Abstract:
A system and method are provided for anchoring a cranial lead or catheter member within a cranial burr hole in a patient, utilizing a feed-through subassembly which permits a lead to be eccentrically positioned with respect to the center of the burr hole, enabling fixation of the lead to the skull while the lead is maintained stereotactically rigid. The feed-through, or anchoring assembly comprises a burr hole element which is positioned within the burr hole, having a radial slit which extends axially through the piece and has a groove for receiving and containing an O-ring, which O-ring is adjustably positioned radially along the slit in accordance with the target position. The O-ring is made of a compressive material, and has a center orifice which closely receives the lead. When the lead is inserted through the O-ring and stereotactically positioned, a clamping element is secured in place above the O-ring, compressing it so as to squeeze it inward, thereby securing the lead while it is still stereotactically fixed.

Description:
FIELD OF THE INVENTION 
     This invention relates to a cranial lead system and, more particularly, a system and method for affixing a brain lead or catheter which is positioned through a cranial burr hole, so that the lead is secured in position relative to the patient&#39;s brain without moving the distal end of the lead. 
     BACKGROUND OF THE INVENTION 
     Systems for providing either electrical stimulation of the brain or coupling as fluid to or from the brain are coming into increased use for various purposes. Electrical stimulation of the brain is utilized for relief of chronic pain and treatment of movement disorders. A typical electrical brain stimulation system comprises a pulse generator operatively connected to the brain by a lead. The lead has one or more electrodes at its distal end, designed to be implanted within the patient&#39;s brain at a precise location, so that the electrode or electrodes are optimally and safely positioned for the desired stimulation. The lead is connected to the pulse generator at its proximal end, and also needs to be anchored with respect to a burr hole drilled in the patient&#39;s skull or cranium, in order to reliably secure the electrodes at the target location. Likewise, in the case of a catheter for providing fluid to the brain or for providing drainage, it is necessary to be able to secure the distal portion of the catheter that passes through the skull and transfers the fluid at a predetermined exact location within the brain. Still further, for a combined catheter and lead member, such secure and reliable anchoring of the member so that the distal end is precisely located within the skull, is very important. As used herein, the term lead, or lead-type member, refers to any such cranial catheter or lead. 
     Reference is made to U.S. Pat. No. 5,464,446, “Brain Lead Anchoring System,” assigned to Medtronic, Inc., which is incorporated herein by reference. The referenced patent illustrates an effective lead anchoring system, and it discusses the method of providing access through the skull by drilling a burr hole with a cranial drill, inserting a stimulation lead through the burr hole and positioning it so that the electrode or electrodes are at the desired stimulation site. The lead is positioned using a stereotactic instrument, which permits a very precise movement within the brain. Once the lead is positioned and tested to determine that the results of stimulation are satisfactory, it is critical that the lead is not moved, since even a small displacement can result in less than optimal results, and even injury to the brain. Accuracy should be maintained with ±0.5 mm. 
     The anchoring system of the &#39;446 patent shows a basic anchor for fixing the lead in place with the distal portion extended through the cranial burr hole, and then securing it by bending it into a slit such that it is held by a friction fit. However, the lead must first be removed from the stereotactic instrument, such that this system does not provide a reliable way for accurately securing the lead, or catheter, before it is bent into the fixation position. Thus, such a system does not reliably preclude a small movement of the distal end of the lead at the time of fixating, or securing the lead in place. Rather, it is required that the lead be removed from the stereotactic device before the lead can be fixed to the skull. 
     In U.S. application Ser. No. 08/705,566, filed Aug. 29, 1996, assigned to the same assignee as this invention, there is shown an apparatus and method wherein a compression screw cap is screwed down onto a compressible seal, the seal being flexible and compressed laterally against the outer wall of the lead. This system provides a substantial improvement over the prior art, and in particular enables securing the lead with respect to the skull before it is stereotactically released. However, it is operative only when the lead is to be positioned in the center of the burr hole. If, however, the target localization procedure indicates that the lead must be inserted off-center, this assembly and the procedure of using it is not adequate; the lead must be bent in order to fix it through the iso-centric burr hole cap, and this bending results in a lead displacement from the stereotactically determined target. There thus remains a need in the art for a reliable system which enables off-center, or eccentric placement of the lead through the burr hole, without requiring stereotactic release of the lead. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a brain treatment system, having a fixation subassembly and procedure for fixing a brain lead off-center, or eccentric from the center axis of the burr hole in the patient&#39;s skull. This objective is to be met without stereotactic release of the lead, so that the lead is secured to the patient&#39;s brain without displacement of the lead distal end from the stereotactically determined target. 
     There is provided a system and method for electrical and/or fluid treatment of a patient&#39;s brain, having a subsystem for anchoring a lead or a fluid catheter within a cranial burr hole within a patient&#39;s skull, wherein the anchoring subsystem has a feed-through burr hole piece, and an adjustable compressive element through which the lead is positioned. The compressible element is movable laterally so that it can be positioned to the required off-center position that has been identified by the target localization procedure. The burr hole feed-through piece contains a radial slit through which the lead passes, the slit further having an upper grooved portion for receiving a compressible O-ring. A compression plate is placed over the O-ring, and pressed down thereupon by a clamping screw, causing compression of the O-ring and radially inward compressive force on the lead outer surface, thereby securing the lead in place with respect to the skull while it is still being stereotactically held. Following fixation by the compressive O-ring, the lead is released from the stereotactic instrument and secured through a burr hole cap, the proximal end of the lead then being connected to an implantable stimulator device or pump. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of the anchoring subassembly of this system, showing a lead being stereotactically held in position, the lead being passed through the anchoring subassembly. 
     FIG. 2 is a top diagrammatic view of the plate that provides downward pressure on the compressive O-ring, in accordance with the invention. 
     FIG. 3A is a top diagrammatic view of the burr hole feed-through piece of this invention, illustrating the slit which is configured to retain the adjustable O-ring and provide for eccentric anchoring of the lead; FIG. 3B is a cross-sectional view taken across lines B—B of FIG. 3A, also showing placement of the compression plate; FIG. 3C is a cross-sectional view of the burr hole feed-through piece taken along lines C—C of FIG. 3A, also showing the compression plate in position; FIG. 3D is a cross-sectional view of the burr hole feed-through piece taken along lines D—D of FIG. 3A, also showing the compression plate; and FIG. 3E is a cross-sectional view similar to FIG. 3C, of an alternate embodiment whereby the lead can be placed at an angle to the burr hole piece axis. 
     FIG. 4A is a diagrammatic view showing the O-ring in position within the retaining groove of the slit in the burr hole piece, with the lead positioned through the center opening of the O-ring, and without any downward force on the O-ring; FIG. 4B is a diagrammatic view the same as FIG. 4A, but with the plate providing downward compression on the O-ring, illustrating the inward compressive force by the O-ring which fixes lead  32 . 
     FIG. 5 is a diagram illustrating the fixation subassembly of this invention in position in a patient&#39;s skull, and illustrating the lead connected to a stimulator or a pump device. 
     FIG. 6 is a flow diagram illustrating the primary steps taken in carrying out the procedure of this invention, either for a test lead or for the final DBS lead. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, there is shown a cross-sectional view illustrating the main components of the burr hole assembly portion of this invention. This drawing is intended to be illustrative, and is not necessarily to scale. A burr hole piece, or element  30  is positioned within a burr hole which has been drilled in the patient&#39;s skull in a known manner. The piece  30  is affixed to the skull in a conventional manner, e.g., by suturing. A lead, or catheter  32  is shown positioned through the burr hole piece, and held stereotactically by a stereotactic member  35 , shown schematically. For an embodiment which utilizes a cranial lead for providing stimulation, the lead carries electrodes positioned at the distal end portion, as indicated at  33 . For an embodiment where fluid is pumped to or withdrawn from the brain, the catheter  32  has an axial lumen for carrying the fluid. As used in this specification, the term “lead” embraces a lead for transmitting stimuli to the brain, and also includes a catheter or combination lead and catheter, and is not limited to any one specific type element. 
     As seen in FIG. 1, the lead  32  is displaced off-center from the central axis of the burr hole, i.e., it is eccentric with respect to the burr hole. As discussed above, the target localization procedure may determine that the proper target does not lie on the center axis of the burr hole which has been drilled, and as a consequence the lead must be positioned off-center. Burr hole piece  30  has a slit portion shown at  36 , wherein is placed an O-ring  37 , which squeezes radially inward to grip lead  32 , in a manner described in more detail below. An annular opening at  38  receives a compression plate  44 , which in turn is clamped by clamping screw  41 , which is screwed into piece  30  on threads  40 . The downward force of plate  44  compresses the O-ring, which is largely contained within slit  36 , such that the O-ring material, e.g., silicone rubber, compresses radially inward and grips lead  32 . When this has been achieved, the lead can be removed from the stereotactic member  35 , and connected to a stimulator or flow delivery device  55 , as illustrated in FIG.  5 . 
     Referring to FIG. 2, there is shown a top diagrammatic view of plate  44 , which is laid down on top of O-ring  37 . Plate  44  has a slit  45 , which runs from about the center axis of the plate radially toward the circumference, having a width which is just larger than the outer circumference of lead  32 . When placing the lead through to the brain, both piece  30  and plate  44  are rotated, so that the slits line up at the correct angle to permit placement of the lead  32  through to the proper position in the brain. 
     Referring now to FIGS. 3A-3D, the important features of a first embodiment of the burr hole piece  30  and the plate  44 , for enabling an eccentric placement of lead  32 , are shown. It is noted that these figures are illustrative of the concepts and elements of the invention, but are not exactly drawn to scale. By way of reference, the burr hole piece  30  may have, e.g. a diameter of 14 mm; and lead  32  has a typical diameter of about 1.3 mm. Referring to FIG. 3A, there is seen a top view, looking in the direction down through the top of the patients skull, at the burr hole element which is positioned within the burr hole. The element is preferably a solid piece of machined metal. A top edge  31 , seen also in FIGS. 3B-3D, is substantially flush with the top of the skull when piece  30  is placed and secured within the burr hole. Within top edge  31  there is a surface  47 , within which is drilled slit  36  which extends to the bottom of the burr hole piece. Slit  36  has top width somewhat less than the diameter of O-ring  37 ; and has an inner recessed groove shown at  48  in FIGS. 3C and 3D, which containingly receives the O-ring  37 . The inner edge of groove  48  is also shown by the dashed line  36 I in FIG.  3 A. 
     FIG. 3B shows a cross-section of burr-hole piece  30  which is taken through the center and along the slit, as indicated at B—B in FIG.  3 A. This view also includes plate  44 , having its slit  45  lined up to coincide with slit  36 . As seen, slit  36  extends to the bottom of element  30 , and is eccentric with respect to the center axis of element  30 . Plate  44  is shown in position, lying on surface  47 , having plate slit  45  aligned with burr hole piece slit  36 . The center axis of lead  32  is shown positioned through the center of O-ring  37 . Referring to FIG. 3C, the view is taken along cross-section C—C indicated in FIG. 3A, meaning that the view is in the direction of slits  36  and  45 . In this case, slit  36  is seen as a narrow width, being just large enough to accommodate the lead  32 . Note that in this view also the slit  45  of plate  44  has a width that is just sufficient to accommodate lead  32 . Note also the containing groove or contour  48  of slit  36 , which receives the O-ring  37 . This groove is configured to match the outer geometry of the O-ring, so that the O-ring is held in place when plate  44  is pressed downward. This groove also holds the small O-ring in place while, e.g., in the package during transportation or during handling by the doctor, whereby there are no loose components that can be lost. FIG. 3D provides yet another view of the same embodiment, showing an off-center view indicating slit  36  with the upper portion thereof defined by containing surface  48 . 
     Referring now to FIG. 3E, there is shown a view similar to that of FIG. 3C, but illustrating an alternate embodiment which enables placement of the lead  32  at an angle with respect to the axis of the burr hole piece. As seen, slit  36  has tapered walls  36 ′, which enables placement of the lead  32  at an angle with respect to burr hole and the axis (A—A) of the burr hole piece  30 . Thus, as illustrated, the lead  32  is positioned by the instrument  35  to be at an angle to the axis which is perpendicular to the top of the skull, thereby providing increased flexibility in directing the lead to the desired brain location. Stated in another way, the direction of the lead can be offset from the perpendicular to the burr hole ring piece. 
     FIGS. 4A and 4B provide a diagrammatic representation of the compressive force of O-ring  47 . Without the plate  44  in position, as shown in FIG. 4A, O-ring  37  fits somewhat loosely in the groove defined by surface  48 , and is not engaging lead  32  which has been positioned through the center of the O-ring. In FIG. 4B, with the compressive plate  44  in position and exerting a downward force, O-ring  37  is squeezed tightly into the cavity provided by groove surface  48 , with a resulting radially inward compressive force which securely grips lead  32 , and holds it in position. The O-ring is preferably made of silicone rubber, but can be made of other materials, and can have a doughnut or other ring-shaped geometry. 
     As seen in FIG. 5, after the lead has been secured within burr hole element  30  by the O-ring, it is released from the stereotactic instrument and passed through a surface cap  52 , and connected to an implantable stimulator or pump device  55 , for chronic operation. Cap  52  may be any conventionally used cap, and may provide an upper surface which is substantially flush with the patient&#39;s skull. Cap  52  conventionally has a pathway for passing the lead  32  laterally to the side of the burr hole, from which position it is then connected to device  55 . Cap  52  and piece  30  are suitably used as shown in U.S. Pat. No. 5,464,446, for passing the lead laterally. As used herein, device  55  communicates with the patient&#39;s brain, either by delivering stimulus pulses or pumping fluid through lead  32 . 
     Referring to FIG. 6, there are shown the primary steps of the method and technique of securing the lead  32  in accordance with this invention. Initially, as indicated at  55 , the burr hole is drilled in the patient&#39;s skull, using known techniques. It is determined whether the procedure is to use a test lead, or the final procedure of implanting the DBS lead, as indicated at  56 ,  58 . For the initial test lead, at  60  physiological target localization is performed. At  61 , the target is identified, and the test lead is removed. Then, at  62 , the burr hole piece is placed and rotated to the proper angle, so that the slit  36  provides entry of the lead  32  to the proper location. Following this, as seen at  63 , for either a test lead or DBS type lead, target localization is performed, to position the lead properly with respect to the brain portion which is to be stimulated, or to which fluid is to be delivered. See, for example, U.S. Pat. No. 5,843,150, filed Oct. 8, 1997. At  64 ,  65 , the loose plate  44  and clamping element  41  are positioned loosely over the lead. The lead then is passed down through the burr hole assembly and stereotactically positioned at the correct position, as indicated at  68 . When the correct position has been confirmed, the loose plate is placed in position on surface  47 , and the clamping element is screwed into place, as indicated at  70 . When this is done, as explained above, the O-ring secures the lead in the proper position, without movement of the distal tip. Following this, at  72  the lead is released from the stereotactic instrument, and at  74  the lead is passed through the upper cap  52 , which cap is then secured to the patient&#39;s skull. Finally, at  75 , the lead is connected to the stimulator or pump device  75 , to complete installation of the system. 
     The burr hole fixation assembly of this invention allows reproducible, non-destructive release of lead  32  from its fixed condition, by unscrewing clamping screw  41 . This feature is very important if, for whatever reason, it is necessary to reposition lead  32 . Thus, stereotactic repositioning can be carried out simply by proceeding backward at any point in the procedure illustrated by FIG. 6, fixing the lead position, and then proceeding forward again.