A bone screw is provided including a longitudinal core member having a longitudinal axis defining a longitudinal direction and having an outer surface and a helical groove in the outer surface, the groove being defined by opposed sidewalls； and a helical thread body configured to be accommodated in the groove. When the thread body is assembled in the groove of the core member and when the core member is straight, the thread body is configured to abut one opposed sidewall without abutting the other opposed sidewall along a full turn of the thread body, the thread body is configured to slide in the groove between the opposed sidewalls of the helical groove parallel to the longitudinal axis, and a first portion of the thread body that is outside the helical groove has a height greater than a second portion of the thread body that is in the helical groove.
