Abstract:
A spine fixation assembly connecting a first vertebra to a second vertebra includes first and second mounting assemblies and a first spinal stabilization component. The first mounting assembly is configured to be attached to a first location of the first vertebra and includes a first bone anchor housing and first and second spinal stabilization component housings extending from the first bone anchor housing. The second mounting assembly is configured to be attached to a first location of the second vertebra and includes a second bone anchor housing and third and fourth spinal stabilization component housings extending from the second housing. The first spinal stabilization component includes an elongated body having a first end and a second end and is configured to connect the first mounting assembly to the second mounting assembly. The first spinal stabilization component housing is adapted to receive and connect to the first end of the spinal stabilization component and the third spinal stabilization component housing is adapted to receive and connect to the second end of the spinal stabilization component.

Description:
CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 60/794,355 filed Apr. 24, 2006 and entitled “IMPROVED SPINE FIXATION METHOD AND APPARATUS, the contents of which are expressly incorporated herein by reference. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an improved spine fixation method and apparatus, and more particularly to a spine fixation method and apparatus that utilizes adjustable, multi-axial mounting assemblies for receiving segments of stabilization elements with various geometries. 
       BACKGROUND OF THE INVENTION 
       [0003]    Several prior art spine fixation assemblies utilize rods and/or plates as connecting and stabilization elements between vertebral elements. The rods are secured to vertebral bones left and right the spinal midline via screws. The screws in some of the prior art assemblies are capable of pivoting around a fixed axis of the stabilization rods to achieve variable angular positions relative to the rods. This limited range of relative angular positioning is acceptable for many spinal pathologies. However, in some cases it is preferred to have screws that provide multi-axial positioning relative to the stabilization rods. 
         [0004]    Single or multilevel segmental posterior fusions are most commonly achieved by contouring a rigid ¼ inch cylindrical rod and attaching it to adjacent pedicle screws on each side of the spine using various connecting assemblies. This longitudinal construction can be made more rigid by connecting the rods to each other to form an “H” configuration. The rod system requires contouring of each rod across several vertebras in many cases. The contouring of each rod depends on the configuration of the pedicle screws and varies from side to side in the same patient and among patients. This may add considerable time to an operation. Recent generations of pedicle screws and rod connectors seek to diminish this drawback by allowing variable axes of movements in the pedicle screw recess for the rod or in the rod connectors. However, in most cases this adds another level of complexity to the operation and often further increases the operative time. This increase in operative time and the complexity of the connectors put substantial stress on the surgeon and the supporting staff. Even in the hands of the best spine surgeon, the rod is often not perfectly contoured to align with the pedicle screws. Hence the surgeon has to use substantial force at multiple points along a rod to hold the rod to the screws or connectors while counteracting the adjacent soft tissues. This maneuver risks soft tissue damage and also puts the dura and the neural contents at risk for dural tears or spinal cord or nerve damage if a holding instrument slips. 
         [0005]    Accordingly, there is a need for an improved spinal fixation device and method that does not require rod contouring and allows multi-axial screw anchoring. 
       SUMMARY OF THE INVENTION 
       [0006]    In general, in one aspect, the invention features a spine fixation assembly for connecting a first vertebra to a second vertebra including first and second mounting assemblies and a first spinal stabilization component. The first mounting assembly is configured to be attached to a first location of the first vertebra and includes a first bone anchor housing and first and second spinal stabilization component housings extending from the first bone anchor housing. The second mounting assembly is configured to be attached to a first location of the second vertebra and includes a second bone anchor housing and third and fourth spinal stabilization component housings extending from the second housing. The first spinal stabilization component includes an elongated body having a first end and a second end and is configured to connect the first mounting assembly to the second mounting assembly. The first spinal stabilization component housing is adapted to receive and connect to the first end of the spinal stabilization component and the third spinal stabilization component housing is adapted to receive and connect to the second end of the spinal stabilization component. 
         [0007]    Implementations of this aspect of the invention may include one or more of the following features. The spinal stabilization component housing comprises a mounting plate extending from the bone anchor housing and a mounting element configured to be removable attached to the mounting plate. The spinal stabilization component housing is rotatable around an axis passing through the center of the bone anchor housing. Any of the bone anchor housings comprise a multi-axial bone anchor housing. The spinal stabilization component may be rods, plates, cables or wires. The geometric configuration of the first and second ends of the elongated body may be a sphere, cylinder, hemisphere, flat plate, cup, hammer, sphere with flat opposite surfaces, circular plate, semicircular plate, polyhedron, ring-shaped and cannulated shape. Any of the mounting assemblies is attached to the vertebral location via a bone anchor configured to be received within the bone anchor housing. The bone anchors may be screws, hooks, pins or poly-axial screws. The mounting elements comprise a seat having a bottom configured to be removable attached to the corresponding mounting plate and a top configured to receive any of the elongated body&#39;s ends and comprising a side portion having an opening through which the elongated body extends. First and second locking elements may secure the first end to the first mounting element and the second end to the third mounting element, respectively. A bone anchor locking element may secure a bone anchor head to any of the bone anchor housings. Any of the locking elements may be a screw, a screw with a flat bottom, a screw with a pointed bottom, a washer, a nut, a snap-in lock, or a breakaway screw. The spine fixation assembly may further include a second spinal stabilization component configured to connect the second mounting assembly to a third mounting assembly configured to be attached to a first location of a third vertebra. The spine fixation assembly may also include a third spinal stabilization component configured to connect the third mounting assembly to a fourth mounting assembly configured to be attached to a first location of a fourth vertebra. The first and second vertebras are adjacent vertebras or not adjacent vertebras. The locations of the vertebras where the mounting assemblies are attached include a pedicle, transverse processes, pars, lamina, vertebral body, sacrum, lateral mass, and occiput. The components of the spine fixation assembly may be made of stainless steel, titanium, gold, silver, nickel, alloys thereof, bone, polymer, composites, ceramics, plastic, absorbable material or combination thereof. The spinal stabilization components may have adjustable lengths. 
         [0008]    In general in another aspect the invention features a mounting assembly configured to be attached to a vertebra including a bone anchor housing and first and second spinal stabilization component housings. The bone anchor housing is configured to receive a bone anchor for attaching the assembly to the vertebra. The first and second spinal stabilization component housings extend from the first bone anchor housing and are adapted to receive and connect to first and second spinal stabilization components, respectively, and thereby to connect the mounting assembly to other mounting assemblies configured to be attached to other vertebras. The bone anchor may be a poly-axial screw. Any of the spinal stabilization component housings may be rotatable around an axis passing through the center of the bone anchor housing. The mounting assembly may further include locking elements for securing the bone anchor to the bone anchor housing and the spinal stabilization components to the spinal stabilization housings, respectively. 
         [0009]    In general, in another aspect, the invention features a method for connecting a first vertebra to a second vertebra including the following steps. First, providing a first mounting assembly comprising a first bone anchor housing and first and second spinal stabilization component housings extending from the first bone anchor housing and attaching the first mounting assembly to a first location of the first vertebra. Next, providing a second mounting assembly comprising a second bone anchor housing and third and fourth spinal stabilization component housings extending from the second housing and attaching the second mounting assembly to a first location of the second vertebra. Next, providing a first spinal stabilization component comprising an elongated body having a first end and a second end and being dimensioned to span the distance between the first mounting assembly and the second mounting assembly and then attaching the first end of the spinal stabilization component to the first spinal stabilization component housing and the second end of the spinal stabilization component to the third spinal stabilization component housing. 
         [0010]    Among the advantages of this invention may be one or more of the following. The improved spinal fixation system allows segmented fixation of the spine in all three directions and multi-axial anchoring of the fixation elements. The use of multiple fixation locations enhances stability and reduces the operating time and risk for spinal injury during surgery. The multi-axial screw housings with the rod stabilization attachments are easy to use and can be easily adjusted before or after implantation. 
         [0011]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and description below. Other features, objects and advantages of the invention will be apparent from the following description of the preferred embodiments, the drawings and from the claims 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Referring to the figures, wherein like numerals represent like parts throughout the several views. Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. 
           [0013]    Referring to the figures, wherein like numerals represent like parts throughout the several views: 
           [0014]      FIG. 1  is a perspective view of a first embodiment of an improved spine fixation apparatus that utilizes multi-axial screw assemblies according to this invention; 
           [0015]      FIG. 2  is an exploded view of the spine fixation apparatus of  FIG. 1 ; 
           [0016]      FIG. 3  is a side view of the spine fixation apparatus of  FIG. 1 ; 
           [0017]      FIG. 4  is a perspective view of another embodiment of an improved spine fixation apparatus that utilizes a multi-axial screw assembly that accommodates both stabilization rods and plates; 
           [0018]      FIG. 5  is a perspective view of the multi-axial screw assembly of  FIG. 4 ; 
           [0019]      FIG. 6  is a partially exploded view of the spine fixation apparatus of  FIG. 4 ; 
           [0020]      FIG. 7  is another partially exploded view of the spine fixation apparatus of  FIG. 4 ; 
           [0021]      FIG. 8  is a perspective view of another embodiment of an improved spine fixation apparatus that utilizes a multi-axial screw assembly; 
           [0022]      FIG. 9  is a perspective view of the multi-axial screw assembly of  FIG. 8  with the mounting plates arranged at 180 degrees relative to each other; 
           [0023]      FIG. 10  is an exploded view of the spine fixation apparatus of  FIG. 8 ; 
           [0024]      FIG. 11  is a perspective view of another embodiment of an improved spine fixation apparatus that utilizes a multi-axial screw assembly; and 
           [0025]      FIG. 12  is an exploded view of the spine fixation apparatus of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    The invention provides a spine fixation apparatus with a multi-axial screw assembly that utilizes a multi-axial screw housing and adjustable, mounting elements for receiving stabilization elements with various geometries 
         [0027]    Referring to  FIG. 1 , a spine fixation assembly  100  includes mounting assemblies  110   a ,  110   b  and stabilization rods  140   a ,  140   b . Stabilization rod  140   b  is placed and secured in the mounting assemblies  110   a ,  110   b  and thereby connects them. Referring to  FIG. 2 , the mounting assembly  110  includes a multiaxial screw housing  111 , two mounting plates  112   a ,  112   b  extending from the housing  111  and two mounting elements  130   a ,  130   b . The screw housing  111  includes a through opening  114  for receiving a bone screw  120 . Opening  114  extends from the top surface of the screw housing  111  to the bottom surface and has a diameter at the top larger than the diameter at the bottom. The bone screw  120  has a body  121  with outer threads and a spherical head  122 . The body  121  is inserted through the opening  114  and is threaded into a vertebral bone (not shown). The spherical head  122  sits in the opening  114  of the screw housing  111  and the bone screw  120  is oriented at an angle  125  relative to the housing  111 . This orientation of the screw  120  relative to the screw housing  111  is secured by a setscrew  150 . Set screw  150  has outer threads that cooperate with inner threads of the opening  114 . In this embodiment mounting plates  112   a ,  112   b  are fixed relative to the screw housing  111  and relative to each other. They have receiving elements  113   a ,  113   b , that are used to attach the mounting elements  130   a ,  130   b  to the mounting plates  112   a ,  112   b , respectively. The mounting elements  130   a ,  130   b  have a cylindrical shape and slot openings  131   a ,  131   b , respectively, shaped and dimensioned to accommodate the ends  144   a ,  142   b  of the stabilization rods  140   a ,  140   b . Each stabilization rod  140   a ,  140   b  has an elongated cylindrical body, a spherical end  144   a ,  144   b  and a slotted flat end  142   a ,  142   b , respectively. The spherical end  144   a  has a flat top  145   a  with a concave dimple  146   a . The slotted end  142   b  of rod  140   b  is placed in the slot opening  131   b  of the mounting element  130   b  and the spherical end  144   a  of rod  140   a  is placed in the slot opening  131   a  of the mounting element  130   a . The flat top  145   a  with the concave dimple  146   a  of end  144   a  faces the same side as the flat surface of end  142   b . The slotted end  142   b  is secured in the opening of the mounting element  130   b  with a set screw  154  that has a flat bottom that sits directly onto the flat surface of the slotted end  142   b . The spherical end  144   a  is secured in the opening of the mounting element  130   a  with a set screw  152  that has a pointed bottom that sits directly into the dimple  146   a  of the spherical end  144   a . Set screws  152 ,  154  secure the angular position of the rods  140   a ,  140   b  relative to the mounting elements  130   a ,  130   b  and therefore relative to the screw housing  111 . 
         [0028]    Referring to  FIG. 4 , in another embodiment, a spine fixation assembly  102  includes a mounting assembly  110  a stabilization rod  140  attached to the mounting assembly  110  and a stabilization plate  160 , also attached to the mounting assembly  110 . Referring to  FIG. 5 , the mounting assembly  110  includes a screw housing  111  and two fixed mounting elements  130   a ,  113   b  extending from the housing  111 . The screw housing  111  includes a through opening  114  for receiving a bone screw  120 . Opening  114  extends from the top surface of the screw housing  111  to the bottom surface and has a diameter at the top larger than the diameter at the bottom. The bone screw  120  has a body  121  with outer threads and a spherical head  122 . The body  121  is inserted through the opening  114  and is threaded into a vertebral bone (not shown). The spherical head  122  sits in the opening  114  of the screw housing  111  and the bone screw  120  is oriented at an angle  125  relative to the housing  111 , as shown in  FIG. 3 . This orientation of the screw  120  relative to the screw housing  111  is secured by a setscrew  150 . Set screw  150  has outer threads that cooperate with inner threads of the opening  114 . In this embodiment the mounting elements  130   a ,  130   b  are fixed relative to the screw housing  111  and relative to each other. The mounting elements  130   a ,  130   b  have a cylindrical shape and threaded openings  131   a ,  131   b , respectively. Referring to  FIG. 6 , end  149  of the stabilization rod  140  is inserted in a bracket  170  that has a cylindrically shaped body  173  for receiving the cylindrically shaped rod end  149 , and a loop  171  extending from the side of the cylindrical body  173 . The loop  171  is placed onto the mounting element  130   b  and is attached to it by inserting a set screw  172  through the loop  171  and screwing it into the opening  131   b . Referring to  FIG. 7 , a cup shaped end  162  of the stabilization plate  160  is placed onto the mounting element  130   a  and is attached to it with a plate screw  164 . Plate screw  164  has a spherical head  165  and a threaded cylindrical bottom  167 . The plate screw  164  is inserted through the cup opening  163  and the cylindrical bottom is screwed into the threaded opening  131   a . The spherical head  165  sits in the cup opening  163 . The plate  160  is positioned at a desired angle relative to the screw housing  111  and the position is locked with a set screw  166  placed on top of the spherical head  165  and tightened down into the cup opening  163 . The set screw surface that interfaces with the spherical heard  165  of the plate screw  164  is concave and concentric with the spherical head  165 . 
         [0029]    Referring to  FIG. 8 , in another embodiment the spine fixation assembly  103  includes mounting assemblies  110   a ,  110   b  (not shown) and stabilization rods  140   a ,  140   b . Stabilization rods  140   a ,  140   b  are placed and secured in the mounting assembly  110   a . Referring to  FIG. 10 , the mounting assembly  110   a  includes a multiaxial screw housing  111 , a fixed mounting plate  112   b  extending from the housing  111  and a movable mounting plate  112   a . The movable mounting plate  112   a  has an end  115  that is inserted in a side opening  119  of the housing  111  and is allowed to swivel around axis  118  of the housing  111  thereby allowing the angle  126  between the mounting plates  112   a ,  112   b  to be adjusted. Axis  118  passes through the center of housing  111 . In other embodiments axis  118  may pass through any other location of the mounting plate  112   a . In the example of  FIG. 8  the angle  126  is set to 90 degrees and in the example of  FIG. 9 , the angle  126  is set to 180 degrees. The screw housing  111  includes a through opening  114  for receiving a bone screw  120 . Opening  114  extends from the top surface of the screw housing  111  to the bottom surface and has a diameter at the top larger than the diameter at the bottom. The end  115  of the movable mounting plate  112  that is inserted in the side opening  119  of the housing  111  also has a through opening  117  that is concentric with the opening  114 . The bone screw  120  has a body  121  with outer threads and a spherical head  122 . The body  121  is inserted through the openings  114  and  117  and is threaded into a vertebral bone (not shown). The spherical head  122  sits in the opening  114  of the screw housing  111  and the bone screw  120  is oriented at an angle  125  relative to the housing  111 . This orientation of the screw  120  relative to the screw housing  111  is secured by a setscrew  150 . Set screw  150  also secures the angle and positioning of the mounting plates  112   a ,  112   b  relative to each other and the housing  111 . The mounting plates  112   a ,  112   b  have receiving elements  113   a ,  113   b , that are used to attach the mounting elements  130   a ,  130   b  to the mounting plates  112   a ,  112   b , respectively. The mounting elements  130   a ,  130   b  have a cylindrical shape and side slot openings  132   a ,  132   b , respectively, shaped and dimensioned to accommodate the ends  149   a ,  148   b  of the stabilization rods  140   a ,  140   b , respectively. Mounting elements  130   a ,  130   b  may also rotate around an axis passing through their center. Each stabilization rod  140   a ,  140   b  has an elongated cylindrical body, and spherical ends  148   a ,  149   a ,  148   b ,  149   b , respectively. The spherical ends  148   a ,  149   a ,  148   b ,  149   b , have flat sides  173   a ,  173   b  opposite to each other. The spherical end  149   a  of rod  140   a  is placed in the slot opening  132   a  of the mounting element  130   a  and the spherical end  148   b  of rod  140   b  is placed in the side slot opening  131   b  of the mounting element  130   b  and are secured with set screws  152 ,  154 , respectively. The flat sides  177   a ,  177   b  are oriented parallel to walls of the side slot openings. Set screws  152 ,  154  secure the angular position of the rods  140   a ,  140   b  relative to the mounting elements  130   a ,  130   b  and therefore relative to the screw housing  111 . 
         [0030]    Referring to  FIG. 11 , in another embodiment  104  of the spine fixation assembly the stabilization rods have hammer shaped rod ends  181   a ,  182   a ,  181   b ,  182   b . The mounting elements  130   a ,  130   b  have a cylindrical shape, side slot openings  132   a ,  132   b , respectively, and accommodate nesting seats  191   a ,  191   b , respectively, shaped and dimensioned to accommodate the hammer shaped ends  182   a ,  181   b  of the stabilization rods  140   a ,  140   b , respectively. 
         [0031]    The screws  120  may be inserted in any location of adjacent vertebras or even in the same vertebra. Typical vertebral location for inserting screws include the pedicles, the vertebral body, the spinous process, the transverse processes the lamina, the sacrum, lateral mass, pars and the occiput. 
         [0032]    In one example, spine fixation assembly  100  is made of titanium metal. In other examples the spine fixation assembly  100  is made of stainless steel, nickel, gold, silver or alloys thereof, composites, ceramics, plastic, bone, absorbable material or combination thereof. In one example, bone screw  120  has a length of 57 millimeters and a diameter of 6.5 millimeters. The stabilization rods may have a length in the range of 20 millimeters to 200 millimeters. Other embodiments include the following. A hook may be used instead for a bone screw. Rotation axis  118  may be perpendicular to plate  112   a  and pass through a location of plate  112   a  between the receiving element  113   a  and end  115 . In this case, receiving element may connect to plate  112   a  via a hinge mechanism or any other connection mechanism that allows rotational motion. Spine fixation assembly  100  may be implanted via a minimally invasive surgical procedure or an open surgery procedure. Spine fixation assembly  100  my be assembled before surgical implantation or after surgical implantation of the components. 
         [0033]    Several embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.