Initial stability of a collarless wedge-shaped prosthesis in the femoral canal.

A collarless wedge-shaped implant was inserted with cementless technique in seven fresh-frozen adult femora. Micromotion of the implant in the proximal femur was evaluated by applying an axial load of 3,000 N or a rotational force of 12 Nm. Six femurs were prepared using a cemented implant, and their stability was similarly determined for comparative purposes. In all tests, the amount of plastic deformation after load relief was quantitated. The cementless prosthesis had excellent initial stability with axial and rotational loading; also the micromotion was similar to that of the cemented implant. Deformation under these experimental conditions was predominantly elastic. The stability demonstrated with this cementless prosthesis satisfies the conditions necessary for bone ingrowth in vivo.