Abstract
There is public concern over the long term systemic health effects of metal released from hip replacement prostheses that use large-diameter metal-on-metal bearings. However, to date there has been no systematic study to determine which organs may be at risk, or the magnitude of any effect. We undertook a detailed cross-sectional health screen at a mean of 8 years after surgery in 35 asymptomatic patients who had previously received a metal-on-metal hip resurfacing (MoMHR) versus 35 individually age and sex matched asymptomatic patients who had received a conventional hip replacement. Total body bone mineral density was 5% higher (mean difference 0.05 g/cm2, P = 0.02) and bone turnover was 14% lower (TRAP 5b, mean difference −0.56IU/L, P = 0.006; osteocalcin, mean difference −3.08 ng/mL, P = 0.03) in the hip resurfacing versus conventional hip replacement group. Cardiac ejection fraction was 7% lower (mean absolute difference −5%, P = 0.04) and left ventricular end-diastolic diameter was 6% larger (mean difference 2.7 mm, P = 0.007) in the hip resurfacing group versus those patients who received a conventional hip replacement. The urinary fractional excretion of metal was low (cobalt 5%, chromium 1.5%) in patients with MoMHR, but creatinine clearance was normal. Diuretic prescription was associated with a 40% increase in the fractional excretion of chromium (mean difference 0.5%, P = 0.03). There was no evidence of difference in neuropsychological, renal tubular, hepatic or endocrine function between groups (P>0.05). Our findings of differences in bone and cardiac function between patient groups suggest that chronic exposure to low elevated metal concentrations in patients with well-functioning MoMHR prostheses may have systemic effects. Long-term epidemiological studies in patients with well-functioning metal on metal hip prostheses should include musculoskeletal and cardiac endpoints to quantitate the risk of clinical disease.
Highlights
There is public concern about the potential systemic health effects of metal exposure in patients who have received large diameter ($36 mm) metal-on-metal hip prostheses [1], there is little data available to quantitate which systems may be affected or the magnitude of any effect [2]
In the metal-on-metal hip resurfacing (MoMHR) group a further 15 patients were excluded for the following reasons: contra-indication to magnetic resonance imaging (MRI) (n = 3), inflammatory arthropathy or metabolic bone disease (n = 3), recent arthroplasty to other joints (n = 3), MoMHR revision (n = 1), use of calcium dietary supplements (n = 2), and current illness (n = 3)
In the total hip arthroplasty (THA) group 28 patients were excluded for the following reasons: complications or revision of the prosthesis (n = 10), failure of the matching criteria (n = 7), inflammatory arthropathy or metabolic bone disease (n = 3), glucocorticoid treatment (n = 3), contra-indication to MRI (n = 3), recent arthroplasty to other joints (n = 1) and subject withdrawal (n = 1)
Summary
There is public concern about the potential systemic health effects of metal exposure in patients who have received large diameter ($36 mm) metal-on-metal hip prostheses [1], there is little data available to quantitate which systems may be affected or the magnitude of any effect [2]. The Food and Drug Administration (FDA) in the United States has recently (May 6th, 2012) instructed manufacturers of large diameter metal-on-metal hip prostheses to conduct cross-sectional studies covering the period from implantation out to 8 years after surgery in order to quantitate the adverse local and systemic effects of metal exposure from these devices (http://www.fda.gov/MedicalDevices/Safety/ AlertsandNotices/ucm335775.htm, accessed May 13th, 2013). We have recently shown that concentrations of cobalt and chromium equivalent to blood levels after MoMHR affect human bone cell viability and function invitro [13]. Linna et al [14], found cobalt workers exposed to a blood cobalt level of 2.5 mg/L over 9 years had echocardiographic evidence of altered left ventricular function versus unexposed controls
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