This study describes the application of the O-arm intraoperative imaging system in odontoid fractures.

Odontoid fractures account for a large proportion of cervical spine fractures in the elderly, causing pain in the occiput and the back of the neck and restricting neck movement. Anterior cervical screw fixation is a common surgical procedure to treat odontoid fractures. Due to the special location and complex anatomy of the odontoid, surgeons need to perform intraoperative fluoroscopies repeatedly to ensure correct screw position and avoid damage to the peripheral nerves and vessels of the odontoid. The traditional anterior cervical screw fixation is usually conducted with the assistance of a C-arm. However, compared to the C-arm, an O-arm intraoperative imaging system can provide 3D images during surgery, which improves the accuracy of screw placement. This study retrospectively analyzed patients with anterior cervical odontoid fractures treated in our hospital. The application of the O-arm intraoperative imaging system for assisting screw placement in the treatment of odontoid fractures can reduce intraoperative blood loss, operation time, and trauma to the patients.

Odontoid fracture is a common form of cervical spine fracture, accounting for approximately 20% of all cervical spine fractures. Odontoid fracture mainly occurs in adults over the age of 65¹. Odontoid process displacement resulting from an external force acting on the cervical spine is the main cause of odontoid process fractures. The main symptoms of odontoid fracture are pain in the occiput and the back of the neck and immobility. According to Anderson's classification², odontoid fractures can be divided into three types. Type I and type III odontoid fractures can achieve satisfactory results with conservative treatments, while patients with type II odontoid fractures often need surgical treatments^3,4.

Current surgical treatments are anterior and posterior screw fixations. The posterior screw fixation technique provides more stable fixation, while the anterior screw fixation technique maintains 80%-100% of the rotational function of the atlantoaxial vertebra. However, because posterior cervical screw fixation causes greater trauma to patients^5,6, treatment of odontoid fractures using anterior screw fixation is increasingly accepted by spine surgeons. The traditional anterior cervical screw fixation is usually conducted with the assistance of a C-arm. However, the complex structures of the anterior neck, the free fracture end, and the size of the patients all obstruct the accurate placement of screws through the anterior neck. High-quality images are desired when navigating accurate screw placement, which is difficult to achieve using the current C-arm system. Therefore, unexpected intraoperative blood loss and longer operation time, as well as more trauma to the patients, may occur when using C-arm to assist the surgery.

The O-arm intraoperative imaging system can provide CT scan images during the operation. Compared with the traditional 2D intraoperative fluoroscopy, the O-arm intraoperative imaging system can detect screw dislocation during the operation, enabling the surgeon to make timely revisions and avoid secondary surgery⁷. The advanced O-arm intraoperative imaging and navigation system can achieve intraoperative 3D CT imaging and provide precise intraoperative navigation. Studies have confirmed that the application of the O-arm navigation-assisted technique in complex surgery can improve the accuracy of screw placement and reduce internal fixation-related complications^6,8,9. Figure 1 shows the application of the O-arm intraoperative imaging system. This study aims to investigate the application of the O-arm intraoperative imaging system in the treatment of odontoid fractures with anterior cervical screws.

This study has been approved by the Ethics Committee of the Third Hospital of Hebei Medical University. The patients signed informed consent, and the patients consented to film and allowed the investigators to use their surgical data. A total of 40 patients were included in this study.

1. Preoperative preparation

1. Select patients based on the following inclusion criteria: i) patients who need surgical treatment due to trauma to the odontoid process of the axis, ii) patients operated by the same surgeon, and iii) cervical MRI images that show no degeneration and obvious edema of the cervical spinal cord.
2. Ensure the following exclusion criteria while selecting patients: i) patients with spinal ankylosis, tumors, and other diseases, ii) combined atlantoaxial joint transverse ligament injury, and iii) severe bleeding tendency or coagulation disorder.
3. Have the patients undergo a routine preoperative examination after admission. Ensure that the patients are accompanied by a doctor to perform imaging examinations, including the anterior and lateral X-ray of the cervical spine, X-ray with mouth open, atlantoaxial CT examination, and the patient's cervical spine MRI.
4. Make it routine for patients to undergo cranial traction (traction weight 2-5 kg) before the operation.
   1. Keep horizontal maintenance traction (traction weight of 2 kg) for patients with no obvious displacement of odontoid fractures.
   2. For those with posterior displacement of the odontoid fractures, perform horizontal traction first, and then increase the traction weight according to the reset situation. After the X-ray shows complete reduction of the fracture end, reduce the traction weight to 2 kg.
5. Review the patients' bedside X-ray films every 2 days. Have the surgeons adjust the position and traction weight according to the displacement of the odontoid process. After the fracture reaches full reduction, perform surgery to fix the fracture. Ensure that the patients have fasted for 12 h before surgery and that the surgical site is well prepared. Take the 20 cm area around the surgical incision as the skin preparation area. Use a razor to remove hair from the skin preparation area.

2. Surgical procedures

1. Place the patient in a supine position on the operating table. Sedate the patient by intravenous administration of propofol, rocuronium bromide, sufentanil, and midazolid at dosages of 2 mg/kg, 0.15 mg/kg, 0.4 µg/kg, and 0.05 mg/kg, respectively.
2. After the patient loses consciousness, perform endotracheal intubation.
   1. Have the anesthesiologist prop up the patient's occiput properly and tilt the head back.
   2. After the patient has inhaled pressurized, pure oxygen through a mask for 3-5 min, have the anesthesiologist open the patient's mouth with the right thumb, forefinger, and middle finger. Hold the laryngoscope with the left hand to expose the glottis and then pass the catheter through the mouth in an arc through the glottis and into the pharynx and trachea with the right hand.
3. Place the tooth pad, take out the laryngoscope, inflate the cuff, and then auscultate both lungs. After confirming the position of the catheter, fix the catheter and the tooth pad with adhesive tape, and connect the ventilator for respiratory support.
4. Take an X-ray before the start of surgery to ensure that the odontoid is in reduction.
5. Perform routine disinfection and draping to the surgical incision site (the right side of the upper edge of the C4-5). Use 2% iodine to sterilize the surgical incision 3x and use 75% alcohol for deiodination and alcohol disinfection 3x. Disinfect up to the lower lip, down to the nipple, and both sides to the front edge of the trapezius muscle. During the drape laying process, take care to move the drape only from the inside to the outside.
6. Use a scalpel to make a 4-5 cm transverse incision on the right side at the upper edge of C4-5. Cut the skin, subcutaneous tissue, and platysma in sequence, and use high-frequency electrocautery to stop the bleeding. Instruct the assistant to use tissue forceps to separate the upper and lower platysma muscle to facilitate retraction and blunt separation of the vascular sheath and visceral sheath. Use the skin retractor to retract to both sides to expose the prevertebral fascia and longus neck muscle and peel it off with a periosteal peeler to separate the prevertebral fascia.
7. Secure the inside of the O-arm workflow with a sterile cloth. Move the O-arm to the surgical site. After turning on the O-arm intraoperative imaging system, perform a 3D scan of the surgical site to determine the C2-3 space.
8. After the C2-3 segment is confirmed, tilt the O-arm 45° to make room for surgery. Use a rongeur to remove a small amount of the labial bone at the lower edge of the C2 vertebra.
9. Under O-arm fluoroscopy, place a 1.5 mm diameter guide wire in the middle of the lower border of the C2 vertebral body. Keep the guidewire in the midsagittal position of the odontoid and tilt it back 15-20°. Under the supervision of the O-arm, drill the guide wire to the tip of the odontoid. Use a hollow drill to create a nail channel along the guide wire and a hollow tap to shape a thread channel.
10. After the guide needle reaches the top of the odontoid, measure the length of the guide wire entering the vertebral body and wait for the surgeon to screw in a 3.5 mm diameter, hollow titanium screw of a suitable length along the guide needle.
11. After screw placement, perform 3D scanning again with the O-arm to observe the screw implantation in all directions and carefully withdraw the guide needle.
12. Fully rinse the wound and perform indwelling drainage. Use a No. 10 thread wire to fix the drainage tube. Suture the platysma muscle with the No. 10 thread, the fascia between the platysma and the skin with the No. 4 thread, and the skin intradermally with the No. 0 thread.

3. Post-surgery

1. Administer antibiotics to the patients for 3 days after the operation. Pull the drainage out 3 days after the operation.
2. Instruct the patients to start walking on the ground while wearing a cervical collar and use the cervical collar continuously for 3 months.

Anterior cervical screw fixations were performed in 40 patients with odontoid fractures, of whom 21 patients underwent surgeries with the assistance of the O-arm intraoperative imaging system (Group O), and 19 patients underwent surgeries with the assistance of the C-arm (Group C). Data are presented as mean (± SD). The average age of Group O was 42.86 (± 10.36) years, while the average age of Group C was 41.05 (± 9.83) years. There was no significant difference in age between the two groups of patients. Both operation time and intraoperative blood loss were significantly lower in Group O than in Group C. The operation times of Group O was 101.90 (± 22.55) min, which is significantly lower than the 126.84 (± 32.28) min (p = 0.007) of Group C. The blood loss of Group O was 98.33 (± 42.20) mL, which is significantly lower than the 145.26 (± 70.35) mL (p = 0.032) of Group C. In Group O, two screws penetrated the cortex, while six screws penetrated the cortex in Group C; there was no significant difference between these two groups (p = 0.178), as shown in Table 1. No surgery-related complications, such as neurovascular injury, were found in these two groups. Figure 2 shows the comparison of the O-arm intraoperative imaging system imaging and traditional intraoperative fluoroscopic imaging.

Figure 1: The O-arm intraoperative imaging system. (A) The O-arm intraoperative imaging system scans the patient's surgical site. (B) After the scan is completed, the three-dimensional structure of the patient's surgical site is displayed on the monitor. (C) The surgeon performs the operation under the O-arm. Please click here to view a larger version of this figure.

Figure 2: Application of the O-arm intraoperative imaging system in treating odontoid fracture with an anterior cervical screw. (A,B) The imaging of the intraoperative O-arm showed that the screw tip was long and broke through the cortical bone, which should be adjusted in time. (C,D) Traditional X-ray fluoroscopy does not facilitate the visualization of fracture reduction and screw position, making it impossible for the surgeon to adjust the screw position in time. Please click here to view a larger version of this figure.

Table 1: Data on the treatment of odontoid fractures with anterior cervical screws. There was a significant difference in the amount of intraoperative blood loss and operation time (p < 0.05) between Groups O and C. There was no significant difference in age, gender, and the number of screws that penetrated the cortex (p > 0.05). Group O: patients who underwent surgeries with the assistance of the O-arm intraoperative imaging system; Group C: patients who underwent surgeries with the assistance of the C-arm system.

Odontoid fractures are usually caused by violent injury; common symptoms are pain and limited mobility. Some patients also experience nerve compression symptoms. In some patients, the degree of fracture displacement is relatively large, and the fracture fragments compress the spinal cord and cause symptoms of paraplegia and neuralgia. Some patients with odontoid fractures also have symptoms of hand weakness and difficulty in walking. Type II odontoid fractures have poor self-healing potential and often require surgical treatments due to poor blood supply to the fracture site, thin cortical bone, and ligament attachment^3,4. Anterior cervical screw fixation involves less trauma to patients and shorter recovery time in the treatment of odontoid fractures⁵, which has unique advantages compared with the posterior screw fixation technique.

In clinical scenarios, anterior cervical screw fixations for odontoid fractures are often performed with the assistance of an intraoperative X-ray. However, with the traditional C-arm fluoroscopy, surgeons usually have difficulties in observing fracture reduction and the position of the screws, which would lead to complications such as excessive screw length and cortical perforation, displacement of fracture ends, and neurovascular injury^10,11. An O-arm navigation assistance technique can help scan the surgical site through the intraoperative imaging system, providing clear, real-time 3D images to guide the placement of screws through the intraoperative navigation system^12,13. The O-arm intraoperative imaging system combined with the navigation system is a multidimensional precise surgical platform, which can ensure the accuracy of difficult surgical operations. In this study, we applied an O-arm intraoperative imaging system to provide high-quality images as well as 3D imaging. Considering that the navigation reference frame is easy to loosen during the anterior surgery, which affects the interpretation of the results by the surgeon, the navigation system was not used in this study. By using an O-arm, surgeons can observe the placement of screws from all levels and, thus, avoid screw penetration into the cortex and damage to important structures. In addition, the O-arm can provide more accurate help to the surgeon to adjust the screw position during the operation, thereby improving the safety of the operation. Studies have demonstrated that using an O-arm can improve the accuracy of screw placement in complex situations and reduce internal fixation-related complications^6,8,14.

Before starting O-arm intraoperative imaging, the O-arm is placed in the scanning position in a lateral position, and during the process of position adjustment, the gantry can be adjusted in various directions without moving the whole machine. After image acquisition is complete, the gantry is tilted to remain in the berth, leaving room for the surgeon to operate. When the image is acquired again, the surgeon only needs to reset the gantry, which saves time compared to the C-arm. During the assisted treatment of odontoid fractures with the O-arm intraoperative imaging system, the surgeon should be as gentle as possible to avoid re-displacement of the patient's odontoid due to excessive force, which increases the difficulty of the operation. When implementing the O-arm scanning process, it is necessary to keep the scanning part free of other objects to prevent disturbance to imaging. In addition, the surgeon must be proficient in the interpretation of the results of O-arm intraoperative imaging. Inaccurate interpretation of the results may lead to increased difficulty in the operation and increased operation time.

In this study, the intraoperative blood loss and operative time in the O-arm group were significantly lower than those of the C-arm group. When using the C-arm for intraoperative X-ray, a radiologist needs to continuously adjust the position of the C-arm to obtain a clear intraoperative image. By contrast, the O-arm intraoperative imaging system conducts 3D scanning on the implanted screws, and as a result, the depth of the implanted screws can be clearly and multi-directionally observed, which can help to prevent the screws from penetrating the cortex. Here, we have shown that the O-arm intraoperative imaging system reduced operation time and intraoperative blood loss. In recent years, studies have shown that in the treatment of type II odontoid fractures by the O-arm intraoperative imaging system, the number of radiations (times fluoroscopy was performed during surgery) and radiation doses received by the operating room staff and patients were lower than those of the C-arm group¹⁵. This may be because the O-arm can provide high-quality intraoperative images, reducing the number of fluoroscopies. Thus, surgeons can apply O-arm to obtain clear X-ray images to improve surgical efficiency¹⁵. Therefore, O-arm intraoperative imaging can be used for CT scanning to generate 3D images and for intraoperative fluoroscopy. However, this study did not find significant differences in the number of screws penetrating the cortex between the two groups, which may be because of the small sample size in this study^16,17.

It is worth noting that, apart from its remarkable advantages, the O-arm intraoperative imaging system also has its disadvantages. To start with, the O-arm intraoperative imaging system is more expensive and requires more operating room space than a C-arm. In addition, the O-arm intraoperative imaging system cannot be widely used in primary hospitals due to its high cost. Therefore, the O-arm system still needs improvements. The O-arm intraoperative imaging system can be used for screw placement in complex operations and in percutaneous kyphoplasty for the treatment of thoracic vertebral compression fractures. Due to the influence of anatomical structures such as the thorax during traditional intraoperative fluoroscopy, the structure presented by lateral imaging is not very clear. Through O-arm intraoperative 3D imaging, the surgeon can clearly observe the positional relationship between the working channel and the fractured vertebral body, reducing the occurrence of bone cement leakage. The O-arm intraoperative imaging system can also be applied to patients with spinal infection in the future, so that the surgeon can define the scope of operation and completely remove the lesions.

The authors declare that there are no conflicts of interest in this study.

None.