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Abstract
Background and purpose — High primary stability is important for long-term survival of uncemented femoral stems. Different stem designs are currently in use. The ABG-I is a well-documented anatomical stem with a press-fit design. The Unique stem is designed for a tight customized fit to the cortical bone of the upper femur. This implant was initially developed for patients with abnormal anatomy, but the concept can also be used in patients with normal femoral anatomy. We present 5-year radiostereometric analysis (RSA) results from a randomized study comparing the ABG-I anatomical stem with the Unique femoral stem.
Patients and methods — 100 hips with regular upper femur anatomy were randomized to either the ABG-I stem or the Unique femoral stem. RSA measurements were performed postoperatively and after 3, 6, 12, 24, and 60 months.
Results — RSA measurements from 80 hips were available for analysis at the 5-year follow-up. Small amounts of movement were observed for both stems, with no statistically significant differences between the 2 types.
Interpretation — No improvement in long-term stability was found from using a customized stem design. However, no patients with abnormal geometry of the upper femur were included in this study.
MN took part in analyzing the data and wrote the manuscript. All the authors took part in later revisions and approved the final manuscript. OF took part in analyzing the data. JK took part in analyzing the data and designing the figures. KH performed the RSA measurements. PB and AA were responsible for development of the custom femoral stem, the design of the study, and collection of data. They also performed most of the surgical procedures together with OSH, who also took part in collecting the data.
None of the authors has received financial support from the manufacturer of the Unique stem (Scandinavian Customized Prostheses (SCP), Trondheim, Norway). AA is an unsalaried member of the Board and is a representative of the research group that took part in the development of the implant.