importing an obj as a shape key on a posed character.

After I posed my character with the meta rig, I exported my character out of blender and into zbrush to create a corrective shape key. i then exported the character out of zbrush as an object and imported back to blender. When I select “join as shape key” and move the slider to 100, it seems that including the bone deformation as well as the modifications made in zbrush. Would greatly appreciate a point in the right direction.