Effect of distal stem geometry on interface motion in uncemented revision total hip prostheses

In this study, we compared differences in motion at the bone-prosthesis interface in femora in which a fluted, tapered, or cylindrical distal stem design had been implanted in a revision total hip arthroplasty model. Paired, fresh-frozen, cadaveric femora underwent resection of the proximal femur to simulate the proximal femoral bone loss often present during revision total hip arthroplasty and implantation with either a fluted, tapered stem or a clinically proven cylindrical stem. Specimens were then preloaded and subjected to a synchronous axial and torsional load with continuous monitoring of axial displacement and rotation. For the fluted, tapered stem, mean axial and rotational displacements were 13.33 microm and 9.81 microm, respectively, compared with 18.37 microm and 13.40 microm for the cylindrical stem (both Ps < .05). Therefore, the fluted, tapered stem design that was tested demonstrated superior initial biomechanical stability compared with that of the clinically proven cylindrical design tested. However, both stems demonstrated motion below the threshold necessary for bony ingrowth. Knowledge of the initial biomechanical properties of different stem designs may assist the revision joint surgeon in choosing the optimal prosthesis for implantation.