Minimally Invasive Lumbar Microdiscectomy: Indications and Techniques

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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.

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).

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).

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.

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