Summary
Prosthetic hip joints consist of two components: the femoral component and the articular interface, each of which may be metallic or non-metallic. Metal-on-metal (MOM) prostheses were previously considered to offer improved durability, and have, in the past, been suggested for hip replacements in younger patients. However, an analysis of data from the National Joint Registry of England and Wales showed poor implant survival for MOM-stemmed prostheses compared with other materials.
MOM prostheses of cobalt and chromium have been associated with high blood concentrations of these metals, and current UK guidelines recommend post-operative monitoring in recipients of an MOM implant. Cobalt and chromium ions cross the placenta and concern has therefore been expressed about potential adverse effects on the developing fetus.
The available data provide no indication of an increased risk of congenital malformation in infants born to women with MOM hip prostheses, but are too limited to conclude that there is no increase in risk. There are currently no reliable data that MOM hip prostheses being in situ during pregnancy increases the risk of other adverse pregnancy outcomes, but data are too limited to permit a robust evidence-based risk assessment.
Additional fetal monitoring may be advisable in cases of high maternal blood concentrations of cobalt or chromium (>7 mcg/L in one or both metals; 119 nmol/L cobalt or 134.5 nmol/L chromium). Other risk factors may also be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments. Discussion with UKTIS is recommended in all cases, but particularly where there is associated maternal toxicity and/or high blood cobalt and chromium concentrations.
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