Abstract:
A vertebral implant ( 10 ) is provided with a concave cut-away section ( 16 ) configured to correspond to the outer circumference of another implant placed adjacently thereto. A specialized distractor tool ( 20 ) with distractor tips ( 21 ) for distracting a vertebral space has two channels ( 26, 27 ) of generally circular profile that overlap in cross-section to accommodate implants according to the present invention.

Description:
BACKGROUND  
       FIELD OF THE INVENTION  
         [0001]    The present application relates to a low profile fusion cage and an insertion set for the low profile fusion cage.  
         BACKGROUND OF THE INVENTION  
         [0002]    Known spinal implants, such as those used for vertebral fusion, are often used in pairs to provide adequate, evenly distributed support and fusion inducement. Because of limited space for implantation and for surgical maneuvering, it is sometimes difficult or unfeasible to implement a pair of implants that otherwise have desirable dimensions and attributes. Certain existing implant designs are configured for close, adjacent placement to other implants, but none achieve optimum performance, versatility or ease of insertion.  
         SUMMARY  
       SUMMARY OF THE INVENTION  
         [0003]    It is an object of the present invention to provide an implant design, and associated instruments and methods, that provide optimum configurations for placement of adjacent implants in close proximity with optimum performance. These objects and others are achieved through the present invention implant configuration and associated instruments and method.  
           [0004]    In a preferred embodiment, a fusion implant according to the present invention is provided with a concave cut-away portion on a circumferential surface of an elongated implant. The concave portion accommodates the outer contour of an adjacently placed implant having a corresponding concave surface. A novel dual tang distractor tool is provided with two over-lapping cross-sectional configurations to facilitate close insertion and placement of implants according to the present invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    Preferred embodiments of the present disclosure are described herein with reference to the drawings wherein:  
         [0006]    [0006]FIG. 1 is a perspective view of the fusion cage of the present disclosure;  
         [0007]    [0007]FIG. 2 is a side view of the fusion cage of FIG. 1;  
         [0008]    [0008]FIG. 3 a  is a cross-sectional view of the fusion cage taken along lines B-B of FIG. 1;  
         [0009]    [0009]FIG. 3 b  is a cross-sectional view of the fusion cage as shown in FIG. 3 a,  with a conventional implant cage of similar view placed adjacently thereto.  
         [0010]    [0010]FIG. 4 is a perspective view of the tang retractor of the present disclosure;  
         [0011]    [0011]FIG. 5 is a perspective view of the guide of the present disclosure;  
         [0012]    [0012]FIG. 6 is a perspective view illustrating attachment of the guide to the tang retractor;  
         [0013]    [0013]FIG. 7 is a perspective view of the plate of the impactor;  
         [0014]    [0014]FIG. 8 is a front, perspective view of an alternative embodiment of the present invention; and  
         [0015]    [0015]FIG. 9 is a front, perspective view of another alternative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    FIGS.  1 - 3   a  illustrate perspective, side and end views of the low profile fusion cage ( 10 ) of the present invention. The present invention cage ( 10 ) is of the type known commercially as the Ray TFC™ Fusion Cage currently marketed by Surgical Dynamics, Inc. The Ray TFC™ Fusion Cage is disclosed in commonly assigned U.S. Pat. No. 4,961,740, the contents of which are incorporated herein by reference.  
         [0017]    The fusion cage ( 10 ) disclosed herein can be implemented with another fusion cage to reduce the total amount of space occupied by two conventional fusion cages placed side by side. The fusion cage ( 10 ) has a helical thread ( 14 ) for facilitating insertion and securing of the cage ( 10 ) in a vertebral disc space. The thread ( 14 ) is carved out to form concave portions ( 16 ,  17 ) to reduce the profile of the thread. As shown, the concave portions ( 16 ,  17 ) are preferably provided 180 degrees apart. If desired, only one concave portion is necessary to carry out the present invention. It is possible, also, to provide more than two concave portions if desired. The concave portions ( 16 ,  17 ) allow two or more cages ( 10 ,  11 ) to be placed close together as the radiused portion of one cage ( 11 ) is placed within the concave portion ( 17 ) of an adjacent cage ( 10 ), as shown in FIG. 3 b.  As can be appreciated, the combined width (transverse space) of the two low profile cages ( 10 ,  11 ) placed in this fashion is less than the combined width if two conventional cages without at least one of them having a concave portion were placed side by side.  
         [0018]    FIGS.  4 - 7   b  illustrate an insertion instrument set for fusion cages according to the present invention. The instrument set includes a tang retractor ( 20 ), a guide ( 30 ) and an impactor ( 40 ) and impactor plate ( 41 ). The tang retractor ( 20 ) includes a pair of spaced apart tangs ( 21 ) which are dimensioned and configured as wedges at the distal end for insertion into and distraction of the disc space. The configuration of the tangs ( 21 ) and the manner in which they distract the disc space is described in pending U.S. patent application Ser. No. 08/889,661, filed Jul. 8, 1997, the contents of which are incorporated herein by reference.  
         [0019]    The tang retractor ( 20 ) includes a pair of proximally extending slotted tabs ( 22 ) for mounting the tabs ( 42 ) of the impactor plate ( 41 ) when the impactor plate ( 41 ) is mounted to the proximal end of the distractor ( 20 ). The tabs ( 42 ) are inserted into the slots ( 23 ) of the tabs ( 22 ) to mount the impactor plate ( 41 ) and the elongated integral impactor ( 40 ), which is connected to the impactor plate ( 41 ) by threads ( 43 ,  45 ), to the tang retractor ( 20 ). The impactor ( 40 ) can then be impacted or tapped at its proximal end ( 47 ) by a suitable tool, such as a hammer, to insert the tang ( 21 ) into a vertebral space. After insertion, the tabs ( 42 ) are slid out of engagement with slots ( 23 ) to separate and remove the impactor ( 40 ) and impactor plate ( 41 ), leaving the tang retractor ( 20 ) in place with the tangs ( 21 ) inserted in the vertebral space.  
         [0020]    The guide ( 30 ) is then attached to tang retractor ( 20 ) by inserting the distal end pin ( 32 ) into the longitudinal slot ( 25 ) of the retractor ( 20 ). The distal end pin ( 32 ) is seated within the slot ( 25 ) so that the guide ( 30 ) can be pivoted, about the pin ( 32 ), with respect to the fixed tang retractor ( 20 ) between alignment with each of the two openings ( 26 ,  27 ) of the tang retractor ( 20 ), respectively. Each of the openings ( 26 ,  27 ) is configured to receive a fusion cage along with a conventional cage insertion tool (not shown). The guide ( 30 ) is rotated about pin ( 32 ) so that its axial bore ( 34 ) is aligned with one of the openings ( 26 ,  27 ) of the tang retractor ( 20 ) during hole preparation through a respective one of the openings. Suitable tools, such as those described in the aforementioned application Serial No. 08/889,661, are inserted through the bore ( 34 ) to prepare the space for fusion cage insertion. Fusion cages such as the type of the present invention, are then inserted via an elongated insertion tool through the bore ( 34 ) and the respective tang retractor opening ( 26 ,  27 ) for placement within the vertebral space. Each cage is placed so that one of the concave portions ( 16 ,  17 ) faces the adjacent opening or bore in the vertebral space. The guide ( 30 ) is subsequently rotated so that axial bore ( 34 ) is aligned with the other opening ( 26 ,  27 ) in the retractor  20 . Another fusion cage, either with or without concave portions, is inserted in a similar manner as described above so that its outer circumferential portion fits within the concave portion ( 16 ,  17 ) of the first-inserted fusion cage.  
         [0021]    It is contemplated that an interlocking device ( 33 ) be provided to retain the guide ( 30 ) in each of its two aligned positions relative to the tang retractor ( 20 ) during site preparation and insertion of a fusion cage therethrough.  
         [0022]    Alternate embodiments of the present invention, such as those shown in FIGS.  8 - 9 , include variously configured implant bodies having a concave portion to facilitate close, adjacent placement with additional implant bodies. For instance, the implant body ( 100 ) in FIG. 8 is a half-oval having a central opening ( 102 ) to facilitate bone fusion, and a concave side wall ( 104 ) configured to matingly receive a circumferential, convex wall ( 106 ) of an adjacent, oval implant ( 108 ). The implant body ( 200 ) of FIG. 9, is generally cylindrical and has a concave channel ( 202 ) aligned generally perpendicularly to a longitudinal axis running between open ends ( 204 ,  206 ).  
         [0023]    It can be appreciated that the tang retractor ( 20 ) having a length approximately equal to its width increases visibility as well as enables the user to more easily remove extraneous disc tissue because of the increased mobility of instruments, e.g. rongeurs, inserted through the retractor  20 . While this is the preferred embodiment, the length of the retractor ( 20 ) may be varied as desired to achieve different advantages.  
         [0024]    While the preferred embodiment has been disclosed herein, it is understood and contemplated that modifications and variations may be employed without departing from the scope of the present invention.