Abstract
Introduction: The Stryker ABG-I Total Hip Arthroplasty system with a Hydroxyapatite coated stem and cup has shown very promising short and mid-term clin-cial results at 2, 5 and 8 years. However, large discrepancies in component survival of the stem and cup have recently been published and require more data and further investigation about the potential causes.
Methods: All peer reviewed publications on the survival of the ABG-I hip prosthesis (9) were analysed regarding clinical results, polyethylene (PE) wear, osteolysis and survival. Own results from the first 250 consecutive ABG-I hips with a long-term follow-up of 10–15 years were added and compared.
Results: In the literature excellent survival rates of the ABG-I stem against osteolysis and aseptic loosening were reported with values ranging between 98%–100% after 5–10 years. In our own series stem survival against aseptic loosening was 100% at 10 years. No radiographic evidence of distal linear lysis was found around any stem. This was confirmed also in a histological investigation.
For the ABG-I cup the literature review gave survival rates between 59%–97% after 8–10 years. In our own study cup survival was 97.4% at 10 years. Looking at PE-wear, the literature gave average wear rates ranging from 0.24 to 0.32mm/year, values clearly above the wear rate boundary of 0.10–0.15mm/year usually considered as critical. In our own study augmented PE-wear (> 0.15mm/year) was noted in 23.6% of all implants. The majority (77%) of these implants were from patients younger than 70 years although this group only represented 57% of the total. The revision rates at 10 years reflect a similar trend with values much higher for patients below 70 years (2.8%) than above(4.9%).
Conclusions: Stem survival in our series was high, comparable to other published series and above the golden standard (cemented Charnley). However, the ABG-I cup showed lower survival rates, elevated PE-wear and augmented osteolysis around the holes. The comparatively high cup survival of our study is partly due to the high proportion of older patients. In the younger patient group PE-wear and revision rates were elevated. PE-wear is multifactorial and depends mainly on use. Some studies speculate it might be accelerated by low PE quality, crosslinking, liner fit or thickness. We found osteolysis not mainly at the rim but mostly around the 12 holes of the metal backed cup pointing at a possible pathway for wear particle migration into the reamed acetabulum as reported for other holed designs (Harris-Galante, Universal, Duraloc). As high wear and cyst formation did not always correlate it seems as if the pumping effect between flexing cup and acetabulum varies with component size, anatomy and bone quality influencing fluid flow, particle migration and osteolytic stimulus. A non-hole cup could alleviate this potential problem.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
