Endoscopic Interlaminar Lumbar Laminectomy

36 Endoscopic Interlaminar Lumbar Laminectomy

Christoph Hofstetter

Summary

The endoscopic interlaminar lumbar laminectomy is becoming the least invasive option to decompress the lumbar spine from a dorsal approach. This technique represents another option in the MIS armamentarium. In this chapter, the reader will obtain extremely valuable information from the expert on how to perform this type of surgery safely, efficiently, some tips and tricks, and also how to avoid complications.

Keywords: ILELL endoscopic spine surgery endoscopic lumbar decompression lumbar spine decompression

36.1 Introduction

Symptomatic lumbar spinal stenosis is a common diagnosis in the elderly population. Pathophysiological processes that lead to spinal stenosis include thickening of the interspinous ligaments and overgrowth of the facet joints. This leads to narrowing of the spinal canal and eventually compression of neural elements with subsequent signs of neural claudication. The feasibility of a unilateral laminotomy for bilateral access to the spinal canal was first demonstrated by Spetzger et al.1^,² This cadaveric study demonstrated that a unilateral approach allowed for bilateral over-the-top decompression of the thecal sac by resection of the ipsilateral facet, the median portion of the lamina arch, the contralateral facet, and the yellow ligament. A case series of 29 patients by the same authors demonstrated feasibility, safety, and favorable clinical outcomes.¹^,² Concurrent development of microendoscopic tubular systems by Foley et al provided a minimally invasive surgical corridor to the spinal canal without detachment of paraspinal muscles.³ Tubular retractors have been used in combination with an operative microscope to achieve bilateral decompression in the setting of lumbar spinal stenosis. A thorough step-by-step description of a minimally invasive lumbar decompression has been recently published.⁴ This technique has been adapted for a working channel endoscope, to allow for decompression of central and lateral recess stenosis in the lumbar spine.⁵^,⁶^,⁷ A prospective randomized controlled study on a total of 161 patients demonstrated favorable functional outcomes at 2-year follow-up with endoscopic technique compared to minimally invasive technique.⁶

36.2 Patient Selection

Case selection: Approach and bony decompression can be challenging in cases with severe spondylotic changes with facet hypertrophy or scoliosis. If these cases are addressed with endoscopic technique, attention to planning the surgical corridor and nonambiguous identification of anatomical landmarks is critical in order to maintain a smooth workflow. Moreover, cases with scoliosis and stable spondylosis require more extensive decompression to allow for sufficient decompression of neural structures during more extensive motion. However, once spondylolisthesis leads to symptomatic foraminal compression of the exiting nerve roots surgical reconstruction of the spinal segment via an arthrodesis procedure should be considered.

In the opinion of the editors, the unilateral tubular “over-the-top” decompression for lumbar spinal stenosis is one of the key competences for a successful minimally invasive surgery (MIS) spine surgeon. Whether or not endoscopic surgery will be able to surpass tubular approaches will depend on its ability to perform this task with the same efficiency and with less patient morbidity. This will need to be established in the upcoming years.

36.3 Indications

Endoscopic interlaminar lumbar laminectomy allows for central and bilateral lateral recess decompression in patients presenting with primarily leg or buttock symptoms with neurogenic claudication. Surgical indications are consistent with open or minimally invasive laminectomies.⁸ Similar to minimally invasive lumbar decompression, decompression of the neural elements is achieved primarily at the level of the disc–facet joint complex; thus, degenerative lumbar spinal stenosis is an appropriate indication for this procedure. In contrast, endoscopic interlaminar decompression may be less effective to achieve sufficient decompression in cases of epidural hematomas, lipomatosis, or phlegma as these pathologies are typically not confined to the disc–facet joint complex but often expand rostrocaudally beyond these structures. Endoscopic interlaminar laminectomy may be combined with resection of synovial cysts, discectomies, and contralateral foraminotomies. Endoscopic technique is in particular advantageous compared to open and MIS technique for spinal decompression in obese patients. A thick subcutaneous fat pannus neither requires additional exposure nor affects the lengths of working corridor or quality of visualization. Grade I spondylolisthesis is not a contraindication as long as there is no dynamic instability on flexion and extension X-rays or vertical foraminal stenosis. Contraindications to endoscopic laminectomies include grade II spondylolisthesis, isthmic spondylolysis, significant lateral listhesis, and significant scoliosis (SVA > 6 cm, lumbar lordosis-pelvic incidence [LL-PI] mismatch > 10 degrees, Coronal Cobb > 20).⁹

36.4 Surgical Technique

36.4.1 Approach

An optimal rostrocaudal approach angle for interlaminar lumbar laminectomies is of extreme importance. Precise determination of his angle enlarges the interlaminar window and greatly reduces the need for bony removal and thereby the operative time. Moreover, an optimized approach angle helps to spare the pars interarticularis, as the spinal canal is approached via the inferior portion of the lamina. An optimal approach angle needs to provide access to spinal canal spanning from the tip of the superior articular process (SAP) to the mid-portion of the pedicle of the caudal segment—this constitutes the goal for the rostrocaudal decompression. For intraoperative determination of the rostrocaudal approach angle, an end plate view of the caudal vertebral body is obtained on anteroposterior (AP) fluoroscopy (Fig. 36.1a). Based on this, angle addition of approximately 10 to 15 degrees of kyphosis is typically required in the lower lumbar levels. The goal is to center the gap between spinous processes over the projection of the disc space (Fig. 36.1a–c). In the lower thoracic and upper lumbar spinal segments, less rostrocaudal angulation should be used. At these levels, spinal stenosis is often caused by overgrowth of the sagittally oriented facet joints. Choosing a too steep rostrocaudal approach angle may interfere with decompression of the caudal aspect of stenosis since the endoscope is deflected by caudal lamina. The incision is marked where the disc space crosses the medial aspect of the facet joint (Fig. 36.1d). A small vertical skin incision is made using an 11-blade. Serial dilators are then advanced with small rostrocaudal movements along the AP trajectory of the fluoroscopy until the medial aspect of the facet joint and the inferior margin of the lamina can be palpated. Beveled dilators may be used to strip muscles off the lamina in order to facilitate the transition from palpation to visualization. Attention should be paid to staying in solid contact with the edge of the lamina. At L5/S1, the dilators may rest on the yellow ligament. In these cases, lateral fluoroscopic images may help to confirm appropriate depth (Fig. 36.1e). Blind penetration of the yellow ligament is not advised as it could lead to damage of neural structures. Following the serial dilation, the working tube is placed with the bevel facing medially (Fig. 38.1f). At this point the endoscope is brought in.

Fig. 36.1 Anteroposterior (AP) fluoroscopic intraoperative images for approach planning. First an AP end plate view of the superior end plate of the caudal level is obtained (L3/L4, arrow) (a). The addition of kyphosis of the rostrocaudal X-ray beam angle moves the projection of the interspinous process space toward the disc space (arrowhead) (b). An ideal rostrocaudal trajectory has been determined (arrow head) (c). The skin incision is marked at the tip of the radiopaque object (d). A lateral X-ray may be obtained to confirm the level (e). Once the working tube is brought into place, an AP X-ray confirms the location of the working tube at the inferior margin of the lamina (arrow) (f).