To compare the mineral density of periprosthetic bone around the two collarless stems, CLS and Alloclassic, which were same in composition and coating, but different in their shape and fit. It is known that the CLS stem is designed for metaphyseal fit and the Alloclassic stem is for upper diaphyseal fit.

In this matched cohort study, we performed DEXA scan using Hologic QDR-1000 on 20 patients, 9 of whom had CLS (Sulzer, Switzerland) femoral stem (group A), and 11 had Alloclassic (Sulzer, Switzerland) femoral stem (group B). BMD was obtained for seven zones of Gruen, and the difference was compared between the two groups.

In group A, there was a significant decrease (P<0.05) of mean BMD in Gruen zones 1, 2 and 7 compared to normal side. In group B, there was a significant decrease (P<0.05) of mean BMD in Gruen zones 1, 2, 3, 4, 6 and 7 compared to normal side. Comparing the percent decreases of BMD, the only significant difference was observed in Gruen zone 1, in which group B showed more than 10% decrease than group A (P<0.05).

Our findings suggest that the design of stem affects postoperative changes of BMD, and that the stem with more proximal fit would behave better in terms of stress shielding.