The cone hip stem: a prospective study of 13 patients followed for 5 years with RSA.

We operated on 13 patients (14 hips) with dysplastic hips, mean age 42 (28-58) years, with a cementless Cone stem and followed them for 5 years, using the Merle d'Aubigné clinical score, conventional radiography and repeated radiostereometry analyses. The clinical scores improved markedly at 4 months and still more throughout the study. None of the patients complained of thigh pain. No stem showed radiographic subsidence, but 3 stems had radiolucent zones probably indicating fibrous ingrowth. Micromigration was measured at 4 months, 1, 2 and 5 years. The mean subsidence after 5 years was 0.27 mm and the mean posterior micromigration of the head was 0.74 mm. Most of the micromigration took place within the first 4 months. We conclude that the uncemented Cone stem used in dysplastic hips has shown a good clinical outcome so far and was found to be stable on conventional radiographs and using RSA technique.