MicroEndoscopic Discectomy (MED)

Evaluation of the "MicroEndoscopic Discectomy": a less invasive method for lumbar discectomy

4th International Congress on MINIMALLY INVASIVE NEUROSURGERY.
Barcelona. Spain
June 17-20. 1999

F. MARTENS and G. DE GEEST *
Department of Neurosurgery
* Director of Clinical Data Onze Lieve Vrouw Clinic, Aalst (B)

INTRODUCTION

When conservative measures fail, the commonly accepted treatment for lumbar disc herniation and radiculopathy is the posterior macro- or microdiscectomy. Continuous amelioration of microscopes and instruments have led to smaller skin incisions (Williams, 1993) and less muscular damage. As experienced by laparoscopic or thoracoscopic surgeons, there is a strong correlation between tissular destruction and pain resulting in a significant decrease in duration of hospitalization and quicker resume of professional activities for endoscopic techniques versus 'open' surgeries. This led to the acceptance of endoscopic or video-assisted surgery as the standard procedure for the correction of various abdominal, orthopedic or even cardiovascular diseases. Beside the benefits to the patient promising economical savings appeal to health administrators resulting in encouragement of further development of this way of thinking. The limiting factor however for the application of endoscopy to the spine is the impossibility to create a working space in a virtual cavity. The only logical solution to this anatomical limitation came when Foley and Smith developed the 'MicroEndoscopic Discectomy'.

This study was realized to evaluate short time and longer time result of the MED and compare the results with microdiscectomy.

TECHNIQUE

The operation has been described in greater detail in previous reports (Foley 1997). In our experience it is preferable to operate on the patient under general anesthesia and placed in a standard knee-chest position using the specific adaptation for the Maquet® operating table. A C-arm fluoroscope is placed to obtain lateral images from the spine and draped with the patient so that images can be obtained at any stage of the intervention (figure). According to the X-ray images a paravertebral 16mm skin incision is made opposite to the pathological disc space. Then a guidewire is inserted and placed on the inferior edge of the superior lamina. Three cannulated soft tissue dilators are inserted over the guidewire and each other. The tubular retractor is then advanced over the last dilator and fixed with a self-retaining arm. The dilators are removed and the endoscope is fixed on the tubular retractor. The further dissection of the ligamentum flavum, exploration of the disc space and nerve root, resection of the hernia and discectomie can be performed similar to a microdiscectomy while following the procedure on the monitor.

Figure: Knee-chest position of the patient with C-arm fluoroscopy in place, the surgeon stands ipsilateral to the disc herniation.

MATERIAL AND METHOD

Between September 1997 and June 1999 362 MEDs were performed by the same surgeon.
The first 100 cases were prospectively studied. All patients presented with a unilateral one-level disc herniation and radicular symptoms resistant to conservative therapy. The mean age was 43 years, there were 44 women, the operated levels were L3-L4 (2), L4-L5 (44%), L5-S1 (54), 43 were right-sided. Complications were recorded.
Clinical results were evaluated after three weeks and six months. Short term results were obtained when the patient presented at the outpatient's clinic for the first time after the operation.
To establish whether the outcome from MED could compare with the 'golden standard' the results after 6 months were compared with 100 consecutive microdiscectomies previously performed by the same surgeon. The technique used was a mailing: patients in both groups were asked to fill out a questionnaire. The mailing was performed and the results statistically analyzed by an independent observer (GDG) not involved with the neurosurgical department. The response was 97 in the MED group and 94 in the 'OPEN' surgeries. The two groups were not clinically significant for age, gender, level of disc herniation or professional activities.

RESULTS

1° Complications

In three patients the operation had to be converted to an 'open' intervention due to a dural tear. However these tears were minor and were not associated with nerve root damage. There was one spondylodiscitis, one superficial wound dehiscence and one deep bleeding needing to evacuation after 24 hours. These complications did not correlate with a bad outcome and for instance the patient with spondylodiscitis recovered completely.
During the 6-month follow-up period there were 4 recurrences of the hernia needing reintervention, two underwent a classic procedure, the remainder had a second MED. This was comparable with the 'OPEN' group were 3 recurrences occurred.

2° Short time results (> 3 weeks)

Complete relief of radicular pain was achieved in 94%, one was unchanged and two patients had worse pain.

3° Results after 6 months

The overall subjective satisfaction rate was good in 74%, partially good in 19% and bad in 7% for the MED. For the 'OPEN' surgeries it was respectively 67%, 23% and 10% (not clinical significant using the Pearson X2 test).
When patients were asked if they would undergo the operation again, 89,9% of the patients in the MED group answered yes, in the 'OPEN' group this was 88,9 % (not clinically significant).

4° Duration of operation, return to work, expenses

The mean duration of the MED was 78,34 minutes, for the OPEN procedure 44.82 (clinical significant t-test p>0.001). The duration of hospitalization was 6.57 days for the OPEN cases and 3,57 days for the MED (clinical significant t-test p>0.001). The patients subjective opinion about their length of stay in the hospital was for the MED acceptable in 67%), too short 31,9% and too long in 1,1%. For the patients operated conventionally it was 81,5%, 25,1% and 0,5% respectively (not clinical significant Pearson x2 test p=0,062).
Mean return to work was 77,49 days in the MED group and 95,57 days in the OPEN group (clinical significant t-test p>0,05). When the global cost of the intervention were calculated in the two groups the MED operation was 31 % cheaper than the OPEN procedure (2285,45 Euro versus 1579,05 Euro).

DISCUSSION AND CONCLUSION

Patients are demanding continuous efforts from their physicians to diminish pain and limit cosmetic side effects from invasive procedures. Endoscopic techniques are the closest in meeting these requirements. However new surgical approaches should be subject to critical analysis. Often double blind prospective studies are not possible or not justified. In the case of the MED the reduction of postoperative pain seemed so obvious that a comparison with an 'historical' control series was preferred. The clinical results regarding radicular relief are comparable and satisfaction rates not clinically significant different from the microdiscectomy. However for a statistically comparable population the results regarding duration of hospitalization and return to work were significantly better for the MED population. In our population one-day-clinic is a realistic goal for the well informed patient (Bouchez 1999). This difference with the classic operation in our opinion can only be explained by the operative approach used. Noteworthy is that this approach is not influenced by the weight of the patient (except in the morbid obese) as this is obviously the case with the OPEN technique. With the MED operation a considerable cost saving can be realized even when patients in the learning curve are included.

REFERENCES

WILLIAMS, lumbar disc disease, Neurosurg Clin North Am, 4, 101, 1993
FOLEY K,SMITH M, microEndoscopic Discectomy (MED): surgical technique and initial clinical results. Presented at the North American Spine Society 12th Annual Meeting, New York City, New York 1997
BOUCHEZ S et al The MED-procedure in outpatients. Minim. Invas. Neurosurg. 42, 107, 1999

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