Comparison of the stability of press-fit hip prosthesis femoral stems using a synthetic model femur.

The motion of three different press-fit hip prosthesis femoral components was compared with that of a cemented stem and an Austin Moore noncemented hemiarthroplasty. Synthetic composite femurs were used as an experimental model to reduce the variations in shape and quality typical among cadaver femurs. Motion was measured under axial and rotational loading approximating a walking load. On the initial application of load, axial subsidence was as much as several millimeters for the noncemented stems. Considerable tightening occurred during the 5,000 walking cycles, such that the motion of the noncemented stems in some directions eventually was as small as that of the cemented stem, on the order of tens of microns.