A randomized study on migration of the Spectron EF and the Charnley flanged 40 cemented femoral stems: secondary analysis of a randomized controlled trial using radiostereometric analysis (RSA) with 10 years’ follow-up

BACKGROUND AND PURPOSE: Our primary aim was to compare the 10-year migration of the proximally roughened Spectron EF stem with the Charnley flanged 40 stems in cemented THA. Secondary aims were to assess the influence of polyethylene type on Spectron EF migration, and clinical outcomes. METHODS: In this randomized trial (NCT00698672), 150 patients (70% women; mean age 70 years) underwent cemented THA with either a Charnley stem (n = 30) or a Spectron EF stem (n = 120, 4 groups with different articulating surfaces). The articulations utilized conventional polyethylene (CPE) or highly crosslinked polyethylene (XLPE) cup liners combined with either cobalt-chromium (CoCr) or Oxinium (OxZr) femoral heads. RSA was performed postoperatively and up to 10 years. Migration was analyzed using linear mixed-effects models. Clinical outcome was assessed with the Harris Hip Score (HHS). RESULTS: After 10 years, 48 patients (14 Charnley, 34 Spectron EF) had evaluable RSA data. Both stems showed posterior translation, subsidence, and retroversion. Retroversion was greater for the Charnley stem than the Spectron EF stem at 3.2° (95% confidence interval [CI] 2.7-3.8) and 1.5° (CI 1.2-1.8), respectively, with a mean difference of 1.7° (CI 1.1- 2.4). The Spectron EF stem had more subsidence at 0.72 mm (CI 0.56-0.88) vs 0.32 mm (CI 0.06-0.57) for the Charnley stem, with a difference of 0.41 mm (CI 0.11-0.71). Spectron EF stems articulating with XLPE had 0.44 mm (CI 0.12-0.76) more subsidence than stems articulating with CPE. HHS improved from 41 (SD 15) to 86 (SD 19) for the Charnley stem and 45 (SD 13) to 86 (SD 15) for the Spectron EF stem with no statistically significant difference between the groups. CONCLUSION: After 10 years, the Spectron EF stem showed less retroversion, but more subsidence than the Charnley stem, with otherwise similar migration and clinical outcomes. XLPE articulating stems had more subsidence than CPE with the Spectron EF stem.