Abstract:
There is disclosed a medical apparatus for positioning and anchoring a lead to a cranium burr hole. The apparatus comprises generally a sleeve and a plurality of springs positioned within the sleeve. The apparatus may be inserted within a conventional burr hole ring or serve as a stand-alone anchoring device that fits within a burr hole. Once a lead is inserted into the sleeve between the plurality of springs, the springs exert a radial force on the lead body, thereby holding the lead in the desired position. The apparatus may also include a circular disc, defining a slot, mountable within the burr hole ring. The circular disc permits the selective positioning of the lead within the burr hole.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for securing implanted medical devices and more particularly to an apparatus for securing implanted medical devices such as electrical stimulation leads or catheters, or a combination thereof, within a cranial burr hole and for varying the functional location of the leads or catheters within the burr hole. 
     2. Description of the Related Art 
     Medical procedures involving access to the brain through a burr hole in the skull are under increasing use. Two such procedures are electrical stimulation of the brain for such purposes as relief of chronic pain and treatment of movement disorders, and the use of parenchymal catheters for infusing pharmaceutical agents. A typical electrical brain stimulation system comprises generally a pulse generator operatively connected to the brain by a lead having at its distal end at least one electrode designed to be implanted within the brain, and having at its proximal end a connector assembly designed to connect to the pulse generator. Use of a parenchymal catheter generally involves the insertion of a catheter within the brain to dispense pharmaceutical agents at a specific targeted location. 
     An important aspect of these procedures, and of any other such procedures that involve instrument access to the brain through a burr hole, is the precision with which any such inserted stimulation devices are placed. As can be appreciated, the functional location of the inserted stimulation device is of critical importance and once an inserted device is properly positioned, it is equally important that the device not be moved. Even one millimeter of travel of a properly positioned stimulation device may cause unsatisfactory results or, in some cases, severe injury to the brain. Accordingly, reliable methods and apparatus for locating and fixing the positioned stimulation device in the cranium burr hole are necessary. 
     Previous designs of systems for securing a positioned device within a burr hole have a number of drawbacks. U.S. Pat. No. 4,328,813 issued to Ray, incorporated herein by reference, discloses a burr hole ring and cap arrangement in which the cap is positioned so as to trap a positioned electrical stimulation lead between the ring and cap by friction. That arrangement involves securing the lead off center from the burr hole in a manner such that during installation of the anchoring cap the lead is secured in place. The lead, however, often needs to be manually supported in place while the anchoring cap is being installed. The lead is thus susceptible to inadvertent movement by the physician during the cap installation period. Further, during the interaction of the cap and ring, the lip of the cap tends to pull on the lead dislodging the lead from the targeted stimulation area. 
     Other current burr hole rings and caps force the lead body to the center of the burr hole ring and, due to the design, to the center of the burr hole itself. Problems occur if the burr hole is not centered on the desired projection path of the lead. The burr hole ring will force the lead body to the center of the burr hole ring, which is offset from the desired lead projection path, thereby placing a load on the lead body tip, which is implanted at the targeted stimulation area in the brain. The load on the lead body tip may force the electrodes away from the targeted stimulation area or it may place an undesirable amount of pressure on the brain. The present invention is directed to overcoming the disadvantages of the foregoing systems. 
     SUMMARY OF THE INVENTION 
     As explained in more detail below, the present invention overcomes the above-noted and other shortcomings of prior burr hole anchoring devices. 
     The present invention preferably comprises an apparatus fixing a lead at a cranial burr hole. One significant feature of the invention anchors the lead before the placement of a cap over the burr hole, thereby reducing the possibility of lead movement. This feature can be implanted directly into a cranium burr hole or it can be installed into a standard burr hole ring which is then implanted into the burr hole. A second significant feature of the present invention functionally locates the lead within a standard burr hole ring, thereby improving the location of the lead at the targeted stimulation area and reducing the possibility of injury to the brain. 
     Briefly, the present invention comprises several embodiments, more fully discussed below. One embodiment generally incorporates a cylindrical sleeve and a plurality of springs mounted within the cylindrical sleeve. The lead is inserted through the cylindrical sleeve between the plurality of springs which retain the lead in a substantially fixed position relative to the cylindrical sleeve. If a burr hole ring is used and mounted in the cranium burr hole, the cylindrical sleeve and accompanying springs are inserted in the burr hole ring. The lead may then be inserted into the sleeve between the springs. The invention accepts the lead and fixes the lead in the desired position before the burr ring cap is placed over the burr hole ring. If a smaller diameter burr hole is desired, for example, 3 or 4 millimeters, the present invention may be used as a stand-alone anchoring device without a burr hole ring, which typically cannot accommodate the smaller size burr holes. With this embodiment, the cylindrical sleeve may have a threaded, serrated, or knurled outer wall which allows the sleeve to be retained in the burr hole. The lead may then be inserted into the sleeve between the springs. 
     Another embodiment of the present invention comprises generally a rotatable disk having a slot. Received within the rotatable disk is a sleeve defining a second slot for capturing and fixing the lead relative to the rotatable disk. The previously identified sleeve and spring assembly may also be mounted in the rotatable disk. Significantly, the rotatable disk permits the implanted lead to be positioned at any location within the burr hole ring and thus anywhere within the burr hole. This functional positioning of the lead within the burr hole compensates for any offset between the burr hole and the desired projection path of the lead. Consequently, with these preferred embodiments, the lead may be located and maintained in a fixed position relative to the brain to allow electrical stimulation and/or drug infusion to the targeted area with improved precision and accuracy. 
     Examples of the more important features of this invention have been broadly outlined above in order that the detailed description that follows may be better understood and so that contributions which this invention provides to the art may be better appreciated. There are, of course, additional features of the invention which will be described herein and which will be included within the subject matter of the claims appended hereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of the invention will be described in relation to the accompanying drawings. In the drawings, the following figures have the following general nature: 
     FIG. 1 is a cross-section view of the lead fixation device of the present invention. 
     FIG. 2 is a top plan view of the invention of FIG.  1 . 
     FIG. 3 is a cross-section view of the invention of FIG.  1 . 
     FIG. 4 is an elevation view of a second embodiment of the lead fixation device of the present invention. 
     FIG. 5 is a plan view of the lead positioning device of the present invention. 
     FIG. 6 is another plan view of the invention of FIG.  5 . 
     FIG. 7 is a cross-section view of the invention of FIG.  6 . 
    
    
     In the accompanying drawings, like reference numbers are used throughout the various figures for identical structures. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-3, a preferred medical lead and catheter fixation device is depicted. The preferred lead fixation device  10  may be used in conjunction with a standard cranial burr ring or as a stand-alone device implanted in a cranial burr hole. Whether or not a separate burr ring is used with a particular patient will depend on the specific circumstances involved in that patient&#39;s case. In addition, the lead fixation device  10  may also be used with the rotatable disc  50 , described more fully below, which is mounted to a standard burr hole ring. 
     The lead fixation device  10  of the present invention defines a sleeve  12 , preferably cylindrical in shape, and a lead-interactive member, preferably a plurality of springs  14 . The lead fixation device  10  is designed to fit within a conventional burr hole ring, or the burr hole ring  52  more fully discussed below, which is then implanted in the cranium. A lead, or cannula if used, is then inserted into the lead fixation device  10 . The lead is anchored within the fixation device with the end of the lead situated within the brain and positioned at the targeted stimulation area. As used herein, the term “lead” may refer to any elongated medical apparatus having an electrode providing electrical stimulation, or a parenchymal catheter for infusing pharmaceutical agents. 
     With regard to the burr rings, as one might imagine, there are many possible sizes and shapes. The selection of one burr ring over another will depend on numerous factors such as the size or shape of the burr hole. Thus, it should be understood that the following description, by way of example, shows exemplary burr ring configurations which may be used in connection with the present invention. 
     The lead fixation device  10  may be formed as a part of a separate member selectively attachable to the burr hole ring, or it may be formed as an integral portion of the burr hole ring. Again, the burr hole ring would typically be pre-placed within the pre-drilled burr hole, with the lead fixation device insertable into the pre-placed burr hole ring. 
     The sleeve  12 , as depicted in FIGS. 1 and 2 as a cylindrical member, further defines inwardly extending circular shoulders  16 ,  18 , a pair of opposing apertures  20 ,  22  at each end of the sleeve  12 , and an inner wall  23 . The sleeve  10  is preferably about 0.15-0.20 inches at its maximum outside diameter and has a preferable length of 0.20-0.30 inches. The sleeve may be made from a biocompatible material, such as, metal or plastic. Those skilled in the art will appreciate that the sleeve may incorporate a variety of other dimensions, depending on the chosen lead, burr hole ring and the desired application. 
     The inward circular shoulders  16 ,  18  are curved or angled at  21  to permit and control the bending of the lead. The curved shoulders allow the lead to be directed radially outward from the sleeve  12  and parallel to the cranium. A small flexible plug, not shown, may be inserted to engage the sleeve  12  and to close off either of the apertures  20 ,  22 . Significantly, with the use of the lead-interactive members  14 , the lead is stabilized prior to the placement of the flexible plug. 
     Seated between the shoulders  16 ,  18  of the sleeve  12  are the lead-interactive members  14 , preferably springs. It is contemplated that other lead-interactive members may be used to fix the lead relative to the sleeve, and still be considered within the spirit and scope of the present invention. As most preferred, two pairs of opposing springs  14  are positioned within the sleeve  12 . These four springs are positioned equidistant around the inner wall  23  of the sleeve  12  resulting in the two pairs of opposing spring sets. The number of springs and their configuration are dictated by the desired amount of radial force to be exerted on the lead. Thus, one should understand that other numbers, arrangements, shapes and sizes of springs may be used with the present invention, depending on the desired amount of radial force on the lead body. The springs  14  may be made of any biocompatible material that exhibits resiliency, such as, metal, plastic or rubber. The selection of the material is dictated, at least in part, by the desired spring force to be applied to the lead body. 
     The springs  14  are formed as thin, elongated members defining a curve  24  located near its longitudinal center. The curve  24  creates the resiliency of the spring  14 . The overall length of the spring, in its unsprung state, is slightly less than the distance between the shoulders  16  and  18 . As most preferred, the spring  14  is fixed at one end to the inner wall  23  and is free at its opposing end. That is, for example, the spring  14  is fixed to the inner wall  23  near the shoulder  16  and is free at the opposite spring end near the shoulder  18 . Space is provided between the end of the spring  14  and the shoulder  18  to accommodate longitudinal movement of the spring end when the lead is inserted into the sleeve, compressing the spring  14 . As preferred, the installed springs  14  create an opening through the sleeve  12  which has an unsprung diameter of 0.040-0.045 inches to accommodate a standard lead with an outer diameter of 0.050 inches. The unsprung diameter is selected to provide a certain radial force on the lead body. Accordingly, it will be appreciated by one skilled in the art that other unsprung diameters may be designed depending on the desired radial force to be exerted on the lead body. 
     Referring to FIG. 3, insertable within the sleeve  12  and between the springs  14  is the lead  31 , or cannula if used. Once the lead  31  is inserted, the resilient springs  14  apply a radial force on the exterior surface of the lead body and, through friction forces between the springs and lead body, the lead is held in place in the desired location. If a cannula is used, the springs depress to accommodate the passage of the cannula through the sleeve  12 . A lead is then inserted into the cannula. Once the cannula is removed leaving the lead in the desired position, the springs  14  snap back to engage the lead, thereby fixing it in place. 
     As conventional, the burr hole ring preferably has one or more lead guides to accept the lead once it has been inserted in the brain. These lead guides direct the lead radially outward from the center of the burr ring and substantially parallel to the cranium. A burr ring cap may then be placed over the burr hole ring and installed sleeve  12 . Thus, the present invention fixes the lead in the desired position prior to the placement of the burr ring cap, thereby removing the possibility of lead movement during such cap placement. 
     Referring to FIG. 4, an alternative embodiment of the sleeve  12  is depicted. As preferred, the sleeve  30  is a stand-alone fixation device which is insertable directly into smaller cranial burr holes, for example, burr holes having a diameter of 3 to 4 millimeters. The sleeve  30  defines a cylindrical sleeve body  32  having either external serrations, threads or knurls  34 , which stabilizes the sleeve  30  in the cranial burr hole. The sleeve  30  also has, at one end, a collar  36  defining an outwardly extending circular shoulder  38  and a tool engaging head  40 . The remaining features of the sleeve  30  are the same as the sleeve  12 , as depicted in FIG.  1 . That is, the sleeve  30  also includes an inner cylindrical wall  23 , apertures  20 ,  22 , and inwardly extending shoulders  16 ,  18 , which receive the lead-interactive members  14 . Upon the insertion of the sleeve  30  into the burr hole in the cranium, the outwardly extending circular shoulder  38  serves to set the depth of the sleeve into the cranium and also serves as a stop to prevent the sleeve from passing through the cranium into the brain. The tool engaging head  40  is preferably hexagonal in shape for engaging a wrench which rotatably positions the sleeve  30  in the burr hole. It should be understood that other tool engaging heads may be used, such as, a round head having either a slot or an internal hexagon, for receiving other types of tools. 
     Referring to FIGS. 5-7, there is shown another embodiment of the present invention that allows the functional positioning of the lead within a cranium burr hole. This embodiment enhances the placement of the lead relative to the targeted stimulation area. As most preferred, a rotatable disc  50  is mounted within a burr hole ring  52 . The rotatable disc  50  defines a slot  54  through the disc body which extends radially from the center of the disc to its periphery. Positioned within the slot  54  is the sleeve  30  or, preferrably, the lead fixation member  56 . The lead fixation member  56  defines a cylindrical sleeve  58  having an integral circular shoulder  60 , and a slot  62  for capturing and fixing the lead body. In use, the sleeve  58  is inserted through the slot  54  with the shoulder  60  seated against the rotatable disc  50 . The sleeve  58  has an external diameter that permits the slidable engagement with the slot  54 . Significantly, the lead fixation member  56  may be located at any position along the slot  54 . Further, with the disc  50  being rotatable within the burr hole ring  52 , the fixation member  56  may be located at any position within the burr hole ring. That is, the lead fixation member  56  may slide within the slot  54  and be rotated within the burr hole ring  52 , permitting full degree of motion of the fixation member  56  within the burr hole. 
     The preferred embodiments of the invention are now described as to enable a person of ordinary skill in the art to make and use the same. Variations of the preferred embodiment are possible without being outside the scope of the present invention. Therefore, to particularly point out and distinctly claim the subject matter regarded as the invention, the following claims conclude the specification.