Abstract:
The invention is based on the use of polyisobutylmethacrylate instead of PMMA as an adhesive or spinal fill material for treating diseases of the spine. Polyisobutylmethacrylate has several advantages over PMMA, mainly less heat is developed during the in situ polymerization process. When using any spinal adhesive of fill material that is light activated, a tube can be used to transmit activating light to the light-activated adhesive or spinal polymerizable fill material at the surgical site. In addition, a mesh bag comprising optical fibers or similar light transmitting material can be employed to receive the injected light-activated fill, with the mesh bag, irradiated externally, for directing the light via the bag to the polymerizable fill.

Description:
BACKGROUND OF THE INVENTION 
     Our earlier filed patent application, Appl. Ser. No. 10/978096, filed 11/01/04, the contents of which are herein incorporated by reference, describes an electrosurgical instrument for removing intervertebral tissue for treating spinal ailments. Among the surgical procedures used for treating spinal ailments are cervical disc surgery (implant of another material as a substitute for a removed cervical disc), vertebroplasty with an adhesive for treatment of osteoporotic fractures, intervertebral disc prosthesis, and mechanical stabilizing of adjacent discs. Many of these procedures and other similar spinal treatments employ as the substitute adhesive material polymethylmethacrylate (PMMA) using in situ chemical activation or visible-light activation. However, adverse events during this procedure with this material may arise, namely, exothermal polymerization of the PMMA causing a temperature elevation high enough to possible lead to soft tissue or bone necrosis. This rise in temperature, which unavoidably accompanies the polymerization process, is exacerbated by the poor heat conduction of the vertebral anatomy. See, for example, “Temperature Elevation After Vertebroplasty With PMMA in the Goat Spine”, by Verlaan et al., Journal of Biomedical Materials Research, 2003 Oct 15; 67B (1): 581-5. 
     SUMMARY OF THE INVENTION 
     An object of the invention is an improved surgical procedure for treating spine ailments involving the use of an adhesive or spinal polymerizable fill material whose temperature rise during polymerization is less than that of PMMA. 
     Another object of the invention is an improved instrument for introducing a light polymerizable adhesive or spinal fill material into spinal anatomy (disk or vertebrae) and that allows polymerizing light to be directly applied to the adhesive or spinal fill material to polymerize same. 
     A feature of the invention is based on the use of polyisobutylmethacrylate instead of PMMA as the adhesive or spinal fill material. Polyisobutylmethacrylate (herinafter “PIBMA”) has several advantages over PMMA for the same purposes that PMMA has been used for surgical spinal procedures. The main advantage is that less heat, compared with PMMA, is developed during the in situ polymerization process, meaning less likelihood of causing soft tissue or bone necrosis. Moreover, the PIBMA material is just as easy to use and to handle for any of these spinal procedures as the PMMA. Further, the PIBMA is dimensionally stable, meaning that when it hardens it tends to retain its injected dimensions. Still further, X-Ray opaque materials, such as radio-opaque Ba or Sr compounds can be added so that the hardened material will be visible in an X-Ray or radiologic examination. 
     The instrument feature of the invention employs as the injecting tube or as an auxiliary tube tubular material that will transmit activating light to a light-activated adhesive or spinal polymerizable fill material at the surgical site. As a further feature, as an improvement on an existing procedure, a mesh bag comprising optical fibers or similar light transmitting material is employed to receive the injected light-activated fill, with the mesh bag, irradiated externally, for directing the light to the polymerizable fill. This has the advantage that the length of working time can be more readily controlled since the polymerization process when light activated can be more consistent. In this aspect of the invention, conventional light-cured polymethacrylate materials may be used, such as urethane dimethacrylate, as well as other non-methacrylate materials. The latter type of light-cured materials may even have a lower curing temperature than that of the PIBMA, and the advantages accompanying the use of light-curable resins will like the use of polyisobutylmethacrylate also be achieved. 
     The surgical procedures employing PIBMA can be the same as those using PMMA, except for the different fill material used and/or the use of light transmitting instruments or mesh bags. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described the preferred embodiments of the invention, like reference numerals or letters signifying the same or similar components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  schematically illustrates part of a spinal column with a cavity adjacent a tubular instrument; 
         FIG. 2  schematically illustrates part of a spinal column with a cavity into which a mesh bag had been introduced via an injecting tube to inject a light-activated fill into the bag; 
         FIG. 3  schematically illustrates a following step in the procedure illustrated in  FIG. 2  in which the injecting tube can be used for illuminating the injected fill with activating light; 
         FIG. 4  schematically illustrates an enlarged view of the end of the injecting tube employed in a somewhat different manner. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The adhesive or spinal flowable polymerizable fill material according to a feature of the invention is PIBMA, polyisobutylmethacrylate. It is generally made up of two constituents that are mixed together by the surgeon outside of the surgical site to form a flowable paste or cream-like consistency that can be injected into the spinal tissue. The resultant cream is then injected into the spinal tissue at the surgical site. The material self-cures in situ in about 6-8 min. The first constituent is liquid monomer isobutylmethacrylate available commercially in liquid form. To it is added finely powered polyisobutylmethacrylate, a solid polymer. Typically, the liquid monomer is added to a suitable container, and sufficient powdered polymer added while mixing with, say, a spatula, until a creamy consistency is formed; the creamy mixture is then poured into the instrument for delivering the mixture, and then injected by the instrument into the spinal area at the surgical site. It begins to harden when exposed to air or liquid and generally sets hard, i.e. polymerizes, after about 6-8 minutes. When hardened it has similar or better properties than PMMA, including strength, retentive ability, and lack of distortion or low curing shrinkage, and importantly lower curing heat. 
     Light-cured plastic materials are also commercially available and include materials such as polyesters and acrylic materials, such as urethane dimethacrylate. Other well-known examples include the camphoroquinone/amine chemistry. Camphoroquinone features an absorption maximum in the visible spectrum at 470 nm (approximately blue light). In conjunction with a suitable amine, as is known, free radical species are generated to cause polymerisation and, therefore, hardening of the material. Polymerisation may be carried out using a suitable UV-generating lamp, such a quartz-halogen, plasma arc, or an argon laser. 
     With both kinds of adhesive or spinal polymerizable fill material a small amount of up to 20% of inert tissue-compatible non-toxic materials can be added to the mix. The inert material may be finely-divided glass, quartz, or ceramics. In addition, to make the hardened fill X-ray visible, a small amount of a known Ba or Sr X-ray opaque compound or material, such as BaSO 4  can be added to the mix. 
     The basic procedure is the same as used for other spinal procedures except for the spinal fill material used or the use of the light-activated fill. Essentially, a tubular member is inserted into the patient as in a conventional percutaneous or endoscopic procedure so that the distal end of the tubular member is at the spinal surgical site where the surgery is to be performed. Conventional instruments can be used to remove any degenerative material or portions of the disc nucleus or the disc itself as required by the selected procedure to forma cavity. Then, through the tube (or cannula as it is sometimes called) can be inserted again a conventional instrument for injecting a suitable spinal fill of adhesive material to fill up a crack in the vertebrae or to fill a cavity created in the nucleus, pulpous, or disc itself All of this can be done as is usual either by percutaneous or radiologic guidance under the view of an endoscopic camera to ensure that the injected fill material is positioned in the proper place. Following the teachings of the invention, the injected adhesive and fill material is the paste mixture of ingredients that will form the polyisobutylmethacrylate when cured, or a paste mixture of ingredients that can be light-activated to harden. If the latter, then after the injection instrument has completed its task, it can be removed from the tubular member and a tubular member having the ability to transmit light inserted in its place. The light transmitting member may be a bundle of optical fibers, known in itself, the distal end of which is placed near the injected material and to the proximal end, outside the patient&#39;s body, is placed a source of UV radiation which travels through the fiber bundle and exits at the surgical site to illuminate the injected fill. If the fill is thick, it may be desirable to carry out this sequence in several small steps, meaning, that first a thin layer of the fill is injected, next the light-transmitting member is inserted to illuminate and cure the initial layer, then the sequence is repeated to form a second cured layer on top of the first cured layer, and so on until the cured fill has the desired size and volume. 
     If the known mesh bag procedure is used, then in an earlier step the mesh bag would be inserted in the cavity and the injection of fill material occur into the open end of the bag using again standard commercially-available instruments for this purpose. This would apply where the fill is the self-curing polyisobutylmethacrylate-forming mixture. Where the light-activated material is used, then as a further alternative the bag mesh can be composed of optical fiber strands so that the incident light is spread around the fill inside the bag by the optical fiber strands. The bag remains in place with the hardened fill. 
     As further alternative, instead of using an optical fiber bundle to transmit the light down the cannula, an additional tubular member with an internal mirrored surface can be inserted and the UV source coupled to the proximal end, such that the UV radiation is tranmitted down the tube by multiple reflections from the internal mirrored surface. The latter can be achieved in a conventional way by plating the inside of the tubular member with a thin layer of nickel as an example, or any other shiny material. 
       FIG. 1  schematically illustrates part of a spinal column  10  with a cavity  12  formed by any suitable instruments such as that described in the referenced patent application, and next to the cavity opening a tubular instrument  14  or cannula, again commercially-available, for injecting a previously-formed polymerizable fill into the cavity using the procedure described above. With the self-curing polymerizable PIBMA, nothing more is required until the fill sets. 
       FIG. 1  also schematically illustrates the part of a spinal column  10  into the cavity  12  of which a mesh bag  16  is shown being introduced in a known way and with the injecting tube  14  in place to inject a light-activated fill into the bag. In this use, it is preferred to employ a cannula  14  containing on its interior two side-by-side internal tubes  18 ,  20 . The latter is illustrated in  FIG. 4 , in which the cannula  14  contains an inner tube  15  containing the two side-by-side internal tubes  18 ,  20 . Between the inner  15  and outer tube  14  is an empty space  22 , the purpose of which will be explained below.  FIG. 1  illustrates that the lower tube  18  can be used to successively inject or administer the tubular mesh  16  and polymerizable fill. The adjacent upper tube  18  can be used for manipulating a guide bar or rod (not shown) to direct the bag to the position desired. Or alternatively, the adjacent upper tube  18  can be used with a viewer for viewing the site during the procedure. In the case illustrated, a spinal tissue has a fracture  24  around which a cavity has been formed and the mesh bag  16  injected from a suitable source  8  is positioned in the cavity alongside the fracture  24 . 
     Either of the tubes can be used for endoscopic viewing of the procedure when the other tube is in use.  FIG. 2  illustrates the spinal fill (not shown) being injected from a suitable supply  9  via one of the tubes  18 ,  20  into the bag  16  to fill same and such that it fills the space alongside the fracture such that when hardened the fractured region is reinforced by the hardened self-polymerized fill. 
     When a light-activated fill is employed, then after the fill has been introduced directly to the surgical site or administered into the mesh bag, it must be illuminated with activating light to polymerize. Preferably, a mesh bag  30  composed of optical fibers is used to help distribute the light around the fill. This embodiment is illustrated in  FIG. 3 , which shows activating light being introduced via one of the inner tubes  18 ,  20  of the cannula  14 . A suitable source is schematically illustrated at  32 , the irradiating light by  34 . In the alternative illustrated in  FIG. 4 , the activating light  36  is shown being introduced directly to a filled cavity or into the mesh bag (not shown) via the space  22  between the inner  15  and outer  14  tubes. 
     In this embodiment, the activating light is provided at the proximal end of the tube outside of the body from, for example, an UV source  32  supplying radiation capable of polymerizing and curing the fill inside the bag. The radiation can be transmitted down the tube  18  by, for example, mirroring the inside surface of the tube, or by extending a bundle of optical fibers that are transparent to the activating radiation down the tube  18  to the vicinity of the mesh opening. To further spread the radiation as completely as possible around the fill inside the mesh bag, the mesh fibers are constructed of thin flexible optical fibers, which are capable of conveying the radiation throughout the bag meshes so that the fill is illuminated from all sides. 
     It will also be apparent to those skilled in this art that the invention should not be limited to the fill injecting or light injecting devices shown as other devices can readily be devised to perform the same function as will be appreciated by the person of ordinary skill in this art. 
     While the invention has been described in connection with preferred embodiments, it will be understood that modifications thereof within the principles outlined above will be evident to those skilled in the art and thus the invention is not limited to the preferred embodiments but is intended to encompass such modifications.