Retrieval analysis of an explanted NuNec cervical disc: A case report

Retrieval analyses allow investigation of the efficacy of artificial implants to replace diseased or damaged natural joints. Implants are not always removed due to mechanical failure; a well-functioning implant may require removal due to causing pain. As an alternative treatment to fusion, total disc replacement is an evolving treatment. Recently, to eliminate the possible failure mechanisms observed in metal-on-polymer and metal-on-metal artificial discs, an all-polymer cervical artificial disc has been introduced. The NuNec cervical arthroplasty system is a self-mating, all-polymer design which utilizes a ball-in-socket configuration with each component made of polyether ether ketone. For the first time, a retrieval analysis of a NuNec cervical disc, which has been removed due to pain from a 54-year-old female patient, has been undertaken. The main reason associated with pain was the size of the implant which was found to be too big for the patient. The time in vivo of the implant was 2 years and at the time of removal, the implant was thought to be functioning well. The average surface roughness values of the socket and the ball of the explanted NuNec disc were measured as 0.067 ± 0.056 μm (Sa) and 0.037 ± 0.023 μm (Sa). Compared to an unused disc, the surface roughness significantly decreased (p = 0.00). The articulating surfaces of the explant had negative skewness and burnished appearances. Evidence for both abrasive and adhesive wear mechanisms was observed on the explant. The hydroxyapatite coatings at the backsides were completely lost.