Open versus endoscopic approaches for disc herniations: case illustrations and a comprehensive literature review

Introduction

The surgical treatment for degenerative disc disease has seen a great evolution from traditional open spine surgery to minimally invasive spine surgery (MISS) including tubular and endoscopic approaches. Starting with the first open discectomy performed in 1934, the treatment for disc herniations slowly migrated to tubular approaches during the last couple decades (1,2). While open microdiscectomy (OMD) has traditionally been regarded as the gold standard, the impetus for transitioning to less invasive approaches was preservation of the extensors muscles, thereby resulting in quicker recovery, and theoretically mitigating subsequent surgeries by preserving the tension band of the posterior spine (3). Endoscopic discectomy (ED) is the newest minimally invasive technique and its global interest is rapidly rising. Since the introduction of percutaneous lumbar discectomy in 1986 by Kambin and Simpson, remarkable advancements in endoscopic techniques and instrumentation have taken place (4,5). Although initially used to treat disc herniations, endoscopic surgical techniques have been more broadly applied to other uses in recent years, such as for spinal canal stenosis and fusion surgeries (6). In this article, we will compare OMD versus ED and discuss their outcomes. This article has the added objective of illustrating the anatomical benefits to a less invasive surgery in both the thoracic and lumbar spine. Finally, we will provide early case illustrations demonstrating how to potentially transition to treating disc herniations via the endoscopic approach. We present this article in accordance with the Narrative Review reporting checklist (available at https://amj.amegroups.com/article/view/10.21037/amj-24-150/rc).

Methods

We performed a literature search through PubMed, focusing primarily on articles published between March 2001 and November 2024 although three studies outside of this timeframe were included for historical reference and technical description of the approach. The search keywords can be found in the table below (Table 1) and are centered around comparing surgical outcomes and technical aspects of OMD vs. ED.

Consideration of the extensor musculature and the theory behind MISS

MISS aims to yield the same results as open spine surgery via smaller incisions. Smaller incisions have become possible with advances in navigation, soft tissue retractors, and improved visualization, which has paved the way for minimal muscle disruption and manipulation of surrounding tissue (7). To appreciate this main concept, it is important to highlight the anatomy of the posterior paraspinal musculature. The paraspinal muscles can be divided into two groups: the deep paramedian transversospinalis muscle group and the erector spinae muscle group. The deep paramedian muscles include the multifidus, interspinalis, intertransversus, and short rotators. The erector spinae muscles include the longissimus, ileocostalis, and spinalis muscles. The multifidus muscle fibers traverse each intervertebral space and extend from the spinous process to the lateral surface of the vertebral lamina, thus making it the most likely muscle to be disrupted during posterior spinal surgery (8). The multifidus muscle is also a major stabilizer of the spine due to its large physiologic cross-sectional area (PCSA) and short fibers (9). Alternatively, muscles like that of the erector spinae group, which act as secondary stabilizers, are positioned lateral to the multifidus muscle and have much longer muscle fibers with a relatively small PCSA (8,10).

The main principles of MISS include the avoidance of self-retaining retractors, the preservation of the midline musculotendinous complex, and the reduction of soft-tissue injury (11). Traditional open spine surgery causes extensive injury to paraspinous soft tissue and can lead to substantial pain and muscular atrophy. Additionally, the self-retaining retractors used in open spine surgery are known to have a tourniquet effect which can cause local ischemia and subsequent reperfusion injury (12). MISS circumvents this issue by using tubular retractors that are placed after sequential tissue dilation. This technique avoids detachment of tendinous origins of the posterior spinal musculature and reduces the likelihood of injuring periarticular tissues (13,14). By minimizing muscle disruption and structural destabilization, MISS has been shown to reduce perioperative pain, blood loss, shorten length of hospital stay, and minimize the need for subsequent surgeries (15,16). Preservation of the soft tissues may further prevent adjacent segment disease by decreasing the flexion moment on the spine via preservation of the extensor musculature, thus preserving overall spinal alignment.

Options for endoscopic techniques—the benefits for an interlaminar or transforaminal approach

The nomenclature for endoscopic spine surgery is based on the properties of the endoscope and the approach angle. The following endoscopes can be utilized depending on the purpose of the surgery: percutaneous endoscope (or full endoscope), microendoscope, biportal endoscope, and epiduroscope (17). Among them, the percutaneous endoscopic technique is the most commonly utilized. Additionally, the two most popular approaches for endoscopic spine surgery are the transforaminal and interlaminar approaches (18).

Both approaches have been well described for treatment of degenerative disc pathology. The decision to use one approach over the other depends primarily on anatomical factors and the clinical conditions of the patient. The transforaminal endoscopic approach was the first of the two approaches to be introduced and is a useful tool for treating disc herniations, especially subarticular and foraminal disc herniations (19). The anatomical landmarks of the intervertebral foramen (IVF) are important to review before discussing the transforaminal approach, since access to the herniation is reached through this window. The boundaries that make up the IVF are the facet joint posteriorly and the intervertebral disc anteriorly (6). The cranial and caudal boundaries of the IVF are created by the inferior and superior vertebral notches, respectively (6).

The transforaminal approach utilizes Kambin’s triangle, a zone that allows for safe access to the spinal canal, and it includes the exiting nerve root (hypotenuse), the superior endplate of the inferior vertebral body (base), and the traversing nerve root (medial border) (20). The transforaminal technique can be performed under local, epidural, or general anesthesia. Once the correct angle of entry has been identified, then the endoscope can be placed to remove the herniated fragments. However, with the advent of the endoscope, there is discussion that Kambin’s triangle should be viewed as a 3D structure and is perhaps better described as a prism to incorporate the superior articular process (SAP). This allows for expansion of the prism (working portal) by sequential removal of the SAP to enlarge the working corridor (21). This is most prescient at the L4–5 level where foraminal stenosis and disc herniations are common. A study comparing a total of 427 Kambin’s triangles found that a cannula with a maximum diameter of 6.11±1 mm could be safely placed within the triangle without contacting the exiting nerve root. Further, only 2% of 8 mm scopes could be placed without displacement of the exiting nerve root in the lumbar spine or removal of the SAP (22). This point is further appreciated by examining patients without exiting nerve root injuries where the root to facet distance was 6.4±1.5 versus 4.1±0.8 mm in those with nerve root injuries. This corresponds to a 23% increase in nerve related complications per 1 mm decrease in distance between the SAP and exiting nerve root at the inferior aspect of the disc space (the base of Kambin’s triangle) (23).

A preliminary study comparing transforaminal endoscopic lumbar discectomy (TELD) and OMD found similar efficacy and recurrence disc herniation rates between the two surgeries (24). Despite displaying promising outcomes for treatment of disc herniation at various levels of the lumbar spine, TELD’s main weakness remains treating the L5-S1 level (25). The transforaminal approach may be difficult to perform at the L5-S1 level due to anatomical limitations such as a high iliac crest and a limited cranial-caudal foraminal height compared to more rostral levels where the dimensions expand (26). Another consideration is the distance and direction a herniation has traveled, since an extensively migrated disc herniation managed through the foramen limit the surgeon's ability to reach cranial or caudal as could be done through an interlaminar approach (6). The interlaminar approach was subsequently developed as an alternative technique to overcome these anatomical constraints.

As mentioned previously, the best indication for the interlaminar approach is the removal of a disc herniation at the L5-S1 level because this approach is not limited by a high iliac crest or a narrow foramen (27) (Figure 1,2). The developers of this approach found that the L5-S1 interlaminar space was usually large enough to pass the endoscope into the epidural space without the need for a laminotomy (28). This technique, which can be done using local, epidural, or general anesthesia, uses a paramedian incision and a posterior interlaminar approach to gain direct access to structures within the central canal and lateral recesses, while preserving the paraspinal musculature (29). The interlaminar space at L4–L5 is often large enough to accommodate the passing through of an endoscope although a small amount of bone resection is common. Levels rostral to L4–5 will need a greater degree of bone resection, making the interlaminar approach a suitable option for the lower lumbar spine. Alternatively, the interlaminar approach is difficult to perform in the upper lumbar spine due to the narrow interlaminar space and difficulty in retracting neural tissue (30). Therefore, the transforaminal approach tends to be the approach of choice for treating pathologies at L4–L5 and above.

Figure 1 Preoperative MRI demonstrating a L5-S1 disc herniation. (A) T2 sagittal MRI scan demonstrating a left sided para-sagittal disc herniation causing severe impingement of the left S1 nerve root. This is an optimal case for a left sided interlaminar approach at L5-S1 to perform an endoscopic discectomy. (B) T2 axial MRI scan demonstrating the left sided disc herniation causing displacement of the traversing S1 nerve root. MRI, magnetic resonance imaging.

Figure 2 AP fluoroscopic image demonstrating targeting of the L5-S1 interlaminar window to access the L5-S1 herniated disc fragment. AP, anterior-posterior.

Comparing surgical techniques and invasiveness

The goal of MISS, which includes OMD and ED, is to reduce recovery time, approach-related injury of collateral tissue, and complications. The main difference between the two approaches is the mode of intraoperative visualization, which can be achieved with either a microscope or an endoscope. The endoscopic technique, coupled with continuous irrigation creates a clear field of vision throughout the operation and may decrease rates of infection (31). A metanalysis reported a significantly lower risk of wound complications and infection in those undergoing percutaneous endoscopic lumbar discectomy (PELD) compared to OMD due to the smaller incision and continuous irrigation of the wound (5).

With these two modalities, comes different parameters for incision length. Goparaju et al. described in their study that of 591 patients the mean microscopic incision length was 30 mm (about 1.18 in), and the mean endoscopic incision length was 11 mm (about 0.43 in). To give context, both incision lengths are significantly smaller than open discectomy, for which this study reports a mean length of 56 mm (about 2.2 in) (32). A study comparing surgical invasiveness between OMD and three different endoscopic techniques for lumbar disc herniation analyzed postoperative creatine phoshokinase, C-reactive protein, and cross-sectional area (CSA) of the high intensity lesion in the paraspinal muscles on MRI (33). The study found that PELD was the least invasive technique based on blood biomarkers and postoperative MRI tissue disruption. The authors believe that this may be due to the muscle stripping technique that is employed in OMD which detaches the paraspinal muscle from the lamina and facet joint whereas PELD employs a muscle splitting technique that preserves the paraspinal muscles (33). The advantages of a more minimally invasive approach seen in transforaminal PELD likely led to the favorable short-term outcomes over OMD, although similar pain relief and functional outcomes at the end of the 2-year follow up period were reported for both OMD and PELD (32).

A randomized MRI study by Tacconi et al. consisting of 50 patients compared paravertebral muscle signal changes within 24 hours postoperatively between PELD and OMD. The group of patients who underwent OMD displayed a significantly increased mean volume of paravertebral muscle signal alterations in both T1- and T2-weighted MRI (34). Compared to PELD, the authors believe OMD causes increased tissue damage by cauterization and compression, which may favor the release of inflammatory cytokines and stress hormones, leading to greater postoperative pain and scar tissue formation (34,35). A similar study collected imaging over a longer term and analyzed surgical approach trauma by using MRI to measure the relative CSA of muscle disruption in 39 patients who either underwent OMD or interlaminar PELD (36). Axial T2-weighted MRI images taken around 11–13 months postoperatively revealed a significantly larger zone of muscular disruption for the OMD cohort than for the interlaminar PELD cohort (62% and 6% respectively) (36).

Although there are many advantages to ED, it is also important to note a few disadvantages, such as a significant learning curve, high cost of instrumentation, and higher radiation exposure compared to other minimally invasive techniques (37). Despite the significant learning curve mentioned by Kim et al., new techniques such as the evolving biportal endoscopic spinal surgery, are showing a shorter learning curve period with lower complication rates during the early learning period, which is promising for spine surgeons with little to no previous endoscopic experience (38).

Regarding short term costs, a single-center retrospective analysis comparing 633 open microscopic decompression, and 195 endoscopic decompression found that the endoscopic approach was associated with an increased total in-hospital costs compared with open decompression procedures (39). This is largely due to the additional disposables required for endoscopic procedures, such as radiofrequency cautery devices and irrigation tubing. Alternatively, a study by Choi et al. concluded that ED was more cost effective compared to OMD at one year follow up and that there was no significant cost difference between the three endoscopic techniques analyzed in this study (40). More cost analyses are needed to better understand the short- and long-term costs of both open and endoscopic techniques.

Lumbar and thoracic disc herniation (TDH)

A lumbar discectomy is one of the most common spine procedures performed worldwide (32). A randomized controlled trial by Gadradj et al. assessed whether transforaminal PELD is non-inferior to OMD in reduction of leg pain (41). At 12 months, the transforaminal PELD group patients had a statistically lower VAS score for leg pain compared with those of the OMD group. In terms of secondary outcomes, the transforaminal PELD group had a reduction of intraoperative blood loss, length of hospital stay, and earlier postoperative mobilization. The authors concluded that although transforaminal PELD resulted in statistically significant and more favorable outcomes of leg pain, back pain, and recovery, the differences may not be large enough to be considered clinically significant (41). Another study comparing transforaminal PELD with OMD, but in active young adults (20–25 years of age) found similar results to that of Gadradj et al., in addition to extremely low level of recurrence rates at 12 months in both groups despite patients undergoing intense physical activity following recovery (42). Thus, transforaminal PELD can be considered a safe and effective alternative to OMD in treating sciatica in adults and symptomatic disc herniation in the younger, more active population.

A common misconception among spine surgeons is that endoscopic lumbar discectomy procedures are limited to small and contained disc herniations. A recent retrospective study investigated this misconception by comparing PELD and OMD for large lumbar disc herniations (43). The authors found that both techniques exhibited significant improvements in leg and back pain postoperatively. The PELD group showed a significantly greater improvement of back pain compared to that of the OMD group. It was also noted that there was a significant decrease in disc height in the OMD group, although this did not change significantly in the PELD group; therefore, PELD can be an effective treatment for large, uncontained lumbar disc herniation and is associated with a rapid recovery and disc height preservation (43).

Although far less represented in the literature, the endoscopic approach can be used to treat TDHs. Thoracic endoscopic techniques were first introduced in the early 1990s and were performed using video-assisted thoracic surgery (VATS) (44). Symptomatic TDH are much less frequent than lumbar disc herniations with most occurring between T8 and L1. The treatment of this pathology is quite challenging due to this area’s complex neural and vascular structure and often required an open transpedicular decompression with fusion (45-47).

The typical options for treating TDH are open decompression with fusion or ED. Most surgical approaches require extensive bony removal, as the spinal cord cannot be retracted; therefore, the open technique almost always requires instrumentation and fusion (48). These patients have a higher risk of postoperative complications, longer hospital stay, larger intraoperative blood loss, and mechanical complications related to instrumentation (48). Alternatively, the endoscopic approach consists of minimal resection of the SAP and inferior pedicle which allows for sufficient transforaminal access to the disc herniation. Because this technique avoids destabilizing the spine, it does not require fusion (49,50). The endoscopic thoracic discectomy may also be performed in awake patients in an outpatient setting with local anesthetic and sedation, which avoids prolonged hospitalization and facilitates quick postoperative recovery (49,51). A study by Gardocki et al. compared the perioperative outcomes, neurological improvement, and cost of surgery between two groups, an open thoracic discectomy (OTD) group and a transforaminal endoscopic thoracic discectomy (TETD) group. Although both groups had similar rates of neurological recovery, the authors found that the TETD group was associated with significantly decreased operative time, estimated blood loss, length of hospital stay, and total cost when compared to the OTD group (50).

Dr. Lambrechts’ experience transitioning to endoscopic surgery from open surgery

It is highly recommended that prior to any endoscopic procedure that you take a formal endoscopic training course, which is often sponsored through companies selling endoscopic equipment (Arthrex, Joimax, RIWOSpine, etc.). After the first formal training course, cadaveric labs may further familiarize surgeons with the L5-S1 interlaminar anatomy and the L4–5 transforaminal anatomy as these are the most common sites of pathology and are workhorse techniques for endoscopic surgery. After the independent cadaveric training, I started my first endoscopic case with an L5-S1 interlaminar approach for an L5-S1 parasagittal disc herniation (similar to Figures 1,2). My next case was an L4–5 transforaminal approach (similar to Figures 3,4). L5-S1 paracentral disc herniations and L4–5 or more rostral level foraminal disc herniations are easier to start with as typically no drilling of the lamina or SAP is required. Further, disc herniations are typically easier cases than central canal stenosis caused by ligamentum flavum hypertrophy or synovial facet cysts. Thecal sac adhesions and greater bone resection require familiarity with endoscopic equipment that may not be suitable to most surgeons beginning their endoscopic learning curve. As a surgeon improves his or her surgical technique, more challenging cases like severe central canal stenosis, especially in the upper lumbar spine may be considered. For these cases, there are typically exceedingly small interlaminar windows and more drilling of the caudal and rostral lamina and medial facet is required. This allows the surgeon to peel off the ligamentum flavum (ideally from the rostral ligamentum flavum origin) thus gaining access to the epidural space. Finally, after a surgeon is comfortable with their endoscopic skillset, transitioning to the thoracic and cervical spine may be considered. Typically, surgeons consider expanding into the cervical and thoracic spine after 40 lumbar cases have been performed, although this is variable across surgeons based on their background and skillset (52).

Figure 3 Preoperative MRI demonstrating a right sided foraminal disc herniation. (A) T2 sagittal MRI demonstrating the L4–5 disc herniation causing displacement of the right L4 nerve with resultant radiculopathy. These are optimal cases for an endoscopic transforaminal approach. (B) T2 axial MRI scan showing the right sided neuroforaminal stenosis at L4–5. MRI, magnetic resonance imaging.

Figure 4 Fluoroscopic images demonstrating appropriate targeting of the right sided L4–5 disc herniation. (A) The AP fluoroscopic view demonstrating targeting of the mid-pedicular line at the L4–5 disc space. (B) Lateral fluoroscopic view targeting the inferior aspect of the L4–5 foramen to maximize distance between the exiting nerve root and portal site. AP, anterior-posterior.

Strengths and limitations of open vs. endoscopic approaches

It is important to note that both open and endoscopic techniques are suitable for the treatment of disc herniation. While surgeons are transitioning to less invasive procedures there is still no conclusive data that any one technique yields substantially better long-term outcomes. Thus, surgeons should perform the procedure they are most comfortable with. However, endoscopes have made discectomies significantly less invasive and as value based care becomes dominant, endoscopic spine surgery will likely grow in popularity.

However, unlike the open approach, most spine surgeons do not receive formal training in endoscopic techniques during their residency or fellowship, thus, those who wish to add this to their practice often receive training via an endoscopic specific fellowship or training course. Because the endoscopic approach is still relatively new, there are few quality clinical studies comparing long term outcomes between tubular and open approaches; therefore, uncertainty remains in its long-term efficacy and disc herniation rate. Despite this, the endoscopic approach has several advantages, including preservation of the spine’s extensor musculature, reduced perioperative pain, intraoperative blood loss, and shorter hospital stay. Another major benefit of the endoscopic approach is seen in thoracic spine surgery where the need for extensive pedicle resection is minimal; and therefore, eliminates the need for fusion.

The endoscopic approach is not without its limitations, its clinical evidence is still limited, it has a steep learning curve, and it is associated with higher radiation exposure. Ultimately, both open and endoscopic techniques provide great outcomes and the decision to use one over the other depends on the patient and surgeon preference.

Conclusions

Both approaches, open and endoscopic, are safe and reliable options for treating symptomatic disc herniation. The main difference between the two is the mode of intraoperative visualization and method by which this visual field is achieved. Although OMD is a low invasiveness approach, it is associated with significantly increased disruption of the paraspinal musculature as opposed to the endoscopic approach, which utilizes a small endoscope to achieve intraoperative visualization thereby reducing damage to peripheral soft tissue. Becoming comfortable with endoscopic spine surgery is quite difficult and is known to have a steep learning curve, although new techniques and updated instrumentation are making the acquisition of these skills easier. Thus, it will take time for this technique to become fully adopted globally. Ultimately, OMD and ED are both valid options for treating degenerative disc disease and the decision to use one technique over the other should be based on the patient and surgeon preference.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://amj.amegroups.com/article/view/10.21037/amj-24-150/rc

Peer Review File: Available at https://amj.amegroups.com/article/view/10.21037/amj-24-150/prf

Funding: None.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://amj.amegroups.com/article/view/10.21037/amj-24-150/coif). M.J.L. reports that he is a consultant for Kuros Biosciences, a member of the advisory editorial board of Spine, Deputy Editor for Primary Research at Clinical Spine Surgery, and Co-Editor-in-Chief of AME Surgical Journal. The other author has no conflicts of interest to declare.

Ethical Statement: The authors are 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.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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