Abstract:
An apparatus and method for fusing opposing spinal vertebrae is disclosed. In an embodiment for a spinal implant of the present invention, the implant includes a body assembly and a retention member coupled to the body assembly. The retention member includes a tang where the tang is extendible from the body assembly. In a method of the present invention, the method includes the step of inserting an implant between adjacent vertebrae with a retention member of the implant in a first retracted configuration. The method also includes the step of configuring the retention member in a second extended configuration wherein when the retention member is in its second extended configuration, a portion of a tang of the retention member extends from the implant and into one of the adjacent vertebrae.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an implant for use in surgical procedures for fusing adjacent bone structures and more specifically adjacent vertebrae. 
     2. Description of the Related Art 
     The fusion of adjacent bone structure is commonly performed to provide for long-term replacement to compensate for degenerative and or deteriorated disorders in bone. In many cases, low back pain can be avoided by preventing relative motion between spinal vertebrae. By fusing the contiguous vertebrae in the lumbar region, lower back pain can be abated. 
     Surgical techniques are known for use in spinal stabilization. Surgical techniques seek to rigidly join the vertebrae that are separated by a degenerated disk. Ideally, the surgery effectively replaces the vertebra-disk-vertebra combination with a single rigid vertebra. Various surgical techniques have been developed to approximate this ideal. 
     Many of the techniques begin by partially removing the degenerative disk material. Where the techniques differ is in their strategy for replacing the disc material. Some procedures fill the void left between the contiguous vertebra with bone graft. Other techniques rely on the use of an implant acting alone or in combination with bone fragments. Usually, initial stabilization is achieved by making the implant diameter slightly larger than the void between the vertebrae. Eventual fusion of the opposing bone segments results from bone growth into and through the implant. 
     In some cases, the above procedures have failed due to shifting of the implant between the adjacent vertebrae during the initial stabilization period, i.e., prior to fusion taking place. This translation of the implant can lead to discomfort and serious consequences for the patient due to the proximity of nerves and blood vessels in the implanted area. 
     Therefore, it is desirable that an improved apparatus and method be provided for fusing opposing spinal vertebrae. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention for a spinal implant includes a body assembly and a retention member coupled to the body assembly. The retention member includes a tang where the tang is extendible from the body assembly. 
     In a method of the present invention, the method includes the step of inserting an implant between adjacent vertebrae with a retention member of the implant in a first retracted configuration. The method also includes the step of configuring the retention member in a second extended configuration wherein when the retention member is in its second extended configuration, a portion of a tang of the retention member extends from the implant and into one of the adjacent vertebrae. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features of the invention will best be appreciated by simultaneous reference to the description which follows and the accompanying drawings, in which: 
     FIG. 1 is a cross-sectional view of an embodiment of a spinal cage in a first configuration in accordance with the principles of the present invention; 
     FIG. 2 is a cross-sectional, partially exploded view of the spinal cage of FIG. 1 in a second configuration; 
     FIG. 3 illustrates the spinal cage between adjacent vertebrae in its first configuration; 
     FIG. 4 illustrates the spinal cage between adjacent vertebrae in its second configuration; 
     FIG. 5 is a side view of the body assembly of the spinal cage of FIG. 1; 
     FIG. 6 is another side view of the body assembly of FIG. 5; 
     FIG. 7 is a top view of the body assembly of FIG. 5; 
     FIG. 8 is a cross-sectional view of the body assembly as taken along line  8 — 8  of FIG. 7; 
     FIG. 9 is a side view of an embodiment of a retention member for the spinal cage in accordance with the principles of the present invention; 
     FIG. 10 is a top view of the retention member of FIG. 9; 
     FIG. 11 is another side view of the retention member of FIG. 9; 
     FIG. 12 is a cross-sectional view of a tang of the retention member of FIG. 9 as taken along line  12 — 12  of FIG. 11; 
     FIG. 13 is a side view of a second embodiment of a retention member for the spinal cage in accordance with the principles of the present invention; 
     FIG. 14 is a top view of the retention member of FIG. 13; 
     FIG. 14 is another side view of the retention member of FIG. 13; 
     FIG. 16 is a cross-sectional view of a tang of the retention member of FIG. 13 as taken along line  16 — 16  of FIG. 15; 
     FIG. 17 is a top view of an embodiment of a deployment device that can be utilized in accordance with the principles of the present invention; 
     FIG. 18 is a cross-sectional view of the deployment device of FIG. 17 as taken along line  18 — 18  of FIG. 17; 
     FIG. 19 is a partial cross-sectional view of an embodiment of a retraction device that can be utilized in accordance with the principles of the present invention; 
     FIG. 20 is a side view of an alternative embodiment of a body assembly in accordance with the principles of the present invention; and 
     FIG. 21 is a side view of another alternative embodiment of a retention member for the spinal cage in accordance with the principles of the present invention. 
    
    
     DETAILED DESCRIPTION 
     An embodiment for the spinal cage  10  of the present invention is illustrated in FIGS. 1 and 2. As can be seen, and as will be described further later in this specification, the spinal cage  10  is comprised of a body assembly  100  and a retention member  200 . Body assembly  100  is comprised of body  110  and end plug  120 . Additionally, body assembly  100  may also include a distal end cap  130 . 
     FIG. 1 illustrates the spinal cage  10  in a first configuration where the retention member  200  is not deployed from the body assembly  100 . FIG. 2 illustrates the spinal cage  10  in a second configuration where the retention member  200  has been deployed from the body assembly  100  such that tangs  220  extend into surrounding bone structure of the patient. 
     As can be seen in FIG. 3, when spinal cage  10  is in its first configuration retention member  200  is not deployed into bone portions  1  and  2 . FIG. 4 illustrates spinal cage  10  in its second configuration where retention member  200  is deployed into bone portions  1  and  2 . 
     As will also be further described later in this specification and as can be seen in FIGS. 17 and 18, a deployment device  300  is utilized to configure spinal cage  10  in its second configuration where tangs  220  are deployed from body assembly  100 . A retraction device  400 , as can be seen in FIG. 19, is utilized to return spinal cage  10  to its first configuration from its second configuration, where tangs  220  are returned to a position within body assembly  100 . 
     Each of the above-described components and procedures will be described in further detail below. 
     As discussed above, spinal cage  10  includes body assembly  100 . Body assembly  100  includes body  110 , which in this embodiment is constructed of allograft cortical bone. In alternative embodiments, body  110  could be comprised of titanium alloy or a bioceramic material. 
     As can be seen in FIG. 8, body  110  is a cylindrical member and includes a hollow bore  111  which extends therethrough. The interior of body  110  is hollow to allow it to be filled with a bone growth medium prior to implantation in the patient. The preferred bone growth medium is a cancellous bone cylindrical plug harvested from the patient. The cylindrical wall  112  of body  110 , which defines bore  111 , includes a plurality of ports  113  which extend completely through wall  112 . Ports  113  may be formed in various configurations, including the circular and oval configurations illustrated. Ports  113  allow bone ingrowth, i.e., bone to grow from outside of body  110 , and thus cylindrical wall  112 , to within body  110  through ports  113 . 
     Body  110  also includes two slots  114  which extend through wall  112 . The two slots  114  are located on opposing sides of wall  112  and are oriented at an angle to the longitudinal axis L 1  of body cylinder  110 . As will be explained, the tangs  220  of retention member  200  are received in, and are extendable through, slots  114 . 
     As can be seen in FIGS. 1 and 2, distal end cap  130  is threadedly received within a distal portion of bore  111  at the distal end  116  of body  110 . After a cancellous bone plug is inserted into the hollow interior, or bore  111 , of body  110 , end cap  130  is threaded into the internal threading included at distal end  116  of body  110 . The end cap  130  is tightened by inserting a complementary-shaped tool into a square-formed slot  132  defined by end plug  130  and further threading end cap  130  into body  110 . 
     End cap  130  utilizes a spherical radius on its exposed surface to prevent irritation to adjacent structures and, in its preferred embodiment, is constructed from a bioabsorbable material such as Poly-L-Lactic Acid (PLLA). End cap  130  will eventually be absorbed by the patient&#39;s body and will, thus, eventually leave the end of the cancellous bone plug inserted within body  110  exposed for further fusion to the patient&#39;s bone. An alternative material for comprising end cap  130  could be allograft cortical bone. 
     End plug  120  is received within a proximal portion of bore  111  at the proximal end  115  of body  110 . End plug  120 , in this embodiment, is comprised of stainless steel; however, other embodiments could be comprised of titanium alloy. In the preferred embodiment, the stainless steel end plug  120  is press-fitted into the allograft body cylinder  110 . However, if titanium alloy is utilized for body  110 , end plug  120  is integrally formed with body  110 , i.e., its features are machined into body cylinder  110 , and a single structure includes all of the features of body  110  and end plug  120 . 
     If two structural components are utilized for end plug  120  and body  110 , a stainless steel pin  150  is press-fitted through body cylinder  110  and end plug  120  to ensure the integrity of the assembly. Even if the body cylinder  110  and end plug  120  are integrally formed, the physical structure of pin  150  may be provided in the integral structure for purposes that will be discussed later. 
     End plug  120  contains internal threading  121  and a counterbore  122 . Similar to body  110 , end plug  120  also contains two slots  123 . The two slots  123  are located on opposing sides of end plug  120  and are oriented at the same angle relative to the longitudinal axis L 1  of body cylinder  110  as are slots  114  of body  110 . As will be explained, the tangs  220  of retention member  200  are received in, and are extendable through, the aligned slots  114  and  123  of the body  110  and end plug  120 , respectively. The slots  114  and  123  are aligned during the process of assembling body  110  and end plug  120 . The aligned slots are oriented 90 degrees from the longitudinal axis of pin  150 . 
     FIGS. 9-12 illustrate a first embodiment for a retention member of the present invention. In this embodiment, retention member  200  is a one piece stainless steel structure consisting of a body  210 , which defines a threaded hole  215  therein, and two tangs  220 . The retention member  200  could also be constructed of titanium alloy or a combination of titanium alloy and nitinol if the other spinal cage components are of titanium alloy. In the embodiment of FIGS. 9-12, the retention member&#39;s tangs  220  have an oval cross-section and a rounded end at the distal tip  225  of each tang  220 . As will be described later in this specification, and as can be seen in FIG. 2, the tangs  220  are deformable such that they are able to extend from body assembly  100  as retention member  200  is moved further into body assembly  100 . 
     Tangs  220  are pre-formed as illustrated in FIG.  9 . Body  210  is cylindrical and includes a multi-faceted flange  212  at its proximal end, which is illustrated as being hexagonal in this embodiment. Threaded hole  215  extends through body  210  and, as will be further explained later in this specification, is utilized for reversing the deployment of retention member  200  from body assembly  100  in the event that the spinal cage must be removed from the patient. 
     Retention member  200  is pre-assembled into body assembly  100 , as can be seen in FIG.  1 . As can also be seen in FIG. 1, retention member  200  is assembled into body assembly  100  with tangs  220  fitted into the slots defined by the body assembly. 
     FIGS. 13-16 illustrate a second embodiment for a retention member of the present invention. Retention member  250  of this embodiment also includes a body  260 , which defines a threaded hole  265  therein, and two tangs  270 . As was body  210  of the previously discussed embodiment, body  260  is also cylindrical and includes a multi-faceted flange  262  at its proximal end, which is also hexagonal in this embodiment. However, the retention member  250  of this embodiment includes tangs  270  which have a triangular cross-section and a sharp end at the distal tip  275  of each tang  270 . Retention member  270  may be comprised of the same materials as retention member  200 . 
     A deployment device  300 , as illustrated in FIGS. 17 and 18, is used to hold and insert the spinal cage  10  as well as to deploy the retention member  200 , as will be explained later in this specification. Deployment device  300  includes a body  310  which has a multi-faceted bore  312  that is complementary in shape to the multi-faceted flange  212  of body  210  of retention member  200 . In this embodiment, and as can be seen in FIG. 17, the bore  312  has a hexagonal shape. Multi-faceted flange  212  is slidably receivable within bore  312 . Distal end  310 A of body  310  includes an anti-rotation slot  314  and retention member tang slots  316 . As will be explained, pin  150  is received within slot  314  and tangs  220  are received within slots  316 . 
     Deployment device  300  also includes collar  320  which is free to rotate and translate about body  310  but is limited in translation by torque arm  330 . Collar  320  contains external threads  322  at a distal end  320 A of collar  320  which are threaded into the internal threads  121  of end plug  120  during use of deployment device  300 . Torque arm  330  is attached to a proximal end  310 B of body  310  and extends perpendicular to the longitudinal axis L 2  of body  310 . A handle  340  includes a hand-grip portion  342  and an externally threaded shaft  344 . The external threads of threaded shaft  344  threadedly engage with the internal threads included at the proximal end  310 B of body  310 . An anvil  346  is included at the distal end of shaft  344 . 
     The use of spinal cage  10  and deployment device  300  will now be further described. The spinal cage is positioned such that the tangs  220  of retention member  200  are deployed parallel to the spinal axis. The deployment device  300  is keyed and marked to facilitate this orientation. The keying of the deployment device  300  is accomplished by slot  314  interfacing with pin  150 . Since torque arm  330  is located 90° angularly with respect to slot  314  and torque arm  330  is marked “align parallel to spinal axis for fixation”, the deployment device  300  is keyed and marked to assure that the tangs  220  deploy parallel to the spinal axis. 
     The deployment device  300  is fitted to the spinal cage  10  when the spinal cage is in its first configuration as shown in FIGS. 1 and 3. The body  310  of deployment device  300  is positioned over the protruding body  210  of retention member  200  such that the retention member body  210  is slidingly received within bore  312  of body  310  of deployment device  300 . The complementary hexagonal shapes of bore  312  of deployment device  300  and flange  212  of body  210  of retention member  200  allow for easy alignment of deployment device  300  and retention member  200 . The slots  316  of body  310  of deployment device  300  are aligned by the operator with the retention member tangs  220  such that, as body  310  of deployment device  300  is pushed into counterbore  122  of end plug  120 , the tangs  220  are received within the slots  316 ; this in-turn will the align anti-rotation slot  314  of body  310  with pin  150  of body assembly  100 . Insertion of pin  150  within slots  314  will prevent rotation of body  310 . 
     Collar  320 , which contains external threading  322  at a distal end  320 A thereof, is threaded into the internal threads  121  of end plug  120 . Body  310  of deployment device  300  is now captivated and restrained against further translation by collar  320  and restrained against further rotation by pin  150 . 
     When torque arm  330  is held parallel to the spinal axis, which is aligned perpendicular with the longitudinal axes of the body assembly  100  and deployment device  300 , the retention member&#39;s tangs  220  will deploy parallel to the spinal axis. To deploy the tangs  220 , the torque arm  330 , which is part of body  310 , is held with one hand of the operator and handle  340  is rotated clockwise with the operator&#39;s other hand. As handle  340  is rotated, the external threads on shaft  344  interact with the internal threads of body  310  at the proximal end  310 B of body  310  to cause anvil  346  to progress towards the distal end  310 A of body  310  and engage with body  210  of retention member  200 . Further distal movement of anvil  346  causes retention member  200  to move distally towards the interior of the body assembly  100  which inturn forces tangs  220  out through the aligned slots  114  of body  110  and slots  123  of end plug  120 , and thus out through body assembly  100  and into the cancellous bone of the vertebra. This process is continued until the retention member body  210  engages with pin  150 . 
     Tangs  220  are deformable such that, as they are forced out of body assembly  100  through the aligned slots  114 ,  123 , they engage with the walls that define the slots. Further distal movement of the tangs  220  through the slots deform the tangs as they are pushed through the slots and extended from body assembly  100 . 
     It can be understood that during deployment of the retention member  200 , because the faceted body  210  of the retention member, e.g., the hexagonal shape, was slidingly received in the complementary-formed faceted bore  312  of the deployment device body  310 , rotation of the retention member body  210  was prevented thus ensuring against any twisting or bending of the retention member tangs  220  during their deployment. 
     FIGS. 2 and 4 illustrate the spinal cage  10  in its second configuration where it is fully deployed into cancellous bone within the cortical bone of the vertebra and the implant is restrained from translation or rotation. Collar  320  is then unthreaded from the spinal cage  10 , and more specifically from end plug  120 , and the deployment device  300  is removed. 
     After removal of the deployment device  300 , proximal end cap  140 , as can be seen in FIG. 2, is threaded into the threaded hole of the retention member&#39;s body, e.g., hole  215  of body  210  for the embodiment of retention member  200  of FIGS.  912 . End cap  140  is utilized to close the trailing end of the spinal cage  10  and avoid irritation to adjacent structures. The exposed surface of end cap  140  has a spherical radius and contains an internal square drive feature, similar to square-formed slot  132  for distal end cap  130 , for use in tightening the proximal end cap  140  in retention member  200 . The threads of end cap  140  are slightly oversized to provide a self-locking feature and prevent inadvertent loosening of the end cap from the retention member. The preferred embodiment of end cap  140  is constructed from Ultra High Molecular Weight Polyethylene (UHMWPE) material. These threads, and end cap  140  as a whole, also prevent any ingrowth into the threaded hole of the retention member to make future removal of the retention member easier, if necessary for any reason. 
     The retention member&#39;s deployment of tangs  220  can be reversed, if necessary, for removal of the spinal cage  10 . In order to retract the tangs  220 , the retraction device  400 , as shown in FIG. 19, is used. Retraction device  400  includes a handle  410 , an externally threaded shaft  420 , which has a threaded stem  425  on a distal end thereof, and a collar  430 . Threaded shaft  420 , and thus threaded stem  425 , are rigidly attached to handle  410 . Collar  430  is threadedly engaged with threaded shaft  420 . A snap-ring  440  may be included on shaft  420  to prevent collar  430  from being inadvertently threaded off of shaft  420 . 
     To retract tangs  220 , end cap  140  is first unthreaded, and thus removed, from retention member  200 . The user then uses retraction device  400  to retract the tangs. The user holds handle  410  and turns it so as to engage threaded stem  425  into the threaded hole of the body of the retention member, e.g., hole  215  of body  210 . When threaded stem  425  is fully engaged in threaded hole  215 , handle  410  is restrained against further rotation and collar  430  is rotated clockwise to thread it distally on threaded shaft  420 , causing it to advance toward the spinal cage  10  due to interaction of the collar&#39;s internal threading with the shaft&#39;s external threading. As stated above, snap ring  440  prevents collar  430  from being inadvertently removed from shaft  420 . As collar  430  advances toward the spinal cage  10 , its leading edge  435  will contact the end plug  120 . Further rotation of collar  430  on shaft  420 , and the contact between collar  430  and end plug  120 , will cause a reaction force on the retention member  200  and will move retention member  200  in the direction R as shown in FIG.  2 . The movement of retention member  200  in this direction will retract tangs  220  from extending outside of body assembly  100  and force the tangs back through slots  114 ,  123 . Further movement of retention member  200  in direction R will pull it from body assembly  100  and into the open area  437  within collar  430 . Through the abovedescribed procedure, the spinal cage  10  can now be removed from the patient&#39;s body. 
     Whereas the above description discussed use of the embodiment of FIGS. 9-12 for the retention member, it is understood that alternative embodiments for the retention member, including the alternative embodiment illustrated in FIGS. 13-16, can be utilized in the present invention. 
     The disclosed embodiments are illustrative of the various ways in which the present invention may be practiced. Other embodiments can be implemented by those skilled in the art without departing from the spirit and scope of the present invention. For example, external threading  512  may be included on a body  510  of a body assembly  500 , as is illustrated in FIG. 20, to further enhance the fusing of the adjacent vertebrae. Additionally, whereas the retention member is illustrated as including two tangs, the present invention may be practiced by only including one tang on the retention member. FIG. 21 illustrates an alternative embodiment for a retention member  600  that only includes one tang  620 . All of the other features of retention member  600  are similar to those as described for the embodiments of retention members  200  and  250 .