Application of Cortical Bone Trajectory Screw for Treating Thoracolumbar and Lumbar Tuberculosis

Summary

This protocol describes the treatment of spinal tuberculosis with cortical bone trajectory screws. CBT screw fixation via the posterior and anterior approaches is a promising technique for the treatment of thoracolumbar and lumbar TB.

Abstract

The common form of extrapulmonary tuberculosis is spinal tuberculosis (TB). Spinal TB can lead to vertebral damage, resulting in kyphosis and neurological impairment. Debridement, bone grafting, and reconstruction are common surgical treatments for spinal TB. Spinal TB patients with anterior-middle spinal column destruction are more likely to experience loosening of internal fixation. Cortical bone trajectory (CBT) screw fixation reduces this complication probability because the entrance trajectory of CBT screws in the sagittal and axial planes substantially interacts with the cortical bone and boosts the screw-bone contact strength interface. The CBT screw insertion path is closer to the spinous process and involves less dissection of the paraspinal muscles; this approach appears to reduce intrinsic injury and postoperative pain. CBT screw is a safe and effective internal fixation method for spinal TB because it can effectively reduce the number of fixed segments, maximize spinal mobility, reduce tissue damage, and alleviate postoperative pain at the surgical site.

Introduction

The most frequent form of extrapulmonary tuberculosis is spinal tuberculosis (TB), of which thoracolumbar and lumbar TB are the common types^1,2. Spinal TB can lead to vertebral damage, resulting in kyphosis and neurological impairment³. Although anti-TB chemotherapy is crucial in treating spinal TB, surgical intervention is often necessary to correct kyphosis and recover neurological function. Debridement, bone grafting, and reconstruction are common surgical treatments for spinal TB⁴. Spinal TB is a disease that primarily results in damage to the anterior-middle vertebral column and presacral or iliopsoas abscess. As a result, many surgeons recommend posterior instrumentation, anterior debridement, and bone grafting to achieve strong internal fixation and enable complete debridement^5,6.

The pedicle screw (PS) fixation technique is considered the gold standard for spinal reconstruction because of its superior biomechanical strength⁷. Conventional PS placement utilizes a lateral route parallel to the axial plane, resulting in the contact strength of the screw-bone interface primarily depending on cancellous bone quality⁸. Individuals with osteoporosis are more likely to experience PS loosening due to bone weakening⁹. TB patients with anterior-middle spinal column injuries may also develop this condition^6,10. Cortical bone trajectory (CBT) screw fixation reduces this complication probability because the entrance trajectory of CBT screws in the sagittal and axial planes substantially interacts with the cortical bone and boosts the screw-bone contact strength interface¹¹. Therefore, CBT screw fixation of spinal TB can effectively reduce the number of fixed segments and maximize the preservation of spinal mobility, especially in the thoracolumbar region.

A previous retrospective study has compared the 3-year clinical effects of CBT screw fixation with conventional screw fixation in the treatment of lumbar TB¹². Both were good, but CBT screw fixation had a more significant improvement in postoperative VAS scores. Therefore, this study aims to further explore the clinical outcomes of CBT screw fixation in the treatment of thoracolumbar and lumbar TB, with a follow-up period extending to 5 years.

Protocol

The Ethics Committee of Hangzhou Red Cross Hospital approved the study. The patients provided written informed consent for the publication of individual clinical details and accompanying images. Patients with lumbar TB were initially diagnosed according to clinical history, clinical signs, radiographic scan results, and laboratory test results. According to the previous study^13,14, this study uses the laboratory test methods of acid-fast staining and microbiological examination of the focal tissue, and rapid liquid culture to diagnose TB. The inclusion criteria for this study were as follows: lesion limited to three or fewer adjacent segments, and the individual experienced spinal instability, nerve dysfunction, and low back pain. The exclusion criteria were as follows: more than three damaged vertebrae, severe kyphosis deformity, vertebral pedicle damage, surgical concerns, and mental disorders. Preoperatively, each patient was administered anti-TB chemotherapy consisting of rifampicin (0.45 g·kg^-1·day^-1), isoniazid (0.3 g·kg^-1·day^-1), ethambutol (0.75 g·kg^-1·day^-1), and pyrazinamide (1.5 g·kg^-1·day^-1) for at least 2 weeks based on the previous report¹². The reagents and the equipment used are listed in the Table of Materials.

1. Preoperative preparation

After general anesthesia induction, the patient was placed prone on a chest pad. The affected vertebral body was identified under C-arm fluoroscopy guidance using anteroposterior and lateral views. The surgical approach side was typically chosen based on the side with the most severe bone destruction, the side of the abscess, and the side with the most pronounced symptoms.

2. Surgical procedure

1. Exposure of the vertebra and identification of the entry point
   A posterior midline incision was centered over the affected vertebral body. The skin, subcutaneous tissue, and deep fascia were incised sequentially. The paraspinal muscle tissues, including the bilateral erector spinae muscle compartments, were dissected. The articular processes and laminae of the responsible vertebrae superior and inferior to the affected vertebra were exposed via the multifidus muscle compartment. The isthmus edge tangent was selected as the reference landmark. The entry point was the intersection of the mid-perpendicular line of the superior articular process and a horizontal line 1 mm inferior to the ipsilateral transverse process. Power instruments may be used to establish the screw pathway, such as employing a burr to open the cortical bone at the entry point.
   NOTE: The burr should be advanced through the cortex until reaching the cancellous bone interface within the pedicle. Due to the relatively hard/dense cortical bone in this region, tapping with a starter awl must be avoided to prevent iatrogenic fracture.
2. Screw placement and trajectory
   During screw placement, the sagittal angle was approximately 25°, and the lateral angle (abduction angle) was approximately 15°¹⁵. For the left pedicle projection, screws were directed from the 5 o'clock position towards the 11-12 o'clock direction. For the right pedicle projection, screws were directed from the 7 o'clock position towards the 12-1 o'clock direction (Figure 1). For lumbar CBT screws, diameters of 4.0-5.0 mm and lengths of 35-40 mm offered relatively good safety. The maximum screw length gradually increased from 32.0 mm at L1 to 35.3 mm at L4, then decreased to 34.8 mm at L5. CBT screws 30 mm in length were safe for the lumbar spine. The maximum screw diameter gradually increased from 4.5 mm at L1 to 7.5 mm at L5. Diameter 4.0 mm CBT screws are recommended for L1-L2; diameter 4.5 mm CBT screws are recommended for L3-L5.
   NOTE: The length, diameter, and trajectory angles of CBT screws must be determined through personalized and precise planning based on preoperative imaging studies.
3. Guide wire placement and fixation
   After determining the entry point, trajectory direction, and angle, a positioning guide wire was inserted into the screw path. The screw path and length were then verified under C-arm fluoroscopy guidance using anteroposterior and lateral views. After confirmation, the guide wire was removed, and appropriately sized CBT screws were inserted into the corresponding vertebral bodies. After pedicle screw placement is completed, appropriately sized titanium rods are selected and secured with the screws. Following meticulous hemostasis, two drainage tubes are placed within the incision and fixed to the skin with silk sutures. The incision is then closed in layers.
   Following the internal fixation, the operating table was then turned 20° away from the surgeon to enhance the view of the surgical area. Then, the retroperitoneal approach was performed through a small incision made in the abdominal wall along the midaxillary line. The side with more severe pathology was then selected as the surgical side, with a lumbar pad supporting the contralateral side. An incision line was marked along the path connecting the tip of the 11th rib to the pubic symphysis on the pathological side. The incision location was determined based on the affected segment and preoperative C-arm localization markings. For different segments, the incision could be shifted cranially or caudally by the height of one vertebra. For the L1-L2 segment, the head of the 11^th rib was resected for 4 cm, followed by a 4 cm anterior extension along the rib, totaling 8 cm. For the L2-L3 and L4-L5 segments, the incision location was chosen based on segmental height, starting from the mid-axillary line and extending anteroinferiorly (Figure 2).
4. Exposure and debridement of the pathological vertebra
   The psoas major muscle was dissected to expose its anterior border, revealing the paraspinal fascia. Segmental vessels of the vertebral body were ligated and coagulated. Dissection continued to expose the affected vertebral body and intervertebral disc. Necrotic bone tissue was resected using an osteotome. Residual sequestra and pathological disc material were curetted perpendicularly toward proximal and distal directions relative to the vertebral body. Necrotic tissue was cleared using suction and pituitary rongeurs. Cold abscesses surrounding the psoas muscle and affected vertebral segments were evacuated.
   NOTE: Ligation and coagulation of segmental vessels must be performed before debriding the pathological vertebral body to minimize intraoperative bleeding.
5. Hemostasis and wound closure
   Hemostasis was meticulously achieved throughout the entire incision, and the wound was repeatedly irrigated with normal saline. One drainage tube was placed within the lesion cavity, brought out through the skin adjacent to the incision, and connected to a drainage bottle at its end. The distinct layers of the external oblique, internal oblique, and transversus abdominis muscles were visible. The incision was closed in layers. The drainage tube was secured to the skin with silk sutures.

3. Postoperative management and follow-up

1. Initial postoperative assessment and wound care
   This was conducted within 24 h postoperatively to evaluate surgical wounds, monitor vital signs, and instruct patients or caregivers on proper wound care and signs of infection.
2. Drain and medication management
   Drainage tubes are removed within 24-48 h postoperatively, depending on drainage output. Antitubercular medications, analgesics, and antibiotics are prescribed as needed, with usage guidance provided.
3. Activity, rehabilitation, and follow-up scheduling
   Early postoperative activities, such as turning and leg lifts, were guided. Follow-up appointments are arranged to track healing progress, address complications, and ensure adherence to rehabilitation protocols.
4. Patient education and emergency protocol
   Resources on postoperative care and rehabilitation are provided, emphasizing medication adherence and the importance of regular follow-ups. Emergency contact information is supplied, and patients are educated on indications for urgent medical care.

Results

The mean follow-up time was 61.9 ± 9.1 months. Table 1 shows the mean operation time and intraoperative blood loss. No instances of screw loosening occurred during follow-up. All cases resulted in complete bony fusion at the final follow-up, and the mean bony fusion time was 4.4 ± 0.9 months. The mean Japanese Orthopedic Association (JOA) and visual analog scale (VAS) scores for low back pain and leg pain significantly improved during follow-up versus preoperation (Figure 3)...

Discussion

Among spinal TB cases, surgery combined with anti-TB chemotherapy can always achieve satisfactory outcomes^16,17. Conservative treatment alone cannot alleviate spinal cord pressure, improve neurological dysfunction, or avoid the development of spinal deformities¹⁸. In contrast, surgical intervention can restore spinal stability and alleviate nerve pressure, thereby contributing to disease treatment. Debridement and effective internal fixati...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Cortical bone trajectory screw	Shandong Weigao Orthopaedic Device Co., Ltd.	WGB1Z-7	Used to internal fixation
Kerrison rongeur	Shanghai Medical Instruments Co., Ltd.	P1Z0303	Used for biting dead bone or repairing bone stumps
Periosteal stripping ion	Shanghai Medical Instruments Co., Ltd.	POK01	Used to peel off or separate the periosteum and soft tissue attached to the bone surface
Power System Tools	Aesculap	GA800	Used to open the cortical bone at the CBT screw entry point
spinal rods	Shandong Weigao Orthopaedic Device Co., Ltd.	GB1Z-1	Used to connect screws