Purpose of study: The purpose of this study was to monitor the course of events after placement of PDN prosthetic disc nucleus devices in the lumbar spine of the baboon and to assess the baboon as a model for future testing.Methods used: Three baboons underwent a lateral surgical approach to the lumbar spine. After discectomy, one animal had two custom-sized PDN implants tethered together and placed using the recommended surgical technique. Two additional animals were implanted but, because of limitations of instrumentation, had a single custom implant placed. Radiographs and computed tomography scans were obtained at 2, 4, 12 and 26 weeks to assess implant movement, disc height and end plate morphology. At 26 weeks, segments were harvested, processed undecalcified and evaluated.of findings: The two animals receiving a single device experienced migration of the implant from the disc in the first 2 weeks. Revision procedures using a technique that disrupted the end plate were performed, and smaller tethered PDN devices were placed. In these two animals, from 2 to 26 weeks after revision, there was progressive loss in disc height, end plate degeneration, implant subsidence, circumferential lucency and increasing sclerosis at adjacent vertebrae. Osteophytes bridged the disc space by 26 weeks. Histology revealed mild inflammation almost completely encapsulating the implants. The animal that received a PDN device pair at the initial surgery showed no signs of implant movement from 2 to 26 weeks, no changes in end plate morphology, no sclerosis, no increase in osteophytosis and only mild focal inflammation.Relationship between findings and existing knowledge: The two animals whose clinical outcome was unfavorable had a primary and revision procedure with focal disruption of the end plate, a possible initiator of osteophytosis. It is unknown whether the outcome would have been favorable at these levels if standard surgical techniques had been employed, but under these conditions, the degenerative changes of the disc and inflammatory response to the PDN devices were significant. In contrast, the animal that underwent only the primary procedure resulted in a favorable clinical outcome. Clinically, there have been reports indicating that the PDN device may be efficacious. There have also been reports on potential complications. The favorable response of one baboon to the implants is similar to reported favorable clinical outcomes. Migration of the PDN device from the disc space has been reported clinically; migration occurred in two baboons. Although there are no known clinical reports on histopathology associated with the PDN device, lucency, subsidence and sclerosis have been reported for interbody fusion devices and disc replacements.Overall significance of findings: These results indicate that the baboon may be an appropriate animal model for intervertebral disc research not only because the anatomy and morphology are similar to humans, but also because the potential complications and degenerative pathology are similar to those reported clinically.Disclosures: Device or drug: PDN prosthetic disc nucleus. Status: investigational.Conflict of interest: Eric Ledet, institutional research grant.