Q: If a person develops heterotopic ossification after a disc replacement in the neck, will it affect how long the implant lasts?

A: It could though not enough research has been done to provide convincing evidence one way or the other to say for sure. Of the studies published, there was a recent one comparing three different types of implants: the Bryan disc, the Mobi-C, and the ProDisc-C.

These three were chosen because they are different in how they are made (material) and how they work (motion system). The Bryan disc is made of titanium and polyurethane. Polyurethane is a resilient, flexible, and durable manufactured material that can be stretched, smashed, or scratched, and remain fairly indestructible.

The Mobi-C implant is composed of titanium and polyethylene (plastic component). And the ProDisc is cobalt chrome and polyethylene. On a continuum of motion provided by each artificial disc, at one end, there's the Bryan disc, which provides the most movement with the least constraint. At the other end, is the ProDisc device with the least motion. The Mobi-C falls somewhere in between.

X-rays were used to look for heterotopic ossification (HO) during the follow-up period after the joint implants were put into place. The length of time between surgery and the development of HO was also recorded.

The overall results showed there was more bone formation than expected and that the type of implant did make a difference. In a group of 170 patients treated in Korea, 40 per cent developed heterotopic ossification.

Occurrence rate was highest in the ProDisc-C group and lowest in the Bryan disc group. And it was serious enough to reduce the life of the implant to an average of only 27 months (less than two and a half years). More study is needed in this area to sort out who develops heterotopic ossification, why, and what can be done to prevent it and protect the implanted discs.

Reference: Seong Yi, MD, PhD, et al. diffeence in Occurrence of Heterotopic Ossification According to Prosthesis Type in the Cervical Artificial Disc Replacement. In Spine