Patent Publication Number: US-2020289145-A1

Title: Method and tools for clearing the epidural space in preparation for medical lead implantation

Description:
TECHNICAL FIELD 
     Embodiments relate to the implantation of medical leads used for stimulation within the epidural space. More particularly, embodiments relate to methods and tools for clearing the epidural space in preparation for implantation of a medical lead. 
     BACKGROUND 
     Various medical conditions may call for therapeutic electrical stimulation within the epidural space of the spine. Therefore, medical leads capable of delivering stimulation signals are implanted within the epidural space. In some cases, it may be necessary to clear the epidural space as well as the entryway to the epidural space of fatty tissue, scar tissue, and the like in order to provide for easier ingress of the medical lead. This is particularly true for paddle leads that are implanted through a surgical procedure due to the relatively wide distal paddle on the medical lead. 
     Conventionally, a rigid plastic tool or a soft plastic tool is inserted into the epidural space through a window created within the vertebral bone and associated ligaments. 
     However, the rigid plastic tool presents multiple issues. A first issue is that the rigid plastic provides minimal deflection when entering the epidural space at an angle through the window and thus creates a potential pressure point along the dura of the spinal cord which can cause discomfort and potential paralysis. Another issue is that once in the epidural space, the rigid plastic tool often has less than adequate clearing ability. The soft plastic also presents multiple issues. Once inside the epidural space the soft plastic may deflect in an undesired direction. Additionally, the soft plastic may not have the stiffness to track in the ideal direction. This is particularly true as the width and length of the paddle continues to grow with newer versions of paddle leads where the increased paddle width increases the likelihood of snagging the blockages within the epidural space. Furthermore, the rigid plastic tool with minimal deflection cannot enter at a shallow enough angle to allow for adequate insertion distance needed to reach and clear the target stimulation site. 
     SUMMARY 
     Embodiments address issues such as these and others by providing methods for clearing the epidural space and implanting the medical lead and for related tools. Once the window is created, a guidewire is introduced into the epidural space and then a clearing tool is inserted along the path created by the guidewire. The clearing tool can thus be flexible and therefore adequately deflect so that the clearing tool can be inserted an adequate distance to reach the target stimulation site. The tool and guidewire can be removed once the epidural space is cleared, and then the medical lead can be inserted into the cleared epidural space. The tool may include additional features to aid in the clearing of the epidural space, such as a distal tip with a width greater than the body of the tool to aid in the clearing of the space, and in some cases the tip may be removable so as to change the size of the tip to meet the circumstances. 
     Embodiments provide a method of implanting a medical lead into an epidural space that involves passing a guidewire through a window to the epidural space created within the spinal column. The method further involves passing a tool through the window and into the epidural space by passing the guidewire through a lumen of the tool and cleaning the epidural space by moving the tool further into the epidural space and then retracting the tool. The method additional involves removing guidewire and tool from the epidural space and after removing the guidewire and tool from the epidural space, inserting the medical lead through the window and into a desired position within the epidural space. 
     Embodiments provide an apparatus for cleaning an epidural space prior to medical lead implantation that includes a flexible elongated body having an inner lumen. The apparatus further includes a guidewire present within the inner lumen and a distal tip present on a distal end of the elongated body, the distal tip having a width greater than a diameter of the elongated body. 
     Embodiments provide a tool for cleaning an epidural space prior to paddle lead implantation that includes a flexible elongated body having an inner lumen and a distal end with a diameter greater than the lead body. The tool further includes a distal tip present on the distal end of the elongated body, the distal tip having a width greater than the distal end of the elongated body. The distal tip is removable from the elongated body by having two tabs with each tab defining an opening with a diameter greater than the distal end of the elongated body, the tabs having a resting state such that the openings of the tabs are eccentrically aligned to lock the distal tip to the distal end, the distal tip being removable upon pressuring the tabs to force the openings of the tabs to become concentric and pass over the distal end. 
     Embodiments provide a method cleaning an epidural space prior to paddle lead implantation that involves passing a guidewire through a window to the epidural space created within the spinal column. The method further involves passing a tool through the window and into the epidural space by passing the guidewire through a lumen of the tool and cleaning the epidural space by moving the tool further into the epidural space causing a body of the tool to deflect within the epidural space in proximity to the window and by then retracting the tool. Additionally, the method involves removing the guidewire and the tool from the epidural space, the body of the tool continuing to deflect as the tool is being removed. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a spine with a window created to access the epidural space. 
         FIG. 2  shows a guidewire being inserted into the epidural space in preparation for insertion of a clearing tool. 
         FIG. 3  shows the insertion of the clearing tool that is being guided by the guidewire into the epidural space. 
         FIG. 4  shows the removal of the clearing tool and guidewire from the epidural space. 
         FIG. 5  shows the insertion of a medical lead into the cleared epidural space. 
         FIG. 6  shows a first example of an apparatus including a guidewire and a clearing tool. 
         FIG. 7  shows a second example of an apparatus including a guidewire and a clearing tool. 
         FIG. 8  shows an example of a removable distal tip of a clearing tool of the second example of an apparatus shown in  FIG. 7 . 
         FIG. 9  shows an axial view of the clearing tool with the removable distal tip example from  FIG. 8  in a locked position. 
         FIG. 10  shows an axial view of the clearing tool with the removable distal tip example from  FIG. 8  in a release position. 
         FIG. 11  shows a longitudinal cross-sectional view of an example of the clearing tool. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments provide methods and tools to clear the epidural space in preparation for implanting a medical lead such as a stimulation lead with a paddle on the distal end. The method involves inserting a guidewire into the epidural space and then using the guidewire to guide a flexible clearing tool into the epidural space and to the target site. Upon removal of the guidewire and tool, the medical lead is then inserted to the target site within the cleared epidural space. The tool may include a distal tip that aids in the clearing process. The distal tip may have a width greater than a body of the tool to further clear the space, and the distal tip may be removable so as to allow for selection of a distal tip with a most appropriate width relative to a given paddle or other width of the medical lead. 
       FIGS. 1-5  illustrate a method of clearing the epidural space and implanting the medical lead within the cleared epidural space.  FIG. 1  shows a spinal region  100  of a patient where the implantation of a medical lead is desired. Prior to clearing the epidural space  108 , a surgeon has created a window  106  in the spinal region  100  in the conventional manner by cutting through any vertebral bone and ligaments that block entryway to the epidural space  108  that occurs between the dura  104  of the spinal cord and the inner surface of the vertebral bone  102 . 
       FIG. 2  shows the insertion of a guidewire  110  into the epidural space  108  by passing the guidewire  110  through the window  106 . As can be seen, the guidewire  110  has deflected to achieve an alignment in the axial dimension of the dura  104 . This deflection may be the result of a pre-formed deflection in the area  112  of the guidewire  110  to ensure that the guidewire does not create undue pressure on the dura  104  when entering the epidural space  108 . The surgeon continues to feed the guidewire along the axial dimension of the dura  104  until approaching the target site. Alternatively, the guidewire may be inserted but not to the target site, and then may be guided to the target site together with the clearing tool as discussed below. The relatively small diameter of the guidewire  110  allows the guidewire  110  to travel through the window  106  and within the epidural space  108  prior to the window  106  and epidural space  108  having been cleared. 
       FIG. 3  shows a clearing tool  114  being inserted through the window  106  and into the epidural space  108  by traveling along the guidewire  110 . As shown below in  FIGS. 6-11 , the clearing tool  114  includes a lumen that the guidewire  110  resides within which allows the clearing tool  114  to be guided to the target site within the epidural space  108 . The guidewire  110  may have a stiffness greater than that of the larger diameter tool  114  which allows the guidewire  110  to effectively control the path of the tool  114  as the tool  114  is being fed to the target site. 
     The guidewire  110  may be constructed of various materials to achieve the stiffness to direct the tool  114  while also having the pre-formed deflection near the distal end. One example of guidewire construction is a stainless steel coil. 
     The body of the tool  114  has a significant amount of flexibility to allow the body of the tool  114  to deflect when entering the epidural space and to allow the tool  114  to extend a significant distance along the axial dimension of the dura  104  while continuing to adequately deflect at the area near the window  106 . The body of the tool  114  may be constructed of various materials to provide such flexibility. Examples of such materials include nylon, high density polyethylene, polyurethane, or polypropylene. To aid the clearing process, the body of the tool  114  may also be made radiopaque by including materials such as platinum/iridium, barium sulfate, gold, and/or tungsten so as to be visible during fluoroscopy. 
     The body of the tool  114  may also include a region  118  that has added stiffness that is small enough to not hinder deflection near the window  106  but aids in the insertion and clearing process by providing axial stiffness without affecting anterior/posterior stiffness. The body of the tool  114  may be relatively soft adjacent to the region  118  and the gradually become stiffer in the proximal direction. For instance, this region  118  may include an inner structure such as a metal braid or a metal coil that allows for some bending yet adds stiffness. Another example is that this region  118  is constructed from a material having a different durometer value from the remaining of the body of the tool  114  to provide the added stiffness. 
     The clearing tool  114  is inserted until a distal tip  116  of the clearing tool  114  has reached or exceeded the target site of stimulation within the epidural space  108 . At that point, the apparatus including the guidewire  110  and clearing tool  114  may be retracted to further clear the epidural space  108  on the exit route back through the window  106 . The retraction of the guidewire  110  and clearing tool  114  is shown in  FIG. 4 . While the guidewire  110  and clearing tool  114  are being retracted, the body of the clearing tool  114  continues to deflect within the epidural space in proximity to the window  106  to direct the tool  114  out through the window  106  while continuing to avoid undue pressure on the dura  104 . 
     Once the guidewire  110  and clearing tool  114  have been removed from the spinal region  100 , the medical lead  120  is then inserted through the window  106  and into the epidural space  108  as shown in  FIG. 5 . The medical lead  120  continues to be inserted until a distal end  122  which may take various forms such as a paddle of the medical lead  120  reaches the target stimulation site along the axial dimension of the dura  104 . Afterward, the medical lead  120  is connected to a medical device that delivers the electrical stimulation signals that are output to through electrodes in the distal end of the medical lead  120 . As shown in  FIG. 5 , the body of the medical lead  120  may exceed that of the clearing tool  114 , but the width of the distal tip  116  of the tool  114  has cleared the epidural space  108  so that the additional width of the medical lead  120  and the distal end  122  are not blocked during ingress by obstructions. 
       FIG. 6  shows one example of the apparatus including the guidewire  110  and the clearing tool  114 . The guidewire  110  includes a proximal hub  124  that a surgeon can manipulate to control and steer the guidewire  110  into position. Likewise, the clearing tool  114  of this example includes a proximal hub  126  that a surgeon can also manipulate to control and steer the clearing tool  114  as it travels along the guidewire  110 . In this example, the clearing tool  114  has a distal tip that is integral to the body of the clearing tool  114 . Therefore, if a particular width to the distal tip  116  is needed, then a clearing tool  114  having a distal tip  116  of the desired width is selected for the clearing procedure. As shown, this fixed distal tip  116  has a domed shaped, which facilitates clearing of the epidural space. However, it will be appreciated that a variety of shapes are applicable for the distal tip  116 . 
       FIG. 7  shows another example of the apparatus including the guidewire  110  and another example of a clearing tool  114 ′. This clearing tool  114 ′ may include the same flexible body as well as the proximal hub  126 . Furthermore, this clearing tool  114 ′ may include a region  118  that has increased stiffness to aid in insertion and clearing. However, the clearing tool  114  has a removable distal tip  116 ′. The removable distal tip  116 ′ allows the distal tip  116 ′ to be swapped for a most appropriate size for a given medical lead to be implanted. Thus, rather than having to choose an entire clearing tool  114 ′ on the basis of the distal tip size needed, only the distal tip  116 ′ is selected and is installed on the distal end of the clearing tool  114 ′. 
       FIG. 8  shows an enlarged view of the distal end  138  of the clearing tool  114 ′ as well as the removable distal tip  116 ′ installed on the distal end  138 . The distal end  138  of the clearing tool  114 ′ of this example has a larger diameter than the remainder of the body of the clearing tool  114 ′. 
     Also in this particular example, the distal tip  116 ′ includes a main body  128  and retention arms  130 ,  134 . Each retention arm  130 ,  134  terminates at a retention ring  132 ,  136 , respectively. The retention rings  132 ,  136  retain the distal tip  116 ′ on the distal end  138  by each providing an opening through which the body of the clearing tool  114 ′ passes, with the openings being eccentric. The eccentricity causes the rings  132 , 136  to abut the larger diameter distal end  138 . 
     This arrangement can be seen in the distal-looking axial view of  FIG. 9  which shows the distal tip  116 ′ in the locked position. The arms  130 ,  134  bias the rings  132 ,  136  in the outward direction to create the eccentricity of the openings defined by the rings  132 ,  136 . As such, the distal end  138  cannot slide through the opening defined by the eccentric rings  132 ,  136  that the main body of the clearing tool  114 ′ passes through. 
     Returning to  FIG. 8 , then main body  128  may have an aperture that receives a portion of the distal end  138  to further stabilize the distal tip  116 ′ on the distal end  138 . In some embodiments, the distal end  116 ′ may have the ability to rotate about the distal end  138 . In other embodiments, the distal end  116 ′ may be prevent from rotating either by the degree of friction of the retention rings  132 ,  136  against the body of the clearing tool  114 ′ and/or by the distal end  138  and an aperture of the main body  128  being keyed to one another. 
       FIG. 10  shows the configuration that occurs when pressure is being applied inwardly on the retention arms  130 ,  134 . The inward pressure brings the rings  132 ,  136  into concentric alignment thus creating a larger diameter opening. This concentric alignment allows the distal end  138  to pass through the opening such that the tip  116 ′ is removed. A tip  116 ′ is installed by also providing the inward pressure on the retention arms  130 ,  134  and sliding the distal end  138  through the resulting opening provided by the concentric rings  132 ,  136 . 
       FIG. 11  shows a longitudinal cross-section to reveal a lumen portion  140  present within the hub  126  as well as a lumen portion  142  present within the body of the clearing tool  114  and a lumen portion  144  present within the integral distal tip  116  of the clearing tool  114  of  FIG. 6 . These lumen portions  140 ,  142 ,  144  create a continuation lumen from end to end and provide a passageway for the guidewire  110  to pass when the clearing tool  114  is being guided into the epidural space  108  by the guide wire  110 . The same lumen portions and resulting continuous lumen are present in the clearing tool  114 ′ of  FIG. 7  as well. 
     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.