Bone screw systems with pressure caps having biasing members

A spinal fixation system, comprising:

• at least one bone screw comprising
• a head at a proximal end;
• and
• a bone connection element at a distal end;
• at least one body comprising
• a proximal end;
• a distal end;
• a mounting rod receiving channel disposed at the proximal end of the body;
• a bone screw head receiving channel disposed at the distal end of the body;
• wherein the proximal end and distal end are disposed along a longitudinal axis;
• and
• wherein a proximal portion of the mounting rod receiving channel comprises an internal thread for receiving a compression element;
• at least one pressure cap comprising:
• a proximal end comprising:
• at least two side walls disposed apart from each other;
• at least one biasing member disposed on a proximal end of the side walls;
• a distal end comprising;
• a surface operable to contact at least a portion of the head of the bone screw;
• wherein the pressure cap is configured to be disposed within the body and between a mounting rod and the bone screw;
• and
• wherein the pressure cap is operable to exert pressure on the bone screw when the mounting rod is biased against the proximal end of the pressure cap.