High early migration of the revised acetabular component is a predictor of late cup loosening: 312 cup revisions followed with radiostereometric analysis for 2-20 years.

INTRODUCTION: Radiostereometric analysis (RSA) is an accurate and precise measurement tool of migration and rotation of implants. We investigated if early migration measured with RSA can be used to predict the risk of later aseptic loosening in acetabular revision surgery. PATIENTS AND METHODS: A total of 312 patients who underwent acetabular revision surgery were followed by RSA measurements for 2 to 20 years. The endpoint was either re-revision due to aseptic loosening or loosening on last available radiographic examination. Cox regression model was used to evaluate the predictive value of early migration.
RESULTS: A total of 16 acetabular cups were re-revised due to aseptic loosening and 7 unrevised cups were radiographically loose. Every mm of proximal migration 2 years postoperatively increased the risk of aseptic loosening by 37% (hazard ratio (HR) 1.37, 95% confidence interval (CI) 1.18-1.58). Adjusting for differences in base line demographics, bone defects and surgical techniques in a Cox regression model, risk of aseptic loosening with every mm of proximal migration was even higher (HR 1.94, 95% CI 1.34-2.82, p<0.001).
CONCLUSIONS: We found a strong relationship between early migration measured by RSA and risk of late aseptic loosening in acetabular revision surgery. Monitoring proximal migration with RSA should be considered as an essential step in quality assessment when new implants and novel techniques are introduced in acetabular revision surgery.