THE UNIQUE CUSTOMIZED PROSTHESIS (UCP) IS MORE STABLE THAN THE CEMENTED ELITE PLUS FEMORAL STEM. A RANDOMIZED PROSPECTIVE STUDY WITH RADIOSTEREOMETRIC ONE YEAR FOLLOW UP

Abstract

New prosthesis designs should be compared to a standard implant in randomized studies evaluated by radiostereometric analysis (RSA). The Unique customized prosthesis (UCP) is a newly developed concept for fitting uncemented prosthesis to the exact internal shape of the proximal femur [1]. We evaluated the new UCP design with the null hypothesis that this implant would be no more stable than a standard cemented implant.

Material and methods: 38 patients, mean age 51.6 years (31–65) were randomized to a UCP HA coated femoral stem or an Elite Plus (DePuy) cemented stem. All patients were implanted with a Duraloc (DePuy) uncemented cup except one patient with a protrusio who was primary impaction grafted with a cemented cup. Most patients received a Zirconium head, and all heads were 28 mm. The femoral stems were fitted with 3 tantalum balls and 4–10 tantalum balls were implanted in the femur during operation. RSA pictures were taken postoperatively, after 6 and 12 months.

Results: The Elite Plus stem rotated more into retroversion after 6 and 12 months (0.79° versus 0.31° after 12 months, P< 0.05). Nearly all of this rotation took place during the first 6 months. The Elite Plus stem migrated medially while the UCP migrated laterally (0.04 mm medially versus 0.03 mm laterally, P=0.06). The Elite Plus stem also migrated more distally than the UCP (0.17 mm versus −0.06 mm, P=0.055).

Discussion: Customized implants were more stable than the cemented Elite Plus prosthesis. Compared to other results with the Elite Plus rotations and migrations were small in this study [2]. Initially all patients had good clinical results, and only by long time follow up any clinical differences due to the small differences in stability as measured by RSA can be found.