Patent Publication Number: US-2005124999-A1

Title: Device and method for radial delivery of a structural element

Description:
This application claims priority to the U.S. Provisional Patent Application No. 60/516,326, filed on Oct. 31, 2003. 
    
    
     FIELD OF THE INVENTION  
      This invention relates generally to the delivery of structural elements into a desired location and, in particular, to a device and methods of percutaneous fixation of a spinal compression fracture and reexpanding a partially collapsed vertebral body by seating a rod-like structure within the vertebral body.  
     BACKGROUND OF THE INVENTION  
      Osteoporotic spinal compression fractures (crushing injuries to one or more vertebrae) represent a major health problem worldwide with as many as 700,000 injuries occurring annually in the United States. Until recently, the treatment of vertebral compression fractures has consisted of conservative measures including rest, analgesics, dietary, and medical regimens to restore bone density or prevent further bone loss, avoidance of injury, and bracing. Unfortunately, the typical patient is an elderly person who generally does not tolerate extended bed rest well. As a result, minimally invasive surgical methods for treating vertebral compression fractures have recently been introduced and are gaining popularity (U.S. Pat. No. 6,595,998).  
      One technique used to treat vertebral compression fractures is the injection of bone filler, such as polymethyl methacrylate (PMMA), into the fractured vertebral body. This procedure is commonly referred to as percutaneous vertebroplasty. But this procedure cannot be used to reestablish lost spinal column height.  
      Kyphoplasty is another vertebral fracture treatment that uses one or two balloons, similar to angioplasty balloons, to attempt to reduce the fracture and restore vertebral height prior to injecting the bone filler. Two balloons are typically introduced into the vertebra via bilateral transpedicular cannulae. The balloons are inflated to reduce the fracture. After the balloon(s) is deflated and removed, leaving a relatively empty cavity, bone cement is injected into the vertebra. In theory, the inflation of the balloons restores vertebral height. However, it is difficult to consistently attain meaningful height restoration. It appears the inconsistent results are due, in part, to the manner in which the balloon expands in a compressible media and the structural orientation of the trabecular bone within the vertebra (U.S. Pat. No. 6,595,998).  
      Recently, another approach to the treatment of the spinal compression fractures have been described in U.S. Pat. No. 6,595,998. The method involves consecutive inserting a plurality of wafers between the tissue surfaces to create a column of wafers. The column expands in a given direction as wafers are consecutively added to the column. However, this method appear to require application of axial force to move a pre-assembled column of the wafers into the bone, which may lead to an inadvertent perforation of the anterior cortex of the target vertebral body by the column. Moreover, the method requires a high precision in aligning and fitting the wafers on top of each other and, thus, is quite laborious.  
      There are many other physical conditions, the treatment of which involves separating two tissue surfaces and their support away from one another. Depending on the condition being treated, the tissue surfaces may be opposed or contiguous and may be bone, skin, soft tissue, or a combination thereof. (U.S. Pat. No. 6,595,998).  
      Outside of the medical field, there is also often a need to provide a structural element that keeps two surfaces away from each other. In certain environments, the delivery of such structural element into the destination must be through a small opening or an access port.  
      Therefore, an unfulfilled need still exists for effective, economical, and simple methods of delivery of structural elements to a particular destination through a small opening.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an object of the present invention to provide simple and effective devices and methods of a radial delivery of a structural element. More particular, it is an object of the invention to provide devices and methods for percutaneous fixation of a spinal compression fracture and reexpanding a partially collapsed vertebral body.  
      These and other objects are achieved in the present invention by utilizing a device for the delivery of a structural element to a destination. The device comprises a channel and a plunger slidably positioned inside the channel. The channel has a proximal end, a distal end, and a barrier formed across the channel at the distal end. The plunger is adapted to move the structural element axially through the channel from the proximal end to the distal end and to push it radially into the destination.  
      In one embodiment, the device is used for percutaneous fixation of a spinal compression fracture and reexpanding a partially collapsed vertebral body. In this embodiment, the structural element may be selected from a group consisting of wafers, rod-like structures, plugs, pledgets of bone matrix material, cadaver bone, and a patient&#39;s autologous bone.  
      In one embodiment, the channel has a side wall and a window formed through the side wall adjacent to the distal end. In this embodiment, the plunger is adapted to push the structural element radially through the window into the destination.  
      In another embodiment, an expandable sack is removably attached to the window in a way such that when the structural elements are pushed radially through the window, they drop into the sack. Thus, in this embodiment, the structural elements are placed into the destination in the sack.  
      In another aspect, the present invention provides another device for percutaneous fixation of a spinal compression fracture and reexpanding a partially collapsed vertebral body. The device comprises: (i) a channel having a side wall, an open proximal end, and an open distal end; (ii) an expandable sack circumferentially removably attached to the open distal end, wherein an opening in the sack communicates with the channel; and (iii) a plunger slidably positioned inside the channel. The plunger is adapted to move a rod-like structure through the channel into the vertebral body, whereby the rod-like structure is placed into the vertebral body in the sack.  
      In still another aspect, the present invention provides a method of a radial delivery of a structural element to a destination. The method comprises providing a delivery device described above; loading the structural element into the channel; pushing the structural element axially with the plunger until it reaches the barrier at the distal end; and applying a radial force to the plunger, whereby the plunger pushes the structural element radially into the destination.  
      The method may be used for percutaneous fixation of a spinal compression fracture and reexpanding a partially collapsed vertebral body in a subject. In one embodiment, rod-like structures are used as a structural element.  
      In yet another aspect, the present invention provides a kit for percutaneous fixation of a spinal compression fracture and reexpanding a partially collapsed vertebral body in a subject. The kit comprises a plurality of structural elements suitable for insertion into the vertebral body; and a delivery device described above.  
      The above-described devices and methods of the present invention provide a number of unexpected advantages over the existing delivery devices and methods. The devices have a simple construction and are easy to use. The devices and methods call for structural elements to be deposited within the target “sideways,” thus avoiding antegrade force from being applied to the structural element. This, in turn, avoids inadvertent perforation of the anterior cortex of the target vertebral body by the structural element.  
      Also, when rod-like structures are being deposited within the target vertebral body, with their gradual and progressive deposition, the height of the partially collapsed vertebral body gradually increases. Such gradual increase makes the procedure safer and easier to perform.  
      The invention is defined in the appended claims and is described below in its preferred embodiments. 
    
    
     DESCRIPTION OF THE FIGURES  
      The above-mentioned and other features of this invention and the manner of obtaining them will become more apparent, and will be best understood by reference to the following description, taken in conjunction with the accompanying drawings, in which:  
       FIGS. 1   a - 1   c  schematically show the operation of the delivery device in accordance with one embodiment of the present invention.  
       FIGS. 2   a  and  2   b  schematically show the operation of the delivery device in accordance with another embodiment of the present invention.  
       FIGS. 3   a - 3   c  schematically show delivery devices in accordance with several embodiments of the present invention.  
       FIGS. 4   a  and  4   b  schematically show the delivery device with an expandable sack in accordance with one embodiment of the present invention. The operation of device ( FIG. 4   a ) and some configurations of the sack ( FIG. 4   b ) are shown.  
       FIG. 5  illustrates a method of the percutaneous fixation of a compression fracture comprising a step of rotating the delivery device in accordance with one embodiment of the present invention.  
       FIGS. 6   a - 6   d  depict some tools that may be used to form a passage through the pedicles for placement of the delivery device of the present invention ( FIGS. 6   a - 6   c ) and a self-installing delivery device ( FIG. 6   d ). 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIG. 1 , in one aspect, the present invention is directed to a device  10  for delivery of a structural element  12  to a destination. The device comprises a channel  13  with a proximal end  14 , a distal end  16 , and a barrier  18  formed across the channel  13  at the distal end  16 . The device further comprises a plunger  20  slidably positioned inside the channel  13 . The plunger  20  is adapted to move the structural element  12  axially i-i through the channel from the proximal end  14  to the distal end  16  and to push it radially ii-ii into the destination.  
      For the purposes of the present invention, the terms “radial” or “radially” mean positioned, occurring, applying force or moving along a ray radiating outward from the longitudinal axis of the channel  13 . Although upward radial movement ii-ii is shown in  FIG. 1   c,  it is to be understood that the phrase “push it radially” is not limited to upward movement of the plunger, but includes all possible radial movements according to the definition of the term “radial” given above.  
      A variety of applications is possible for the delivery device  10  of the present invention. For example, it may be used to deliver a broad range of agents and structural elements to different sites within the body. Within the vertebral body and other bones, the device may be used to deposit wafers, rod-like structures, plugs or pledgets of bone matrix material, cadaver bone or the patient&#39;s autologous bone with or without bone morphogenetic protein (BMP). Radiophamaceuticals/radiation sources, chemotherapeutic drugs, or biological agents (such as stem cells or gene therapy vectors) for the treatment of cancer or a host of degenerative diseases may also be deposited within bone, bodily organs or the brain of a human or an animal. These and other structural elements and agents are known and commonly used by those skilled in the medical and veterinary arts. Accordingly, the known features of such structural elements and agents will not be discussed here in detail.  
      Outside of the field of medicine, this device employing the radial delivery of some agent or a structural element may be used in manufacturing or mining, especially where one needs to fill a cavity through a small opening or an access port.  
      Referring to  FIGS. 2   b - 2   e,  in one embodiment, the channel  13  has a side wall  21  and a window  22  formed through the side wall adjacent to the distal end  16 . The plunger  20  is adapted to push the structural element  12  radially through the window into the destination ( FIGS. 2   d - 2   e ). The channel may be inside a pipe-like holder ( FIG. 3   a ) or inside a half-pipe holder ( FIG. 3   b ). Preferably, the window  22  has a length that is about the same as a length of the structural element. In one embodiment, the delivery device  10  comprises at least one additional window.  
      Referring to  FIG. 3   b,  in another embodiment, the delivery device  10  comprises an expandable sack  25  removably attached to the window  22  in a way such that when the structural elements are pushed radially through the window, they drop into the sack. According to this embodiment, the structural elements are placed into the desired destination in the sack  25 . The sack may separate from the delivery device when a predetermined number of structural elements is accumulated in the sack or/and the delivery device  10  is withdrawn from the body.  
      Referring to  FIGS. 2   b - 2   e,  in one embodiment, the structural element  12  is a rod-like structure. The rod-like structure may be an intramedullary rod made of a metal, an alloy, a polymer, a cadaver bone material, or a composite. In one embodiment shown in  FIGS. 2   d  and  2   e,  the rod-like structure has a front end  50  and a back end  52 . The plunger  20  engages the back end  52  of the rod-like structure  12  with its first end  53  to move the rod-like structure axially through the channel. To facilitate the engagement between the plunger  20  and the rod-like structure  12 , the first end  53  of the plunger and the back end of the rod-like structure  52  are beveled. In one embodiment, to improve sliding of the rod-like structure through the channel, the rod-like structure  12  has a rounded front end  50 .  
      The rod-like structure, the channel and the plunge may be made of any durable material including, but not limited to, the same or different metal or plastic materials. The rod-like structures may be of any shape as long as they fit in and may be moved through the channel first axially and, then, radially. For example, the rod-like structures may have a cross-section that is normal to its longitudinal axis and wherein the cross-section is selected from a group consisting of circles, ovals, polygons, and figures combining curved and straight sides. In one embodiment, the rod-like structures have a length of 1.5-2 cm and a diameter of about 13 gauge.  
      In another embodiment, the rod-like structure has a leading edge  54  on its side to facilitate its entry into the vertebral body. In yet another embodiment, the channel, the rod-like structure, or both have a lubricated coating that facilitates movement of the rod-like structure through the channel  13 .  
      Referring to  FIG. 3   c,  the delivery device  10  may further comprise a plunger-advancing mechanism  30  in communication with the plunger  20 . In one embodiment, the plunger  20  is advanced with the aid of a screw-like mechanism, which generates the radial force necessary to extrude the structural element into the desired destination, such as vertebral body. In this embodiment, the plunger has a threaded portion  60  with an external thread and the plunger-advancing mechanism comprises a sleeve  62 , defining an interior channel having an internal thread complimentary to the external thread of the plunger. The threaded portion of the plunger  60  is received through the sleeve  62  whereby the external thread of the plunger mates with the internal thread of the sleeve. The plunger advancing mechanism further comprises a nut or a handle  64  attached to the threaded portion of the plunger  60 , wherein rotation of the nut or the handle  64  advances the plunger  13  forward into the channel or retrieves it therefrom.  
      In one embodiment, the screw-like device provides sufficient radial force to plunger to enable its radial movement. In another embodiment, the delivery device comprises an additional mechanism, such as a spring-loaded mechanism, that enables radial movement of the plunger  20  inside the channel  13 . In still another embodiment, a portion of the channel  13  containing the window is detachable from the rest of the channel and may be left in the subject.  
      The delivery device  10  may further comprise a feeder  40  operatively connected with the channel  13 . The feeder  40  is adapted for holding a plurality of the structural elements  12 , such as rod-like structures, and for placing them into the channel sequentially and on demand. The feeder may further comprise a trigger mechanism for forcing structural elements  12  into the channel  13 . Those skilled in the art are familiar with various types of feeders and would be able to select one suitable for the instant application based on the disclosure provided herein. For example, the feeder may work similar to an ammunition clip for an automatic weapon. Each time the plunger is sufficiently withdrawn, it allows another structural element to be spring-loaded into the channel  13 . Another suitable feeder is described in the U.S. Pat. No. 6,595,998, the entire content of which is incorporated herein by the reference.  
      In reference to  FIGS. 4   a  and  4   b,  in another aspect, the present invention provides a device for percutaneous fixation of a spinal compression fracture and reexpanding a partially collapsed vertebral body in a subject by seating a rod-like structure within the vertebral body. The device comprises a channel  13  having an open proximal end  40  and an open distal end  42 . The device also includes an expandable sack  44  circumferentially removably attached to the open distal end  42  in a way that ensures that an opening in the sack  46  communicates with the channel  13 . A plunger  20  is slidably positioned inside the channel  13 . The plunger is adapted to move a structural element, such a rod-like structure  12 , through the channel into the vertebral body, whereby the rod-like structure is placed into the vertebral body in the sack  44 .  
      The sack may be made of any durable and biocompatible material. For example, the material for the sack  44  may be selected from a group consisting of a metal, a metal alloy, or a plastic. Some embodiments of the sack  44  of the present inventions include, but are not limited to, a thin-walled tantalum or elgiloy metal tube with multiple linear fenestrations ( FIG. 4   b (i)); a compressed tube constructed from a thin braided metal or metal alloy wires ( FIG. 4   b (ii)); or a polymer mesh ( FIG. 4   c (iii)). Optionally, the sack may be removably attached to distal end  42  by any suitable method, including, but not limited to, a thin latex, adhesive, or an elastic sheath.  
      In another aspect, the present invention provides a method of a radial delivery of a structural element to a destination. The method, which is illustrated in  FIGS. 2   a - 2   e,  comprises: (a) providing a delivery device  10  having a channel  13  with a distal end  16  and a barrier  18  formed across the channel at the distal end; and a plunger  20  slidably positioned inside the channel  13  ( FIGS. 2   b  and  2   c ); (b) loading the structural element  12  into the channel; (c) pushing the structural element  12  axially (marked as a direction i-i)with the plunger  20  ( FIG. 2   c ) until it reaches the barrier  18  at the distal end ( FIG. 2   d ); and (d) applying a radial force ii-ii to the plunger  20 , whereby the plunger  20  pushes the structural element  12 , such as a rod-like structure, radially into the destination.  
      In the embodiment shown in  FIGS. 2   a - 2   e,  the channel has a side wall  21  and a window  22  formed through the side wall adjacent to the distal end. In this embodiment, the method further comprises steps of sliding the plunger between the structural element and the side wall and pushing the structural element radially through the window  22 . The method of the present invention may also include a step of placing the delivery device proximate to the target destination, such as a collapsed vertebral body, and with the window facing the destination. In another embodiment, the method further comprises a step of withdrawing the plunger from the channel after pushing one structural element through the window to allow the loading of the next structural element.  
      A plurality of the structural elements may be deployed into the destination by sequentially repeating steps (b)-(e) of the method above with each structural element. Referring to  FIG. 5 , in yet another embodiment, the method further comprises a step of rotating the delivery device ( FIG. 5 (ii)) after placing one structural element ( FIG. 5 (i)) and before placing next structural element into a different location within the destination. Such rotation of the delivery device would direct the placement of structural elements, such as minirods, either cephalad or caudad, in order to achieve the desired effect of restoring the vertebral body&#39;s height. As shown in  FIG. 5 (iii), the turning the delivery device after placing a structural element, ensures more even, multi-directional distribution of the structural elements in the target area, such as bone.  
      In one embodiment, the delivery device is used for stabilizing spinal compression fractures and reexpanding partially collapsed vertebral bodies. In this embodiment, the device may be inserted bilaterally transpedicularly into the affected vertebral body. This may be accomplished under fluoroscopic guidance by first driving 11-gauge bone biopsy needles  80  ( FIG. 6   a ) through the pedicles and into the affected body. The stylet of these needles is replaced with an 0.038″ guidewire or surgical K-wire over which is inserted an 8-gauge metal sheath  82  with a central metal dilator ( FIGS. 2   a  and  6   b ). The sheath is inserted to the pedicle-body junction bilaterally. A small hand drill  84  may be inserted through these sheaths and rotated to create a pathway anterior to the metal sheaths for the subsequent insertion of an 11-gauge metal delivery tube device to deliver and deploy multiple rod-like structures.  
      In another embodiment, the present invention provides a self-installing delivery device  10  having a sharp-needle like distal end  16  that facilitates its insertion without a need for all or some of the installation tools described above. The delivery device also has window  22  for radial ejection of structural elements from the delivery device.  
      The structural elements may be “minirods” having a length of 1.5-2 cm and a diameter of about 13 gauge. In one embodiment, the delivery device for the minirod is an 11-gauge metal tube with a sealed distal end and a distal side window with a length approximately the same as the minirod. Minirods may be sequentially deployed within the vertebral body by pushing the minirod to the distal end of the delivery tube with a plunger advanced forward by a screw mechanism, much the same as the screw mechanism used in balloon angioplasty inflation syringes. Once the minirod reaches the side window zone of the distal delivery tube, further advancement of the plunger causes the minirod to be pushed out radially from the lumen of the delivery tube, compacting the soft demineralized bone of the partially collapsed vertebral body. Accordingly, advancing the plunger completely to the end of the lumen of the delivery tube results in the total extrusion of the minirod from the delivery tube. The plunger may then be withdrawn from the delivery lumen (by disengaging the screw mechanism and pulling it back), thus allowing the insertion of the next minirod.  
      At the conclusion of the procedure, the 8-gauge metal sheaths are removed from the pedicles and the skin incisions are sterilely dressed. The entire procedure may be performed under fluoroscopic guidance with the patient in the prone position. I.V. sedation with local anesthesia or general endotracheal anesthesia may be utilized.  
      In addition to restoring vertebral body height, the structural elements of the present invention may act as multiple intramedullary rods, stabilizing the fractured vertebral body, and increasing its tensile strength.  
      In another embodiment, the methods of the present invention may further comprise a step of injecting a polymer or a bone matrix material within and around the rod-like structures placed into the vertebral body. The bone matrix material may comprise an osteoconductive or an osteoinductive material, such as bone morphogenetic protein (or BMP). The polymer may be polymethyl methacrylate (PMMA) or a biocompatible polyurethane preparation. Polymers and bone matrix material would act to enhance fracture stabilization and bone tensile strength. The injection may be made through the delivery device prior to its removal.  
      In another aspect, the present invention provides a kit for percutaneous fixation of a spinal compression fracture and reexpanding a partially collapsed vertebral body in a subject. The kit comprises a plurality of structural elements suitable for insertion into the vertebral body; and a delivery device of the present invention as described above. The structural elements may have the same, or a different, size. Referring, for example, to  FIG. 3   a,  in one embodiment, the structural elements of at least two different sizes are used and the window  22  is sized to accommodate the longest structural element.  
      It will be apparent to those skilled in the art that various modifications and variations can be made in system and methods of the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention cover modifications and variations of this invention that come within the scope of the appended claims and their equivalents.