In vitro study of initial stability of a conical collared femoral component

This in vitro experimental study compared the initial stability of an uncemented conical collared femoral component to that of the same component with the collar removed. The two configurations examined simulated joint resultant forces encountered in single leg stance and stair climbing. For the simulated single leg stance loads, the data do not allow any inferences about relative component stability. With the exception of one collarless control, all micromotion for single leg stance loading was under 150 microns, measured approximately 1.5 cm below the resection line. For scaled stair-climbing loads, however, the conical collared component group was significantly more stable than the collarless control group in transverse (primarily rotational) micromotion. The overall average measured transverse motion for the collarless control group was more than 3.7 times greater than that of the conical collar group at scaled stair-climbing loads. The two conical collared components loaded to full peak stair-climbing load (2,100 N) exhibited micromotion under 160 microns. The results suggest that the conical collar may improve stability of an uncemented prosthesis under loads that include an out-of-plane (rotational) component.