Metal ion levels in the blood of patients with metal-on-metal hip prostheses.

BACKGROUND A BHR (Birmingham hip resurfacing) prosthesis was implanted in 445 people in Norway. Adverse reactions can arise as a result of the release of metal ions from metal-on-metal joint surfaces made from cobalt-chromium alloy. The aim of the study was to analyse the release of metal ions during the first five years after surgery in patients with a BHR prosthesis and to investigate whether this was linked to clinical complications. MATERIAL AND METHOD Forty-four male patients (median age 53 years) implanted with a BHR prosthesis at the Coastal Hospital at Hagevik in the period October 2009 to May 2013 were monitored by means of blood samples before implantation and three months, one year, three years and five years afterwards. Analyses of cobalt and chromium in whole blood were performed. Function scoring was used to clinically assess the prosthetic joint. RESULTS Metal ion concentrations increased between the surgery date and one year later (p < 0.001), and subsequently remained stable. After five years, the median concentrations (min.- max.) of cobalt and chromium were 1.1 µg/L (0.4-6.3 µg/L) and 1.4 µg/L (0.4-11.7 µg/L) respectively for unilateral prostheses (n = 36), and 2.3 µg/L (1.6-28.5 µg/L) and 2.6 µg/L (1.7-14.1 µg/L) respectively for bilateral prostheses (n = 8). Five patients underwent revision surgery, while other patients had good hip function. INTERPRETATION Patients with a BHR prosthesis had a significant increase in cobalt and chromium in their blood one to five years after surgery, but the median levels were still well below the threshold value of 7 μg/L, which indicates an increased risk of complications.