To compare the incidence of early dislocation in a series of a small femoral heads with a series of larger femoral heads.

This study analyzed 84 primary total hip arthroplasties, which were performed between January 2002 and January 2006 and were followed more than 6 months. The cases were divided into two groups, a smaller head group (28 & 32 mm) and a larger head group (36 mm). The incidence of dislocation was recorded for both groups during the first 3 months after surgery. The probability that the incidence of dislocation between both groups was significantly different from the expected dislocation rate was assessed based on the assumed risk of an early dislocation of 2%. The two groups were compared with regard to the size of the acetabular cup.

There were 6 early dislocations in the smaller head group, while no dislocations occurred in the larger head group. The incidence of expected dislocation, assuming a 2% dislocation rate, was similar for the smaller head group but different for the larger head group. The size of the acetabular cup was similar in both groups.

These results highlight the advantage of a larger femoral head in reducing the early dislocation rates.