Feasibility of the Runt Cow for In Vivo Testing of a Spinal Interbody Prosthesis with Preliminary Results

Background: The optimal lumbar spinal disc prosthesis has yet to be developed. Failures of clinical device studies may be minimized by appropriate large animal preclinical studies. The lumbar spine of the mature "runt" cow, Corrientes breed, has been shown to have a number of desirable characteristics to the human. This study assessed the feasibility of the "runt" cow for in vivo testing of human-sized lumbar interbody implants and the ability to perform common analyses of explants. Methods: Eight cows (four experimental and four controls) were compared. The experimental animals had transosseous implantation of the disc prosthesis at L4-L5, and their spines were harvested at four or six months. They were evaluated for the ease of surgical access and healing, motion segment mobility, ability to remove the implant nondestructively, and microradiography and histomorphology. Results: All animals had successful implantation. All explantations were performed without alteration to the devices. All animals had surgical healing and intended device motion, and histology found device stability by demonstrating bone ingrowth into the device's porous plates. There was a significant 46% increase in the amount of trabecular bone adjacent to the implants. Conclusion: The mature runt cow allows for implantation of human-sized interbody and intrabody spinal prostheses. This animal model allowed for macro-and histological analysis of the implant and surrounding tissues. In vivo stability was demonstrated for the disc prosthesis while also allowing for evaluation of intended mobility. Additionally, this is the first study to suggest increased bone density supporting an interbody prosthesis.