Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 16804267
Source of Support: None, Conflict of Interest: None
Background: Lumbar disc prolapse is a common problem and the current surgical standard for its treatment is a microsurgical discectomy. Microendoscopic discectomy (MED) is a minimally invasive spinal procedure being done successfully for prolapsed intervertebral disc disease. Aims: We report the technique, outcome and complications seen in 107 cases of prolapsed lumbar intervertebral disc who underwent MED. Setting and Design: The study was carried out at the Department of Neurosurgery, at a tertiary hospital in South India and the data was collected prospectively. Materials and Methods: 107 patients with prolapsed lumbar intervertebral disc who were seen at our institution between November 2002 and January 2006 were included in the study. Data was collected prospectively. The METRx system (Medtronic Sofamor Danek, Memphis,TN) was used to perform MED. Outcome assessment was done by the modified Macnab criteria. Results: 107 patients (67 males, 40 females) underwent MED for prolapsed lumbar intervertebral disc. Follow up ranged from 2 to 40 months with a mean follow up 12.9 months. Seventy six patients had an excellent outcome, 22 patients had a good outcome, 5 patients had a fair outcome and 3 patients had a poor outcome. One patient with a long dural tear required conversion to a standard microdiscectomy and was excluded from outcome assessment. Complications included dural puncture with K-wire (1), dural tear (2), superficial wound infection (1), discitis (1) and recurrent disc prolapse (2). Conclusions: Microendoscopic Discectomy (MED) is a safe and effective procedure for the treatment of prolapsed lumbar intervertebral disc.
Keywords: Discectomy, microendoscopic, MED
The surgical treatment of prolapsed lumbar intervertebral disc has evolved since the initial report of lumbar discectomy by Mixter and Barr in 1934. The standard operations include fenestration, hemilaminotomy and microdiscectomy., Microsurgical discectomy or microdiscectomy is the currently accepted surgical procedure for lumbar disc prolapse with which all other techniques are compared. The minimally invasive techniques which have been used to treat contained lumbar disc prolapse and discogenic back include chemonucleolysis with papain, various modifications of percutaneous discectomy, percutaneous laser discectomy, percutaneous endoscopic discectomy and intradiscal electrothermy. However they are mainly intradiscal procedures with a posterolateral approach to intervertebral disc and cannot be used for extruded disc fragments. Microendoscopic discectomy (MED) is a procedure which combines spinal endoscopy and the techniques used in microdiscectomy and this directly deals with offending prolapsed or extruded disc fragment and decompresses the nerve root. In addition lateral and foraminal stenosis can also be tackled. The advantages of minimally invasive techniques have included smaller incision, less peri-operative pain, early ambulation, short hospital stay and early return to work.,,,,, We report our results in 107 patients who underwent MED for prolapsed lumbar intervertebral disc.
One hundred and seven patients with prolapsed lumbar intervertebral disc who were seen at our institution between November 2002 and January 2006 were included in the study. Data was collected prospectively. Pre-operatively all patients had a trial of conservative therapy before surgery was offered. This included a minimum period of 6 weeks of analgesics and rest. All patients had a pre-operative MRI of the lumbar spine. Lateral recess stenosis at the involved level was not a contraindication to MED. Informed written consent was taken from all patients. In 2 patients with central disc prolapse, MED was attempted unsuccessfully and the surgery was converted to the standard microsurgical discectomy. Subsequently MED was not attempted for central disc prolapse.
Operative technique: Under general anesthesia the patient was positioned prone. Skin preparation was done with betadine. The METRx system (Medtronic Sofamor-Danek, Memphis, TN)) was used for the procedure. Under X-ray control a spinal needle was placed paramedian (1 cm lateral to midline) on the side of disc herniation and the position of the needle was adjusted till it was parallel to the center of the involved disc space. Subsequently a small incision was made and a K wire was placed under X-ray control at the offending disc level parallel to the disc space. Serial dilators were then passed over this. Finally, an operating post of 16 mm diameter was placed. The endoscope was then brought in and fixed to this port using an adapter. Endoscope was connected to monitor and rest of procedure was carried out using the image displayed on monitor like any other endoscopic procedure. The laminae, facet and ligamentum flavum were identified and a proper orientation and focus was achieved by adjusting the endoscope. Laminotomy and medial facetectomy was done. Ligamentum flavum was then cut using a knife and flavectomy achieved using a Kerrison rongeur. The nerve root and dural tube were identified. Discectomy and rhizolysis of the involved nerve root was carried out. Where necessary posterior osteophytes could also be removed and lateral recess could also be adequately decompressed. Closure involved subcuticular absorbable stitches. Perioperative antibiotics were given for 48 hours. The patients were ambulated as soon as the effects of general anaesthesia wore off (usually within 6 hours of the surgery) and were discharged on the 2nd post operative day. Outcome assessment was done using the modified Macnab criteria [Table - 1].
One hundred and seven patients underwent MED at our institution between November 2002 and January 2006. There were 67 males and 40 females. The age group ranged from 17 years to 73 years. All patients had a posterolateral disc herniation [Figure - 1][Figure - 2] and of these 5 patients also had associated lateral recess stenosis [Figure - 3][Figure - 4]. L4-5 and L5-S1 were the most commonly involved levels [Table - 2]. All patients were ambulated within 6 hours of the surgery and were discharged within 48 hours of the surgery. During the latter part of series, patients were discharged within 24 hours of surgery. This excluded the patient with long dural tear in whom a conversion to the open procedure was done. Duration of post operative follow ranged from 2 months to 40 months with a mean follow up of 12.9 months.
There were a total of seven complications (6.54%). This included 1 case of dural puncture during K wire insertion which did not require any specific treatment. There was one case of superficial wound infection which was treated with antibiotics and daily dressings. One patient had a long dural tear which required conversion to an open procedure while a small dural tear in a patient did not require any intervention. There were 2 cases of recurrent disc prolapse which occurred 1 month and 14 months after the MED. The first patient underwent a microdiscectomy with a good outcome while the second patient refused surgical intervention. One patient had a post operative discitis/vertebral osteomyelitis which was successfully treated with antibiotics and bed rest.
Outcome assessment was done for 106 patients using the modified Macnab criteria. The patient with dural tear which required conversion to the standard microdiscectomy was excluded from outcome assessment. Seventy six patients had excellent outcome, 22 patients had a good outcome, 5 had a fair outcome while 3 patients had a poor outcome. Thus, overall success rate was 92.4% in our series. The mean operative time was 120 minutes. The cases done early in the series took a longer time upto 180 minutes, however after gaining experience, the average time taken for surgery is about 90 minutes. The difficult cases which included axillary fragments and those with associated stenosis took a longer time, even after familiarization with the technique and equipment.
The relationship between lumbar disc herniation and the syndrome of lumbago/sciatica has been well recognized since the 1930's. Since then it has been a constant endeavor to achieve the decompression of the offending nerve root by various operative techniques and innovations. Undoubtedly, the gold standard for lumbar disc surgery - microsurgical discectomy, was introduced by Yasargil and Casper separately in 1977. Available evidence suggests that Prof. Yasargil was the first person to introduce this technique.
The success rates for microdiscectomy range from 88 to 98.5% in various series. It was established that this procedure reduces the incision size, blood loss and morbidity. It faced the same skepticism at that time which is being faced by MED at present. However, with time, the benefits of operating microscope in terms of illumination, magnification, minimal retraction of neural structures and direct visualization of the disc space became evident and the procedure was adapted widely. It became a standard with which other procedures on prolapsed lumbar disc started being compared.
There have been several percutaneous systems introduce for lumbar disc prolapse such as chemonucleolysis, percutaneous lumbar discectomy (manual and automated) and percutaneous laser assisted discectomy. The advantages cited for these techniques have been surgery under local anesthesia, early mobilization, non disturbance of posterior structures such as laminae, facet and ligamentum flavum, less manipulation in the intraspinal space thus reducing the possibility of epidural fibrosis. The indications for these procedures are discogenic back pain and sciatica secondary to contained disc prolapse. These procedures cannot be used in cases of extruded disc fragments causing compression of the nerve root and they do not address the concomitant bony and ligamentous compression of the nerve root. The results of these procedures have been very variable and satisfactory results have ranged from 29 to 92%. One randomized controlled trial comparing automated percutaneous lumbar discectomy (APLD) with microdiscectomy for contained lumbar disc herniations showed that only 29% of the patients undergoing APLD had a satisfactory outcome when compared to 80% undergoing microdiscectomy.
The technique of MED was described by Foley et al in 1997. This procedure is a combination of endoscopy and the technique of standard microscopic discectomy using a posterior approach similar to that of microdiscectomy. The indications for this procedure are postero-lateral disc herniation with or without lateral recess stenosis, foraminal and extra-foraminal disc herniations.,, MED has also been successfully used for recurrent disc prolapse. This minimally invasive procedure has also been applied for decompression of lumbar stenosis and lateral recess stenosis secondary to facet or ligamentum flavum hypertrophy. Its use is also being extended for cervical foramenotomies and minimally invasive spinal instrumentation.
The advantages of MED over standard microdiscectomy include smaller incision, lesser post operative pain, early ambulation, short hospital stay, shorter time to return to work and lesser cost of treatment.- The patient's ability to return to the previous employment is a measure of success of the surgical procedure. Bookwalter et al reported that 40% of their patients returned to work in fewer that 5 weeks after microdiscectomy while Casper et al reported a mean return-to-work time of 18.6 weeks. Palmer reported a mean return-to-work time of 32 days following MED while Perez-Cruet et al reported a mean return-to-work time of 17 days following MED. The cost benefit analysis has also been established in an insurance driven practice such as in the USA. One study comparing the intraoperative electromyography (EMG) in the lower limb between MED and microdiscectomy showed that there was lesser irritation of the nerve root in the MED group. Good to excellent outcomes have been reported in upto 94% of patients undergoing MED., This correlates well with the success rate seen in current series (92.4%). There are no reported randomized clinical trials comparing MED and microdiscectomy but there is one non-randomized prospective study in which the authors have compared MED with microdiscectomy. In this study the average low back pain outcome score improvement was of clinical significance in both patient groups and there was no difference between the two groups. However, patients in the MED group required less postoperative analgesia during their stay. The authors concluded that MED is as effective as microsurgical discectomy for the treatment of uncontained or large contained disc herniations.
The complications reported in patients undergoing MED,,, include wound infections (0-0.8%), discitis (0-0.8%), dural tears (2.3-7.1%) and recurrent disc prolapse (2.6-2.9%).
The complications reported in large series with patients undergoing microdiscectomy,,, are also similar and include wound infections (0-7.2%), discitis (0-0.8%), dural tears (0-6.7%) and recurrent disc prolapse (3-14%). The complications seen in our series is comparable to the other MED series.
Lack of depth perception and stereoscopic vision associated with a learning curve have always been the problems associated with endoscopic surgeries. The METRx system can allow the use the use of microscope for initial familiarization in this minimally invasive approach. However, once the surgeon becomes familiar with the system, a 3 dimensional image can be conceptualized. The endoscope with a 25 degree angle also allows a better visualization under the nerve root. The system also has the advantage of both hands free and therefore two separate instruments can be used simultaneously. A recent study assessing the learning curve for lumbar MED by a single surgeon, states that approximately 30 cases are required to overcome the learning curve and before the operative time and complications reduce. The best methods to learn MED are skill development in cadaveric workshops and clinical supervision in a learning environment. The specific skills required in MED include visuo-spatial orientation, handling of endoscopic equipment and working through a small field of view. Surgeons who are experienced in the standard microdiscectomy may be better equipped to overcome the learning curve faster. Our results and conclusions are based on 107 patients who have undergone MED for posterolateral lumbar disc herniations. We have also applied the METRx system for single level lumbar laminectomy, drainage of tuberculous abscess and removal of an extradural spinal tumor and a few technical points from our experience are summarized.
a. For a proper disc removal, it is imperative that the tubular retractor is placed parallel to the disc space. Hence if a two level discectomy is being attempted, it is incorrect to angle the tubular retractor to reach the disc space. Instead the skin incision has to be extended to the appropriate level and the tubular retractor is placed parallel to the disc space being operated. That is the only way to enter the disc spaces to remove disc fragments.
b. It is possible do a good ligamentous and bony decompression of the contralateral nerve root by angulating the tubular retractor. However, it is dangerous to approach the contralateral disc space as the contralateral nerve root can get injured.
c. A point dural puncture can be left alone as the muscle splitting technique allows the muscle to approximate and CSF leak is not a problem.
d. An intra-operative X-ray using the C-arm is mandatory. A lateral view of the lumbar spine is sufficient.
e. In the early stages of learning, it is helpful to use the operating microscope with a 350 mm lens to visualize the structures through the tubular retractor and even do the surgery.
f. It is possible to remove a central disc prolapse by introducing two tubular retractors simultaneously, but is technically more demanding and time consuming. Standard microdiscectomy remains the standard for treating a central disc herniation.
g. Fogging of the lens, especially if bipolar is being used and occasional blood stain over the lens, can impair the vision and requires frequent cleaning. Instead of removing it time and again for cleaning, a good result can be obtained by warm saline irrigation in the operating port.
h. The METRx set can be autoclaved. However, it is found that at times moisture enters the system from inside. This can be removed by focusing the endoscopic light source over the lens. The heat generated cleans the lens.
Microendoscopic Discectomy (MED) is a safe and effective procedure for the treatment of prolapsed lumbar intervertebral disc. Its results are comparable to standard microdiscectomy. The current indications for this procedure include posterolateral disc herniations and/or lateral recess stenosis.
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4][Table - 1], [Table - 2]