Abstract:
An anchor system for securing a lead to a patient&#39;s skull is disclosed. The lead is of the type that passes through a burr hole created in the patient&#39;s skull and includes a distal end which is implanted within the patient&#39;s brain at a target site. The anchor, according to a first embodiment of the invention includes a stem, an integrally formed rim plate, and a peripheral clamping structure. The clamping structure is adapted to receive and snugly hold a portion of the lead. The stem is sized and shaped to fit within the burr hole, leaving the rim plate positioned flush with the patient&#39;s skull. A flared passage is provided within the stem and rim plate so that the lead may pass through the stem and into the rim plate, at which point the lead follows the contours of the flared passage and communicates with the peripheral clamping structural. The clamping structure holds a portion of the lead so that any tension of the lead will not be transmitted past the anchor and the distal end of the lead will not become displaced from the target site. According to a second embodiment, the peripheral clamping structure includes several flexible loops that are sized and spaced from each other to allow a lead to be laced through the loops as the lead extends about the periphery of the rim plate.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to anchoring systems for securing an implanted tubular medical device to a patient, and more particularly, to such anchoring systems for securing intracranial tubular medical devices to the patient&#39;s skull. 
         [0003]    2. Description of the Prior Art 
         [0004]    Surgical procedures of a patient&#39;s brain often require implanting a medical device to a prescribed intracranial target site. The implanted medical device typically requires long-term communication between the target site and a remote site located outside the patient&#39;s skull. The device can be electrically-based wherein power or signal lead wires must link the device at the target site to the outside world, or the device may be a catheter implanted to administer a drug from a remote location precisely at the target site within the brain or perhaps positioned to shunt fluid from the target site, or a catheter that includes mapping or stimulating electrodes at its distal end. 
         [0005]    Either the electrical lead or the catheter reaches the brain by passing through a predrilled hole in the patient&#39;s skull, called a burr hole. 
         [0006]    Electrical stimulation of the brain can be used for a variety of therapeutic treatments including relief of chronic pain and control of movement disorders. A typical electrical brain-stimulation system includes a pulse generator operatively connected to at least one electrode by a lead. The lead is connected to the electrodes at its distal end. The electrodes are implanted within the patient&#39;s brain at a precise location to optimize the applied stimulation. The lead is connected to the pulse generator at its proximal end. To prevent dislodging the implanted distal end of each electrode, a portion of the lead must be anchored in position, usually at the point of entry, the burr hole. 
         [0007]    It is also common to use catheters to either introduce fluids (such as drugs) to or collect biological fluids from a specific target site within the patient&#39;s brain to treat brain disorders such as malignancies or neurodegenerative diseases. Another example is to position an implantable deep-brain infusion catheter in the striatum or putamen to deliver a pharmaceutical agent to treat movement disorders such as Parkinson&#39;s Disease. Typically, these implantable catheters are vary delicate being only about 1 mm to 1.5 mm in outer diameter and are therefore prone to kinking and abrasive damage during handling and especially during use over their lifetime. As with the above-described electrical application, the delicate catheter must be secured so that the distal portion of the catheter remains at the target site within the brain, regardless of the patient&#39;s movement or the movement of the catheter outside the brain, and also must prevent or at least discourage trauma that may kink or otherwise damage the catheter. 
         [0008]    In order to insert the lead or catheter into the patient&#39;s brain, a surgeon first drills a hole in the patient&#39;s cranium using a surgical burr or a cranial perforator. The hole size will vary depending on the particular procedure being performed. The drill cuts a clean straight hole into the patient&#39;s skull and often leaves a sharp edge along the upper rim of the burr hole. Any inserted lead or catheter must be protected from this sharp edge. To do this, a burr hole ring is often inserted into the burr hole before the catheter or lead wire is inserted through the hole into the patient&#39;s brain to the target site. This ring is often used to cooperate with an insert to anchor the exiting catheter or lead wire. Previously, intracranial catheters have been sutured directly to the periosteum, which is a fibrous membrane covering the surface of bone. The periosteum does not provide as much stability as desired, and movement of the catheter anchor may result in displacement of the catheter tip. 
         [0009]    Another method of attaching a catheter tube to a patient included the steps of first coiling the tube to form a loop, applying a strip of adhesive tape over the loop and attaching the opposite ends of each strip of tape to the patient&#39;s skin. The function of the loop was to act as a strain-relief so that the implanted distal end of the catheter tube is not displaced or disturbed even when unexpected tension is applied to the tubing. 
         [0010]    For situations wherein an implanted intracranial medical device must remain operational for long periods of time, it is even more important to safely and effectively anchor the leads and/or catheters to a patient&#39;s skull to prevent displacement of the distal ends within the patient&#39;s brain regardless of the relative motions of these leads and/or catheters outside the patient&#39;s skull. 
         [0011]    Obviously, a patient with such intracranial leads and/or catheters in place, whether in a hospital recovery ward, or leading an active life will invariably challenge the integrity and strength of the anchoring system. Typically, during normal patient activities, the communicating leads located outside the patient&#39;s skull will become entangled and snagged on various things and will become tugged or even violently jerked. The anchoring system must be strong enough to resist such trauma to the delicate catheter and also prevent dislodgement of the distal tip from the target site. To achieve this, current anchors are often secured directly to the patient&#39;s skull using fasteners or an appropriate adhesive or both. 
         [0012]    One system for fixing a cranial lead is disclosed in U.S. Pat. No. 4,328,813. This patent discloses a socket and plug anchoring system wherein the lead is engaged by and held within a neck portion of the socket and recessed portion of the plug. However, in this arrangement the lead may easily be moved, particularly axially, when the plug is forced into engagement with the socket. This system uses the shape of the plug to force the exiting lead into a friction bend. This system cannot be used with catheters and any tension applied to the remote portions of the leads will act to directly remove the plug and also the socket, which will then release the lead and easily risk displacement of its distal end. This system fails to offer any strain-relief structure that allows remote applied tension to the leads to be absorbed without dislodging the implanted distal ends from the target site. 
         [0013]    Another brain-lead anchoring system is disclosed in U.S. Pat. No. 5,464,446, “Brain Lead Anchoring System,” assigned to Medtronic, Inc., which is incorporated herein by reference. The anchoring system of this referenced patent includes several parts, a plug, a cap and a socket, that must all be assembled by the surgeon and secured within the burr hole of the patient&#39;s skull and around either a lead or a catheter. A plug and socket use mere friction within the burr hole to hold the anchor and lead in place to the patient&#39;s skull. The cap covers the burr hole and allows two exiting passages. A first one is sharply angled for a lead wire and a second passage that is straight for accommodating catheters, which cannot handle the sharp bend of the first passage. 
         [0014]    Although the anchoring system of U.S. Pat. No. 5,464,446 is versatile by allowing both a lead wire and a catheter to exit a patient&#39;s skull atraumatically, the device is too difficult to assemble, will not hold up to even moderate applied tension, and forces a catheter to exit normal to the patient&#39;s skull thereby causing difficultly in allowing the patient to perform normal activities or even hide their medical disposition—for example, the patient cannot wear a hat without potentially kinking or damaging the catheter. Also, the device of this prior art patent fails to offer a strain-relief function that can mitigate the displacement of the distal end of the implanted lead or catheter due to remote applied tension. 
       SUMMARY OF THE INVENTION 
       [0015]    An object of the invention is to provide a system and method for easily and effectively securing a catheter or electrical lead from a burr hole of a patient in such a manner that ensures that the catheter or lead is anchored with respect to a target site within the patient&#39;s brain and so that tension applied to the catheter or lead will not cause damage to the same. 
         [0016]    Another object of the invention is to provide such an anchor that safely and atruamatically redirects the exterior portion of an implanted catheter or lead wire from a perpendicular trajectory (exiting from the burr hole) to a tangential path immediately adjacent the patient&#39;s scalp. 
         [0017]    An anchor system for securing a lead to a patient&#39;s skull is disclosed. The lead is of the type that passes through a burr hole created in the patient&#39;s skull and includes a distal end, which is implanted within the patient&#39;s brain at a target site. The anchor, according to a first embodiment of the invention includes a stem, an integrally formed rim plate, and a peripheral clamping structure. The clamping structure is adapted to receive and snugly hold a portion of the lead. The stem is sized and shaped to fit within the burr hole, leaving the rim plate positioned flush with the patient&#39;s skull. A flared passage is provided within the stem and rim plate so that the lead may pass through the stem and into the rim plate, at which point the lead follows the contours of the flared passage and communicates with the peripheral clamping structural. The clamping structure holds a portion of the lead so that any tension of the lead will not be transmitted past the anchor and the distal end of the lead will not become displaced from the target site. 
         [0018]    According to a second embodiment, the peripheral clamping structure includes several flexible loops that are sized and spaced from each other to allow a lead to be laced through the loops as the lead extends about the periphery of the rim plate. 
         [0019]    The accompanying drawings show examples of embodiments of the present invention. They illustrate how the invention achieves the above stated advantages and objectives. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a perspective view of a lead-anchor having a rim plate, a stem, a flared passage, and a peripheral lead-encapsulating structure, according to a first embodiment of the present invention, shown without a lead or catheter in place; 
           [0021]      FIG. 2  is a top plan view of the lead-anchor, according to the first embodiment of the present invention, showing a representative lead in an anchored position exiting the flared passage and being secured within the peripheral lead-encapsulating structure; 
           [0022]      FIG. 3  is a bottom plan view of the lead-anchor, according to the first embodiment of the present invention, showing details of the stem with the representative lead in the anchored position; 
           [0023]      FIG. 4  is a rear elevation view of the lead-anchor, according to the first embodiment of the present invention, showing details of the lead-encapsulating structure holding the representative lead in the anchored position; 
           [0024]      FIG. 5  is a side elevation view of the lead-anchor, according to the first embodiment of the present invention, showing details of the lead-encapsulating structure including an anchor sleeve and also the representative lead in the anchored position; 
           [0025]      FIG. 6  is a front elevation view of the lead-anchor, according to the first embodiment of the present invention, showing details of the lead-encapsulating structure including an anchor bridge and with the representative lead in the anchored position; 
           [0026]      FIG. 7  is a sectional side elevation view of the lead-anchor, according to the first embodiment of the present invention, showing details of the flared passage, the stem and the rim plate, with the representative lead in the anchored position; 
           [0027]      FIG. 8  is a perspective view of the lead-anchor, according to the first embodiment of the invention, showing the device fastened to a representative section of a patient&#39;s skull; 
           [0028]      FIG. 9  is a perspective sectional view of the lead-anchor of  FIG. 8  showing details of a stem portion and the positioning of a lead wire exiting the patient&#39;s skull; 
           [0029]      FIG. 10  is a perspective view of a lead-anchor, according to a second embodiment of the invention, showing peripheral lead-loops and a lead wire located in an anchored position; 
           [0030]      FIG. 11  is a top plan view of the lead-anchor, according to the second embodiment of the invention, with the lead wire in place; 
           [0031]      FIG. 12  is an elevation view of the lead-anchor, according to the second embodiment of the invention, with the lead wire in place; and 
           [0032]      FIG. 13  is a perspective view of the lead-anchor, according to the second embodiment of the invention, showing details of the lower surface of the anchor and with the lead wire in place. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    At the start of the surgical procedure for implanting the distal end of either a lead wire or a catheter into a patient&#39;s brain to a target site, a carefully drilled hole (called a burr hole) having a predetermined inside diameter is formed through the patient&#39;s skull. If the lead or catheter is meant to remain at the target site for a long period of time, the portion of the lead wire or catheter that extends beyond the patient&#39;s skull will be highly susceptible to entanglement and tension which may result in an undesirable displacement of the implanted distal end from the target site. To prevent this potential displacement from occurring, the lead or catheter is typically anchored to the patient&#39;s skull. The present invention is an improved anchoring device used to secure a portion of a lead wire or a catheter leaving a burr hole formed in a patient&#39;s skull. 
         [0034]    Referring now to  FIGS. 1 through 9 , a lead anchor  10  for securing communicating lead wires and catheter conduits (herein after collectively referred to as “lead  11 ”) from intracranially implanted devices is shown, according to a first embodiment of the invention. In its basic form, as is apparent in the figures, anchor  10  is similar in shape to that of a small rubber funnel and includes a generally circular rim plate  12  and an integrally formed hollow lower stem  14 . As can be seen in  FIGS. 4 ,  5 ,  6 ,  7 , and  9 , lower stem  14  includes a generally cylindrical outside shape and an internal flared passage  16 . Flared passage  16  connects a small lower opening  18  located at the bottom of lower stem  14  to rim plate  12  so that the flared passage  16  looks similar to the cusp shape of a trumpet horn, opening to a larger diameter at the top adjacent the rim plate  12  and defining a cusp-shaped inside surface  19 . Rim plate  12  defines an upper surface  21  and a lower surface  23 . 
         [0035]    Although it is preferred that rim plate  12  be generally circular, as shown in the figures of this application, rim plate  12  can be oval or ellipsoid in plan-view shape without departing from the invention. For the purposes of explaining the present invention, the rim plate  12  will be considered circular in shape. 
         [0036]    As shown in  FIGS. 1 ,  2 ,  4 ,  5 ,  6 , and  7 , rim plate  12  defines a periphery  20  to which a rim lead-holder  22  is integrally formed. As can be seen in  FIG. 2 , rim lead-holder  22  extends approximately 180 arc degrees around rim plate  12 . Located along the entire 180 arc degree curved length of rim lead-holder  22  is a channel  24  that is defined by a passage  26  and a side slit  28 . This rim lead-holder  22 , also called a “middle tube” preferably extends between 90 and 270 arc degrees about the periphery  20 . Passage  26 , which includes entry/exit ends  27 , is sized and shaped to snugly receive lead  11 . Side slit  28  is formed integrally during the molding of anchor  10  and has a resting width that is less than the diameter of lead  11  so that a lead  11  can be effectively captured by passage  26  and held in place by the natural resiliency of the rim lead-holder  22 . Side slit  28  preferably further includes opposing beveled or rounded outer edges  30 . As can be appreciated by one skilled in the art, the purpose of side slit  28  is to provide quick access to passage  26  so that a surgeon may quickly press a lead  11  through side slit  28  and into the holding confines of passage  26 . The purpose of the preferred beveled outer edges  30  is to help the surgeon guide the lead  11  along the length of the side slit  28  and to further encourage its quick entry into passage  26 . 
         [0037]    As shown in  FIGS. 1 ,  2 ,  4 ,  6 , and  7 , rim plate  12  further includes an anchor bridge  32  which is preferably integrally formed along upper surface  21  of rim plate  12  and generally opposite rim lead-holder  20 . The purpose of anchor bridge  32  is to receive and hold a lead  11  exiting the flared passage  16  and also to help encourage a relatively atraumatic transition of the exiting lead  11  to a more tangential trajectory that is coplanar with rim plate  12 , as lead  11  is captured within passage  26 . Lead  11  is gently directed to bend at the point of anchor bridge  32  and the resulting friction generated at this bend point will help hold lead  11  in a stable position about anchor  10  and thereby will discourage any dislodgement of its distal end from the target site located within the patient&#39;s brain. 
         [0038]    As is illustrated in  FIGS. 1 and 2 , located between anchor bridge  32  and both entry/exit ends  27  of rim lead-holder  22  are positioned rim anchor sleeves  34 . These sleeves are short anchoring structures that are integrally formed with rim plate  12 . Each of these sleeves includes an arcuate passage  36  which is sized and shaped to receive lead  11  and which align with arcuate passage  26  of rim lead-holder  22 . Rim anchor sleeves  34  are tubular in that they do not include a side slit, as rim-lead-holder  22  does. The purpose of rim anchor sleeves  34  is to provide a guided entry into and a guided exit from the passage  26  of rim channel  22 . Anchor sleeves  34  prevent any tension of lead  11  from forcing the captured portion of lead  11  to dislodge itself from the friction hold of passage  26  through side slit  28 . 
         [0039]    As shown in  FIGS. 1 ,  2 , and  3 , the relative size, shape and positions of rim lead-holder  22  and rim anchor sleeves  34  define spaces  38  therebetween. These spaces  38  offer the surgeon room to manipulate the end of the lead  11  and feed the same into passage  36  of anchor sleeves  34  and rim lead-holder  22  using a pair of hemostats or his or her fingers, as necessary. 
         [0040]    Referring now to  FIGS. 1 ,  2 ,  8  and  9 , rim plate  12  includes at least two opposing bores  40  that are sized and shaped to receive appropriate fasteners  42  for securing anchor  10  to the outside surface  44  of a patient&#39;s skull  46  (only a representative circular portion of a skull  46  is shown in  FIG. 8 and 9 ). As shown in  FIGS. 8 and 9 , fasteners  42 , when securing anchor  10  to skull  46  do not interfere with lead  11  as it is held in position about anchor  10 . Fasteners  42  are preferably made from titanium (or any other biocompatible material that is preferably non-magnetic) and further includes any appropriate drive head, such as a square drive head, a Torx® drivehead, or an Allen drive head allowing the surgeon to confidently apply the required torque to penetrate the patient&#39;s skull  46  to secure the anchor thereto. 
         [0041]    An important feature of the present invention is to provide not only an anchor for intracranially implanted lead wires or catheters, but also a transition point that smoothly and atraumatically redirects a perpendicularly-exiting lead  11  from a patient&#39;s skull to a path that is generally tangent to the patient&#39;s skull. This redirection allows any leads and catheters to exit the patient&#39;s skull and atraumatically bend so that they can be positioned under the patient&#39;s scalp in a manner that is more accommodating to the patient&#39;s movements and general life style. A patient can more easily hide their medical disposition if lead  11  can be guided close to their scalp without concern that any harm will come lead  11  or the pinpoint positioning of its distal end. 
         [0042]    Anchor  10  is preferably made from a biocompatible polymer material including thermoplastic elastomers, such as Santoprene®, preferably having a durometer of about 87 Shore A. Anchor  10  may also be made from an implantable-grade radio-opaque, MRI-safe silicone rubber that preferably has a durometer of between 50 and 100 Shore A. The level of durometer should offer anchor  10  semi-rigidity, a level of flexibility that allows fasteners  42  to secure rim plate  12  firmly against the patient&#39;s skull  46  without causing the material to collapse and unduly deform under the compression forces of the tightened fasteners  42 . If the material is made too flexible (e.g, a durometer less than 30 Shore A), fasteners  42  would merely deform the local areas of contact and the anchor  10  would not function properly and could slip entirely over the heads of the fasteners. If the material is made too rigid, anchor  10  would not properly conform to the curvature of the patient&#39;s skull  46  (or other irregularities found on the skull) and could fracture under the compressive forces as fasteners  42  are tightened. Another consideration in selecting an appropriate material for anchor  10  is that the material&#39;s coefficient of friction should be relatively high so that the material will form a high friction surface bond when contacting the lead. 
         [0043]    Although not shown, Applicants contemplate an anchor  10  that is co-molded with two materials, each of a different durometer. In this arrangement, rim plate  12  is made from a more rigid material, while stem  14 , anchor sleeves  34 , anchor bridge  32  and rim lead-holder  22  are made from a more flexible (softer) material. This would allow sufficient support for anchor  10  to be secured to the patient&#39;s skull  46  and yet still provide soft sealing and lead-gripping structures to function effectively. As those skilled in the art will appreciate, well known co-molding and/or over-molding techniques could be used to manufacture this version of anchor  10 . 
         [0044]    As is well know, the thickness of a patient&#39;s skull  46  will vary depending on the location about the cranium and also from patient to patient. As discussed in greater detail below, before anchor  10  is fitted to the patient&#39;s skull  46 , the thickness of the skull at the location of a burr hole  48  is measured and the hollow lower stem  14  is then cut (shortened) to an appropriate length based on the measurement. As is illustrated in the section view of  FIG. 9 , once cut, the stem  14  can be fitted within the burr hole and anchor  10  subsequently secured using fasteners  42 . It can be appreciated that the outside cylindrical shape of stem  14  is similar to the shape of burr hole  48  formed in the patient&#39;s skull  46  so that a snug fit will be realized. It is preferable that the outside diameter of stem  14  actually be slightly larger than the inside diameter of the burr hole  48  so that when fitted, stem  14  of anchor  10  forms an even tighter fit within burr hole  48 . 
         [0045]    As shown in  FIGS. 7 and 9 , the shape of stem  14  (after being cut to the proper length) is such that anchor  10  can be advanced into burr hole  48  sufficiently that lower surface  23  of rim plate  12  contacts the outside surface  44  of the patient&#39;s skull  46 . An appropriate biocompatible sealant or adhesive can be used to seal the space between the inside surface of the burr hole  48  and the outside surface of the stem  14 . Such a sealant or adhesive may further be used between the outside surface  44  of the patient&#39;s skull  46  and the underside of rim plate  12  to provide an additional barrier against infection to the brain. 
         [0046]    In use of this anchoring device, an incision is first made in a patient&#39;s scalp and the scalp is drawn from a desired drill-site. The surgeon uses a cranium perforator (or other drilling device) to create a carefully positioned burr hole  48 . The outside diameter and depth of the burr hole  48  will vary from patient to patient and based on the location of the skull. Once burr hole  48  is created, the surgeon will verify the depth of the hole and will cut stem  14  of the present anchor  10  based on the measurement so that when fitted, the stem  14  will fit properly into the burr hole. Once cut to length, the surgeon inserts stem  14  of the present anchor  10  into burr hole until the lower surface  23  of rim plate  12  contacts the patient&#39;s skull. As described above, fasteners  42  are then inserted into bores  40  of rim plate  12  and the anchor  10  secured to the patient&#39;s skull. Of course, as can be appreciated by those skilled in the art, appropriate pre-drilling into the patient&#39;s skull may be required to effectively receive fasteners  42 . 
         [0047]    As mentioned above, prior to fitting the anchor  10  into burr hole  48 , an appropriate sealant or adhesive may be applied to the lower surface  23  of rim plate  12  and possibly within the burr hole itself. 
         [0048]    Once the present anchor  10  is fastened to the patient&#39;s skull, the surgeon uses instrumentation, usually including stereotactic guidance to insert and position the distal end of lead  11  to a target site within the patient&#39;s brain. Lead  11  passes through flared passage  16  (the wide end first) and then the smaller opening  18  located at the bottom of stem  14  before entering the patient&#39;s brain. Once the distal end of lead  11  reaches the desired target site within the brain, the proximal end of lead  11  (located outside the patient&#39;s skull) is threaded through anchor bridge  32 , as shown in  FIGS. 8 and 9 , and then threaded into either anchor sleeve  34 , and then guided into passage  26  by pressing lead  11  gently, but firmly through side slit  28 . Once lead  11  follows around rim plate  12  into passage  26 , the surgeon then threads its proximal end into the other anchor sleeve  34  and finally lead  11  is guided under the patient&#39;s scalp to exit therefrom at an appropriate opening located near the patient&#39;s neck. Finally, the patient&#39;s scalp is sutured closed over lead  11  and the entire anchor  10 . Anchor  10  is made low profile and therefore can easily be accommodated under the patient&#39;s scalp. 
         [0049]    Although not shown in the figures, to prevent or at least discourage infection to the patient&#39;s brain, an appropriate seal (such as a well known duckbill seal or a membrane seal) may be incorporated into the passage  16  to help seal this entry into the brain. In such instance, lead  11  must pass through the seal as it is advanced through passage  16  during initial insertion. 
         [0050]    Once the anchor device  10  is firmly affixed to the user&#39;s skull, should the proximal end of lead  11  be pulled, the patient&#39;s scalp will function as a tension relief, but even if the tensile force reaches the anchor, the force will act mostly on the exiting anchor sleeve  34 . Under such tensile forces, lead  11  will gently bind within passage  26 , owing to the relatively large surface contact with lead  11 . The end result is that the torturous (but atraumatic) path of lead  11  around anchor  10  prior to entering the patient&#39;s brain will help discourage any displacement of the distal end of the implanted lead  11  from the target site. 
         [0051]    Referring now to  FIGS. 10-13 , a lead-anchor  100 , according to a second embodiment is shown. Similar to the first embodiment shown in  FIGS. 1-9  and described above, anchor  100  is similar to a funnel and includes a generally circular rim plate  102  and an integrally formed hollow lower stem  104 . As before, this anchor  100  includes an internal flared passage  106  that has a small lower opening  108  that opens up to the larger diameter of the rim plate  102 . 
         [0052]    The purpose of this second embodiment is to show a skull-secured lead-anchor  100 , which includes a different peripheral structure to hold a lead  11  in place. In this second embodiment, as described in greater detail below, the lead-holding peripheral structure includes at least two loops  150 . Each loop  150  defines an opening  152  through which a lead  11  may pass. Loops  150  are made from a flexible material (preferably having a durometer between 30 and 80 Shore A, and more preferably between 30 and 50 Shore A) which allows a surgeon to easily spread open each loop wide enough to receive any connector (not shown) that may be secured to the proximal end of lead  11  (for example, a luer lock may be pre-secured to the proximal end of a catheter lead  11  or similarly, an appropriate electrical connector may be pre-secured to the end of an electrical lead wire  11 ). By making loops  150  very flexible, each loop can flex around the relatively large connector. The loops  150  should be made from a material that affords them sufficient stretchability and flexibility so that they can be selectively enlarged to accommodate large lead-connectors and yet have “memory” so that after stretched, the loops  150  will return to their original size, shape and orientation. Loops  150  should also not be so flexible that they do not provide some influence on the path of the lead that is laced through the loops about the periphery of the rim. In other words, the loops should gently force the lead to bend so that the lead follows a somewhat serpentine path about the anchor. This sinuous path is what helps hold the lead in place. 
         [0053]    As can be seen in  FIGS. 10-13 , anchor  100  does not include any anchor bridge  32  as the above described first embodiment does. This second embodiment is meant to show an easy-to-manufacture and easy-to-use version. The anchor  100  shown in  FIGS. 10-13  can be made using a simple planar type mold wherein no core plates or caming is required, as can be appreciated by those skilled in the art. 
         [0054]    As already mentioned, the anchor  100  shown in  FIGS. 10-13  has a different peripheral anchoring structure, but retains much of the structure of the above-described anchor  10 , shown in  FIGS. 1-9 . For example, both embodiments of this anchor includes a rim plate ( 12 ,  102 ), a stem ( 14 ,  104 ), a flared passage ( 16 ,  106 ) and opposing bores ( 40 ,  140 ). The surgeon secures both anchors  10 ,  100 , to the patient&#39;s skull  46  within a burr hole  48  in a similar manner, using fasteners  42 . Once the anchor is secured to the patient&#39;s skull and the lead  11  is in the desired position, the surgeon secures lead  11  to anchor  100  differently. The surgeon merely threads the lead  11  through each loop  150  around the rim plate  102 , like lacing a shoe. Since there is no anchor bridge  32  in this version, the surgeon can start with any of the loops and finish with any of the loops around rim plate  102 . 
         [0055]    As can be seen in  FIG. 12 , each loop  150  is formed within a plane that is angled with respect to upper surface  121  of rim plate  102 . The preferred angle between these two planes is between 0 and 45 arc degrees, and more preferably between 10 and 20 arc degrees. This allows the surgeon a choice of holding friction. If lead  11  is laced through loops  150  in a clockwise direction, as shown in  FIG. 10 , the lead will experience an easier path since each angled loop is angled to provide a straighter path around rim plate  102 . A lead laced within the loops in this direction will cause less trauma to the lead and therefore may be appropriate for a catheter. In contrast, a lead laced within loops  150  in the opposite (counter clockwise) direction, not shown, the lead would have to follow a more torturous path because in this direction each angled loop provides a less straight path forcing the lead to bend sharply below each loop before entering its respective opening  152 . Of course the “trauma” to the lead  11  in either direction is still relatively minimal because the loops are preferably made from a flexible material and will be somewhat forgiving. 
         [0056]    As shown in  FIG. 10 , each loop  150  preferably includes a cross-section that is wide so that opening  152  is relatively small and the surface area that contacts lead  11  when lead  11  is laced through loops  150  is maximized to increase holding friction. These loops  150  are designed to contort and bind against the surface of the laced lead when the lead is pulled, thereby preventing any tension generated at the proximal end of the lead from transmitting to the distal end within the brain. The loops  150  ensure that the distal end of the lead within the brain remains exactly at the target site. 
         [0057]    The number, size and exact shape of loops  150  can vary to meet the exact requirements of the particular anchoring application. Of course, the angle of each loop  11  in this second embodiment shown in  FIGS. 10-13  may also vary depending on the design particulars, as can the exact durometer of the material used to make either anchor. 
         [0058]    As can be seen in  FIGS. 10 ,  11 , and  13 , rim plate  102  includes cutouts  154  along the periphery  120 . The purpose of cutouts  154  is to offer a less sharp path for lead  11  to make the transition from vertically exiting flared passage  106  from the patient&#39;s brain to the more horizontal orientation about the rim plate  102  and through the loops  150 . The lead  11  passes gently into any of the cutouts about the periphery  120  before entering any of the loops  150 . 
         [0059]    As shown in  FIG. 13 , the anchor  100  of this second embodiment further includes a sealing ring  156  located on the lower surface  123  of rim plate  102 . This sealing ring  156  is meant to be integrally formed with rim plate and is preferably made from a very soft durometer material. The purpose of this sealing ring  156  is to first contact the surface of the patient&#39;s skull  46  and to create an effective seal about the burr hole  48 . The sealing ring will compress against the patient&#39;s skull as the fasteners  42  are tightened, as can be appreciated by those skilled in the art.