Transforaminal percutaneous endoscopic lumbar discectomy: technical tips to prevent complications

Abstract

Transforaminal percutaneous endoscopic lumbar discectomy is regarded as an effective alternative to open discectomy. Remarkable technical evolution now enables selective endoscopic removal of an epidurally extruded disc fragment. As a result, the surgical indications for this technique are becoming broader. However, as the use of endoscopic techniques increases in spinal procedures, related complications emerge as important problems. These include postoperative dysesthesia, dural tears, hematoma, infection and visceral injury. There are several technical guidelines to increase the effectiveness of endoscopic techniques and prevent complications. Initial landing should be as close to the target as possible. Complete herniotomy after thorough release of annular anchorage is a key to success. The definitive end point of the procedure is free mobilization of neural tissues, not direct exposure of neural tissues.

Keywords::

• complication
• endoscopic
• herniotomy
• lumbar discectomy
• selective discectomy
• transforaminal

Figure 1. Schematic drawings demonstrating the adequate transforaminal approach in different situations.

According to the zone of herniation, the landing point and approach angle should be adjusted; for central and subarticular disc herniation, the horizontal approach to the medial pedicular line is recommended (A). For foraminal and far-lateral disc herniation, the steep approach angle to the lateral pedicular line is recommended (B). The landing point and approach angle can be changed according to the level. For upper lumbar levels, such as L1-L2 and L2-L3, a steeper approach and lateral landing are recommended (C). For lower lumbar levels, such as L4-L5 and L5-S1, a more horizontal approach and medial landing are recommended (D).

Figure 2. Regardless of the approach angle and landing point, the exiting nerve root should be protected during the approach.

The leading edge of any instrument should be located away from the trajectory of the exiting nerve root. A more caudal approach along the superior facet surface is a useful technique to avoid the exiting nerve root injury.

Figure 3. Schematic drawings demonstrating the importance of annular release and complete herniotomy.

The herniated fragment should be separated from the tight annular anchorage and freed before removal. The releasing procedure can be performed using a side-firing laser and annulus cutter (A). Then, complete removal of the whole hernia fragment in both the epidural and the intradiscal space should be performed to prevent recurrence (B).

Figure 4. The ideal end point is free mobilization of neural tissue with complete herniotomy, not full exposure of the nerve root.

An attempt to achieve wide exposure of the neural tissue involves the risk of neural damage. (A) In the intradiscal view, we can identify the annular fissure (arrow heads), decompressed dural sac through the undersurface of the annulus (a) and intradiscal space (b). (B) In the lateral view, we can see the anatomical layers such as the dural sac in the epidural space (a), the remaining annulus (b) and the intradiscal space (c).Reproduced with permission from [14].

Transforaminal percutaneous endoscopic lumbar discectomy (PELD) is regarded as a safe and effective procedure for treating soft disc herniation. The advantages of this procedure include preservation of posterior structures and a similar effectiveness to that of traditional open discectomy [1–4]. Recently, PELD has undergone remarkable technical evolution. In the early era of this procedure, the basic concept was to achieve indirect neural decompression within the central nucleus region. Subsequently, the decompression focus moved onto subannular-protruded disc herniation. As the working zone has now been shifted towards epidurally extruded disc herniation, the current aim of this procedure is to achieve selective epidural fragmentectomy and direct neural decompression, while preserving the central nucleus [5,6]. Several randomized controlled studies have demonstrated the effectiveness of this novel procedure [2,7–9]. However, with the increase in use of PELD, various adverse events or complications of this procedure are emerging [10–13]. The purpose of this article is to describe various complications associated with PELD and discuss technical tips in order to increase effectiveness of PELD and prevent complications.

Surgical technique

The procedures are performed according to the standard transforaminal endoscopic selective discectomy technique under local anesthesia [2,6,7,9,14]. The patient is placed prone on a radiolucent table and kept conscious during the procedure to enable monitoring of any changes in symptoms and signs. The skin entry point is typically approximately 8–13 cm from the midline. The entry point is dictated by the size of the patient, the dimensions of the facet joints and the desired location for the tip of the needle in the triangular working zone. To determine the appropriate entry point, preoperative imaging studies and intraoperative fluoroscopy should be performed. An 18-gauge spinal needle is inserted after infiltration of local anesthetic. The needle tip is positioned at one point of the medial-to-lateral pedicular line on the anteroposterior fluoroscopic projection and at the posterior vertebral line on the lateral projection. Before the insertion of the needle, a preemptive epidural blockade with 0.5% lidocaine is performed to prevent approach-related pain. After the insertion of the needle into the disc, 1 ml of indigocarmine dye is mixed with 6 ml contrast medium and injected into the nucleus pulposus. Pathological structures within the disc are stained and can be easily distinguished from normal disc tissues, which are firm, resilient and unstained. This intraoperative discography procedure is useful for the selective removal of herniated fragments under fluoroscopic and endoscopic visualization. The needle is then replaced by a guide wire and an obturator with a small stab incision. The tapered cannulated obturator is slid over the guide wire and introduced gently into the disc through the foraminal window. A bevel-ended working cannula is then introduced over the obturator. During this step, a moderate to severe approach-related pain may develop because of irritation to the exiting nerve root or any inflamed epidural tissues. To help reduce approach-related pain and exiting nerve root irritation, serial dilation of the annulotomy hole before obturator insertion and introduction of a sharp, bevel-ended working cannula instead of a standard working cannula after obturator insertion can be performed. After the obturator is withdrawn, an ellipsoidal endoscope, with an eccentrically placed working channel and two irrigation channels, is inserted. At first, the surgeon can see the subannular, intradiscal space through endoscopic visualization. Initial subannular decompression can be performed with forceps and a bipolar coagulator. After the initial decompression step, the ‘layers’ of endoscopic anatomy, including the dural sac, epidural fat, posterior longitudinal ligament, inflamed annulus and disc material, can be discriminated. Through this endoscopic window, the surgeon can recognize the herniated disc fragment and annular fissure. The herniated fragment is usually anchored by a fibrotic annular fissure, and the release of annular anchorage before discectomy is essential. The releasing step can be performed using an annulus cutter and a side-firing holmium:yttrium-aluminum-garnet laser. As the fibrotic annular anchorage is released and the annular fissure is opened widely, the blue-stained herniated disc fragments become loose and mobile. The free fragment is then removed using endoscopic forceps and laser. As the decompression process gradually reduces the back muscle tension, the angle of the endoscope can become more horizontal, thereby pivoting on the foramen. The surgeon can adjust the approach angle as needed. The flexibility of the approach angle is one of the benefits of the transforaminal approach in comparison to the conventional posterior approach [6,15]. With this levering technique, the surgeon can examine the full undersurface of the annulus and even remove the epidurally herniated disc fragments. Finally, epidural dissection is performed, and the decompressed dural sac or nerve roots are identified. When the end point of the procedure – that is, free mobilization of neural tissue – is achieved, the endoscope is withdrawn and a sterile dressing is applied over a one-point subcutaneous suture. In the absence of postoperative problems, all patients are permitted to go home within 24 h.

Discussion

Several randomized controlled trials have been performed to determine the effectiveness of PELD in comparison to conventional open discectomy [2,7–9]. Hermantin et al. (n = 60) demonstrated that the rate of satisfactory outcomes was the same in the endoscopy and open discectomy groups [2]. However, the period of postoperative disability or narcotic use was shorter in the endoscopy group. Ruetten et al. (n = 178) reported that the clinical outcomes of the endoscopic technique are equal to those of the microsurgical technique, with significant advantages in back pain, return to work, complications and traumatization [9]. However, the current level of evidence on the effectiveness of transforaminal PELD is low because most studies have substantial design weaknesses in the randomization method or outcome measures with a high risk of bias. Only one adequately randomized controlled study [2] has been identified so far. Therefore, high-quality randomized controlled trials with sufficiently large sample sizes are required to provide valid information on the effectiveness of PELD in the future. Technical evolution of PELD now enables the selective removal of epidurally extruded disc fragments in the lumbar spine. Ironically, the occurrence of complications in PELD may be closely related to its technical evolution. As surgeons become overconfident in performing the technique and the use of PELD is broadened to include cases of greater complexity, the risk of unexpected adverse events may increase.

Injury to neural structures & dural tear

The most common neural problem is approach-related irritation of the exiting nerve root, dorsal root ganglia or possibly the furcal nerve in the foraminal area [6,9,13–17]. Approach-related irritation can be caused by the approach needle, bulky obturator or the working cannula during the approach step. During the procedure, patients are conscious under local anesthetic; therefore, neural irritation by approach instruments may cause severe pain, because of which the procedure may have to be stopped. Postoperative dysesthesia from exiting nerve root damage may cause significant sequelae. If neural injury occurs during the posterior open discectomy, it may occur on the traversing nerve root, which is already compromised. In PELD, however, the injury may occur on the fresh dorsal root ganglion, and the patient may complain of a new symptom: postoperative dysesthesia [16]. The occurrence of this complication may be particularly stressful for the surgeon, because the dysesthesia usually affects the dermatome of the exiting nerve root, and the symptoms differ from the patient’s preoperative symptoms. A deviation of the needle, dilator and cannula to the cranial part of the neuroforamen can affect the exiting nerve root. Excessive intraoperative manipulation by instruments or laser can also cause this complication. The less common, but more serious, complication of neural tissue is an intraoperative dural breach [5]. Dural injury may occur in two forms: a mechanical tear caused by surgical tools, or thermal injury caused by laser. If dural injury is unrecognized or untreated, serious neurological deficits may develop. Our own published data [5] demonstrated that patients in the unrecognized dural tear group showed less-favorable clinical outcomes than the patients with recognized dural tear did, with substantial motor weakness.

Injury to vascular structures & hematoma

Although the occurrence of hematoma is relatively rare, vascular damage usually develops into a postoperative hematoma. The unique hemorrhagic complication of this procedure is a retroperitoneal hematoma [10,13]. Injury to the radicular lumbar artery or its branches during the transforaminal approach or extraforaminal instrumental work may result in hematoma formation in the loose retroperitoneal space [10]. In the case of a large hematoma (>500 ml), urgent surgical evacuation is required. Another possible vascular event is a postoperative epidural hematoma, the incidence and risk factors of which are not clear. In most cases, postoperative epidural hematoma is subclinical or self-limiting. However, occasionally, revision surgery may be required, especially after extensive epidural exploration or bony sculpturing.

Injury to abdominal contents

The approach needle can perforate the peritoneal sac during its course to the foraminal window if the skin entry point is chosen too far laterally and the trajectory is kept vertical. An inadvertent tap of the intestine during initial needle insertion may contaminate the disc space, leading to secondary spondylodiscitis after PELD [18–20]. Another possible scenario is inadvertent advancement of a needle or other instruments beyond the anterior disc margin. Bowel or ureter injury resulting from inadvertent use of a laser or biting instrument beyond the anterior annulus has been reported [21,22]. To avoid these complications, the needle or instrument position should be regularly confirmed on fluoroscopic views, especially the lateral view. It is important to keep the needle tip posterior to the posterior vertebral line. If intestinal injury is suspected, the needle should be changed immediately.

Infections

The most common problematic infection is spondylodiscitis [19,20]. According to published data [20], the occurrence of postoperative spondylodiscitis is relatively rare after PELD compared with open surgery. However, the clinical manifestations of spondylodiscitis progress rapidly and are of a serious nature. The typical symptoms are severe back pain, possibly combined with leg pain, several days after the procedure. Elevated laboratory markers, such as erythrocyte sedimentation rate and C-reactive protein, appear to be more reliable than radiological findings in the early postoperative stage [23,24]. Early MRI is not reliable as the sole method for detecting septic spondylodiscitis [25,26]. For definitive bacteriological diagnosis, disc punctures under fluoroscopic or endoscopic guidance are recommended. First-line treatment consists of appropriate antibiotic therapy with motion restriction. In case of unresponsiveness to medical therapy, decisive surgery such as an open debridement or interbody fusion is required [27].

Incomplete decompression & reherniation

Incomplete decompression occurs because of a missed fragment or remanent lateral recess stenosis that significantly compresses the nerve root [13]. The patients usually still suffer from radicular pain without a pain-free interval and frequently require a second surgery. Incomplete decompression occurs due to technical difficulties or the failure to recognize if the decompression is sufficient. Incomplete decompression is more likely to occur in cases of migrated disc herniation or large central disc herniation with high canal compromise [13,28,29]. To prevent this problem, adequate knowledge about the anatomical relationships and the ability to recognize the end point of the procedure are essential. Another problem of incomplete decompression is reherniation of disc fragments after a pain-free period. After surgery, a hidden intradiscal herniated fragment may extrude from the same side or the contralateral side. A reliable recurrence rate of herniation after PELD has not been established, but some data demonstrate that the recurrence rate is similar to that of traditional open discectomy [13]. To reduce recurrence, complete removal of the hernia mass (herniotomy), including the basal part and extruded parts, is important. However, herniotomy is not a radical removal of the disc; rather, it is the removal of a fragment that is sequestered from the maternal disc.

Technical tips & tricks to prevent complications

PELD has a steep learning curve, and the surgical outcome tends to be different between experts and beginners [30]. Furthermore, surgeons usually do not learn endoscopic techniques during their residency or training course. There are several technical guidelines to increase the effectiveness of endoscopic techniques and prevent complications. These guidelines can be summarized by three key words: landing, herniotomy and ending.

Landing (as near to the target as possible)

Adequate landing, which means an adequate transforaminal approach through the foraminal window, is the most important key to achieving success and preventing complications. The basic principle is that the landing point should be as close to the target as possible and that the exiting nerve root should not be irritated. According to the zone of herniation, the landing point and approach angle can be adjusted. For central and subarticular disc herniation, a horizontal approach to the medial pedicular line (shallow transforaminal approach) is recommended, and for foraminal and far-lateral disc herniation, the steep approach angle to the lateral pedicular line (steep extraforaminal approach) is recommended (Figure 1) [31,32]. The landing point and approach angle can be changed according to the level. For upper lumbar levels such as L1-2 and L2-3, a steeper approach and lateral landing are recommended. For lower lumbar levels, such as L4-5 and L5-S1, a more horizontal approach and medial landing are recommended (Figure 1). At the L5-S1 level, a high iliac crest may be a major obstacle to the standard transforaminal approach. In cases of low iliac crest, a shallow transforaminal approach is possible. However, in cases of high iliac crest, a modified technique with a more medial placement of the skin window and resection of the superior facet tip (endoscopic foraminotomy) should be applied [6,33]. Regardless of the approach and landing used, the exiting nerve root should be protected during the approach. The leading edge of any instrument should be located away from the trajectory of the exiting nerve root. A more caudal approach along the superior facet surface is a useful technique to avoid the exiting nerve root (Figure 2). This prevents approach-related pain and postoperative dysesthesia. Finally, all instruments should be kept posterior to the posterior vertebral line before entry into the disc space. This is essential to prevent abdominal damage and injury to the radicular lumbar artery. Therefore, the initial needle insertion should be performed under lateral fluoroscopic guidance rather than the anteroposterior view.

Releasing herniotomy (removal of the whole ‘iceberg’)

The herniated fragment should be separated from the tight annular anchorage and freed before removal. Complete release of annular anchorage can be performed using a side-firing laser and annulus cutter (Figure 3). This releasing step is critical in PELD because the instruments are relatively smaller and weaker than those used in conventional microdiscectomy. In general, the herniated fragment is composed of an epidurally extruded part and an intradiscal part, just like an iceberg. The whole ‘iceberg’ must be removed, not just the tip. If any part of the iceberg is left, incomplete decompression or delayed reherniation may occur. To identify a perfect herniotomy, there is a simple tip: ‘see the contralateral annular fissure.’ This is a useful indicator of a complete herniotomy.

Ending (free mobilization)

Many beginners usually ask: ‘What is the end point of PELD?’ The end point may be different according to the situation. The recommended end point is free mobilization of neural tissue after complete herniotomy. In the surgical field, the end point can be recognized by seeing the whole annular fissure and strong epidural pulsation of the dural sac and nerve root. At this point, the dural sac and the nerve root can be seen to ‘breathe.’ However, direct exposure of the traversing nerve root or dural sac is not recommended. An attempt to achieve wide exposure of the neural tissue involves the risk of dural tear or neural damage by instruments or laser. Moreover, excessive removal of the outer layer of the annulus or other mechanical barriers, including the epidural fat and various ligamentous structures, may cause recurrence, dysesthesia, epidural fibrosis or postoperative instability. Therefore, an ideal end point of PELD is complete herniotomy with an intact annular barrier, free mobilization of epidural neural tissues, and intact epidural fat and ligamentous structures (Figure 4).

Expert commentary

The current concept of transforaminal endoscopic discectomy is a targeted epidural fragmentectomy, while preserving the central nucleus. Technical evolutions have broadened the surgical indications and have improved the clinical effectiveness of transforaminal endoscopic discectomy. However, procedure-related complications have emerged as important clinical issues. Careful technical considerations should be kept in mind to prevent these complications.

Five-year view

Currently, patients with central stenosis and calcified disc herniation cannot be treated with PELD. Technical innovation will overcome these limitations in the near future. New instruments such as tip-control burrs, endoscopic punches, navigational/steerable forceps and high-resolution cameras will enable the definitive decompression of harder lesions, such as hypertrophied facets, thickened ligamentum flavum, calcified disc herniation and far-migrated disc fragments in regions of difficult access. Moreover, the development of endoscopes with a smaller outer sheath will provide a safer and easier approach.

Key issues

• • The technical evolution of endoscopic lumbar discectomy has been remarkable. The basic concept has changed from central disc decompression to selective removal of extruded disc fragments.

• • As the use of endoscopic techniques increases in spinal procedures, related complications such as postoperative dysesthesia, dural tear, hematoma, infection and visceral injury may emerge as important problems.

• • Accurate landing through the foraminal window is the most important key to achieve success. Remember this: as near to the target as possible!

• • Adequate release of the herniated fragment from tenacious annular anchorage enables definitive removal of herniated fragments using small surgical instruments.

• • Complete herniotomy, which means removal of the whole fragment (including epidural and intradiscal hidden fragments), is important to prevent recurrence. In addition, careful consideration of the ongoing disc degeneration and the characteristics of the annular defect are also important.

• • The recommended end point is free mobilization of neural tissue with visualization of natural pulsation, not full exposure of the nerve root.

Financial & competing interests disclosure

The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.