Abstract:
Bone anchoring devices for anchoring medical devices to bones and for reducing bone fractures are provided. The devices include a bone anchor portion designed to allow for bony ingrowth and secure fixation to a bone and an internal fastener designed to resist bony ingrowth and facility easy removal of the fastener from a patient.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/828,113, filed on Jul. 25, 2007, which claims the benefit of U.S. Provisional Patent Application Nos. 60/834,011, filed Jul. 28, 2006, and 60/841,729, filed Sep. 1, 2006, all of which are hereby incorporated by reference, in their entirety, for any and all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention generally relates to medical devices and anchoring mechanisms. More specifically, a bone anchoring device is disclosed which is capable of anchoring a medical device to bone or reducing a bone fracture with an internal fastener nested within a bone anchor. 
       BACKGROUND 
       [0003]    In some medical applications, it is required or at least desired, that a medical device be firmly anchored to a bone. For example, in correcting certain conditions of the spine, it is desirable to firmly anchor a spinal stabilization device to one or more vertebra. In such cases, a device may be anchored to a bone via bone screws. The bone screws used in such applications may be constructed of a material which promotes or allows for tissue or bony ingrowth throughout or through a portion of the bone screw, thereby effectively preventing the removal of the bone screw and device from the subject without significant difficulty or trauma to the surrounding bone and tissue. While in some cases it is desired that a medical device permanently remain within a patient, in other cases, after the medical device in a patient has served a useful purpose or needs repair or replacement, it is desirable or necessary to remove the device from a patient&#39;s body. Similarly, bone screws may be used in reducing fractures and the like. However, after the repair is complete, removal of the bone screw may or may not be desired. 
       SUMMARY 
       [0004]    Bone screw devices and anchoring devices for attaching medical devices to bone are provided. In some embodiments, the device comprises a bone anchor comprising an elongated shaft having a cannula running through at least a portion of the length of the shaft. The bone anchor has a proximal end and a distal end, wherein the proximal end may form a head and the distal end may form a tip. In some embodiments, the internal surface of the shaft, which defines the cannula, provides an internal thread. The external surface of the shaft defines an external thread, which allows the bone anchor to be screwed into a bone in order to anchor a device to the bone, or to assist in the healing of a bone fracture. In other embodiments, the internal surface of the shaft comprises at least one retaining member to permanently engage an internal fastener. 
         [0005]    Desirably, at least a portion of the external surface of the bone anchor is made from, or coated with, a porous material that allows for bone ingrowth into the material, helping to secure the bone anchor to the bone. In some embodiments, the porous coating is cobalt chromium alloy, cobalt chromium molybdenum alloy, or porous titanium. As an alternative to, or in addition to, the porous material, the bone anchor may include fenestrations, channels or cavities built into its external surface, such that bone growth into the fenestrations, channels or cavities helps to secure the bone anchor to the bone. 
         [0006]    The device further includes an internal fastener. In some embodiments the internal fastener is capable of removably being engaged in the cannula of the bone anchor, comprising an elongated shank and having a proximal end, which may form a head, and a distal end, which may form a tip. The elongated shaft of the internal fastener may comprise an external thread on the surface of the elongated shank, thereby defining an internal screw, the proximal end forming a screw head, and the distal end forming a screw tip. In some embodiments, the external thread of the internal screw is designed to compliment the internal thread of the bone anchor such that the internal screw may be screwed into the cannula of the bone anchor. In other embodiments, the internal fastener may be permanently engaged in the bone anchor. In such embodiments, the internal fastener is capable of being permanently engaged in the bone anchor via a mechanism such as lock and key; an annular ring on the elongated shaft internal fastener and at least one retaining member on the internal surface of the cannula of the bone anchor; at least one recess on the elongated shaft of the internal fastener and at least one retaining member on the internal surface of the cannula of the bone anchor; a bayonet style connection; a pin that is inserted through the bone anchor and internal fastener in a direction that is transverse to a longitudinal axis of both the bone anchor and internal fastener; or other mechanism known to those of skill in the art. In some embodiments, the internal fastener is an intramedullary nail. 
         [0007]    The internal fastener may be made from a material that does not allow bone ingrowth and, therefore, facilitates the easy removal of the internal fastener (and any devices mounted thereto) from the bone. In some embodiments, the bone anchor is an implant or implantable device, and in other embodiments, the bone anchoring device is an implant or implantable device. 
         [0008]    Methods for using the present devices are also provided. In some embodiments, the methods comprise inserting the bone anchor of the device in a bone, engaging the internal fastener in the cannula of the bone anchor, and securing the internal fastener in the bone anchor. In some such embodiments, the engaging comprises screwing the internal screw in the cannula, and the securing comprises tightening the internal screw in the cannula. In some embodiments, the methods further comprise connecting a medical device to a bone with the bone anchoring device. In other embodiments, the methods further comprise removing the internal fastener from the bone anchor, while leaving the bone anchor fixed within a patient&#39;s bone. In some embodied methods, where the internal fastener is to be permanently engaged in the bone anchor, the internal fastener is inserted into the cannula of the bone anchor by pushing the annular ring past the retaining member such that the internal fastener is permanently engaged in the bone anchor. In other embodiments, the method comprises pushing the internal fastener into the cannula of the bone anchor until the at least one retaining member engages the at least one recess of the shaft of the internal fastener. 
         [0009]    In some embodiments, the combination of a medical device and a bone anchor device comprise a medical device assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a cross-sectional view of a bone anchor according to one embodiment of the present invention. 
           [0011]      FIG. 2  is a side view of an internal fastener according to one embodiment of the present invention. 
           [0012]      FIG. 3  is a cross-sectional view of a bone anchor inserted in a bone, an internal screw nested within the bone anchor, and a medical device anchored to the bone according to one embodiment of the present invention. 
           [0013]      FIG. 4  is a cross-sectional view of a bone anchor and internal fastener, in which the internal fastener is permanently engaged with the bone anchor, according to one embodiment of the present invention. 
           [0014]      FIG. 5  is a cross-sectional view of a bone anchor and internal fastener, in which the internal fastener is permanently engaged with the bone anchor, according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    In one aspect of the present invention, a bone anchoring device is provided. The bone anchoring device is a multi-part anchoring device for anchoring orthopedic devices to bone or for use in the reduction of fractures of bones. Referring to  FIG. 1 , a bone anchoring device comprises at least two parts, a bone anchor  10  and an internal fastener  20 . In some embodiments, and as illustrated in  FIG. 1 , the internal fastener  20  may be a screw, however other fasteners are known to those of skill in the art. For example, other types of fasteners may include, but are not limited to bayonet-style fasteners, lock-and-key mechanism style fasteners, and the like. The bone anchor  10  comprises an elongated hollow shaft  105 , the internal surface  112  of which defines a cannula  110 . The shaft has a proximal end, which defines the head  100  of the shaft, a distal end, which defines the tip  120  of the shaft, an external thread  140  on the external surface of the elongated hollow shaft  105 , and in some embodiments, an internal thread  130  along at least a portion of the internal surface  112 . In other embodiments, the internal surface  112  of the shaft comprises a locking mechanism for other types of fasteners described above. The internal fastener  20  comprises an elongated shank  230  having a proximal end, which forms the head  210  of the fastener, a distal end, which forms the tip  220  of the fastener, and, in embodiments where the internal fastener  20  is an internal screw, a thread  240  on at least a portion of the external surface of the elongated shank  230 . In some embodiments, the bone anchoring device is used to anchor an orthopedic device to one or more bones. 
         [0016]    The bone anchor  10  may comprise a self-tapping tip such that the bone anchor  10  may be started directly into bone without pre-drilling a pilot hole for the bone anchor  10 , or a pilot hole may first be drilled. At least a portion of the external surface of the bone anchor (i.e., a portion of the external surface that is to be in contact with a bone) may be coated with, or made from, a porous material that allows for bone ingrowth. As shown in  FIG. 1 , the bone anchor  10  may also comprise fenestrations  150  that run transverse to the cannula  110 . Fenestrations  150  allow for tissue or bone ingrowth into the bone anchor  10 . In other embodiments, the bone anchor  10  is an implant or an implantable device. 
         [0017]    The head  100  of the bone anchor  10  may comprise a driving mechanism known to those of skill in the art. For example, a triangular, square, or hexagonal drive recess may be incorporated into the head  100  of the bone anchor  10 , such that the recess may be engaged by a drive device having a complimentary shape. Other drive recess shapes may correspond to those used with Philips head screwdrivers, slotted screw drivers, star-head drivers, and the like. The bone anchor  10  may also be driven into bone using a driving device having a threaded tip such that the internal threads  130  are engaged by threads on a drive device that then may be removed by reversing the turn of the drive device, thus leaving the bone anchor  10  in the bone. 
         [0018]    The bone anchors of the present invention may be made of any material known to those of skill in the art to be compatible with orthopedic usage. For example, the bone anchor may be made of titanium, titanium alloys, stainless steel, stainless steel alloys, chrome cobalt, graphite ceramics, biocompatible polymers, carbon-reinforced composites, and the like. Suitable biocompatible polymers include, but are not limited to, polyethylene (e.g., ultra high molecular weight polyethylene) and polyether ester ketone. The bone anchor may also be coated with materials that promote bone growth such as, but not limited to, hydroxyapatites, plasma spray coatings, porous coatings, and the like. Porous coatings include porous coated alloys such as, but not limited to cobalt chromium alloy or cobalt chromium molybdenum alloy on a porous layer of beads, or porous titanium. 
         [0019]    In embodiments where the internal fastener  20  is an internal screw, the threads  240  of the internal fastener  20  are died such that they correspond to the tap of the internal threads  130  of the bone anchor  10 . The head  210  of the internal fastener  20  may comprise a driving mechanism known to those of skill in the art. For example, a triangular, square, or hexagonal drive recess may be incorporated into the head  210  of the internal fastener  20 , such that the recess may be engaged by a drive device having a complimentary shape. Other drive recess shapes may correspond to those used with Philips head screwdrivers, slotted screw drivers, star-head drivers, and the like. Although the distal end of the internal fastener  20  of  FIG. 3  is shown extending all the way to the distal end of the bone anchor  10 , it is possible to design the device such that the internal fastener  20  extends only part way down the length of the cannula  110  in the bone anchor  10  when the device is in place in a patient. In these latter embodiments, bone growth into a lower portion of the cannula (below the distal end of the internal fastener) may further assist in fixing the bone anchor to a bone. Bone growth into the lower portion of the cannula may be enhanced by providing fenestrations in the lower portion of the bone anchor to allow bone growth through the fenestrations and into the cannula. 
         [0020]    The internal fastener  20  may be made of any material known to those of skill in the art to be compatible with orthopedic usage. For example, the internal fastener  20  may be made of titanium, titanium alloys, stainless steel, stainless steel alloys, ceramics, biocompatible polymers, carbon-reinforced composites, and the like. However, desirably the internal fastener  20  is made of a material that does not allow for bone ingrowth into the material or incorporation of the internal fastener  20  into the bone. In such embodiments, the internal fastener  20  (and any medical device attached thereto) is capable of being removed relatively easily, even if bone ingrowth into the anchor has taken place. An associated medical device and bone anchor device may be referred to as a medical device assembly. In some embodiments, the internal fastener  20  may be a screw similar to those described in U.S. Pat. Nos. 5,474,555 and 5,466,237, however such an internal fastener engages a bone anchor rather than directly engaging bone. 
         [0021]    In another aspect, an internal fastener  30  is provided for use with a bone anchor  20 , wherein the internal fastener  30  is capable of being permanently engaged in the bone anchor  40  having at least one thread  460  for securing the bone anchor  40  in a bone. One such non-limiting example of a permanently engaging anchoring device is illustrated in  FIG. 4 , showing the internal fastener  30  and bone anchor  40 . A locking mechanism between bone anchor  40  and internal fastener  30  provides the permanent engagement. The internal fastener  30  has a proximal end comprising a head  410  and a distal end comprising a tip  420 , the head  410  and the tip  420  being separated by an elongated shaft  430 . The external surface of the elongated shaft  430  comprises an annular ring  450 . The surface of the cannula of the bone anchor  40  comprises at least one retaining member  440 , such that when the internal fastener  30  is inserted in the bone anchor  40  and the annular ring  450  is pushed past the at least one retaining member  440 , the internal fastener  30  is prevented from being removed and is permanently engaged in the bone anchor  40 . In some embodiments, the annular ring  450  may snap past the retaining member  440 , acting as a snap feature. The annular ring  450  provides a continuous surface with which the internal fastener  30  is retained in the bone anchor  40  by the at least one retaining member  440 , such that turning of the internal fastener  30  does not result in its removal. In such embodiments, a plurality of annular rings and retaining members may be used. The option of such embodiments, removable and permanent engagement of an internal fastener in a bone anchor, allow one of skill in the art to determine in advance if a removable internal fastener or a permanently engaged internal fastener is required. 
         [0022]      FIG. 5  is another, non-limiting illustration of permanently engaging an internal fastener  50  in a bone anchor  60 . As shown, the internal fastener  50  has an elongated shaft comprising at least one recess  550 , the bone anchor  60  has at least one retaining member  540 , and the bone anchor  60  may also comprise at least one fenestration  560  and threading  570  for securing the bone anchor  60  in a bone. In such embodiments, the at least one recess  550  engages the at least one retaining member  540  such that removal of the internal fastener  50  from the bone anchor  60  is prevented. A plurality of recesses and retaining members may be used. 
         [0023]    Alternatively, the locking mechanism may be a lock and key type mechanism. For example, the elongated shaft of an internal fastener may have a cross-sectional shape other than completely round and a cannula of a bone anchor has a shape that is complementary, such that when the internal fastener is inserted into the bone anchor, rotation of the internal fastener is prevented by the shape matching. In such cases, permanent attachment of the internal fastener in the bone anchor may be achieved by providing at least one retaining member on the surface of the elongated shaft of the internal fastener and at least one retaining member on the internal surface of the cannula in a position that will engage the at least one retaining member. 
         [0024]    Internal fasteners intended for permanent engagement in a bone anchor may or may not be made of materials that allow for bone ingrowth. For example, the internal fastener may be made of the materials identified above for those internal fasteners that do not allow for bone ingrowth, or they may be made of materials similar to the bone anchor in which bone growth is promoted and encouraged by porous surfaces and porous coatings. 
         [0025]    In some embodiments, the internal fastener may be used to reduce fractures. For example, a bone anchor may be secured in a bone and an internal fastener inserted through another bone, or fragment of bone, the internal fastener then being engaged within the bone anchor to reduce the fracture. Such internal fasteners may also be an intramedullary (IM) nail. IM nails are typically inserted lengthwise through bone to secure and realign broken or misshapen bones. The internal fastener, or IM nail, may be inserted through a bone lengthwise and inserted into a bone anchor secured in another bone such that when the IM nail extends through the bone, it may be permanently engaged in the bone anchor, thus securing the bone requiring realignment or reshaping. Such an engagement allows a surgeon to make the connection without the need for securement by transverse pins through the bone and into the IM nail. 
         [0026]    In another aspect, methods of using the bone screw device are provided. In one method, the bone anchor  10  is driven into a bone  310 , as illustrated in  FIG. 3  using an appropriate drive device. A medical device  320  is then placed over the head  100  and the cannula  110  of the bone anchor  10  and the internal fastener  20  is inserted through the medical device  320  and into the cannula  130  before being secured in the bone anchor  10  by driving until tight. Over time, a bone reduction will set and heal or a medical device may become unnecessary or need to be replaced or repaired. However, due to the porous coating or materials used to construct the bone anchor  10 , removal of that part of the device may be difficult without causing severe trauma to the area. The method thus may further comprise removing the internal fastener  20  from the bone anchor  10 , thereby freeing the device  320  from the bone, while leaving behind a minimal amount of foreign material (i.e., bone anchor  10 ) in the subject. Because the internal fastener  20  does not allow for bone ingrowth, removal of the internal fastener  20  may cause less trauma to the bone and surrounding tissue. Bone may then continue to grow into the cannula  110  of bone anchor  10 , thus incorporating the bone  10  anchor wholly into the bone over time. Alternatively, an internal fastener  20  may be reinserted into the bone anchor  10  after a device has been removed, so that the cannula in the bone anchor remains bone-growth-free and may be reused to re-anchor another medical device, should the need arise. In other embodiments, the internal fastener  20  is inserted through a bone prior to insertion into the bone anchor  10  to reduce a fracture. 
         [0027]    In another embodied method, the bone anchor  10  is driven into a bone  310 , as illustrated in  FIG. 3  using an appropriate drive device. The internal fastener  20  is then inserted into the cannula  130  before being secured in the bone anchor  10  by driving until tight with the head  210  of the internal fastener  20  adjacent to the head  100  of the bone anchor  10 . The result is a completely nested internal fastener in bone anchor, without an attached medical device. 
         [0028]    In yet another embodied method, the bone anchor  40  is driven into a bone, using an appropriate drive device. The internal fastener  30  is then inserted into the cannula of the bone anchor  40 , and is pushed in to such a depth that the annular ring  450  passes the at least one retaining member  440 . The result is that the internal fastener  30  is permanently engaged within the bone anchor  40 . In such embodiments, the internal fastener may be used to reduce a bone fracture, or align a bone. In embodiments where the internal fastener  30  and bone anchor  40  secure a medical device, the internal fastener  30  is first inserted through an attachment bore on the medical device before inserting into the bone anchor  40 . 
         [0029]    Referring to  FIG. 5 , in yet another method, the internal fastener  50  is inserted into the bone anchor  60  such that the at least one retaining member  540  engages the at least one recess  550  thereby preventing removal of the internal fastener  50  from the bone anchor  60 . 
         [0030]    Examples of medical devices that may be anchored to bones with one or more of the present devices include, but are not limited to, spinal stabilization devices, such as those described in U.S. Patent Application Publication No. 2005/0113927, intervertebral disc prostheses, such as those described in U.S. Patent Application Publication No. 2005/0071007, and prosthetic vertebral bodies, such as those described in U.S. Patent Application Publication No. 2005/0137707. For example, a stabilizing rod or plate may be connected to an internal fastener which takes the form of the “anchor,” as described in U.S. Pat. No. 5,474,555 or U.S. Pat. No. 5,466,237, and the internal fastener may then be secured to a bone anchor, rather than directly engaging a bone. In some embodiments, the medical device that may be anchored to a bone is a rod, a plate, a disc, a cervical device, a lumbar device, or other device known to those of skill in the art. The bones with which the bone anchor devices of the present invention may be used, include bones not only associated with the spinal column, but any bones within the body. For example, the bones to be secured or to which a medical device may be secured by bone anchor devices of the present invention include bones associated with, but not limited to, the arms, legs, spinal column, ribs, skull, hip, knee, ankle, foot, and hand. 
         [0031]    For the purposes of this disclosure and unless otherwise specified, “a” or “an” means “one or more”. All patents, applications, references and publications cited herein are incorporated by reference in their entirety to the same extent as if they were individually incorporated by reference. 
         [0032]    While some detailed embodiments have been illustrated and described, it should be understood that such detailed embodiments are merely exemplary and changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the invention in its broader aspects as defined in the following claims.