[Primary rotatory stability of hip endoprostheses stems after manual and robot assisted implantation]. / Primäre Rotationsstabilität von roboterunterstützt und manuell implantierbaren Hüftendoprothesenschäften.

AIM: In our study we compared the primary rotatory stability of hip endoprostheses which were implanted with the help of a robot with that of manually implanted stems. METHOD: We examined three different types of prosthesis-stems: Osteolock (Stryker-Howmedica), CBC (Mathys), Excia (Aesculap). Furthermore, we examined two types of prostheses which could not be implanted with a robot (Sl-Plus/Endoplus; Hipstar/Stryker-Howmedica). 10 stems of each prosthesis type were implanted in identical polyurethane foam blocks; 5 of them were implantated manually, 5 with the help of a robot (CASPAR, URS-Ortho). After implantation, a defined rotatory stress was put on the stem with the help of a torquing machine. The torsional moment which was necessary until the stem broke out of the foam was documented with the help of special software. RESULTS: In all types of prostheses the use of the robot system led to a higher rotatory stability compared to the manual group. Among the three tested types of prosthesis stems, the CBC stem is significantly more 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. The Zweymüller stem and the Hipstar prosthesis did very well, even in comparison to the robot-implanted group. The results of the Zweymüller stem and the robot-implanted CBC Stem were similar, and a significantly higher rotatory stability of the Hipstar prosthesis compared to every other stem was observed. CONCLUSION: Using a robot, the rotatory stability of hip endoprostheses can be improved. However, the design of the stems seems to be even more important for the stability than the implantation technique.

[Primary rotatory stability of robot-assisted and manually implanted hip endoprosthesis stems]. / Primäre Rotationsstabilität von roboterunterstützt und manuell implantierten Hüftendoprothesenschäften.

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.

[Biomechanical examinations of the efficacy of wrist guards in inline skating]. / Biomechanische Untersuchungen zur Effektivität von Handgelenksprotektoren für das Inline-Skating.

INTRODUCTION: Fractures of the wrist and forearm are the most frequent injuries in Inline-Skating. Clinical experience has shown that these injuries can be prevented the use of wrist protectors. But various authors have shown that fractures can also occur despite the use of wrist protectors. Aim of this study was to examine different wrist protectors in a biomechanical set up. METHOD: A standardized trauma was simulated using an artificial hand with a certain weight. The forces with or without protective devices have been recorded by a force moment sensor. The results of different protectors have been compared. RESULTS: A mean force of 956 N was measured without the use of a protective device. With the application of a wrist protector these forces were reduced between 4 and 20 %. The best values have been reached with models with a strong base plate. CONCLUSIONS: The results of the present study may explain the clinical observation that wrist and forearm fractures can occur despite the use of a wrist guard. The protective effect of a wrist protector depends highly on the model that is used.

[The Kiel arthrograph--an instrument for recording active and passive shoulder joint mobility]. / Der Kieler Arthrograph--Ein Gerät zur Aufzeichnung der aktiven und passiven Schultergelenksbeweglichkeit.

The authors describe a new method for measuring the flexibility of the shoulder. They have designed a device consisting of two electrical goniometers to measure the horizontal and the vertical position of the humerus. A computer registers these signals, calculates the region of mobility as a sperical segment centered to the shoulder joint (caput humeri). This region is displayed in a map, called arthrogram. Slightly modified, the arthrograph measures the rotation of the humerus and depicts the rotation angle into the map, at the site of the measurement. First results are reported. The procedure is reproducible with an error less than 5 degrees. Arthrograms of sound persons are compared to those of different pathological symptoms. Arthrograms show more information than single angular values. They can be viewed easily, e.g. to control the success of a treatment.