Polyaxial bone screw with shank articulation pressure insert and method

A pivotal bone anchor assembly for securing an elongate rod to a bone, the pivotal bone anchor assembly comprising

• a receiver having an interior cavity communicating with an upper open channel, the interior cavity in communication with a bottom surface of the receiver through a lower opening, the interior cavity having at least one non-deformable internal insert engaging surface, the open channel being configured to receive the elongate rod and a closure above the elongate rod to secure the elongate rod to the receiver;
• a shank having an upper portion and a body for fixation to the bone, the upper portion being pivotably positioned within a lower portion of the receiver interior cavity with the shank body extending downward through the lower opening;
• and
• a pressure insert at least partially positionable within the open channel and having an outer profile with a receiver engaging surface, the pressure insert being manipulated by a tool into an overlapping engagement position between the insert receiver engaging surfaces and the at least one non-deformable internal insert engaging surface within the receiver interior cavity to provide a frictional articulatable arrangement for the receiver relative to the shank until both are locked relative to each other with the elongate rod and closure positioned within the open channel after the tool has been removed,
• wherein the pressure insert is manipulated by the tool into the overlapping engagement position so that the insert receiver engaging surface comes into a compressive overlapped contact with the receiver internal insert engaging surface to resist any upward movement of the pressure insert within the receiver open channel, thereby providing the frictional articulatable arrangement for the pivotal bone anchor assembly prior to the assembly being locked with the closure, and
• wherein the engaging surfaces on the insert and receiver remain in biased contact with each other after coming into the overlapping engagement so as to cooperate in resisting any upward loosening forces that might move the pressure insert with respect to the receiver so as to affect the frictional articulatable arrangement therebetween.

A bone anchor assembly for securing an elongate rod to a bone, the bone anchor assembly comprising:

• a shank having a proximal capture portion and an anchor portion extending distally from the proximal capture portion for fixation to the bone;
• a receiver having a longitudinal axis, an upper portion defining an open channel with inner sidewall surfaces configured to receive the elongate rod, and a lower portion defining a cavity having an internal surface communicating with the open channel and a receiver bottom opening, the proximal capture portion of the shank positionable within the cavity, the inner sidewall surfaces including a helically wound guide and advancement structure and a rigid engagement structure formed in the receiver between the helically wound guide and advancement structure and the cavity;
• a closure rotatably positionable within the receiver open channel;
• and
• a pressure insert sized and shaped to be displaceable within the receiver into a frictional biased overlapping engagement with the receiver rigid engagement structure using a tool, after the shank proximal capture portion is positioned within the cavity of the receiver, so as to prevent the pressure insert from moving back up within the receiver due to the frictional biased overlapping engagement therebetween, the receiver rigid engagement structure being formed into the receiver prior to the pressure insert being positioned into the receiver,
• wherein the closure is spaced apart from the pressure insert when the closure and the elongate rod are positioned in the receiver open channel in a locked orientation.