Background: Systemic cobalt dissemination from the Metasul
Co-28Cr-6Mo-0.2C metal-on-metal total hip prosthesis has been demonstrated in
the first year after implantation. The aim of this prospective study was to
monitor the serum cobalt concentrations in patients during the first five
years after total hip arthroplasty with a metal-on-metal articulation.
Methods: A total hip arthroplasty was performed without cement in
100 consecutive patients who had either unilateral osteoarthritis or
unilateral osteonecrosis. Fifty patients were randomized to be treated with a
metal-on-metal articulation, and fifty patients, with a
ceramic-on-polyethylene bearing. The femoral stem was made of a Ti-6Al-7Nb
alloy, and the threaded acetabular cup was made of commercially pure titanium.
Blood samples were taken before the operation and at multiple time-points for
five years after the operation. Serum cobalt concentrations were measured with
use of atomic absorption spectrometry.
Results: In the metal-on-metal group, the median serum cobalt
concentration was 1 µg/L at one year after surgery and 0.7 µg/L at five
years. The median of the serum cobalt concentrations measured from three to
twelve months did not differ from the median of subsequent measurements, with
the numbers available. The median serum cobalt level in the control group of
patients treated with the ceramic-on-polyethylene articulation was below the
detection limit at all time-points.
Conclusions: Systemic cobalt release from Metasul metal-on-metal
articulations was demonstrated throughout the five-year study period. The
median serum cobalt concentrations were found to be slightly above the
detection limit and remained in a constant range. The serum cobalt
concentrations did not reflect a so-called run-in wear period of the
Level of Evidence: Therapeutic study, Level I-1a
(randomized controlled trial [significant difference]). See Instructions to
Authors for a complete description of levels of evidence.