Two-Year Prospective RSA Measured Migration of a Third-Generation Taper Wedge Cementless Femoral Stem

Implant migration is a concern with newly designed cementless femoral stems for total hip arthroplasty. Radiostereometric analysis (RSA) is the most accurate technique available to measure implant migration following total hip arthroplasty (THA). The objective of this study was to establish the migration pattern of a cementless tapered wedge stem during the first two years after implantation using RSA as well as assess clinical results.

Thirty patients underwent a primary THA with a morphometrically designed cementless stem. RSA was completed immediately after surgery and at three-, six-, 12- and 24-month intervals. Subsidence after two years was compared to the migration thresholds, and survivorship and clinical outcome scores were obtained.

After two years, the mean subsidence (distal migration) of the stem within the canal was 0.08mm (standard deviation [SD] 0.036mm), the mean retroversion was 0.301mm (SD 0.362), and the maximal total point motion was 0.764mm (SD 0.195). All stems demonstrated stable motion patterns beyond six months (p=0.99). Patient outcome data highlighted a statistical and clinically significant improvement (p<0.05) after hip arthroplasty at six months, and then there were modest changes at subsequent follow ups.

The femoral stem tested in this study was designed to provide adequate implant stability in total hip arthroplasty patients in the short term. We found stable fixation of the third-generation tapered wedge stem two years postoperatively and clinical improvements in patient-reported outcomes.