Modular spinal fixation screw
A modular spinal fixation screw capable of rapid linear engagement of a bone screw and a rod member. The fixation screw is coupled to a connector formed from a clamp and a collet. The collet incorporates the use of a T-shaped living hinge which facilitates both attachment of the connector to a bone screw and lessens the resistance of the collet for locking to the bone screw and rod member. The collet further includes scallops that facilitates the insertion of the spherical end of the bone screw into the collet. The clamp can be moved from a first unlocked position used for installation to a locked position securing the rod member to a pedicle bone. The clamp compresses the collet which holds the hold rod member to the bone screws in a pre-selected position by linear movement of the clamp.
1. A modular spinal fixation screw comprising:
a bone screw having a first end and a second end with a threaded shank therebetween, said first end for penetrating securement to bone, said second end forming a spherical head portion;
a connector consisting of a collet operatively associated with a clamp, said collet having a lower end spaced apart from an upper end with a cylindrical shaped side wall therebetween, said upper end forming a header which protrudes outwardly from said side wall with a tapered section extending from said side wall to said upper end, a u-shaped receptacle extending beneath said upper end constructed and arranged to receive a rod member, said collet lower end having an inner side wall forming a receptacle surface sized for coupling to said head portion of said bone screw, said receptacle surface having at least one T-shaped living hinge formed therein from a first relief cut extending from said collet lower end to a perpendicular positioned relief cut juxtapositioned to said lower receptacle surface, said collet including a split line extending between said receptacle surface and said lower end; said relief cuts placed between said living hinge and said split line, said collet including first and second vertically disposed pin slots extending along a length of said side wall;
said clamp having an elongated body with an interior wall and an exterior wall, said interior wall including at least one annular bulge constructed and arranged to change the diameter of said collet sidewall when said clamp is drawn over said collet, a rod slot constructed to accept a rod member, said clamp including a first and second pin holes extending between said interior wall and said exterior wall; and
first and second pins, said first pin coupled to said first pin hole and extending into said first pin slot, said second pin coupled to said second pin hole and extending into said second pin slot wherein said pins regulate linear movement of said collet;
wherein said collet is linearly traversable between a first position and a second position by application of a linear force applied along a longitudinal axis of said clamp, whereby traversal of said collet from said first position to said second position causes said collet to cooperate with said at least one annular bulge to apply concurrent compressive forces to simultaneously immobilize movement between said connector and said rod member and immobilize movement between said connector and said bone screw.
2. The modular spinal fixation screw according to claim 1 wherein said collet includes a second pair of relief cuts placed between said split line and said living hinge.
3. The modular spinal fixation screw according to claim 1 including side wall reliefs to facilitate securing said collet to said bone screw head.
4. The modular spinal fixation screw according to claim 1 wherein said collet includes at least one inner annular ridge constructed and arranged to engage said at least one annular bulge in an overlapping manner while said collet is in said second position, whereby engagement of said at least one bulge and said at least one ridge applies compressive forces to said clamp for immobilizing said clamp to said head of the anchored bone screw.
5. The modular spinal fixation screw according to claim 1 wherein said collet includes one inner annular surface constructed and arranged to engage said at least one annular upper bulge in an overlapping manner while said collet is in said second position, whereby engagement of said at least one annular upper bulge and said at least one annular surface applies compressive forces to said clamp for immobilizing said clamp to said rod member.
6. The modular spinal fixation screw according to claim 1 wherein said at least one annular bulge is constructed and arranged to cooperate with said collet to apply compressive forces to said clamp for immobilizing connections between said rod and said anchored bone screw.
7. The modular spinal fixation screw according to claim 1 wherein said bone screw includes at least one helical thread for penetrating and engaging a bone and wherein said head portion is at least partially spherical in shape.
8. A modular spinal fixation screw comprising:
a bone screw having a first end and a second end with a threaded shank therebetween, said first end for penetrating securement to bone, said second end forming a spherical head portion;
a connector consisting of a collet operatively associated with a clamp, said collet having a lower end spaced apart from an upper end with a cylindrical shaped side wall therebetween, said upper end forming a header which protrudes outwardly from said side wall with a tapered section extending from said side wall to said upper end, a u-shaped receptacle extending beneath said upper end constructed and arranged to receive a rod member, said collet lower end having an inner side wall forming a receptacle surface sized for coupling to said head portion of said bone screw, said receptacle surface having at least one T-shaped living hinge formed therein from a first relief cut extending from said collet lower end to a perpendicular positioned relief cut juxtapositioned to said lower receptacle surface, said collet including a split line extending between said receptacle surface and said lower end, said collet includes relief cuts placed between said living hinge and said split line, said collet including first and second vertically disposed pin slots extending along a length of said side wall;
said clamp having an elongated body with an interior wall and an exterior wall, said interior wall including at least one annular bulge constructed and arranged to change the diameter of said collet sidewall when said clamp is drawn over said collet, a rod slot constructed to accept a rod member, said clamp including a first and second pin holes extending between said interior wall and said exterior wall; and
a first pin coupled to said first pin hole and extending into said first pin slot, and a second pin coupled to said second pin hole and extending into said second pin slot, wherein said pins regulate linear movement of said collet to the length of each pin slot;
wherein said collet is linearly traversable between a first position and a second position by application of a linear force applied along a longitudinal axis of said clamp, whereby traversal of said collet from said first position to said second position causes said collet to cooperate with said at least one annular bulge to apply concurrent compressive forces to simultaneously immobilize movement between said connector and said rod member and immobilize movement between said connector and said bone screw.
9. The modular spinal fixation screw according to claim 8 including side wall reliefs to facilitate securing said collet to said bone screw head.