Chapter 162 Minimally Invasive Lumbar Microdiscectomy

Indications and Techniques

Since Mixter and Barr first elucidated the pathophysiology of lumbar radiculopathy in 1934, each subsequent generation of spine surgeons has made contributions to the surgical treatment of lumbar radiculopathy to lessen the trauma to the paraspinous muscles, optimize visualization of the neural elements, and minimize the incision.^1,2 Dandy first described a complete laminectomy and transdural removal of the disc fragment.¹ Thereafter, Scoville and Williams made significant refinements that eventually yielded the current technique of a laminoforaminotomy and microdiscectomy.³ The introduction of the operating microscope in 1977 by Caspar and Yasargil optimized visualization and further reduced the exposure needed to safely perform the operation.^4,5 In 1997, Foley took the next step in refining microdiscectomy and introduced a muscle-splitting approach employing a series of concentric dilators to access the lumbar spine.⁶ This technique avoids the midline structures and the muscle-stripping technique and minimizes the size of the incision needed to expose the requisite anatomy. The principle of a table-mounted tubular retractor, as opposed to a self-retaining retractor, decreases the pressure at the muscle-retractor interface, which can lessen postoperative discomfort and subsequent muscle atrophy.^7,8

Since its introduction in 1997, the minimally invasive technique for lumbar microdiscectomy has continued to undergo refinements and become more commonplace as more surgeons familiarize themselves with the technique. In this chapter, we describe their surgical technique for a minimally invasive lumbar microdiscectomy with a tubular retractor system. We then review the lessons learned from our first 100 cases and discuss operative nuances to this technique.

Patient Positioning and Room Setup

The setup for a minimally invasive lumbar microdiscectomy requires an adequately sized room that can comfortably accommodate the operating table, the fluoroscopic unit and monitor, and the operating microscope. Any operating table may be used, but we prefer a Jackson table with a Wilson frame. The Jackson table allows free passage of the fluoroscopic unit, without the hindrance of the pedestal. Regardless of the table used, the patient should be positioned prone with the spine flexed to optimally open the interlaminar space. The various minimally invasive sets have a table-mounted clamp, which should be placed opposite to the side being operated upon. For example, for a right L4–5 microdiscectomy, the clamp should be placed on the left at the base of the Wilson frame. This facilitates placement of the retractor arm, which is used to secure the tubular retractor (Fig. 162-1).

FIGURE 162-1 Operating room setup. A, The operating room should comfortably accommodate a fluoroscopic unit and operating microscope. We prefer a Wilson frame atop a Jackson table to facilitate fluoroscopy. B, The clamp for the table mounted retractor is secured at the base of the Wilson frame opposite to the side of the operation.

Technique

Incision

To work through a small incision, precise planning is essential given the limited field of view through the tubular retractor. A critical component of this planning is the trajectory of the tube. The optimal location of the incision is at a point where the tubular retractor lies in a trajectory parallel to the disc space (Fig. 162-2).

FIGURE 162-2 Intraoperative lateral fluoroscopic images demonstrating the importance of trajectory. A, This image confirms the L5–S1 level with an 18-gauge spinal needle. Note the trajectory of the needle veering away from the disc space. An incision based on this mark will be too low and adjustments will need to be made to optimize visualization of the nerve root and the disc. The visualization will remain suboptimal because of the trajectory required to access the disc space from this incision. B, The trajectory of the needle in this image is parallel to the disc space. Once the muscle is dilated and the retractor is placed, no adjustments will be required to optimize visualization.

The patient’s lower lumbar area is draped widely because no preoperative imaging is performed in order to minimize fluoroscopy time. The midline is marked by palpating the spinous processes, the level is approximated by palpating the bony landmarks, and a mark 2 cm from midline is made. After all the drapes are placed, the fluoroscopic unit is brought into the field and remains in position until the tubular retractor is secured to the table-mounted arm. Prior to making an incision, a 20-gauge spinal needle is placed to confirm the level. Once again, the needle is placed at a point on the skin that allows a trajectory parallel to the disc space, which is typically 2 cm lateral from the corresponding interspinous process space. This is confirmed with the first lateral fluoroscopic image.

Once an optimal point has been identified, a vertical incision is marked. To minimize trauma to the skin edges, the incision should be 2 mm longer than the diameter of the tubular retractor that will be used. For example, if a 16-mm tubular retractor will be used, an 18-mm incision should be planned, centered around the entry point of the spinal needle. we prefer to infiltrate the incision with a lidocaine-bupivacaine local anesthetic containing epinephrine, both superficially and deep within the muscle layer. This minimizes bleeding from the muscle and provides excellent postoperative pain control.

Dilator Insertion

Despite the numerous publications that detail the use of a K-wire for puncturing the fascia and docking onto the laminofacet complex, we refrain from using this technique out of concern that the wire might advance into the interlaminar space and enter the canal. Nevertheless, several publications have reported the safe use of this technique.^6,9 Instead, we prefer to sharply divide the fascia with either Metzenbaum scissors or Bovie cautery. Once the fascia has been divided, the first dilator may be safely passed and docked onto the laminofacet junction (Fig. 162-3).

FIGURE 162-3 A, After dividing the fascia with either Bovie cautery or Metzembaum scissors, the first dilator is passed and docked onto the inferior aspect of the rostral lamina. Careful palpation with the dilator is used until the medial aspect of the facet is determined. B, Subsequent dilators are used with intermittent fluoroscopic guidance to ensure a satisfactory trajectory.

To optimize the position of the first dilator, we palpate the bony anatomy in the immediate vicinity with the dilator itself. Once fluoroscopic guidance has been used to confirm the level, the inferior aspect of the lamina is determined with careful probing and, in a similar fashion, the medial aspect of the facet is identified. It is important to keep in mind while probing with the first dilator that it is small enough to enter the canal when the spine is flexed. Once the position of the first dilator is anchored into position with one hand, sequential dilators of increasing size are passed until the desired diameter is reached (Fig. 162-4). As each dilator is passed, the risk of inadvertently entering the canal with the dilator decreases.

FIGURE 162-4 Sequential dilation of the paraspinous muscles. Gentle wanding of the dilator minimizes the subsequent need for tissue resection. The retractor is secured with downward pressure (see Fig. 162-5), and a final fluoroscopic image is obtain to ensure the trajectory has remained unchanged.

The term wanding

Buy Membership for Neurology Category to continue reading. Learn more here

Related posts:

Hearing Prosthetics: Surgical Techniques Surgical Management of Cerebrospinal Fluid Leakage after Spinal Surgery Surgical Management of Sphenoid Wing Meningiomas Surgical Management of Chronic Subdural Hematoma in Adults Arachnoid, Suprasellar, and Rathke’s Cleft Cysts Management of Skull Base Trauma

Schmidek and Sweet Operative Neurosurgical Techniques Indication