Continued mid-term stability of a novel cementless femoral stem design: A radiostereometric analysis study.

Abstract

Measuring early micromotion using radiostereometric analysis is the gold standard to evaluate new implant performance. The aim of this study was to assess the continued stability of a new cementless Paragon stem at 5 years. Secondary aims were to assess patient reported outcomes and compare the continued stability between 2 and 5 year to an existing gold standard, the Corail stem. This is a brief follow-up report of a radiostereometric analysis study. Of the original 46 patients in the 2 year study, four patients were lost to follow-up, three had died, five relocated interstate and seven withdrew from the study. We prospectively reviewed 27 primary total hip arthroplasty patients who underwent radiographic examinations at 5 years for beaded radiostereometric analysis measurements of stem translational and rotation migration. Median subsidence of the Paragon stem at 5 years was -0.428 mm (range - 0.107 to -1.092) and the median stem subsidence between 2 and 5 years was -0.010 mm (0.115 to -0.269). When compared to the historical Corail stem stability between two and six years, the Paragon stem demonstrated similar subsidence (p = 0.09); and significantly less medial translation (p = 0.0033), anterior translation (p < 0.0001), anterior tilt (p = 0.0004) and anteversion (p = 0.015) between 2 and 5 years. The mean Oxford Hip Score improved substantially within the first year and did not decrease between 2 (44.7, SD 5.9) and 5 years (44.0, SD 8). The Paragon stem showed continued stability up to 5 years follow-up which is encouraging for the further clinical use of this new design.