In vitro biomechanical testing of the stability of primary and revision hip acetabular implants

Hip acetabular stability is the capability of acetabular implants to resist to the forces acting in the acetabulum during patient activities after surgery. If implant motions are sufficiently low, primary stability is achieved and the osteointegration process between the implant and the surrounding bone may occur. In this context, measuring implant motions is essential to predict the implant failure. In clinical practise, these measurements are limited to implant migration, while elastic motions and periacetabular strains are not monitored. So far, to obtain a complete set of stability measurements in vitro testing is the most reliable option. Despite the importance of the experimental analysis, a general consensus about the application of biomechanical tools to solve clinical problems is still missing. The aim of my Ph.D project was to develop and apply reliable in vitro methods to assess the hip acetabular stability in case of primary and revision reconstructions. First, two methodological studies were conducted (1) to define and implement a robust reference frame for the human hemipelvis based on a morphological analysis of this anatomical district and (2) to create a robust procedure to measure the implant motions and the periacetabular strains with the Digital Image Correlation technique. Secondly, I applied these methods to answer the following clinical questions: 1. How do changes in the motor task affect the cup stability and the periacetabular strains? 2. Does the cup medialization affect implant stability? 3. Which is the effect on cup stability of defect reconstructions with an innovative synthetic bone substitute or with human bone graft in revision surgery? All these clinical questions were answered in three experimental studies. In conclusion, this project provided a reliable set of in vitro methods to perform biomechanical testing on human hemipelvis and to assess the stability of acetabular reconstructions by mean of Digital Image Correlation.