Polyaxial Pedicle Screw Assembly

Abstract

A fastener and a bone fixation assembly for the internal fixation of vertebral bodies such as a pedicle screw is provided which allows a detachable tulip to be provisionally locked to a pedicle screw, while separately, the rod securely locks to the tulip. According to one exemplary embodiment, the tulip assembly includes a tulip body and an inner tulip member, the tulip body having a non-circular surface disposed on an outer surface. Additionally, a fastener is coupled to the tulip assembly and positionable to retain the tulip assembly on the head of a screw. Further, a cap having an outer surface and a plurality of inner protrusions is provided, wherein the plurality of inner protrusions are configured to mateably connect to the non-circular surface on the tulip body to compress the tulip assembly and secure a rod.

1 . A pedicle screw assembly comprising:
 a threaded screw, the screw having a threaded portion, a spherical head and an interface for driving the screw;   a tulip assembly including a tulip body and an inner tulip member, the tulip body having non-circular surface disposed on an outer surface;   a fastener coupled to the tulip assembly and positionable to retain the tulip assembly on the head of the screw; and   a cap having an outer surface and a plurality of inner protrusions, wherein said plurality of inner protrusions are configured to mateably connect to said non-circular surface to compress said tulip assembly.   
   
   
       2 . The pedicle screw assembly of  claim 1  wherein said fastener comprises a compression ring configured to receive and be positioned around at least a part of the head portion of said threaded screw. 
   
   
       3 . The pedicle screw assembly of  claim 2  wherein said compression ring comprises a split in the ring that permits the diameter of the ring to vary from a first, larger diameter to a second, smaller diameter. 
   
   
       4 . The pedicle screw assembly of  claim 1 , wherein said tulip body comprises an internal wall region defining a bore;
 said bore being configured to receive said fastener and said inner tulip member.   
   
   
       5 . The pedicle screw assembly of  claim 4 , wherein:
 said bore extends from a top region of the tulip to a lower region of the tulip;   said bore is sized to receive said spherical head of said screw; and   said bore includes an expansion channel shaped to facilitate coupling of said fastener to said spherical head of said screw when inserted in said bore.   
   
   
       6 . The pedicle screw assembly of  claim 5 , wherein said expansion channel further comprises a seating taper disposed on a lower portion of said expansion channel; and
 a taper disposed on a lower portion of said fastener corresponding to said seating taper;   wherein said seating taper and said taper on said fastener are configured to constrict said fastener about said spherical head of said screw.   
   
   
       7 . The pedicle screw assembly of  claim 1 , wherein said cap further comprises a plurality of protruding members on an inner surface of said cap;
 wherein said protruding members are configured to selectively engage said inner tulip member and impart a translating force on said inner tulip member.   
   
   
       8 . The pedicle screw assembly of  claim 7 , wherein said protruding members comprise inclined planes. 
   
   
       9 . The pedicle screw assembly of  claim 7 , wherein said inner tulip member is coupled in said tulip body adjacent to said fastener such that downward translation of said inner tulip member translates said fastener into a seating taper. 
   
   
       10 . The pedicle screw assembly of  claim 9 , wherein said protruding members are configured to impart a translating force on said inner tulip member sufficient to seat said fastener in said seating taper lock an angular position of said tulip assembly relative to said threaded screw. 
   
   
       11 . The pedicle screw assembly of  claim 7 , wherein said cap has a first position and a second retained position;
 wherein said first position engages said protruding members and said inner tulip member to lock a relative angle between said tulip assembly and said threaded screw; and   wherein said second retained position engages said inner protrusions with said non-circular surface to compress said tulip assembly to lock a rod within said tulip assembly.   
   
   
       12 . The pedicle screw assembly of  claim 1 , wherein said tulip body further comprises at least one compression relief 
   
   
       13 . The pedicle screw assembly of  claim 1 , further comprising a coupling member formed on said tulip body;
 wherein said coupling member defines a single channel, said non-circular surface being disposed in said channel; and   wherein said inner protrusions in said cap connect to and are rotated in said channel.   
   
   
       14 . The pedicle screw assembly of  claim 1 , wherein said cap further comprises a tool receiving driving feature. 
   
   
       15 . A tulip assembly configured to be coupled to a head of a bone fixation device comprising:
 an outer member including a non-circular surface;   at least one inner member disposed in said outer member, said at least one inner member being configured to fix said tulip assembly to said head of a bone fixation device;   a channel formed in said tulip assembly to receive a rod; and   a cap having an outer surface and a plurality of inner protrusions, wherein a first set of said plurality of inner protrusions is configured to mateably connect to said non-circular surface to compress said channel.   
   
   
       16 . The tulip assembly of  claim 15 , wherein said at least one inner member further comprises:
 a first inner member disposed in a lower portion of said outer member;   a second inner member disposed in an upper portion of said outer member;   wherein said first inner member is elastically expandable to receive said head of a bone fixation device; and   wherein said second inner member is configured to interact with said rod when said channel is compressed.   
   
   
       17 . The tulip assembly of  claim 16 , wherein said second inner member comprises:
 a main body;   at least one extension proximally protruding from said main body;   an inner bore formed in a distal end of said main body; and   a compression surface formed on a distal end of said main body;   wherein said compression surface is configured to contact said first inner member and selectively seat said first inner member in a seating taper, said seating taper being configured to constrict said first inner member about said head of a bone fixation device to fix a position of said tulip assembly relative to said bone fixation device.   
   
   
       18 . The tulip assembly of  claim 17 , wherein said cap has a first position and a second retained position;
 wherein said first position is configured to engage a second set of said plurality of inner protrusions with said first inner member to seat said first inner member and to lock a relative angle between said tulip assembly and said threaded screw; and   wherein said second retained position engages said first set of said plurality of inner protrusions with said non-circular surface to compress said channel to lock a rod within said tulip assembly.   
   
   
       19 . A pedicle screw assembly comprising:
 a threaded screw, the screw having a threaded portion, a spherical head and an interface for driving the screw;   a tulip assembly including a tulip body and an inner tulip member, the tulip body including an inner surface and an outer surface, said inner surface defining a bore for receiving said inner tulip member, and a non-circular surface disposed on said outer surface;   a split ring fastener coupled to the tulip assembly and positionable to retain the tulip assembly on the head of the screw; and   a cap having an outer surface and a plurality of inner protrusions, wherein said cap has a first position and a second retained position, wherein said first position engages a first group of said inner protrusions with said inner tulip member to lock a relative angle between said tulip assembly and said threaded screw, and wherein said second retained position engages a second group of said inner protrusions with said non-circular surface to compress said tulip assembly to lock a rod within said tulip assembly.   
   
   
       20 . The pedicle screw assembly of  claim 19 , wherein:
 said bore extends from a top region of the tulip to a lower region of the tulip;   said bore is sized to receive said spherical head of said screw; and   said bore includes an expansion channel shaped to facilitate coupling of said fastener to said spherical head of said screw when inserted in said bore;   wherein said expansion channel further comprises a seating taper disposed on a lower portion of said expansion channel, and a taper disposed on a lower portion of said fastener corresponding to said seating taper, wherein said seating taper and said taper on said fastener are configured to constrict said fastener about said spherical head of said screw.   
   
   
       21 . The pedicle screw assembly of  claim 19 , wherein said first group of said inner protrusions comprise inclined planes. 
   
   
       22 . The pedicle screw assembly of  claim 19 , wherein said inner tulip member is coupled in said tulip body adjacent to said split ring fastener such that downward translation of said inner tulip member translates said split ring fastener into a seating taper. 
   
   
       23 . The pedicle screw assembly of  claim 19 , wherein said tulip body further comprises at least one compression relief. 
   
   
       24 . The pedicle screw assembly of  claim 19 , further comprising a coupling member formed on said tulip body;
 wherein said coupling member defines a single channel, said non-circular surface being disposed in said channel; and   wherein said second group of inner protrusions in said cap connect to and are rotated in said channel.   
   
   
       25 . A method of fixing a tulip assembly to a pedicle screw comprising:
 inserting said pedicle screw into a bone, said pedicle screw including a head portion;   expanding a first inner member of said tulip assembly over a head portion of said pedicle screw after said pedicle screw is inserted into a bone;   inserting a rod in said tulip assembly;   coupling a cap to a single channel of said tulip assembly;   rotating said cap to a first position to fix an angle of said tulip assembly; and   rotating said cap to a second position to compress an outer housing of said tulip assembly to lock said rod in said tulip assembly.   
   
   
       26 . The method of  claim 25 , wherein rotating said cap to a first position to fix an angle of said tulip assembly comprises:
 engaging a protrusion on said cap with a first inner member of said tulip assembly to generate a compressive force on said inner member;   transmitting said compressive force through said inner member to a second inner member, wherein said compressive force seats said second inner member in a seating taper.   
   
   
       27 . The method of  claim 26 , wherein rotating said cap to a second position to compress an outer housing of said tulip assembly to lock said rod in said tulip assembly comprises:
 engaging a compression tab of said cap with a non-circular surface of said outer housing to create interference;   wherein said interference compresses said outer housing to frictionally secure said rod in said tulip.   
   
   
       28 . The method of  claim 27 , wherein said interference further compresses said first inner member about said rod. 
   
   
       29 . A cap for compressing a tulip assembly comprising:
 an inner bore; and   a plurality of graduated tabs configured to compress said tulip assembly.   
   
   
       30 . A tulip assembly comprising:
 a tulip body; and   an inner tulip member;   wherein said tulip body includes a non-circular surface disposed on an outer surface, said non-circular surface being configured to interact with a cap to compress said tulip body about a rod, securely coupling said rod.