The application relates to a bone screw assembly for fixation into a bone, comprising a first screw element with a body including a threaded first end with a first external screw thread having a first handedness and a first lead length. The first screw element comprises an internal thread feature with a second handedness and a second lead length located within a bore within said body. The screw assembly includes a second screw element comprising a second external screw thread with the second handedness and the second lead length. Said second screw element is arranged within said bore and said second external screw thread is engaged with said internal thread feature. The second screw element is movable from a first implantation configuration where the second screw element is arranged completely within said bore and a second implantation configuration where the second screw element protrudes from said bore.
