Introduction

Percutaneous lumbar nucleotomy as a minimally invasive procedure for lumbar disc herniation was firstly reported in 1975 ₆ . Afterwards, percutaneous lumbar disc surgery evolved including percutaneous nucleotomy using automated disc removal devices ₁₂ , spinal endoscopy ₁₅ , and the laser ₃ . These procedures used posterolateral or para-foraminal approach, and the indications for these procedures have been limited to contained lumbar disc herniations. Furthermore, they have not proven to be as effective as standard open lumbar discectomy, because of longer operation times and some technical problems in addressing all the different aspects of lumbar disc disease ₈ .

On the other hand, microendoscopic discectomy (MED), one of the minimally invasive spine surgery systems for lumbar disc herniation, was introduced by Smith and Foley in 1997 ₄ . This MED system is characterized by a tubular retracter system and oblique endoscope lens. A muscle dilating postrerior approach reduces the approach site comorbidity and the angled endoscope may yield visualization beyond the confines of the tubular retractor. However, there is a steep learning curve to master this procedure ₁₃ . Actually, many surgeons prefer the METRx -MD system ( Medtronic Sofamor Danek, Memphis TN )which allows the surgeons to operate under direct vision through the microscope. However, once this endoscopic technique is mastered, the modularity of the MED system also allows for the development of expanded applications beyond lumbar nerve root decompression ₁, ₂, ₅, ₉, ₁₆ .

From 1998, we introduced MED system and applied it not only in several types of lumbar disc surgery, but also decompression surgery of spinal stenosis, cervical radiculopathy and cervical myelopathy. In this article, based on our experiences ₁₁, ₁₇, ₁₈, ₁₉, ₂₀ we describe the surgical technique and clinical results in lumbar disc disease.

Methods

Patients

Technical note

Patient positioning

Approach site identification

Dilator insertion and tubular retractor insertion

Endoscope Insertion and focus and image orientation

Interlaminar space identification

All soft tissue should be removed to maximize the working space within the tubular retractor. Meticulous hemostasis was needed, and provided by the bipolar cautery. After detaching the ligamentum flavum from the lamina using up-going angled curette, the trailing edge of the upper lamina and the medial part of facet was removed by Kerrison punch to enlarge the interlaminar window to secure an adequate working space (Figure 1). To prevent an iatrogenic instability, medial facetectomy should be minimized as much as possible.

Figure 1

Figure 1: Enlargement of interlaminar window. To detach the ligamentum flavum from the lamina, an up-going angled curette is used. After that, the trailing edge of lamina and medial facet is removed by Kerrison punch. (Figure 1 to 5 are from Nakagawa Y, Yoshida M. Microendoscopic discectomy (MED) for lumbar disc herniation. In Takaoka K ed. New OS NOW No. 27, Medical View, Tokyo, 2005: 47-54, partially modified.)

Flavectomy

The dorsal layers of ligamentum flavum were cut by a microknife perpendicularly to the fibers of the ligament, leaving some ventral layers (Figure 2).

Figure 2

Figure 2: Cutting the dorsal surface of ligamentum flavum. The Cut edge is dissected back bilaterally by using the tip of sucker, knife and angled curette and removed.

If the dorsal surface of the ligamentum flavum was degenerated and thickned ₁₄ , degenerative tissue should be removed by pituitary ronguer until the elastic ligament tissue appears. The dorsal surface of the ligament was dissected from the cut edge by using a tip of microknife and suction tube, or a curette bilaterally and removed, and then, the ligament of the ventral layer is split gently by a Penfield dissector. The epidural fat tissue appeared after penetrating the ligamentum flavum (Figure 3).

Figure 3

Figure 3: Ventral layer of ligamentum flavum is split gently by Penfield dissector. The epidural fat tissue will emerge after penetrating the ligament. Ligamentum flavum is removed by a small Kerrison punch while protecting the neural tissue, and flavectomy should proceed to ensure an adequate exposure.

Ligamentum flavum was removed by small Kerrison punch while protecting the thecal sac, and flavectomy was performed to ensure an adequate exposure.

Nerve root exploration , discectomy and closure

Resection of the ligamentum flavum proceeded from medial to lateral until the nerve root was identified. The nerve root was retracted medially using a Penfield dissector or suction retractor (Figure 4).

Figure 4

Figure 4: Nerve root retraction. The nerve root is retracted medially using a Penfield dissector or suction retractor in a standard fashion.

If an annulotomy was necessary, it was accomplished with a microknife while protecting the nerve root with suction retractor. The herniated disc fragment was removed by pituitary rongeur (Figure 5).

Figure 5

Figure 5: Discectomy. The herniated disc is removed by pituitary rongeur. Take care not to put the pituitary rongeur too deeply into the intradiscal space.

This procedure was the same fashion of Love's style ₁₀ . We took care to avoid putting the pituitary rongeur too deeply into the intradiscal space. After removal of the herniated fragment and nerve root decompression, the disc space was thoroughly irrigated with saline to remove any free fragments. Any bleeding in the epidural space was controlled with bipolar cautery. A suction drain was placed if needed, and the fascia and skin was closed in the standard fashion. The suction drain was taken off after one or two days postoperatively. The techniques mentioned above are also available in a briefly summarized video (Video 1).

Video 1: The patient was 41-year old female, with L5-S1 disc herniation on the right sided. Video starts from the procedure of flavectomy. Top of the screen indicates medial, bottom is lateral (right side), right is cephalad, and left is caudal.

Postoperative care

Outcome measures

Clinical outcome was assessed using Japanese Orthopaedic Association scoring system for lumbar disease (JOA score) ₇ , with an average 2-years follow-up after surgery. Perioperative complications, frequency of revision surgery, operation time and blood loss were also investigated.

Results

JOA score in lumbar disc herniation patients improved from 13.4 ± 5.1 preoperatively to 26.3 ± 3.1 postoperatively, and 27.6 ± 2.2 at the final follow-up (mean 2 years). With regard to posterior osseous endoplate lesion patients, JOA score also recuperated from 16.9 ± 3.6 preoperatively to 27.1 ± 2.3 postoperatively, and 28.2 ± 1.6 at the final follow-up (Figure 6). Mean operation time was 95.3 minutes and mean blood loss was 67.5 ml. There was no case of permanent neural injury, but perioperative complications occurred in 16 cases (4.0%), including 6 dural tears, 3 misjudgements of operative site (wrong level), 4 epidural hematomas, 1 pyogenic spondylitis and 2 transient muscle weaknesses. Revision surgeries were performed in 12 cases (3%) and consisted of 9 recurrence of disc herniations, 2 epidural hematomas and 1 inadequate decompression.

According to the development of operation time of senior author, it seems that the surgical skill had been established after completing 30 cases (Figure 7). Furthermore, operation time and blood loss in the latest 30 cases were significantly less than those of the first 30 cases (Figure 8). These data were previously reported ₁₉ .

Figure 6

Figure 6: Clinical outcome of posterior microendoscopic discectomy (MED) of lumbar disc herniation and posterior osseous endoplate lesion.

Figure 7

Figure 7: Relationship between the number of cases and the operation time

Figure 8

Figure 8: Comparison of operation time and blood loss between first 30 cases and latest 30 cases.

Discussion

MED is an excellent technique which could replace a conventional open procedure if the learning curve could be overcome. Minimally invasive surgery including MED provides manifold benefits such as a small skin incision, reduced postoperative pain, shorter hospital stay, faster mobilization, shorter rehabilitation, reducing pain medication usage and antibiotics, quick recovery to daily life or work, and so on. Moreover, the endoscope allows the surgeon to obtain more wide visualization through the oblique lens, so it can be possible to operate in the field beyond the confines of the tubular retractor. Additionally, the ability to get the endoscope close to the neural tissue pathology provides the surgeon with a clearer view. The 3CCD camera head also contributes to the improvement of image quality, which allows surgeons to facilitate the MED technique to more difficult pathologies. The first generation of the MED system could not provide such a clear image due to its disposable, one-tip camera head. This fact is one of the reasons that many surgeons gave up the MED system, and the MED system has not been widespreadly used. However, the progress of the image quality changed the situation. The versatility of this technique was seen in its ability to treat various lumbar disc pathologies including far lateral disc herniations, concomitant lateral recess stenosis, and noncontained disc herniation ₅₉₁₇₁₉ . With regard to clinical outcomes, our mid-term results are equivalent to open procedures ₁₈ .

On the other hand, it has been pointed out that the endoscopic procedure has a steep learning curve. Actually, most complications in this series were encountered in the early learning curve period. According to our experiences, surgical skill had been established after 30 cases of MED. MED procedure can be applied to other spine pathology and decompression surgery such as far lateral disc herniation, spinal stenosis, cervical radiculopathy or cervical myelopathy. To achieve safe and effective operation, it is crucial to master the MED technique in the first place and then apply to other pathologies.

Conclusions

The MED system is safe and effective method for surgical management of lumbar disc diseases. However, because there is a learning curve, it is advisable to start with herniated free fragments in younger patients, and only later treat older patients with bony and ligamentous pathology associated with disc herniation. The MED procedure will be able to become the new gold standard for lumbar disc surgery in near future.

Acknowledgments

Correspondence to

Yukihiro Nakagawa, M.D., Ph, D. Department of Orthopaedic Surgery, Wakayama Medical University 811-1, Kimiidera, Wakayama, 641-8510, Japan phone +81 73 447 0645 fax +81 73 448 3008 E-mail: nakagawa@wakayama-med.ac.jp