[Method of non-destructive mechanical testing of new surface coatings for prostheses]. / Methodik zur zerstörungsfreien Testung von Oberflächenbeschichtungen in der Endoprothetik.

Research into new surface coatings and surface processing methods for prostheses is subject to numerous studies. The aim of this study was to test an innovative biomechanical measuring method for the examination of the ingrowth of bone implants. Using a transcortical model, coated (n=14) or uncoated (n=14) titanic cylinders were implanted into the lateral condyle of 28 New Zealand White Rabbits. After 6 weeks or 6 months the animals were sacrificed and the osseointegration of the implants was evaluated biomechanically and histologically. Up to traction of 50 N the load dependent movement between bone and testing cylinder did not lead to a destruction of the bone-implant-interface. Therefore, biomechanical and histological investigations could be performed in the same specimen. The results of both evaluations showed a significant correlation (correlation coefficient -0.79; p < 0.01) and were absolutely reproducible. With the method of non-destructive mechanical testing, it is possible to halve the number of required animals. Additionally, the results of the biomechanical and histological analysis can be compared and thus serve as an internal control. In summary, the method of non-destructive mechanical testing represents an ideal tool to study new surface coatings and surface processing methods for prostheses.

Robotically-milled bone cavities: a comparison with hand-broaching in different types of cementless hip stems.

We performed an experimental study to compare the effectiveness of robotic bone milling (Robodoc and CASPAR) with hand-broaching as regards primary rotational stability of 7 different cementless stems. Using 48 synthetic femora and a specially-designed apparatus, we compared the implant stability of proximal and distal rotational stem displacement (slip) in relation to the cortex. We also measured stem deformation (twist) and the location of torque transfer from stem to cortex (i.e., fixation pattern). 5-ROM, Antega, and ABG stems were more stable in hand-broached femora. Osteolock stems showed no difference between CASPAR and hand preparation, but rotational stability was better in the Robodoc group. G2, VerSys ET and Vision 2000 stems gave increased rotational stability in the robotic groups. When placed too laterally, Vision 2000 showed a pattern of more distal fixation. The findings emphasize the current difficulties in creating a perfect match of robotically-milled cavity and stem geometry to achieve enhanced primary rotational stability. The pattern of fixation seems to depend not only on stem design, but also on canal preparation and stem positioning.