Patent Publication Number: US-2011054408-A1

Title: Delivery systems, devices, tools, and methods of use

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation in part of U.S. application Ser. No. 12/205,539 filed Sep. 5, 2008, which is a continuation in part of U.S. application Ser. No. 12/171,168 filed Jul. 10, 2008, which claims benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/948,866 filed Jul. 10, 2007, U.S. Provisional Application No. 61/040,531 filed Mar. 28, 2008, and U.S. Provisional Application No. 61/040,537 filed Mar. 28, 2008; the present application is a continuation in part of U.S. application Ser. No. 12/171,125, filed Jul. 10, 2008, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/948,866 filed Jul. 10, 2007, U.S. Provisional Application No. 61/040,531 filed Mar. 28, 2008, and U.S. Provisional Application No. 61/040,537 filed Mar. 28, 2008; the present application claims benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/152,057 filed Feb. 12, 2009, U.S. Provisional Application No. 61/154,673, filed Feb. 23, 2009, U.S. Provisional Application No. 61/154,689 filed Feb. 23, 2009, and U.S. Provisional Application No. 61/154,679 filed Feb. 23, 2009. The contents of all above referenced applications are hereby incorporated herein by reference in their entirety. 
    
    
     FIELD 
     A delivery system for delivering a substance or material to a surgical site is provided. More particularly, a delivery system comprising a covering and a substance, the covering being configured for at least partially retaining the substance provided therein until the delivery system is placed at a surgical site, and thereafter facilitating transfer of the substance or surrounding materials, is provided. 
     BACKGROUND 
     The use of bone grafts and bone substitute materials in orthopedic medicine is known. While bone wounds can regenerate without the formation of scar tissue, fractures and other orthopedic injuries take a long time to heal, during which time the bone is unable to support physiologic loading unaided. Metal pins, screws, rods, plates and meshes are frequently required to replace the mechanical functions of injured bone. However, metal is significantly more stiff than bone. Use of metal implants may result in decreased bone density around the implant site due to stress shielding. Physiologic stresses and corrosion may cause metal implants to fracture. Unlike bone, which can heal small damage cracks through remodeling to prevent more extensive damage and failure, damaged metal implants can only be replaced or removed. The natural cellular healing and remodeling mechanisms of the body coordinate removal of bone and bone grafts by osteoclast cells and formation of bone by osteoblast cells. 
     Conventionally, bone tissue regeneration is achieved by filling a bone repair site with a bone graft. Over time, the bone graft is incorporated by the host and new bone remodels the bone graft. In order to place the bone graft, it is common to use a monolithic bone graft or to form an osteoimplant comprising particulated bone in a carrier. The carrier is thus chosen to be biocompatible, to be resorbable, and to have release characteristics such that the bone graft is accessible. Generally, the formed implant, whether monolithic or particulated and in a carrier, is substantially solid at the time of implantation and thus does not conform to the implant site. Further, the implant is substantially complete at the time of implantation and thus provides little ability for customization, for example by the addition of autograft. 
     The use of bone grafts is generally limited by the available shape and size of grafts. Bone grafts using cortical bone remodel slowly because of their limited porosity. Traditional bone substitute materials and bone chips are more quickly remodeled but cannot immediately provide mechanical support. In addition, while bone substitute materials and bone chips can be used to fill oddly shaped bone defects, such materials are not as well suited for wrapping or resurfacing bone. 
     Thus, it would be useful to provide a delivery system for delivering a substance, such as bone graft, to a surgical site that conforms to the surgical site, that maintains a substance provided therein in a coherent mass, and that can be customized at the time of implantation. 
     SUMMARY 
     A delivery system for delivering a substance or material to a surgical site is provided. The delivery system comprises a covering and a substance to be retained within and delivered by the covering. Generally, the covering may be a single or multi-compartment structure capable of at least partially retaining a substance provided therein until the covering is placed at a surgical site. In some examples, upon placement, the covering facilitates transfer of the substance and/or materials from the covering to the surgical site. The covering may participate in, control, or otherwise adjust, the release of the substance or penetration of the covering by surrounding materials, such as cells or tissues. 
     In accordance with another embodiment, a delivery system comprising a plurality of operably linked segments of at least two types is provided. The first segment type of the delivery system comprises a covering material defining at least one compartment containing a bone growth substance, and the second segment type is configured to connect segments of the first type. In further embodiments of the delivery system, each of the first segment types contain the same or different amounts and/or types of bone growth substance. In some embodiments, the segments of the first type vary in size and/or covering material. In still further embodiments, the second segment type is also made of a covering material that is unfilled or partially filled with a bone repair substance. 
     In accordance with another embodiment, a delivery system comprising linked segments of at least two types, the delivery system is designed for use in a sternum closure procedure, or filling an irregular shaped bone void is provided. When used to fill an irregular void, many embodiments of the delivery system include at least two segments of the first type within the bone void packed substantially in parallel. In still further embodiments, the delivery system is terminally sterilized, for example by gamma radiation, electron beam radiation, UV irradiation, cobalt source radiation; autoclaving, dry heating, EtO, EtOH, and by supercritical fluid exposure. In still other embodiments, the bone growth substance is sterilized by a method other than that used to sterilize the covering material. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description. As will be apparent, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the detailed description is to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION 
         FIG. 1   a  illustrates a delivery system comprising a relatively narrow tubular covering and a particulated substance, in accordance with one embodiment. 
         FIG. 1   b  illustrates an alternative view of the delivery system of  FIG. 1   a.    
         FIG. 2   a  illustrates a delivery system comprising a relatively wide tubular covering and a particulated substance, in accordance with one embodiment. 
         FIG. 2   b  illustrates an alternative view of the delivery system of  FIG. 2   a.    
         FIG. 2   c  illustrates an accordion-style covering, in accordance with one embodiment. 
         FIG. 3  illustrates a two-compartment covering comprising two single-compartment coverings coupled together, in accordance with one embodiment. 
         FIG. 4  illustrates a tubular covering for delivery in a catheter, in accordance with one embodiment. 
         FIG. 5   a  illustrates a perspective view of a covering having an elongated containment portion, in accordance with one embodiment. 
         FIG. 5   b  illustrates a top view of the covering of  FIG. 5   a.    
         FIG. 5   c  illustrates an end cross-sectional view of the covering of  FIG. 5   a.    
         FIG. 6   a  illustrates a perspective view of an alternative embodiment of a covering having an elongated containment portion. 
         FIG. 6   b  illustrates a top view of the covering of  FIG. 6   a.    
         FIG. 6   c  illustrates an end cross-sectional view of the covering of  FIG. 6   a.    
         FIG. 7   a  illustrates a perspective view of yet an alternative embodiment of a covering having an elongated containment portion. 
         FIG. 7   b  illustrates a top view of the covering of  FIG. 7   a.    
         FIG. 7   c  illustrates an end cross-sectional view of the covering of  FIG. 7   a.    
         FIG. 8  illustrates a first embodiment of a multi-compartment covering having an elongated containment portion. 
         FIG. 9  illustrates a second embodiment of a multi-compartment covering having an elongated containment portion. 
         FIG. 10  illustrates a dual-compartment covering comprising first and second compartments situated side-by-side and separated by a barrier, in accordance with one embodiment. 
         FIG. 11  illustrates a nested dual-compartment covering, in accordance with one embodiment. 
         FIG. 12   a  illustrates a covering comprising as a plurality of compartments separated by perforations, in accordance with one embodiment. 
         FIG. 12   b  illustrates a top view of a multi-compartment covering configured to be foldable and stackable, in accordance with one embodiment. 
         FIG. 12   c  illustrates a side view of a multi-compartment covering configured to be foldable and stackable, in accordance with one embodiment. 
         FIG. 12   d  illustrates a stacking sequence of a multi-compartment covering configured to be foldable and stackable, in accordance with one embodiment. 
         FIG. 12   e  illustrates a top view of another embodiment of a foldable and stackable covering where there may be a segment of a first type and a segment of a second type. 
         FIG. 12   f  illustrates a side view of another embodiment of a foldable and stackable covering where there may be a segment of a first type and a segment of a second type. 
         FIG. 12   g  illustrates another side view of another embodiment of a foldable and stackable covering where there may be a segment of a first type and a segment of a second type. 
         FIG. 13   a  illustrates a covering having a hook attachment mechanism, in accordance with one embodiment. 
         FIG. 13   b  illustrates a covering having a screw attachment mechanism, in accordance with one embodiment. 
         FIG. 13   c  illustrates a covering having a mechanical attachment mechanism, in accordance with one embodiment. 
         FIG. 13   d  illustrates a covering having a tab attachment mechanism, in accordance with one embodiment. 
         FIG. 13   e  illustrates a covering having a suture attachment mechanism, in accordance with one embodiment. 
         FIG. 13   f  illustrates a covering having a wrap attachment mechanism, in accordance with one embodiment. 
         FIG. 13   g  illustrates a covering having an adhesive attachment mechanism, in accordance with one embodiment. 
         FIG. 13   h  illustrates a covering having an adhesive attachment mechanism, in accordance with a further embodiment. 
         FIG. 14   a  illustrates a tension band and covering embodiment, in accordance with one embodiment. 
         FIG. 14   b  illustrates tension band comprising covering including spreaders, in accordance with one embodiment. 
         FIG. 15   a  illustrates a cage for use with a cartridge covering, in accordance with one embodiment. 
         FIG. 15   b  illustrates a cartridge covering, in accordance with one embodiment. 
         FIG. 15   c  illustrates a delivery system comprising a cage and a cartridge covering, in accordance with one embodiment. 
         FIG. 15   d  illustrates a cartridge for use in a delivery system, in accordance with one embodiment. 
         FIG. 15   e  illustrates a first graft-containing covering for use in a cage delivery system, in accordance with one embodiment. 
         FIG. 15   f  illustrates a second graft-containing covering for use in a cage delivery system, in accordance with one embodiment. 
         FIG. 15   g  illustrates how the first and second graft-containing coverings are placed in the cage delivery system, in accordance with one embodiment. 
         FIG. 15   h  illustrates the placement of the cage delivery system in a target site, in accordance with one embodiment. 
         FIG. 15   i  illustrates a one piece covering and cage delivery system, in accordance with another embodiment. 
         FIG. 15   j  illustrates a one piece covering for use in a cage delivery system, in accordance with one embodiment. 
         FIG. 15   k  illustrates another view of the one piece covering wrapped around itself, in accordance with one embodiment. 
         FIG. 16  illustrates a delivery system comprising a cage and a cartridge covering, in accordance with another embodiment. 
         FIG. 17  illustrates a delivery system comprising a cage and a cartridge covering wherein the cartridge covering is oversized with respect to the cage, in accordance with yet another embodiment. 
         FIG. 18   a  illustrates a cage with three containment areas for receiving cartridge coverings, in accordance with one embodiment. 
         FIG. 18   b  illustrates a delivery system comprising a cage and three cartridge coverings, in accordance with one embodiment. 
         FIG. 19  illustrates a delivery system comprising a hip stem and a cartridge covering, in accordance with one embodiment. 
         FIG. 20  illustrates a tubular covering partially divided into compartments, in accordance with one embodiment. 
         FIG. 21   a  illustrates a delivery system comprising a cage and a wrapping covering, in accordance with one embodiment. 
         FIG. 21   b  illustrates a delivery system comprising a cage, a cartridge covering, and a wrapping covering, in accordance with one embodiment. 
         FIG. 21   c  illustrates an embodiment of a curved covering with a shaping or reinforcing structure, in accordance with one embodiment. 
         FIG. 21   d  illustrates a top view of assembly of the curved covering of  FIG. 21   c.    
         FIG. 21   e  illustrates a side view of assembly of the curved covering of  FIG. 21   c.    
         FIG. 22   a  illustrates a cup-shaped embodiment of a covering, in accordance with one embodiment. 
         FIG. 22   b  illustrates another view of a cup-shaped embodiment of a covering with a flange extending at least partially around the rim of the covering, in accordance with one embodiment. 
         FIG. 23  illustrates a U-shaped covering, in accordance with one embodiment. 
         FIG. 24   a  illustrates a substantially solid delivery container covering, in accordance with one embodiment. 
         FIG. 24   b  illustrates a cap interlocking with a tube of a substantially solid delivery container covering via press fitting. 
         FIG. 24   c  illustrates a solid delivery container covering used in femoral head AVN, in accordance with one embodiment. 
         FIG. 24   d  illustrates a solid delivery container covering used in treatment of a tibial compression fracture, in accordance with one embodiment. 
         FIG. 24   e  illustrates a solid delivery container covering used in ankle fusion, in accordance with one embodiment. 
         FIG. 24   f  illustrates the assembly of a covering comprising two layers of material, in accordance with one embodiment. 
         FIG. 24   g  illustrates a coving comprising two layers of material that is open at one end, in accordance with one embodiment. 
         FIG. 24   h  illustrates a carrier that may be inserted into a covering, in accordance with one embodiment. 
         FIG. 24   i  illustrates a multi-compartment covering that may house a carrier, in accordance with one embodiment. 
         FIG. 25  illustrates a delivery gun for covering placement, in accordance with one embodiment. 
         FIG. 26   a  illustrates a tamper insertion tool, in accordance with one embodiment. 
         FIG. 26   b  illustrates a covering surrounding a tamper insertion tool ready for placement in a site, in accordance with one embodiment. 
         FIG. 26   c  illustrates a TLIF opening in a disc space in preparation for a covering insertion, in accordance with one embodiment. 
         FIG. 26   d  illustrates the covering and insertion tool being inserted into the prepared site, in accordance with one embodiment. 
         FIG. 26   e  illustrates the covering inserted into the TLIF opening in the disc space, in accordance with one embodiment. 
         FIG. 26   f  illustrates the insertion tool pushing the covering anteriorly in the disc space, in accordance with one embodiment. 
         FIG. 26   g  illustrates another view of the covering inserted into the TLIF opening, in accordance with one embodiment. 
         FIG. 26   h  illustrates the coving being pushed into position by the insertion tool, in accordance with one embodiment. 
         FIG. 27   a  illustrates a tubular insertion instrument, in accordance with one embodiment. 
         FIG. 27   b  illustrates coverings prior to insertion in a tubular insertion instrument and after delivery from a tubular insertion instrument, in accordance with one embodiment. 
         FIG. 27   c  illustrates inserting a covering into the chamber of a tubular insertion instrument, in accordance with one embodiment. 
         FIG. 27   d  illustrates a plunger inserted in the receiving end of the tubular insertion instrument to compress the covering toward the form area. 
         FIG. 27   e  illustrates the covering being compressed by the plunger toward the discharge area. 
         FIG. 27   f  illustrates delivery of the covering, which has been inserted into the target site. 
         FIG. 28  illustrates a covering being loaded with a substance using a syringe, in accordance with one embodiment. 
         FIG. 29  illustrates a tubular covering with pre-tied sutures at both ends, in accordance with one embodiment. 
         FIG. 30   a  illustrates elongated coverings folded like a U and an L, in accordance with one embodiment. 
         FIG. 30   b  illustrates a folded covering placed in a site, in accordance with one embodiment. 
         FIG. 31   a  illustrates a cage with graft being inserted, in accordance with one embodiment. 
         FIG. 31   b  illustrates a cage containing graft inserted into a site and surrounded by a folded covering, in accordance with one embodiment. 
         FIG. 32   a  illustrates two vertebra bodies and a disc to be prepared for discectomy, in accordance with one embodiment. 
         FIG. 32   b  illustrates preparation of the site whereby the lip of the vertebra are removed, in accordance with one embodiment. 
         FIG. 32   c  illustrates where a covering containing graft will be placed in the site, in accordance with one embodiment. 
         FIG. 32   d  illustrates insertion of the covering containing graft in the site, in accordance with one embodiment. 
         FIG. 32   e  illustrates the complete placement of the covering containing graft in the site, in accordance with one embodiment. 
         FIG. 32   f  illustrates a curved covering in an insertion tool or device, in accordance with one embodiment. 
         FIG. 32   g  illustrates a curved covering inserted through a TLIF entrance with the reinforcing extending proximally therefrom, in accordance with one embodiment. 
         FIG. 32   h  illustrates a curved covering inserted via an ALIF procedure, in accordance with one embodiment. 
         FIG. 32   i  illustrates a top view of a curved covering inserted via an ALIF procedure, in accordance with one embodiment. 
         FIG. 33   a  illustrates a view of a tube covering with a generally flat central section, in accordance with one embodiment. 
         FIG. 33   b  illustrates a side view of a tube covering with a generally flat central section, in accordance with one embodiment. 
         FIG. 34   a  illustrates a facet fusion joint where a posterolateral fusion may take place, in accordance with one embodiment. 
         FIG. 34   b  illustrates a generally square covering with a tab attachment mechanism, in accordance with one embodiment. 
         FIG. 34   c  illustrates a view of the covering bridging the facet joint, in accordance with one embodiment. 
         FIG. 34   d  illustrates another view of the covering bridging the facet joint, in accordance with one embodiment. 
         FIG. 34   e  illustrates another view of the covering bridging the facet joint, in accordance with one embodiment. 
         FIG. 35   a  illustrates generally where an incision for a posterior cervical approach may be, in accordance with one embodiment. 
         FIG. 35   b  illustrates the spine stabilized after the posterior cervical approach with coverings on either side of the lateral mass screws, in accordance with one embodiment. 
         FIG. 35   c  illustrates the spine stabilized after the posterior cervical approach with two coverings, one on either side of the lateral mass screws, in accordance with another embodiment. 
         FIG. 35   d  illustrates the spine stabilized after the posterior cervical approach with a U-shaped covering on the interior side of the lateral mass screws, in accordance with another embodiment. 
         FIG. 36   a  illustrates a covering with openings to fit around screws, in accordance with one embodiment. 
         FIG. 36   b  illustrates an embodiment wherein a single wide covering is provided longitudinally with pedicle screws placed through the covering and into the bone, in accordance with one embodiment. 
         FIG. 36   c  illustrates an embodiment wherein a first covering is provided on a first side of pedicle screws and a second covering is provided on a second side of pedicle screws, in accordance with one embodiment. 
         FIG. 37   a  illustrates the relationship between the C1, C2, C3 vertebrae and the occipital bone. 
         FIG. 37   b  illustrates a U-shaped covering used to fuse the C1 and C2 vertebra in an occipital cervical procedure, in accordance with one embodiment. 
         FIG. 37   c  illustrates U-shaped coverings used in an occipital cervical procedure, wherein the C1 and C2 vertebrae are fused, and the occipital and C1 are also fused. 
         FIG. 37   d  illustrates another view of the U-shaped covering for use in an occipital cervical procedure. 
         FIG. 38   a  illustrates a generally square bag covering, in accordance with one embodiment. 
         FIG. 38   b  illustrates using generally square bag coverings to form a continuous bridge in the front of the spine, in accordance with one embodiment. 
         FIG. 38   c  illustrates a tubular covering placed longitudinally acting as a bridging scaffold on the outside of the vertebral bodies, in accordance with another embodiment. 
         FIG. 38   d  illustrates a top view of a covering with a generally spherical central containment portion, in accordance with one embodiment. 
         FIG. 38   e  illustrates a perspective view of a covering with a generally spherical central containment portion, in accordance with one embodiment. 
         FIG. 38   f  illustrates the implant site where the covering of D1 and D2 will be used, in accordance with one embodiment. 
         FIG. 38   g  illustrates a covering of D1 and D2 placed in, covering, and bridging the defect, in accordance with one embodiment. 
         FIG. 38   h  illustrates the defect where a covering will be placed, in accordance with one embodiment. 
         FIG. 38   i  illustrates a cup shaped covering placed in the defect with the flange resting on the acetabular/pelvic rim, in accordance with one embodiment. 
         FIG. 38   j  illustrates a covering that may have cancellous chips or other graft material placed on it and formed to a generally spherical diameter for receipt of an implant, in accordance with one embodiment. 
         FIG. 38   k  illustrates an acetabular implant shell placed over the graft material, in accordance with one embodiment. 
         FIG. 38   l  illustrates a thru-hole defect in an acetabular medial wall where a covering may be placed, in accordance with one embodiment. 
         FIG. 38   m  illustrates a bridge/restrictor covering placed in the thru hole, in accordance with one embodiment. 
         FIG. 38   n  illustrates bone cement used to fill the void between the covering and the shell implant, in accordance with another embodiment. 
         FIG. 39   a  illustrates an anterior view of a graft-containing covering placed into the tunnel entrance of a bone-tendon-bone graft of an ACL reconstruction surgery, in accordance with one embodiment. 
         FIG. 39   b  illustrates a medial view of a graft-containing covering placed into the tunnel entrance of a bone-tendon-bone graft of an ACL reconstruction surgery, in accordance with one embodiment. 
         FIG. 39   c  illustrates an anterior view of a graft-containing covering used in a looped graft of an ACL reconstruction surgery, in accordance with another embodiment. 
         FIG. 39   d  illustrates a medial view of a graft-containing covering used in a looped graft of an ACL reconstruction surgery, in accordance with another embodiment. 
         FIG. 40   a  illustrates a tibial implant that must be removed. 
         FIG. 40   b  illustrates the large defect left when cement is removed from a joint replacement implant and a rasping tool used to smooth the defect, in accordance with one embodiment. 
         FIG. 40   c  illustrates where a doughnut shaped covering may be placed in the smoothed site, in accordance with one embodiment. 
         FIG. 40   d  illustrates a tapered impactor used to position the placed covering, in accordance with one embodiment. 
         FIG. 40   e  illustrates a new impact placed over the covering, in accordance with one embodiment. 
         FIG. 41   a  illustrates how a continuous covering may be formed to a hollow cone, in accordance with one embodiment. 
         FIG. 41   b  illustrates how a continuous covering formed around a hollow cone may comprise a coupled first and second layer, in accordance with another embodiment. 
         FIG. 42   a  illustrates an original metal implant cemented in the tibia prior to revision joint surgery, in accordance with one embodiment. 
         FIG. 42   b  illustrates the large defect created when the impact and cement of an original metal implant are removed, in accordance with one embodiment. 
         FIG. 42   c  illustrates a forming instrument used to compress a covering placed in the defect, in accordance with one embodiment. 
         FIG. 42   d  illustrates a revision implant seated and void filler placed between the revision impact and the covering, in accordance with one embodiment. 
         FIG. 42   e  illustrates a perspective view of a covering configured as an end-cap for treatment of an amputation, in accordance with one embodiment. 
         FIG. 42   f  illustrates a side view of a covering configured as an end-cap for treatment of an amputation, in accordance with one embodiment. 
         FIG. 42   g  illustrates a top view of a covering configured as an end-cap for treatment of an amputation, in accordance with one embodiment 
         FIG. 42   h  illustrates the covering placed at the end of a femur in the above-the-knee amputee, in accordance with one embodiment. 
         FIG. 43   a  illustrates a covering formed as a long tube or snake and where it can be placed in a site, in accordance with one embodiment. 
         FIG. 43   b  illustrates a snake covering placed in a site, in accordance with one embodiment. 
         FIG. 44   a  illustrates a defect that can be filled by a covering, in accordance with one embodiment. 
         FIG. 44   b  illustrates a covering that is partially filled with graft and partially empty, in accordance with one embodiment. 
         FIG. 44   c  illustrates placement of the partially filled and partially empty covering in the defect, in accordance with one embodiment. 
         FIG. 44   d  illustrates removal of the empty portion of the covering from the site, in accordance with one embodiment. 
         FIG. 44   e  illustrates a first embodiment of a foldable and stackable covering used to treat an irregular bone void, in accordance with one embodiment. 
         FIG. 44   f  illustrates a second embodiment of a foldable and stackable covering used to treat an irregular bone void, in accordance with one embodiment. 
         FIG. 44   g  illustrates a third embodiment of a foldable and stackable covering used to treat an irregular bone void, in accordance with one embodiment. 
         FIG. 44   h  illustrates a covering used as a sternum closure after open heart surgery, in accordance with one embodiment. 
         FIG. 44   i  illustrates a covering used as a sternum closure after open heart surgery placed in the site, in accordance with one embodiment. 
         FIG. 45  illustrates a covering comprising a first sheet and a second sheet with a substance being provided therebetween, in accordance with one embodiment. 
         FIG. 46  illustrates a covering comprising a first sheet and a second sheet configured as a drug release system, in accordance with one embodiment. 
         FIG. 47  illustrates a drug delivery from the drug release system of  FIG. 46 , in accordance with one embodiment. 
         FIG. 48  illustrates a cylindrical covering, in accordance with one embodiment. 
         FIG. 49  illustrates a pouch covering, in accordance with one embodiment. 
         FIG. 50   a  illustrates a tubular covering having a hollow central core for use in repairing a segmental defect. 
         FIG. 50   b  illustrates a tubular covering having a hollow central core used in segmental reconstruction. 
     
    
    
     DEFINITIONS 
     Bioactive Agent or Bioactive Compound, as used herein, refers to a compound or entity that alters, inhibits, activates, or otherwise affects biological or chemical events. For example, bioactive agents may include, but are not limited to, osteogenic or chondrogenic proteins or peptides, anti-AIDS substances, anti-cancer substances, antibiotics, immunosuppressants, anti-viral substances, enzyme inhibitors, hormones, neurotoxins, opioids, hypnotics, anti-histamines, lubricants, tranquilizers, anti-convulsants, muscle relaxants and anti-Parkinson substances, anti-spasmodics and muscle contractants including channel blockers, miotics and anti-cholinergics, anti-glaucoma compounds, anti-parasite and/or anti-protozoal compounds, modulators of cell-extracellular matrix interactions including cell growth inhibitors and antiadhesion molecules, vasodilating agents, inhibitors of DNA, RNA or protein synthesis, anti-hypertensives, analgesics, anti-pyretics, steroidal and non-steroidal anti-inflammatory agents, anti-angiogenic factors, angiogenic factors, anti-secretory factors, anticoagulants and/or antithrombotic agents, local anesthetics, ophthalmics, prostaglandins, anti-depressants, anti-psychotic substances, anti-emetics, and imaging agents. In certain embodiments, the bioactive agent is a drug. In some embodiments, the bioactive agent is a growth factor, cytokine, extracellular matrix molecule or a fragment or derivative thereof, for example, a cell attachment sequence such as RGD. A more complete listing of bioactive agents and specific drugs suitable for use in the present invention may be found in “Pharmaceutical Substances: Syntheses, Patents, Applications” by Axel Kleemann and Jurgen Engel, Thieme Medical Publishing, 1999; the “Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals”, Edited by Susan Budavari et al., CRC Press, 1996; and the United States Pharmacopeia-25/National Formulary-20, published by the United States Pharmacopeial Convention, Inc., Rockville Md., 2001, each of which is incorporated herein by reference. 
     Biocompatible, as used herein, refers to materials that, upon administration in vivo, do not induce undesirable long-term effects. 
     Bone, as used herein, refers to bone that is cortical, cancellous or cortico-cancellous of autogenous, allogenic, xenogenic, or transgenic origin. 
     Demineralized, as used herein, refers to any material generated by removing mineral material from tissue, e.g., bone tissue. In certain embodiments, the demineralized compositions described herein include preparations containing less than 5% calcium and preferably less than 1% calcium by weight. Partially demineralized bone (e.g., preparations with greater than 5% calcium by weight but containing less than 100% of the original starting amount of calcium) is also considered within the scope of the invention. In some embodiments, demineralized bone has less than 95% of its original mineral content. Demineralized is intended to encompass such expressions as “substantially demineralized,” “partially demineralized,” and “fully demineralized.” 
     Demineralized bone matrix, as used herein, refers to any material generated by removing mineral material from bone tissue. In preferred embodiments, the DBM compositions as used herein include preparations containing less than 5% calcium and preferably less than 1% calcium by weight. Partially demineralized bone (e.g., preparations with greater than 5% calcium by weight but containing less than 100% of the original starting amount of calcium) are also considered within the scope of the invention. 
     Osteoconductive, as used herein, refers to the ability of a non-osteoinductive substance to serve as a suitable template or substance along which bone may grow. 
     Osteogenic, as used herein, refers to the ability of an agent, material, or implant to enhance or accelerate the growth of new bone tissue by one or more mechanisms such as osteogenesis, osteoconduction, and/or osteoinduction. 
     Osteoimplant, as used herein, refers to any bone-derived implant prepared in accordance with the embodiments of this invention and therefore is intended to include expressions such as bone membrane, bone graft, etc. 
     Osteoinductive, as used herein, refers to the quality of being able to recruit cells from the host that have the potential to stimulate new bone formation. Any material that can induce the formation of ectopic bone in the soft tissue of an animal is considered osteoinductive. For example, most osteoinductive materials induce bone formation in athymic rats when assayed according to the method of Edwards et al., “Osteoinduction of Human Demineralized Bone: Characterization in a Rat Model,”  Clinical Orthopaedics  &amp;  Rel. Res.,  357:219-228, December 1998, incorporated herein by reference. 
     Superficially demineralized, as used herein, refers to bone-derived elements possessing at least about 90 weight percent of their original inorganic mineral content, the expression “partially demineralized” as used herein refers to bone-derived elements possessing from about 8 to about 90 weight percent of their original inorganic mineral content and the expression “fully demineralized” as used herein refers to bone containing less than 8% of its original mineral context. 
     DETAILED DESCRIPTION 
     I. Introduction 
     A delivery system for delivering a substance or material to a surgical site is provided. In various embodiments, the delivery system comprises a covering and a substance for delivery by the covering. The covering provides superior containment of the substance, such as graft material, which helps focus and concentrate materials that provide healing at the surgical site. In some embodiments, the covering also helps the surgeon perform less invasive procedures, by delivering a contained unit of grafting material to the surgical site. 
     The delivery system may be used to treat a wide variety of bone or soft tissue defects including surgically created or pre-existing (such as by trauma) defects. In some embodiments, the delivery system may be used to treat contained bony voids or contained defects. Such bony voids are voids or cavities that have a cortical shell on three sides. In some embodiments, the delivery system may be used to treat critical defects. Generally, critical defects are defects that will not heal spontaneously and must be grafted in order to assure healing. In some embodiments, the delivery system may be used to treat segmental defects. Segmental defects are defects in the cortical shaft of a long bone in which a segment is missing. In some embodiments, the delivery system may be used to treat contained or non-critical defects wherein the delivery system may act as a plug to assist healing. Other applications for the delivery system are discussed herein and none are intended to be limiting. 
     The delivery system comprises a covering and a substance wherein the substance is provided within the covering for delivery to the surgical site. The delivery system provides increased handling properties, ability to place grafting material reliably using minimally invasive procedures, and improved delivery characteristics such as graft retention compared with other systems. In some embodiments, upon placement, the covering facilitates transfer of the substance and/or materials to the surgical site. In some embodiments, for example wherein the covering holds graft materials, the covering substantially prevents graft migration. The covering may participate in, control, or otherwise adjust, the release of the substance from the covering or penetration of the covering by surrounding materials, such as cells or tissues. 
     Generally, the covering may be a single or multi-compartment structure capable of at least partially retaining a substance provided therein until the covering is placed at a surgical site. In some embodiments, the covering may be substantially non-expandable or minimally deformable. In some embodiments, the covering may be a temporary covering wherein the covering is substantially resorbable. For example, in some embodiments, the covering may be formed of a material that is substantially resorbed within 2 weeks, within 4 weeks, within 12 weeks, or within other suitable time frame. Accordingly, in some embodiments a delivery system including the covering may be a temporary delivery system. The covering may include one or more attachment mechanisms for retaining the covering at the surgical site. The attachment mechanism may be a mechanical attachment mechanism, a physical attachment mechanism, a biological attachment mechanism or a chemical attachment mechanism, or may employ combinations of these. The attachment mechanism may be used to attach the covering to skeletal or soft tissue proximate the surgical site. 
     In some embodiments, the covering may be used for containment of particulate or morselized materials (the substance provided in the covering), optionally to provide a focus or concentration of biological activity. In some embodiments, the covering may be used for containment of a substance one or more of bone particles, bone fibers, other osteoinductive or osteoconductive materials, BMP, antibiotics, or other materials. 
     In some embodiments, the covering may be used for maintaining materials (the substance provided in the covering) in spatial proximity to one another, possibly to provide a synergistic effect. In some embodiments, the covering may be used to control availability of a substances provided within the covering to cells and tissues of a surgical site over time. In some embodiments, the covering may be used for delivery through a limited opening, such as in minimally invasive surgery or mini-open access. In some embodiments, the covering may be used to deliver morselized or particulated materials (the substance provided in the covering) in pre-measured amounts. In other embodiments, the substance may be liquid or flowable, or combinations of these with particulate, morselized, and/or other materials. 
     In various embodiments, the covering may contain a substance or material such as a graft material. The covering limits, and in some embodiments eliminates, graft migration and maintains graft density. The delivery system, with contained substance or material, may be configured to conform to surrounding bony contours or implant space. In some embodiments, the delivery system provides a pathway for healing/cell penetration and tissue ingrowth. Thus, the covering may facilitate transfer or diffusion of materials into and out of the covering. For example, the covering may facilitate diffusion from the covering of a substance provided within the covering or may facilitate diffusion into the covering of materials in the surgical site, such as cells and tissues, into the covering. The covering may be configured to permit diffusion of some materials while substantially preventing diffusion of other materials. Further, in various embodiments, the covering may be configured such that diffusion is permitted into or out of certain portions of the covering but not other portions of the covering. In some embodiments, the covering may merely retain a substance at the surgical site. 
     The covering may have a single compartment or may have a plurality of compartments. Thus, in one embodiment, the covering is dual-compartment and comprises first and second compartments. A first substance may be provided in the first compartment and a second substance may be provided in the second compartment. The second compartment may be adjacent to, apart from, inside, or surrounding the first compartment. Materials forming the first compartment and the second compartment may be the same or may be different. Selection of materials, positioning of the compartments, and other factors relating to the first and second compartments may be chosen to achieve simultaneous or sequential delivery or release of a substance or substances. 
     II. Covering Material 
     The covering may comprise a structural material and, in some embodiments, a functional material. The structural material may comprise a mesh material, a polymeric material, a substantially solid material, or other. The functional material may comprise, for example, a radiopaque material, a bacteriocidal material, or other. 
     Structural Material Characteristics 
     In various embodiments, in accordance with the specific application for which the covering is being used, the covering may be rigid, may be flexible, may be non-elastic, or may be elastic. The covering material may be braided, woven, non-woven shape memory, particulate, threaded, porous, non-porous, or substantially solid. While the term “structural” is used to describe the material forming the main structure of the covering, it is to be appreciated that this is not intended to imply that the covering need have structural or load-bearing characteristics. 
     The covering may participate in, control, facilitate, prevent, or otherwise adjust the release of the substance. For example, the covering may act as a selectively permeable membrane and/or may be porous, with the level of porosity being related to the nature of the substances inside the covering. Thus, the material for and configuration of the covering may be selected or adjusted based on desired release characteristics. Specific properties of the structural material that may be adjusted include thickness, permeability, porosity, strength, flexibility, elasticity, and others. It is to be appreciated that some of these properties may depend on others. For example, the thickness and porosity of the material may contribute to its strength, flexibility, and elasticity. In some embodiments, the covering may be made of a squishy, moldable, sticky, and/or tacky material to facilitate placement and packing of the covering. 
     In some embodiments, the covering may be porous to fluid and/or cells, may be biocompatible, and may be resistant to rupture (including should the substance provided therein swell). In some embodiments, the covering with the substance provided therein may be load-bearing. The covering may be resorbable or non-resorbable. The covering may provide increased handling properties, may have irrigation resistance, may have material retention characteristics, and/or may support cellular penetration. Flexibility of the covering may be selected to suit particular applications. In some applications, it may be desirable to have a flexible covering. 
     If the covering is made from a resorbable material, the covering degrades and disappears after a period of time. The covering thus may be considered a temporary covering. If the covering is not made of a resorbable material, the covering remains in the body. Tissue ingrowth may occur to bind the host tissue to the substance provided within the covering. Tissue ingrowth through and around the covering, between the host tissue and the substance provided within the covering, may be promoted via openings in the covering. 
     In various embodiments, the covering may comprise a porous material or a mesh material. The size of the pores of the covering may be designed to permit cellular infiltration (approximately several microns to several millimeters), but may also be designed specifically to exclude cells from the inside of the covering (e.g. approximately 0.45 microns) and only allow diffusion of small molecules (proteins and hormones). Thus, the covering may act to control access to the interior of the delivery system by cells. U.S. Patent Application Publication No. 2005/0283255 for Tissue-Derived Mesh for Orthopedic Regeneration describes suitable manners for forming a mesh for use with a covering as provided herein and is herein incorporated by reference in its entirety. 
     The covering may be formed of a resorbable or nonresorbable, natural or synthetic, biocompatible material. In some embodiments, more than one material may be used, including as multiple layers. For example, in an embodiment comprising two compartments, one or more materials may be used for the first compartment and a different material or materials may be used for the second compartment. For example, one compartment or portions thereof may be made of material or materials that provide a desired property or properties relative to other compartments or portions thereof, such as increased or decreased resorbability or stiffness, or the different compartments or portions thereof may be imparted with different drug delivery properties, etc. Alternatively, all compartments may comprise the same material or mixtures of materials. Where the characteristics of the material are varied between compartments, or over the surface of a single compartment, the pores of the first compartment or portion thereof may be larger than the pores of the second compartment. 
     The covering may comprise any suitable structure for delivering a substance in vivo. Thus, as described, the covering may comprise a mesh. In other embodiments, the covering may comprise a polymeric structure with a chamber provided therein. The chamber may be filled with a substance for delivering in vivo, such as autograft, demineralized bone matrix, or others disclosed herein. 
     In embodiments comprising more than one compartment, characteristics of the covering material may be varied between compartments. Generally, the porosity, flexibility, strength, or any other characteristic of one compartment may vary from that characteristic of the other compartment. Further, characteristics of the covering may vary at different positions of the covering regardless of compartmental configuration of the covering. 
     In some embodiments, the covering may expand when placed in the body. Expansion can be provided in at least two ways: the covering may be compressed such that the covering expands when placed in the body or the covering may be made of a material that expands when it comes in contact with water or other bodily fluids, either by way of liquid absorption, or by stretching when the materials inside it absorb liquid and themselves expand. In some embodiments, the covering may comprise a shape memory material such as copper-zinc aluminum-nickel alloy, copper-aluminum-nickel alloy, and nickel-titanium (NiTi) alloy. Reinforcing materials such as cortical bone, calcium phosphates, etc. may be incorporated into the structure of the covering to reinforce it. In other embodiments, the covering may be substantially non-expandable or minimally deformable. 
     The covering may be configured for specific compressive strength and rigidity by adjusting density and resorption time of the covering. In some embodiments, a coating may be provided over the covering. For example, the coating may be a compound of poly-L-lactide, of polyglycolic acid, or their polymers, or polyhydroxyalkanoates (polyhydroxybutyrates and polyhydroxyvalerates and copolymers). The coating may be selected such that it has a resorption time wherein it is resorbed by the body and the material within the covering is permitted to exit through openings in the covering. 
     Exemplary Covering Materials 
     Polymeric material (for example, see U.S. Pat. Nos. 6,696,073, 6,478,825, 6,440,444, and 6,294,187 and U.S. Patent Publications Nos. 2006/0216323 and 2005/0251267, all herein incorporated by reference in their entirety); woven material and braided material (for example, see U.S. Patent Publication No. 2005/0283255, herein incorporated by reference in its entirety); non-woven materials; shape memory material; porous materials; and non-porous materials may be used. In some embodiments, outer particles may be used to contain inner particles; particles may be attached to threads of material, and/or porosity may be added to mesh fibers. In some embodiments, materials may be used for portions of the covering, such as for a compartment of the covering, that are substantially impenetrable. 
     In some embodiments, the covering may comprise a mesh material. Suitable mesh materials include natural materials, synthetic polymeric resorbable materials, synthetic polymeric non-resorbable materials, and other materials. Natural mesh materials include silk, extracellular matrix (such as DBM, collagen, ligament, tendon tissue, or other), silk-elastin, elastin, collagen, and cellulose. Synthetic polymeric resorbable materials include poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(lactic acid-glycolic acid) (PLGA), polydioxanone, PVA, polyurethanes, polycarbonates, polyhydroxyalkanoates (polyhydroxybutyrates and polyhydroxyvalerates and copolymers), polysaccharides, polyhydroxyalkanoates polyglycolide-co-caprolactone, polyethylene oxide, polypropylene oxide, polyglycolide-co-trimethylene carbonate, poly(lactic-co-glycolic acid), and others. See Chen and Wu, “The Application of Tissue Engineering Materials,” Biomaterials, 2005, 26(33): p. 6565-78, herein incorporated by reference in its entirety. Other suitable materials include carbon fiber, metal fiber, polyertheretherketones, non-resorbable polyurethanes, polyethers of all types, polyethylene terephthalte, polyethylene, polypropylene, Teflon, and various other meshes. In other embodiments, the covering may comprise non-woven material such as spun cocoon or shape memory materials having a coil shape or shape memory alloys. Alternatively, any of these materials may be used in a non-mesh form. 
     Generally, the covering may be formed of any natural or synthetic structure (tissue, protein, carbohydrate) that can be used to form a covering configuration. Thus, the covering may be formed of a polymer (such as polyalkylenes (e.g., polyethylenes, polypropylenes, etc.), polyamides, polyesters, poly(glaxanone), poly(orthoesters), poly(pyrolicacid), poly(phosphazenes), polycarbonate, other bioabsorbable polymer such as Dacron or other known surgical plastics, a natural biologically derived material such as collagen, gelatin, chitosan, alginate, a ceramic (with bone-growth enhancers, hydroxyapatite, etc.), PEEK (polyether-etherketone), dessicated biodegradable material, metal, composite materials, a biocompatible textile (e.g., cotton, silk, linen), extracellular matrix components, tissues, or composites of synthetic and natural materials, or other. Various collagen materials can be used, alone or in combination with other materials, including collagen sutures and threads. Any suitable collagen material may be used, including known collagen materials, or collagen materials as disclosed in U.S. patent application Ser. No. 12/030,181, filed Feb. 12, 2008, hereby incorporated by reference in its entirety, which discloses collagen materials that may be used for forming a covering. Some examples include polymer or collagen threads woven, or knitted, into a mesh. Other suitable materials include thin polymer sheets molded in the presence of a porogen and having underwent leaching; polymer sheets or naturally derived sheets such as fascia and other collagen materials, small intestinal submucosa, or urinary bladder epithelium, the sheets being punctured to introduce porosity; specific shapes printed using available or future printing technologies; naturally secreted materials such as bacterial cellulose grown within specific molds; etc. 
     In some embodiments, mesh fibers may be treated to impart porosity to the fibers. This may be done, for example, to PLA, PLGA, PGA, and other fibers. One suitable method for treating the mesh fibers comprises supercritical carbon dioxide treatment to partially solubilize the particles. This treatment may further be carried out for viral inactivation. Another suitable method for treating the mesh fibers comprises explosive decompression. Explosive decompression generates porosity and leads to controlled permeability. The mesh material further may be loaded with cells, growth factors, or bioactive agents. 
     In further embodiments, fibers of a mesh material may be treated such as by having particles adhered thereto. The particles may be, for example, bone particles. Thus, in one embodiment, the covering may comprise a plurality of threads formed into a fabric. The threads may have particles adhered thereto. For example, the threads may have particles strung on the thread. In an alternative embodiment, the covering may be formed of a material and the material may be coated with particles. 
     In yet other embodiments, the covering may comprise a non-porous material, which may be permeable. A non-porous material may be used for later (or delayed) delivery of a substance provided therein. Such substance may comprise, for example, cells, growth factors, or bone morphogenetic proteins. Accordingly, in one embodiment, a delivery system for delayed delivery of cells, growth factors, or bone morphogenetic proteins is provided comprising a non-porous covering. 
     While certain embodiments are described with respect to having mesh characteristics, it is to be appreciated that not all embodiments may have such mesh characteristics. Further, the material used for the covering and its characteristics may be selected for specific applications. For example, in some embodiments, the covering may be formed of a resorbable material, such as formed as a resorbable container or capsule. Such resorbable material may be useful in delivering, for example, antibiotic to a site by an outer resorbable material, and then gradually exposing inner graft material after the infection is cleared. In such embodiments, the delivery system comprises a temporary delivery system. 
     Functional Material Characteristics 
     The covering material may have functional characteristics. Alternatively, other materials having functional characteristics may be incorporated into the covering. Functional characteristics may include radiopacity, bacteriocidity, source for released materials, tackiness, etc. Such characteristics may be imparted substantially throughout the covering or at only certain positions or portions of the covering. 
     Suitable radiopaque materials include, for example, ceramics, mineralized bone, ceramics/calcium phosphates/calcium sulfates, metal particles, fibers, and iodinated polymer (see, for example, WO/2007/143698). Polymeric materials may be used to form the covering and be made radiopaque by iodinating them, such as taught for example at (http://www.teamreva.com/tech_bioresorbable.html and http://www.teamreva.com/company_news_xray.html and U.S. Pat. No. 6,585,755, herein incorporated by reference in its entirety. Other techniques for incorporating a biocompatible metal or metal salt into a polymer to increase radiopacity of the polymer may also be used. Suitable bacteriocidal materials may include, for example, trace metallic elements. In some embodiments, trace metallic elements may also encourage bone growth. 
     Functional material, such as radiopaque markers, may be provided at one or more locations on the covering or may be provided substantially throughout the covering. Thus, for example, in a tubular covering, a radiopaque marker may be provided at a tip of the tubular covering. Such marker may facilitate placement of the covering. Radiopaque materials may be incorporated into the covering and/or into the substance for delivery by the covering. Further, radiopaque materials may be provided at only some locations on the covering such that visualization of those locations provides indication of the orientation of the covering in vivo. 
     The covering itself may be designed to release materials during degradation of the covering material. Thus, bone morphogenic proteins (BMPs), growth factors, antibiotics, angiogenesis promoting materials (discussed more fully below), bioactive agents (discussed more fully below), or other actively releasing materials may be incorporated into the covering material such that as the covering material is degraded in the body, the actively releasing material is released. For example, an actively releasing material may be incorporated into a biodegradable polymer covering such as one manufactured of a biodegradable polyester such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(lactic-co-glycolic acid) (PLGA), or polyhydroxyalkanoates (polyhydroxybutyrates and polyhydroxyvalerates and copolymers). In some embodiments, poly(ethylene glycol) (PEG) may be incorporated into the biodegradable polyester to add hydrophilic and other physico-chemical properties to enhance drug delivery. In some embodiments, composites of allograft bone and biodegradable polymers (for example, PLEXUR® products available from Osteotech) may be used in the covering. 
     In some embodiments, the covering may comprise a material that becomes tacky upon wetting. Such material may be, for example, a protein or gelatin based material. Tissue adhesives, including mussel adhesive proteins and cryanocrylates, may be used to impart tackiness to the covering. In further examples, alginate or chitosan material may be used to impart tackiness to the covering. In further embodiments, an adhesive substance or material may be placed on a portion of the covering or in a particular region of the covering to anchor that portion or region of the covering in place at an implant site. 
     In one embodiment of a covering comprising two compartments, first and second materials may be used for the first and second compartments, respectively. The first material may release or expose a growth factor according to a first rate and the second material may release a growth factor according to a second rate. Further, the growth factors released by the first and second compartments may be the same or may be different. For example, an angiogenic growth factor may be provided with the first compartment and an osteoinductive growth factor may be provided with the second compartment. 
     Mesh Formulation 
     Any suitable technique may be used for forming a material for the covering. Generally, the material may be formed as a substantially solid material, as a sheet, as a mesh, or in other configuration. In some embodiments, the material may be a textile type material. Thus, for example, the material may be formed using a textile approach such as be weaving, rug making, knitting, etc. Such formation may be by a mechanical or industrial method. In another embodiment, a substantially solid sheet may be formed and may be treated to assume a configuration penetrable by cells, fluids, and proteins. For example, the sheet may be perforated, may be expanded to create openings, or other. Also, it would be perfectly suitable to take a thin sheet of the covering material, and to perforate it, expand it to create openings, or otherwise make it penetrable by cells, fluids and proteins. 
     In one embodiment, elongated bone-derived particles or fragments of small intestinal submucosa (for example, approximately 6) may be combined longitudinally into three small bundles, each having, for example, from about 1 to about 3 tissue particles. The three bundles may then be braided. Various methods of braiding and types of braids any of which may be useful in producing the material of the invention herein are also described, e.g., by Shaw, KNOTS—Useful &amp; Ornamental, Bonanza Books, New York (1983), incorporated herein by reference. The ends of the braided tissue-derived particles may then be glued together using a fixation agent to prevent their unraveling, or they may be held together with a biocompatible polymer or metal band. 
     In an alternative embodiment, bone-derived particles are combined with a solvent to form a material. Exemplary solvents include water, lower alkanols, ketones, and ethers and mixtures of any of these or other materials. The material may then be extruded at an appropriate temperature and pressure to create a thread. Threads may also be produced by spinning, drawing, rolling, solvent-extruding, cutting or laser cutting from a sheet or bar stock. The material may alternatively be cast or molded into a solid sheet or bar stock and then cut into thin threads. These may be used immediately or woven into a mesh. Alternatively or in addition, they may be spliced, wrapped, plied, cabled, braided, woven, or some combination of these. The material may be shaped by thermal or chemical bonding, or both. In one embodiment, a portion of the solvent is removed from the material before extrusion. 
     Alternatively or in addition, the material may be cast as a slurry, extruded, or molded. A variety of materials processing methods will be well known to those skilled in the art. For example, the material may be solvent cast using a press such as a Carver press to spread the material into a film. Solvent evaporation will yield a porous film. Alternatively, the material may be compression molded into a film. The mesh size or porosity of the film will depend on the thickness of the film and the viscosity of the precursor and can be easily manipulated by one skilled in the art. Where elongated particles are used in an extruded aggregate, they will tend to be aligned roughly parallel to one another. 
     In an alternative embodiment, a thread of a biocompatible natural or synthetic material, for example, polylactide or collagen, may be coated with tissue-derived or other elements, for example, by dubbing. For example, a polymer fiber may be coated with an adhesive, for example, lecithin, and bone particles or other osteoconductive or osteoinductive fibrils allowed to adhere to the thread. The thread may then be twisted on itself or with a second or a plurality of similarly treated threads. Alternatively or in addition, the threads may be braided. The adhesive may be a lipid that is waxy at room temperature, for example, a di- or tri-glyceride that is solid at room temperature. Alternatively or in addition, the adhesive may be a phosphocholine or phosphatidylcholine. In some embodiments, the adhesive is a material that binds both the thread and the material that is used to coat the thread (e.g., bone particles) but that does not degrade either. Non-aqueous adhesives may improve the stability of the final aggregate as compared to aqueous adhesives. 
     Suitable fibers may be formed utilizing well known techniques, e.g., braiding, plying, knitting, weaving, felting, that are applied to processing natural fibers, e.g., cotton, silk, etc., and synthetic fibers made from synthetic bioabsorbable polymers, e.g., poly(glycolide) and poly(lactic acid), nylon, cellulose acetate, etc. See, e.g., Mohamed, American Scientist, 78: 530-541 (1990). For example, U.S. Pat. No. 5,378,469, herein incorporated by reference in its entirety, describes the braiding of crosslinked and non crosslinked collagen threads using a harness braiding machine (New England Butt Co., Providence, R.I.). Specifically, collagen thread is wound onto cylindrical stainless steel spools. The spools are then mounted onto the braiding carousel, and the collagen thread is then assembled in accordance with the instructions provided with the braiding machine. In one particular run, a braid was fowled of four collagen threads, which consisted of two threads of non-crosslinked collagen and two threads of crosslinked collagen. One skilled in the art will recognize that these techniques may be applied to the other fibrous materials described herein. 
     Fibers and more evenly dimensioned particles may also be plied into yarns using the same methods and same machinery known to those skilled in the art in plying threads made out of other material, e.g., cotton, polyester, etc. For example, U.S. Pat. No. 5,378,469 describes the production of a 60 ply yarn from non-crosslinked collagen threads. Four collagen threads were twisted together. Three of the resultant 4-ply strands were then twisted together in the opposite direction, and then 5 of the resultant 12 ply strands were twisted in the opposite direction. 
     Elongated materials including multistranded materials, e.g., braids, plied yams, cables, etc., may be knitted into tubular or flat fabrics by using techniques known to those skilled in the art of producing fabrics manufactured from other types of threads. Various biologically active substances can be incorporated in, or associated with, the braided, knitted, or woven materials. Particles and fibers and materials of these (including multistranded materials) may alternatively or additionally be assembled into a material by non-woven methods such as laying, needle-punching, and hooking (as for a rug). For example, a thread may be attached to another thread or a pressed film. 
     Regardless of the assembly method, the material shape, mesh size, cable thickness, and other structural characteristics, e.g., architecture, may be customized for the desired application. For example, where a two dimensional aggregate is used to retain a thixotropic material within a gap, a tight weave is preferred to prevent leakage. To optimize cell or fluid migration through the mesh, the pore size may be optimized for the viscosity and surface tension of the fluid or the size of the cells. For example, pore sizes on the order of approximately 100-200 μm may be used if cells are to migrate through the mesh. Mesh size may be controlled by physically weaving strands of the material by controlling the ratio of solvent to solids in a precursor material. 
     Cells may be seeded onto the material, or contained within it. In one embodiment, cells may be encapsulated in a matrix such as alginate or collagen gel and the capsules placed on the material. Methods for encapsulating cells are well known to those skilled in the art; an exemplary method is disclosed in U.S. Pat. No. 4,391,909, herein incorporated by reference in its entirety. Seeded materials generally do not need to be incubated for long periods of time in solutions that could partially dissolve the binding agent. Instead, the capsules may be placed on the material or covering shortly before implantation. In another embodiment, cells are simply mixed with a gel which is then combined with the material. Alternatively, a material or covering may be cultured with cells before implantation. In one embodiment, thicker materials are used for culturing to increase mechanical integrity during implantation. Any class of cells, including connective tissue cells, organ cells, muscle cells, nerve cells, and stem cells, may be seeded onto the implant. In an exemplary embodiment, connective tissue cells such as osteoblasts, osteoclasts, fibroblasts, tenocytes, chondrocytes, and ligament cells and partially differentiated stem cells such as mesenchymal stem cells and bone marrow stromal cells are employed. 
     III. Covering Configuration or Form 
     The shape, configuration, or form of the covering may be selected for particular applications. Such shape and configuration may include, for example, the basic shape of the covering (e.g., a cylinder or a bag), whether the covering has a single or a plurality of compartments, and whether the covering includes attachment mechanisms. The covering (or delivery system) may be configured to conform to surrounding bony contours of the space in which it is placed. 
     Form 
     As previously discussed, the covering may be formed of as a mesh. Thus, the covering may comprise a woven material. The woven material may have varying degrees of permeability. It may be permeable, semi-permeable, or non-permeable. Permeability may be with respect to cells, to liquids, to proteins, to growth factors, to bone morphogenetic proteins, or other. In further embodiments, the material may be braided. 
     In alternative embodiments, the covering may comprise a substantially solid structure, such as a polymer structure with a chamber, or a spun cocoon. 
     Shape 
     The covering may have any suitable configuration. For example, the covering may be formed as a ring, a cylinder, a cage, a rectangular shape, a mesh, a suture-like wrap, a continuous tube, or other configuration. In specific embodiments, the covering may be formed as a thin tube designed to be inserted through catheters or an introducer tube, a rectangular shape designed to fit adjacent to spinal processes for posterolateral spine fusion, a cube like structure designed to fit between vertebral bodies or within cages for interbody spinal fusion, a tube-like shape where the ends are designed to be fitted onto nonunion long bone defects, relatively flat shapes designed to fill cranial or maxillofacial defects, rectangular structures designed for osteochondral defects, structures pre-shaped to fit around various implants (e.g. dental, doughnut with hole for dental implants), or relatively elastic ring-like structures that will stretch and then conform to shapes (e.g. rubber band fitted around processes). In an embodiment wherein the covering is formed as a cage, the cage may comprise a plurality of crossed filaments which define between them a series of openings for tissue ingrowth. Any of these shapes may be used for a covering comprising a plurality of compartments. For example, in a tubular embodiment, the tube may be formed into a plurality of compartments by tying a cord around the tube at one or more points, or by other suitable mechanism such as crimping, twisting, knotting, stapling, sewing, or other. The configuration of the covering may be determined by the substance to be provided within the covering. For example, if the substance to be contained comprises fibers, the covering may be formed as strings or sutures that are wrapped around the fibers. 
     A covering as provided herein may further comprise an attachment or coupling mechanism. Any suitable attachment mechanism can be used, such as a tab, loop, tack or other structure adapted for attachment at the site. Also, for example, a covering may include a hook-and-eye (Velcro) portion. The hook-and-eye portion may be used to couple the covering to a tissue structure, such as bone, or to another covering. For example, as shown in  FIG. 3 , a dual compartment covering  21  may be formed by two single-compartment coverings  22 ,  24  coupled at portion  26  at complementary ends thereof. In the embodiment shown, the coupling portion  26  may comprise overlapping/mating Velcro portions. The size and shapes of the single compartment coverings  22 ,  24  may be the same or may be different. Further, the materials of the compartment coverings  22 ,  24  and the substances provided therein may be the same or may be different. The coupling may be done pre-implantation or post-implantation. In post-implantation embodiments, the coupling may be done by inserting first and second coverings through an opening into a space and coupling the coverings within the space. Other suitable attachment, or coupling, mechanisms are described more fully below. 
       FIGS. 1   a  and  1   b  illustrate a delivery system comprising tubular covering  10  and particulated substance. In the embodiment of  FIGS. 1   a  and  1   b , the covering  10  is relatively narrow. In contrast,  FIGS. 2   a  and  2   b  illustrate a delivery system comprising relatively wide covering  20 . In the embodiments shown in  FIGS. 1   a ,  1   b ,  2   a , and  2   b , the coverings  10 ,  20  comprise a mesh material. The particulated substance is provided within the coverings  10 ,  20 . 
       FIG. 2   c  illustrates a further embodiment wherein the covering  23  has a generally accordion shape. In such embodiment, the covering may expand to take on configurations of areas where grafting is desired. 
     A covering as provided herein may further comprise an attachment or coupling mechanism. Any suitable attachment mechanism can be used, such as a tab, loop, tack or other structure adapted for attachment at the site. Also, for example, a covering may include a hook-and-eye (Velcro) portion. The hook-and-eye portion may be used to couple the covering to a tissue structure, such as bone, or to another covering. For example, as shown in  FIG. 3 , a dual compartment covering  21  may be formed by two single-compartment coverings  22 ,  24  coupled at portion  26  at complementary ends thereof. In the embodiment shown, the coupling portion  26  may comprise overlapping/mating Velcro portions. The size and shapes of the single compartment coverings  22 ,  24  may be the same or may be different. Further, the materials of the compartment coverings  22 ,  24  and the substances provided therein may be the same or may be different. The coupling may be done pre-implantation or post-implantation. In post-implantation embodiments, the coupling may be done by inserting first and second coverings through an opening into a space and coupling the coverings within the space. Other suitable attachment, or coupling, mechanisms are described more fully below. 
     In some embodiments, the covering may be labeled. Such labeling may be done in any suitable manner and at any suitable location on the covering. In some embodiments, labeling may be done by using a silk screen printing, using an altered weaving or knotting pattern, by using different colored threads, or other. The labeling may indicate information regarding the covering. Such information might include part number, donor id number, number, lettering or wording indicating order of use in the procedure or implant size, etc. 
     Compartments 
     Single Compartment 
     As shown in  FIGS. 1   a ,  1   b ,  2   a , and  2   b  the covering may comprise a single compartment covering  10 ,  20 . Those figures illustrated generally tubular embodiments. In further embodiments, such as shown in  FIG. 4  the covering  30  may be a narrow tube for delivery through a catheter  32 . For example, the covering may be delivered percutaneously using a catheter through which it is inserted. Thus, as shown, the covering  30  may have dimensions suitable for receipt in the catheter. Optionally, the covering  30  may be stiffened to facilitate insertion into the catheter  32 . Such stiffening may be achieved through choice of material for the covering, by treating the material of the covering, or other. In some embodiments, the covering  30  may be coated with a material to facilitate sliding engagement with the catheter  32 . 
       FIGS. 5   a - 5   c  illustrate a covering embodiment  200  having an elongated containment portion  202  for housing a substance for delivery, and having first and second ends  204 ,  206 . One or both of the first and second ends  204 ,  206  may have an attachment mechanism  208 . Any suitable attachment mechanism may be used. In the embodiment shown, each of the first and second ends  204 ,  206  comprises a tab attachment mechanism  208 . One or both of the first and second ends  204 ,  206  further may be sealed. In the embodiment shown, the first end  204  is sealed. The seal  210  may comprise a portion of the tab  208 , as shown, or may be separate from the tab  208 . The seal  210  may have a width and a thickness suitable for maintaining a seal with the substance provided within the containment portion. For example, the seal  210  may have a length of approximately 0.6 cm, with the tab  208 , including the seal  210 , having a length of approximately 1.0 cm. Accordingly, the tab  208  is coextensive with the seal  210  for approximately 0.6 cm and extends approximately 0.4 cm beyond an outer edge of the seal  210 . In some embodiments, one or both ends  204 ,  206  may be unsealed such that the covering  200  may be filled with a substance and sealed, for example via heat sealing, in the operating room. The elongated containment portion  202  comprises a length, a width, and a cross section. The length may be, for example, approximately 5 cm, approximately 10 cm, approximately 20 cm, or any other suitable length. The width may be, for example, approximately 1 cm. The length to width ratio may vary depending on application. In the embodiment of  FIGS. 5   a - 5   c , the containment portion  202  has a generally circular cross-sectional shape with an approximately 1.0 cm diameter. While exemplary dimensions are provided with respect to  FIGS. 5   a - 5   c , these dimensions are intended for illustration only and are not limiting. 
       FIGS. 6   a - 6   c  illustrate an alternative embodiment of a covering  220  having an elongated containment portion  222  for housing a substance for delivery, and having first and second ends  224 ,  226 . In the embodiment of  FIGS. 6   a - 6   c  the containment portion  222  has a generally oval cross-sectional shape. In various embodiments, the covering  220  may have a width of approximately 2.5 cm, a containment portion  222  length of approximately 5 cm or approximately 10 cm, and a tab  228  length of approximately 0.5 cm. In the embodiment of  FIGS. 6   a - 6   c , a seal  230  is provided at the first end of the covering and extends over substantially the entire length of the tab  228  at the first end  224 . While exemplary dimensions are provided with respect to  FIGS. 6   a - 6   c , these dimensions are intended for illustration only and are not limiting. 
       FIGS. 7   a - 7   c  illustrate an alternative embodiment of a covering  240  having an elongated containment portion  242  for housing a substance for delivery, and having first and second ends  244 ,  246 . The embodiment of  FIGS. 7   a - 7   c  is substantially similar to the embodiment of  FIGS. 6   a - 6   c  except for the tabs  248  at the first and second ends  244 ,  246 . In the embodiment of  FIGS. 7   a - 7   c , the tabs  248  have a length of approximately 1.0 cm and the associated seal  250  of the tab at the first end  244  has a length of approximately 0.6 cm. Accordingly, the tab  248  is coextensive with the seal  250  for approximately 0.6 cm and extends approximately 0.4 cm beyond an outer edge of the sea  250 . While exemplary dimensions are provided with respect to  FIGS. 7   a - 7   c , these dimensions are intended for illustration only and are not limiting. 
       FIGS. 5   a - 5   c ,  6   a - 6   c , and  7   a - 7   c  illustrate various alternative embodiments of a covering having an elongated containment portion for housing a substance for delivery, and having first and second ends. In each of the embodiments shown, the first and second ends include a tab attachment mechanism. In alternative embodiments, only one of the ends may have an attachment mechanism. Further, the attachment mechanism may have an alternative configuration, such as a bore for receiving a screw.  FIGS. 5   a - 5   c ,  6   a - 6   c , and  7   a - 7   c  illustrate generally circular and generally oval cross-sectional shapes. In alternative embodiments, any cross-sectional shape, such as a generally rectangular, generally square, generally star, or any other suitable shape may be used. The length, width, and length-to-width ratio may vary depending on the application for the covering. 
     In one embodiment of a single compartment covering, a plurality of substances may be provided within the covering based on characteristics of the substances. For example, where it is desirable to include a particulated first substance within a material having mesh openings larger than the substance, a second substance may be provided surrounding the particulated first substance to reduce the likelihood of release of particles of the first substance from the mesh. Thus, for example, a particulated first substance and a particulated second substance may be provided wherein the particles of the first substance have a smaller size than the particles of the second substance. A covering is provided comprising a mesh having mesh openings or pores larger than the particles of the first substance. For use, the first substance is provided generally centrally within the covering, the second substance is provided around the first substance and thus between the first substance and the second substance. In further embodiments, the second substance may be coated, for example via spray coating or solvent casting. 
     In yet a further embodiment, a single compartment covering may be used as a spacer for nonunion. For example, the covering may be placed in a canal of a long bone. 
     Multi Compartment 
     In alternative embodiments, and as briefly discussed with respect to  FIG. 3 , the covering may comprise a plurality of compartments. Further, the covering may generally comprise an open compartment area. In various embodiments, the covering may comprise nested coverings, coverings coupled via a temporary barrier, coverings separated with a boundary, and others, described below. In embodiments comprising two compartments, a second compartment may be adjacent, apart from, inside, or surrounding a first compartment. Materials for the first compartment and the second compartment (which may be designated first and second substances) may be the same, partially the same, or different. The materials for the first compartment and the second compartment may have different release profiles, different porosities, and other different characteristics. Selection of materials, positioning of the compartments, and other factors relating to the first and second compartments may be chosen to achieve simultaneous or sequential delivery or release of a substance or substances. A first substance may be provided in the first compartment and a second substance may be provided in the second compartment. In some embodiments, an osteoinductive substance may be placed in a compartment generally adjacent tissue being treated as implanted and an osteoconductive substance may be placed in a compartment not adjacent tissue being treated. Release rates for the materials provided in the first compartment and the second compartment may be different. In some embodiments, at least one of the compartments may be unfilled at the time of surgery and autograft or other material may be provided therein in the operating room or at the surgical site. In some embodiments, the covering may form a 3D scaffold. 
     The embodiments of  FIGS. 5   a - 5   c ,  6   a - 6   c , and  7   a - 7   c  may further be configured as multi-compartment embodiments.  FIG. 8  illustrates an exemplary multi-compartment embodiment of a covering  260  having an elongated containment portion  262  for housing a substance for delivery, and having first and second ends  264 ,  266 . In the embodiment of  FIG. 8 , the elongated containment portion  262  comprises first and second compartments  268 ,  270  extending substantially the entire length of the elongated containment portion  262 . As shown, the first and second compartments  268 ,  270  extend side-by-side with each of the first and second compartments  268 ,  270  extending from the first end  264  of the covering  260  to the second end  266  of the covering  260 . Alternatively, the first and second compartments may extend one over the other, such as the first compartment arranged over the second compartment. 
       FIG. 9  illustrates an exemplary multi-compartment embodiment of a covering  280  having an elongated containment portion  282  for housing a substance for delivery, and having first and second ends  284 ,  286 . In the embodiment of  FIG. 9 , the elongated containment portion  282  comprises first and second compartments  288 ,  290  with one compartment  288  provided adjacent the first end  284  and one compartment  290  provided adjacent the second end  286 . The compartments  288 ,  290  may have substantially the same length, as shown, or may have different lengths. 
     With each of the embodiments of  FIGS. 8 and 9 , the compartments may be separated by a seal, may communicate therebetween, may be substantially separate, or may be otherwise divided with respect to other multi-compartment embodiments. 
     In one multi-compartment embodiment, shown in  FIG. 10 , the covering  50  comprises first and second compartments  52 ,  54  situated side-by-side and separated by a barrier  56 . The barrier  56  may be temporary or may be substantially permanent (remaining for the life of the covering  50 ). A temporary barrier may be a sheet or a masking agent. A boundary may be provided for dividing between two tissue types, for example between intervertebral disk and bone, between tendon and bone, between meniscus and bone, or between cartilage and bone. The barrier  56  may be integral with the covering  50 , integral with one of the first and second compartments  52 ,  54 , or may be coupled to the covering  50  or compartments  52 ,  54 . 
       FIG. 11  illustrates a nested dual-compartment embodiment  60 . As shown, a second compartment  64  is provided within a first compartment  62 . Selection of materials for provision in each of the first and second compartments may be based on release kinetics from the first compartment and from the second compartment (provided within the first compartment and thus also within the material provided in the first compartment). In one embodiment, smaller particles of a substance are provided within the first compartment and the first compartment accordingly comprises a tighter mesh while larger particles of a substance are provided within the second compartment and the second compartment comprises a looser mesh. Either or both of the first compartment  62  and the second compartment  64  may be preloaded. Alternatively, either or both of the first compartment  62  and the second compartment  64  may be left empty at manufacture for loading in the operating room or at the surgical site. In one embodiment, the first compartment may be preloaded and a port provided to access the second compartment in the operating room or at the surgical site. In some embodiments, a nesting configuration may comprise a wrapped configuration. 
     In some embodiments, at least one but not all of the compartments may be weight-bearing. In other embodiments, all of the compartments may be weight-bearing. 
     In some embodiments, the covering may be perforated between compartments for separation. For example,  FIG. 12   a  illustrates a covering  70  comprising a plurality of compartments  72 ,  73 ,  74 , and  75  separated by perforations  76 . The surgeon may select the number of compartments desired for placement and cut or pull/tear along a perforation  76  providing that number of compartments. If the covering is made of a material that is brittle or strain hardens, the surgeon may separate the compartments by bending the selected portion back upon itself and reversing until the segments separate. In such embodiment, every other compartment, for example, may be preloaded or filled with a substance for delivery. Alternatively, only some of the compartments may be preloaded, for example, every other compartment may be preloaded such that alternating compartments may be filled in the operating room or at the surgical site. 
     In one embodiment, the covering may comprise a penetrable material at a first compartment configured for placement adjacent bone and a substantially impenetrable material at a second compartment configured for placement adjacent soft tissue. Alternatively, the material of the compartments may have substantially identical characteristics. The covering then can be positioned in any desirable manner. By way of example only, a covering may have a porous surface that is positioned adjacent bone, and a separate or opposite surface that has a generally impenetrable surface that is positioned adjacent soft tissue. Alternatively, a covering may have one compartment that comprises a porous material, and a second compartment that comprises a substantially impenetrable material. 
     In another embodiment, the covering may comprise a continuous tube wherein the tube may be twisted to divide portions of the tube. The tube thus may be divided into a series of implants, each having ends that may be twisted or heat treated. Any suitable manner of dividing the tube into a plurality of compartments may be used. For example, the tube may be crimped, heat treated, twisted, knotted, stapled, sewn, or otherwise divided. Any suitable tool may be used for dividing the tube into such compartments including, for example, a crimper, a heat tool, or other. 
     In some embodiments, a multi-compartment covering may be configured to be foldable and stackable. A first embodiment of a foldable and stackable covering is shown in  FIGS. 12   b - 12   d .  FIG. 12   b  illustrates a top view and  FIG. 12   c  illustrates a side view. As shown, the covering  1010  comprises a series of individual segments including segments of a first type  1012 , segments of a second type  1014 , and segments of a third type  1016 . The segments of a first type  1012  are generally longer lengths of covering that may be filled with a substance for delivery. The segments of a second type  1014  extend between the segments of the first type  1012  and the segments of the third type  1016 . The segments of the second type  1014  may be generally short lengths of covering and may be left unfilled. In some embodiments, the segments of the second type  1014  may not be formed as a covering and may simply be a material spanning the segments of a first type  1012  and the segments of a third type  1016 . The segments of the third type  1016  are generally shorter lengths of covering. The length of the segments of a third type  1016  generally correlates to a length less than a stacked height of two segments of the first type  1012 .  FIG. 12   d  thus illustrates a stacking sequence of the covering of  FIGS. 12   b  and  12   c . As shown, segments of the first type  1012  are generally stacked on top of one another, segments of the third type  1016  extend along a side of the stacked segments of the first type  1012 , and segments of the second type  1014  span between the segments of the first type  1012  and the segments of the third type  1016 . It will be understood that the number of types of segments and their length can be varied depending upon the requirements of the surgical site. 
     Second and third embodiments of a foldable and stackable covering are shown in  FIGS. 12   e - 12   g .  FIG. 12   e  illustrates a top view and  FIGS. 12   f  and  12   g  illustrate side views. As shown, the foldable and stackable coverings may comprise a segment of a first type  1018  and a segment of a second type  1020 . The segments of the first type  1018  may be filled with a substance for delivery. The segments of a second type  1020  extend between the segments of the first type  1018 . The segments of the second type  1020  may be unfilled coverings or may be provided as, for example, a material spanning segments of the first type  1018 . In the embodiment of  FIG. 12   f , each of the segments of the first type  1018  are approximately equally filled. Thus, when stacked, each of the segments of the first type provide approximately equal height. In the embodiment of  FIG. 12   g , the segments of the first type  1018  alternate between first  1022  and second fill levels  1024 . Thus, when stacked, the segments of the first type  1018  provide different heights. In the embodiment shown, every other segment of the first type  1018  has like fill levels. In alternative embodiments, every third, every fourth, or other segment of the first type may have like fill levels. 
     Any other suitable conformation or shape or combination of these also may be used. 
     For both single and multi-compartment coverings, the covering may be closed after filling substances. Further, the covering may be left substantially open—with one or more unsealed ends. Accordingly, the covering may be provided in an unfilled, unsealed state. After a substance for delivery is placed in the covering, the covering may be permanently or temporarily closed. Permanent closure may be, for example, by heat sealing, stitching, adhesion, or other methods. Temporary closure may be by tying, fold lock, cinching, and etc. A temporarily closed covering can be opened without damaging to the covering during surgical implantation to add or remove substances in the covering. 
     Attachment Mechanisms 
     The covering may be configured with structures to permit attachment at the surgical site, such as to skeletal tissue or to soft tissue structures, or for attachment to other coverings, or for attachment to adjacent implantable medical devices or products (such as a rod or screw or cross-brace of a pedicle screw fixation system, a hip prosthesis, a bone plate, and the like). Generally, the attachment mechanism may be used to retain the covering at the surgical site and any mechanisms capable of doing so may be used. The attachment may be to bone or to adjacent tissues such as muscle, tendon, or ligament. Where the covering retains a bone graft substance, the covering may be held in a relatively stable position relative to bone (or relative to the surgical site or surgical defect) to promote bone growth. Accordingly, in some embodiments, the delivery system may be suitable for assisting in attaching tendons, artificial tendons, or ligaments to bone or other structure. 
     The bone or soft tissue to which the covering is attached may be prepared for receiving the attachment mechanism(s). For example, in spinal applications, slots or perforations may be provided in posterior elements such as transverse processes, spinous processes, or other bone or tissue to receive the attachment mechanism. 
     Any suitable attachment mechanism may be used, including mechanical, physical, chemical, and biological attachment mechanisms. The attachment mechanism may be provided at an end of the covering, centrally in or on the covering, generally in or on the body of the covering, or any combinations of these. U.S. Pat. No. 5,899,939 describes attachment mechanisms that may be adapted for use with a covering as provided herein, and is herein incorporated by reference. When an attachment mechanism is used to couple first and second coverings to one another, such attachment or coupling may be done pre-implantation or post-implantation. In post-implantation embodiments, the coupling may be done by inserting first and second coverings through an opening into a space and coupling the coverings within the space. In some embodiments, the covering may be provided with attachment mechanisms to facilitate suturing or other attachment of the covering in vivo. 
     In some embodiments, a covering may include an area for receipt of an attachment mechanism. For example, a covering may include a tab for receipt of a screw. In other embodiments, an attachment mechanism may interface with any portion of the covering. For example, a screw attachment mechanism may be threaded through a covering at any location, including central to a containment area of the covering. In some embodiments, a screw attachment mechanism may be threaded through the covering and the substance provided in the containment area of the covering. 
     A further method of attachment may comprise suturing or otherwise attaching the covering to a tether, anchor, or screw embedded in a bony structure, e.g. a pedicle screw of a spinal stabilization system. Such screw, anchor, or tether may pass through the covering and its contained contents to provide fixation, or through a tab at a margin of the covering, or through other structure of the covering. 
       FIGS. 13   a - 13   c  illustrate a covering with a mechanical attachment mechanism.  FIG. 13   a  illustrates a covering  200  comprising a compartment  202  with a mechanical attachment mechanism  204 , such as a hook, as shown, at an end thereof.  FIG. 13   b  illustrates a covering  200  comprising a compartment  202  and ends  206  with a mechanical attachment mechanism  204  comprising openings  208  at each end  206  of the covering  200  and a screw  210  for placement through the opening  208 .  FIG. 13   c  illustrates a covering  200  with a mechanical attachment  204  provided at an end thereof. In various embodiments, the mechanical attachment mechanism  204  of  FIG. 13   c  may be a hook, barb, staple, screw, cap screw, nail or tack, bolt, button, tab, flap, hook-and-eye material, loop, rivet, stud, or cam lock (or other conformant fastener), clamp (or cramp), clasp, grommet, pin, retaining ring, rivet, snap, staple, tack, toggle, zipper, or other configuration. In some embodiments, hinges, springs, or like mechanisms may be used as attachment mechanisms. Any of these fasteners may be made of any suitable material, including metal, ceramic, tissue such as allograft, xenograft, autograft, collagen, any of the materials listed above in the section entitled Exemplary Covering Materials, or combinations of these. In a further embodiment, the attachment mechanism may comprise a press-fit system. In a specific screw attachment mechanism, attachment may be done via interference screw fixation. For example, attachment may be via biodegradable interference screw fixation. Combinations of these also may be used. 
       FIG. 13   d  illustrates a covering having a tab attachment mechanism. As shown, the covering  200  is generally square shaped with a thinner portion  201  at one end thereof. The thinner portion  201  includes a tab  203  with thru holes  205  for receiving screws. In the embodiment shown, two thru holes  205  are provided. The tab  203  may be integrally formed with the material of the covering  200  or may be separately formed and coupled with the covering  200 . The tab  203  thus may be formed of the same material as the covering  200  or may be formed of a different material as the covering  200 . In some embodiments, the tab may be formed of a reinforced material relative the material of the covering. In some embodiments, more or fewer thru holes may be provided. Further, while  FIG. 13   d  illustrates a tab at one end of the covering, it is to be appreciated that such a tab may be provided at more than one end, margin, edge, or other of the covering. 
       FIGS. 13   e  and  13   f  illustrate embodiments of physical attachment mechanisms, e.g., wherein the attachment mechanisms comprise a band-like structure.  FIG. 13   e  illustrates a covering  200  comprising a compartment  202  and ends  206 . Sutures  204  are provided through the ends  206  of the covering  200 . In alternative embodiments, sutures  204  may be provided through the compartment  202 .  FIG. 13   f  illustrates a covering  200  comprising a compartment  202  and a wrap attachment mechanism  204 . The wrap is provided around the compartment  202  and is generally centrally placed. Further physical attachment mechanisms suitable for use, for example in the embodiment of  FIG. 13   f , may comprise wraps, sutures, wires, strings, elastic bands, cables, ropes, chains, plastic wrap, strap, tie, cable tie, or other mechanisms. These mechanisms may be coated, such as with plastic. In some embodiments, a plurality of mechanisms, such as a multiple parallel wires, may be joined together, for example with a plastic strip coating. Suitable techniques for using such attachment mechanisms may include suturing, stitching, knotting, twisting, cinching, knot tying, and similar techniques. Any of these physical fastening materials may be made of any suitable material, including metal, tissue such as allograft, xenograft, autograft, collagen, any of the materials listed above in the section entitled Exemplary Covering Materials, or combinations of these. 
     Chemical attachment mechanisms may comprise, for example, a bioadhesive or glue, cement, tape, tissue adhesives, or similar mechanism. Chemical attachment mechanisms may further comprise mechanisms that facilitate cross-linking. In further embodiments, attachment mechanisms such as crimping, welding, soldering, or brazing may be used. For example, tissue welding may be used (see, for example, http://www.lasertissuewelding.com/laser_mediated_tissue_soldering and http://www.csmgtechinternational.com/presentation.html). Further, attachment may be achieved via friction.  FIGS. 13   g  and  13   h  illustrate coverings with chemical attachment mechanisms.  FIG. 13   g  illustrates a covering  200  with a compartment  202 . An adhesive is placed over a surface of the compartment  202 .  FIG. 13   h  illustrates a covering  200  with a compartment  202  and ends  206 . An adhesive  204  is placed over the ends  206 . Suitable adhesives for use with the embodiments of  FIGS. 13   g  and  13   h  include, for example, cyanoacrylates (such as histoacryl, B Braun, which is n-Butyl-2 Cyanoacrylate; or Dermabond, which is 2-octylcyanoacrylate); epoxy-based compounds, dental resin sealants, dental resin cements, glass ionomer cements, polymethyl methacrylate, gelatin-resorcinol-formaldehyde glues, collagen-based glues, inorganic bonding agents such as zinc phosphate, magnesium phosphate or other phosphate-based cements, zinc carboxylate, L-DOPA (3,4-dihydroxy-L-phenylalanine), proteins, carbohydrates, glycoproteins, mucopolysaccharides, other polysaccharides, hydrogels, protein-based binders such as fibrin glues and mussel-derived adhesive proteins, and any other suitable substance. Adhesives may be selected for use based on their bonding time; e.g., in some circumstances, a temporary adhesive may be desirable, e.g., for fixation during the surgical procedure and for a limited time thereafter, while in other circumstances a permanent adhesive may be desired. Where the compartment  202  is made of a material that is resorbable, the adhesive can be selected that would adhere for about as long as the material is present in the body. In some embodiments, the covering material may be treated to form chemical linkages between the covering and adjacent tissue, whether bone or soft tissue. 
     In some embodiments, biological attachment may be via mechanisms that promote tissue ingrowth such as by a porous coating or a hydroxyapatite-tricalcium phosphate (HA/TCP) coating. Generally, hydroxyapatite bonds by biological effects of new tissue formation. Porous ingrowth surfaces, such as titanium alloy materials in a beaded coating or tantalum porous metal or trabecular metal may be used and facilitate attachment at least by encouraging bone to grow through the porous implant surface. These mechanisms may be referred to as biological attachment mechanisms. 
     Generally, any combination of mechanical, physical, chemical, or biological attachment mechanisms may be used. 
     Any of the various attachment mechanisms may be provided as part of the covering or may be supplied separately. In various embodiments, the attachment mechanisms may be integral to the covering. Alternatively, the attachment mechanisms may be secured to the covering, for example, by stitching, welding, crimping, or other. The attachment mechanisms may have any suitable geometric configuration and may optionally include apertures for receiving other components for coupling in vivo, such as an aperture for receiving a screw. Thus, for example, an attachment mechanism may be provided configured for receiving an anchor for fixation to bone. Generally, any number of attachment mechanisms may be provided at any suitable location on the covering. 
     The attachment mechanisms may be manufactured of the same material as the portion of the covering to which it is coupled or may be manufactured of a different material from the portion of the covering to which it is coupled. The attachment mechanism may be resorbable or nonresorbable. The material of the attachment mechanism may be selected to allow anchoring the covering to an adjacent covering having a complementary attachment mechanism or to another structure. In various embodiments, the attachment mechanism may comprise, allograft, synthetic materials, demineralized bone, nondemineralized bone, other material, or combinations of these. The shape and size of the attachment mechanism may be selected based on application. 
     In some embodiments, the covering may be tubular and have threaded ends such that the ends may be threaded with a reciprocal thread of a further device or implant. For example, the covering may be used with interference screws. In some embodiments, the covering may include extensions or tabs that may be used for wrapping around or suturing to the surgical site. Alternatively, the covering may be sutured directly to the surgical site. The ends of the covering may be presealed or may be sealed after introduction of contents. Sealing may be done by using adhesives, heating, solvent treatment, suturing, knotting, or any other means. 
     Spinal Tension Band 
     A further embodiment is shown in  FIGS. 14   a  and  14   b . Those figures illustrate an embodiment comprising a tension band including a covering for delivering a substance or material. In accordance with the embodiments shown in  FIGS. 14   a  and  14   b , the covering may comprise any of the materials described herein with respect to other embodiments. 
     Spinal fusion is frequently used as a treatment for various spinal disorders and is achieved by formation of a bony bridge between adjacent vertebral bodies eliminating the intervertebral joint. Spinal fusion can be accomplished within the disc space, anteriorly between adjacent vertebral bodies and/or posteriorly between consecutive processes, e.g., transverse processes, laminae or other posterior elements of the vertebrae. 
     One frequently used spinal fusion technique involves removal of the intervertebral disc and insertion of an anterior supporting structure, e.g., bone grafts, bone substitutes, plugs, bone dowels, cages, and the like, into the intervertebral disc space to prevent collapse of the disc space and promote fusion of the adjacent vertebrae. To ensure proper growth and fusion between the affected adjacent vertebrae, the posterior side of the spine may be stabilized by utilizing a rigid metallic implant, e.g., a plate, rod, wire or strip, which spans the adjacent vertebrae to re-create a load distribution similar to that of the intact spine. These metallic implants are commonly referred to throughout the relevant scientific and medical literature as “tension bands.” U.S. Pat. No. 6,752,831 teaches a biocompatible osteogenic band to stabilize the spine and is herein incorporated by reference in its entirety. As taught therein, the osteogenic band may be fabricated in whole or in part from various materials, particularly connective type biological material obtained from human and animal tissues, plants, and insects which include, but are not limited to, e.g., bone, tendon, ligament, silk, collagen, elastin, reticulin, cellulose, alginic acid, chitosan, small intestine submucosa or combinations thereof. The biological material can be autogenic, allogenic, transgenic, or xenogenic in origin. 
       FIG. 14   a  illustrates a tension band and covering embodiment  80  comprising a tension band or cable  82  and covering  84 . As shown, the covering structure  84  is provided over the tension band or cable  82 . The tension band  82  may comprise an osteogenic material, as described above, or may comprise other suitable material such as synthetic polymer, titanium, stainless steel, or other. The covering structure  84  may be filled with a substance  86 , as described herein. In some embodiments, the substance  86  may comprise an osteogenic particulate material. The overall dimensions of the tension band and covering delivery system  80  can vary widely depending on the distance between affected vertebrae, the site, and the method of affixation. In some embodiments, the dimensions of the tension band and covering delivery system  80  may range from about 1 cm to about 1 meter in length, or from about 3 cm to about 8 cm in length, from about 2 mm to about 30 mm in thickness, or from about 2 mm to about 10 mm in thickness, and from about 2 mm to about 30 mm in width, or from about 2 mm to about 10 mm in width. 
     The tension cable or band  82  includes first and second end portions  88  for coupling with first and second end portions  90  of the covering structure  84 . Coupling may be achieved in any suitable manner such as by adhesive, by mechanical coupling, or other. The tension cable or band  82  further comprises first and second ends  92  affixing or coupling to the vertebrae. The ends  92  may be cut or machined to include threads, grooves, driver head, fasteners, rivets, screws, bolts, pins, etc., to aid in affixing each end portion of the elongated section to the vertebrae. The tension cable or band and covering structure delivery system  80 , including material, may have dimensions such that, as formed, the system  80  extends between and cover the spinal processes at each end of the system  80 . The tension cable or band  82  may be affixed to the spinal processes by any of the mans disclosed in U.S. Pat. No. 6,752,831. 
       FIG. 14   b  illustrates a tension band and covering embodiment  100  wherein the covering  102  includes spreaders  104  such that the covering  102  forms the tension band. In the embodiment shown in  FIG. 14   a , the covering structure  100  has sufficient strength to support the spine. The spreaders  104  substantially prevent the covering  102  from compressing under load. The covering structure  100  includes first and second ends  106 , the ends  106  being formed for affixation to the spinal processes. As shown, the ends  106  may be formed into cable structures. First and second spreaders  104 ′ may be provided proximate first and second ends of the covering structure. The spreaders  104  may have any suitable configuration. In some embodiments, the spreaders may comprise discs. In other embodiments, as shown, the spreaders may comprise rings. The spreaders  104  may be formed of any biocompatible material including, for example, a polymer, a metal, or a natural material such as bone. Generally, flexible spreaders may exhibit less strength under loads. 
     The tension band and covering embodiments shown in  FIGS. 14   a  and  14   b  may further comprise a substance or material provided in the covering structure. The substance or material may be osteogenic, such as demineralized bone, provided in fiber, liquefied, particulate, chunk, or monolithic form. The substance or material may be an osteogenic protein or extract in a suitable carrier. Generally, the substance or material may be osteoinductive and/or osteoconductive. The substance or material may be any material described herein for provision in a covering. 
     Cartridge 
     In various embodiments, a compartment may be configured for placement in a device for use as a delivery system. For example, a cartridge covering may be configured for placement in an interbody fusion cage, in a hip stem, or in other implant devices for delivering a substance. Thus, in some embodiments, the compartment may encourage ingrowth through the implant device.  FIGS. 15   a - 15   c  illustrate a cage  200 , a cartridge covering  202 , and a delivery system  204  comprising the cartridge covering  202  in the cage  200 , respectively. In various embodiments, the covering may be sized to be slightly larger than the cavity of a cage into which it is to be inserted. 
       FIGS. 15   d - 15   h  illustrate further embodiments of a cartridge delivery system placed in a cage. As shown, a cage  200  or allograft implant may be used along with first  201  and second graft-containing coverings  203 . As shown in  FIG. 15   g , The first covering  201  may be configured to fit inside the cage&#39;s central cavity, while the second covering  203  may be elongated and may be placed around the cage  200 . As shown in  FIG. 15   h , the first  201  and second coverings  203  may be placed into position during the surgery, and inserted into the site  207 . 
     In another embodiment, a delivery system such as that shown in  FIGS. 15   d - 15   h  may be formed with a one piece covering  209  and a cage  200  as shown in  FIG. 15   i . As shown in  FIG. 15   j , the one piece covering  209  may have a body portion  211 , an optional hinge  213 , and a protuberance  215 .  FIG. 15   k  shows a one piece covering  209  wrapped around itself. The protuberance may be folded into the cavity of the cage while the body portion is wrapped around part or all of the cage before insertion. 
     In other embodiments, a cartridge covering may form an insert and a second covering may form the implant device for receiving the cartridge covering. The second covering may, in some embodiments, have a structural or mechanical component configured for supporting loads such that the second covering may function as a cage. The cartridge covering may have a biologically active material provided therein. 
       FIG. 16  illustrates an embodiment of a delivery system  204  wherein the covering comprises a cartridge covering  206  for placement in an interbody fusion cage  208 . The interbody fusion cage  208  may be any suitable cage, such as one suitable for anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), or other procedure, or may be other suitable implant device. The cage  208  may be formed of metal, polymer, PEEK, biocomposite, allograft, xenograft, other materials, or combinations of these. The cage  208  may have any suitable dimensions. The cage may have substantially solid sides, may have mesh sides, may have slotted sides, may have some open sides and some solid sides, or any combination thereof. 
     In some embodiments, such as shown in  FIG. 16 , the cage  208  may be provided with an opening  210  for receiving the cartridge covering  206 . The opening  210  may be positioned and sized for receiving the cartridge covering  206  before or after cage placement. Accordingly, the opening  210  may be positioned based on direction of insertion of the cage  208  such that the opening  210  faces the surgeon after insertion of the cage  208 . The cartridge covering  206  may be sized and shaped with particularity for the interbody fusion cage  208  or may be selected merely such that it is accommodated by the cage  208 , for example by being smaller than the cage  208 . A tool may be provided with the cartridge covering for holding the cartridge covering  206  in a position for insertion through the opening  210  of the cage  208  after placement of the cage  208  in vivo. 
     In alternative embodiments, the cartridge covering may be placed in the cage prior to insertion of the cage in vivo. As shown in  FIG. 17 , the cage  208  may be sized such that the cartridge covering  206  is oversized with respect to the cage  208 . In such embodiments, the cartridge covering  206  thus may contact vertebrae when the cage  208  is inserted in vivo. 
     In some embodiments, a cage may be provided with containment areas for receiving more than one cartridge covering. In the embodiment of  FIG. 18   a , the delivery system  211  comprises a cage  212 , including three containment areas  214 ,  216 , and  218 , and corollary cartridge coverings for placement in each containment area. As shown, the containment areas  214 ,  216 , and  218  may be generally uniformly sized and shaped. Alternatively, the containment areas  214 ,  216 , and  218  may have varying sizes or shapes and/or varying materials characteristics. The materials provided in the cartridge coverings provided in each containment area may vary depending on the general position of the cartridge covering as placed in vivo. Thus, for example, a different material may be provided in a cartridge covering for placement in containment area  214  than in a cartridge covering for placement in containment area  216 . Further, in some embodiments, a plurality of cartridge coverings may be provided in a single containment area. 
       FIG. 18   b  illustrates an alternative embodiment of a cage delivery system  221  comprising a cage  222  having a plurality of cartridge coverings  224 ,  226 ,  228  provided therein. In the embodiment of  FIG. 18   b , a single containment area  230  is provided with three cartridge coverings  224 ,  226 ,  228  provided therein. The cartridge coverings  224 ,  226 ,  228  are provided generally vertically stacked. The coverings may be provided in any desired configuration. Thus, as placed in vivo, the top and bottom cartridge coverings  224  and  228  are closest to host bone. Thus, the top and bottom cartridge coverings  224  and  228  may have osteoconductive materials provided therein. In contrast, the middle cartridge covering  226  is separated from host bone by the top and bottom cartridges  224  and  228 . Thus, for example, osteoinductive materials may be provided in the middle cartridge covering  226 . In alternative embodiments, separate containment areas may be provided for each of the cartridge coverings  224 ,  226 ,  228 . 
     In some embodiment, it may be useful to provide a cage having specific characteristics. For example, the cage may be provided with openings, via mesh structure, slots, or other, on surfaces generally adjacent vertebrae to encourage ingrowth through the cage to the covering cartridge within the cage. Further, the cage may be specifically configured for accommodating a cartridge covering, for enhancing specific characteristics of a material delivered by the cartridge covering, or other. In some embodiments, the cage may be formed to increase exposure area to the interior of the cage such that exposure of the cartridge covering within the cage is enhanced. Thus, exposure of the cartridge covering to the vertebral body may be enhanced. 
     It is to be appreciated that such cartridge coverings may be provided for placement in any suitable implant device for delivering a material in vivo or for enhancing healing of the body, such as via bone ingrowth through the implant. Thus, as shown in  FIG. 19 , in yet a further embodiment, a delivery system  240  may comprise a hip stem  242  and a cartridge covering  244  for delivery of material in the hip stem  242  to encourage ingrowth to the stem. Accordingly, the hip stem  242  may include a window  246  for receiving the cartridge covering  244 . Osteoinductive and/or osteoconductive materials may be provided within the cartridge covering. For example, in one embodiment, DBM may be provided within the cartridge covering  244 . 
     Coverings such as disclosed herein may further be useful in osteonecrosis. In osteonecrosis of the femoral head, one treatment method comprises drilling a hole through the trochanter and through the femoral neck, into the femoral head. This drill hole may be grafted, for example using graft material in a tube implant device. In certain embodiments, coverings may be filled (pre-filled or filled by the surgeon) with graft materials for insertion in the drill tract directly or for insertion into a tube implant device for placement in the drill tract. The covering may be dimensioned for delivery into the tube implant device or through the drill tract, for example generally long and thin. In further embodiments, a thread may be provided on an end of the covering to assist in loading of the covering into, for example, a tube for placement in the drill tract. Alternatively, the covering may be provided as a series of small coverings and these coverings iteratively placed into the tube or drill tract. Using a covering such as provided herein, the procedure for placing the covering in osteonecrosis may be minimally invasive or open. 
     In some embodiments, cartridge coverings may be used with an implant such as a mechanical or structural support device to deliver materials in weight-bearing applications. The cartridge covering facilitates spatially controlled delivery of materials. 
     Cartridge coverings may be provided singly or in series. For example, a series of cartridge coverings may be provided in a manner similar to the embodiment of tubular covering  120  of  FIG. 20 , described further below. Generally, the wrapping covering may be formed of any materials discussed with respect to other covering embodiments described herein. 
     Any of the materials described herein may be provided in the cartridge covering. In specific embodiments, a collagen sponge may be provided in a cartridge covering and the cartridge covering delivered in the cage or implant. Materials such as BMP-2 may be added to the material, may be injected into the material, or may be the primary material for delivery by the cartridge covering. Other bioactive agents and bioactive compounds may be used, as desired. 
     Wrapping 
     In accordance with further embodiments, a covering may be provided for wrapping around an implant, such as a cage. Thus, for example, as shown in  FIG. 21   a , a wrapping covering  250  may be wrapped around a cage  252 . Further, as shown in  FIG. 21   b , a cartridge covering  254  may be placed within the cage  252 , as described above, and a wrapping covering  250  wrapped around the cage  252 . In some embodiments, the wrapping covering  250  may comprise an elastic mesh containment ring. In alternative embodiments, the wrapping covering  250  may be formed of any materials discussed with respect to other covering embodiments described herein. The wrapping covering may be wrapped around the cage before or after insertion of the cage in vivo. Wrapping of the covering  250  may comprise extension (and subsequent retraction) of an elastic wrapping covering around the cage, may comprise tying of a wrapping covering around the cage, may comprise hooking of a wrapping covering on hooks or other coupling mechanisms on the cage, or other. Further, the wrapping covering  250  may extend around the entire cage  252  or over only a portion of the cage  252 . While specific reference is made herein to a wrapping covering wrapped around a cage such as an interbody fusion cage, it is to be appreciated that such wrapping covering may be used with any suitable implant. 
     In further embodiments, an implant may be fit within a covering. For example, in joint revision surgeries, a covering may be provided in a defect created by removal of an original implant and cement from the implant and a revision implant may be placed centrally of the covering. 
     In yet further embodiments, a covering may be provided surrounding another structure. For example a covering may be provided around a cylinder configured for receipt in a long bone segmental defect, such as in trauma or tumor situations. The covering may hold a graft and maintain the graft in the defect, excluding soft tissue, to provide apposition to the segment ends. 
     Curved 
     In some embodiments, a delivery system such as provided herein may comprise a curved covering. In some embodiments, the curved covering may have a shaping or reinforcing structure. In some embodiments, the shaping or reinforcing structure may be resorbable. Such shaping or reinforcing structure may be, for example, a rod or wire. The shaping or reinforcing structure may be formed out of metal or other radiographic material such that it may act as a radiographic marker. The shaping or reinforcing structure may be removed after delivery device placement or may be kept in place. In some embodiments, the shaping or reinforcing structure may add rigidity to the covering device and thus facilitate impaction into a defect. In some embodiments, a substantially straight shaping or reinforcing structure may be provided in a covering to act as a radiographic marker or as an instrument interface. In some embodiments, the curved covering may be preassembled or formed with a resorbable shaping or reinforcing structure. 
       FIG. 21   c  illustrates an embodiment of a curved covering with a shaping or reinforcing structure. As shown, the curved covering  1030  may have a central containment portion  1032  and first  1036  and second end portions  1038 . The central containment portion  1032  may be filled with a substance for delivery. The end portions  1036 ,  1038  may be unfilled. A shaping or reinforcing structure  1034  such as a rod, bar, or wire is provided along the containment portion  1032 , for example centrally on the containment portion  1032  and running from a first end portion  1036  to a second end portion  1038 , for forming the covering into the curved shape. 
       FIG. 21   d  illustrates a top view of assembly of the curved covering of  FIG. 21   c .  FIG. 21   e  illustrates a side view of assembly of the curved covering of  FIG. 21   c . As may be appreciated, a covering  1040  is provided and a shaping or reinforcing structure  1042  is provided. The covering  1040  may be provided in a filled or unfilled condition. Generally, the covering  1040  and the shaping or reinforcing structure  1042  may have complementary lengths. In the embodiments shown, the covering  1040  and reinforcing structures  1042  have approximately equal lengths. In other embodiments, the shaping or reinforcing structure may be longer than the covering such that, after assembly, the shaping or reinforcing structure extends beyond at least one end of the covering. As shown, the shaping or reinforcing structure  1042  is combined with the covering  1040  to form a curved covering  1044 . Such combination  1044  may be in any suitable manner including placement of the shaping or reinforcing structure  1042  in the covering  1040 , threading of the shaping or reinforcing structure  1042  through the covering  1040 , adherence of the shaping or reinforcing structure  1042  on the covering  1040 , or other. 
     Cup Shape 
       FIGS. 22   a  and  22   b  illustrate a cup-shaped embodiment. As shown, the covering  1050  may have a substantially cup-shaped configuration comprising a first layer  1052  and a second layer  1054 . The first layer  1052  and the second layer  1054  may be coupled together along a rim  1058  of the covering  1050 . Such coupling may be done, for example, by suturing the first layer  1052  and the second layer  1054  together. The covering may further include a flange  1056  extending at least partially around the rim  1058  of the covering  1050  and formed by the coupled first layer  1052  and second layer  1054 . Graft material or other substance may be provided between the first layer  1052  and the second layer  1054 . 
     Pad 
     In accordance with further embodiments, a delivery system such as provided herein may be used to deliver a layer of osteoinductive and/or osteoconductive material to encourage ingrowth of bone. For example, a compartment may be configured for delivering a mat of DBM underneath a tibial tray in a total knee replacement to encourage ingrowth. In accordance with such an embodiment, the covering may deliver DBM or other graft material. In some configurations, the covering may capture fibers of DBM but allow protrusion of some of the fibers. Alternatively, a compartment may be configured as a pad for applications such as building up a cheekbone for plastic surgery, as a cranioplasty covering, or other. 
     In a further pad or mat embodiment, a delivery system such as provided herein may be formed as a mat for use in the occipital/cervical region of the spine. A covering for such delivery system may be substantially U-shaped and generally configured to fit the cranio-cervical junction. In certain embodiments, the covering may be filled with BMP or similar material. Such covering may be useful for fusion from C1-C2.  FIG. 23  illustrates a U-shaped pad  231 . 
     In accordance with some embodiments, a covering may be used in a cemented total joint arthroplasty. The covering, with material provided therein, may be used to create a lining between a cement mantle and the host tissue. 
     Solid Covering 
     In some embodiments, the covering may be a substantially solid delivery container.  FIG. 24   a  illustrates such a covering. The graft material may be, for example, a mixture of demineralized bone particles and pressed bone fibers. In some embodiments, the graft material may further include an antibiotic, drug powder, or other material(s) such as disclosed herein. The covering  410  may be a generally tubular body formed of, for example, a polymer such as disclosed in U.S. Pat. No. 6,696,073 and U.S. patent application Ser. No. 11/625,086 (published as US2008/0069852), herein in incorporated by reference in their entireties. Alternatively, other polymers or other materials may be used. The graft material  412  may be placed in the covering  410 . A first end  414  of the covering  410  may be sealed in a non-removable fashion (such as by forming the tube with a closed end) and a second end of the covering may have a removable cap  416 . The cap  416  may interlock with the tube  410  via threading, a press fit, or other.  FIG. 24   b  illustrates the cap  416  being press fit on a covering  410  holding graft material  412 . The covering may be factory assembled with the graft material therein or may be intraoperatively assembled. 
       FIGS. 24   c - 24   e  illustrate example applications of such a covering. As shown in  FIG. 24   c , the substantially solid covering  410  may be used in femoral head avascular necrosis  418 . As shown in  FIG. 24   d , the substantially solid covering  410  may be used in treatment of a tibial  420  compression fracture. As shown in  FIG. 24   e , the substantially solid covering  410  may be used in joint fusion, such as ankle fusion. Joint fusion, including ankle fusion, generally comprises decorticating the articular surface of the joint to be fused and drilling a hole that encompasses faces of each of the two adjacent bones to be fused. A delivery system, including covering and graft material for example, such as disclosed herein may be placed into the drilled hole, such that both bones are contacted. 
     Shapes and Configurations 
     As discussed herein, coverings may be provided in a plurality of shapes and generally may be configured for desired applications. Coverings may be configured for receipt directly in vivo or for placement in an implant device. The size and shape, as well as material from which it is manufactured, may be selected for a desired application. Generally, a covering may be provided as a plug (such as a cylinder with a tapered or blunt end), as a generally flat mat (with captured particles or woven to surround a generally flat plane of material), as a tube, a snake (generally long tube, such as may be subdivided), as a block, as a sphere, as an ovoid, as a molded shape (geometric, such as based on an atomic CT or other scan), as a U-shape, as an L-shape, as a tape, as a film, or shaped to substantially mimic a skeletal bone. In further embodiments, a covering may be provided in other configurations such as a sealed, perforated film, as a twin compressing fibers or other materials, as a resorbable container or capsule, or as a cage or container such as providing mechanical support. 
     Packing 
     The substance may be packed in the covering at any suitable density. For some applications, the substance may be loosely packed in the covering to enhance manipulability. In some embodiments, the material may be packed in the covering such that the covering retains flexibility and may be folded over itself. In other applications, the substance may be tightly packed in the covering to provide a relatively stiff delivery system, and it may be weight bearing. 
     In some embodiments, the covering may be configured to facilitate placement of graft material in the covering. Thus, for example,  FIGS. 24   f  and  24   g  illustrate a covering  1060  comprising two layers  1062 ,  1064  of material. The two layers  1062 ,  1064  of material meet one another to form four sides of the covering. Three of the sides are sealed  1066 . The fourth side  1068  is unsealed. At the fourth side  1068 , one layer of material  1064  has a length more than the other layer of material  1062 . Thus, a fold-over tab  1070  is formed. The covering  1060  may be opened to add or remove materials from the covering  1060 . In some embodiments, the fold-over tab  1070  may be sutured, crimped, or otherwise manipulated to fixedly close the covering  1060 . It is to be appreciated that the fold-over tab  1070  also facilitates adjustability of the size of the bag. Thus, for example, the fold-over tab  1070  may be used to fold a portion of the covering  1060  including both layers of material  1062 ,  1064  to reduce the size of the covering  1060 . Accordingly, the embodiment of  FIGS. 24   f  and  24   g  may be used to manipulate the size of the covering  1060  or volume of materials inside of the covering  1060 . 
     IV. Substance for Delivery by Covering 
     A substance is provided in the covering, before or during surgery (as described below), for delivery in vivo. Generally, the substance or material may be homogenous or heterogeneous. The substance or material may be selected to exhibit certain gradients. For example, the substance or material may be selected to exhibit a gradient to guide, lure, or attract cells along a pathway. Such gradient may comprise a cell gradient, a cell type gradient (for example transitioning from bone cells to cartilage cells or transitioning from bone cells to tendon cells), a gradient of conductivity, or a gradient of density/porosity. In some embodiments, the substance or material may comprise a sequence of ingredients. 
     The covering may be used to deliver a substance comprising any suitable biocompatible material. In specific embodiments, the covering may be used to deliver surface demineralized bone chips (cortical or cancellous), optionally of a predetermined particle size, demineralized bone fibers, optionally pressed, and/or allograft. For embodiments wherein the substance is biologic, the substance may be autogenic, allogenic, xenogenic, transgenic, or combinations of these. Each of these tissue types includes any tissue of bone origin, connective tissue origin, or any collagen containing material including organ tissues. Other suitable materials that may be positioned in the covering include, for example, protein, hormones, nucleic acid, carbohydrate, lipids, collagen (autograft, allograft, or xenograft from musculoskeletal or organ systems), allograft bone, autograft bone, cartilage stimulating substances, allograft cartilage, TCP, TCP/calcium sulfate, calcium carbonate, calcium phosphates, bioactive glasses, glass ceramics, magnesium phosphates, phosphates containing any biocompatible metal ion, porous implants of all types including trabecular metal, biocompatible metals including stainless steel, cobalt-chrome, titanium, titanium alloys, polymers such as polylactic acid, polyglycolic acid, polycaprolactone, polyglycolide-co-caprolactone, polyethylene oxide, polypropylene oxide, polyglycolide-co-trimethylene carbonate, poly(lactic-co-glycolic acid), poly-L-lactide, polyethylene glycol, polyetheretherketones, polyurethanes, polyethers of all types, poly ethylene terephthalte, polyethylene, polypropylene, Teflon, chondroitin sulfate, hyaluronic acid and its salts, chitosan and derivatives, natural polymers such as silk, collagen, polysaccharides, polyhydroxyalkanoates, polymers combined with bone or collagen or both from any source (allograft, xenograft, transgenic, autograft), hydroxyapatite, calcium sulfate, polymer, nanofibrous polymers, growth factors, carriers for growth factors, growth factor extracts of tissues, demineralized bone matrix, dentine, bone marrow aspirate, bone marrow aspirate combined with various osteoinductive or osteoconductive carriers, concentrates of lipid derived or marrow derived adult stem cells, umbilical cord derived stem cells, adult or embryonic stem cells combined with various osteoinductive or osteoconductive carriers, transfected cell lines, bone forming cells derived from periosteum, combinations of bone stimulating and cartilage stimulating materials, committed or partially committed cells from the osteogenic or chondrogenic lineage, platelets, activated platelets, antibiotics, substances with antimicrobial properties, or combinations of any of the above. In accordance with one embodiment, the substance is a bone matrix compositions such as described in U.S. patent application Ser. No. 12/140,044 and U.S. Patent Publications Nos. 2007/0098756 and 2007/0110820 all for Bone Matrix Compositions and Methods, herein incorporated by reference in their entireties. Suitable materials for preparing biocomposites for placement in the covering are disclosed in U.S. Patent Publication Nos. 2007/0191963, 2006/0216323, and 2005/0251267, U.S. Pat. Nos. 6,696,073, 6,478,825, 6,440,444, and 6,294,187, all herein incorporated by reference in their entireties for all purposes. 
     In some embodiments, the substance or material for delivery may comprise a biodegradable polyester such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(lactic-co-glycolic acid) (PLGA), or polyhydroxyalkanoates (polyhydroxybutyrates and polyhydroxyvalerates and copolymers), polysaccharides, polyhydroxyalkanoates, polyglycolide-co-caprolactone, polyethylene oxide, polypropylene oxide, and polyglycolide-co-trimethylene carbonate. In some embodiments, poly(ethylene glycol) (PEG) may be incorporated into the biodegradable polyester to add hydrophilic and other physico-chemical properties to enhance drug delivery. In some embodiments, composites of allograft bone and biodegradable polymers (for example, PLEXUR® products available from Osteotech) may be delivered by the covering. 
     In some embodiments, the substance may be pressed before placement in the covering. A substance provided within the covering may be homogenous, or generally a single substance, or may be heterogeneous, or a mixture of substances. In some embodiments, the substance may be designed to expand in vivo. U.S. Patent Publications No. 2008/0091270 describes an osteoimplant that expands in vivo and is herein incorporated by reference in its entirety. Such an embodiment may be used to fill a space and create contact with congruent surfaces as it expands in vivo, for example for interbody fusion. Thus, in some embodiments, the delivery system may be used in the disc space, between implants, or inside a cage. In some embodiments, the substance may include a natural and/or synthetic expandable material. The expandable material may comprise bone particles, a polymer, a hydrogel, a sponge, collagen, or other material. In various embodiments, the expandable material comprises bone allograft comprising demineralized bone particles, and the demineralized bone particles may be a blend of cortical and cancellous bone. For example, the expandable material may comprise demineralized cortical fibers and demineralized cancellous chips, wherein the demineralized cancellous chips may create a healthy matrix for the incorporation of new bone and add advanced expansion characteristics. 
     In addition to bone particles, an expandable polymer, a collagen sponge, compressed and/or dried hydrogels, or other materials may be used. In addition to expansion properties, the material may exhibit osteoinductive and/or osteoconductive properties. For example, cancellous bone particles may exhibit osteoconductive properties while demineralized cortical bone particles may exhibit osteoinductive properties. 
     The expandable material may be compressed during formation to aid in subsequent expansion. Generally, increased compression leads to increased expansion characteristics in the osteoimplant. Compressed materials and certain non-compressed materials may be constrained such that, absent the constraint, the material is free to expand. A constrained material is one that embodies energy, such as a bent, spring-loaded, or coiled material, or any other material that is artificially prevented from expanding or conforming to its natural configuration. The expandable material may include a covering material that partially or wholly surrounds the material. The covering material may be provided also expand as the expandable material expands. 
     Expansion may be activated in any suitable manner. For example, expansion may be activated by exposure to air, water, blood, heat, removal of a constraint, or otherwise. In one embodiment, the expandable material may be provided compressed and dried. Upon exposure to liquid in vivo, the expandable material may expand. In another embodiment, the expandable may be compressed and at least partially constrained by a covering material. Upon exposure to liquid in vivo, the covering material may expand or disintegrate, as the expandable material expands. The expandable material may expand as a function of time. In yet another embodiment, the expandable material may have a first state at approximately 60 degrees F. and an expanded state at approximately 98 degrees F. such that, upon implantation in vivo and exposure to body heat, the expandable material may expand. In a further embodiment, the expandable material may be vacuum-sealed during manufacture and, when unsealed and exposed to air, the expandable material may expand. 
     The covering retains the substance in place by pressure against the covering. The covering thus may, in some embodiments, maintain particles of substance in close proximity (for example, where the covering retains a substance comprising bone particles). Generally, the ratio of covering material to substance for placement within the covering may be low. For example, in some embodiments, the ratio of covering material to substance, by weight, may be approximately 1:1,000, 1:100, 1:50, 1:25, 1:1, or any suitable ratio that may be higher or lower than these. 
     In some embodiments the substance delivered by the covering may include or comprise an additive such as an angiogenesis promoting material or a bioactive agent. It will be appreciated that the amount of additive used may vary depending upon the type of additive, the specific activity of the particular additive preparation employed, and the intended use of the composition. The desired amount is readily determinable by one skilled in the art. Angiogenesis may be an important contributing factor for the replacement of new bone and cartilage tissues. In certain embodiments, angiogenesis is promoted so that blood vessels are formed at an implant site to allow efficient transport of oxygen and other nutrients and growth factors to the developing bone or cartilage tissue. Thus, angiogenesis promoting factors may be added to the substance to increase angiogenesis. For example, class 3 semaphorins, e.g., SEMA3, controls vascular morphogenesis by inhibiting integrin function in the vascular system, Serini et al.,  Nature,  (July 2003) 424:391-397, incorporated by reference herein, and may be included in the recovered hydroxyapatite. 
     In accordance with some embodiments, the substance may be supplemented, further treated, or chemically modified with one or more bioactive agents or bioactive compounds. Bioactive agent or bioactive compound, as used herein, refers to a compound or entity that alters, inhibits, activates, or otherwise affects biological or chemical events. For example, bioactive agents may include, but are not limited to, osteogenic or chondrogenic proteins or peptides; demineralized bone powder as described in U.S. Pat. No. 5,073,373; collagen, insoluble collagen derivatives, etc., and soluble solids and/or liquids dissolved therein; anti-AIDS substances; anti-cancer substances; antimicrobials and/or antibiotics such as erythromycin, bacitracin, neomycin, penicillin, polymycin B, tetracyclines, biomycin, chloromycetin, and streptomycins, cefazolin, ampicillin, azactam, tobramycin, clindamycin and gentamycin; bacteriaphages; immunosuppressants; anti-viral substances such as substances effective against hepatitis; enzyme inhibitors; hormones; neurotoxins; opioids; hypnotics; anti-histamines; lubricants; tranquilizers; anti-convulsants; muscle relaxants and anti-Parkinson substances; anti-spasmodics and muscle contractants including channel blockers; miotics and anti-cholinergics; anti-glaucoma compounds; anti-parasite and/or anti-protozoal compounds; modulators of cell-extracellular matrix interactions including cell growth inhibitors and antiadhesion molecules; vasodilating agents; inhibitors of DNA, RNA, or protein synthesis; anti-hypertensives; analgesics; anti-pyretics; steroidal and non-steroidal anti-inflammatory agents; anti-angiogenic factors; angiogenic factors and polymeric carriers containing such factors; anti-secretory factors; anticoagulants and/or antithrombotic agents; local anesthetics; ophthalmics; prostaglandins; anti-depressants; anti-psychotic substances; anti-emetics; imaging agents; biocidal/biostatic sugars such as dextran, glucose, etc.; amino acids; peptides; vitamins; inorganic elements; co-factors for protein synthesis; endocrine tissue or tissue fragments; synthesizers; enzymes such as alkaline phosphatase, collagenase, peptidases, oxidases, etc.; polymer cell scaffolds with parenchymal cells; collagen lattices; antigenic agents; cytoskeletal agents; cartilage fragments; living cells such as chondrocytes, bone marrow cells, mesenchymal stem cells; natural extracts; genetically engineered living cells or otherwise modified living cells; expanded or cultured cells; DNA delivered by plasmid, viral vectors, or other means; tissue transplants; autogenous tissues such as blood, serum, soft tissue, bone marrow, etc.; bioadhesives; bone morphogenic proteins (BMPs); osteoinductive factor (IFO); fibronectin (FN); endothelial cell growth factor (ECGF); vascular endothelial growth factor (VEGF); cementum attachment extracts (CAE); ketanserin; human growth hormone (HGH); animal growth hormones; epidermal growth factor (EGF); interleukins, e.g., interleukin-1 (IL-1), interleukin-2 (IL-2); human alpha thrombin; transforming growth factor (TGF-beta); insulin-like growth factors (IGF-1, IGF-2); parathyroid hormone (PTH); platelet derived growth factors (PDGF); fibroblast growth factors (FGF, BFGF, etc.); periodontal ligament chemotactic factor (PDLGF); enamel matrix proteins; growth and differentiation factors (GDF); hedgehog family of proteins; protein receptor molecules; small peptides derived from growth factors above; bone promoters; cytokines; somatotropin; bone digesters; antitumor agents; cellular attractants and attachment agents; immuno-suppressants; permeation enhancers, e.g., fatty acid esters such as laureate, myristate and stearate monoesters of polyethylene glycol, enamine derivatives, alpha-keto aldehydes, etc.; and nucleic acids. 
     In certain embodiments, the bioactive agent may be a drug. In some embodiments, the bioactive agent may be a growth factor, cytokine, extracellular matrix molecule, or a fragment or derivative thereof, for example, a protein or peptide sequence such as RGD. A more complete listing of bioactive agents and specific drugs suitable for use in the present invention may be found in “Pharmaceutical Substances: Syntheses, Patents, Applications” by Axel Kleemann and Jurgen Engel, Thieme Medical Publishing, 1999; the “Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals”, Edited by Susan Budavari et al., CRC Press, 1996; and the United States Pharmacopeia-25/National Formulary-20, published by the United States Pharmacopeial Convention, Inc., Rockville Md., 2001. 
     In one embodiment of a covering comprising two compartments, a first growth factor may be provided for delivery by the first compartment and a second growth factor may be provided for delivery by the second compartment. The first and second growth factors may be provided with other substances. The first and second growth factors may be selected (and placed in respective compartment for positioning in vivo) based on desired characteristics of the growth factor. For example, an angiogenic growth factor may be provided in the first compartment and an osteoinductive growth factor may be provided in the second compartment. 
     Similarly, the substance delivered by the first compartment and the substance delivered by the second compartment may be selected based on desired characteristics of the compartment according to its placement in vivo. Thus, for example, one compartment may have a substance that is substantially osteoclast stimulating while another compartment may have a substance that is substantially osteoblast stimulating. 
     In one embodiment, demineralized bone fibers may be provided in the first compartment and surface demineralized bone chips may be provided in the second compartment. In this embodiment, the demineralized bone fibers may generally provide osteoinductive characteristics and the surface demineralized chips may generally provide osteoinductive and/or osteoconductive characteristics. In use, the covering may be laid flat on the transverse process and positioned such that the first compartment, holding the demineralized bone fibers, is nearest the vertebral body and the second compartment, holding the surface demineralized bone chips, is farther from the vertebral body, or the compartments may be positioned in any other desired configuration. In another embodiment, a covering may comprise first and second compartments wherein autograft may be placed in one of the compartments prior to placement of the covering in vivo, described more fully below. In other embodiments, three or more compartments may be used, as appropriate for the materials being delivered and the application of the compartmented implant. More than one substance may be provided in a compartment. For example, surface demineralized bone chips and demineralized bone fibers may be mixed and provided within a single compartment. Such mixture of substances within a single compartment may be a substantially uniform mix or may be a plurality of substances placed in the compartment separately such that they are substantially unmixed. When multiple compartments are used, each compartment may contain one or more substances. Exemplary substances that may be provided in one or more compartments of the delivery system include cells from the osteogenic precursors, growth factors, angiogenic factors and other active proteins including bone morphogenic proteins, and cellular scaffolding materials of natural or synthetic origin, antibiotics, and other substances described below. 
     In some embodiments, other medical devices may be provided within the covering. For example, one or more electrical stimulator electrodes may be provided within the covering. 
     Generally speaking, any suitable substance or material may be delivered using coverings as provided herein. Such substances may include bone, cartilage, tendon, ligament, muscle, skin, nerve, collagen, calcium sulfate (CaSO 4 ), calcium phosphate (CaPO 4 ), betaTCP, hydroxyapatite, bioglass, silicon-containing calcium phosphates, cells, autograft, or other. 
     Particulate Substance 
     In some embodiments, a particulate substance may be delivered by the covering. For example, the covering may be used to delivery a particulate bone graft. 
     Growth Factors or Other Active Substances 
     Growth factors or other active substances may be delivered by the covering. Active substances may include, for example, growth factors such as BMP-2 (Infuse) and/or other growth proteins, as well as drugs, antibiotics, etc. In some embodiments, a carrier for the growth factors or other active substances may be incorporated into the delivery system. Thus, for example, as shown in  FIG. 24   h , a carrier  1400  such as a collagen sponge or collagen fibers may be provided. The carrier  1400  may be loaded with growth factors or other active substances. The loaded carrier  1400  then may be placed in the covering. 
       FIG. 24   i  illustrates an example embodiment of a covering  1402  with such carrier  1400 . As shown, a covering  1402  is provided comprising three compartments: a central covering  1404  and first  1406  and second lateral coverings  1408 . In one embodiment, the central covering  1404  receives a carrier  1400  such as shown in  FIG. 24   h  and the lateral coverings  1406 ,  1408  include a material such a osteoconductive and/or osteoinductive material such as DBM. Such embodiment may be used for, for example, spinal fusion. In further embodiments, additional coverings may be included. Such additional coverings may be filled with, for example, DBM, a calcium phosphate, a polymer, a combination material, an osteoconductive material, and/or an osteoinductive material. While a multi-compartment covering is shown, it is to be appreciated that a carrier may alternatively be used in a single compartment embodiment. 
     V. Sterilization 
     The delivery system, including covering and substances for delivery, may be terminally sterilized. Sterilization may be done using any technique now or later known including, for example, gamma radiation, electron beam radiation, UV, cobalt source radiation; autoclaving, dry heat, and by supercritical fluids. 
     Further, in various embodiments, an portion of the delivery system, such as the covering of the substance for delivery by the covering may be separately sterilized prior to assembly of the delivery device. Different sterilization methods can be used for different parts of the delivery system. Thus, the sterilization method used may be customized for the materials of the portion of the system being sterilized. For example, a synthetic calcium phosphate filler may be sterilized using radiation while a resorbable polymer covering may be sterilized with EtO or EtOH. Further, only some portions of the delivery system maybe sterilized. 
     Generally, in some embodiments, the delivery system (assembled and filled covering; placed in final packaging) may be processed under aseptic conditions from sterile components. Such processing results in a sterile delivery system without a terminal sterilization step. 
     VI. Kit and Tools 
     In some embodiments, kits may be provided with a plurality of differently sized or differently shaped coverings. For example, a kit may comprise a set of bag-shaped coverings of different sizes or a set of tubular coverings of different sizes. In some examples, kit sizes may be, for example, a small covering (such as sized for fitting in the medullary cavity in a fibula), a medium covering (such as sized for fitting in the medullary cavity in a humerus), and a large covering (such as sized for fitting in the medullary cavity in a tibia or femur). The kits may be provided for specific procedures or for different vertebral levels (for example, a single level kit or a multiple level kit, as in spinal surgery), or for use in unilateral or bilateral procedures. In some embodiments, a kit for a given level may have a bag-shaped covering and a tubular covering such that the surgeon may choose the appropriate covering for the procedure based on evaluation of the disc space. The coverings may be pre-filled in the kit or may be provided empty or partially empty for filling by the surgeon. In some embodiments, the coverings may be individually packaged in a kit. 
     In some embodiments, a kit may include osteoconductive materials and osteoinductive materials for mixing and placing into the covering at the time of surgery. The kit may include a drug such as an antibiotic, analgesic, anabolic, bisphosphonate, growth factor, cells or instruments to procure and optionally concentrate cells, in addition to its other components. Trial implant(s) may be provided in some embodiments included to facilitate sizing of the site to be filled by the covering and its contents. In further embodiments, a kit may contain instrumentation (disposable or re-usable), sutures, attachment implants, etc. to prepare, fill, deliver and attach the coverings to the surgical site. For example, with the kit may include one or more tools for placing the covering. These may include, for example, a cutter, a caulker or insertion tool, an assessment tool, or other tool. 
     In one embodiment, a cutter/sealer tool may be provided to manipulate the size of a covering. For example, using a covering comprising a tube, the tube may be cut and sealed for specific sizes. In alternative embodiments, the tube may be cut and left open. In yet alternative embodiments, the tube may be cut and sutured. In some embodiments, the cutter may be a gastrointestinal cutter. 
     In further embodiments, an assessment tool may be provided for assessing the area in which the covering is to be placed. Thus, for example, the assessment tool may provide a general measurement of the space for receipt of the covering such that an appropriately sized covering may be selected and/or an appropriate amount of graft material may be placed in the covering. Such assessment tool may be, for example, a balloon device. In some embodiments, the balloon device may be coupled to a fluid source and may be radiopaque. Thus, under visualization, the balloon may be inflated (such as by delivery of fluid into the balloon) until the balloon fills the space. A correlation then may be made between the amount of fluid used to fill the balloon and the available space for the covering and graft. 
     Tools 
     Various insertion tools (also referred to as delivery devices) may be used with coverings provided herein. Such insertion tools may include, for example, a delivery gun, a scraper, an injector instrument, or other suitable tool. Such tools may be provided separately or may be provided as part of a kit. 
     In some embodiments, an insertion tool such as a delivery gun  900 , as shown in  FIG. 25 , may be provided. For example, a delivery device may comprise a chamber  904  terminating in a discharge opening  908 , and a trigger  906 . The chamber  904  may be configured to receive a covering, such as a tubular covering. Accordingly, the chamber  904  may be sized and shaped to compliment a specific covering configuration. In one embodiment, the chamber  904  is configured to receive a tubular covering that is approximately 0.5 cm in width. In other embodiments, the chamber may be configured to receive one or more coverings of any size or shape. The chamber terminates in a discharge opening  908  for delivery of the covering. The chamber may be tilted or angled to facilitate entry into the disc space. In some embodiments, a portal tube  902 , such as used for minimally invasive procedures, may be attached to the discharge opening. Alternatively, as shown in  FIG. 25 , the discharge opening  908  may be formed into a portal tube  902 . In various embodiments, the discharge opening or the end of the portal tube may be radiopaque to facilitate visualization during placement. 
     In some embodiments, the insertion tool may be pre-loaded, for example, with one, two, three or more coverings provided in the chamber. In other embodiments, the insertion tool may be provided empty and may be loadable by the surgeon. In some embodiments, the insertion tool may have a removable tube for loading. Thus, for example, a covering may be placed in the removable tube and the tube placed in the chamber. In some embodiments, the tube may be formed of sterile plastic. In some embodiments, a covering for placement in the tube may comprise several short lengths of tube connected together. The covering, with graft material therein, may be pre-wetted for malleability before placement in the delivery gun. In some embodiments, a covering for placement using the delivery gun, as shown in  FIG. 25 , may include a radiopaque tip. 
     In a further embodiment, an insertion instrument may be provided suitable for use in minimally invasive surgeries and thus configured, for example, to go through a portal for minimally invasive surgery. Thus, for example, the delivery gun  500  may have a nozzle  502  configured for interfacing with such portal. 
       FIG. 26   a  illustrates a tamper insertion tool  520 . As shown, the insertion tool  520  includes a handle  522 , an elongated body  524 , and an insertion head  526 . The elongated body  524  and the insertion head  526  may be disposable. Alternatively, the insertion head  526  may be disposable. As shown, a suture retainer mechanism  528  is provided proximally on the elongated body.  FIG. 26   b  illustrates an embodiment of a covering  500  that may be inserted using the tamper insertion tool  520 . As shown, the covering  500  is generally elongated and has sutures  530  at each end thereof.  FIG. 26   b  illustrates the insertion head  526 , the suture retainer mechanism  528 , and a portion of the elongated body  524  of the tamper insertion tool  520  with the covering  500  placed thereon for insertion. As shown, the covering  500  may be folded over the insertion head  526  with the sutures  530  extending proximally and through the suture retainer mechanism  528 . The sutures  530  create tensioning of the covering  500  and retain the covering  500  in a desired position on the insertion head  526 . 
       FIGS. 26   c - 26   h  illustrate insertion of a covering using the tamper insertion tool of  FIGS. 26   a  and  26   b . It is to be appreciated that these Figures are for illustration of use of the tool only and are not intended to be limiting. As shown, a disc space  340  between first  342  and second vertebral bodies  344  is prepared with a TLIF opening  346 . Generally, the disc space  340  may have a height of approximately 10 mm to approximately 14 mm and the TLIF opening  346  may have a height of approximately 7 mm. The covering, in a wet and compressed condition folded over the insertion tool  520 , may fit through the TLIF opening  346 .  FIGS. 26   d  and  26   e  show the covering  500  inserted into the disc space  340  by inserting the insertion head  526  of the insertion tool  520  through the TLIF opening  346 . As shown, the sutures  530  extend proximally from the opening.  FIGS. 26   f - 26   h  illustrate the covering  500  pushed anteriorly in the disc space  340  using the insertion tool  520 . The insertion tool  520  pushes the covering  500  and compresses/shapes the covering  500  in another direction such that the covering  500  contacts the endplates  532 . The covering  500  may be pressed to the end plates  532  of the disc space  340  to form and fill the height of the disc space  340 . As shown, the sutures  530  remain extending proximally from the disc space  340 . After the covering  500  is in place, the sutures  530  may be pulled out and removed. In some embodiments, further coverings may be inserted after each covering is placed. It is to be appreciated in this and similar embodiments that the term “suture” is intended to refer to any filament or like structure useful for facilitating handling of the covering. 
     In yet a further embodiment, shown in  FIG. 27   a , an insertion instrument  500  may comprise a tubular insertion instrument  502  and associated plunger  504 . The tubular insertion instrument  502  includes a chamber  506 , a plunger receiving end  508 , and a discharge opening  510 . The chamber  506  may have a diameter approximately equal to the diameter of a covering to be placed by the insertion instrument  550 . In some embodiments, the chamber  506  may taper along a channel  512  towards the discharge opening  510  to form the covering to fit into a specific incision or defect. The chamber  506  thus may include a loading area (into which it is initially placed) and a form area  514  (in which it is compressed into an appropriate configuration). Thus, for example, the channel  506  may taper to an oval shape cross section in the form area  514  with the discharge opening  510  being formed in the oval shape.  FIG. 27   b  illustrates the change in the covering before placement in the tool and after delivery from the tool. A covering  500  is shown before placement  580  in the tool  550  and having a generally round diameter of approximately 14 mm. The covering  500  after placement in and delivery  584  from the tool and having an ovoid cross section approximately 7 mm high and 12 mm wide is also shown. Any suitable dimensions, however, may be used. 
       FIGS. 27   c - 27   f  illustrate insertion and expulsion of a covering into and from the insertion instrument. As shown in  FIG. 27   c , a covering  500  may be inserted in the chamber  506 . In the embodiment shown, the covering  500  is slip fit into an appropriately sized opening in the plunger receiving end  508  of the tool. In other embodiments, the covering may be inserted into the chamber through the discharge opening  510 , by opening the chamber (for example, where the chamber has hinged walls), or other. A plunger  504  may be inserted in the plunger receiving end  508  of the insertion instrument  502  and used to compress the covering toward the form area  514 , shown in  FIG. 27   d . The insertion instrument may be positioned such that the discharge opening  510  is at or proximate a location for the covering  500  and the plunger  504  further used to expel the covering  500  from the discharge opening  510 , shown in  FIG. 27   e . The covering  500 , as expelled from the discharge opening  510 , generally has the cross sectional shape of the discharge opening  510 .  FIG. 27   f  thus shows the covering  500  being inserted in the disc space  340 . 
     In further embodiments, a scraper insertion tool may be provided in some embodiments. Such scraper may have a length and a width. Generally, the width may be selected to minimize the possibility of puncturing a covering with the insertion tool. A first end of the insertion tool may comprise a nose. The nose may be configured for contacting the covering and thus may have a width slightly more than the width of the remainder of the tool. 
     In some embodiments, two insertion tools may be provided, the first being substantially straight or linear and the second being curved. 
     VII. Method of Use 
     The covering delivers the substance or substances in vivo. Such delivery may be active, passive, by diffusion, or other. Active delivery may include the degradation or decomposition of the covering with the interaction of body fluids, extracellular matrix molecules, enzymes or cells. It may also include the cleavage of physical and/or chemical interactions of substance from covering with the presence of body fluids, extracellular matrix molecules, enzymes or cells. Further, it may comprise formation change of substances (growth factors, proteins, polypeptides) by body fluids, extracellular matrix molecules, enzymes or cells. 
     The covering is loaded with the substance for placement in vivo. The covering may be pre-loaded, thus loaded at manufacture, or may be loaded in the operating room or at the surgical site. Preloading may be done with any of the substances previously discussed including, for example, DBM, synthetic calcium phosphates, synthetic calcium sulfates, enhanced DBM, collagen, carrier for stem cells, and expanded cells (stem cells or transgenic cells). Loading in the operating room or at the surgical site may be done with any of these materials and further with autograft and/or bone marrow aspirate. 
     Any suitable method may be used for loading a substance in the covering in the operating room or at the surgical site. For example, the substance may be spooned into the covering, the substance may be placed in the covering using forceps, the substance may be loaded into the covering using a syringe (with or without a needle), or the substance may be inserted into the covering in any other suitable manner.  FIG. 28  illustrates loading the covering  110  with a syringe  112 . As shown, in some embodiments, the covering  110  may include a port  114  or other structure for receiving the syringe  112  or similar instrument. Specific embodiments for loading at the surgical site include for vertebroplasty or for interbody space filler. 
     For placement, the substance or substances may be provided in the covering and the covering placed in vivo. The covering may be delivered using any of the insertion tools provided herein or may be otherwise delivered. In one embodiment, the covering is placed in vivo by placing the covering in a catheter or tubular inserter and delivering the covering with the catheter or tubular inserter. The covering, with a substance provided therein, may be steerable such that it can be used with flexible introducer instruments for, for example, minimally invasive spinal procedures. For example, the osteoimplant may be introduced down a tubular retractor or scope, during XLIF, TLIF, or other procedures. In other embodiments, the covering (with or without substance loaded) may be placed in a cage, for example for interbody fusion. In some embodiments, the covering may be wet prior to placement. Wetting of the covering may enhance manipulability and/or flexibility of the covering. Wetting may be done using, for example, water, blood, marrow, saline, or other fluid. The covering may be delivered using any of the insertion tools provided herein or may be otherwise delivered. 
     In continuous tube embodiments, the surgeon may divide the tube into the desired number of compartments, using a crimper, heat tool, or other.  FIG. 20 , previously discussed, illustrates an embodiment of a tubular covering  120  partially divided into compartments  122 . As shown, the tubular covering  120  includes a further portion  124  that may be divided into compartments. After subdivision into compartments  122 , one or more compartments  122  may be removed from the tube  120  for implantation. Alternatively, in an embodiment wherein the tube is perforated into a plurality of compartments, the surgeon may select the number of compartments desired and cut along the applicable perforation. In some embodiments, some of the compartments may be pre-filled with a substance for delivery and other compartments may be empty for filling by the surgeon. For example, ever other compartment between perforations may be preloaded or filled. The osteoimplant thus may be customized by filling the empty compartments with a desired substance. 
     For example, in some embodiments, a portion of the covering for example, one compartment of a multi-compartment covering, may be filled with autograft. Thus, the covering may be substantially empty prior to surgery. During surgery, a surgeon may remove autograft from the patient and place the autograft in the substantially empty compartment. Such placement may be done in any suitable manner. In one embodiment, the covering may be provided with a port for receiving an opening of an injection device and the autograft may be injected into the covering. Alternatively, the autograft may be mixed with allograft, synthetics, or any other desired substances or combination of substances. 
     Attachment mechanisms provided on the covering may be used to couple the covering to a site in vivo. 
     VIII. Applications 
     Coverings and delivery systems as provided herein may be used in any suitable application. In some embodiments, the covering and associated delivery system may be used in spinal interbody fusion, posterolateral fusion, healing of vertebral compression fractures, minimally invasive procedures, correction of adult or pediatric scoliosis, treatment of long bone defects, treatment of osteochondral defects, ridge augmentation (dental/craniomaxillofacial, e.g. edentulous patients), beneath trauma plates, treatment of tibial plateau defects, filling of bone cysts, wound healing, around trauma, contouring (cosmetic/plastic/reconstructive surgery), and others. Generally, delivery systems such as provided herein may be used in bone or hard tissue applications as well as soft tissue applications including plastic and reconstructive surgery. The delivery system may be used in a minimally invasive procedure via placement through a small incision, via delivery through a tube, or other. The size and shape of the covering and associated delivery system may be designed with restrictions on delivery conditions. 
     Spinal Fusion 
     One application for using a delivery system as disclosed is fusion of the spine. Spinal fusion is a surgical procedure used to combine two or more vertebrae. It involves adding bone graft or bone graft substitute to an area of the spine to set up a biological response, which causes the bone to grow between the two vertebral elements and thereby stop motion at that segment. Spinal fusion may be used to eliminate pain caused by motion of the vertebrae, or compression of the disc space, by immobilizing the vertebrae themselves. 
     Spinal fusion may generally be done in, for example, the lumbar, cervical, or thoracic areas of the spine. Patients with the following conditions, for example, may require spinal fusion: degenerative disc disease, spinal disc herniation, discogenic pain, spinal tumor, vertebral fracture, scoliosis, kyphosis, spondylolisthesis, spondylosis, posterior rami syndrome, other degenerative spinal conditions, or any other condition that causes instability of the spine. 
     Generally there are two main types of lumbar spinal fusion that may be used together or separately: posterolateral fusion and interbody fusion. Posterolateral fusion inserts the bone graft between the transverse processes in the back of the spine. Generally, the vertebrae may then be fixed in place with screws and/or wire through the pedicles of each vertebra, for example, that attach to a fixation device on each side of the vertebrae. In some embodiments, a covering such as provided herein may form such fixation device or may attach to such fixation device. Interbody fusion comprises inserting the bone graft in the intervertebral space. Prior to spinal fusion, the disc is removed to open the disc space for such bone graft. A delivery system as provided herein may be placed between the vertebra to maintain spine alignment and disc height and to help the fusion process. The fusion occurs between the endplates of the vertebrae. If both types of fusion are used together, it is known as a 360-degree fusion. 
     In clinical use, a delivery system comprising a covering and delivered substance may be used in any type of spinal fusion procedure including, for example, posterolateral fusion, interbody fusion (of any type), facet fusion, spinous process fusion, anterior only fusion, or other fusion procedure. The covering and delivered substance may be used, for example, to bridge the gap between the transverse processes of adjacent vertebral bodies. The delivery system may also be used to bridge two or more spinal motion segments. Generally, the delivery system may be used in other fusion procedures. For all fusion procedures, the covering may surround the substance to be implanted, and contain the substance to provide a focus for healing activity in the body. The covering generally retains the substance in appropriate position and substantially prevents migration of the substance from the fusion site (referred to as graft migration). 
     All spinal fusion techniques described below may be conducted using fixed protective tubes to protect surrounding neurological and vascular structures, known as minimally invasive procedures, or through an unprotected open procedure. The discussed techniques and procedures may be done using mini-open, endoscopic, or minimally invasive techniques using different parameters including, for example, incision size, location, and instruments. Variation of such parameters is within the skill of someone skilled in the art. Discussion of any non-minimally invasive techniques for such procedures thus is not intended to be limiting. 
     Posterior Lumbar Interbody Fusion (PLIF) 
     In one application, the covering and delivery system may be used in posterior lumbar interbody fusion (PLIF). According to this technique, the vertebrae are reached through an incision in the patient&#39;s middle back, which allows direct access to the area being treated. In this procedure, prior to surgery visualization may be performed to determine the size of the area to be treated. A 3-6 inch incision is made in the back of the patient and the spinal muscles are retracted, or separated, in order to access the vertebral disc. A laminectomy is performed to provide visual and physical access to the nerve roots. In some cases, the facet joints that lie directly over the nerve roots may be trimmed to create more room for the nerve roots. The affected disc and surrounding tissue is removed. The bone surfaces of the adjacent vertebrae are prepared for fusion. After preparation of the disc space, the delivery system may be implanted. 
     The delivery system of the present invention in one embodiment may include a covering with a cartridge covering for placement in an interbody fusion cage for a PLIF procedure. In use, coverings may be placed into the interbody space and cages placed thereafter. In some embodiments, the coverings may be configured as, for example, small tubes or small bags. The interbody fusion cage may be any suitable cage, such as one suitable for PLIF, may have any suitable dimensions, and may be made of any suitable material. The containment area(s) of the cage may be filled with a covering and substance as provided herein and may also be filled with bone graft, allograft, BMP or other suitable material to promote fusion between the vertebrae. Additional instrumentation may be used, such as rods, screws, wires or the like to further stabilize the spine. For a standard PLIF procedure, the bone graft and/or instrumentation is performed on both sides. 
     Transforaminal Lumbar Interbody Fusion (TLIF) 
     In another application, the covering and delivery system may be used with transforaminal lumbar interbody fusion (TLIF), which is a refinement of PLIF. TLIF fuses the anterior and posterior columns of the spine through a single posterior approach. The anterior portion of the spine may be stabilized by a bone graft and an interbody spacer, whereas the posterior column may be locked in place with a cage and/or pedicle screws, and/or rods, and bone graft. Only one side of the back is accessed and affected in TLIF. Accordingly, TLIF involves approaching the spine through a midline incision in the back of the patient using a transforaminal approach that is both posterior and lateral. 
     Using this approach may reduce the amount of surgical muscle dissection needed and may also minimize the nerve manipulation required to access the vertebrae, discs and nerves. As with PLIF, disc material is removed from the spine and may be replaced with the delivery system of the present disclosure. 
     One difficulty to be overcome in the TLIF procedure is the poorer ability to visualize and prepare the endplates, and to place grafting material properly. Generally, minimally invasive surgical procedures have not been widely used for TLIF because it can be difficult to place a graft in suitable position for the procedure. A portal opening for a TLIF procedure generally ranges from approximately 10 mm to approximately 20 mm, with 16 mm being an acceptable average. Coverings such as provided herein facilitate insertion using minimally invasive techniques. The covering may be sized specifically for the procedure. Further, the covering substantially retains graft material in position and, thus, reduces any chance of the material falling into interbody space. 
     In one embodiment, as shown in  FIG. 29 , a tubular covering  500  may be provided with pre-tied sutures  330  at both ends for ease of placement. In some embodiments, the sutures may be radiopaque to facilitate visualization of the ends of the covering. In one embodiment, a tab may be provided on an end of the covering and the suture provided through the tab. In some embodiments, the sutures may be removed after placement of the covering or prior to placement if not desired. To place such a covering, an insertion tool may be pressed midway on the length of the covering with the covering folded about the end of the insertion tool. The sutures may be pulled proximally (towards the surgeon) to facilitate bending of the covering. The covering thus is in a generally U-shape over the insertion tool. The insertion tool, with covering folded thereover may be inserted through a portal into an access portion and then further into the disc space. The sutures then may be pulled out while holding the insertion tool and covering in position. The insertion tool may be used to direct the covering in an anterior and lateral direction. In some embodiments, the covering may be cut and crimped to customize the size of the covering. 
     As shown in  FIGS. 30   a  and  30   b  from the anterior aspect or surgical approach direction, an elongated covering  600  may be folded into a U-shape  604  or an L-shape  602  and placed into the surgical site  606  with one or both ends of the covering  600  protruding. As shown in  FIGS. 31   a  and  31   b , a cage  200  containing graft  608  may be placed over the top of the folded covering  600 . In an alternate embodiment, the ends may be folded over the exposed surface of the cage  610 . The surgical site then may be closed as known by those skilled in the art. In yet another embodiment, the covering may be used without a cage, as long as a structural member, such as a cervical plate for example, is used in conjunction with the covering. It is to be appreciated that this approach, using a covering folded over an insertion tool, may be useful in any of several interbody approaches including, at least, ALIF and PLIF as well as TLIF. 
     In one embodiment, a covering is at least partially wrapped around a cage. In some embodiments, the covering may be sutured or otherwise fixed to the cage. The cage, with the covering wrapped therearound, is impacted into the vertebral space. In some embodiments, the cage with the covering wrapped therearound may be placed through a minimally invasive cannula/portal system. 
     In another embodiment, the covering (for example a tubular or generally cylindrical covering) may be placed as a first implant and a fusion device, such as a cage, may be placed as a second implant. This order facilitates placing of implants in the proper location. 
     In a further embodiment, a covering configured as a tube may be placed into the disc space with a leading end first directed into the disc space. The covering may then be packed into the disc space. To place the covering, the covering may be provided in a tubular insertion tool. Such insertion tool may have a diameter approximately matching a diameter of the covering. The insertion tool may be placed into a minimally invasive portal for accessing the disc space. A plunger mechanism may be used to expel the covering from the insertion tool. In some embodiments, a single covering may be placed using the insertion tool. In other embodiments, a plurality of coverings, for example, generally smaller coverings, may be placed in a single procedure using the insertion tool. 
     In another embodiment, as shown in  FIGS. 32   a - 32   e , the site to be treated comprises two vertebral bodies  620  and an intervening disc  622 , and an annulus covering. A partial or complete discectomy is performed to prepare the site  628 , and the lip of the vertebra  624  is removed. The covering containing graft material  626  is placed into the site  628  against the opposing surface  630 . The opposing surface  630  may be remaining disc material, annulus, or other graft. The covering  626  may be packed with graft material at a relatively low density to facilitate manipulation and shape changing without significant deformation of the covering. The graft-containing covering (or delivery system)  626  may be placed manually or with an instrument, such as a bone tamp, or other suitable instrument, and adjusted until it conforms to the surgical site. 
     In another embodiment, one or more coverings may be inserted into a cage. For example, two tubular coverings may be inserted into a TLIF cage. In some embodiments, such coverings may be approximately 2.5 cm long and approximately 0.5 cm wide. As discussed previously, the interbody fusion cage may be any suitable cage, such as one suitable for TLIF, may have any suitable dimensions, and may be made of any suitable material. 
     In embodiments wherein the covering is manually positioned in the disc space, the surgeon may percutaneously feed a needle or suture passed through from the contra-lateral side to the TLIF side, sew the covering onto the suture and pull the suture to the other side. This can ensure that the covering extends to the contra-lateral side. 
     In an alternative embodiment, a covering with graft material provided therein may be delivered using a pre-loaded gun delivery device such as described with respect to  FIG. 25 . Such delivery device may facilitate delivery of the covering to the contra-lateral side. 
       FIGS. 32   f  and  32   g  illustrate a curved covering  1320  used in a TLIF procedure.  FIG. 32   f  illustrates a curved covering  1320  in an insertion tool or device  1322 . As shown, in a TLIF procedure, a shaping or reinforcing structure  1324  of the curved covering  1320  may extend out of and interface with an insertion tool or device  1322 .  FIG. 32   g  illustrates a curved covering  1320  inserted through a TLIF entrance  1326  with the reinforcing  1324  extending proximally therefrom. The shaping or reinforcing structure  1324  facilitates positioning of the covering  1320  maintaining the covering  1320  in a curved configuration. After placement of the covering  1320 , the shaping or reinforcing structure  1324  may be removed with the covering  1320  or left in place. 
     After placement of the covering and/or cage, free space in the disc space may be filled with further coverings such as small bag coverings or small tube coverings. 
     Suitable coverings for use in TLIF procedures may be, for example, tubular coverings having dimensions of approximately 5 cm long and approximately 0.5 cm wide. 
     The space that is filled in a TLIF procedure is generally about 20 mm×25 mm×7 mm. Thus, for example, the covering may be filled with approximately 3.5 cc of graft material. 
     Anterior Lumbar Fusion (ALIF) 
     In another application, the covering and delivery system may be used with an anterior lumbar fusion (ALIF) procedure. Whereas PLIF and TLIF access the spine via the patient&#39;s back, ALIF approaches the spine from the front of the patient&#39;s body. Generally, a 3-5 inch incision is made in the lower abdomen, or the side of the patient. In some cases it may be necessary to cut through the muscles of the lower abdomen, which would require later repair. The abdominal muscles and blood vessels may be retracted in order to access the vertebrae. The disc and disc material may then be removed. As with PLIF and TLIF, an embodiment of the present disclosure may be inserted in the space where the disc and disc material were. 
     In various embodiments, the covering or delivery system may be customized for spinal fusions. For example, for ALIF procedures, a covering configured as a bag may be provided that is sized slightly lager than the cavity of a cage for use in the fusion surgery. In some embodiments, a kit for ALIF procedures may be provided including three differently sized coverings. Generally, the covering may be larger than approximately 1 cm×1 cm. 
     In one embodiment, a first covering may be placed in the a cavity of the cage and graft material inserted into the covering. Second and third coverings then may be placed on each side of the first covering to fill the cavity. In some embodiments, a plurality of coverings of different sizes may be provided such that a surgeon may select appropriately sized coverings for the procedure. 
     In a further embodiment, a first covering may be positioned against the annulus posteriorly. The covering may be, for example, a tubular covering sized approximately 5 cm in length and approximately 0.5 cm in width. A cage may be filled with a graft material and inserted into the disc space. In alternative embodiments, the cage may be filled with a delivery system as provided herein. A second covering may be placed on one side of the cage and a third covering placed on the other side of the cage. The second and third coverings may be configured generally the same as the first covering or may be configured differently. In some embodiments, ends of the second and third coverings may be tucked into the disc space laterally of the cage. The cage and coverings may be impacted into the disc space. In some embodiments, a fourth covering may be placed in front of the cage. In some embodiment, an additional covering may be placed over the first covering before placement of the cage. As may be appreciated by those skilled in the art, in an ALIF procedure, the anterior annulus may be split and sutured back together after placement of the cage and covering(s). 
     In yet a further embodiment, a curved covering may be used for an ALIF procedure.  FIGS. 32   h  and  32   i  illustrate a curved covering  1330  inserted via an ALIF procedure. As shown, the curved covering  1330  has the form of a curve and thus complements the curve of the anterior endplate  1332 . The curved covering  1330  may be in a curved configuration by provision of a shaping or reinforcing structure  1334 . 
     Antero-Lateral IBF Approach (XLIF Approach) 
     In another embodiment, the covering and delivery device may be used in an extreme lateral interbody fusion (XLIF). XLIF involves a minimally invasive approach to the anterior spine that avoids an incision that traverses the abdomen and also avoids cutting or disrupting the muscles of the back. In XLIF, the disc space is accessed from a very small incision, for example approximately 1-3 inches, on the side or flank of the patient. Another small incision, for example approximately 1 inch long, may be made just behind the first incision. Retractors and a fluoroscopy machine may be used to provide real-time visualization of the spine. Special monitoring equipment may also be used to determine the proximity of the working instruments to the nerves of the spine. The disc material is removed from the spine. An embodiment of the present disclosure may be inserted in the space where the disc and disc material were. 
     For XLIF approaches, the covering may comprise a tube and may be used with a vertebral cage. In one embodiment, the covering  601  may comprise a tube having a generally flat central section  602 , as shown in  FIGS. 33   a  and  33   b . The generally flat central section  602  facilitates conformation of the covering  601  around an interbody graft. The covering may be, for example, approximately 5 cm in length. 
     In use, a covering may be placed generally on top of the disc space and a cage may be placed on top of the covering. In some embodiments, the covering may be tubular. The cage, positioned over the covering, may be pushed into the disc space. The covering thus is positioned generally in front of, in back of, and to the contra-lateral side of the cage. In an alternative positioning, the covering may be guided into the interbody space with a first end leading. 
     In a further embodiment, a covering for XLIF procedures may comprise a tubular covering subdivided into a plurality of smaller covering tubes. Radiopaque markers may be provided along the covering to aid in placement. 
     AxiaLIF 
     In yet other embodiments, the delivery system may be used in AXIALIF, using a Trans 1 system. Such procedure is described, for example, at http://www.trans1.com/axiaLif_axiaLif_technology.html and enters near the top of the coccyx for an L5-S1 fusion. The technique involves accessing the lumbar spine through a percutaneous opening adjacent to the sacral bone, alleviating the need for the surgeon to cut through soft tissues like muscles and ligaments. 
     Minimally Invasive Posterolateral Fusion 
     In a further embodiment, the delivery system may be used with a posterolateral fusion operation. In contrast to PLIF, a posterolateral fusion operation keeps the disc space intact and the bone graft or cage is placed between the transverse processes in the back of the spine. In the posterolateral fusion operation the bone may heal and stabilize the spine from the transverse process of one vertebra to the transverse process of the next vertebra. A smaller incision may be used to make the posterolateral fusion minimally invasive. After the small incision, for example approximately 3 cm, is made in the patient&#39;s lower back, the muscles surrounding the spine may be dilated in order to permit access to the section of the spine to be stabilized. The lamina is facilitate visualization of the nerve roots to be seen. The facet joints may be trimmed to give the nerve roots more room. A covering and associated delivery system as provided herein may be laid between the transverse processes in the back of the spine. 
     In one embodiment the tension band and covering illustrated in  FIG. 14   a  or  14   b  may be used for posterior lateral fusion procedures. 
     In a further embodiment, a facet fusion covering may be provided, as shown in  FIGS. 34   a - 34   e . The facet is a small joint in the posterior of the spine and is part of the articulation of vertebral bodies. A covering such as provided herein may be attached to the upper vertebra and drawn down into/between the prepared fact joint.  FIG. 34   a  illustrates a facet fusion joint  702 , the two vertebra bodies  620 , and the disc  622 .  FIG. 34   b  illustrates a covering  600  comprising a generally square covering  650  and having an attachment mechanism  652  on one end thereof. In the embodiment shown, the attachment mechanism  652  may be a tab  654  with thru holes  656  for receiving screws  658 .  FIGS. 34   c ,  34   d , and  34   e  illustrate the covering  600  bridging the facet joint  702 . Extra sutures may be used to aid in contact of the covering across the joint. 
     A further embodiment may comprise a covering that may be fixed in place using a facet screw to bridge a facet joint for fusion. 
     Posterior Cervical Approach 
     In another embodiment, a covering and associated delivery system may be used with a posterior cervical fusion procedure. This procedure approaches the spine through the back of a patient&#39;s neck. The procedure involves joining two or more neck vertebrae into one solid section of bone. The procedure is generally performed to remedy neck fractures and dislocations and to remedy deformities in the curve of the neck. The patient lies face down during the procedure. An incision may be made down the middle of the back of the neck. Retractors are used to separate and hold the neck muscles and soft tissues apart to provide a space for the surgeon to work. A layer of bone may be shaved from the surface of the lamina of each vertebra that will be fused in order to stimulate healing. A covering as provided herein may be laid over the back of the spinal column. 
     As shown in  FIGS. 35   a - 35   d , one or more coverings may be placed adjacent lateral mass screws in the posterior cervical spine.  FIG. 35   a  shows generally where an incision  670  for this procedure may be located.  FIGS. 35   b - 35   d  illustrate the spine stabilized after the procedure using different embodiments. 
       FIG. 35   b  illustrates a covering that may be used, for example, to delivery antibiotics or other materials to the site but that does not span the vertebrae. As shown, the covering  672  is provided generally around the sides of the lateral mass screw  676 . 
       FIG. 35   c  illustrates an embodiment comprising two coverings placed on either side of two or more lateral mass screws. As may be seen, a first covering  671  may be placed on one side of the lateral mass screws  676  and a second covering  673  may be placed on the other side of the lateral mass screws  676 . The first covering  671  and the second covering  673  may be fixed to the vertebrae and/or may be fixed to one another. In the embodiment shown, the first covering  671  and the second covering  673  are fixed together via sutures. 
       FIG. 35   d  illustrates a further embodiment comprising a single covering  675  folded into a U-shape around the lateral mass screws  676 . 
     In some embodiments, the coverings may be tubular and may have dimensions of approximately 5 mm to approximately 10 mm long and approximately 0.5 cm to 1 cm wide. The tubular coverings may be substantially flat or may be substantially round in cross section. In some embodiments, the covering may be sutured or screwed to substantially fix the covering in place. It is to be appreciated that these dimensions are for the purposes of illustration only and other dimensions may alternatively be used. 
     Posterior Lumbar Fusion 
     In another embodiment, the covering and associated delivery system may be used with a posterior lumbar fusion procedure. Posterior lumbar fusion is a general term referring to a surgical procedure where two or more lumbar spine bones are fused together along the sides of the bone. Bone graft is placed along the side of the spine bones, as opposed to between the disc spaces as with interbody fusion. This procedure is performed through an incision in the lower middle of the back, which reaches to the spinous processes (the bony projections off the back of the vertebrae). The incision may be, for example, approximately 4-8 cm. The tissues and small muscles along the side of the low back are separated and lifted off of the vertebrae in order to expose the target area. A laminectomy may be performed. Prior to fusion, a layer of bone from the back surfaces of the spinal column may be shaved. A covering and associated delivery system may be placed over the back of the spinal column. Additional instrumentation, such as plates, rods, screws, or other, may also be used to fix the bones in place and prevent the vertebrae from moving. Coverings such as provided herein may be used in traditional posterior lumbar fusion procedures or in minimally invasive posterior lumbar fusion procedures. 
     In various embodiments, coverings for use in posterior lumbar fusion may be generally tubular and may have dimensions of approximately 2.5 cm wide and approximately 5 cm to approximately 10 cm in length. Generally, wider coverings may be used in the lumbar region and narrower coverings may be used in the thoracic region. A covering with graft material contained therein substantially retains the graft material in the disc space. As shown in  FIG. 36   a , in one embodiment, a covering  600  may be placed between a plurality screws  680 . Accordingly, the covering  600  may include openings to fit around the screws  680 , or to interdigitate between them, as shown. The screws may be, for example, pedicle screws in adjacent or non-adjacent levels in the spine. In some embodiments, the covering may be fixed in place, such as by suturing the covering to or through the transverse process. 
       FIG. 36   b  illustrates a generally wide covering  1340  placed in a posterolateral site. As shown, attachment mechanisms, such as pedicle screws  1342  may be placed directly through the covering and its contents and into the pedicle of the vertebra. In alternative embodiments, a covering such as shown in  FIG. 36   b  may be coupled to a fixation system. 
     In some embodiments, two coverings may be used, for example, placed on either side of pedicle screws.  FIG. 36   c  illustrates an embodiment wherein a first covering  1080  is provided on a first side of pedicle screws  1084  and a second covering  1082  is provided on a second side of pedicle screws  1084 . As shown, the first  1080  and second coverings  1082  may be coupled to one another and/or to surrounding soft tissue. Such coupling may be done using any suitable attachment mechanism. For example, such coupling may be done by suturing  1086 . 
     In yet further embodiments, a covering may be placed under hardware such as a rod. Placement of the covering may be done, for example, using a delivery gun such as provided herein, sliding the covering over K-wires, or by other method. The covering and its contents may have a concavity, or be placed and positioned to provide a concavity into which the rod fits. 
     Cervical Interbody Fusion 
     In another application the covering and delivery system may be used with an anterior or posterior cervical interbody fusion procedure. An incision may be made in either the anterior or the posterior of the patient. The procedure is similar to the posterior cervical fusion, except that in the cervical interbody fusion an entire disc may be removed and a covering and associated delivery system may be placed in the disc space. The covering may be provided as a cartridge for placement in an interbody fusion cage. As discussed previously, the interbody fusion cage may be any suitable cage, such as one suitable for cervical interbody fusion, may have any suitable dimensions, and may be made of any suitable material. Generally, cages for cervical placement have small cavities for receipt of graft materials. Small coverings may be placed in the cages and filled with suitable graft material, such as bone graft, allograft, BMP, or any other suitable material. A covering may be filled with material before or after placement in the cage. The cage may receive the covering before or after placement in the spine. Coverings may be useful, for example, for fusion of 2 or more levels. In one embodiment, a covering for use in posterior cervical interbody fusion may be a generally small flat covering having dimensions of approximately 1 cm×5 cm. Radiopaque markers may be provided to facilitate imaging and to confirm final seating location. In some embodiments, a covering such as provided herein may be used in a Harms cage for corpectomy procedures. Additional instrumentation may be used, such as rods, screws, wires or the like to further stabilize the spine. 
     Occipital Cervical Fusion 
     In another embodiment, the covering and associated delivery system may be used with an occipital cervical fusion procedure. Occipital cervical fusion involves fusion of the occiput to the cervical spine with possible instrumental fixation. Following placement of Mayfield tongs on the skull, a patient may be turned prone onto bolsters. The head and neck may be immobilized, in a Mayfield extension frame, for example. Visualization may be performed to confirm reduction of the occipital-cervical junction. Following prepping and draping of the posterior occipital-cervical region, as well as the iliac crest, a midline incision may be performed and exposure of the occiput, inion, arch of C1 and posterior elements of C2 and C3, for example may be performed. The covering may comprise a cartridge for placement in a cervical fusion cage. Such a cage may have any suitable dimensions and may be made of any suitable material. The containment area(s) of the cage may be filled with the covering/delivery system and may further be filled with bone graft, allograft, BMP or any other suitable material to promote fusion between the vertebrae. Additional instrumentation may be used, such as rods, screws, wires, or the like, to further stabilize the spine. 
     As shown in  FIGS. 37   a - 37   d  in some embodiments, a generally U-shaped covering may be used for occipital cervical procedures. A covering as provided herein may be used to fuse the C1 and C2 vertebrae. C1 and C2 are cervical vertebrae that work together to support the head. As shown in  FIG. 37   a , the C2 vertebra  1362  has a dens that projects upwardly into the space of the C1 vertebra  1360 . The occiput (or occipital bone)  1364  of the lower skull articulates against the C1 vertebra  1360  on two condyles. In a fusion procedure, the condyles are decorticated and a covering  1370  is placed over the condyles. The covering  1370  thus facilitates fusion of the skull to the first cervical vertebra (C1)  1360 . In a further embodiment, a fusion procedure is performed wherein the condyles and the articular facet of the dens are decorticated with the covering placed to facilitate fusion of the skull to the first and second vertebrae. In another embodiment, as shown in  FIG. 37   c , in addition to fusing the C1  1360  and C2  1362  vertebra, the C1 vertebra  1360  could also be fused to the occiput  1364 . 
     In a further embodiment, a covering for use in occipital cervical fusion may be a generally flat covering having dimensions of approximately 2 cm in width and approximately 10 cm in length. 
     Anterior Lumbar Spine—Deformities 
     As shown in  FIGS. 38   a  and  38   b , in one embodiment, a covering formed as a generally square bag may be used in treating anterior lumbar spine deformities. As shown in  FIG. 38   a , the covering  600  may be, for example, approximately 2.5 cm×2.5 cm. Treatment of the anterior vertebral bodies  730  may thus comprise trimming down the cortical bone such that the surface of the vertebral body is raw and placing the square coverings  600  on top of the surface. The coverings  600  may be screwed into the vertebral body. A continuous bridging in the front of the spine is thus provided, as shown in  FIG. 38   b.    
     As shown in  FIG. 38   c , in a further embodiment, one or more tubular coverings  740  may be placed longitudinally. More specifically, a trough may be cut into the front of the vertebral bodies  730 , a covering  740  placed in the trough and fixed with screws or other attachment mechanisms. The covering  740  thus acts as a bridging scaffold on the outside of the vertebral bodies  730 . This provides a vascularized area with a peritoneum put back on top of it. 
     In some embodiments, a covering may be placed anteriorly. Such placement may use the covering as a fixation element and may obviate the need for a buttress plate or other fixation system. 
     In some embodiments, a covering may be placed in front of the disc space over a cage. It may be fixed with a plate on top from vertebral body to vertebral body or may be fixed directly into the vertebral body by screws through the covering. 
     Other Vertebral Applications 
     Generally, a covering may be configured for any vertebral application. For example, long narrow tubular coverings may be suitable for pediatric cervical spine or pediatric thoracic hemi vertebrae applications. 
     Returning to  FIGS. 34   a - 34   e , they illustrate an embodiment suitable for facet fusion, discussed previously above.  FIG. 34   a  illustrates a facet fusion joint  702 , two vertebra bodies  620 , and a disc  622 .  FIG. 34   b  illustrates a covering  600  comprising a generally square covering  650  and having an attachment mechanism  652  on one end thereof. In the embodiment shown, the attachment mechanism  652  may be a tab  654  with thru holes  656  for receiving screws  658 .  FIGS. 34   c ,  34   d , and  34   e  illustrate the covering bridging the facet joint  702 . Extra sutures may be used to aid in contact of the covering across the joint. 
     A further embodiment may comprise a covering that may be fixed in place using a facet screw to bridge a facet joint for fusion. 
     Small Joint Fusion 
     In other applications, the delivery system may be used in small joint fusion. For example, the delivery system may be placed between wrist or ankle bones, metatarsals, phalanges, metacarpals, or other to create fusion. For example, in one embodiment, a hole may be drilled that encompasses a portion of each articular surface and the covering may be placed into the hole, thus spanning the spacing between the articular surfaces. In another embodiment, endplates of the bones may be rasped or otherwise prepared and a covering placed therebetween. 
     Deformity/Trauma 
     In some embodiments, coverings may be provided for treatment of deformity or trauma. For example, a covering may be generally configured as a bag and have dimensions of approximately 20 mm×20 mm. The covering may be pierced to facilitate placement on a pedicle screw or pushing down a guide wire. Thus, in one embodiment, such covering may be used in a Wiltse approach wherein the covering is pushed along a K-wire. In further embodiments, coverings may be provided as long strips for placement across facets, fractures, or as desired in a surgical site. 
     In yet a further embodiment, coverings may be provided for placement over the head of a pedicle screw. Thus, for example, a covering may be formed as a small generally flat square. Such coverings may be placed over the heads of 2 pedicle screws. After threading of the screws, the coverings provide overlap between the screw heads. 
     Revision of a Failed Temperomandibular Joint (TMJ) 
       FIGS. 38   d - 38   g  illustrate an embodiment wherein the covering is configured as a defect bridge and restrictor. The covering may be used to treat eroded fossa from disease, trauma, or failed implant. In one embodiment, the covering may be used to treat a failed temperomandibular joint.  FIG. 38   d  illustrates a top view and  FIG. 38   e  illustrates a perspective view of the covering  1150 . As shown, the covering  1150  includes a generally spherical central containment portion  1152 . A flange portion  1154  extends from the containment portion  1152 . The containment portion  1152  may be configured to receive a substance for retention or delivery at a surgical site such as to bridge a defect. The flange portion  1154  may be used to fix the covering at the surgical site. 
       FIG. 38   f  illustrates the implant site. As shown, eroded fossa  1156  presents in temporal bone  1158  near the mandible  1160 .  FIG. 38   g  illustrates a covering  1150  placed in the defect. As shown, the covering  150  bridges and fills the defect. The covering  1150  may be fixed at the surgical site using an attachment mechanism. For example, the covering may be tacked or micro-screwed. Soft tissue flaps may be used to cover the covering. After healing, the site may be prepared for an implant. 
     Repairing the Floor of the Orbit 
     In a further embodiment, a covering and associated delivery system may be used to repair the floor of the orbit. Orbit and orbital floor fractures are common midface fractures. When only the orbital floor is fractured, this is known as a blowout fracture. When orbital floor fractures are also associated with orbital rim and lateral buttress fractures, they are known as tripod fractures. The orbital floor is concave inferolaterally and is typically more convex medially and becomes substantially convex posteriorly behind the equator of the globe. When repairing the floor of the orbit, it may also be necessary to repair the orbital walls and recreate the orbital volume, in order to allow repositioning of the globe into its normal anatomical position. 
     Several surgical approaches exist to gain access to the orbital floor, for example, transconjunctival, subciliary, and subtarsal being among the most common. It will be recognized by those skilled in the art, however, that any suitable approach may be used to gain access to the orbital floor. Regardless of the approach used, the repair procedures are substantially the same. The area is dissected. The globe or optic nerve must not be retracted too forcefully or blindness may result. The contents of the floor are removed from the maxillary sinus. A covering may be placed in the defect to keep the maxillary sinus contents from regressing. In some embodiments, the covering may have a plate-like configuration. 
     Cranioplasty or Burr Hole Defects 
     In further embodiments, a covering and associated delivery system may be used for cranioplasty or to treat burr hole defects. Cranioplasty is reconstructive surgery to repair large defects in the frontal and neurocranial areas of the skull caused by, for instance, trauma or intercranial surgery. The main purpose in performing cranioplasty is to protect the brain because when the protective bones of the cranium are missing, the brain is only covered by skin, scar tissue and the meninges. Reconstruction will also attempt to create harmonic contours with an aesthetic appearance. The covering generally fits against all the borders of the bone defect and also resembles the aesthetic, harmonic, and symmetric contour of a normal skull. Generally, a cranioplasty procedure may involve exposing the bony margins of a patient&#39;s defects by separating the covering skin from the meninges. The covering may then be placed and fixed with appropriate attachment mechanisms, such as with titanium microscrews. 
     Similarly, burr hole defects resulting, for example, from cranial trepanation, can be very noticeable when they occur in areas that are not covered by hair. A covering as provided herein may be placed in the burr hole defect. In one embodiment of the present invention the covering and delivery system may be used to either “tent-over” the defect, or be directly placed into the defect with the edges reaching into the margins. 
     Osteonecrosis 
     In yet a further embodiment, a covering and associated delivery system may be used to treat osteonecrosis. Osteonecrosis, also known as avascular necrosis, aseptic necrosis and ischemic necrosis, is a disease resulting from the temporary or permanent loss of blood supply to the bones. The bone tissue dies and causes the bone to collapse without blood. If this process occurs near a joint, it may lead to collapse of the joint surface. Though most commonly this disease affects the ends of the femur, it may affect any bone, including but not limited to the tibia, upper extremity, foot, ankle, knee, shoulder, and jaw. The disease may affect only one bone, more than one bone at the same time, or more than one bone at different times. 
     Several treatments are available depending on the stage and location of the disease. Core decompression involves surgically removing the inner cylinder of bone to reduce the pressure within the bone allowing more blood to flow there. A covering and associated delivery system may be implanted into the cored space to stimulate new vascular growth. Osteotomy involves reshaping the bone to reduce the amount of stress on the affected area. The substance within the covering may be a bone graft and, in some embodiments, a vascular graft. In other embodiments, a vascular graft may be added around the delivery system. Such vascular graft may increase the blood supply to the affected area. Finally, arthroplasty, or total joint replacement may be used. This procedure involves replacing the diseased joint with artificial parts. 
     Iliac Crest Defects 
     In another embodiment, a covering and associated delivery system may be used to treat an iliac crest defect. Iliac crest defects may result from trauma or from surgery, particularly donor site surgery. Reconstructing the iliac crest may be associated with significantly lower intensity and incidence of pain than in those with unreconstructed iliac crest defects. Additionally, reconstructing the iliac crest defect may be substantially superior cosmetically. A covering thus may be configured to conform to the space of the iliac crest defect. 
     Segmental Bone Defects 
     In a further embodiment, the covering may be used in a variation of the Masquelet technique. The Masquelet technique is used in long bone trauma applications where there is a large intercalary defect, such as where a segment of a long bone is missing. The Masquelet technique typically comprises two stages, a first stage wherein a spacer is placed and soft tissue forms around the spacer, and a second stage wherein the spacer is removed and a bone graft is placed in the space left by the spacer. The formed soft tissue (a kind of periosteum) fauns vascularized fibrous sheath. This sheath acts as a prepared environment for bone graft and is used to cover the bone graft. The spacer may be, for example, PMMA cement with an antibiotic. The spacer thus helps clear the infection and causes inflammation at the site, which in turn leads to formation of the soft tissue. After removal of the spacer, the soft tissue (or periosteum like layer) facilitates new bone growth around the to-be-placed graft material. 
     In some embodiments, a covering such as provided herein may be similarly used for trauma repair in a long bone segmental defect. For example, a covering may be provided with a substance (such as a graft material) provided therein suitable for trauma repair. The covering may be formed as a temporary covering where, for example, the covering is designed to be resorbed in a relatively short time frame. The covering thus is used to hold the space (excluding soft tissue) in the long bone and have soft tissue form therearound. The covering may be resorbable and may have materials such as antibiotics provided therein (in the material of the covering or in the substance within the covering). Like the spacer of the Masquelet technique, the covering can assist in reducing infection and may also stimulate inflammation to cause formation of a periosteum-like layer. The covering acts as a temporary covering and is resorbed by the body. After resorption of the covering, the graft material is exposed and facilitates new bone growth. Unlike the Masquelet technique, which requires a second surgery step to remove the spacer and place the graft material, the entire process is stimulated with a single surgical step. 
     In alternative embodiments, as depicted in  FIG. 50 , a covering material may be provided as a cylinder  272  defining a hollow core  276  or tube. The cylinder may have an outer covering material  275  defining an outer radius R of the cylinder  272 . The hollow core may be defined by an inner covering material  274  further defining an inner radius r of the cylinder. The cylinder shaped covering material may be used to deliver graft materials for segmental reconstruction of a bone  272 , in revision implants for the proximal femur, or for other sites. 
     Acetabular Defect 
     Pelvic discontinuity may be encountered during acetabular revision in patients with severe acetabular bone loss or defects. Recognition of the discontinuity and appropriate intraoperative treatment contribute to a successful clinical outcome. The treatment for the discontinuity depends on how much host bone remains, the potential for healing of the discontinuity, and the potential for biologic ingrowth of acetabular components. If healing potential of the discontinuity exists, the discontinuity may be treated in compression with a posterior column plate and structural allograft or with an internal plate. If healing potential for the discontinuity does not exist, the discontinuity may be bridged and treated in distraction with an acetabular transplant supported with a cage. In various embodiments, a covering such as provided herein may be configured as a structural implant for healing the discontinuity. In other embodiments, a covering such as provided herein may be configured to bridge the defect. Large acetabular defects can be reconstructed with various methods depending on size and location of the defect. 
     A cup-shaped acetabular covering may be used to treat, for example, a pelvic-acetabular defect.  FIGS. 38   h - 38   k  illustrate an embodiment for treatment of a large acetabular defect through the medial wall.  FIG. 38   h  illustrates the defect. Remnant acetabulum  1170  is shown in the pelvic bone  1172  and terminating at the medial wall  1174 . An example width of such remnant acetabulum  1170  is approximately 80 mm.  FIG. 38   i  illustrates a cup shaped covering  1176  placed in the defect with the flange resting on the acetabular/pelvic rim  1178 . Once positioned, the covering is secured at the site. In the embodiment shown, the covering  1176  is secured using screw attachment mechanisms  1180 . The screws  1180  may be threaded through the flange  1182  of covering  1176 . The width of the open acetabular region  1170  may then reduced to approximately 66 mm. In some embodiments, a graft material may be placed over the covering. For example, as shown in  FIG. 38   j , cancellous chips or other graft material  1184  may be placed on the covering  1176  and formed to a generally spherical diameter for receipt of an implant.  FIG. 38   k  thus illustrates an acetabular implant shell  1186  placed over the graft material  1184 . In alternative embodiments, the acetabular implant shell  1186  may be placed directly over the covering  1176 . The acetabular implant shell  1186  may be fixed using attachment means such as screws  1180 . The screws  1180  may extend through the implant shell  1186 , the graft material  1184 , and the covering  1176 . 
     In some embodiments, an acetabular cup may be placed over a bridge/restrictor covering as previously discussed with respect to  FIGS. 38   d  and  38   e . Such embodiment may be useful for acetabular medial wall reconstruction.  FIG. 38   l  illustrates a thru-hole defect  1200  in an acetabular medial wall  1202 .  FIG. 38   m  illustrates a bridge/restrictor covering  1204  placed in the thru hole. Graft material  1206  is placed over the covering  1204  to substantially fill the void between the covering and the acetabular cup  1208 . In an alternative embodiment, shown in  FIG. 38   n , bone cement  1210  is used to fill the void between the covering  1204  and the shell implant  1208  and is provided in sufficient amount to facilitate wall healing. 
     Guided Bone Regeneration (GBR) 
     In yet another embodiment, a covering and associated delivery system may be used in guided bone regeneration. GBR is a surgical procedure using barrier membranes to direct growth of new bone at sites having insufficient volumes or dimensions for function or prosthesis placement. GBR is directed to the development of hard tissue. GBR may be applied, for example, in the oral cavity to support new hard tissue growth on the alveolar ridge to allow stable placement of dental implants. GBR may also be used for augmentation around implants placed in immediate or delayed extraction sockets, or for localized ridge augmentation for later implantation, filling bone defects after root resection, cystectomy, removal of retained teeth, or guided bone regeneration in dehiscense defects. 
     Generally, GBR is performed by first closing the wound to promote undisturbed and uninterrupted healing, whereupon angiogenesis occurs. A space is created to facilitate bone in-growth. A covering, forming a barrier membrane, may be implanted into the space. The covering may be configured to be resorbable or non-resorbable and, in some embodiments, may comprise a collagen material. The wound is stabilized to induce blood clot formation and to allow for uneventful healing. 
     ACL Reconstruction Surgery 
     As shown in  FIGS. 39   a - 39   d , in a further embodiment, a covering may be used in a surgery for a torn Anterior Cruciate Ligament (ACL), which is one of the ligaments that connects the tibia  750  to the femur  752 . A Bone-Tendon-Bone graft  754  may be used as a replacement of the ACL as shown in  FIG. 39   a  in the anterior view, and  FIG. 39   b  in the medial view. In this case, the knee is placed in flexion, and a drill is used to create a tunnel from the tubercle region of the tibia  750  into the femur  752 . The implant is placed using standard techniques, and fixed into the tunnel. The graft-containing covering  756 , in one embodiment, may be placed into the tunnel entrance, to close it off and to encourage bone growth up to the bone block anchored in the tibia, as shown in  FIGS. 39   a  and  39   b.    
     In another embodiment, shown in  FIGS. 39   c  and  39   d , a looped graft  760 , such as some synthetic grafts, hamstring grafts, and some tendon grafts, may be used. In this case, the loop is captured across a pin  766  in the femur  752 , and the tibial  750  portion is tightened into place using an interference screw  764 . The entry hole for the pin  766  can be plugged or capped using the covering  756 , by pushing or packing it into position. 
     Revision Joint Surgery 
     In one application, a covering and associated delivery system may be used in a simplified approach to repairing a defect created by the removal of a joint implant such as tibial implant. Generally, such covering may be used for proximal tibial, distal femoral, and proximal femoral revision joint surgery. The approach thus may be used for the femoral component of a hip implant, or in other revision joint arthroplasty applications. Typically joint replacement implants are cemented implants.  FIG. 40   a  illustrates a tibial implant to be removed. The tibial bone  769  has a metallic prosthesis  767  with cement  768  holding the prosthesis  767  in the bone  769 , with a polyethylene insert  766  placed on top. As illustrated in  FIG. 40   b  during removal of the cement  768 , a large volume of the cancellous bone may be removed as well, thereby creating a defect  770 . This defect can be prepared to an even, smooth and, for example, conical geometry by reaming or rasping with an appropriate instrument  772 . Tubular or cylindrical shaped preparation beds may also be accommodated. A tubular, tapered or doughnut shaped covering containing graft material  776  may be placed into the prepared site  778 , as shown in  FIG. 40   c . Several sizes of coverings may be provided to accommodate any variety of defect. A tapered impactor  782  may be used to press against the inner surface of the covering  776 , and force the covering into the reamed, tapered surface  778 . This is similar to “impaction grafting”. A new implant  784  is then placed, for example by cementing in place. 
     In accordance with one embodiment, as shown in  FIGS. 41   a  and  41   b , the covering may be a continuous covering  790  formed to a hollow cone  792 . The covering  790  may comprise first and second layers of, for example, mesh, that are overlapped and coupled (such as by stitching)  794 , as shown in  FIG. 41   b.    
       FIGS. 42   a - 42   d  illustrate placement of an impaction graft in the tibia  750 .  FIG. 42   a  illustrates an original metal implant  810  cemented in place in the tibia  750 . The implant  810  and cement are removed, thus creating a large defect void  812 , shown in  FIG. 42   b . A covering  816  is placed in the defect void  812  and a forming instrument  814  may be used to compress the covering  816  into a suitable shape, shown in  FIG. 42   c . A revision implant  818  then may be seated and void filler  818  placed between the revision implant and the covering  816 , as shown in  FIG. 42   d.    
     Amputation 
     When performing an amputation, surgeons generally cut above the diseased or injured area so that a portion of healthy tissue remains to cushion bone. Sometimes the location of a cut may depend in part on its suitability to be fitted with an artificial limb, or prosthesis. The first step in performing an amputation involves ligating the supplying artery and vein, to prevent hemorrhage. The muscles are transected, and finally the bone is sawed through with an oscillating saw Skin and muscle flaps are then transposed over the stump, occasionally with the insertion of elements to attach a prosthesis. 
     In some embodiments, a covering may be configured as an end-cap for treatment of an amputation, to provide a more stable site for a bony fixed prosthesis or to solidify the bony support for an externally attached prosthesis.  FIG. 42   e  illustrates a perspective view,  FIG. 42   f  illustrates a side view, and  FIG. 42   g  illustrates a top view of such embodiment. As shown, the covering  1218  may be formed as a substantially flat and circular bag. Flanges may extend from the covering  1220 . A single flange may be provided around substantially the entire perimeter of the covering or one or more flanges may be provided extending from the covering. In the embodiment shown, two flanges  1220  are provided on generally opposite ends of the covering  1218 . 
     After preparing the bony surface, and optionally, elevating the periosteum, such covering may be placed, at the end of a femur in an above-the-knee amputee.  FIG. 42   h  illustrates the covering as placed. The covering  1218  is placed on an end of the bone  1222 , over the cortical bone, or may also be placed inside the intramedullary canal. The containment area of the covering may thus extend partially into the intramedullary canal  1224 . The covering  1218  may be fixed via the flanges  1220 . In some embodiments, sutures or other attachment mechanisms may be used to clamp the flange(s) to the bone. Muscle flap may be positioned over the covering once the covering is fixed in place. 
     Other 
     Generally, the delivery system may be applied to a pre-existing defect, to a created channel, or to a modified defect. Thus, for example, a channel may be formed in a bone, or a pre-existing defect may be cut to form a channel, for receipt of the delivery system. The covering may be configured to match the channel or defect. In some embodiments, the configuration of the covering may be chosen to match the channel or defect. In other embodiments, the channel may be created, or the defect expanded or altered, to reflect a configuration of the covering. The covering may be placed in the defect or channel and, optionally, coupled using attachment mechanisms. Similarly, a covering may be used to fill a gap created by fracture in vertebroplasty or kyphoplasty. 
       FIG. 43   a  illustrates a covering formed as a long tube  830 , generally referred to as a snake structure. The covering  830  may be placed in a cyst or tumor site that has been evacuated  832 . Placement may be done percutaneously or in an open procedure. In another embodiment, as shown in  FIG. 43   b , a defect may be filled with a long ribbon-like or “snake” covering containing graft  830 . The covering may be inserted into the defect by folding the covering upon itself to completely fill and pack the defect. 
     In some embodiments, a covering may be used to fill a concave defect. The covering may be provided such that substantially complete filling of the defect does not substantially deform the covering material. Further, the covering may be provided in a pre-filled configuration. In a further embodiment, a covering and associated delivery system may be used to fill a concavity, which is a contained defect. A covering that is at least partly filled with graft materials may be used to fill a defect  832 , which is shown in  FIG. 44   a . Several different sizes of coverings, representing different filling volumes may be provided. A “trial” implant may be used to identify the volume of the defect and to select an appropriately sized covering.  FIG. 44   b  shows a covering  850  that is partially filled with graft material  852 , and partially empty  854 .  FIG. 44   c  shows the graft material  852  is packed into the space, and carries the covering in as it is packed into the defect. Packing can be performed manually, or by using a tamp, for example. As the graft material is packed into position, graft inside the covering may be manipulated into the defect or out into the unfilled end. The end of the covering containing empty space  854  and any unused graft materials is collected, and the covering is re-sized by any suitable means, such as by crimping, clipping, tying, twisting and tying, heat sealing, suturing or sewing, etc. Optionally, the excess bag material might be cut and removed, as shown in  FIG. 44   d.    
       FIG. 44   e  illustrates a first embodiment of a foldable and stackable covering  1230  used to treat an irregular bone void  1232 . As shown, the foldable and stackable covering  1230  includes segments of a first type  1234 , segments of a second type  1236 , and segments of a third type  1238 . The segments of the first type  1234  are generally stacked on one another to fill a height of the void  1232 . The segments of the third type  1238  extend along the sides of the segments of the first type  1234  and thus assist in filling the width of the void  1232 . The segments of the second type  1236  span the segments of the first type  1234  and the segments of the third type  1238 . 
       FIG. 44   f  illustrates a second embodiment of a foldable and stackable covering  1240  used to treat an irregular bone void  2142 . As shown, the foldable and stackable covering  1240  includes segments of a first type  1244  and segments of a second type  1246 . The segments of the first type  1244  are generally evenly sized and evenly filled. The segments of the second type  1246  are sized such that the segments of the first size  1244  may be folded over 180°. Thus, as stacked in a bone void  1242 , the segments of the first type  1244  stack generally evenly on top of one another. 
       FIG. 44   g  illustrates a third embodiment of a foldable and stackable covering  1250  used to treat an irregular bone void  1252 . As shown, the foldable and stackable covering  1250  includes segments of a first type  1254  and segments of a second type  1258 . The segments of the first type  1254  are generally evenly sized but alternate between a first fill level  1256  and a second fill level  1260 . The segments of the second type  1258  are sized such that the segments of the first size  1254  may be folded over 180°. Thus, as stacked in a bone void  1252 , the segments of the first type  1254  stack generally evenly on top of one another but with differing heights contributed by the different fill levels in the segments of the first type  1254 . Such configuration facilitates tighter packing of the bone void  1252  and deforms to larger covering profiles. 
       FIGS. 44   h  and  44   i  illustrate a covering used as a sternum closure after open heart surgery. As shown, the covering includes segments of a first type  1270  and segments of a second type  1272 . The segments of a first type  1270  may be filled with a substance such as a graft material. The segments of a first type  1270  may be generally sized and spaced to correspond with rib locations. The segments of a second type  1272  extend between the segments of the first type  1270  and may comprise unfilled covering or may comprise other material.  FIG. 44   i  illustrates the covering as placed. Closure wires  1274  are placed through the segments of a second type  1272 . The segments of a first type  1270  generally align with the ribs  1276 . 
     In alternative embodiments, such covering configuration may be used to treat non-unions and in reoperations. A broken bone that does not grow back together is called nonunion. This can happen with certain types of fractures. Nonunion can be treated by replacing the affected joint with an artificial joint or by bone grafting. Bone grafting involves placing additional bone around the area of the nonunion. Additionally, some patients who have had, for example, spinal fusion, may require reoperation if symptoms return after several years. About 10% to 20% of people who have had surgery need to have surgery again. Reoperation may be necessary if, for instance: spinal stenosis develops in another area of the spine; an earlier surgical procedure was not effective in controlling symptoms; instability develops, or fusion does not occur: or regrowth of tissue (lamina) presses on the spinal cord or spinal nerve roots. A covering such as provided herein may be configured to span ends of a broken bone in a nonunion, as an implant for an artificial joint, etc. 
     At the time just prior to when the delivery system is to be placed in a defect site, optional materials, e.g., autograft bone marrow aspirate, autograft bone, preparations of selected autograft cells, autograft cells containing genes encoding bone promoting action, etc., can be combined with the covering and/or with a substance provided within the covering. The delivery system can be implanted at the bone repair site, if desired, using any suitable affixation means, e.g., sutures, staples, bioadhesives, screws, pins, rivets, other fasteners and the like or it may be retained in place by the closing of the soft tissues around it. 
     Collagen Covering 
     Collagen materials may be used to form the covering. The collagen material may be processed to any suitable level. For example, the collagen material may be minimally processed. The collagen material may be treated with enzymes. For example, human-derived collagen may be enzymatically treated to yield a collagen material having a preserved amount of native constituents but with immunologically active glycoproteins and recombinant collagen removed. Collagen material may be constructed from collagen fibers, fibrils, microfibrils, particles, threads, strands, etc. The materials may be processed by chemical treatments (e.g., with enzymes, enzyme deactivation solutions, alcohols and/or cross-linking agents) and/or by physical treatments (e.g., blending, freezing, lyophilizing, casting, pressing, molding). The collagen material may be provided as a sheet, may be woven (using, for example, textile techniques), knitted, braided, non-woven (using, for example, felting processes), may be formed as a film, or may be provided in any suitable configuration. In embodiments wherein the collagen material is provided as a sheet, the sheet may have holes created therein and, further, may be stretched to increase the size of the holes. The collagen material may be treated to have different properties when wetted—such as increased flexibility or malleability. Such wetting may be, for example, by any fluid including blood, serum, saline, and water. In accordance with one embodiment, the collagen material is a collagen product disclosed in U.S. Patent Publication Nos. 2008/0195202 for Methods for Collagen Processing and Products Using Processed Collagen and 2008/0260794 for Collagen Products and Methods for Producing Collagen Products, herein incorporated by reference in their entireties for all purposes. 
     In accordance some embodiments, a covering may be configured as a pad or sheet and formed for drug release. Accordingly, as shown by  FIGS. 45-47 , a delivery system  300  may include a covering comprising a first layer  314  and a second layer  312  and a substance placed and contained therebetween. In some embodiments, the first  314  and second layers  312  may comprise a material such as a collagen material. In various embodiments, the collagen material may be processed.  FIGS. 45 and 46  illustrate formation of the covering  300 . As shown, a first sheet  314  is provided. The sheet  314  may be wet, for example, to facilitate adherence of a substance  316  for delivery on the sheet. A substance  316  for delivery is then provided on the sheet  314 . As shown in  FIG. 45 , the substance  314  may comprise a drug powder  316  that is sprinkled on or otherwise provided on or adhered in or to the first sheet  314 . The second sheet  312  is then placed over the first sheet  314  and the material  316 , as shown in  FIG. 46 . In some embodiments, the second sheet  316  may be wet.  FIG. 47  illustrates drug delivery from the delivery system  300 . Generally, with biological fluid and cells permeating the first and second sheets, the substance provided therebetween is released in a relatively controlled manner. 
     In further embodiments, more than two sheets or layers of material may be used. For example, a delivery system may be provided including a covering having first, second, third, and fourth layers of material. Substances may be provided between each of the layers. The substances may be the same or different between layers. For example, a bone graft material may be provided between the second and third layers with a different substance, such as an active substance or an antibiotic, may be provided between the first and second layer and between the third and fourth layer. 
     A delivery system such as shown in  FIGS. 45-47  may be further configured. For example, as shown in  FIG. 48 , a generally cylindrical delivery system  10  may be formed from the delivery system  300  of  FIGS. 45-47 . This form may be achieved, for example, by rolling the delivery system  300  into a tubular or generally cylindrical form. An adhesive may be used on the delivery system  300  to facilitate formation into the generally cylindrical form. Attachment mechanisms may be provided on the delivery system, for example at ends of a tubular configuration. 
     In yet a further embodiment, shown in  FIG. 49 , one or more sheets may be coupled to form a pouch or bag covering  20 . Alternatively, the sheet (combined with other sheets as appropriate) may be formed into a tube, a pillow, or any other desired shape. The sheets may comprise a single layer of material or may comprise a multi-layer construct such as shown in  FIGS. 45-47 . As shown in  FIG. 49 , two layers  22  and  24  may be coupled along, for example, first, second, and third edges to form a covering. Coupling may be by, for example, sealing the first layer and the second layer together. Such sealing may be done by welding, suturing, adhesives, or other. In the embodiment shown, sutures  26  are used for coupling the first layer  22  to the second layer  24 . In some embodiments, one edge of the covering may be left open. In the embodiment shown, the upper edge  28  is left unsealed. A substance for delivery thus may be inserted into the covering  20  through the open edge  28 . That edge may be closed after filling the covering or may be left open. In one embodiment, a pillow may be formed where the outer layer of the pillow includes two layers, with an active substance between the two layers; the pillow further comprises an interior, into which another active substance (in addition to or instead of the active substance between the layers of the covering) may be provided, such as a bone growth material (demineralized bone, or bone morphogenetic protein). 
     Soft Tissue Augmentation 
     In some embodiments, a covering may be used for skin or other soft tissue augmentation. For example, a covering may be configured as a relatively thin tube and may be filled with a material such as collagen, artificial skin, cells, or other material useful in soft tissue augmentation. The covering may be delivered, for example, into wrinkles or other soft tissue. In some embodiments, the covering may be delivered via injection. 
     Testing Applications 
     In some embodiments, a delivery system such as provided herein may be used in testing bone, either in vitro or in animal in vivo assays. For example, in in vitro applications, a covering comprising a mat may contain a graft and may be placed in a petri dish. Alternatively, a covering comprising a cylinder may be placed in a bioreactor. In in vitro applications, a covering may be used to deliver DBM ectopically in an athymic rat assay. Similarly, a delivery system may be used in mosaic plasty-like applications such as where cartilage is grown on a surface of a cylinder of material using tissue engineering methods such as a bioreactor. 
     IX. CONCLUSION 
     In accordance with various embodiments, a delivery system for delivery a substance in vivo is provided. The delivery system comprises a covering and a substance. The covering may be a single or multi-compartment structure capable of at least partially retaining a substance provided therein until the covering is placed at a surgical site. Upon placement, the substance may be released (actively or passively) to the surgical site. The covering may participate in, control, or otherwise adjust, the release of the substance. The delivery system may be used to control availability of a substances provided within the delivery system to cells and tissues of a surgical site over time. 
     Various delivery techniques may be used for implanting or placing a delivery system such as provided herein. These include attaching the covering to bone, attaching the covering to soft tissue (such as muscle, ligament, or tendon), delivering the covering through a cannula, delivering the covering through a drill hole or tract, placing the covering in an open or mini-open procedure, wrapping the covering around threads of another device (such as a cage, screw, dental implant, or similar), placing the covering a two-part procedure (delivering the covering to the site and filling the covering at the site), as part of a minimally invasive procedure, and in a procedure generally comprising “dumping” the delivery system at the site. 
     U.S. Pat. No. 4,430,760 for Nonstress-bearing Implantable Bone Prosthesis, U.S. Pat. No. 6,740,093 for Method and Apparatus for Treating a Vertebral Body, U.S. Pat. No. 4,755,184 for Bone Augmentation Implant, U.S. Pat. No. 5,571,189 for Expandable Fabric Implant for Stabilizing the Spinal Motion Segment, U.S. Pat. No. 7,220,282 Annulus-Reinforcing Band, U.S. Pat. No. 7,208,015 for Bone Repair Device, and U.S. Patent Publication No. 2007/0073401 for Method for Repairing Bone disclose various fabrics and structures for containing materials for implanting in the body and are herein incorporated by reference in their entireties. 
     Although the invention has been described with reference to preferred embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.