Abstract:
A spinal implant for insertion between adjacent vertebrae to function as a disc prosthesis. The prosthesis is formed from two plates fastened to adjacent vertebrae facing each other. The facing sides of the plates have a donut shaped cushioning coupler to replicate the displaced disc material. Stabilizing links are positioned along the edge of the plates to prevent over compression of the shaped cushioning coupler in a bending moment. Adjustable mounting brackets are used to secure the implant to the spine.

Description:
PRIORITY CLAIM 
     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 to U.S. provisional patent application Ser. No. 61/800,476, filed on Mar. 15, 2013, entitled “SPINAL DISC PROSTHESIS”, the contents of which are hereby expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of orthopedic surgery and, more particularly, to implants to be placed between vertebrae in the spine. 
     BACKGROUND OF THE INVENTION 
     Spinal prosthesis used for replacement of missing or excised disk material to replicate the function of the missing tissue is known. However, improvements in the area are timely and invited. Spinal prosthesis implants are disclosed in U.S. Pat. Nos. 4,759,769; 5,246,458; and 6,228,118. 
     SUMMARY OF THE INVENTION 
     Disclosed is a spinal implant for insertion between adjacent vertebrae to function as a disc prosthesis. The prosthesis is formed from two plates fastened to adjacent vertebrae facing each other. The facing sides of the plates have a donut shaped cushioning coupler to replicate the displaced disc material. The cushioning coupler is a compressible elastic hollow body which is secured between the two plates. The hollow body can be filled with an incompressible fluid. In addition, stabilizing links are positioned along the edge of the plates to prevent over compression of the shaped cushioning coupler in a bending moment. 
     It is an objective of the invention to provide an intervertebral prosthesis wherein undesired tensile stresses under unilateral loads is reduced or eliminated 
     It is another object of the invention to provide a compressible prosthesis which is able to accept edge loading in with a controlled reinforcement. 
     Other objectives 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 
         FIG. 1  is a pictorial view of the spinal implant inserted in the intervertebral space; 
         FIG. 2  is a pictorial view of the spinal implant; 
         FIG. 3  is a pictorial view of the spinal implant and various components thereof; 
         FIG. 4  is a side view of the spinal implant depicting the shaped cushioning coupler; 
         FIG. 5  is a pictorial view of the spinal implant. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The spinal implant  10  is inserted in the intervertebral space to replace damaged, missing or excised disk material ( FIG. 1 ). The implant  10  is formed from an upper plate  11  having a first inwardly facing surface  14  with a shaped body  16  and a lower plate  12  having a second inwardly facing surface  20  with a shaped body  22 . The facing sides of the plates support a donut shaped cushioning coupler  24  to replicate the displaced disc material ( FIGS. 2-4 ). 
     The cushioning coupler  24  is a compressible elastic hollow body formed as a toroidal ring secured between the plates. An annular cavity of the hollow body can be filled with an incompressible fluid such as physiological sodium chloride or a silicon oil. Alternatively a highly elastic polymer, for example polyurethane, can be used. With a fluid medium which is incompressible under the occurring loads, the elastic compressible hollow body maintains a constant volume. Under “decentralized” loads, the liquid content in the cavity of the hollow body shifts within the annular cavity and leads to an expansion of the body in that region. Thus, tensile stresses are reduced or even avoided. 
     In addition, stabilizing links  27  are positioned along four corners of the implant for use in securing the plate  11  and  12  together, but also to prevent over compression of the shaped cushioning coupler  24  in a bending moment ( FIGS. 2, 3 ). The stabilizing links  27  are also made of an elastic or compressible polymer. The links or bushings are comprised of a resilient material with a fiberous laminate skeleton which provides both compression and tension resistance. Excessive bending of the implant can result in the expansion of the body in a radial direction under compressive stress which can be limited if the radial limit of the body is reinforced by a stabilizing links  27  reinforcing means. Compression along one edge results in expansion along an opposite edge, the stabilizing links accommodating this reaction. 
     Plates  11  and  12  include adjustable mounting brackets or depth stops  30  and  31 . The upper plate  11  includes a mounting bracket or depth stop  30  having a base or elongated planar body  42  that is slidable within the recesses, grooves or receptacle  40 . Locking screws  43  maintain the base to the receptacle at a position selected by the surgeon. Teeth or sharp protuberances  45  engage the bone and prevent movement upon placement. Similarly, lower plate  12  includes a mounting bracket  31  having a base or planar body  32  that is slidable within receptacle  41 . Locking screws  36 , maintain the base or planar body  32  to the receptacle  41  at a position selected by the surgeon. As illustrated in  FIGS. 1, 2 and 3 , the mounting brackets can be positioned at different positions to accommodate the individual situation. 
     With the above description providing certain details, embodiments of the device(s) are provided. 
     In preferred embodiments a spinal implant comprises an upper endplate  11 , a lower endplate  12 , a cushioning coupler  24 , a stabilizing linker  27 , an adjustable mounting bracket or depth stop  30 ,  31 , a bone screw  80  or combinations thereof ( FIG. 3 ). 
     In preferred embodiments, the upper  11  and lower endplates  12  comprise a planar surface  60 , pointed, rounded or curved  61  edges. 
     In preferred embodiments, the upper  11  and lower  12  end plates comprise an outward facing surface  15  and  17  respectively, for receiving the depth stop  30 ,  31  and engaging a vertebra; an inward facing surface  14 ,  20  for engaging the cushioning coupler  24 . The outward facing surfaces of the upper and lower plates comprise one or more receptacles, recesses or grooves  40  for receipt of the depth stop  30 ,  31 . 
     In other preferred embodiment, the inward facing surface comprises a shaped body  16 ,  22 , the shaped body comprising a convex dome, a concave dome, a shaped protuberance, or a recess, and, one or more slots or recesses  70  for receiving one or more stabilizing linkers  27 , the stabilizing linkers  27  being detachably fastened to the upper and lower plates by a pin  81  ( FIGS. 3, 4, 5 ). The stabilizing linkers comprising one or more holes  83 , aligned with the holes  82  of the upper and lower endplates ( FIGS. 3 and 5 ). In preferred embodiments, the stabilizing linkers further serve the purpose of a spinal ligament allowing for a degree of movement and stability. 
     In preferred embodiments, the pins  81  are inserted into one or more holes  82 , tunneled horizontally through each plate through to the slot  70 , and aligned with a pin receiving aperture  83  in the stabilizing linker  27 . 
     In preferred embodiments, the stabilizing linkers  27  are blocked shaped having planar, curved, concave or a convex surface. However, it is to be understood that these linkers can have any shape or size and can be placed at varying distances and positions from each other, depending on the position of the slots or recesses in the upper and lower plates. 
     In a preferred embodiment, the cushioning coupler  24  is removable, and is shaped and dimensioned for disposition between the upper  11  and lower  12  endplates, within the confines of the stabilizing linker  27  disposed on the periphery or edges  61  of the upper and lower endplates ( FIG. 4 ). 
     In preferred embodiments, the cushioning coupler  24  comprises a doughnut or toroid shape, square shape, spherical shape, oval or elliptical shaped. Preferably, the cushioning coupler  24  is toroid shaped. The shaped body  16 ,  22 , can thus be shaped, dimensioned or patterned to accommodate the cushioning coupler  24 . The cushioning coupler is optionally fillable with volumetric fluids comprising: saline, gels, latex, polymers, polyethylenes, silicones, polyurethanes, collagen, or hydrogels. 
     In preferred embodiments, the cushioning coupler  24  is a compressible elastic body. 
     In another preferred embodiment, the retractable bracket or depth stop  30  comprises an elongated planar body  42  with at least one sharp protuberance  45  disposed on the surface of the planar body  42 , the planar surface having a first end  46  for sliding into the recesses or grooves  40  of the outward facing surfaces  15 ,  17  of the upper  11  and lower  12  endplates, a second end  47  which is perpendicular to the planar body, comprising an aperture  48  for receipt of a bone screw  80  ( FIG. 3 ). Similarly, the retractable bracket or depth stop  31  comprises an elongated planar body  32  with at least one sharp protuberance  45  disposed on the surface of the planar body  32 , the planar surface having a first end  37  for sliding into the recesses or grooves  40  of the outward facing surfaces  15 ,  17  of the upper  11  and lower  12  endplates, a second end  33  which is perpendicular to the planar body, comprising an aperture  34  for receipt of a bone screw  80 . The sharp protuberances  45  engage the bone and prevent movement upon placement of the retractable brackets or depth stops  30 ,  31  ( FIG. 3 ). 
     In yet another preferred embodiment, the planar body  42 ,  32  comprises one or more apertures  49 ,  35  for receipt of a set screw  43 ,  36  for securing the depth stop or mounting bracket  30 ,  31  to the upper and lower plates and to fix the position of the depth stop. 
     In preferred embodiments, the bone screw  80  attaches the device to the intervertebral space. 
     In other preferred embodiments, the device and components thereof are formed from biocompatible materials, such as titanium, or any conventional material used for surgical implants, such as stainless steel and its many different alloys, titanium alloys, metallic alloys, polymeric materials, plastics, plastic composites, elastic materials, shape memory alloys (e.g. nitinol), shape memory polymers, stainless steel and alloys thereof, thermoplastics, thermoplastic composites, organic polymer thermoplastics, plastics, plastic composites, ceramic or combinations thereof and any other metal or material with the requisite strength and biologically inert properties. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and/or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” 
     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. 
     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.