[Primary rotatory stability of robot-assisted and manually implanted hip endoprosthesis stems].

In our study we compared the primary rotatory stability of hip endoprostheses implanted with the help of a robot and manually implanted stems. We examined three different types of prosthesis stems: Osteolock (Stryker-Howmedica), CBC (Mathys), and Excia (Aesculap). Ten stems of each prosthesis type were implanted in identical polyurethane foam blocks: five were implanted manually and five with the help of a robot (CASPAR, URS-Ortho). After implantation, the stem was subjected to a defined rotatory stress. The torsional moment necessary to break the stem out of the foam was documented with the help of special software. The force-displacement diagrams after robot-assisted implantations were homogeneous for each type of prosthesis. After manual preparation, the diagrams were very inhomogeneous. The rotatory test also showed very consistent results for the robot-implanted stems. The range of results after manual implantation was much higher. In all types of prostheses the use of the robot system led to a higher rotatory stability compared to the manual group. The CBC stem was most stable for rotatory forces after robot-assisted implantation compared to the other two types. After manual implantation there was no difference in stability between the different stems.