The success of the cemented arthroplasty is due primarily due to excellent initial stability, intimate contact with the prepared bone and the isoelastic properties provided by the cement. In an experimental in vitro study, the initial stability of both the cemented and uncemented femoral components was measured and it was found that they were both very stable in simulated single limb stance (maximum motion of less than fifty microns). However, in simulated stair climbing, the uncemented components were more unstable than the cemented components (maximum micromotion of 76 microns for cemented and 280 microns for uncemented), and this relative instability of the uncemented femoral components could compromise the bone ingrowth. Studies on femurs retrieved at autopsy from patients who underwent cemented total hip arthroplasty two week sup to seventeen years earlier and were functioning well, have shown that the failure of cemented femoral components is initiated primarily by mechanical factors, consisting of debonding at the cement-prosthesis interface and fractures of the cement rather than lack of bone ingrowth or fibrous tissue formation at the interface. Thus the problems with using cemented femoral components involve the poor strength of the cement-prosthesis interface and the cement, while the problems with cementless components involve the difficulties in precisely machining the femoral canal, and providing rigid stability as well as accurate fit.