A new methodology for improving and testing the performance of hip prosthesis through advanced severe plastic deformation processes

Modern Total Hip Arthroplasty (THA) has evolved allowing orthopaedic surgeons for an exact reconstruction of hip biomechanical parameters thanks to modularity. Modular hip replacement represents, in fact, the best way to reconstruct the joint compared to conventional femoral stems. However, the modular implants are not massively used because of the high risk of breakage. One of the most common causes of their failure is the fretting corrosion at the neck-head interface combined with their relative micro-motion. Thus, the neck component undergoes major wear stresses leading to the implant failure. In order to avoid the risk of failure due to the corrosion fretting, it is necessary to improve the contact surfaces. Furthermore, available actual standards provide long testing procedure for verifying the overall modules fatigue performance thus discouraging researchers to search for possible solutions by changing the manufacturing process of the modules. This work presents a viable manufacturing technique for producing high performance neck components, proposing, at the same time, a faster and reliable testing procedure to predict the wear rate and its driving mechanism affecting the module. Thus, Ti6Al4V neck components have been manufactured by means of burnishing process at varying processing conditions which led to different surface characteristics. Different necks have been tested under real conditions for fretting fatigue simulating a walking loading cycle. Relative micromotions, together with information related to wearing path and operating conditions have been extracted online while testing, using the phase-based motion estimation method (PBME). The overall results demonstrate that burnishing process can tremendously improve the performance under service of the neck component and the proposed testing methodology is able to drastically reduce the testing time improving the reliability of the results.