007. Influence du diamètre de la tête fémorale sur le cône Morse - Influence of head diameter on Fretting and Corrosion of the Morse Taper

Ph Hernigou (Créteil))

Taper corrosion in THA was identified as a clinical concern in the 1980s and was believed to have been addressed. However, implant corrosion has recently been reintroduced as a clinical issue in modular large head, metal on metal designs, two pieces modular femoral stems and even metal on PE design.

We based our cohort design on the collection of 300 revision arthroplasties in our hospital. The ceramic-metal taper cohort included both C-O-C and/or C-PE bearings and included both alumina and zirconia heads. These components were cemented, therefore cement is not considered to be a confounding factor for this study. The metal femoral head in the metal-metal taper cohort was composed of CoCr or steel. The metallic stem material compositions were confirmed with manufacturers and were composed of titanium alloy or CoCr.

Composite fretting and corrosion damage at the modular CoCr head and metal stem interfaces were characterized using a scoring technique with a score of 1 indicating minimal fretting or corrosion (fretting on < 10% surface and no corrosion damage); 2 indicating mild damage (fretting on>10% surface and/ or corrosion attack confined to one or more small areas); 3 indicating moderate damage (fretting >30% and/or aggressive local corrosion attack with corrosion debris); and 4 indicating severe damage (fretting >50% with severe corrosion attack and abundant corrosion debris). We analyzed metal transfer to the inner taper of the ceramic heads using a similar 4-point scoring technique with a score of 1 indicating minimal metal transfer (< 10% of the taper surface), 2 indicating metal transfer over 10%, 3 indicating metal transfer over 30%, and 4 indicating metal transfer over more than 50% of the inner head taper. Tissue samples from the hips obtained at revision were analysed to research debris of metal.

Evidence of fretting and corrosion consistent with a score of 1 to 2 was observed in stems in the ceramic-metal taper, whereas for stems in the metal-metal taper cohort, the score was 3 to 4. We observed dark corrosion deposits outside the head-neck taper junctions in 10% of the metal-metal taper cohort and zero (0%) of the ceramic-metal taper cohort. Stem alloy (titanium alloy better than chrome cobalt), femoral head size (small size better than large size) , the ceramic material formulation (alumina better than zirconia), neck size (short better than  medium better than long) and decreased stem flexural rigidity were predictors of stem fretting and corrosion damage and metal transfer for the ceramic-metal taper cohort.

Metal debris in tissues were less important with 32 mm alumina head on a large (14-16) diameter taper than with a 32 mm head on a medium (12-14) diameter taper or with a 28 mm alumina head on a small (12-10) diameter taper, or with a 28 mm zirconia head both on a large, medium or a small diameter taper, or with a metal head whatever the size of the taper. In absence of detectable wear on PE cups, osteolysis and metal particles on the calcar were more important with zirconia 28 mm diameter head on a small diameter taper than on a large diameter taper, with alumina long neck heads than with alumina short neck heads, which suggests that wear of PE is not the only cause of osteolysis in hip arthroplasty.

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