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 . fig1 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 . fig1 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 . 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 ). fig2 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 ,” publication no . us - 2008 - 0147156 - a1 ( 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 ,” publication no . us - 2008 - 0140169 - a1 ( 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 . the hard tissue anchors 600 of the present invention include bone tacks and bone screws . fig3 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 fig4 . 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 . 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 . fig5 illustrates a side view of an embodiment of a tack 601 having such a channel 608 along the top of the head 602 , and fig6 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 fig7 . 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 . fig8 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 . in some embodiments , the tack 601 includes a grommet 606 , as illustrated in fig9 a - 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 . fig1 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 . fig1 a , 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 the front view illustrated in fig1 a , tack 601 includes head 602 and penetrating end 604 . as shown in fig1 a , head 602 can be shaped like an incomplete ring to include aperture 607 and channel 608 . head 602 can have a 0 . 060 inch diameter , aperture 607 can have a 0 . 040 inch diameter , and channel 608 can be 0 . 008 inches wide , for example . the penetrating end 604 can have serrations which taper from a first serration 611 to a second serration 613 to a point 615 . for example , first serration 611 can have a width of approximately 0 . 045 inches and extend outwards at an angle of approximately 50 degrees , second serration can have a width of approximately 0 . 035 inches and extend outwards at an angle of approximately 50 degrees , and penetrating end 604 can have a length of approximately 0 . 105 inches from the center of aperture 607 to point 615 . additionally , the distance from the center of aperture 607 to neck 609 can be approximately 0 . 029 inches , the distance from the center of aperture 607 to first serration 611 can be approximately 0 . 043 inches , and the distance from the center of aperture 607 to second serration 613 can be approximately 0 . 068 inches . neck 609 of the penetrating end 604 can attach to head 602 , and can extend outwards at an angle of approximately 30 degrees . fig1 b shows a side view of bone tack 601 , including head 602 and penetrating end 604 having first serration 611 , second serration 613 , and point 615 . as shown in fig1 b , penetrating end 604 can come to a sharp point 615 at an angle of approximately 40 degrees . furthermore , the distance from second serration 613 to point 615 can be approximately 0 . 034 inches , for example . fig1 c shows a top view of bone tack 601 . head 602 can have a depth of approximately 0 . 009 inches , and penetrating end 604 can have a depth of approximately 0 . 025 inches , for example . fig1 d illustrates point 615 of penetrating end 604 . 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 . 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 . 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 . 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 fig1 , 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 . fig1 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 fig1 . 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 . in some embodiments , the distal end 304 is comprised of an insert that is inserted into the elongate body 300 . fig1 a - 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 . fig1 a 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 . fig1 b illustrates an embodiment of an elongate body 300 having a length of 0 . 105 inches and a width of 0 . 28 inches . fig1 c 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 fig1 d . in this embodiment , the slot 303 has a depth of 0 . 105 inches and a width of 0 . 028 inches . fig1 e 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 fig1 , the aperture 607 of the bone tack 601 is exposed to allow an element to pass therethrough . referring back to fig1 e , in this embodiment , the notch 305 has a width of 0 . 033 inches . it may be appreciated that the dimensions noted herein are examples . 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 . 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 . fig1 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 . 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 fig4 . 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 fig7 . optionally , the bone screw 650 may include a grommet having similar features to the grommet 606 described previously in relation to bone tacks 601 . fig1 a - 17e provide various views of one embodiment of a bone screw 650 of the present invention . fig1 a illustrates a perspective view of a bone screw 650 similar to the bone screw of fig1 . however in this embodiment , the penetrating end 654 has a thread which is more suitable for penetrating cancellous bone . fig1 b illustrates a side view of the bone screw 650 of fig1 a . 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 fig1 e ). referring to fig1 c and its cross - section shown in fig1 d , 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 . 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 . 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 fig1 a - 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 . fig1 a 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 . fig1 b 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 . 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 . 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 .
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 .