Influence of Femoral Implant Alignment in Uncemented Total Hip Replacement Arthroplasty: Varus Insertion and Stress Shielding

Background: The influence of varus insertion of femoral implants in uncemented total hip replacement arthroplasty (THR) remains unclear. Thus, in this study, we retrospectively assessed the clinical impact of uncemented THR with femoral implants that were inserted in varus on the basis of radiological findings. Materials and Methods: The study participants included 89 patients who underwent uncemented THR for 106 joints and were followed-up for > 3 years. From clinical records, we retrieved Japanese Orthopaedic Association (JOA) pain scores and the range of motion (ROM) of flexion and abduction both preoperatively and at the final follow-up. The presence of varus insertion of the femoral implant and stress shielding were also retrospectively reviewed from X-rays. We defined varus insertion of the femoral implant as the axis of the femoral implant that was inclined to the femoral shaft by 2 or more. Stress shielding was judged in accordance with Engh's classification system. Results: Of the 106 joints, varus insertion was observed in 40 (37.3%) (the varus group) but not in 66 (62.3%) (the non-varus group). The JOA pain score significantly improved in both groups; however, there were no significant differences between the groups. Although ROM improved in both groups, there were no significant differences between the groups. The appearance rate of stress shielding of >= third degree in the varus group was significantly greater than that in the non-varus group. Conclusion: These results revealed that varus insertion of femoral implants had no influence on short to mid-term clinical outcomes because the pain score and ROM significantly improved in both the varus and non-varus groups. However, high rates of severe stress shielding appeared with varus insertion of femoral implants, suggesting an influence on long-term clinical outcomes.