Abstract:
An implantable spacer body ( 44 ) configured to be positioned between the spinous process portions of adjacent vertebrae in such a manner that the spinous process of the superior vertebra rests on and is supported on the spacer body. A pair of extension arms ( 54, 56 ) extend from each side of the spacer body and are adapted to be fixed to bone fasteners ( 86 ) which engage a region of the inferior vertebral body in locations other than the spinous process, preferably engaging the pedicle regions of the inferior vertebra. Alternatively, the extension arms can be fixed to spinal rods ( 90, 92 ) that are fastened to multiple vertebrae in a typical spinal rod assembly.

Description:
RELATED APPLICATIONS  
       [0001]     None.  
       TECHNICAL FIELD  
       [0002]     The present invention relates to implantable spacers for implantation between two vertebral segments and, more particularly, to a spacer that permits controlled movement while providing support between adjacent vertebrae with optimal load distribution.  
       BACKGROUND OF THE INVENTION  
       [0003]     In spinal orthopedic surgical techniques and procedures, it is common to replace and/or supplement injured, diseased, worn or otherwise deficient components of the spine including vertebrae and disc tissue between vertebrae. While in some cases, fusion is desired, in other cases it is desirable to provide a dynamic intervertebral spacer assembly which permits controlled movement along with support for sufficient vertebral spacing and stability.  
         [0004]     The various known systems for allowing controlled movement of spinal reconstructions have shortcomings. Such shortcomings include: overloading a specific area such as a disc or disc region by concentrating load which by nature is meant to be distributed among additional vertebral components; permitting over-bending of a repaired spinal section so as to increase risk of over-stretching and injury; requiring highly invasive procedures for installation; lacking versatility to adapt to varying sizes and configurations; and lacking overall stability.  
       OBJECTS OF THE INVENTION  
       [0005]     It is an object of the present invention to provide an implantable, dynamic intervertebral spacer assembly that overcomes the above-mentioned shortcomings and that achieves additional, inherent objectives apparent from the description set forth below.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention comprises an implantable spacer body configured to be positioned between the spinous process portions of adjacent vertebrae in such a manner that the spinous process of the superior vertebra rests on and is supported on the spacer body. A pair of extension arms extend from each side of the spacer body and are adapted to be fixed to bone fasteners which engage a region of the inferior vertebral body in locations other than the spinous process, preferably engaging the pedicle regions of the inferior vertebra. Alternatively, the extension arms can be fixed to spinal rods that are fastened to multiple vertebrae in a typical spinal rod assembly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a diagrammatic sideview of a pair of adjacent vertebrae for use in illustrating application of the present invention.  
         [0008]      FIG. 2  is a diagrammatic top view of a vertebra for use in illustrating application of the present invention.  
         [0009]      FIG. 3  is a perspective view of a first preferred embodiment of a device according to the present invention.  
         [0010]      FIG. 4  is a perspective view of a second preferred embodiment of a device according to the present invention assembly.  
         [0011]      FIG. 5  is a diagrammatic top view of an assembly according to the first embodiment of the present invention.  
         [0012]      FIG. 6  is a partial, perspective view of a component of the device according to  FIG. 3 , having a fastener attached thereto.  
         [0013]      FIG. 7  is a diagrammatic top view of an assembly according to the first embodiment of the present invention, having a pair of fasteners attached thereto.  
         [0014]      FIG. 8  is a diagrammatic end view of the assembly shown in  FIG. 7 .  
         [0015]      FIG. 9  is a diagrammatic end view of an alternative assembly according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     In describing and illustrating the preferred embodiments, reference is made to the diagrammatic representations of vertebral components shown in  FIGS. 1 and 2 . A pair of adjacent vertebrae are represented as a superior vertebra ( 10 ) and an inferior vertebra ( 12 ), described with reference to orientation arrows shown in  FIG. 1  as: a superior direction ( 14 ), and inferior direction ( 16 ), an anterior direction ( 18 ), and a posterior direction ( 20 ). The first and second vertebrae have various components that are common to different regions of the spine such as cervical, thoracic, and lumbar regions, even though the actual shapes and details of individual vertebra vary among such regions. Despite minor differences, the presently claimed invention has application that is not limited to any one of these regions and has the versatility to be configured in a manner in which it is applicable to any region.  
         [0017]     The first vertebra ( 10 ) has a body ( 22 ) with an upper end face ( 24 ), a lower end face ( 26 ), a pedicle region ( 28 ) on each side, and a spinous process ( 30 ). The second vertebra ( 12 ) has a body ( 32 ) with an upper end face ( 34 ), a lower end face ( 36 ), a pedicle region ( 38 ) on each side, and a spinous process ( 40 ). A vertebral space ( 42 ) exists between the adjacent vertebrae ( 10 ,  12 ) and is ordinarily occupied by vertebral disc tissue (not shown).  
         [0018]     A first embodiment of the present invention is shown in  FIG. 3 , and comprises a body portion ( 44 ) having generally symmetrical and generally parallel disc-shaped sections ( 46 ,  48 ) joined by a middle portion ( 50 ) of a smaller diameter than the disc-shaped sections ( 46 ,  48 ) such that the middle portion ( 50 ) forms a generally horizontal axis when the disc-shaped portions ( 46 ,  48 ) are aligned with an imaginary vertical axis ( 52 ). A first arm ( 54 ) and a second arm ( 56 ) each extend from a respective one of said disc-shaped sections ( 46 ,  48 ) away from the center of the body portion ( 44 ) and, preferably, at an angle (α) with respect to an imaginary horizontal centerline ( 58 ) as shown by dotted lines in  FIG. 3  extending from a distal end of each arm ( 54 ,  56 ). Each disc-shaped section ( 46 ,  48 ) has an interior face ( 60 ,  62 ) and an exterior face ( 64 ,  66 ).  
         [0019]     A second embodiment of the present invention is shown in  FIG. 4 , and comprises a body portion ( 68 ) having generally symmetrical and generally parallel disc-shaped sections ( 70 ,  72 ) joined by a middle portion ( 74 ) of a smaller diameter than the disc-shaped sections ( 70 ,  72 ) such that the middle portion ( 74 ) forms a generally horizontal axis when the disc-shaped portions ( 70 ,  72 ) are aligned with an imaginary vertical axis ( 76 ). A first arm ( 78 ) and a second arm ( 80 ) each extend from a respective one of said disc-shaped sections ( 70 ,  72 ) away from the center of the body portion ( 68 ) along an imaginary horizontal centerline ( 82 ) as shown by dotted line in  FIG. 4 . Each disc-shaped section ( 70 ,  72 ) has an interior face ( 74 ,  76 ) and an exterior face ( 78 ,  80 ).  
         [0020]     As shown in the diagrammatic view of  FIG. 5 , a device according to the first embodiment ( FIG. 3 ) is inserted between vertebrae ( 10 ,  12 ) in a manner such that the center portion ( 50 ) is placed underneath the superior spinous process ( 30 ), supporting a portion of vertical load transmitted through the superior spinous process ( 30 ). While  FIG. 5  shows the insertion of the first embodiment device, the second embodiment device (illustrated in  FIG. 4 ) is inserted and held in essentially the same manner as shown in  FIG. 5  and in the successive drawing figures.  
         [0021]      FIG. 6  illustrates the end of arm ( 54 ) which preferably has a round diameter and is compatible with a screw retaining rod adapter ( 84 ) of any type generally known that fixes a pedicle screw ( 86 ) or other bone fastener to a rod-shaped member, in this case the arm ( 54 ). Such a rod adapter ( 84 ) is used in conjunction with and to facilitate application of the present invention. Other types of fastener adapters, including those that could adapt to the arm ( 54 ) if it were not of round cross-section, could be used to perform the same function. Alternatively, a bone-engaging fastener could be permanently attached to the arm ( 54 ) or integrally formed therewith (not shown).  
         [0022]     Referring to  FIG. 7 , the components as shown in  FIG. 5  are illustrated with the addition of rod adapters ( 84 ) on each arm ( 54 ,  56 ) retaining pedicle screws thereon. As shown in  FIG. 8 , these pedicle screws ( 86 ) are fastened to the pedicle regions ( 38 ) of the inferior vertebra ( 12 ). The center portion ( 50 ) of the body ( 44 ) supports the superior spinous process ( 30 ) and transfers vertical load of the superior vertebra ( 10 ) through each arm ( 54 ,  56 ), through each rod adapter ( 84 ) and each pedicle screw ( 86 ), and finally to each pedicle region ( 38 ) of the inferior vertebra ( 12 ). The center portion ( 50 ) as well as any portion of the body ( 44 ) is not permitted to contact or transfer any vertical load to the inferior spinous process ( 40 ). Such an assembly applied as illustrated in  FIGS. 7-8  is sized and configured to prevent over-rotation in the direction shown by arrow ( 88 ) in  FIG. 1 , and to distribute vertical load between the vertebrae ( 10 ,  12 ) during normal posture so that all the existing vertical load is not concentrated through the end faces ( 26 ,  34 ) via disc material or a disc prosthetic or implant.  
         [0023]     As shown in  FIG. 9 , an alternative assembly using a device according to the embodiment of  FIG. 3  comprises attaching the body ( 44 ) via the arms ( 54 ,  56 ) to first and second rods ( 90 ,  92 ) of a rod assembly of a type generally known in which rod couplers ( 94 ) of a type generally known are used to attach the arms ( 54 ,  56 ) to the rods ( 90 ,  92 ). The rods ( 90 ,  92 ) are attached as is generally known to vertebral bodies through bone fastener assemblies ( 96 ) of a type generally known, such as pedicle screws. The embodiment of  FIG. 4  could also be implemented with the assembly of  FIG. 9  in essentially the same manner as the embodiment of  FIG. 3  is implemented.  
         [0024]     The components of the assemblies according to the preferred embodiments may be made of any suitable, implantable material of sufficient strength and having additional characteristics suitable for such use. Such materials include but are not limited to surgical metals and alloys, composites and ceramics.  
         [0025]     While the preferred embodiments of the present invention have been described, various modifications can be made without departing from the scope of the invention.