Abstract:
The present invention is directed to implantable devices for stabilizing or fusing bone structures within the spine. More specifically, the present invention is a spinal plate assembly that includes an automatic mechanism for blocking the pathway of a bone fastener once inserted to prevent unwanted backwards migration of the bone screw.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    In accordance with 37 C.F.R 1.76, a claim of priority is included in an Application Data Sheet filed concurrently herewith. Accordingly, the present invention claims priority under 35 U.S.C. §119(e), 120, 121, and/or 365(c) to U.S. Provisional Patent Application No. 61/542,873, entitled, “SPINAL PLATE ASSEMBLY”, filed on Oct. 4, 2011. The contents of each of the above referenced applications are herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to instruments and methods for the fixation and/or stabilization of spinal bones. More specifically, the present invention relates to a spinal plate assembly for fixation and/or stabilization of spinal column bones. The spinal plate includes a blocking mechanism that prevents unwanted backing out of the screws utilized to secure the plate to the bone(s) once installed. 
       BACKGROUND OF THE INVENTION 
       [0003]    A normal human spine is segmented with seven cervical, twelve thoracic and five lumbar segments. The lumbar portion of the spine resides on the sacrum, which is attached to the pelvis. The pelvis is supported by the hips and leg bones. The bony vertebral bodies of the spine are separated by intervertebral discs, which reside sandwiched between the vertebral bodies and operate as joints, allowing known degrees of flexion, extension, lateral bending and axial rotation. 
         [0004]    The intervertebral disc primarily serves as a mechanical cushion between adjacent vertebral bodies, and permits controlled motions within vertebral segments of the axial skeleton. The disc is a multi-element system, having three basic components: the nucleus pulposus (“nucleus”), the anulus fibrosus (“anulus”) and two vertebral end plates. The end plates are made of thin cartilage overlying a thin layer of hard, cortical bone that attaches to the spongy, richly vascular, cancellous bone of the vertebral body. The plates thereby operate to attach adjacent vertebrae to the disc. In other words, a transitional zone is created by the end plates between the malleable disc and the bony vertebrae. The anulus of the disc forms the disc perimeter, and is a tough, outer fibrous ring that binds adjacent vertebrae together. The fiber layers of the anulus include fifteen to twenty overlapping plies, which are inserted into the superior and inferior vertebral bodies at roughly a 40-degree angle in both directions. This causes bi-directional torsional resistance, as about half of the angulated fibers will tighten when the vertebrae rotate in either direction. It is common practice to remove a spinal disc in cases of spinal disc deterioration, disease or spinal injury. The discs sometimes become diseased or damaged such that the intervertebral separation is reduced. Such events cause the height of the disc nucleus to decrease, which in turn causes the anulus to buckle in areas where the laminated plies are loosely bonded. As the overlapping laminated plies of the anulus begin to buckle and separate, either circumferential or radial anular tears may occur. Such disruption to the natural intervertebral separation produces pain, which can be alleviated by removal of the disc and maintenance of the natural separation distance. In cases of chronic back pain resulting from a degenerated or herniated disc, removal of the disc becomes medically necessary. 
         [0005]    In some cases, the damaged disc may be replaced with a disc prosthesis intended to duplicate the function of the natural spinal disc. In other cases it is desired to fuse the adjacent vertebrae together after removal of the disc, sometimes referred to as “intervertebral fusion” or “interbody fusion.” In this process, spondylodesis or spondylosyndesis is used to join two or more vertebrae to eliminate pain caused by abnormal motion, degradation, fractures or deformities of the vertebrae. 
         [0006]    Spinal plates have become one common approach to attaching one adjacent vertebra to another. A spinal plate generally includes an elongated plate of a metal such as titanium or stainless steel. The plate includes a plurality of apertures positioned to allow a surgeon to attach the plate across at least two vertebras with screws. The combination of the plate and screws serve to hold the adjacent vertebra together while the intervertebral fusion occurs. 
         [0007]    One shortcoming to this approach relates to the screws utilized to hold the plate to the bone. As the person who had the plate installed continues with his/her everyday life, the plate is repeatedly loaded and twisted. Each motion that the person makes applies a dynamic load to both the screws and the plate. This repeated loading and unloading places tremendous stress on the plate and particularly on the screws that interface with the soft bone. These stresses tend to cause the screws to back out of the bone over time. The backing out of the screws can cause complications that not only affect the fusion of the bone, but may also damage nerves and tissues in the proximity of the implant. Additional issues such as osteoporosis may exacerbate the problem. Additional surgeries may therefore be required to repair or remove loosened screws or implants. 
         [0008]    A number of plate assembly designs have been proposed in attempts to prevent screws from pulling away or withdrawing from the bone and/or to prevent the screws from backing out, pulling away or withdrawing from the surface of the spinal plate. Some of these devices include rotating or sliding plates that cover a top surface of the screw. Other devices include set screws that apply pressure to the top of the screw. All of these devices require secondary action by the surgeon to activate or set the mechanisms that prevent the screws from backing out. Because the parts are very small, the risk of losing a part into the patient or improperly assembling the locking devices is unreasonably high. 
         [0009]    Another type of system for preventing screw back out includes springs that automatically snap over a portion of the bone screw as it is inserted into the plate and thus the bone. For example, U.S. Pat. Nos. 7,008,426, 7,070,599, and 7,204,837 disclose a bone plate having an elongated slot extending the length of the plate between the top and bottom surfaces of the plate. A pair of elongated strips of material are positioned within the slot with springs therebetween to force the strips toward the outer portions of the slot. The slot and the strips are positioned to require movement of one of the strips as the head portion of the bone screws enter the plate. 
         [0010]    A shortcoming to this type of device relates to longitudinal movement of the strips during insertion of the bone screws. As designed, the screw head was intended to pass the strip and force it medially with respect to the plate and snap back to cover a portion of the screw to prevent the screw from backing out after the screw head passed the strip. However, in practice a surgeon will generally install all of the screws partially into the bone. An x-ray is then taken to assure the proper positioning of the screws before they are finally tightened. Because partial placement of the screws causes both strips to move medially at the same time with respect to the plate, the strips lose contact with the plate, causing them to be free for longitudinal movement. Because the spring pressure causes the strip to bear against the side of the screws, rotation of any of the screws causes displacement of the strips longitudinally with respect to the plate. This movement prevents the strips from functioning for their intended purpose and requires the plate to be removed from the patient. 
         [0011]    A further shortcoming to this device is the locking strips prevent windows from being positioned in the plate to allow visualization through the plate. This construction makes positioning of the plate more difficult for the surgeon. 
         [0012]    Therefore, there is a need in the art for a spinal plate that includes a locking mechanism that allows increased versatility in screw placement. The locking mechanism should operate automatically, e.g. without manual manipulation of the locking mechanism, as any number of screws are secured to bone through the plate to positively prevent back out of the bone screw(s). The locking mechanism should also allow for partial insertion of the bone screws without longitudinal displacement of the locking mechanism. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention is directed to implantable devices for stabilizing or fusing bone structures within the spine. More specifically, the present invention is a spinal plate assembly that includes an automatic mechanism for blocking the pathway of a bone fastener once inserted to prevent unwanted backwards migration of the bone screw. The automatic mechanism generally includes a central base portion, a pair of spring loaded blades and a pair of anchors. The central base portion is substantially rigid having a pair of leaf type springs extending outwardly therefrom; each left type spring having a blade member mounted on a distal end thereof. The central base portion also includes a second pair of leaf springs extending outwardly therefrom in an opposite direction with respect to the first leaf springs. A pair of anchor members are secured to the distal ends of the second pair of leaf springs to engage pockets formed into the bone plate. In this manner, each spring loaded blade may be operated independently or simultaneously without dislodging the connection between the anchors and the bone plate. 
         [0014]    Accordingly, it is an objective of the instant invention to provide a spinal plate for stabilization and/or fusion of adjacently positioned spinal bones. 
         [0015]    It is a further objective of the instant invention to provide a spinal plate that includes an automatically operating screw locking mechanism for preventing screws from backing out of position once properly seated within the spinal plate. 
         [0016]    It is yet another objective of the instant invention to provide a spinal plate that includes a locking mechanism that includes two locking blades connected to a central base via independent spring members so that the blades can function individually or simultaneously. 
         [0017]    It is a still further objective of the invention to provide a spinal plate that includes a locking mechanism that includes two anchor members connected to a central base via independent spring members so that the anchors remain independent with respect to operation of the locking blades to prevent dislodgement of the locking mechanism during operation thereof. 
         [0018]    It is still yet another objective of the invention to provide a spinal plate with a locking mechanism wherein the spinal plate includes windows for visualization through the plate. 
         [0019]    Other objects and advantages of this invention will become apparent from the following description taken in conjunction with any accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. Any drawings contained herein constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0020]      FIG. 1A  is a perspective view of a prior art bone plate with locking member in place; 
           [0021]      FIG. 1B  is a perspective view of the locking member of the prior art illustrated in  FIG. 1A ; 
           [0022]      FIG. 2  is a partial view of the embodiment illustrated in  FIG. 1A  illustrating one shortcoming of the design; 
           [0023]      FIG. 3  is a perspective view of one embodiment of the present invention illustrated with multiple locking mechanisms in place; 
           [0024]      FIG. 4  is a partial section view taken along lines  4 - 4  of  FIG. 3 ; 
           [0025]      FIG. 5  is a partial section view taken along lines  5 - 5  of  FIG. 3 ; 
           [0026]      FIG. 6  is a top view partially in phantom illustrating one embodiment of the present invention; 
           [0027]      FIG. 7A  is a top view of the embodiment illustrated in  FIG. 3 ; 
           [0028]      FIG. 7B  is a side view of the embodiment illustrated in  FIG. 3 ; 
           [0029]      FIG. 8  is a top view of one embodiment of the locking mechanism of the present invention; 
           [0030]      FIG. 9  is a side view of the locking mechanism embodiment illustrated in  FIG. 8 ; 
           [0031]      FIG. 10  is a top view of one embodiment of the locking mechanism of the present invention; and 
           [0032]      FIG. 11  is a side view of the locking mechanism embodiment illustrated in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred, albeit not limiting, embodiment with the understanding that the present disclosure is to be considered an exemplification of the present invention and is not intended to limit the invention to the specific embodiments illustrated. 
         [0034]    Referring to  FIGS. 1A and 1B , a prior art spine plate assembly  10  is illustrated. The bone plate  10  includes an elongated slot  12  extending the length of the plate between the top  14  and bottom  16  surfaces of the plate. A member  18  including a pair of elongated strips  20  of material are positioned within the slot with springs  23  therebetween to force the strips toward the outer portions of the slot  12 . The slot and the strips are positioned to require movement of one of the strips as the head portion  22  of the bone screws  24  enter the plate  10 . A shortcoming to this type of device relates to longitudinal movement of the strips  20  during insertion of the bone screws  24 . As designed, the screw head  22  was intended to pass the strip  20  to force the strip medially with respect to the plate  10  and snap back to cover a portion of the screw to prevent the screw from backing out after the screw head passed the strip. However, in practice a surgeon will generally install all of the screws partially into the bone. An x-ray is then taken to assure the proper positioning of the screws  24  before they are finally tightened. Partial placement of the screws causes both strips  20  to move medially at the same time, as illustrated in  FIG. 2 ; the strips  20 , therefore, lose contact with the plate  10  causing the strips to be free for longitudinal movement. The spring pressure causes the strip to bear against the side surface of the screw head  22 , whereby rotation of any of the screws causes displacement of the strips longitudinally with respect to the plate. This movement prevents the strips from functioning for their intended purpose and requires the plate to be removed from the patient for replacement with another device. A further shortcoming to this type of device relates further to the elongated locking strips. The elongated locking strips extend the full length of the plate. This construction prevents sight windows from being positioned in the plate between the bone apertures to allow visualization through the plate. The lack of sight windows makes positioning of the plate more difficult for the surgeon. 
         [0035]    Referring to  FIGS. 3-7 , a spinal plate assembly  30  is illustrated. The spine plate assembly  30  generally includes a spine plate  32 , a locking member  34  and a plurality of bone screws  36 . The spine plate  32  is preferably constructed from a biocompatible material such as titanium, and includes a bottom surface  38 , a top surface  40 , a pair of side surfaces  42  and a pair of end surfaces  44 . At least two bores  46  extend through the top and bottom surfaces  38 ,  40 , each of the bores are sized for passage of a bone screw  36 . In addition, each bore  46  includes a counterbore  48  extending downwardly from the top surface  40 . The counterbore is sized and shaped to substantially contain a head portion  50  of the bone screw. The counterbore may be of any shape desirable to match with the bone screw. For example, the counter bore may be spherical, square, truncated or any suitable combination thereof. A segmented T-slot  52  extends between the pair of end surfaces  44  and substantially parallel to the top surface  40 . A first leg  54  of the T-slot extends through the top surface  40  while portions of the second and third legs  56 ,  58  extend into each counterbore  48 . The segments of the T-slot  52  are separated by sight windows  60  extending between the top and bottom surfaces. The sight windows  60  aid the surgeon in placement of the spinal plate  32  by allowing the surgeon to view anatomical features through the plate. The spinal plate also preferably includes at least one, and more preferably two anchor pockets  62 . The anchor pockets are generally constructed and arranged to cooperate with a portion of the locking member  34  to secure the locking member to the spinal plate. The anchor pockets  62  extend downward from the top surface  40  to about the same depth as the second and third legs  56 ,  58  of the T-slot  52  and are wider than the T-slot  52  when viewed from an end surface  44  of the spinal plate  32 . The anchor pockets  62  include side surfaces  64  and end surfaces  66  which cooperate with the locking member  34 . The spinal plate  32  may additionally include tool apertures  68  which aid in the placement of the plate. The tool apertures  68  are preferably sized for cooperation with a gripping tool or K-wire, whereby the plate may be more easily maneuvered into position within the anatomy of a human or animal in vivo. The tool aperture may additionally function as windows for the surgeon once the plate has been maneuvered into position. 
         [0036]    Referring to  FIGS. 3-11 , a locking member  34  is illustrated. The locking member is generally constructed and arranged to fit substantially within the T-slot  52  with portions extending into the counterbores  48  for blocking backwards migration of the bone screws  36  after insertion. The locking member includes a central base portion  70  having at least one, and more preferably two leaf springs  72  extending outwardly therefrom in a first direction. A blade portion  74  is secured to a distal end of each leaf spring  72  to contact the first side wall of the second leg of the T-slot  52  whereby a portion of each blade  74  extends into at least one counterbore  48 . At least one and more preferably two anchor portions  76  extend outwardly from the base portion in a direction different from the leaf spring  72 . Each anchor portion  76  terminates in an anchor foot  78  whereby each anchor foot  78  is constructed and arranged to fit into a respective anchor pocket  62 . The anchor foot  78  cooperates with the pair of anchor pocket side walls  64  and end wall  66  to prevent movement of the locking member during movement of the blade portion away from the side surfaces of the second and third legs  56 ,  58  of the T-slot  52 . In at least one embodiment, the anchor portion is constructed to function as a leaf spring and may further be constructed to apply a preload force to the side and/or end surfaces of the anchor pocket to further secure the locking member to the spinal plate. The locking member  34  is preferably constructed from a relatively thin biocompatible material, such as but not limited to Nitinol, having a spring temper. In one embodiment, the thickness  80  of the locking member is about 0.015 thousandths of an inch. 
         [0037]    Referring to  FIGS. 3 ,  6  and  7 , spinal plates  32  having different lengths are illustrated. As shown in  FIG. 6 , an embodiment is illustrated having two sets of through bores  46 . It should be appreciated that each set of through bores include one locking member  34 . This construction permits the same locking member construction to be utilized across an entire series of spinal plates having different lengths and different number of through bores. 
         [0038]    All patents and publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains. All patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. 
         [0039]    It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and any drawings/figures included herein. 
         [0040]    One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as, those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.