Abstract:
This invention relates to implantable bone fill materials, systems and methods of treating bone abnormalities such as compression fractures of vertebrae, bone necrosis, bone tumors, cysts and the like. In an exemplary embodiment, the bone abnormality is accessed and a space is created by bone removal or compaction. An exemplary implant of the invention has a substantially fluid impermeable surface portion and an interior portion including an in-situ hardenable bone cement. The method of the invention includes applying energy to the fill material to accelerate polymerization and hardening of the material for supporting the bone.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of Provisional U.S. Patent Application Ser. No. 60/571,753 filed May 17, 2004 (Docket No. S-7700-010) titled Composite Implant and Method for Treating Bone Abnormalities, which is incorporated herein by this reference. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    This invention relates to implants and methods for treating abnormalities in bones such as a compression fracture of a vertebra. More in particular, the invention relates to a plurality of elongated, flexible sleeve-like members that can be packed and entangled in a bone and wherein the members have fluid impermeable surfaces with an interior core that includes materials that can be polymerized in situ to provide a rigid bone support structure. 
       SUMMARY OF THE INVENTION 
       [0003]    The invention provides a method of correcting bone abnormalities including bone tumors and cysts, avascular necrosis of the femoral head, tibial plateau fractures and compression fractures of the spine. In an exemplary embodiment, the system of the invention provides flexible filament-like structures that are packed into a bone that are controllably hardened by application of energy from a remote source to cause in-situ polymerization and hardening of materials within the filament-like structures. 
         [0004]    The abnormality may be corrected by first accessing and boring into the damaged tissue or bone and reaming out the damaged and/or diseased area using any of the presently accepted procedures, or the damaged area may be prepared by expanding a structure within the damaged bone to compact cancellous bone. After removal and/or compaction of the damaged tissue, the bone can be stabilized with the in-situ polymerized filament-like structures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    In the following detailed description, similar reference numerals are used to depict like elements in the various figures. 
           [0006]      FIG. 1  is a side view of a segment of a spine with a vertebra having a compression fracture that can be repaired with the present invention, showing an introducer in a method of the invention for creating at least one space in the vertebral body. 
           [0007]      FIG. 2  is a cross-sectional view of the vertebra and abnormality of  FIG. 1  with spaces created therein by cutting, reaming or compaction means. 
           [0008]      FIGS. 3A-3C  are cross-sectional views of exemplary polymerizable element corresponding to the invention; 
           [0009]      FIG. 3A  illustrating an ultrasound fragmentable barrier between first and second components of a bone cement such as PMMA; 
           [0010]      FIG. 3B  illustrating a cross-sectional view of a sleeve with fragmentable microspheres containing first and second components of a bone cement; and 
           [0011]      FIG. 3C  illustrating a member with a bore extending therethrough for receiving an elongated ultrasound device for mixing polymerizable components. 
           [0012]      FIG. 4  is a perspective view of a portion of an alternative implant for creating an in-situ hardenable bone support material. 
           [0013]      FIG. 5  is a cross-sectional view of a portion of the bone support material of  FIG. 4 . 
           [0014]      FIG. 6  is a cut-away view of a portion of an alternative structure for containing an in-situ hardenable bone cement. 
           [0015]      FIG. 7  is a schematic view of the use of an implant as in  FIG. 6  or preventing extravasion of an in-situ hardenable bone cement. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 1  shows a spine segment  100  wherein vertebra  102   a  has a compression fracture  104  that has caused a collapse in vertebral height. The cancellous bone  106  in the interior of the vertebra has been treated to provide a cavity or space  110  therein. The space or spaces  110  as indicated in  FIG. 2  can be created with cutting and extraction tools indicated at  112  in  FIG. 1 , compaction of cancellous bone by means of ultrasound or a low frequency mechanical vibrating device, compaction by a balloon, or the space can created by a combination of compaction and cutting. There can be a single space or a multiplicity of spaces  110  as in  FIG. 2 . 
         [0017]      FIG. 3A  illustrates an exemplary implant body  120 A of the invention that comprises a polymer sleeve or monolithic polymer body that has a substantially fluid impermeable surface  122 . The body has an initial flexible, deformable condition, similar to a monofilament fish line, that is stiff enough to allow it to be pushed and thereafter packed and convoluted into cavity  110  in a bone after being introduced through the bore of a small diameter sleeve  123  (see  FIG. 2 ). The interior of body  120 A carries first and second polymerizable components  124 A and  124 B that when exposed to one another cause a chemical interaction to thereby polymerize the components and alter the implant body to a inflexible, high modulus, substantially rigid and non-deformable condition. 
         [0018]    In one embodiment, the implant body  120 A has a surface  122  of any biocompatible polymer  125  (e.g., Teflon, Dacron, silicone rubber, polysulfone, etc.) and the polymerizable components  124 A and  124 B are independent agents that separated in by an intermediate sacrificial element  128  that when perforated, obliterated or sacrificed allows the components to intermix to cause a chemical reaction process herein described generally as a polymerization process (see  FIG. 3A ). For example, the polymerizable components can be PMMA precursors. This polymerization process allows the body  120 A to transform irreversibly into its rigid or inflexible state. In body  120 A of  FIG. 3A , the polymerizable components  124 A and  124 B are in concentric sleeve portions separated by sacrificial or disintegratable element  128 . The element  128  preferably disintegrates in response ultrasound energy, although other stimulus such as heat caused by an Rf or light source are also possible. Rf can be coupled to element  128  by electrical leads wherein the element has conductive particles of microfilaments therein to allow heating and melting of the element  128 . In  FIG. 3B , either or both polymerizable components  124 A and  124 B are microencapsulated wherein the disintegrable element  128  comprises the polymer of the capsule material. The sacrificial element  128  preferably is sacrificial in response ultrasound energy or heat from inductive heating as in known in the art. The fragmentable component  128  can carry any suitable biocompatible material that cooperates with photonic energy, electrical energy or magnetic energy to elevate its temperature. Light sources, Rf sources and magnetic emitters are known and can be used to deliver energy to the implant, e.g., as disclosed in the author&#39;s U.S. patent application Ser. No. 09/473,371 filed Dec. 27, 1999 (now U.S. Pat. No. 6,306,075), incorporated herein by reference. The detail of the energy source need not be further described herein. In  FIGS. 3A-3B , the member is illustrated as having an exterior sleeve, but it should be appreciated that the member can be a solid low-modulus polymer with the first and second polymerizable materials dispersed therein together with a surface modification that makes the surface substantially fluid-impermeable. 
         [0019]    Still other alternative embodiments are contemplated wherein the energy can be light energy, microwave energy, inductive heating energy, mechanical forces, shear forces, tension forces and/or changes in pressure. 
         [0020]    In the embodiments of  FIGS. 3A-3B , the polymerization process results in a hardened material such as PMMA in the interior of the implant body. PMMA can be provided as a two-part mixable polymer with one powder component and one liquid component. The scope of the invention includes any polymer precursors  124 A and  124 B that yield a rigid biocompatible polymer. When such components are carried in an implant body  120 A, the compositions that are polymerizable to make the body rigid preferably comprise at least about 50% of the body by volume, and more preferably at least about 80% by volume. The body  120 A can be provided in selected lengths—or can be cut to length after introducing into a bone cavity  110  (see  FIG. 2 ). The lengths of each implant body can be from about 5 mm to 100 mm. or more. 
         [0021]      FIG. 3B  illustrates an implant body  120 B comprises a thin, closed-end sleeve  130  that carries any polymer precursors  124 A and  124 B that when exposed to one another result in a polymerization process that yields a rigid biocompatible polymer. Again, PMMA can be provided as a two-part mixable polymer with one powder component and a microencapsulated liquid component, with both components carried in the sealed, closed-end sleeve  130 . The sleeve  130  has a substantially fluid impermeable surface to thereby provide means to assure that the polymer cannot leak out during the polymerization process. Again, the implant body  120 B has an initial flexible state for introduction and packing into space  110  in a bone. In this embodiment, the microencapsulated components (either  124 A or  124 B) can have any form of sacrificial surface  128  that when perforated, obliterated or sacrificed allows the components to intermix to cause the polymerization process to irreversibly rigidify the body. It should be appreciated that microencapsulation of polymerizing components is one preferred aspect of invention, any other sacrificial elements intermediate the first and second components  124 A and  124 B within body  120  are possible, such as an element that extends at least one of axially, cross-axially, or helically or concentrically as described above at any microscale or macroscale. 
         [0022]      FIG. 3C  illustrates an alternative preferred implant body  120 C that comprises a thin-wall, closed-end sleeve  130 ′ that has a passageway  132  extending therethrough for receiving an energy delivery member  140  (phantom view) such as a ultrasound member. In all other respects, the implant body is as described previously. In preferred embodiments, the sleeve  130  or  130 ′ is of a substantially non-distensible polymer. 
         [0023]    In a preferred embodiment, the implant body ( 120 A- 120 C) has a mean cross section of less that 5 mm. More preferably, the implant body a mean cross section of less that about 4 mm. but can have any suitable cross section. 
         [0024]    In preferred embodiments, the polymer of the implant body or sleeve ( 130  or  130 ′) and/or at least one of the first and second components  124 A and  124 B carries filaments for reinforcing the rigid state of the implant following the polymerization process. The filaments or fibers can be any suitable reinforcing material known in the art such as Kevlar, carbon fiber, titanium stainless steel or another metal. 
         [0025]    In another embodiment, the implant body  120 C can include a sleeve wall  130 ′ ( FIG. 3C ) comprising knit, woven or braided filaments  144  as is known in the art of fabricating biocompatible implants. 
         [0026]    In preferred embodiments, the body  120 A- 120 C can carry additional filler materials that are responsive to energy delivery to cause agitation, mixing, stirring, turbulent flows and the like to cause optimal chemical interaction of the components that form a hardened material. In one embodiment, a filler comprising an ultrasound responsive material such as high-impedance compositions or elements that wiggle (e.g., a metal or ceramic element) or an encapsulated gas that cavitates, explodes or the like. The filler can also comprise elements that are magnetically responsive to an oscillating magnetic source to allow agitation and mixing of polymerizing components. Electrical energy from an Rf source can be used to agitate and heat the polymerizing components by means of conductive fillers in the hardenable material. The conductive filler comprises filaments, particles, microspheres, powders or crystals. The conductive filler is a least one of titanium, tantalum, stainless steel, silver, gold, platinum, nickel, tin, nickel titanium alloy, palladium, magnesium, iron, molybdenum, tungsten, zirconium, zinc, cobalt, chromium or carbon. 
         [0027]    In preferred embodiments, the implant body  120 A- 120 C includes at least portions of the surface material polymer that are bioerodible, biodegradable, bioabsorbable and/or bioexcretable. By this means, natural bone infill can migrate into the body after implantation. 
         [0028]    In another embodiment shown in  FIG. 4 , each polymer implant body  145  has a non-smooth exterior surface  146  with an interior volume of hardenable bone cement so that when the bodies are compacted together into cavity  110  in a bone ( FIG. 5 ) there will exist open spaces  150  between the surfaces  146  that will remain open for natural bone ingrowth. For example, each implant body can have a grooved exterior surface  148  with the polymer surface having a suitable modulus that will prevent collapse of the grooved structure. The grooved exterior surface can have grooves that extend at least one of axially, helically and circumferentially. In general, the polymer body  145  has substantial surface relief elements for providing interstitial spaces after packing of at least one polymer structure in a cavity  110  in a bone. 
         [0029]    In any embodiment, the implant body  120  further carries a radiopaque composition in either the polymer body or in at least one of the first and second components  124 A and  124 B. 
         [0030]      FIG. 2  illustrates a procedure wherein at least one implant body ( 120 A- 120 C) is injected and packed into space  110 . Of particular interest, energy is applies to the implant body to irreversibly transform the volume into a polymerized composite that has high strength to support bone. Embodiments with reinforcing fibers can reduce a fracture, such as a vertebral fracture, in a manner that is improved over the injection of a conventional bone cement. The system of the invention entirely eliminates the possibility of cement and monomer extravasion (leakage) from the targeted interior region of the bone. Of particular interest, the implant prevents leakage of bone cement precursors that can damage nerves or migrate into the patient&#39;s blood stream. 
         [0031]    It should be appreciated that the implant body can carry a polymer together with any of the following: cortical bone material, synthetic cortical replacement material, demineralized bone material, autograft and allograft materials. The implant body also can include drugs and agents for inducing bone growth, such as bone morphogenic protein. 
         [0032]    The inventive implant bodies  120 A- 120 C of  FIGS. 3A-3C  can have any suitable length. Substantially short implants may be injected toward the end of the procedure to assure the correct selection of total volume. Alternatively, the bodies can be a continuous element that is injected with the trailing end cut when the space  110  is filled. Such a continuous body with microencapsulating polymerizing elements  124 A and  124 B with a substantially solid polymer body can be compared to self-healing plastics that carry such microencapsulated agents for polymerizing following shear stresses. 
         [0033]    In another embodiment, at least the exterior surface layer of the implant carries polymers or polymer precursors that cross-link and fuse together after the body is packed and convoluted in a bone cavity  110  ( FIG. 5 ). For example, such surface cross-linking can be caused by a selected temperature increase that results from the polymerization process of PMMA or another bone cement that is ongoing in the interior of the implant. 
         [0034]    As can be seen in  FIG. 5 , the packed, convoluted implants when in a final state in a bone cavity comprises a composite monolith that includes networked open spaces  150  and also includes a fiber-reinforced, high strength bone cement contained with a fluid impermeable polymer sleeve  125 ,  130 ,  130 ′. Of particular interest, the PMMA or other similar high strength polymer at all times is contained within the fluid impermeable surfaces to prevent contact with nerves and the patient&#39;s blood stream. 
         [0035]      FIG. 6  illustrates an alternative implant  200  and aspect of the invention for controlling extravasion of cement and monomers of bone cement when treating bone. As can be seen in the cut-away view of  FIG. 6 , the implant body  200  comprises a plurality of distensible or non-distensible concentric, fluid permeable shell elements  202   a - 202   d  (collectively  202 ) that can be collapsed, crushed or rolled into a compact form for introduction into bone through a small diameter introducer. The shell elements can number from about 2 to 20 and are substantially porous with pores  205  therein. The shell elements can be perforated, knit, woven, braided and an combination thereof. Suitable biocompatible materials are nylons, urethanes, Dacron and Teflons. In one aspect of the invention, the plurality of shell elements are inserted into a bone space  110  (cf.  FIG. 2 ), and then an, introducer  208  is penetrated through the shells  202  into an interior of the shell assembly. A radiopaque marker is carried on at least one interior shell. Thereafter, a bone cement such as PMMA is directly injected into the interior region  210  and the elements deform as expand to the irregular surface of bone space  110  (cf.  FIG. 2 ). At the same, the shell elements overlap and cause limited registration of pores  205 . As the shell elements  202  expand further, the outward pressures of the cement progressively cause the collective surfaces of the shell elements  202  to form a substantially fluid impermeable surface. The shell elements also can be inserted directly into cancellous bone an filled with a bon cement to provide a similar method fro preventing extravasion or leakage of bone cement. 
         [0036]      FIG. 7  illustrates the use of implant  200  of  FIG. 6 . The deformable implant is useful in containing bone cement within an assembly that becomes substantially fluid impermeable after filling with cement which prevents migration of the bone cement or monomers into the blood stream or into contact with nerves. The use of such elements solves a problem associated with prior art procedures wherein PMMA bone cement is injected directly into a bone cavity and its components can cause damage to nerves or can enter circulatory system and have serious consequences on the patient&#39;s health. While described in conjunction with a compression fracture of vertebra, it should be appreciated that the implant for sealing the extremities of a bone cavity from bone cement migration extends to similar uses in all bones such as the tibia and femur that are often treated with bone cement. 
         [0037]    The implants of the invention also can carry suitable radiovisible elements, for example as longitudinal stripes, at ends of each elongate element or any other form. The implants also can carry any suitable pharmacological agent for immediate or timed release. 
         [0038]    In another embodiment, a composite implant is provide that carries self-healing polymer components, for example microencapsulated components, that initiate a polymerization process when disrupted by shear forces in months or years following their implantation. The use of self-healing polymers has been proposed for polymer materials in industrial uses. The self-healing polymer implants of the invention are for the first time disclosed for use in a biomedical implant. Of particular interest, the self-healing polymer may be adapted for use in minimally invasive prophylactic procedures for needle injection into cancellous bone in elderly patients. Upon a compression fracture, the shear forces would release the self healing polymer to stabilize or support the bone defect. 
         [0039]    The above description of the invention intended to be illustrative and not exhaustive. A number of variations and alternatives will be apparent to one having ordinary skills in the art. Such alternatives and variations are intended to be included within the scope of the claims. Particular features that are presented in dependent claims can be combined and fall within the scope of the invention. The invention also encompasses embodiments as if dependent claims were alternatively written in a multiple dependent claim format with reference to other independent claims.