Pedicle screw assembly

Abstract

A pedicle screw assembly having an axial load element engaging the structure joining the screw and the rod retainer. The axial load element generally holds the rod retainer in place with respect to the screw, while allowing manual movement when desired. In one embodiment, the pedicle screw assembly includes a ball-and-socket joint joining the screw head to the rod retainer. The assembly may include a saddle configured to secure a ball at the head of the screw within a socket in the rod retainer. The saddle may provide resilient compression in the axial direction. For example, the saddle may include a pair of axially-offset slots that extend partially across the saddle from opposite sides to define a bridge section. The resiliency of the saddle may be controlled by varying the characteristics of the slots and consequently the bridge section.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
         1 . A pedicle screw assembly comprising:
 a screw;   a rod retainer configured to selectively receive a rod, said rod retainer pivotally joined to said screw at a joint;   a saddle disposed within said rod retainer, said saddle including at least one slot formed into said saddle and extending in a generally transverse direction to provide said saddle with resiliency in an axial direction and said saddle applying a resilient bias to said joint in an axial direction, said bias tending to hold said rod retainer in place with respect to said screw at said joint, said saddle being compressed between said rod retainer and said screw even in an absence of a rod, whereby said joint receives a resilient bias even in an absence of a rod; and   a rod locking structure configured to secure a rod to said rod retainer.   
     
     
         2 . The assembly of  claim 1  wherein said joint is a ball-and-socket joint. 
     
     
         3 . The assembly of  claim 2  wherein said ball-and-socket includes a ball disposed about a head of said screw and a socket defined within said rod retainer. 
     
     
         4 . The assembly of  claim 3  wherein said ball includes two split ball halves closed about said screw head, said resilient load member configured to engage and assist in retaining together said split ball halves. 
     
     
         5 . The assembly of  claim 3  wherein said saddle is fitted within and secured to said rod retainer to hold said ball within said socket. 
     
     
         6 . The assembly of  claim 5  wherein said saddle includes at least two slots, each of said slots extending in a generally transverse direction to provide said saddle with resiliency in said axial direction. 
     
     
         7 . The assembly of  claim 5  wherein said saddle includes a pair of axially offset slots extending in a generally transverse direction, said slots cooperatively defining a resilient bridge section to provide said saddle with resiliency in said axial direction. 
     
     
         8 . The assembly of  claim 7  wherein said slots are defined in said saddle from opposite directions. 
     
     
         9 . The assembly of  claim 8  wherein said saddle includes a ball seat at one end and a rod seat at an opposite end. 
     
     
         10 . The assembly of  claim 9  wherein said saddle includes at least two ears for interlocking said saddle within said rod retainer. 
     
     
         11 . The assembly of  claim 10  wherein said rod retainer defines an annular groove configured to receive said ears, said saddle being rotatable within said rod retainer when said ears are disposed within said annular groove. 
     
     
         12 . The assembly of  claim 11  wherein said rod retainer defines at least two recesses configured to receive said at least two ears, said recesses axially offset from said annular groove, whereby said saddle may be moved axially within said rod retainer to move said ears from said annular groove into said recesses. 
     
     
         13 . A pedicle screw comprising:
 a rod retainer having an internal space;   a screw having a ball seated within said rod retainer;   a saddle fitted within said internal space under compression between said rod retainer and said ball, said saddle having an axially-extended body having a rod seat at a first end and a ball seat at a second end, said rod seat capable of seating a rod for connecting one pedicle screw to another pedicle screw, said ball seat configured to pivotally engage said ball, said body defining a first slot configured to provide said body with resiliency in an axial direction.   
     
     
         14 . The screw of  claim 13  wherein said saddle is generally cylindrical and is configured to be fitted within a generally cylindrical opening in a rod retainer, said rod seat disposed at said first end of said cylinder and said ball seat disposed at said second opposite end of said cylinder. 
     
     
         15 . The screw of  claim 14  wherein said body defines a second slot cooperating with said first slot to provide said body with resiliency in the axial direction. 
     
     
         16 . The screw of  claim 15  wherein said first slot and said second slot extend into said body from substantially opposite sides of said body, said first slot and said second slot being axially offset from one another to define a bridge section. 
     
     
         17 . The screw of  claim 16  wherein said body includes at least one protrusion extending radially outwardly from said body at said first end for securing said saddle within a rod retainer. 
     
     
         18 . The screw of  claim 16  wherein said body includes a pair of ears extending radially outwardly from said body at said first end for securing said saddle within a rod retainer. 
     
     
         19 . A pedicle screw assembly comprising:
 a screw with a shaft and a head, said screw having a ball at said head;   a rod retainer mounted to said screw, said rod retainer defining a socket receiving said ball, said rod retainer being pivotally movable about said ball; and   a saddle installed within said rod retainer to secure said ball in said socket, said saddle being resilient in an axial direction and being installed into a compressed state between said ball and said rod retainer under an axial load, whereby said saddle provides a bias compressing said ball within said socket in an axial direction to hold said rod retainer in a fixed position relative to said screw in an absence of an external force and in absence of a rod within said rod retainer.   
     
     
         20 . The assembly of  claim 19  wherein said saddle includes a first end defining a rod seat and a second end defining a ball seat, said rod seat configured to seat a rod for connecting the pedicle screw to a rod, said ball seat configured to pivotally engage said ball. 
     
     
         21 . The assembly of  claim 20  wherein said saddle defines first and second slots extending generally transversely into saddle from opposite sides, said first and second slots being axially offset from one another to define a bridge section that provides said saddle with resiliency in the axial direction. 
     
     
         22 . The assembly of  claim 21  wherein said saddle includes at least two ears extending from said first end, said ears extending radially outward to engage said rod retainer. 
     
     
         23 . The assembly of  claim 22  wherein said ball is defined by a pair of split ball halves closed on said screw head, said split ball halves engaging one another alone a plane extending generally parallel to an axis of said screw, said ball seat including a generally spherical surface engaging both of said split ball halves, said axial load in said saddle causing said ball seat to urge together said split ball halves.