Roentgen stereophotogrammetric analysis of prosthetic fixation in the hip and knee joint.

Using highly accurate roentgen stereophotogrammetric analysis (RSA), migration and cyclic displacement of prosthetic components can be assessed. In arthroplasty of the knee, all tibial components migrate during the first year but stabilize thereafter in a majority of cases. They also display inducible displacement in response to external forces. The effects of alterations in design or different modes of fixation may be readily detected using this noninvasive method. Three patients, who later developed mechanical loosening, migrated continuously and were identified by RSA already during the first year, indicating a clinical significance of continuous migration in terms of future mechanical loosening. Also in the hip, abnormally migrating femoral and acetabular components may be identified at an early stage. Using conventional clinical assessment, ten years and a large number of patients are often needed, while with RSA, new prosthetic devices may be assessed at a much earlier stage.