Pyrolytic carbon (pyrocarbon) was hailed at the time of its introduction for use in small joint arthroplasty as an ideal material because of its excellent wear characteristics and biological compatibility with joint tissues. In this article, Sweets and Stern present the longest-term follow-up to date of pyrolytic carbon implants for proximal interphalangeal joint arthroplasty in patients with osteoarthritis. At an average of fifty-five months, with over half the patient cohort followed for more than five years, the authors noted a high rate of failure after proximal interphalangeal joint arthroplasty with pyrolytic carbon implants, including dislocation, subsidence and loosening, implant fracture, and joint contracture, with a reoperation rate of 19%.
The literature on the use of pyrolytic carbon implants for the proximal interphalangeal joint has shown mixed results, including a previous study by one of the authors (P.J.S.) that noted high patient satisfaction but squeaking, loosening, contracture, and dislocations at the time of the thirteen month follow-up1. Chung et al., in a study of twenty-one proximal interphalangeal joint arthroplasties with pyrolytic carbon implants, reported improvements in the Michigan Hand Outcomes Questionnaire scores and patient satisfaction, but noted three dislocations and slight motion loss at the time of the twelve-month follow-up2. Nunley et al. found no improvement in either range of motion or outcomes scores at an average of seventeen months, and noted loosening and joint contractures in five patients with posttraumatic osteoarthritis3. Herren et al. also reported radiographic migration of one or both components in eight of seventeen proximal interphalangeal joints, with radiolucent lines seen in three more joints, although pain relief was sustained at 20.5 months in all patients4. The only study with a follow-up interval comparable to that in the current article is the investigation by Bravo et al., who reported on a mixed population of patients with osteoarthritis, posttraumatic arthritis, and rheumatoid arthritis, with an average thirty-seven-month follow-up5. In that study, decreased pain scores, improved grip and pinch, and subjective patient satisfaction were noted. Those authors noted that additional procedures were needed in 28% of the joints, including four that were revised for instability (although dislocation was not specifically reported) and four that were revised for loosening. Bravo et al. also noted that 40% of the implants showed radiographic position changes at the time of the final evaluation but did not appear to be loose, attributing these changes to the way in which pyrolytic carbon implants react with the surrounding bone.
While the wear properties and inert biochemical profile of pyrolytic carbon have been shown from its long-term use in cardiac valve replacement6, the interaction of pyrolytic carbon within the bone microenvironment may not be as favorable, as shown by this article. In the short term, most investigations have noted high patient satisfaction, but nearly all studies have described some radiographic or clinical loosening. In the only other long-term study5, patient satisfaction was sustained at thirty-seven months, but nearly one-third of the joints required further surgery. The reported signs of radiographic change at the implant-bone interface at the time of final follow-up are the more concerning outcome from that study. In combination with the findings by Sweets and Stern, who reported that nearly half of the pyrolytic carbon implants demonstrated radiographic signs of loosening, the clinical outcomes suggest that the surrounding bone does not form a stable interface with these implants.