Patent Publication Number: US-10758362-B1

Title: Motion preserving spinal implant for total disc replacement

Description:
The current application claims a priority to the U.S. Provisional Patent application Ser. No. 62/828,584 filed on Apr. 3, 2019. The current application also claims a priority to the U.S. Provisional Patent application Ser. No. 62/837,474 filed on Apr. 23, 2019. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to human body implants. More particularly, the present invention relates to a motion preserving spinal implant for replacement of a spinal disc. 
     BACKGROUND OF THE INVENTION 
     Spinal implants are intended to treat degenerative disc disease (DDD) or other disc injuries. Spinal fusion treatment is a widely used treatment to alleviate pain, but limits range of motion and mobility for a patient. Total disc replacement is another treatment for disc degenerative disease that aims to preserve motion and limit complications related to spinal fusion such as adjacent level wear and disc degeneration. Total disc replacement is an effective solution for degenerative disc disease and gaining interest due to increasing prevalence of neck pain, lower back pain, and pain in general. Thus, there is a need for functional improvement. For an example, without limitations, there is a need for total disc replacement spinal implants that reduce wear due to metal to metal sliding and corrosive surfaces, increase cushioning, improve shock absorption, reduce wear debris of metal, and maintain spinal motion range. 
     The present invention solves these problems by providing a treatment solution that reduces degeneration due to metal wear because of no sliding between metal plates, increases cushioning with effective inner core design features, and uses special polymeric and elastomeric materials having varying hardness and physical properties such as silicone or liquid silicon rubber that also provides shock absorption, and maintains range of motion due to effective outer core design, its features, and choice of materials. All components in the assembly are designed such that it can effectively resist compression forces, shear-compression forces, and torsion forces. 
     Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Additional advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the detailed description of the invention section. Further benefits and advantages of the embodiments of the invention will become apparent from consideration of the following detailed description given with reference to the accompanying drawings, which specify and show preferred embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of the present invention. 
         FIG. 2  is an exploded perspective view of the present invention. 
         FIG. 3  is a front view of the present invention. 
         FIG. 4  is a rear view of the present invention. 
         FIG. 5  is a top view and a side sectional view of the present invention. 
         FIG. 6  is a top view and a front sectional view of one of the end plates of the present invention. 
         FIG. 7  is a top view, a side sectional view, and a side view of the inner core of the present invention. 
         FIG. 8  is a top view, a side sectional view, and a side view of the outer core of the present invention. 
         FIG. 9  is a top view and a side sectional view of an alternative embodiment of the present invention incorporating anchoring protrusions. 
         FIG. 10  is a top view and a side sectional view of one of the end plates in the alternate embodiment. 
         FIG. 11  is a top view and a side sectional view of the outer core in the alternate embodiment. 
     
    
    
     DETAIL DESCRIPTIONS OF THE INVENTION 
     All illustrations of the drawings are for the purpose of describing selected versions of the present invention and are not intended to limit the scope of the present invention. The present invention is to be described in detail and is provided in a manner that establishes a thorough understanding of the present invention. There may be aspects of the present invention that may be practiced or utilized without the implementation of some features as they are described. It should be understood that some details have not been described in detail in order to not unnecessarily obscure focus of the invention. References herein to “the preferred embodiment”, “one embodiment”, “some embodiments”, or “alternative embodiments” should be considered to be illustrating aspects of the present invention that may potentially vary in some instances, and should not be considered to be limiting to the scope of the present invention as a whole. 
     The present invention is a spinal implant intended for use in total replacement of a degenerated spinal disc. In general, referring to  FIGS. 1-5 , the present invention comprises a first end plate  1 , a second end plate  2 , an inner core  3 , and an outer core  4 . In the preferred embodiment of the present invention, the first end plate  1 , the second end plate  2 , the inner core  3 , and the outer core  4  each have generally radial geometry, though it may be noted that other geometries may be utilized as desired or useful. The inner core  3  and the outer core  4  are generally disc-shaped, being substantially wider than tall, having a radial axial cross section and a certain thickness, or axial height. The inner core  3  is positioned concentrically within the outer core  4 , and the outer core  4  is connected between the first end plate  1  and the second end plate  2  through a plurality of interlocking members  5 . Thus, the inner core  3  and the outer core  4  are sandwiched by the first end plate  1  and the second end plate  2 . More specifically, the outer core  4  comprises an inner cavity  40  that centrally and axially traverses through the outer core  4 . The inner core  3  is positioned within the inner cavity  40  of the outer core  4 , such that the inner core  3  is sealed by the outer core  4 , the first end plate  1  and the second end plate  2 . In some embodiments, the internal lateral geometry of the inner cavity  40  may be determined by the external lateral geometry of the outer core  4 . 
     In the preferred embodiment, the inner core  3  is constructed of a medical or implant grade polymeric or elastomeric material which may have varying hardness and other physical properties in various embodiments. In some embodiments, the inner core  3  is constructed of a silicone material. In some embodiments, the inner core  3  is constructed of a medical or implant grade silicone elastomer with a hardness ranging from 60 shore A to 90 shore A. In some embodiments, the inner core  3  may be constructed of a liquid silicone rubber (LSR) material. Such material is inert and widely used in medical breast implants. Silicone rubber has the ability to retain its initial shape and mechanical stress under high compression, shear-compression, flexural, torsional, and tensile stresses and has excellent creep properties. In other embodiments, other appropriate materials may be used to manufacture the inner core  3 . The inner core  3  serves as a solid “diaphragm” or cushion that resists and withstands localized compression, shear-compression, torsion, and other forces. In various embodiments, the diameter of the inner core  3  may range from approximately 0.125 inches to 2.25 inches, but it should be understood herein that various dimensions of the present invention may vary without departing from the intended spirit and scope of the present invention. 
     In the preferred embodiment, the inner core  3  comprises a first core convexity  30  and a second core convexity  31 , as shown in  FIGS. 5 and 7 . The first core convexity  30  and the second core convexity  31  are positioned axially opposite each other along the inner core  3 . The first core convexity  30  and the second core convexity  31  are essentially bulges centrally positioned on the inner core  3  that contribute to the inner core&#39;s  3  capabilities to resist and withstand any forces the inner core  3  is subject to while installed in a human spine. The first core convexity  30  and the second core convexity  31  further correspond to and mate with inner concavities on the first end plate  1  and the second end plate  2 , as will be discussed hereinafter. In various embodiments, a convexity angle of the first core convexity  30  and the second core convexity  31  may range from 5 degrees to 60 degrees, and an outer radius of the first core convexity  30  and the second core convexity  31  may range from 0.075 inches to 2 inches in various embodiments. In some embodiments, the inner core  3  further comprises a lateral wall with a convex curvature, whose radius may range in various embodiments from 0.063 inches to 2.250 inches, but it should be understood herein that various dimensions of the present invention may vary without departing from the intended spirit and scope of the present invention. 
     The outer core  4  acts as a sealing ring for the inner core  3  and provides the necessary motion to the spine once the present invention is implanted in a human body. In the preferred embodiment, the outer core  4  is constructed of a polymeric or elastomeric material with varying hardness and other physical properties in various embodiments. 
     In some embodiments, the outer core  4  may be constructed of an ultra-high molecular weight polyethylene (UHMWPE) material. In some embodiments, the outer core  4  may be constructed of a medical grade polypropylene (PP) material, though the material of the outer core  4  may vary in different embodiments as desired. In general, it is desired to use a material with superior abrasive and corrosive resistance, high strength, light weight, and low coefficient of friction in the outer core  4 . In various embodiments, the diameter of the outer core  4  may range from 0.175 inches to 2.375 inches, though as previously mentioned, any dimensions listed for the various components of the present invention should not be considered to be limiting and may vary in different embodiments. 
     In the preferred embodiment, the first end plate  1  and the second end plate  2  are each constructed of a polyether ether ketone (PEEK) material, though the material of the first end plate  1  and the second end plate  2  may vary in different embodiments. PEEK is increasingly employed as a biomaterial for trauma treatments, orthopedic, and spinal implants. It is inherently strong, inert, and biocompatible. Properties that make PEEK a material of choice for the end plates include: modulus similar to bone, reduced stress shielding, artifact-free imaging, and an osteoconductive surface for bone on-growth. Alternatively or additionally, PEEK material can be used in combination with a titanium material or with a titanium plasma spray on the external surfaces of the outer core  4 . The first end plate  1  and the second end plate  2  may be externally treated with a titanium material in order to promote strength, abrasion resistance, and friction reduction. 
     In the preferred embodiment, as shown in  FIGS. 1-6 , the first end plate  1  and the second end plate  2  each comprise a plate body  20 , an inner side  21 , an outer side  22 , a plate convexity  23 , and a concavity  24 , wherein a thickness of the plate body  20  extends between the inner side  21  and the outer side  22 . In various embodiments, the diameter of the plate body  20  may range from 0.375 inches to 2.5 inches, while the thickness may range from 0.031 inches to 0.375 inches, but it should be understood herein that various dimensions of the present invention may vary without departing from the intended spirit and scope of the present invention. 
     In the preferred embodiment, the plate body  20  of the first end plate  1  and the plate body  20  of the second end plate  2  are oriented at a specified tilt angle  6  to each other, as illustrated in  FIG. 1 . The specified tilt angle  6  defines a deviation of the plate bodies of the first end plate  1  and second end plate  2  from being oriented parallel to each other. The specified tilt angle  6  may vary in different embodiments, mainly to correspond with different spinal disc types to replace. In various embodiments, the specified tilt angle  6  may range from 0.5 degrees to 15 degrees. In some embodiments, the specified tilt angle  6  may be less than 0.5 degrees. In some embodiments, the specified tilt angle  6  may be 0 degrees, such that the first end plate  1  and the second end plate  2  are oriented parallel to each other. In some embodiments, the specified tilt angle  6  may exceed 15 degrees. 
     The plate convexity  23  is centrally positioned on the outer side  22  of the plate body  20  for each of the first end plate  1  and the second end plate  2 , similarly, the concavity  24  is centrally positioned on the inner side  21  of the plate body  20  for each of the first end plate  1  and the second end plate  2 . In some embodiments, the thickness of the plate body  20  is constant, and the plate convexity  23  and the concavity  24  are formed through a deviation from the generally flat geometry of the plate body  20 , such that the thickness of the end plates at the plate convexity  23  and concavity  24  is equal to the thickness of the end plates at their perimeter. In other embodiments, the plate convexity  23  and the concavity  24  of the first end plate  1  and the second end plate  2  may be formed independently of each other. In some embodiments, a fillet may be formed between the plate body  20  and the plate convexity  23  with a radius of, for example, but not limited to, a range from 0.015 inches to 0.5 inches. The fillet serves to reduce any polymeric stress due to vertical localized compression forces on the first and second end plates  2 . The first core convexity  30  is positioned within the concavity  24  of the first end plate  1 , and the second core convexity  31  is positioned within the concavity  24  of the second end plate  2 . 
     As previously mentioned, the outer core  4  is connected between the first end plate  1  and the second end plate  2  through the plurality of interlocking members  5 . In some embodiments, the inner core  3  is further connected between the first end plate  1  and the second end plate  2  in the same manner through the plurality of interlocking members  5 , though this is not considered a requirement. More particularly, the inner side  21  of the first end plate  1  is connected to the outer core  4  through the plurality of interlocking members  5 , and the inner side  21  of the second end plate  2  is connected to the outer core  4  opposite the first end plate  1  axially along the inner core  3  through the plurality of interlocking members  5 . 
     In some embodiments, the first end plate  1  and the second end plate  2  each further comprise an attachment flange  25  and at least one fastener aperture  26 . The attachment flange  25  may be used to anchor the present invention to adjoining vertebrae through one or more implant screws. The inclusion of the attachment flange  25  in various embodiments will depend on end product requirements. The attachment flange  25  is perpendicularly and perimetrically connected to the plate body  20 , and extends away from the inner side  21 , past the outer side  22  for each of the first end plate  1  and the second end plate  2 , wherein the attachment flange  25  is connected along a flange arc segment of the perimeter of the plate body  20 . Preferably, the attachment flange  25  does not extend past the inner side  21 , though this may vary in different embodiments. The at least one fastener aperture  26  traverses through the attachment flange  25  for each of the first end plate  1  and the second end plate  2 . Each of the at least one fastener aperture  26  may be a counterbore hole, a countersink hole, a through hole, or other types of holes suitable for receiving various fasteners in different embodiments. 
     Furthermore, in some embodiments, the attachment flange  25  comprises an inner groove  27 . The inner groove  27  traverses into and radially through the attachment flange  25  along the flange arc segment adjacent to the outer side  22  of the plate body  20  and adjacent to a perimeter of the plate body  20  for each of the first end plate  1  and the second end plate  2 . The inner groove  27  serves to provide clearance to the edge of adjoining vertebra where the total disc replacement is being performed to reduce any wear from vertebral edges. 
     In the preferred embodiment, referring to  FIGS. 2 and 5-7 , the outer core  4  comprises a first plurality of core interlocking members  50  and a second plurality of core interlocking members  51  from the plurality of interlocking members  5 , wherein the first plurality of core interlocking members  50  and the second plurality of core interlocking members  51  are positioned axially opposite each other along the outer core  4 . Further, the first end plate  1  and the second end plate  2  each further comprise a plurality of plate interlocking members  52  from the plurality of interlocking members  5 . The plurality of plate interlocking members  52  is positioned concentrically around the convexity on the inner side  21  of the plate body  20  for each of the first end plate  1  and the second end plate  2 . The first plurality of core interlocking members  50  of the outer core  4  is engaged with the plurality of plate interlocking members  52  of the first end plate  1 , and the second plurality of core interlocking members  51  of the outer core  4  is engaged with the plurality of plate interlocking members  52  of the second end plate  2 . 
     Furthermore, in some embodiments, the present invention further comprises a plurality of interlocking member receiving channels  7 , as shown in  FIGS. 2, 5, 6, and 8 . Each of the plurality of interlocking member receiving channels  7  is positioned concentrically with and adjacent to one of the plurality of interlocking members  5 , and each of the plurality of interlocking members  5  is positioned within one of the plurality of interlocking member receiving channels  7 . The plurality of interlocking members  5  and the plurality of interlocking member receiving channels  7  are configured to resist extrusion of the inner core  3  and outer core  4  when the inner core  3  and outer core  4  are subject to external forces. The specific configuration and shape of the plurality of interlocking members  5  and the plurality of interlocking member receiving channels  7  may vary in different embodiments. For example, in some embodiments, the plurality of interlocking members  5  and the plurality of interlocking member receiving channels  7  have a dovetail mating configuration as shown in  FIGS. 2 and 5-8 , wherein a cross section width of each of the plurality of interlocking members  5  increases with distance away from the axial center of the outer core  4 , and wherein each of the plurality of interlocking member receiving channels  7  is shaped inversely to the plurality of interlocking members  5  to accommodate them. In some embodiments, a cross section of each of the plurality of interlocking members  5  resembles a “tooth”, having an angled protrusion with a circular element at the end, wherein the cross section of the interlocking member receiving channels  7  would have correspondingly negative geometry to receive the tooth. In either case, the distal geometry of the interlocking members  5  has a greater radial width than the remainder of the interlocking members  5 , facilitating securement of the interlocking members  5  within the interlocking member receiving channels  7 . Alternatively, in some embodiments, the interlocking members  5  and receiving channels  7  may not vary in thickness, as shown in  FIG. 9 . 
     More particularly,  FIGS. 9-11  illustrate an alternative embodiment wherein each of the plurality of interlocking members  5  is oriented at a specified anti-extrusion angle  53  in order to adequately resist extrusion of the inner core  3  and/or outer core  4  as previously described. In such an embodiment. More particularly, each of the first plurality of core interlocking members  50 , the second plurality of core interlocking members  51 , and the plurality of plate interlocking members  52  is oriented at the specified anti-extrusion angle  53 . The specified anti-extrusion angle  53  may be defined in various ways, but herein the specified anti-extrusion angle  53  is defined in relation to a central axis  15  of the present invention. The central axis  15  may be considered to be an axis about which the radial features of the present invention, such as, but not limited to the inner core  3  and the outer core  4 , and the plate body  20  are positioned concentrically about. Separate central axes may be defined as appropriate for the inner core  3 , outer core  4 , and plate body  20  in order to account for any angular discrepancies due to the specified tilt angle  6 . 
     It may be understood herein that due to the specified tile angle  6 , true central axes of the plate body  20 , inner core  3 , and/or outer core  4  may not be positioned exactly coincidental with each other. However, that is considered to be the case herein for the sake of simplicity. 
     It is important to define herein that the specified anti-extrusion angle  53  should be oriented radially outward from the central axis, such that an imaginary line extending outward from any given member of the first plurality of core interlocking members  50  or the second plurality of core interlocking members  51  does not intersect with the central axis. This is important because an inwardly-oriented anti-extrusion angle  53  would not be effective or as effective and may not provide effective interlock as an outwardly-oriented anti-extrusion angle. 
     As previously mentioned, the plurality of interlocking members  5  and the plurality of interlocking member receiving channels  7  function primarily to secure the inner core  3  to the first end plate  1  and the second end plate  2 , but also secondarily to resist extrusion of the outer core  4  (and inner core  3 , in applicable embodiments) when the present invention is subjected to external forces, compressive forces in particular. When the present invention is subjected to an axial compressive force, the inner core  3  and outer core  4  will tend to deform a certain amount in compression axially and in expansion laterally. Thus, is it a concern that subject to such forces, portions of the inner core  3  and outer core  4  will “extrude” out of their designated positions and potentially become misaligned or damaged. The plurality of interlocking member receiving channels  7  may function to provide some space to accommodate such extrusion, and moreover the physical interlocking between the interlocking members  5  and interlocking member receiving channels  7  prevents the inner core  3  and outer core  4  from becoming dislodged from their positions relative to the first end plate  1  and the second end plate  2 . The quantity of both the plurality of interlocking members  5  and the plurality of interlocking member receiving channels  7  may vary in different embodiments, from 1 to 9, for example, though any quantity of interlocking members  5  and interlocking member receiving channels  7  may be included as desired in various embodiments. 
     As previously mentioned, in various embodiments, the first end plate  1  and the second end plate  2  may be oriented at a specified tilt angle  6  to each other in order to imitate the geometry of a spinal disc to be replaced by the present invention. As such, the plate body  20  of the first end plate  1 , the plate body  20  of the second end plate  2 , the inner core  3  and the outer core  4  may be understood to extend in a longitudinal direction between a proximal end  8  and a distal end  9 . The proximal end  8  and the distal end  9  are positioned diametrically opposite each other for each of the plate body  20 , the inner core  3 , and the outer core  4 . The proximal ends  8  are defined herein to be radially aligned with each other and the distal ends  9  are radially aligned with each other for each of the plate bodies of the first end plate  1  and the second end plate  2 , the inner core  3 , and the outer core  4 . Thus, in some embodiments, the specified tilt angle  6  is defined in a plane coincident with the proximal ends  8  and the distal ends  9 . In some embodiments comprising the flange attachment, the flange attachment is positioned at the proximal end  8  for each of the first end plate  1  and the second end plate  2 . In various embodiments, the orientation and alignment of the specified tilt angle  6  may vary however, and should not be considered to be limited to the foregoing description. 
     Moreover, referring to  FIGS. 7-8 , in some embodiments, the specified tilt angle  6  may be realized through a diametrical difference in thickness of the inner core  3  and the outer core  4 , so that the axial outer ends of the inner core  3  and outer core  4  are oriented at the specified tilt angle  6  to each other, and thus the first end plate  1  and the second end plate  2 , being generally flat, are oriented at the specified tilt angle  6  to each other as a result. As such, a proximal thickness  10  and a distal thickness  11  of both the inner core  3  and the outer core  4  may be defined, wherein the proximal thickness  10  of the outer core  4  is the thickness of the outer core  4  at the proximal end  8  of the outer core  4 , the distal thickness  11  of the outer core  4  is the thickness of the outer core  4  at the distal end  9  of the outer core  4 , the proximal thickness  10  of the inner core  3  is the thickness of the inner core  3  at the proximal end  8  of the inner core  3 , and the distal thickness  11  of the inner core  3  is the thickness of the inner core  3  at the distal end  9  of the inner core  3 . 
     Thus, in some embodiments, the proximal thickness  10  of the inner core  3  is greater than the distal thickness  11  of the inner core  3 , and the proximal thickness  10  of the outer core  4  is greater than the distal thickness  11  of the outer core  4 . Thus, the specified tilt angle  6  may be determined in some embodiments by the difference between the proximal thicknesses  10  and the distal thicknesses  11 . In other embodiments, the specified tilt angle  6  may be determined through other means; for example, the thickness of the inner core  3  and outer core  4  may be constant, while the thickness of the first end plate  1  and second end plate  2  may vary instead. 
     In some embodiments of the present invention, as shown in  FIG. 9 , as an alternative to the attachment flange  25 , the first end plate  1  and the second end plate  2  further comprise a plurality of anchoring protrusions  12 . The plurality of anchoring protrusions  12  serve as an alternative means of mounting the first end plate  1  and the second end plate  2  to adjacent vertebrae. The anchoring protrusions  12  are connected to the outer side  22  and are preferably oriented perpendicular to the plate body  20 . The anchoring protrusions  12  are distributed around the outer side  22  in any desirable configuration, such as, but not limited to, four anchoring protrusions positioned in a concentric 90 degree pattern around the plate convexity  25 . Furthermore, each of the anchoring protrusions  12  may comprise a plurality of teeth  13  positioned at a distal end  14  of the anchoring protrusions  12 . 
     The components of the present invention may be manufactured through any desirable manufacturing process, such as, but not limited to, 3D printing, CNC machining, injection molding, compression bolding, or other manufacturing processes. The inner core  3  is preferably injection molded through an insert molding process where the first end plate  1  and the second end plate  2  serve as inserts. Alternatively, the inner core  3  can be produced independently through an injection molding, compression molding, or 3D printing process and is subsequently assembled with the first end plate  1  and the second end plate  2 . The outer core  4  is preferably either injection molded or compression molded using an insert molding process where an assembly of the first end plate  1 , second end plate  2 , and inner core  3  serve as inserts. Alternatively, the outer core  4  can be produced independently through injection molding, compression molding, or 3D printing and subsequently assembled with the first end plate  1 , second end plate  2 , and inner core  3 . Furthermore, in the preferred embodiment, at every stage of assembly of the present invention, the external surfaces of the various components of the present invention are treated to increase surface bonding to achieve sufficient covalent, cohesive and/or adhesive bonds. 
     Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.