In-depth oxidation and strain profiles in UHMWPE acetabular cups non-destructively studied by confocal Raman microprobe spectroscopy

Raman spectroscopy is used for the characterization of the two main mechanisms responsible for the degradation of acetabular cups in hip joints: creep deformation and oxidation. The term creep refers to the permanent deformation that occurs under the effect of body weight and does not completely recover after load release. This mechanism involves no mass loss from the sample, but packing and adjustment of the polyethylene molecules in their reciprocal positions under pressure. Conversely, oxidation triggers wear, which is accompanied by irreversible mass loss from the material: surface molecules of the polyethylene body oxidize, delaminate and are progressively peeled off, involving volumetric changes and resulting in debris formation. Both degradation mechanisms negatively interact and converge toward cup loosening, which requires revision surgery. In this paper, we show that confocal Raman spectroscopy can be used to separate the contributions to the dimensional change observed in acetabular cups arising from creep and from wear. Raman measurements are completely non-destructive and contactless, and can guide surgeons and materials technologists to optimize surface treatments and molecular structure of polyethylene cups, thus maximizing their in vivo lifetime. (C) Koninklijke Brill NV, Leiden, 2009