There’s a trend toward bone preservation in human joint repairs that’s possible in part to a specialty implant material called pyrolytic carbon, or pyrocarbon for short. The traditional materials used for implants are metals such as cobalt-chrome and titanium or plastics such as ultra-high molecular weight polyethylene.
Pure pyrocarbon implants are said to offer advantages over polyethylene and metal implants. For starters, pyrocarbon has an elastic modulus very similar to cortical bone, of the two types of tissue that form bones. This results in better biological fixation to the existing bone and reduced stress. Pyrocarbon is also thromboresistant , that is, it resists blood clotting.
In addition, pyrocarbon has been found to have excellent long-term biological compatibility. The material has already been widely used in mechanical heart valves and in finger joint implants.
To make pyrocarbon-coated orthopedic implants, a graphite substrate is placed in a chamber and heated to between 1,200 and 1,500C. A hydrocarbon gas, such as propane, is inserted into the chamber. The heat breaks the hydrogen bonds and releases a carbon atom. This carbon atom then deposits itself onto the graphite substrate. Over time, the substrate is coated with pyrolytic carbon.
The physical and mechanical properties of pyrocarbon lie between graphite and diamond, two other materials of the same carbon family.
Pyrcocarbon was originally developed for nuclear reactors, and in 1996 a pure carbon implant material was introduced. They are currently marketed for implants by Tornier and Ascension Orthopedics.
Tornier, for example, offered several joint replacement or joint spacer devices made from pyrocarbon in the hand, wrist and elbow, and recently announced a pyrocarbon shoulder implant.
The first product offered by Ascension Orthopedics, founded in Austin, TX in 1992, was a pyrolytic carbon total joint replacement for the MCP joint of the hand. Its joint replacement product line has since expanded to include implants for the shoulder, elbow, wrist, hand, foot and ankle.