Stabilizing bones using screws and rods

An orthopedic fixation device for affixing a screw head of a polyaxial pedicle screw, comprising:

• a tulip comprising:
• a tulip body forming an interior cavity;
• two opposed arms extending away from a proximal end of the body;
• cooperating threads disposed on mutually facing sides of each arm;
• at least one radially extending pin;
• and
• a ramp positioned at a distal end of the tulip body at an entrance to the cavity, a saddle sized and dimensioned to be insertable into the tulip body, the saddle comprising:
• a U shaped groove at a proximal end sized to receive a spinal fixation rod inserted between the tulip arms;
• and
• a mating connection portion on a peripheral surface of a distal end of the saddle, and
• a ring for engaging the screw head, the ring having a first diameter smaller than a widest diameter of the screw head, wherein the ring is configured to be formable into a second diameter larger than the widest diameter of the screw head when the screw head is passed into the ring, wherein the ring comprises:
• a mating connection portion mateable with the mating connection portion of the saddle, whereby the ring and the saddle are mutually releasably connectable;
• a ramp cooperative with the ramp of the tulip;
• and
• one or more axially extending kerfs,
• wherein the screw head is clampable within the tulip body interior cavity in a position between the saddle and the ring when the saddle is urged in a distal direction towards a tulip ledge and the ramp of the ring slides against the ramp of the tulip, and the pin of the tulip is configured to extend into a kerf of the ring as the ring is moved axially, the pin thereby guiding movement of the ring and blocking movement of the ring beyond an axially extending length of the kerf,
• at least one kerf extending from a proximal surface of the ring and extending axially to a length less than an axial length of the ring, and at least one kerf extending from a distal surface of the ring and extending axially to a length less than an axial length of the ring, the ring thereby compressible about a proximal periphery and compressible about a distal periphery.