Radiostereometric analysis (RSA) is the most accurate method to measure acetabular migration in vivo. RSA migration measurements at two years have been shown to predict long term loosening [1]. New implant designs now require clinical evidence to gain CE marking due to changes to European Union Medical Device Regulations in 2021. It would be optimal to have the shortest validated clinical surrogate measure for long term success. Hence the aim of this meta-analysis was to investigate if RSA migration measurements earlier than two years can predict later loosening.
A systematic review of all RSA acetabular migration studies was performed in accordance with PRISMA guidelines (PubMed, Scopus and Embase databases). Migration results of each reported cohort were analysed at all early timepoints including three months, six months, one year and two years. Implant type, fixation method and additional screw fixation were investigated as independent factors that may influence the pattern of early migration.
61 RSA studies (including 1579 acetabular components) reported two year migration results of 33 different implants. There was no difference in the median migration of cemented (0.16mm) and uncemented (0.14mm) components at two years (p=0.36). The migration of uncemented components with additional screw fixation (0.157mm) was not significantly different to components without screws (0.161mm, p=0.94). RSA migration was reported at both one and two years for only 25 cohorts and 11 of these cohorts had mean migration above the recommended threshold of 0.2mm at two years. One year migration data correctly identified 10 of these 11 cohorts having a mean migration above the threshold at one year.
This meta-analysis provides the first evidence that RSA migration measurements at one year may be used to predict long-term loosening of acetabular components. This is significant for orthopaedic companies requiring the earliest clinical evidence available to introduce new implants.