Chapter 81 Minimal Access and Percutaneous Lumbar Discectomy
Minimal Access Lumbar Discectomy
Lumbar discectomy has become the most common neurosurgical procedure in the United States, with nearly 300,000 procedures performed each year. Herniated lumbar discs and resultant radiculopathy lead to approximately 15 million physician visits per year and have created a financial burden on society exceeding $50 billion annually.1–3
Historical Review
The operative treatment of lumbar disc disease has challenged spine surgeons since the first reported case of Dandy in 1929.4 The operating microscope revolutionized the operation. It improved the ability to visualize the neural elements and disc material, decreased surgical morbidity, and decreased incision size.5 Yasargil popularized the operating microscope in the mid-1960s, although it was not until the 1970s that the first publications by Yasargil6 and Caspar began to appear separately.7 In 1978 Williams reported on 532 patients who had undergone lumbar microdiscectomy through an intralaminar approach.8 These publications detailed the usefulness of the microscope and the appearance of lumbar microdiscectomy.
Since these early descriptions, surgeons have sought to decrease the incision size and iatrogenic morbidity associated with the operation. Faubert and Caspar in 1991 reported the use of a muscular retractor system9 rather than subperiosteal dissection to facilitate visualization of smaller operative corridors. The endoscope was also applied for the treatment of spine pathology.10
True minimally invasive lumbar microdiscectomy was first described by Foley and Smith11 in 1997. They reported the use of a microendoscopic discectomy system that entailed the use of tubular dilators to facilitate muscle sparing, a tubular retractor system, and an endoscope coupled with microsurgical techniques and instrumentation. This approach (microendoscopic discectomy) revolutionized minimal access spine surgery and paved the way for minimally invasive surgery (MIS) laminectomy and fusion techniques. The goal of these MIS approaches is to achieve clinical outcomes similar to those of standard approaches yet minimize the iatrogenic injury encountered during the approach to the spine.
Microsurgical (Microlumbar) Discectomy
General Principles
The technique requires a blunt paravertebral muscle-splitting approach. Recent evidence has suggested that the approach is characterized by less postoperative pain, shorter hospitalization, and faster return to work.12 The subperiosteal approach, by contrast, requires a larger incision and the detachment of the tendinous insertions of the paraspinal muscles and their retraction from the spinous process. The paravertebral muscles are rich in proprioceptors and may be injured when retracted. There are reports on the correlation between denervation and retraction-ischemia of the muscles and postoperative pain.12
The microsurgical approach to a herniated lumbar disc entails several modifications of the standard approach: surgical planning, positioning of the patient, and intraoperative imaging. Some of these modifications may appear as disadvantages to those surgeons not experienced with microsurgery. The surgical corridor to the target area is very limited, so the localization of the skin incision has to be determined very precisely. Once the skin incision has been placed, there is no way of altering the approach other than by enlarging the incision. The approach uses the same instruments that are used in standard lumbar discectomy but have been modified for use through small tubular retractors. The instruments are usually bayoneted and are of a dark color to reduce glare from the light source. A high-speed drill with a long, tapered, and gradually bent tip is designed to be used through these tubular retractors.
Surgical Technique
Step 2: Dilator Insertion
The smallest dilator is then inserted through the incision and is docked on the inferior aspect of the cranial lamina (Fig. 81-1). That is the L4 lamina for an L4-5 disc herniation. This is confirmed with lateral fluoroscopy. Remember that the edge of the lamina is caudal to the disc space. The anatomy should be palpated with the dilator, and a three-dimensional image of the anatomy should be formed in the surgeon’s mind. The inferior edge of the lamina is determined as well as the facet/lamina junction. The dilator may then be used to clear soft tissue from the lamina and medial facet. Care should be taken not to allow the dilator to slip into the intralaminar space.
Step 3: Sequential Dilator and Tubular Retraction Insertion
Sequentially place the second, third, and fourth dilators over the initial dilator down to the lamina, and then place the working channel (tubular retractor) over the final dilator (Fig. 81-2). We do not check fluoroscopy after each dilator placed but do so after the last is secured. Continued soft tissue is dissected from the lamina during subsequent dilator placement. The length of the final working tubular retractor is determined from markings on the largest dilator. The length and width of the tube are determined, and the tube is placed over the dilator to dock on the edge of the lamina. Fluoroscopy is used to verify placement of the tube (Fig. 81-3). We then direct the distal end of the tube somewhat medially.
The tube is then fixed to an arm, which is then attached to the operating table (Fig. 81-4). Once it has been attached, the dilators are removed and a corridor is established percutanously to the lamina and interlaminar space. We place a Penfield no. 4 under the edge of the lamina to confirm correct level localization on the lateral image (Fig. 81-5) and also confirm medial-lateral position on the anteroposterior image.
Step 4: Soft Tissue Removal and Laminar Identification
At this point, the operating room microscope or endoscope is brought into the field to provide illumination and magnification. Soft tissue usually will need to be removed from the laminae by using a Bovie with an extended tip and rongeur. The inferior (caudal) edge of the lamina should be identified as well as the medial facet joint (Fig. 81-6). Visualization of the fibers of the facet capsule ensure that one does not inadvertently enter the joint or remove too much of the joint and cause potential instability.
Step 7: Discectomy and Root Decompression
Once the disc space is visualized, the disc material is removed as for any standard discectomy. We prefer to only remove herniated disc material. If an anulotomy is required, a small one is made in a horizontal fashion (medial/lateral) with a no. 11 blade or a sheathed microknife (Fig. 81-7).
