In vivo corrosion of modular hip prosthesis components in mixed and similar metal combinations. The effect of crevice, stress, motion, and alloy coupling

Abstract

One hundred forty-eight retrieved modular hip prostheses of both mixed (Ti-6Al-4V/Co-Cr) and similar (Co-Cr/Co-Cr) metal combinations were examined and positive evidence of corrosive attack was found in the conical taper region between head and stem. Significant corrosion was observed in both mixed and similar metal combinations with 16% of necks and 35% of heads (for mixed-metal cases), and 14% of necks and 23% of heads (for similar-metal cases) showing moderate to severe corrosive attack. There was a significant correlation between the percentage of prostheses with moderate to severe corrosion and the duration of implantation for both mixed and similar metal cases, indicating that this corrosion process is progressive in time. Moderate to severe corrosion was seen as early as 2.5 and 11 months (mixed and similar metals, respectively). Scanning electron microscopy and x-ray analysis identified several forms of corrosive attack in the cobalt-based component of the taper. These included, for both mixed and same metal combinations: preferential dissolution of cobalt, fretting, and pitting; mixed metals only: the formation of a Ti-Cr-Mo interfacial phase and interdendritic corrosion; and for similar metals: intergranular attack adjacent to grain boundaries enriched in molybdenum and silicon. It is hypothesized that the restricted crevice environment, coupled with high cyclic stresses which cause repeated fracture of the passive oxide films in the taper, result in an unstable electrochemical environment within the crevice for both the cobalt alloy and Ti-alloy passive films. The passivity of these alloys is subsequently lost and active attack of the taper results. Also, the repeated fracturing of the passive films will result in large amounts of corrosion products being formed. This corrosion and particulate accumulation could result in loss of mechanical integrity of the implants in vivo, create particles for third body wear, and release particles into the surrounding tissues.

Metal release and corrosion effects of modular neck total hip arthroplasty

“…Such particles may get trapped between the articulating surfaces of the artificial joint resulting in third-body wear [21]. Furthermore, mechanically assisted crevice corrosion (as a combination of fretting and crevice corrosion) may attack the alloy and lead to implant failure [7]. Modularity is often associated with corrosion effects and is seen as a weak link with a possible source of complications [24].…”

Effect of impact assembly on the fretting corrosion of modular hip tapers

“…[1][2][3][4][5][6][7][8][9][10][11][12] Initially, corrosion was thought to result from a galvanic process due to the coupling of Ti-6Al-4V alloy with CoCrMo alloy. 2 This hypothesis was rejected by the finding of comparable corrosion products in similar alloy (CoCrMo/CoCrMo) couples.…”

“…Gilbert et al found evidence of moderate to severe corrosion in 16% of necks and 35% of heads in mixed metal couples, and 14% of necks and 23% of heads in similar metal couples, in a retrieval study of 148 modular hip implants of several designs. 3 In a more extensive retrieval study, Goldberg et al evaluated more than 200 modular implants, 7 finding that several variables affected fretting and corrosion, including material combination, metallurgical condition (i.e., cast vs. wrought), implantation time, and flexural rigidity of the neck.…”

Characterisation of the surface topography, tomography and chemistry of fretting corrosion product found on retrieved polished femoral stems

“…A study by Gilbert et al (Gilbert et al, 1993;Gilbert and Engh, 1995;Jacobs et al, 1998) -C within modular head-C C M…”