Patent Publication Number: US-2019183537-A1

Title: Spinal implant assembly

Description:
FIELD OF THE INVENTION 
     The invention relates to a spinal implant assembly. More specifically the invention relates to assemblies with parts for implantation into intervertebral space between adjacent vertebrae of the spine. 
     BACKGROUND TO THE INVENTION 
     The spine or vertebral column comprises a plurality of separate vertebrae. The vertebrae are movable relative to one another, and separated from one another by fibrocartilage called inter-vertebral discs. 
     In its entirety, the spinal column is highly complex in that it houses and protects critical elements of the nervous system which have innumerable peripheral nerves and arterial and venous bodies in close proximity. In spite of these complexities, the spine is a highly flexible structure, capable of a high degree of curvature and twist through a wide range of motion. The intervertebral discs provide mechanical cushion between adjacent vertebrae. Genetic or developmental irregularities, trauma, chronic stress, tumors, and disease, however, can result in spinal pathologies which either limit this range of motion, or which threaten the critical elements of the nervous system housed within the spinal column. A variety of systems have been disclosed in the art which achieve immobilization by implanting artificial assemblies in or on the spinal column. 
     In order to treat certain injuries or conditions of the spinal column an intervertebral device may be placed in the intervertebral disc space to fuse or promote fusion of adjacent vertebrae. Such fusion devices are often used in combination with stabilisation systems wherein a metal rod that is bendable to match the natural curvature of the spine is mechanically attached at strategically selected vertebrae, allowing the rod to be rigidly fixed to the spine. This provides a rigid support to the spinal column. For this, pedicle screws located in the bone structure are typically fixed to a specially designed clamp to attach to a spinal rod. A problem with these stabilisation systems is that parts of the vertebra cannot stably receive a bone screw, or can only receive a bone screw screwed in at a certain angle. Also, for spinal fixings for small animals, within the confined spaces allowed therein, conventional rod anchoring methods are not suitable since the placement of the pedicle screw and the direction of the rod cannot be matched adequately. A system that can be used in small animals is needed, wherein confined spaces make conventional rod anchoring systems unsuitable. Furthermore, many devices for providing positioning of bone screws with respect to a stabilising rod loosen over time, providing an unstable joint. There is therefore a need for a solution that overcomes one or more of these problems. 
     SUMMARY OF INVENTION 
     According to a first aspect of the invention there is provided a spinal implant assembly comprising an intervertebral device configured to be installed in a spinal disc space, the intervertebral device having a head component and a body component, the spinal implant assembly further comprising a coupling body for coupling the head component of the intervertebral device and an elongate member, the coupling body and head component each having a longitudinal axis, wherein the head component can be received by the coupling body with the longitudinal axis of the head component at a selected angle within a predetermined range of angles relative to the longitudinal axis of the coupling body. Suitably the head component can be adjusted polyaxially relative to the coupling body. 
     The intervertebral device provides a stable anchorage for the spinal stabilisation system provided by the elongate member. 
     Suitably the spinal implant assembly can be adapted to provide a locked configuration, wherein the head component and/or elongate member are locked in position relative to the coupling body, and an adjustable configuration, wherein the position of the head component and/or elongate member relative to the coupling body can be adjusted. 
     Preferably the assembly further comprises an elongate member, the coupling body receiving the elongate member and the head component of the intervertebral device when assembled. 
     The head component and body component can be integral, however preferably are releasably attachable to one another. 
     Preferably the head component of the intervertebral device is releasably attachable to the body component via a threaded connection. 
     Preferably the head component has a head portion and a shank portion, the shank portion being at least partially externally threaded, the body component having a bore with a first open end, the bore being at least partially internally threaded, the internal threads of the bore corresponding with the external threads of the shank portion of the head component such that the head component is releasably attachable to the body component. 
     Preferably the head portion of the head component is at least partially spherical. 
     Preferably the coupling body comprises a hollow tubular body, the head portion of the head component being receivable in the hollow tubular body. 
     Preferably the coupling body has a first opening in a first end and a second opening in a second end, the first opening being larger in diameter than that of the head portion and the second opening being smaller in diameter than that of the head portion, a portion of the inner surface of the coupling body having a concavely curved inner surface, the curved inner surface corresponding with the at least partially spherical head portion, such that the head component may be positioned polyaxially relative to the coupling body when assembled. 
     Preferably the coupling body has at least a first slot. Suitably the elongate member suitably extends through the first slot when assembled with the coupling body. The slot communicates with the first open end of the coupling body. In some embodiments, when assembled, the elongate member can pivot relative to the coupling body, within the first slot, over a pre-determined range of motion. 
     Preferably the coupling body has a second slot. Suitably the elongate member extends through the second slot when assembled with the coupling body. The first and/or second slots preferably are elongate, the or each slot having a longitudinal axis parallel with the longitudinal axis of a bore of the coupling body. Where the elongate member is a rod, the elongate member will extend through both the first and second slots when assembled, the first and second slots effectively providing a rod receiving channel. 
     Preferably the elongate member comprises a rod. 
     Preferably the elongate member has a first end that is at least partially spherical. Preferably the elongate member has a second end that is at least partially spherical. 
     Preferably the assembly further comprises a washer for location between the head component and the elongate member when assembled. 
     Preferably the washer has first and second opposing surfaces, the first surface being concavely curved and facing the first end of the elongate member when assembled. Such a washer will be used to engage the elongate member when it has a first end that is at least partially spherical. 
     Preferably the washer has first and second opposing surfaces, the first surface having an elongate groove for receiving the elongate member when assembled. Such embodiments are suitable for use with a rod-like elongate member. 
     Preferably the washer has first and second opposing surfaces, the second surface being concavely curved and facing the head component when assembled. 
     Preferably at least part of the body component of the intervertebral device is externally tapered. 
     Preferably the body component has a proximal end and a distal end and the external taper of the body component tapers towards the proximal end of the bolt. In this context the term proximal used in relation to parts of spinal implants or spinal fixings means located nearer or towards the centre of the subject&#39;s body or spine when the implant part or fixing part is installed and distal means located away from the centre of the body or spine when the implant part or fixing part is installed. The term subject as used herein can be a human or animal subject. 
     The maximum diameter of the body component at any point along its longitudinal axis is greater than the opening in the second open end of the coupling body. In this way, the coupling body can be compact whilst the body component can be large in diameter, suitable for vertebral distraction and stable anchoring in the disc space. 
     Preferably at least part of the body component is externally threaded. 
     Preferably the body component has a hollow bore. 
     Preferably the head component has a shank portion insertable within the hollow bore of the body component, the shank portion of the head component being shorter in length than the hollow bore of the body component such that with the shank portion fully inserted in the body component, at least some hollow space in the hollow bore remains unoccupied by the shank portion. This allows for bone ingrowth into the body component when installed, thus improving the stability of the anchorage. 
     Preferably the body component has at least one aperture, the aperture communicating with the hollow bore. Suitably said at least one aperture is not obscured, or is only partially obscured, by the shank portion of the head component when assembled, such that the aperture communicates with the hollow bore when the spinal implant assembly is assembled. 
     Preferably at least part of the body component is hydroxyapatite coated. 
     Preferably the assembly further comprises a compression member for compressing the elongate member and the head component in locking engagement within the coupling body. 
     Preferably the compression member is a locking screw. The locking screw may be externally threaded, the coupling body having a bore with first and second open ends, at least part of the bore being internally threaded, the internal threads of the bore corresponding with the external threads of the locking screw. Preferably the assembly further comprises a ring, configured to be received around the coupling body when assembled. 
     There is also provided a spinal implant system comprising two or more spinal implant assemblies according to any previous aspect of the invention and an elongate member, wherein the assemblies are configured to be coupled together using the elongate member. This provides a system wherein a first implant assembly can be installed in a first disc space and a second implant assembly can be installed in a second, adjacent disc space, and the spine can be stabilised by the coupling of the implant assemblies using the elongate member. Further implant assemblies installed in further disc spaces can be assembled, all being coupled by a single elongate member. Alternatively a first implant assembly can be installed in a disc space and a second implant assembly can be installed in the same disc space. 
     The assembly can also be used as part of a spinal implant system comprising a spinal implant assembly according to any preceding claim and an elongate member, wherein the system further comprises a spinal fixing comprising a bone fastener configured to be installed into bone and a coupling body for receiving the bone fastener and said elongate member such that the elongate member couples the spinal implant assembly and spinal fixing when the system is assembled. The bone fastener may be a pedicle screw for example, suitable for installation into a vertebra. 
     There is also provided a kit for assembly into a spinal implant assembly or system, wherein the kit comprises the parts of the assembly according to any previous aspect of the invention. A modular kit can be provided wherein intervertebral devices of differing dimensions are provided, for example. 
     There is also provided a computer program embodied on a computer readable medium for manufacturing a spinal implant assembly or system to any previous aspect of the invention. 
     There is also provided a method of installing a spinal implant assembly, the method comprising the steps of providing a spinal implant assembly, the spinal implant assembly comprising an intervertebral device configured to be installed in a spinal disc space, the intervertebral device having a head component and a body component, the spinal implant assembly further comprising a coupling body for coupling the head component of the intervertebral device and an elongate member, the coupling body and head component each having a longitudinal axis, wherein the head component can be received by the coupling body with its longitudinal axis at a selected angle within a predetermined range of angles relative to the longitudinal axis of the coupling body, the method further comprising
         implanting the body component of the intervertebral device between adjacent vertebrae or between a vertebra and the sacrum;   coupling the intervertebral device with the coupling body, before or after implanting the body component, wherein the head component can be received by the coupling body such that its longitudinal axis is at a selected angle within a predetermined range of angles relative to the longitudinal axis of the coupling body.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the present invention will now be more particularly described by way of example only with reference to the accompanying drawings, wherein: 
         FIG. 1  is an exploded view of a spinal implant assembly; 
         FIG. 2  is a perspective view of the assembly of  FIG. 1 , assembled together; 
         FIG. 3  is a side view of the assembly of  FIG. 2 , but with the longitudinal axis of the intervertebral device shown non-parallel with that of the coupling body; 
         FIG. 4  is a cross-sectional view of the assembly of  FIG. 2 ; 
         FIGS. 5 to 7  show another embodiment, similar to that of  FIGS. 1 to 4 , but wherein the elongate member is a dumbbell rather than a rod; 
         FIG. 5  is an exploded view of a spinal implant assembly; 
         FIG. 6  is a perspective view of the assembly of  FIG. 4 , assembled together; 
         FIG. 7  is a cross-sectional view of the assembly of  FIG. 6 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present embodiments represent currently the best ways known to the applicant of putting the invention into practice. But they are not the only ways in which this can be achieved. They are illustrated, and they will now be described, by way of example only. 
     Referring to  FIG. 1 , this shows a spinal implant assembly  10  according to a first embodiment. The assembly can be used to fuse two or more vertebra together, in order and to provide stabilisation of the spine. The assembly  10  comprises an intervertebral device  20 , an elongate member  30  and a coupling body  40 . The assembly is designed such that the intervertebral device  20  can be coupled for multiaxial positioning relative to the coupling body  40  and elongate rod  30 . 
     The intervertebral device  20  comprises a body component  20   a  and a head component  20   b . The body component  20   a  of the intervertebral device is configured for installation in a spinal disc space between any two vertebrae of a subject, including the space between the sacrum and the adjacent vertebra. The body component  20   a  of the intervertebral device is a tapered bolt that can be used to induce fusion and distraction when implanted. The bolt  20   a  has a proximal end  21  and a distal end  22 , and is tapered towards the proximal end  21 . The external surface of the bolt  20   a  is threaded with deep threads for cutting into vertebral bone on either side of the spinal disc space. The threads are thin in section and very pronounced, to cut into the bone and aid the insertion process. 
     The bolt  20   a  has a hollow bore. The proximal end  21  is closed and the distal  22  end is open. Alternatively, the proximal end  21  may be open. The hollow bore is internally threaded, at least partially, at or near the distal end  22  of the bolt. 
     The bolt has a first elongate slot  23 , having a longitudinal axis running parallel with the longitudinal axis of the bolt  20 . The bolt has a second elongate slot opposite the first elongate slot (not visible in the figures). The bolt may have more than two elongate slots. The outer surface of the bolt  20  may have a hydroxyapatite coating to stimulate bone ingrowth. 
     The head component  20   b  of the intervertebral device has a head portion  51  and a shank portion  52 . The shank portion  52  has an externally threaded portion  53  and an enlarged shoulder  54 . The externally threaded shank portion  52  is receivable within the hollow bore of the bolt  20   a , the external threads of the shank portion  52  corresponding with the internal threads of the hollow bore of the bolt  20   a , such that the head component  20   b  is releasably attachable to the bolt  20   a . The enlarged shoulder  54  butts up against the distal end  22  of the bolt  20   a  when the shank portion  52  is fully inserted in the bolt  20   a.    
     The head portion  51  and shank portion  52  of the head component  20   b  are preferably integral with one another. The head portion  51  comprises a substantially spherical head with a female recess  55  at its distal end. The recess is hexagonal in shape. The recess  55  can receive a wrench or other torque-transferring tool, for transferring torque to the head component  20   b  during assembly, to assemble it to the bolt  20   a . Alternatively, the recess  55  may be a shape other than hexagonal, the shape being suitable for receiving torque transfer from a suitable tool. In an alternative embodiment the head portion  51  can comprise a part-spherical portion and removable rocker, to form a substantially complete ball end. The term part-spherical as used herein refers to a surface that comprises a portion of a sphere. 
     The coupling body  40  comprises a tubular, hollow body. The coupling body  40  has a bore  41  having first and second open ends. The first and second open ends each have an opening that is circular in shape  42 , 43 , the first opening communicating with first and second elongate slots  44 ,  45 , disposed in opposite sides of the coupling body  40 . The elongate slots  44 , 45  extend from the first opening  42 , part of the way down the side of the coupling body  40 . The elongate slots  44 ,  45  form a channel for receiving the elongate member  30  when assembled. The second opening  43 , in the proximal end, is smaller in diameter than the first opening  42 . The first opening  42  is large enough to receive the head portion  51  of the head component  20   b  therethrough. The second opening  43  is surrounded by a curved inner surface, internally to the coupling body  40 . The curvature of the curved inner surface corresponds to the curvature of the head portion  51 , such that the head portion  51  can pivot smoothly in the coupling body  40  within a pre-determined range of angles relative to the coupling body  40  when the head component  20   b  is received within the coupling body  40 . 
     The assembly further comprises a washer  60 , located between the head component  20   b  and the elongate member  30  when assembled. The washer  60  is circular in shape, having first and second opposing surfaces  61 ,  62  (top and bottom surfaces, or distal and proximal surfaces). The first surface  61  has an elongate groove  63  for receiving the elongate member  30  when assembled. The second surface  62  is concavely curved (not visible in the figures). The groove  63  in the first surface and concavely curved second surface form sockets for receiving the elongate member  30  and head portion  51  respectively. The intermediate conforming washer  60  increases the surface contact area that would exist between the head portion  51  and the elongate member  30 , if the washer were not present. The washer allows the distribution of loads evenly between the head portion  51  and the elongate member  30 . 
     In some embodiments the sockets in the washer conform in shape with the corresponding piece of the assembly to be received therein. In alternative embodiments, the first and second surfaces of the washer may include one or more points or edges that, when the assembly is subjected to compressive force by a locking member  70  (described below), bite into the respective members the washer engages with. The axial mouth of the groove  63  may have a transverse diameter that is smaller than the radius of the elongate member. Similarly the radius of curvature of the second surface  62  may be slightly less than the radius of curvature of the head portion  51 . This non-conformance between the sockets in the first and second surfaces of the washer and the corresponding head portion and elongate member provides an edge contact between the socket and the member to be received therein, which enhances the locking mechanism provided by the washer. 
     The elongate extension  30  is a rod. The rod may of course be long or short, and may be fixed to the subject using another fixing device at its end or at one or more points along the length of the rod. The rod may be longer than as shown in  FIGS. 1 to 3 . The rod may be straight or curved. The rod may be flexible, such that it can be curved into a desired shape by the surgeon during installation. 
     The assembly further comprises a locking screw  70 , which acts as a compression member in use, to compress the elongate member  30 , washer  60 , and head component  20   b  together, against the inside of the coupling body  40 , and therefore to lock the head component  20   b  at a selected angular orientation relative to the coupling body  40 . The locking screw  70  has a circular cross-section, and has externally threaded sides. The coupling body  40  has internal threading on at least part of its internal surface, near to the first opening  42 . The internal threads of the coupling body  40  correspond with the external threads of the locking screw  70 . The locking screw  70  can be screwed into the first opening  42  of the coupling body, thus providing a compressive force on the elongate member  30 , washer  60  and head component  20   b . The locking screw  70  has a hexagonal shaped recess  71  in its top surface (distal surface), which can receive a hexagonal shaped torque-transferring tool for tightening the locking screw  70  in threaded engagement in bore  41 . Alternatively the recess  71  may be a shape other than hexagonal, the shape being suitable for receiving torque transfer from a suitable tool. 
     The  FIG. 1  embodiment also includes a further optional feature, ring  80 . The ring  80  is a circular piece which is shaped and dimensioned to sit in a recessed region  46  in the outer wall of the distal end of the coupling body  40 , as shown assembled in  FIG. 2 . The ring  80  is placed in the recessed region  46 , the ring  80  butting up against a shoulder on the outer wall of the coupling body  40 . The ring  80  is usually placed around the coupling body  40  before the locking screw  70  is tightened. The ring  80  captivates the distal end of the coupling body  40 , preventing the split distal end of the coupling body from springing apart as the locking screw  70  is tightened. The ring is shown in the embodiment of  FIGS. 1 to 4 , but it is an optional part of the assembly. 
     In operation, in order to assemble the spinal implant assembly and install it in a subject, the shank portion  52  of the head component  20   b  is inserted, through the first opening  42 , then through the second opening  43  of the bore  41  of the coupling body  40 , until the head portion  51  butts up against the internal edges of the second opening  43 . A torque-transferring tool, such as a wrench, is received in recess  55  to threadedly secure the head component  20   b  to the bolt  20   a . The bolt  20   a  may already be installed in a subject&#39;s disc space or may be installed in a subject&#39;s disc space after the head component  20   b  with coupling body  40  assembled thereto is secured to the bolt  20   a.    
     When installing the bolt  20   a  in the subject it is inserted in the disc space between adjacent vertebrae or at the lumbo-sacral joint. The threads on the external surface of the bolt  20   a  cut into the bone during insertion. The hollow bore of the bolt  20   a  can be impregnated with bone graft before insertion of the bolt  20   a  in the subject. The subject&#39;s bone will ingrow, through the elongate slots  23 , and attach with the bone graft inside the hollow section of the bolt  20   a . This further anchors the bolt  20   a  in the subject. Even if no bone graft is inserted in the hollow of the bolt  20   a  before implantation of the bolt  20   a  into the subject, cutting of the subject&#39;s bone by the bolt threads as the bolt is inserted will create bone debris that will accumulate, via the elongate slots  23 , in the hollow bore of the bolt  20   a . The subject&#39;s bone will ingrow, through the elongate slots  23 , and attach with the accumulated bone debris, further anchoring the bolt  20   a  against rotation. 
     The washer is then inserted in the coupling body, with the second surface  62  facing the head component  20   b , then the elongate member  30  is inserted in the slots  44 ,  45  of the coupling body  40 . 
     With the assembly assembled as described above, the coupling body  40  can pivot relative to the anchored intervertebral device  20  (comprising the bolt  20   a  and head component  20   b ), giving rise to polyaxial positioning within a predetermined angle range. Therefore, the assembly is in this adjustable configuration, it provides a polyaxial or universal joint between the bolt  20   a  and the coupling body  40  and also between the bolt  20   a  and the elongate member  30 . The elongate extension can slide within the slots  44 ,  45 , relative to the coupling body  40 . The locking screw  70  can be tightened within the threaded bore  41 , with the ring  80  in place around the coupling body  40 , to compress the head component  20   b , washer  60  and elongate member  30  together, against the inside of the coupling body  40 , until the elongate member  30  and intervertebral device  20  are locked, relative to the coupling body, such that they can no longer be positionally adjusted. An assembled device is shown in  FIG. 2 . A further assembled device in which the longitudinal axis of the intervertebral device  20  is non-parallel with that of the coupling body  40  is shown in  FIG. 3 . 
     The spinal implant assembly can be provided as part of a system in which two or more spinal implant assemblies, as described above, are coupled by a single elongate member  30 . A first implant assembly can be installed in a first disc space and a second implant assembly can be installed in a second, adjacent disc space, and the spine can be stabilised by the coupling of the implant assemblies using the elongate member. Alternatively a first implant assembly can be installed in a disc space and a second implant assembly can be installed in the same disc space. 
     Instead of a bolt, the body component  20   a  may be an interbody cage. 
     The spinal implant assembly can also be provided as part of a system in which one or more spinal implant assemblies, as described above, are coupled to at least one spinal fixing having a simple pedicle screw or other bone fixing means, which is coupleable to the elongate member  30  via a suitable coupling body. 
       FIGS. 5 to 7  show an alternative embodiment for a spinal implant assembly  110  similar to that of  FIGS. 1 to 4 . The same reference numerals have been used in  FIGS. 5 to 7  to refer to components which are substantially the same as those in the previous embodiment. The implant assembly  110  differs from that of  FIGS. 1 to 4  in that the elongate member  130  in the  FIG. 5  embodiment has first and second ball ends  131 ,  132  joined by a rod portion  134 . Each ball end  131 ,  132  is substantially spherical, such that the elongate member  130  is like a dumbbell. Each ball end  131 ,  132  can have a diameter that is substantially the same as that of the head portion  51  of head component  20   b.    
     For the embodiment of  FIG. 5 , both the first and second surfaces  161  of the washer  160  will be concavely curved. The washer  161  has a notch  164  extending between the first surface  161  and the side of the washer. When assembled, the notch  164  faces toward the rod portion  134  of the elongate member  130 . 
     The coupling body  141  only has one slot  144  (although it can have a second slot on the opposing side). 
     The underside  171  of the locking screw  170  has a concavely curved surface corresponding with the curvature of the first ball end  131  of the elongate member  130 . The elongate member can pivot relative to the coupling body  140 , along the axis of slot  144 , when the locking screw  170  is not fully tightened. The notch  164  in the washer  160  allows for a greater range of movement when the elongate member  130  pivots within slot  144 . 
     The second ball end  132  can be received within the coupling body  40  of a second spinal implant assembly like that of  FIG. 5 , or some other spinal implant assembly (such as an assembly including a pedicle screw rather than an intervertebral device with detachable head component). 
     In alternative embodiments, the elongate member  130  may have only a first ball end  130  which is received by the coupling body  40 , the elongate member forming a simple rod extending from the first ball end  130 . 
     Like the embodiment of  FIGS. 1 to 4 , the assembly of  FIGS. 5 to 7  allows polyaxial positioning of the bolt  20   a  relative to the coupling body  140  when the assembly is in an adjustable configuration (when the locking member  170  is not tightly compressing the assembly components) but not when the assembly is in a locked configuration (when the locking member not tightly compressing the assembly components). 
     The embodiment of  FIGS. 5 to 7  is installed in a very similar manner to that of  FIGS. 1 to 4 .