Orthopedics This Week—March 12, 2012
Timothy Wright, Ph.D., Kirby Chair of Orthopedic Biomechanics at Hospital for Special Surgery (HSS), and Douglas Padgett M.D., chief of Adult Reconstruction and Joint Replacement with HSS, have just completed a study that gives the first comprehensive look at the modes of failure in metal-on-metal (MOM) total hip replacements.
Dr. Wright tells OTW, "There is a long history of analyzing retrieved implants and making observations about the kinds of damage you see on the surface...but little comprehensive information about the mechanism behind the damage. I think it's fair to say that we don't have our arms around the problem yet.
"We looked at how we could begin to match our observations of the damage modes on the surface with quantitative measurements of how much the component wore in the damaged areas as well as with other factors such as metal ion levels, MRI imaging, and the surgical positioning of components, manufacturer, and head size. We found seven distinct damage modes, some of them obvious as to the underlying mechanisms of failure.
This is important because in the second part of our study, we are working with a company that has the technology to tell us where material has been removed. So if I'm staring at the head, where is the geometry altered? If you now take the descriptors of what the surface looks like, together with how the material was removed, it gives us more confidence in trying to understand mechanisms."