Corrosion of Polished Cobalt-Chrome Stems Presenting as Cobalt Encephalopathy

Abstract

Adverse reactions to metallic debris from corrosion of polished cobalt-chromium–cemented femoral stems are reported. Cobaltism (systemic cobalt poisoning) has not been reported from this phenomenon. Three patients presented to their surgeon for ongoing care 10-20 years after primary metal-on-plastic hip arthroplasty with the same polished cobalt-chromium–cemented femoral stems (Heritage, Zimmer). Urine cobalt was elevated, and the patients had symptoms consistent with cobaltism. Quantitative-F 16 DG-PET-CT brain imaging was performed showing generalized and focal brain hypometabolism consistent with cobalt encephalopathy. At revision, all stems were well fixed and grossly corroded. At 1 year after revision, cobalturia and cognitive symptoms were resolved or improved. Mechanically assisted crevice corrosion at the polymethylmethacrylate interface is a complication of polished cobalt-chromium–cemented stems that can result in systemic cobalt exposure and toxic encephalopathy. Our cases had only minor periprosthetic symptoms. Patients implanted with polished cobalt-chromium–cemented stems warrant monitoring with urine cobalt. Patients with cobaltemia warrant an evaluation for toxic encephalopathy.

Titan – ein zementierbarer Werkstoff für die Endoprothetik

“…Factors That Promote Crevice Corrosion: 1. Implant Design Hydrolysis and corrosion processes occur not only with titanium alloys, but also with cobalt-chrome alloys [22]. By nature, titanium alloys are described as being highly resistant to corrosion, since a passive oxide layer forms in the physiological environment.…”

“…Begünstigende Faktoren für Spaltkorrosion: 1. Implantatdesign Hydrolyse-und Korrosionsvorgänge treten nicht nur bei Titan-, sondern auch bei Kobalt-Chrom-Legierungen auf [22]. Naturgemäß werden Titanlegierungen als sehr korrosionsbeständig beschrieben, da sich im physiologischen Milieu eine passive Oxidschicht formiert.…”

Corrosion of Metals During Use in Arthroplasty

“…62 Electrochemically, behind the moving asperities that scrape the protective metallic oxide films, corrosive oxide debris and particles are released, together with oxide dissolution and repassivation taking place, which leads to more accumulation of cations within the crevice and electrons on the implants, causing electropotential drop. 26,31,61 Furthermore, diffusion of chloride ions into the crevices to maintain neutrality/balance cation release will cause the formation of more acidic solution that favors more corrosion process. 38 Examples include a retrieval study, which examined fretting corrosion and material losses for an MDM liner taper.…”

“…The main standard of metallic implant biocompatibility has been that the more corrosion resistance potential, the more biocompatible the metal should be as an implant . A metal could achieve biocompatibility by the possession of a low dynamic force for corrosion, as in noble metals, or through the possession of a protective kinetic barrier bestowed by a thin passive metallic-oxide film at the surface . Movements and cyclic loads occurring through an arthroplastic implant can induce micro-oscillatory motions between the components, resulting in subsequent disruption of the protective kinetic barrier. ,, When this happens, the protected underlying metal is exposed, but repassivation usually occurs, thus restoring the passive integrity and pH of the local environment.…”

Note From the Editor

“…Brian J. McGrory, MD, MS, Editor Emeritus, had the vision to recognize the instructive value of case reports; as such, one of the initial intents of Arthroplasty Today was to provide a platform for their publication. The case reports selected for this Highlights issue all illustrate the potential adverse consequences of modularity [ [1] , [2] , [3] ]. The 2 surgical technique articles we chose are particularly practical, simple techniques that practicing surgeons can readily adapt to their practices [ 4 , 5 ].…”