Abstract:
In a first broad aspect, there is provided herein a bioactive device and system for fusion between two bones, two parts of a bony joint, or a bony defect, such as of the spine. The fusion device includes a screw having a head and a threaded shaft. The fusion device also includes a bone dowel having an internal bore of which at least a distal portion is threaded to engage the threads of the screw shaft. The bone dowel is made of a bone-like, biocompatible, or allograft material to provide a layer of bone-like, biocompatible, or allograft material between the screw and the spinal bone. The device is generally coaxial and is further described in the drawings and description herein.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/593,270, filed Jan. 31, 2012, the disclosure of which is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    The invention was not made with government support, and the government has no rights in the invention. 
       TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY 
       [0003]    This invention relates, in part, to a bioactive system for fusion between two bones, two parts of a bony joint, or a bony defect, such as of the spine. This invention also relates, in part, to methods of making and methods of using such a bioactive system for fusion. 
       BACKGROUND OF THE INVENTION 
       [0004]    Over 650,000 spine surgeries are performed annually in the United States, with the majority being decompressive laminectomies for spinal stenosis. Spinal stenosis is a narrowing of the spinal canal housing the spinal cord, which is generally caused by arthritis of articulating bones of the vertebral column and/or bulging of the intervertebral discs. Eighty percent of the population report having back pain, with over 400,000 patients per year diagnosed with spinal stenosis. The majority age group is 65 or older. The diagnosis of spinal stenosis and, therefore, need for treatment is likely to escalate rapidly when U.S. census data is applied. For example, the U.S. population of individuals over 65 represented 12.4% (about 35 million) in 2000 and is projected to represent 19.6% (million) by the year 2030. 
         [0005]    The most common treatment for spinal stenosis involves a midline approach with a decompressive laminectomy to address the stenosis. Although highly effective in relieving the clauditory symptomotology, there is growing evidence and concern over the need for reoperation to address reoccurrence of symptoms related to progression of spondylolisthesis, or slippage, at the site of decompression. Slippage rates post-surgery have been reported as high as 20% in “no preop slip” patients and from 40% to 100% in “preop slip present” patients. The reoperation rate for each of these groups varies and is dependent on many factors. Reported reoperation rates average around 18% for the “no preop slip” group and upward of 30% for the “preop slip present” group. 
         [0006]    The concern for further slippage and need for reoperation has fostered a treatment method involving the use of dynamic or motion sparing devices placed without a fusion to give some amount of “stiffness” to prevent further slippage and yet allow for some motion, avoid excessive loading of adjacent segments, and hopefully avoid adjacent segment disease. Such devices have been successful in limiting the progression of slip in stable spine constructs. However, there are recent reports of instrumentation failures and the need for revision surgery. Thus, the uses of dynamic systems are not always clinically successful and may defeat the attempt to limit reoperations. Furthermore, it is reported that adjacent segment disease continues similar to patients with rigid fusions. Furthermore, the need to utilize pedicle screw technology and approaches with such dynamic systems makes the muscle trauma morbidity comparable to undergoing a fusion surgery with screws and/or rods. Thus, alternative instrumentation is being explored by surgeons and engineers alike. 
       SUMMARY OF THE INVENTION 
       [0007]    In a first broad aspect, there is provided herein a bioactive device and system for fusion between two bones, two parts of a bony joint, or a bony defect, such as of the spine. The fusion device includes a screw having a head and a threaded shaft. The fusion device also includes a bone dowel having an internal bore of which at least a distal portion is threaded to engage the threads of the screw shaft. The bone dowel is made of a bone-like, biocompatible, or allograft material to provide a layer of bone-like, biocompatible, or allograft material between the screw and the spinal bone. The device is generally coaxial and is further described in the drawings and description herein. 
         [0008]    In another aspect, a method of fixation of two bones, two parts of a bony joint, or a bony defect, such as of the spine is disclosed. For example, a method of fixation of a facet joint of two vertebrae includes the step of inserting a fusion device through the inferior articular process of a first vertebra, transversely across a facet joint, and into the superior articular process of a second adjacent vertebra. The fusion device includes a screw having a head and a threaded shaft and a bone dowel having an internal bore, of which least a distal portion is threaded to engage the threads of the screw shaft. The bone dowel is made of a bone-like, biocompatible, or allograft material to provide a layer of the bone-like, biocompatible, or allograft material between the screw and the spinal bone. The screw is threaded into the bore of the dowel to secure the two vertebrae together across the facets. 
         [0009]    An advantage of the fusion device is reduced medical costs from a less invasive surgical procedure. Another advantage is the reduced amount of slippage and re-operations that are required. A further advantage is the achievement of comparable stabilization of the spine with minimal invasiveness. 
         [0010]    Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawings, incorporated herein and forming a part of the specification, illustrate the present invention in its several aspects and, together with the description, serve to explain the principles of the invention. In the drawings, the thickness of the lines, layers, and regions may be exaggerated for clarity. 
           [0012]      FIG. 1  is an elevational view showing two vertebrae in a portion of a human spine. 
           [0013]      FIG. 1A  is an enlarged view of portions of the two vertebrae illustrated in  FIG. 1  and including a schematic representation of a fusion device fixing such vertebrae together in accordance with this apparatus and method of this invention. 
           [0014]      FIG. 1B  illustrates a first exemplary manner in which a first embodiment of the fusion device of this invention can be installed on the two vertebrae illustrated in  FIG. 1 . 
           [0015]      FIG. 1C  illustrates a second exemplary manner in which the first embodiment of the fusion device of this invention can be installed on the two vertebrae illustrated in  FIG. 1 . 
           [0016]      FIG. 2  is an enlarged elevational view of a first embodiment of a bone screw portion of the first embodiment of the fusion device. 
           [0017]      FIG. 3  is an enlarged elevational view of a second embodiment of a bone screw portion of the first embodiment of the fusion device. 
           [0018]      FIG. 4  is an enlarged elevational view of a bone dowel portion of the first embodiment of the fusion device. 
           [0019]      FIG. 5  is an enlarged perspective view of a bone dowel portion of the first embodiment of the fusion device illustrated in  FIG. 4 . 
           [0020]      FIG. 6  is an enlarged perspective view of the second embodiment of the bone screw portion illustrated in  FIG. 3  coaxially aligned with the bone dowel portion of the first embodiment of the fusion device. 
           [0021]      FIG. 7  is an enlarged elevational view of the second embodiment of the bone screw portion illustrated in  FIG. 3  partially threaded within the bone dowel portion of the first embodiment of the fusion device. 
           [0022]      FIG. 8  is an enlarged elevational view of the second embodiment of the bone screw portion illustrated in  FIG. 3  fully threaded within the bone dowel portion of the first embodiment of the fusion device. 
           [0023]      FIG. 9  is an enlarged perspective view, partially in phantom, of the second embodiment of the bone screw portion illustrated in  FIG. 3  fully threaded with the bone dowel portion of the first embodiment of the fusion device. 
           [0024]      FIG. 10  is another enlarged perspective view, partially in phantom, of the second embodiment of the bone screw portion illustrated in  FIG. 3  fully threaded with the bone dowel portion of the first embodiment of the fusion device. 
           [0025]      FIG. 11  is an elevational view of a second embodiment of a fusion device in accordance with this invention. 
           [0026]      FIG. 12  is a perspective view of the second embodiment of a fusion device illustrated in  FIG. 11 . 
           [0027]      FIG. 13  is an exploded perspective view of the second embodiment of a fusion device illustrated in  FIGS. 11 and 12 . 
           [0028]      FIG. 14  is a perspective view of a full bone screw and bone screw and internal metal screw. 
           [0029]      FIG. 15  illustrates how the fusion device of this invention passes through the lamina of the spine and then through the facet joint. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0030]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. All references cited herein, including books, journal articles, published U.S. or foreign patent applications, issued U.S. or foreign patents, and any other references, are each incorporated by reference in their entireties, including all data, tables, figures, and text presented in the cited references. 
         [0031]    Unless otherwise indicated, all numbers expressing ranges of magnitudes, such as quantities of ingredients, properties such as molecular weight, reaction conditions, dimensions, and so forth as used in the specification and claims are to be understood as being modified in all instances by the term “about.” Any numerical values inherently contain certain errors necessarily resulting from error found in their respective measurements. Accordingly, unless otherwise indicated, the numerical properties set forth in the specification and claims are approximations that may vary depending on the desired properties sought to be obtained in embodiments of the present invention. All numerical ranges are understood to include all possible incremental sub-ranges within the outer boundaries of the range. Thus, a range of 30 degrees to 90 degrees discloses, for example, 35 degrees to 50 degrees, 45 degrees to 85 degrees, and 40 degrees to 80 degrees, etc. 
         [0032]      FIG. 1  is an elevational view showing two vertebrae  22  and  22 ′, such as in a portion of a human spine. Although this invention will be described and illustrated in the context of a fusion of a facet joint between the two vertebrae  22  and  22 ′, it will be appreciated that this invention may be practiced for any other purpose in any other environment. For example, this invention may be practiced to perform a fusion between two bones, two parts of a bony joint, or a bony defect. 
         [0033]    As shown in various embodiments in  FIGS. 1A ,  1 B, and  1 C, a first embodiment of a fusion device  70  includes a hollow bone dowel portion  72 . The illustrated hollow bone dowel portion  72  is internally threaded for at least a distal portion of its length, although such is not required. A bone screw portion  74  of the fusion device  70  can be disposed within the hollow bone dowel portion  72 . For example, the bone screw portion  74  of the fusion device  70  can be externally threaded and be threaded within the hollow bone dowel portion  72 . The screw portion  74  of the fusion device  70  can be formed from any desired material including, for example, a metallic material such as titanium. As shown in  FIG. 2 , the screw portion  74  of the fusion device  70  can be formed from a solid body of material having an external helical thread or other similar structure provided thereon. Alternatively, as shown in  FIG. 3 , the screw portion  74  can be formed from a ribbon of material having a helical or other similar shape. 
         [0034]    The bone dowel portion  72  of the fusion device  70  can be formed from a bone-like or allograft composition and may include one or more external threads  76  for insuring insertion and resisting backwards slipping in or relative to the vertebrae  22  and  22 ′. Alternatively, the bone dowel portion  72  of the fusion device  70  may include one or more other structures, such as, for example, barbs, teeth, ribs and the like, for this purpose. At a distal end  78  of the dowel  72 , a flexible flange  80  may be provided to aid in seating and/or compression relative to the vertebrae  22  and  22 ′. The distal end  78  of the dowel  72  may be internally threaded so as to cooperate with the externally threaded screw portion  74  for a purpose that will be explained below. Some or all of the bone dowel portion  72  of the fusion device  70  (including the flange  80 ) may be made of a flexible biocompatible polymer, such as polyaryletherketone (“PAEK”), polyetherketone (“PEEK”) or UHMWPE or antioxidant stabilized UHMWPE. Such devices are sometimes referred to as PEEK constructs. When the screw  74  is threaded completely into the bone dowel  72 , the screw head  75  seats against the proximal end  73  of the bone dowel  72 . Continued turning of the screw  74  pulls the internally threaded distal portion  78  of the bone dowel  72  in a proximal direction and flattens the flanges  80  radially outwardly from a relaxed orientation (shown in  FIGS. 4 through 7 ) to a compressed orientation (shown in  FIGS. 8 through 10 ). Such deployment of the flanges  80  facilitates the installation of the fusion device  70  relative to the vertebrae  22  and  22 ′, as shown in  FIGS. 2 and 3 . 
         [0035]    The bone dowel portion  72  of the fusion device  70  can have any desired shape or size. In one embodiment, the diameter of the bone dowel  72  can range from about 3 mm to about 7 mm. In another embodiment, the diameter of the bone dowel  72  can range from about 4 mm to about 6 mm. Similarly, the length of the bone dowel  72  can range from about 16 mm to about 26 mm, or from about 20 mm to about 24 mm. The distal portion  78  of the bone dowel  72 , including the uncompressed flange  80 , can range from about 4 mm to about 8 mm long. The screw portion  74  can have a shaft of about 2 mm in diameter and, in certain preferred embodiments, is sufficiently long to engage the threaded distal portion of the bone dowel  72 . 
         [0036]      FIGS. 1A ,  1 B, and  1 C show how the fusion device  70  can be positioned relative to the vertebrae  22  and  22 ′. Each of the vertebrae  22  and  22 ′ includes laminae  30  that extend between a spinous process  32  and respective transverse processes  34 . As shown in  FIG. 1B , the fusion device  70  may be inserted through an inferior articular process  38  of the upper vertebra  22 , across a facet joint gap  50 ,  50 ′ between the vertebrae  22  and  22 ′, and into a superior articular process  36  of the lower vertebra  22 ′. The fusion device  70  may optionally extending into a pedicle  26  of one of the vertebrae  22  and  22 ′. 
         [0037]    Alternatively, as shown in  FIG. 1C , the fusion device  70  may be inserted through the inferior articular process  38  of the upper vertebra  22 , across the facet joint gap  50 ,  50 ′ between the vertebrae  22  and  22 ′, and into the superior articular process  40  of the lower vertebra  22 ′. However, in  FIG. 1C , the fusion device  70  extends through a pedicle  26  and into the vertebral body  24  of the vertebra  22 . As compared with the approach of  FIG. 1B , the angle of insertion in  FIG. 1C  is more aligned anterior-posterior, and the angle of insertion the fusion device  70  forms with respect to the facet faces  41 ,  42  is more oblique.  FIG. 1A  shows how the fusion device  70  transects the surfaces  41 ,  42  of the facets, rather than being in the interfacet space between the vertebrae  22  and  22 ′. 
         [0038]    During the installation of the fusion device  70 , the surgeon only needs a minimal incision, for example, a very small standard midline approach, allowing the surgeon to work in his/her “comfort zone” for the midline partial laminectomy. In such a manner, the pars of the vertebra are preserved and up to 60% of the inferior facet is preserved, thus allowing for a fusion and stabilization across the facet joint. The fusion device  70  is placed in a minimally invasive procedure, thus minimizing the need for muscle retraction or dissection, often required to place “pedicle-based” stabilization systems. 
         [0039]    Once surgically inserted, the closer the facet fusion device is located to the Center of Rotation (COR), the smaller and yet stronger the actual fixation of the device is within the vertebra. There is no “rod” per se like the pedicle screw/rod constructs. In this embodiment, the facet fusion device  70  harnesses the most “physiologic rod” of all, the bone across the facet joint  50 ,  50 ′ and the pars areas above and below the facets. This “living, dynamic rod” allows for some flex without detrimental loosening of the facet fusion device. There is more “motion” than a rigid screw/rod construct, but there is also a solid locking implant and fusion across the facet joints (the only true joint in the spine), thus preventing further slippage, facet joint pain, etc. Additional levels of decompression are all linked together through this “living bone rod construct.” 
         [0040]    For an even more rigid construct in patients with greater instability, degenerative disc disease, etc. an interbody cage may optionally be added to the surgery, still preserving the lamina and facet construct. Alternatively, an interspinous fusion can be done with facet screws for further rotational stability. 
         [0041]    The fusion device  70  described herein can provide the stability and, at the same time, deliver the bone graft material of the bone dowel portion  72  around the screw  74  directly at the fusion site. Thus, the fusion device  70  delivers bone graft material (when required) by bridging technology without an additional procedure and without compromising the stability of the fixation. As well as reducing the time required to perform surgery, the use of this fusion device  70  allows the surgeon to operate via a smaller incision. Both factors may contribute to a shorter recovery time for the patient. This fusion device  70  also reduces the likelihood of pseudoarthrosis. 
         [0042]      FIGS. 11 through 13  illustrate a second embodiment of a fusion device, indicated generally at  100 , in accordance with this invention. As shown therein, the fusion device  100  includes a screw portion  101  having a first externally threaded portion  102  and a second externally threaded portion  103 . The screw portion  101  may be formed from any desired material, including that described above in connection with the bone screw  74 . The fusion device  100  also includes a hollow bone dowel portion  104  that, when assembled, extends about the screw portion  101 . The bone dowel portion  104  may include an internally threaded portion (not shown) that engages the second externally threaded portion  103  of the screw portion  101 , although such is not required. The fusion device  100  further includes a head portion  105  having an internally threaded portion (not shown) that engages the second externally threaded portion  103  of the screw portion  101 . As a result, the hollow bone dowel portion  104  is retained about the screw portion  101  between the head portion  105  and the first externally threaded portion  102 , as best shown in  FIGS. 11 and 12 . The fusion device  100  can be sized and shape as desired to deliver the bone graft material of the bone dowel portion  104  directly at the fusion site in the manner described above. 
         [0043]      FIG. 14  is a perspective view of a full bone screw and bone screw and internal metal screw. 
         [0044]      FIG. 15  illustrates how the fusion device of this invention passes through the lamina of the spine and then through the facet joint. 
       Other Embodiments 
       [0045]    Hybrid Cage 
         [0046]    The fusion device of this invention can be used in conjunction with an inter-body cage or/and interspinous fusion device. In one non-limiting example, a hybrid cage can be used as a non fusion device (disc-like action) or used as inter body fusion device in conjunction with proposed facet screws. 
         [0047]    Dynamic Interspinous Device 
         [0048]    In the last several years, the interspinous fusion procedure in patients above 65 is becoming a standard practice. In one non-limiting example, a dynamic interspinous device can be used in conjunction with a bone screw of the fusion device of this invention to increase its stability. 
         [0049]    While the invention has been described with reference to various and preferred embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the essential scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. 
         [0050]    Therefore, it is intended that the invention not be limited to the particular embodiment disclosed herein contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. 
         [0051]    The publication and other material used herein to illuminate the invention or provide additional details respecting the practice of the invention, are incorporated by reference herein, and for convenience are provided in the following bibliography. 
         [0052]    Citation of the any of the documents recited herein is not intended as an admission that any of the foregoing is pertinent prior art. All statements as to the date or representation as to the contents of these documents is based on the information available to the applicant and does not constitute any admission as to the correctness of the dates or contents of these documents. 
         [0053]    The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.