Abstract:
Implants sized to be inserted into an intervertebral space between first and second vertebral members, and related methods. The spinal implant may have a body extending along a longitudinal axis with opposing first and second longitudinal ends. An end cap is mounted to the body at one of the ends and disposed longitudinally outboard of the corresponding end. The end cap comprises a first portion, a second portion, and an annular elastic element, such as an O-ring. The first and second portions are disposed circumferentially around the longitudinal axis. The annular elastic member circumferentially surrounds the first portion, the second portion, and the longitudinal axis. The annular elastic member applies a compressive force that urges the first and second portions together in a direction transverse to the longitudinal axis. The end cap may be flat or angled. Other implants and related methods are disclosed.

Description:
BACKGROUND 
       [0001]    The present application is directed to devices and methods for stabilizing vertebral members, and more particularly, to intervertebral implants and methods of use for replacing an intervertebral disc, vertebral member, or combination of both to distract and/or stabilize the spine. 
         [0002]    The spine is divided into four regions comprising the cervical, thoracic, lumbar, and sacrococcygeal regions. The cervical region includes the top seven vertebral members identified as C1-C7. The thoracic region includes the next twelve vertebral members identified as T1-T12. The lumbar region includes five vertebral members L1-L5. The sacrococcygeal region includes nine fused vertebral members that form the sacrum and the coccyx. The vertebral members of the spine are aligned in a curved configuration that includes a cervical curve, thoracic curve, and lumbosacral curve. Intervertebral discs are positioned between the vertebral members and permit flexion, extension, lateral bending, and rotation. 
         [0003]    Various conditions may lead to damage of the intervertebral discs and/or the vertebral members. The damage may result from a variety of causes including but not limited to a specific event such as trauma, a degenerative condition, a tumor, or infection. Damage to the intervertebral discs and vertebral members can lead to pain, neurological deficit, and/or loss of motion. 
         [0004]    Various procedures include replacing the entirety or a section of a vertebral member, the entirety or a section of an intervertebral disc, or both. One or more replacement implants may be inserted to replace the damaged vertebral members and/or discs. The implants are configured to be inserted into the intervertebral space and contact against the remaining adjacent vertebral members. The implants reduce or eliminate the pain and neurological deficit, and increase the range of motion. 
         [0005]    While a number of implant designs have been proposed, they have not proven ideal for all situations. As such, there remains a need for alternative intervertebral implant designs, particularly designs that allow for easy adaptation to spinal morphology. 
       SUMMARY 
       [0006]    The present application describes a spinal implant and associated method. In one embodiment, a spinal implant for insertion into an intervertebral space between first and second vertebral members comprises a body extending along a longitudinal axis with opposing first and second longitudinal ends. An end cap is mounted to the body at one of the ends and disposed longitudinally outboard of the corresponding end. The end cap comprises a first portion, a second portion, and an annular elastic element. The first and second portions are disposed circumferentially around the longitudinal axis. The annular elastic member, such as an O-ring, circumferentially surrounds the first portion, the second portion, and the longitudinal axis. The annular elastic member applies a compressive force that urges the first and second portions together in a direction transverse to the longitudinal axis. The end of the body having the end cap mounted thereto may comprise a plurality of projections projecting away from a center of the body, with at least some of the projections inter-engaged with the end cap to mount the end cap to the body. 
         [0007]    In another embodiment, an intervertebral implant comprises a body extending along a longitudinal axis with opposing first and second longitudinal ends; the body comprising a first section that includes the first end and a second section that includes the second end; wherein the second section is adjustably longitudinally positionable relative to the first section while coupled thereto. The first end has a plurality of protrusions extending longitudinally away from the second end; at least two of the protrusions having undercuts. An end cap is mounted to the body at the first end and disposed opposite to the second section relative to the first section. The end cap comprises a first circumferential segment having a first lip, and a second circumferential segment distinct from the first segment and having a second lip. The first and second segments are coupled together and disposed circumferentially around the longitudinal axis, with the first lip engaging a first of the undercuts and the second lip engaging a second of the undercuts. The first and second segments define at least in part a longitudinally extending bore through the end cap. The end cap includes an annular elastic member that circumferentially surrounds the first segment, the second segment, and the longitudinal axis. The annular elastic member applies a compressive force that urges the first and second segments together in a direction transverse to the longitudinal axis so as to maintain the first and second lips in engagement with their respective undercuts. Sometimes, the first and second portions of the end cap are mirror images of each other, with each of the first and second portions extending for a circumferential arc of at least 90° relative to the longitudinal axis. 
         [0008]    In another embodiment, a method of assembling a spinal implant comprises: providing a body extending along a longitudinal axis with opposing first and second longitudinal ends; the body comprising a first section that includes the first end and a second section that includes the second end; wherein the second section is adjustably longitudinally positionable relative to the first section while coupled thereto. An end cap having a first portion and a second portion distinct from the first portion is provided. The method includes mating the first portion of the end cap to the body at the first end of the body by moving the first portion transversely to the longitudinal axis. Thereafter, the second portion of the end cap is mated to the body at the first end of the body by moving the second portion transversely to the longitudinal axis. Thereafter, the first portion of the end cap is bound to the second portion of the end cap by circumferentially surrounding the first and second portions with an annular elastic member that urges the first and second portions together in a direction transverse to the longitudinal axis; wherein the annular elastic member circumferentially surrounding the first portion, the second portion, and the longitudinal axis. 
         [0009]    The various aspects of the various embodiments may be used alone or in any combination, as is desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of an implant according to one embodiment of the present invention. 
           [0011]      FIG. 2  is a partially exploded view of the implant of  FIG. 1 . 
           [0012]      FIG. 3  is a partially exploded view of a portion of the implant body and the corresponding end cap of  FIG. 1 . 
           [0013]      FIG. 4  is a top view of  FIG. 3  in the assembled condition. 
           [0014]      FIG. 5  is a cross-section along line V-V of  FIG. 4 . 
           [0015]      FIG. 6  shows an angled type end cap according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The present application is directed to intervertebral implants for spacing apart vertebral members. The implant  20  is intended to be positioned within an intervertebral space formed between vertebral members. The implant  20  includes a body  30  and at least one end cap  50 . The end cap  50  includes at least two distinct portions (or segments)  60 , 70  that are held together by an annular elastic element  80 , such as an O-ring. The annular elastic element  80  urges the two portions  60 , 70  together, keeping the end cap  50  mounted to the body  30  as discussed further below. The implant  20  may also include a second end cap  51  positioned at the opposite end. The second end cap  51  may be the same or different than the first end cap  50 . 
         [0017]      FIG. 1  shows one embodiment of the implant  20  in an assembled state. As more clearly shown in the partially exploded view of  FIG. 2 , the implant  20  includes a body  30  and at least one end cap  50 . The body  30  in combination with the end cap  50  is sized to fit within the intervertebral space. The body  30  extends along a longitudinal axis  32  and includes a first end  34  and a second end  36 . In some embodiments, the body  30  is of a fixed length along the longitudinal axis  32 . In other embodiments, the length L of the body  30  along axis  32  is adjustable. For example, the body  30  may have two or more sections  44 , 46  that can be adjustably positioned relative to each other. The first section  44  may include the first end  34 , and the second section  46  may include the second end  36 , and the second section  46  may be telescopically received in the first section  44 . A suitable locking mechanism  48 , such as a pin or locking collar or the like, may be used to lock the relative positions of the first and second sections  44 , 46 . For additional information about adjustable height implants, see, e.g., U.S. Patent Application Publications 2007/0255408; 2007/0255409; 2008/0114467; 2008/0177387; 2009/0164017, the disclosures of which are incorporated herein by reference in their entirety. In some embodiments, one or more apertures may extend through one or more sections of the body  30  to a hollow interior, such as for receipt of bone growth material. In some embodiments, the second end  36  may include a plurality of teeth designed to engage with the corresponding vertebral member. 
         [0018]    The first end  34  of the body  30  includes a plurality of protrusions  37  which extend outwardly away from the body  30 , advantageously generally parallel to the longitudinal axis  32 . The protrusions  37  are advantageously about six in number, but other numbers of protrusions  37  are within the scope of the invention. The protrusions  37  are advantageously arranged symmetrically about the longitudinal axis  32 , at a common distance therefrom. The protrusions  37  may take the form of short posts, each with a pointed top  38 . Advantageously, the protrusions  37  are all identical, but such is not required in all embodiments. Two or more of the protrusions  37  may include undercuts  39  that face radially outward, see  FIG. 3  and  FIG. 5 . 
         [0019]    End cap  50  is mounted to first end  34  of body  30 . End cap  50  includes first portion  60 , second portion  70 , annular elastic member  80 , and alignment pins  84 . When assembled, end cap  50  forms an annular body of approximately the size of end  34  in a plane perpendicular to the longitudinal axis  32 . The center of the annular body  30  includes a central bore  52  that is defined by the first and second portions  60 , 70 . The central bore  52  advantageously includes a plurality of lobes  54 , with the number of lobes  54  corresponding to the number of protrusions  37 . The lobes  54  are advantageously symmetrically and evenly disposed about axis  32 . The lobes  54  may all be identical, or the lobes  54  may have two or more configurations. For example, the middle lobe  54   b  of first portion  60  may be narrower than the outboard lobes  54   a , 54   c , as shown in  FIG. 4 . Likewise, the middle lobe  54   e  of second portion  70  may be narrower than outboard lobes  54   d , 54   f . The end cap  50  optionally includes teeth  56  projecting outward away from the body  30 , advantageously generally parallel to the longitudinal axis  32 . The teeth  56  are configured to bite into the corresponding vertebra, and may take any form known in the art. 
         [0020]    First and second portions  60 , 70  are advantageously mirror images of each other; as such, the present discussion will focus on first portion  60 , it being understood that the description may apply as well to second portion  70 . First portion  60  forms a circumferential section of end cap  50 . When there are two portions, the first portion  60  advantageously forms a 180° circumferential segment, but other amounts of circumferential sweep are within the scope of the present invention. In the illustrated embodiment, the first portion  60  has three recesses on its inner face which form three lobes  54  of the central bore  52 . The center points of each of these three lobes  54  are advantageously located approximately 60° apart in circumferential sweep, with the middle lobe  54   b  disposed in the center of the first portion  60 . A circumferential groove  62  extends around the exterior of first portion  60 , between its upper surface  57  and its lower surface  58 . The groove  62  is sized to receive the annular elastic member  80 . Near the centers of the lobes  54 , the groove  62  may open directly into the recesses forming the lobes  54 . A lip  64  is formed in this location, which is sized to fit in the undercuts  39  of protrusions  37 , see  FIG. 5 . The first portion  60  also includes two holes  66  that face the second portion  70 . These holes  66  are sized to receive the alignment pins  84 . The upper surface  57  of the first portion  60  may include one or more of the teeth  56 . 
         [0021]    Second portion  70  likewise includes a groove  72  and a retaining lip  74 , and includes corresponding lobes  54   d - f , if desired. In some embodiments, the second portion may likewise have holes  76  for the alignment pins  84 . As mentioned above, the second portion  70  may be a substantial or complete mirror image of the first portion  60 . 
         [0022]    The annular elastic member  80  may take any suitable form. For example, the annular elastic member  80  may be an O-ring made from suitable biocompatible material(s). Alternatively, the annular elastic member  80  may be an elastic band of any suitable type, an end-to-end-joined coil spring, a cinched elastic cord, or other elastic member. The annular elastic member  80  should be sized to fit at least partially in grooves  62 , 72  and be sized to be under at least some tension when the end cap  50  is assembled. 
         [0023]    The implant  20  may be assembled in a variety of ways. For example, alignment pins  84  may be placed in holes  66  of the first portion  60 . The first portion  60  is then coupled to the body  30  by sliding the first portion  60  onto the first end  34  from a direction normal to the longitudinal axis  32 . Such an approach allows the lips  64  of first portion  60  to slide under/into the corresponding undercuts  39  on the corresponding protrusions  37 . It should be noted that in the embodiments where the protrusions  37  are evenly spaced about the first end  34 , the first portion  60  of the end cap  50  need not be positioned in a single particular orientation relative to the body  30 , but can be put at any one of a variety of functionally equivalent positions. For example, if there are six protrusions  37 , then the first portion  60  of the end cap  50  can be joined to the body  30  in any one of six different relative positions. After the first portion  60  of the end cap  50  is joined to the body  30 , the second portion  70  is then slid into position from the opposite direction, with the alignment pins  84  being received in the holes  76  of the second portion  70 . As with the first portion  60 , the lips  74  of the second portion  70  are captured in the corresponding undercuts  39 . Joined in this manner, the first and second portions  60 , 70  are prevented from moving longitudinally away from the body  30  so as to become disconnected from the body  30 . This type of engagement is maintained by urging the first portion  60  toward the second portion  70  (and vice-versa) so that the lips  64 , 74  remain captured by the undercuts  39 . The force F to urge the first and second portions  60 , 70  toward each other is supplied by the tension in the annular elastic member  80 . 
         [0024]    In some embodiments, the second end  36  of body  30  may also have an end cap  51  mounted thereto. The second end cap  51  may be identical to the first end cap  50 , or may be different, as is desired. 
         [0025]    Once assembled, the implant  20  may be used in a conventional fashion. For example, the implant  20  may be placed into an intervertebral space that has been prepared in a conventional fashion, and then the length L or operational height of the implant  20  may be adjusted as desired for those embodiments having height adjustments. The teeth  56  on the end cap  50 , if present, help secure the implant  20  in place by biting into the bone of the associated vertebra. Suitable bone growth material may then be added to the implant  20 , and/or the bone growth material may be added to the implant  20  prior to implantation. The implantation is then terminated in a conventional fashion. It should be noted that the implants  20  described herein may be implanted within a living patient for the treatment of various spinal disorders. The implants  20  may also be implanted in a non-living situation, such as within a cadaver, model, and the like. The non-living situation may be for one or more of testing, training, and demonstration purposes. 
         [0026]    In the embodiments discussed above, flat style end caps  50  have been used for illustrative purposes. When assembled to the body  30 , the flat style end caps  50  have upper surfaces  57  and lower surfaces  58  that are generally parallel to each other, and disposed at a common angle to the longitudinal axis  32 , such as perpendicular thereto. However, in some embodiments, one or both end caps  50  may be of an angular style, such that the upper surface  57  and lower surface  58  of the end cap  50  are not parallel, but are each disposed at respective different angles that are both transverse to the longitudinal axis  32 . The respective angles may vary from each other by, for example, 4°-15° or other desired amounts. 
         [0027]    The discussion above has assumed that the alignment pins  84  are distinct from the first and second portions  60 , 70 . With such an arrangement, the first and second portions  60 , 70  can be, if desired, mirror images of each other. However, such is not required, and the alignment pins  84  can be made integral with one or both of the first and second portions  60 , 70 . Further, while simple pins  84  have been used for illustrative simplicity, other alignment approaches, such as rails and grooves, tapered and interleaving projections/recesses, or the like could alternatively be used to help align the second portion  70  relative to the first portion  60 . 
         [0028]    The discussion above has also used a round shape for the end cap  50 . However, the end cap  50  need not be round, and other regular shapes, such as octagonal, square, oval, football-like, or semi-symmetric or irregular shapes can alternatively be employed without departing from the present invention. Likewise, the discussion above has used an end cap  50  of two distinct peripheral portions  60 , 70  as an illustrative embodiment. However, the periphery of end cap  50  may be formed of more than two distinct peripheral portions, such as three, four, or more portions, without departing from the present invention. For example, the end cap  50  may be formed of four portions, each sweeping a peripheral arc of 90°. For such an arrangement, there should be at least four protrusions  37  with undercuts  39  disposed in the corresponding locations. The various peripheral portions help form the overall outer periphery of the end cap  50  and surround the central bore  52 . 
         [0029]    The discussion above has assumed that the end cap  50  will remain removable from the body  30 , such as by removing the annular elastic member  80  and sliding the first and second portions  60 , 70  out of engagement with the body  30 . However, in some embodiments, the end cap  50  may be permanently mounted to the body  30 , such as through the addition of adhesives, welding, staking, locking detents, or other comparable means. If desired, the end cap  50  or body  30  may have roughed surfaces, which may facilitate locking together of the components. 
         [0030]    The discussion above has sometimes used an O-ring as an example of the annular elastic member  80 . While O-rings are typically circular in their undeformed state, both in top view and in cross-section, there is no requirement that the annular elastic member have such characteristics in all embodiments. Indeed, the annular elastic member  80  may have any suitable cross-sectional shape, such as trapezoidal, oval, octagonal, star, or any other desired shape including irregular shapes. Likewise, the annular elastic member  80 , in its undeformed (e.g., unloaded) state, may have a shape in top view that is oval, octagonal, square, or any other desired shape that loops back on itself, including irregular shapes. 
         [0031]    The components described above may be made from any suitable biocompatible material known in the art, such as titanium and its alloys, polymers such as PEEK or silicones, etc. By way of non-limiting example, the annular elastic element  80  may be made from silicone or stainless steel, and may advantageously be superelastic if desired. 
         [0032]    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. 
         [0033]    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. 
         [0034]    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. 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.