Abstract
The rotational stability of cementless hip prostheses corresponds to their appropriate contour design. The appropriate contour design of a femoral stem is important for secure primary fixation. This paper addresses the issue of the fixation method of hip stems and their rotational stability. Specimens were four kinds of hip prostheses. The rotational displacement was measured and analyzed by applying a reproduced torsion moment. Different kinds of finite element models of four femoral stems were constructed for computer simulation. The measurements were accomplished by real stems used in clinical scene. Common conditions of analyses and measurements were: (i) a torsion load of 18.9 Nm was applied to the proximal femur as the intra-rotation; (ii) a stepping load of 1800 N was applied to the proximal tip of the stem; and (iii) rigid contact of the distal end of the model femur with the rigid base. As a result, it was found that the relative rotational displacement obtained by FEM was 0.21 mm in the Intra-Medullary Cruciate stem. For the VerSys stem, the relative rotational displacement was 0.10 mm. The relative rotational displacement of the PerFix SV stem was 0.67 mm. The relative rotational displacement of the Duetto SI stem was 0.03 mm. The relative rotational displacement obtained by laser displacement sensor was 0.37 mm in the Intra-Medullary Cruciate stem, 0.25 mm in the VerSys stem, 1.87 mm in the PerFix SV stem, and 0.17 mm in the Duetto SI stem. Judging from rotational displacement obtained by two approaches, three types of stem (Intra-Medullary Cruciate stem, VerSys stem, Duetto SI stem) provided rotational stability.
