Micro-endoscopic-discectomy (MED) for far lateral disc herniation in the lumbar spine. Technical note

Acta Neurochir (2005) [Suppl] 92: 99–101 6 Springer-Verlag 2005

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Micro-endoscopic-discectomy (MED) for far lateral disc herniation in the lumbar spine. Technical note

P. Cervellini, G. P. De Luca, M. Mazzetto, and F. Colombo

Department of Neurosurgery, Vicenza Hospital, Vicenza, Italy

Summary

This study describes a new experience of the authors in the treat- ment of extraforaminal disc herniation via the micro-endoscopic far lateral approach to establish a less traumatic approach to extra- foraminal disc herniation with less stay in hospital and less cost.

Seventeen patients who underwent surgery for extraforaminal disc herniation were analysed and long-term follow up was done revisit- ing all of them in hospital. The results of surgical decompression via the micro-endoscopic far lateral approach were good in all patients with minimal discomfort. There was complete resolution of leg pain presented. Dysesthesia subsided after 2–3 weeks. Extraforaminal disc herniation can be diagnosed with the aid of CT scan and MRI.

The minimally invasive surgical treatment via the micro-endoscopic far lateral approach, in our initial experience, has a high rate of succes.

Keywords: Lateral disc herniation; paramedian approach dis- cectomy; micro-endoscopic approach.

Introduction

About 7–10% of lumbar disc herniations are lo- calized in the intervertebral foramen and extrafora- minally with compression signs of the extraforaminal nerve root and lumbar pain [1, 2, 7, 11, 15, 16, 20, 26, 27]. Foley and Smith recently have described a new technique of micro-endoscopic-discectomy for disc herniation excision with minor tissue damage, reduced scarring as compared to standard microdiscectomy [10, 13, 14, 19]. This technique is commonly used in our Department with good results. Standard micro- discectomy for lateral, intra and extraforaminal disc herniation is more traumatic, the surgical skin incision is larger and muscle traction and damage is more im- portant [6, 8, 21–24].

Materials and methods

17 patients with extraforaminal disc herniations were operated with far lateral micro-endoscopic discectomy; 10 in L4-L5 and 7 in L3-L4 (Fig. 1). In L5-S1 space this approach is not possible.

Following induction of general endotracheal anaesthesia, the pa- tient is placed in the prone position on a lumbar frame with thighs flexed at 30 degrees permitting the use of x-ray in lateral and antero- posterior position. The operative site is prepared in the usual fashion.

A needle guide is introduced directly to the transverse process [12, 25] with x-ray control (CT scan and MRI images were evaluated before to calculate the distance from the midline). The correct posi- tion of the needle is on the supero-medial portion of the inferior transverse process to the level of approach, few millimetres lateral of the articular process. Under x-ray confirmation the dilators are in- serted over the guide needle reaching the bigger of 17 mm of diame- ter (Figs. 2–3). The last dilator is positioned with the inferior border to the superior portion of the transverse process. After the introduc-

Fig. 1. Magnetic resonance imaging obtained of a left L3-L4 far

lateral disc herniation

tion of the optic fibers the intertransverse muscle is dissected expos- ing the intertransverse ligament. This is divided with accuracy in the supero-external portion. In this way we can see the root superiorly pushed from the disc herniation. Care must be taken to avoid trau- matizing or transmitting electrical energy from the coagulation apparatus to the underlying root and ganglion. Disc fragments are removed using small grasping instrumentation. It is also possible to reach the disc space and to remove additional disc material.

Results

In our series, 17 patients presented with a volumi- nous far lateral disc herniation confirmed at surgery.

Removal was easy in all cases using the endoscopic technique. Operative time ranged from 45 to 120 mi-

nutes. All patients were discharged home within 35 hours. The results were good and reported according to Macnab criteria (Table 1). The follow up period ranged from 1 to 4 years. There was no postoperative pain or dysesthesia secondary to the trauma of dissec- tion and/or coagulation. The patients were immedi- ately mobilized and discharged the day after surgical treatment. In the operated patients there was no neu- rological impairment and all of them had complete regression of radicular pain.

Discussion

The incidence of far lateral lumbar disc fragments is approximately 7–10% of all lumbar disc herniations [4, 17, 18]. The wide use of CT scan and lumbar MRI detect the disc fragments with increasing frequency [3, 5]. These herniation produce pain and radicular symptoms. In the past, the most common surgical approach was via a midline hemilaminectomy expo- sure that often requires destruction of the facet joint with subsequent instability. The other possibility is now the paramedian muscle splitting approach with microdiscectomy avoiding the facetectomy and insta- bility [9, 11, 20]. This is the new concept of minimally invasive surgery with little discomfort, cosmetic dis- figurement and towards day hospital surgery. A recent new evolution of this technique is the microendoscopic discectomy (MED) using dilators. This muscle split- ting approach is the most direct route to the lumbar disc herniations lateral to the neural foramen and is greatly implemented by the use of video assisted mi- croendoscopic technique. Radiographic view of the transverse process is mandatory for the correct posi- tion of the guide needle and dilators to avoid lesions to the root. Another point is the fat tissue that has to be measured before on the CT scan and MRI to permit the use of dilators that have now a limited length of 20 cm. This problem can be solved in the future by modifying the length of dilators. We are also working to change from general to spinal anaesthesia reducing

Fig. 2. Fluoroscopic lateral control of the ball-tip probe medial to the exiting nerve root searching for more disc fragments

Fig. 3. Fluoroscopic AP control of straight ball-tip probe under the pedicle and exiting L3 nerve root

Table 1. Outcome after endoscopic discectomy

Outcome N

of patients

Macnab criteria

– Excellent 9

– Good 8

– Fair 0

– Poor 0

100 P. Cervellini et al.

both hospital stay and cost. An absolute contraindica- tion for this approach is the hypertrophic articular process that doesn’t permit medial positioning and view of the optic fibers inside dilators. We never per- formed an approach at level L5-S1 because of the iliac crest.

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Correspondence: P. Cervellini, U.O. di Neurochirurgia, Ospe- dale Civile, Viale Rodolfi, 36100 Vicenza, Italy. e-mail: patrizioce@

hotmail.com

Micro-endoscopic-discectomy (MED) for far lateral disc herniation in the lumbar spine. Technical note 101