Should total hip arthroplasty femoral components be designed to subside? Aradiostereometric analysis study of the Charnley Elite and Exeter stems

The Charnley Elite and the Exeter sterns have different design concepts: Th e former is designed not to subside, whereas the latter is expected to subs ide. This radiostereometric analysis Study compares the early migration of the 2 steins. For both implants, the Ist year migration was about 4 times f aster than the 2nd year. The Exeter migration was predominantly distal (1 m m/y in the 1st year). It also showed slight collapse into valgus, and the h ead migrated slowly posteriorly (0.3 mm/y in the 1st year). In contrast, th e Elite had slow distal migration (0.2 mm/y in the 1st year) and rapid post erior head migration (0.8 mm/y in the 1st year). Four Elites and no Exeters had rapid posterior head migration rates (mean 2.8 mm/y in the 1st year an d 0.8 mm/y in the 2nd year). The Elite and the Exeter stems have fundamenta lly different early patterns of migration, which affect their long-term fun ction; 20% of the Elites and none of the Exeters had rapid posterior head m igration in the 1st year and the 2nd year and are likely to fail early. Pol ished, collarless, tapered designs, such as the Exeter, may be more forgivi ng than conventional stems designed not to subside.