Introduction: Cementless implantation of acetabular cups is the standard procedure of choice nowadays. We report on a new hemispheric acetabular socket with Trabecular-Metal-Surface made out of tantalum for cement-less implantation that meets all the requirements that are considered essential for direct osseointegration of cementless implants like porosity, surface roughness and biocompatibility. This multi-center study reports on the surgical technique and the early 5-year clinical results with this implant at three orthopaedic institutions.

Material und Methods: Since 1998 a total of 186 of these cups were implanted in three orthopaedic departments. All patients were followed-up prospectively. 32 implantations were performed with computer-assisted navigation, all others were done manually. In 18 cases the ceramic-on-ceramic articulation was used, all the other patients received Ceramic-on-HDPE as the standard articulation. The cup was combined with different stems including cementless Zweymueller stem, the cementless SBG stem and the cemented Weber-Stuehmer stem. A standard lateral or antero-lateral approach was used in all the patients. The first 112 consecutively patients with a minimum follow-up of 5 years were evaluated.

Results: Postoperative Harris-Hip-Score could be improved to median 92. The positions of all the cups implanted with computer navigation were within a +/−3 range with respect to the intended target whereas manual implantation yielded differences of up to 10. Radiographically all cups showed full osseointegration after one year in all zones. Initial gaps in zone II in 7 cases were filled-up completely. There was no migration and no radiolucency. Two well-fixed cups had to be removed because of infection around the stem. We encountered two dislocations within the first six weeks in patients with Ceramic-on-HDPE-articulation. Both of them could be successfully treated by closed reduction. There were no clinical or radiographic signs of aseptic loosening. No other complications like deep vein thrombosis, hematoma or wound infection did occur.

Conclusion: The new tantalum surface showed excellent osseointegration in all patients. Even in those cases of infection the cup was well-fixed. Due to its hemispheric surface it can be positioned quite easily and shows excellent primary stability. This new poro-coating surface ensures firm fixation of the implant and promises an unprecedented long-term stability.