I have been tasked with running a compression test on a femur bone, by applying boundary conditions to reference points and then getting the force displacement from them. however the model seem to rotate when I use tie functions to connect them with the element sets I have created, but works fine when applying the boundary conditions directly to the sets. 

below is my set up for the ties. I am a bit new to abacus so any advice on how to fix this would be appreciated:

element Set 1 has been applied to the bottom of the femur along with a reference point, the tie has been set up with the reference point as the main and element set as secondary. an encaser boundary condition has been applied to the reference point, in initial step

element Set 2 has been applied to the top edge curve along with a reference point, the tie has been set up with the reference point as the main and element set as secondary. a displacement lock boundary condition has been applied to the reference point preventing movement in x-y and Z rotational directions in initial step

element Set 3 has been applied to the top of the model along one of the shoulders with a reference point in the same area, the tie has been set up with the reference point as the main and element set as secondary. a displacement boundary condition has been applied to the reference point moving it in the z direction to simulate compression in step 1

(see below for positions I am basing my model on)