Abstract:
An improved anchoring mechanism for an implantable lead is discussed. The anchoring mechanism consists of a tine enclosed in a housing structure. Deployment and retraction of the tine is controlled by the rotation of a stylet releasable connected to the tine. The stylet is inserted through the lead and engages the tine at an interface between them. The stylet is rotated. This serves to rotate the tine to thereby secure the lead connected to an anchor housing from which the tine emerges to body tissue.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from U.S. Provisional Application Ser. No. 61/116,718, filed Nov. 21, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related generally to implantable medical electrical leads. More specifically, the present invention is related to implantable neurological leads. 
     2. Prior Art 
     Spinal cord and other neurological stimulations by electrical leads are used for many purposes, including pain masking. These electrical leads emit a voltage or current which mimics the body&#39;s electrical response and masks a patient&#39;s pain. 
     As such, these leads must be precisely placed near a specific nerve or series of nerves to provide the required therapy. It is therefore critical that the correct nerve or nerves are targeted and that the lead does not move once in place. Lead migration, defined as the undesirable movement of a lead in the body over time, causes the stimulation therapy to become ineffective. Additional surgery is therefore required to reposition the lead and correct the problem. 
     One such neurological electrical stimulation lead is the percutaneous lead, which is well suited for stimulating nerve tissue. A percutaneous lead is a relatively long, slender, cylindrical lead with a small diameter and a series of electrode bands that wrap around the outside surface. The relatively long length and small cylindrical diameter allow for easy and unimpeded access to the nerve tissue along the spinal column through a small incision in the body. The series of electrode bands are programmed to emit an electrical signal such as a voltage or current that provides pain relief by targeting a specific nerve or nerves. However, the long, slender, cylindrical construction of percutaneous leads which make them advantageous for intricate placement and unimpeded advancement about the tight confines of the spinal column also make them prone to movement and migration. 
     One such solution to prevent lead migration is a suture type of lead fixation device. As discussed in U.S. Pat. Nos. 5,843,146 and 6,473,654 to Cross and Chinn, respectively, implanted leads are secured through the use of sutures designed to tie the implanted lead to bodily tissue. 
     The problem is that the use of sutures is not ideal in securing the lead to delicate neurological tissue, which may easily tear. Furthermore, suturing neurological stimulation leads requires invasive surgery to gain access to the spinal column area, which would defeat the minimally invasive benefits of the percutaneous lead. In addition, sutures can make it difficult to easily move the stimulation lead to a new desired location. A physician would have to perform another invasive surgery to gain access to the spinal column area to remove the old sutures and re-suture the lead to the new location. 
     Helical screw anchoring mechanisms are another means of fixating implanted leads. Such mechanisms are disclosed in U.S. Pat. No. 6,711,443 and U.S. Patent application publication 2007/0299493, both to Osypka. Helical fixation mechanisms are primarily used in the placement of cardiac leads. This fixation mechanism is beneficial in cardiac applications since the strong fibrous tissue of the heart muscle captures and prevents the embedded helical structure from becoming unsecured. 
     Helical fixation mechanisms, however, are not ideal in securing a lead to neurological tissue. The drilling action of the helix destroys the delicate neurological tissue as it bores into the tissue. In addition, since neurological tissue is not as strong and fibrous as that of cardiac tissue, the helical structure would easily rip out of and damage the delicate neurological tissue. 
     Hook style lead anchoring mechanisms have also been developed to secure cardiac leads to heart tissue. Two previous hook type anchoring mechanisms have been disclosed in U.S. Pat. Nos. 4,858,623 and 5,871,532 by Bradshaw et al. and Schroeppel, respectively. However these specific prior art anchoring examples are not well suited for anchoring to delicate neurological tissue. They could easily be dislodged through movement as a patient goes about their daily activities. As stated in column 4, line 65 of the &#39;623 patent, “a slight tug on the lead will cause the hook to rotate about its pivot point to a position beyond the tip, thereby allowing the lead to be withdrawn”. Such inadvertent dislodgement could occur through the movement of a patient&#39;s spinal column as they move. 
     Accordingly, what is desired is a percutaneous neurostimulator lead with a fixation mechanism that provides long term secure anchoring, prevents inadvertent lead dislodgement, minimizes neurological tissue damage and does not compromise the minimally invasive benefits of the lead. 
     SUMMARY OF THE INVENTION 
     The present invention is broadly directed to an improved percutaneous lead anchoring mechanism that affords the physician long term secure lead anchoring stability, prevents inadvertent dislodgement and allows for precise anchor deployment control. 
     The improved anchoring mechanism, which is located in the anchor housing at the distal end of the neurological lead, comprises a curved sharpened hook that pierces the neurological tissue and secures the implanted lead in place. 
     Movement of the anchor hook is controlled by rotation of a removable stylet from outside a patient&#39;s body. The stylet is first inserted through the lead. The stylet shaft connects to a tine at a socket opening of the anchor housing. Rotation of the stylet causes the tine to rotate which, in turn, deploys the connected anchor hook from the housing. Once the anchor hook is fully deployed and the lead is securely attached to the neurological tissue, the stylet is removed. 
     Importantly, the stylet can be re-inserted into the socket of the housing at a later time to retract the anchor hook from the tissue. This means the lead can be moved to a new location without the need for invasive surgery. Once the lead is repositioned, the anchor hook is re-deployed again to secure the lead in place. This process can be repeated as many times as needed. The anchor hook, however, cannot be moved without rotation of the internal tine by the stylet. Therefore, inadvertent dislodgement of the anchor hook is prevented, which keeps the lead from migrating from its intended location. 
     The anchor housing, which contains the anchor deployment mechanism, is designed with a flat planar bottom surface meeting a curved sidewall and curved distal end. This shape allows for relatively easy and unimpeded insertion of the lead into the narrow confines adjacent to the spinal column. The bottom flat planar housing surface allows for the lead to be positioned in close proximity to the desired neurological nerve tissue. It is from this flat bottom surface of the housing that the hook emerges. 
     These and other aspects of the present invention will become more apparent to those skilled in the art by reference to the following description and the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a prior art neurological stimulator lead  10 . 
         FIG. 2  is a perspective view of the present invention comprising a neurological stimulator lead  20  with the anchor housing  40  and stylet  30 . 
         FIG. 3  shows an elevated view of the anchor housing  40 . 
         FIG. 3A  shows a cross-sectional view taken along line  3 A- 3 A of  FIG. 3 . 
         FIG. 4  shows an elevated view of the stimulator lead  20  plugged into the socket opening  37  of the anchor housing  40 . 
         FIG. 4A  shows a cross sectional view taken along line  4 - 4  of  FIG. 4 . 
         FIG. 4B  illustrates as alternate embodiment for connecting the distal end  18 B of the stylet  18  to the tine  49 . 
         FIG. 5  is a perspective view of the lead  20  connected to the anchor housing  40  prior to deployment of the anchor hook  49 . 
         FIG. 6  is a perspective view of the lead  20  connected to the anchor housing  40  shown in  FIG. 5  during initial deployment of the anchor hook  49 . 
         FIG. 7  is a perspective view of the anchor housing  40  midway through deployment of the anchor hook  49 . 
         FIG. 7A  is a bottom plan view of the anchor housing  40  shown in  FIG. 7 . 
         FIG. 8  is a perspective view of the anchor housing  40  shown in  FIG. 6  with a fully deployed the anchor hook  49 . 
         FIG. 9  shows a perspective view of the present invention that has been inserted in a catheter sheath  52 . 
         FIG. 10  is an enlarged view of the indicated area in  FIG. 9  showing the anchor housing  40  protruding from a catheter sheath  52 . 
         FIG. 11  shows a schematic view of the stimulation lead  20  of the present invention inserted in the spinal column  64  of a patient. 
         FIG. 12  shows an enlarged, cross-sectional view taken along line  12 - 12  of  FIG. 11  of the anchor housing  40  positioned next to neurological tissue  66  prior to deployment of the anchor hook  49 . 
         FIG. 13  shows an enlarged, cross-sectional view taken along line  13 - 13  of  FIG. 11  showing the anchor housing  40  attached to neurological tissue  66  after deployment of the anchor hook  49 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a generalized view of a prior art neurological stimulation lead  10 . The lead  10  comprises a cylindrical lumen  16  with a series of proximal metal electrode bands  14  and a series of distal metal electrode bands  12 . As those skilled in the art are readily aware, the proximal electrode bands  14  are designed to connect to the header (not shown) of an implantable medical device, for example, a cardiac pacemaker, a cardiac defibrillator, a neurostimulator, a drug pump, a bone growth stimulator, and the like. The distal electrode bands  12  are intended to be placed proximate body tissue, such as neurological tissue  66  ( FIG. 13 ) comprising the spinal column system  64  ( FIG. 11 ). That is for the purpose of providing electrical stimulation to the body tissue. 
       FIG. 2  illustrates the present invention neurological stimulation lead  20  with an anchoring housing  40  connected to the distal end thereof. As the illustration shows, the stimulation lead  20  has an elongate body comprising a sidewall  16  that extends from a proximal region  16 A to a distal region  16 B. 
     Within the proximal lead region  16 A is a discrete series of metal electrode bands  14  that extend circumferentially around the outside surface thereof. The distal lead region  16 B comprises a separate series of discrete metal electrode bands  12  that extend circumferentially around the lead sidewall  16 . As is well known by those skilled in the art, the distal and proximal electrodes  12 ,  14  are electrically connected to each other by electrical conductors (not shown) extending along the lead body between respective ones of them. As will be described in greater detail hereinafter, an anchoring tine  49  ( FIGS. 4 ,  6  to  8 ,  13  and  14 ) is contained within the anchor housing  40  connected to the distal lead region  16 B. 
     The lead  20  has a hollow lumen  22  ( FIGS. 4 and 4A ) extending from its proximal region  16 A to the distal region  16 B. This lumen  22  is sized to receive a stylet  18  ( FIG. 2 ) provided with a manipulatable handle  30  at its proximal end. In use, the stylet  18  is advanced through the lead lumen  22  to the anchor housing  40  where its distal end  18 A connects to the tine  49  in a releasable engagement. Then, rotational movement of the stylet handle  30  causes the tine  49  to deploy from and retract into the anchor housing  40 . This movement will be described in greater detail hereinafter. 
       FIG. 3  shows an enlarged view of the anchor housing  40 . The anchor housing  40  is composed of a rigid biocompatible polymeric material, preferably of polyurethane. However, other polymeric materials not limited to polyethylene, polyether ether ketone, including silicone, and polyimide can also be used. In addition to polymeric materials, metals not limited to titanium, MP35N, platinum, niobium, gold, palladium, and their alloys can also be used to construct the anchor housing  40 . 
     In that respect, the anchor housing  40  is preferably a molded member extending along a central longitudinal axis A-A and comprising a main housing portion  41  having a radiused sidewall  42  extending to a planar bottom surface  38  connected to a nose housing portion  43 , also having a radiused sidewall  42 A, extending to a curved nose  44  and a planar bottom surface  38 A. Chamfers  42 B,  42 C ( FIG. 5 ) are provided where the sidewalls  42 ,  42 A and  44  meet the planar bottom surfaces  38 ,  38 A. 
     The curved sidewalls  42 ,  42 A and  44  of the housing  40  facilitate advancement of the lead  20  through the narrow confined passages of the spinal column with minimal interference. The planar bottom surfaces  38 ,  38 A enable the anchor housing  40  to be placed in close proximity to the body tissue, such as neurological tissue to which the lead  20  will be anchored. A fin  38 B protrudes from the bottom planar surface  38  at the proximal region of the main housing portion  41 . With the lead  20  connected to the anchor housing  40  as shown in  FIGS. 4 to 8 , the fin  38 B facilitates movement of the anchor housing  40 /lead  20  assembly through body tissue without that portion of the lead adjacent to the planar bottom surface  38  snagging on body tissue. 
     The main housing portion  41  comprises a proximal end  35  having a lead opening  33  sized to receive the distal lead region  16 B. The lead  16  is preferably secured in the position shown in  FIGS. 2 and 4  to  8  by a suitable adhesive. The lead opening  33  in turn communicates with a housing channel  46  extending longitudinally through the main housing portion  41  to a tine passage  48 . 
     The tine passage  48  communicates with a housing opening  41  where the main housing portion  41  connects to the nose housing portion  43 . The tine passage  48  is a semi-circular passageway aligned perpendicular to the axis A-A within which the anchor tine  49  ( FIG. 4 ) can freely rotate in an arcuate path. Tine passage  48  has a width extending along the longitudinal axis and communicates with the housing opening  41  having a similar width and located between the planar bottom surfaces  38 ,  38 A of the main and nose housing portions  41 ,  43 , respectively. 
     The housing channel  46  comprises a frusto-conical portion  46 A extending distally from the lead opening  33  at the proximal housing end  35 . The frusto-conical channel portion  46 A tapers downwardly and inwardly to a distal channel portion  46 B of a reduced diameter. The distal channel portion  46 B communicated with the tine passage  48 . 
     The anchor tine  49  comprises a proximal leg  49 A that is preferably of a circular cross-section connected to a lateral portion  49 B that connects to a distal, arc-shaped tine portion  49 C. The arc-shaped tine portion  49 C extends to a tine point  49 D. 
     A sleeve  47  is connected to the proximal tine leg  49 A. The sleeve is of a similar material as that of the tine  47 . In an alternate embodiment, the sleeve  47  can be replaced by a bore drilled or otherwise provided in the proximal tine leg portion  49 A. Either the sleeve  47  or the bore in the proximal tine portion provide a lumen into which the stylet  18  is received in a releasable friction fit relationship. The purpose of this relationship will be described in detail hereinafter. 
     To construct the anchor housing  40 , the proximal tine leg  49 A supporting the sleeve  47  is first received in the distal channel portion  46 B while the lateral and distal, arc-shaped tine portions  49 B,  49 C are in the tine passage  48 . Then, the nose housing portion  43  is secured to the main housing portion  41  at seam  41 A ( FIGS. 3 and 4 ). This serves to capture the tine  47  inside the housing. Tine  49  is preferably composed of a metallic or polymeric material and rotate freely (both clockwise and counter clockwise) inside the tine passage  48 . The pointed tip  49 D is designed to pierce through neurological tissue with minimal tissue damage. 
     The tine  49  and sleeve  47  are preferably composed of a biocompatible metal, preferably of titanium. Alternate metals that could also be used include, but are not limited to, the following: MP35N, nitinol, platinum, niobium, gold, palladium, and their alloys. Additionally rigid biocompatible polymers could be used to construct the tine  49  and sleeve  47 . These materials include but are not limited to polyurethane, polyethylene, silicone, polyether ether ketone, and polyimide. 
     The length of the anchor housing  40  measured along the longitudinal axis A-A is from about 0.0125 inches to about 0.50 inches. The height of the anchor housing measured from the planar bottom surfaces  38 ,  38 A to the apex of the radiused sidewalls  42 ,  42 A is from about 0.01 inches to about 0.10 inches. The diameter of the sidewalls  42 ,  42 A is measured from one edge of the planar bottom surfaces  38 ,  38 A to the other perpendicular to the longitudinal axis A-A. This also defines the width of the planar bottom surfaces  38 ,  38 A which are from about 0.02 inches to about 0.10 inches. 
     As shown in  FIGS. 3 and 4 , an inlet  42 A is formed part way into the thickness of the sidewall  42  of the main housing portion  41 . The inlet  42 A is shaped and formed to receive the tongue  52 A of a catheter sheath  52  ( FIG. 10 ). That way, the inlet  42 A helps align the sheath  52  with the anchor housing  42 . While the inlet  42 A is shown positioned on the top surface of the housing sidewall  42 , that is only exemplary. Such an inlet  42 A or a combination of multiple inlets could be positioned anywhere along the circumferential extent of the outer shell  42  to perform the function of receiving the catheter tongue  52 A to align the sheath  52  with the lead  20  and anchor housing  40 . 
     In use, the catheter  60  including the sheath  52  is first moved over the lead  20  until its tongue  52 A is received in the inlet  42 A provided in the sidewall  42  of the main housing portion  41 . The stylet  18  is then moved through the lumen  16  in the lead  20  until the distal stylet end  18 A is received in the lumen provided by the sleeve  47  or by the bore in the proximal tine portion  49 A. The lumen in the sleeve  47  or the tine bore (not shown) is sized so that the distal end  18 A of the stylet is received therein in a releasable friction fit relationship. 
     This assembly in then inserted into a body and advanced to a tissue of interest that is intended to be electrically stimulated or otherwise assisted in a beneficial manner. Once the target tissue has been reached, the stylet handle  30  is rotated in either a clockwise or counter clockwise manner. This causes the stylet  18  and the proximal leg  49 A of the anchor tine  49  to rotate. As the tine  49  rotates, its arc-shaped portion  49 C rotates along the tine passage  48 . This movement causes the pointed tip  49 D to pierce into body tissue situated proximate the planar anchor housing surfaces  38 ,  38 A. Further rotational movement causes the tip  49 D to move through an arc in the tissue and back into the housing opening  41 . That way, the tine  49  pierces into and then out of body tissue, thereby preventing longitudinal movement of the lead  20  along the axis A-A of the housing  40 . As this rotational movement takes place, the catheter  60  serves as a counter balance to prevent the lead  16  and anchor housing  40  from rotating along with the tine  49 . 
     The stylet  18  is next removed from its engagement with the anchor housing by applying a slight tugging or pulling force on the handle  30 . This is sufficient to separate the distal stylet end from its friction fit relationship with the proximal tine bore  49 A. Finally, the tongue  52 A of the catheter sheath  52  is removed from the inlet  42 A in the anchor housing  40  and the sheath is completely removed from the body. 
       FIG. 5  shows a perspective view of the distal-end of the present invention prior to deployment of the anchor hook  49  through the housing opening  41 . Once the hook  49  is fully deployed and has pierced through the body tissue  66 , the pointed tip  49 D enters the opening  41  on the opposite side thereof. This ensures that the anchor hook  49  does not become dislodged from the tissue to which it is anchored. 
       FIG. 6  shows the anchor tine  49  beginning to emerge from the anchor housing  40  through the opening  41 . The tine point  49  is just beginning to emerge from the housing  40 . 
       FIG. 7  shows the anchor tine  49  continuing to be deployed from the anchor housing  40  through the opening  41 . As the illustration shows, the anchor tine  49  passes through an arcuate path. 
       FIG. 7A  shows the view of the emerging tine  49  from the perspective of the bottom planar surface  38 A of the housing. One can see the opening  41  across the width of the bottom surface  38 A. 
       FIG. 8  shows the anchor tine  49  in a fully deployed position. The pointed tip  49 D has traversed from the right side to the left side of the opening  41  and now resides back inside the housing  40 . 
       FIG. 9  shows the present invention inserted through an implantation catheter  60  comprising a sheath  52  connected to a catheter handle  62 . The stylet shaft  18  is shown inserted through the catheter handle  62  and catheter sheath  52 . 
       FIG. 10  shows an enlarged view of the distal end of the sheath shown in  FIG. 9 . The smooth surface of the catheter sheath  52  is aligned with the anchor housing  40 . The tongue  52 A of the sheath  52  is aligned with the housing shell inlet  42 A. 
     The neurological lead  20  is now ready for implantation into the spinal column of a patient. A minimally invasive incision is first cut into the patient and the neurological lead  20  which is encased in the catheter sheath  52  as shown in  FIGS. 9 and 10 , is inserted into the body through the incision. The catheter sheath  52  encased lead  20  is then advanced in the body to its intended location along the spinal column  64 . The catheter handle  62  is used to steer the lead  20  into position. 
       FIG. 11  shows the neurological lead  20  in place and secured along the spinal column  64 . The distal electrodes  12  are shown in close proximity to the spinal column  64 . 
       FIG. 12  shows an exploded cross-sectional view of the housing  40  shown in  FIG. 11  prior to deployment of the anchor hook  49 . As  FIG. 12  shows, the anchor housing  40  has been positioned adjacent to the neurological tissue  66 . The flat planar bottom surface  38  of the hosing  40  allows the lead  20  to be positioned in close proximity to the targeted neurological tissue. 
       FIG. 13  shows an enlarged cross-sectional view of the anchor tine  49  in its fully deployed position. The pointed tip  49 D of the tine  49  has pierced and penetrated through the adjacent body tissue  66 . A portion of the tine  49  has completed its arc path through the tissue  66  and now resides in the opposite side of the tine  49 . The tine  49  is locked into place with the tip  49 D embedded in the body tissue. This prevents the tine  49  from becoming detached from the tissue  66 . 
     An important aspect of the present invention is that the lead  20  can be removed from the body tissue. That may be because a new one is needed, or the present lead needs to be repositioned. In either case, the catheter  60  including the sheath  52  is moved over the lead  20  until the tongue  52 A reengages the inlet  42 A. The stylet  18  is moved through the proximal end  16 A of the lead  20  until the distal stylet end  18 A engages with the sleeve  47  or the bore provided in the proximal tine portion  49 A. The stylet handle  30  is then rotated in an opposite direction to that used to originally secure the anchor housing to the body tissue. This serves to rotate the tine  49  out of the body tissue and back into the anchor housing. Once completely inside, the entire assembly including the lead  20  with the anchor housing  40 , the catheter  60  and the stylet  18  can be removed completely from the body of move to a new location for redeployment. 
       FIG. 4B  shows another aspect of the present invention is that the distal end  18 A of the stylet need not necessarily connect to the tine  49  using the sleeve  47  or a bore in the tine. Instead, one of the distal stylet end  18 A and the proximal tine portion  49 A can have a Philips or standard-type end  18 B that is received in a mating receptacle  47 A provided in the other of them. That is in a similar manner as a screw driver and screw is connected to each other to insert a screw-type fastener into a piece of wood, and the like. 
     It is appreciated that various modifications to the inventive concepts described herein may be apparent to those of ordinary skill in the art without departing from the scope of the present invention as defined by the appended claims.