A prospective multicentric study was carried out in patients having metal-onmetal METASUL components (Sulzer Medica, Winterthur, Switzerland) in order to check the following null hypotheses: H1: The concentration of Co, Cr, Ni, and Mb in blood and urine is not modified by the implant of a hip prosthesis with METASUL components at 6 months. H2: The incidence of markers of chromosomal damage [sister chromatid exchanges (SCEs) and micronuclei (Mni)] in lymphocytes is not modified by the implant of METASUL components at 6 months. H3: The concentrations of Co, Cr, Ni, and Mb in blood and urine did not correlate with the incidence of the markers of chromosomal damage. The measurements showed a 2-fold increase of Co in blood, a 10-fold increase of Co in urine, a 1.5-fold increase of Cr in the blood, and a 3-fold increase of Cr in the urine at a follow-up of 6 months from the operation; there was also a significant increase in the Ni blood concentration at the 7 day checkup. The study cohort did not show any modification in the frequency of markers of chromosomal damage in the peripheral lymphocytes at any of the observation times. The amount of the SCEs and Mni recorded at all the observation times did not correlate with each other or with any of the ion levels measured in the blood and in the urine.

We report a study of 85 Symax femoral stems that were followed at regular intervals with radiographs at 6, 12, 24 and 36 months. The radiological migration of each stem was measured using the computer-assisted EBRA -FCA method. In 30 cases in which the EBRA method did not provide a complete measurement another computer-assisted method (Roman version 1.7) was employed. In all cases the distal migration of the stems was minimal, The threshold migration value used to define the stability of a stem was 1.5 mm at 24 months. The mean migration within the first two years was -0.17 mm (+/- 0.3) at 6 months, -0.31 mm (+/- 0.4) at 12 months and -0.45 mm (+/- 0.5) at 24 months. Only two cases exceeded the threshold limit of 1.5 mm at the two-year follow-up, but both values were lower than 2 mm. In the 25 cases which reached three-year follow-up the mean distal migration was -0.84 (+/-0.7). In four of them the subsidence exceeded 1.5 mm, but only one exceeded 2 mm. These data represent a positive predictive factor for the minimal risk of future aseptic loosening.

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