In-vivo degradation mechanism of Ti-6Al-4V hip joints

In-vivo exposed Ti-6Al-4V implants were investigated to determine the degradation mechanism occurring during the articulating movements of the hip joint in the human body. Failed implants were compared to Ti-6Al-4V samples, which were tested in the laboratory for their tribocorrosion performance. The results strongly indicate that degradation of Ti-6Al-4V has occurred with the same mechanism for both the implants and the laboratory tested samples and, hence, block-on-ring tribocorrosion testing was found to be a useful tool for mimicking the degradation occurring in the body. gradation mechanism was concluded to be of combined mechanical and chemical nature. Wear debris is formed and accumulated in large flakes (> 100 μm). Upon further sliding the flakes are pressed into the surface and ultimately crushed into small, brittle particulate debris (< 5 μm), which is released from the surface. It is suggested, that the small brittle particulate debris has a more detrimental effect in the hip joint than the large flakes due to a stronger reaction of the peri-prosthetic tissue. Also, Al-oxide particles are formed as part of the degradation mechanism.