Abstract: A lag screw for connecting a bone portion separated from the femur, by fracture, to the main portion thereof is fixedly secured in the separated bone portion and extends through main portion of the femur. A nail member is installed in the femur in order to fix the lag screw to the femur. The lag screw is secured in the nail member by a set screw inserted into an outer end of the nail member. In order to prevent the rotation of the separated bone portion about the lag screw, an auxiliary connector is inserted through the nail member between the lag screw and the set screw. The lag screw is clamped by the set screw via a spacer for transmitting a clamping force.