Instrument and method for provisionally locking a polyaxial screw

A screw head locker assembly for provisionally tightening a screw body member to a head of a polyaxial bone screw the screw head locker assembly comprising:

• a bushing configured to be seated between the head and the screw body member of the polyaxial bone screw, the bushing having a concave surface having a radius of curvature Rb;
• a barrel body having a proximal end and a distal end, the distal end having a pair of tangs for releasably engaging a pair of screw body pockets on the screw body member, and a pair of cut outs opposite of each other and open to the distal end of the barrel body;
• an inner shaft disposed within the barrel body, the inner shaft having a distal engagement portion with a pair of opposing protrusions extending from a longitudinal axis of the inner shaft, the pair of opposing protrusions cooperatively having a length LP and a radius of curvature Rp which substantially equals the radius of curvature Rb of the concave surface of the bushing of the screw body member, the pair of cutouts spaced apart from each other a length Wb, wherein the length Lp is greater than Wb;
• a load link assembly operably coupling the inner shaft to the body, and
• a lever extending from the load link assembly, the lever being movable to actuate the load link assembly, wherein the actuation of the load link assembly displaces the pair of opposing protrusions to engage the bushing disposed between the screw body member and the head of the polyaxial bone screw.

A screw head locker assembly for provisionally tightening a screw body member to a head of a polyaxial bone screw, the screw head locker assembly comprising:

• a bushing configured to be seated between the head and the screw body member of the polyaxial bone screw, the bushing having a concave surface having a radius of curvature Rb;
• a barrel body having a proximal end and a distal end, the distal end having a pair of rotatable tangs configured to engage the screw body member, and a pair of cut outs opposite of each other and open to the distal end of the barrel body;
• an inner shaft including a proximal end and a distal end configured to engage a bushing within the screw body member, the bushing having a concave surface having a curvature of radius Rb, the inner shaft having a distal engagement portion with a pair of opposing protrusions extending from a longitudinal axis of the inner shaft and configured to be seated within a respective cut out of the pair of cut outs, the pair of protrusions cooperatively having a length LP, the two opposing protrusions having a radius of curvature Rp which substantially equals the radius of curvature Rb of the concave surface of the bushing of the screw body member, wherein the pair of cutouts are spaced apart from each other a length Wb, wherein the length Lp is greater than Wb;
• a handle and a lever coupled to the proximal end of the barrel body, the lever pivotally coupled to one of the handle and the barrel body;
• and
• a load link assembly operably coupled to the inner shaft and the lever, wherein actuation of the lever towards the handle causes the load link assembly to longitudinally displace the pair of opposing protrusions toward the distal end to contact the bushing and advance the bushing into a frictional fit between the screw body member and the head of the polyaxial bone screw.