Percutaneous Endoscopic Lumbar Diskectomy for Migrated Lumbar Disk Herniation

4 Percutaneous Endoscopic Lumbar Diskectomy for Migrated Lumbar Disk Herniation

Akarawit Asawasaksakul, Gun Choi, and Ketan Deshpande

4.1 Introduction

In the years since the introduction of the concept of percutaneous posterolateral nucleotomy by Kambin in 1973, percutaneous endoscopic lumbar diskectomy (PELD) has evolved.1,2,3,4,5,6,7 PELD is increasingly the preferred treatment for lumbar disk herniation. The transforaminal approach offers several advantages: First, it provides protection of the posterior ligamentous and bony structures, with a lower incidence of postoperative instability,^8,9,10 facet joint arthropathy, and disk space narrowing.^{2,3,4,5,11,12,13,14,15,16,17,18,19,20,21} Second, there is no interference with the epidural venous system that could lead to chronic neural edema and fibrosis.^{2,14,15,16,22} Last, epidural scarring, a common sequel to open diskectomy, and which leads to clinical symptoms in more than 10% of patients, is rare with PELD.^23,24,25

The narrow transforaminal window provides limited access that proves adequate for the removal of nonmigrated or low-grade migrated disk herniation, but the limited access may render the PELD procedure ineffective in cases of high-grade migrations.^6,7,25 Migrated intracanalicular disk herniation, especially high-grade migration, poses a greater challenge, even for an experienced endoscopic surgeon. The success of the PELD procedure depends considerably on appropriate placement of the working instruments in an optimal trajectory to directly visualize and access the migrated ruptured fragment.^19,26,27 Improper trajectory is an important cause of failure of the procedure, and the biggest difficulty encountered during retrieval of high-grade migrated disk herniation is obtaining the optimal trajectory,²⁶ because it is significantly hindered by the natural obstacles of the normal anatomy and is worsened by the degenerative changes.

Because of these limitations, foraminoplasty helps in addressing this issue. We define foraminoplasty as widening of the foramen by undercutting a ventral (nonarticular) part of the superior facet and sometimes the upper part of the inferior pedicle, along with ablation of the foraminal ligament to visualize the anterior epidural space and its contents. This can be achieved with the help of bone trephines or reamers, an endoscopic drill, endoscopic chisels, and side-firing holmium:yttrium-aluminum-garnet (Ho:YAG) laser (Video 4.1, Video 4.2, and Video 4.3).

4.2 Anatomical Considerations

Foraminoplasty is needed, especially to access high-grade migrated intracanalicular disk herniation, because of the following:

• Lumbar disk herniation is common at the lower levels, where the diameter of the intervertebral foramen is small in comparison to the diameter at the higher levels.²⁸

• Degenerative changes leading to hypertrophy, overriding of facets, and thickening of the foraminal ligament may cause additional narrowing of the transforaminal window.

Table 4.1 Obstacle structures

1	Superior articular process (SAP)
2	Cranial part of the lower pedicle
3	Osteophyte from posterior vertebral body
4	Inferior articular process (IAP)

• High-grade migrated disk herniation lies in the region of the spinal canal that is hidden from the endoscopic view by natural anatomical barriers.

• The barriers prevent direct access to the migrated fragment (Table 4.1).

• Min et al²⁹ have demonstrated that the dimensions of the working zone in the sagittal plane, specifically the base dimension, are of clinical importance in the current practice of endoscopic surgery.

• Foraminoplasty provides adequate working space for excision of the ruptured fragment under direct endoscopic vision through the enlarged foramen.

4.3 Migrated Disk Herniation

• Whether extruded or not, herniation displaced either above or below the end plate level is called migrated disk herniation.

• Migrated disk herniation is classified into two grades depending on the extent of migration.

• If the extent of migration is greater than the measured height of the posterior marginal disk space on T2-weighted sagittal MRI, it is called a high-grade migration.^26,27,30,31

• Migration smaller than the height of the disk space is classified as a low-grade migration (Fig. 4.1).³²

Fig. 4.1 The degree of migration of the herniated fragment in relation to the posterior height of the disk space.

Fig. 4.2 Anatomical change of the neural foramen (a) before and (b) after foraminoplasty.

Fig. 4.3 Partial pediculectomy. Removal of the upper and medial walls of the pedicle (a), along with the undercutting of the superior facet (b), can aid visualization of, and access to, the ruptured fragment.

Fig. 4.4 Preoperative planning. Axial MRI or CT is used to calculate the distance of the skin entry point of the needle from the midline, and the needle trajectory is aimed to target the ruptured fragment while avoiding the contents of the peritoneal sac.

4.4 Types of Foraminoplasty

Foraminoplasty is classified into two types depending on the extent of bony resection.

4.4.1 Conventional Foraminoplasty

• Conventional foraminoplasty essentially involves undercutting of the nonarticular part of the superior facet and removal of the lateral edge of the ligamentum flavum in cases of downward-migrated disk herniation.

• It involves the release of the superior foraminal ligament and the ligamentum flavum in cases of upward-migrated disk herniation.

• The need for undercutting of the facet may diminish at lumbar levels above L3–L4.

• Because the upper part of the foramen is wider than the lower part and there is no superior facet to obstruct visualization of the anterior epidural space, bone cutting is not needed in cases of upward-migrated disks (Fig. 4.2).

4.4.2 Extended Foraminoplasty (Foraminoplasty with Partial Pediculectomy)

• In severely downward-migrated disk herniation where the ruptured fragment lies in close contact with the medial wall of the pedicle, the upper part of the inferior pedicle may prevent its direct visualization.

• Removal of the upper and medial wall of the pedicle along with undercutting of the superior facet can help in visualizing and accessing the ruptured fragment (Fig. 4.3).

• The downward inclination of the endoscopic trajectory enables oblique cutting of the upper part of the pedicle.

4.5 Surgical Technique

4.5.1 Position and Anesthesia

• PELD is performed under local anesthesia with the patient in the prone position on a radiolucent table under the guidance of C-arm fluoroscopy.

• Conscious sedation with midazolam and fentanyl allows continuous feedback from the patient during the entire procedure to avoid causing damage to the neural structures.

• Midazolam is administered in the dose of 0.05 mg/kg IM 30 minutes before surgery, followed by another dose intravenously during surgery if required.

• Fentanyl dosage is 0.8 µg/kg intravenously 10 minutes before surgery, followed by additional doses intraoperatively if required.

4.5.2 Preoperative Planning

• Axial MRI or CT is used to calculate the distance of the needle’s skin entry point from the midline.

• The scans are also used to calculate the needle trajectory, targeting the ruptured fragment while avoiding the contents of the peritoneal sac (Fig. 4.4).

4.5.3 Needle Insertion Technique

• It is imperative to achieve proper placement of the needle, which is facilitated by following these guidelines:

The site of annular puncture by the needle tip should be at a medial pedicular line in the anteroposterior view and at a posterior vertebral line in the lateral view on fluoroscopic imaging (Fig. 4.5). This corresponds to the Kambin safe triangle between exiting and traversing nerve roots.

The midpedicular line should be considered for upper lumbar disk herniation (L3, L4, and above) to avoid neural injury, because the dural sac is bigger, with more nerve tissue, and lies more laterally due to the narrow width of the pedicles at the upper levels.33,34,35,36

Fig. 4.5 Fluoroscopic views showing the position of the needle tip (a) at the medial pedicle line in the AP view and (b) at the posterior vertebral line in the lateral view. Note the downward inclination of the needle trajectory on the AP view.

Only gold members can continue reading. Log In or Register to continue