Design, application, and evaluation of a novel method for determining optimal trajectory of thoracic pedicle screws

Intraoperative lateral wall breach simulation in the cadaveric spine and the impact of thread designs of screws on pullout strength in the osteoporotic thoracic vertebrae: A biomechanical study in human cadavers

OBJECTIVE

This study aimed (1) to simulate pedicle screw pullout after intraoperative external wall perforation and (2) to assess restoration strength with different thread designs in the pedicle screw instrumentation for osteoporotic thoracic vertebrae.

METHODS

Twenty fresh-frozen human cadaveric thoracic vertebra bodies were prepared and divided into 4 groups: group 1, 5.5 mm × 45 mm polyaxial single thread pedicle screws (PASTS); group 2, after wall injury 5.5 mm × 45 mm PASTS; group 3, 6.5 mm × 45 mm PASTS after wall injury; and group 4: 6.5 mm × 45 mm polyaxial mixed-threaded screws after wall injury. While group 1 was the control group, groups 2, 3, and 4 were used as study groups after the lateral wall breach. All prepared screw units were placed on a universal pullout measurement testing device.

RESULTS

The mean bone mineral density for 20 thoracic vertebrae was 0.57 ± 0.12 g/cm2 (range 0.53-0.6 g/cm2 ). The mean pullout strength was 474.90 Newtons (N) for group 1, 412.85 N for group 2, 475.4 N for group 3, and 630.74N for group 4. The lateral wall breach caused a 14.1 % decrease in average pullout strength compared with the initial screw pullout. Mixed (double)-threaded screws increased pullout strength compared to 6.5 mm screws (P=.036) Conclusion: Using a 1 mm thicker polyaxial pedicle screw or mixed (double)-threaded pedicle screw seems to increase pullout strength; however, this was statistically significant only for group 4. In the thoracic spine, the redirection possibility of the pedicle screw is limited, and augmentation with cement will not be appropriate due to the risk of wall injury-related leakage. Therefore, care should be taken to avoid violating the lateral cortex by using appropriate pedicle entry points and trajectories.

Clinical applications and prospects of 3D printing guide templates in orthopaedics

Background

With increasing requirements for medical effects, and huge differences among individuals, traditional surgical instruments are difficult to meet the patients' growing medical demands. 3D printing is increasingly mature, which connects to medical services critically as well. The patient specific surgical guide plate provides the condition for precision medicine in orthopaedics.

Methods

In this paper, a systematic review of the orthopedic guide template is presented, where the history of 3D-printing-guided technology, the process of guides, and basic clinical applications of orthopedic guide templates are described. Finally, the limitations of the template and possible future directions are discussed.

Results

The technology of 3D printing surgical templates is increasingly mature, standard, and intelligent. With the help of guide templates, the surgeon can easily determine the direction and depth of the screw path, and choose the angle and range of osteotomy, increasing the precision, safety, and reliability of the procedure in various types of surgeries. It simplifies the difficult surgical steps and accelerates the growth of young and mid-career physicians. But some problems such as cost, materials, and equipment limit its development.

Conclusions

In different fields of orthopedics, the use of guide templates can significantly improve surgical accuracy, shorten the surgical time, and reduce intraoperative bleeding and radiation. With the development of 3D printing, the guide template will be standardized and simplified from design to production and use. 3D printing guides will be further sublimated in the application of orthopedics and better serve the patients.

The translational potential of this paper

Precision, intelligence, and individuation are the future development direction of orthopedics. It is more and more popular as the price of printers falls and materials are developed. In addition, the technology of meta-universe, digital twin, and artificial intelligence have made revolutionary effects on template guides. We aim to summarize recent developments and applications of 3D printing guide templates for engineers and surgeons to develop more accurate and efficient templates.

[Clinical application of three-dimensional printing technique combined with thoracic pedicle screw track detector in thoracic pedicle screw placement]

OBJECTIVE

To investigate the clinical application of three-dimensional (3D) printing technique combined with a new type of thoracic pedicle screw track detector in thoracic pedicle screw placement.

METHODS

According to the characteristics of thoracic pedicle and common clinical screw placement methods, a new type of thoracic pedicle screw track detector was independently developed and designed. The clinical data of 30 patients with thoracic vertebrae related diseases who underwent posterior thoracic pedicle screw fixation between March 2017 and January 2020 were retrospectively analysed. Among them, there were 18 males and 12 females with an average age of 56.3 years (range, 32-76 years). There was 1 case of thoracic disc herniation, 4 cases of thoracic canal stenosis, 2 cases of ossification of posterior longitudinal ligament of thoracic vertebra, 16 cases of thoracic trauma, 2 cases of thoracic infection, and 5 cases of thoracic canal occupation. Three-dimensional CT of the thoracic vertebra was routinely performed preoperatively, and the model of the patient's thoracic vertebra was reconstructed and printed out. With the assistance of the model, preoperative simulation was performed with the combination of the new type thoracic pedicle screw track detector, and detected no nails after critical cortical damage. During operation, one side was randomly selected to use traditional hand screws placement (control group), and the other side was selected to use 3D printing technique combined with new type thoracic pedicle screw track detector to assist thoracic pedicle screws placement (observation group). The single screw placement time, adjustment times of single screw, and blood loss during screw placement were compared between the two groups. The accuracy of screw placement in the two groups was evaluated according to postoperative CT imaging data.

RESULTS

The single screw placement time, adjustment times of single screw, and blood loss during screw placement in the observation group were significantly less than those in the control group ( P<0.05). Postoperative CT examination showed that the observation group had 87 screws of grade 1, 3 screws of grade 2, and the acceptable screw placement rate was 100% (90/90); the control group had 76 screws of grade 1, 2 screws of grade 2, 11 screws of grade 3, and 1 screw of grade 4, and the acceptable screw placement rate was 86.7% (78/90); showing significant difference in screw placement between the two groups ( χ 2=12.875, P=0.001). All patients were followed up 6-18 months, with an average of 11.3 months. There was no complication of vascular, nerve, spinal cord, or visceral injury, and screws or rods broken, and no patient was revised.

CONCLUSION

The 3D printing technique combined with the new type of thoracic pedicle screw track detector assisted thoracic pedicle screw placement is convenient, and significantly improves the accuracy and safety of intraoperative screw placement, and overall success rate of the surgery.