Burr hole cap and methods of use

In one embodiment, an apparatus for securing a lead within a burr hole comprises: an annular body structure adapted to be at least partially inserted within the burr hole; a lead retainer structure mechanically coupled to the annular body structure and adapted to be rotated along an inner perimeter of the annular body structure; the lead retainer structure including a lead engaging member for capturing the lead, wherein the lead engaging member pivots relative to the lead retainer structure; and a fixation member that is adapted to lock the lead retainer structure in place after the lead has been captured by the lead engaging member.

TECHNICAL FIELD

The present application is generally related to burr hole cap devices which are used to hold a lead, catheter, or cannula within a burr hole in a patient's skull.

BACKGROUND

Deep brain stimulation (DBS) refers to the delivery of electrical pulses into one or several specific sites within the brain of a patient to treat various disorders. For example, DBS has been proposed as a clinical technique for treatment of chronic pain, essential tremor, Parkinson's disease (PD), dystonia, epilepsy, depression, obsessive-compulsive disorder, and other disorders.

A DBS procedure typically involves first obtaining preoperative images of the patient's brain (e.g., using computer tomography (CT) or magnetic resonance imaging (MRI)). The imaging process sometimes involves first affixing to the patient's skull fiducial markers that are discernable on the images produced by the imaging process. The fiducial markers assist in registering the preoperative images to the actual physical position of the patient in the operating room during the subsequent surgical procedure. Using the preoperative images, the neurosurgeon can select a target region within the brain, an entry point on the patient's skull, and a desired trajectory between the entry point and the target region. The entry point and trajectory are carefully selected to avoid intersecting or otherwise damaging critical brain structures.

In the operating room, the patient is immobilized and the patient's actual physical position is registered. The physician marks the entry point on the patient's skull and drills a burr hole at that location. A mechanism is provided to precisely control the path through the patient's brain to the desired location. Specifically, a positioning error on the order of a millimeter can have a significant negative effect on the efficacy of the DBS therapy. Stereotactic instrumentation and trajectory guide devices are commercially available products that facilitate the control of the trajectory and positioning of a lead during the surgical procedure.

A microdrive introducer can be used to insert a deep brain stimulation lead toward the selected region of the brain along the selected trajectory. The lead provides one or several conductive paths to deliver stimulation pulses to the selected region. The lead includes a very small diameter insulative lead body with one or several conductors (e.g., stranded wires) embedded in the insulative material. The lead also includes one or several electrodes at a distal end of the lead that are electrically coupled to respective conductors. The electrodes can be used to record signals within the brain and/or to deliver electrical stimulation pulses to brain tissue. Often, the electrical activity adjacent to one or several electrodes is analyzed to determine whether the recorded signals are consistent with the targeted region of the brain. If the recorded signals are not consistent with the targeted region, an adjustment to the lead's position can be made as appropriate.

A burr hole plug or cap structure is typically utilized to retain the lead in the desired position. A burr hole structure generally includes (i) a ring or grommet-like element that is inserted into the hole first so as to protect the edges of the burr hole and (ii) a cap or plug device that is inserted into the ring or grommet-like element to secure the lead and plug the hole.

By way of example, in U.S. Pat. No. 6,044,304, a burr ring is disclosed that is secured to the skull. The burr hole plug of the '304 patent also has an upper flange portion and circumferential ribs used to position the plug in the cranium. Also, the burr hole plug described in the '304 patent includes an aperture capable of accepting a lead through a septum.

In U.S. Pat. No. 5,954,687, a device is disclosed for securing a catheter within a burr hole. The device has a series of spaced septum elements that can be selectively penetrated for fluid communication with a reservoir in the apparatus. The main objective of the device is to allow fluid access to the patient's brain through a burr hole. Anchoring of the device is not taught and there are a limited predetermined number of septum holes that can be accessed.

U.S. Pat. No. 5,927,277 describes a burr hole ring for retaining a probe relative to the skull. The burr hole ring has an engaging member with holes to receive a probe. The '277 patent also describes a method for securing a device at a desired orientation within the burr hole. Since a fixed spacing between holes is described, the device can be placed in a limited number of locations through the burr hole.

U.S. Pat. No. 5,865,842 discloses a system and method for anchoring a lead in a burr hole. The disclosed system consists of a base-plate, adaptor, seal, and screw cap. The lead is anchored mechanically at the burr hole at a 90 degree angle relative to the burr hole.

U.S. Pat. No. 5,843,150 discloses an annular clamping means with a compressible feed-through member for receiving a lead. The described order for anchoring the lead includes making the burr hole, inserting the plug ring, inserting the lead, and engaging the clamping member.

Other burr hole plug assemblies and features of burr hole plugs are taught in U.S. Pat. No. 5,464,446 (burr hole plug with a central lumen and a cap that engages with the flange of the plug); U.S. Pat. No. 4,998,938 (a device that facilitates insertion of an instrument into a patient's cranial cavity); U.S. Pat. No. 4,328,813 (a burr hole plug with a cap that anchors the lead); and U.S. Pat. No. 4,245,645 (a probe and system that is used to perform stereoelectroencephalographic exploration).

SUMMARY

In one embodiment, an apparatus for securing a lead within a burr hole comprises: an annular body structure adapted to be at least partially inserted within the burr hole; a lead retainer structure mechanically coupled to the annular body structure and adapted to be rotated along an inner perimeter of the annular body structure; the lead retainer structure including a lead engaging member for capturing the lead, wherein the lead engaging member pivots relative to the lead retainer structure; and a fixation member that is adapted to lock the lead retainer structure in place after the lead has been captured by the lead engaging member.

The foregoing has outlined rather broadly certain features and/or technical advantages in order that the detailed description that follows may be better understood. Additional features and/or advantages will be described hereinafter. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the appended claims. The novel features, both as to organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the appended claims.

DETAILED DESCRIPTION

Referring now to the drawings,FIG. 1depicts burr hole cap100in a partially disassembled form according to one representative embodiment. Burr hole cap100preferably comprises multiple components that are assembled at the time of lead implantation. For the purpose of this application, when the term “lead” is employed, it is intended to be interpreted broadly to include stimulation leads, infusion catheters, cannulas, and similar medical devices that can be retained within a burr hole cap device. As shown inFIG. 1, burr hole cap100includes cap base101, insert assembly102, and snap on cap103. Insert assembly102fits within the central opening of cap base101. Snap on cap103covers insert assembly102and is retained on cap base101via coupling of projections113to elements111of cap base101. An assembled version of these components is shown in the illustration of burr hole cap100inFIG. 4.

In use, cap base101is secured to a patient's skull. Specifically, surgical screws (not shown) are inserted through cap base101into the patient's skull. Cap base101could alternatively be affixed to the patient's skull using an exterior threaded structure that fits into threads formed in the burr hole of the patient as an example. Cap base101further includes opening112through which the lead exits from the burr hole cap100to be coupled to a pulse generator.

Insert assembly201is shown in a disassembled form inFIG. 2according to one representative embodiment. Insert assembly201is adapted to be partially located within the burr hole of the patient and to be mechanically coupled with cap base101. Insert assembly201includes the components that enable a lead to be secured at a desired location anywhere within the burr hole. As shown inFIG. 2, insert assembly201comprises retainer201, lead retainer202, and housing structure203. In preferred embodiments, housing structure203and lead retainer201are shipped in a permanently coupled configuration with a distal portion of lead retainer202placed between the two components, although the components could be connected at the time of surgery in alternative embodiments.

When mated, housing structure203and lead retainer201define an annular channel in which a distal portion of lead retainer202sits. Preferably, flange204of housing structure203comprises a lip (shown inFIG. 5A) on its underside and interior circumference. A suitable structure (e.g., a pivot pin306as shown inFIG. 3) is preferably implemented on lead retainer202that extends into the space behind the lip. Accordingly, the lip ensures that pin306and, hence, the distal end of lead retainer202is retained within the annular channel defined by housing structure203and lead retainer201.

FIG. 5Adepicts a cut-away view of housing structure203and retainer201showing annular channel501according to one representative embodiment. Lip502is also shown on the underside of flange204.FIG. 5Bdepicts a top view of housing structure203and the path through which lead retainer202may be traversed according to one representative embodiment. As shown inFIG. 5B, the annular channel enables lead retainer202to rotate along the circumferential path defined by housing structure203.FIG. 5Cshows lead retainer202fully pivoted in the clockwise position and having pivotal freedom in the counter-clockwise direction.FIG. 5Dshows lead retainer202fully pivoted in the counter-clockwise position and having pivotal freedom in the clockwise direction. Additionally, lead retainer202has some radial degree of freedom (not shown) that results from movement of the pin306within the radial width defined of annular channel501. By allowing lead retainer202to be rotated and pivoted within the burr hole, the lead can be captured irrespective of the lead's position within the burr hole.

FIG. 3depicts a disassembled view of lead retainer202according to one representative embodiment. Lead retainer202comprises lead holder base structure303which includes pivot pin306and clamp pin307. One end of clamp307fits over clamp pin307and rotates about pin307. After lead holder base307is rotated and/or pivoted as shown inFIGS. 5B-5Dsuch that the lead350is positioned within the recess of lead holder base structure303, clamp307is rotated about pin307to capture lead350. Set screw305is rotated to cause pressure foot302(which is attached to lead holder base307through pins301) to expand (the combined width of lead holder base structure303and pressure foot302is increased). The expansion of pressure foot302locks the lead retainer202in place and consequently causes lead350to be held at the desired position. That is, the expansion of the pressure foot302causes lead retainer202to contact the upper and lower surfaces of channel501(shown inFIG. 5A) with some amount of force. The contact requires a significant frictional force to be exerted on lead retainer202to move lead retainer202thereby locking lead retainer202in place. Although a fixation member is shown integrated with lead retainer202, one or several fixation members could be employed elsewhere. For example, housing204could be implemented to selectively fix lead retainer202at a given position and orientation.

FIG. 6depicts a flowchart for placing a lead within the skull of a patient in conjunction with use of the present burr hole cap according to one representative embodiment.

In step601, fudicial markers are affixed to the patient's skull. In step602, imaging of the patient's brain occurs. Any suitable imaging technology can be utilized such as MRI systems, CT systems, etc. The imaging may also involve functional analysis of the brain in response to specific stimuli. For example, a functional MRI process may be performed in which stimuli is provided to the patient and the MRI imaging is utilized to identify the specific structures in the brain that respond to the stimuli. In step603, based upon the imaging information, a target location is identified. Commercially available navigational software can be used to relate the fudicial markers to desired target location. Specifically, the navigational software uses the identified target location with the imaging information of the patient's brain and the fiducial markers to calculate a location for the burr hole and a path for traversal of the DBS lead to the target location. The location of the burr hole and the path are selected to avoid damaging relevant structures of the brain.

In step604, the patient is placed within a stereotactic frame in a head rest. In step605, one or several incision(s) may be made on the patient's scalp. In step606, an identification of the area for the burr hole is made on the patient's skull within the area exposed by the incision(s). In step607, the burr hole is drilled. In step608, the base of the burr hole cap is attached to the patient's skull using surgical screws. In step609, the insertion assembly is placed within the burr hole cap base and into the burr hole.

In step610, a microelectrode recording drive is positioned using a stereotatic arc (in relation to the fudicial markers) and the stored navigational data and a microelectrode cannula is placed within the drive. In step611, the microelectrode is advanced along the predetermined tract and the brain signals detected by the microelectrode are recorded. In step612, the target brain tissue is identified using the recorded information. In step613, the microelectrode cannula and microelectrode are removed.

In step614, a macroelectrode is inserted into a larger diameter cannula. In step615, the macroelectrode is advanced to the identified location using a microdrive. In step616, electrical stimulation is provided to the identified location using the macroelectrode to verify that the expected result occurs from the stimulation, such as reduced tinnitus effects, reduced tremor, improved mood, etc. Variation in stimulation parameters (pulse amplitude, pulse frequency, pulse width, etc.) May occur at this stage for the purpose of obtaining optimal results from the stimulation. Also, some variation in positioning of the macroelectrode can occur for the purpose of obtaining optimal results. In step617, the cannula and macroelectrode are removed.

In step618, a DBS lead and cannula are placed. In step619, the lead is advanced with a stylet to the target stimulation site. In step620, a trial stimulator is used to perform the desired stimulation to verify the expected result of the stimulation. Some variation in positioning may occur for the purpose of obtaining optimal results. In step621, the lead retainer is rotated, pivoted, and/or radially translated to place the recess structure of the lead retainer against the DBS lead. In step622, the clamp of the lead retainer is adjusted to capture the DBS lead. In step623, the pressure foot of the lead retainer is expanded to lock the lead retainer with the DBS lead in place. In step624, the stylet and the cannula are removed. In step625, the DBS lead is adjusted to allow the cap to be placed on the burr hole base structure.

Although DBS leads are discussed according to one representative embodiment, some representative embodiments can be utilized to secure any suitable type of lead, catheter, or probe. For example, a paddle-style cortical lead that is placed extradurally within a patient's skull could be secured according to one alternative embodiment. Alternatively, a catheter for drug infusion could be secured according to another representative embodiment.