Abstract:
A spinal implant having a series of sections or units hinged together and a balloon connected to at least some of the sections, the balloon having a curved configuration. The implant has a first delivery configuration and a second curved placement configuration, wherein it has a more linear configuration in the first delivery configuration than in the second curved configuration. The implant assumes the first delivery configuration during delivery to the disc space and maintains the curved configuration after placement within the disc space. The curved configuration can result from filling or expanding the balloon.

Description:
This application claims priority from provisional application Ser. No. 60/859,357 filed Nov. 16, 2006, the entire contents of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     This application relates to a spinal implant and more particularly to a spinal disc implant that can be inserted minimally invasively. 
     2. Background of Related Art 
     After removal of the intervertebral disc, it has been recognized that the disc space needs to be filled between the adjacent vertebrae. There are two approaches in the prior art to fill the space: one involving placement of a fusion cage and the other involving an artificial disc. Fusion cages are essentially metallic cages packed with bone to promote bone ingrowth. The fusion cages, designed to promote fusion, provide support between the vertebrae, but eliminate motion. Thus, to achieve stability, they sacrifice mobility. 
     Artificial disc prostheses of the prior art take many forms. Each form is essentially designed to strike a balance between sufficient stability to support the high loads of the vertebrae and sufficient mobility so as not to curtail movement of the patient. To date, attempts to strike such balance have met with limited success, with the artificial disc providing either stability or mobility, but not both. The need therefore exists for a disc replacement that can better simulate the natural disc by combining adequate support with flexibility. 
     Additionally, in many intervertebral procedures, major open surgery is required. The advantages of endoscopic (minimally invasive) procedures are well known, e.g. smaller incision causing less trauma and reduced infection potential, shorter hospital stays, lower costs, reduced patient recovery time, and reduced pain for the patient. Therefore, it would be advantageous if such an artificial disc, which achieves a beneficial balance between mobility and stability, could be inserted minimally invasively. 
     SUMMARY 
     The present invention provides a spinal implant having a series of sections or units hinged together and a balloon connected to at least some of the sections, the balloon having a curved configuration. The implant has a first delivery configuration and a second curved placement configuration, wherein it has a more linear configuration in the first delivery configuration than in the second curved configuration. The implant assumes the first delivery configuration during delivery to the disc space and maintains the curved configuration after placement within the disc space. The curved configuration can result from filling or expanding the balloon. 
     In one embodiment, a support strip is positioned on an outer surface of the hinged sections. In an alternate embodiment, it is positioned on the inner surface. 
     In the embodiment wherein a support strip is provided of shape memory material, the support strip can move the hinged sections to the curved configuration, and then the balloon filled to maintain the shape and support the sections. Alternatively, both the expanded balloon and support can together move the hinged sections to the curved configuration. 
     In one embodiment, the balloon in the expanded configuration has a first area and a smaller area having a smaller transverse cross section, each area extending along a length of the balloon. 
     The present invention also provides a method of minimally invasively inserting a spinal implant in a disc space. The method comprises providing a delivery instrument containing the spinal implant in a first configuration, the spinal implant having a plurality of hinged sections and a balloon connected thereto, inserting the delivery instrument to the disc space, deploying the implant from the delivery instrument to position the implant in the disc space, expanding the balloon to maintain the hinged sections in a substantially horseshoe shaped configuration, and removing the delivery instrument and leaving the implant in place. 
     In one embodiment the step of expanding the balloon expands the hinged section in a direction transverse to a plane of the disc space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiment(s) of the present disclosure are described herein with reference to the drawings wherein: 
         FIG. 1  is a perspective view of a cannula for receiving a disc removal device for use in the intra-vertebral space (the soft tissues are not shown); 
         FIG. 2  is a close up top view of the spinal disc nucleus being removed by a disc removal device; 
         FIG. 3  is a close up perspective view of a portion (two sections) of an implant device of the present invention; 
         FIG. 4  is a top plan view of the implant device of  FIG. 3  shown in the curved deployed (placement) position; 
         FIG. 5  is an exploded view of the portion of the implant of  FIG. 3 ; 
         FIG. 6  is a close up exploded view of the hinging element of the implant of  FIGS. 3 and 4 ; 
         FIG. 7  is a plan view of the spinal implant of  FIGS. 3 and 4  being delivered from the cannula of  FIG. 1 ; 
         FIG. 8  is a top view of the implant of  FIG. 4  shown in place between the vertebral bodies, the drawing further showing the cannula being removed; 
         FIG. 9  is an enlarged partially exploded view of an alternate embodiment of the implant of the present invention; and 
         FIG. 10  is a close up perspective view of an alternate embodiment of a hinge for connecting adjacent implant sections. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now in detail to the drawings where like reference numerals identify similar or like components throughout the several views, several different embodiments of the spinal implant of the present invention are described herein. 
     The spinal implants of the present invention are designed to be inserted minimally invasively into the disc space, thus enabling a smaller incision to be used in the procedure. This is achieved by the implants being deflectable laterally to a substantially linear configuration. That is, the implant is in a more straightened shape to enable minimally invasive insertion through a cannula. Once ejected from the delivery instrument at the desired site, i.e. the disc space between adjacent vertebrae, the balloon will be filled and the implant maintained in a curved configuration. Implanted in the disc space, the spinal implant is radially compressible in response to vertebral loads placed thereon. 
     Turning first to the instrumentation for minimally invasively preparing the disc space and for minimally invasively delivering the spinal implant, and with initial reference to  FIGS. 1 and 2 , a device used in the intra-vertebral space to remove the spinal disc nucleus in a minimally invasive fashion is illustrated. The disc removal device  10  has an elongated tubular portion  12  which is inserted through an arthroscopic cannula  14  and has a pair of cutting jaws  16  which are operatively connected to and remotely manipulated, i.e. opened and closed, by a proximal handle (not shown) to cut and remove the disc nucleus. Insertion through arthroscopic cannula  14  enables the disc to be removed minimally invasively rather than through a larger incision during an open more invasive surgical procedure. 
     As the nucleus is removed endoscopically, i.e. through a cannula forming a small incision, the implant of the present invention that is designed to replace the removed disc is also advantageously inserted minimally invasively. A delivery instrument (not shown) containing the spinal implant  30  within a distal portion is inserted through cannula  14 . Implant  30  is maintained in the delivery instrument in a substantially straightened (linear) configuration. 
       FIG. 7  illustrates the implant  30  partially ejected from the device;  FIG. 8  illustrates the implant  30  fully deployed and implanted in the disc space. As can be appreciated, as the implant  30  is ejected it moves from its more straightened configuration toward its curved configuration described below. After placement of the implant  30 , the delivery device and cannula are removed from the body. 
     As can be appreciated in the plan view of  FIG. 8 , the implant  30  is substantially horseshoe-shaped or substantially C-shaped in configuration as it extends circumferentially along the periphery of the disc space, thus providing support along the periphery or circumference of the disc space. That is, adjacent individual implant sections  32  are linked and form the curved shaped in a plane defined as lying perpendicular to the spine and parallel to the disc space defined between upper and lower vertebral bodies. It is also contemplated that the implant could be a closed loop, e.g. circular, or extend more than 360 degrees so the end portions overlap. In each of these instances, the implant would be delivered in a substantially straighter configuration and move to its curved shape for placement in the disc space. 
     With reference to  FIGS. 3 and 4 , the implant  30  is composed of a series of sections  32  linked together (only some of which are labeled for clarity). The linked sections  32  can be composed of a shape memory material, stainless steel, or other material to provide sufficient support. Each of these sections is preferably C-shaped or U-shaped in configuration with a lip  34  formed at the ends of its arms or upper and lower walls  35 ,  37 . A textured surface such as protrusions  36  can be formed on the upper and lower surfaces  38 ,  39 , respectively, of walls  35 ,  37  to increase surface friction between the implant and the opposing bone/vertebrae. Although protrusions are shown, other friction enhancing surfaces can be provided such as recesses, textured surfaces, different shaped projections and coatings. The walls  35 ,  37  can move toward each other due to the forces of the vertebral bodies between which it is inserted. 
     Adjacent sections  32  are hinged to enable movement from a more linear configuration for delivery through the cannula to the curved configuration shown in  FIG. 4 .  FIG. 6  is an enlarged view of one embodiment of the hinged structure showing ball  42  received and snapped in a slot formed on the underside of connector  44 . This frictional engagement interlocks adjacent sections  32  while still enabling lateral and pivotal movement with respect to one another. 
     A support or strut  48  illustratively in the form of an elongated flat strip is attached to the outer surface  33  of the hinged sections  32 , preferably extending along the entire length. This strip  48  is preferably composed of metal and provides support for the hinged sections and assists in linking of the sections. 
     In one embodiment, the support is made of shape memory, such as Nitinol, a nickel titanium alloy, although other shape memory metals or polymeric materials are contemplated, and has a shape memorized configuration of a substantially horseshoe shape or substantially C-curve as shown in  FIG. 4 . In this manner, the support  48  is maintained in a substantially straightened configuration for delivery. Once ejected from the delivery device, it will move to its memorized configuration, cooperating with the balloon explained below to move the hinged sections  32  into the curved configuration of  FIG. 4 . 
     A balloon is designated by reference numeral  50  and shown in the inflated (filled) position in  FIGS. 3-5 . The balloon has a reduced diameter section  52  (see arrow D) along its length to fit within the open arms  35 ,  37  of the hinged sections  32 . The balloon is substantially horseshoe shaped and functions to give the hinged sections the substantially horseshoe or curved shape shown in  FIG. 4 . The larger cross-section area  54  has a curved outer surface  56  and remains outside the hinged sections  32 . A portion abuts lip  34 . The balloon is filled with a gas or liquid after placement of implant  30  in the disc space to expand and extend in the curved configuration. The substantially horseshoe shape of the balloon thus forces the attached hinged sections  32  to form and/or maintain a curved shape, thereby providing the curved shape to the implant. The balloon  50  can also apply a force against the walls  35 ,  37  of the implant  30  (i.e. in a direction transverse to a plane of the disc space) and in some embodiments slightly expands these walls to further move surfaces  38 ,  39  against the vertebrae. The balloon materials and pressure can vary to thereby vary the degree of compressibility, cushioning and rigidity of the implant. That is, the variations of the balloon can affect the movement of adjacent vertebrae. For example, a less compressible balloon will increase stability but further restrict movement of the vertebrae; a more compressible balloon will provide more movement and mobility. 
     In the alternate embodiment of  FIG. 9 , the metal support strip  160 , shown rectangular in cross section, is positioned inside the open arms  135 ,  137  of implant  130 . The surface  152  of the balloon  150  is attached to the strip  160 . The opposite surface  162  of the strip is attached to the inner surface of hinged sections  132 . Metal strip  160  functions in a similar manner to strip  48  of  FIG. 3 . 
       FIG. 10  illustrates an alternate way to connect the implant units (sections)  230 . Two engaging closed loops  232 ,  234  are linked to provide the attachment. This connection provides for movement of adjacent sections  230 , while maintaining the inter-lock. It also helps to maintain the linked sections  32  in the curved configuration. 
     It is also contemplated that the support  48  (or  160 ) constitutes the element for moving the hinged sections to the curved configuration, with the balloon being moved to its curved shape by the hinged sections  32  and then maintaining the shape and support of the sections. Alternatively, the balloon can be the sole element moving the hinged sections  32  to the curved shape, with the support following the movement of the sections  32  to subsequently support the sections. Alternatively, both the balloon and support  48  (or  160 ) cooperate together to move and maintain the hinged sections. 
     Each of the implants assumes a substantially straightened configuration for delivery to the surgical site. Once delivered to the disc space, the hinged sections and the inflated balloon provide sufficient springiness in response to vertebral loads placed on the device by the spine. This provides both support for the vertebral bodies plus the desired flexibility. As noted above, variations in the balloon can vary the support and flexibility for the vertebral bodies. 
     Any of the foregoing implants can be provided with a roughened surface, such as a textured surface, to enhance bone ingrowth to enhance implant retention in the disc space. Surface finishes such as hydroxyapatite, calcium silicate and calcium phosphate could also be applied to allow for bone ingrowth. 
     In use, the disc nucleus is removed arthroscopically, i.e. through cannula  14 , by device  10 . Cannula  14  can optionally be placed by first inserting a needle and wire, removing the needle and sequentially placing and removing dilators of progressively increasing diameter over the wire until the desired cannula diameter is reached. After removal of the disc, device  10  is withdrawn through cannula  14  and then a delivery device, containing any of the foregoing implants, is inserted through the cannula. The implant is contained within the delivery device in a substantially straightened configuration with the balloon in the collapsed (unexpanded) configuration. The implant is then ejected from the delivery device and implanted in the disc space between the vertebral bodies, with the balloon filled to expand and maintain the curved configuration. The delivery instrument and cannula  14  are withdrawn from the body.  FIG. 8  illustrates the implant  30  positioned within the disc space. 
     While the above description contains many specifics, those specifics should not be construed as limitations on the scope of the disclosure, but merely as exemplifications of preferred embodiments thereof. For example, in addition to the substantially C-shaped cross-sectional configurations, substantially circular, rectangular, hexagonal, substantially octagonal as well as other configurations are contemplated. Also the length of the implant could be longer than that shown in the drawings for assuming the curved shape. Those skilled in the art will envision many other possible variations that are within the scope and spirit of the disclosure as defined by the claims appended hereto.