In vitro test methods for seating and fretting corrosion behavior of modular metal‐on‐metal acetabular tapers

Abstract

Retrieval studies show that metal-on-metal acetabular shell-liner tapers are susceptible to corrosion, which is hypothesized to arise from mechanically-assisted crevice corrosion (MACC). The role of materials on MACC of acetabular tapers has not been previously studied. In vitro tests of seating, pushout, and fretting corrosion performance of acetabular tapers are presented to assess the role of material combinations (Ti-6Al-4V shells, HC CoCrMo, LC CoCrMo, and 316L SS liners). The acetabular tapers were wetassembled to a seating load of 1,000 N. The liner load-displacement seating mechanics were measured. Fretting corrosion currents were evaluated using a uniaxial incremental cyclic compression test up to 4,000 N, with the load applied at a 55°angle to the taper interface. Fretting currents, fretting onset loads, taper disengagement strength were measured and load-displacement plots were obtained. Pushout tests were also performed pre-and post-fretting corrosion. The average liner seating displacements varied from 134 to 226 μm across groups. Fretting currents at 3,600 N cyclic load were low and ranged between 0.05 and 0.27 μA and were independent of material combination (p > 0.05), reflecting small amounts of fretting. Fretting corrosion onset loads were between 1,800 and 2,100 N, and did not differ across groups (p > 0.05). Pushout loads were 27-43% of the maximum load applied. Fretting corrosion levels were very low for all material combinations and not different from one another. The seating and pushout responses were also not material dependent. The low fretting currents measured imply that MACC may not be a major cause for acetabular taper corrosion.

Nontribological corrosion modes dominate wrought CoCrMo acetabular taper corrosion: A retrieval study

“…In engagement regions, there is some evidence of material transfer from the interfacing titanium shells, visible as light contrast regions in backscatter SEM mode, and confirmed by EDS analysis. A recent study by Shenoy et al 13 shows the actual area in contact is minimal compared to the entire shell-liner taper interface available for contact, which explains the low fretting currents (under 1 μA) recorded in the short-term in vitro fretting corrosion tests. This was corroborated in this study, where we found dispersed regions of fretting, indicating minimal direct contact within the engagement region.…”

“…Note the antirotation tabs and the lower engagement region (marked in red) and the noncontact region between the tabs (white arrow). Figure adapted from Shenoy et al 13 backscattered image, since these generate the most backscattered electrons. Thus, we can distinguish between different surface features compositionally using SEM imaging.…”

“…[7][8][9] Retrieval analysis studies of acetabular components have reported similar findings. 1,2,[10][11][12] However, a recently published in vitro study has found that MACC may not be a significant driver of taper corrosion in titanium shell-CoCrMo liner acetabular tapers, 13 especially when compared with head-neck tapers with the same material combination.…”

Fretting corrosion testing of acetabular modular tapers for total hip replacements: A comparison of two designs

“…Tribocorrosion performance of two commercial modular acetabular designs was assessed during a long term, three million cycle intermittent test. Previous studies have not been performed for this duration (roughly 3 years of clinical use) 12 . This method provides a quantitative assessment based on fretting currents, resulting in a comparative analysis of fretting corrosion damage in the taper designs in vitro.…”

Adverse loading effects on tribocorrosive degradation of 28 mm metal-on-metal hip replacement bearings

“…This interface has been of increasing interest in recent years as a possible source of debris and ions. [42][43][44] While not part of the bearing surface degradation here is still relevant to device performance. With increased inclination the load vector will have shifted more to one side of the cup, closer to the vertical, possibly resulting in a more severe fretting interface.…”