Abstract

Introduction Fusion has been the gold standard as the surgical treatment for DDD, but disc arthroplasty is gaining more popularity based on motion-preserving characteristics and theoretically, preventing accelerated disc degeneration at adjacent levels. NuNec is a novel cervical device developed to maintain motion, while not interfering with MRI/ CT and incorporating a fixation system that does not require over distraction or keel cutting of bone. Design Similar to most cervical disc arthroplasty devices, NuNec has an inner ball/socket articulation. The device is manufactured from PEEK-OPTIMA with hydroxyapatitecoated outer surfaces and is fixated by a unique CAM interference screw locking mechanism. Fixation strength was tested with bench-top pullout testing and bony ingrowth was examined in a pilot study with an in-vivo caprine model. Wear testing of the device was conducted following ASTM/ISO recommendations. Most cervical arthroplasty devices are of metal-on-metal or metal-on-UHMWPE, resulting in strong MRI/CT artifacts prohibiting accurate future diagnosis on the index level. NuNec is made from radiolucent PEEK and will not interfere with MRI and CT. For fixation of the endplates to the adjacent vertebrae, most devices use keels, flange screws or spikes. Keel designs have the potential risk of spinal cord injury during keel cutting and splitting of the vertebral body, especially for multi-level disc arthroplasty. Spikes need overdistraction for implantation of the device. Also most devices have roughened, plasma-sprayed metallic surfaces to enhance by bone in growth. The CAM design of NuNec offers implantation with zero profile and fixation by rotating interference CAM’s into the endplates. Bench-top pullout testing has shown this CAM design has a fixation force higher than most keel and flange-screw designs. The hydroxyapatite coating does not affect the chemical and mechanical properties of the device; 3-month results from an in-vivo caprine model have shown excellent bony apposition to the coating/PEEK with no adverse histological response. Wear testing shows a wear rate comparable to other devices. Conclusion NuNec is the first articulating radiolucent cervical arthroplasty device in combination with a unique, instinctive mechanical fixation with a hydroxyapatite coating. These design benefits have been demonstrated through preclinical testing and have allowed for advancement to the clinical stage.