Unilateral Biportal Endoscopic Decompression for Thoracic Spinal Stenosis Secondary to Ossification of the Ligamentum Flavum

0:00 Title Page

We are presenting the surgical technique of interlaminar approach for unilateral biportal endoscopic decompression in patient who had thoracic spinal stenosis due to ossification of ligamentum flavum.

0:12 Introduction

Ossification of the ligamentum flavum (OLF), is the primary cause of thoracic spinal stenosis [1]. particularly prevalent in East Asian populations with a higher incidence noted in Korea and China [2]. OLF often associated with other spinal conditions, notably lumbar and cervical canal stenosis [3]. This condition, often accompanied by local thoracic pain and progressive myelopathy, necessitates immediate medical attention and surgical intervention [4,5].

0:37 Treatment

The treatment options range from open surgery, to minimally invasive techniques like percutaneous endoscopic thoracic decompression. Today, we focus on the unilateral biportal endoscopic (UBE) decompression, which minimizes damage to surrounding structures and enhances postoperative recovery

0:48 Advantage of UBE Decompression

UBE decompression offers a magnified surgical view under continuous saline irrigation, reducing postoperative complications such as infection, instability and back pain. This method preserves key musculoligamentous structures and facilitates complete spinal cord decompression with minimal facet violation [6].

1:20 Patient Preparation and Anesthetic Technique

Patients undergo general anesthesia and are positioned prone on a radiolucent table and Wilson frame. Intraoperative neuromonitoring [7] is utilized to detect any potential damage to the spinal cord, with optimal hydrostatic pressure maintained between 30–50 mmHg to minimize risk. In this case, we use gravity to control water pressure.

1:40 Surgical Instrument

In preparation for surgery, we assemble key instruments: a 0°, 4-mm endoscope for visualization; shavers and drills, including a 4- or 5-mm diamond cutting burr; radiocrequency probes with a 90°, ball-tip for precise tissue management; a curette for scraping; and a scalpel handle with serial dilators to establish the surgical pathway.

2:04 Surgical Approach and Steps

We first mark the correct spot on the surgical level by putting a needle where we plan to operate. We then use a C-arm fluoroscope, to check the needle's position. After that, we inject a methylene blue. When we see the dye at the place we're working, it confirms we have the right spot for the surgery.

We start with 2 incisions on medial of the upper and lower pedicles—1 for the endoscope and 1 for the instruments. Then, we gently create a tunnel using a scalpel with a blunt tip and a dilator, a tool that helps enlarge the tunnel. Finally, we place a plastic cannula into both incisions. This keeps them open and allows easy access for the endoscope and surgical instruments during the procedure.

While making working space, we ensure that both surgical instruments are precisely positioned over upper lamina and interlaminar space.

2:54 Bone Drilling Stage

We start drilling at the ipsilateral spinolaminar junction and proceed until the spinal canal's midline is discernible, which can be recognized by the ligamentum flavum's midline gap, resembling a butterfly-like figure. Following this visual guide, we continue to drill at the 4 sides where the ligamentum flavum is anchored, allowing us to fully detach and remove it.

3:16 Drilling Zone

We categorize the drilling areas by risk level. The 'safe zone' in green is just next to the medial border of the pedicle and extends beyond the lamina's attachment. Here, drilling is generally safer. The 'intermediate risk zone,' shown in yellow, covers the ligamentum flavum areas where there's no spinal compression. The 'high risk zone' in red indicates areas of thoracic OLF, where the spinal cord is compressed.

We adapt to these zones with a range of drill tips, chosen for their ability to safely navigate through each area. We initiate drilling in the safe zone, which is clear of critical structures, then proceed cautiously into the intermediate zone, taking care not to compress the spinal cord.

4:01 Ligamentum Flavum Removal

With all margins of danger identified, we meticulously confirm the boundaries before proceeding with the removal of the thoracic ossified ligamentum flavum. Our goal is to prevent early exposure of the dura and avoid drilling directly into ossified regions, which could be isolated.

To mitigate the risk of injury, sharp tools are set aside in favor of blunt instruments. These tools are carefully maneuvered to lift the ligamentum flavum away from the delicate spinal cord, ensuring a safer removal process.

4:32 In Case of Severe Stenosis

In situations where we encounter ossification of the dura along with OLF or significant narrowing of the spinal canal, our surgical objective is to simultaneously remove the ossified layers while carefully preserving the arachnoid membrane. Utilizing a water-based surgical approach assists in gently separating the layers of the arachnoid from the dura. This meticulous preservation is key to preventing leaks of cerebrospinal fluid, ensuring that the patient’s recovery after surgery proceeds without unnecessary delays.

5:00 Case Presentation

We are presenting the case of an 81-year-old male experiencing ataxia, along with numbness and weakness in his lower extremities for the past 2 months. Physical assessment shows an ataxic gait, inability to walk without assistance, diminished leg muscle strength, reduced sensation below the T12 level, and loss of proprioceptive sensation in both legs.

5:21 Preoperative Imaging

The preoperative imaging reveals a ossification of ligamentum flavum in the central canal of T9–10 region, resulting in severe central canal stenosis of thoracic spine. The magnetic resonance imaging (MRI) also showed the spinal cord signal change at the affected level.

Endoscopic Video

5:38 Bone Drilling Step

We initiate drilling at the ipsilateral spinolaminar junction. We advise starting with the outer cortex, then proceeding to the cancellous bone, and finally the inner cortex. This approach helps prevent jamming of bone and instruments during the surgery. We continue drilling until the midline gap of the ligamentum flavum becomes visible.

6:01 Identification of Midline

Once the midline of the ligamentum flavum and spinal canal is confirmed, we continue with bone drilling toward the safe zone. This includes the 4 attachment sites of the ligamentum flavum: the medial part of the contralateral superior articular process (SAP) or just lateral to the medial border of the pedicle, the upper part of the lower lamina, the medial part of the ipsilateral SAP, and the upper lamina.

During drilling, it is important to avoid pressing on the spinal cord and the ligamentum flavum to prevent any additional damage.

6:38 Thinning the Attachment Site

After all borders of the ligamentum flavum are clearly visible, we carefully drill at the attachment sites, thinning the bone until it is sufficiently detached from its insertion and can be easily removed with a curette.

The drilled and thinned bony margin was cut using a curette and 1-mm Kerrison rongeur along each attachment site.

7:10 Ligamentum Flavum Removal

We carefully removed the detached laminar flap and the attached ligamentum flavum using dissectors and a punch, working from the ipsilateral SAP and upper lamina to the contralateral SAP and lower lamina. During this process, caution is exercised to avoid damaging any adhesions between the dura and ligamentum flavum. If necessary, small Penfield elevators or blunt dissectors can be employed to gently separate any adhesions before completing the removal.

After we completely removed the ligamentum flavum, we trimmed the sharp bony edges and coagulated the bleeding soft tissue and bone. We also placed a vacuum drain to prevent postoperative epidural hematoma.

8:36 Postoperative Imaging

Following the en bloc removal of the ossified ligamentum flavum, depicted in the lower right image, postoperative imaging confirms the total excision of the OLF. The MRI show full decompression of the spinal canal and expansion of the dural sac, with the integrity of the facet joints maintained. Despite these improvements, postoperative images indicate persistent spinal cord signal changes.

8:59 Surgical Outcome

The operation, lasting about 60 minutes with minimal blood loss, demonstrated no immediate perioperative complications. Postoperative evaluations showed improved back pain and proprioception, with the patient able to ambulate independently using a walker by the second postoperative day.

9:15 Conclusion

In our conclusion, UBE surgery stands out for its muscle and facet joint preservation, offering stabilization benefits. With preoperative imaging, we pinpoint safe and dangerous zones, allowing for safer and more efficient surgical procedures. Depending on the severity of the OLF, we employ various removal techniques, from piece-meal to en bloc, tailoring our approach to each case.