Metal-on-Metal Hip Prostheses and Systemic Health: A Cross-Sectional Association Study 8 Years after Implantation
Patients with well-functioning metal-on-metal (MoM) hip resurfacing prostheses may experience systemic effects from chronic exposure to low elevated metal concentrations, according to a British study published online this month in the journal PLOS ONE. Investigators performed a cross-sectional health screen of 35 asymptomatic patients who had undergone MoM hip resurfacing and 35 age- and sex-matched patients who had undergone conventional hip replacement with a variety of bearing surfaces (metal-on-polyethylene ; ceramic-on-ceramic ; and ceramic-on-polyethylene ), at a mean follow-up of 8 years. Total body bone mineral density was 5 percent higher—and bone turnover was 14 percent lower—in the hip resurfacing patients compared to traditional hip replacement patients. In addition, in the hip resurfacing group, left ventricular and end-diastolic diameter was 6 percent larger, and cardiac ejection fraction was 7 percent lower. “Our data suggest mixed health effects, including potentially positive effects on systemic bone mass, but potentially deleterious effects on left ventricular function,” note the researchers. They call for the use of musculoskeletal and cardiac endpoints in future long-term epidemiologic studies to determine the risk of clinical disease.
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.
Citation: Prentice JR, Clark MJ, Hoggard N, Morton AC, Tooth C, et al. (2013) Metal-on-Metal Hip Prostheses and Systemic Health: A Cross-Sectional Association Study 8 Years after Implantation. PLoS ONE 8(6): e66186. doi:10.1371/journal.pone.0066186
Editor: Joel Joseph Gagnier, University of Michigan, United States of America
Received: December 21, 2012; Accepted: May 2, 2013; Published: June 10, 2013