Percutaneous Endoscopic Lumbar Diskectomy: Extraforaminal Approach

3 Percutaneous Endoscopic Lumbar Diskectomy: Extraforaminal Approach

Akarawit Asawasaksakul, Alfonso García, and Gun Choi

3.1 Introduction

Extraforaminal disk herniations, or “the hidden zone,” as described by Macnab, extend out from the far lateral reaches of the spinal canal. These regions of the canal have only recently been understood, because the myelographic contrast material used to delineate the pathology was unable to reach the far lateral region. McCulloch and Young also described how patients who underwent an exploratory surgery awoke with leg pain because the disk was located outside the spinal canal, lateral to the pars.1 The clinical syndrome became clear only after Abdullah,² in 1974, described extreme lateral disk herniation.

The diagnosis of extraforaminal disk herniation (EFDH) became more frequent owing to the availability of modern imaging methods like CT and MRI. But the surgical procedure still involved either removal of a significant portion of the facet joint or pars articularis resection, leading to instability and back pain.^3,4,5,6,7 The introduction of the paraspinal muscle-splitting (Wiltse’s) approach changed the outcome, and success rates of 71 to 88% were reported.^2,3,4

The development of surgical techniques and tools, such as the endoscope, the laser with a side-firing probe, and the steerable radiofrequency probe, made the percutaneous approach possible and helps to avoid postoperative instability.^8,9,10,11,12 Choi et al have reported an endoscopic extraforaminal approach called the targeted fragmentectomy approach.¹³ This approach has some distinct features in comparison to the regular transforaminal approach:

• More medial entry point

• Steep needle angle

• Target fragmentectomy with very little or no removal of intradiskal contents

3.2 Clinical Presentation

The clinical presentation of an EFDH differs from canalicular disk herniation in many distinct ways:

• More common in young patients (average age 40 ± 2 years)

• Radicular pain is frightfully more severe

• Less significant back pain

• Valsalva maneuvers (coughing or sneezing) do not increase the pain

• Referred groin pain, from irritation of the psoas muscle

3.3 Surgical Technique

3.3.1 Position and Anesthesia

• Percutaneous endoscopic lumbar diskectomy (PELD) by the extraforaminal approach is performed with the patient under conscious sedation in the prone position on a radiolucent operating table.

• Patient’s hips and knees should be in flexion to avoid stretching the lumbosacral plexus.

• Level marking is done before scrubbing/draping to facilitate changes in position if needed.

• Conscious sedation provides adequate analgesia and simultaneously allows continuous feedback from the patient, which helps avoid damage to neural structures.

• Midazolam is administered in a dose of 0.05 mg/kg IM half an hour before surgery, followed by 50 μg of fentanyl or remifentanil intraoperatively as necessary for pain.

3.3.2 Skin Entry Point

• Preoperative axial MRI or CT is used to approximate the distance from the skin entry point to the midline, and the needle trajectory is aimed to target the ruptured fragment while avoiding the contents of the peritoneal sac (Fig. 3.1).

3.3.3 Needle Insertion

• Target-level disk spaces are marked under the image intensifier, and they should be made parallel to each other by tilting the image intensifier in a cranial to caudal angulation.

• The spinous process and the iliac crest are marked in similar fashion.

• The point of entry, as calculated on preoperative CT or MRI axial images, is marked from the spinous process on the symptomatic side.

• The target point is the midpedicular line close to the superior end plate of the caudal vertebra on AP view and the posterior vertebral body margin on LAT view (Fig. 3.2).

• After skin infiltration with 1% lidocaine, an 18 G spinal needle is navigated under fluoroscopic guidance toward the target point.