Abstract:
Implants, tools and techniques facilitate a percutaneous posterior lateral approach to the placement of an in-situ cage, and an inventive cage design to meet this objective. In terms of apparatus, the invention includes a laterally expandable cage, including a locking gate, enabling the system to be introduced into an intradiscal space through a minimally invasive percutaneous posteo-lateral approach. In addition to the cage designs, adapted to hold bone graft and/or other biologic materials, the invention includes other novel instruments, including an introducer associated with cage placement, deployment and closure.

Description:
REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority from U.S. Provisional Patent Application Ser. No. 60/516,209, filed Oct. 31, 2003. This application is also a continuation-in-part of U.S. patent application Ser. No. 10/462,498, filed Jun. 16, 2003, which claims priority from U.S. Provisional Patent Application Ser. No. 60/388,974, filed Jun. 14, 2002. The entire content of each application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to development of tools and techniques for percutaneous posterior lateral approach to place a modified in-situ cage.  
       BACKGROUND OF THE INVENTION  
       [0003]     One of the most common causes of chronic back pain is degenerative disc disease. The degeneration may start after a particular injury, or many occur due to multiple injuries over time. Degeneration usually takes several years. As the vertebrae grow closer, the openings in the back of the spine where the nerve roots leave the spinal canal become narrower. This can lead to pinching and irritation on the nerves, causing pain.  
         [0004]     There are many surgical approaches and methods used to fuse the spine. Most involve the placement of a bone graft between the vertebrae. Supplemental hardware, such as plates, screws and cages may or may not be used, depending upon the indication.  
         [0005]     An early cage design is described in U.S. Pat. No. 4,501,269 to Bagby, entitled “PROCESS FOR FUSING BONE JOINTS.” According to the method, a hole is bored transversely across the joint and a slightly larger cylindrical basket is driven into the hole, thereby spreading the bones in resistance to the tensile forces of the surrounding tissue. Immediate stabilization of the joint is achieved by the implantation of the rigid cylindrical basket. Subsequent bone-to-bone fusion is achieved, both through and about the basket, which is filled with bone fragments produced during the boring step.  
         [0006]     The Bagby patent states that the process is applicable to any human or animal joint formed by opposed contiguous bony surfaces which are covered and separated by intervening cartilage and are surrounded by ligaments which resist expansion of the joint. Specific examples of such joints are a spinal joint between adjacent vertebrae or the ankle joint.  
         [0007]     This stand-alone interbody fusion technique continued to evolve with material changes and the design of threaded cages to increase stability and decrease displacement rates. Bilateral, parallel implants were designed for use in the lumbar spine, with the first human implantation occurring in the early 1009s. The cylindrical titanium cages were threaded to screw into the endplates, thereby stabilizing the device and allowing for increased fusion rate with a stand-alone anterior device.  
         [0008]     Ray and colleagues developed a similar titanium interbody fusion device which was initially used in posterior lumbar interbody fusions (PLIF), but expanded to include ALIF procedures (anterior lumbar interbody fusions). In 1985, Otero-Vich reported using threaded bone dowels for anterior cervical arthrodesis, and femoral ring allograft bone has subsequently been fashioned into cylindrical threaded dowels for lumbar application.  
         [0009]     Currently, there are a wide number of available interbody fusion devices of varying design and material, including: 
        1) Cylindrical threaded titanium interbody cages;     2) Cylindrical threaded cortical bone dowels; and     3) Vertical interbody rings, boxes and wedges.        
 
         [0013]     A typical intervertebral fusion cage is a large, hollow cylinder made of some type of metal, usually titanium. It is designed as a “cage” so that bone graft can be placed inside the hollow cylinder. Holes throughout the cage allow bone to form around and through the cage to allow a spinal fusion to occur between two vertebrae. Many of the newer types of intervertebral fusion cages are also designed to facilitate an open incision or a laproscopic procedure.  
         [0014]     An intervertebral fusion cage serves a couple important purposes. First, it distracts the vertebrae, making more room for the nerves, thereby decreasing pinching and irritation. The strong ligaments that surround the disc are also tightened, which decreases the segmental instability between the two vertebrae and decreases the mechanical pain in the spine. The cage also hold the two vertebrae in the correct position until a fusion occurs.  
         [0015]     There are several drawbacks with existing approaches and techniques, such that further research and improved designs are desirable. Increased morbidity of anterior in-situ cage placement is not justified when less anatomic correction of the disc space is possible. Additionally, current PLIF and transverse lumbar interbody fusions (TLIF) cage and allograft placements require large dissections for exposure. PLIF and TLIF approaches also weaken existing posterior elements via bony destruction resulting from the operative procedure used to access the disc space.  
         [0016]     My co-pending U.S. patent application Ser. No. 10/462,498, incorporated herein by reference, improves upon existing solutions by providing a spinal fusion system including a cage with a fillable volume and removable locking gate. This enables the fillable volume to be packed with graft, biologic or other materials prior to the gate being closed and locked. In the preferred embodiment, the locking gate is positioned anteriorally, though lateral, posterior, and combinations thereof are also possible.  
       SUMMARY OF THE INVENTION  
       [0017]     This invention broadly resides in implants, tools and techniques facilitating a percutaneous posterior lateral approach to the placement of an in-situ cage, and an inventive cage design to meet this objective.  
         [0018]     In terms of apparatus, the invention includes a laterally expandable cage, including a locking gate, enabling the system to be introduced into an intradiscal space through a minimally invasive percutaneous posteo-lateral approach.  
         [0019]     In addition to the cage designs, adapted to hold bone graft and/or other biologic materials, the invention includes other novel instruments, including an introducer associated with cage placement, deployment and closure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a perspective view of a preferred laterally expandable cage according to the invention;  
         [0021]      FIG. 2  is a perspective view of an alternate laterally expandable cage;  
         [0022]      FIG. 3  is a perspective view of a variable-length locking gate;  
         [0023]      FIG. 4A  is a drawing of an instrument according to the invention that may be used both to overdistract a disc space and expand a novel cage according to the invention  
         [0024]      FIG. 4B  is a drawing of the expander portion of the device of  FIG. 4A , with three millimeters of expansion in both superior and inferior directions;  
         [0025]      FIG. 5A  is a drawing of the device of  FIG. 4  with a cage coupled thereto prior to expansion;  
         [0026]      FIG. 5B  is a drawing of the device of  FIG. 5A , having expanded a cage in position;  
         [0027]      FIG. 6A  is a drawing of a gate introducer according to the invention is a predeployed state;  
         [0028]      FIG. 6B  is a drawing of the introducer of  FIG. 6A  in an opened state;  
         [0029]      FIG. 7A  is a drawing which shows the instrument of  FIG. 4 , loaded with an expandable cage as shown in  FIG. 5 , being introduced into an intradiscal space through a cannulated opening;  
         [0030]      FIG. 7B  shows the instrument and cage of  FIG. 9A , having been rotated 90 degrees to facilitate overdistraction;  
         [0031]      FIG. 7C  shows the instrument being deployed, pushing the side walls of the cage outward laterally;  
         [0032]      FIG. 7D  shows the way in which the intervertebral bodies are “overdistracted” through the action of the instrument;  
         [0033]      FIG. 7E  illustrates the removal of the instrument, leaving the cage in place following the overdistraction;  
         [0034]      FIG. 8A  is a top-down view of instrument removal, leaving a U-shaped cage in position;  
         [0035]      FIG. 8B  shows the way in which high speed burrs are used to roughen the endplates;  
         [0036]      FIG. 8C  is a drawing which shows the way biologics may be inserted into the cage prior to closure;  
         [0037]      FIG. 8D  is a drawing which shows the way that autograft/allograft and/or other biologic materials are tamped into the cage prior to closure;  
         [0038]      FIG. 8E  is a drawing which shows the introduction of the locking gate;  
         [0039]      FIG. 8F  is a drawing which shows the removal of the gate introduction tool; and  
         [0040]      FIG. 9  is a perspective view drawing showing the expanded, filled cage in position between upper and lower vertebral bodies. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     This invention resides in an expandable, locking intervertebral cage facilitating a minimally invasive percutaneous posteo-lateral approach.  FIG. 9  is a perspective view drawing showing the expanded, filled cage in position between upper and lower vertebral bodies. In this description, the cage designs and novel instruments will first be introduced, followed by a detailed description of the preferred surgical procedure.  
         [0042]     The cage is preferably radiolucent, being composed of a carbon fiber, but with one or more radiopaque markers to provide a certain degree of visualization. Full or partial metal or ceramic construction may also be used. Some or all of the walls of the cage may include superior and/or inferior surface features to enhance positioning and/or minimize back-out, and the posterior wall may be indented to prevent neurocompression. The sidewalls of the cage may further include a recessed face with nipple indents and locking fasteners. Multiple cages may provided, each being shaped differently for use at different spinal levels. For example, the cage may be larger and more trapezoidally-pronounced for the L5-S1 levels, or smaller and less trapezoidally pronounced for the T and L2 levels.  
         [0043]      FIG. 1  is a perspective view of a preferred laterally expandable cage according to the invention. The cage, depicted generally at  100 , includes side arms  102 ,  104 , connected through a back wall  106  which is laterally expandable, creating an adjustable C-shaped implant. In the preferred embodiment, the back wall includes ratchets  110  which allow the cage to be expanded but not contracted once in position, leading to an expanded wall  106 ′ associated with the expanded cage  100 ′.  
         [0044]     Note that the forward portions of the arms  102 ,  104  include indents  120 . The purpose of these indents is to receive the ends of an expandable gate described with reference to  FIG. 3 .  FIG. 2  is a drawing which shows an alternate embodiment of a gate according to the invention, wherein arms  204 ,  206  overlap with one another at the back wall, and one or both includes multiple screw holes such as  210 , enabling a fastener to be used to lock the arms into a desired width through the use of an appropriate fastener. Again, the area shown in  302  would be closed with the gate of the type depicted in  FIG. 3 , which shows an expandable gate according to the invention, and a collapsed state at  302 , and an expanded state at  302 ′. In the preferred embodiment, the gate is spring-loaded to expand into position, facilitating introduction in the collapsed state  302 .  
         [0045]      FIG. 4A  is a drawing which shows a multi-purpose distracter/introducer according to the invention. Generally speaking, the tool includes upper and lower expansion portions  402 ,  404  used to “overdistract” a disc space for tool removal and cage placement, the advancement of these sections being controlled by a manually operated feature  410  which, when pulled toward the user, causes the plates  402 ,  404  to expand on the order of one to three millimeters or more. The tool further includes side expanders  412 ,  414  which expand under control of a different manually operated feature  420 .  FIG. 4B  shows the control  410  being pulled, causing the plates  402 ,  404  to expand outwardly. The tool would be providing in different sizes, with, for example, a height on the eight millimeters for a 10 millimeter cage, 10 millimeters for a 12 millimeter cage, 12 millimeters for a 14 millimeter cage, and so forth, such that through overdistraction on the order of three millimeters in each case, the tool may be removed, leaving the cage in position.  
         [0046]      FIG. 5A  shows a cage of the type in FIGS.  1  or  2 , without the gate of  FIG. 3 , being loaded onto the tip of the tool, and  FIG. 5B  shows the cage being expanded through operation of control  20 , as described with reference to  FIG. 4A .  FIG. 6A  is a drawing which shows the gate introducer, according to the invention, including a set of claws  602  which are expanded through a control  604 , as shown in  FIG. 6B . Thus, utilizing the spring-loaded gate of  FIG. 3 , it may be introduced in a collapsed position, then expanded using the control  604  to leave it in place as discussed in further detail below.  
         [0047]     In terms of operative procedure, the patient is under general anesthetic, in a prone position on a C-arm capable table. A surface grid of the type described in my co-pending patent application Ser. No. 10/689,123, or other localizing device, is used to assist with finding anatomic entry point outside pedicle, below the traverse process, and into disc space using a posterior lateral approach (known to those of skill as an IDET approach).  
         [0048]     A guide wire is inserted into the disc space using a handheld instrument or assisted using the navigable radiolucent forceps of the type described in my co-pending patent application Ser. No. 10/268,373. A 2-plane check is then carried out using the C-arm to ensure that the tip of the guide wire is in anterior opposite quadrant, with the guide wire parallel to endplates.  
         [0049]     A penetrating guide sleeve is placed over the guide wire and advanced to center of disc. The puncture incision is enlarged and a series of soft tissue dilators are inserted to desired mm height (i.e., up to 12 mm for a 12 mm cannula).  
         [0050]     A specific sized cannula (ex. 12 mm) is inserted over the dilator and docked onto disc space. The dilator is held against the disc space, and an endoscope is optionally inserted to check anatomic position.  
         [0051]     The guide wire and dilator are removed, keeping the cannula against disc space. A sharp coring biopsy tool is then used to create an opening into disc space. Ronguers and/or rasps are inserted, and serrated scrappers are used to remove disc material.  
         [0052]     A series of disc space dilators are next inserted up to desired cage height (i.e., 10, 12, 14 mm, color coded). The last dilator is removed and replaced with cage/overdistractor tool of specific cage, loaded with correct, color-coded cage. The cage is oriented with the cage sides facing endplates. This and any of the following steps may be checked with the C-arm, as appropriate. The tool and (attached cage) are rotated 90 degrees, to deploy the side walls and “overdistract” by 1-4 mm over the actual height of cage.  
         [0053]      FIG. 7A  is a drawing which shows the instrument of  FIG. 4 , loaded with an expandable cage as shown in  FIG. 5 , being introduced into an intradiscal space through a cannulated opening.  FIG. 7B  shows the instrument and cage of  FIG. 9A , having been rotated 90 degrees to facilitate overdistraction.  FIG. 7C  shows the instrument being deployed, pushing the side walls of the cage outward laterally.  FIG. 7D  shows the way in which the intervertebral bodies are “overdistracted” through the action of the instrument.  FIG. 7E  illustrates the removal of the instrument, leaving the cage in place following the overdistraction.  
         [0054]      FIG. 8A  is a top-down view of instrument removal, leaving a U-shaped cage in position.  FIG. 8B  shows the way in which high speed burrs are used to roughen the endplates.  FIG. 8C  is a drawing which shows the way biologics may be inserted into the cage prior to closure. These biologics, which may be inserted or injected, include BMP, HEALOS, VITOSS, autograft, allograft, and so forth.  FIG. 8D  is a drawing which shows the way that autograft/allograft and/or other biologic materials are tamped into the cage prior to closure.  
         [0055]      FIG. 8E  is a drawing which shows the introduction of the locking gate using the tool of  FIG. 6 . The release spring is used to expand the gate and slide it to the outer end of cage where it is clicked into position.  FIG. 8F  is a drawing which shows the removal of the gate introduction tool. The cannula is removed and the wound is closed.  FIG. 9  is a perspective view drawing showing the expanded, filled cage  900  in position between upper and lower vertebral bodies  902 ,  904 .