Outpatient toxicology clinic experience of patients with hip implants

With regard to biological effects, the increasing number of early failure of metal-on-metal (MoM) hip arthroplasties and possible parenteral exposure to orthopedic metal alloys have caused concern for patients and providers alike.

We sought to characterize our outpatient clinical experience of patients with MoM and other forms of hip implants and associated serum/blood chromium and cobalt levels, with a focus on possible systemic sequelae.

This was an observational and retrospective chart review of consecutive patients presenting to two outpatient medical toxicology clinics from January 1, 2010-June 1, 2012 with history of hip implants. Presenting signs, symptoms, and interventions were reviewed. Available cobalt and chromium levels were summarized as median concentration with interquartile range.

A total of 39 patients were analyzed; of the 39 patients, 26 had MoM hip implants while 13 did not. Twelve patients exhibited no symptoms and nine sought evaluation for fatigue while two other patients had been previously diagnosed with fibromyalgia. Tinnitus/hearing loss was also a frequent complaint noted in 12 patients (one presenting complaint), however there was no difference between the incidence of this symptom between the MoM and non-MoM groups. Three patients were provisionally diagnosed with demyelinating neuropathy with one patient demonstrating marked (subjective and objective) improvement after revision. Patients with MoM arthroplasties generally exhibit an approximately tenfold increase in metal ion levels than traditional arthroplasties. Finally, 20 (51.2%) patients had replacement or revision of their hip implant with subsequent decreases in metal ion levels.

A majority of our patients had minor symptoms (fatigue and muscle aches) or no symptoms (n = 23 or 59%). Documented peripheral neurotoxicity is uncommon. The decision for hip revision solely for toxicologic reasons is rare and usually involves a multidisciplinary approach.

Most patients seeking toxicologic referral may be minimally symptomatic and seek guidance regarding elevated blood or serum metal ions; however, solely toxicologic-based interventions are unusual. Revision was associated with a decrease in metal ion levels; however, subjective complaints did not correlate with metal ion levels.