gms | German Medical Science

Objective: The development of new materials for spine implants, e. g. with osteoinductive properties, is in the focus of experimental and preclinical research. For in vivo examinations, these studies commonly use large animal models, e. g. in sheep, while small animal models are uncommon. However, a murine spine model would be advantageous because of the broad availability of transgenic strains necessary to study osteointegration on the cellular level. In this proof of principle study, the feasibility of a murine model to perform a vertebral body replacement with an individually 3D printed implant was evaluated.

Methods: 3 C57BL/6NRj mice were euthanized. The cervicothoracic spine was scanned in a µCT. The scan data was segmented and exported as a 3D model to a 3D software. Next the cervical vertebral bodies C4 and C5 were virtually removed and a tube shaped intervertebral implant with additional plate for fixation was designed. The implant was then fabricated on a stereolithography 3D printer measuring 4100 µm (+/- 40) x 1600 µm (+/- 12). In a next step the implants were implanted into 9 mouse cadavers after removal of 2 cervical vertebrae with a micro drill via an anterior approach and fixed with micro screws. After the preparation, all cadavers received transcardiac and esophageal perfusion with a radiopaque casting agent. The samples then underwent µCT scanning.

Results: The surgical procedure was carried out in 9 murine cadavers. In the first 4 cases, a fracture of the implant or bone occurred during insertion. These cases were excluded from further analysis. In the further cadavers, the surgical procedure was carried out successfully. The aim of implant and screw placement, and µCT scanning was achieved in all 5 cases. Mean surgical time was 35 min +/- 13 min. In 2 of the 5 cases vertebrae C4/5 and in 3 of the 5 cases vertebrae C5/6 were successfully removed. A screw deviation with intraspinal screw position was observed in 7/10 screws (70%). Other gross misalignments of the implants were not observed. Leaking of the contrast agent indicating lesions of the carotid arteries or the esophagus were not observed.

Conclusion: Our study demonstrates that a murine model for spine implants is feasible from the surgical and imaging perspective, while especially the screw fixation of the implants still needs to be improved. Our 3D printing technique allows fast fabrication of individual implants. Animal studies will be needed to test the feasibility of the model for in vivo examinations.