A Modified Eggshell Technique for Sclerosing Thoracic Disc Herniation

Summary

This protocol introduces a modified eggshell surgical technique used for treating sclerosing thoracic disc herniation.

Abstract

Sclerosing thoracic disc herniation refers to a condition in which the intervertebral disc in the thoracic region protrudes and becomes calcified, causing compression on the spinal cord and/or nerve roots. Sclerosing herniation of the thoracic disc poses a significant danger as it can lead to serious complications like paraplegia during or after surgery. Iatrogenic spinal cord injury is a common risk for individuals diagnosed with sclerosing thoracic disc herniation due to the inflexible protrusion of the sclerosing disc into the spinal canal and its adhesion to the ventral side of the dural sac. The challenging and crucial aspect of the surgery is how to safely and efficiently eliminate the hardened tissue. The eggshell method is a surgical procedure that addresses the kyphosis abnormality of the spinal column by excavating the vertebral body via the pedicles and subsequently inserting the kyphotic fracture block into the excavated vertebral body. In this article, a revised surgical method using the eggshell technique will be presented for the treatment of sclerosing thoracic disc herniation. The surgical procedure briefly involves hollowing out the anterior intervertebral space of the hardened disc tissue to create an eggshell-like structure, with the sclerotic tissue forming the posterior wall. Subsequently, the sclerotic disc tissue is pushed into the hollow intervertebral space to achieve complete decompression of the ventral spinal cord. The safety and effectiveness of this approach for treating sclerosing thoracic disc herniation have been confirmed.

Introduction

In medical situations, thoracic disc herniation is categorized into three types: central, paracentral, and lateral. Spinal cord injury (SCI) symptoms are predominant in central protrusion, whereas radicular symptoms are commonly observed in lateral protrusion. Central and paracentral protrusions account for approximately 70%. Predominant segments affected are T11 and T12 (26%), with 75% of thoracic disc herniation occurring between T8 and T12, and the subsequent thoracic vertebrae exhibiting the highest incidence^1,2,3.

When nerve compression occurs, the thoracic spinal canal typically becomes smaller than the cervical and lumbar spinal canal, resulting in reduced space for spinal cord escape^4,5,6. Once patients exhibit symptoms, many are accompanied by signs of spinal cord injury^7,8. The effectiveness of conservative treatment is generally poor, necessitating eventual surgical intervention.

The primary objective of thoracic disc herniation surgery is to alleviate pressure on the spinal cord⁸. Surgical approaches include two types - anterior and posterior approaches. Anterior surgery directly alleviates compression on the spinal cord, while posterior surgery indirectly relieves this compression. Even for skilled surgeons capable of directly removing compression from the anterior sclerotic disc, anterior surgery is technically demanding and poses a high risk to patients. Complications, including spinal cord injury, worsening symptoms, leakage of cerebrospinal fluid (CSF), and infection, were observed in a range of 9.6% to 40.8%^9,10,11.

A major factor contributing to the elevated surgical risk is the relative fragility of the dorsal subarachnoid space and the ventral spine's dura. Even slight increased backward traction on the spinal cord can lead to disastrous outcomes¹². Furthermore, detaching the dural sac from the thoracic spine and applying pressure often results in electrophysiological warning occurrences, significantly increasing the chances of spinal cord damage^13,14,15. Additionally, anterior thoracic spinal stenosis surgery often requires thoracotomy and is more traumatic.

Posterior surgery, achieved by removing the posterior structure of the spinal canal, allows the spinal cord to have a certain backward movement space, indirectly relieving compression from the sclerotic disc to the spinal cord^9,16,17. Both surgical approaches can yield certain surgical effects, but anterior surgery, influenced by the presence of lungs, blood vessels, and nerves, increases the surgical difficulty¹⁸. In contrast, posterior surgery's effect on spinal cord decompression is limited for patients^9,16,17, and complete relief of compression may not be achieved. However, the advantage lies in the absence of vital vascular nerves and organs at the back, making it easily exposed and convenient for surgical operations¹⁵. Nevertheless, there is still debate on which surgery constitutes the gold standard for thoracic disc herniation.

Severe symptoms can manifest when the spinal cord or nerve roots are compressed due to the herniation and calcification of the thoracic intervertebral disc, a condition known as sclerosing thoracic disc herniation¹⁹. Because of the typical positioning of the hardened disc on the ventral side of the spinal cord, direct visual removal of the hardened disc is often unfeasible. Our team previously reported a posterior modified eggshell surgical technique for treating sclerosing thoracic disc herniation²⁰. This modified eggshell technique, performed under direct vision, enables complete spinal cord decompression in all directions. The modified eggshell approach can completely remove the sclerotic disc, thereby reducing the risk of SCI. Treating sclerosing thoracic disc herniation with this surgical method is both safe and efficient. This article introduces and demonstrates the surgical procedure.

Protocol

This protocol has received approval and adheres to the guidelines established by The Ethics Committee of Hebei Medical University Third Hospital. Patient data were collected after obtaining informed consent from them. The inclusion criteria for patients were as follows: patients suffering from symptoms of spinal cord damage with ineffective conservative treatment, the presence of hardened tissue observed on X-ray, computer tomography (CT), and magnetic resonance imaging (MRI) on the ventral side of the spinal cord, and complete clinical data with regular follow-ups. Patients with coexisting contraindications such as infection or tumor, or those unable to tolerate the operation, were excluded from the surgery. The surgical tools and equipment used for this study are listed in the Table of Materials.

1. Preoperative preparation

1. Allow the patient to fast for 6 h and proceed with anesthesia via endotracheal intubation²⁰ following institutionally approved protocols.
2. Position the patient in the prone position.
3. Perform a double disinfection of the surgical area using povidone-iodine, followed by two rounds of alcohol. Place sterile sheets to cover the surgical site.
4. Mark the positions for surgical incisions with a marker. Place a Kirschner needle horizontally and perpendicular to the spine on the surgical area. Verify the needle placement using a C-arm fluoroscope.

2. Exposing the surgical site

1. Make an incision along the posterior midline of the designated surgical site, approximately 10 cm in length. Successively expose the skin, subcutaneous tissues, and paraspinal muscles. Completely expose the upper and lower vertebral segments²⁰.
2. Carefully peel the soft tissue away from the bone surface to prevent damage to the intercostal nerve, arteries, and veins. Expose the bony protrusion of the spine, both above and below, as well as the joints.

3. Inserting pedicle screws

1. Insert pedicle screws into the decompression section of the spinal column. Identify the intersection of the vertical line of the lateral margin of the pedicle and the midline of the transverse process as the location for inserting pedicle screws.
2. Use a rongeur to remove part of the cortical bone from the articular process where a pedicle screw is to be inserted. Establish the pathway of a pedicle screw using an awl, then use a probe to confirm the integrity of the pedicle pathway and measure the length of the pedicle screw pathway. Insert the pedicle screw into this pathway.
3. Verify the suitability of the pedicle screw instrumentation using intraoperative fluoroscopy²⁰. Ensure that the pedicle screws remain within the pedicle pathways, avoiding extension beyond the anterior edge of the vertebrae and surpassing the central axis of the spinal column. This indicates the appropriate location of the pedicle screws.

4. Posterior decompression

1. Use lamina forceps to extract the bone situated at the intersection of the vertebral lamina and the inner side of the pedicle. Employ the uncover technique to eliminate the spinous process and lamina²⁰.
2. Remove the bilateral facet joints using a rongeur to fully expose the dura mater and spinal cord (see Figure 1A and Figure 2A).

5. Modified eggshell technique

1. Use a clamp to remove the vertebral body corner and cut open the annular fibrosis with a No. 11 scalpel blade.
2. Hollow out the intervertebral disc by extracting the disc tissue from the intervertebral space, retaining only the anterior and a portion of the lateral section of the annulus (see Figure 1B and Figure 2B).
3. Employ a nerve retractor crook or hook blade to detach the adhesion between the herniated calcified disc and dura mater. Subsequently, use a reverse-angled curette to push the hardened disc tissue into the anterior intervertebral space (see Figure 1C and Figure 2C).
   NOTE: This procedure is known as the "modified eggshell procedure," and the surgical tools used are depicted in Figure 3.
4. Utilize a curved clamp to remove the hardened disc tissue.
5. To detach the hardened disc from surrounding tissues, use a grinding drill to remove the hardened tissues. If the adhesion between the hardened tissues and spinal dura mater is severe and poses a risk, consider making it 'floating' rather than attempting a risky removal.

6. Strengthening the stability of the spine

1. Fill the cages with bone harvested from the spinous, lamina, and articular processes.
2. Implant a cage vertically on both sides into the intervertebral space, maintaining a minimum distance of 0.5 cm between the back edge of the cage and the back edge of the vertebral body.
3. Secure the pedicle screw-rod system in its current position. Press the pedicle screws longitudinally along the rod and secure the rods with nuts. Prevent any minor alteration in curvature following decompression and minimize harm to the spinal cord (see Figure 1D and Figure 2D).

7. Suturing the incision

1. Check for bleeding and completely stop it using electrocautery.
2. Thoroughly clean the incision with saline. Insert a drainage set.
3. Suture the incision layer by layer. Use an absorbable suture No.7 for the fascia layer, an absorbable suture No.4 for the subcutaneous tissues, and a silk suture No.4 for the skin.

8. Postoperative procedures

1. Administer preventive antibiotics to patients for 2 days following the operation.
2. Prescribe bed rest for 1 week.
3. Initiate ambulation with a lumbar brace for patients starting at 1 week after surgery.

Results

As reported in our previous study²⁰, the modified eggshell surgery was successfully performed on 25 patients. The sclerotic tissues of four patients were extensively adhered to the dural sac, making it impossible to fully remove the tissues. However, the compression force on the spinal cord caused by the anterior sclerotic tissue was completely relieved. In two patients, dural sac rupture occurred due to the intraoperative separation of sclerotic tissue and the dural sac, but CSF leakage stopped a...

Discussion

The primary application of this surgical procedure is to achieve thorough decompression of the spinal cord from all angles, utilizing the posterior pathway of the thoracic spine. Serious complications are common in patients with thoracic disc herniation, primarily due to the anatomy of the thoracic spine. According to Min et al.¹⁸, anterior decompression using an anterior method has a definite impact but requires a challenging procedure. Furthermore, the extensive trauma it induces, substantial di...

Materials

Name	Company	Catalog Number	Comments
Bipolar electrocoagulation tweezers	Juan'en Medical Devices Co.Ltd	BZN-Q-B-S	1.2 mm x 190 mm
Bone wax	ETHICON	W810T	2.5 g
Curette	Qingniu	20739.01	300 x Ø9 x 5°
Curette	Qingniu	20739.02	300 x Ø9 x 15°
Curette	Qingniu	20739.03	300 x Ø9 x 30°
Curette	Qingniu	20739.04	300 x Ø9 x 45°
Double jointed forceps	SHINVA	286920	240 mm x 8 mm
High frequency active electrodes	ZhongBangTianCheng	GD-BZ	GD-BZ-J1
Laminectomy rongeur	Qingniu	2054.03	220 x 3.0 x 130°
Pedicle screw	WEGO	800386545	6.5 mm x 45 mm
Pedicle screw	WEGO	800386550	6.5 mm x 50 mm
Rod	WEGO	800386040	5.5 mm x 500 mm