Patent Publication Number: US-11376130-B2

Title: Intervertebral prosthetic disc

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/167,763, filed May 27, 2016, now U.S. Pat. No. 10,357,376, which is a continuation of U.S. patent application Ser. No. 14/287,709, filed May 27, 2014, now U.S. Pat. No. 10,342,671 which is a continuation of Ser. No. 12/759,460 filed Apr. 13, 2010, which is a continuation of Ser. No. 12/101,664 filed Apr. 11, 2008, now U.S. Pat. No. 10,342,670, which application is a continuation of Ser. No. 10/855,817 filed May 26, 2004 (now U.S. Pat. No. 7,442,211), which is a non-provisional of U.S. Provisional Application Nos. 60/473,802 and 60/473,803, both of which were filed May 27, 2003; the full disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to medical devices and methods. More specifically, the invention relates to a prosthetic disc for intervertebral insertion, such as in the lumbar and cervical spine. 
     In the event of damage to a lumbar or cervical intervertebral disc, one possible surgical treatment is to replace the damaged disc with a disc prosthesis. Several types of intervertebral disc prostheses are currently available. For example, one type of intervertebral disc prosthesis is provided by Waldemar Link GmbH &amp; Co under the trademark LINK® SB Charite. This prosthesis includes upper and lower prosthesis plates or shells which locate against and engage the adjacent vertebral bodies, and a low friction core between the plates. The core has upper and lower convexly curved surfaces and the plates have corresponding, concavely curved recesses which cooperate with the curved surfaces of the core. This allows the plates to slide over the core to allow required spinal movements to take place. The curved recesses in the plates are surrounded by annular ridges which locate, at the limit of sliding movement of the plates over the core, in opposing upwardly and downwardly facing, peripheral channels surrounding the curved surfaces of the core. 
     This type of disc configuration is described in EP 1142544A1 and EP 1250898A1, assigned to Waldemar Link GmbH &amp; Co. A drawback of such configurations is that the provision of the peripheral ribs and channels limits the areas available for bearing and sliding contact between the plates and core, and accordingly the loads which can be transmitted by the prosthesis. As a result of the relatively small bearing areas, it is believed that at least the core will be subject to rapid wear and have a relatively short lifespan. Also, because the core is in effect merely “clamped” between the plates, this configuration does not allow for secure retention of the core. In one alternative arrangement, the curved surfaces of the core carry opposing, elongate keys that locate in elongate grooves in the plates and another alternative arrangement in which the plates have opposing elongate keys that locate in elongate grooves in the opposite curved surfaces of the core. These key and groove arrangements allow the plates to slide over the core within the limits of the length of the grooves, in one direction only. Although allowance is made for some lateral play of the keys in the grooves, very little sliding movement of the plates over the core can take place in the orthogonal vertical plane, and this is considered to be a serious drawback of this design. 
     Other currently available intervertebral disc prostheses have similar and/or other drawbacks. Typically, drawbacks include insufficient resistance to wear and tear, restricted range of motion and/or insufficient ability of the prosthesis to adhere to vertebral bone. 
     Therefore, a need exists for improved intervertebral disc prostheses. Ideally, such improved prostheses would resist wear and tear, provide a desired range of motion and adhere well to vertebral bone. At least some of these objectives will be met by the present invention. 
     2. Description of the Background Art 
     Published US patent applications 2002/0035400A1 and 2002/0128715A1 describe disc implants which comprise opposing plates with a core between them over which the plates can slide. The core receives one or more central posts, which are carried by the plates and which locate in opposite ends of a central opening in the core. Such arrangements limit the load bearing area available between the plates and core. 
     Other patents related to intervertebral disc prostheses include U.S. Pat. Nos. 4,759,766; 4,863,477; 4,997,432; 5,035,716; 5,071,437; 5,370,697; 5,401,269; 5,507,816; 5,534,030; 5,556,431; 5,674,296; 5,676,702; 5,702,450; 5,824,094; 5,865,846; 5,989,291; 6,001,130; 6,022,376; 6,039,763; 6,139,579; 6,156,067; 6,162,252; 6,315,797; 6,348,071; 6,368,350; 6,416,551; 6,592,624; 6,607,558 and 6,706,068. Other patent applications related to intervertebral disc prostheses include U.S. Patent Application Publication Nos.: 2003/0009224; 2003/0074076; 2003/0191536; 2003/0208271; 2003/0135277; 2003/0199982; 2001/0016773 and 2003/0100951. Other related patents include WO 01/01893A1, EP 1344507, EP 1344506, EP 1250898, EP 1306064, EP 1344508, EP 1344493, EP 1417940, EP 1142544, and EP 0333990. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect of the present invention, an intervertebral prosthetic disc for insertion between adjacent vertebrae comprises: upper and lower plates having outer surfaces locatable against the respective vertebrae and inner, curved surfaces; a core between the plates, the core having upper and lower curved surfaces complementary in shape to the inner, curved surfaces of the plates to allow the plates to slide over the core; and at least one projection extending from at least one of the upper and lower curved surfaces of the core into at least one recess of one of the inner surfaces of the plates, the recess being oversize with respect to the projection to allow sliding movement of the plate over the core while retaining the core between the plates during such sliding movement. 
     Some embodiments further include multiple projections extending from the upper and lower surfaces of the core. For example, the multiple projections may include two elevated rings projecting from a peripheral portion of each of the upper and lower surfaces of the core into ring-shaped recesses on the upper and lower plates. In other embodiments, the multiple projections may comprise multiple surface features projecting from a peripheral portion of each of the upper and lower surfaces of the core into multiple recesses on the upper and lower plates. In yet other embodiments, the multiple projections may comprise respective ends of an elongate, upright element extending axially through the core, the ends projecting beyond the upper and lower core surfaces. For example, the upright element may comprise a rod extending through an axial passage through the core. In some embodiments, such a rod and passage may be complementarily threaded for engagement with one another. 
     In some embodiments, the disc further includes at least one fin extending from each of the outer surfaces of the plates to promote attachment of the plates to the vertebrae. In some embodiments, each fin extends from its respective outer surface at a 90.degree. angle. In other embodiments, each fin extends from its respective outer surface at an angle other than 90.degree. In some embodiments, each fin includes at least one hole for promoting attachment of the plates to the vertebrae. For further promoting attachment of the plates to the vertebrae some embodiments include outer surfaces of the plates that are textured. For example, in some embodiments the textured surfaces comprise multiple serrations. 
     The plates may have any of a number of different configurations, sizes, or the like. In one embodiment, the outer surfaces of the plates are flat. In one embodiment, lateral edge portions of the upper and lower plates are adapted to contact one another during sliding movement of the plates over the core. 
     In another aspect of the present invention, an intervertebral prosthetic disc for insertion between adjacent vertebrae comprises: upper and lower plates having outer surfaces locatable against the respective vertebrae and inner, curved surfaces, at least one of the inner surfaces having at least one recess; a core between the plates, the core having upper and lower curved surfaces complementary in shape to the inner, curved surfaces of the plates to allow the plates to slide over the core, and an axial passage extending through the core; and a rod extending through the axial passage into the at least one recess in the inner surface(s) of the plate(s). The recess are oversize with respect to the projection to allow sliding movement of the plate over the core while retaining the core between the plates during such sliding movement. 
     Optionally, the rod and passage may be complementarily threaded for engagement with one another. In some embodiments, the rod is movably engaged with a first oversized recess on the upper plate and a second oversized recess on the lower plate. In various embodiments, the plates and core may have any of the features or characteristics described above. 
     In another aspect of the invention, an intervertebral prosthetic disc for insertion between adjacent vertebrae includes: upper and lower plates having outer surfaces locatable against the respective vertebrae and inner, curved surfaces; a core between the plates, the core having upper and lower curved surfaces complementary in shape to the inner, curved surfaces of the plates to allow the plates to slide over the core; and a flexible tie member extending laterally through the core and having ends outside the core which are engaged with one or both of the plates to retain the core between the plates when the plates slide over the core. The flexible tie member, for example, may extend through a lateral passage through the core and may include ends engaged with at least one of the upper and lower plates. In some embodiments, the flexible tie member comprises a flexible cable or cord. 
     In yet another example of the present invention, an intervertebral prosthetic disc for insertion between adjacent vertebrae comprises: upper and lower plates having textured outer surfaces locatable against the respective vertebrae, each of the outer surfaces having at least one vertical fin and an edge portion adapted to contact a corresponding edge portion of the other plate, and inner, curved surfaces; and a core between the plates, the core having upper and lower curved surfaces complementary in shape to the inner, curved surfaces of the plates to allow the plates to slide over the core. The curved surfaces of the plates and core include formations which cooperate with one another to retain the core between the plates when the plates slide over the core. The formations include recesses and projections received by the recesses, and the recesses and projections are located between a central axis of the relevant curved surface and an outer periphery thereof. 
     In some embodiments, for example, the projections may comprise two elevated rings projecting from a peripheral portion of each of the upper and lower surfaces of the core into ring-shaped recesses on the upper and lower plates. In other embodiments, the projections may comprise multiple surface features projecting from a peripheral portion of each of the upper and lower surfaces of the core into multiple recesses on the upper and lower plates. Again, the plates and core may include any of the features described above. 
     These and other aspects and embodiments are described more fully below with reference to the drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a cross-sectional anterior view of a prosthetic disc according to one embodiment of the invention, with the prosthesis plates and core in vertical alignment; 
         FIG. 2  shows a cross-sectional side view of the disc of  FIG. 1 , after sliding movement of the plates over the core; 
         FIG. 3  shows a cross-sectional side view of the disc of  FIG. 1 , after translational movement of the plates relative to the core; 
         FIG. 4  shows a cross-sectional side view of the disc of  FIG. 1 , with the plates and core in vertical alignment; 
         FIG. 5  shows a plan view of the core of the disc of  FIG. 1 ; 
         FIG. 6  shows a plan view of the upper plate of the disc of  FIG. 1 ; 
         FIG. 6A  shows a plan view of a disc, as in  FIGS. 1 and 6 , with a fin rotated away from the anterior-posterior axis; 
         FIG. 7  shows a cross-sectional anterior view of a prosthetic disc according to another embodiment of the invention with a flexible tie member engaged with one plate and  FIG. 7A  shows a cross-sectional anterior view of another prosthetic disc with a flexible tie member engaged with both plates; 
         FIG. 8  shows a cross-sectional side view of the prosthetic disc of  FIG. 7 ; 
         FIG. 9  shows a cross-sectional anterior view of a prosthetic disc according to another embodiment of the invention; 
         FIG. 10  shows a cross-sectional side view of the prosthetic disc of  FIG. 9 ; and 
         FIG. 11  shows a cross-sectional side view of another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1-4  illustrate a prosthetic disc  10  for intervertebral insertion between two adjacent spinal vertebrae (not shown). The disc  10  comprises three components, namely an upper plate or shell  12 , a lower plate or shell  14  and a core  16  located between the plates. 
     The upper plate  12  includes an outer surface  18  and an inner surface  24  and may be constructed from any suitable material or combination of materials, such as but not limited to cobalt chrome molybdenum, titanium (such as grade  5  titanium) and/or the like. In one embodiment, typically used in the lumbar spine, the upper plate  12  is constructed of cobalt chrome molybdenum, and the outer surface  18  is treated with aluminum oxide blasting followed by a titanium plasma spray. In another embodiment, typically used in the cervical spine, the upper plate  12  is constructed of titanium, the inner surface  24  is coated with titanium nitride, and the outer surface  18  is treated with aluminum oxide blasting. An alternative cervical spine embodiment includes no coating on the inner surface  24 . In some embodiments, it may be useful to couple two materials together to form the inner surface  24  and the outer surface  18 . For example, the upper plate  12  may be made of an MRI-compatible material, such as titanium, but may include a harder material, such as cobalt chrome molybdenum, for the inner surface  24 . Any suitable technique may be used to couple materials together, such as snap fitting, slip fitting, lamination, interference fitting, use of adhesives, welding and/or the like. Any other suitable combination of materials and coatings may be employed in various embodiments of the invention. 
     In some embodiments, the outer surface  18  is planar. Oftentimes, the outer surface  18  will include one or more surface features and/or materials to enhance attachment of the prosthesis  10  to vertebral bone. For example, the outer surface  18  may be machined to have a serrations  20  or other surface features for promoting adhesion of the upper plate  12  to a vertebra. In the embodiment shown ( FIG. 6 ), the serrations  20  extend in mutually orthogonal directions, but other geometries would also be useful. Additionally, the outer surface  18  may be provided with a rough microfinish formed by blasting with aluminum oxide microparticles or the like. In some embodiments, the outer surface may also be titanium plasma sprayed to further enhance attachment of the outer surface  18  to vertebral bone. 
     The outer surface  18  may also carry an upstanding, vertical fin  22  extending in an anterior-posterior direction. The fin  22  is pierced by transverse holes  23 . In an alternative embodiment, as shown in  FIG. 6A , the fin  22  may be rotated away from the anterior-posterior axis, such as in a lateral-lateral orientation, a posterolateral-anterolateral orientation, or the like. In some embodiments, the fin  22  may extend from the surface  18  at an angle other than 90.degree. Furthermore, multiple fins  22  may be attached to the surface  18  and/or the fin  22  may have any other suitable configuration, in various embodiments. In some embodiments, such as discs  10  for cervical insertion, the fins  22 ,  42  may be omitted altogether. 
     The lower plate  14  is similar to the upper plate  12  except for the absence of the peripheral restraining structure  26 . Thus, the lower plate  14  has an outer surface  40  which is planar, serrated and microfinished like the outer surface  18  of the upper plate  12 . The lower plate  14  optionally carries a fin  42  similar to the fin  22  of the upper plate. The inner surface  44  of the lower plate  14  is concavely, spherically curved with a radius of curvature matching that of the inner surface  24  of the upper plate  12 . Once again, this surface may be provided with a titanium nitride or other finish. 
     The core  16  of the disc  10  is made of a low-friction material, such as polyethylene (Chirulen™). In alternative embodiments, the core  16  may comprise any other suitable material, such as other polymers, ceramics or the like. For wear resistance, the surface zones of the core  16  may be hardened by an appropriate cross-linking procedure. A passage  32  extends axially through the core. The passage is provided with an internally threaded sleeve  33  of titanium or other suitable material. An elongate element in the form of a round cross-section, threaded rod  34  extends axially through the passage and is in threaded engagement with the sleeve  33 . The length of the rod is greater than the axial dimension of the core, with the result that the opposite ends  36  of the rod project from the curved surfaces  28  and  30  of the core. In the assembled disc  10 , these ends  36  locate in the recesses  26 . The diameter of the rod is less than that of the recesses  26  so there is substantial room for the rod ends to move laterally in the recesses. 
     In use, the disc  10  is surgically implanted between adjacent spinal vertebrae in place of a damaged disc. The adjacent vertebrae are forcibly separated from one another to provide the necessary space for insertion. The disc is inserted, normally in a posterior direction, into place between the vertebrae with the fins  22 ,  42  of the plates  12 ,  14  entering slots cut in the opposing vertebral surfaces to receive them. After insertion, the vertebrae, facets, adjacent ligaments and soft tissues are allowed to move together to hold the disc in place. The serrated and microfinished surfaces  18 ,  40  of the plates  12 ,  14  locate against the opposing vertebrae. The serrations  20  and fins  22 ,  42  provide initial stability and fixation for the disc  10 . With passage of time, enhanced by the titanium surface coating, firm connection between the plates and the vertebrae will be achieved as bone tissue grows over the serrated surface. Bone tissue growth will also take place about the fins  22 ,  40  and through the transverse holes  23  therein, further enhancing the connection which is achieved. 
     Referring to  FIG. 5 , the core  16  may be formed with narrow, angularly spaced, blind passages  61  which accommodate titanium pins  64 . In many embodiments, the core  16  itself is transparent to X-radiation and so is invisible in a post-operative X-ray examination. The pins  64  serve as radiographic markers and enable the position of the core  16  to be ascertained during such examination. 
     In the assembled disc  10 , the complementary and cooperating spherical surfaces of the plates and core allow the plates to slide or articulate over the core through a fairly large range of angles and in all directions or degrees of freedom, including rotation about the central axis  40 .  FIGS. 1 and 4  show the disc  10  with the plates  12 ,  14  and core  16  aligned vertically with one another on the axis  40 .  FIG. 2  illustrates a situation where maximum anterior flexion of the disc has taken place. Such flexion is enabled by the ability of the ends  36  of the rod to move laterally in all directions and through a fairly large distance, in the recesses  26 . At the position of maximum flexion, the ends  36  of the rod abut the sides of the recesses as illustrated. At the same time, the plates  12 ,  14  abut one another at the periphery of their curved surfaces. Similar principles apply to maximum posterior flexure of the plates  12 ,  14  over the core, i.e. during spinal extension and/or in the event of maximum lateral flexure. 
       FIG. 3  illustrates how the disc  10  can also allow for translational movement of the plates relative to the core. In the illustrated situation there has been lateral translation of the plates relative to the core. The limit of lateral translation (not shown) is again reached when the ends  36  of the rod abut laterally against the sides of the recesses  26 . 
     In each case, the cooperating retaining formations, i.e. the ends  36  of the rod and the recesses  26  cooperate with one another to prevent separation of the core from the plates. In other words, the cooperation of the retaining formations ensures that the core is held captive between the plates at all times during flexure of the disc  10 . In other embodiments of this version of the invention, the rod can be mounted fixedly to the core by means other than the illustrated threaded connection. In other embodiments, the rod may be replaced by separate elements projecting respectively from the upper and lower curved surfaces of the core. 
       FIGS. 7 and 8  illustrate another embodiment of the invention. In this embodiment, the core  16  is formed with a lateral passage  50  extending diametrically through it. The passage is provided with a sleeve  52  of titanium or other suitably wear resistant material. A flexible tie means, in this embodiment in the form of a cable  54  of braided titanium construction, passes with clearance through the sleeve  52 . The ends of the cable  54  are flexed upwardly and enter passages  56  in the upper plate  12 . The extremities of the cable carry crimped retention lugs or ferrules  58  anchored in blind ends of the passages  56 . The flexible tie member  54  extends laterally through the core  16  and has ends outside the core which are engaged with one ( FIG. 7 ) or both ( FIG. 7A ) of the plates  12 ,  14  to retain the core between the plates when the plates slide over the core. 
     The cable  54  holds the core  16  captive during sliding movement of the plates  12 , 14  over the core, whether in flexion, extension or translation. The cable can flex through a wide range of angles to allow sliding movement or articulation of the plates relative to the core to take place. The slack in the cable also allows a degree of rotational movement of the plates relative to the core. As illustrated in  FIG. 7 , the ends of the passage  50  and sleeve  52  are belled to accommodate movements of the cable during sliding movements. Also, surfaces  60  of the plates  12 ,  14  are inclined to accommodate the cable when sliding has taken place, so that the cable does not act directly on the plates. 
       FIGS. 9 and 10  illustrate another embodiment of a prostheses  10 . In this embodiment, the curved surfaces  24  of the plates  12 ,  14  are formed, at positions between the central axis and their peripheries, with continuous, inwardly directed ribs  62  of annular shape. These ribs locate, with considerable clearance, in annular channels  64  provided at corresponding positions in the upper and lower curved surfaces of the core  16 . Once again, cooperation between the retaining formations, i.e. the ribs and channels, holds the core captive between the plates when the plates slide over the core during flexion, extension or translation. At the limit of sliding movement in each case, the rib  62  will abut against a side of the channel. The channel may be provided with a wear resistant lining as described previously. 
       FIG. 11  illustrates another embodiment of a prosthesis. In this case, the core carries continuous, annular ribs  70  on its upper and lower surfaces which locate with clearance in channels  72  in the plates  12 ,  14 . The ribs  70  may be lined with wear resistant material as described previously. 
     In each of the later versions, i.e. those of  FIGS. 7 to 11 , the core  16  may be provided with radiographic markers as described previously. Also, in each of these versions, the outer surfaces of the plates  12 ,  14  may have the same configuration as described in relation to the first version of  FIGS. 1 to 6 . 
     In  FIGS. 1-6 and 9-11 , embodiments are illustrated in which retaining formations are provided that cooperate with one another between both plates and the core. In other embodiments, core retention may be achieved by cooperation between retaining formations which only act between one of the plates, either the upper plate  12  or the lower plate  14 , and the core. In one embodiment, for example, there may be a single projection, which extends from the upper (or lower) curved surface of the core and a corresponding recess in the inner surface of the lower (or upper) plate. 
     Although the foregoing is a complete and accurate description of the invention, any of a number of modifications, additions or the like may be made to the various embodiments without departing from the scope of the invention. Therefore, nothing described above should be interpreted as limiting the scope of the invention at it is described in the claims.