The Effect of 3D-printed Titanium Cage Used in Atlantoaxial Lateral Mass Joints on Cervical Realignment Introduction: Research on the effect of using 3D-printed cage in the atlantoaxial lateral mass joint on cervical sagittal realignment remains few. The purpose of this study is to investigate the effects of using inter-atlantoaxial lateral mass joint 3D-printed titanium cage on cervical sagittal realignment in atlantoaxial dislocation surgery compared with traditional Harms rod-screw fixation systems without inter-atlantoaxial lateral mass joint cage.

Methods: Seventeen atlantoaxial dislocation patients treated with atlantoaxial lateral mass joint 3D-printed cage (Cage group) with a 1:1 matched patient without cage (non-cage group) were collected during the same period. Preoperative, last follow-up cervical upright lateral radiographs were collected. Cervical sagittal parameters including slope of Frankfort horizontal line (sFH), orbital tilt (OrT), occipital incidence (OI), occipital slope (OS), cervical sagittal vertical axis (cSVA), occiput-C1 Cobb angle (O-C1 CA), occiput-C2 Cobb angle (O-C2 CA), C1-C2 Cobb angle (C1-C2 CA), C2-7 Cobb angle (C2-7 CA), T1 slope (T1s), thoracic inlet angle (TIA), and neck tilt (NT) were measured. Finally, the cervical sagittal parameters were compared between cage group and non-cage group. A t-tests was used to analyze these parameters.

Results: The average operative time and blood loss were more in cage group but with no significant difference. The gender, age, hospital stay, all cervical alignment parameters and intraoperative complications were not significant different between two groups. Solid bone fusion could be observed in all inter-atlantoaxial lateral mass joints in 3 mons after surgery. Cervical alignments were improved in all Pts at two groups after surgery, However, OrT, O-C1 CA, O-C2 CA, C2-7 CA and T1S were improved significantly in cage group. The values of ΔsFH, ΔOrT, ΔO-C1 CA, ΔO-C2 CA, ΔC2-7 CA reflecting the postoperative improvement of cervical alignments compared with the preoperative also significantly changed in cage group.

Conclusion: In the surgical treatment of atlantoaxial dislocation, the placement of a 3D-printed titanium cage between the atlantoaxial lateral mass joints did not increase the surgery related complications. However, it did significantly realign the cervical spine better compared to the traditional Harm screw-rod system without cage through improving the value of atlantoaxial regional alignment.