Cobalt–Chromium Metallosis With Normal Electroretinogram

Abstract

Background Ocular cobalt toxicity is a rare phenomenon reported with increased frequency due to the rise of cobalt-chromium metal hip implants. We report the case of a 66 year-old previously healthy man who developed decreased vision due to cobalt-chromium toxicity from a metal-on-metal hip arthroplasty. Our objective was to determine whether the origin of his visual loss was due to toxicity of the optic nerve, of the retina, or of both. Methods Ocular examination, 10–2 SITA-Standard Humphrey Visual Field (VF), standard full-field electroretinogram (ERG) as indicated by the International Society for Clinical Electrophysiology of Vision (ISCEV), multifocal electroretinogram (mfERG), multifocal visual evoked potentials (mfVEP), and optical coherence tomography (OCT) were conducted. Results Ocular examination revealed decreased visual acuity, poor color vision, normal funduscopy, and cecocentral scotomas on visual field. As his right eye was amblyopic since childhood, test results from only the left eye are shown. Electrophysiology studies revealed an ISCEV standard full-field ERG with photopic and scotopic responses within normal limits, mfERG with amplitudes and latencies within normal limits, and mfVEP with latencies within normal limits, but with decreased central amplitudes. Peripapillary and macular OCT showed retinal nerve fiber layer (RNFL) and retinal ganglion cell-inner plexiform layer (RGC-IPL) thickness within normal limits. Conclusion As decreased color vision and cecocentral scotoma on 10–2 VF are most consistent with toxic optic neuropathy, and decreased central amplitudes on mfVEP are suggestive of neural dysfunction, we hypothesize that our patient presented with an early stage of optic nerve toxicity that was not yet apparent as a structural abnormality on OCT.

Metallosis Die Hard

“…Metallosis is defined as aseptic fibrosis, local necrosis, or loosening of a device secondary to metallic corrosion and release of wear debris [5]. It can be related to many different types of metal implants, such as titanium [5,6], cobalt/chromium [6][7][8] or different joint replacements such as hip, knee and shoulder [6,[9][10][11][12].…”

Metal-on-metal hip arthroplasty

“…The composite score for ocularvestibular symptoms increased from 54% to 57%-68% with rising threshold value (120-170 or 220 nmol/L), which suggests a correlation between ion concentration and symptomprevalence. Subjects in the current study reported tinnitus and hearing loss far more often than patients in the general population [53,56,57]. Also, more subjects were found with tinnitus in the high cobalt ionconcentration group at higher thresholds and with increasing threshold values.…”

“…These concentrations might be influenced by a variety of parameters, which can be divided into patient factors (female sex, age at surgery (young), time since implantation), implant factors (bilateral, small femoral HRA components, design, type of implant (HRA/LHMoM)) and surgical factors (acetabular component malposition, reduced contact patch to rim distance) [55]. There was a concern that increased cobalt and chromium ion concentrations increased the risk for cancer, but this was proven otherwise in large comparative studies [56,57]. Nevertheless, in 2012, the NetherlandsOrthopaedicAssociation (NOV) advised against the use of any MoM hip arthroplasty [58,59].…”