Fixation of the modular total hip femoral component in cementless total hip arthroplasty.

Cementless femoral component fixation with a modular design that achieved tight fit in the proximal and distal femur was evaluated. The base of the femoral neck made the most important contribution, but diaphyseal bony interlock also contributed significantly to immediate torsional fixation. Fluted surface and slotted distal design produced fixation that was superior to fully porous-coated and cemented cylindrical stems. Early cyclical loading improved fixation, and under moderate torsional loads (up to 20 N-m), no measurable interface slippage occurred with the modular implant.