely used in the clinical treatment of LDH and has achieved favourable clinical outcomes [4]. PELD includes two different surgical approaches, namely percutaneous endoscopic transforaminal discectomy (PETD) and percutaneous endoscopic interlaminar discectomy (PEID), each with its own advantages in treating LDH [6].

Compared with PEID, PETD removes the herniated disc through the "safety triangle" of the intervertebral foramina without laminectomy and dural retraction, causing less damage to the spinal canal and the soft tissues of the lumbar spine [7, 8]. Some researchers believe that PETD can more effectively relieve postoperative pain and reduce blood loss and hospital stay [8]. However, for L5–S1 disc herniation, PETD still faces significant technical challenges due to its challenging anatomical characteristics such as a high position of iliac crest, narrow intervertebral foramen, and facet hypertrophy [6, 9]. On the other hand, PEID benefits from a wider interlaminar space and easier localization; thus, some scholars believe that it is a better choice for treating L5–S1 disc herniation and may facilitate surgery and shorten operative time [10]. Nevertheless, Yeung et al. [11] demonstrated that PETD can be successfully used in treating disc herniation at all lumbar levels, including L5–S1. Therefore, it is still controversial which surgical approach yields better outcomes in the treatment of L5–S1 disc herniation. In this study, we retrospectively analysed the clinical outcomes of patients with L5–S1 disc herniation who underwent two different surgical approaches. Our findings illuminate their comparative clinical safety and efficacy and provide some clinical rationale for selecting surgical methods.

LDH is a chronic progressive disease that clinically presents with low back pain, radicular symptoms in the lower limbs, and sensory disturbances in the corresponding dermatomes [19]. Surgical intervention is required for patients with LDH who do not respond to conservative treatment. [3, 20]. Traditional open surgery is a classic approach for treating LDH but necessitates it involves extensive dissection of the paraspinal muscles and wide removal of the lamina, and facet joints, which can lead to postoperative complications such as refractory low back pain, muscle denervation, and lumbar instability [7, 21]. With the advancement of endoscopy techniques, several studies have shown that endoscopic treatment of LDH can achieve similar clinical outcomes as open surgery, with advantages such as less trauma, faster recovery, and fewer complications [4, 5]. Currently, PEID and PETD are widely used in the treatment of patients with LDH, with specific clinical characteristics [22]. However, for L5–S1 disc herniation, the specific advantages and disadvantages of these two different surgical approaches are still unclear due to their unique anatomical characteristics.

During the endoscopic treatment of L5–S1 disc herniation, the presence of the high iliac crest and a narrow intervertebral foramen can hinder the entry of the working cannula, and the hyperplastic facet joints can also obstruct the protruding disc [6]. The lateral approach has a limited perforation angle, necessitating excessive intraoperative removal of facet joints that compromise the biomechanical stability of the spine. These limitations increase the difficulty of intraoperative accurate puncture positioning and adequate surgical decompression for PETD, necessitate repeated fluoroscopy, and increase radiation exposure for both patients and spine surgeons [9]. Excessive X-ray exposure is a serious concern and can have significant health implications for medical personnel in the long term [23]. In addition, due to the obstruction caused by the superior margin of the iliac crest and the narrow intervertebral foramen, the operating space during PETD is insufficient, which may lead to incomplete removal of the protruding disc in the far region. The residual disc tissue increases the risk of recurrent disc herniation, which can seriously affect the treatment outcome [6]. Therefore, it is usually recommended to remove the L5–S1 disc through a wide interlaminar space during PEID. In the L5–S1 segment, the sacral one nerve root originating from the dural sac is positioned high in the plane of the intervertebral spaces, The herniated disc tissue can be removed intraoperatively from the shoulder or axilla of the nerve root according to the actual situation, which is easier and safer in this segment than in other segments. However, PEID necessitates the removal of the ligamentum flavum and a part of the lamina, which may interfere with the dural sac and increase the risk of injury to the dural sac or cauda equina [24]. Therefore, caution is needed during PEID to reduce the incidence of postoperative complications.

In our study, we observed that both PEID and PETD for L5–S1 disc herniation showed no significant difference in clinical functional scores and imaging. VAS scores for back and leg pain and ODI index of all patients significantly improved after the surgery, meeting the criteria for MCID. Therefore, both minimally invasive surgical techniques are safe and effective treatments for L5–S1 disc herniation, leading to favourable clinical outcomes. However, despite similar clinical outcomes of the two surgical approaches, they still have distinct characteristics in treating L5–S1 herniated discs. We found that the PEID group had significantly shorter operation time and lower frequency of fluoroscopy than the PETD group, suggesting the superiority of PEID over PETD in reducing surgical time and radiation exposure. The advantages of PEID may be related to several factors: (i) PEID uses an interlaminar approach, which is familiar to most spine surgeons and easier compared with PETD; (ii) PEID is not technically limited by the obstruction of the high iliac crest and narrow intervertebral foramen, allowing rapid and precise puncture positioning, and easy targeting of the L5–S1 herniated disc within a wide interlaminar space; (iii) PEID provides a spacious operating space, allowing better mobility of the working cannula for complete removal of the protruding disc; and (iv) PEID directly visualizes the protruded or extruded disc under endoscopy, enabling full decompression of central and paracentral disc herniation [6].

Although PETD for L5–S1 disc herniation is more challenging and requires higher proficiency of spine surgeons, it has its advantages and indications. PETD demands entering the spinal canal through a physiologically formed safe triangle of the intervertebral foramen, avoiding the blockade of the dural sac and nerve root traction during the surgery. Thus, PETD can reduce the incidence of complications, such as dural tear and nerve root injury. Besides, PETD is a better choice for patients with recurrent LDH as it can effectively avoid the influence of scar tissue from previous surgeries through the intervertebral foramen approach [10]. PETD can treat almost all types of L5–S1 disc herniations, including central, paracentral, foraminal, and far lateral types. However, giant herniated discs are relative contraindications for PETD, primarily due to limited surgical space caused by the obstruction of the superior margin of the iliac crest and the narrow intervertebral foramen, which can lead to inadequate decompression of the herniated disc. On the other hand, PEID has advantages for central, paracentral, and freely isolated types of disc herniations since it is not limited by the iliac crest blockade and offers advantages such as rapid puncture positioning, shorter operation time, and lower frequency of fluoroscopy.

In our study, all patients were successfully operated under endoscopy without any severe complications, such as dural tears or disc space infections. Four patients experienced postoperative complications. Two patients in the PEID group and one patient in the PETD group suffered from aggravating radicular symptoms within three days after surgery. The symptoms of patients improved by nerve nutrition, hormone therapy, and rehabilitation. One patient in the PETD group experienced LDH recurrence at 12 months postoperatively, and the symptoms improved after conservative treatment. There was no statistically significant difference in the incidence of complications between the two groups (P > 0.05). In addition, the results of imaging revealed that the mobility of the responsible segment increased postoperatively compared with before surgery, implying that we should attempt to damage as little as possible of the original lumbar spine when decompressing the disc. Previous studies have shown that loss of structures such as facet joints, and intervertebral discs, can all affect lumbar spine biomechanics [25, 26]. In our study, both PETD and PEID were performed without intraoperative resection of the high-weight-bearing area of facet joints, which had less impact on segmental stability. After recovery from surgical trauma and lumbar functional exercises, the mobility of the responsible segment was restored, and no patient experienced segmental instability during follow-up. However, whether postoperative disc degeneration and decreased disc height affect patients' surgical prognosis needs further studies.

In summary, both PEID and PETD for L5–S1 disc herniation can achieve favourable clinical outcomes. However, PEID has advantages over PETD, with reduced operation time and fluoroscopy exposure. There are some limitations to the current study. First, it was a retrospective study, and we could not completely eliminate subjective factors in case selection during the study period. We also could not achieve random grouping. Although we used PSM to minimize confounding factors, some biases might still exist. Second, although the results of imaging were averaged after 3 measurements by 3 independent reviewers, measurement error might still exist. Thirdly, the sample size was relatively small, the follow-up period was short, and it was a single-centre study, which might influence the results.