Imprinting and Column Damage on CoCrMo Head Taper Surfaces in Total Hip Replacements

Abstract

Material degradation within taper junctions of modular total hip replacements remains of great concern. Imprinting and column damage are two damage modes that frequently occur on head taper surfaces. Both can cover large areas and therefore can be associated with significant material loss. It was the purpose of this study to determine the prevalence of imprinting and column damage on a group of retrievals collected at our medical center and to identify damage pathways on selected cases. We asked two research questions: (1) How do CoCrMo stems imprint into CoCrMo heads? (2) Does alloy microstructure influence the column damage pattern in CoCrMo heads? In order to answer these questions, we conducted a retrieval study on moderately to severely worn femoral head taper surfaces that were paired with stems of different materials. All components were viewed under a stereo-light microscope to determine the presence of imprinting and column damage. Selected cases were further studied by means of scanning electron microscope, interferometry, and metallography to determine damage mode and the potential role of alloy microstructure. Our results demonstrated that imprinting is independent of the stem material but highly dependent on its topography. The imprinting process is at least initially driven by fretting and the generation of oxide particles. Column damage on the other hand is highly dependent on the microstructure of wrought CoCrMo alloys, which can exhibit banding resulting from slight alloy segregations that were characterized by molybdenum depletion. Therefore, column damage may be prevented by avoiding banding of the alloy during the thermomechanical processing. This study demonstrates that it is important to consider differences among the occurring degradation mechanisms and to understand how they relate to material and design factors.

Alloy Microstructure Dictates Corrosion Modes in THA Modular Junctions

“…This finding is important because (1) alloys from all manufacturers were affected; (2) the head taper surface aligns with a deviation of only 2.838 from the longitudinally oriented banded microstructure; and (3) both the E corr and the I corr are unfavorable in this orientation. We have recently shown by EDS mapping that the banded microstructure was linked to areas of local molybdenum depletion [18]. This finding aligns well with the observed inferior corrosion behavior of surfaces with a banded microstructure, because molybdenum is known to enhance the stability of the alloy's protective passive film and thus the alloy's resistance to corrosion [12].…”

“…Of greatest concern are corrosion products generated from CoCrMo alloy, where it has been shown that cobalt can be especially detrimental at elevated concentrations [8,27]. Histopathologically, ALTRs are often associated with the accumulation of lymphocytes in the presence of chromium phosphate particles [18,22], yet the concept of modularity and the use of CoCrMo alloys bear considerable advantages. Modularity provides the surgeon with valuable flexibility during surgery.…”

In Vitro Evidence for Cell‐Accelerated Corrosion Within Modular Junctions of Total Hip Replacements

“…Specifically, these features were usually seated within areas of column damage. Column damage is characterized by long etched troughs running along the taper axis, and is associated with banding of the CoCrMo alloy microstructure . Considering our findings in this study, it is probable that fretting within modular taper junctions will eventually release particles from the crevice.…”

“…The contribution of CAC to material loss cannot be easily quantified and may differ broadly. At least in the case of column damage, one can estimate that the contribution is significant as it covers large areas and leaves troughs with a depth of several tens of micrometers . Column damage is also inherently related to the alloy microstructure as are other damage modes such as phase boundary corrosion and intergranular corrosion .…”

Mechanical, chemical and biological damage modes within head‐neck tapers of CoCrMo and Ti6Al4V contemporary hip replacements

“…18 Most interestingly there was a direct relationship between the observed column like damage pattern and a banded structure within the wrought alloy. 18,31 It appears that banding within the alloy make the head taper surface vulnerable to corrosion under harsh chemical conditions. 31 Previous studies noted a similarity of the column damage feature with damage causes by erosion corrosion 14 or described it as scratches caused during the assembly process that subsequently underwent corrosion 32 .…”