Abstract:
An intervertebral prosthesis implantable within a disc space and disposed between upper and lower vertebral endplates is provided. The prosthesis comprises a plurality of prosthesis components insertable into the disc space, wherein the components have at least one set of complementarily-shaped and sized surfaces, and wherein the at least one set of complementarily-shaped surfaces comprises a slot, and a rod that fits in the slot. A method of implanting an intervertebral prosthesis according to the present invention also is provided.

Description:
FIELD OF INVENTION 
       [0001]    The present invention is directed to spinal nucleus replacement implants, and systems and methods for implanting the nucleus replacement implants. 
       BACKGROUND 
       [0002]    This disclosure is related to Application Ser. No. 12/356,702 (Atty Dkt. P26987.00), Ser. No. 12/356,713 (Atty Dkt. P26228.00), and Ser. No. 12/356,743 (Atty Dkt. P32043.00), each of which is hereby incorporated by reference in their entireties. 
         [0003]    The present disclosure relates generally to devices and methods for relieving disc degeneration or injury, and more particularly, to devices and methods for augmenting or replacing a nucleus pulposus. Within the spine, the intervertebral disc functions to stabilize and distribute forces between vertebral bodies. The intervertebral disc comprises a nucleus pulposus which is surrounded and confined by the annulus fibrosis (or annulus). 
         [0004]    Intervertebral discs are prone to injury and degeneration. For example, herniated discs typically occur when normal wear, or exceptional strain, causes a disc to rupture. Degenerative disc disease typically results from the normal aging process, in which the tissue gradually loses its natural water and elasticity, causing the degenerated disc to shrink and possibly rupture. 
         [0005]    Intervertebral disc injuries and degeneration may be treated by fusion of adjacent vertebral bodies or by replacing the intervertebral disc with a prosthetic. To maintain as much of the natural tissue as possible, the nucleus pulposus may be supplemented or replaced while maintaining all or a portion of the annulus. 
         [0006]    It would be advantageous to keep any incision in the annulus minimal, in order to avoid injuring healthy tissue. Accordingly, it is desirable to provide a prosthetic device that requires a relatively small opening or incision in the annulus when being inserted into the disc space. 
       SUMMARY OF THE INVENTION 
       [0007]    An intervertebral prosthesis implantable within a disc space and disposed between upper and lower vertebral endplates is provided. The prosthesis comprises a plurality of prosthesis components insertable into the disc space, wherein the components have at least one set of complementarily-shaped and sized surfaces, and wherein the at least one set of complementarily-shaped surfaces comprises a slot, and a rod that fits in the slot. The components have surfaces configured to engage within the disc space in a manner such that the components form an assembled prosthesis of a size substantially preventing it from being outwardly expelled from the disc space through an opening in the disc space, and the components have bearing surfaces slidably engageable with the endplates to permit articulation between upper and lower vertebral endplates. 
         [0008]    In certain embodiments, the prosthesis has a lower surface that is relatively flat. In some embodiments, the prosthesis has an upper surface that comprises a generally hemispherically-shaped surface. In some embodiments, the prosthesis has a lower surface that comprises a generally hemispherically-shaped surface. Also, in certain embodiments, the prosthesis is configured such that in its final shape, it is generally pear shaped. 
         [0009]    In some embodiments, when the prosthesis is in its final shape, the plurality of components are locked together with a locking mechanism. Typically, each component of the prosthesis can be inserted into the disc space by being inserted through an opening in the annulus between the upper and lower vertebral endplates. 
         [0010]    According to the invention, each of the multiple components has an insertion rod attached to the component for inserting the respective component to which the insertion rod is attached into the disc space. In such embodiments, a first insertion rod of a first component has a slot in which at least a second insertion rod of a second component can be inserted and used to guide the at least second component into the disc space. Typically, the insertion rods are configured such that each can be detached from their respective components. 
         [0011]    A method of implanting an intervertebral prosthesis within a disc space between upper and lower vertebral endplates also is provided. In some methods, the prosthesis comprises at least a first component and a second component, and the method comprises using a first insertion rod attached to the first component to insert the first component through an incision in an annular wall and into the disc space, using a second insertion rod attached to the second component to insert the second component through the incision in the annular wall and into the disc space, and after the first component and second component are in their respective final positions in the disc space, detaching the first and second insertion rods from their respective components. 
         [0012]    In certain methods according to the present invention, wherein prior to insertion through the annular wall and into the disc space, the method of implanting an intervertebral prosthesis further comprises rotating at least one of the components approximately 90 degrees so that the at least one component is inserted through the incision and into the disc space in a vertical position. With using such methods, the at least one component may be rotated approximately 90 degrees back to its original, more horizontal position that has less of a vertical profile. 
         [0013]    In some methods according to the present invention, the first insertion rod has a slot and the second insertion rod fits in the slot to enable the second component to cooperate with the first component and be guided into a desired location in the disc space. Also, in certain methods, after the first and second insertion rods are detached from their respective components, the insertion rods may be removed from the disc space and the body. 
         [0014]    Additional aspects and features of the present disclosure will be apparent from the detailed description and claims as set forth below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cross-sectional lateral view of a section of a spinal column; 
           [0016]      FIG. 2  is an exemplary disc incision in the anterior wall of an annulus fibrosus; 
           [0017]      FIG. 3  is a cut-away, cross-sectional view of the layer of spinal column of  FIG. 2 ; 
           [0018]      FIG. 4  shows an isometric view of a first module of a prosthesis according to the present invention; 
           [0019]      FIG. 5  shows an isometric view of a second module of a prosthesis according to the present invention; 
           [0020]      FIG. 6  shows an isometric view illustrating the manner in which the first and second modules of a prosthesis of the present invention cooperate; 
           [0021]      FIG. 7  shows an isometric view illustrating the cooperation of the first and second components of a prosthesis; 
           [0022]      FIG. 8  shows an isometric view of the manner in which the first and second components of a prosthesis cooperate after their respective insertion rods have been detached; 
           [0023]      FIG. 9  shows an isometric view of a first module of a second embodiment of a prosthesis according to the present invention; 
           [0024]      FIG. 10  shows a side view of a second module of the second embodiment of the prosthesis according to the present invention; 
           [0025]      FIG. 11  shows an isometric view illustrating the manner in which the first and second modules of the second embodiment of the prosthesis of the present invention cooperate; and 
           [0026]      FIG. 12  shows an isometric view of the manner in which the first and second components of the second embodiment of the prosthesis of the present invention cooperate after their respective insertion rods have been detached. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments, or examples, illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
         [0028]    Referring first to  FIG. 1 , the reference numeral  10  refers to a vertebral joint section or a motion segment of a vertebral column. The joint section  10  includes adjacent vertebral bodies  12  and  14 . The vertebral bodies  12  and  14  include endplates  16  and  18 , respectively. An intervertebral disc space  20  is located between the endplates  16  and  18 , and an annulus fibrosus  22  surrounds the space  20 . In a healthy joint, the space  20  contains a nucleus pulposus  24  within the disc space  20 , which helps maintain the distance between endplates  16  and  18 , known as the disc height  15 . Proper disc height  15  may vary for a particular patient, but medical experts understand how to determine a range of desired disc height  15 . The nucleus pulposus  24  may degenerate with age, disease or trauma, permitting the endplates  16  and  18  to move closer together. 
         [0029]    Referring now to  FIGS. 2 and 3 , an exemplary disc incision  26  is shown in the anterior wall of the annulus fibrosus  22 . Disc incision  26  breaches the annulus fibrosus  22  to the disc space  20 . As necessary, nucleus pulposus  24  may be removed from the disc space  20  in order to accommodate the insertion of a prosthesis. Illustratively (representatively shown empty in  FIG. 2 ), the disc incision  26  is longitudinal in order to attempt to minimize trauma to the annulus fibrosus  22 . The anterior wall of the annulus fibrosus  22  is shown, but the depicted procedure and device are not limited by the example. The particular surgical professional performing the procedure may choose to enter the annulus fibrosus  22  from anterior oblique, posterior, posterior oblique, lateral, transforaminal, or any other approach judged suitable with regard to other factors. The particular surgical professional also may choose to orient the disc incision  26  differently. 
         [0030]    A dilator may be used to dilate the disc incision  26 , making it large enough to deliver the implant to replace or augment the disc nucleus. The dilator may stretch the disc incision  26  temporarily and avoid tearing so that the disc incision  26  can return back to its undilated size after the dilator instrument is removed. Although some tearing or permanent stretching may occur, the dilation may be accomplished in a manner that allows the disc incision  26  to return to a size smaller than the dilated size after the implantation is complete. 
         [0031]      FIGS. 4-8  show various isometric views of a specially designed prosthesis  100  embodying principles of the present invention.  FIG. 4  shows a first module  30 A, which comprises a first component  30  and a first insertion rod  32 . The first component  30  has a cross section that is generally pear-shaped, having a round portion at its proximal end  31  and a pointed portion at its distal end  39 . The first component  30  has a relatively flat base or lower surface  33 . The first component  30  also has a cut-away portion  35 , which has a generally circular shape, at the proximal end  31  of its upper surface. The first insertion rod  32  and the cut-away portion  35  of the first component  30  each contain a slot  34  that is co-linear as it extends through the first insertion rod  32  and through the cut-away portion  35 . As shown in  FIG. 4 , the slot  34  is centered in the middle of the first insertion rod  32  and in the upper surface of the first insertion rod  32 . Similarly, as shown in  FIG. 4 , the slot  34  is centered in the middle of the cut-away portion  35  of the first component  30 , and the slot is continuous through both the first insertion rod  32  and the cut-away portion  35 . 
         [0032]      FIG. 5  shows a second module  40 A, which comprises a second component  40  and a second insertion rod  42 . The second component  40  has an overall shape that is generally hemispherical, with a cross section that is generally circular. In accordance with the invention, the second component  40  is intended to cooperate with or mate with the first component  30 . As shown in  FIG. 5 , the second insertion rod  42  of second module  40  is shaped so that it can cooperate, or fit within, and slide along slot  34  of first insertion rod  32 . 
         [0033]    In operation, the nucleus pulposus  24  is removed, as necessary, from the disc space  20  in order to accommodate the insertion of a prosthesis  100  according to the present invention. The first module  40  is inserted through the incision  26  in the annulus  22  and into the disc space  20  with the aid of the first insertion rod  32 . That is, the distal end  39  passes through the incision  26  and penetrates the disc space  20  first, while the surgeon is holding onto a proximal end (not shown) of the first insertion rod  32 , i.e., the end opposite the first component  30 . After the first component is in the desired position in the disc space  20 , the surgeon then inserts the second component  40  through the incision  26  and into the dis space  20 . The surgeon places the second insertion rod  42  into the proximal end of slot  34  and slides the second insertion rod  42  through the slot  34 , as shown in  FIG. 6 , until the second component  40  cooperates with the first component  30  in the disc space  20 . As shown in  FIG. 7 , this is achieved when the second component  40  cooperates or mates with the cut-away portion  35  of the first component  30 . In addition, a locking mechanism can be utilized to know when the second component is in its desired position and has properly mated with the first component  30 . As examples, a quick connect, snap fit, living hinge or other mechanism may be utilized. For example, as shown in  FIG. 5 , on the distal end of the second insertion rod  42 , there is a slight lip or protrusion  44  that can engage a corresponding hole or gap in slot  34 . 
         [0034]    After both the first component  30  and the second component  40  are in desired position in the disc space  20  and properly mated, the insertion rods  32  and  42  may be separated from their respective components or detached in some manner by the surgeon and done in a way that detaches the rods from the components at the respective proximal ends of the components  30  and  40 . For example, the insertion rods  32  and  42  may be snapped off from their respective components at their respective proximal ends. Various mechanisms can be used to accomplish this. For example, a perforation type of mechanism at these points will facilitate such a breaking or snapping off of the rods  32  and  42 . Thus, after the insertion rods  32  and  42  are separated from their respective components, and the insertion rods  32  and  42  are removed from the disc space and from the body, the prosthesis  100  according to the present invention will remain in the disc space  20 . As shown in  FIG. 8 , the prosthesis includes the first component  30  and the second component  40 . 
         [0035]    There are various benefits of the prosthesis of  FIGS. 4-8 . For example, the second component  40  is of a spherical shape to fit in the nuclear recess, i.e., particularly in the caudal-rostral dimension to restore disc height and to re-stabilize the disc space  20  and adjacent vertebrae  12  and  14 . This overall spherical shape of the exposed part of the second component  40  also utilizes the endplate geometry for adequate fixation, while retaining motion and even stress distribution in the lateral direction. In addition, the first component  30  allows for a larger foot print on the inferior endplate, which is designed to minimize the extent of subsidence of the prosthesis  100 . 
         [0036]    Further, with the particular shape of the first component  30 , i.e., with the relatively narrow or pointed portion at its distal end  39 , the first component  30  is self-distracting to allow for an easy insertion of the first component  30  through the incision  26  and into the disc space  20 . In particular, as shown in the figures, the upper surface of the first component  30  has a rise from the relatively narrow or pointy distal end  39  as it moves toward the cut-away portion  35 . This can be described as being in the sagittal plane, or in the caudal-rostral dimension. In addition, however, there is an increase in width, or a similar rise, in the direction perpendicular to this one (in the transverse plane). As shown in  FIG. 4 , for example, component  30  is wider and has a larger angle of inclination in the transverse plane than it does in the sagittal plane. Thus, where more distraction is desired, component  30  can be inserted between the vertebrae when it is turned on its side, or approximately 90 degrees, with respect to the view shown in  FIG. 4 . With a mostly vertical incision  26  in the annular wall  22 , this position also is desirable, as the component  30  would be oriented vertically and therefore could reduce further damage to the annular wall  22 . Once in the disc space  20 , the component  30  can be turned back “upside right” and assume the position as shown in  FIG. 4 , i.e., namely that with the lower surface  33  abutting the upper surface or endplate  18  of the inferior vertebra  14 . 
         [0037]    In addition, the insertion rods  32  and  42  provide for simple, safe and accurate implantation, and even re-positioning of the prosthesis  100  before the rods  32  and  42  are detached. Further, the slot aspect of how the two insertion rods  32  and  42  are designed not only facilitates implanting of the second component  40 , but prohibits the two components  30  and  40  from detaching from each other once in proper position in the disc space  20 . Also, as demonstrated, the prosthesis  100  of the present invention requires only a relatively small opening (or incision  26 ) in the annulus  22  so that the prosthesis  100  may be inserted into the disc space  20  by using multiple components, with each having a smaller profile than the final design. 
         [0038]      FIGS. 9-12  show various views of a specially designed prosthesis  200  embodying principles of the present invention.  FIG. 9  shows a first module  130 A, which comprises a first component  130  and a first insertion rod  132 . The first component  130 A has a cross section that is generally pear-shaped, having a round portion at its proximal end  131  and a pointed portion at its distal end  139 . As opposed to the first component  30 A of  FIGS. 4-8 , however, the first component  130  has a rounded lower surface. In this way, the first component  130  is shaped like half a pear after a whole pear is cut along its longitudinal axis, as shown in  FIG. 9 . The first insertion rod  132  and the first component  130  has a slot  134  that is co-linear as it extends through the first insertion rod  132  and through the first component  30 . As shown in  FIG. 9 , the slot  134  is centered in the middle of the first insertion rod  132  and in the upper surface of the first insertion rod  132 . Similarly, as shown in  FIG. 9 , the slot  134  is centered in the middle of the first component  30  and along its longitudinal axis, and the slot  134  is continuous through both the first insertion rod  132  and the first component  130 . 
         [0039]      FIG. 10  shows a side view of second module  140 A, which comprises a second component  140  and a second insertion rod  142 . As with the first component  130 , the second component  140  has a cross section that is generally pear-shaped, having a round portion at its proximal end  141  and a pointed portion at its distal end  149 . Also, the second component  140  has a rounded upper surface. Similar to the first component  130 , the second component  140  is shaped like half a pear after a whole pear is cut along its longitudinal axis, as shown in  FIG. 10 . The second insertion rod  142  is co-linear and continuous as it extends along the base of the second component  140  and extends from the proximal  141  away from the distal end  149  of the second component  140 . As shown in  FIG. 10 , the second insertion rod  142  is centered in the middle of the second component  140  and along its longitudinal axis. Also as shown in  FIG. 10 , the second insertion rod  142  of second module  140  is shaped so that it can cooperate, or fit within, and slide along slot  134  of first insertion rod  132 . 
         [0040]    In operation, after the nucleus pulposus  24  is removed, as necessary, from the disc space  20 , the first module  130  is inserted through the incision  26  in the annulus  22  and into the disc space  20  with the aid of the first insertion rod  132 . That is, the distal end  139  passes through the incision  26  and penetrates the disc space  20  first, while the surgeon is holding onto a proximal end (not shown) of the first insertion rod  132 , i.e., end opposite the first component  130 . After the first component  130  is in the desired position in the disc space  20 , the surgeon then inserts the second component  140  through the incision  26  and into the disc space  20 . The surgeon places the second insertion rod  142  into the proximal end of slot  134  and slides the second insertion rod  142  through the slot  134  (similar to that of  FIG. 6 ), until the second component  140  cooperates with the first component  130  in the disc space  20 . As shown in  FIG. 11 , this is achieved when the second component  40  cooperates or mates with the first component  130 . In addition, a locking mechanism can be utilized to know when the second component  140  is in its desired position and has properly mated with the first component  130 . Examples of such locking mechanisms for prosthesis  200  are similar to those that can be used for prosthesis  100  of  FIG. 4-8 . For example, as shown in  FIG. 10 , on the distal end of the second insertion rod  142 , there is a slight lip or protrusion  144  that can engage a corresponding hole or gap in slot  134 . 
         [0041]    As with the prosthesis  100  of  FIG. 4-8A , after both the first component  130  and the second component  140  are in desired position in the disc space  20  and properly mated, the insertion rods  132  and  142  may be snapped off by the surgeon and done in a way that breaks the rods off at the respective proximal ends of the components  130  and  140 . A perforation type of mechanism at these points will facilitate such a breaking off of the rods  132  and  142 . Thus, after the insertion rods  132  and  142  are separated from their respective components, the prosthesis  200  according to the present invention will remain in the disc space  20 . As shown in  FIG. 12 , the prosthesis includes the first component  130  and the second component  140 . 
         [0042]    Some of the same benefits of the prosthesis  100  of  FIGS. 4-8  are present with the prosthesis  200  of  FIGS. 9-12 . For example, both second components  130  and  140  are of a spherical shape to fit in the nuclear recess, i.e., particularly in the caudal-rostral dimension to restore disc height and to re-stabilize the disc space  20  and adjacent vertebrae  12  and  14 . The overall spherical portion of the prosthesis  200  also utilizes the endplate geometry for adequate fixation, while retaining motion and proper stress distribution in the lateral direction. 
         [0043]    In addition, with the particular shape of each component  130  and  140 , i.e., with the relatively pointed portion at their respective distal ends, each component  130  and  140  is self-distracting to allow for an easy insertion of the component  130  and  140  through the incision  26  and into the disc space  20 . In particular, as shown in the figures, the distal ends of each component  130  and  140  are relatively narrow and rises up to meet the generally spherically-shaped proximal end, thereby giving it a generally pear-shaped appearance. As described above with respect to component  30 , where more distraction is desired, either component  130  or  140  can be inserted between the vertebrae when it is turned on its side, or approximately 90 degrees, with respect to the views shown in  FIGS. 9 and 10 . With a mostly vertical incision  26  in the annular wall  22 , this position also is desirable, as the components  130  or  140  would be oriented vertically and therefore could reduce further damage to the annular wall  22 . Once in the disc space  20 , the components  130  can be turned back “upside right” and assume the positions as shown in  FIGS. 9 and 10 . With prosthesis  200 , however, one may not want to perform this “turning upside right” step until the second component  140  has been inserted. That is, if it is desirable to have a greater amount of distraction when component  140  is inserted, the insertion rods  132  and  142  should align, so one should maintain both components  130  and  140  aligned vertically until both are in the desired position in the disc space  20 . 
         [0044]    In addition, the insertion rods  132  and  142  provide for simple, safe and accurate implantation, and even re-positioning of the prosthesis  200  before the rods  132  and  142  are detached. Further, the slot aspect of how the two insertion rods  132  and  1142  are designed not only facilitates implanting of the second component  140 , but prohibits the two components  130  and  140  from detaching from each other once in proper position in the disc space  20 . Also, as demonstrated, the prosthesis  200  of the present invention requires only a relatively small opening (or incision  26 ) in the annulus  22  so that the prosthesis  200  may be inserted into the disc space  20  by using multiple components, with each having a smaller profile than the final design. 
         [0045]    The present invention does not depend on the materials of the constituent parts, but any of the components or modules may be made of any biocompatible materials that are typically used in the intra-discal area. Examples of suitable materials include, but are not limited to, metals such as cobalt-chromium alloys, stainless steels, titanium and titanium alloys. Examples of other materials include, but are not limited to, polymers such as polyetherether ketone (“PEEK”), polyether ketone (“PEK”), polyethylene, and polyurethanes. In addition, various ceramics, biologics and resorbable materials also could be used. Also, a portion of a component or module can be made of a different material than the remainder of the component or module such that the prosthesis can have variable stiffness. Similarly, parts of certain components or modules that occupy the central area of a prosthesis  100  or  200  can be made of a compressible material to provide different load bearing characteristics. 
         [0046]    Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this disclosure. An example of such a modification would be modifying the overall shape of prosthesis  100  or  200 , and/or using more than two components to create a prosthesis  100  or  200 . That is, a prosthesis according to the principles of the present invention may be made with more than two constituent components. For example, multiple slots also may be utilized. 
         [0047]    Accordingly, all such adjustments and alternatives are intended to be included within the scope of the invention, as defined exclusively in the following claims. Those skilled in the art should also realize that such modifications and equivalent constructions or methods do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alternations herein without departing from the spirit and scope of the present disclosure. Furthermore, as used herein, the terms components and modules may be interchanged. It is understood that all spatial references, such as “anterior,” “posterior,” “inward,” “outward,” and “sides” are for illustrative purposes only and can be varied within the scope of the disclosure.