The “inside out” transforaminal technique to treat lumbar spinal pain in an awake and aware patient under local anesthesia: results and a review of the literature

Contraindications

Endoscopic removal of disc herniation is only limited by the accessibility of endoscopic instruments to the herniation site. The location of the disc herniation, the extent of the extrusion and sequestration, and the experience level of the surgeon are vital considerations for patient selection. Some patients with high iliac crests, horizontal L5-S1 disc spaces, or degenerative scoliosis make surgical access through the foramen difficult. Contraindications thus are relative, and depend on the anatomic factors involved.

Postoperative Regimen

Prior to removal of the access cannula, routine use of depomedrol 80 mg delivered with .5% marcaine (1-2 cc) will provide immediate postoperative analgesia; although there may be increased risk of infection, there have been no incidence of infection attributed to the use of steroids. In the absence of damaged tissue, discitis is very low. Post-op antibiotics may be considered for 24 hours post op when patient morbidity dictates its use. A postoperative lumbar corset will make the patient feel more comfortable. The patient should be instructed to avoid bending, lifting, and twisting for 4-6 weeks to allow the annulus to heal and to reduce the incidence of recurrent disc herniation from the foraminal access portal and from an annular defect of the disc herniation as well. Physical therapy is helpful, but not required, but can be considered on an individual basis. Patients are instructed to use their pain as a guide after the 6 week period. Some patients return to work and limited activity as soon as one day after surgery.

Complications and Avoiding Pitfalls

As with arthroscopic knee surgery, the risks of serious complications or injury are low—approximately 1% or less in the authors’ experience. As with any surgery, there are the usual risks of infection, nerve injury, dural tears, bleeding, and scar-tissue formation. Transient dysesthesia, the most common postoperative complaint, occurs in approximately 5%-15% of cases, and is almost always transient. Its cause remains incompletely understood and may be related to nerve recovery, operating adjacent to the dorsal root ganglion of the exiting nerve, furcal nerves or a small hematoma adjacent to the ganglion of the exiting nerve, as it can occur days or even weeks after surgery. There are also anomalous nerve fibers in the annular tissue which may be furcal nerves or nerves growing into an inflammatory membrane in the area of the foramen that is not the traversing or exiting nerve. It could show up in the surgical specimen without permanent effect on the patient, but may cause temporary dysesthesia. Using blunt techniques to dilate the annular fibers has limited surgical morbidity but dysesthesia cannot be avoided completely. It can occur even when there were no adverse intraoperative events and in cases where the continuous electromyography (EMG) and somato-sensory evoked potentials (SEP) did not show any nerve irritation. The symptoms are sometimes so minimal that most endoscopic surgeons do not report it as a “complication.”

The more severe dysesthetic symptoms are similar to a variant of complex regional pain syndrome, but usually less severe, and without the skin changes. postoperative dysesthesia is treated with transforaminal epidurals, sympathetic blocks, and the off-label use of Pregabalin or Gabapentin (Pfizer, Inc., New York, New York, USA) titrated to as much as 1800-3200 mg/day. Gabapentin is FDA-approved for post-herpetic neuralgia, but effective in the treatment of neuropathic pain.

A thorough study of pre operative imaging and attention to details of the anatomy and its alterations can avoid the pitfalls in TFE.

History of traditional TFE

True minimally invasive treatment of the disc started in 1963 with Lyman Smith injecting chymopapain in discs.^11–13 In 1977, Hijikata did Percutaneous Manual Discectomy¹⁴; then in 1984, Ascher did Percutaneous Laser Discectomy (nonspecific depressurization) and in 1985, Onik proposed Automated Percutaneous Lumbar Discectomy (nonspecific disc deflation in the absence of visualization) using a probe and published their work. These methods of pure intradiscal decompression surgery typically gave more effective and faster results as compared to waiting for natural, nonsurgical resolution of the painful condition.^{15, 16} Percutaneous discectomy thus started as a “blind” fluoroscopically guided method used for merely intradiscal debulking or volume and pressure reduction of the disc. The surgical goal was mechanical decompression and was blind and fluoroscopically guided as pain was thought to be only due to increased pressure inside the disc and around the root and DRG.

In 1988, Kambin and Sampson described a purely endoscopic visualized technique (full endoscopy (FE) TFE) as an extraforaminal approach, for non-sequestrated intracanal discal hernia.¹⁷ This technique and its outcomes have evolved with time, including translaminar dorsal access surgery and simultaneous use of an arthroscope through access cannulas. The present day foraminal approach is credited in 1996 to Mathews: Transforaminal Endoscopic Micro discectomy when he emphasized extending intradiscal therapy to decompressing the foramen through an endoscope. Matthews was developing a fiber optic endoscope for Sofamor Danek.¹⁸ Yeung and Kambin, before Matthew's publication, had already began to use a working channel endoscope by Smith and Nephew, exploring the epidural space, but only the YESS scope was commercialized by Richard Wolf.

In the 1990s, many switched from open discectomy with the naked-eye to microscope assisted discectomy. This refined version of open disc surgery uses the microscope to magnify and visualize the target. Endoscope assisted surgery per Foley, ¹⁹ but developed earlier by Destandau ²⁰ as a custom endoscope aided system, evolved around 1995 but in all these developments understanding and philosophy did not change with respect to traditional goals of ONLY mechanical disc decompression. Historically, Destandeau preceded Foley although Foley published first. This may be labelled as early period of the TFE.

It was in 1991 that Kuslich first described surgery for lumbar disc herniation and stenosis under progressive local anesthesia in 193 patients. This study made an important contribution to our understanding of tissue origin of low back pain and sciatica and gave us the concepts of pain generators, pain patterns by answering the fundamental question: where is the pain coming from?²¹ Thus identifying the physiological target. This also fundamentally made surgery possible under local anesthesia as significant pain was not seen in paraspinal structures during transforaminal access. Another important conceptual change around that time (1995) was a study of foraminal anatomy and its relation to size of cannulas that the foramen can accept. A study by Mirkowitz supervising his then resident David Swartz, highlighted the maximum size of cannulas which we can safely put in the foramen for safe endoscopic surgery.²² This facilitated transforaminal access. TFE really started changing around this time.

In the same period, Siebert: Endoscopic Laser Disc Surgery - the Foraminal Approach, Leu: Percutaneous Foraminoscopy, and Casper: Foraminal Laser Endoscopic Disc Ablation published their work. Martin Knight around same time, ^23–26 however, was the first to use laser for foraminal decompression for lateral and subarticular stenosis, which further set the stage for Yeung's evolution of his technique for inside out disc surgery and surgery for foraminal stenosis, using a combination of laser and mechanical trephines, kerrisons, and burrs by working outside the disc through a working channel endoscope. Yeung was already proficient with the transforaminal approach developed by Kambin, which emphasized decompression of the epidural space indirectly, and avoiding the epidural space in order to spare its vasculature and theoretically avoid scarring. The access then evolved further as a direct epidural access by undercutting the facet by “outside in access”. This has been popularized by Hoogland et al's Thessys technique.^27–30 Some variation in trajectory and angle of access also has been proposed by Hoogland, Ruetten and Choi, et al. when targeting inferior and superior migrated fragments. This targeted entry, which can vary from extreme lateral from the midline to a more moderate 35-45 degree angle, and is directed to traverse the foramen toward the disc extrusion or osteophyte. Since the “out-side in” procedure is partially blind and dependent on serial dilation to retract nerves, it usually involves foraminalplasty with trephines and reamers as well as discectomy. While this approach is better understood by traditional surgeons using dilation techniques for MIS surgery, this simplified approach ignores anomalous anatomy such as furcal nerves, sympathetic nerves and other and anomalous nerves documented and described by Yeung and Gore. Complications and adverse risks of dysesthesia is therefore anticipated to be higher. Ruetten has also described interlaminar access with the same instruments, mainly for L5-S1 access.

Pathologies visualized through scope and conditions ideal for the transforaminal approach

An inflammatory membrane is identified in the epidural space containing multiple nerves entering the disc through a grade V annular defect as seen from inside by an endoscope (Figure 17). Illustration of a Grade IV Annular tear. Annular tears can be graded according to Adam's Classification. It can be visualized intradiscally and treated with tools utilizing bipolar flextip Radiofrequency, laser, tissue sealants, and biologics that enhance tissue healing.

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Fig. 17

Annular tears.

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Fig. 18

Radiofrequency Thermal Modulation of a Grade IV annular tear in a tall disc.

Intraoperative PA and lateral discogram demonstrating a grade V annular tear (Figure 19A-E). Annular defect identified after removing the degenerative nucleus. The defect was visualized with a 70-degree scope. The nerve and dura was protected by an intact PLL between the annular defect and epidural space, shielding the nerve from chemical irritation. The tear would open and close with the patient's breathing. The nerve and epidural space was shielded by the PLL. Note mildly inflamed disc annulus and blue stained nucleus material (Figure 19F). Thermal modulation with a bipolar flex probe (using a biportal technique) ablated the inflammatory and disc tissue and partially contracted the hole in the annulus (Figure 19G). After thermal modulation, a valve-like flap would open and close the hole (Figure 19H). Discectomy specimen contained 4 grams of soft, degenerative nucleus pulposus. This patient remains asymptomatic after 5 years.

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Fig. 19

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Fig. 20

A: This saggital MRI demonstrates two dark discs on T2 imaging, but does not show significant disc protrusion or the presence of an HIZ. It could be interpreted as “normal.” Positive evocative discography identified a painful grade IV annular tear. B: The annular tear is identified endoscopically and successfully treated with foraminal discectomy and thermal annuloplasty.

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Fig. 21

This MRI demonstrates a bulging disc with an annular tear that progressed to in an eventual herniation. The patient had intermittent, but debilitating pain at this stage. Earlier definitive treatment of this condition with Disc FX or selective endoscopic discectomy would have mitigated the years of prolonged and debilitating symptoms (Figure 22). The patient progressed to herniation without radiculopathy initially. Back pain and sciatica later on was constant. An extruded free fragment was found at surgery.

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Fig. 22

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Fig. 23

A. Cannula placement for foraminalplasty. B. Kerrison foraminoplasty. C. Diamond burr decompressing ventral aspect of the SAP. D. Relationship of the exiting nerve with the SAP. E. Bony specimen and foraminal disc fragment removed following foraminoplasty. F. The ligamentum flavum seen well.

The newer emphasis is on cases of FBSS where we can now visualize the hidden zone of Mcnab and relieve the likely common cause of failure by decompressing the axilla between the traversing and exiting nerve (Figure 24). Patho-anatomy such as recurrent/ residual HNP, lateral stenosis, ostephytosis, synovial cysts have all been identified in the absence of obvious abnormal MRI and CT scan imaging. Imaging studies in this “pain generating” region do not always have clear findings. The application of diagnostic and therapeutic injections performed by the operating MIS surgeon will provide a prognosis for this type of decompression without “burning any bridges for subsequent more traditional decompression and fusion.^{31, 32}

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Fig. 24

Advantages of TFE access and surgery:

1. Muscle trauma: Wolfgang Rauschning's work on the macro-and micro-anatomy of degenerative disc disease, and the importance of preserving the dorsal muscle column serves as a guide for the ideal minimal approach in the lumbar spine. (³¹) Post-surgical specimens of patients who had posterior lumbar surgery all have extensive scar formation of the dorsal column muscles, even with smaller incisions. According to Rauschning, not only were the erector spinae muscles affected, but so were the deep short oligosegmental muscles which account for proprioception and fine tuning of segmental mobility. Rauschning concluded that surgery should avoid traumatizing the dorsal muscle column.

2. In the transcanal approach, surgeon is limited with exposure, he is also limited by the approach itself. Resection of lamina, ligamentum flavum, and annulus may be necessary to reach the herniation, thus potentially destabilizing the spinal segment. Even after reaching the herniation site, the surgeon still cannot see inside the disc to inspect for residual fragments. In the TFE approach there is no destabilization and no access related morbidity but we can see inside of the disc well. IN cases of central disc herniation it may very easy to target and remove a central herniated contained protrusion or fragment by transforaminal access staying inside the disc.(³) Further, the translaminar approach does not allow the surgeon to visualize the nucleus inside the disc in order to determine if all of the loose nuclear tissue was removed. This is important to prevent early recurrence. The extent of nucleus removal remains unresolved among traditional surgeons utilizing the posterior approach. Some surgeons remove only the disc sequestrum and others remove all the disc they can extract through the annulotomy site. Surgeon philosophy dictates the technique that is followed.

3. Annular tears come in all sizes and shapes. Granulation tissue in annular defects (tears) can be visualized and ablated and closed using a RF electrode. It is best identified by discography, not always on MRI. Endoscopy can successfully identify and treat painful annular tears and is much more effective than the image guided techniques of IDET and variations of surgical disc decompression.

4. Selective nerve root block and epidurography is performed by the surgeon, and can be considered a pre-surgical trial that provides prognostic information.(³²) The resulting foramino-gram will then provide the surgeon with additional imaging information by the contrast pattern outlined at the surgical site. This will be anatomical input. A favorable response to interventional therapeutic injections can be correlated with longer term favorable results of foraminal decompression, nerve ablation and disc decompression. Conditions such as foraminal osteophytes tethering the nerve, and lateral recess stenosis are often underestimated by traditional imaging. With diagnostic and therapeutic injections, providing additional information about the pain generator, both surgeon and patient can come to an informed joint decision with respect to determining the likelihood of surgical success. This is especially true given that surgery of discectomy can be combined with foraminal decompression and ablation, making it more likely that the surgeon will be able to remove the source of pain.

5. The learning curve may be steep³³ but once the technique is mastered, the surgeon is able to extract contained and non-contained disc herniation from within the disc or directly from the epidural space.

6. The Holmium-YAG laser, in a straight fiber or a reflected 70 degree fiber has the unique ability to divide shrink, ablate, and cut collagenous tissue and vaporize bone.

7. The foraminal approach is more versatile than the posterior approach, the more cephalad the herniation level. From T-10 to L-2, the foraminal posterolateral approach offers the greatest and most flexible access to the lumbar disc without the need for laminectomy.

8. In surgical discectomy by any approach, the paradoxical effect of nucleus pulposus removal and the amount of postoperative instability created by removing and decompressing the disc should be considered by the surgeon. Annular fenestration has been studied, ranging from dilation of the annulus to cutting out an annular window. In most instances, a sharp annulotomy knife or trochar is used to perform, at minimum, a cruciate incision. It will be necessary to remove the hernia at its weakest point during a transcanal approach, weakening the annulus further and making it more susceptible for a recurrent herniation.

9. Foraminoplasty: IN comparison to trans laminar decompression, there is less instability produced by decompression, as the articular surface area of the facet joints are preserved.(34) More widening is achieved by transforaminal access in a case of stenotic lateral canal than by a medial facetectomy, which adds instability too.

10. Transforaminal and translaminar endoscopy access inherently avoids excessive removal of ligamentum flavum in the interlaminar area. IT may be important to retain that barrier between dura and muscles. Our technique preserves ligamentum flavum and that is significant in preventing scar formation. (35)

11. Visualization A: has been touted as an important factor by traditional surgeons in choosing their method of disc excision. Most who are familiar with the microscope tout it as being un-surpassed for visualization, emphasizing the 3-Dimensional capability of binocular vision, as the best visualized technique. For teaching purposes, the assistant can also see. With the new glass rod-lens endoscopes, however, it only requires side-by-side comparison of images to dispel the notion that visualization is inferior. While the microscope is capable of giving great visual detail, the endoscope can match the detail and with magnification as well. In a learning situation, the entire OR crew can see what is happening on the video screen.

12. Visualization B: The advantage of the endoscope is the ability to place the lens and surgical instruments closer to the pathology, which requires less magnification for the same detail. The ability to manipulate the endoscope for viewing the pathology at slightly different angles and varied depths, the ability to manipulate normal and patho-anatomy, and the ability to visualize the disc intradiscally as well as the foramen overcomes any concern about the lack of 3-Dimensional visualization. This happens in a awake and aware patient. Accomplished surgeons have also used the endoscope in all fields of surgery with no problems from the lack of 3-D visualization.

13. Once the learning barriers are overcome, however, surgeons who are competent in both techniques may prefer the posterolateral endoscopic disc surgery to microdiscectomy or micro-endodiscectomy for selected herniations. It is better for the patient, has less surgical morbidity, has equivalent results, and will not affect a subsequent posterior surgical approach if needed. Cadaveric-experimental studies comparing the transcanal approach and the foraminal approach clearly showed that both approaches to the lumbar discs carry potential risk for injury or violation of blood vessels and spinal nerves. When a surgeon limits his exposure, there is a learning curve, and complications may arise because of unfamiliarity with the limited surgical view in both techniques.

14. If we consider all these advantages TFE is a matter of choice by default. It can deliver same results with less of morbidity and complications.

A review of the literature

Looking at studies before 1995,^36–46 we find that surgery was mainly under fluoroscopy and in later years visualized. Annular opening was done after fenestrating the annulus nerve by blunt palpation. Contraindications of those years were sequestrations, calcified or narrow disc, cauda equina syndrome, previous same level surgery, instability, large extra ligamentous disc, high iliac crest, stenosis, listhesis. Over years we have standardized our technique and overcome all contraindications except instability and central canal stenosis. We need to combine TFE with stabilization and in stenosis we may need additional interlaminar surgical access(Table 1).

There are 15 studies during the period from 1995 to 2005.^47–59 This was a time when spine endoscopy was in flux and evolving, after the YESS system received FDA approval in 1998. A study focusing on identification of pain generators 1991, and the anatomy of the foramen in 1995 were published with studies supporting and validating these ideas and mainly standardizing the instruments. Even though there were not many randomized controlled trials, first prospective randomized controlled trial was published by Hermantin et al in 1999 and a sound and strong base was created for taking these ideas further by adding many other complementary technologies like RF, laser and improvements in optics and surgical instruments. It was established that without any posterior midline access we could deliver same or better results. It also established precision needed for adoption of the technique. The indications and inclusions have changed to include sequestrations, prior surgery and even nerve deficits. The exclusions have narrowed. The reoperation rates are around 5% and complications are low. The surgery has now essentially become intra and extradiscal, and use of YESS system has become common by 2005 (Table 2).

There are 9 significant studies after 2005^60–68 when spine endoscopy was technologically maturing producing relatively consistent results. The inclusion criteria show that we are able to include a vast range of symptoms and degenerative conditions of an aging spine affecting the functional spinal unit. It also identifies where we fall short in patients with instability, central canal stenosis where even today we are in search of complementary solutions. More recent studies in press are addressing instability and failed back surgery syndrome with endoscopic transforaminal fusion and neuromodulation of the Dorsal root ganglion. Spine endoscopy can be done in awake and aware patients thus extending its benefits to medically compromised patients (Table 3).

Since we introduced the methodology of spine endoscopy in 2001 we are able to compare results of TFE Vs micro discectomy during that period, using a group practice that offers both techniques. There is a very extensive study of MLD vs Endoscopy also reported by Kotilainen in 1994.⁶⁹

In a 2006 study by Lee et al.⁷² post op radiological evaluation based study. Although the clinical outcomes were similarly satisfactory in both groups, PELD is a less invasive procedure for the muscles and soft tissues of the back than open microdiscectomy in selected cases. A 2007 study by Sasani⁶⁷ about far lateral herniations treated by TFE, a report of 66 patients. It was effective in removal of total fragment and achieve a pain free status in majority.

Following 2 studies of 2008 and 2009 by Ruetten^{73, 74} are comparative studies of TFE and MLD one for standard virgin untreated herniations and one for recurrences. They have been summarized in Table 4. The clinical results of the full-endoscopic technique were equal to those of the microsurgical technique. TFE had reduced traumatization. Full-endoscopic surgery (including interlaminar FE) is a sufficient and safe supplementation and alternative to microsurgical procedures.⁴⁶ Lee et al.⁷⁵ found bothoth PELD and repeat OLM showed favorable outcomes for recurrent disc herniation, but PELD had advantages in terms of shorter operating time, hospital stay, and disc height preservation. The prevention of recurrence was achieved in interlaminar access by annular sealing mainly in percutaneous interlaminar FE.⁷⁶ Another study in 2009 has demonstrated that FE can be day care surgery and achieved similar results.⁷⁷

In 2010 in a systematic review,⁷⁸ a randomized controlled trial, 7 non-randomized controlled trials, and 31 observational studies were identified. The data from these 31 studies have been sourced and reanalyzed in Table 1, Table 2, Table 3. Studies were heterogeneous regarding patient selection, indications, operation techniques, follow-up period and outcome measures, and the methodological quality of these studies was poor.

The eight trials (randomized and non-randomized; Table 5) did not find any statistically significant differences in leg pain reduction between the transforaminal endoscopic surgery group (89%) and the open microdiscectomy group (87%); overall improvement (84 vs. 78%), re-operation rate (6.8 vs. 4.7%) and complication rate (1.5 vs. 1%), respectively. There has been an added detailed review of evolution of disc surgery in 2011 by Postachini.⁷⁹

In 2013 a study comparing learning curve of MLD and FE it was found it is steep but not hard to master.⁸¹ There is a recent French instructional course on disc surgery 2013⁸² by A. Blamoutier that compares microdiscectomy and full endoscopy.

Ruetten et al. reported no difference in terms of lumbar or radicular pain, or Oswestry or North American Spine Society (NASS) pain or neurology scores at 2 years’ follow-up. Gotfryd and Avanzi⁸³ and Nellensteijn ⁷⁸ performed systematic literature reviews. The former compared standard discectomy (SD), micro- or microlumbar discectomy (MD) and endoscopy (MED and FE). Endoscopy and MED were preferable to SD in terms of hospital stay and bleeding but not of clinical result. The latter assessed efficacy in FE and MED, they concluded that there was no difference between the techniques in terms of pain, complications or recurrence.

Mixed randomized controlled trials

Two randomized controlled trials by Ruetten^{73, 74} (n = 200 and n = 100 respectively) allocated patients either to interlaminar or transforaminal approach, or to microdiscectomy. The interlaminar approach was generally used for herniations inside the spinal canal and TF for intra- and extra-foraminal herniations, although the final decision was at the discretion of the surgeon.

One study included patients with first time disc herniations,⁷⁴ the other only patients with recurrent disc herniations who previously had discectomy surgery⁷³ at the same level. These studies were both judged to have a high risk of bias. As such all pooled analyses provide low quality evidence. There is Level 4 evidence that the effects of minimally invasive surgery (IL or TF) for patients with first time⁷⁴ and recurrent disc herniations⁷³ are not different to MD on back pain, leg pain or function at any time point.

The results being same or similar, it would be important to know how these results are achieved. It is not possible to ignore the morbidity with open surgery and limitation which medical comorbidities will have on choice of surgery. In patients with severe medical comorbidities only way we can offer pain relief is surgery under awake and aware status under local anesthesia.