Laminectomy for the Removal of Thoracic Ossification of the Ligamentum Flavum (TOLF) Using Ultrasonic and Conventional Osteotomes

Summary

We present a methodology for using an ultrasonic osteotome combined with a conventional osteotome for laminectomy in thoracic ossification of the ligamentum flavum. This is a relatively safe and easy-to-learn method that avoids the perioperative complications associated with the conventional method.

Abstract

Thoracic ossification of the ligamentum flavum (TOLF) is a common cause of progressive thoracic myelopathy. TOLF is typically treated with surgical decompression. A variety of surgical techniques, including laminoplasty, laminectomy, and lamina fenestration, are used for the effective treatment of TOLF. However, traditional methods are associated with a substantial risk of perioperative complications, including dural laceration and/or iatrogenic spinal cord injury. Therefore, it is important to develop an efficient and secure surgical technique for TOLF. Herein, we describe a method for laminectomyperformed at the thoracic spine using an ultrasonic osteotome combined with a conventional osteotome. This technique can reduce intraoperative complications. This is a relatively safe and easy-to-learn method that should be recommended for the treatment of TOLF.

Introduction

Thoracic ossification of the ligamentum flavum (TOLF) is one of the major causes of thoracic spinal stenosis and has been established as the primary cause of thoracic myelopathy^1,2,3. TOLF is characterized by the replacement of the ligamentum flavum by ectopic new bone formation. The incidence of TOLF is as high as 36% in Japan and 63.9% in China. Most patients show slow progression to symptomatic thoracic canal stenosis or thoracic myelopathy⁴. Decompression is the only effective treatment for TOLF once it becomes symptomatic since conservative treatment is usually ineffective⁵.

Laminoplasty, laminectomy, and lamina fenestration are three surgical techniques that have been demonstrated to be effective for TOLF^6,7,8. However, the surgical outcomes are not always satisfactory. The conventional methods can result in a high rate of perioperative complications such as dural laceration and/or iatrogenic spinal cord injury^9,10. Therefore, it is important to develop a more efficient and secure surgical technique for TOLF.

Here, we describe in detail a method for laminectomy of the thoracic spine using an ultrasonic osteotome combined with a conventional osteotome to resect the lamina (Figure 1). An ultrasonic osteotome is a precision tool that uses ultrasonic oscillations in its blade to selectively cut mineralized tissue, preventing collateral tissue damage¹¹. The technique presented herein is a relatively safe and easy-to-learn method that should be recommended for the treatment of TOLF.

An ultrasonic osteotomy system is designed to cut hard bone structures effectively while preserving soft tissues by converting the electrical input signal into vertically mechanical oscillations at an amplitude of 0-120 µm and a frequency of 39 kHz. The system consists of a power unit, a handpiece, several tips, and a footswitch. An irrigation pump is also integrated into the system, and this delivers saline to the cutting edge to reduce local thermal necrosis.

Presented here is a case of 57 year old male patient who presented with lower limb weakness with unsteady walking for 3 years. The symptoms were more pronounced on the right side. Physical examination revealed that the patient's muscle strength grade¹² was 5 (barely detectable weakness) for both the lower limbs. Additionally, numbness of the skin occurred when acupuncture was applied below the left inguinal plane, hypoesthesia was observed when needling the skin in the saddle area, the deep tendon reflexes were slightly increased in both lower limbs, and the Babinski sign¹³ was positive. X-ray, CT, and MRI showed thoracic ossification of the ligamentum flavum at T10-11. The preoperative data are presented in Figure 2.

Protocol

Ethical approval was obtained from the Medical Ethics Committee of the authors' hospital. Informed consent was obtained from each patient.

1. Inclusion/exclusion criteria and preoperative preparation

1. Include patients with the following preoperative symptoms: unable to walk steadily, numbness of the lower limbs, atrophy of the lower limbs, leg weakness, uncontrolled movement of the lower extremities, or sphincter dysfunction, etc., as well as signs and imaging data consistent with thoracic myelopathy.
2. Exclude patients based on the following criteria: the presence of cervical spinal stenosis or lumbar spinal stenosis (confirmed by MRI), thoracic disk herniation or ossification of the posterior longitudinal ligament (confirmed by CT), fracture, or an infection or tumor of the spine.
3. Place the patient in a prone position under general anesthesia.
4. Conduct neurophysiological monitoring involving somatosensory evoked potentials (SSEPs) and motor-evoked potentials (MEPs) throughout the surgery.
5. Identify the TOLF levels with the C-arm before the operation.

2. Incision and approach

1. Disinfect the surgical area using povidone-iodine (PVP-I), and drape the area with sterile surgical towels.
2. Identify the involved levels of the TOLF preoperatively using the C-arm X-ray machine.
3. Make a longitudinal midline incision over the spinous processes using a scalpel, extending from the spinous process above to the spinous process below the level of the TOLF.
   NOTE: One segment is about 10 cm long. The incision should extend from the spinous process above to the spinous process below the level of the TOLF.
4. Expose the posterior bony structure, including the spinous processes, bilateral lamina, and zygapophyseal joints of the involved levels using a unipolar electrotome.
5. Determine the pedicle screw entry points (the intersection between the midlines of the facet joint and transverse process). Insert pedicle marker pins to mark the pedicle screw entry points, and use these as a reference for the lateral border of the thoracic spinal cord.
6. Define a rectangular decompression zone as the area between the midpoint of the facet joints bilaterally and between the inferior portions of the superior lamina (beneath the caudal edge of the pedicle, which can be located by the pedicle marker pins) and the superior portions of the inferior lamina (above the cranial edge of the pedicle) of the involved TOLF segments (Figure 3).

3. Decompression

1. Remove the spinous processes, along with the supraspinous and interspinous ligaments, using a bone rongeur from the cranial to the caudal end of the decompression zone. Usually, maintain a part of the spinous process to help in removing the lamina.
   1. Irrigate the incision with saline to identify bleeding sites, and block any bleeding sites with sterilized medical styptic gauge on the residual supraspinous.
2. Use an ultrasonic osteotome to cut the lamina horizontally on the cranial and the caudal ends of the decompression zone and longitudinally between the midpoint of the facet joints bilaterally. Perform the cutting until the surgeon feels the lamina has been cut through (The cutting can be done multiple times).
3. Use a conventional osteotome to lever the lamina upward and turn it from side to side. A cracking sound of the bone indicates that the lamina has been completely cut off (Figure 4).
4. After the lamina has been loosened, use one or two towel clamps to clamp the root of the spinous process, and elevate the entire lamina carefully. When there is adhesion between the ossified tissue and the dura mater, use a nerve dissector for disattachment.
5. Trim the remaining articular process and the edge of the lamina on both sides with Kerrison rongeurs to ensure full decompression.

4. Internal fixation

1. After thorough hemostasis with bipolar electrocoagulation and styptic cream, cover the dural surface with a gelatin sponge, or fluid gelatin, and neurosurgical sponge (e.g., Cottonoid). Then, replace the pedicle marker pins with pedicle screws.
2. Connect the screws with titanium rods, and tighten the screw nuts.
3. Mince the bone fragments from the vertebral lamina, and implant the fragments bilaterally between the transverse processes. Throughout the operation, achieve hemostasis using bipolar electrocoagulation and styptic cream.

5. Postoperative treatment

1. Perform Jackson-Pratt drainage routinely for 24-48 h in patients without dural tears¹⁴. Administer dehydration management and neurotrophic medications after the operation.
2. Administer intravenous methylprednisolone (40 mg) for 3 days.
3. Instruct the patients to perform rehabilitation exercises to help functional recovery.

Results

Representative case results
On the first postoperative day, the CT scans revealed that the ossification had been fully removed, and the spinal cord had been completely decompressed (Figure 5). The patient could walk steadily. The muscle strength of both lower limbs was 5. The patient was discharged 3 days after the operation.

A total of 71 patients were enrolled in the study. All surgeries were carried out satisfactorily. The mean duration of ...

Discussion

Laminectomy is the conventional treatment method for thoracic ossified ligamentum flavum. However, the improper use of traditional bone-cutting equipment, such as high-speed drills and revolving burrs, can result in nerve thermal injury, grasping the soft tissue, tearing the dura mater, and mechanical injury^15,16,17. An ultrasonic osteotome is a novel bone-cutting tool used for precise osteotomies. This device allows for bone di...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
C-arm X-ray machine	GE	20192060063	/
Cera styptica	Johnson&Johnson (China) Medical Equipment Co., Ltd	W810T	/
Conventional osteotome	Suzhou qingniu medical instrument co.	10012.01	/
Cottonoids	Piaoan Holding Group Co., Ltd	20182640073	/
Fluid gelatin	Johnson&Johnson (China) Medical Equipment Co., Ltd	20183142459	/
Gelatin sponge	B.Braun Melsungen AG	20163642299	/
Jackson–Pratt drainage	Suzhou Weikang Medical Equipment Co., Ltd	20162140955	/
Kerrison Rongeurs	Jinzhong Medical Instruments Co., Ltd	2100888	/
Nerve dissector	Jinzhong Medical Instruments Co., Ltd	p23110	/
Pedicle screw	Medtronic	76446545	/
Towel clamps	KEWEIDUN	10058468134417	/
Ultrasonic Osteotomy Surgical System	SMTP Technology Co.	FD880A	/
Unipolar/bipolar electrotome	Shanghai Hutong Electronics Co., Ltd	20143251899	/