19-Microendoscopic Lumbar Discectomy
19-Microendoscopic Lumbar Discectomy
19-Microendoscopic Lumbar Discectomy
OBJECTIVE: The microendoscopic discectomy (MED) technique was initially developed in 1997 to treat herniated lumbar disc disease. Since then, thousands of cases have been successfully performed at more than 500 institutions. This article discusses the technical aspects of this procedure and presents a consecutive case series. METHODS: A total of 150 consecutive patients underwent MED. MED is performed by a muscle-splitting approach using a series of tubular dilators with consecutively increasing diameters. A tubular retractor is then inserted over the final dilator, and a specially designed endoscope is placed inside the tubular retractor. The microdiscectomy is performed endoscopically while the surgeon views the procedure on a video monitor. RESULTS: Clinical outcomes were determined using a modified MacNab criteria, which revealed that 77% of patients had excellent, 17% had good, 3% had fair, and 3% had poor outcomes. The average hospital stay was 7.7 hours. The average return to work period was 17 days. Complications primarily included dural tears, which occurred in 8 patients (5%) and were seen early on in the patient series. Complication rates diminished as the surgeons experience with this technique increased. CONCLUSION: MED for lumbar herniated disc disease can be performed safely and effectively, resulting in a shortened hospital stay and faster return to work; however, there is a learning curve to this procedure.
KEY WORDS: Discectomy, Endoscope, Herniated disc, Lumbar, Microendoscopic, Minimally invasive
Neurosurgery 51[Suppl 2]:129136, 2002 DOI: 10.1227/01.NEU.0000031004.69814.2D www.neurosurgery-online.com
n 1997, the microendoscopic discectomy (MED) system was introduced; it allowed spinal surgeons to decompress a symptomatic lumbar nerve root Reprint requests: reliably using an endoscopic, Richard G. Fessler, M.D., Ph.D., minimally invasive surgical apSection of Neurosurgery, MC 3026, University of Chicago, 5841 proach (7, 18). Since January South Maryland Avenue, Chicago, 1997, more than 6000 MED proIL 60637. cedures have been performed in Email: more than 500 institutions. This rfessler@surgery.bsd.uchicago.edu system offers many advantages over other minimally invasive surgical lumbar discectomy techniques (2, 6, 8, 16, 17); it reduces tissue trauma, allows direct visualization of the nerve root and disc disease, and enables bony decompression. In addition, the system comes with long, tapered instrumentation designed specifically for use in a small working space. The approach used is anatomically familiar to spine surgeons, and excellent clinical results have been achieved on an outpatient basis. However, there were limitations to the initial MED system. The endoscope was not reusable, image quality was inconsistent, and the working space within the tubular retractor was limited. The next generation MED system, called the METRx,
Chicago Institute for Neurosurgery and Neuroresearch, Rush-Presbyterian-St. Lukes Medical Center, Chicago, Illinois
was developed to address these limitations. Compared with the initial MED system, the METRx system has additional advantages, including improved image quality, decreased endoscopic diameter, variable tubular retractor size, increased available working room within the tubular retractor, and decreased per-case cost. Unlike percutaneous approaches, the METRx system allows surgeons to address not only contained lumbar disc herniations, but also sequestered disc fragments and lateral recess stenosis. A prospective multicenter clinical study has shown the efficacy of this system in treating lumbar disc disease (3). The modularity of the METRx system also allows for the development of expanded application beyond lumbar nerve root decompression (1, 1114). In addition, the tubular retractor system developed for use with an endoscope has been modified for use with a microscope, which allows for three-dimensional visualization and improved image quality. This latter technique has been more readily adopted because of the familiarity of most surgeons with the microscope. However, we think the endoscopic technique has advantages in providing visualization beyond the confines of the tubular retractor, which is made possible by the 30-degree angled working endoscope. This is particularly useful during contralateral spinal decompression from an ipsilateral approach (13). In addition, the
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microscope lens apparatus tends to get in the way of instruments going in and out of the tube and can be less ergonomically friendly for the surgeon because the microscope must be positioned to look straight down the tube, which is not necessary in the heads-up monitor display provided with the endoscopic set-up. The MED system was developed to perform minimally invasive lumbar discectomy with excellent clinical results and, because of reduced tissue trauma compared with more traditional discectomy techniques, it allows patients to be treated on an outpatient surgical basis. The MED system endoscope is intended for use in visualizing lumbar herniated disc material, aiding in the search for and removal of disc material, and aiding bony decompression.
TABLE 16.2. Modified Macnab criteria used to assess clinical outcome in 150 consecutive patients undergoing microendoscopic discectomy Excellent Free of pain No restriction of mobility Able to return to normal work and activities Good Occasional nonradicular pain Relief of presenting symptoms Able to return to modified work Fair Some improved functional capacity Still handicapped and/or unemployed Poor Continued objective symptoms of root involvement Additional operative intervention needed at the index level, irrespective of repeat or length of postoperative follow-up
TABLE 16.1. Clinical characteristics of 150 consecutive microendoscopic discectomy patients Age (yr) Male:female ratio Workers compensation Level L2L3 L3L4 L4 L5 L5S1 Far lateral location 18 76 (mean, 44) 93:57 14 3 12 53 82 11
FIGURE 16.1. MED system of dilators, K-wire, tubular retractor, and flexible arm assembly.
ment is secured to the endoscope via a dovetail locking mechanism. Suction tubing is then connected to the aspiration port. After the camera/endoscope complex is assembled, the camera head light cable inputs are passed off the surgical field and connected to the video integrator. The endoscope is whitebalanced by placing a white, nonreflective object 1 cm from the lens while pressing the white balance button on the video integrator. For best results, the entire endoscopic image should be white. The distal tip of the endoscope should then be cleaned with antifog solution (which is found in the MED procedure kit). The METRx endoscope has the following spec-
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Dilator Insertion
The initial cannulated soft tissue dilator was inserted over the K-wire using a twisting motion while avoiding excessive downward force. Once the fascia was penetrated and the initial dilator was docked on bone, the K-wire was removed. Placement of the initial dilator was confirmed by lateral fluoroscopy. The tip of the dilator was used to sweep the paraspinal musculature off the laminar edge while being careful not to enter the interlaminar space (Fig. 16.6A). This maneuver not only allowed for palpation of the lamina but also expedited soft-tissue removal once the tubular retractor and endoscope were in place. By keeping the dilator tip in the subperiosteal plane, the dissection was essentially bloodless; however, care must be exercised to prevent advancing the initial dilator into the spinal canal. Until comfortable, this procedure should be performed under fluoroscopy.
FIGURE 16.2. Standard video equipment used for the MED procedure.
ifications: working length, 100 mm; angle of view, 25 degrees; field of view, 90 degrees; and depth of field, 5 to 50 mm. The wide depth of field enables a clear anatomic view through the length of the retractor tube. The METRx endoscope is compatible with V-Mount and certain three-chip camera heads.
TECHNIQUE
The back of the patient was washed and draped in a standard surgical fashion. The lumbar level to be approached was confirmed using lateral fluoroscopy, and then a 20-gauge spinal needle was inserted into the paraspinal musculature ap-
Endoscope Insertion
The endoscope was then inserted into the tubular retractor and secured to the tubular retractor using the locking arm on the ring attachment (Fig. 16.6C). The endoscope can be placed
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FIGURE 16.5. Operating room set-up for MED procedure. Fluoro, fluoroscopy.
FIGURE 16.4. Instruments used to perform MED procedure. Bayoneted instruments and a long, thin, tapered drill simplify the procedure.
anywhere within the 360-degree periphery of the tubular retractor and retracted or extended for variable magnification. The initial placement of the endoscope was in the most retracted position to avoid endoscope contact with soft tissue. Smudging the endoscope with soft tissue will dramatically reduce visualization. When this occurred, the endoscope was removed from the tubular retractor and the lens was cleaned
FIGURE 16.6. A, illustrations showing initial dilator in place sweeping paraspinal musculature off lamina, B, sequential dilators for musclesplitting approach, and C, tubular retractor with endoscope in place.
using antifog solution and gauze. Irrigating with plain saline solution while the endoscopic assembly was in the tubular retractor was also done to clear the camera.
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FIGURE 16.8. A, hemilaminotomy being preformed with a Kerrison punch, B, removal of ligamentum flavum with up-going curette, C, exposure of dura and traversing nerve root, and D, removal of disc herniation under retracted nerve root.
towards the center of the tube, with final removal of soft tissue using a pituitary rongeur. In this manner, the medial facet and lamina were exposed. A frequent on-and-off Bovie technique in the tube was used to prevent smoke accumulation that could fog the camera lens. It is essential to remove all soft tissue exposed in the operative corridor to maximize the working space within the tubular retractor.
FIGURE 16.7. Illustration of endoscopic image on the video monitor showing the initial image orientation to be incorrect (A). Proper orientation is achieved by turning the gold ring on the endoscopic assembly so that the V-shaped indicator (B) is in the same position on the video monitor as the endoscope is within the tubular retractor. At completion (C), the medial anatomy is at 12 oclock and the lateral anatomy is at 6 oclock on the video screen to give the surgeon proper orientation for performing MED.
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POSTOPERATIVE CARE
Patients were evaluated in the postoperative area and sent to the ambulatory ward. Patients and interested family members were instructed on operative findings, wound care, and further follow-up. Once the patient ambulated and voided, he or she was discharged home with a family member or friend.
and safely. Because most surgeons use an operative microscope or loop magnification, looking up at a video monitor to perform microdiscectomy seems cumbersome at first. With repeated use, the surgeon becomes more proficient, operative times decrease, and overall satisfaction with this system increases. To facilitate the use of the tubular retractor system, the METRx MD system (Sofamor Danek, Memphis, TN) was developed for use with the operative microscope. The advantage of this system over the endoscopic METRx MED system is three-dimensional operative visualization and surgeon familiarity with using the microscope. However, as the operative indications for this technique using a 30-degree operative lens increase, its usefulness, particularly in looking beyond the confines of the tubular retractor, will be better appreciated. Microendoscopic decompression for lumbar stenosis is facilitated by angled endoscopic visualization during contralateral sublaminar decompression and foraminotomy (13). Furthermore, once the surgeon is comfortable performing lumbar MED, further indications for the use of this technique include posterior cervical laminoforaminotomy and discectomy (1, 14), thoracic discectomy, lumbar laminectomy for stenosis (13), far lateral lumbar discectomy (11), and interbody lumbar fusion (12). In our experience, we have found high patient satisfaction with minimally invasive spinal procedures. The potential complications of the METRx system are not significantly different from those encountered performing standard microdiscectomy. The most frequently stated risks are dural tear, bleeding, neurological damage, damage to the surrounding soft tissue, and infection. In the early learning period, there may be a slightly higher incidence of dural tears, but these can be avoided with careful attention to operative technique. Dural tears, if they occur, are difficult to repair primarily through the working tube. A small piece of DuraGen dural graft matrix (Integra NeuroSciences, Plainsboro, NJ) covered with fibrin glue can be applied through the tubular retractor. Alternatively, a lumbar drain can be placed percutaneously above or below the operative site and left in place 2 to 3 days postoperatively. No cerebrospinal fluid leaks required repair through an open procedure, and all were treated through the tubular retractor by placing sealant and/or a percutaneous lumbar drain at an adjacent level. Additional risks specific to the METRx system can include instrument malfunction, such as bending, fragmentation, loosening, and/or breakage (whole or partial). Because this is a delicate instrument, it is important not to force the endoscope into position on the tubular retractor. The locking lever that attaches the endoscope system to the tubular retractor must to be fully released before rotating the endoscope into position on the tubular retractor. Also, to prevent inadvertently hitting the endoscope system during the procedure, the locking arm affixed to the operative table and METRx system and cables must be positioned out of the surgeons way. High-energy radiation light emitted from the illuminating fiber at the distal end of the scope may give rise to temperatures exceeding 41C within 8 mm in front of the scope. Therefore, do not leave the endoscope tip in direct contact with the patients tissue or combustible materials or burns may result.
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average follow-up of 12 months (range, 324 mo), 77% of patients had excellent, 17% good, 3% fair, and 3% poor outcomes (Fig. 16.9). The recent development of the MED system precludes extensive clinical outcome data; however, a prospective multicenter study with 13 months of mean follow-up (3), along with the results reported above, showed excellent clinical efficacy for this procedure.
CONCLUSIONS
The MED system is safe and effective for performing minimally invasive lumbar microdiscectomy. Careful attention to surgical technique will ensure that complications are minimized and will optimize patient outcomes. Dural tear was the most frequently recognized complication, and it is reduced with increased experience with this surgical technique. In essence, the MED system provides a conduit to the numerous benefits of minimally invasive spinal surgery. Further randomized, prospective investigations are needed to evaluate fully the impact of the MED system and other minimally invasive spinal discectomy techniques on clinical outcomes.
FIGURE 16.9. Patient outcomes as defined by the modified MacNab criteria showing data from 150 consecutive cases performed using the MED system.
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