Abstract:
A bone fixation device having an elongate body, an actuateable gripper disposed on the elongated body, an actuator operably connected to the gripper to deploy the gripper from a retracted configuration to an expanded configuration, and a membrane surrounding at least a portion of the elongate body or the gripper is disclosed. Also disclosed are systems, surgical kits and methods of using a bone fixation device with a membrane cover.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. § 119 of U.S. provisional application Ser. No. 60/949,071, entitled “FRACTURE FIXATION DEVICE, TOOLS AND METHODS”, filed Jul. 11, 2007, the disclosure of which is incorporated herein by reference. 
       INCORPORATION BY REFERENCE 
       [0002]    All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to methods and systems for providing reinforcement of bones. More specifically, the present invention relates to methods and systems for providing reconstructive surgical procedures and devices for reconstruction and reinforcement bones, including diseased, osteoporotic and fractured bones. 
         [0004]    Bone fractures are a common medical condition both in the young and old segments of the population. However, with an increasingly aging population, osteoporosis has become more of a significant medical concern in part due to the risk of osteoporotic fractures. Osteoporosis and osteoarthritis are among the most common conditions to affect the musculoskeletal system, as well as frequent causes of locomotor pain and disability. Osteoporosis can occur in both human and animal subjects (e.g. horses). Osteoporosis (OP) and osteoarthritis (OA) occur in a substantial portion of the human population over the age of fifty. The National Osteoporosis Foundation estimates that as many as 44 million Americans are affected by osteoporosis and low bone mass, leading to fractures in more than 300,000 people over the age of 65. In 1997 the estimated cost for osteoporosis related fractures was $13 billion. That figure increased to $17 billion in 2002 and is projected to increase to $210-240 billion by 2040. Currently it is expected that one in two women, and one in four men, over the age of 50 will suffer an osteoporosis-related fracture. Osteoporosis is the most important underlying cause of fracture in the elderly. Also, sports and work-related accidents account for a significant number of bone fractures seen in emergency rooms among all age groups. 
         [0005]    One current treatment of bone fractures includes surgically resetting the fractured bone. After the surgical procedure, the fractured area of the body (i.e., where the fractured bone is located) is often placed in an external cast for an extended period of time to ensure that the fractured bone heals properly. This can take several months for the bone to heal and for the patient to remove the cast before resuming normal activities. 
         [0006]    In some instances, an intramedullary (IM) rod or nail is used to align and stabilize the fracture. In that instance, a metal rod is placed inside a canal of a bone and fixed in place, typically at both ends. See, for example, Fixion™ IM(Nail), www.disc-o-tech.com. This approach requires incision, access to the canal, and placement of the IM nail. The nail can be subsequently removed or left in place. A conventional IM nail procedure requires a similar, but possibly larger, opening to the space, a long metallic nail being placed across the fracture, and either subsequent removal, and or when the nail is not removed, a long term implant of the IM nail. The outer diameter of the IM nail must be selected for the minimum inside diameter of the space. Therefore, portions of the IM nail may not be in contact with the canal. Further, micro-motion between the bone and the IM nail may cause pain or necrosis of the bone. In still other cases, infection can occur. The IM nail may be removed after the fracture has healed. This requires a subsequent surgery with all of the complications and risks of a later intrusive procedure. 
         [0007]    External fixation is another technique employed to repair fractures. In this approach, a rod may traverse the fracture site outside of the epidermis. The rod is attached to the bone with trans-dermal screws. If external fixation is used, the patient will have multiple incisions, screws, and trans-dermal infection paths. Furthermore, the external fixation is cosmetically intrusive, bulky, and prone to painful inadvertent manipulation by environmental conditions such as, for example, bumping into objects and laying on the device. 
         [0008]    Other concepts relating to bone repair are disclosed in, for example, U.S. Pat. No. 5,108,404 to Scholten for Surgical Protocol for Fixation of Bone Using Inflatable Device; U.S. Pat. No. 4,453,539 to Raftopoulos et al. for Expandable Intramedullary Nail for the Fixation of Bone Fractures; U.S. Pat. No. 4,854,312 to Raftopolous for Expanding Nail; U.S. Pat. No. 4,932,969 to Frey et al. for Joint Endoprosthesis; U.S. Pat. No. 5,571,189 to Kuslich for Expandable Fabric Implant for Stabilizing the Spinal Motion Segment; U.S. Pat. No. 4,522,200 to Stednitz for Adjustable Rod; U.S. Pat. No. 4,204,531 to Aginsky for Nail with Expanding Mechanism; U.S. Pat. No. 5,480,400 to Berger for Method and Device for Internal Fixation of Bone Fractures; U.S. Pat. No. 5,102,413 to Poddar for Inflatable Bone Fixation Device; U.S. Pat. No. 5,303,718 to Krajicek for Method and Device for the Osteosynthesis of Bones; U.S. Pat. No. 6,358,283 to Hogfors et al. for Implantable Device for Lengthening and Correcting Malpositions of Skeletal Bones; U.S. Pat. No. 6,127,597 to Beyar et al. for Systems for Percutaneous Bone and Spinal Stabilization, Fixation and Repair; U.S. Pat. No. 6,527,775 to Warburton for Interlocking Fixation Device for the Distal Radius; U.S. Patent Publication US2006/0084998 A1 to Levy et al. for Expandable Orthopedic Device; and PCT Publication WO 2005/112804 A1 to Myers Surgical Solutions, LLC for Fracture Fixation and Site Stabilization System. Other fracture fixation devices, and tools for deploying fracture fixation devices, have been described in: U.S. Patent Appl. Publ. No. 2006/0254950; U.S. Ser. No. 60/867,011 (filed Nov. 22, 2006); U.S. Ser. No. 60/866,976 (filed Nov. 22, 2006); and U.S. Ser. No. 60/866,920 (filed Nov. 22, 2006). 
         [0009]    In view of the foregoing, it would be desirable to have a device, system and method for providing effective and minimally invasive bone reinforcement and fracture fixation to treat fractured or diseased bones. 
       SUMMARY OF THE INVENTION 
       [0010]    Fracture fixation devices, and tools for deploying fracture fixation devices, have been described. See, e.g., U.S. Patent Appl. Publ. No. 2006/0254950; U.S. Ser. No. 60/867,011 (filed Nov. 22, 2006); U.S. Ser. No. 60/866,976 (filed Nov. 22, 2006); and U.S. Ser. No. 60/866,920 (filed Nov. 22, 2006). 
         [0011]    The fracture fixation device of the invention is adapted to be inserted through an opening of a fractured bone, such as the radius (e.g., through a bony protuberance on a distal or proximal end or through the midshaft) into the intramedullary canal of the bone. In some embodiments, the fixation device has two main components, one configured component for being disposed on the side of the fracture closest to the opening and one component configured for being disposed on the other side of the fracture from the opening so that the fixation device traverses the fracture. 
         [0012]    The device components cooperate to align, fix and/or reduce the fracture so as to promote healing. The device may be removed from the bone after insertion (e.g., after the fracture has healed or for other reasons), or it may be left in the bone for an extended period of time or permanently. 
         [0013]    In some embodiments, the fracture fixation device has one or more actuatable anchors or grippers on its proximal and/or distal ends. These anchors may be used to hold the fixation device to the bone while the bone heals. 
         [0014]    In some embodiments, to aid in insertion into the intramedullary canal, at least one component of the fracture fixation device has a substantially flexible state and a substantially rigid state. Once in place, deployment of the device also causes the components to change from the flexible state to a rigid state to aid in proper fixation of the fracture. At least one of the components may be substantially rigid or semi-flexible. At least one component may provide a bone screw attachment site for the fixation device. 
         [0015]    In some embodiments, a bone fixation device is provided which includes an elongate body, an actuateable gripper disposed on the elongated body, an actuator operably connected to the gripper to deploy the gripper from a retracted configuration to an expanded configuration, and a membrane surrounding at least a portion of the elongate body or the gripper. 
         [0016]    In some embodiments, a surgical kit is provided which includes a bone fixation device having an elongate body, an actuateable gripper disposed on the elongated body, and an actuator operably connected to the gripper to deploy the gripper from a retracted configuration to an expanded configuration, and a membrane configured to surround at least a portion of the bone fixation device. 
         [0017]    In some embodiments, a method of repairing a fracture of a bone is provided. One such method includes covering at least a portion of a bone fixation device with a flexible membrane, inserting the device and the membrane into an intramedullary space of a bone to place a first portion of the device on one side of a fracture and a second portion of the device on another side of the fracture; and operating an actuator to deploy at least one gripper of the device to engage an inner surface of the intramedullary space to anchor the fixation device to the bone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0018]    A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
           [0019]      FIG. 1  shows a fracture fixation device according to one embodiment of this invention and two possible insertion paths: one near the bone end and another at midshaft. 
           [0020]      FIGS. 2 and 3  show the fracture fixation device of  FIG. 1  in place within fractured bones. 
           [0021]      FIG. 4  shows an embodiment of a fracture fixation device with a curved hub at one end and a straight hub at another end. 
           [0022]      FIG. 5  shows another embodiment of a fracture fixation device inserted into an intramedullary space of a fractured bone. 
           [0023]      FIGS. 6 and 7  show yet another embodiment of a fracture fixation device being inserted into a fractured bone. 
           [0024]      FIG. 8  shows the device of  FIG. 6  in an undeployed configuration. 
           [0025]      FIG. 9  is a cross-sectional view of the device of  FIG. 8 . 
           [0026]      FIG. 10  shows the device of  FIG. 6  in a deployed configuration. 
           [0027]      FIG. 11  is a cross-sectional view of the device of  FIG. 10 . 
           [0028]      FIG. 12  shows the deployed device of  FIGS. 10 and 11  within a fractured bone. 
           [0029]      FIGS. 13-18  show details of one embodiment of an actuatable gripper for use with a fracture fixation device. 
           [0030]      FIGS. 19-21  show yet another embodiment of a fracture fixation device according to the invention. 
           [0031]      FIG. 22  shows a portion of fracture fixation device of  FIGS. 19-21  in a deployed configuration. 
           [0032]      FIGS. 23-25  show the fracture fixation device of  FIGS. 19-22  deployed within a bone. 
           [0033]      FIGS. 26-31  show details of a gripper for use with a fracture fixation device. 
           [0034]      FIGS. 32 and 33  show yet another embodiment of a fracture fixation device according to the invention. 
           [0035]      FIGS. 34-39  show a deployment tool for use with a fracture fixation device of this invention. 
           [0036]      FIGS. 40-41  show another embodiment of a deployment tool for use with a fracture fixation device of this invention. 
           [0037]      FIGS. 42-43  show the interaction between a flexible screw driver and the actuator of a fixation device. 
           [0038]      FIGS. 44-48  show another embodiment of a gripper for use with a fracture fixation device. 
           [0039]      FIGS. 49-50  show another embodiment of a fracture fixation device similar to the device shown in  FIGS. 19-25  using a distal gripper similar to that shown in  FIGS. 44-48  but using an alternative actuator/locking mechanism. 
           [0040]      FIGS. 51-52  show yet another embodiment of a fracture fixation device similar to the device shown in  FIGS. 49-50  but using another alternative actuator and an alternative flexible body. 
           [0041]      FIGS. 53-59  show alternative designs for the flexible body of a fracture fixation device according to this invention. 
           [0042]      FIGS. 60 and 61  show an alternative embodiment of a fracture fixation device according to this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]    By way of background and to provide context for the invention, it may be useful to understand that bone is often described as a specialized connective tissue that serves three major functions anatomically. First, bone provides a mechanical function by providing structure and muscular attachment for movement. Second, bone provides a metabolic function by providing a reserve for calcium and phosphate. Finally, bone provides a protective function by enclosing bone marrow and vital organs. Bones can be categorized as long bones (e.g. radius, femur, tibia and humerus) and flat bones (e.g. skull, scapula and mandible). Each bone type has a different embryological template. Further each bone type contains cortical and trabecular bone in varying proportions. The devices of this invention can be adapted for use in any of the bones of the body as will be appreciated by those skilled in the art. 
         [0044]    Cortical bone (compact) forms the shaft, or diaphysis, of long bones and the outer shell of flat bones. The cortical bone provides the main mechanical and protective function. The trabecular bone (cancellous) is found at the end of the long bones, or the epiphysis, and inside the cortex of flat bones. The trabecular bone consists of a network of interconnecting trabecular plates and rods and is the major site of bone remodeling and resorption for mineral homeostasis. During development, the zone of growth between the epiphysis and diaphysis is the metaphysis. Finally, woven bone, which lacks the organized structure of cortical or cancellous bone, is the first bone laid down during fracture repair. Once a bone is fractured, the bone segments are positioned in proximity to each other in a manner that enables woven bone to be laid down on the surface of the fracture. This description of anatomy and physiology is provided in order to facilitate an understanding of the invention. Persons of skill in the art will also appreciate that the scope and nature of the invention is not limited by the anatomy discussion provided. Further, it will be appreciated there can be variations in anatomical characteristics of an individual patient, as a result of a variety of factors, which are not described herein. Further, it will be appreciated there can be variations in anatomical characteristics between bones which are not described herein 
         [0045]      FIG. 1  shows a fracture fixation device  10  according to one embodiment of the invention.  FIG. 2  shows device  10  in place within an intramedullary space of a fracture bone  12  and spanning a fracture site  14  after having been inserted an opening  11  or  13  formed in the bone  12 . Device  10  has a flexible-to-rigid component  16  that may be compressed by an actuator (such as the actuator  62  shown in  FIG. 6 ) from its flexible state to be made substantially rigid. Device  10  also has two actuatable grippers  18  and  20  and two hubs  22  and  24 . In the configuration shown in  FIG. 1 , flexible-to-rigid component  16  is in its flexible state, and grippers  18  and  20  are in their unactuated state. In this embodiment, component  16  is formed as a unitary spirally wound element with wavy intersections between the turns. In the flexible state, there is a slight gap between the turns to permit the component  16  to bend. When compressed by an actuator, component  16  is foreshortened to bring the wavy spiral turns into compressive contact, thereby making component  16  rigid. The waves of the spiral also interact to permit the device to bend and to transmit torque, even in the device&#39;s flexible state. 
         [0046]    In  FIGS. 2 and 3 , component  16  has been actuated to its rigid state, and grippers  18  and  20  have been actuated to grip the interior of the bone. Grippers  18  and  20  in conjunction with flexible-to-rigid member  16  provide fixation to stabilize bone fragments. Optionally, one or more bone screws  26  may be inserted through the bone or fragments thereof into either or both hubs  22  and  24  to stabilize the device within the bone and to fix any bone fragments to the device as shown in  FIG. 2 . The bone screws can be inserted at any point along the hub(s) along any orientation desired. Attachment features  29  may be provided on the hubs to permit attachment of the fixation device to a deployment tool.  FIG. 3  shows device  10  in use to repair a fracture having multiple bone fragments at the fracture site  14 . 
         [0047]      FIG. 4  shows an embodiment of a fracture fixation device  10 ′ similar to device  10  of  FIGS. 3 and 1 . In this embodiment, the straight hub at one end of the device has been replaced with a curved hub  28 . The curve of hub  28  is preferably selected to match the curve of an access opening in the bone to help anchor the device within the bone. Either one or both hub configurations may be used in different types of fractures. 
         [0048]      FIG. 5  shows another embodiment of a fracture fixation device  30  inserted into an intramedullary space through an access opening  31  or  33  formed in a fractured bone  32  to span a fracture site  34 . Like the device shown in  FIG. 3 , device  30  has a flexible component  36  formed as a wavy spiral that may be actuated by the compressive forces of an actuator (such as actuator  62  shown in  FIG. 6 ) to become substantially rigid. Device  30  also has one or more pairs of actuatable grippers  38  and  40  and a hub  42 . Bone screws  44  have been inserted through bone  32  and hub  42  to stabilize the device within the bone and to fix any bone fragments to the device and to the rest of the bone. 
         [0049]      FIG. 6  shows yet another embodiment of a fixation device  50  of the invention in the process of being inserted through an opening  51  into a fractured bone  52  to span a fracture site  54 . As shown in additional detail in  FIGS. 7-12 , device  50  has three actuatable flexible-to-rigid components  55 ,  56  and  57  and four actuatable grippers  58 - 61 . At one end, device  50  has an actuator  62  with a blunt end  64  to help guide the device within the bone and to push aside any soft bone material within the bone  52 . Actuator  62  is threaded and passes through an internally threaded head  66  disposed proximal to the grippers and flexible components through the interior of device  50  to a distal screw head  68 . By rotating screw head  68  and actuator  62  (by using, e.g., a flexible screw drive  69 , as shown in  FIG. 7 ), threaded head  66  travels distally with respect to the grippers and the flexible-to-rigid components while hub  68  remains stationary. This action foreshortens device  50  to deploy grippers  58 - 61  and to rigidize components  55 - 57 . When deployed to the configuration shown in  FIGS. 10-12 , grippers  58 - 61  tilt outward to dig their tips into the interior surface of the bone, as shown in  FIG. 12 . To reposition or remove device  50  from bone  52 , the actuator may be rotated in the other direction to release the grippers and to permit the flexible-to-rigid components to become flexible again. 
         [0050]    In  FIGS. 3-12 , the flexible-to-rigid members such as  16 ,  30 ,  56  and the rigid members such as hub  42  that traverse the fracture are designed with substantially larger external diameters than the rest of the assembly. The larger diameter will limit the amount of bone in-growth that the fracture may experience and thus leave a passage large enough for the ease removal of the rest of the components such as the grippers  60  and  58 . 
         [0051]      FIGS. 13-15  show details of an actuatable gripper  70  for use with, e.g., the fracture fixation device embodiments described above. In this embodiment, gripper  70  has two rotatable cams  72  and  74 . Cams  72  and  74  are attached by pins  73  and  75  to cam arms  76  and  78 , respectively. Cam arms  76  and  78  attach by pins  77  and  79  to flanges  80  and  82 , respectively. Flanges  80  and  82  connect with the components on either end of the device. In the undeployed configuration shown in  FIGS. 13 and 14 , cams  72  and  74  are oriented such that the sharp tips  85  and  87  of cam  72  and the sharp tips  81  and  83  of cam  74  do not extend from the cylinder of the gripper. When foreshortened during deployment, however, movement of flanges  80  and  82  toward each other causes cam arms  76  and  78  to rotate about pins  77  and  79  with respect to flanges  80  and  82  and causes cams  72  and  74  to rotate about pins  73  and  75  with respect to cam arms  76  and  78  so that the sharp tips swing out from the cylinder of the gripper, as shown in  FIG. 15 . Thus, when part of a fracture fixation device that has been inserted into a bone, deployment of the gripper  70  causes the sharp tips of the cams to dig into the bone to anchor the device. An alternative design combines cams  72  and  74  into one integral component. 
         [0052]    In order to prevent inadvertent deployment of the gripper, one or more optional lock wires may be inserted into the gripper. As shown in  FIG. 13 , lock wire channels  84  and  86  may be formed in flanges  80  and  82 , and corresponding channels may be formed in flange  80 . Likewise, lock wire channels may be formed in the cams, such as channel  88  formed in cam  74 , to line up with the lock wire channels formed in the flanges when the gripper is in its undeployed configuration, thereby permitting a lock wire  89  to be inserted through the gripper, as shown in  FIG. 14 . Lock wire  89  must be removed before the gripper can be rotated to its foreshortened deployed configuration, as shown in  FIG. 15 . A lock wire may also be inserted across the gripper through holes  71 . 
         [0053]      FIGS. 16-18  show a gripper  90  for use on one end of an actuatable fracture fixation device according to one embodiment of the invention. In this embodiment, a threaded flange  92  replaces flange  82  of the earlier gripper embodiment. Internal threads  94  in flange  92  interact with a threaded actuator, such as actuator  62  shown in  FIGS. 6-12 , for use in foreshortening during deployment. 
         [0054]      FIG. 18  also demonstrates an advantage of the grippers  70  and  90  shown in  FIGS. 13-18 . During insertion into the interior of a bone along a curved insertion path, grippers  70  and  90  can adapt to the curve of the insertion path, as shown by the curved line in  FIG. 18 . 
         [0055]      FIGS. 19-21  show yet another embodiment of a fracture fixation device  100  according to the invention. In this embodiment, device  100  has a first gripper  102  constructed, e.g., like the grippers described above with respect to  FIGS. 13-18 , and a second gripper  104 . Extending between grippers  102  and  104  is a flexible-to-rigid body  106 . A threaded actuator  108  with a blunt end  110  extends through grippers  102  and  104 , body  106  and an internally threaded head  112 . A tool engagement feature  114  extends from one end of actuator  108  to enable a screw driver or other tool to rotate actuator to actuate, foreshorten and rigidize fixation device  100 . A curved hub  116  is attached to the device distal to gripper  104 . Pins  111  secure hub  116  axially to the actuator and device while still permitting the actuator and/or device to rotate with respect to the hub. A flange  113  formed in tool engagement feature  114  engages a lip  109  formed on the inside of hub  116  to transfer any loads from the actuator directly to the hub without overloading pins  111 . Internal threads  118  in hub  116  provide for attachment to a deployment tool (such as, e.g., tool  300  shown in  FIGS. 34-41 ) or for the insertion of a plug (not shown) after deployment of fracture fixation device  100  within a fractured bone. Hub  116  that transverses the fracture is designed with a larger external diameter than the rest of the device. This features in the hub  116  limits, during the healing process of the fracture, the amount of bone in-growth and calluses that would otherwise prevent the removal of the device. The external diameter of the hub  116  is preferably also tapered to facilitate the release and removal of the device. The larger diameter of the hub  116  during withdrawal leaves behind an opening larger than the rest of the device such as the grippers  104 ,  108  and flex-to-rigid body  106  and thus facilitates the removal of the device. 
         [0056]      FIG. 22  shows device  100  of  FIGS. 19-21  without hub  116 , actuator  108  and blunt end  110 . As shown, grippers  102  and  104  have been actuated to a deployed configuration. 
         [0057]      FIGS. 23-25  show fracture fixation device  100  of  FIGS. 19-22  deployed within a space  118  formed in a bone  120 . Device  100  has been inserted through an opening  122  formed in a bony protuberance of bone  120 , and the grippers  102  and  104  have been actuated to grip the interior of the bone. Appropriate tools (such as those discussed below) have been used to form space  118  with a curved distal portion extending proximally from opening  122  to a substantially straight proximal portion through one or more fracture areas, such as fracture lines  124  and  126 . As shown, hub  116  is disposed within the curved portion of space  118  while flexible-to-rigid body  106  and the grippers  102  and  104  are disposed in the substantially straight portion of space  118 . During delivery to space  118  in the device&#39;s undeployed configuration, grippers  102  and  104  and body  106  are substantially flexible so as to accommodate the curve of the distal portion of the opening. After actuation, however, the device body  106  becomes rigid through the compression and interaction of its segments during foreshortening and deployment of grippers  102  and  104 . 
         [0058]    In this embodiment, hub  116  is substantially rigid and has a curve approximating that of the curved portion of opening  118 . In some embodiments of the method of this invention, some or all of hub  116  is placed on one side of a bone fracture while the remainder of the fracture fixation device is placed on the other side of the fracture. 
         [0059]    In some embodiments, hub  116  is made of PEKK or PEEK implantable grade material and may be injection molded. Using the tools of this invention, a hole through bone  120  may be drilled at any angle and through any portion of hub to permit a screw to be inserted through the bone and fixation device. In  FIG. 23 , one screw  128  has been inserted through hub  126  to help anchor device  100  within the bone and to hold bone fragment  125  to the main portion of the bone. In  FIGS. 24 and 25 , multiple screws  128  have been inserted in various positions and orientations. These figures illustrate the ability to place screws wherever needed and at whatever orientation required. 
         [0060]      FIGS. 26-31  show details of a gripper  104  for use with a fracture fixation device, such as the devices of  FIGS. 1-5 ,  6 - 12  or  19 - 25 .  FIGS. 26 and 27  show gripper  104  in an undeployed configuration.  FIGS. 28-31  show gripper  104  in deployed configurations. Gripper  104  has three sets of anchor elements, with each set including a first anchor leg  130  and a second anchor leg  132 . Anchor leg  130  is connected to flange  134  and extends toward flange  136 , and anchor leg  132  is connected to flange  136  and extends toward flange  134 . Legs  130  and  132  are rotatably connected by a pin  138  that is welded to leg  130 . Leg  132  rotates freely about pin  138 . A larger head portion  139  on pin  138  keeps leg  132  rotatably mounted on pin  138 . Alternatively, a washer may be added to pin  138  at the end opposite of the head  139 . The pin  138  may then be welded to the washer instead of leg  130 . In this arrangement the washer and head  139  retains pin  138  within the holes in leg  132  and leg  130  such that the pin and washer may rotate freely within both legs  130  and  132 . This washer arrangement provides a lower stress concentration on the weld, which can result in a more reliable connection in some embodiments. 
         [0061]    In the undeployed configuration of  FIGS. 26 and 27 , legs  130  and  132  lie substantially parallel to each other within the cylinder of flanges  134  and  136 . When the fracture fixation device is actuated by, e.g., turning an actuator  108  to foreshorten the device (as shown in  FIG. 31 ), flanges  134  and  136  are moved closed together. This movement causes the outer edges  140  and  142  of legs  130  and  132 , respectively, to rotate outward to grip the inside surface of the bone in a deployed configuration, as shown, e.g., in  FIGS. 23-25 . Movement of flanges  134  and  136  away from each other retracts legs  130  and  132  toward and into their undeployed configuration for repositioning and/or removal of the device from the bone. Cut-outs  135  formed in gripper  104  mate with corresponding shapes in the hub to provide a rotational keying feature enabling the transmission of torque from the hub to the rest of the device without overloading the pins connecting the hub to gripper  104 , as shown in  FIGS. 29 and 31 . 
         [0062]      FIGS. 32 and 33  show yet another embodiment of a fracture fixation device according to the invention. Like the embodiment shown in  FIGS. 19-31 , device  200  has a curved hub  216 , a distal gripper  204  (formed, e.g., like gripper  104  of the prior embodiment), a flexible body  206  and two proximal grippers  201  and  202  (each formed, e.g., like gripper  102  of the prior embodiment). Pins  211  attach hub  216  to gripper  204 . As in the embodiment of  FIGS. 19-31 , a threaded actuator  208  cooperates with an internally threaded head  212  to foreshorten and actuate the device. The sectional view of  FIG. 33  shows a threaded plug  217  that has been inserted into the distal opening of hub  216  to seal the device after actuation. 
         [0063]    As seen from the discussion above, the devices of this invention can be easily modified by adding grippers or by placing grippers in different positions on the device to address fractures where more gripping forces are needed. 
         [0064]      FIGS. 34-39  show a deployment tool  300  for use with a fracture fixation device  100  of this invention. As shown in  FIG. 34 , the hub  116  of fixation device  100  connects to a stem  302  of tool  300 . Hub  116  may be provided with, e.g., connection features  115  for this purpose, as shown, e.g., in  FIG. 23 . This connection orients fixation device  100  with tool  300 . In particular, tool  300  aids in the use of a fixation device actuation tool and alignment of a drill with the fixation device&#39;s hub after the device has been deployed within a fractured bone and in the insertion of screws into the hub and bone. 
         [0065]    Access to the interior of fixation device  100  is provided by a port  304  through stem  302  so that, e.g., a flexible screw driver  306  may be inserted through hub  116  to device actuator  108 , as shown in  FIG. 36 . Rotation of flexible screw driver  306  and actuator  108  moves device  100  from an undeployed configuration to a deployed configuration, as shown in  FIGS. 42 and 43  (which show the interaction of flexible screw driver  306  and fixation device  100  outside of tool  300 ). A flexible ring  308  may be provided to interact with a groove  310  formed in flexible screw driver  306  to provide proper axial positioning between the screw driver and the tool engagement feature  114  of actuator  108  while still permitting the flexible screw driver to rotate. 
         [0066]    Tool  300  also helps orient a drill and enables it to find the hub of the fixation device even when the fixation device is inside the bone and cannot be seen by a user. When fixation device  100  is properly attached to stem  302 , the bore  321  of drill guide  320  points toward the device&#39;s hub  116  even when the drill guide is rotated along curved guide  300  or translated along grooves  326 . In order to provide the user with flexibility in drill placement (e.g., in order to place one or more screws through hub  116  as shown in  FIGS. 23-25 ), tool  300  permits drill guide  320  to be moved with respect to stem  302  and attached hub  116 . Drill guide  320  may be translated proximally and distally with respect to hub  116  by loosening knob  322  and moving support  324  along grooves  326 . In addition, drill guide  320  may be rotated about hub  116  by loosening knob  328  and moving drill guide  320  along curved groove  330 . 
         [0067]      FIGS. 37-41  show tool  300  being used to guide a drill  332  toward and through hub  116  (and through the bone, as shown in  FIG. 41 ). The drill sleeve  333  surrounding drill bit  332  is held in place within bore  321  by a set screw  334 . An external x-ray visible aim  340  may extend from drill guide  320  to show on x-rays the orientation of the drill bit  332  within the patient&#39;s bone, as shown in  FIG. 41 . The drill bit may be provided with a scale to show depth of the drilled hole and, therefore, the length of the screw needed. In some embodiments, the drill  332  may have a sharp tip to reduce skittering of the drill against the device hub and/or bone during drilling. The tip included angle may be less than 100° and preferably between 25° and 35° to ensure penetration of the hub. 
         [0068]      FIGS. 40-41  show an alternative planar tool  1300  being used to guide a drill  1332  toward and through the hub  116  of a fracture fixation device. As with the earlier embodiment, access to the interior of fixation device  100  is provided by a port  1304  through a stem  1302  so that, e.g., a flexible screw driver may be inserted through hub  116  to device actuator  108 . A flexible ring  1308  may be provided to interact with a groove formed in the flexible screw driver to provide proper axial positioning between the screw driver and the tool engagement feature  114  of actuator  108  while still permitting the flexible screw driver to rotate. 
         [0069]    Like the deployment tool described above, tool  1300  also helps orient a drill and enables it to find the hub of the fixation device even when the fixation device is inside the bone and cannot be seen by a user. When fixation device  100  is properly attached to stem  1302 , the bore of drill guide  1320  points toward the device&#39;s hub  116  even when the drill guide is translated along grooves  1326  or is rotated above the axis of knob  1322 . In order to provide the user with flexibility in drill placement (e.g., in order to place one or more screws through hub  116  as shown in  FIGS. 23-25 ), tool  1300  permits drill guide  1320  to be moved with respect to stem  1302  and attached hub  116 . Drill guide  1320  may be translated proximally and distally with respect to hub  116  by loosening knob  1322  and moving support drill guide  1320  along grooves  1326 . In addition, drill guide  1320  may be rotated about stem  1302  and hub  116 . 
         [0070]      FIGS. 44-48  show another embodiment of a gripper  350  for use with a fracture fixation device. As shown, gripper  350  is designed to be used on the leading end of the fixation device. It should be understood that this gripper could be used at other points in the fixation device as well. 
         [0071]    Extending between flange  352  and nose cone flange  354  are two sets of anchor elements. Anchor legs  356  are rotatably attached to flange  352  and extend toward flange  354 , and split anchor legs  358  are rotatably attached to nose cone flange  354  and extend toward flange  352 . Anchor legs  356  are disposed in the split  357  of anchor legs  358 . Legs  356  and  358  are rotatably connected by a pin  360 . In the undeployed configuration of  FIGS. 44 and 45 , legs  356  and  358  lie substantially parallel to each other within the cylinder of flanges  352  and  354 . When the fracture fixation device is actuated by, e.g., turning an actuator to foreshorten the device, flanges  352  and  354  are moved closer together. This movement causes the outer edges  362  and  364  of legs  356  and  358 , respectively, to rotate outward to grip the inside surface of the bone in a deployed configuration, as shown, e.g., in  FIGS. 46-48 . Movement of flanges  352  and  354  away from each other retracts legs  356  and  358  toward and into their undeployed configuration for repositioning and/or removal of the device from the bone. A lock wire (shown in phantom in  FIG. 44 ) disposed in channels  366  formed in projections  368  extending between the two sides of the proximal anchor legs  358  prevents inadvertent actuation of the anchors. Stop surfaces  370  and  372  on flanges  352  and  354 , respectively, meet to provide a limit to extension of gripper  350 , as shown in  FIG. 48 . 
         [0072]      FIGS. 49-50  show another embodiment of a fracture fixation device  400  similar to device  100  shown in  FIGS. 19-25  using a distal gripper  402  similar to that shown in  FIGS. 44-48 . Instead of a threaded rotating actuator, however, device  400  uses a ratcheting actuator  408 . Actuator passes through device hub  416 , gripper  402  and flexible body  406  to a flange (not shown) at the other end of the fixation device. To foreshorten and actuate the fixation device (thereby extending the grippers and rigidizing the flexible body), actuator  408  is tensioned by pulling in the direction of the arrow in  FIG. 49 . As it moves distally, ridges  410  formed in actuator push against a cam surface  412  formed in crown  414  in ratchet  417 , expanding the crown enough to permit the ridges to pass through. After passing through the crown, surface  420  of ridge  410  meets a stop surface  422  of ratchet crown  414 , thereby preventing proximal movement of actuator  408  after it has been tensioned. After deployment of the fracture fixation device within a fractured bone, the portion of actuator  408  extending from the end of the device after suitable tensioning may be cut and removed. A tool (not shown) may be used to release the ratchet in the event fixation device  400  must be repositioned or removed. 
         [0073]      FIGS. 51-52  show yet another embodiment of a fracture fixation device  500  similar to that of  FIGS. 49-50 . Flexible body has two concentric tubular members  506 A and  506 B with opposing clockwise/counterclockwise helical cuts. In order to rigidize flexible body  506  and deploy gripper  502 , actuator  508  is tensioned in the direction of the arrow in  FIG. 51 . As it moves in that direction, ridges  510  of actuator  508  move against cam surfaces  512  of ratchet members  514 , which rotate outwardly around pins  516 . The interaction of face  518  of ridge  510  with face  520  of ratchet member  514  prevents actuator  508  from moving back the direction it came. The actuator  508  may be released from the ratchet by using a tool (not shown) to move the ratchet members  514  to the position shown in  FIG. 52 . 
         [0074]      FIGS. 53-59  show alternative designs for the flexible body of a fracture fixation device according to this invention.  FIGS. 53 and 54  show helical wavy cuts formed in the flexible-to-rigid body so that it is flexible when not compressed and rigid when foreshortened and compressed.  FIG. 55  shows a canted helical wavy cut formed in the flexible-to-rigid body.  FIGS. 56 and 57  show canted angles formed in the helical cuts of the flexible-to-rigid body.  FIGS. 58 and 59  show a helical cut to form the flexible-to-rigid body. As in the earlier embodiments, the shape of the helical turns enables the transmission of bending and torque along the flexible-to-rigid body, in addition to the rigidizing function the body performs. 
         [0075]      FIGS. 60 and 61  show an embodiment of a fracture fixation device having a flexible membrane cover. Like some earlier embodiments, fixation device  700  has a hub  702 , expandable and releasable grippers  704  and  706  and a flexible-to-rigid body  708 . A threaded actuator  710  extends through the device. A tubular flexible membrane  712  covers the grippers and flexible-to-rigid body and conforms to the device&#39;s outer shape. As shown in  FIG. 61 , when the fixation device is actuated to extend grippers  704  into the interior space  714  formed in a bone and to rigidize body  708 , the flexible membrane  712  stretches and forms a tent-like envelope that keeps debris and bone ingrowth away from the device, thereby facilitating subsequent removal of the device from the bone. The flexible membrane can be used with any of the previously described embodiments of the fracture fixation device, or with similar implanted devices as well, with or without grippers. 
         [0076]    The membrane may serve one or more other purposes instead of or in addition to facilitating removal of a device that has been implanted in the body for a period of time. For example, the membrane may provide corrosion resistance to the implanted device, and/or may reduce inflammation caused by the implanted device. The membrane may deliver therapeutic agents inside the body over a predetermined period of time, such as for the treatment of the central nervous system. The membrane may also comprise, contain or otherwise deliver biologically active material or proteins that provide some benefit to the body, anatomy, immunological, or biochemical response by the patient. For example, a bioactive agent may be used for the stimulation of bone growth or the prevention of infection. Immunological agents may be used for the treatment of immuno-deficiencies. In some embodiments, the membrane may comprise matter that prevents or inhibits bone ingrowth. The membrane may also contain radio-opaque material, such as barium sulfates or other metals, to allow the membrane to be seen on x-rays or with other imaging. This can be useful for checking the integrity of the membrane after implanting and/or to determine if it has migrated. 
         [0077]    The flexible membrane may be made from a thermoset or thermoplastic material. Exemplary materials that may be used include, thermoplastic elastomer TPE, silicon rubber, Teflon®, PTE or flexible PTFE. Inert polyethylene, polypropylene or other long term biocompatible materials such as PEEK or PEKK may be used for the membrane. Additional materials suitable in some embodiments, and that may be used alone or in combination with other materials include polymeric materials such as Dacron (the general category polyester), polyolefin (the general category of straight chain carbon polymers such as polypropylene, polyethylene), polysilanes (the general category of silicon backbone polymers), polymers of aromatic hydrocarbon backbone (polycarbonates, polysulfones, polymers that contain a benzene ring), epoxide type polymers that are thermoset or thermoplastic (the general class of polymers that contain the strained carbon-oxygen-carbon bridge), hydrogels, ionomers, and metalocenes. Inorganic materials that include calcium salts, calcium containing ceramics, calcium phosphates, and hydroxyapitite may also be used. Inorganic materials that include heavy metals such as palladium, cobalt 60, iridium, platinum, and strontium for nuclear medical treatments may be used. Therapeutic agents loaded into any of the above are contemplated, including Warfarin, opiates for pain, pharmaceuticals for red cell, white cell, and platelet production, T-cell enhancement pharmaceuticals, and bone morphogenic proteins. 
         [0078]    Depending on the application, the materials described above may form the membrane substrate itself, may be co-extruded or co-molded with the membrane material(s), and/or may be coated on the inner or outer surface of the membrane. The membrane can be formed from a dipping process. In the dipping bath the above constituents may be present. In some embodiments, the material may be a liquid, gel, powder or other form of material contained within the membrane. The membrane can be configured to be porous to allow any material contained therein to pass through the membrane at a predetermined rate, or the membrane can be configured to be generally impervious. Pore sizes may range from 0.1 nanometers to 100 microns in some embodiments. 
         [0079]    In some embodiments, the thickness of the membrane is between about 0.010 inches to about 0.030 inches, before deployment of any grippers, depending on the size and nature of the fracture fixation device it covers. The membrane may stretch and become thinner in some regions when grippers are deployed. In other embodiments, the membrane thickness may be between about 0.01 microns and about 5 milimeters. In some of these embodiments, the membrane is not thick enough to be self-supporting, but rather is a coating over the implantable device. The membrane thickness need not be uniform, but may be made thicker is some regions. For instance, the regions around the grippers may be made thicker to prevent or inhibit the grippers from puncturing the membrane when expanded against the bone. A radius or chamfer or a blunt tip may be provided at the gripping points of the gripper&#39;s arm to also prevent or inhibit puncturing the membrane. Depending on the load required by the bone fixation, in some embodiments, it may be desirable to allow the grippers to penetrate the membrane in order to obtain a better hold between the grippers and the bone. 
         [0080]    The membrane may be formed by injection molding, liquid injection molding, transfer molding, extrusion, or other suitable manufacturing method such as overmolding on the fixation device and grippers. The membrane may be closed or semi-closed at one or both ends, such as the semi-closed distal end shown in  FIGS. 60 and 61 . In other words, the distal end of actuator  710  may be covered by membrane  712 , or may protrude through membrane  712  as shown. One or both ends may be open, such as the open proximal end shown in  FIGS. 60 and 61 . The membrane may be configured to cover the entire device, or just one or more portions of the device. 
         [0081]    Various methods may be employed to secure membrane  712  to fixation device  700 . In some embodiments, membrane  712  may be secured by being stretched over a portion of device  700 , and/or held in place by an adhesive. In some embodiments a tie, strap, snap ring, clamp, sleeve, or similar element may surround one or more portions of membrane  712  and device  700 . A groove may also be provided in device  700 , as shown in  FIGS. 60 and 61 , to receive a portion of membrane  712  and/or a securing element. A snap ring or similar retaining element may be molded into the membrane during fabrication to aid in assembly. An otherwise open end of a membrane may extend beyond an end of device  700  and tied or otherwise secured to itself. An end of a membrane may wrap around an end of the device and be secured within and interior cavity of the device, such as with a press-fit plug. 
         [0082]    In some embodiments, multiple membranes may be provided, one over the other(s), for redundant layers in case one or more membranes are ruptured. Extra layers may be provided over the entire protected area of the device, or in just limited areas such as the grippers. Multiple layers or varying membrane thicknesses may also be useful in controlling diffusion gradients across the membrane. Multiple membrane sleeves may only partially overlap each other, each covering one end or portion of the fixation device. Multiple layers may be stretched over one another, thermally bonded together, and/or secured in place with adhesive. The membrane and device may be configured to provide a hermetic seal around all or a portion of the implanted device to prevent or impede material ingress and egress, or the membrane may merely surround the device to inhibit bone ingrowth. 
         [0083]    It is envisioned that the membrane and fixation device may be provided in an operating room as a single, preassembled unit. This unit may be provided in a pre-sterilized condition, or be ready for sterilization just prior to the surgical procedure it is to be used in. Alternatively, the fixation device and membrane may be provided in a surgical kit as separate units in the same or separate packaging. The fixation device and membrane may then be assembled, either before or after sterilization, if not already sterilized before packaging. 
         [0084]    While various embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention.