A bone fixation assembly comprises a tulip-shaped assembly and a bone fixation device such as a surgical or pedicle screw, comprising a head and a bone fixation portion. The tulip assembly comprises an upper portion to receive a rod and a lower portion that has a cavity in which the head of the bone fixation device rests. The cavity has an aperture below. The aperture has a length through which the tulip assembly may slide with respect to the bone fixation device, for movement of the tulip assembly when the bone fixation device is in place, while also maintaining the angular movement of the tulip assembly. The bone fixation device may comprise an aperture engaging part, which locks the bone fixation device position on the aperture length. A tulip assembly translation mechanism comprises a head, a cavity, an aperture to the cavity.
