Biomechanical Comparison of Impaction Techniques and Cross-Sectional Femoral Stem Shapes for Cementless Total Hip Arthroplasty

Abstract

Introduction. Traditional mallet broaching and stem seating for cementless total hip arthroplasty (THA) could lead to femoral stem misalignment therefore decrease implant survivability. The specific aim of this study was to compare the pull-out strength of cementless THA femoral stem with different cross-sectional design resulting from powered impactor method versus traditional mallet method.

Methods. Twenty-four polyurethane foam femurs along with two size 5 femoral bone preservation stems with different proximal cross-sectional shapes (double taper: ACTIS and flat taper: TRI-LOCK) were utilized. Each femur was prepared with either the powered impactor or mallet impaction methods. Each femur was broached from size 0 to size 5 in the standard fashion. Broaching time and component implantation times were recorded. A load-to-failure pullout strength test was performed, and the ultimate pullout load was recorded.

Results. The broaching time for TRI-LOCK stem was statistically significant between two impaction methods (powered: 37 seconds, mallet: 75 seconds, p=0.002), but not statistically significant detected for ACTIS stem between two impaction methods (powered: 47 seconds, mallet: 59 seconds). There was a statistically significant difference in pullout strength between the two impaction groups, and this strength was impacted by the implant cross sectional shape (ACTIS: 774N versus 679N, p=0.018; TRI-LOCK: 616N versus 819N, p<0.001).

Conclusions. The femoral bone preparation technique (powered impactor technique versus mallet technique) and the cross-sectional design of the cementless femoral stem play an important role in achieving initial stem stability and influencing operation time.