Introduction: The acetabular component in primary THA is placed on pathologic bone stock. Little is known about histology and its impact on aseptic cup loosening. We therefore investigated undecalcified acetabular bone biopsies taken prior to primary THA and at the time of revision surgery. Study design: In a prospective study, starting 01/1993, a bone biopsy of the acetabulum out of zone 1 according to De Lee and Charnley is taken in each primary THA in a standardized manner. In case of revision surgery of the cup, another biopsy is taken again. Between 01/1993 and 08/1997 351 cementless titanium shells with screws cups have been implanted at our institution. The average age at operation was 68 years (range 29–90 years). In 88% osteoarthritis was the primary diagnosis. Biopsies were classified as normal bone (type I), increased sclerosis (type II), restless bone (type III) or dead bone (type IV) according to a classification developed in our institution. Biopsies with a special entity such as rheumatoid arthritis are grouped «others». The initial diagnosis on the pre-operative X-ray was correlated to the results of the biopsies. Signs for aseptic loosening of the cup were defined on the complete x-ray series. All explanted cups were analysed for signs of impingement or increased wear.

Results: 8 cups (8 patients) had to be revised until August 2004 (average age at revision 63.6years, range 49.6–77.8 years). The initial diagnosis was osteoarthritis in 5 cases, twice avascular necrosis of the femoral head and 1 rheumatoid arthritis. 5 times we found metal-on-metal, 3 times PE-ceramic bearings. We found one of each biopsies in type I and type IV, 2 in type II and type III. 2 biopsies had to be grouped «others». At time of revision one biopsy initially grouped as type III had to be reclassified as «others». 2 cups were revised due to late haematogenous infection. 3 cases showed a direct relation between the result of the biopsy and failure of the cup. In 1 case we found surgical failure, though impingement and a type IV biopsy as combined reasons for failure. 2 cups (2 patients) revised after 1.2 years, immunhistological reaction due to metal-on-metal could have been the reason for failure (still under investigation).

Discussion: Surgical failures and implant related factors are accused as major reasons for loosening of the cup in THA, patient related factors often neglected. The acetabular bone quality, as one patient related factor, showed in almost half of the cases analysed a correlation with later acetabular loosening. One should therefore be aware of acetabular bone quality as one factor for loosening of the cup when monitoring acetabular implants, especially when newly introduced.