Abstract:
The present invention provides devices, systems and methods for anchoring medical devices to hard tissues, such as bones or bony structures, particularly vertebrae. By anchoring these medical devices directly to the surrounding hard tissue, the devices are anchored closer to the source of treatment. This provides additional stability and reduces migration of the device at the treatment site. Also, by attaching to hard tissue rather than soft tissue, a stronger attachment is often able to be made.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority of provisional patent application No. 60/873,549 (Attorney Docket No. 10088-708.101), filed on Dec. 6, 2006, which is incorporated herein by reference for all purposes. 
     
    
     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
       [0002]    NOT APPLICABLE 
       REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK 
       [0003]    NOT APPLICABLE 
       BACKGROUND OF THE INVENTION 
       [0004]    A variety of implantable medical devices are used to treat portions of the anatomy which reside near bones or bony structures within the body of a patient. Such devices are typically anchored in place by suturing portions of the device to surrounding soft tissue. Often the device includes suture holes designed specifically for this purpose at predetermined locations along the device. Thus, the device may only be sutured at these locations, limiting the areas and types of tissue available for suturing thereto. Often, the location is far from the treatment site. Such distance and instability of anchoring tissue can contribute to lead migration and pull-out. 
         [0005]    For example, conventional spinal cord stimulators (SCS) are positioned along the spinal column to treat pain. A conventional SCS system comprises an implantable lead and an implantable power source or implantable pulse pulse generator IPG. Using fluoroscopy, the lead is implanted into the epidural space of the spinal column and positioned against the dura layer of the spinal cord. The lead extends from the spinal column to the IPG which is remotely implanted. Typically, the lead is sutured to soft tissue remote from the point of entry into the epidural space. And, lead migration and pull-out are common problems associated with SCS. 
         [0006]    Therefore, it is desired to provide a more stable anchoring system for implantable devices, such as leads. Such an anchoring system should provide anchoring at desired locations rather than merely at locations along the device which are predesigned for anchoring. Such anchoring should also assist in resisting migration and pull-out. At least some of these objectives will be met by the present invention. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention provides devices, systems and methods for anchoring medical devices to hard tissues, such as bones or bony structures, particularly vertebrae. A variety of medical devices are used to treat portions of the anatomy which reside near bones or bony structures within the body of a patient. The devices and systems of the present invention are suitable for use with many of such medical devices and specialized devices used for particular treatments. By anchoring these directly to the surrounding hard tissue, the devices are anchored closer to the source of treatment. This provides additional stability and reduces migration of the device at the treatment site. Also, by attaching to hard tissue rather than soft tissue, a stronger attachment is often able to be made. 
         [0008]    In a first aspect of the present invention, a hard tissue anchor is provided for securing an element to a hard tissue. In some embodiments, the hard tissue comprises a penetrating end shaped for penetrating the hard tissue, and a head having an aperture, wherein the aperture is configured to receive the element therethrough and wherein the head is configured to secure the element within the aperture. Typically, the element comprises a lead, however catheters or other devices may be used. 
         [0009]    In some embodiments, the head includes a channel connected to the aperture, wherein the channel is configured allow passage of the element from outside of the head to the aperture. In some instances, the head is adjustable to close the channel, such as by deformation of the head. Optionally, deformation of the head may secure the element within the aperture. In some embodiments, the head further comprises a grommet disposed within the aperture. The grommet may assist in holding the element within the aperture. 
         [0010]    In some embodiments, the penetrating end has a tapered, conical, notched, barbed or serrated shape. In such instances, the hard tissue anchor is considered a tack and is pressed into the hard tissue. In other embodiments, the penetrating end has a shank with a helical thread. In these instances, the hard tissue anchor is considered a screw and is rotated into the hard tissue. 
         [0011]    In a second aspect of the present invention, a method is provided for anchoring an element to a hard tissue in a body: In some embodiments, the method comprises advancing a hard tissue anchor toward the hard tissue, wherein the anchor has a penetrating end and a head having an aperture, positioning the element within the aperture, and applying pressure to the head so as to drive the penetrating end at least partially into the hard tissue. 
         [0012]    In some embodiments, applying pressure comprises applying pressure to the head so as to secure the element within the aperture. Optionally, applying pressure comprises deforming the head so as to secure the element within the aperture due to friction. 
         [0013]    In some instances, the method further comprises implanting the element in the body. Such implanting may occur before the positioning step of positioning the element within the aperture. This allows the hard tissue anchors to be utilized with existing implanted systems. 
         [0014]    In still further embodiments, the anchor includes a channel connected to the aperture and the method further comprises passing a portion of the element through the channel to the aperture. Optionally, applying pressure comprises deforming the head so as to at least partially close the channel. 
         [0015]    To deliver a hard tissue anchor of the present invention, such methods may include mounting the head of the anchor on a distal end of an applicator. In some situations, advancing the hard tissue anchor toward the hard tissue comprises advancing the distal end of the applicator through a percutaneous access opening. In such instances, the applicator has a low profile suitable for such percutaneous delivery. 
         [0016]    In some embodiments, applying pressure to the head comprises applying pressure to the applicator. Optionally, applying pressure to the applicator may comprise deforming the head by force of the applicator so as to secure the element within the aperture due to friction. 
         [0017]    In a third aspect of the present invention, an applicator is provided for delivering a hard tissue anchor. In some embodiments, the applicator comprises an elongate body having a proximal end and a distal end, wherein the distal end is configured to receive a head of the hard tissue anchor, and a handle attached to the proximal end of the elongate body so that force applied to the handle is translatable to the head of the hard tissue anchor. Optionally, the elongate body may be shaped for passage through a percutaneous access opening. 
         [0018]    In some embodiments, the applicator further comprises a release button for releasing the hard tissue anchor from the distal end of the elongate body. The distal end may include a recess for receiving the head, from which the hard tissue anchor is releasable. 
         [0019]    When the hard tissue anchor comprises a bone tack, the force typically comprises longitudinal force which is translatable to a downward force on the head of the hard tissue anchor. When the hard tissue anchor comprises a bone screw, the force typically comprises rotational force which is translatable to rotation of the head of the hard tissue anchor. In such instances, the distal end may comprise a rotatable member joinable with the head, wherein the rotation force rotates the rotatable member. 
         [0020]    Other objects and advantages of the present invention will become apparent from the detailed description to follow, together with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  illustrates a hard tissue anchor of the present invention used with a conventional SCS system. 
           [0022]      FIG. 2  illustrates a hard tissue anchor of the present invention used with a lead which is implanted near a DRG to provide selective stimulation thereto. 
           [0023]      FIG. 3  illustrates an embodiment of a bone tack of the present invention. 
           [0024]      FIG. 4  illustrates an embodiment of a bone tack having an element threaded through its head prior to implantation of the element. 
           [0025]      FIG. 5  illustrates a side view of a tack having a channel along the top of the head. 
           [0026]      FIG. 6  illustrates a top view of such the tack of  FIG. 5 . 
           [0027]      FIG. 7  illustrates passing an element through a channel in the head of a bone tack. 
           [0028]      FIG. 8  illustrates a lead surrounded by a silicone tube positioned within arms of the head of a bone tack. 
           [0029]      FIGS. 9A-9B  illustrate an embodiment of a bone tack having a grommet. 
           [0030]      FIG. 10  illustrates a tack having a grommet wherein the channel of the grommet has been closed by crimping of the head. 
           [0031]      FIGS. 11A ,  11 B,  11 C,  11 D illustrate front, side, top and bottom views, respectively, of one embodiment of a bone tack of the present invention. 
           [0032]      FIG. 12  illustrates an applicator for delivery of a bone tack to a portion of a hard tissue. 
           [0033]      FIG. 13  illustrates a distal end of the applicator having a recess for receiving a head of a bone tack. 
           [0034]      FIG. 14  illustrates a bone tack securely fixed to an applicator during insertion via friction fit with a grommet. 
           [0035]      FIGS. 15A ,  15 B,  15 C,  15 D,  15 E illustrates various views elongate body of an applicator having an insert positionable within its distal end. 
           [0036]      FIG. 16  illustrates an embodiment of a bone screw of the present invention. 
           [0037]      FIGS. 17A ,  17 B,  17 C,  17 D,  17 E illustrate various view of an embodiment of a bone screw. 
           [0038]      FIGS. 18A-18B  illustrate an applicator for delivery of a bone screw to a portion of a hard tissue. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    The present invention provides devices, systems and methods for anchoring medical devices to hard tissues, such as bones or bony structures, particularly vertebrae. A variety of medical devices are used to treat portions of the anatomy which reside near bones or bony structures within the body of a patient. For example, spinal cord stimulators (SCS) are positioned along the spinal column to treat pain.  FIG. 1  illustrates a conventional SCS system comprising an implantable lead  100  and an implantable power source or implantable pulse pulse generator IPG. Using fluoroscopy, the lead  100  is implanted into the epidural space E of the spinal column S and positioned against the dura layer of the spinal cord. The lead  100  is implanted either through the skin via an epidural needle (for percutaneous leads) or directly and surgically through a mini laminotomy operation (for paddle leads). In either case, the leads  100  extend from the spinal column S to the IPG which is remotely implanted. Typically, the leads  100  are sutured to soft tissue remote from the point of entry into the epidural space E. Such suturing is often insufficient to adequately the implanted lead  100 , thus leading to migration or pull-out.  FIG. 1  illustrates a hard tissue anchor  600  of the present invention used in conjunction with the conventional SCS system to anchor the implantable lead  100 . As shown, the anchor  600  can be used to attach the lead  100  a hard tissue, such as a vertebrae V near the point of entry to the epidural space E. This provides more secure anchoring by fixing to a harder tissue and reduces the distance between the distal portion of the lead and the site of anchoring. This assists in reducing migration and pull-out of the lead  100 . 
         [0040]    In addition, the devices, systems and methods of the present invention may be used to anchor other types of medical devices, in particular various other types of leads used to selectively stimulate the spinal anatomy, particularly the dorsal root or dorsal root ganglion (DRG).  FIG. 2  illustrates a lead  150  which is implanted near a DRG to provide selective stimulation thereto. Examples of such leads are provided in U.S. patent application Ser. No. 11/952,049, filed Dec. 6, 2007, entitled “Grouped Leads For Spinal Stimulation”, (Attorney Docket No. 10088-706.201/Client Ref No. SM-00610US) and U.S. patent application Ser. No. 11/952,053, filed Dec. 6, 2007, entitled “Grouped Leads For Posterior Access Of Directed Spinal Stimulation” (Attorney Docket No. 10088-707.201/Client Ref No. SM-00710US), both incorporated herein by reference. As shown, a hard tissue anchor  600  of the present invention may be used to anchor the lead  150  to a portion of the vertebrae V which is near the DRG. This anchors the lead  150  close to the stimulation site and reduces migration or pull-out of the lead  150 . 
         [0041]    The hard tissue anchors  600  of the present invention include bone tacks and bone screws.  FIG. 3  illustrates an embodiment of a bone tack  601  of the present invention. The bone tack  601  can be used to anchor an element, such as a lead or catheter, to a bone or bony structure, such as near to a site of an intended application. In this embodiment, the bone tack  601  has a head  602  and a penetrating end  604  opposite the head  602 . The penetrating end  604  may have a tapered, conical, notched, barbed, serrated or otherwise shaped end which is suitable for penetrating bone B, as shown. The head  602  includes an aperture  607  through which the element  152  can be threaded prior to implantation of the element  152 , as illustrated in  FIG. 4 . The bone tack  601  is advanced along the element  152  to the desired anchoring position. Force is then applied to the head  602  to advance the penetrating end  604  into the bone B, thereby fixing the element  152  to the bone B at that location. This may be achieved during the implantation procedure of the element  150 . 
         [0042]    Other embodiments of the bone tack  601  are particularly suited for anchoring the element  150  at an anchoring location when it is less desirable to pre-load the anchor on the element  150 . This may be the case when the element  150  is already implanted or it is not possible to advance an anchor over the element  150 , such as from one of the ends of the element  150  to the anchoring location. In some of these embodiments, the head  602  of the bone tack  601  includes a channel  608  which connects to the aperture  607 .  FIG. 5  illustrates a side view of an embodiment of a tack  601  having such a channel  608  along the top of the head  602 , and  FIG. 6  illustrates a top view of such a tack  601 . The tack  601  can be slipped over the element  150  through the channel  608  in the head  602  so that the element  150  passes through the aperture  607 , as illustrated in  FIG. 7 . Thus, the tack  601  can be positioned at any location along the element  150 . The channel  608  can then be closed by deformation of the head  602 . Further deformation of the head  602  crimps the head  602  onto the element  150  resisting relative motion. 
         [0043]      FIG. 8  illustrates a lead  610  surrounded by a silicone tube  612  positioned within arms  614  of the head  602  of a bone tack  601 . Deforming or crimping of the head  602  (at least one arm  614 ) holds the silicone tube  612  in relation to the head  602  and further crimping holds the lead  610  in relation to the silicone tube  612 . Thus, various degrees of deformation may be used to provide differing desired results. 
         [0044]    In some embodiments, the tack  601  includes a grommet  606 , as illustrated in  FIGS. 9A-9B . The grommet  606  includes a channel which is alignable with the channel  608  of the head  602 . Thus, an element  150  may be passed through the channel  608  of the head  602  and the aligned channel of the grommet  606 . The grommet  606  assists in applying friction to the element  150  and protects the element  150  from possible damage. Deformation or crimping of the head  602  applies further friction to the element  150 , such as fixing the element  150  within the grommet  606 .  FIG. 10  illustrates a tack  601  having a grommet  606  wherein the channel of the grommet  606  has been closed by crimping of the head  602 . This illustrates the reduction in size of the aperture an therefore increased friction against the element  150 . 
         [0045]      FIGS. 11A ,  11 B,  11 C,  11 D provide front, side, top and bottom views, respectively, of one embodiment of a bone tack  601  of the present invention. In this embodiment, the tack  601  has a 0.060 inch diameter head  602  with a 0.040 inch diameter aperture  607 . Further, the head  602  has a 0.008 inch channel  608 . This embodiment also includes a penetrating end  604  having serrations which taper from a first serration having a width of 0.045 inches to a second serration having a width of 0.035 inches to a point. The penetrating end  604  has a length of 0.105 inches from the center of the aperture  607 . Thus, the bone tacks  601  of the present invention typically have a small size to allow positioning in confined or hard to reach areas of the anatomy. It may be appreciated that such dimensions are exemplary and are not intended to limit the scope of the present invention. 
         [0046]    The head  602  and a penetrating end  604  are typically formed from the same material and may comprise any biocompatible and/or bioresorbable material including but not limited to cobalt chromium, cobalt chromium alloys, titanium, titanium alloys, stainless steel, resorbable PGA or PLA, and PEEK. 
         [0047]    The grommet  606  may be comprised of any soft biocompatible and/or bioresorbable material including but not limited to silicone or polyurethane. The grommet  606  could be an assembly or molded onto the tack  606 . 
         [0048]    The bone tacks  601  of the present invention are driven into a portion of bone B by mechanical force, such as tapping or pressing. Referring to  FIG. 12 , an applicator  620  is provided for delivery of the bone tack  601  to a portion of a bone B. The applicator  620  is designed so that the tack  601  can be delivered through a percutaneous access opening and positioned at an anchoring location via fluoroscopy or other imaging techniques. Typically, the applicator  620  comprises an elongate body  300  with a low profile to assist in accessing a variety of target locations within the body. The elongate body  300  has a proximal end  302  and a distal end  304 , wherein the distal end  304  is configured to receive the hard tissue anchor  600 . In most embodiments, the applicator  620  also includes a handle  306  attached to the proximal end  302  of the elongate body  300 . 
         [0049]      FIG. 13  illustrates an embodiment of a distal end  304  of the applicator  620  having a recess  624  for receiving a head  602  of a bone tack  601 . In some embodiments, the bone tack  601  is securely fixed to the applicator  620  during insertion via friction fit with the grommet  606 , as illustrated in  FIG. 14 . The tack  601  is penetrated and anchored into the bone B via the penetrating end  604 , by application of downward or longitudinal force on the tack  601  by the applicator  620 . Thus, force applied to the handle  306  is translatable to the head  602  of the hard tissue anchor  600  and drives the anchor  600  into the hard tissue. In some embodiments, such force also then crimps the head  602  onto an element passing through the aperture  607 . The tack  601  can then be released from the applicator  620 , such as with the use of a release button  626 . The tack  601  is then left behind with the element passing therethrough. 
         [0050]    In some embodiments, the distal end  304  is comprised of an insert that is inserted into the elongate body  300 .  FIGS. 15A-15E  illustrate various views of an elongate body  300  having an insert  301 . Typically the insert  301  is formed or machined so that together the insert  301  and the elongate body  300  desirably receive the bone tack  601 .  FIG. 15A  illustrates a side view of an insert  301  having a recess  624  for receiving a bone tack  601 . Here the recess  624  has a depth of 0.050 inches and a width of 0.060 inches.  FIG. 15B  illustrates an embodiment of an elongate body  300  having a length of 0.105 inches and a width of 0.28 inches.  FIG. 15C  illustrates a bottom view of an insert  301  showing recess  624 . The insert  301  is inserted into a slot  303  in the elongate body  300 , illustrated in  FIG. 15D . In this embodiment, the slot  303  has a depth of 0.105 inches and a width of 0.028 inches.  FIG. 15E  illustrates a side view of the elongate body  300  having a notch  305 . When a bone tack  601  is inserted into the distal end  304 , as illustrated in  FIG. 14 , the aperture  607  of the bone tack  601  is exposed to allow an element to pass therethrough. Referring back to  FIG. 15E , in this embodiment, the notch  305  has a width of 0.033 inches. It may be appreciated that the dimensions noted herein are examples. 
         [0051]    Example methods of installing a bone tack  601  of the present invention are described herein. In one embodiment, a tack  601  of the present invention is mounted in an applicator  620  as described above. An element, such as a lead  610 , is threaded through the aperture  607  of the tack  601  while the tack  601  is held in the applicator  620 . The tack  601  is inserted into a percutaneous access site, locating the target bone or bony structure via fluoroscopy or other imaging method. The lead  610  is positioned as desired for its intended therapeutic purpose. The bone tack  601  is then tapped into place so that the penetrating end  604  sufficiently penetrates the target bone or bony structure and the head crimps the lead. The applicator  620  is then removed. 
         [0052]    Thus, the bone tacks  601  of the present invention can be used to secure various devices without the use of sutures. Further, such securing or anchoring can be achieved in percutaneous procedures without the need for a large surgical exposure. And, such securing and anchoring is easily achievable without excessive manipulation, particularly with the use of the deformable head which secures the lead during insertion of the tack into bone. Likewise, this action is assisted by the use of the applicator which is able to hold the tack and deform the head while inserting the tack into the bone. 
         [0053]      FIG. 16  illustrates an embodiment of a bone screw  650  of the present invention. The bone screw  650  can also be used to anchor an element, such as a lead or catheter, to a bone or bony structure near to a site of an intended application. The bone screw  650  has a head  652  and a penetrating end  654  opposite the head  652 . Typically, the penetrating end  654  has a tapered shank with a helical thread which is suitable for turning or twisting into bone. In some embodiments, the thread is particularly suitable for penetrating cortical bone. Cortical thread forms are generally finer pitched (more threads per inch) and shallower than thread forms designed to penetrate cancellous bone. In some embodiments, the helical thread has a pitch of 0.020-0.200 inches, more particularly 0.029 inches. Typically, the penetrating end  654  is self-tapping and does not require the use of a bone tap to implant the bone screw  650  into the hard tissue. In some embodiments, the penetrating end  654  has an acute nose angle to assist in self-tapping, such as a 60 degree nose angle. In some embodiments, a wedge is added to further assist in self-tapping, such as a 30 degree wedge. 
         [0054]    The head  602  includes an aperture  657  through which the element  152  can be threaded prior to implantation of the element  152  in a manner similar to the bone tack  601  of  FIG. 4 . Or, the screw  650  can be slipped over a portion of the element  152  through a channel  658  in the head  652  which connects to the aperture  657  in a manner similar to the bone tack  601  of  FIG. 7 . Optionally, the bone screw  650  may include a grommet having similar features to the grommet  606  described previously in relation to bone tacks  601 . 
         [0055]      FIGS. 17A-17E  provide various views of one embodiment of a bone screw  650  of the present invention.  FIG. 17A  illustrates a perspective view of a bone screw  650  similar to the bone screw of  FIG. 16 . However in this embodiment, the penetrating end  654  has a thread which is more suitable for penetrating cancellous bone.  FIG. 17B  illustrates a side view of the bone screw  650  of  FIG. 17A . In this embodiment, the head  652  has a diameter of approximately 0.14 inches and an aperture  657  having a diameter of approximately 0.06 inches. Likewise, the head  652  has a 0.03 inch channel  658 . The penetrating end  654  has a length of 0.38 inches from the center of the aperture  657  and a diameter of approximately 0.10 inches (as illustrated in the top view of  FIG. 17E ). Referring to  FIG. 17C  and its cross-section shown in  FIG. 17D , the penetrating end  654  has a shank with a helical thread with a pitch of 0.075 inches. Thus, the bone screws  650  of the present invention typically have a small size to allow positioning in confined or hard to reach areas of the anatomy. It may be appreciated that such dimensions are exemplary and are not intended to limit the scope of the present invention. 
         [0056]    The head  652  and a penetrating end  654  of the bone screws  650  are typically formed from the same material and may comprise any biocompatible and/or bioresorbable material including but not limited to cobalt chromium, cobalt chromium alloys, titanium, titanium alloys, stainless steel, resorbable PGA or PLA, and PEEK. 
         [0057]    The bone screws  650  of the present invention are driven into a hard tissue, such as a portion of bone B, by rotational force. Referring to  FIGS. 18A-18B  an applicator  660  is provided for delivery of the bone screw  650  to a portion of a bone B. The applicator  660  is designed similarly to the bone tack applicator  620  in that it has a low profile so that the screw  650  can be delivered through a percutaneous access opening and positioned at an anchoring location via fluoroscopy or other imaging techniques. Again, the applicator  660  typically comprises an elongate body  670  having a proximal end  672  and a distal end  662 , wherein the distal end  662  is configured to receive the hard tissue anchor  600 . In most embodiments, the applicator  660  also includes a handle attached to the proximal end  672  of the elongate body  670 . 
         [0058]      FIG. 18A  illustrates an embodiment of a distal end  662  of the applicator  660  having a recess  664  for receiving a head  652  of a bone screw  650 . The applicator  660  includes a rotatable member  661  which is joinable with the bone screw  650 .  FIG. 18B  illustrates a bone screw  650  securely fixed to the rotatable member  661  via friction, such as with a grommet. The screw  650  is penetrated and anchored into the bone B via rotation of the penetrating end  604  by rotating the member  661 . When it is desired to deform or crimp the head  652 , force may be applied to the handle and translated to the head  652  which crimps the head  652  onto an element passing through the aperture  657 . The screw  650  can then be released from the applicator  660 , such as with the use of a release button. 
         [0059]    One challenge of a twisting or screw-type penetration is that the orientation of the aperture  657  depends on how the screw  650  is screwed in. Also, placing the lead into the aperture  657  after delivery may be difficult due to its orientation. These challenges are overcome by the bone screws  650  of the present invention. The bone screw  650  may be screwed in place at a desired location first and then the element, such as a lead, is loaded through the channel  658  in the head  652 . The lead is then advanced to a desired position for the therapeutic application and secured in place by crimping of the head  652 . 
         [0060]    Although the foregoing invention has been described in some detail by way of illustration and example, for purposes of clarity of understanding, it will be obvious that various alternatives, modifications and equivalents may be used and the above description should not be taken as limiting in scope of the invention.