An in vitro assessment of the mechanical performance of 10 types of external femoral stabilization allowed the amplitudes of fracture site displacements during the initial loading phase of a comminuted fracture treated by external fixation to be established. The largest displacement to load ratios were observed in the sagittal plane for all tested configurations. The highest fixator stiffnesses were obtained by using large diameter tubes and pins. The most rigid fixators have a derigidification system which creates the problem of choosing the ideal time to change the rigidity.