Abstract:
Spinal alignment apparatus including rods, pedicle screws, and hinged connectors for rigidly immobilizing the vertebrae of the spine. The hinged connectors allow angular motion between the pedicle screws and the connectors when the connectors are in an open or unlocked position. The hinged connectors hold the head of the pedicle screw tightly, thus preventing angular motion, when the connector is forced closed. The hinged connector and rod are held closed by a cap or strap over the rod and connector.

Description:
REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims benefit from U.S. Provisional Patent Application Serial No. 60/301,181, filed Jun. 27, 2001, the entire contents of which being incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates generally to instrumentation and techniques associated with spinal fixation and, in particular, to apparatus and methods facilitating alignment of the spine.  
           [0004]    2. Description of the Related Art  
           [0005]    Various methods of spinal immobilization have been known and used for many years in the treatment of spinal instability and displacement. As surgical techniques have become more sophisticated, various methods of internal and external fixation have been developed.  
           [0006]    External fixation involves at least some portion of the stabilization device which is external to the patient&#39;s body. Internal fixation, which is the preferred method, refers to methods of stabilization which are wholly internal to the patient, and commonly involve devices such as screws, plates and rods.  
           [0007]    The first successful internal fixation method for surgically treating scoliosis used the Harrington instrumentation system. According to this technique, a rigid rod with hooks at each end is implanted adjacent the concave side of the scoliotic spine. The spine is manually straightened to a desired extent and a distraction rod is used to maintain the correction by exerting vertical forces at each end. The rod commonly has a ratcheted end over which hooks are slidably mounted and locked into place. The Harrington instrumentation system has been successfully used for some time, but because the distraction rod is fixed to the spine in only two places, failure at either end causes the entire system to fail.  
           [0008]    An alternative treatment has since evolved which takes advantage of segmented fixation. According to this method, a rod is fixed to the spine at multiple points by means of sublaminar wires, hooks, or pedicle screws.  
           [0009]    U.S. Pat. No. 4,611,581 uses pedicle screws that attach to plates on the posterior aspect of the spine. However, the plates can be difficult to insert over pedicle screws angled in several different directions.  
           [0010]    U.S. Pat. No. 4,805,602 uses rods that attach to pedicle screws. The device allows angular motion between the pedicle screw and a component that connects the screw to the rod. The motion between the connector component and the screw is restricted by forcing the rod against the pedicle screw. However, the immobilization of the screw is not as rigid as the immobilization of the device taught in &#39;581 patent.  
           [0011]    U.S. Pat. No. 4,946,458, like the &#39;602 patent, uses a connector component that allows angular motion of the screw relative to the connector component. The &#39;458 patent teaches the use of nuts on a threaded rod to force two halves of the connector component, contained by a ring, around the screw head, thus immobilizing the screw within the connector component. However, the connector component will fail to hold the screw or the rod if one of the two halves of the connector dissociates from the retaining ring. Furthermore, the device taught in the &#39;458 patent relies on nuts driven on threaded rods. Threaded rods are weaker than rods without threads. Lastly, the use of wrenches on nuts threaded longitudinal rods is cumbersome.  
           [0012]    U.S. Pat. No. 5,540,689 uses a shape-memory alloy rod which is deformed at the time of surgery to accommodate the existing curvature of the patient&#39;s spine and segmentally affixed using bone clamps, and then heated to effect shape recovery and thereby apply corrective forces to the spine.  
           [0013]    While these devices can be adequately used for surgically treating abnormal curvatures of the spine, a need exists for a system that rigidly immobilizes polyaxial pedicle screws within connector components, yet uses rods without threads and has a connector closing mechanism that sits on top of the connector.  
         SUMMARY OF THE INVENTION  
         [0014]    It is therefore an object of the present invention to provide a device which uses polyaxial pedicle screws which can be securely connected to a solid cylindrical unthreaded rod.  
           [0015]    It is a further object to the present invention to provide a spinal alignment system which uses segmented fixation with pedicle screws having connectors through which a cylindrical rod is rigidly affixed at each screw.  
           [0016]    It is a still further object of the present invention to provide a pedicle screw system which allows angular motion relative to the rod and connector to achieve maximum holding power without undue stress on the system.  
           [0017]    These and other objects of the present invention will be more readily apparent from the description and drawings that follow.  
           [0018]    This invention resides in spinal fixation apparatus, including implantable components, instrumentation, and methods of use. In broad and general terms, the preferred embodiment includes pedicle screws that are attached to longitudinal rods by hinged connectors.  
           [0019]    The connectors include a hinge feature that permits angular motion of the pedicle screw when open and rigidly immobilizes the pedicle screw when closed. A strap, cap, or clip may be used to hold the hinged connector in position and the rod within the connector.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a lateral view, partly in cross-section, of a preferred embodiment of the device of the present invention with the rod and pedicle screw locked in position;  
         [0021]    [0021]FIG. 2 is a lateral view of the device shown in FIG. 1 with the connector in an unlocked position;  
         [0022]    [0022]FIG. 3 is an exploded view of the device shown in FIG. 1;  
         [0023]    [0023]FIG. 4 is a lateral view of the cap of the device with the cam in the unlocked position;  
         [0024]    [0024]FIG. 5 is a lateral view of the cap shown in FIG. 4 with the cam in the locked position;  
         [0025]    [0025]FIG. 6 is a lateral view, partly in cross-section, of an alternative embodiment of the device of the present invention with the rod and pedicle screw locked in position; and  
         [0026]    [0026]FIG. 7 is a lateral view of the device shown in FIG. 6 with the connector in an unlocked position.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    Referring now to FIG. 1, there is shown a locking device for a spinal fixation system, generally indicated at  10 , according to the present invention. Devcie  10  includes a hinged connector  12  which is locked around a pedicle screw  14 . Hinged connector  12  is formed from two opposing sets of arms  12   a ,  12   b  which are each hinged at a pivot  16 . Any number of arm sets  12   a ,  12   b  more than two can be used. Arm sets  12   a ,  12   b  are adjustable from a normal at rest position shown in FIG. 3 to a locking position shown in FIG. 1. In one embodiment, arms  12   a ,  12   b  may be biased away from each other in their normal at rest position by a spring or other biasing means known in the art. Each of arms  12   a ,  12   b  contain a notched portion  18 .  
         [0028]    Pedicle screw  14  consists of an exteriorly threaded portion  14   a  and a spherical head portion  14   b . Threaded portion  14   a  is capable of being threadedly affixed to a vertebra, while head portion  14   b  is sized such that connector  14  may be inserted over threaded portion  14   a  of screw  14  until it contacts head portion  14   b , allowing rotating motion of connector  12  about head portion  14   b . Head portion  14   b  contains a recess  20 , such as a hexagonal recess, to facilitate the installation of pedicle screw  14  into bone by use of a suitable tool.  
         [0029]    A cylindrical rod  22  used to couple vertebrae together is positioned above spherical head portion  14   b  of each pedicle screw  14  which has been inserted into a vertebra at points deemed to be useful to the attending surgeon. Rod  22  may be formed to restore or maintain proper alignment of the spine during the installation procedure of spinal fixation device  10 . When locked securely in place by connector  12 , neither rod  22  nor screw  14  can move within connector  12 .  
         [0030]    A cap  24  for locking connector  12  in position about rod  22  and head portion  14   b  of screw  14  contains a flat planar surface  26  with downwardly depending tabs  28  at each end terminating with inwardly turned edges  30 . Edges  30  are sized to fit tightly within notched portions  18  of connector  12  when in the locked position. A cam operated device  32  is rotatably coupled within cap  24  which serves to lock rod  22  in position within connector  12  when device  10  is in use.  
         [0031]    [0031]FIG. 2 illustrates hinged connector  12  in the unlocked position about screw  14 . Screw  14  is free to change angular motion within connector  12  when connector  12  is not held closed or locked by cap  24 . Furthermore, cap  24  can be removed, unlocking rod  22  and screw  14 , as necessary to reposition rod  22  or screw  14 . The distance between screws  14  can be varied by sliding screws  14  and connectors  12  along rod  22  prior to closing locking cap  24 . For example, two consecutive screws  14  can be forced apart with an instrument to distract the vertebrae. Head  14   b  of screw  14  and/or the interior surface of hinged connector  12  can be grooved, sand blasted, or otherwise roughed to increase the friction fit between the head of screw  14  and hinged connector  12 .  
         [0032]    [0032]FIG. 3 shows the insertion sequence of the spinal system. Pedicle screw  14  is inserted through hinged connector  12 . Once assembled, each pedicle screw  14  is threaded into a vertebra. Rod  22  is contoured and cut to length to fit the portion of the spine containing pedicle screws  14 . Distraction or compression of screws  14  is performed as necessary. A pliers-like instrument (not shown) is used to force the sides of the hinged connector  12  closed. Edges  30  of cap  24  are slid into notches  18  on the hinged connector  12  once connector  12  is closed. The pliers-like instrument can be removed once the cap  24  is partially placed on connector  12 . A pliers-like instrument can also be used to force the partially inserted cap  24  completely onto connector  12 . Once cap  24  is properly positioned, cam device  32  is rotated 90 degrees, locking rod  22  within connector  12 .  
         [0033]    [0033]FIG. 4 shows cam device  32  in the unlocked position. Cap  24  can be slid onto connector  12  and over rod  22  when cam device  32  is in the unlocked position. FIG. 5 shows cam  32  in the locked position. Cam  32  fits tight against rod  22  in the locked position, between cam device  32  and head  12   a  of screw  12 .  
         [0034]    [0034]FIGS. 6 and 7 show an alternative device, generally designated at  10   a , for locking rod  22  in position against pedicle screw  14 . Referring now to FIG. 6, connector  12  has two opposing sets of arms  12   a ,  12   b  which are each hinged at a pivot  16 . In this embodiment,  12   a ,  12   b  are biased away from each other in their normal at rest by a spring or other biasing means known in the art, as can be seen in FIG. 7. At the end of each arm  12   a  opposite pivot  16 , a lever  40  is rotatably coupled to arm  12   a  by a pivot  42 . Lever  40  terminates in a handle portion  44 . Also rotatably coupled to lever  40  is a locking strap  46 . At the end of each arm  12   b  opposite pivot  16 , a hook section  50  is formed.  
         [0035]    The operation of device  10   a  can now be described. A screw  14  is inserted through connector  12  up to spherical head  14   b , and then section  14   a  is threaded into a vertebra. Rod  22  is contoured and cut to length to fit the portion of the spine containing pedicle screws  14 . Distraction and compression of screws  24  is performed as necessary. In the unlocked position, screw  14  is free to change angular motion within connector  12 , and rod  22  can be repositioned.  
         [0036]    When device  10   a  is in the desired position relative to rod  22 , lever  40  is rotated about pivot  42  to a point where strap  46  can pass over hook  50  of each arm  12   b . After strap  46  is passed over hook  50 , handle  44  of lever  40  is rotated about pivot  42  in the opposite direction, causing rod  22  to be captured in position between strap  46 , head  14   b  of pedicle screw  14 , and arms  12   a ,  12   b  of connector  12 . Connector  12  can be unlocked to reposition rod  22  relative to connector  12  or screw  14 .  
         [0037]    While the present invention has been shown and described in terms of several preferred embodiments thereof, it will be understood that this invention is not limited to these particular embodiments and that changes and modifications may be made without departing from the true spirit and scope of the invention as defined in the appended claims.