[Long-term results of the cementless conical balgrist expansion cup--comparison analysis to the Zweymüller-Alloclassic screw cup].

AIM

The press-fit fixation of the conical Balgrist expansion cup (Allo Pro, Baar, Schweiz) is realised by the help of a (titanium alloy) split ring and a metal-backed inlay. The results and fixation principles of the cement-free Balgrist hip socket are analysed within a clinical and radiological long-time study and compared with those of the conical Zweymüller-Alloclassic CFS (Zimmer-GmbH, Winterthur, Schweiz) screw cup for a concluding evaluation.

METHOD

Between 1993 and 2003, 277 Balgrist hip sockets and between 1994 and 2000 130 Alloclassic-Zweymüller screw cups were performed consecutively in 364 patients considering similar indications with an average age of 54.6 years and 51.9 years, respectively. The clinical investigation was carried out with the Harris hip score (HHS). Radiological evaluation included a manual migration analysis according to Sutherland et al., Nunn et al. and Effenberger et al.; radiolucent lines were registered according to the zones of DeLee and Charnley. The survival rate of both cups was calculated on the basis of the Kaplan-Meier and the life-table analyses.

RESULTS

Besides 4 (1.4%) aseptic loosenings, 5 Balgrist cups (1.8%) had to be replaced because of infection and another 1 (0.8%) because of persisting pain. Three Balgrist sockets (1.1%) showed a migration > 2 mm. In the Alloclassic group 1 cup (0.8%) was considered as being migrated, another cup (0.8%) had to be replaced due to infection. Considering aseptic loosening and radiological migration as an end point, the cumulative survival of the Balgrist cup at 13 years was 97.3%, that of the Zweymüller-Alloclassic cup at 10 years was 99.2%. In comparison with the Alloclassic group, the Balgrist hip sockets showed increased radiolucent lines of zone 1 (p < 0.001), without any effects on the survival time or the clinical result however. Both cups resulted in good to excellent clinical results in the HHS (91 points).

CONCLUSION

The long-term analysis of the Balgrist hip socket proved that the concept of the retightening conical expansion cup leads to good clinical results and fulfils the minimum survival rate of 95% at 10 years as demanded by Delaunay and Kapandji. The good results obtained with the aid of this concept are comparable to those of the Alloclassic screwing cup.