Radiostereometric analysis (RSA) can detect early micromovement in unstable implant designs which are likely subsequently to have a high failure rate. In 2010, the Articular Surface Replacement (ASR) was withdrawn because of a high failure rate. In 19 ASR femoral components, the mean micromovement over the first two years after implantation was 0.107 mm (sd 0.513) laterally, 0.055 mm (sd 0.204) distally and 0.150 mm (sd 0.413) anteriorly. The mean backward tilt around the x-axis was -0.08° (sd 1.088), mean internal rotation was 0.165° (sd 0.924) and mean varus tilt 0.238° (sd 0.420). The baseline to two-year varus tilt was statistically significant from zero movement, but there was no significant movement from one year onwards.
We conclude that the ASR femoral component achieves initial stability and that early migration is not the mode of failure for this resurfacing arthroplasty.
We wish to thank Project Nurse A. Gam-Pedersen, the technical staff at the RSA unit and statistician L. Korsholm for their help.
The author or one or more of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. In addition, benefits have been or will be directed to a research fund, foundation, educational institution, or other non- profit organisation with which one or more of the authors are associated.
- Received January 14, 2012.
- Accepted May 2, 2012.
- ©2012 British Editorial Society of Bone and Joint Surgery