Abstract:
Instruments and methods for reducing and stabilizing bone fractures are presented, which include providing a cavity in bone, such as a vertebra, wherein the cavity is proximate to an endplate of the bone, such as a vertebra endplate, and wherein the cavity extends radially from a passage into the cavity. The methods further include providing a device, such as an inflatable device, into the cavity and manipulating the device for expansion. The cavity may be expanded thereby reducing and/or stabilizing the fracture. The fracture may be further reduced and/or stabilized by adding a material into the cavity.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/140,413 filed May 27, 2005, which claims the benefit of U.S. Provisional Patent Application No. 60/575,635 filed May 28, 2004. The entirety of both patent applications are hereby incorporated by reference to the fullest extent allowable. 
    
    
     BACKGROUND 
     The invention described generally relates to instruments and methods for application with skeletal disorders, and, in particular relates to instruments and methods for the reduction and stabilization of skeletal fractures. 
     Fracture reduction and/or stabilization are generally practiced to substantially restore or repair skeletal structures to their pre-fractured state. In practice, materials, such as in-situ curable materials (e.g., bone cements) and/or implants are often used to help stabilize fractured bone. In one clinical procedure known as vertebroplasty, bone cement is injected into a fractured vertebral body to stabilize bone fragments. This and other procedures may also additionally use one or a number of devices for reduction and stabilization of a fracture. For vertebroplasty, a device is used to assist in the formation of a cavity in the vertebra prior to injection of the in-situ curable material. Another device used with some procedures is a bone tamp used to reduce the fracture. 
     SUMMARY 
     The present invention solves many problems associated with current methods and devices for reduction, stabilization, restoration, and repair of skeletal fractures. 
     Generally, and in one form described herein are methods of reducing and/or stabilizing a fracture in bone. The method includes cutting a portion of the bone having a fracture to create a cavity. The cavity may be substantially axisymmetric and may be cut using any suitable device, such as a tissue cavitation device. The cavity is then expanded to reduce the fracture. A suitable expanding device includes a medical balloon as an example. The expanding device is typically positioned proximate to cortical bone. The fracture may be further reduced by filling the cavity with a material. The material may fully or partially fill the cavity. Examples of suitable materials include implants and in-situ materials that are curable or hardenable. Such materials may be permanent, resorbable, penetrating and combinations thereof. The material filling the cavity offers stabilization to the fracture. Any bone fragments near the fracture may also be stabilized. When suitable, the cutting of a portion of the bone having a fracture is preceded by the formation of at least one passage to the fracture site. Depending on the type of bone having the fracture, the passage(s) may be intracortical, extracortical, intrapedicular, extrapedicular, and combinations thereof. 
     Additionally, described herein is a method for treating bone comprising the steps of: forming a passage in a vertebra; forming a cavity in the vertebra, wherein the cavity at least extends radially from the passage, wherein the cavity has a first size and a first portion of the cavity is proximate to a vertebral endplate; providing an inflatable device configured for expansion; introducing the inflatable device configured for expansion into the cavity; and expanding the inflatable device configured for expansion to provide an expansion force sufficient to enlarge the cavity to a second size. The expansion force may be provided proximate to the vertebral endplate, comprising a first endplate and a second endplate. The expansion force may be provided to reduce a vertebral compression fracture. The first endplate may be a superior endplate and the second endplate may be an inferior endplate. Forming the cavity comprises a method of cutting bone, the method of cutting bone selected from the group consisting of shearing, cutting, scraping, and combinations thereof. The inflatable device may be a balloon. The inflatable device may be non-compliant. The inflatable device may be semi-compliant. The inflatable device may be configured to manipulate cortical bone to reduce a fracture. The method may further comprise filling the cavity with a material after expanding the inflatable device, the material selected from the group consisting of implantable material, in-situ curable material, in-situ hardenable material, permanent material, resorbable material, penetrating material, and combinations thereof. The passage in the vertebra may comprise forming an entry hole from which the cavity is formed. Forming the cavity may further comprise cutting bone. The cavity may be substantially axisymmetric. The cavity may be substantially non-axisymmetric. In one form, the second size of the cavity has an increased volume as compared with a volume associated with the first size of the cavity. Forming the passage in the vertebra may precede forming the cavity. Forming the passage in the vertebra may occur substantially concomitantly with forming the cavity. 
     Still further, described herein is a method for treating bone comprising the steps of: forming a passage in a vertebra along a linear axis; providing a tissue cavitation device; forming a cavity in the vertebra with the tissue cavitation device, wherein the cavity has first volume that extends from the passage proximate to a first vertebral endplate; providing an inflatable device configured for expansion in the cavity; and expanding the inflatable device configured for expansion within the cavity to expand the cavity to a second volume, wherein the second volume is greater than the first volume. The cavity is proximate to a second vertebral endplate. The cavity is proximate to but separated from the first vertebral endplate by a layer of cancellous bone. The cavity has a boundary and a portion of the boundary consists of cortical bone. The cavity has a boundary and a portion of the boundary consists of cancellous bone. The inflatable device configured for expansion is a balloon. In one form, expanding the inflatable device manipulates cortical bone to reduce a fracture. The method may further comprise filling the cavity after expanding with a material, wherein the material is a filling material selected from the group consisting of implant material, in-situ curable material, in-situ hardenable material, permanent material, resorbable material, penetrating material, and combinations thereof. In one form, forming the passage in the vertebra comprises forming an entry hole about which the cavity is formed. Forming the cavity in the vertebra may comprise disrupting bone. The cavity may be substantially axisymmetric. The cavity may be substantially non-axisymmetric. The cavity may be formed with rotational actuation of the tissue cavitation device. Forming the passage in the vertebra may precede forming the cavity. Forming the passage in the vertebra may occur substantially concomitantly with the step of forming the cavity. 
     Also described herein is a method of treating bone comprising the steps of: forming a passage in a vertebra; providing a tissue cavitation device, inserting the tissue cavitation device into the passage; forming a cavity with the tissue cavitation device along a central portion of the vertebra, wherein the cavity extends proximate to a vertebral body endplate; providing an inflatable device configured for expansion with a working fluid; inserting the inflatable device into the cavity that is the central portion of the vertebra; and expanding the inflatable device to expand the cavity. The cavity may be proximate a first region of the vertebral body endplate which includes cortical bone. The cavity may be proximate a second region of the vertebral body endplate which includes cortical bone, wherein the first region is a superior endplate and the second region is an inferior endplate. The cavity may be proximate a first region of the vertebral body endplate and separated from the first region by a layer of cancellous bone. In one form, the cavity has a boundary, a portion of which is cortical bone. The cavity may also have a boundary, a portion of which is cancellous bone. Forming the cavity may comprise a method of separating bone, the method of separating bone selected from the group consisting of shearing, cutting, scraping, and combinations thereof. The inflatable device may be a balloon. The inflatable device may be substantially non-compliant. The inflatable device may be semi-compliant. The inflatable device may be used to manipulate cortical bone to reduce a fracture. The method may further comprise filling the cavity with a material, wherein the material is a filling material selected from the group consisting of implant material, in-situ curable material, in-situ hardenable material, permanent material, resorbable material, penetrating material, and combinations thereof. The cavity may be substantially axisymmetric. The cavity may be substantially non-axisymmetric. In one form, a working end of the tissue cavitation device is transformable between a first shape for entry into the passage and a second shape for forming the cavity. In one or more embodiments, the tissue cavitation device comprises: a shaft having a diameter and a longitudinal axis; and flexible cutting element associated with the shaft, wherein the flexible cutting element is configured to assume a first shape for insertion and configured to assume a second shape suitable for forming the cavity that has a diameter greater than a diameter of the shaft when the shaft is rotated about the longitudinal axis of the shaft. The cavity is formed with rotational actuation of the tissue cavitation device. Wherein forming the passage in the vertebra may precedes forming the cavity. Wherein forming the passage in the vertebra may occur substantially concomitantly with forming the cavity. In some forms, expanding the inflatable device provides a distraction force. 
     A method for treating bone is also described that comprises: forming a passage in a vertebra along a linear axis; providing a tissue cavitation device; forming a cavity in the vertebra with the tissue cavitation device by separating bone, wherein the cavity is formed with rotational actuation of the tissue cavitation device, wherein the cavity extends from the passage; providing an inflatable device configured for expansion; and expanding the inflatable device configured for expansion within the cavity to enlarge the cavity. 
     Those skilled in the art will further appreciate the above-noted features and advantages of the invention together with other important aspects thereof upon reading the detailed description that follows in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
         FIG. 1  is a superior view of a human bone; 
         FIG. 2A  is another superior view of a human bone showing the bone a working channel; 
         FIG. 2B  is a cross-sectional view of the bone in  FIG. 2A  or  FIG. 1  showing a fracture; 
         FIG. 3  is a schematic of a device useful with the present invention showing (A) a side view, (B) a perspective view, and (C) a detailed perspective view of a portion of the device; 
         FIG. 4A  is a superior view of the bone of  FIG. 1  with a fracture site and after performing a step of the present invention; 
         FIG. 4B  is a cross-sectional view of the bone of  FIG. 4A  showing the step of  FIG. 4A  and a cavity within the bone; 
         FIG. 5A  is a superior view of the bone of  FIG. 4A  when performing another step of the present invention; 
         FIG. 5B  is a cross-sectional view of the bone of  FIG. 5A  showing the step of  FIG. 5A  and an expanding device in the cavity of the bone; 
         FIG. 6A  is a superior view of the bone of  FIG. 5A  when performing yet another step of the present invention; 
         FIG. 6B  is a cross-sectional view of the bone of  FIG. 6A  showing the step of  FIG. 6A  and a restored bone; 
         FIG. 7A  is a superior view of the bone of  FIG. 5A  when performing still another step of the present invention; and 
         FIG. 7B  is a cross-sectional view of the bone of  FIG. 7A  showing the bone with an in-situ material in the cavity. 
     
    
    
     DETAILED DESCRIPTION 
     Although making and using various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many inventive concepts that may be embodied in a wide variety of contexts. The specific aspects and embodiments discussed herein are merely illustrative of ways to make and use the invention, and do not limit the scope of the invention 
     In the description which follows like parts may be marked throughout the specification and drawing with the same reference numerals, respectively. The drawing figures are not necessarily to scale and certain features may be shown exaggerated in scale or in somewhat generalized or schematic form in the interest of clarity and conciseness. 
     Instruments and methods will be disclosed for reducing and stabilizing bone fractures. The method may be useful for fractured bone, including vertebral bone. Typically, vertebral bone fractures in compression. This type of fracture is most common in the thoracic and/or lumbar regions of the spine and may coincide with regions of osteoporotic bone. 
     Common medical nomenclature may be used when describing aspects of the present invention. As used herein, superior is nearer the head in relation to a specific reference point, inferior is nearer the feet in relation to a specific reference point, anterior is forward in relation to a specific reference point and posterior is rearward in relation to a specific reference point. The midsagittal plane is an imaginary plane dividing the body into a right side and left side. A frontal plane is any imaginary vertical plane orthogonal to the midsagittal plane. 
     Referring not to  FIG. 1 , the figure shows anatomical structures of a human bone. In this example, the bone is vertebra  1  in a superior view. Vertebra  1  is comprised of body  2  and posterior elements  3 . Posterior elements  3  include pedicle  4 . An edge view of midsagittal reference plane  18  is shown in  FIG. 1  as line X-X. Body  2  is generally comprised of two types of bone: cortical bone  12  and cancellous bone  14 . In contrast to cortical bone, cancellous bone has a substantial degree of porosity. In addition there are transition regions of varying porosity between cancellous and cortical bone. For the present invention, the bone does not necessarily require all the above-identified elements. For example, some bone do not comprise pedicle  4 ; other bone may be more symmetrical in shape when shown in superior view. All bone, however, will include a body with some degree of cancellous bone and some degree of cortical bone. 
     Vertebral  1  of  FIG. 1  is shown in a superior view in  FIG. 2A .  FIG. 2B  shows relevant cortical bone  12  structures including superior endplate  8 , inferior endplate  8 ′, and side wall  10 . As a possible site of fracture, fracture  16  is shown to include side wall  10  and cancellous bone  14 . Fractures may also occur in locations such as superior endplate  8  and inferior endplate  8 ′, as examples. 
     Continuing to refer to  FIG. 2A  and  FIG. 2B , passage  70  is formed within body  2  using any of a number of methods and surgical instruments known to one of ordinary skill in the art. Examples of possible surgical instruments used to create passage  70  include a bone biopsy needle, guide pin, stylet, stylus, drill-bit instrument, and obturator. Referring again to  FIG. 2A , working channel  20  is typically used to pass instruments into and out of body  2 . While body  2  will typically have a working channel, the formation of passage  70  may not be essential. In some instances, a drill-bit instrument is used within working channel  20  to create passage  70 , wherein the diameter of passage  70  is similar to the inner diameter of working channel  20 . Other appropriate instruments may also be used with the working channel. Working channel  20  typically remains in position for additional steps of the present invention. As shown in  FIG. 2A , access to body  2  is thru pedicle  4  (intrapedicular); however access may also include one or a number of posterior elements  3  or may be outside pedicle  4  (extrapedicular). The surgical approach typically depends on the site of the fracture, the patient, and/or surgeon preferences. 
     The term “tissue cavitation device” as used herein will refer to a device useful with the present invention. This device is capable of separating a portion of bone having a fracture and providing a cavity in the portion of the bone including or near the site of the fracture. By use of such a device, the device may separate the bone by cutting, shearing or scraping the bone, as examples. The separation creates a cavity that is typically substantially larger in diameter than the access passage, as shown in  FIG. 2A  as passage  70 . A suitable device and use of such a device is described in U.S. Pat. No. 6,746,451 to Middleton et. al, which is hereby incorporated by reference. The Middleton device is comprised of a rotatable shaft interconnected to a flexible cutting element. The flexible cutting element has a first shape suitable for minimally invasive passage into tissue, and the flexible cutting element has a means to move toward a second shape suitable for forming a cavity in the tissue, such as bone. Several embodiments of the Middleton device may also be adapted to a powered and/or a manual surgical drill, as needed. 
     Referring now to  FIG. 3A ,  FIG. 3B , and  FIG. 3C , examples of a suitable device are shown. Device  30  comprises a flexible cutting element  32 , a shaft  34 , a serration  36 , and a T-handle  38 . T-handle  38  allows the user (e.g., surgeon) to rotate device  30  during use or in the formation of a cavity. 
     Referring now to  FIG. 4A  and  FIG. 4B , vertebra  1  is shown with cavity  72  provided after use of a device, such as device  30  shown in  FIG. 3 . Here, cavity  72  was created by using a device, such as device  30 , within passage  70  to cut a portion of the bone, the bone being cancellous bone  14  and/or cortical bone  12 . Although passage  70  is useful to position device  30 , it is contemplated that a cavity  72  can be made without requiring passage  70 . Cavity  72 , as shown in  FIG. 4A  and  FIG. 4B , is generally spherical, although other shapes are also contemplated, such as cylindrical and elliptical shapes, as examples. In general, it is desirable to extend the boundary of cavity  72  so that it at least partially includes, or is in proximity of, superior endplate  8  and inferior endplate  8 ′. Hence, cavity  72  is typically in proximity to cortical bone  12 . Accordingly, cavity  72  may be bound, in part, by cortical bone  12 . Cavity  72  is initially formed by device  30 ; in which device  30  cuts, shears, and/or scrapes a portion of bone near the fracture. Cavity  72  is not initially formed by compacting the bone using an expanding device. 
     Often, it is desirable to have the height and width of cavity  72  be of similar or equal dimensions. Therefore, an axisymmetric shape of cavity  72  is useful, although non-axisymmetric shapes are also contemplated. For example, device  30 , shown in  FIG. 3 , may be designed, through the use of available materials and geometry, to effectively cut cancellous bone but ineffectively cut cortical bone which may lead to a non-axisymmetric bone cavity, despite complete rotation of shaft  34  during use of device  30 . Alternatively, both cancellous and cortical bone may be cut by device  30 . Thus, the boundaries of the cavity may be cortical and/or cancellous bone. Various elements of the present invention, to include position and size of the bone cavity, will become apparent to one of ordinary skill in the art. 
     A further step to reduce the fracture includes expansion of the cavity with an expanding device. The expanding device is one that expands the shape of the cavity in at least one dimension. The device, itself may be involved in the expansion. Alternatively, one or more materials may be used with the device for such expansion. Example of expanding devices are a medical balloon or SKy Bone Expander (Disc Orthopaedic Technologies Inc., New Jersey, USA). Other suitable expandable means may also be used. Referring now to  FIG. 5A  and  FIG. 5B , expanding device  40  is positioned within cavity  72 . For  FIGS. 5A and 5B , expanding device  40  is a medical balloon which is inflated with working substance  46 , such as a fluid or saline. Readily available surgical inflation devices, including a syringe and syringe-like devices, are suitable for pressurizing the expanding device. Not every expanding device, however, will require pressurization. Each expanding device will have components and functions known to those skilled in the art. For example, expanding device  40  as shown in  FIG. 5A  and  FIG. 5B , typically comprises an expandable portion  41 , inner cannula  42 , and outer cannula  44 . The expandable portion  41  may be constructed of a number of materials, such as a non-compliant or semi-compliant material (e.g., poly(ethylene terephthalate) or Nylon). For any expanding device, the expanding portion may be resorbable, nonresorbable, porous or nonporous. 
     In general, because cortical bone is stiffer and stronger as compared with cancellous bone, expanding device  40  may be positioned initially at or in proximity to cortical bone  12 . The position of expanding device  40  is typically based on the size, shape, and location of cavity  72 . For example, with expanding device  40  as a medical balloon, the top and bottom surface of expandable portion  41  may be initially positioned at or in proximity of cortical bone  12  upon initial pressurization of expandable portion  41 . Therefore expandable portion  41  may provide relatively direct distraction forces against superior endplate  8  and inferior endplate  8 ′ upon pressurization of expandable portion  41 . The width of expandable portion  41  relates to the vertical distraction forces expandable portion  41  provides for a given pressure. Relative to passage  70 , cavity  72  is typically larger, allowing pressurization of a relatively large expandable portion  41 . Thus, for a given pressure, a larger expanding expandable portion  41  would generally provide greater distraction forces. Or, for a required distraction force, a larger expanding portion  41  generally requires lower pressure. Typically, a larger expanding device provides greater surface area for distraction and provides broader, more uniform distraction, while avoiding local pressure concentrations. Referring to  FIG. 5B , H 1  represents the height of body  2  prior to reduction of the fracture. Inflation of expandable portion  41  is intended to reduce the fracture in the form of an increased body height of the bone in at least one dimension. 
     Referring now to  FIG. 6A  and  FIG. 6B , body  2  is shown following inflation of expanding device  40  of  FIG. 5  and removal of expanding device  40 . An expanding device may include an implantable portion subsequently left in the patient to become permanent or later resorbed. In suitable embodiments, an expandable portion of expanding device  40  may remain in cavity  72 ′ and be filled with a material further described below. The material and/or the expandable portion may remain permanently in cavity  72 ′ or be later resorbed. 
     Referring specifically to  FIG. 6B , a new vertebral body height, H 2 , is established in the cavity, reflecting partial or significant restoration toward the pre-fractured height of body  2 . In addition, cavity  72 , as initially shown in  FIG. 4 , is now enlarged or otherwise modified, as represented in  FIG. 6A  and  FIG. 6B  by cavity  72 ′. Cavity  72 ′ may, thus, be associated with a reduction of the fracture. This may include, for example as described above, a change in the spatial relationship between endplate  8  and endplate  8 ′. 
     The fracture may be further reduced and/or stabilized by any of a number of means, including introduction of a material. Some examples of suitable materials include an implant, a support, an in situ material that is hardenable or curable, and other equivalents. An example of a material used for further reduction is shown in  FIG. 7A  and  FIG. 7B . Here, cavity  72 ′ is filled with in-situ material  50  to provide stability and strength to body  2 . The in-situ material  50  may fully or partially fill the volume of cavity  72 ′, including between any bone fragments and any related fractures, especially fracture fissures interconnected directly to cavity  72 ′. In-situ curable material  50  may also penetrate the pores of cancellous bone  14 . The in-situ material may be a permanent material or may be resorbable. Alternatively, the Suitable in-situ materials that be hardened or curable include polymethylmethacrylate-based bone cements and bone substitute materials, such as calcium sulfate compounds, calcium phosphate compounds, demineralized allografts, hydroxyapetites, carbonated apetites (e.g., Synthes&#39; Norian Bone Void Filler), collagen mixtures, mineral and cytokine mixtures, terpolymer resins, difunctional resins (e.g., Orthovita&#39;s CORTOSS®), and combinations thereof, as examples. Any passage to cavity  72  and  72 ′, if present, such as working channel  20  or passage  70 , is either filled or allowed to heal. Any components used for the introduction of material  50  (or its equivalents) are similarly removed. 
     The instruments and methods presented in this disclosure are used as examples of the present invention. Those skilled in the art will be able to develop modifications and variants that do not depart from the spirit and scope of the present invention. Variations include using a porous expanding device. Alternately, an expanding device may be filled with a material (e.g., implant or in-situ material that is curable or hardenable) and subsequently left in the patient to become permanent or later resorbed. It is also understood that the expanding device may be an implant or include an implant and, thus, all or part of the device may remain in cavity  72 ′. Such implants may be metallic or nonmetallic, coated or noncoated. 
     Alternate surgical approaches are also within the scope of the present invention. For example the instruments and methods may be used on the right side and left side of a body of a bone, such as in a bipedicular approach for vertebral bone. The present invention is applicable to the reduction and stabilization of any bone or fracture site, including fractured vertebra. Accordingly, the present invention offers restoration and repair of a fractured bone comprising cortical and/or cancellous bone. 
     Additional objects, advantages and novel features of the invention as set forth in the description, will be apparent to one skilled in the art after reading the foregoing detailed description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instruments and combinations particularly pointed out here.