Brain structure and function in patients after metal-on-metal hip resurfacing.

M. J. Clark,M. N. Paley,J. R. Prentice,N. Hoggard,M. Hadjivassiliou,J. M. Wilkinson

doi:10.3174/ajnr.a3922

Abstract

Hip prostheses that use a metal-on-metal articulation expose the brain to elevated metal concentrations that, in acute excess due to prosthesis malfunction, is associated with neurologic damage, including visual and hearing loss and motor deficits. Here, we examined whether chronic exposure to lower elevated metal levels, typical of well-functioning prostheses, also affects brain structure and function. We compared brain volumes, metal deposition, and gray matter attenuation by MR imaging and clinical neurologic function in patients 8 years after receiving a metal-on-metal hip resurfacing versus a matched group of patients with the same duration exposure to a conventional hip prosthesis. Twenty-nine patients (25 men; mean, age 59±7 years) after metal-on-metal hip resurfacing and 29 patients (25 men; 59±8 years) after total hip arthroplasty were compared. Whole blood cobalt and chromium concentrations were 5-10 times higher in the metal-on-metal hip resurfacing group (P<.0001). Occipital cortex gray matter attenuation tended to be lower (P<.005 uncorrected, P>.05 corrected), and the optic chiasm area tended to be lower (mean difference, -2.7 mm2; P=.076) in the metal-on-metal hip resurfacing group. Subgroup analyses in 34 patients (17 per group), after exclusion of primary ocular pathology, showed the same trend in gray matter attenuation in the occipital cortex and basal ganglia and a smaller optic chiasm in the metal-on-metal hip resurfacing group (mean difference, -3.9 mm2; P=.048). No other structural or functional differences were found between the groups. Chronic exposure to metal-on-metal hip resurfacing is associated with subtle structural change in the visual pathways and the basal ganglia in asymptomatic patients.

Highlights

BACKGROUND AND PURPOSEHip prostheses that use a metal-on-metal articulation expose the brain to elevated metal concentrations that, in acute excess due to prosthesis malfunction, is associated with neurologic damage, including visual and hearing loss and motor deficits
Chronic exposure to metal-on-metal hip resurfacing is associated with subtle structural change in the visual pathways and the basal ganglia in asymptomatic patients
We examined whether prolonged exposure to circulating metal after metal-on-metal hip resurfacing (MoMHR) is associated with differences in brain structure and function assessed by MR imaging and clinical neurologic assessment in a group of clinically healthy patients after MoMHR versus an age, sex, diagnosis, and time since surgery–matched group of patients who received a conventional total hip arthroplasty (THA) that did not use a metal-on-metal bearing to determine whether this choice of prosthesis has implications for brain health

Summary

Methods

Metal deposition, and gray matter attenuation by MR imaging and clinical neurologic function in patients 8 years after receiving a metal-on-metal hip resurfacing versus a matched group of patients with the same duration exposure to a conventional hip prosthesis. All patients underwent clinical neurologic examination, including an assessment of extrapyramidal tract function by using the Unified Parkinson’s Disease Rating Scale (UPDRS), Part 2 (activities of daily living) and Part 3 (motor). The UPDRS is a standardized scale used to assess the severity of Parkinson disease symptoms and has previously been applied to the quantitation of movement disorders associated with metal neurotoxicity.[16,17] Blood and plasma Co and Cr levels were measured by inductively coupled plasma–mass spectroscopy, as described previously.[15]

Results

Discussion

Conclusion