This article report cases underwent upper cervical spine reconstruction or AAD reduction with personalized 3D printed implants. The results showed that 3D printed implants for upper cervical surgery is sufficient to provide good stability and prognosis. In addition, the advanced planning of instruments and screw paths by simulating surgery can simplify the operation process and improve the accuracy, which plays a good auxiliary role in the upper cervical surgery with high accuracy requirements.
In our preliminary report of the first 3D printed C2 vertebral body replacement in 2016, we described this new implant design, which was suitable for the patient's anatomical structure to increase the contact area between adjacent vertebrae, with the additional feature of zero-profile fixation, and improved conduciveness to bone-ingrowth due to their trabecular pores [13]. In 2022, Hu et al. of our center conducted a comparative study of conventional titanium mesh and 3D printed AVB for reconstruction after resection of C2 tumor, which showed that personalized AVB can provide reliable reconstruction [21]. Laratta et al. proposed that the advantage of 3D printed AVB for postoperative fusion is its dense reticular structure, which can increase the interaction with surrounding bone and promote bone growth inward without bone grafting [22]. In addition, Zhou et al. analysed 23 patients who underwent reconstruction after en bloc resection of thoracolumbar tumors, and confirmed that 3D printed implants can effectively promote bone growth and have lower subsidence rate and stronger stability [19, 23]. In this study, we also observed a conclusion consistent with these findings, that is, 3D printed implants have excellent stability and prognostic effects.
Although there are other technologies for manufacturing implants, 3D printing can produce more uniform porosity in terms of aperture and shape. In addition, the screw paths can be planned in advance to improve the safety and accuracy of screw insertion.
Because of more confidence in the strength of fixation, shorter posterior instrumentation and fusion was attempted. It seems that 3D printed implants are strong enough to save the occipital-atlantic joint. This will enable patients to obtain better results in terms of function, because most of the head flexion and extension is achieved through movement between atlas and occipital bone. In addition, thanks to the better short-term postoperative stability provided by the customized 3D printed implants, the patients were allowed to walk on the first day after surgery only with the Philadelphia collar. This is in contrast with the postoperative recovery after traditional surgery, which requires a longer course of non-ambulation and a sternal-occipital-mandibular immobilizer (if not a Halo vest).
However, there are also shortcomings that cannot be ignored. First of all, because the 3D printed implants are designed according to the bone structure reconstructed by CT images, it is necessary to thoroughly expose the bone surface which needs to contact with the implants, which will prolong the operation time and increase the risk of bone damage, especially in the case of poor bone quality. And sometimes we can’t reach exactly the value of tumor removal, so accurately inserting the implants into right place requires experience and patience. Secondly, the design and manufacture of individualized implants requires longer preoperative preparation time and higher labor and economic costs.
In short, 3D printed implant is an ideal substitute for high cervical surgery, which is accurate and safe. The patients who used 3D printed implants had good prognosis, and showed acceptable stability and effect on spinal reconstruction, reduction and fixation. At present, there is no absolute standard to guide the selection of using 3D printed implants or traditional surgical methods. However, based on the experience of surgeons, when traditional surgical instruments or methods cannot meet the needs, 3D printed implants are an alternative choice. It can be predicted that this kind of individualized implants will be paid more and more attention.