Assessment of the initial stability of the Symax femoral stem with EBRA-FCA: a multicentric study of 85 cases.

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.