Effect of Inner Taper Angle of Acetabular Metal Shell on the Malseating and Dissociation Force of Ceramic Liner

Background Malseating of ceramic liner appeared as a matter of concern in multibearing metal, although multibearing cup can be coupled with hard liners as well as polyethylene liner. In this metal shell, the inner taper angle should be 10° for the modularity, while standard metal shells for ceramic liner have an inner taper angle of 18°. However, there has been no study in the effect of taper angle to the risk of malseating. We evaluated whether the taper angle of metal shell might affect the malseating of ceramic liner, and dissociation force of ceramic liner from metal shell. Methods Three surgeons manually inserted ceramic liners into two designs of metal shell with different tapers angles (10° and 18°). We compared malseating rates of ceramic liners and push-out strengths, which means dissociation force of the ceramic liner from the metal shell, between these two metal shell designs. Results The malseating rates in 10° metal shell were higher than those in 18° metal shell (23.3% vs 0%, P < .05). The mean dissociation force (1148.8 ± 46.7 N) in 10° taper cup was higher than that (389.7 ± 108.3 N) in 18° taper cup (P < .01). Conclusion Our results suggest that surgeon should be cautious about malseating of ceramic liner when using multi-bearing metal shell with inner taper angle of 10°. Clinical relevance When surgeon use multi-bearing metal shell with inner taper angle of 10°, our results suggest that surgeon should be cautious about malseating of ceramic liner.