Abstract:
A surgical implant is provided with upper and lower telescoping members which move axially between extended and retracted positions. A fixed length sleeve fits over the telescoping members. The sleeve is load bearing to support axial loads. The sleeve also prevents the telescoping members from retracting and encloses an internal cavity within the implant for packing bone fusion material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of application Ser. No. 13/409,357, filed Mar. 1, 2012, which claims priority to Application No. 61/448,981 filed Mar. 3, 2011, all of which are hereby incorporated by reference in their entireties. 
     
    
     FIELD 
       [0002]    The invention relates to an expandable corpectomy cage having non-weight bearing telescoping members which are expandable and retractable and a weight-bearing sleeve fit over the telescoping members so that the sleeve bears axial loads when the assembled cage is implanted in a patient. 
       BACKGROUND 
       [0003]    A corpectomy is a surgical procedure wherein a portion of the vertebral body and adjacent intervertebral discs are removed to relieve pressure or decompress the spinal cord and nerves. A corpectomy cage is used to fill the space created by the vertebrae removal. Two types of cages are generally available: A solid fixed height cage and an expandable cage. Fixed cages are manufactured in various heights so that one cage can be selected to best fit the cavity created by the removed vertebral body. Alternatively, an expandable cage having a variable height can be used to maintain spacing of the vertebrae above and below the removed body material. Such expandable cages typically include telescoping members with a physical mechanism to retain the members at the selected height. For example, telescoping members are formed with threaded or ratcheting interconnections, or the use of pins, set screws and the like, to fix the members at a selected height. 
         [0004]    Both types of cages have limitations and problems. Fixed or solid cages have excellent structural integrity, but are cumbersome to place. The fixed cage must be exactly the right height. Otherwise, if the cage is too big, it can cause over distraction to the vertebral bodies or damage the vertebral body above and below the cage. If the cage is too small, it can move out of position. Expandable cages are much easier to place and size correctly. However, the mechanical mechanism used to expand the cage may fail in vivo, which can lead to catastrophic results. The telescoping members are weight bearing so as to support the axial loads on the cage when the cage is implanted. Thus, the strength of the case depends upon the inner connection between the telescoping members. If the physiologic load becomes too great, the cage will collapse, thereby causing potentially serious medical problems for the patient. Thus, the structural integrity of an expandable case is less than a fixed or solid cage. 
         [0005]    Some commercially available expandable cage are made of metal. These metal cages cause artifact on MRI or CT scans, thereby decreasing the ability to visualize nearby anatomy. Metal cages are also much harder than bone, and can telescope into the vertebral bodies above and below the cage. Commercially available fixed cages are made of other materials, such as carbon fiber, or plastic, which eliminate artifacts on MRI and CT scans. 
         [0006]    Accordingly, a primary objective of the present invention is the provision of an improved expandable corpectomy cage which overcomes the problems of the prior art. 
         [0007]    Another objective of the present invention is the provision of an expandable corpectomy cage having structural integrity and which is easy to use. 
         [0008]    Still another objective of the present invention is the provision of an expandable corpectomy cage which is made of non-metallic materials so as to avoid scanning and imaging artifacts. 
         [0009]    Yet another objective of the present invention is the provision of a corpectomy cage having telescoping members which are non-load bearing, and a load-bearing sleeve around the telescoping members. 
         [0010]    A further objective of the present invention is the provision of a corpectomy cage having C-shaped telescoping members with aligned openings for receiving bone fusion material, and a sleeve to cover the openings so as to retain the fusion material within the cage. 
         [0011]    Still another objective of the present invention is the provision of an improved corpectomy cage having minimal weight and increased strength. 
         [0012]    A further objective of the present invention is the provision of an improved corpectomy cage which is economical to manufacture, and safe and durable in use. 
         [0013]    These and other objectives will become apparent from the following description of the invention. 
       SUMMARY 
       [0014]    The expandable corpectomy cage of the present invention includes upper and lower telescoping members or segments which are movable axially between extended and retracted positions. Each segment has an internal cavity for receiving bone fusion material. A C-shaped sleeve or cover removably fits over the opening in opposite sides of the telescoping members. The primary function of the sleeve is to support axial loads on the assembly to prevent the telescoping members from retracting or collapsing. The sleeve also encloses the cavity, which is free from obstructions. The sleeve is retained on the telescoping members by a snap fit, fasteners, or other locking means. The assembly may have a substantially square cross-section or a circular cross-section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIGS. 1A-14D  of the drawings show a first embodiment of the corpectomy cage of the present invention having a square cross-section. 
           [0016]      FIGS. 15-21  show a second embodiment of the corpectomy cage of the present invention having a round cross-section. 
           [0017]      FIG. 1A  is a perspective view of the first embodiment of the corpectomy cage according to the present invention. 
           [0018]      FIG. 1B  is a perspective view of the telescoping members of the first embodiment. 
           [0019]      FIG. 2  is a sectional view taken along lines  2 - 2  of  FIG. 1A . 
           [0020]      FIG. 3  is an exploded view of the telescoping members and sleeve of the corpectomy cage of the first embodiment. 
           [0021]      FIG. 3A  is an exploded view of an alternate embodiment with ratcheting side walls on the telescoping member. 
           [0022]      FIG. 4  is a plan view from one side of the cage. 
           [0023]      FIG. 5  is a sectional view taken along lines  5 - 5  of  FIG. 4 . 
           [0024]      FIG. 6  is a perspective view of a shortened sleeve for the corpectomy cage. 
           [0025]      FIG. 7A  is a perspective view of the inner telescoping members. 
           [0026]      FIG. 7B  is an end view of the inner telescoping members shown in  FIG. 7A . 
           [0027]      FIG. 7C  is an elevation view of one side of the inner telescoping member. 
           [0028]      FIG. 7D  is an end view from the opposite end of  FIG. 7B . 
           [0029]      FIG. 7E  is another elevation view of the inner telescoping member. 
           [0030]      FIG. 8A  is a perspective view of the outer telescoping members. 
           [0031]      FIG. 8B  is an end view of the outer telescoping members shown in  FIG. 8A . 
           [0032]      FIG. 8C  is an elevation view of one side of the outer telescoping member. 
           [0033]      FIG. 8D  is an end view from the opposite end of  FIG. 8B . 
           [0034]      FIG. 8E  is another elevation view of the outer telescoping member. 
           [0035]      FIG. 9A  is a perspective view of the sleeve of the corpectomy cage. 
           [0036]      FIG. 9B  is a top plan view of the sleeve. 
           [0037]      FIG. 9C  is an elevation view from one side of the sleeve. 
           [0038]      FIG. 9D  is an elevation view from another side of the sleeve. 
           [0039]      FIG. 10  is an exploded view of an alternative embodiment of the corpectomy cage. 
           [0040]      FIG. 11  is a perspective view of a shortened sleeve for the cage of  FIG. 10 . 
           [0041]      FIG. 12A  is a perspective view of the inner telescoping member of the corpectomy cage shown in  FIG. 10 . 
           [0042]      FIG. 12B  is an end view of the inner telescoping members shown in  FIG. 12A . 
           [0043]      FIG. 12C  is an elevation view of one side of the inner telescoping member shown in  FIG. 12A . 
           [0044]      FIG. 12D  is an end view from the opposite end of  FIG. 12B . 
           [0045]      FIG. 12E  is another elevation view of the inner telescoping member of  FIG. 12A . 
           [0046]      FIG. 13A  is a perspective view of the outer telescoping member of the cage shown in  FIG. 10 . 
           [0047]      FIG. 13B  is an end view of the outer telescoping members shown in  FIG. 13A . 
           [0048]      FIG. 13C  is an elevation view of one side of the outer telescoping member shown in  FIG. 13A . 
           [0049]      FIG. 13D  is an end view from the opposite end of  FIG. 13B . 
           [0050]      FIG. 13E  is another elevation view of the outer telescoping member of  FIG. 13A . 
           [0051]      FIG. 14A  is a perspective view of the sleeve of the corpectomy cage shown in  FIG. 10 . 
           [0052]      FIG. 14B  is a top plan view of the sleeve of  FIG. 14A . 
           [0053]      FIG. 14C  is an elevation view from one side of the sleeve shown in  FIG. 14A . 
           [0054]      FIG. 14D  is an elevation view from another side of the sleeve of  FIG. 14A . 
           [0055]      FIG. 15  is a perspective view of the round embodiment of the corpectomy cage of the present invention. 
           [0056]      FIG. 16  is another perspective view of the round corpectomy cage. 
           [0057]      FIG. 17  is an exploded view of the round corpectomy cage. 
           [0058]      FIG. 18  is an enlarged view taken along line  18  of  FIG. 16 . 
           [0059]      FIG. 19  is a side elevation view of the round corpectomy cage. 
           [0060]      FIG. 20  is a sectional view taken along lines  20 - 20  of  FIG. 19 . 
           [0061]      FIG. 21  is a sectional view taken along lines  21 - 21  of  FIG. 19 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0062]    A square embodiment of the corpectomy cage of the present invention is designated by the reference numeral  10  in  FIGS. 1A-14D .  FIGS. 15-21  show a round embodiment of the corpectomy cage designated by the reference numeral  10 A. The cage  10  has three primary components: an inner telescoping member  12 , and outer telescoping member  14  and a sleeve or cover  16 . Similarly, the cage  10 A has three primary components: an inner telescoping member  12 A, an outer telescoping member  14 A, and a sleeve or cover  16 . The cages  10  and  10 A, and their components, function similarly to one another in implantation and in use. 
         [0063]    The inner telescoping member  12  has opposite sides  18  with an inner connecting web or back wall  20 , with an opening  22  opposite the web  20 . Thus, the inner telescoping member  12  has a general C-shape with squared corners. The outer telescoping member  14  has opposite sides  24 , with an inner connecting web or back wall  26 , with an opening  28  opposite the web  26 . Thus, the outer telescoping member  14  has a C-shape with squared corners. The sidewalls  18  of the member  12  have a narrower spacing than the side walls  24  of the member  14 , such that the members  12 ,  14  can be assembled for axial movement relative to one another. 
         [0064]    In the alternative embodiment shown in  FIG. 3A , the sides  18  have external ratchets  19  and the side  24  have internal ratchets. The ratchets  19 ,  24  matingly overlap and allow the telescoping members to be extended one step at a time, such as 1 mm increments. 
         [0065]    The inner and outer telescoping members  12 A,  14 A each have cylindrical side walls  18 A,  24 A, respectively, with enlarged openings therein. The diameter of member  12 A is smaller than the diameter of member  14 A, so that the members can be assembled for axial movement relative to one another. 
         [0066]    The sleeve  16  includes opposite sides  30  with a web or front wall  32  extending between the opposite sides, and an opening  34  opposite the web  32 . The sleeve  16  has a C-shaped profile with squared corners. Similarly, the sleeve  16  has opposite sides  30 A with an opening  34 A. 
         [0067]    The inner and outer telescoping members  12 ,  14  each have an end plate  36 ,  38 , respectively. Similarly, the inner and outer round telescoping members  12 A,  14 A have respective end plates  36 A,  38 A. 
         [0068]    The inner and outer telescoping members  12 ,  14  and  12 A,  14 A are adapted to matingly and slidably fit together in a telescoping manner for axial expansion and retraction. The sleeve  16  is adapted to matingly fit over the outer telescoping member  14 A, with the opposite ends of the sleeve  16  engaging the inner surfaces of the end plates  36 ,  38 . Similarly, the sleeve  16  is adapted to matingly fit over the outer telescoping member  14 A, with the ends of the sleeve  16  abutting the inner surfaces of the end plates  36 A,  38 A. This assembly of the inner and outer telescoping members and the sleeve forms the cage  10 ,  10 A with the sleeve  16 ,  16  being load bearing. Thus, with this cage configuration of the present invention, the sleeves  16 ,  16  bear the axial loads from the vertebral bodies on the end plates  36 ,  38  or  36 A,  38 A. The sleeves  16 ,  16  thereby preclude or prevent the telescoping members  12 ,  14  and  12 A,  14 A from collapsing or retracting in vivo relative to one another. Also, the sleeves  16 ,  16  eliminate the need for a fastener between the inner and outer telescoping members, as in the prior art, to fix the relative positions of the telescoping members relative to one another. Thus, the telescoping members  12 ,  14  and  12 A,  14 A are non-load bearing. 
         [0069]    Preferably, the inner and outer telescoping members  12 ,  14  have overlapping or interlocking structure so that these members slide axially without transverse separation. More particularly, in the preferred embodiment, the inner telescoping member  12  has an external tongue or lip  40  extending outwardly from each side  18 . The outer telescoping member has internal grooves  42  on each side  24  to slidably receive the tongues or lips  40  on the inner telescoping member  12 . For the round inner and outer telescoping members  12 A,  14 A, the circular shape controls the sliding axial movement of the members relative to one another. 
         [0070]    The sleeve  16  can be retained on the telescoping members  12 ,  14  in any convenient manner. In a preferred embodiment, the sleeve  16  snap fits onto the outer telescoping member  14 . More particularly, the outer telescoping member  14  has an axially extending external projection or bead  44  with a beveled surface and a retention shoulder extending along each side  24 . The sleeve  16  has an internal groove  46  along the inside of each side wall  30 . The sides  30  of the sleeve are resilient such that the sleeve snap fits over the beads  44 , which are matingly received within the grooves  46  of the sleeve  16 . Thus, the sleeve  16  is retained on the outer telescoping member  14  by the overlapping beads  44  and grooves  46 . The sleeve  16  can be removed from the outer telescoping member  14  by spreading the sides  30  to disengage the beads  44  and grooves  46 . 
         [0071]    In an alternative embodiment shown in  FIGS. 10-14D , the sleeve  16  is retained on the telescoping members  12 ,  14  using screws  48  which extend through the sleeve and into threaded holes in the telescoping members  12 ,  14 . For the round cage  10 A, the sides  30 A of the sleeve  16  are resilient, such that the sleeve  16  can be snap fit over the telescoping members  12 A,  14 A. 
         [0072]    It is understood that the sleeve  16 ,  16  is generally selected by the surgeon performing the corpectomy from a set of sleeves having various heights or lengths, such that the assembled cage  10 ,  10 A will properly fit between the upper and lower vertebral bodies. For example,  FIGS. 1A-4  show a longer or taller sleeve  16 , while  FIG. 6  shows a shorter sleeve. Similarly,  FIG. 11  shows a shorter sleeve compared to the longer sleeve shown in  FIG. 14A . 
         [0073]    While the sleeve  16 ,  16  prevents the telescoping members  12 ,  14  and  12 A,  14 A from being retracted toward one another, in another alternative embodiment, the sleeve can prevent extension of the telescoping members relative to one another. For example, in the round cage  10 A shown in  FIGS. 15-21 , the sleeve  16  has a radially directed lip  50  extending inwardly from each end for receipt in a groove  42  on each telescoping member  12 A,  14 A. The lips  50  of the sleeve  16  are received in the grooves  52  of the telescoping members  12 A,  14 A to prevent the members from expanding axially. 
         [0074]    The cages  10 ,  10 A of the present invention are implanted using conventional methodology. For example, the tips of a hand held expanding tool are received in holes  54  in the end plates  36 ,  38  of the telescoping members  12 ,  14 , or in a perimeter groove  56  in the end plates  36 A,  38 A of the telescoping members  12 A,  14 A. After the telescoping members  12 ,  14 ,  12 A,  14 A, are implanted and bone fusion material is added to the cage cavity, the sleeve  16 ,  16  is placed over the telescoping members so as to fix the height of the cage  10 ,  10 A. The axial loads on the cage  10 ,  10 A are then born by the sleeve  16 ,  16 , rather than by the telescoping members  12 ,  14  and  12 A,  14 A. The cages  10 ,  10 A have enlarged fusion openings  58 ,  58 A to accommodate bone growth around and through the cage. The center cavity of the cage is substantially unobstructed for improved or enhanced bone growth and fusion. 
         [0075]    Since the sleeve  16 ,  16  has a fixed length so as to be load bearing, the telescoping segments  12 ,  14  and  12 A,  14 A, as well as the sleeves  16 ,  16 , can be made of non-metallic material which does not interfere or otherwise produce artifacts when scanned or imaged. Thus, the cages  10 ,  10 A can be made of any high strength, lightweight, biocompatible material. 
         [0076]    The invention has been shown and described above with the preferred embodiments, and it is understood that many modifications, substitutions, and additions may be made which are within the intended spirit and scope of the invention. From the foregoing, it can be seen that the present invention accomplishes at least all of its stated objectives.