Radiostereometric migration analysis of the Lubinus SP II hip stem: 59 hips followed for 2 years

The aim of this prospective study was to analyze the migration pattern of the Lubinus SP II hip stem and to evaluate the clinical results. Fifty-nine patients were followed for 2 years. Translational and rotational micromotion of the implant was measured by radiostereometric analysis (RSA) and the Harris hip score (HHS), and the Charnley classification was used to assess the clinical outcome. Although there was a very small, but statistically significant, distal migration of 0.04±0.83 mm, the prosthesis was found stable at 2 years of follow-up. The main migration in this direction took place between 6 months and 1 year. Maximum total point motion (MTPM) showed a mean of 0.99±0.69 mm. Good clinical outcome with HHS results of 42±11 before and 79±16 at 2 years after surgery was observed. The Charnley classification showed increasing additional impairments in the 2-year interval, which is likely to influence the HHS results of future follow-ups. The migration values measured in the present study are far below the thresholds considered clinically relevant in literature. Thus, the conclusion can be drawn that the implant is not at risk for early aseptic loosening. Long-term RSA is required to assess possible late migration.