Abstract:
An interbody fusion device, or bone dowel for mending of joints is disclosed herein. The device comprises anti-migration ridges having optimum geometry to avoid failure during the insertion process while providing boney ingrowth in the body&#39;s natural healing process. A tapered head portion and a cylindrical body without threads are further included herein. Also, the device provides novel means for engagement to an insertion tool. Additional methods are disclosed herein to maintain and insert a device without torsional stresses due to torquing.

Description:
PRIORITY CLAIM 
       [0001]    This utility patent application contains subject matter claiming benefit of the priority date of U.S. Provisional Patent Application Ser. No. 61/277,475, filed on Sep. 26, 2009, accordingly, the entire contents of this provisional patent application is hereby expressly incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention pertains generally to devices and methods useful in surgical processes that require fusion of joints. More specifically, the present invention is particularly but not exclusively useful as an allograft fusion implant for interbody spinal fusion and related procedures. 
         [0004]    2. Description of the Prior Art 
         [0005]    Spinal fusion has been known as a procedure improving articular movement and providing stabilization of the spine for sufferers of a variety of aliments including degenerative disc disease, spinal disc herniation, discogenic pain, spinal tumor, vertebral fracture, scoliosis, kyphosis, spondylolisthesis, spondylosis, Posterior Rami Syndrome, and other degenerative spinal conditions. In performing this procedure, implants are applied to an area once occupied by the intervertebral disc between adjacent vertebrae. When the disc is removed, the space between vertebrae endplates will tend to collapse. Accordingly, this space is first reamed to maintain the proper geometry prior to the implant insertion. The implants may also be referred to as dowels, cages, or bone grafts (as the implants are preferably made from allograft material). 
         [0006]    Following the implant procedure, the natural osteoblastic process will produce ingrowth from the normal bone healing response. Hence, a high quality allograft bone obtained from organ donors is much preferred over artificial implants. The use of a bone graft presents challenges because they have relatively brittle material properties as compared to plastic or titanium and therefore will fracture more easily under stresses of insertion. Also complicating the problem is that bone from tissue donors is relatively expensive to acquire. 
         [0007]    Many proposed designs have been granted U.S. patent protection to include: U.S. Pat. No. 5,593,409, entitled “Interbody Spinal Fusion Implants” to Michelson, U.S. Pat. No. 5,814,084, entitled “Diaphysial Cortical Dowel” to Frivas et al., U.S. Pat. No. 6,371,988 entitled “Bone Grafts” to Pafford et al., and U.S. Pat. No. 6,447,544 entitled “Lordotic Interbody Spinal Fusion Implants” also to Michelson, and U.S. Pub. Pat. App. No. 2010/0057207 entitled “Bone Gratis” to Ray III et al. One problem with many prior solutions is that they provide a tapered dowel along its entire length believing that this is the optimum choice the procedure. Conversely, while many younger healthy spines will have a tapered area between vertebrae, an older spine will more likely have more of a flat area in the disc space. However not so intuitively, the patients needing this procedure are more likely to be older with applicable conditions worsening with age. Also, the ream used to maintain proper space are currently not tapered and thus a tapered design would more likely break during the insertion process. Other improvements to processes and devices for spinal fusion are also needed within the art. 
         [0008]    In light of the above, an object of the present invention is to provide an Interbody Fusion Device that has a cylindrical design to closely mirror the space it is to occupy. It is a further object of the present invention to provide an implant design that will promote proper bony ingrowth from the body&#39;s natural healing process. It is still further an object of the present invention to provide an implant design having improved features to engage an insertion tool used in the spinal fusion process. It is still further an object of the present invention to provide a tapered leading edge to a cylindrical design to facilitate implant insertion. Yet still further, it is an object of the present invention provide an optimum design for ridges with optimum geometry. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The present invention specifically addresses and alleviates the above mentioned deficiencies associated with the prior art. More particularly, the present invention in a first aspect, is directed to an interbody fusion device comprising: a tapered head portion; a cylindrical body portion having an inner diameter and an outer diameter; and an end portion opposite the head portion, the end portion additionally comprising a disc shaped protrusion, the disc shaped protrusion having a carve out having a hexagonal shape, the carve out further including a threaded inner cavity for engaging a tool for insertion of said device. 
         [0010]    In this aspect, the invention is additionally characterized in that the body portion further comprises a cavity about an axis aligned perpendicular to a longitudinal axis. Also, the body portion further comprises a plurality of anti-migration ridges including a “Z” shape having a peak followed by perpendicular ridge relative to a longitudinal axis, and followed by an angled constant slope to an adjacent peak. Further, the invention is characterized wherein the inner diameter corresponds to a width of the disc shaped protrusion. 
         [0011]    In a preferred embodiment, the plurality of anti-migration ridges comprises no more and no fewer than four anti-migration ridges for optimum bony ingrowth and brittle fracture properties. Also according to a preferred embodiment, the disc protrusion further comprises two diametrically opposed cut-outs in the disc protrusion, the diametrically opposed cut-outs for further engaging an insertion tool. Further in this aspect, the invention is characterized wherein the tapered head portion further comprises a frustum conical shape however having rounded edges. 
         [0012]    In yet another aspect, the invention is characterized as an interbody fusion device comprising: a tapered head portion; a cylindrical body portion having a first quarter portion, a second quarter portion, a third quarter portion, and a fourth quarter portion, wherein the first and third quarter portions comprise a cavity therethrough, and wherein the first and third quarter portions further comprise a plurality of anti-migration ridges, and wherein the second and fourth quarter portions comprise a smooth surface. An end portion is also provided opposite the head portion, the end portion configured to engage an insertion tool. 
         [0013]    An additional embodiment for an end portion is characterized as comprising a hexagonal protrusion having a surface area for engaging the insertion tool; and a threaded cavity for further engaging the insertion tool. 
         [0014]    These, as well as other advantages of the present invention will be more apparent from the following description and drawings. It is understood that changes in the specific structure shown and described may be made within the scope of the claims, without departing from the spirit of the invention. 
         [0015]    While the apparatus and method has or will be described for the sake of grammatical fluidity with functional explanations, it is to be expressly understood that the claims, unless expressly formulated under 35 USC 112, are not to be construed as necessarily limited in any way by the construction of “means” or “steps” limitations, but are to be accorded the full scope of the meaning and equivalents of the definition provided by the claims under the judicial doctrine of equivalents, and in the case where the claims are expressly formulated under 35 USC 112 are to be accorded full statutory equivalents under 35 USC 112. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
           [0017]      FIG. 1A  is a perspective view of a first preferred interbody fusion device of the present invention; 
           [0018]      FIG. 1B  is a cross-sectional view of the interbody fusion device taken along sectional line  1 B- 1 B in  FIG. 1A ; 
           [0019]      FIG. 1C  is an enlarged view of the area bound by line  1 C in  FIG. 1B ; 
           [0020]      FIG. 1D  is a top plan view of the first preferred embodiment; 
           [0021]      FIG. 1E  is an end view illustrating an end portion of the present invention; 
           [0022]      FIG. 1F  is a profile view of the first invention embodiment; 
           [0023]      FIG. 1G  illustrates an interbody fusion device(s) in a disc space of a spine; 
           [0024]      FIG. 1H  is an additional illustration of an interbody fusion device (2) being employed between vertebrae; 
           [0025]      FIG. 2A  is a perspective view of a second preferred embodiment of the present invention; 
           [0026]      FIG. 2B  illustrates a cross-sectional view of the second embodiment taken along sectional line  2 B- 2 B in  FIG. 2A ; 
           [0027]      FIG. 2C  is an end view of an end portion of the invention illustrated in relation to  FIG. 2B ; 
           [0028]      FIG. 2D  is a top plan view of the second preferred embodiment; 
           [0029]      FIG. 2E  is a profile view illustrating an end portion of the second preferred embodiment of the present invention; 
           [0030]      FIG. 3A  is a perspective view of another invention embodiment; 
           [0031]      FIG. 3B  is an end view thereof; 
           [0032]      FIG. 4A  is a perspective view of still another invention embodiment; 
           [0033]      FIG. 4B  is an end view thereof; 
           [0034]      FIG. 5A  is a perspective view of yet still another invention embodiment; 
           [0035]      FIG. 5B  is an end view thereof; 
           [0036]      FIG. 6A  is a perspective view of still further another invention embodiment; 
           [0037]      FIG. 6B  is an end view thereof; 
           [0038]      FIG. 7A  is a perspective view of an additional embodiment for engaging an insertion tool; 
           [0039]      FIG. 7B  is an end view thereof; 
           [0040]      FIG. 7C  is a perspective view showing a notch in addition to the diametrically opposed cut-outs for engaging a insertion tool; 
           [0041]      FIG. 7D  is an end view thereof; 
           [0042]      FIG. 8A  is a perspective view of an alternative design for a cylindrical body portion; 
           [0043]      FIG. 8B  is an top plan view thereof; 
           [0044]      FIG. 9A  is a perspective view of an alternative end portion of the present invention; and 
           [0045]      FIG. 9B  is an end view thereof. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0046]    Referring initially to  FIG. 1A , a perspective view of a first preferred embodiment of an interbody fusion device  100  is shown. This particular embodiment contains a cavity  129  that will naturally occur when a sample is obtained from femoral bone of an organ donor due to an existing canal within the femur. Coincidentally, the cavity  129  is beneficial to spinal fusion due to properties promoting bony ingrowth. Also importantly, when the device  100  is in place in the space formerly occupied by the intervertebral disc, the cavity should be aligned upward. Hence, the device  100  is actually illustrated on a side and accordingly  FIG. 1D  is described as the top plan view. 
         [0047]    Also referring to  FIG. 1B , a cross-sectional view of the invention embodiment  100  shown in  FIG. 1A  is provided. Herein, the device comprises a leading head portion  110  and a disc protrusion  130  at opposing ends. There between, a cylindrical body portion  120  has anti-migration ridges  123  as further detailed herein. The end portion  130  is configured to receive an insertion device; wherein according to this example  100 , the end contains a hexagonal insert  131 . At the end portion, the insertion device would be configured to engage the hexagonal insert  131 . Referring to  FIG. 1C , the insertion device will contain a threaded pin to matingly engage a threaded hole  132  of the present invention. Therefore for example, a fusion device  100  will not become unsecured from an insertion device when it is held upside down. 
         [0048]    Also with regard to  FIG. 1B  and  FIG. 1C , close inspection of the fusion device  100  reveals that it contains an inner  121  and an outer  122  diameter. The outer diameter  122  will correspond to peaks  124  of a plurality of ratcheted anti-migration ridges  123  or fins. The ridges  123  will help the fusion device  100  to remain in place as well as promote bony ingrowth. Generally, the device is cylindrical in shape and hence the outer diameter  122  is constant over the length of the device  100 . The inner diameter  121  will correspond to a width of the end portion  130  and also to base points  124   a  on the plurality of ridges  123 . Also generally, the ridges  123  are “Z” shaped having a peak  124  followed by a perpendicular ridge  125  (perpendicular to the length of the device  100 , i.e. its longitudinal axis) to a base point  124   a , and followed by an angled  126  constant slope to the next peak  123 . In a preferred embodiment, the angle is 45°. In the example, eleven (11) peaks  123  are shown; however other designs with different peaks  123 ,  223  may be employed as further detailed herein. Since cavity  129  size is relatively constant, the present invention attempts to employ an optimum number of ridges  123 ,  223  so that ridges will not migrate forward with a reduced chance that expensive devices  100 ,  200 ,  300 ,  400 ,  500 ,  600 ,  700 ,  800 ,  900  will not fail due to brittle fracture during the insertion process. A design  100 ,  200  employing less ridges/peaks would make the ridges  123 ,  223  relatively thicker and more robust as further detailed herein. Also for optimum migration without fracture of the device  100 , the last peak  127  closest to the end portion  130  comprises a different shape the having a flat summit  128  instead of a point  124 . 
         [0049]    The tapered head portion  110  provides a different shape than in prior art devices. The shape is essentially that of a truncated cone or frustum, i.e. a cone having an apex cut off by a parallel plane. However the truncated cone is further configured with a rounded tip to the frustum. The tapered head portion  110  will facilitate insertion of the spinal fusion device  100 .  FIG. 1E  provides another view of an end portion  110  of the present invention showing hexagonal insert  131  with threaded hole  132 . 
         [0050]      FIG. 1D  illustrates a top plan view of the present invention as the device  100  is typically inserted with the cavity  129  aligned upward, as illustrated in  FIG. 1G , for example. With regard to  FIG. 1F , a profile view of the invention embodiment  100  is illustrated. In this side aspect, the device  100  appears to have an hourglass shape due to the cavity  129 .  FIG. 1G  illustrates a device inserted between adjacent vertebrae  911 ,  912  in the lumbar region of the spine, for example. 
         [0051]      FIG. 2A  through  FIG. 2D  illustrate an alternative embodiment  200  of the present invention. Similar to the first embodiment, the device comprises a tapered head portion  210  and a protruding end  230 . As before, the end portion  230  has a hexagonal insert  231  and is configured to receive an insertion device. Importantly, this example comprises four (4) anti-migration ridges  223  as deemed to be an optimum number to prevent brittle fracture during insertion while additionally preventing post operative migration. Further as stated, cavity  229  has a fixed size. Additionally the invention herein  100 ,  200 ,  300 ,  400 ,  500 ,  600 ,  700 ,  800 ,  900  is devoid of threads to the cylindrical body portion so that impacting is only required and not torquing during insertion. This feature  123 ,  223  lowers a risk of failure due to fracture, and further eliminates one step in the insertion method. Similar to the first preferred embodiment  100 , the ridge  227  closest to the end portion  230  has a flat summit  228  to facilitate insertion and to prevent migration thereafter. 
         [0052]      FIG. 3A  and  FIG. 3B  illustrate an alternative triangle insert  331  for engagement for an insertion tool. Similarly,  FIG. 4A ,  FIG. 4B ,  FIG. 5A , and  FIG. 5B  show square  431  and rectangle  531  inserts respectively. As shown, body portions  320 ,  420 ,  520 , are coupled to ends  330 ,  430 ,  530  having female inserts  331 ,  431 ,  531 , with female threaded cavities  332 ,  432 ,  532 . 
         [0053]    In the  FIG. 6A  and  FIG. 6B  example  600 , a cylindrical body portion  620  has a protruding end  630  as stated herein. However, in this embodiment  600 , a flat head screwdriver insert  631  is provided. For this, the insertion device would have a working end resembling a flat head screw driver however modified with a threaded pin as discussed herein. The configuration includes a slot  631  to receive the flat head portion of the insertion device. As shown, the slot  631  is aligned perpendicular to the cavity  629  ( FIG. 6A ). If the slot  631  were alternatively aligned with the cavity, it would result in a relatively weak area in the material between the cavity  629  and the slot  631 . Similarly, it should be appreciated that the long axis of the insert  531  in  FIG. 5A  should be aligned perpendicular to its cavity  529 ; and further insert  731  with diametrically opposed cut-outs  733 ,  734  ( FIG. 7A  and  FIG. 7B ) are aligned perpendicular to its cavity  729  as detailed herein. 
         [0054]    With regard to  FIG. 7A  and  FIG. 7B , an additional embodiment  700  of an end portion  730  for engaging an insertion tool is provided. In this example, the threaded cavity  132 ,  232 ,  332 ,  432 ,  532 ,  632 ,  932  is absent and replaced with a pair of diametrically opposed cut-outs  733 ,  734 . The diametrically opposed cut-outs  733 ,  734  together with a hexagonal insert  731  provide a friction fit to an insertion tool. In a preferred embodiment, the diametrically opposed cut-outs  733 ,  734  will further each have a notch  735  that extends a few millimeters into the body portion  720 . 
         [0055]    Now turning to  FIG. 8A  and  FIG. 8B  an additional embodiment  800  to a cylindrical body portion  820  is provided. Initially, it should be appreciated that cavity  829  is aligned upward in use, so the illustration in  FIG. 5A  depicts a device lying on its  800  side. Therefore,  FIG. 8B  is a top plan view. Herein, cylindrical body portion  820  comprises four quarter portions, namely first  851  second  852  third (not shown, however identical to first  851  quarter portion) and fourth  853  quarter portions. The first  851  and third quarter portions comprise the anti-migration ridges  823  carved out of a smooth surface  852 ,  854 , since these portions ( 851 ,  853 ) will have the most direct contact with adjacent vertebrae  911 ,  912  ( FIG. 1G ). Second  852  and fourth  854  quarter portions will comprise a smooth surface without ridges  823 , for enhanced strength of the device  800 , as desired by a user. 
         [0056]    With regard to  FIG. 9A  and  FIG. 9B , yet another alternative  900  for an end portion  930  for engaging an insertion tool is provided. Whereas previous embodiments provided female-female  131 ,  132  connection, this embodiment is female-male  930 ,  932 . Hence, an insertion tool can fit over the hexagonal protrusion  930  and fit into the threaded cavity  932 . This option  900 ,  930  provides more surface area  930  for rotation in an event that rotational adjustment is needed. 
         [0057]    The invention also provides novel processes and method for fusion of vertebrae  911 ,  912 . The method comprises proving a cadaver femoral bone; machining a tool to cut a spinal fusion device having a proper geometry; and freeze drying the device so it can be preserved and stored for when it&#39;s needed without having to rely on freezer storage and dry ice for transportation. Next proper space is maintained in the area between the vertebrae  911 ,  912  to prepare for the insertion process. Next, the device is impacted into place and not torqued or screwed. 
         [0058]    Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims. For example, notwithstanding the fact that the elements of a claim are set forth below in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different elements, which are disclosed in above even when not initially claimed in such combinations. 
         [0059]    While the particular Interbody Fusion Device as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims. 
         [0060]    Insubstantial changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of the claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements.