Prof. Dr. Stefan Budde, Bielefeld, presented exciting results of an RSA migration analysis of the A2® short stem at the German Congress for Orthopedics and Trauma Surgery (DKOU) in Berlin. Radiostereometry analysis (RSA) is a precise method to measure the smallest movements of an implant postoperatively. For this purpose, tantalum beads are introduced as markers in order to illustrate the migration of the implant in three-dimensional space with a simultaneously created stereo X-ray image and with the help of mathematical calculations. This makes it possible to understand the migration behavior and the process of osseointegration of a joint implant very well.

Half of the 60 patients included in the study were randomly assigned to receive the A2® short stem with titanium plasma spray coating (TPS), the other half received the A2® short stem with an additional BONIT® calcium phosphate coating. RSA was performed at baseline measurement before the first exercise and at follow-ups at 1 week, 6 weeks, 3 months, and 6 months.

The results show that 67% of the stems reached their final position after just one week. “That’s earlier than I would have thought,” said Prof. Dr. Budde during his lecture in Berlin. Over time, the implants showed rapid and complete stabilization and good osseointegration, which suggests a good long-term prognosis.

Although both stem surfaces (TPS and TPS+BONIT®) showed very good stabilization, it was interesting that the additional calcium phosphate coating did not have a positive effect on implant migration. In comparison, the stems with the additional coating had significantly higher and longer-lasting migration in the early phase than the stems with only TPS coating. The roughness of the implant surface may play a role in the initial stability in the early phase, as was discussed in the Berlin session. In addition, the hydrolysis of calcium phosphate layers could have an impact on the migration behavior of hip stems. Two thirds of the short stems examined achieved stability after just one week. This is earlier than a biological coating can show its benefits, stated Prof. Dr. Budde in Berlin.