Abstract
Aim: In alumina-on-alumina (Al/Al) THA, microsepa-ration is reported to accelerate wear and to be a risk factor of alumina cup fracture. While microseparation after THA is detected during walking, microseparation also occurs in relation to the hip position. Using Al/Al THA with cemented polyethylene-back alumina cup, the microseparation is clearly visible on plain roentgen-ograms. The aim of this study is to investigate the factors that affect hip position related microseparation. Materials and Methods: We performed 65 primary Al/Al THA. An average age at operation was 61.1 years and an average follow-up period was 29.5 months. Roentgenograms were taken in hip neutral position, abduction, adduction, external rotation and internal rotation. Results: Microseparation was observed in 15 hips (23.1%); 10 hips with hip external rotation and 5 hips with hip abduction. An average abduction angle of the cup was 33.5±9.8 degrees with microseparation and 36.6±7.3 degrees without microseparation. An average anteversion of the cup was 9.7±6.7 degrees and 7.8±5.8 degrees, respectively. The factors that brought about microseparation were postoperative muscle weakness in 3 hips, impingement in 9, cup malposition (abduction angle: 19, 23 degrees) in 2, and short off-set stem in one. Discussion and Conclusions: It should be noted that microseparation is not a rare phenomenon and it occurs in hip particular position even if it can not be detected on routine roentgenograms.
Theses abstracts were prepared by Professor Dr. Frantz Langlais. Correspondence should be addressed to him at EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
