Abstract:
The function of a strain relief loop of an implantable medical lead is preserved by inhibiting restriction of the strain relief loop from tissue growth onto the strain relief loop. The restriction may be inhibited by either obstructing tissue growth and/or by utilizing a mechanical advantage to overcome the restriction. The tissue growth may be obstructed be isolating the interior of the strain relief loop such as by enclosing the strain relief loop or including an object within the loop. The mechanical advantage to overcome restriction from tissue growth may be provided in various ways such as utilizing a spring loaded mechanism or a structure such as an elastic mesh, tube, or mold having an inherent bias toward a steady state position.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments relate to strain relief loops of implantable medical leads. More particularly, embodiments relate to inhibiting tissue growth from restricting strain relief loops. 
       BACKGROUND 
       [0002]    Implantable medical systems include implantable stimulators that are positioned at an implantation site and implantable medical leads that extend from the implantation site to a target site within the body of a patient. The implantable medical leads have a proximal end that is coupled to the implantable stimulator and have a distal end that includes electrodes at the target site. The implantable medical leads include conductors within a lead body, and these conductors carry electrical stimulation signals from the electrical stimulator to the electrodes to deliver the electrical stimulation signals to the tissue at the target site. 
         [0003]    An issue that occurs for a period of time immediately following implantation of the medical lead involves the distal end of the lead being displaced from the target site due to certain bending movements of the patient prior to the distal end of the lead being adequately encapsulated by tissue growth. To address this displacement issue, during implantation a strain relief loop is created with the lead in order to allow the patient to move while allowing the distal end of the lead to remain positioned at the target site. However, the strain relief loop may experience encapsulation from tissue growth prior to the distal end of the lead being adequately encapsulated by tissue. This encapsulation of the strain relief loop limits the ability of the strain relief loop to function properly to maintain the position of the distal end of the lead. 
       SUMMARY 
       [0004]    Embodiments address issues such as these and others by providing methods and devices that inhibit tissue growth from restricting the function of the strain relief loop of the implantable medical lead. One manner of doing so is to inhibit the tissue growth from encapsulating the strain relief loop. This may be done in various ways, such as by obstructing at least the interior of the loop so that tissue does not fill the interior and adhere to the loop and/or by utilizing a tissue growth inhibitor as a coating or dopant of the lead or the object obstructing the interior of the loop. Another manner of doing so is to establish a mechanical advantage by applying a bias onto the loop which allows the loop to function to provide slack but biases the loop toward a steady state size when the loop size changes from the steady state due to movements by the patient. 
         [0005]    Embodiments provide a method of inhibiting tissue growth from restricting a strain relief loop of an implantable medical lead. The method involves positioning a lead body of the implantable medical lead to produce a strain relief loop. The method further involves coupling an object to the lead such that the object obstructs an area defined by an inner circumference of the loop while allowing the strain relief loop to provide strain relief. 
         [0006]    Embodiments provide a method of inhibiting tissue growth from restricting a strain relief loop of an implantable medical lead. The method involves providing a lead body of the lead with a tissue growth inhibitor. The method further involves positioning the lead body of the implantable medical lead to produce a strain relief loop such that the tissue growth inhibitor is present at the loop. 
         [0007]    Embodiments provide a method of inhibiting tissue growth from restricting a strain relief loop of an implantable medical lead. The method involves providing a lead body that forms a strain relief loop. The method further involves providing an object that is coupled to the strain relief loop, that has a steady state position providing a first diameter of the strain relief loop, and that applies a bias toward the steady state position when force applied to the implantable lead causes the strain relief loop to have a second diameter that differs from the first diameter. 
         [0008]    Embodiments provide an apparatus that inhibits tissue growth from restricting a strain relief loop. The apparatus includes an implantable lead forming the strain relief loop and an object that is coupled to the strain relief loop. The object has a steady state position providing a first diameter of the strain relief loop, and the object applies a bias toward the steady state position when force applied to the implantable lead causes the strain relief loop to have a second diameter that differs from the first diameter. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  shows an implantable medical system including a lead having a strain relief loop. 
           [0010]      FIG. 2  shows the strain relief loop portion of the lead with a first embodiment of a strain relief holder that inhibits restriction by tissue growth. 
           [0011]      FIG. 3  shows the strain relief loop portion of the lead with a second embodiment of a strain relief holder that inhibits restriction by tissue growth. 
           [0012]      FIGS. 4A and 4B  show embodiments of the strain relief loop portion of the lead that inhibits restriction by tissue growth. 
           [0013]      FIGS. 5A and 5B  show two states of the strain relief loop portion of the lead with a third embodiment of a strain relief holder that inhibits restriction by tissue growth. 
           [0014]      FIGS. 6A and 6B  show two states of the strain relief loop portion of the lead with a fourth embodiment of a strain relief holder that inhibits restriction by tissue growth. 
           [0015]      FIGS. 7A and 7B  show two states of the strain relief loop portion of the lead with a fifth embodiment of a strain relief holder that inhibits restriction by tissue growth. 
           [0016]      FIGS. 8A and 8B  show two states of the strain relief loop portion of the lead with a sixth embodiment of a strain relief holder that inhibits restriction by tissue growth. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Embodiments provide an implantable medical system including an implantable medical lead that may be coupled to a stimulation device where the implantable medical lead has a strain relief loop. According to various embodiments, a strain relief loop holder and/or the strain relief loop of the lead itself inhibits restriction by tissue growth of the function of the strain relief loop. This allows the strain relief loop to assist in maintaining the position of the distal end of the lead at the target site during movements of the body of the patient. 
         [0018]      FIG. 1  shows an example of an implantable medical system  100 . In this particular view, the implantable medical system  100  is implanted within tissue  101  of a patient. The implantable medical system  100  includes a stimulation device  102  that includes a housing  106  that encloses a stimulation engine  110 . A header  108  that is affixed to the housing  106  or is integral to the housing  106  receives a proximal end of an implantable medical lead  104  to establish electrical connectivity to conductors within the lead. The lead  104  provides an electrically conductive pathway from the implantable device  102  to electrodes  118  at a distal end  116  of the lead  104  which is positioned at a target site  120  within the patient. Here, the electrodes  118  are in close proximity to tissue  122  to be stimulated, such as neurological tissue or cardiac tissue. 
         [0019]    A lead body  112  of the lead  104  forms a strain relief loop  114  where various embodiments may be present to inhibit restriction of the strain relief loop  114  by tissue growth  124  that otherwise adheres to the strain relief loop  114  within the patient. Here, the electrodes  118  are in close proximity to tissue  122  to be stimulated, such as neurological tissue or cardiac tissue. 
         [0020]    A lead body  112  of the lead  104  forms a strain relief loop  114  that is subject to restriction by tissue growth  124 . Various embodiments may be present at the strain relief loop  114  to inhibit restriction by the tissue growth  124  that otherwise adheres to the strain relief loop  114 .  FIGS. 2-8B  show examples of these various embodiments which include various objects and/or coating/dopant configurations for obstructing tissue growth as shown in  FIGS. 2-4B . These various embodiments also include various objects that create a mechanical advantage to overcome restriction by tissue growth as shown in  FIGS. 5A-8B . 
         [0021]      FIG. 2  shows an embodiment of an object in the form of a strain relief loop cover  202  that is an enclosure that surrounds the strain relief loop  114 . The cover  202  has an entry aperture  204  and an exit aperture  206  that allows the lead body  112  to enter and exit the holder  202  while forming the loop  114  inside of the holder  202 . The interior of the cover  202  may be empty space as shown or may have interior details for structural support so long as such details do not restrict the function of the loop  114 . The cover  202  obstructs the tissue from being able to grow within the loop  114  as the loop  114  and in particular the surface  115  of the lead body  112  that forms the inner circumference of the loop  114  is effectively isolated from surrounding tissue and tissue growth. 
         [0022]    The strain relief loop cover  202  may be constructed of various biocompatible materials, including compliant materials such as polymers including silicones, poly(ethylene), polyurethanes, poly (vinyl chloride), and polylactides and/or rigid materials such as ceramics and metals including stainless steel, cobalt alloys, and titanium alloys. Additionally, the strain relief loop cover  202  may include either a coating or dopant of material  210  that inhibits tissue growth, and in particular inhibits monocyte adhesion and collagen growth. Examples of such a material  210  include synthetic polymers including poly (vinyl alcohol), poly (lactic co-glycolic) acid and poly (lactic acid), oxymatrine, and hydrogels such as poly (hydroxyethyl methacrylate) and polyethylene glycol, and phospholipid-containing materials. This material  210  may be present throughout the cover  202  or at least in areas surrounding the entry aperture  204  and exit aperture  206  so help prevent tissue growth within the apertures  204 ,  206  that might otherwise restrict the function of the loop  114 . 
         [0023]      FIG. 3  shows an example of an object in the form of a mesh structure  302  that is present within the loop  114  and is adhered to the surface  115  of the lead body  114  that forms the inner circumference of the loop  114 . The mesh structure  302  obstructs the interior of the loop  114  to inhibit tissue from growing through the interior of the loop  114  while being compliant to allow the loop  114  to function. Examples of the material that forms the mesh structure  302  include polymers including silicones, poly(ethylene), polyurethanes, poly (vinyl chloride), and polylactides. 
         [0024]    To aid the mesh structure  302  in eliminating tissue growth from the interior of the loop  114 , the mesh structure  302  may have a tissue growth inhibitor as a dopant or coating material  304 . This material  304  may be the same as the material  210  discussed above in relation to  FIG. 2 . This material  304  reduces the occurrence of tissue growth onto the mesh structure  302  so that the mesh structure  302  maintains adequate compliance for the loop  114  to function. 
         [0025]      FIG. 4A  shows an example where there is no object such as a holder or a mesh structure associated with the loop  114 . Instead, the lead body  112  has a dopant or coating of material  402  at least in the section forming the loop  114  where the material  402  inhibits tissue growth. While tissue may grow to some degree within the loop  114 , the ability of the tissue to grow onto the loop  114  is reduced to thereby preserve at least some of the function of the loop  114 . The material  402  may be the same as the material  210  discussed above in relation to  FIG. 2 . 
         [0026]      FIG. 4B  shows an example where there is a mesh structure  404  like the mesh structure  302  of  FIG. 3 , and the lead body  112  also has a dopant or coating of material  402  at least in the section forming the loop  114  where the material  402  inhibits tissue growth as in  FIG. 4A . Tissue growth is obstructed within the loop  114  while the ability of the tissue to grow onto the loop  114  is also reduced to further preserve the function of the loop  114 . 
         [0027]      FIG. 5A  shows an example of an object  502  that creates a mechanical advantage to overcome restriction by tissue growth. The object  502  of this example is a pair of arms  504 ,  508  connected at a hinge point  512  which provides a scissor-like operation. One arm  508  is attached at fixed points  510  along the loop  114  to the lead body  112 . The fixation may be provided by a clamping structure on the ends of the arm  508 , by an adhesive, by a weld, and the like. The other arm  504  has ends  506  that are loosely coupled to the loop  114  to allow the ends  506  to slide along the loop  114 . The arms  504 ,  508  may be constructed of various rigid and biocompatible materials such as biocompatible plastics or metals. 
         [0028]    The arms  504 ,  508  are biased relative to one another to a steady state position shown in  FIG. 5A . The bias may be provided by a spring  514  located at the hinge  512  where one side of the spring  514  is attached to the arm  504  and the other side is attached to the arm  508 . The arm  504  may be anchored by the presence of tissue and/or by being surgical anchored via suturing or another anchoring technique. The spring  514  causes the arm  508  to resist motion relative to the arm  504 , although providing less resistance to motion than the resistance to motion of the distal end  116  of the lead  104 . Upon a force  516  being applied due to movement of the patient, the proximal end of the lead moves which overcomes the bias of the spring  514  without dislodging the distal end  116  and causes the arm  508  to rotate away from the steady state position as shown. This rotation in opposition to the bias from the spring  514  results in the state of the object  502 ′ shown in  FIG. 5B , where the loop  114 ′ now has a different diameter than the steady state diameter and the spring  514 ′ is stressed relative to the steady state position. 
         [0029]    In this example, the force  516  has produced a smaller diameter loop  114 ′ which produces excess lead length that extends toward the proximal end to relieve tension on the distal end  116 . When the movement of the patient returns, the excess lead length produced by the reduction in loop diameter should be regained by the loop  114  to increase the loop diameter back to the steady state configuration of  FIG. 5A . However, the tissue growth around the loop  114  may constrain the ability of the excess length of the lead body  112  to return to the loop  114 , especially considering the loop is compliant and may tend to buckle. The mechanical advantage provided by the bias of the stressed spring  514 ′ effectively pulls the excess length of the lead body  112  back into the loop by the return rotation  518  of the arm  508  as shown in  FIG. 5B . 
         [0030]      FIG. 6A  shows an example of another object  602  that creates a mechanical advantage to overcome restriction by tissue growth. The object  602  of this example is an elastic mesh  602  connected to the surface  115  forming the inner circumference of the loop  114 . The elastic mesh  602  has a steady state position shown in  FIG. 6A  and may resist motion in all directions, although to a lesser degree than the resistance to motion of the distal end  116  of the lead. The elastic mesh  602  may be constructed of various biocompatible materials such as polymers including silicones, poly(ethylene), polyurethanes, poly (vinyl chloride), and polylactides which provide the mechanical advantage by attempting to return to the steady state position. Upon a force  604  being applied due to movement of the patient, the proximal end of the lead moves which causes the mesh  602  to crumple away from the steady state position to the crumpled mesh  602 ′ of  FIG. 6B . This movement and resulting crumpling in opposition to the bias from the mesh  602  results in the loop  114 ′ having a different diameter than the steady state diameter. 
         [0031]    In this example, the force  604  has produced a smaller diameter loop  114 ′ which produces excess lead length that extends toward the proximal end to relieve tension on the distal end  116 . When the movement of the patient returns, the excess lead length produced by the reduction in loop diameter should be regained by the loop  114  to increase the loop diameter back to the steady state configuration of  FIG. 6A . However, the tissue growth around the loop  114  may constrain the ability of the excess length of the lead body  112  to return to the loop  114 , especially considering the loop is compliant and may tend to buckle. The mechanical advantage provided by the bias  606  of the crumpled mesh  602 ′ forcing the smaller loop  114 ′ to grow in diameter back to the steady state effectively pulls the excess length of the lead body  112  back into the loop  114 . 
         [0032]    The primary benefit of the mechanical advantage is to assist the strain relief loop in countering the forces exerted by the tissue encapsulation. The goal is to have tissue encapsulation occurring at the strain relief loop last, as per the cover and doping mechanisms discussed above, or in the case of mechanical advantage embodiments, having the effect of the encapsulation (i.e., resisted motion) occurring at the strain relief loop last relative to the effect of the encapsulation at the electrodes. 
         [0033]      FIG. 7A  shows an example of another object  702  that creates a mechanical advantage to overcome restriction by tissue growth. The object  702  of this example is a loop holder in the form of a tubular loop  702  having an entry aperture  704  and an exit aperture  706 . The lead body  112  passes through the tubular loop  702  to form the loop  114 . The tubular loop  702  has a steady state position shown in  FIG. 7A  and may resist motion in all directions, although to a lesser degree than the resistance to motion of the distal end  116  of the lead. The tubular loop  702  may be constructed of various materials such as polymers including silicones, poly(ethylene), polyurethanes, poly (vinyl chloride), and polylactides which produce the mechanical advantage by attempting to return to the steady state position. Upon a force  708  being applied due to movement of the patient, the proximal end of the lead  104  moves which causes the tubular loop  702  to bend to a greater degree away from the steady state position to the smaller diameter tubular loop  702 ′ of  FIG. 7B . This movement and resulting reduction in loop diameter in opposition to the bias from the tubular loop  702  results in the loop  114 ′ also having a different diameter than the steady state diameter. 
         [0034]    In this example, the force  708  has produced a smaller diameter loop  114 ′ which produces excess lead length that extends toward the proximal end to relieve tension on the distal end  116 . When the movement of the patient returns, the excess lead length produced by the reduction in loop diameter should be regained by the loop  114  to increase the loop diameter back to the steady state configuration of  FIG. 7A . However, the tissue growth around the loop  114  may constrain the ability of the excess length of the lead body  112  to return to the loop  114 , especially considering the loop is compliant and may tend to buckle. The mechanical advantage provided by the bias  710  of the tubular loop  702 ′ forcing the smaller loop  114 ′ to grow in diameter back to the steady state effectively pulls the excess length of the lead body  112  back into the loop  114 . 
         [0035]      FIG. 8A  shows an example of another object  802  that creates a mechanical advantage to overcome restriction by tissue growth. The object  802  of this example is a holder in the form of a polymer mold  802 . The lead body  112  is press fit into the polymer mold  802 , where the mold  802  may either deform to receive the lead body  112  or may have a pre-formed channel  806  to receive the lead body  112 . The lead body  112  forms the loop  114  where the loop  114  is then held by the mold  802 . The mold  802  has a steady state position shown in  FIG. 8A  and may resist motion in all directions, although to a lesser degree than the resistance to motion of the distal end  116  of the lead. The mold  802  may be constructed of various materials such silicones, poly(ethylene), polyurethanes, poly (vinyl chloride), and polylactides which produce the mechanical advantage by attempting to return to the steady state position. Upon a force  804  being applied due to movement of the patient, the proximal end of the lead  104  moves which causes the mold  802  to deform away from the steady state position to the smaller diameter mold  802 ′ of  FIG. 8B  having the ripples  808 . This movement and resulting reduction in loop diameter in opposition to the bias from the mold  802  results in the loop  114 ′ also having a different diameter than the steady state diameter. 
         [0036]    In this example, the force  804  has produced a smaller diameter loop  114 ′ which produces excess lead length that extends toward the proximal end to relieve tension on the distal end  116 . When the movement of the patient returns, the excess lead length produced by the reduction in loop diameter should be regained by the loop  114  to increase the loop diameter back to the steady state configuration of  FIG. 8A . However, the tissue growth around the loop  114  may constrain the ability of the excess length of the lead body  112  to return to the loop  114 , especially considering the loop is compliant and may tend to buckle. The mechanical advantage provided by the bias  810  of the mold  802 ′ forcing the smaller loop  114 ′ to grow in diameter back to the steady state effectively pulls the excess length of the lead body  112  back into the loop  114 . 
         [0037]    While embodiments have been particularly shown and described, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.