Abstract:
A surgical spacer comprising first and second hollow support members, a flexible container, and a compressible material disposed in the container is disclosed. The first and second support members each have an exterior and an interior cavity. The exteriors of the first and second support members are affixed together and the interior cavities of the first and second support members are connected via a connecting opening. The container is disposed in the interior cavities and extends through the connecting opening. In addition, the container is substantially impermeable to the compressible material. The first and second support members are more rigid than the flexible container. A combination of the first and second support members controls the shape of the flexible container, with the compressible material disposed therein, in response to a compressive load applied to an exterior of the spacer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS/PATENTS 
       [0001]    This application is a continuation of prior application Ser. No. 11/438,891, filed May 23, 2006, the entirety of which is incorporated herein by reference. 
         [0002]    In addition, this application contains subject matter which is related to the subject matter of the following applications. Each of the below listed applications is hereby incorporated herein by reference in its entirety: “Surgical Spacer,” by Anderson (U.S. patent application Ser. No. 11/438,940); and “Systems and Methods for Adjusting Properties of a Spinal Implant,” by Trieu et al. (U.S. patent application Ser. No. 11/439,006). 
     
    
     TECHNICAL FIELD 
       [0003]    The present invention generally relates to surgical spacers for spacing adjacent body parts. More particularly, the present invention relates to surgical spacers having a flexible container for containing a material that is compressible during end use, the container being substantially impermeable to the material, and a structure for controlling at least part of a shape of the container when containing the material. 
       BACKGROUND OF THE INVENTION 
       [0004]    The human spine is a biomechanical structure with thirty-three vertebral members, and is responsible for protecting the spinal cord, nerve roots and internal organs of the thorax and abdomen. The spine also provides structural support for the body while permitting flexibility of motion. A significant portion of the population will experience back pain at some point in their lives resulting from a spinal condition. The pain may range from general discomfort to disabling pain that immobilizes the individual. Back pain may result from a trauma to the spine, the natural aging process, or the result of a degenerative disease or condition. 
         [0005]    Procedures to address back problems sometimes require correcting the distance between spinous processes by inserting a device (e.g., a spacer) therebetween. The spacer, which is carefully positioned and aligned within the area occupied by the interspinous ligament, after removal thereof, is sized to position the spinous processes in a manner to return proper spacing thereof. 
         [0006]    Dynamic interspinous spacers are currently used to treat patients with a variety of indications. Essentially, these patients present a need for distraction of the posterior elements (e.g., the spinal processes) using a mechanical device. Current clinical indications for the device, as described at SAS (Spine Arthroplasty Society) Summit 2005 by Guizzardi et al., include stenosis, disc herniation, facet arthropathy, degenerative disc disease and adjacent segment degeneration. 
         [0007]    Marketed interspinous devices include rigid and flexible spacers made from PEEK, titanium or silicone. Clinical success with these devices has been extremely positive so far as an early stage treatment option, avoiding or delaying the need for lumbar spinal fusion. However, all devices require an open technique to be implanted, and many require destroying important anatomical stabilizers, such as the supraspinous ligament. 
         [0008]    Current devices for spacing adjacent interspinous processes are preformed, and are not customizable for different sizes and dimensions of the anatomy of an interspinous area of an actual patient. Instead, preformed devices of an approximately correct size are inserted into the interspinous area of the patient. Further, the stiffness or flexibility of the devices must be determined prior to the devices being inserted into the interspinous area. 
         [0009]    Thus, a need exists for improvements to surgical spacers, such as those for spacing adjacent interspinous processes. 
       SUMMARY OF THE INVENTION 
       [0010]    Briefly, the present invention satisfies the need for improvements to surgical spacers by providing shape control. A flexible container is provided that is fillable in situ to a desired amount, with a structure for at least part of the container providing shape control thereto. An optional conduit coupled to the container allows for filling of the container, for example, by injecting a material into the container. 
         [0011]    The present invention provides in a first aspect, a surgical spacer. The surgical spacer comprises a flexible container for containing a material that is compressible during end use, wherein the container is substantially impermeable to the material. The surgical spacer further comprises a structure for at least part of the container when containing the material, wherein the structure controls at least part of a shape of the surgical spacer. 
         [0012]    The present invention provides in a second aspect, an interspinous spacer. The interspinous spacer comprises a flexible container for containing an injectable material that is compressible during end use, wherein the container is substantially impermeable to the injectable material. The interspinous spacer further comprises a conduit coupled to the container for accepting the injectable material, and a structure for at least part of the container when containing the material, wherein the structure has a shape during end use to fit between adjacent spinous processes. 
         [0013]    The present invention provides in a third aspect, a method of controlling at least part of a shape of a surgical spacer. The surgical spacer comprises a flexible container for containing a material that is compressible during end use, wherein the container is substantially impermeable to the material. The surgical spacer further comprises a structure for at least part of the container when containing the material. The method comprises creating the structure with at least one material for controlling at least part of a shape of the surgical spacer during end use. 
         [0014]    The present invention provides in a fourth aspect, a method of spacing adjacent spinous processes. The method comprises providing an interspinous spacer, the interspinous spacer comprising a flexible container for containing an injectable material that is compressible during end use, wherein the container is substantially impermeable to the injectable material. The interspinous spacer further comprises a conduit coupled to the container for accepting the injectable material, and a structure for at least part of the container when containing the material, wherein the structure has a shape during end use to fit between adjacent spinous processes. The method further comprises implanting the interspinous spacer between adjacent spinous processes, and injecting the injectable material into the container through the conduit such that the shape is achieved. 
         [0015]    Further, additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0017]      FIG. 1  depicts adjacent vertebrae of the lumber region of a human spinal column. 
           [0018]      FIG. 2  depicts a more detailed view of a portion of a human spinal column including the vertebrae of  FIG. 1 . 
           [0019]      FIG. 3  depicts the spinal column portion of  FIG. 2  after implantation and filling of one example of an interspinous spacer in accordance with an aspect of the present invention. 
           [0020]      FIG. 4  is a partial cut-away view of one example of an unfilled surgical spacer with the container in the structure, in accordance with an aspect of the present invention. 
           [0021]      FIG. 5  depicts an example of a surgical spacer with integrated container and structure, in accordance with an aspect of the present invention. 
           [0022]      FIG. 6  is a cross-sectional view of one example of a surgical spacer with external container, in accordance with an aspect of the present invention. 
           [0023]      FIG. 7  depicts one example of the construction of a structure for use with one example of a surgical spacer, in accordance with another aspect of the present invention. 
           [0024]      FIG. 8  depicts another example of a surgical spacer with integrated container and structure, in accordance with another aspect of the present invention. 
           [0025]      FIG. 9  depicts one example of a structure for a surgical spacer including at least one substantially inflexible shaped member, in accordance with another aspect of the present invention. 
           [0026]      FIG. 10  depicts another example of a structure for a surgical spacer including at least one substantially inflexible shaped member, in accordance with another aspect of the present invention. 
           [0027]      FIG. 11  depicts still another example of a structure for a surgical spacer including a supra-structure, in accordance with another aspect of the present invention. 
           [0028]      FIG. 12  depicts a portion of a surgical spacer with a structural mesh coupled at least one least one substantially inflexible shaped member, in accordance with another aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    A surgical spacer of the present invention can be formed in situ during a procedure. The spacer includes the following basic aspects: a flexible container, and a structure for at least part of the container that controls at least part of the shape of the surgical spacer. The flexible container can be filled or injected through an optional conduit after placement. Further, the structure may be folded or otherwise reduced in size prior to use in some aspects. Together with an unfilled container, in some aspects, the spacer can create a smaller footprint during implantation. Once filled, the structure provides support and containment for the container, as well as providing shape control for at least part of the spacer. 
         [0030]      FIG. 1  depicts adjacent vertebrae  100 ,  102  of the lumbar region of a human spinal column. As known in the art, each vertebrae comprises a vertebral body (e.g., vertebral body  104 ), a superior articular process (e.g., superior articular process  106 ), a transverse process (e.g., transverse process  108 ), an inferior articular process (e.g., inferior articular process  110 ), and a spinous process (e.g., spinous process  112 ). In addition, between vertebral bodies  104  and  114  is a space  116  normally occupied by an intervertebral disc (see  FIG. 2 ), and between spinous processes  112  and  118  is a space  120  normally occupied by an interspinous ligament (see  FIG. 2 ). 
         [0031]      FIG. 2  depicts the vertebrae of  FIG. 1  within an area  200  of the lumbar region of a human spine. As shown in  FIG. 2 , spinous processes  112  and  118  are touching and pinching interspinous ligament  202 , calling for spacing of the spinous processes. 
         [0032]      FIG. 3  depicts spinous processes  112  and  118  after spacing with an interspinous spacer  300  in accordance with one aspect of the present invention. As shown in  FIG. 3 , interspinous ligament  202  has been removed in a conventional manner prior to insertion of spacer  300 . Although shown in its filled state, in this example, spacer  300  is implanted in its unexpanded state, as described more fully below. The spacer is filled with a material described below through a conduit  302  after implantation. For example, the material may be injected into the spacer through the conduit (e.g., a one-way valve). Prior to implantation and filling, measurement of the space between the interspinous processes and determination of the spacer size and desired amount of filling can be performed. Conventional methods can be used, such as, for example, the use of templates, trials, distractors, scissor-jacks or balloon sizers. 
         [0033]      FIG. 4  depicts a partially cut-away view of one example of a spacer  400 , in accordance with one aspect of the present invention. As shown in  FIG. 4 , the spacer comprises an unfilled container  402  inside a structure  404 . Preferably, the container is in an evacuated state during implantation and prior to being filled. Where a valve (e.g., a one-way valve) is coupled to the container, the container is preferably evacuated prior to or during the process of coupling the valve thereto. In the present example, the structure is outside the container. However, as will be described in more detail below, the container can be outside the structure, or the container and structure can be integrated. In addition, although the structure is shown to be roughly H-shaped to fit between adjacent spinous processes, the structure can have any shape necessary for the particular surgical application. For example, the structure could instead have a roughly cylindrical shape to replace an intervertebral disc. As another example, the structure could be spherically or elliptically shaped to replace part of the intervertebral disc, for example, the nucleus pulpous, leaving the rest of the disc intact. Further, although the structure is shown enveloping the container, the structure could be for only a portion of the container, depending on the particular application. For example, it may be desired to prevent bulging of the container only in a particular area. Coupled to the container is an optional conduit  406  for accepting a material that is compressible during end use. The structure provides support for and containment of the container when filled. 
         [0034]    The container is flexible and substantially impermeable to the material it will be filled with. However, depending on the application, the container may be permeable to other materials, for example, it may be air and/or water permeable. In the present example, the container takes the form of a bag or balloon, but can take other forms, so long as flexible and substantially impermeable to the material it will be filled with. Thus, the container must be substantially impermeable to the filling material, for example, in a liquid state during filling and prior to curing. Examples of container materials include silicone, rubber, polyurethane, polyethylene terephthalate (PET), polyolefin, polycarbonate urethane, and silicone copolymers. 
         [0035]    Conduit  406  accepts the material being used to fill the container. Preferably, the conduit comprises a one-way valve, however, a two-way valve is also contemplated, as another example. The conduit can comprise any material suitable for implanting, for example, various plastics. Also preferably, the conduit is constructed to be used with a delivery system for filling the container, such as, for example, a pressurized syringe-type delivery system. However, the delivery system itself forms no part of the present invention. As noted above, the conduit is optional. Other examples of how to fill the container comprise the use of a self-sealing material for the container, or leaving an opening in the container that is closed (e.g., sewn shut) intraoperatively after filling. Using a curable material to fill the container may also serve to self-seal the container. 
         [0036]    In use, the container is filled with a material that is compressible during end use. The compressibility characteristic ensures that the material exhibits viscoelastic behavior and that, along with the structure, the spacer can accept compressive loads. Of course, the degree of compressibility will depend on the particular application for the surgical spacer. For example, if a spacer according to the present invention is used between adjacent spinous processes, the spacer would need to accept compressive loads typically experienced in the posterior region of the spine, for example, up to about 80 shore A. In other words, the spacer is preferably capable of resisting compressive motion (or loads) with a stiffness of about 40 to about 240 N/mm (newtons per millimeter). The material is preferably injectable, and may be compressible immediately or after a time, for example, after curing. For purposes of the invention, the compressibility characteristic is necessary during end use, i.e., after implantation. Materials that could be used include, for example, a plurality of beads (e.g., polymer beads) that in the aggregate are compressible, or materials that change state from exhibiting fluid properties to exhibiting properties of a solid or semi-solid. Examples of such state-changing materials include two-part curing polymers and adhesive, for example, platinum-catalyzed silicone, epoxy, polyurethane, etc. 
         [0037]    As noted above, the structure provides support for and containment of the container when filled, as well as at least partial shape control of the spacer. The structure comprises, for example, a structural mesh comprising a plurality of fibers and/or wires  408 . Within the structural mesh are shape-control fibers and/or wires  410 . In one example, shape control is provided by wires of a shape-memory alloy (e.g., Nitinol). The shape-memory alloy wire(s) can be coupled to the structural mesh (inside or outside), or weaved into the mesh (i.e., integrated). Coupling can be achieved, for example, by stitching, twisting, or closing the wire on itself. Alternatively, shape control can be provided by other wires or fibers that do not “give” in a particular direction, for example, metal or metal alloys (e.g., tantalum, titanium or steel, and non-metals, for example, carbon fiber, PET, polyethylene, polypropalene, etc.). The shape-memory alloy can be passive (e.g., superelastic) or active (e.g., body-temperature activated). The use of metal, metal alloy or barium coated wires or fibers can also improve radiopacity for imaging. The remainder of the structure can take the form of, for example, a fabric jacket, as shown in  FIG. 4 . Although the shape-memory alloy wires make up only a portion of the structural mesh of  FIG. 4 , it will be understood that there could be more such wires, up to and including comprising the entirety of the mesh. The fabric jacket in this example contains and helps protect the container from bulging and damage from forces external to the container, while the shape-memory alloy provides shape control of the spacer in a center region  412 . The fibers of the jacket comprise, for example, PET fabric, polypropylene fabric, polyethylene fabric and/or steel, titanium or other metal wire. Depending on the application, the structure may be permeable to a desired degree. For example, if bone or tissue growth is desired to attach to the structure, permeability to the tissue or bone of interest would be appropriate. As another example, permeability of the structure may be desired to allow the material used to fill the container to evacuate air or water, for example, from the container, in order to prevent bubbles from forming inside. Where a mesh is used, for example, the degree of permeability desired can be achieved by loosening or tightening the weave. 
         [0038]    Although the structure is shown in a roughly H-shape in the example of  FIG. 4 , it will be understood that in practice, the structure can be made to be folded, unexpanded, or otherwise compacted. This is particularly true where, for example, the structure comprises a fabric or other easily folded material. A folded or unexpanded state facilitates implantation, allowing for a smaller surgical opening, and unfolding or expansion in situ upon filling of the container. Further, the structure can have a different final shape, depending on the shape-control material used. For example, the shape-memory wires in  FIG. 4  may be in their inactive state, whereupon activation by body temperature causes contraction thereof, making the spacer of  FIG. 4  “thinner” than shown in the center region. 
         [0039]    One example of the construction of a structural mesh  700  for use as one example of a structure of the present invention will now be described with reference to  FIG. 7 . Two roughly cylindrical members  702  and  704  are sewn together around a periphery  706  of an opening along a side (not shown) in each. Each member in this example comprises a fabric mesh (e.g., fabric mesh  714 ) similar in composition to the fabric jacket of  FIG. 4 . Interwoven with the fabric are a plurality of shape-memory alloy wires both horizontally (e.g., wire  716 ) and vertically (e.g., wire  718 ). An opening  708  is created in one of the members for accepting the container, for example, by laser cut. In one example, a conduit described above would poke through opening  708 . The ends of the cylindrical members (e.g., end  710 ) are then trimmed and sewn shut, as shown in broken lines (e.g., lines  712 ) in  FIG. 7 . 
         [0040]      FIG. 5  depicts an outer view of another example of a surgical spacer  500  in accordance with an aspect of the present invention. A container conduit  501  is shown pointing outward from an opening  503 . As shown, the structure  502  delimits the final shape of the spacer, in this example, a rough H-shape. The structure comprises a mesh  504  of shape-memory alloy wire, that is soaked through with a dispersion polymer  506  (e.g., silicone). The dispersion polymer (after curing) acts as the container and is shown filled in  FIG. 5 . This is one example of the container and the structure being integral. Although the mesh of  FIG. 5  is described as being all shape-memory alloy wire, it will be understood that, like  FIG. 4 , the shape-memory alloy could only form a part of the structure. 
         [0041]      FIG. 6  is a cross-sectional view of another example of a surgical spacer  600  in accordance with the present invention. Surgical spacer  600  is similar to the spacer of  FIG. 5 , except that instead of being soaked in a dispersion polymer, a structural mesh  602  of a shape-memory alloy wire is coated with a dispersion polymer (e.g., silicone)  604  or other curable liquid appropriate for the container material, creating an outer container. The coating can be done in a conventional manner, for example, by dip molding on the outside of the mesh. 
         [0042]      FIG. 8  depicts another example of a surgical spacer  800  with an integrated container and structure, in accordance with another aspect of the present invention. The container and structure in the example of  FIG. 8  both comprise a single layer  802  of rubber that is thick enough for a given application to perform the functions of both the container and structure (including shape control). Such a rubber shell would be able to return to its original shape when unconstrained. In addition, spacer  800  preferably includes a conduit  804  (preferably, a one-way valve) for filling internal space  806 . The material can be any of the filling materials described above, for example, silicone. Where the spacer is used, for example, to space adjacent spinous processes, the thickness of layer  802  is preferably in the range of about 0.2 mm to about 2.5 mm. A layer of rubber of that thickness will contain the material chosen, and, when filled, will sufficiently maintain the shape of the spacer for the intended use. 
         [0043]    In an alternate aspect, the rubber shell of  FIG. 8  can be augmented with internal, external, or integrated features to further control shape. Examples of such features include thread, wires (e.g., metal, including shape-memory alloys), cables, tethers, rings or a mesh. 
         [0044]      FIG. 9  depicts one example of a structure for a surgical spacer including at least one substantially inflexible shaped member, in accordance with another aspect of the present invention. The substantially inflexible member(s) are used to achieve at least part of a preformed shape for a given application. Structure  900  comprises blades  902  and  904  that are substantially inflexible and are substantially straight. In one example, the blades comprise metal, such as, for example, a nickel-titanium alloy. The blades provide a specific shape for at least part of the surgical spacer. Coupling the blades is, for example, a structural mesh  906 . The structure can be paired with any of the types of containers described herein. In addition, the structural mesh can take any of the forms described herein. For example, the structural mesh could take the form of a PET fabric mesh, with or without other shape-enhancing elements (e.g., shape-memory alloy fabric or wire). In one example, the mesh covers the blades. In another example, the mesh is coupled at a periphery of the blades. 
         [0045]    As shown in the example of  FIG. 12 , a portion of a surgical spacer  1200  comprises a blade  1202  and structural mesh  1204 . At the periphery  1206  of the blade, the mesh is coupled to the blade by stitching through a plurality of holes (e.g., hole  1208 ). 
         [0046]    Similarly,  FIG. 10  depicts another example of a structure  1000  including at least one substantially inflexible shaped member. In this example, there are two substantially inflexible shaped members  1002  and  1004 , each being roughly U-shaped. In one example, the U-shaped members comprise metal blades, such as, for example, nickel-titanium alloy blades. Coupling the blades is, for example, a structural mesh  1006  similar to that described above with respect to  FIG. 9 . In addition, as also noted above with respect to  FIG. 9 , the structure of  FIG. 10  can be paired with any of the containers described herein. 
         [0047]      FIG. 11  depicts still another example of a structure  1100  for a surgical spacer, in accordance with another aspect of the present invention. In this example, the structure comprises a supra-structure  1102  coupled to a main structure  1104 . The main structure need not provide shape control, since that is provided by the supra-structure, however, it could also provide shape control. For example, the main structure could provide shape control in one or more directions, while the supra-structure provides shape control in one or more other directions. Of course, the supra-structure could provide shape control uniformly, e.g., if added to all surfaces. In one example, the main structure comprises a fabric mesh (e.g., PET fabric) with or without added shape memory control fibers or wires. In one example, shown inset in  FIG. 11 , supra-structure  1102  comprises a plurality of interlocking links  1106 , the links comprising, for example, a shape-memory alloy. The links could provide resistance to expansion in one or more directions or uniformly, and/or could allow pliability, permitting deformation in one or more directions. The supra-structure can be loosely or rigidly coupled to the main structure, for example, via loops, hooks, stitches or frictional mechanisms. Of course, the supra-structure could instead be coupled to an inside  1108  of the main structure in another example. As with other embodiments herein, the shape-memory alloy can be passive (e.g., superelastic) or active (e.g., body-temperature activated). 
         [0048]    Although preferred embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.