| BackgroundClinically,internal fixation surgery is often necessary to treat cervical disorder resulting from congenital malformations,trauma,infection or tumor.Of all fixation techniques,pedicle screw system appears to be the most popular approach because it can offer better biomechanical stability,higher fusion rate and less demand of fusion segments than other methods of internal fixation.Because the surgeons could not have a direct view of the pedicle structure in surgery,there is a risk of injury to the vertebral artery and spinal cord during the operation.This region is considered a high-risk area for surgery,therefor the principle of individualization and precision should be emphasized in these surgeries.Currently,the main navigational methods that can be used to assist screw placement in the cervical spine are computer-aided navigation technology,bioelectric impedance measuring technology,robotic technology,and individualized navigation template technology.These methods can improve the accuracy of screw positioning,but involve some limitations.Such as high medical cost,long learning curve and radioactive contamination.So,it is necessary to develop a cost-effective,safe and user-friendly navigational method.By 3D metal printing technology,metal parts can be directly formed with complex structure,high density,high precision and good mechanical properties.Its characteristics of high degree of individualization and precision can meet the need of of spine surgery.On the bases of the reported literatures,we improve the design and molding process by innovatively combining the 3D metal printing technology with cervical spine fixation surgery.And its accuracy would be evaluated.Objective1.The objective of this study was to design and fabricate a novel cervical screw guide template with high accuracy,good mechanical properties and biocompatibility by 3D metal printing technology.2.To explore the accuracy of novel metal navigational template in cervical pedicle screw placement by comparing with conventional resin navigational template in a cadaver study.3.To evaluate the benefits of using 3D-printed metal surgical templates in complicated upper cervical surgery in clinic.Methods1.Design a new type of cervical screw guide template with three-dimensional reconstruction technique,reverse engineering and 3D metal printing technology.Design concept:According to the literature and our experience in the non-metallic navigational template,we learned that reliability of the printing process,mechanical properties of the materials and the stability of the navigational template are the keys to accurate screws placement.By 3D metal printing technology,metal parts could be directly formed with complex structure,high density,high precision and good mechanical properties,making it possible to modify the conventional navigational template.And two anchors on both sides of the guide template were designed so that the guide template could be temporarily fixed on the lamina,which can effectively prevent the displacement of the guide template.Preparation of the individualized navigation template:Fine-cut CT scan of the cervical spine was performed,CT imaging data stored in DICOM format was imported into a computer workstation to design the individualized drill guide template,finally the template was fabricated by a 3D metal printer.2.Cadaveric pedicel screw insertion and assessment of navigational accuracy.Six formalin-preserved cervical cadavers(rang C1-C6)were obtained.The soft tissue on posterior surface of the laminar was cleared.All specimens underwent thin slice CT scan,significant bone defects were eliminated.The specimens were randomly divided into two groups,and underwent pedicle screw insertion surgery.The metal group(Group A)were operated under the guidance of novel metal navigational template,and the resin group(Group B)were operated by using conventional resin navigational template.The accuracy of the screw positioning was evaluated by postoperative CT.3.The clinical effect was observed in a group of patients applied with novel metal navigational templateBetween August 2015 and October 2017,7 patients(6 males and 1 female;age range:3-36 years old,mean age 10.7 years old)underwent posterior cervical fixation surgery guided by the novel metal navigational templates.After surgery,the screw trajectory was evaluated by CT scan.Result1.Individualized metal screw guide templates were successfully designed in line with the characteristics of 3D metal printing and meet the quality requirements.All the templates were successfully produced with thicknesses and volumes much smaller than those of the resin templates and no fractures or deformation during use.The templates were found to be perfectively fit with the corresponding bone structure without any free movemet.2.Assessment and analysis of the postoperative CT scan showed that:In each group 36 screws were inserted.The accuracy score in group A was:2 points in 30 screws(83.3%),3 points in 4 screws(11.1%),4 points in 1 screw(2.7%),5 points in 1 screw(2.7%);The accuracy score in group B was:2 points in 22 screws(61.1%),3points in 8 screws(22.2%),4 points in 4 screws(11.1%),5 points in 1 screw(2.7%),6 points in 1 screw(2.7%).Statistic analysis showed that there was significant difference between two groups(P<0.05).3.All seven surgeries were successfully performed with the placement of a total of nine pedicle screws and five lamina screws.Postoperative CT confirmed that all fourteen screws were accurately positioned.No spinal cord injuries,vertebral artery injuries or other complications occurred.Conclusion1.Using 3D metal printing technique,the authors was able to develop an individualized metal screw guide template for screw placement with good mechanical property and high accuracy,which could meet the demand of surgical use.2.The cadaver study showed that:Compared with the conventional resin navigational template,the novel metal navigational template was more accurate.3.The accuracy and safety of the use of a 3D-printed metal screw guide template in cervical spine fixation were high,which could effectively reduce the risk of surgery and improve the success rate. |
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