Tulip head and collet for a poly axial screw

A system for connecting a fusion rod to a poly axial screw, the system comprising:

• a u-shaped tulip head with partially threaded side walls;
• a tulip collet;
• and
• a poly axial screw with ball head,
• wherein the collet includes:
• an upper saddle part with a base and two saddle horns;
• and
• a lower jaw joint part,
• wherein the saddle, its base and its two saddle horns are configured to receive a fusion rod, wherein the fusion rod sits across the saddle base, and is cradled by the two horns,
• wherein the jaw joint is configured to assume an open and a closed position, and comprises a plurality of jaw joint members that are configured to be separated in the open position, and to make contact with each other in the closed position,
• wherein each saddle horn defines an inwardly projecting, opposing lip along a top end thereof, wherein when said rod is seated in said collet said opposing lips project towards each other and flank the rod;
• wherein the tulip head comprises:
• an upper chamber;
• and
• a lower chamber,
• wherein the upper chamber is wider than the lower chamber, and the upper chamber is configured to loosely accommodate the ball head of the poly axial screw and the collet with its jaw joint in the open position;
• wherein the lower chamber is narrower than the upper chamber and the lower chamber is configured to fit tightly around the collet with its jaw joint in the closed position around the ball head of the poly axial screw and thus to lock the tulip in position while allowing it to rotate and pivot against the ball head upon actuation of manual force;
• wherein the top part of the tulip head is configured to engage with a fastener to allow fixation of the connection to a fusion rod in its final position.

A method of assembly of a poly axial screw from a tulip head and tulip collet onto an implanted screw during spinal fusion surgery, the method comprising:

• implanting the screw into a bone, including the pedicle of a vertebrae;
• and
• mounting the tulip head and collet onto a ball head of the screw by actuating a downward force upon the top of the tulip collet, thus moving the collet into a lower chamber of the tulip head,
• wherein the collet includes:
• an upper saddle part having a base and two saddle horns;
• and
• a lower jaw joint part configured to assume an open and a closed position, and comprising a plurality of jaw joint members that are configured to be separated in the open position, and to make contact with each other in the closed position,
• wherein each saddle horn defines an inwardly projecting, opposing lip along a top end thereof,
• wherein when said rod is seated in said collet said opposing lips project towards each other and flank the rod;
• wherein the tulip head comprises an upper chamber and a lower chamber,
• wherein the upper chamber is wider than the lower chamber, and the tulip head is configured to loosely accommodate a ball head of the poly axial screw and the collet with its jaw joint in the open position,
• wherein the lower chamber is narrower than the upper chamber and is configured to fit tightly around the collet with its jaw joint in a closed position around the ball head of the poly axial screw and thus to lock the tulip in position while allowing it to rotate and pivot against the ball head upon actuation of manual force;
• wherein when the collet is moved into the lower chamber of the tulip head the walls of the narrower lower chamber squeeze the jaw joint members circumferentially onto the ball head thereby achieving a locked position that remains rotatably and pivotably adjustable by manual force.