MIGRATION AND WEAR OF HYDROXYAPATITE-COATED PRESS-FIT CUPS IN REVISION HIP-ARTHROPLASTY - A RADIOSTEREOMETRIC STUDY

Screw-fixated and hydroxyapatite-coated press-fit cups were studied us ing radiostereometry in 29 revision and 14 primary arthroplasties. The acetabular defects in the revision cases varied from none to type 3 ( wall defects) according to Gustilo-Pasternak, Morsellized allograft wa s used in 25 revisions. Nine of these cups rested on less than 50% liv ing bone. After 2 years, the mean migration in the revised group reach ed 0.36, 0.21, and 0.49 mm in the horizontal, longitudinal, and antero posterior (AP) directions. The mean rotations varied between 0.5 degre es and 0.7 degrees depending on direction. The primary implants displa yed smaller mediolateral migration and AP till. The mean proximal wear rate far the whole group was 0.11 mm/y. A central gap on the postoper ative AP view implied less migration. The size of the preoperative bon e defects or amount of bone-graft used had no influence on the migrati on. Despite extensive use of morsellized allograft, this implant displ ayed the smallest migration so far reported in revision hip arthroplas ty.