DOES TAPER ANGLE CLEARANCE INFLUENCE THE FRETTING CORROSION BEHAVIOUR OF MODULAR THA COMPONENTS? A MATCHED COHORT STUDY

Introduction Recent implant design trends have renewed concerns regarding metal wear debris release from modular connections in THA. Previous studies regarding modular head-neck taper corrosion were largely based on cobalt chrome (CoCr) alloy femoral heads. Comparatively little is known about head-neck taper corrosion with ceramic femoral heads or about how taper angle clearance influences taper corrosion. This study addressed the following research questions: 1) Could ceramic heads mitigate electrochemical processes of taper corrosion compared to CoCr heads? 2) Which factors influence stem taper corrosion with ceramic heads? 3) What is the influence of taper angle clearance on taper corrosion in THA? Methods 100 femoral head-stem pairs were analyzed for evidence of fretting and corrosion. A matched cohort design was employed in which 50 ceramic head-stem pairs were matched with 50 CoCr head-stem pairs based on implantation time, lateral offset, stem design and flexural rigidity. Fretting corrosion was assessed using a semi-quantitative scoring scale where a score of 1 was given for little to no damage and a score of 4 was given for severe fretting corrosion. The head and trunnion taper angles were measured using a roundness machine (Talyrond 585, Taylor Hobson, UK). Taper angle clearance is defined as the difference between the head and trunnion taper angles. Results The fretting corrosion scores were significantly lower for the stems in the ceramic head cohort when compared with the CoCr cohort. Stem alloy and stem flexural rigidity were predictors of stem fretting and corrosion damage in the ceramic head cohort, however not for the CoCr cohort. The mechanism of mechanically assisted crevice corrosion was the same in the two cohorts, with the exception being that, only one of the two surfaces (i.e., the trunnion) engaged in the oxide abrasion and repassivation process in the ceramic cohort. There was no significant correlation observed between taper angle clearance and visual fretting-corrosion scores for trunnions in the ceramic cohort (Rho=−0.17), trunnions in the CoCr cohort (Rho=0.24), or the femoral head tapers in the metal cohort (Rho=−0.05) (Figure 1). Additionally, visual fretting-corrosion scores in the metal cohort were similar between components with distal contact (negative taper angle clearance) and components with proximal contact (positive taper angle clearance) (p=0.43 and 0.56 for head and trunnion scores, respectively). Conclusions The results suggest that by using a ceramic femoral head, CoCr fretting and corrosion from the modular head-neck taper may be mitigated, but not completely eliminated. The findings of this study support further study of the role of ceramic heads in potentially reducing femoral taper corrosion. Taper angle clearance was not correlated with the visual fretting-corrosion scores in the ceramic or CoCr cohort in the present study. The effects of taper angle clearance may not be significant compared to other factors leading to material loss or the lack of correlation may be due to the limitations in the visual scoring method. Research is underway quantify the volume of material release from explants to better understand the reasons for reduced fretting and corrosion observed in the ceramic head cohort.