Abstract:
Methods and apparatus for implanting a neural stimulation lead in a patient&#39;s body are described. A lead assembly comprises a pointed-tip stylet, a stimulation lead, and an optional tube to deploy a fixation element attached to the lead. One embodiment of the implant methods starts with inserting the pointed-tip lead assembly directly into tissue. After the desired implant position is determined, the pointed-tip component is separated from the stimulation lead and removed from the tissue, leaving the stimulation lead implanted. After confirmation that the stimulation lead is in the right tissue location, the pointed-tip component is removed from the body, leaving the stimulation lead in place. The stimulation lead can be connected to a neurostimulator to delivery therapies to treat neural disorders, such as urinary control disorders, fecal control disorders, sexual dysfunction, and pelvic pain, etc.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/033,592, filed on Sep. 23, 2013, now U.S. Pat. No. 8,781,603, which is a divisional of U.S. patent application Ser. No. 12/506,282, filed on Jul. 21, 2009, now U.S. Pat. No. 8,634,932, which claims priority from U.S. Provisional Application Ser. No. 61/082,271, filed Jul. 21, 2008. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a neural stimulation lead assembly and minimally invasive implant methods associated with use of the described lead assembly. More specifically, the present invention relates to a lead assembly including a stimulation lead and a pointed-tip stylet received in a lumen of the lead. Minimally invasive method involves inserting the lead assembly into tissue without using a dilator. 
       BACKGROUND OF THE INVENTION 
       [0003]    Many people suffer from an inability to control urinary function, i.e., urinary incontinence. Different muscles, nerves, organs and conduits within the urinary tract cooperate to collect, store and release urine. A variety of disorders may compromise urinary tract performance and contribute to incontinence. Many of the disorders may be associated with aging, injury or illness. For example, aging can often result in weakened sphincter muscles, which cause incontinence, or weakened bladder muscles, which prevent complete emptying. Some patients also may suffer from nerve disorders that prevent proper triggering and operation of the bladder or sphincter muscles. 
         [0004]    Fecal incontinence is the inability to control bowel function. Fecal incontinence may be attributable to many physiological conditions, such as damage to the muscles of the rectum (e.g., the anal internal or external sphincters), nerve damage, loss of storage capacity within the rectum, and pelvic floor dysfunction. 
         [0005]    Electrical stimulation of nerves may provide an effective therapy for a variety of disorders, including urinary incontinence and fecal incontinence. For example, an implantable neurostimulator can deliver electrical stimulation to the sacral nerve to induce sphincter constriction and thereby close or maintain closure of the urethra at the bladder neck. In addition, electrical stimulation of the bladder wall may enhance pelvic floor muscle tone and assist fluid retention in the bladder or voiding fluid from the bladder. 
         [0006]    In current clinical practice to minimally implant a sacral stimulation lead, the procedure starts with a kit comprising a needle and a dilator that are particularly adapted to enable introduction of a neurostimulation lead into a foramen to locate a distal lead electrode(s) in operative relation to a sacral nerve. The needle is adapted to be inserted through an entry point of the skin or a skin incision posterior to the sacrum. The needle is guided along an insertion path into a foramen to locate at least a distal portion thereof extending alongside a sacral nerve. A proximal portion of the needle extends from the entry point away from the patient&#39;s skin. The dilator is inserted over the needle proximal end and advanced distally over the needle to dilate the insertion path. to that of the dilator diameter. The needle is then withdrawn through the dilator body lumen. The stimulation lead can now be advanced through the dilator body lumen to locate the lead electrode into operative relation with the sacral nerve. The dilator is then withdrawn over or removed from the stimulation lead body. 
         [0007]    The above practice requires multiple steps and disposable components in a kit to implant the stimulation lead. This takes time and creates extra trauma around the stimulation lead. Therefore, in the current invention, a simplified implant method, and a modified stimulation lead and kit are described. 
       SUMMARY OF THE INVENTION 
       [0008]    A minimally invasive implant method starts with inserting a. pointed-tip lead assembly directly into tissue. The desired implant position is determined by electric stimulation either through the stimulation lead or the pointed tip. Afterwards, the pointed-tip component is separated from the stimulation lead and removed from the tissue, leaving the stimulation lead implanted. In one variation, a needle is first inserted to identify the optimal stimulation site. After marking the needle path and position, the needle is removed and a pointed-tip stimulation lead. assembly is inserted along the marked needle path. After confirmation that the stimulation lead is in the right tissue location, the pointed-tip component of the lead assembly is removed from the body, leaving only the stimulation lead in place. This minimally invasive implant method can be practiced in a wide variety of neural stimulation applications, including sacral nerve stimulation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  shows an embodiment of an implanted neurostimulator. 
           [0010]      FIG. 2  shows a lengthwise cross-section view of stimulation lead assembly, with the proximal end of the pointed-stylet attached to the stimulation proximal end via a cap. 
           [0011]      FIG. 2A  is a cross-sectional view taken along line  2 A- 2 A of  FIG. 2 . 
           [0012]      FIG. 2B  is a cross-sectional view taken along line  2 B- 2 B of  FIG. 2A . 
           [0013]      FIG. 3  shows the proximal end of the stylet uncoupled from stimulation lead of  FIG. 2  by removing the cap. 
           [0014]      FIG. 4  shows how a tube being pushed over the lead to extend fin-type fixation elements attached at the lead intermediate section. 
           [0015]      FIG. 5  shows the stimulation lead in a deployed state after separately removing the stylet and the tube used for activating the fixation elements on the lead body. 
           [0016]      FIG. 6  shows a cross-section view of a stimulation lead assembly inserted through tissue and into a foramen, led by the pointed-tip stylet at the distal end. 
           [0017]      FIG. 7  shows the stylet retracted from the distal end of  FIG. 6  and placement of the stimulation lead. at the stimulation site. 
           [0018]      FIG. 8  shows a cross-section view of a tube being pushed over the implant lead to activate the fixation element on the intermediate portion of the lead. 
           [0019]      FIG. 9  is a cross-sectional view showing deployment of the fixation element in tissue by the tube. 
           [0020]      FIG. 10  shows a stimulation lead design with multiple fixation elements attached at different locations along the lead intermediate section. 
           [0021]      FIG. 11  shows a cross-section view taken along line  11 - 11  of  FIG. 10 . 
           [0022]      FIG. 12  shows an activation tube used to deploy the fixation elements shown in  FIG. 10 . 
           [0023]      FIG. 13  shows a cross-sectional view along line  13 - 13  of  FIG. 12 . 
           [0024]      FIG. 14  shows tapered coils as fixation elements along a stimulation lead. 
           [0025]      FIG. 15  shows the implant of stimulation lead assembly and deployment of tapered coil fixation in tissue. 
           [0026]      FIG. 16  shows a stimulation lead assembly having an elongated pointed-tip lead carrier. 
           [0027]      FIG. 17  shows a cross-sectional view of the lead assembly with the pointed-tip lead carrier disengaged from the lead. 
           [0028]      FIG. 18  is a cross-sectional view taken along line  18 - 18  of  FIG. 16 . 
           [0029]      FIG. 19  shows a cross-sectional view of the disengagement of lead carrier from lead via rotation. 
           [0030]      FIG. 20  shows a complete disengagement of the lead carrier from the lead after being rotated out of the way. 
           [0031]      FIG. 21  shows a cross-sectional view of the lead after implantation, with both the stylet and the lead carrier. removed from the implant site. 
           [0032]      FIG. 22  is a flowchart of a first minimally invasive method embodiment. 
           [0033]      FIG. 23  is a flowchart of a second minimally invasive method embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]      FIG. 1  shows an embodiment of an implanted neurostimulator  26  for stimulating sacral nerves  27  located near the sacrum  28 . The sacral nerves are accessible through an entry point in the skin along an insertion path  33  into a foramen  31  to reach a desired location  35 . A neurostimulation system can include a stimulation lead  30 , an optional lead extension  32 , an implantable neurostimulator  26 , a physician programmer (not shown), and a patient programmer (not shown). The stimulation lead  30  has electrical contacts  34  positioned on the distal end to stimulate nerves, and connectors (not shown) on the proximal end to connect to a lead extension or directly to the implantable neurostimulator  26 . 
         [0035]    The implantable neurostimulator  26  provides a programmable stimulation signal that is delivered to a desired location to stimulate selected nerves. The implantable neurostimulator  26  is typically implanted in a subcutaneous pocket around the upper buttocks, sometime after the stimulation lead  30  has been implanted and its effectiveness verified. The physician programmer is used by the clinician to program the stimulation signal produced by the implantable neurostimulator  26 . The patient programmer allows the patient to communicate with the implantable neurostimulator to control certain parameters of the stimulation signal typically selected by a clinician. For example, with a pelvic floor disorder, a patient can typically control stimulation signal parameters such as voltage amplitude. 
         [0036]    As a preferred embodiment of the current. invention,  FIG. 2  shows a lead assembly  36  comprising a stimulation lead.  37  and a pointed tip stylet  60 . The stimulation lead  37  has a proximal portion  38 , a distal portion  40  and an intermediate portion  39 . As one of the preferred embodiments, the distal portion has four electrical contacts  44 ,  46 ,  48  and  50  serving as stimulation electrodes. These contacts can be made of iridium/platinum alloy rings. The lead proximal portion also has four electrical connectors  52 ,  54 ,  56  and  58  for connecting the lead proximal portion  38  to the neurostimulator  26 . These electric connectors can be made of stainless steel rings. 
         [0037]    Electric pulses from the neurostimulator  26  run through the proximal connectors  52 ,  54 ,  56  and  58  and along the lead body to the distal electrodes  44 ,  46 ,  48  and  50  via respective electrical wires  61 A,  61 B,  61 C and  61 D ( FIG. 2A ). For example, as shown in  FIGS. 2 ,  2 B and  3 , the distal electrode  44  is connected by wire  66 D to the proximal connector  52  and electrode  48  is connected by wire  66 B to the proximal connector  56 . These wires are embedded in the lead insulation body  70  ( FIG. 2A ). The connection of a wire at its ends to a distal electrode and a proximal connector can be achieved by various means, for example, laser welding. This is shown in  FIG. 2A  where a laser welded connection  68  links wire  61 A to electrode  50 . 
         [0038]    Typically the insulation portion of the lead body is made of biocompatible silicone or polyurethane. As shown in  FIGS. 2 and 3 , the proximal connectors  52 ,  54 ,  56  and  58  and distal electrodes  44 ,  46 ,  48  and  50  can be partially embedded in the lead body to form a diametric profile and to minimize trauma during lead implant. This partial embedding can be achieved by grinding or thermal reflow. 
         [0039]    The lead body has a central lumen  41  extending from the proximal portion  38  to the distal end  40 . The stylet  60  runs through the central lumen thereof. The stylet  60  has a distal end  64  with a pointed tip  65 . In use, the distal end  64  extends out of the lead body a sufficient distance to expose the pointed tip  65 . The stylet  60  also has a coupling element  62  at its proximal portion  63  that couples with the lead proximal portion  38 . As shown in  FIG. 2 , this coupling element  62  can be a removable cap attached at the stylet proximal end  63 . As a variation in a preferred embodiment, this coupling element can also be removably attached to the stylet proximal end  63  and lead proximal portion  38 , for example a clamp holding the lead and the stylet together. 
         [0040]    During insertion of the lead assembly  36  into tissue, the coupling element  62  helps prevent stylet movement inside the lumen  41 . That is so the lead assembly  36  can be inserted as a single unit by holding both its intermediate portion  39  and optionally its proximal portion  38 . 
         [0041]    As shown in  FIG. 3 , after the lead  36  assembly is inserted into tissue, the coupling element  62  is removed and the stylet  60  moved back and forth within the central lumen  41  by pulling or pushing its proximal end against the lead proximal portion  38 . The stylet  60  can be made of metal that is electrically conductive. That is so electric pulses can be fed from its proximal end into its distal end  64  where the pulses will evoke a patient motor or sensory response. To enhance the accuracy and localization during the desired stimulation site probing process, the stylet distal end can be partially insulated, for example by a thin layer of polytetrafluoroethylene (PTFE), with only the tip  65  being left exposed. By moving the pointed-tip stylet freely inside the lead central lumen  41 , a desired stimulation location can be probed by the stylet  60 , preferably aided by the patient motor or sensory response. 
         [0042]    Once a desired stimulation location has been identified using the tip  65  of the stylet  60 , the lead  37  is positioned close to the desired location by holding the intermediate portion  39  and pushing the lead forward over the stylet. To facilitate lead advancement through tissue over the stylet,  FIG. 2B  shows a tapered end  42  at the lead distal portion  40 . The final location of the lead can be verified by feeding electric pulses from at least one of the lead proximal connectors  52  to  58  to at least one of the distal electrodes  44  to  50 . 
         [0043]    Once verification of the desired lead placement is complete, it is necessary to anchor the lead, for example by a fixation element build on the stimulation lead  37 . This fixation element is deployed into tissue surrounding the lead. Once deployed, the fixation element prevents lead movement in both longitudinal and lateral directions. 
         [0044]    As shown in  FIGS. 2 ,  4  and  5 , one preferred embodiment of a fixation element is of a fin-like structure  66 . The fins  66  are finger-like structures having an length. substantially longer than their diameter or width taken along a cross-section. perpendicular to the length thereof. They are preferably of an elastic material, for example, of polyurethane or silicone and only one of their ends is attached on the outer surface of the lead intermediate portion  39 . Attachment can be achieved by injection molding or adhesive bonding. Before the fixation fins  66  are deployed into tissue, the opposite ends of the fins should be pointed toward the lead proximal portion  38 . That is in order to reduce resistance when entering tissue during the lead insertion process. After the desired stimulation location is identified and the fixation fins  66  are ready to be deployed, a preferred embodiment of the current invention includes a tube  72  ( FIG. 4 ). The tube  72  is positioned over the lead body and pushed down from the proximal portion  38  toward the lead intermediate portion  39  until the distal tube end  74  touches the fixation fins  66 . Tube  72  first touches the non-attached ends of the fins  66  and pushes them away from the lead intermediate portion  39 . This movement stops when the tube  72  contacts the attached ends of the fins  66 . Thus, the fixation element is moved from its initial state ( FIG. 2 ) into its final deployed state ( FIG. 4 ) via tube  72 .  FIG. 5  shows the lead with the fixation fins  66  deployed and the tube  72  removed from the lead  37 . 
         [0045]    As a preferred embodiment of the current invention,  FIGS. 6 to 9  show a minimally invasive method for implanting the above-described stimulation lead-stylet assembly  36  percutaneously. The method is also described in the flowchart of  FIG. 22 . 
         [0046]    Briefly, a local anesthetic is typically applied to the area where the stimulation lead-stylet assembly  36  will be implanted, for example, posterior to the sacrum  28 . By using local anesthesia, an implanting clinician can include the patient&#39;s conscious sensory responses to electric stimuli to aid in placing the stimulation lead-stylet assembly  36 . 
         [0047]    The lead-stylet assembly  36  is hand guided  98  into the foramen  31  along an insertion path  33 . The foramen&#39;s  31  approximate location can be found using anatomical landmarks, fluoroscopy or x-ray images. Once the lead-stylet assembly  36  has been placed inside the foramen  31 , the coupling  62  between the stimulation lead and stylet is removed. The desired stimulation site can be first probed by the stylet and sensed by a variety of means such as by applying electric pulses to the stylet  60  at its proximal end  63  to evoke a patient response, such as a motor or sensory response. As shown in  FIG. 7 , once the stylet is in place, the tapered stimulation lead can be pushed over the stylet and moved into the identified stimulation site. 
         [0048]    Before anchoring the lead with the fixation element  66  using the tube  72 , however, verification of lead placement at the desired location should be made. This is done by feeding electric pulses to at least one of the lead proximal electric connectors  52 ,  54 ,  56  and  58 , and sensing or stimulating by at least one of the lead distal electrodes  44  to  50 . 
         [0049]      FIGS. 8 and 9  show the step  100  of anchoring the lead  36 . This is done by pushing the tube  72  over the lead-stylet assembly  36  until the tube contacts the fixation element  66 . The force exerted by the tube distal end  74  on the fixation fins  66  pushes their non-attached ends away from the surface of the lead intermediate portion  39  and into the tissue, preferably at a fascia layer, such as the lumbosacral fascia layer. The lubosacral fascial layer may be located at different depth from the skin for different patient. For that reason, the provision of multiple fixation fins enables the clinician to successfully deploy at least one of them at the preferred lumbosacral layer are described. 
         [0050]    A preferred embodiment comprising multiple fixation fins supported on a stimulation lead  37  is shown in  FIG. 10 . By way of example, this embodiment has three fin-like fixation elements  66 A,  66 B and  66 C, each having only one end attached to the lead body. The opposite end of the fins extends away from the lead surface when it is deployed by tube  72  in a similar manner as shown in  FIG. 4 . These fixation elements can be made of material having elastic properties, such as polyurethane or silicone, and are similar to the fins  66  described in  FIGS. 2 ,  4  and  5 . However, they are attached to the lead intermediate portion  39  at different axial locations. Initially, the non-attached ends point to the lead proximal portion  38  during insertion of the lead-stylet assembly  36 . Once deployed into tissue, as shown in the cross-sectional view of  FIG. 11 , the three fixation elements are preferably about  120  degrees from each other. 
         [0051]    The deployment tube  72  shown in  FIG. 12  has three slots  76 ,  78  and  80  with different lengths measured from the tube  72  distal end at the tube distal portion  74 . As shown in  FIG. 13 , these slots are also about 120 degrees apart from each other. That is so when the tube  72  is pushed over the lead-stylet assembly  36 , the length and orientation of the various slots deploys only one of the fixation fins  66 A to  66 C. For example, slot  76  only deploys fixation element  66 A, slot  78  only deploys a respective fixation element  66 B, and slot  80  only deploys fixation element  66 C. 
         [0052]      FIG. 14  shows another preferred embodiment of a fixation structure. In this embodiment, there are three tapered coils  82 A,  82 B and  82 C, each having a smaller diameter end and a larger diameter end. Only the smaller diameter end is attached to the surface of the lead intermediate portion  39  with the remainder of the coil surrounding the perimeter of the lead. The tapered coils can be twisted in one direction at their larger end. This causes their larger diameters to shrink so that the coil fits into a tube  73  whose inner diameter is smaller than the coil&#39;s uncoiled diameter. The lead-stylet assembly in this case will also include the tube  73  covering only the lead intermediate portion  39  and part of lead distal portion  38  (not shown). 
         [0053]    During the implanting process shown in  FIG. 15 , the entire lead assembly including the tube  73  is inserted into body tissue. After the desired stimulation site has been identified by the pointed stylet  60  and the fixation elements  82 A,  825  and  82 C are ready to be deployed, the tube  73  is retracted from the stimulation lead. As this movement takes place, the coils are released from inside the tube  73  and expand like a torsion spring surrounding the lead. At least one of the tapered coils is preferably expanded within the lumbosacral fascial layer. These tapered coils are preferably made of biocompatible metals, such as stainless steel, platinum, titanium, NP35N, or nitinol. 
         [0054]    While the larger ends of the coils are shown facing distally, that is not necessary. In an alternative embodiment, the larger coil ends can face proximally. Still further, one of the coils could have its larger end facing distally while another has its larger end facing proximally. 
         [0055]    Referring back to the flowchart  92  shown in  FIG. 22 , after deployment of the fixation element into tissue, preferably in the lumbosacral fascial layer, the point-tip stylet  60  is removed  102  via the lead central lumen  41 . To make sure there is no displacement of the stimulation lead during deployment of the fixation elements  66  and removal of the tube  72  or tube  73  and stylet  60 , re-verification of lead position at the desired stimulation site should be repeated as described previously. Afterwards, a skin incision is made for implanting the neurostimulator, i.e., the implantable pulse generator (IPG). The lead proximal portion  38  is tunneled under the skin to bring it adjacent to the implanted IPG and then to the lead proximal connectors  52 ,  54 ,  56  and  58  are connected  106  to the appropriate IPG receptacles (not shown). After the IPG is activated, patient feedback is acquired to make sure the desired neural stimulation is achieved. Finally, the skin incisions for both the lead entry point and the IPG implant site are closed  108 . 
         [0056]      FIG. 23  shows a variation  94  of the preferred embodiment in  FIG. 22  of the current invention. Instead of inserting a whole lead-stylet assembly  36 , a needle similar to the stylet  60  and having a diameter much smaller than the assembly  36  is inserted first  110  to probe the desired stimulation site  112 . Once the desired site is identified, the implant clinician records the needle depth and orientation as a reference, and the needle is removed. The recorded needle depth and orientation information is then used to guide insertion  96  of lead-stylet assembly  36 . The remainder of the procedure steps is the same as in flowchart  92 . However, comparing the flowcharts  92  and  94 , it is seen that the latter enables an implant clinician to probe several sites with relatively more ease before implanting the lead assembly  36  than in the former. This helps reduce trauma to the patient and enhance therapy effectiveness. 
         [0057]    Another variation of the preferred embodiment of the lead-stylet assembly  36  is the implant assembly shown in  FIGS. 16 and 17  having an elongated carrier body  84 , a lead body  37  and a stylet  88 . The lead body  37  has a central lumen  41 , which does not run through to the lead tip. This means that the distal end of the stylet  88  within the lead body  37  is not exposed out from the distal end of the lead tip  40 . In this embodiment, the carrier body  84  has a pointed tip  86  for cutting through tissue during implantation. The side wall of the carrier body  84  is sized to accommodate the lead body  37 . With the lead body  37  nested in the carrier body, the lead tip  40  resides in a longitudinal cavity  90  extending along the distal end of the carrier. 
         [0058]    The distal end of the carrier  84  is then inserted into tissue in a similar manner as previously described with respect to the assembly  36 . To disengage the carrier body  84  from the lead body  37 , the clinician holds the lead body  37  and stylet  88  in place and pushes the carrier body  84  further forward, as shown by the arrow in  FIG. 17 . This caused the lead distal end  40  to separate from the carrier body cavity  90 . To remove the carrier body  84  from the tissue, the carrier body  84  is rotated out of the way relative to the lead body  37  ( FIG. 19 ). This ensures that the cavity  90  does not re-engage with the lead tip  40  during removal ( FIG. 20 ). After the carrier body is removed, the lead is implanted into body tissue using either the previously described fixation fins  66  or the tapered coils. The stylet  88  is then removed, from the lead central lumen with only the stimulation lead  35  being left in place ( FIG. 21 ). 
         [0059]    Thus, embodiments of minimally invasive sacral lead implantation methods  92  and  94  are disclosed with many benefits. Embodiments of the methods can simplify the implant procedure, reduce trauma to the patient during implant procedure, reduce patient recovery time, and reduce healthcare costs. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.