How to perform a lumbar microdiscectomy

Laminotomy

The goal of laminotomy is to remove enough bone to release the underlying ligamentum flavum from its attachments on the operative side and access the herniation site.

The laminotomy size is determined by ligamentum flavum attachments: superiorly to the anterior L4 lamina at mid-height, and inferiorly to the superior L5 lamina margin. Medially, the spinous process base serves as the landmark. Laterally, the pars interarticularis should be preserved.

1. Laminotomy is performed using a high-speed burr requiring precise control of bone thickness, or more safely with Kerrison rongeurs that remove controlled bone bites. The lamina can be thinned with a burr and completed with Kerrison, or performed entirely with Kerrison alone.

2. The drilling of bone is started at the base of the spinous process along the inferior edge of the L4 lamina. This starting point enables following the lamina-flavum interface cranially, maintaining the ligamentum flavum intact at this point. The inferior lamina bone averages 6-8 mm thick, varying between individuals.

3. Drilling, or alternatively using Kerrison rongeurs, proceeds cranially with controlled passes progressively thinning the bone.
   
   The ligamentum flavum thins as it approaches its attachment point at approximately the midpoint of the superior lamina, making it a particularly vulnerable area for dural injury, so precise control with the instrument is needed.
   
   
   

4. Irrigation removes bone debris, enhancing visualization throughout this process.

5. When the laminar bone is breached, the yellow hue of the ligamentum flavum becomes visible.

6. A dissector is used to verify detachment of the superior attachment of the ligamentum flavum. Often, the separation of the flavum from its laminar attachment is also visually apparent.

7. The laminotomy is completed superiorly using a Kerrison rongeur until the ligamentum flavum is fully detached from its superior attachments.

8. A dissector is used to separate the inferior attachment of the ligament from the superior edge of the L5 lamina.

9. When the ligament is breached, the inferior attachment is released fully by taking small bites with the Kerrison of the L5 laminar bone, which is relatively thin, 1-2 mm, at its superior portion.

10. The ligamentum flavum is now free from its superior and inferior attachments.

Removing the ligamentum flavum

The goal is to detach the ligamentum flavum medially and laterally and remove it to gain access to the spinal canal.

1. A dissector is used to carefully separate possible adhesions of the flavum to dura.

2. Complete removal requires mobilizing the lateral attachment by dissecting along the bone-flavum interface, typically necessitating removal of 1-2 mm of the medial facet edge. Care must be taken to preserve the pars interarticularis of the posterior vertebral arch when extending the laminotomy laterally.

3. A blunt-tipped nerve hook is used to free the remaining medial attachments and verify that no adhesions between the flavum and dura exist.

4. In visual control, the Kerrison is used to remove the final medial attachments.

5. In most cases, the ligamentum flavum is not removed as a single piece, as seen here, but rather resected in multiple segments.

6. After the removal of the ligament, epidural fat, and typically also the dural sac, becomes visible underneath, and access to the spinal canal is gained.

Exposing the dural sac and the nerve root

After access to the spinal canal has been made, the goal is to expose the lateral margin of the dural sac and the shoulder region of the traversing L5 nerve root, where it emerges from the sac.

These structures need to be exposed enough to allow their safe medial retraction, providing access to the herniated disc material located ventrally.

1. Residual ligamentum flavum and partly the medial edge of the facet joint are still limiting the initial visualization of the dural sac. The Kerrison is used to obtain exposure laterally while keeping the neural structures protected.

2. The ball tip hook can be used to gently explore the spinal cavity anatomy to locate the traversing nerve root and the herniation.

3. Some of the epidural fat is removed to provide better visualization of the dural sac.

4. As additional tissue is carefully removed from the medial facet inferiorly, the traversing L5 nerve root begins to emerge. A ball-tipped dissector is used to gently protect the neural structures at all times when working with the Kerrison near the neural structures.

5. Adequate exposure has been achieved when the traversing nerve root and the lateral margin of the dural sac are clearly visualized and can be gently retracted medially from the shoulder region of the nerve root, revealing the herniation site underneath.

Retracting the dural sac and nerve root

Medial mobilization of the neural structures is performed at the shoulder level of the nerve root. This level of retraction provides optimal exposure to the underlying disc space, where the herniation is located in this case.

1. Retraction is applied gently at the shoulder level of the nerve root with a retractor, just enough to reveal and access the herniation site.
   
   Gentle handling is crucial to prevent dural tear or neurological stretch injuries. If the neural elements resist mobilization, this typically indicates compression by the herniated disc material. In such cases, additional working space can be created by extending the exposure laterally with careful resection of the medial facet margin, rather than applying excessive retraction force.
   
   

2. The neural elements are now adequately retracted and the disc herniation site is in view.

Exposing the disc herniation site

The visible surface of the herniated disc should be cleared and any overlying veins coagulated. This is done to ensure that no neural elements remain in the incision field and to prevent obscuring bleeding when the disc capsule, or annulus fibrosus, is opened.

1. Suction is used to maintain visibility.
   
   

   Bipolar electrocautery forceps coagulate the overlying small veins.
   
   

2. With coagulation complete and neural structures protected, the herniation site is now prepared for safe incision of the annulus fibrosus.

Removing the hernia

The goal is to remove the herniated disc fragment and decompress the nerve root, not to evacuate the disc space itself. In a contained disc herniation, the extruded nuclear material remains covered by intact but bulging annular fibers or the posterior longitudinal ligament. A precise incision through this outer layer is required to access the herniated nucleus pulposus.

1. A small incision is made on the annulus using a long bayonet-handled blade, while the neural elements are protected medially.

2. The herniated disc fragment is grasped with pituitary rongeurs and carefully mobilized to release it from adhesions, maintaining awareness of potential connections to the disc space.

3. Once the fragment is freed from surrounding tissue, it is extracted with the help of another pair of rongeurs.

4. The extracted material consists of herniated nucleus pulposus.

5. All herniation fragments should be extracted from the pocket.
   
   Occasionally, a communication exists between the herniation cavity and the intervertebral disc space. Only loose fragments at this junction should be carefully extracted. Intrusion into the actual disc space must be avoided, as the unnecessary removal of intact nucleus pulposus can lead to disc height collapse, altered biomechanics, and increase the risk of recurrent herniation at the same level.
   
   Advancing too far anteriorly into the actual disc space carries additional rare but serious risks, including potential injury to major vascular structures such as the aorta, iliac vessels, and inferior vena cava, which lie directly anterior to the anterior longitudinal ligament of the lumbar spine.
   
   

Verification of decompression

The herniation pocket should be thoroughly explored to reduce the risk of incomplete hernia removal and residual compression.

1. The ball-tipped probe gently palpates beneath and around the neural structures to confirm adequate decompression.

2. The annular defect and surrounding area are probed to ensure removal of extruded disc fragments while preserving intact nucleus pulposus.

3. The retractor is removed and the successful decompression is verified by observing unrestricted passage of the neural structures. Typically, pulsation of the dural sac resumes once decompression has been achieved.

4. A probe is passed under the bony margins, ensuring no residual compression remains.

5. Fluoroscopy with a radiopaque marker positioned at the surgical site documents the level of disc herniation addressed.

Hemostasis

Before closure, careful evaluation of possible bleeding sources is essential to prevent postoperative epidural hematoma formation that can compress the nerves, requiring emergency reoperation for evacuation to prevent permanent ischemic damage.

1. Evaluation of hemostasis.

2. Hemostatic agents are not applied routinely but can be used to address small venous oozing, as is done here.

3. In cases of concern about complete hemostasis, a surgical drain can be placed to prevent hematoma accumulation into the epidural space.

Closure

1. Closure begins with approximating the fascia with non-absorbable thread.

2. The subcutaneous layer is closed with absorbable thread in one to two layers, depending on its thickness.

3. The skin can be closed using staples, absorbable sutures, or non-absorbable sutures.

4. The wound is covered with wound tape.