Muscle Preserving Lumbar Microdiscectomy

33 Muscle Preserving Lumbar Microdiscectomy


Mick J. Perez-Cruet and Moumita S.R. Choudhury


Abstract


Herniated lumbar disc was perhaps the first indicated pathology for the minimally invasive surgery (MIS) muscle preserving approach. This approach allows spine surgeons to reliably decompress a symptomatic lumbar nerve root using a microscope while preserving the normal anatomical integrity of the spine. This technique has been expanded to perform cervical foraminotomy, lumbar laminectomy for stenosis, and more complex fusion and instrumentation. It offers many advantages over other MIS lumbar discectomy techniques by reducing tissue trauma, allowing direct visualization of the nerve root and disc pathology, and enabling bony decompression with instruments 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. The potential complications with the use of the tubular system are not significantly different from those encountered when performing standard microdiscectomy. Prospective multicenter clinical study has shown the efficacy of this system in treating lumbar disc disease. The approach described allows the development of expanded application beyond lumbar nerve root decompression and the tubular retractor system developed for use with an endoscope has been modified for use with a microscope, which allows excellent three-dimensional visualization and improved image quality. Surgeons familiar with the microscope have more readily adopted this latter technique.


Keywords: minimally invasive spine, muscle-sparing approach, muscle-splitting approach, One-Step Dilator, BoneBac Press, tubular retractor, microdiscectomy


33.1 Introduction


The microdiscectomy procedure is considered the gold standard for patients who require surgery for symptomatic lumbar disc herniation causing radiculopathy that has not improved with conservative measures.1 Lumbar disc herniation is the most common cause of nerve root pain and yet responsible for less than 5% of all lower back problems.2 Except when there is a considerable or emergent neurologic deficit, conservative medical management is approached preferred for at least 6 weeks since the onset of symptoms. If there is no improvement in 6 weeks, surgical intervention is considered. Microdiscectomy is the gold standard treatment for uncomplicated disc herniation. Surgical discectomy for carefully selected patients with sciatica due to lumbar disc herniation provides faster relief from the acute attack than conservative management, although any positive or negative effects on the lifetime natural history of the underlying disc disease are still unclear.3 A qualitative and quantitative analysis was performed on articles published between January 1975 and December 2012, relating to the optimum time of surgery in patients with lumbar disc herniation. The results indicated that longer duration of sciatica led to poorer patient outcomes.4


Removal of a herniated disc using the operative microscope was first performed by Yasargil in 1977.5 Microscope use during spinal procedures became more prevalent during the late 1980s.6 By the 1990s, many spinal surgeons adopted the routine practice of microdiscectomy abandoning the open non-microscope visualization method.7


In 1997, the microendoscopic discectomy (MED) system was introduced, which allowed spine surgeons to reliably decompress a symptomatic lumbar nerve root via an endoscopic, minimally invasive surgical (MIS) approach.8,9 This system offered many advantages over other MIS lumbar discectomy techniques by reducing tissue trauma, allowing visualization of the nerve root and disc pathology, and enabling bony decompression.10,11,12,13,14 In addition, the system came with long, tapered, bayonetted instruments designed specifically for use in a small working tubular retractor (image Fig. 33.1). The approach used is anatomically familiar to spine surgeons and excellent clinical results have been achieved on an outpatient basis.


Unlike percutaneous approaches, the METRx Microdiscectomy System (Medtronic, Memphis, TN) allows surgeons to address not only contained lumbar disc herniations, but also sequestered disc fragments, lateral recess stenosis, and bone and ligamentous compression. Prospective multicenter clinical study has shown the efficacy of this system in treating lumbar disc disease.15 The modularity of the METRx system also allows the development of expanded application beyond lumbar nerve root decompression.16,17,18,19,20 In addition, the tubular retractor system developed for use with an endoscope has been modified for use with a microscope, which allows three-dimensional visualization and improved image quality. Surgeons familiar with the microscope have more readily adopted this latter technique. The evolution of many tubular retractor systems including expandable tubes has further facilitated the muscle-splitting approach to the spine. The endoscopic technique appears to be replaced by the microscope, which provides improved visualization and potentially reduced cost. Additionally, we have found that the need to clean the endoscope during the case causes undesirable delays. Other even less invasive techniques to perform microdiscectomy, such as the transforaminal endoscopic approach, have been described. However, Nellensteijn et al,21 in a comparative analysis between transforaminal endoscopic and microdiscectomy, found no statistically significant variation in techniques when comparing leg pain reduction, overall patient improvement, reoperation rate, and complications.


33.2 Surgical Approach


33.2.1 Patient Positioning and Operating Room Setup


Microdiscectomy can be successfully performed on an ambulatory basis with the patient under spinal or general anesthesia. The patient is positioned prone with the spine flexed to aid in intraoperative exposure of the interlaminar space typically using a Wilson frame. Alternatively, a Jackson table can be used. Abdominal compression is avoided by properly positioning the patient on a frame, Jackson table, or rolls to reduce intraoperative venous bleeding (see image Fig. 8.3). The table and frame should be compatible with lateral fluoroscopy to allow for fluoroscopic viewing of the spine.



A set of fine-bayonetted instruments and a long tapered drill help optimize the working space within the tubular retractor. We typically use a cutting matchstick M8 burr on the drill. The drilled bone is collected using the BoneBac Press (Thompson MIS, Salem, MA) and used to reconstruct the laminotomy defect after completion of the microdiscectomy. We have found that this may help reduce perineural scar formation by removing the dead space created by the laminotomy defect. Thus, this technique may potentially improve patient outcomes (image Fig. 33.2).


Postoperative imaging studies after laminectomy with autologous bone graft reconstruction have shown excellent healing after decompression with restoration of the lamina defect and reduced perineural scar formation (image Fig. 33.3).


The operating room should be large enough to comfortably accommodate the fluoroscopic unit, fluoroscopic monitor, and microscope. The microscope is typically set up on the opposite side of the table to the surgeon after being properly balanced.


33.3 Surgical Technique


The patient’s back is prepped and draped in standard surgical fashion. With the patient in the prone position on a radiolucent Wilson frame, the level is identified with a spinal needle and lateral fluoroscopic image. An incision is made directly overlying the disc space of interest and lateral to the midline approximately one finger-breadth. The fascia is cut with a Bovie cautery. A muscle-splitting approach system has been developed that eliminates the Kirschner wire (K-wire) and muscle dilators that can potentially enter the canal and cause neural injury (image Fig. 33.4).



Benefits of Muscle-Sparing Approach Using One-Step Dilator


This approach to spine surgery without K-wire or sequential muscle dilators:


Facilitates and makes safer MIS surgery.


Is easy to use.


Reduces approach-related complications.


Is more efficient.


On redo operations where scar is present, the One-Step Dilator is docked above the spine and the approach completed under direct microscope visualization. This helps avoid penetration of the canal and neural injury or dural tear. A tubular retractor is placed to establish an operative corridor to the lamina and interlaminar space. Fluoroscopy confirms appropriate positioning (image Fig. 33.5).


33.3.1 Soft-Tissue Removal and Laminar Identification


It is essential to remove sufficient soft tissue exposed in the operative corridor to maximize the working space within the tubular retractor. The soft tissue over the lamina is removed using Bovie electrocautery, which prevents bleeding from the soft tissue during removal. A final confirmatory lateral fluoroscopic image can be taken to assure the proper disc space and tubular retractor location.




The soft tissue is removed circumferentially from the edge of the tubular retractor to maximize the working area and to prevent bleeding. Starting at the lateral aspect, bony landmarks are identified and soft tissue is removed by keeping the Bovie tip on the bone and turning the soft tissue inward toward the center of the tube. Final removal of soft tissue is achieved using a pituitary rongeur. In this manner, the medial facet and lamina are adequately exposed. A frequent on-and-off Bovie technique and use of sucker in the tube prevents smoke accumulation that can obscure visualization.


33.3.2 Laminar and Interlaminar Space Identification


A hemilaminotomy/medial facetectomy is then performed with a Kerrison punch and/or high-speed drill. We prefer to use an M8 cutting burr and collect all drilled bone for bone reconstruction of the laminotomy defect at the completion of the case using the BoneBac Press (image Fig. 33.2). The smooth tip of the cutting M8 matchstick burr allows for bone to be removed safely over the ligamentum flavum. Bone removal via drilling is started at the lateral caudal aspect of the lamina where the ligamentum flavum protects the dura. With the ligamentum flavum exposed laterally, the drilling can proceed safely over the ligament to remove the more rostral and then medial aspect of the lamina (image Fig. 33.6).


Oct 17, 2019 | Posted by in NEUROSURGERY | Comments Off on Muscle Preserving Lumbar Microdiscectomy
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