Abstract:
A method and apparatus for stabilizing adjacent vertebrae. Upper and lower interlocking brackets are insertable in a prepared intervertebral space between adjacent vertebrae. The brackets are affixed to the vertebrae at attachment plates. A rib on one side of one bracket interlocks with a rib receiving groove in the other bracket to stabilize the spinal column without eliminated mobility (forward and rearward flexion) of the column. Various embodiments include additional shock absorption features.

Description:
[0001]    This is a divisional application of co-pending U.S. patent application Ser. No. 09/627,261, filed Jul. 28, 2000, now U.S. Pat. No. 6,610,093, issued Aug. 26, 2003. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to an intervertebral disk stabilizing implant and a method of stabilizing two adjacent vertebrae. More specifically, the present invention relates to upper and lower interlocking brackets which attach to adjacent vertebrae sufficiently to stabilize the vertebrae but allow for some forward flexion and rearward extension of the spine with slight lateral displacement. An alternative embodiment provides for stability of the spinal column, with flexion and extension with spinal shock absorption.  
           [0003]    The spine is a flexible structure comprised of thirty-three vertebrae. The vertebrae are separated and cushioned from each other by fibrous cartilage in structures called intervertebral disks. If the spine is injured or becomes diseased, surgical intervention involving removal of one or more of these disks and fusion of the adjacent vertebrae, may be indicated. Such disk injuries can happen in the neck, in the thoracic region and in the lumbar region. The more frequent injuries are in the lower lumbar and in the lower cervical regions.  
           [0004]    Treatment of a herniated disk in the neck and in the lumbar region continues to be a challenging field of medicine. The classical treatment for a ruptured disk continues to be removal of the disk from between the vertebrae. By this process of removing the disk, overall spinal instability is increased. This may aggravate the patient to some degree after the operation. Another procedure previously employed is to replace the disk space with a bone graft, bringing about fusion of the vertebrae above and below the disk, eliminating the empty space between the vertebrae and improving stability.  
           [0005]    Theoretically a diskectomy with fusion is a satisfactory procedure, though not ideal because the replaced bone does not have the principal functions of the cartilage tissue of the disk. This fusion procedure is technically demanding and has medical complications because of several physiological factors.  
           [0006]    It must be remembered that the disk primarily serves as a mechanical cushion while permitting limited mobility. For any replacement system for a disk to be truly effective, it must allow for mobility within the natural limits of the original disk. In other words, the replacement should match appropriate joint rheology (movement behavior). The natural disk allows about 11 degrees of flexion-extension, limited lateral bending of 3 to 5 degrees, and very restricted rotation of about 1 degree.  
           [0007]    Various prosthetic devices and implants are disclosed in the art, but all are characterized by compromises to the full functions of a natural disk discussed above. Examples of the prior art include the following U.S. Pat. Nos. 5,893,890; 5,693,100; 5,658,336; 5,653,761; 5,653,762; 5,390,683; 5,171,278; and 5,123,926. The present invention improves upon the state of the art including the inventor&#39;s own prior inventions by more closely approximating the natural function of the disk, including extension-flexion, slight lateral bending, and very slight rotation.  
         SUMMARY OF THE INVENTION  
         [0008]    This present invention provides a method and apparatus for providing vertebral stabilization while further providing shock absorption; flexion and extension (mobility); slight lateral bending; and very slight rotation about the spinal column; and, still achieving spinal stability. The vertebral disk stabilizer of the present invention has upper and lower brackets with vertebral attachment plates. Arcuate surfaces on the brackets provide for a structural configuration which conforms to the shape of the intervertebral space. The upper and lower brackets are linked or attached to one another by complimentary ribs and rib receiving grooves or a “ball and socket” linkage. The stabilizer is vertically affixed to the outer cortial surface of adjacent vertebrae by conventional medical fasteners which extend through the bracket plates into the vertebrae bodies.  
           [0009]    An independent intervertebral disk member is disposed and retained between the upper and lower brackets. The disc member may be, alternatively: (a) a compressible composition; (b) a metal disk member with a mechanical spring mechanism affixed between the upper and lower brackets; or (c) a combination of compressible material and mechanical spring. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a lateral view of a portion of a human spinal column having a preferred embodiment of the vertebral disk stabilizer of the present invention inserted therein.  
         [0011]    [0011]FIG. 2 is a side elevation view of the present invention illustrating the medical fasteners.  
         [0012]    [0012]FIG. 2A is a top plan view of the upper bracket of the present invention.  
         [0013]    [0013]FIG. 2B shows a top plan view of the intervertebral cushion member of the present invention.  
         [0014]    [0014]FIG. 2C is a top plan view of the lower bracket of the present invention.  
         [0015]    [0015]FIG. 3 illustrates an exploded perspective view of one embodiment of the present invention.  
         [0016]    [0016]FIG. 4 illustrates an exploded perspective view of another embodiment of the present invention.  
         [0017]    [0017]FIG. 4A illustrates an exploded perspective view of an alternative disk of the present invention.  
         [0018]    [0018]FIG. 4B illustrates an exploded perspective view of yet another disk of the present invention.  
         [0019]    [0019]FIG. 4C illustrates an exploded perspective view of an additional disk of the present invention.  
         [0020]    [0020]FIG. 5 illustrates an exploded perspective of an embodiment of the present invention with an arcuate rib having inwardly slanting side walls.  
         [0021]    [0021]FIG. 6 illustrates an exploded perspective of an embodiment of the present invention with a “ball and socket” linkage.  
         [0022]    [0022]FIG. 6A illustrates in detail the intervertebral disk of one embodiment of the present invention which utilizes the “ball and socket” linkage.  
         [0023]    [0023]FIG. 7 shows a partial cutaway perspective view of yet another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Referring now to the figures, a first embodiment of a disk stabilizer constructed in accordance with the teachings of the present invention is shown implanted in a human spinal column in FIG. 1. The vertebral disk stabilizer, indicated generally at reference numeral  10 , is implanted between the bodies  12  and  14  of adjacent vertebrae  16  and  18 , respectively, in the disk space (not numbered) from which a portion of the invertebral disk  20  is removed, i.e., by simple diskectomy and small laminotomy.  
         [0025]    In FIG. 2, the stabilizer  10  is comprised of an upper bracket  22 , a lower bracket  24 , and an invertebral disk  26 . Brackets  22  and  24  may be composed of a strong, thin, non-porous material. Suitable materials for the brackets include carbon fiber, modified carbon, titanium, surgically compatible steel, physiologically inert and/or medically compatible polymers such as urethane or DELRIN® polymers, or any surgical implant or any biologically compatible material.  
         [0026]    In the presently preferred embodiment shown, the means for mounting the invention to the spine takes the form of fasteners  30  passing through bores  32  in vertical vertebral attachment plates  34  and into the bodies  12  and  14 . The plate ends are tapered for a smooth contour fit to the bodies  12  and  14 . The brackets  22  and  24  are linked to the disk  26  by ribs  38  and  40 . Ribs  38  and  40  are generally cylindrical protrusions extending transversely partially across the bottom surface of the brackets. Alternatively, one rib could be affixed to the upper bracket  22  and one rib could be attached to the underside of the disk. Thus, the disk rib would be a generally cylindrical protrusion extending transversely partially across the bottom surface of the disk member  26 .  
         [0027]    Bracket rib  38  is received and retained in rib receiving groove  39  in the upper surface of disk  26  (FIG. 2B). The rib  38  and groove  39  act as hinge elements or bearing elements and are sized such that the rigid rib  38  is retained into engagement in the groove, but the cylindrical shapes of the rib and groove interlock to resist disengagement. In the alternative where a rib is affixed to the disk, the disk rib would be received and retained in a rib receiving groove in the upper surface of the lower bracket  24 .  
         [0028]    It is important to understand that the size of effective diameter d 1  of a rib  38  or  40  is less than the size or effective diameter d 2  of the grooves  39  or  41 . This allows for movement of the rib within the groove, but not so much movement as to result in vertebral instability. As will be seen below the groove depth must be sufficient to allow the rib to move vertically in a cushioning or shock absorbing mode of the device  10 .  
         [0029]    The intervertebral disk  26  may be composed of any number of compressible physiologically inert and/or medically compatible polymers. Again, only by way of example and not as a limitation, the disk could be made of urethane or a DELRIN® polymer. The purpose of the compressible composition is to provide shock absorption between the interlocked brackets  22  and  24 . Later it will be shown that mechanical springs may be substituted for the compressible disk composition. In such a case the disk may be constructed by carbon fiber, modified carbon, titanium, surgically compatible steel, or any other rigid material acceptable in such operations.  
         [0030]    It should be noted that the outer ends  42  and  44  of disk  26  may be chamfered to allow flexion and extension of the spine through movement of the stabilizer forwardly and rearwardly (shown by arrows in FIG. 2). The desired range of flexion and extension is adjusted by the angle of the chamfer, as the patient bends or leans forward or backwards.  
         [0031]    As may be seen in FIGS. 1, 2,  3 , and  4 , the disk ends  42  and  44  may be chamfered at both ends, one end, or no end. Where flexion and extension require, the bracket ends  17  and  19  may be chamfered and upon rotation the disk  26  will halt the degree of rotation as will be understood by on skilled in the art. For example, FIG. 2 shows bracket ends  17  and  19  chamfered and disk end  44  squared off. Again, the arrows in FIG. 2 illustrate that flexion and extension are available with the present invention. FIG. 2 further shows that when the present invention  22  is assembled the plates  34  align substantially along the same longitudinal axis L.  
         [0032]    In more detail, now referring to FIG. 3, it may be seen that the top arcuate side  23  of upper bracket  22  and the bottom arcuate side  25  of lower bracket  24  are roughened or textured. These bi-convex sides  23  and  25  of stabilizer  10  are provided with a plurality of teeth or ridges  50  for biting or gripping into the adjacent vertebrae  16  and  18 . Those skilled in the art who have the benefit of this disclosure will recognize the sides  23  and  25  of the stabilizer  10  need not define a true arch which is symmetrical. It will also be recognized that the sides  23  and  25  need not be provided with the serrations  50  to bite into the vertebrae. This biting function can also be accomplished by providing the sides  23  and  25  with multiple steps formed in right angles along sides  23  and  25  or by simply knurling the surfaces of these sides.  
         [0033]    Another feature of the present invention illustrated in FIG. 3 is the incorporation of bearing surfaces  52  and  54  in disk member rib receiving grooves  39  and  41 . These surfaces are intended to reduce friction and extend the life of the parts. It should be understood that low friction surface materials may be substituted for any type of mechanical bearing.  
         [0034]    An alternative preferred embodiment  10 A is illustrated in the exploded perspective view of FIG. 4. In most ways stabilizer  10 A is identical to stabilizer  10  except that a mechanical shock absorption mechanism is provided. Disk  26 A is provided with two central depressions  60  of sufficient depth and diameter to allow compression springs  64  and  65  to be fitted and retained in depressions  60  (the second depression is on the underside of the disk  26 A in FIG. 4). Spring  65  may be attached to bottom surface  69  of the lower bracket  24 A in complimentary depression  80 . Spring  64  may likewise be attached to the bottom surface  66  of upper bracket  22 A. Springs  64  and  65  thus result in a means for varying the degree of shock absorption which may be achieved by the stabilizer  10 A.  
         [0035]    FIGS.  4 A- 4 C illustrate alternative disk arrangements available to provide for shock absorption. In FIG. 4A, disk  26 C is provided with a multiplicity of depressions  80 A along its top surface  47  (and, if desired, bottom surface  37 ). The depressions are sized to accept and retain compression pillars  64 A. By varying the composition and quantity of pillars the physician is able to control the compressive force absorption in each stabilizer. Further, the pillars will allow for a slight degree of lateral vertebral movement. However, the relationship between the diameters d 1  and d 2  of the ribs and grooves, respectively, controls the total amount of movement available in any embodiment.  
         [0036]    [0036]FIG. 4B illustrates the utilization of leaf-type springs  64 B on this disk embodiment  26 D. Further, a unitary spring, a single pillar, or a combination may be used. FIG. 4C shows compression element  64 C passes through the disk member  26 E through opening  80 C and is attachable to the upper and lower brackets, as would be readily understood by one skilled in the art.  
         [0037]    Again, it should be understood that any combination of compressible materials and mechanical springs may be employed to absorb shock in the present invention The disk could be metal with compressible pillars; it could be a compressible composition with compressible pillars; or it could be a compressible composition with metal springs.  
         [0038]    Turning to FIG. 5, another embodiment of the present invention  10 F may be seen. The key distinction of this embodiment relates to the interlocking ribs  38 F and  40 F. The central height H c  of the ribs on the bottom side  69  of brackets  34  is greater than the end height He of the inwardly slanting side walls  91 . The grooves  39 F and  41 F in disk  26 F have depths D g  which are greater than the central height H c . This arrangement, in coordination with the slanting walls  91 , allows for the brackets (attached to the vertebrae) to flex, extend, and move laterally with a very slight twisting operation. At the same time, the spinal column is stabilized. As may be seen in FIG. 5, the grooves  39 F and  41 F may be fitted with roller bearings  52  and  54  to reduce frictional forces as previously discussed with FIG. 3  
         [0039]    The embodiment  10 G of FIG. 6 utilizes a unique ball and socket linking arrangement. The brackets are provided with a ball  41 G at the end of a neck  96 G attached to the underside of the bracket. Also attached to the underside are rigid stop pegs  92 G and  94 G. The pegs  92 G and  94 G cooperate with stop notches  90 G in the invertebral disk  26 G to limit excessive lateral motion and rotation of the elements of the device  10 G. The pegs  94 G have diameters smaller than the diameters of the notches and generally do not contact the notches except when the lateral motion or rotation becomes excessive.  
         [0040]    The balls  41 G cooperate with the sockets  38 G to both receive and retain the interlocking relationship of the separate elements of the invention. The socket has a greater diameter than the ball. The socket wraps over half of the ball diameter to keep the ball from being dislocated during flexion/extension of the spine.  
         [0041]    [0041]FIG. 6A shows how the ball  38 G at the end of neck  96 G extends downwardly from the upper bracket into and is retained in the socket  39 G in the disk  26 G.  
         [0042]    It should be understood that the tolerances of the interlocking and cooperating parts are intended to allow for the normal range of movements discussed above. Thus the target range of flexion/extension is 9-12 degrees, lateral bending in the range of 3 to 5 degrees, and a very slight 0.5-1.5 degrees rotation of adjacent joined vertebrae.  
         [0043]    Yet another embodiment of the present invention  10 B is shown in FIG. 7. Upper bracket  22 B has a vertical vertebral attachment plate  34 B with bores  32 B for receiving fasteners to attach the stabilizer  10 B to the first vertebrae body  12 . A linking hook  70  is attached to the plate and is arcuated. A rib  72  is formed in the top side  74  of the hook  70 . Lower bracket  24 B also has a vertical disk attachment plate  34 B with bores  32 B. An opening  76  is formed in the lower bracket  24 B to receive and retain the linking hook  70 . An interlocking arcuate cavity  78  is also formed in lower bracket  24 B. A rib receiving groove  79  allows the flexion (shown in arrows in FIG. 5) of the stabilizer  10 B. There is sufficient “play” or clearances between the hook  70  and rib  72  within the rib receiving groove  79  to maintain stability but allow for limited mobility (flexion).  
         [0044]    In each embodiment of the present invention the separate parts are sized to facilitate insertion within the intervertebral space created and sustained between adjacent vertebrae during the medical insertion procedure.  
         [0045]    It is anticipated that the stabilizer  10  of the present invention will be fully assembled prior to insertion into the intervetebral space. Thus, by varying the compressive force mechanism and the size of the brackets and disk, the physician will be able to utilize the present invention with any number of different size patents.  
         [0046]    The use of the stabilizer  10  of the present invention in, for instance, a method of intervertebral disk stabilization is illustrated in FIG. 1. Surgery is performed as a simply diskectomy and the intervertebral disk  20  is exposed. The natural deteriorated disk material is removed and any nerve root compression is corrected. Any ligament, muscle, or cartilage covering the vertebrae are moved or removed until the surface of the bodies  12  and  14  of adjacent vertebrae  16  and  18 , respectively, are exposed above and below the disk space.  
         [0047]    Using spreaders the vertebrae  16  and  18  are distracted to open the disk space sufficient to inset the stabilizer.  
         [0048]    A stabilizer  10  having a height and width selected to fit the disk space is then mounted to an applicator (not shown) as is well known in the art. The appropriate sized stabilizer  10  is then inverted into the disk space with the stabilizer oriented so that the upper convex side  23  of bracket  22  and bottom convex side  25  of bracket  24  engage the bodies  12  and  14  of adjacent vertebrae  16  and  18 , respectively. The vertical attachment plates or plates  34  are vertically aligned with the vertebrae. Fasteners  30  are then passed through bores  32  thereby securing the upper and lower brackets to the spinal column.  
         [0049]    Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. On the contrary, various modifications of the disclosed embodiments will become apparent to those skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover such modifications, alternatives, and equivalents that fall within the true spirit and scope of the invention.