Tubular Endoscopic Lumbar Laminoforaminotomy and Diskectomy [1]

13 Tubular Endoscopic Lumbar Laminoforaminotomy and Diskectomy [1]

Mick Perez-Cruet and Mengqiao Alan Xi

13.1 Introduction

Minimally invasive surgical (MIS) approaches to spine decompression were developed with the goal of preserving paraspinal soft tissues. A microscope is typically used in MIS procedures to provide a three-dimensional (3D) view of the regional anatomy.1,2,3 However, endoscopic approaches have been described as well.^4,5 Muscle dilators of increasing diameters can be used to approach the spine while sparing the paraspinal musculature. However, recent developments in retractor systems allow an approach to the spine in a muscle-sparing fashion but reduce the risk of insertion of K-wire or muscle dilators into the spinal canal (Fig. 13.1). Additionally, we have tended away from the endoscopic system and toward use of the microscope, which provides excellent 3D visualization of the anatomy and helps to facilitate the procedure (Video 13.1).

The METRx System (Medtronic, Memphis, TN) was one of the earliest and is one of the most frequently used tool sets in minimally invasive microdiskectomy. Our group has substantial experience with this system. The assembly consists of serial muscle dilators and a tubular retractor available in 14-, 16-, 18-, and 20-mm stainless or 18-mm disposable. The bayoneted instruments are slender and therefore greatly minimize crowding within the working channel.^6,7 This chapter describes the use of the microscope for performing minimally invasive muscle-sparing lumbar microdiskectomy and foraminotomy.

13.2 Operating Room Setup and Patient Preparation

There should be sufficient space in the operating room to accommodate the microscope and C-arm fluoroscopy, while leaving abundant working area for the surgeon and operating room personnel. The patient is placed in a prone position under general anesthesia. The patient’s abdomen is supported with rolls or frames to prevent excessive venous bleeding that may obscure the intraoperative view. The patient’s back is sterilized and draped in a routine fashion (Fig. 13.2). The microscope is balanced and surgically draped with a viewing port for the surgeon and assistant (Fig. 13.2).

Fig. 13.1 (a,b) Illustrations, (c) photo, and (d) intraoperative fluoroscopic images showing the application of the BoneBac One-Step Dilator (Thompson MIS, Salem, NH) used in a muscle-splitting approach to the spine. The technique prevents muscle damage while approaching the spine in a bloodless fashion, and it eliminates the need for K-wire and sequential muscle dilators.

Fig. 13.2 (a) Operating room setup allowing the surgeon to visualize the workspace with minimal effort. (b) The microscope is balanced and surgically draped with a viewing port for the surgeon and assistant.

13.3 Muscle-Sparing Approach to the Spine

The level is identified using an 18 G spinal needle and lateral fluoroscopy. The needle is positioned 1.5 cm lateral to the midline and directly over the disk space of interest. Once the level is identified, the needle is removed and an incision is made 1.5 cm or a finger-breadth lateral to the midline over the disk space of interest. The lumbodorsal fascia is cut with Bovie cautery parallel to the spinous processes. The BoneBac One-Step Dilator (see Fig. 13.1) or K-wire and serial muscle dilators can be used to approach the spine with the aid of lateral fluoroscopy to guide the approach (Fig. 13.3). The incision should be only as large as the diameter of the final tubular retractor (usually < 20 mm). Care is taken not to advance the K-wire or muscle dilators into the canal. We frequently dock above the spine, especially in a redo operation, and then approach the spine directly under microscope visualization. The One-Step Dilator or muscle dilators can be used to perform this portion of the procedure by docking directly on visualized laminar facet bone. Using this method, we have not experienced any dural tears or neural injury.

The first dilator is placed over the K-wire and is advanced through the soft tissue using a twisting motion. Once the dilator docks on the bony surface and its location is confirmed on fluoroscopy, the K-wire is removed. Fluoroscopic guidance should be used for this process. It is important to pay attention to the depth of the dilator tip so that it does not enter the spinal canal. The second, third, and fourth dilators are telescoped over the initial dilator in sequence down the working trajectory onto the laminar surface (Fig. 13.4). The tubular retractor is then placed over the final dilator until it docks on the laminofacet junction. The distal end of the retractor features a 20° bevel tip shaped to the curvature of the bone, facilitating tight contact and preventing soft tissue from creeping under the tip and obstructing the view. Applying downward force on the retractor toward the lamina also prevents soft tissue creep. Next, the tubular retractor is secured to the flexible arm. The muscle dilators are removed, exposing a clear tubular corridor through which the procedure can be performed. A final lateral fluoroscopic image is used to confirm that the retractor is firmly in place and at the appropriate level. If repositioning is necessary, the tubular retractor is unlocked from the flexible arm, wanded toward the desired location, and locked again to the flexible arm. This maneuver enables the surgeon to place objects of interest in the center of the surgical field and facilitates the procedure.

Fig. 13.3 (a,b) The One-Step Dilator (Thompson MIS) is introduced and deployed, allowing a cylindrical working channel to be established via the tubular retractor. This eliminates the need for K-wire and multistep dilators.

Fig. 13.4 Illustrations showing (a) K-wire and (b) sequential muscle dilators over which (c) a tubular retractor is placed.

13.4 Laminoforaminotomy and Removal of Ligamentum Flavum

From this point, the surgeon will encounter five anatomical layers, from superficial to deep: soft tissue, bony lamina and facet, ligamentum flavum, neural structures, and the intervertebral disk in question. The first three layers are removed sequentially. Note that each of the three layers should be cleared to a sufficiently large extent before pursuing a deeper layer. Otherwise, the opening becomes successively smaller at each deeper level, restricting the working space for the final diskectomy.

The bony facet and lamina can be palpated with a Bovie tip. The soft tissue is then circumferentially removed with Bovie cautery to expose the lamina and medial facet complex. Care is taken not to disrupt the synovial capsule overlying the facet joint; however, we have encountered no adverse clinical event if this occurs.

Once the lamina and medial facet joint are exposed, an M8 cutting bur is used to perform the laminotomy. All drilled bone is collected using the BoneBac Press and is used to reconstruct the laminar defect at completion of the decompression (Fig. 13.5).

Once adequate laminotomy has been performed, a small curet is used to separate the ligamentum flavum from the ventral underside of the lamina. The ligament flavum is left intact to cover the underlying neural structures during bone removal. A hemilaminotomy and medial facetectomy are performed using either a Kerrison punch or drill. The ligamentum flavum is detached from the inferior cut edge of the superior lamina using a small up-going curet and by sweeping under the lamina to detach the ligament. Utmost care is taken to avoid accidental dural tear. The ligamentum flavum is peeled back dorsally and caudally using a twisting motion and then is removed with a Kerrison punch (Fig. 13.6).

Fig. 13.5 Intraoperative photos showing use of BoneBac Press (Thompson MIS, Salem, NH) to collect the patient’s drilled autograph bone for fusion material.

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