A Comparative Study of Metal Ion Analysis with Metal-on-Metal (MoM) Hip Resurfacing and 28mm MoM Total Hip Replacement (THR): Data at Medium-term

Institution: The Rizolli Institute, Italy
Investigator: Professor Antonio Moroni
Stream: Research Fellowship
Topic: Lower Limbs/Biology (Hip)
Status: Completed

Modern metal-on-metal (MoM) hip resurfacing has been introduced as a less invasive method of joint reconstruction for young-active patients. The use of large diameter MoM has also gained popularity. The advantages of using this procedure include: wider range of motion, better functional outcomes and lower rate of dislocation.

Considering the large diameter of the coupling components, there are concerns regarding the quantity of metal ions released. In vitro studies on the effect of bearing diameter on wear reveal a two-phase effect. Smaller bearings such as those of 22mm diameter have higher wear rates with increasing diameters, as expected in bearing in boundary lubrication mood. In larger bearings of 28mm and above, the wear rate decreases with increasing diameter, as expected from mixed or fluid film lubrication.

In our previous study, we found no differences in metal ion levels between BHR patients and 28mm Metasul THR patients at two years follow up. The reason for these results remain unclear and could be explained according to the classic elastrohydrodynamic theory, which suggests that fluid-film is more likely in larger diameters, and hence, it is inferred that wear will be reduced. Possible difference in the tribology of the two types of prosthesis, in the radial clearance or ions dissociation from the stem taper-neck junction could also explain this result.

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