Comparison of Periprosthetic Femoral Bone Remodeling After Total Hip Arthroplasty with Zimmer VerSys Taper Stem or VerSys Midcoat Stem: Long-Term Outcomes

Background/Objectives: We compared long-term radiological femoral bone remodeling after total hip arthroplasty (THA) with either the VerSys Taper stem (T) or VerSys Midcoat stem (M). Methods: Of 206 patients who underwent unilateral primary THA, 157 (T group: 65; M group: 92) were followed up for >15 years. Stress shielding was evaluated according to Engh’s classification, cancellous condensation and cortical hypertrophy in each zone were assessed according to Gruen’s zone, and fixation was evaluated using Engh’s classification. We investigated the grade of each stem at each point in stress shielding. Results: Grade 3 or 4 stress shielding incidence was higher in the T group than in the M group, and stress shielding grades at each time point were significantly higher in the T group. The stress shielding grade showed progressively greater divergence in the T group, consistent with a significant stem × time interaction. The generalized linear mixed model showed significant zonal variation in cancellous condensation but no effects of stem type or stem × zone interaction. Similarly, cortical hypertrophy showed no significant effects of stem type, zone, or their interaction. There were no cases of unstable fixation in either group; however, 90.2% of patients in the M group had bone ingrowth, whereas 23.1% of patients in the T group had fibrous stability. There were no cases of revision owing to aseptic loosening in either group. Conclusions: These findings suggest that the primary long-term difference between the stem designs lies in the trajectory of stress-shielding progression rather than in zonal bone responses.