Bone Ingrowth in Retrieved Bryan Cervical Disc Prostheses

In Brief Study Design. Explant analysis for bone ingrowth of retrieved cervical disc prosthesis in chimpanzees and humans. Objectives. To assess the bone ingrowth into retrieved Bryan Cervical Discs. Summary of Background Data. Bone ingrowth in cervical disc prothesis has not been documented in the literature. Methods. Chimpanzee: Two chimpanzees underwent placement of the Bryan disc at C3–C4 and 3 months later had explantation and interbody fusion. Human: Two patients had removal of their Bryan disc and interbody fusion for failure to resolve symptoms at 8 and 10 months. The explants were analyzed for bone ingrowth. Results. Chimpanzee: Histologic analysis showed bony ingrowth through the interstices of the porous coating and apposition ranging from 10% to 50% of toluidine blue-stained sections. New ingrowth, rather than bony impaction, was confirmed with fluorochrome-labeled sections Human: Bone ingrowth was a mean of 30.1% (12% SD). No difference was observed between peripheral, intermediate, or central locations. Conclusions. Adequate bony apposition was found in all primate device-to-vertebral body interfaces. Human retrievals also demonstrated significant ingrowth in all four surfaces. This compares with hip and knee arthroplasty percent ingrowth rates of 10% to 30%. All implants had stable fixation judged by radiographs and at the time of implant removal. Bone ingrowth into the Bryan Cervical Disc prostheses was assessed in chimpanzees after 3 months of implantation and from 2 cases of retrievals from humans. Ingrowth was robust, averaging 30.2%. Despite successful ingrowth, device removal, and interbody fusion or implantation of a new prosthesis was possible.