Three-dimensional printing, also known as additive manufacturing, is a kind of rapid prototyping technology. Medical 3DP is based on human anatomy to accurately make physical models of human organs and tissues. The applications of 3DP for clinical purposes have grown rapidly over the past decade. In the 1980s, it was first applied to engineering by Chuck Hull through computer modeling. The medical application was developed in 1990, and a skull was printed based on the CT scan data. Currently, 3DP plays an important role in orthopedics: in clinical teaching assistance, doctor-patient communication, diagnosis of complex diseases, preoperative planning and surgical simulation training, surgical navigation, 3DP prosthesis implantation and bone tissue engineering.[11–14]
Spinal deformity is one of the toughest challenges faced by spine surgeons and neurosurgeons. It is difficult for surgeons to evaluate and understand the exact pathological anatomical structure through traditional imaging examination, especially for congenital scoliosis caused by vertebra formation defect and failure of segmentation. However, with the emergence and development of 3DP technology, the situation has greatly improved[15, 16].
Li et al. made 3DP models of 22 patients with cervical deformations, and simulated posterior cervical operations were conducted on the models to obtain accurate screw placement routes and angles. The screw accuracy was improved and no vertebral artery was injured. Sixteen severe scoliosis patients were treated with the help of 3DP technology, and the best screw placement angle and depth were obtained in the simulated surgery on the 3DP spine models before operation. Li et al. randomly divided 53 patients with scoliosis into the control and 3DP groups, and the statistical data showed that the operation time was shorter and screw placement accuracy was better in the 3DP group.
It is challenging for surgeons to implant pedicle screws accurately in the deformed spine, which is usually accompanied by vertebra rotation, thin pedicle, hemivertebra, unsegmented vertebra, or multi-segment fused vertebra. Severe spine deformity cases treated by posterior pedicle screw fixation and fusion in our center were comprehensively compared between 3DP spine model-assisted group and free-hand group using PSM method in this study, and the results showed that pedicle screw placement was more accurate and operation time was much shorter with the guidance of the printed model. The operation time was shortened by 33 minutes on average, which would reduce surgery-related and anaesthesia-related complications and improve the efficiency of operating room staff.
The severe spine deformity often requires spinal osteotomies to achieve good correction. The higher the osteotomy grade, the better the correction effect, but also comes with a higher risk. The osteotomy plan was made by the surgeon based on cognition of the spinal anatomy structure. It has been reported that preoperative familiarity of oncologic pathology based on 3D models in orthopaedics helps to increase the accuracy of bone resection and to decrease operative time. In this study, surgeons were more inclined to performed more advanced osteotomies with the help of 3DP spine models. In the meanwhile, neurological complications rate was reduced and operation time was shortened significantly.
Traditionally, CT scan and reconstraction images help us a lot to evaluate the spine deformity. Zheng et al. reported that compared with reconstructed 3D-rendered images in preoperative planning, the utilizing of 3DP models could significantly improve surgical plan quality. The authors postulated that the 3DP models may have improved the understanding of the anatomically complex sites of skeletal structure. 3DP models allowed surgeons to appreciate the structure and relations of the relevant anatomy much better than the visualization provided by two-dimensional CT images conventionally used. Inspection of these models also revealed structural abnormalities not appreciated on CT which altered the surgical approach in a significant number of cases. Luo et al. demonstrated that accuracy of the surgical technique using spinal 3D printing technology in patients with severe congenital scoliosis was higher than that of the free-hand technique, and it appeared to shorten operative time.
It is reported that the intraoperative navigation system or robotic assistant system have been used to enhance the accuracy of pedical screw insertion in the treatment of spine degenerative and some spine deformity disease, and it turns out to be fesiable and effective.[24, 25] However, in severe spine deformity surgery, the evidence was unpowered and insufficient. Yang et al. reported that 3D technology could reduce the misplacement rate, operating time and blood loss in patients with preoperative mean Cobb angle only > 50°. According to our experience, the application of robotic navigation technology in the operation of severe spinal deformity was not accurate and convenient enough.
The cost of 3DP full spine model varies from $400 to $500, which is much less than the surgical robot or surgical navigation. Thus, in the area of severe spine deformity surgery exhibiting the advantage of cost-effectiveness and reducing radiation exposure.[28, 29]
Currently, the progress of the surgeons’ surgical skill learning curve mainly depends on clinical practice, cadaveric simulation, and digital imaging technology training, such as virtual reality and augmented reality. For surgeons in training, getting a chance to operate is competitive, especially in the developing countries where medical resources are inadequate, and this limits the training of surgeons. In addition, cadaveric training has significant limitations in cost, quality, and availability.
3DP technology has also been adopted for the surgeons’ training and teaching purposes, whereby the design flexibility in terms of geometry and material properties (tissue density, hardness, flexibility) enables simulation of a range of clinical scenarios for surgical training[30, 31] or anatomical learning without the associated ethical and cost barriers, as well as anatomical variation, that can be present in cadaveric study. Especially for the complex spinal deformities, printed models can improve the junior doctors' understanding of the pathological structure of the spine. Zhao et al. trained junior surgeons by conducting simulated surgery with 3DP models. The accuracy of screw placement on the model reached 93.75% after 3-months of training. After 6 months of training, all junior surgeons could implant pedicle screw accurately and independently, which greatly reduced the training time. Besides, many studies have indicated that 3DP spine model could promote surgical education, team communication and patient understanding.[34–37]
In conclusion, it is worthwile to apply the 3DP technology in severe spinal deformity surgery concerning the following advantages. Firstly, 3DP spine model improves the understanding of the anatomical structure of the surgical site and can be used for surgical rehearsal to accelerate the learning curve of surgeons and improve the quality of clinical education. Secondly, it improves surgical safety by increasing screw accuracy and reducing fluoroscopy exposure[17, 18, 38, 39]. Thirdly, it improves surgical efficiency by shortening the operation time. At last, 3D-printed spinal models make it easier for doctors to convince the patients and families about treatment plan, surgical complications, and rehabilitation program.
We suggest that 3DP models should be incorporated into the workflow in the surgical treatment of complex and severe spine deformity. It is believed that 3DP technology has great potential to become popular in the field of orthopedics. The medical 3DP industry may experience a period of rapid development.