Aims: We compared the primary rotatory stability of robot implanted hip endoprostheses with manually implanted stems. We examined three different types of prosthesisstems: Osteolock, CBC, Excia. Methods: 10 stems of each prosthesis type were implanted in identical polyurethan foam blocks: 5 manually, 5 robot assisted (CASPAR-System). The forces, which were necessary for the implantation of the stem were documented digitally. Now a deþnated rotatory stress was put on the stem with a torquing machine. The torsional moment was also documented digitally. Results: The strengthway- diagram of the implantation in robot assisted reamed foam blocks was homogeneous at each type of prosthesis. At the manually reamed blocks, the diagrams were very inhomogeneous.

The rotatory test showed also very unitary results at the robot implanted stems with only minimal variations of the results from the median. The range of results after manually implantation was much higher. In all types of protheses the use of the robot system lead to a signiþcantly higher rotatory stability. CBC stem is signiþcantly most stable for rotatory forces after robot assisted implantation compared to the other two types. After manual implantation there was no differrent stability between the CBC and the Osteolock stem. The Excia stem showed the signiþcantly lowers rotatory stability after manual and robot assisted implantation. Conclusions: With a robot system the primary rotatory stabilty of hip endoprosthesis is improved indenpendtly of the type of the prosthesis. The inßuence of the stem design is also important for the rotatory stability, too.