Abstract
Background
The failure and subsequent withdrawal of the ASR device in both its resurfacing and THR form has been well documented. The National Joint Registry report of 2010 quoted figures of 12–13% failure at five years. Adverse reaction to metal debris (ARMD) is a poorly understood condition and patients developing severe metal reactions may go unrecognised for sometime.
Patients and Methods
In 2004 a single surgeons prospective study of the ASR bearing surface was undertaken. We present the ARMD failure rates of the ASR resurfacing and ASR THR systems. The diagnosis of ARMD was made by the senior author and was based on clinical history, examination, ultrasound findings, metal ion analysis of blood and joint fluid, operative findings and histopathological analysis of tissues retrieved at revision. Mean follow up was 52 months (24–81) and 70 patients were beyond 6 years of the procedure at the time of writing. Kaplan Meier survival analysis was carried out firstly with joints designated “failure” if the patient had undergone revision surgery or if the patient had been listed. A second survival analysis was carried out with a failure defined as a serum cobalt > 7µg/L. Full explant analysis was carried out for retrieved prostheses.
Results
There were 505 ASR patients in total.
657 metal ion samples were available at the time of writing (152 repeats).
Survival analysis using revision/listed as end point (at 6 years):
ASR resurfacing: 26.1% failure. ASR THR: 55.5% failure.
Survival using ion analysis (at 5 years):
ASR resurfacing: 50.1% failure. ASR THR: 66.5% failure.
The median (range) volumetric wear rate of failed prosthesis was 8.23mm3/year (0.51–95.5).
Conclusion
A number of design flaws in the ASR has led to excessive wear of the bearing & taper leading to catastrophic failure secondary to ARMD.
