Modified Posterior Vertebral Column Resection for Patients with Thoracolumbar Kyphotic Deformity

Summary

We describe a modified technique for resecting the posterior vertebral column unilaterally based on a modified trephine for patients with thoracolumbar kyphotic deformity.

Abstract

Old compression vertebrae fracture or congenital kyphoscoliosis with abnormal vertebral body development and other diseases that invade the spine may cause severe thoracolumbar kyphotic deformity, often accompanied by intractable low back pain or compression of the spinal cord, leading to severe neurological symptoms or even paralysis. If conservative treatment cannot relieve the symptoms or correct the deformities, surgical treatment is usually needed. For severe kyphotic deformity, reconstruction of the physiological curvature and rigid fixation determine the prognosis of the patients. Osteotomy and orthopedics are the standard procedure for deformities with severe compression of the front and middle column, but the trauma to the patients is high, with a long operation time and massive blood loss. To avoid these disadvantages, we have developed a modified technique to remove the diseased vertebra unilaterally. In this technique, we use a modified trephine to resect the vertebral columns like in the pedicle screw technique by adding a locking instrument that can restrict the trephine to lower the risk of osteotomy and shorten the surgery time and blood loss.

Introduction

Thoracolumbar kyphotic deformity is a primary or secondary disease generally caused by vertebrae fracture, vertebral body development, ankylosing spondylitis, and spinal tuberculosis^1,2,3,4. Severe kyphotic deformity often induces spinal cord compression or severe low back pain. Once conservative treatment becomes ineffective, a surgical approach is necessary due to the complications caused by the deformity. However, the appropriate surgical treatment remains controversial.

The surgical approach to treat severe kyphotic deformity usually needs grade 3 or higher osteotomy⁵. Pedicle subtraction osteotomy (PSO) is a technique in which a three-column osteotomy can be achieved, which is reported with correction between 30° and 40°⁶. When the kyphotic deformity is more than 40°, vertebral column resection is recommended, but it can shorten the spine and induce spinal cord bulk⁷. Partial body and disc resection (BDBO; grade 4) and posterior vertebral column resection (PVCR; grade 5) require complete interception of the anterior and middle columns of the spine, which may cause huge damage to the spine with severe neurologic complications due to spinal instability in the operation or postoperative implant settlement^7,8. For general operators, the technique is hard to master, and the surgical damage is enormous for the patients. Thus, a method that is easier to perform with less damage is needed.

In this report, we introduce a refined surgical technique with a modified trephine to treat thoracolumbar kyphosis by removing the vertebral and adjacent discs unilaterally and placing a titanium mesh with autologous bone on the same side. This technique aims to minimize the damage to the patient while achieving good results. In our previous research, the refined surgical procedure showed significantly greater outcomes and reduced the damage to the spine through the preservation of the contralateral pedicle and part of the vertebral body⁹.

Protocol

The protocol follows the guidelines of the Ethics Committee of the Third Hospital of Hebei Medical University. Informed consent was obtained from the patients for including them and the data generated as a part of this study.

1. Pre-operative preparation

1. Select patients according to the following inclusion and exclusion criteria. For the patients undergoing the surgeries, the inclusion criteria are as follows: 1) nerve compression due to thoracolumbar kyphosis, 2) severe low back pain due to kyphosis, 3) patients with Kummell disease, 4) kyphosis deformity left over by a cured infectious disease. The exclusion criteria are as follows: 1) bone destruction due to a spinal tumor, 2) infectious diseases of the spine in the active phase.
2. After the administration of general anesthesia with endotracheal intubation, place the patient on the operating table in the prone position.
3. Use a C-arm to localize the lesioned segment. Mark and label the location to indicate the lesion and the adjacent upper and lower vertebral bodies and make an incision trace. Then, disinfect the surgical area with iodine and alcohol and drape with sterile sheets.

2. Lesion exposure

1. Make a median dorsal incision centered on the diseased vertebra with a scalpel, covering two vertebral bodies above and below. To ensure the pedicle screw can be placed in, keep the length of the incision longer than the two vertebrae adjacent to the lesion on each side.
2. Use a scalpel to cut the skin and subcutaneous tissue vertically along the mark. Use bipolar coagulation to stop the bleeding. Then, use an electrocoagulation electrotome to separate the latissimus dorsi and multifidus muscles along the muscle attachment points until the posterior spinous process and vertebral plate are revealed.
3. Use osteoforceps to remove part of the facet joints of the two vertebrae above and below the lesion until the articular surface is exposed completely. Then, use the positioning needle to confirm the correct position of the pedicle screws under C-arm guidance.
4. Choose the entry point 3 mm caudal to the junction of the transverse process in the thoracic vertebra¹⁰; the entry point of the lumbar vertebra is the intersection of the horizontal line of the transverse process' midpoint and the vertical line of the superior articular process.
5. Insert eight pedicle screws bilaterally in the upper and lower segments using a reaming probe to expand the path. Depending on the disease, insert another pedicle screw on one side of the lesioned segment. If the patient suffers from osteoporosis, use bone cement-injectable cannulated pedicle screws to strengthen the vertebral bodies.
6. Place a temporary fixation rod opposite to the osteotomy side on the pedicle screw caps, and screw and fasten the nuts. Then, use a rongeur to excise the lesioned segment's spinous process.
7. Next, use the laminectomy rongeur to remove the lamina adjacent to the spinous process and the inferior articular process on the osteotomy side. Following these procedures, use the rongeur to cut off the transverse process on the same side.
   ​NOTE: The removal of the rib head is needed for better exposure of the thoracic vertebrae.

3. Deformity correction

1. Use a modified trephine (Figure 1) to perform the osteotomy in the surgery^9,11.
   1. First, insert the pedicle probe into the lesioned vertebra. Then, use a modified trephine to remove the bone by twisting the handle into the vertebra. When the top of the trephine reaches the tip of the probe, the locking instrument will restrict its movement and prevent the serrated top from injuring the anterior tissue.
2. Hold on to the trephine and probe and slowly pull them out. Collect the cancellous bone in the trephine for later use. Then, repeat the same procedure to remove the bone quickly. Sometimes, the bone may not come out with the trephine; use a nucleus pulposus clamp to remove it.
3. By changing the angle of the probe and making sure the trephine does not injure the nerves, remove the contralateral bone, preserving the vertebral arch and part of the bone.
4. After the removal of most of the bone roughly, use the laminectomy rongeur and nucleus pulposus clamp to remove the remaining small cancellous bone fragments and discs. Then, use a curette to scrape the upper and lower endplate cartilage. When the space is large enough to implant the titanium mesh, the osteotomy is complete.
5. Under the isolation of the dura by the nerve dissector, use the reverse curette and osteotome to remove the posterior wall of the vertebra. Once the compression to the spinal cord is relieved, gently pull the spinal cord into a position where the titanium cage can be safely implanted. Be careful not to damage the spinal dura mater to avoid cerebrospinal fluid leakage.
6. Remove the temporary fixation bar and change it to an orthopedic rod (pre-corrected to the proper curvature), and screw and fasten the nuts on the opposite of the osteotomy.
7. Fill an appropriately size titanium cage with the amputated autologous bone, and then place it in the correct position to prevent forward flexion of the spine. Implant the autologous fragmented bones peripherally.
8. Place another fixing rod with the same curvature as the rod placed previously on the osteotomy side, and screw and fasten the nuts.

4. Closing the incision

1. Use a large amount of saline to flush the operative field and stop active bleeding with bipolar electrocoagulation. Then, use gelatin sponges to fill the void and insert one or two closed suction drains to prevent postoperative hematoma.
2. Close the incision layer-by-layer and ensure that each layer is not sutured to the drains. Use interrupted suture to suture the muscle and continuous suture to close the fascia by using absorbable suture material (size 1-0 for muscle and deep fascia, size 2-0 for superficial fascia). Use a skin stapler to suture the skin.

5. Post-operative care

1. Measure the blood loss through the drain by observing the blood in the drainage bottle each day. The surgeons should also evaluate hidden blood loss to make sure the patients can obtain fast recovery¹². Remove the drain when the blood loss is less than 50 mL per day.
2. Allow patients to walk with a thoracolumbosacral orthosis if no venous thromboembolism is detected by a deep vein ultrasound scan. The orthosis is usually used for more than 3 months.

Representative Results

About 330° decompression can be achieved by using the unilateral PVCR technique. The transverse process and the rib head need to be removed to make sure the abduction angle is enough to remove the contralateral bone.

By using the modified trephine, the bone of the diseased vertebrae can be removed easily by rotating it with mild stress. When the trephine is locked, one should pull out the trephine and probe together, and then a cylinder of cancellous bone can be obtained (Figure 2).

Not all patients require a pedicle screw implantation in the osteotomy segment. For some patients with mild vertebral compression and preoperative computed tomography showing there is enough space to implant a pedicle screw, the screw can be implanted on the opposite side of the osteotomy segment. The screw does not need to be taken out once it is implanted because instability can happen without screw fixation. If a patient is eligible for the implantation, it means the patient's segment that needs osteotomy has enough bones. The range of osteotomy can be reduced appropriately on the opposite side as long as it does not interfere with the osteotomy side.

In previous studies, compared to traditional PVCR, unilateral PVCR achieved a satisfactory result but reduced the operating time (174.6 min ± 26.7 min vs. 226.4 min ± 32.6 min), the blood loss (870.3 mL ± 92.5 mL vs. 997.4 mL ± 107.3 mL), and the incidence of nerve root impingement (4.3% vs. 8.7%)¹³. With the use of the modified trephine, we further shortened the osteotomy time and gained satisfactory treatment results¹¹. In addition, we were able to combine the unilateral PVCR technique and modified trephine to remove the lesions and rebuild spinal stability for patients with Kummell disease (Figure 3 and Figure 4)^9,14, especially for patients with kyphotic deformity and obvious nerve-oppressed symptoms.

Figure 1: The modified trephine with the locking instrument. Use the probe to stab into the cancellous bone, and then rotate and push the trephine until it is locked. Put on the handle, and then pull out the probe and trephine together. This figure has been modified from Wang et al.¹¹. Please click here to view a larger version of this figure.

Figure 2: The bone removed by the trephine. Grab the handle of the probe and pull it out, and a columnar bone can be harvested. This figure has been modified from Wang et al.¹¹. Please click here to view a larger version of this figure.

Figure 3: Preoperative images of the unilateral PVCR technique. Preoperative images of X-ray, computed tomography, and magnetic resonance imaging of a patient with Kummell Disease. This figure has been modified from Yang et al.⁹. Please click here to view a larger version of this figure.

Figure 4: Postoperative images of the unilateral PVCR technique. Postoperative images of X-ray and computed tomography of a patient with Kummell Disease after the treatment of modified posterior vertebral column resection. This figure has been modified from Yang et al.⁹. Please click here to view a larger version of this figure.

Discussion

The steps of placing the temporary fixation rod and the deformity correction mentioned in the protocol are the critical steps during the surgery. By preserving one side of the pedicle and loading a temporary fixation bar, stability is preserved during the osteotomy procedure. During the surgical progress of the deformity correction, the nerve roots must be protected to prevent serious postoperative neurological complications. If the surgeons are uncertain about the location of the nerve roots, the exposure of the nerve roots after removing the vertebral plate and the articular process is necessary. When removing the wall of the vertebral canal, blood loss can be huge due to the venous plexus. Although blood loss may be reduced using bipolar electrocoagulation to stop the bleeding, accompanied by gelatin sponges and brain cotton pieces layer-by-layer, the long surgery time is a big problem. The surgeons can prepare blood transfusion in advance and use an autologous blood transfusion system because of the long operation time and huge blood loss. If a dural matter tear happens during the surgery, the surgeons can use dural suture to fix the damage; a pedicled multifidus muscle flap is also useful according to previous research¹⁵. To prevent damage to the abdominal aorta or thoracic aorta, surgeons must be careful in removing the bone near the anterior longitudinal ligament. In addition, a C-arm can be used to detect the position of the pedicle probe to avoid over-insertion damage caused by the serrated top of the trephine. The cancellous bone collected by the trephine can be directly used in the titanium cage for the autologous bone graft.

The unilateral PVCR technique shortens the operation time compared to the classic PVCR as only one side of the vertebral pedicle access is required. Subsequently, the unilateral PVCR technique reduces the stimulation to the spinal cord and nerve roots. By using this approach, the contralateral vertebral pedicle and parts of the vertebra can be saved to increase the stability and bone fusion rate compared to total laminectomy. However, this technique is solely based on classic PVCR with the innovation of the tools. Therefore, similar to the original PVCR, the implant-related complications would still happen due to osteotomy¹⁶.

With the use of modified trephine, bone excision becomes easier and more controllable than the traditional use of a high-speed drill and osteotome. Surgeons with the ability of pedicle screw placement can master the refined technique quickly. The unilateral PVCR technique with the modified trephine provides a quicker way to resect and collect the bone, shortening the surgical time for surgeons to do more delicate operations. It is shown that the reconstruction of physiological curvature and the correction of spinal deformity can alleviate patients' symptoms, including low back pain¹⁷. Therefore, this unilateral PVCR technique can reconstruct spinal stability and rigid fixation to achieve satisfactory treatment effects with less trauma to the patients.

Materials

Name	Company	Catalog Number	Comments
Adhesive	Biatain	3420	12.5 cm x 12.5 cm
Bipolar electrocoagulation tweezers	Juan'en Medical Devices Co.Ltd	BZN-Q-B-S	1.2 mm x 190 mm
Bone wax	ETHICON	W810T	2.5g
Curette	Qingniu	20739.01	300 x Ø9 x 5°
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°
Laminectomy rongeur	Qingniu	2058.03	220 x 5.0 x 130°
Pedicle screw	WEGO	800386545	6.5 mm x 45 mm
Pedicle screw	WEGO	800386550	6.5 mm x 50 mm
Pituitary rongeur	Qingniu	2028.01	220 mm x 3.0 mm
Pituitary rongeur	Qingniu	2028.02	220 mm x 3.0 mm
Rod	WEGO	800386040	5.5 mm x 500 mm
Surgical drainage catheter set	BAINUS MEDICAL	SY-Fr16-C	100-400 mL
Surgical film	3L	SP4530	45 cm x 30 cm
Titanium cage	WEGO	9051228	19 mm x 80 mm
Trephine	NATON MEDICAL GROUP	DJD04130	12 mm/10 mm