Spinal stabilization system

Abstract

The present invention is directed to a spinal implant system that incorporates unique snap, or spring loaded, features to assist the surgeon in the placement of screws, rods, hooks and transverse connectors. The poly-axial movement also uses a more direct loading lower saddle into the bone screw to improve locking of the construct.

1 . A bone anchor assembly, comprising:
 a first fixation element configured to couple to a bone, the fixation element having a shank portion and a fixation head portion, the shank portion having an external thread form to engage bone;   a housing portion having an internal bore extending there through, the housing portion having at least two sidewalls forming a first channel adapted to receive a connecting rod;   an insert sized and configured for insertion into the internal bore of the housing portion, the insert having an upper receiver portion for making a first provisional connection to the connecting rod, the insert further having a lower receiver portion for making a second provisional connection to the fixation head portion of the fixation element.   
     
     
         2 . The bone anchor assembly of  claim 1 , wherein the upper receiving portion making the first provisional connection selectively retains the connecting rod within the first channel but allows the connecting rod to slide along a longitudinal axis of the connecting rod within the first channel of the housing portion. 
     
     
         3 . The bone anchor assembly of  claim 1 , wherein the lower receiver portion for making the second provisional connection engages the fixation head portion and applies sufficient frictional resistance between the lower receiver portion and the fixation head portion to inhibit free rotational movement of the fixation head portion relative to the insert but allow rotational movement of the fixation head portion relative to the insert upon application of an outside force. 
     
     
         4 . The bone anchor assembly of  claim 1 , wherein advancement of a set screw into the housing converts the first and the second provisional connections into a first and a second permanent connection, whereby the first permanent connection inhibits relative movement between the insert and the connecting rod, and the second permanent connection inhibits relative rotation between the fixation head and the insert. 
     
     
         5 . The bone anchor assembly of  claim 1 , wherein the upper receiver portion includes a plurality of flexible fingers extending upwardly from the insert, at least two of the flexible fingers being spaced apart a first distance at a location distal from the insert, the first distance being less than a diameter of the connecting rod. 
     
     
         6 . The bone anchor assembly of  claim 1 , wherein the lower receiver portion includes a plurality of flexible fingers extending downwardly from the insert, at least two of the flexible fingers being spaced apart a first distance at a location distal from the insert, the first distance being less than a diameter of the fixation head portion. 
     
     
         7 . The bone anchor assembly of  claim 1 , wherein the insert includes a plurality of anchoring tabs projecting outward from a generally cylindrical periphery of the insert, the anchoring tabs sized and configured to engage with a plurality of pockets formed into an inner surface of the housing portion when the insert is assembled to a desired position within the housing portion. 
     
     
         8 . A surgical construct comprising:
 a bone screw having a threaded shaft and a screw head;   a rod holding body for accommodating at least a portion of a connecting rod, the rod holding body including a screw hole, a chamber and a threading area, wherein the screw hole has a smaller inner diameter than an outer diameter of the screw head;   an insert sized and configured to fit within the chamber, the insert including a central body, an upper rod receiving portion and a lower screw head receiving portion;   the upper rod receiving portion including at least two rod fingers extending distally upward from the central body, a spacing between the at least two rod fingers at a location distal from the central body being less than an outer diameter of the connecting rod such that, when the connecting rod is positioned within the rod receiving portion, the rod fingers contact the connecting rod with sufficient frictional force to inhibit but not preclude movement of the rod relative to the upper rod receiving portion;   the lower screw head receiving portion including at least two screw fingers extending distally downward from the central body, a spacing between the at least two screw fingers at a location distal from the central body being less than an outer diameter of the screw head such that, when the screw head is positioned within the lower screw head receiving portion, the screw fingers contact the screw head with sufficient frictional force to inhibit but not preclude movement of the screw head relative to the lower screw head receiving portion.   
     
     
         9 . The surgical construct of  claim 8 , wherein the central body of the insert is formed in a generally concentric cylindrical shape, and the chamber of the rod holding body is formed in a generally non-concentric cylindrical shape. 
     
     
         10 . The surgical construct of  claim 8 , wherein the insert further comprises at least one securement tab extending outward from the central body, the securement tab sized and configured to engage with at least one pocket formed in an inner surface of the chamber. 
     
     
         11 . The surgical construct of  claim 8 , wherein the central body of the insert between the upper rod receiving portion and the lower screw head receiving portion comprises a generally cylindrical shape. 
     
     
         12 . The surgical construct of  claim 8 , wherein at least one of the at least two rod fingers is flexible. 
     
     
         13 . The surgical construct of  claim 8 , wherein at least one of the at least two screw fingers is flexible. 
     
     
         14 . The surgical construct of  claim 10 , wherein the at least one securement tab is flexible. 
     
     
         15 . A surgical construct for use in spinal corrective procedures, comprising
 a bone screw;   a housing;   an insert;   an elongated rod; and   a set screw;   the bone screw comprising:
 a threaded portion, and 
 a head comprising a housing engaging surface and an insert engaging surface; 
   the housing comprising:
 a bone facing surface and a top edge with at least one sidewall extending therebetween; 
 a throughhole extending from the top edge to the bone facing surface, the throughhole including at least one insert locking surface; 
 at least a pair of opposing slots proximate the top edge; and 
 a screw head seating surface, the screw head seating surface capable of engaging the housing engaging surface at a plurality of polyaxial orientations to allow polyaxial locking of the bone screw relative to a vertical axis of the housing when the set screw is in a locked configuration; 
   the insert comprising:
 a screw head engaging surface, the screw head engaging surface shaped to cooperatively engage the insert engaging surface to allow polyaxial orientation of the bone screw relative to a vertical axis of the housing, the screw head engaging surface including at least one flexible tab that contacts the head of the bone screw and retains at least a portion of the insert engaging surface in intimate frictional contact with at least a portion of the screw head engaging surface; 
 a rod receiving surface shaped to seat a portion of the elongated rod, the rod receiving surface aligning with the pair of opposing slots, the rod receiving surface including at least one elongated finger that contacts the elongated rod and retains at least a portion of the elongated rod in frictional contact with at least a portion of the rod receiving surface, wherein the elongated rod is seatable on the rod receiving surface; and 
 a housing locking surface, the housing locking surface including at least one outwardly extending member that contacts the insert locking surface and secures the insert within the throughhole. 
   
     
     
         16 . The surgical construct of  claim 15 , wherein when the surgical construct is in an unlocked configuration the housing engaging surface of the bone screw does not contact the screw head seating surface of the housing. 
     
     
         17 . The surgical construct of  claim 15 , wherein the rod receiving surface of the insert further comprises two generally opposing elongated fingers. 
     
     
         18 . The surgical construct of  claim 15 , wherein the screw head engaging surface of the insert comprises at least two generally opposing flexible tabs. 
     
     
         19 . The surgical construct of  claim 16 , wherein when the surgical construct is in a locked configuration the housing engaging surface of the bone screw directly contacts the screw head seating surface of the housing. 
     
     
         20 . The surgical construct of  claim 15 , wherein when the surgical construct is in an unlocked configuration the head of the bone screw can rotate relative to the insert and the elongated rod can slide along a longitudinal rod axis relative to the insert, but when the surgical construct is in a locked configuration the head of the bone screw is rotationally locked between the screw head engaging surface and the screw head seating surface; and the elongated rod is immovably secured between the rod receiving surface and a rod contacting surface of the set screw.