A prospective study of the migration of two acetabular components. PCA versus RM cups.

Fifty-nine PCA cups and 61 hydroxyapatite-coated RM cups were included in a prospective randomised study with a mean follow up of 5.2 years. Clinical evaluation revealed better results with the RM cup. Radiological criteria of loosening could be applied only with considerable restrictions as different parameters were assessed: progressively loosened beads in PCA cups and faded contour in RM cups. Migration was measured by a computer assisted method (EBRA). PCA cups showed significantly more longitudinal migration 2 years after operation and subsequently. High migration values correlated with a limp. Loosening as defined by migration was of clinical relevance, could be measured early and predicted the survival rate.