Abstract:
Craniotomy closure systems comprising surgical fasteners and a protective covering over the dura are described for use in reattaching a skull flap removed from the skull of a patient during brain surgery. Methods of using the same are also described. Surgical strips optionally used in combination with the craniotomy closure systems are shaped to follow the perimeter contour of the skull flap. The craniotomy closure systems are designed to encourage bone growth and healing of the skull flap and they can be used to deliver medication and bone growth enhancement materials to the surgical site.

Description:
FIELD OF THE INVENTION 
     The invention relates to craniotomy closure systems used in reattaching a skull flap removed during brain surgery and methods of reattaching the skull flap using the systems. More specifically, the invention relates to craniotomy closure systems comprised of surgical fasteners used in combination with a protective layer for covering the dura, the protective layer also being referred to herein as a dura cover. The invention also concerns methods of implanting the closure systems and methods which enhance bone growth and the consequent healing of the skull flap and the skull. 
     BACKGROUND OF THE INVENTION 
     Surgical access to the brain for neurosurgical procedures is created by removing a portion of the patient&#39;s skull to provide an exposed area of dura and permit access to the soft tissue of the brain for surgery, a procedure termed a craniotomy. The craniotomy is determined by the location of the pathology within the brain, the safest/easiest access route and the degree of exposure required for the procedure. Once the location is determined, the first step is to create an initial perforation of the full thickness of the skull. Special skull perforators are available to create perfectly round holes but most surgeons simply use a rounded, end-cutting burr to create the perforation. Typically the perforation is in the range of about 11-15 millimeters (mm) in diameter. A surgeon may choose to create more than one perforation around the perimeter of the planned craniotomy. Some surgeons prefer a single perforation and others use more than one, but there is no standard number. Once this hole is created, it allows the insertion of a rotary powered surgical instrument (e.g., a craniotome) which is used to create a continuous cut (also called an osteotomy cut or a kerf) around the perimeter of the craniotomy. This kerf begins and ends at the perforation when there is one perforation or it runs from one perforation to another when more than one perforation is made in the skull. The kerf is made with a side cutting burr which is shielded from the dura (outer covering of the brain) by a foot plate on the craniotome. The foot plate extends below and forward of the cutting burr and the surgeon keeps the tip of the foot plate in contact with the inner surface of the skull as he performs the craniotomy. The typical kerf is made freehand with an approximately 2 mm diameter burr. The shape of the craniotomy is therefore highly variable and the kerf is not always oriented perpendicular to the skull. The kerf may be larger than 2 mm in some areas as well. Over the course of the kerf, the skull thickness will vary, typically over the range of 3-8 mm in adults. 
     Once the cut is complete, the skull flap is removed from the skull and placed on the sterile back table for reinsertion at the end of the procedure. The dura is then cut to provide access to the soft tissue of the brain. After completion of the soft tissue surgery (typically 1-6 hours), the dura is sutured back together, and the skull flap then is inserted back into the craniotomy and fixated to prevent movement and restore the original contour of the skull. The surgeon may bias the skull flap toward one side or another to create bone-to-bone contact in a particular area or he may leave a gap around the entire flap. The scalp is then closed and the patient is sent to the neurosurgical intensive care unit for recovery. 
     If complications develop while the patient is in the hospital, there may be the need for emergency access to the brain through the craniotomy site. In addition, some patients may return for subsequent craniotomies in the same region, particularly in cases of recurrent tumors. Postoperative imaging studies (MRI or CT) are generally conducted on all patients. There is no clear evidence that the skull flap ever completely heals (solid bony union) in adults. It is more likely that a combination of new bone formation and fibrous connective tissue fills the gap between the skull and the skull flap. 
     From a surgeon&#39;s perspective, the method of reattaching the bone flap must be safe, simple to use, be rapidly applied, permit emergent re-entry, not interfere with postoperative imaging studies, provide stable fixation and have an acceptably low profile. The ideal method would result in complete fusion of the bone flap to the native skull with no long term evidence of prior surgery. 
     Current methods of reattaching the skull flap include drilling a series of small holes in the edge of the skull and the edge of the flap. Sutures are then passed through the corresponding holes and the flap is secured back into the skull opening from which it was taken. Because the fit is not exact due to the material removed by the craniotome, the flap can sag and sit slightly below the surface of the skull resulting in a depressed area that is obvious through the skin. 
     Another common reattachment method substitutes stainless steel wire for the suture material and fewer holes are used. There is still the risk of a cosmetically objectionable depressed area resulting. Metallic cranial fixation is (generally) only ever removed if it becomes symptomatic or if it interferes with subsequent surgeries. 
     More recently, surgeons have begun to use the titanium micro plates and screws that were developed for internal fixation of facial and finger bones. While this method results in a more stable and cosmetic result, it is relatively expensive, does not insure fusion and leaves foreign bodies at the surgical site. 
     All of these methods take ten minutes to one hour of additional surgery after the soft tissue (brain) surgery. 
     There is another method in which a titanium rivet (or clamp) is placed inside the skull with the stem of the rivet (clamp) passing between the skull and the flap. A large “pop rivet” type tool is used to force an upper titanium button down over the stem of the rivet, locking the flap and the skull in place between the upper and lower buttons. Three or four of these rivets and buttons are used to secure the flap in place. This method can be faster than other methods and less expensive than the titanium plates, but more expensive than sutures or wires. Just as with titanium plates and screws, fusion is not assured and foreign bodies remain in the patient. 
     According to the present invention we have developed new systems for, and methods of, reattaching a skull flap in a skull opening. The fixation provided utilizing a fastener and dura cover of the invention and practicing the methods of the invention is secure and cosmetically acceptable. The fastener and dura cover can be used in combination with materials which can enhance bone growth in a manner which causes healing by means of bone-to-bone reattachment of the skull flap to the skull. 
     The term “perimeter contour” as used herein with reference to the skull flap means “the shape of the outer boundary around the skull flap.” 
     The term “shaped to follow the perimeter contour” means “formed around the perimeter contour.” 
     SUMMARY OF THE INVENTION 
     After a skull flap is removed from a patient and the soft tissue surgery on the brain is completed, a dura cover of the invention is placed over all or at least a portion of the dura uncovered by the skull flap before the skull flap is reattached using the surgical fasteners of the invention. The surgical fasteners are designed to allow the surgeon to reattach the skull flap in generally the same position from which it was removed, thereby maintaining the contour of the skull in a manner which is cosmetically desirable. The fasteners also position the flap in the skull in a manner which provides a generally even gap (the kerf) between the flap and the skull around the perimeter of the flap. The dura cover is made from a sheet of generally even thickness and can be in one piece or more than one piece. When the dura cover is placed over only a portion of the dura exposed by removal of the skull flap, it is at least placed over the portion of the dura located directly below the kerf. Flexible surgical strips can be used in combination with the surgical fasteners and the dura cover. These strips can be shaped to follow the perimeter contour of the skull flap and, consequently, the contour of the opening in the skull from which the flap was removed. The strips are placed or implanted in the kerf between the flap and the skull. In a preferred embodiment, a craniotomy closure system of the invention is comprised of at least two fasteners, used to reattach the skull flap, a dura cover and one or more than one surgical strip. 
     The dura cover of the invention can be made from various biocompatible bioabsorbable materials. The cover is sized to fit over the portion of the dura which is exposed by removal of the skull flap. In a preferred embodiment, the dura cover should be slightly larger than the opening in the skull so that the edges of the dura cover can be tucked under the skull before the skull flap is reattached. 
     The surgical fastener of the invention comprises a flange which is disposed over and adjacent to the skull flap and the skull. A projection extends from the underside of the flange. The projection extends into the kerf and acts as a spacer between the skull flap and the skull to make the generally even gap. In some embodiments, the projection can be flexible and somewhat wider than the kerf to make a snug fit. But the flexibility of the projection should be somewhat limited so that the function of the projection to act as a spacer is not compromised. 
     A strip or ribbon of material can comprise the element of the surgical strip which is shaped to follow the perimeter contour of the skull flap. Some embodiments of the surgical strip are provided with one or more cavities disposed along its length. The cavities generally are located in the strip so that they are disposed between the skull flap and the skull when the strip is implanted in a patient. For example, the cavity may have a uniform cross section along the entire length of the strip such as in the shape of a U, V, J, W or pleats or corrugations or it may be a closed tube or a solid having the cross-sectional shape of a circle, oval, ellipse, square, rectangle, triangle or any other closed geometric shape. 
     The strip can also be a moldable material which may be, for example, in the form of a putty, paste or gel (i.e., a putty-like, paste-like or gel-like material) or a compressible material or any other material that is formable and which is rolled before it is implanted by insertion into the kerf or which is implanted by pressing, pouring, squeezing or injecting the material into the kerf and the material then takes its shape as a strip following implantation. 
     The outer width of the cross-section of a strip is sometimes referred to herein as the outer width of the channel. References to such strip shapes herein each refer to the shape of a cross-section taken transverse to the length of the strip. In other embodiments one or more tubular elements are used to make the strip and these are disposed between the skull flap and the skull when the strip is implanted in a patient. 
     The surgical strips have side portions which are disposed between the skull flap and the skull when the strip is implanted. These side portions can optionally have openings such as holes, slits or lateral slots which permit bone regrowth. Additionally the slits may be oriented along a transverse axis through one sidewall and a portion of the bottom section of the strip, allowing the strip additional flexibility. The strips also can have a bottom portion. The tubular and solid shaped elements have bottom and top portions and these bottom and/or top portions also can have openings such as holes or lateral slots. 
     As a further option the cavities or tubular elements can be filled or partially filled with medication, bone paste, bone growth enhancers and the like. The putty-like, paste-like, gel-like or compressible material referred to herein also can be comprised of or impregnated with medication, bone paste, bone growth enhancers and the like. 
     Other variations and embodiments are described in more detail below and in the drawings and further variations will be apparent to those skilled in the art based upon the principles of the invention set forth herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The appended drawings are not intended to illustrate every embodiment of the invention but they are representative of embodiments within the principles of the invention. The drawings are for illustrative purposes and are not drawn to scale. 
         FIG. 1  is a representative view of a human skull showing one possible location and configuration of a craniotomy skull flap. 
         FIGS. 1A and 1B  are section views of portions of skull bone and cranial cavity. 
         FIG. 2  is a perspective view of a fastener of the invention having a V-shaped projection extending from the bottom of a flange. The projection has an aperture therethrough.  FIG. 2A  is a top view of the fastener and  FIG. 2B  is a section view.  FIG. 2C  illustrates a fastener with a solid V-shaped projection.  FIG. 2D  is a perspective view of the  FIG. 2  fastener having a strip threaded through the aperture thereof and  FIG. 2E  is a section view of  FIG. 2D . 
         FIGS. 3 ,  3 A,  3 B and  3 C are top views illustrating various shapes of the flange portion of the same type of fastener as illustrated in  FIG. 2 . 
         FIG. 4  is a perspective view of a fastener of the invention having a “W” shaped projection extending from the bottom of the flange. 
         FIG. 5  is a perspective view of a fastener of the invention having a Y-shaped flange and two V-shaped projections. 
         FIG. 6  is a perspective view of the underside of a fastener of the invention having an X-shaped flange and two V-shaped projections wherein each projection is connected on one side and the connections are on opposite sides of an opening in the flange. 
         FIG. 7  is a perspective view of a fastener of the invention having a Y-shaped flange and two projections from the underside. 
         FIG. 8  is a perspective view of a fastener of the invention having a severed V-shaped projection. 
         FIG. 9  is a perspective view of a fastener of the invention having a modified conical projection. 
         FIG. 10  illustrates a craniotome having a cutting diameter of generally the same width as the projection of a fastener. 
         FIG. 11  is a perspective view of a skull flap having three fasteners positioned thereon for affixation thereto. 
         FIG. 12  illustrates a skull flap reattached to a skull using the fasteners of the invention which have been installed with screws. 
         FIG. 13  is a section view of a skull flap reattached to a skull including a section of a fastener and a section of a dura cover of the invention. 
         FIG. 14  illustrates in section a conventional craniotome cut to remove a skull flap from a skull. 
         FIG. 14A  illustrates in section a more angled cut (sometimes referred to herein as a “pumpkin cut”) to remove a skull flap from a skull. 
         FIG. 15  is a perspective view of a woven strip with leaders to thread the strip through apertures in the projections of the fasteners of the invention. 
         FIG. 16  illustrates a rolled strip of a putty-like, paste-like, gel-like or compressible material which can be used as a strip of the invention. 
         FIG. 17  is a section view illustrating the relationship of the strip of  FIG. 16  to the dura cover, the skull flap and the skull. 
         FIG. 17A  is a section view illustrating the relationship to the dura cover, the skull flap and the skull of a strip  161  which has been pressed into the kerf and formed in situ. And  FIG. 17   b  illustrates the use of a J-shaped strip as a supplemental “floor” for strip  161 . 
         FIGS. 18 and 18A  illustrate openings in the skull covered by dura covers comprised of more than one piece of material. 
         FIG. 19  is a perspective view of an embodiment of a strip of the invention comprising a perforated, U-shaped, flexible strip and  FIG. 19A  is a section view of the  FIG. 19  embodiment. 
         FIG. 20  is a perspective view of an embodiment of a strip of the invention comprising a V-shaped flexible strip and  FIG. 20A  is a section view of the  FIG. 20  embodiment. 
         FIG. 20B  is a perspective view of the  FIG. 20  embodiment which is straight rather than pre-curved. 
         FIG. 21  is a perspective view of an embodiment of a strip of the invention comprising a W-shaped flexible strip and  FIG. 21A  is a section view of the  FIG. 21  embodiment. 
         FIG. 22  is a perspective view of a strip of the invention having a flexible strip comprised of three stacked tubes and  FIG. 22A  is a section view of the  FIG. 22  embodiment. 
         FIGS. 22B and 22C  are perspective views of flexible tubular strips which also can be filled or solid. In  FIG. 22C  the tubular strip has a helical slit along its length. 
         FIG. 23  is a perspective view of fasteners of the invention in combination with a perforated, J-shaped, flexible strip.  FIG. 23A  is a top view and  FIG. 23B  is a section view of the  FIG. 23  embodiment. 
         FIG. 24  is a perspective view of a fastener of the invention which can be used in conjunction with various strips.  FIG. 24A  is a bottom view and  FIGS. 24B  and C are section views of the  FIG. 24  fastener.  FIGS. 24D and 24E  are top views of the  FIG. 24  fastener, each illustrating the fastener with a different strip threaded through the aperture. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For reference, a human skull  1  with a craniotomy skull flap  2  (also referred to herein as a flap) is shown in  FIG. 1 . The skull flap  2  is defined by a burr hole  3  and the connecting osteotomy cut or kerf  4 , wherein the skull portion of the burr hole is designated in  FIG. 1  as  3   a  and the skull flap as  3   b . The skull flap  2  has a perimeter contour  5  but it need not be of the particular shape shown and may have any number of burr holes  3 . On the opposing sides of the osteotomy cut  4  is the respective bone edge surface  6  of the skull flap  2  and the surrounding bone  7  of the skull  1 , respectively. The bone edge surface  6  has a perimeter contour  5  matching the contour of the surrounding bone  7  of skull  1 . 
     The skull  1  and skull flap  2  are either made from bone that has a three layer composition, as shown in  FIG. 1A , or a single layer as shown in  FIG. 1B . Referring to  FIG. 1A , the outermost layer is the outer cortical bone  8  and the innermost layer is the inner cortical bone  9 . Between these two stiff layers is a relatively soft middle layer of cancellous bone known as the diploe  10 . Interior to the inner cortical bone  9  is the cranial cavity  11  housing the brain  12  and its surrounding dura matter  13 .  FIG. 1B  illustrates the condition wherein the skull bone is comprised entirely of cortical bone  14 . 
     The present invention is particularly adapted for securing a craniotomy skull flap  2  to the skull  1 , but may be Used in other situations where appropriate. The present illustrative discussion assumes that a surgical strip of the invention is being used in combination with a craniotomy closure system of the invention to close a craniotomy skull flap  2  having one burr hole  3  but the same principles apply if the surgeon makes more than one burr hole in order to open up the skull for surgery. The kerf  4  may be normal to the surface of the skull  1  or at an angle thereto. As we shall explain in more detail below, angled cuts are presently preferred wherein the angle is such that the top of the skull flap  2  is larger relative the bottom than it would be if a cut normal to the surface of the skull was made. This is sometimes referred to herein as a “pumpkin cut” because the cut is similar to one made when cutting the top of a pumpkin to make a jack-o-lantern. 
     The term “surgical strip” is used herein to mean a surgical strip which is used in combination with a craniotomy closure system of the invention. 
     The surgical strips of the invention, also referred to herein as strips, can be made straight or with a precurvature to reduce kinking when they are shaped to follow the perimeter contour of the skull flap. 
     The strips also can be made from a moldable material that has, for example, a putty-like, paste-like or gel-like consistency or a compressible material or any other material that is formable into a shape that will fit in the kerf. Strips of this type may be pressed, poured, squeezed or injected into a kerf and formed in situ. For example, a strip can comprise a paste-like or putty-like material containing bone, either allograft or autogenous bone, and/or other bone growth enhancing material. 
     Combinations of two or more than two strips of the invention can be used. Numerous variations are possible when such combinations are used as will be apparent to those skilled in the art based on the disclosures herein. For example, one strip may contain bone particulate and/or growth enhancers and another may contain antibiotics or other medications. Alternatively, one strip may be used as a “floor” for another strip. This would be supplemental to the “floor” created by the dura cover of the invention. For example, a U, V. W or J-shaped strip or mesh or tubular strip may be threaded through or affixed to the projections of the fasteners to create a floor for a putty-like, paste-like, gel-like or compressible strip. 
     The closure systems and the surgical strips of the invention can be made of various biocompatible materials and combinations of biocompatible materials. Suitable materials include biocompatible metals, alloys, plastics and reinforced plastics which are commonly used in surgical implants of all kinds. Such materials include materials that have sufficient strength and flexibility to meet the objectives of the invention. The materials also can optionally be porous, semi-porous, semi-permeable or maleable. Many of the materials that have been approved by the United States Food and Drug Administration (FDA) for surgical implant applications are also suitable. Some examples of suitable materials include DuraGen® dural graft matrix, available from Integra Lifesciences Corporation, 311 Enterprise Drive, Plainsboro, N.J. 08536, USA and Gelfoam® sterile compressed sponge, a product of Pfizer distributed by Pharmacia &amp; Upjohn Company, Division of Pfizer Inc., New York, N.Y. 10017. DuraGen is a particularly suitable material for making the dura cover of the invention. 
     Generally speaking, there are three main types of alloys used in biocompatible metals today, titanium alloys, cobalt alloys and stainless steel alloys. An exhaustive list is available on the FDA website which also provides the reference numbers and effective dates of the ASTM or ISO standards for many of the materials that are suitable. Some examples include unalloyed titanium and titanium alloyed with aluminum, niobium and/or vanadium; stainless steel and other irons alloyed with molybdenum, chromium, cobalt, tungsten, aluminum, nickel, manganese or vanadium in various combinations, various other stainless steels and other iron alloys, for example, with aluminum oxides, zirconium oxides, tantalum and calcium phosphates. This list is not intended to be exhaustive. 
     Numerous types of high strength polymers also are employed to make implants and many of these are identified not only on the FDA website mentioned above but also on the ASTM website. Examples of suitable high strength polymers include polyetheretherketone (PEEK), epoxys, polyurethanes, polyesters, polyethylenes, vinyl chlorides, polysulfones, polytetrafluoro-ethylene (PTFE), polycarbonates, polyaryletherketone (PAEK), polyoxymethylene, nylon, carbon fiber polyester, polyetherketoneetherketoneketone (PEKEKK), silicones, hydrogels and the like. When a polymer is used, a small wire or other radiopaque material can be incorporated in the main body of the base for purposes of x-ray detection. 
     The foregoing lists of materials may have application in some embodiments of the present invention but not in others as will be apparent to those skilled in the art based on requirements of strength, flexibility, machinability and the like for the particular application. The lists are intended to be illustrative and not exhaustive. Other materials and new materials may be employed based upon the principles of the invention as set forth herein. 
     For purposes of this specification, the term “high strength polymer(s)” is defined as any biocompatible non-bioabsorbable polymer, copolymer, polymer mixture, plastic or polymer alloy having sufficient strength to withstand without failure the stresses that a fastener of the invention would normally be subjected to during surgery or in the body. 
     Bioabsorbable material can also be used to make all or a portion of one or more of the component parts of the fasteners, dura covers or strips of the invention and/or the bioabsorbable material can be applied as a partial or complete coating on such component parts. Some component parts can be made from different materials than others as will be apparent to those having skill in the art based on the disclosures herein. 
     The term “bioabsorbable material” as used herein includes materials which are partially or completely bioabsorbable in the body. 
     Suitable bioabsorbable materials include DuraGen, Gelfoam, collagen, polyglycolide, poly(lactic acid), copolymers of lactic acid and glycolic acid, poly-L-lactide, poly-L-lactate; crystalline plastics such as those disclosed in U.S. Pat. No. 6,632,503 which is incorporated herein by reference; bioabsorbable polymers, copolymers or polymer alloys that are self-reinforced and contain ceramic particles or reinforcement fibers such as those described in U.S. Pat. No. 6,406,498 which is incorporated herein by reference; bioresorbable polymers and blends thereof such as described in U.S. Pat. No. 6,583,232 which is incorporated herein by reference; copolymers of polyethylene glycol and polybutylene terephthalate, and the like. The foregoing list is not intended to be exhaustive. Other bioabsorbable materials can be used based upon the principles of the invention as set forth herein. Some of the most common: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Poly-L-lactic acid (PLLA) 
                 Poly-DL-lactic acid (PDLLA) 
               
               
                   
                 Polyglycolic acid (PGA) 
                 Polydioxanone (PDS) 
               
               
                   
                 Polyorthoester (POE) 
                 Poly-C-capralactone (PCL) 
               
               
                   
                   
               
             
          
         
       
     
     Bioactive materials can be admixed with the bioabsorbable materials, impregnated in the bioabsorbable materials and/or coated on the outer surface thereof. Bioactive materials, including natural and/or synthetic materials, also can be used to fill cavities in the fasteners and the surgical strips. These materials can include, for example, bioactive ceramic particles, bone chips or paste, platelet rich plasma (PRP), polymer chips, synthetic bone cement, autologous materials, allograft, cadaveric materials, xenograft, nanoparticles, nanoemulsions and other materials employing nanotechnology, capsules or reinforcement fibers. And they can contain, for example, antimicrobial fatty acids and related coating materials such as those described in Published U.S. Patent Application No. 2004/0153125 A1; antibiotics and antibacterial compositions; immunostimulating agents; tissue or bone growth enhancers and other active ingredients and pharmaceutical materials known in the art. 
     The products of the invention which are made with bioabsorbable material can be made by molding, extrusion, heat shrinking or coating the bioabsorbable material on a base which has been provided with attachment means such as those described in our pending patent application Ser. No. 11/025,213 filed Dec. 29, 2004 which is incorporated herein by reference. Some of the screws and other fastening devices described in our pending patent application Ser. No. 11/025,213 filed Dec. 29, 2004 can also be used in or in combination with the surgical strips and fasteners of the present invention. When the bioabsorbable material will have functional mechanical properties which are not made from the base material, the bioabsorbable material can be molded onto the base in the desired shape. Alternatively, the bioabsorbable material also can be coated, shrink wrapped or molded onto the base. If necessary, the bioabsorbable material can be machined to the desired shape and/or dimensions. 
     As will be apparent to those skilled in the art, the sizes of the surgical strips and fasteners of the invention can be varied to meet their intended applications. The shapes can take various forms in addition to those illustrated without deviating from the principles of the invention. And the sizes, lengths and widths can be varied for particular applications within the principles of the invention set forth herein. 
     The size of the dura cover will be dictated by the surgeon. In some cases the surgeon may elect to use more than one piece of material to make the dura cover. The cover may be sized to cover a portion of the opening in the skull or may be the same size as the opening in the skull or may be larger than the opening if the surgeon wishes to tuck a portion of the dura cover under the skull to extend it slightly beyond the size of the opening. The dura cover may be cut from a sheet of material in the operating room and may comprise one piece or more than one piece of material. One of the purposes of the dura cover is to protect the portion of the soft tissue located directly below the kerf. Another purpose is to cover the sutures that are used to put the dura back together after the soft tissue surgery. The thickness of the dura cover will generally be uniform and should be from about 0.5 to about 3 millimeters thick. 
     Various methods can be used to employ the craniotomy closure systems of the invention as will be apparent to those skilled in the art based upon the embodiment(s) of the fasteners and optional surgical strips selected for use by the practitioner. For example, the fasteners may be attached to the skull flap first, then the skull flap would be positioned in the skull opening following placement of the dura cover over the exposed dura. The fastener would then be attached to the skull. In a preferred embodiment, the fasteners are made from a material that allows the flange to be intraoperatively bent so that the fastener and reattached flap will follow the original contour of the skull. The flange can be bent, for example, before it is affixed to the skull flap or after it is affixed to the skull flap, but normally it is automatically bent by the pressure imparted by the fasteners (screws, tacks, other means) when it is affixed to the skull. This could be followed by affixing one or more cranial plugs in the burr hole or holes as needed as described in our copending patent application Ser. No. 11/333,102 filed Jan. 17, 2006, the disclosure of which is incorporated herein by reference. When surgical strips are used, antibiotics, bone growth enhancers or other materials disclosed herein could be added in cavities in the surgical strips and/or fasteners before or after the skull flap is reattached to the skull, as will be apparent to those having ordinary skill in the art. It should be noted that the terms “affixing”, “affixed” or “affix” as used herein include “snap-fit” and “press-fit” as well as the other means such as screws, staples, tacks, adhesives and the like as described herein. Other methods will be apparent to those having skill in the art depending upon the characteristics of the skull and/or skull flap, the type of surgery involved and the likelihood or unlikelihood of the need to re-open the surgical site. 
     As noted above, the surgical strips of the invention can be formed around the perimeter contour of the skull flap and attached to the skull flap or the strips can be attached to the fasteners before or after the fasteners are attached to the skull flap and before attachment of the flap to the skull. Alternatively, the fasteners can be attached to the skull flap and then the skull followed by insertion of a strip or strips. The step of attaching the fasteners to the skull flap, and optionally bending the flanges to conform with the skull contour, can be done by operating room personnel while the surgeon is performing surgery. This saves substantial time when the skull flap is reattached following surgery. The previously attached fasteners support the skull flap and insure that the top of the flap coincides with the top surface of the skull. As noted above, the shape of the skull flap is highly variable and when it is reattached to the skull it is positioned in a manner to match the position from which it was removed, similar to replacing a piece of a jigsaw puzzle. 
     There are numerous suitable options for fastening the fasteners of the invention to the skull flap and the skull. These include screws, staples, tacks, glues, adhesives, peel off adhesives, press-fit, snap-fit and combinations of two or more thereof. For example, a fastener may be stapled onto the skull flap and then press-fit into the opening in the skull. These fastening methods may be used to affix the fasteners to any contacting surface of either the skull flap or skull. 
       FIG. 2  is a perspective view of a fastener  20  of the invention.  FIG. 2A  is a top view and  FIG. 2B  is a section view. A continuous elongate flange  21  has lower surfaces  28  which overlay both sides of the kerf when the fastener is affixed to the skull and skull flap. Optional holes  22  can be provided for screws or other devices for affixing the fastener to the skull and skull flap. A V-shaped projection  23  extends from the underside of the flange. The projection  23  has an aperture  26  having a central axis a-a disposed in parallel with lower surfaces  28  and a surgical strip  27  can be threaded through the aperture as illustrated in  FIG. 2D  and the section view thereof,  FIG. 2E . Optional opening  24  provides access to aperture  26  after fastener  20  is installed in a patient. The opening  24  opens from the upper surface of the flange  21  into the aperture  26  and can be used to assist in threading a strip or strips through the aperture and/or to insert medication, bone growth enhancers and the like into the fastener. 
       FIG. 2C  illustrates an alternative embodiment of the fastener wherein the projection  25  is solid and does not have an aperture or an optional opening through the flange. 
       FIGS. 3 ,  3 A,  3 B and  3 C are top views of fasteners of the invention having flanges of various shapes. Flange  32  is T-shaped, flange  34  is Y-shaped, flange  36  is L-shaped and flange  38  is X-shaped. Other shapes can be used without departing from the invention. 
     The projections from the undersides of the flanges can also have various shapes without departing from the invention and there can be one or more than one projection from the underside of a flange.  FIG. 4  illustrates a fastener having projections  43  which make up a W-shape extending from elongate flange  41 .  FIG. 5  illustrates a fastener having Y-shaped flange  51  having V-shaped projections  53  and  54  extending from the underside thereof. Apertures  56  in the projections are coaxial. An X-shaped flange  61  is provided in the fastener of  FIG. 6 . One leg of projection  63  is connected to the underside of the flange on one side of opening  65  and one leg of projection  64  is connected to the underside of the flange on the opposite side of opening  65 . The unconnected legs of the projections allow for enhanced flexibility. The fastener illustrated in  FIG. 7  is comprised of a Y-shaped flange  71  and projections  73  and  74 . Flange  81  of the fastener illustrated in  FIG. 8  has projections  83  and  84  which together form the shape of a V which has been severed at point  85 . A modified conical or bullet-shaped projection  93  extends from the bottom of flange  91  in the fastener of  FIG. 9 . Projection  93  can be solid or hollow. 
     In the prior art, flat plates were typically used to reattach a skull flap to a skull. The plates did not have projections as described herein. By sizing the projection so that its width corresponds to the diameter of the cutting burr of a craniotome cutter, and consequentially the width of the kerf around the skull flap, the projection centers the flap and allows the surgeon to place the flap in the position it occupied before it was cut out of the skull. The projection also acts as a buttress to resist inward displacement of the flap and can serve to intraoperatively bend the flange of the fastener or assist the manual bending of the flange to match the contour of the skull. Because the skull flap is cut out in a single pass with the craniotome, the resulting gap (the kerf) between the native skull and flap necessarily corresponds to the width (diameter) of the cutting burr. To replace the flap in its original position, the surgeon needs to maintain this uniform gap around the periphery of the flap as he/she applies the rigid fixation using the fasteners. By matching the width of the projection on the fastener to the diameter of the cutter, this is automatically accomplished. 
       FIG. 10  illustrates a craniotome  101  with a footplate  103  and a cutting burr  102  having relatively the same diameter D as the width W of projection  23  from fastener  20 . 
     In a preferred surgical method, the fasteners  20  are affixed to the skull flap  2  before the skull flap is reattached to the skull. This is illustrated in  FIG. 11  wherein one side of each projection  23  is butted up against and in contact with the perimeter of the flap, the side being approximately tangential to the edge of the flap at the point of contact. The number of fasteners employed is at the discretion of the surgeon. We recommend using at least two and preferably three fasteners or more to insure proper placement of the flap into its original position. 
     Following placement of the dura cover  211  over the dura  13  (see  FIGS. 13 and 17 ) the flap  2  is replaced in the skull  1  and the fasteners  20  insure an even gap (i.e., the kerf  4 ) around the periphery thereby returning the flap to its original position as illustrated in  FIG. 12 . Screws  29  are used to affix the fasteners  20  to the skull flap and skull in the illustration but it is understood that other devices or adhesives can be used to affix the fastener as previously described herein. 
       FIG. 13  is a section view of a portion of  FIG. 12  illustrating the relationship of the fastener  20  to the skull flap  2  and skull  1  after the skull flap has been reattached to the skull. The projection  23  fits snugly between the sidewalls of the kerf  4  and the central axis a-a of aperture  26  is approximately in parallel with the side walls at the points of contact of the projection with the sidewalls. Stated another way, the central axis a-a of the aperture is approximately in parallel with the perimeter (or a tangent t-t to the perimeter) at the point of contact of the projection with the surface of the perimeter. The dura cover  211  in  FIG. 13  is sized only to cover the opening in the skull without being tucked under the portion of the skull adjacent the opening. 
     Restoration of the original flap position provides the optimum cosmetic result and the consistent peripheral gap (the kerf) allows for the optional insertion of a uniform volume of material all around the flap. This inserted material comprises one or more strips of the invention. For example, the material could be autologous bone graft as described above, autogenous bone mixed with blood and/or saline, a filler material such as collagen, DuraGen, Gelfoam or the like, or a combination of bone graft material and filler. These materials act as strips whether or not they are supported by the fasteners. 
     When cutting the flap, the surgeon will keep the craniotome angled perpendicular (normal) to the curvature of the skull or more likely, he/she will deliberately tilt the cutter to produce an angled cut through the skull to make a pumpkin cut as described above. This is illustrated in  FIGS. 14 and 14A  wherein the cut in  FIG. 14  is normal to the skull and the cut in  FIG. 14A  is a pumpkin cut. 
     Both methods produce a flap that is widest at its outer or top surface and tapers to a smaller dimension across its inner or bottom surface. The corresponding sidewalls of the kerf  4  are generally in parallel. While neither flap would fall freely through the corresponding hole in the skull, allowing the bone flap to move or settle inwardly would cause the inner surface of the flap to impinge on the brain and would secondarily result in a cosmetically unacceptable depression of the patient&#39;s scalp. Rigid fixation of the flap to the skull solves this problem. Prior art metallic plates without a projection span the gap between flap and skull and are generally affixed with screws anchored into the bone. But the projection beneath the flange of the fastener of the invention adds an additional element of strength. It does so without adding any additional material to the surface of the skull which would increase the chance that the fixation system of the invention would be palpable to the patient. 
     The fastener has a top flange that functions much like a standard bone plate but the addition of the projection beneath the flange fills the gap created by the osteotomy cut (kerf) and acts as a buttress to further resist any downward force on the flap. Because the width of this projection is matched to the craniotome cutting burr, the lateral walls of the projection are either in contact with or in very close proximity to the parallel sidewalls of the flap and skull as shown in  FIG. 13 . Any inwardly directed force on the flap must now overcome not only the resistance of the flange (in bending) and screws or other anchoring devices but also must crush the projection which fills the gap. 
     Because the width (or diameter) of the projection on the fastener matches the diameter of the craniotome cutting burr, the projection effectively restores the removed bone volume at each fastener location. This allows it to function as a three-dimensional spacer, automatically restoring the flap location side-to-side as well as re-establishing the correct depth of the flap relative to the skull as shown here. 
     There is one other advantage attributable to the underside projection on the fastener. The difficulty of bending plastic plates (without heating and softening) can be overcome with the fastener design. When the flap with attached fastener is reinserted into the skull opening, the projection will be pushed slightly toward the side of the flap. This in turn will bend the flange of the fastener slightly downwardly. Because the projection is trapped in the gap between the flap and the skull, this bend is maintained. The surgeon simply pushes the flap down (inward) and the non-secured end of the flange bends to meet the skull. The surgeon then fastens this side in place with the appropriate affixation device or adhesive. This feature allows a fastener to be made with a flange that is only slightly precurved knowing that it will self-bend when the flap is inserted into the skull opening. Because the projection provides added support, this flange can be made more flexible than a traditional plate to enhance this property. 
       FIG. 15  illustrates a mesh strip  150  having a curved leader  152  affixed to one end thereof. An optional leader  154  affixed to the other end is also illustrated. The leader or leaders can be pre-curved, straight or intraoperatively curved. This embodiment can be used when the strip is to be threaded through the apertures  26  in the fasteners. The leader is used in a similar manner to a needle when sewing with a needle and thread. Any of the strips of the invention that are sufficiently flexible can be combined with a leader in this manner. 
       FIG. 16  illustrates a strip  160  made from a putty-like or gel-like material. This can be made in the form of a rolled material as illustrated or it can be hand rolled or compressed and pressed into the kerf after the skull flap is reattached to the skull (illustrated as strip  161  in  FIGS. 17A and 17B ). Alternatively, this type of filler material can simply be pressed, poured or injected into the kerf after reattachment of the flap, effectively creating a strip of material in situ in the kerf extending from one fastener to another. As noted above, the objectives of all of the strips of the invention are to close the openings in the skull and optionally to enhance bone regrowth, provide medication and the like. 
     The strips also can serve to provide a supplemental “floor” to the kerf in addition to the “floor” provided by the dura cover. This may allow the surgeon to apply greater pressure to filler strips (implanted following implantation of the strip or strips which provide a supplemental floor) such as autologous bone which are pressed into the kerf, without pressing against the dura cover. Furthermore, the strips which serve to provide a supplemental floor replace some of the volume of the bone removed with the craniotome so that collected bone from the craniotome will be adequate to fill the volume remaining in the kerf. 
     The strips of the invention can be made from various materials and in various shapes. They can be affixed to the skull flap before it is reattached to the skull, they can be affixed to the fasteners before or after they are affixed to the skull or they can be implanted after reattachment. Some of them can be threaded through apertures in the fasteners, others can be affixed to or implanted adjacent to the sidewall of the skull flap and others can simply be inserted adjacent the fasteners and in attachment with or in contact with the fasteners or without necessarily being attached to or in contact with the fasteners. 
       FIG. 17  is a section view of strip  160  implanted between a skull flap  2  and a skull  1 . Dura cover  211   a  is also illustrated over the dura  13 . The dura cover is placed over the dura before the skull flap is reattached. The portion of the dura uncovered by the skull flap is covered with the dura cover and the dura cover is optionally sized slightly larger than the opening in the skull so that a portion of the dura cover can be tucked under the portion of the skull adjacent the opening as illustrated in  FIG. 17 . In other words, the dura cover is sized to cover a portion of the soft tissue located under the skull and adjacent the kerf. The dura cover effectively provides a floor under the kerf  4  so that the material of strip  160  (or any other material or strip in the place of strip  160 ) will not impinge upon the dura or migrate into the cranium. As noted above, a suitable material for the dura cover is any biocompatible bioabsorbable material, for example, DuraGen. 
     In  FIGS. 17A and 17B  the strip  161  is comprised of a putty-like, paste-like, gel-like or compressible material which is pressed into the kerf  4  to form a strip in situ.  FIG. 17B  illustrates an embodiment employing a J-shaped strip  221  which is used as a supplemental floor for the strip  161 . Of course, various other strips of the invention can be used as a supplemental floor or as a filler to provide medication, enhanced bone regrowth, etc., as will be apparent to those having skill in the art based on the disclosures herein. 
       FIG. 18  illustrates an opening  182  in a skull, the dura  13  which has been sutured with sutures  183  and a dura cover made up of four pieces,  211   b ,  211   c ,  211   d  and  211   e . Additional dura cover material can be cut in strips (not shown) and used to cover the sutures at the surgeon&#39;s discretion. 
       FIG. 18A  illustrates an opening  184  in a skull. Two pieces of dura cover,  211   f  and  211   g , are used to cover all of the exposed area of the dura and edge portions are tucked under the skull. Sutures  183  are covered by the dura cover. 
       FIGS. 19 and 19A  illustrate a strip  170  having a U-shape which is pre-curved and sufficiently flexible to be shaped to follow the perimeter contour of a skull flap. Multiple holes  171  are disposed around the inside perimeter  172  and the outside perimeter  173  of U-shaped strip  170 . The holes  171  permit bone growth for bone to bone reattachment of the skull to the skull flap or they can be used to affix the sidewalls of the strip to the edges of the skull flap. Bone growth can be enhanced by filling the U-shaped strip  170  with known bone growth enhancers and/or other bioactive materials as described above. This can be done before and/or after the strip  170  is implanted in the patient. This concept can be adapted by those skilled in the art to strips of other cross sections disclosed herein. 
       FIGS. 20 and 20A  illustrate a strip  180  comprised of a V-shaped strip which is pre-curved and sufficiently flexible to be shaped to follow the perimeter contour of a skull flap. Multiple slots serve the same function as the holes  171  described in respect of the  FIG. 19  embodiment and the V-shaped strip  180  can be filled with known bone growth enhancers and/or other bioactive materials and/or medications as described above.  FIG. 20B  is a perspective view of the  FIG. 20  embodiment which has not been pre-curved. 
     The strip  190  illustrated in  FIG. 21  is comprised of a W-shaped strip which is pre-curved and sufficiently flexible to be shaped to follow the perimeter contour of a skull flap. Slots  191  or holes (not shown) can optionally be provided through the W-shaped strip to serve the same functions as described above. 
     Strip  200  illustrated in  FIG. 22  is comprised of one or more flexible tubes  201  (three illustrated) which are pre-curved and sufficiently flexible to be shaped to follow the perimeter contour of a skull flap. The terms “tubular” or “tube” as they are used herein are not meant to restrict the lateral cross-section of the tube to only a circular profile. Oval, elliptical, rectangular or other closed geometric shaped tubular structures (not shown) are also within the meaning of “tubular” or “tube” and can be used with this design. A tube of the invention can be hollow, filled or solid. Multiple slits  202  or holes or slots (not shown) can optionally be provided in the tubes  201  as with many of the other embodiments discussed above. The slits  202  are narrow cuts made through the tubes  201 . The tubes  201  also can be filled with known bone growth enhancers and/or other bioactive materials as described above. These tubular strips may be packaged (sterile) with the bioactive materials already filling the cavities. This is also possible for the other configurations but obviously much more practical for a tubular profile. 
     As discussed above in respect of the tubular strip of  FIG. 22 , the tubes of  FIGS. 22B and 22C  can have various cross sections. In  FIG. 22B , tube  203  of strip  204  can be made from a solid, porous, semi-porous, semi-permeable or woven material and/or it can have holes or slots or slits. 
     Strip  205  in  FIG. 22C  is comprised of a tube  206  having a helical slit  207  which runs the entire length of the tube. 
     Multiple tubes of the kind illustrated and described in respect of  FIGS. 22B and 22C  can be arranged together. For example, they can be stacked as in  FIG. 22  or arranged in rows or combinations of rows and stacks or the like. Combinations of tubes  203  and  206  can also be used in such multiple tube embodiments. Tubes may also be made in a rolled form and bone growth enhancers and/or medications can be incorporated into the rolled tubular strip. These rolled strips may be sufficiently flexible (or soft) such that they readily conform to the size and shape of the kerf when inserted in a patient&#39;s skull. 
     The strip  220  illustrated in  FIGS. 23 ,  23 A and  23 B is comprised of a J-shaped flexible strip  221  which is pre-curved and sufficiently flexible to be shaped to follow the perimeter contour of a skull flap. This embodiment has been illustrated with fastener  230  which is a slight variant of the fastener  20  as explained in the below discussion of  FIG. 24 . In this embodiment, the projection  233  purposely positions the J-shaped cavity of the strip  221  below the level of the underside of the flange  231  to insure that the J-shaped flexible strip  221  remains below the top surface of the skull and skull flap. In this embodiment the strip can be affixed to the skull flap before or after the fasteners are affixed to the flap or the strip can be affixed to the fasteners before the fasteners are affixed to the flap. Any strip having an open upper portion such as a U, V. W or J-shaped strip can be used with a fastener having a compatibly shaped projection. 
       FIG. 24  illustrates a perspective view of a fastener  230  with a continuous elongate flange  231  creating lower surfaces  238  each of which will be affixed to one side of the kerf when the fastener is implanted in a patient. Optional fastener holes  232  are shown in the flange. A V-shaped projection  233  having an aperture  236  projects from the underside  234  of the flange and the aperture is illustrated with a compatibly shaped flexible strip  180 . In other words, the strip  180  is threaded through the aperture  236  in the V-shaped projection  233  of fastener  230 .  FIG. 24A  is a view of the underside of  FIG. 24 ,  FIG. 24B  is a section view taken through section line  24 B- 24 B of  FIG. 24A  and  FIG. 24C  is a section view taken through section line  24 C- 24 C of  FIG. 24A .  FIG. 24D  is a top view of a fastener  230  with a V-shaped strip  180  threaded through the aperture thereof. Of course, strips of many other shapes could be threaded through the aperture as long as they can be pulled through the aperture. A flexible strip such as, for example, a woven strip or a flexible tube can be threaded through the aperture even if the cross-section is wider than the aperture. In that case, it will simply be squeezed within the aperture but allowed to expand to its original size on both sides of the aperture. This is illustrated in  FIG. 24E  wherein a woven strip  150  has been threaded through the aperture of the fastener and the strip  150  is wider than the aperture. 
     Optional tabs  235  on the inside of the aperture  236  position the strip  180  at a distance below the underside of the flange  234 . The fasteners could be affixed to the strip or could be able to slide along its length. Obviously other strip cross-sections (U, J, W, tubular) could be used in a similar manner.