US20200376264A1 - Device and method for percutaneous placement and anchoring of stimulating electrodes in spine - Google Patents

Abstract

A system and method for anchoring an electrode that stimulates a dorsal root ganglion. The anchoring device includes a screw, collet, and locking cap. The screw is inserted into bone of the pars interarticularis and the electrode is inserted through the screw and positioned next to the dorsal root ganglion for stimulation. The screw includes a recess that is shaped to fit the collet. The collet has flexible arms. When assembled, the locking cap forces the collet into the recess thereby moving the flexible arms inward radially, impinging on the electrode and holding the electrode in place adjacent the dorsal root ganglion.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. application Ser. No. 15/724,208, filed Oct. 3, 2017, now U.S. Pat. No. 10,751,527 granted on Aug. 25, 2020, which claims priority benefit from U.S. Provisional Application No. 62/403,492 filed Oct. 3, 2016. Each patent application identified above is incorporated here by reference in its entirety to provide continuity of disclosure.
BACKGROUND OF THE INVENTION
• Mechanical compression or injury to spinal nerves with resulting radicular pain can develop in response to a variety of conditions, including spondylolisthesis, osteoarthritis, and degenerative disc disease, among others. Nerve root irritation can also result in numerous symptoms aside from the radicular pain, including both sensory and motor deficiencies, such as numbness of the extremities, weakness, and difficulty with or loss of dexterity and muscle control.
• One method for controlling pain resulting from irritation of a nerve root is electrical stimulation of the dorsal nerve rootlet and associated dorsal root ganglion, effected by an electrode array implanted peripheral to the dorsal rootlet. The dorsal rootlet transmits sensory signals, and stimulation of the dorsal rootlet can alleviate painful sensations without interfering with motor functions, which are transmitted through the adjacent ventral rootlet.
• The dorsal root ganglion is located along the dorsal rootlet and contains the cell bodies of the neurons whose axons traverse the dorsal root. Stimulation of the dorsal root ganglion is a promising treatment for neuropathic pain. Research shows that over half of patients with chronic back pain see a reduction in symptoms with nerve stimulation, or neuromodulation, procedures.
• To maximize the efficacy of dorsal root stimulation, implantation of the electrode array should be proximate to the dorsal root ganglion. Location at greater distances requires increased amounts of energy to be delivered to the electrode array to achieve the desired stimulation, which depletes energy sources more quickly. Prior art solutions, such as implantation of an electrode array on the exterior of the vertebrae running parallel to the spinal column, suffer from this problem. Furthermore, location outside the spinal vertebrae leaves the electrical stimulation signal subject to dissipation due to bulk conductivity of the surrounding soft tissues and cerebrospinal fluid.
• The technical skill required to properly locate the electrode adjacent the dorsal root ganglia presents a challenge because of the anatomical orientation of the nerve rootlet and dorsal root ganglion within the intervertebral foramen. Additionally, the site of the ganglia varies depending on the location of the vertebrae of a single patient. For example, one survey found the location of the dorsal root ganglia in the fourth lumbar spine to be intraspinal (“IS”) in approximately 6% of patients, intraforminal (“IF”) in approximately 48% of patients, and extraforminal (“EF”) in 41% (5% were not identified). In the fifth lumbar spine, the same population had 10% IS, 75% IF, and 6% IS (with 9% not identified) dorsal root ganglia.
• Prior art techniques address this problem by percutaneously injecting the electrode through the intervertebral foramen via a needle, laying it alongside the spinal nerve root. However, this technique leaves the electrode suspended in the intervertebral foramen without firm fixation. Hence, the electrode array is prone to migration, which both diminishes the efficacy of the stimulation technique and can cause other complications necessitating surgical correction of the migration or removal of the electrode array.
• Percutaneous injection is also not an ideal solution because it carries with it all the risks, costs, and time constraints normally associated with surgery. Further, surgery may not be an option for certain patients because of risk factors such as age, clotting, prior injuries, and pre-existing epidural scars.
• The problem of electrode array migration has been addressed by other prior art techniques, but has not been adequately resolved. For example, prior art techniques to anchor the electrode include an anchoring hook that is engaged in the fibrous fascia layer surrounding the nerve root. The anchoring hook must pierce the nerve fascia layer. But, piercing the nerve fascia layer with a hook presents risk of nerve damage. Migration also remains a problem with this technique.
• U.S. Publication No. 2017/0021180 to Datta discloses a method for implantation of a neural stimulator comprised of electrodes attached to a generator. The electrodes are connected to the generator via a subcutaneous lead with connector plugs. However, the method anchors the electrode to the soft tissue near the targeted nerve, which leaves the electrode susceptible to migration.
• U.S. Publication No. 2016/0199112 to Kim discloses a medical insertion apparatus comprised of a screw nail body to be implanted in a boney structure that includes an electrode. The screw nail body includes an electrode connected to a lead which runs along the length of the screw nail body either inside a cavity or along the outside edge, or a combination thereof. The position of the electrode is fixed at the terminal end of the screw nail body, requiring the screw nail body to be located immediately peripheral to the targeted nerve, which is not always possible when targeting the dorsal root ganglion. Furthermore, the screw nail body must be seated perpendicularly to the surrounding bone, prohibiting an electrode position parallel to the nerve root. Alternatively, using an array of electrodes that extends beyond the tip of the screw nail body leaves the array adrift in the epidural space, with no way to position the array precisely and no way to control electrode migration. U.S. Pat. No. 6,356,792 to Errico, et al. discloses an assembly for securing an electrode inside a patient's skull. A skull port member is affixed to the skull. An electrode is placed inside the skull and the connecting lead is run through the skull port member. The electrode is secured by a mechanism that seats in the skull port member and crimps the connecting lead. However, the electrode is susceptible to movement when the operator inserts the lead-locking mechanism into the skull port member and crimps the connecting lead. The nature of the mechanism also limits the possible materials and possible sizes of the assembly, as thinner and lighter materials in the connecting lead would be likely to break when crimped in place by the lead locking mechanism. Furthermore, the design is ill-suited for use in the spine, as there is no way to position the electrode perpendicular to the direction of the skull port member, which is desirable for stimulation of spinal nerves.
• U.S. Pat. No. 9,737,233 to Londot discloses an assembly having a pedicle screw with an electrically-conductive longitudinal member that is used to propagate a signal along the exterior of the pedicle screw. However, the assembly does not allow for placement of the electrode beyond the pedicle screw and limits locations to which electrical stimulation can be applied.
• U.S. Pat. No. 9,579,222 to Branemark, et al. discloses a percutaneous gateway for transmission of signals from a patient's nervous system to a robotic prosthesis. The system discloses an apparatus for mounting a prosthesis and preserving the percutaneous transmission of signals with appropriate seals to prevent infection after long-term use, as well as use with stimulating electrodes that may optionally be implanted. However, the system does not disclose a method for locating the electrodes relative to targeted nerves, anchoring the position of the electrodes, or implantation in the spine.
• Hence, there remains a need for an electrode array and implantation technique that can reliably locate the array within close proximity to the dorsal root ganglion, regardless of the ganglion site, and effectively anchor the array in place to reduce or eliminate future migration.
SUMMARY OF THE INVENTION
• This disclosure provides for anchoring an electrode that stimulates a dorsal root ganglion. The electrode is anchored to the bone of the pars interarticularis using a set of tools that implant an anchoring device.
• The disclosure further provides a device and method for percutaneous placement of a stimulating electrode into the spine using minimally-invasive surgery (MIS) techniques. The disclosure also provides a method for anchoring the electrode, which is resistant to migration. The disclosure also provides a method of electrode implantation accurately even in the presence of a pre-existing epidural scar. Reduced radiation from fluoroscopy for the technician is also anticipated.
• A preferred embodiment consists of a cannulated anchoring screw which is placed fluoroscopically into the pars interarticularis using MIS techniques. A hole is drilled through the pars either under fluoroscopy or with the aid of electrophysiological monitoring of the nerve root. A pliable percutaneous lead with nickel-titanium alloy “memory metal” stylet is then advanced fluoroscopically through the anchor screw along the course of the nerve root to lay parallel to the dorsal root ganglion. The stylet is removed and a locking cap is deployed over the screw to anchor the electrode array.
• The disclosure also provides a preferred set of tools, that when used together, allow for implanting the anchoring device and electrode adjacent the dorsal root ganglion and anchoring it permanently to the pars interarticularis.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a median view of the human spine, showing the different types of vertebrae and their approximate location.
• FIG. 2 is an axial view of a lumbar vertebra, showing the various bone features.
• FIG. 3 is a sagittal view of a lumbar vertebra, showing the structure and foramen where spinal nerves are located.
• FIG. 4A depicts the attachment of the nerve roots to the spinal cord.
• FIG. 4B is a frontal X-ray image of a patient's lumbar region, showing the possible locations of the dorsal root ganglion.
• FIG. 5 is a view of a preferred embodiment of an electrode array that is used with an anchoring device.
• FIG. 6A is a cross section view of a screw of a preferred embodiment of an anchoring device.
• FIG. 6B is a top view of a preferred embodiment of an anchoring device.
• FIG. 6C is a cross section view of a screw of an alternate embodiment of an anchoring device.
• FIG. 6D is a top view of an alternate embodiment of an anchoring device.
• FIG. 6E is a cross section view of an alternate embodiment of an anchoring device.
• FIG. 6F is a top view of an alternate embodiment of an anchoring device.
• FIG. 7A is a cross section view of a preferred embodiment of a collet.
• FIG. 7B is a top view of a preferred embodiment of a collet.
• FIG. 7C is a cross section view of a preferred embodiment of a collet.
• FIG. 7D is a top view of a preferred embodiment of a collet.
• FIG. 8A is a cross section view of a preferred embodiment of a locking cap.
• FIG. 8B is a top view of a preferred embodiment of a locking cap.
• FIG. 8C is a cross section view of an alternate embodiment of a locking cap.
• FIG. 8D is a top view of an alternate embodiment of a locking cap.
• FIG. 8E is a bottom view of an alternative embodiment of a locking cap.
• FIG. 8F is a cross section view of a preferred embodiment of a locking cap.
• FIG. 8G is a bottom view of a preferred embodiment of a locking cap.
• FIG. 9 is an exploded view of a preferred embodiment of an electrode array threaded with an anchoring device.
• FIG. 10 is a view of a preferred embodiment of a needle used with a preferred embodiment of an anchoring method.
• FIG. 11 is a view of a preferred embodiment of a guide tube used with a preferred embodiment of an anchoring method.
• FIG. 12 is a view of a preferred embodiment of a guidewire used with a preferred embodiment of an anchoring method.
• FIG. 13 is a view of a preferred embodiment of a dilator tube used with a preferred embodiment of an anchoring method.
• FIG. 14A is a side view of preferred embodiment of an insertion tool used with a preferred embodiment of an anchoring method.
• FIG. 14B is a bottom view of a preferred embodiment of an insertion tool used with a preferred embodiment of an anchoring method.
• FIG. 15 is a view of a preferred embodiment of a drill a preferred embodiment of an anchoring method.
• FIG. 16A is a side view of a preferred embodiment of a driver used with a preferred embodiment of an anchoring method.
• FIG. 16B is a bottom view of a preferred embodiment of a driver used with a preferred embodiment of an anchoring method.
• FIG. 17 is a view of a preferred embodiment of a stylet used with a preferred embodiment of an anchoring method.
• FIG. 18 is a cutaway view of a preferred embodiment of an assembled tool set comprising a dilator tube, a guide tube, and a needle.
• FIG. 19 is a cutaway view of a preferred embodiment of an assembled tool set comprising a dilator tube, an insertion tool, a drill, a depth stop, and an anchoring device.
• FIG. 20 is a cutaway view of a preferred embodiment of an assembled tool set comprising a dilator tube, a driver, an electrode, a stylet, an anchoring device, a collet, and a locking cap.
• FIGS. 21A and 21B are a flowchart of a preferred embodiment of a method for implanting an anchoring device.
• FIG. 22 is a flowchart of a preferred embodiment of a method for removing an anchoring device.
• FIG. 23 is an oblique view of a lumbar vertebra with the anchoring device fixed to the bone of the Pars.
• FIG. 24 is a cutaway view of a lumbar vertebra and the anchoring device showing the anchoring device in place.
DETAILED DESCRIPTION OF THE INVENTION
• FIG. 1 shows a drawing of the human spine includingspinal column100.Spinal column100 is comprised of a number of vertebrae, categorized into four sections, thelumbar vertebrae102, thethoracic vertebrae104, thecervical vertebrae106 and thesacral vertebrae108. Starting at the top of the spinal column,cervical vertebrae106 include the 1st cervical vertebra (C1) through 7th cervical vertebra (C7). Just below the 7th cervical vertebra is the first of twelvethoracic vertebrae104 including the 1st thoracic vertebra (T1) through 12th thoracic vertebra (T12). Just below the 12ththoracic vertebrae104, are fivelumbar vertebrae102 including the1st lumbar vertebra (L1) through 5th lumbar vertebra (L5). The 5th lumbar vertebra is attached to the sacral vertebrae108 (S1 to S5), thesacral vertebrae108 being naturally fused together in the adult.
• FIG. 2 shows an axial view of representativelumbar vertebrae102. Representativelumbar vertebra200 has a number of features which are shared with thethoracic vertebrae104 andcervical vertebrae106, although the feature thicknesses and shapes may vary. The thick oval segment of bone forming the anterior aspect oflumbar vertebra200 is thevertebral body201.Vertebral body201 is attached to a bonyvertebral arch203 through which the neural elements run.Vertebral arch203, forming the posterior oflumbar vertebra200, is comprised of twopedicles205, which are short stout processes that extend from the sides ofvertebral body201, and twolaminae207, the broad flat plates that project frompedicles205 and join in a triangle to form a hollow archway, thespinal canal209.Spinous process211 protrudes from the junction oflaminae207.Transverse processes213 project from the junction ofpedicles205 andlaminae207. The structures of the vertebral arch protect the spinal cord and/or spinal nerves that run through the spinal canal.
• InFIG. 3, a representativelumbar vertebra300 is shown from a lateral view.Lumbar vertebra300 has a number of structural features enabling it to house spinal nerves and connect with the vertebrae superior and inferior to it. Interiorvertebral notch303 aligns with the vertebra inferior tolumbar vertebra300 to formintervertebral foramen305.Lumbar vertebra300 articulates with adjacent vertebra via the superiorarticular process307 and inferiorarticular process309. Thespinous process311 protrudes from the junction of the laminae. The pars interarticularis313 is the thin wall of bone located between the superiorarticular process307 and inferiorarticular process309. In most cases, the minimum depth of the Pars is about 4 mm, but can be as much as 8 mm, depending on the patient and the vertebral position.Lumbar vertebra300 joins to superior and inferior vertebrae by discs that attach superior and inferior to thevertebral body315.Transverse processes317 protrude laterally fromvertebra300.
• InFIG. 4A, a representativespinal cord segment400 is shown in axial cross-section. The nerve structures are housed in the foramen shown inFIG. 3.Spinal cord401 is situated in the vertebral foramen.Ventral root403 anddorsal root405 join to formspinal nerve root407, which routes through intervertebral foramen.Dorsal root ganglion409 is located alongdorsal root405.
• One of the challenges faced by traditional spinal nerve stimulation techniques is positioning the electrode near the dorsal root ganglion. Maximum efficacy is achieved when the electrode is positioned adjacent to thedorsal root ganglion409. However, the position ofdorsal root ganglion409 varies from patient to patient, with some dorsal root ganglia being lateral to the pedicle, outside theintervertebral foramen305 while others are located medial to thepedicle205.
• InFIG. 4B, an X-ray image of the lower lumbar spine is shown. Three dots show possible locations of thedorsal root ganglion409.Position411 shows the extraforamenal site (EF), located outside theintervertebral foramen305.Position413 shows the intraforamenal site (IF), located inside theintervertebral foramen305.Position415 shows the intraspinal site (IS), located within the vertebral foramen.
• Referring toFIG. 5,electrode500 is a stimulating electrode array that contains one or more electrodes atdistal tip502. The interior ofelectrode500 has astylet channel504 along a central axis to facilitate directional control ofelectrode500 insertion. The electrode array includesannular electrode contacts506 and annular insulatingbands508. In a preferred embodiment, the electrode is comprised of a pellethane or silastic outside sheeth with platinum-iridium electrode contacts. Wires (not shown) proceed through the stylet channel and connect the electrode array to a current source to supply stimulation once the electrode is firmly implanted.
• Referring then toFIGS. 6A and 6B, a preferred embodiment of cannulated lockingscrew600 of an anchoring device, will be described.Screw600 has self-tapping right-handedthreads602 on its exterior.Flange608 is positioned above the threads and forms a cylindrical shelf which functions to limit the depth that screw600 can penetrate into the bone and to seat the screw against the bone surface.Flange608 contains fourdetent indentions610 which engageinsertion tool1400, which will be later described. In a preferred embodiment,underside609 offlange608 can be knurled to increase the friction between the flange and the bone surface. Screw600 contains arecess606 which engagescollet700 to anchorelectrode500 withinlumen612 ofscrew600,lumen704 ofcollet700, andlumen804 of lockingcap800. In a preferred embodiment, the recess is elliptical in shape, having a minor radius of about 2 mm and a major radius of about 3 mm. Left-handedthreads604 allowscrew600 to be attached and secured to lockingcap800.Screw600 is preferably composed of titanium or an alloy thereof. In a preferred embodiment, the diameter “g” offlange608 is about 10 mm, with the largest diameter “e” ofrecess606 starting at about 6 mm and narrowing to match the 2 mm diameter “f” oflumen612. The total height “d” ofscrew600 is about 10 mm, with right-handedthreads602 running for a distance “c” of 5 mm, separated from the left-handedthreads604 having a height “a” of about 3 mm by theflange608 having a height “b” of about 2 mm. Other dimensions can be envisioned to accommodate differing surgical conditions.
• Referring toFIGS. 6C and 6D, an alternate embodiment of cannulated lockingscrew601 of an anchoring device will be described. Lockingscrew601 has self-tapping right-handedthreads632.Flange638 is positioned adjacent the threads and limits the depth that lockingscrew601 can penetrate into the bone.Flange638 contains fourdetent indentions640 which engageinsertion tool1400. Lockingscrew601 contains arecess636 which engagescollet700 to anchorelectrode500 withinlumen642 of lockingscrew601,lumen704 ofcollet700, andlumen804 of lockingcap801.Bayonet mount634 allows lockingscrew601 to be attached and secured to lockingcap800 by 60° of rotation, as will be further described. The bayonet mount may be used instead of the threads between the locking screw and the locking cap in the various embodiments. Lockingscrew601 is preferably composed of titanium an alloy thereof or a suitable medical plastic.
• Referring toFIGS. 6E and 6F, an alternate embodiment of cannulated lockingscrew611 of an anchoring device will be described.Screw611 has self-tapping right-handedthreads643.Flange648 is adjacent the threads and limits thedepth screw611 can penetrate into the bone.Flange648 contains fourdetent indentions650 which engage withinsertion tool1400. Screw611 contains arecess646 which engages collet701 to anchorelectrode500 withinlumen652 ofscrew611,lumen704 of collet701, andlumen804 of lockingcap801. In a preferred embodiment, the recess is frustoconical in shape, having an incline as measured from a central longitudinal axis of between about 25° and about 45°. Other inclines are envisioned.Bayonet mount644 allowsscrew611 to be attached and secured to lockingcap800 by 60° of rotation, as will be further described.Screw611 is preferably composed of titanium, an alloy thereof, or a suitable medical plastic. The dimensions of lockingscrew601 are similar to those ofscrew600.
• Referring toFIGS. 7A and 7B,collet700 is fabricated from a biocompatible polymer such as polytetrafluoroethylene.Collet700 has two or moreflexible arms702 separated byslots706. Four slots are shown. However, between two and eight slots are envisioned in other embodiments. Each of the flexible arms comprises an ellipticaloutside surface703 with a minor radius of about 2 mm and a major radius of about 3 mm. The flexible arms of the collet are designed to fit within the recess of the locking screw. The flexible arms are designed to bend inward when the locking cap forces the collet into the recess of the locking screw due to the outside shape of arms and the inside shape of the recess.
• In other embodiments, outsideshape713 of the collet may be frustoconical, as shown inFIGS. 7C and 7D. The incline of the outside shape in a preferred embodiment, is about 30°, but may be between about 25° and about 45°. Other inclines are envisioned.Collet710 includesflexible arms712,slots716, andcentral lumen714.Collet710 is designed to mate withrecess646 of lockingscrew611.
• Referring toFIGS. 8A and 8B, lockingcap800 is described. The outside surface of lockingcap800 preferably designed to fit a standard hex-head spanner to simplify manufacture. Other spanner head shapes can be employed. Lockingcap800 has left-handedthreads802 that are designed to mate with left-handedthreads604 ofscrew600 or601. Lockingcap800 also has acentral lumen804 sized to allowelectrode500 andinsertion tool1400 to pass through. The underside of lockingcap800 has a recessedseat806 designed to accommodate the outer diameter of the collet. The collet is designed to nest inside recessedseat806 and be held in place by a press fit tolerance. In a preferred embodiment, the diameter of recessedseat806 is 6 mm. An inert epoxy may be employed to fix the collet in the seat. Lockingcap800 is preferably composed of titanium or a biologically inert alloy thereof.
• Referring toFIGS. 8C, 8D and 8E,alternate locking cap801 is described. Lockingcap801 includes an integrally formedelliptical protrusion807 that matches the shape ofrecess606 or636. The elliptical protrusion includes fourflexible arms808 separated byslots809. Other numbers of arms and slots are envisioned, as required.Lumen804 extends through the top of lockingcap800 to the tip of the elliptical protrusion, culminating in one ormore teeth810.Teeth810 protrude from and are integrally formed with the flexible arms. The teeth extend radially inward intolumen804. When assembled and implanted, the flexible arms are forced inward by the recess andclamp electrode500 to prevent electrode migration. In a preferred embodiment, the locking cap is machined from polyoxymethylene or poly-tetrafluoroethylene. In another embodiment, the locking cap can be machined from a titanium alloy.
• Referring then toFIGS. 8G and 8F, analternate locking cap803 is described. Lockingcap803 includesbayonet mount827 that is designed to matchbayonet mount644 ofscrew611. Lockingcap803 includescentral lumen824 sized to allowelectrode500 andinsertion tool1400 to pass through. The underside of lockingcap801 includes recessedseat826 designed to accommodate the outer diameter of the collet. The collet is designed and nest inside recessed seat and be held in place by a pressed fit tolerance. In a preferred embodiment, the diameter of the recessed seat is about 6 mm. In another alternative embodiment, the collet may be fixed within the recessed seat by a suitable medical epoxy. In a preferred embodiment, the locking cap is composed of a titanium alloy.
• Referring toFIG. 9, anchoringdevice900 includesscrew600,collet700, and lockingcap800.Electrode500 is inserted through thecentral lumen804 of lockingcap800,central lumen704 ofcollet700, endcentral lumen612 ofscrew600. When lockingcap800 is tightened, the collet is forced downward into the recess.Flexible arms702 ofcollet700 are then compressed and crimpelectrode500. The friction between the interior of the arms and the exterior of the electrode prevents movement of the electrode, relative to the collet, and the locking screw.
• Referring toFIG. 10, Jamshidi (PAK)needle1000 includesrigid needle1002,awl tip1004, and handle1006.Needle1000 is sized to fit withinguide tube1100.Rigid needle1002 allows for piercing the soft tissue between the incision site and the pars interarticularis, and for creating a lead hole in the Pars for insertion of the locking screw.
• Referring theFIG. 11,guide tube1100 includesbody1102,lumen1104 withinbody1102,frustoconical end1106, anddistal tip1108. In a preferred embodiment, the distal tip is shaped as a reverse ellipse, which forms a concave transition from the cylindrical outside surface to the open lumen.Body1102 is generally cylindrical and designed to fit withinguide tube1100 with a tolerance sufficient to allow longitudinal movement, but restrict lateral movement.Lumen1104 has a diameter that is substantially equal to that ofrigid needle1002 ofPAK needle1000. The lumen is sized to allow longitudinal movement, but constrict lateral movement ofPAK needle1000 fromguide tube1100. Whenneedle1000 is fully inserted intoguide tube1100, the top ofguide tube1100 abuts the bottom ofhandle1006 andawl tip1004 extends fromdistal tip1108.
• Referring toFIG. 12, guidewire (Kirschner wire)1200 is of a similar diameter to that ofelectrode500. The guidewire, when in use, is placed into the guide hole in the Pars created by the needle. In a preferred embodiment, the guidewire is a titanium alloy of sufficient diameter to fit withinlumen1104 and be visible fluoroscopically.Guidewire1200 is used to guidescrew600,collet700, and lockingcap800 to the implantation site prior to the insertion ofelectrode500 at the implantation site.
• Referring toFIG. 13,dilator tube1300 includeslumen1302 withinbody1304 andsemi-conical nose1306 at distal tip1308. The body ofdilator tube1300 is generally cylindrical and is made of rigid non-conducting material such as poly-ether-ether-ketone (PEEK). The lumen is sized to fit the outside diameter ofinsertion tool1400 and allow longitudinal movement, but prevent lateral movement. The diameter of distal tip1308 ofdilator tube1300 is substantially equal to the diameter offlange608.
• Referring toFIGS. 14A and 14B,insertion tool1400 includes one ormore handles1402,lumen1404 withinbody1410, and taperedprojections1406.Tapered projections1406 fit intodetent indentions610 of the locking screw prior to assembly of the screw with the collet and the locking cap. Torque is applied to the insertiontool using handles1402.Insertion tool1400 has slightly taperedprojections1406 which engage the detent indentions on the locking screw with a press fit tolerance sufficient to hold the locking screw during the insertion procedure, but release it after the screw is tapped into the Pars. The insertion tool includesstop1408 which is designed to limit the longitudinal travel of the drill, which will be further described.
• Referring toFIG. 15,drill1500 includeshandle1502,depth nut1504,lock nut1505,shaft1508, anddrill bit1510.Shaft1508 includesdiameter reductions1511 and1513 to avoid interference with the alignment of the shaft in the lumen of the insertion tool. Whendrill1500 is placed intoinsertion tool1400,drill1500 can only be advanced untildepth nut1504 reaches stop1408 ofinsertion tool1400. In a preferred embodiment, left-handedthreads1506 are left-handed to allow for adjustment ofdepth nut1504 to control the depth thatdrill bit1510 will reach. Looking downward at the tool, rotatingdepth nut1504 counterclockwise with respect toshaft1508 causesdepth nut1504 to move downwards towardsshaft1508 which shortens the maximum depth reachable bydrill bit1510. Conversely, rotating the depth nut clockwise causesdepth nut1504 to move upwards towardshandle1502, thereby increasing the maximum depth reachable bydrill bit1510. The diameter ofshaft1508 corresponds with the diameter ofinner lumen1404 ofinsertion tool1400. The diameter ofdrill bit1510 corresponds with the inner diameter of the lumen in the locking screw.Lock nut1505 is advanced to a positionadjacent depth nut1504, and then torqued into a constricted position against the depth nut so that neither can move, thereby allowing the position ofdepth nut1504 to be fixed on the threaded shaft.
• Referring toFIGS. 16A and 16B, lockingcap driver1600 includeshandle1602,lumen1604,driver head1606 anddriver body1605.Lumen1604 allows for threadinglocking cap driver1600 ontoelectrode500.Driver head1606 is shaped to fit lockingcap800, which, in a preferred embodiment, is a hexagonal spanner head. Lockingcap driver1600 includesratchet mechanism1603.Ratchet mechanism1603 is torque limited to preventovertightening locking cap800 during the installation of the anchoring device. In a preferred embodiment, the torque is limited to approximately3 ft./lbs. This torque limit may be adjusted. This torque is sufficient to allow lockingcap800 to compress the arms ofcollet700, but yet prevent extraction ofscrew600. In a preferred embodiment,driver body1605 is made of a rigid plastic such as poly-ether-ether-ketone (PEEK) to allow radiolucency. In another preferred embodiment,driver body1605 is made of titanium alloy for situations where exacting torque or angular placement are required. In a preferred embodiment, the ratchet is reversible so that the tool may be used to extract the locking screw if need be.
• In another preferred embodiment, lockingcap driver1600 can be provided as two separate tools, one which only provides torque in a clockwise direction so that the only use is to insert the anchoring device and another which only provides torque in a counterclockwise direction so that the only use is to extract the anchoring device. By providing two separate tools confusion may be reduced, thereby preventing unintentional over insertion of the anchoring device into the pars during an extraction procedure.
• Referring toFIG. 17,stylet1700 includeshandle1702 andbend1704.Stylet1700 is sized to fit withinstylet channel504 ofelectrode500. In a preferred embodiment,stylet1700 is made from nickel-titanium. The nickel-titanium alloy possesses a unique crystaline structure that exhibits “superelasticity,” allowingstylet1700 to deform significantly under stress and yet return to its original shape once the stress is released. In a preferred embodiment,stylet1700 can be formed to have a predetermined curve for locating theelectrode500. Once in this curved shape, thestylet1700 can be straightened in order to be inserted through thestraight lumen1604 of lockingcap driver1600. Once the tip ofstylet1700 emerges fromscrew600 in the intervertebral foramen, the alloy returns to its curved shape, thereby positioning the tip of theelectrode500 parallel to the nerve root and facilitating location of theelectrode500 peripheral to the dorsal root ganglion.
• Referring toFIG. 18, assembledtool1800 will be described.Assembled tool1800 includesdilator tube1300,guide tube1100, andneedle1000.Dilator tube1300 haslumen1302 with a diameter corresponding to the outer diameter ofguide tube1100, allowingguide tube1100 to be inserted intodilator tube1300. In a preferred embodiment, the outer diameter ofguide tube1100 and diameter oflumen1302 indilator tube1300 are about 10 mm.Needle1000 has an outer diameter corresponding to the inner diameter ofguide tube1100, allowingneedle1000 to be inserted intoguide tube1100. In a preferred embodiment, the outer diameter ofneedle1000 and inner diameter ofguide tube1100 are about 2 mm. When assembled, all the parts of the tool should be free to move longitudinally, but yet be substantially coaxial.
• Referring toFIG. 19, assembledtool1900 will be described.Assembled tool1900 includesdilator tube1300,insertion tool1400,drill1500, and screw600.Insertion tool1400 has an outer diameter corresponding to the inner diameter oflumen1302 ofdilator tube1300, allowinginsertion tool1400 intodilator tube1300. In a preferred embodiment, the outer diameter ofinsertion tool1400 is about 10 mm.Insertion tool1400 has taperedprojections1406 that engagedetent indentions610 ofscrew600, allowinginsertion tool1400 to turnscrew600 and advance self-tapping right-handedthreads602 into the pars.Drill1500 hasshaft1508 with a diameter corresponding to the inner diameter oflumen1404 ininsertion tool1400 and adrill bit1510 that corresponds to the inner diameter oflumen612 inscrew600.Drill1500 can therefore be advanced intoinsertion tool1400, allowingdrill bit1510 to protrude beyondscrew600 by a distance determined by the adjustment ofdepth nut1504 andlock nut1505. When assembled, all parts of the tool should be free to move longitudinally, but should be held in a substantially coaxial orientation.
• Referring toFIG. 20, assembledtool2000 will be described.Assembled tool2000 includesdilator tube1300, lockingcap driver1600,screw600,collet700, lockingcap800,electrode500, andstylet1700. Lockingcap driver1600 has an outer diameter corresponding to the inner diameter oflumen1302 indilator tube1300.Stylet1700 is inserted intoelectrode500 and used to advanceelectrode500 through thelumen1604 of lockingcap driver1600, throughlumen804 of lockingcap800, throughlumen704 ofcollet700, and throughlumen612 ofscrew600, into the intervertebral foramen. The collet is fit within the seat of the locking cap.Driver head1606 engages lockingcap800 and allows lockingcap driver1600 to advance lockingcap800 ontoscrew600, causingcollet700 to engageelectrode500. The parts of the assembly tool should be free to move longitudinally, but be substantially coaxial.
• Referring toFIGS. 21A and 21B,method2100 is used to positionelectrode500 next to the spinal nerve root.
• Atstep2102, both anteroposterior and lateral fluoroscopy are utilized to visualize the pars interarticularis overlying the target nerve root.
• Atstep2104, a small incision is made in the skin overlying the location of the radiographic projection.
• Atstep2106, a PAK needle is assembled fromneedle1000 and guidetube1100.Rigid needle1002 is placed throughlumen1104 ofguide tube1100 by sliding it throughlumen1104 ofguide tube1100.
• Atstep2108, the assembled tool comprisingguide tube1100 andPAK needle1000 is inserted into the incision.
• Atstep2110, handle1006 is impacted with a mallet to embedawl tip1004 and thefrustoconical end1106 ofguide tube1100 into the bone of the pars interarticularis.
• Atstep2112,PAK needle1000 is then withdrawn.
• Atstep2114, guidewire1200 is inserted throughlumen1104 ofguide tube1100.
• Atstep2116,dilator tube1300 is then placed overguide tube1100 until distal tip1308 meets bone of the pars interarticularis.Semi-conical nose1306 allows passage through muscle tissue.Dilator tube1300 is inserted overguide tube1100 to create a larger opening in the soft tissue around the incision site to make room for implantingscrew600. Atstep2118,guide tube1100 is removed.
• Atstep2120,screw600 is attached toinsertion tool1400 by matchingdetent indentions610 withtapered projections1406.
• Atstep2122,screw600 andinsertion tool1400 are placed down thelumen1302 ofdilator tube1300 with thecentral lumen612 ofscrew600 passing alongguidewire1200.
• Atstep2124,insertion tool1400 is manually rotated clockwise usinghandles1402 to engage self-tapping screw right-handedthreads602 ofscrew600 into the hole in the bone made byawl tip1004 and guide tubefrustoconical end1106.Screw600 is then advanced untilflange608 meets the bone.Flange608centers dilator tube1300 as theflange608 impinges upon theinner lumen1302 ofdilator tube1300.
• Atstep2126, guidewire1200 is removed fromscrew600 anddilator tube1300.
• Atstep2128,drill1500 is then inserted throughlumen1404 ofinsertion tool1400.
• Atstep2130,drill bit1510 at a distal tip ofdrill1500 passes throughlumen612 ofscrew600.
• Atstep2132,drill1500 is rotated clockwise usinghandle1502 to drivedrill bit1510 through the bone of the pars interarticularis.
• Atstep2134,depth nut1504 is adjusted as a mechanical stop againststop1408 ofinsertion tool1400. Left-handedthread1506 allowsdepth nut1504 to be adjusted without self-advancing asdrill1500 is turned clockwise. The mechanical stop is a safety mechanism to preventdrill1500 from advancing too far intoinsertion tool1400 and to preventdrill bit1510 from damaging the spinal nerve root.Lock nut1505 is then advanced into a locking position against the depth nut.
• Atstep2136,drill bit1510 is advanced into the bone to its final depth. The final depth is determined by examination of the lateral fluoroscopic visualization, or by stimulated electromyographic (EMG) recording of the underlying nerve root. In the latter case, the cathode of a pulsed current source is attached to drill1500 which is insulated bydilator tube1300. The current source anode is attached to the body at a remote location. An example current source waveform might be a square wave with amplitude 7 mA, frequency 1 Hz,pulse duration 500 microseconds. Asdrill bit1510 breaches the underlying cortex of the pars interarticularis, the current density becomes sufficient to stimulate the underlying nerve root and elicit an electromyographic response.
• Atstep2138,drill1500 is withdrawn.
• Atstep2140,insertion tool1400 is disengaged fromscrew600 and removed, leavingdilator tube1300 in place.
• Atstep2142, bone residue is removed through irrigation and suction vialumen1302 ofdilator tube1300.
• Atstep2144,stylet1700 is inserted intostylet channel504 ofelectrode500.
• Atstep2146,electrode500 withstylet1700 is inserted through theinner lumen1604 of lockingcap driver1600.
• Atstep2148, thedistal tip502 of theelectrode500 is then sequentially inserted throughlumen804 of lockingcap800 and throughlumen704 ofcollet700.
• Atstep2150, in one embodiment,collet700 is press-fit into lockingcap800 which in turn is press-fit intodriver head1606 end of lockingcap driver1600. In embodiments where the cap and collet are integrally formed, this step is omitted.
• Atstep2152,electrode500 is withdrawn untildistal tip502 is atslot706 ofcollet700.
• Atstep2154, lockingcap driver1600 withelectrode500, lockingcap800 andcollet700 are then placed throughlumen1302 ofdilator tube1300.
• Atstep2156, under fluoroscopy theelectrode500 is advanced throughscrew600,recess606, andlumen612 to exit the under surface of the pars interarticularis through the hole that was previously drilled. The trajectory and position ofelectrode500 is then guided under fluoroscopy by advancingstylet1700 while twistinghandle1702.
• Atstep2158, theelectrode500 is optimally placed parallel to the dorsal root ganglion to facilitate bipolar stimulation.
• Optionally atstep2160, ifelectrode500 does not properly drive within the foraminal zone, thendistal tip502 is positioned at the underside of the pars interarticularis bone hole and monopolar stimulation is employed.
• Atstep2162, the threads of the locking cap are engaged with the threads of the screw. Handle1602 of lockingcap driver1600 is turned counter-clockwise to tighten the locking cap. This compresses the collet against the screw and the recess to drive the flexible arms of the collet against the electrode, which locks the electrode into position. The initial tightening prevents movement of the electrode, but is still light enough that the stylet can be removed from the electrode.
• Atstep2164, after theelectrode500 is in optimal position and lockingcap800 has been initially tightened, thestylet1700 is removed.
• Atstep2166, a final tightening of the locking cap to the screw is performed with lockingcap driver1600. The ratchet is advanced until the torque limit is triggered, thereby forcing the flexible arms of the collet inward, further into the lumen and compressing the electrode exterior. Removal ofstylet1700 allows for additional compression ofelectrode500 and further reduces the ability ofelectrode500 to slip with respect to screw600.
• Atstep2168,Locking cap driver1600 anddilator tube1300 are then removed.
• Referring toFIG. 22,method2200 allows for the electrode and screw assembly to be removed when necessary.
• Atstep2202,guide tube1100 is placed overelectrode500 and pushed through the soft tissue untildistal tip1108 ofguide tube1100 meets lockingcap800.
• Atstep2204,dilator tube1300 is then placed overguide tube1100 to engageflange608 ofscrew600.
• Atstep2206, stainless steellocking cap driver1600 is threaded overelectrode500.
• Atstep2208, lockingcap driver1600 is inserted intolumen1302 ofdilator tube1300.
• Atstep2210, lockingcap driver1600 engages hex-head locking cap800.
• Atstep2212, handle1702 of r lockingcap driver1600 is not torque-limited and is turned counter-clockwise to removescrew600 from the pars interarticularis.
• Atstep2214, lockingcap driver1600 is then extracted.
• Atstep2216,electrode500 is grasped and pulled.Electrode500 is still secured by the force of lockingcap800 and screw600 ontocollet700 that is pinchingelectrode500. Pullingelectrode500 applies a force to screw600 removing the anchoring device, lockingcap800,collet700, andelectrode500 from the implantation location.
• Atstep2218, thedilator tube1300 is then removed.
• Referring toFIG. 23, a representativelumbar vertebra2300 is shown.Anchoring device2302 is shown installed in pars interarticularis2306 as described above. The anchoring device is shown holdingelectrode2304 in place to prevent migration.
• FIG. 24 shows a cross sectional view of the pars interarticularis in which the anchoring device is installed.Electrode500 extends throughlumen804 of lockingcap800,lumen704 ofcollet700,lumen612 ofscrew600, and throughhole2402 in pars interarticularis2404 drilled bydrill1500.Electrode contacts506 are placed inside the intervertebral foramen adjacent the root ganglion. The force exerted oncollet700 by lockingcap800 forces the flexible arms of the collet into the recess, thereby causing them to move together and exert a frictional clamping force on the electrode.
• It will be appreciated by those skilled in the art that modifications can be made to the embodiments disclosed and remain within the inventive concept. Therefore, this invention is not limited to the specific embodiments disclosed, but is intended to cover changes within the scope and spirit of the claims.

Claims (22)

1. An anchoring device configured to anchor an electrode to a pars interarticularis over a dorsal root ganglion, the electrode configured to stimulate the dorsal root ganglion, the anchoring device comprising:

a screw;

a locking collet;

a recess, within the screw and shaped to fit the locking collet; and,

whereby a force pressing the locking collet into the recess causes the locking collet to impinge on the electrode.

2. The anchoring device ofclaim 1, wherein the screw further comprises:

a first set of screw threads that embed the anchoring device into the pars interarticularis; and,

a screw flange that limits a depth that the screw can be embedded into the pars interarticularis.

3. The anchoring device ofclaim 1, wherein the locking collet further comprises:

a locking cap and a removable collet adjacent the locking cap.

4. The anchoring device ofclaim 3, wherein the screw further comprises:

a second set of screw threads, matched to a set of locking cap threads in the locking cap, to secure the screw to the locking cap and to provide the force to the collet; and,

a screw lumen along a central longitudinal axis of the screw and through which the electrode is passed.

5. The anchoring device ofclaim 4, wherein the locking collet further comprises:

a collet lumen along a central axis of the collet and through with the electrode is passed; and,

a set of collet arms shaped to fit the recess of the screw and to constrict the electrode in response to the force.

6. The anchoring device ofclaim 5, wherein the locking cap further comprises:

a locking cap lumen along a central axis of the locking cap and through with the electrode is passed.

7. A system for implanting an anchoring device for an electrode into a pars interarticularis, over a dorsal root ganglion, the electrode configured to stimulate the dorsal root ganglion, the system comprising:

a guide tube having a first lumen; and,

a first configuration wherein a needle, having an awl tip, is positioned in the first lumen, and is adapted to create a hole in the pars interarticularis.

8. The system ofclaim 7 further comprising:

a second configuration wherein:

a dilator tube, having a second lumen, is positioned over the guide tube; and,

a guidewire is positioned in the first lumen.

9. The system ofclaim 8 further comprising:

a third configuration wherein:

an insertion tool, having a third lumen, is attached to the anchoring device and is positioned in the second lumen; and,

the guidewire is positioned in a fourth lumen of the anchoring device.

10. The system ofclaim 9 further comprising:

a third configuration wherein:

a drill is positioned in the third lumen and the fourth lumen.

11. The system ofclaim 9 further comprising:

a mechanical stop, at a proximal end of the insertion tool, for limiting a depth of the hole.

12. The system ofclaim 10 further comprising:

a fourth configuration wherein:

the anchoring device further comprises a screw section, a collet adjacent the screw section and a locking cap adjacent the collet;

the screw section further comprises a fifth lumen;

the collet further comprises a sixth lumen;

the locking cap further comprises a seventh lumen;

the electrode further comprises an eighth lumen;

a locking cap driver, fitted to the locking cap;

wherein a stylet is positioned in the eighth lumen; and,

the electrode is positioned in the sixth lumen and the seventh lumen.

13. The system ofclaim 12 wherein the collet is integrally formed with the screw section.

14. The system ofclaim 12 wherein the screw section further comprises:

a seating flange adapted to be positioned against the pars interarticularis.

15. The system ofclaim 12 wherein the locking cap engages the screw through a bayonet mount.

16. The system ofclaim 12 wherein the locking cap engages the screw through a first threaded connection.

17. The system ofclaim 16 wherein the screw section engages the hole with a second threaded connection.

18. The system ofclaim 17 wherein the first threaded connection is an opposite thread direction from the second threaded connection.

19. The system ofclaim 12 wherein the collet further comprises a compressible clamping section adjacent the electrode.

20. The system ofclaim 19 wherein the screw section further comprises:

a compression receiver, adjacent the compressible clamping section, for controllably deforming the compressible clamping section.

21. The system ofclaim 12 further comprising:

a fifth configuration wherein:

the locking cap driver is positioned in the second lumen.

22. The system ofclaim 21 further comprising:

a sixth configuration where:

the collet is compressed in a compression chamber of the screw section, by the locking cap, so as to impinge on the electrode.

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