Wear studies on hip joints have been mainly focused on ultra high molecular weight polyethylene (UHMWPE) acetabular components since they can liberate a substantial number of particulate debris into the joint space, able to trigger osteolysis (bone dissolving disease) in the soft tissue of the periprosthetic area. However, also metallic and ceramic femoral components may contribute to the osteolysis phenomenon. To minimize wear and thus the production of wear particles, the choice of the two sliding materials and their intrinsic parameters (i.e. diameter of the components, roughness of the surfaces...) are decisive for the long-term success of a joint prosthesis. The success of these devices greatly depends on the smoothness of the harder femoral head, since increased roughness of the counterface may dramatically accelerate abrasive polyethylene wear. To gain more insights into this subject at molecular level, in vivo worn UHMWPE acetabular cups (follow-up of 11-12 years) coupled to ceramic or metal femoral heads were analysed by micro-Raman spectroscopy and the obtained results were related to the Ra and Rsk roughness data obtained on their femoral counterface. Moreover, selected alumina femoral heads were analysed by micro-Raman and fluorescence spectroscopy, according to a widely used piezospectroscopic technique applied to the study of alumina- and zirconia-based ceramics. In this work we focused our attention on the analysis of the R1 and R2 Cr3+ fluorescence bands of alumina as well as its Raman band at about 417 cm−1. The micro-Raman spectroscopic data showed that the wear of polyethylene correlated with the surface finishing of the counterface, since the UHMWPE acetabular cups articulating against alumina were significantly different from those coupled with metal femoral heads. The cup (pz_10) that articulated against the most worn alumina femoral head (as detected by roughness, micro-Raman and fluorescence measurements) was characterised by an orthorhombic into monoclinic phase transformation. The presence of the monoclinic form has been identified as a sign of polymer crystals under stress since shear and/or compression are required for the occurrence of the transformation into the monoclinic form. This phenomenon was not observed in the cups coupled to metal heads characterised by low wear; the latter underwent an increase in the orthorhombic phase content. Therefore, the obtained results showed that the surface finishing of the femoral head determined the morphological changes experienced by polyethylene at the molecular level.
The influence of the roughness of the femoral head on the in vivo wear behaviour of the polyethylene acetabular cup: a Raman investigation
TOZZI, SILVIA;TADDEI, PAOLA
2014
Abstract
Wear studies on hip joints have been mainly focused on ultra high molecular weight polyethylene (UHMWPE) acetabular components since they can liberate a substantial number of particulate debris into the joint space, able to trigger osteolysis (bone dissolving disease) in the soft tissue of the periprosthetic area. However, also metallic and ceramic femoral components may contribute to the osteolysis phenomenon. To minimize wear and thus the production of wear particles, the choice of the two sliding materials and their intrinsic parameters (i.e. diameter of the components, roughness of the surfaces...) are decisive for the long-term success of a joint prosthesis. The success of these devices greatly depends on the smoothness of the harder femoral head, since increased roughness of the counterface may dramatically accelerate abrasive polyethylene wear. To gain more insights into this subject at molecular level, in vivo worn UHMWPE acetabular cups (follow-up of 11-12 years) coupled to ceramic or metal femoral heads were analysed by micro-Raman spectroscopy and the obtained results were related to the Ra and Rsk roughness data obtained on their femoral counterface. Moreover, selected alumina femoral heads were analysed by micro-Raman and fluorescence spectroscopy, according to a widely used piezospectroscopic technique applied to the study of alumina- and zirconia-based ceramics. In this work we focused our attention on the analysis of the R1 and R2 Cr3+ fluorescence bands of alumina as well as its Raman band at about 417 cm−1. The micro-Raman spectroscopic data showed that the wear of polyethylene correlated with the surface finishing of the counterface, since the UHMWPE acetabular cups articulating against alumina were significantly different from those coupled with metal femoral heads. The cup (pz_10) that articulated against the most worn alumina femoral head (as detected by roughness, micro-Raman and fluorescence measurements) was characterised by an orthorhombic into monoclinic phase transformation. The presence of the monoclinic form has been identified as a sign of polymer crystals under stress since shear and/or compression are required for the occurrence of the transformation into the monoclinic form. This phenomenon was not observed in the cups coupled to metal heads characterised by low wear; the latter underwent an increase in the orthorhombic phase content. Therefore, the obtained results showed that the surface finishing of the femoral head determined the morphological changes experienced by polyethylene at the molecular level.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
