Percutaneous Endoscopic Lumbar Diskectomy with Foraminotomy

5 Percutaneous Endoscopic Lumbar Diskectomy with Foraminotomy

Akarawit Asawasaksakul, Gun Choi, and Alfonso García

5.1 Introduction

Herniated nucleus pulposus is one of the most common spine problems in the modern world, and it can be treated endoscopically, but there are some challenges in the endoscopic technique for treating difficult or complicated herniations, such as in the case of highly downward-migrated or upward-migrated disks or in patients with a narrow foraminal diameter. The main challenge is the space limitation that prevents tilting the scope and visualizing all the related structures and that limits the trajectory of the endoscopic instruments. In this situation, foraminoplasty is a great help, because it enlarges the foraminal diameter to accommodate the need for space (Video 5.1).

5.2 Foraminal Anatomy

5.2.1 Normal Arrangement

Before attempting foraminoplasty, knowledge of normal foraminal anatomy is crucial for surgical planning and preparing for unexpected situations. See Chapter 1 for a complete discussion of the anatomy.

Because the exiting nerve root courses underneath the cephalad pedicle, the exiting root can be visualized on the surgeon’s left in the left transforaminal approach. Vascular structures usually run along the nerve root and are rarely encountered in normal situations. Lateral extension of the ligamentum flavum can also be clearly visualized through the endoscope.

5.2.2 Possible Obstacle

Foraminal cut MRI is very helpful in determining what to expect during the procedure and which wall of the foramen will need to be partially removed. The considerations include disk position, the size of the foramen, and whether any bony part of the foraminal wall impinges on the nerve root. For example, if the disk is highly downward-migrated, partial caudad pediculectomy should be considered to allow better angulation for the endoscopic procedure, or, if are there any bony spurs from the posterior vertebral body, if the ventral part of the superior articular process impinges on exiting nerve root, or if the foramen is too small to accommodate the endoscope, removal of the impingement together with enlargement of the foraminal diameter is important.

Foraminal vessels, especially arteries, should also be kept in mind for potential bleeding. An artery that is situated in the inferior third of the foramen is the most at risk.

5.3 Migrated Disk Herniation

We usually use posterior marginal disk height to determine the extent of migration. If the disk has migrated more than the posterior marginal disk height as measured from the adjacent end plate level, it is considered a high-grade migrated herniation; if it has migrated less, it is called low-grade migration.^1,2,3

Most of the time that foraminoplasty is considered, the disk has gone beyond low-grade migration (Fig. 5.1).

5.4 Patient Selection

Possible indications for the procedure include:⁴

1. Predominant unilateral leg pain with or without associated back pain

2. Positive nerve root tension sign

3. Corresponding findings on CT and MRI

4. Soft disk herniation

5. Failure of conservative treatment for more than 6 weeks

Possible contraindications include:

1. Associated bony spinal stenosis

2. Calcified disk

3. Spinal instability

4. Herniation at the L5–S1 level with high iliac crest and thick transverse process

5.5 Surgical Technique

Most cases that need foraminoplasty involve downward-migrated herniation, especially highly migrated cases. With upward-migrated herniation, because the working site is in the upper, larger part of the foramen, foraminoplasty is usually not necessary.

5.5.1 Step 1: Patient Position and Preoperative Planning

• The patient is placed in the prone position with hips and knees flexed.

• Local anesthesia plus conscious sedation is preferable.

• The skin entry point can be calculated using axial MRI.

5.5.2 Step 2: Needle Insertion

• Needle insertion depends on the location of the migrated fragments, but usually the inclination of the trajectory is at an angle of ~ 30 degrees to the end plate.

• For caudal migration, the trajectory of the needle should be cephalocaudal.

Thus, the skin entry point should be cephalad to the level of the disk.

• When inserting the needle, try to aim toward the disk fragments.

• The final position of the needle should be at the medial pedicular line on the anteroposterior (AP) view for L4–L5 and below; for the upper lumbar spine (L3–L4 and above), the midpedicular line is safer to avoid neural injury, because the dural sac is larger, with more nerve tissue.5,6,7,8 On lateral view, the tip of the needle should be on the posterior vertebral line^{9,10,11,12,13,14,15,16} (Fig. 5.2).