Abstract:
An implant for insertion between vertebral members in which an inner member, intermediate member, and outer member are concentrically disposed. The inner and outer members may comprise end plates to contact the vertebral members. The outer member may include a tapered interior wall. A locking element is movably contained within an opening that extends through a sidewall of the intermediate member. The intermediate member is displaceable longitudinally in first and second directions relative to the outer member. Displacement of the intermediate member in the first direction tends to force the locking element laterally into contact with the inner and outer members. A biasing member may urge the intermediate member in the first direction. Displacement of the intermediate member in the second direction allows the locking element to be laterally displaced out of contact with the inner member.

Description:
BACKGROUND  
       [0001]     Spinal implants are often used in the surgical treatment of spinal disorders such as degenerative disc disease, disc herniations, scoliosis or other curvature abnormalities, and fractures. Many different types of treatments are used, including the removal of one or more vertebral bodies and/or intervertebral disc tissue. In some cases, spinal fusion is indicated to inhibit relative motion between vertebral bodies. In other cases, dynamic implants are used to preserve motion between vertebral bodies. In yet other cases, relatively static implants that exhibit some degree of flexibility may be inserted between vertebral bodies.  
         [0002]     Regardless of the type of treatment and the type of implant used, surgical implantation tends to be a difficult for several reasons. For instance, access to the affected area may be limited by other anatomy. Further, a surgeon must be mindful of the spinal cord and neighboring nerve system. The size of the implant may present an additional obstacle. In some cases, a surgeon may discover that an implanted device has an inappropriate size for a particular application, which may require removal of the implant and insertion of a different implant. This trial and error approach may increase the opportunity for injury and is certainly time-consuming. Expandable implants are becoming more prevalent as a response to some of these concerns. However, the expansion mechanism in some of these devices tends to be complex and large. In some devices, the expansion mechanism is a ratcheting mechanism that provides limited positional resolution. Consequently, existing devices do not appear to address each of these issues in a manner that improves the ease with which the device may be surgically implanted.  
       SUMMARY  
       [0003]     Illustrative embodiments disclosed herein are directed to an implant for insertion between vertebral members in which an inner member, intermediate member, and outer member are concentrically disposed. Each member may have a circular cross section or asymmetric cross section to maintain relative clocking between the members. The inner and outer members may comprise end plates to contact the vertebral members. The outer member may include a tapered interior wall. A locking element is movably contained within an opening that extends through a sidewall of the intermediate member. In one embodiment, the locking element is a sphere. In one embodiment, the locking element is a cylinder. The intermediate member is displaceable longitudinally in first and second directions relative to the outer member. Displacement of the intermediate member in the first direction tends to force the locking element laterally into contact with the inner and outer members. A biasing member may urge the intermediate member in the first direction. Displacement of the intermediate member in the second direction allows the locking element to be laterally displaced out of contact with the inner member. Moving the inner member in the second direction may expand the implant. Moving the intermediate member in the second direction while moving the inner member in the first direction may compress the implant. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  is a side elevation view of a vertebral implant according to one embodiment positioned between vertebral bodies;  
         [0005]      FIG. 2  is a perspective view of one embodiment of a vertebral implant;  
         [0006]      FIG. 3  is an exploded perspective view of one embodiment of a vertebral implant;  
         [0007]      FIG. 4  is a longitudinal cross section view of a vertebral implant according to one embodiment depicted in a locked state;  
         [0008]      FIG. 5  is a longitudinal cross section view of a vertebral implant according to one embodiment depicted in an unlocked state;  
         [0009]      FIG. 6  is an axial cross section view according to the section lines VI-VI in  FIG. 5 ;  
         [0010]      FIG. 7  is an axial cross section view according to the section lines VII-VII in  FIG. 4 ;  
         [0011]      FIG. 8  is a longitudinal cross section view of a vertebral implant according to one embodiment;  
         [0012]      FIG. 9  is a longitudinal cross section view of a vertebral implant according to one embodiment;  
         [0013]      FIG. 10  is an axial cross section view of a vertebral implant according to one embodiment; and  
         [0014]      FIG. 11  is a longitudinal cross section view of a vertebral implant according to one embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0015]     The various embodiments disclosed herein are directed to vertebral implants that are expandable to achieve a desired distraction between vertebral bodies. The vertebral implant includes a locking mechanism that permits infinite adjustability in an expansion direction while restricting motion in an opposite direction. An exemplary implant  10  for supporting vertebral bodies is illustrated in  FIG. 1 . In one embodiment, the implant  10  is a vertebrectomy implant positionable within an intervertebral space to span one or more vertebral levels along the longitudinal axis of the spinal column. Although the illustrated embodiment of the implant  10  spans two vertebral levels, it should be understood that the implant  10  may be configured to span a single vertebral level or three or more vertebral levels.  
         [0016]     A perspective view of the implant  10  is provided in  FIG. 2 . An exploded assembly view of the implant  10  is provided in  FIG. 3 . The device  10  comprises a first member  20 , a second member  30 , and a lock  40 . Generally, the first member  20  and second member  30  are expandably coupled to one another. That is, the second member  30  is disposed within the first member  20  and is expandable in the direction of the arrow labeled E in  FIG. 1 . The lock  40  generally prevents motion of the second member  30  relative to the first member  20  in the substantially opposite direction (i.e., compression). However, as will be explained below, the lock  40  may be released to allow compression. A similar configuration for the lock  40  is disclosed in commonly assigned U.S. patent application Ser. No. 11/335,389, filed Jan. 19, 2006, the relevant portions of which are hereby incorporated by reference herein.  
         [0017]     The first member  20  includes a first end member  12  disposed at an end of a first body  16 . Similarly, the second member  30  includes a second end member  14  disposed at an end of a second body  18 . The end members  12 ,  14  are adapted to engage the endplates of upper and lower vertebral bodies V 1 , V 2  as shown in  FIG. 1 . Accordingly, the end members  12 ,  14  may be shaped and/or sized to match the anatomy of the endplates. The end members  12 ,  14  may be wider than the respective bodies  16 ,  18 , though this is not explicitly required. As a result of the expandable nature of the implant  10 , the end members  12 ,  14  may be distracted a desired amount to maintain an intervertebral axial space S between the upper and lower vertebral bodies V 1 , V 2  following the removal of one or more vertebral levels (shown in phantom). To facilitate insertion of the implant  10 , first and second members  20 ,  30  may be collapsed relative to each other. Once the implant  10  is inserted between the vertebral bodies V 1 , V 2 , the end members  12 ,  14  may be distracted using a surgical tool T (represented by dashed lines) to maintain the desired intervertebral spacing S.  
         [0018]     The implant  10  and its various components may be constructed a variety of biocompatible materials. Some non-limiting examples include non-metallic substances such as, for example, carbon fiber materials, polymers, or copolymers, including varieties made from materials such as PEEK and UHMWPE. In further embodiments, the implant  10  may be formed of metals, such as, for example, stainless steel, titanium, cobalt-chrome, and shape memory alloys.  
         [0019]     The first member  20 , in one embodiment, includes a hollow elongated first body  16  having an open interior  22  that extends through the length. Similarly, the second member  30  includes a hollow elongated second body  18  having an open interior  22  that extends through the length. The open interior of the first member  20  and second member  30  provides a cavity in which bone growth promoting materials such as bone grafts or BMP may be inserted. Alternatively, the second body  18  may be solid. One embodiment of the lock  40  includes a lock body  31  having one or more openings  33  in a lower section. One embodiment of the lock  40  includes one or more locking elements  41  that fit within the openings  33 . Locking elements  41  may move within the openings  33  between the locked and unlocked positions.  FIG. 3  also shows a retainer  80  and biasing member  75  that cooperate to retain the lock body  31  within the open interior  22  of the first member  20 . As described below, the biasing member  75  may also maintain the locking elements  41  in the locked position.  
         [0020]      FIG. 4  illustrates a longitudinal cross section of one embodiment of the implant  10 . In this embodiment, the first body  16  includes an elongated length extending between a first end  23  and a second end  24 . In another embodiment, first body  16  includes a shorter length extending around the second body  18  of the second member  30 . For example, in certain applications, the implant  10  may be used in disc replacement surgery or for the replacement of a single vertebral level. In these cases, a shortened body  16  may be appropriate. The first body  16  may be hollow forming the interior section  22  that extends the length. In one embodiment, first body  16  includes a substantially circular cross-sectional shape with the interior section  22  also being substantially circular. In other embodiments, first body  16  and the interior section  22  include non-circular cross-sectional shapes. Generally, for either configuration, the first body  16 , lock body  31 , and second body  18  may be concentric. The interior section  22  tapers from a first width at wall  26  disposed towards the first end  23  to a second, narrower width at wall  28  disposed towards the second end  24 . A tapered wall  25  is disposed therebetween and provides a transition between the different widths.  
         [0021]     In one embodiment, the lock  40  includes lock body  31  sized to fit within the interior section  22 . In one embodiment, a limited section of the second member  30  fits within the interior section  22 . In one embodiment as illustrated in  FIG. 3 , lock body  31  includes an interior section  36  that extends the length and is sized to receive the second body  18 . One or more openings  33  may extend through the lock body  31  and each is sized to receive a locking element  41 . Openings  33  may be positioned along the length of the lock body  31  at a variety of locations. In one embodiment as illustrated in  FIG. 4 , openings  33  are positioned at a lower section of the lock body  31  to interact with the tapered wall  25  of the first body  16  as will be explained in detail below. In one embodiment, a single opening  33  is positioned within the lock body  31 . In one embodiment, the lock body  31  includes three openings  33  that are aligned within a common plane and spaced about 120 degrees apart around the lock body  31 .  
         [0022]     One embodiment of the lock body  31  further includes a neck section  34  with a reduced width that is spaced inward from the inner sidewalls of first body  16 . A shelf  35  having a larger width is positioned at one end of the neck section  34  in one embodiment. A cap  37  including a larger width may be positioned at an upper end of the lock body  31 .  
         [0023]     In one embodiment, the lock  40  includes one or more locking elements  41  movably positioned at the openings  33 . In one embodiment, locking elements  41  comprise spherical balls, such as ball bearings. In another embodiment, locking elements  41  include other shapes. For example, in one embodiment described below, the locking element  41  includes a substantially cylindrical shape. In embodiments having plural locking elements  41 , each of the elements  41  may include the same or different shapes and sizes. In one embodiment, each locking element  41  travels back and forth relative to the opening  33 . As illustrated in the embodiment of  FIG. 4 , a thickness of the locking element  41  is greater than a thickness of the lock body  31  forming the opening  33  (other sections of the lock body  31  may include a greater thickness than the locking element). Therefore, downward movement of the lock body  31  relative to the first member  20  causes the locking elements  41  to move radially inward when sliding along the tapered wall  25 . It is worth noting that in  FIG. 4 , the implant  10  is depicted with the lock  40  in the locked position.  
         [0024]      FIG. 5  illustrates one embodiment in the unlocked position. In this embodiment, second member  30  extends through the hollow interiors  22 ,  36  of the first member  20  and lock body  31 . In one embodiment, second member  30  is aligned with a centerline of a longitudinal axis A that extends through the second body  18  of first member  20  and lock body  31  of lock  40 . The lock body  31  is positioned within the first member  20  with the opening  33  positioned at wall  26  where the interior section  22  includes a wider first width. In one embodiment, a space formed between second body  18  of the second member  30  and the sidewall  26  of the interior section  22  is greater than the thickness of the locking elements  41  allowing the locking elements  41  to freely move thus preventing binding with the second member  30 .  
         [0025]      FIG. 6  is a cross-sectional view of the device of  FIG. 5  cut along the section line VI-VI. In this embodiment, space  90  formed between the second body  18  and the interior sidewall  26  of the first body  16  is greater than the thickness of the locking elements  41 . Thus, the locking elements  41  may move within the space  90  and the second member  30  may move axially relative to the first member  20 , including in compression.  
         [0026]      FIGS. 4 and 7  illustrate one embodiment of an implant  10  in the locked position. In this configuration, the lock body  31  is moved downward within the first body  16 . Openings  33  are now aligned at tapered wall  25  where the space  90  formed between the second body  18  and the first body  16  is less than the thickness of the locking elements  41 . This causes the locking elements  41  to deflect inward through the openings  33  and into contact with second body  18 . In one embodiment, this contact locks the second member  30  to the first member  20  and prevents compression.  
         [0027]     However, due to the orientation of the tapered wall  25 , the second member  30  may still extend relative to the first member  20 . Furthermore, the tapered wall  25  produces a decreasing width of the interior section  22  in the compression direction. The decreasing width creates greater interference to prevent compression of the implant  10 . Therefore, the locking elements  41  may apply a greater force on the second member  30  the further the second wall  18  and lock body  31  are inserted downward into the first member  20 .  
         [0028]     In one embodiment, a biasing mechanism  75  is positioned between the first member  20  and lock  40 . In one embodiment, a first end of the biasing mechanism  75  contacts the shelf  35  of the lock body  31 . In one embodiment, a retainer  80  attached to the inner wall of the first body  16  forms a contact surface for a second end of the biasing mechanism  75 . The biasing mechanism  75  in one embodiment includes a cylindrical configuration that is disposed around the neck  34 . In one specific embodiment, biasing mechanism  75  is a coil spring. In one embodiment, biasing mechanism  75  applies a force on the lock body  31  to maintain the lock  40  towards the locked position. The force may be adequate to lock the implant  10  against compression between the first member  20  and second member  30 . Unlocking the implant  10  may require moving the lock body  31  away from the first member  20 . Unlocking the implant  10  may require moving the lock body  31  against the biasing force applied by the biasing mechanism  75 . In one embodiment, grasping and pulling the cap  37  towards the second end member  14  will unlock the lock  40 . Unlocking the implant  10  may require moving the lock body  31  upward to a point where the recesses  33  are positioned in a region of the interior section  22  having a larger interior width.  
         [0029]     Locking elements  41  may further include a variety of shapes and sizes. Embodiments as illustrated in  FIGS. 3-7  incorporate a locking element  41  including a spherical shape that moves within the openings  33 . Another embodiment such as that illustrated in  FIG. 8  incorporates a locking element  141  that includes a different shape. In one embodiment, locking element  141  is contained within an opening  33  within the lock body  31 . In another embodiment as illustrated in  FIG. 8 , locking element  141  is positioned outside of the lock body  31  and at a position to be contacted by the lock body  31 . Locking element  141  may be operatively connected to the lock body  31 , or may be unconnected.  
         [0030]     The number of locking elements  41  may vary depending upon the application. Certain embodiments feature multiple locking elements  41 . For embodiments with multiple locking elements  41 , the elements  41  may be positioned within the same plane relative to the lock body  31 . In other embodiments, two or more of the locking elements  41  may be positioned within different planes. In one embodiment, a single locking element  41  locks the device  10 . For example,  FIG. 9  depicts an embodiment in which a single, ring shaped locking element  241  is used. The ring shaped locking element  241  may be split to allow radial compression of the locking element  241  or form a continuous ring to resist radial compression.  
         [0031]     The end members  12 ,  14  may be disposed at various angles relative to a longitudinal axis of the implant  10 . The orientation of the end members  12 ,  14  may be varied to accommodate a desired angle between vertebral bodies (e.g., to achieve desired lordotic or kyphotic curvatures). For instance,  FIG. 4  shows angles α and β respectively describing the angle between end members  12 ,  14  and longitudinal axis A. In one embodiment, angles α and β may be substantially 90 degrees, which implies that the end members  12 ,  14  are substantially parallel. In other embodiments, the end members  12 ,  14  may be parallel but disposed at some acute or obtuse angle relative the axis A. In other embodiments the end members  12 ,  14  may be disposed at different angles α and β relative to axis A.  
         [0032]     It may be desirable to maintain the angles α and β aligned about a common anatomic plane. For instance, a surgeon may wish to orient the angles α and β within a sagittal or coronal plane. Further, it may be desirable to maintain the angles α and β at some relative clocking position (including aligned or misaligned) relative to each other. Accordingly, in one embodiment shown in  FIG. 10 , the bodies  116 ,  118  of the first member  20  and second member  30  are asymmetric or non-cylindrical. In the illustrated embodiment, the first body  116  and the second body  118  are substantially D-shaped with each having a single flat sidewall  120 ,  122 . The flat sidewalls  120 ,  122  maintain a keyed or clocked relationship between the first member  20  and second member  30 . In other embodiments, the first body  116 , and second body  118  may include additional flat surfaces. For example, the first and second bodies  116 ,  118  may be substantially triangular, square, or polygonal. Other asymmetric configurations that do not have flat sidewalls  120 ,  122  may be used. For example, both bodies  116 ,  118  may include an elliptical cross section. A non-spherical locking element  141  may be used at the interface between the flat sidewalls  120 ,  122 . In one embodiment, the locking element  141  is cylindrical as depicted in  FIG. 10 .  
         [0033]     Embodiments above have incorporated a lock body  31  as part of the lock  40 . The lock body  31  offers several advantages, including but not limited to providing a recess  33  in which the locking elements  41  are retained as well as providing a release mechanism by which the first member  20  and second member  30  may be compressed. Nevertheless, it is certainly possible to incorporate the locking elements  41  in the implant  10  without the use of a separate lock body  31 . For example, in an embodiment shown in  FIG. 11 , the implant  210  includes a first member  220 , a second member  30 , and locking element  41 . More than one locking element  41  may be distributed radially about the implant  210 . In the illustrated embodiment, the first member  220  includes an opening  233  extending through a sidewall of the implant in which the locking element  41  is positioned. A comparable configuration may be arranged where the locking elements  41  are retained in openings in the second member  30 . In contrast with previous embodiments, the opening  233  is slanted in a way that permits extension of the second member  30  relative to the first member  220 . However, the slanted orientation of the opening  233  creates greater interference as second member  30  is compressed relative to the first member  20 . In fact, the locking elements  41  may apply a greater force on the second member  30  the further the second member  30  is inserted downward into the first member  220 . If desired, a retainers  212 ,  214  may be included to keep the second member  30  within the first member  220  and further to keep the locking element  41  in the opening  233 .  
         [0034]     The various Figures and embodiments disclosed herein have depicted spinal implant devices that are inserted between or adjacent vertebral bodies. However, the teachings disclosed are certainly applicable to other types of spinal implant devices, including interspinous spacers, rods, and other implants that are coupled to vertebrae V 1 , V 2 .  
         [0035]     Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description.  
         [0036]     As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.  
         [0037]     The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. For instance, the embodiments disclosed herein have contemplated a single implant positioned between vertebral bodies V 1 , V 2 . In other embodiments, two or more smaller implants may be inserted between the vertebral bodies V 1 , V 2 . The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.