Systems and methods for electrosurgery

Methods and apparatus for selectively applying electrical energy to a target location within a patient's body, particularly including tissue in the spine. In a method of the invention high frequency (RF) electrical energy is applied to one or more active electrodes on an electrosurgical probe in the presence of an electrically conductive fluid to remove, contract or otherwise modify the structure of tissue targeted for treatment. In one aspect, a dura mater and spinal cord are insulated from the electrical energy by an insulator positioned on a non-active side of the probe. In another aspect, a plasma is aggressively formed in the electrically conductive fluid by delivering a conductive fluid to a distal end portion of the probe and aspirating the fluid from a location proximal of the return electrode. In another aspect, a distal end of an electrosurgical probe having at least one electrode on a biased, curved, bent, or steerable shaft is guided or steered to a target site within an intervertebral disc having a disc defect for treatment of tissue to be treated at the target site by the selective application of electrical energy thereto.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the spine. The present invention is particularly suited for the treatment of herniated discs and other disorders of intervertebral discs. This invention also relates to treatment of an intervertebral disc by guiding an electrosurgical probe to a target site within an intervertebral disc.

The major causes of persistent, often disabling, back pain are disruption of the disc annulus, chronic inflammation of the disc (e.g., herniation), or relative instability of the vertebral bodies surrounding a given disc, such as the instability that often occurs due to a degenerative disease. Spinal discs mainly function to cushion and tether the vertebrae, providing flexibility and stability to the patient's spine. Spinal discs comprise a central hydrophilic cushion, the nucleus pulposus, surrounded by a multi-layered ligament, the annulus fibrosus. As discs degenerate, they lose their water content and height, bringing vertebrae closer together. This results in a weakening of the shock absorption properties of the disc and a narrowing of the nerve openings in the sides of the spine which may lead to pinching of the nerve root. This disc degeneration can cause back and leg pain. Weakness in the annulus fibrosus of degenerative discs, or disc injury, can allow fragments of the nucleus pulposus to migrate from within the disc into the annulus fibrosus or the spinal canal. Displaced annulus fibrosus, or protrusion of the nucleus pulposus, e.g., herniation, may impinge on spinal nerves or nerve roots. The mere proximity of the nucleus pulposus or a damaged annulus to a nerve can cause direct pressure against the nerve, resulting in pain and sensory and motor deficit.

Often, inflammation from disc herniation can be treated successfully by non-surgical means, such as rest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosteroids. In some cases, the disc tissue is irreparably damaged, thereby necessitating removal of a portion of the disc or the entire disc to eliminate the source of inflammation and pressure. In more severe cases, the adjacent vertebral bodies must be stabilized following excision of the disc material to avoid recurrence of the disabling back pain. One approach to stabilizing the vertebrae, termed spinal fusion, is to insert an interbody graft or implant into the space vacated by the degenerative disc. In this procedure, a small amount of bone may be grafted and packed into the implants. This allows the bone to grow through and around the implant, fusing the vertebral bodies and preventing reoccurrence of the symptoms.

Until recently, spinal discectomy and fusion procedures resulted in major operations and traumatic dissection of muscle and bone removal or bone fusion. To overcome the disadvantages of traditional traumatic spine surgery, minimally invasive spine surgery was developed. In endoscopic spinal procedures, the spinal canal is not violated and therefore epidural bleeding with ensuring scarring is minimized or completely avoided. In addition, the risk of instability from ligament and bone removal is generally lower in endoscopic procedures than with open discectomy. Further, more rapid rehabilitation facilitates faster recovery and return to work.

Minimally invasive techniques for the treatment of spinal diseases or disorders include chemonucleolysis, laser techniques and mechanical techniques. These procedures generally require the surgeon to form a passage or operating corridor from the external surface of the patient to the spinal disc(s) for passage of surgical instruments, implants and the like. Typically, the formation of this operating corridor requires the removal of soft tissue, muscle or other types of tissue depending on the procedure (i.e., laparascopic, thoracoscopic, arthroscopic, back, etc.). This tissue is usually removed with mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders and the like. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, these instruments might sever blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon's view of the target site.

Once the operating corridor is established, the nerve root is retracted and a portion or all of the disc is removed with mechanical instruments, such as a pituitary rongeur. In addition to the above problems with mechanical instruments, there are serious concerns because these instruments are not precise, and it is often difficult, during the procedure, to differentiate between the target disc tissue, and other structures within the spine, such as bone, cartilage, ligaments, nerves and non-target tissue. Thus, the surgeon must be extremely careful to minimize damage to the cartilage and bone within the spine, and to avoid damaging nerves, such as the spinal nerves and the dura mater surrounding the spinal cord.

Lasers were initially considered ideal for spine surgery because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, bones, ligaments and spinal nerves often lie within close proximity of the spinal disc, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.

Monopolar and bipolar radiofrequency devices have been used in limited roles in spine surgery, such as to cauterize severed vessels to improve visualization.

Monopolar devices, however, suffer from the disadvantage that the electric current will flow through undefined paths in the patient's body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient's body. In addition, since the defined path through the patient's body has a relatively high impedance (because of the large resistance or resistivity of the patient's body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.

There is a need for an apparatus or system including an electrosurgical instrument, such as a catheter or probe, wherein the instrument can be introduced into an intervertebral disc during an endoscopic procedure, and the distal portion of the instrument can be guided to a target site within the disc, wherein the target site can be treated with minimal or no damage to surrounding, non-target tissue. The instant invention provides such an electrosurgical system and methods for treating tissue by a cool ablation mechanism involving generation of a plasma in the presence of an electrically conductive fluid and molecular dissociation of tissue components, as is described in enabling detail hereinbelow.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods for selectively applying electrical energy to structures within a patient's body, such as tissue within or around the spine. The systems and methods of the present invention are particularly useful for ablation, resection, aspiration, collagen shrinkage and/or hemostasis of tissue and other body structures in open and endoscopic spine surgery.

In one aspect of the invention, a method is provided for treating discs within a patient's spine. Specifically, a method of the present invention comprises positioning at least one active electrode within close proximity of a disc in the spine (either endoscopically, or through an open procedure). The dura mater tissue that surrounds the spinal cord is insulated from the active electrode(s) and a high frequency voltage is applied between the active electrode(s) and one or more return electrodes to apply sufficient energy to the disc tissue to reduce the volume of the disc.

In one embodiment, the high frequency voltage is sufficient to ablate at least a portion of the nucleus pulposus, either the extruded portion outside the annulus or a portion or all of the nucleus pulposus within the annulus. In another embodiment, the active electrode is advanced into the annulus and sufficient high frequency voltage is applied to contract or shrink the collagen fibers within the nucleus pulposus. This causes the pulposus to shrink and withdraw from its impingement on the spinal nerve. In other embodiments, the present invention may be used to both ablate the extruded portion of the nucleus pulposus, and then to contract or shrink the inner disc material to allow repair of the annulus.

In a specific configuration, electrically conducting fluid, such as isotonic saline, is directed to the target site between the target disc tissue and the active electrode. In monopolar embodiments, the conductive fluid need only be sufficient to surround the active electrode, and to provide a layer of fluid between the electrode and the tissue. In bipolar embodiments, the conductive fluid preferably generates a current flow path between the active electrode(s) and one or more return electrodes.

In procedures requiring contraction of tissue, high frequency voltage is applied to the active electrode(s) to elevate the temperature of collagen fibers within the tissue at the target site from body temperature (about 37° C.) to a tissue temperature in the range of about 45° C. to 90° C., usually about 60° C. to 70° C., to substantially irreversibly contract these collagen fibers. In a preferred embodiment, an electrically conductive fluid is provided between the active electrode(s) and one or more return electrodes positioned on an electrosurgical probe proximal to the active electrode(s) to provide a current flow path from the active electrode(s) away from the tissue to the return electrode(s). The current flow path may be generated by directing an electrically conductive fluid along a fluid path past the return electrode and to the target site, or by locating a viscous electrically conducting fluid, such as a gel, at the target site, and submersing the active electrode(s) and the return electrode(s) within the conductive gel. The collagen fibers may be heated either by passing the electric current through the tissue to a selected depth before the current returns to the return electrode(s) and/or by heating the electrically conductive fluid and generating a jet or plume of heated fluid which is directed towards the target tissue. In the latter embodiment, the electric current may not pass into the tissue at all. In both embodiments, the heated fluid and/or the electric current elevates the temperature of the collagen sufficiently to cause hydrothermal shrinkage of the collagen fibers.

In procedures requiring ablation of tissue, the tissue is removed by molecular dissociation or disintegration processes. In these embodiments, the high frequency voltage applied to the active electrode(s) is sufficient to vaporize an electrically conductive fluid (e.g., gel or saline) between the active electrode(s) and the tissue. Within the vaporized fluid an ionized plasma is formed, and charged particles (e.g., electrons) cause the molecular breakdown or disintegration of several cell layers of the tissue. This molecular dissociation is accompanied by the volumetric removal of the tissue. This process can be precisely controlled to effect the volumetric removal of tissue as thin as 10 microns to 150 microns with minimal heating of, or damage to, surrounding or underlying tissue structures. A more complete description of this phenomenon is described in commonly assigned U.S. Pat. No. 5,683,366, the complete disclosure of which is incorporated herein by reference.

In another aspect of the invention, the present invention is useful for performing spinal surgery. The method comprises positioning an electrosurgical instrument in close proximity to an intervertebral disc. An electrically conductive fluid is delivered toward a distal tip of the electrosurgical instrument. A high frequency electrical energy is applied to the active electrode such that the conductive fluid completes a current flow path between the active electrode and a return electrode. The conductive fluid is aspirated through an aspiration lumen positioned proximal of the return electrode. Because the aspiration lumen is positioned away from the fluid delivery lumen and proximal of the return electrode, a plasma can be aggressively created and the tissue can be ablated or contracted more efficiently.

The tissue may be completely ablated in situ with the mechanisms described above, or the tissue may be partially ablated and partially resected and aspirated from this operating corridor. In a preferred configuration, the probe will include one or more aspiration electrode(s) at or near the distal opening of an aspiration lumen. In this embodiment, high frequency voltage is applied between the aspiration electrode(s) and one or more return electrodes (which can be the same or different electrodes from the ones used to ablate tissue) to partially or completely ablate the tissue fragments as they are aspirated into the lumen, thereby preventing clogging of the lumen and expediting the tissue removal process. In other configurations, the aspiration electrodes can be disposed within the aspiration lumen.

The present invention offers a number of advantages over current mechanical and laser techniques for spine surgery. The ability to precisely control the volumetric removal of tissue results in a field of tissue ablation or removal that is very defined, consistent and predictable. The shallow depth of tissue heating also helps to minimize or completely eliminate damage to healthy tissue structures, cartilage, bone and/or spinal nerves that are often adjacent the target tissue. In addition, small blood vessels within the tissue are simultaneously cauterized and sealed as the tissue is removed to continuously maintain hemostasis during the procedure. This increases the surgeon's field of view, and shortens the length of the procedure. Moreover, since the present invention allows for the use of electrically conductive fluid (contrary to prior art bipolar and monopolar electrosurgery techniques), isotonic saline may be used during the procedure. Saline is the preferred medium for irrigation because it has the same concentration as the body's fluids and, therefore, is not absorbed into the body as much as certain other fluids.

Apparatus according to the present invention generally include an electrosurgical probe or catheter having a shaft with proximal and distal ends, one or more active electrode(s) at the distal end and one or more connectors coupling the active electrode(s) to a source of high frequency electrical energy. For endoscopic spine surgery, the shaft will typically have a distal end portion sized to fit between adjacent vertebrae in the patient's spine. In some embodiments, the distal end portion can have an active side which has the active electrodes and an insulated non-active side. In a specific use, the insulator can be used to protect the dura mater (and spinal column) from iatrogenic injury.

Some embodiments of the electrosurgical probe can include a fluid delivery element for delivering electrically conductive fluid to the active electrode(s). The fluid delivery element may be located on the probe, e.g., a fluid lumen or tube, or it may be part of a separate instrument. In an exemplary embodiment, the lumen will extend through a fluid tube exterior to the probe shaft that ends adjacent the distal tip of the shaft.

Alternatively, an electrically conducting gel or spray, such as a saline electrolyte or other conductive gel, may be applied to the target site. The electrically conductive fluid will preferably generate a current flow path between the active electrode(s) and one or more return electrodes. In an exemplary embodiment, the return electrode is located on the probe and spaced a sufficient distance from the active electrode(s) to substantially avoid or minimize current shorting therebetween and to shield the return electrode from tissue at the target site.

In a specific configuration, the electrosurgical probe will include an electrically insulating electrode support member having a tissue treatment surface at the distal end of the probe. One or more active electrode(s) are coupled to, or integral with, the electrode support member such that the active electrode(s) are spaced from the return electrode. In one embodiment, the probe includes an electrode array having a plurality of electrically isolated active electrodes embedded in the electrode support member such that the active electrodes extend about 0.2 mm to about 10 mm from the tissue treatment surface of the electrode support member.

In other embodiments, the probe can include one or more lumens for aspirating the electrically conductive fluid from the target area. In an exemplary embodiment, the lumen will extend along the exterior of the probe shaft and end proximal of the return electrode. In a specific configuration, the aspiration lumen and fluid delivery lumen both extend along the exterior of the probe shaft in an annular configuration. The fluid delivery lumen will extend to the distal tip of the shaft while the aspiration lumen will extend only to a point proximal of the return electrode.

In yet another aspect, the present invention provides a method of treating an intervertebral disc having a nucleus pulposus and an annulus fibrosus. The method comprises advancing a distal end of an electrosurgical instrument into the annulus fibrosus. The distal end of the electrosurgical instrument is moved, typically biased or steered, to a curved configuration that approximates a curvature of an inner surface of the annulus fibrosus. A high frequency voltage is delivered between an active electrode and a return electrode that are positioned on the distal end of the electrosurgical instrument to treat the inner surface of the annulus fibrosus.

In yet another aspect, the present invention provides a method of treating an intervertebral disc. The method comprises positioning a distal end of an electrosurgical probe within close proximity of an outer surface of the intervertebral disc. A high frequency voltage is delivered between an active electrode and a return electrode. The high frequency voltage is sufficient to create a channel in the disc tissue. The active electrode is then advanced through the channel created in the intervertebral disc. The distal end of the electrosurgical instrument is moved to a curved configuration that approximates a curvature of an inner surface of the annulus fibrosus. A high frequency voltage is delivered between the active electrode and the return electrode to treat the inner surface of the annulus fibrosus.

In a further aspect, the present invention provides an apparatus for treating an intervertebral disc. The apparatus comprises a steerable distal end portion that is moveable to a curved configuration that approximates the curvature of the inner surface of an annulus fibrosus. At least one active electrode and a return electrode are positioned on the distal end of the apparatus. A high frequency energy source is configured to create a voltage difference between the active electrode and the return electrode. Preferably, the return electrode is positioned proximal of the active electrode so as to draw the electric current away from the target tissue.

In another aspect, the present invention provides a method of using an electrosurgical system for treating a disorder of an intervertebral disc of a patient, wherein the electrosurgical system includes a power supply coupled to at least one active electrode disposed on a shaft distal end of an electrosurgical probe. Such disc disorders include fragmentation and migration of the nucleus pulposus into the annulus fibrosus, discogenic or axial pain, one or more fissures in the annulus fibrosus, or contained herniation (a protrusion of the nucleus pulposus which is contained within the annulus fibrosus) of the disc. The method includes inserting the shaft distal end within the intervertebral disc such that the active electrode is in the vicinity of the tissue targeted for treatment (fissure, contained herniation, etc.), and thereafter applying a high frequency voltage between the active electrode and a return electrode sufficient to ablate target tissue. In preferred embodiments, the voltage generates a plasma in the vicinity of the target site and tissue at the target site is ablated by the molecular dissociation of disc tissue components to form low molecular weight ablation by-products, the latter being readily aspirated from the target site or tissue being treated.

In one embodiment, the shaft may be guided by a combination of axial translation of the shaft and rotation of the shaft about its longitudinal axis. In one aspect of the invention, the shaft has a pre-defined curvature, both before and after the shaft has been guided to the vicinity of the contained herniation. The pre-defined curvature may include a first and a second curve in the shaft, the second curve being proximal to the first curve.

In another aspect of the invention, the shaft may lack a pre-defined curvature, and may be bent to a suitable conformation prior to a particular surgical procedure. In yet another aspect of the invention, the shaft may lack a pre-defined curvature, and the shaft distal end may be steered during a surgical procedure so as to adopt a suitable conformation, thereby allowing the shaft distal end to be guided to a target site within an intervertebral disc.

By applying a high frequency voltage between the active electrode and the return electrode, disc tissue at the target site undergoes molecular dissociation. In one embodiment, the active electrode includes an electrode head having an apical spike and a cusp, wherein the electrode head is adapted for providing a high current density in the vicinity of the electrode head when a high frequency voltage is applied between the active electrode and the return electrode. The method may be conveniently performed percutaneously, and one or more stages in the treatment or procedure may be performed under fluoroscopy to allow visualization of the shaft within the disc to be treated.

Further aspects, features, and advantages of the present invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention provides systems and methods for selectively applying electrical energy to a target location within or on a patient's body, particularly including tissue or other body structures in the spine. These procedures include laminectomy/disketomy procedures for treating herniated disks, decompressive laminectomy for stenosis in the lumbosacral and cervical spine, medial facetectomy, posterior lumbosacral and cervical spine fusions, treatment of scoliosis associated with vertebral disease, foraminotomies to remove the roof of the intervertebral foramina to relieve nerve root compression and cervical and lumbar diskectomies, shrinkage of vertebral support tissue, and the like. These procedures may be performed through open procedures, or using minimally invasive techniques, such as thoracoscopy, arthroscopy, laparascopy or the like.

In the present invention, high frequency (RF) electrical energy is applied to one or more active electrodes in the presence of electrically conductive fluid to remove and/or modify the structure of tissue structures. Depending on the specific procedure, the present invention may be used to: (1) volumetrically remove tissue, bone, ligament or cartilage (i.e., ablate or effect molecular dissociation of the body structure); (2) cut or resect tissue or other body structures; (3) shrink or contract collagen connective tissue; and/or (4) coagulate severed blood vessels.

In some procedures, e.g., shrinkage of nucleus pulposus in herniated discs, it is desired to shrink or contract collagen connective tissue at the target site. In these procedures, the RF energy heats the tissue directly by virtue of the electrical current flow therethrough, and/or indirectly through the exposure of the tissue to fluid heated by RF energy, to elevate the tissue temperature from normal body temperatures (e.g., 37° C.) to temperatures in the range of 45° C. to 90° C., preferably in the range from about 60° C. to 70° C. Thermal shrinkage of collagen fibers occurs within a small temperature range which, for mammalian collagen is in the range from 60° C. to 70° C. (Deak, G., et al., “The Thermal Shrinkage Process of Collagen Fibres as Revealed by Polarization Optical Analysis of Topooptical Staining Reactions,” Acta Morphologica Acad. Sci. of Hungary, Vol. 15(2), pp 195–208, 1967). Collagen fibers typically undergo thermal shrinkage in the range of 60° C. to about 70° C. Previously reported research has attributed thermal shrinkage of collagen to the cleaving of the internal stabilizing cross-linkages within the collagen matrix (Deak, ibid). It has also been reported that when the collagen temperature is increased above 70° C., the collagen matrix begins to relax again and the shrinkage effect is reversed resulting in no net shrinkage (Allain, J. C., et al., “Isometric Tensions Developed During the Hydrothermal Swelling of Rat Skin,” Connective Tissue Research, Vol. 7, pp. 127–133, 1980). Consequently, the controlled heating of tissue to a precise depth is critical to the achievement of therapeutic collagen shrinkage. A more detailed description of collagen shrinkage can be found in U.S. patent application Ser. No. 08/942,580, filed Oct. 2, 1997, entitled “Systems and Methods for Electrosurgical Tissue Contraction,” previously incorporated herein by reference.

The preferred depth of heating to effect the shrinkage of collagen in the heated region (i.e., the depth to which the tissue is elevated to temperatures between 60° C. to 70° C.) generally depends on (1) the thickness of the tissue, (2) the location of nearby structures (e.g., nerves) that should not be exposed to damaging temperatures, and/or (3) the volume of contraction desired to relieve pressure on the spinal nerve. The depth of heating is usually in the range from 0 to 3.5 mm. In the case of collagen within the nucleus pulposus, the depth of heating is preferably in the range from about 0 to about 2.0 mm.

In another method of the present invention, the tissue structures are volumetrically removed or ablated. In this procedure, a high frequency voltage difference is applied between one or more active electrode(s) and one or more return electrodes to develop high electric field intensities in the vicinity of the target tissue site. The high electric field intensities lead to electric field induced molecular breakdown of target tissue through molecular dissociation (rather than thermal evaporation or carbonization). Applicant believes that the tissue structure is volumetrically removed through molecular disintegration of larger organic molecules into smaller molecules and/or atoms, such as hydrogen, oxides of carbon, hydrocarbons and nitrogen compounds. This molecular disintegration completely removes the tissue structure, as opposed to dehydrating the tissue material by the removal of liquid within the cells of the tissue and extracellular fluids, as is typically the case with electrosurgical desiccation and vaporization.

The high electric field intensities may be generated by applying a high frequency voltage that is sufficient to vaporize an electrically conductive fluid over at least a portion of the active electrode(s) in the region between the distal tip of the active electrode(s) and the target tissue. The electrically conductive fluid may be a gas or liquid, such as isotonic saline, delivered to the target site, or a viscous fluid, such as a gel, that is located at the target site. In the latter embodiment, the active electrode(s) are submersed in the electrically conductive gel during the surgical procedure. Since the vapor layer or vaporized region has a relatively high electrical impedance, it minimizes the current flow into the electrically conducting fluid. This ionization, under optimal conditions, induces the discharge of energetic electrons and photons from the vapor layer and to the surface of the target tissue. A more detailed description of this cold ablation phenomenon, termed Coblation®, can be found in commonly assigned U.S. Pat. No. 5,683,366 the complete disclosure of which is incorporated herein by reference.

The present invention applies high frequency (RF) electrical energy in an electrically conductive fluid environment to remove (i.e., resect, cut or ablate) or contract a tissue structure, and to seal transected vessels within the region of the target tissue. The present invention is particularly useful for sealing larger arterial vessels, e.g., having a diameter on the order of 1 mm or greater. In some embodiments, a high frequency power supply is provided having an ablation mode, wherein a first voltage is applied to an active electrode sufficient to effect molecular dissociation or disintegration of the tissue, and a coagulation mode, wherein a second, lower voltage is applied to an active electrode (either the same or a different electrode) sufficient to achieve hemostasis of severed vessels within the tissue. In other embodiments, an electrosurgical probe is provided having one or more coagulation electrode(s) configured for sealing a severed vessel, such as an arterial vessel, and one or more active electrodes configured for either contracting the collagen fibers within the tissue or removing (ablating) the tissue, e.g., by applying sufficient energy to the tissue to effect molecular dissociation. In the latter embodiments, the coagulation electrode(s) may be configured such that a single voltage can be applied to coagulate with the coagulation electrode(s), and to ablate or contract with the active electrode(s). In other embodiments, the power supply and electrosurgical probe are configured such that the coagulation electrode is used when the power supply is in the coagulation mode (low voltage), and the active electrode(s) are used when the power supply is in the ablation mode (higher voltage).

In the method of the present invention, one or more active electrodes are brought into close proximity to tissue at a target site, and the power supply is activated in the ablation mode such that sufficient voltage is applied between the active electrodes and the return electrode to volumetrically remove the tissue through molecular dissociation, as described below. During this process, some vessels within the tissue may be severed. Smaller vessels will be automatically sealed with the system and method of the present invention. Larger vessels, and those with a higher flow rate, such as arterial vessels, may not be automatically sealed in the ablation mode. In these cases, the severed vessels may be sealed by activating a control (e.g., a foot pedal) to reduce the voltage of the power supply into the coagulation mode. In this mode, the active electrodes may be pressed against the severed vessel to provide sealing and/or coagulation of the vessel. Alternatively, a coagulation electrode located on the same or a different probe may be pressed against the severed vessel. Once the vessel is adequately sealed, the surgeon activates a control (e.g., another foot pedal) to increase the voltage of the power supply back into the ablation mode.

The present invention is particularly useful for removing or ablating tissue around nerves, such as spinal or cranial nerves, e.g., the spinal cord and the surrounding dura mater. One of the significant drawbacks with the prior art cutters, graspers, and lasers is that these devices do not differentiate between the target tissue and the surrounding nerves or bone. Therefore, the surgeon must be extremely careful during these procedures to avoid damage to the bone or nerves within and around the spinal cord. In the present invention, the Coblation® process for removing tissue results in extremely small depths of collateral tissue damage as discussed above. This allows the surgeon to remove tissue close to a nerve without causing collateral damage to the nerve fibers.

In addition to the generally precise nature of the novel mechanisms of the present invention, applicant has discovered an additional method of ensuring that adjacent nerves are not damaged during tissue removal. According to the present invention, systems and methods are provided for distinguishing between the fatty tissue immediately surrounding nerve fibers and the normal tissue that is to be removed during the procedure. Peripheral nerves usually comprise a connective tissue sheath, or epineurium, enclosing the bundles of nerve fibers to protect these nerve fibers. The outer protective tissue sheath or epineurium typically comprises a fatty tissue (e.g., adipose tissue) having substantially different electrical properties than the normal target tissue, such as the disc and other surrounding tissue that are, for example, removed from the spine during spinal procedures. The system of the present invention measures the electrical properties of the tissue at the tip of the probe with one or more active electrode(s). These electrical properties may include electrical conductivity at one, several or a range of frequencies (e.g., in the range from 1 kHz to 100 MHz), dielectric constant, capacitance or combinations of these. In this embodiment, an audible signal may be produced when the sensing electrode(s) at the tip of the probe detects the fatty tissue surrounding a nerve, or direct feedback control can be provided to only supply power to the active electrode(s) either individually or to the complete array of electrodes, if and when the tissue encountered at the tip or working end of the probe is normal (e.g., non-fatty) tissue based on the measured electrical properties.

In one embodiment, the current limiting elements (discussed in detail below) are configured such that the active electrodes, will shut down or turn off when the electrical impedance reaches a threshold level. When this threshold level is set to the impedance of the fatty tissue surrounding nerves, the active electrodes will shut off whenever they come in contact with, or in close proximity to, nerves. Meanwhile, the other active electrodes, which are in contact with or in close proximity to target tissue, will continue to conduct electric current to the return electrode. This selective ablation or removal of lower impedance tissue in combination with the Coblation® mechanism of the present invention allows the surgeon to precisely remove tissue around nerves or bone.

In addition to the above, applicant has discovered that the Coblation® mechanism of the present invention can be manipulated to ablate or remove certain tissue structures, while having little effect on other tissue structures. As discussed above, the present invention uses a technique of vaporizing electrically conductive fluid to form a plasma layer or pocket around the active electrode(s), and then inducing the discharge of energy from this plasma or vapor layer to break the molecular bonds of the tissue structure. Based on initial experiments, applicants believe that the free electrons within the ionized vapor layer are accelerated in the high electric fields near the electrode tip(s). When the density of the vapor layer (or within a bubble formed in the electrically conductive liquid) becomes sufficiently low (i.e., less than approximately 1020atoms/cm3for aqueous solutions), the electron mean free path increases to enable subsequently injected electrons to cause impact ionization within these regions of low density (i.e., vapor layers or bubbles). Energy evolved by the energetic electrons (e.g., 4 eV to 5 eV) can subsequently bombard a molecule and break its bonds, dissociating a molecule into free radicals, which then combine into final gaseous or liquid species.

The energy evolved by the energetic electrons may be varied by adjusting a variety of factors, such as: the number of active electrodes; electrode size and spacing; electrode surface area; asperities and sharp edges on the electrode surfaces; electrode materials; applied voltage and power; current limiting means, such as inductors; electrical conductivity of the fluid in contact with the electrodes; density of the fluid; and other factors. Accordingly, these factors can be manipulated to control the energy level of the excited electrons. Since different tissue structures have different molecular bonds, the present invention can be configured to break the molecular bonds of certain tissue, while having too low an energy to break the molecular bonds of other tissue. For example, fatty tissue, (e.g., adipose tissue) has double bonds that require a substantially higher energy level than 4 eV to 5 eV to break (typically on the order of about 8 eV). Accordingly, the present invention in its current configuration generally does not ablate or remove such fatty tissue. However, the present invention may be used to effectively ablate cells to release the inner fat content in a liquid form. Of course, factors may be changed such that these double bonds can be broken (e.g., increasing the voltage or changing the electrode configuration to increase the current density at the electrode tips).

The electrosurgical probe or catheter will comprise a shaft or a handpiece having a proximal end and a distal end which supports one or more active electrode(s). The shaft or handpiece may assume a wide variety of configurations, with the primary purpose being to mechanically support the active electrode and permit the treating physician to manipulate the electrode from a proximal end of the shaft. The shaft may be rigid or flexible, with flexible shafts optionally being combined with a generally rigid external tube for mechanical support. Flexible shafts may be combined with pull wires, shape memory actuators, and other known mechanisms for effecting selective deflection of the distal end of the shaft to facilitate positioning of the electrode(s) or electrode array. The shaft will usually include a plurality of wires or other conductive elements running axially therethrough to permit connection of the electrode array to a connector at the proximal end of the shaft.

For endoscopic procedures within the spine, the shaft will have a suitable diameter and length to allow the surgeon to reach the target site (e.g., a disc) by delivering the shaft through the thoracic cavity, the abdomen or the like. Thus, the shaft will usually have a length in the range of about 5.0 cm to 30.0 cm, and a diameter in the range of about 0.2 mm to about 20 mm. Alternatively, the shaft may be delivered directly through the patient's back in a posterior approach, which would considerably reduce the required length of the shaft. In any of these embodiments, the shaft may also be introduced through rigid or flexible endoscopes. Specific shaft designs will be described in detail in connection with the drawings hereinafter.

In one embodiment, the probe may comprise a long, thin needle (e.g., on the order of about 1 mm in diameter or less) that can be percutaneously introduced through the patient's back directly into the spine (seeFIGS. 34–36). The needle will include one or more active electrode(s) for applying electrical energy to tissues within the spine. The needle may include one or more return electrodes, or the return electrode may be positioned on the patient's back, as a dispersive pad. In either embodiment, sufficient electrical energy is applied through the needle to the active electrode(s) to either shrink the collagen fibers within the intervertebral disk, or to ablate tissue within the disk.

The current flow path between the active electrode(s) and the return electrode(s) may be generated by submerging the tissue site in an electrically conductive fluid (e.g., within a liquid or a viscous fluid, such as an electrically conductive gel) or by directing an electrically conductive fluid along a fluid path to the target site (i.e., a liquid, such as isotonic saline, or a gas, such as argon). This latter method is particularly effective in a dry environment (i.e., the tissue is not submerged in fluid) because the electrically conductive fluid provides a suitable current flow path from the active electrode to the return electrode. A more complete description of an exemplary method of directing electrically conductive fluid between the active and return electrodes is described in U.S. Pat. No. 5,697,536, previously incorporated herein by reference.

The electrically conductive fluid should have a threshold conductivity to provide a suitable conductive path between the return electrode(s) and the active electrode(s). The electrical conductivity of the fluid (in units of millisiemens per centimeter or mS/cm) will usually be greater than 0.2 mS/cm, preferably will be greater than 2 mS/cm, and more preferably greater than 10 mS/cm. In an exemplary embodiment, the electrically conductive fluid is isotonic saline, which has a conductivity of about 17 mS/cm. Alternatively, the fluid may be an electrically conductive gel or spray, such as a saline electrolyte gel, a conductive ECG spray, an electrode conductivity gel, an ultrasound transmission or scanning gel, or the like. Suitable gels or sprays are commercially available from Graham-Field, Inc of Hauppauge, N.Y.

In some procedures it may also be necessary to retrieve or aspirate the electrically conductive fluid after it has been directed to the target site. In addition, it may be desirable to aspirate small pieces of tissue that are not completely disintegrated by the high frequency energy, or other fluids at the target site, such as blood, mucus, the gaseous products of ablation, etc. Accordingly, the system of the present invention will usually include a suction lumen in the probe, or on another instrument, for aspirating fluids from the target site. In addition, the invention may include one or more aspiration electrode(s) coupled to the distal end of the suction lumen for ablating, or at least reducing the volume of, non-ablated tissue fragments that are aspirated into the lumen. The aspiration electrode(s) function mainly to inhibit clogging of the lumen that may otherwise occur as larger tissue fragments are drawn therein. The aspiration electrode(s) may be different from the ablation active electrode(s), or the same electrode(s) may serve both functions. A more complete description of probes incorporating aspiration electrode(s) can be found in commonly assigned, co-pending patent application Ser. No. 09/010,382 filed Jan. 21, 1998, the complete disclosure of which is incorporated herein by reference.

The present invention may use a single active electrode or an electrode array distributed over a contact surface of a probe. In the latter embodiment, the electrode array usually includes a plurality of independently current-limited and/or power-controlled active electrodes to apply electrical energy selectively to the target tissue while limiting the unwanted application of electrical energy to the surrounding tissue and environment resulting from power dissipation into surrounding electrically conductive liquids, such as blood, normal saline, electrically conductive gel and the like. The active electrodes may be independently current-limited by isolating the electrodes from each other and connecting each electrode to a separate power source that is isolated from the other active electrodes. Alternatively, the active electrodes may be connected to each other at either the proximal or distal ends of the probe to form a single wire that couples to a power source.

In some embodiments, the active electrode(s) have an active portion or surface with surface geometries shaped to promote the electric field intensity and associated current density along the leading edges of the electrodes. Suitable surface geometries may be obtained by creating electrode shapes that include preferential sharp edges, or by creating asperities or other surface roughness on the active surface(s) of the electrodes. Electrode shapes according to the present invention can include the use of formed wire (e.g., by drawing round wire through a shaping die) to form electrodes with a variety of cross-sectional shapes, such as square, rectangular, L or V shaped, or the like. Electrode edges may also be created by removing a portion of the elongate metal electrode to reshape the cross-section. For example, material can be ground along the length of a round or hollow wire electrode to form D or C shaped wires, respectively, with edges facing in the cutting direction. Alternatively, material can be removed at closely spaced intervals along the electrode length to form transverse grooves, slots, threads or the like along the electrodes.

Additionally or alternatively, the active electrode surface(s) may be modified through chemical, electrochemical or abrasive methods to create a multiplicity of surface asperities on the electrode surface. These surface asperities will promote high electric field intensities between the active electrode surface(s) and the target tissue to facilitate ablation or cutting of the tissue. For example, surface asperities may be created by etching the active electrodes with etchants having a pH less than 7.0 or by using a high velocity stream of abrasive particles (e.g., grit blasting) to create asperities on the surface of an elongated electrode.

The active electrode(s) are typically mounted in or on an electrically insulating electrode support that extends from the electrosurgical probe. In some embodiments, the electrode support comprises a plurality of wafer layers bonded together, e.g., by a glass adhesive or the like, or a single wafer. The wafer layer(s) have conductive strips printed thereon to form the active electrode(s) and the return electrode(s). In one embodiment, the proximal end of the wafer layer(s) will have a number of holes extending from the conductor strips to an exposed surface of the wafer layers for connection to electrical conductor lead traces in the electrosurgical probe or handpiece. The wafer layers preferably comprise a ceramic material, such as alumina, and the electrode will preferably comprise a metallic material, such as gold, copper, platinum, palladium, tungsten, silver or the like. Suitable multilayer ceramic electrodes are commercially available from e.g., VisPro Corporation of Beaverton, Oreg.

In one configuration, each individual active electrode in the electrode array is electrically insulated from all other active electrodes in the array within the probe and is connected to a power source which is isolated from each of the other active electrodes in the array or to circuitry which limits or interrupts current flow to the active electrode when low resistivity material (e.g., blood, electrically conductive saline irrigant or electrically conductive gel) causes a lower impedance path between the return electrode and the individual active electrode. The isolated power sources for each individual active electrode may be separate power supply circuits having internal impedance characteristics which limit power to the associated active electrode when a low impedance return path is encountered. By way of example, the isolated power source may be a user-selectable constant current source. In this embodiment, lower impedance paths will automatically result in lower resistive heating levels since the heating is proportional to the square of the operating current times the impedance. Alternatively, a single power source may be connected to each of the active electrodes through independently actuatable switches, or by independent current limiting elements, such as inductors, capacitors, resistors and/or combinations thereof. The current limiting elements may be provided in the probe, connectors, cable, controller or along the conductive path from the controller to the distal tip of the probe. Alternatively, the resistance and/or capacitance may occur on the surface of the active electrode(s) due to oxide layers which form selected active electrodes (e.g., titanium or a resistive coating on the surface of metal, such as platinum).

The tip region of the probe may comprise many independent active electrodes designed to deliver electrical energy in the vicinity of the tip. The selective application of electrical energy to the conductive fluid is achieved by connecting each individual active electrode and the return electrode to a power source having independently controlled or current limited channels. The return electrode(s) may comprise a single tubular member of conductive material proximal to the electrode array at the tip which also serves as a conduit for the supply of the electrically conductive fluid between the active and return electrodes. Alternatively, the probe may comprise an array of return electrodes at the distal tip of the probe (together with the active electrodes) to maintain the electric current at the tip. The application of high frequency voltage between the return electrode(s) and the electrode array results in the generation of high electric field intensities at the distal tips of the active electrodes with conduction of high frequency current from each individual active electrode to the return electrode. The current flow from each individual active electrode to the return electrode(s) is controlled by either active or passive means, or a combination thereof, to deliver electrical energy to the surrounding conductive fluid while minimizing energy delivery to surrounding (non-target) tissue.

The application of a high frequency voltage between the return electrode(s) and the active electrode(s) for appropriate time intervals effects cutting, removing, ablating, shaping, contracting or otherwise modifying the target tissue. The tissue volume over which energy is dissipated (i.e., a high current density exists) may be precisely controlled, for example, by the use of a multiplicity of small active electrodes whose effective diameters or principal dimensions range from about 5 mm to 0.01 mm, preferably from about 2 mm to 0.05 mm, and more preferably from about 1 mm to 0.1 mm. Electrode areas for both circular and non-circular electrodes will have a contact area (per active electrode) below 25 mm2, preferably being in the range from 0.0001 mm2to 1 mm2, and more preferably from 0.005 mm2to 0.5 mm2. The circumscribed area of the electrode array is in the range from 0.25 mm2to 200 mm2, preferably from 0.5 mm2to 100 m2, and will usually include at least two isolated active electrodes, preferably at least five active electrodes, often greater than ten active electrodes and even fifty or more active electrodes, disposed over the distal contact surfaces on the shaft. The use of small diameter active electrodes increases the electric field intensity and reduces the extent or depth of tissue heating as a consequence of the divergence of current flux lines which emanate from the exposed surface of each active electrode.

The area of the tissue treatment surface can vary widely, and the tissue treatment surface can assume a variety of geometries, with particular areas and geometries being selected for specific applications. Active electrode surfaces can have areas in the range from 0.25 mm2to 75 mm2, usually being from about 0.5 mm2to 40 mm2. The geometries can be planar, concave, convex, hemispherical, conical, linear “in-line” array or virtually any other regular or irregular shape. Most commonly, the active electrode(s) or active electrode(s) will be formed at the distal tip of the electrosurgical probe shaft, frequently being planar, disk-shaped, or hemispherical surfaces for use in reshaping procedures or being linear arrays for use in cutting. Alternatively or additionally, the active electrode(s) may be formed on lateral surfaces of the electrosurgical probe shaft (e.g., in the manner of a spatula), facilitating access to certain body structures in endoscopic procedures.

It should be clearly understood that the invention is not limited to electrically isolated active electrodes, or even to a plurality of active electrodes. For example, the array of active electrodes may be connected to a single lead that extends through the probe shaft to a power source of high frequency current. Alternatively, the probe may incorporate a single electrode that extends directly through the probe shaft or is connected to a single lead that extends to the power source. The active electrode may have a ball shape (e.g., for tissue vaporization and desiccation), a twizzle shape (for vaporization and needle-like cutting), a spring shape (for rapid tissue debulking and desiccation), a twisted metal shape, an annular or solid tube shape or the like. Alternatively, the electrode may comprise a plurality of filaments, a rigid or flexible brush electrode (for debulking a tumor, such as a fibroid, bladder tumor or a prostate adenoma), a side-effect brush electrode on a lateral surface of the shaft, a coiled electrode or the like. In one embodiment, the probe comprises a single active electrode that extends from an insulating member, e.g., ceramic, at the distal end of the probe. The insulating member is preferably a tubular structure that separates the active electrode from a tubular or annular return electrode positioned proximal to the insulating member and the active electrode.

In some embodiments, the electrode support and the fluid outlet may be recessed from an outer surface of the probe or handpiece to confine the electrically conductive fluid to the region immediately surrounding the electrode support. In addition, the shaft may be shaped so as to form a cavity around the electrode support and the fluid outlet. This helps to assure that the electrically conductive fluid will remain in contact with the active electrode(s) and the return electrode(s) to maintain the conductive path therebetween. In addition, this will help to maintain a vapor or plasma layer between the active electrode(s) and the tissue at the treatment site throughout the procedure, which reduces the thermal damage that might otherwise occur if the vapor layer were extinguished due to a lack of conductive fluid. Provision of the electrically conductive fluid around the target site also helps to maintain the tissue temperature at desired levels.

The voltage applied between the return electrode(s) and the electrode array will be at high or radio frequency, typically between about 5 kHz and 20 MHz, usually being between about 30 kHz and 2.5 MHz, preferably being between about 50 kHz and 500 kHz, more preferably less than 350 kHz, and most preferably between about 100 kHz and 200 kHz. The RMS (root mean square) voltage applied will usually be in the range from about 5 volts to 1000 volts, preferably being in the range from about 10 volts to 500 volts depending on the active electrode size, the operating frequency and the operation mode of the particular procedure or desired effect on the tissue (i.e., contraction, coagulation or ablation). Typically, the peak-to-peak voltage will be in the range of 10 volts to 2000 volts, preferably in the range of 20 volts to 1200 volts and more preferably in the range of about 40 volts to 800 volts (again, depending on the electrode size, the operating frequency and the operation mode).

As discussed above, the voltage is usually delivered in a series of voltage pulses or alternating current of time varying voltage amplitude with a sufficiently high frequency (e.g., on the order of 5 kHz to 20 MHz) such that the voltage is effectively applied continuously (as compared with e.g., lasers claiming small depths of necrosis, which are generally pulsed about 10 Hz to 20 Hz). In addition, the duty cycle (i.e., cumulative time in any one-second interval that energy is applied) is on the order of about 50% for the present invention, as compared with pulsed lasers which typically have a duty cycle of about 0.0001%.

The preferred power source of the present invention delivers a high frequency current selectable to generate average power levels ranging from several milliwatts to tens of watts per electrode, depending on the volume of target tissue being heated, and/or the maximum allowed temperature selected for the probe tip. The power source allows the user to select the voltage level according to the specific requirements of a particular spine procedure, arthroscopic surgery, dermatological procedure, ophthalmic procedures, FESS procedure, open surgery or other endoscopic surgery procedure. A description of a suitable power source can be found in U.S. Provisional Patent Application No. 60/062,997 entitled “Systems and Methods for Electrosurgical Tissue and Fluid Coagulation,” filed Oct. 23, 1997, the complete disclosure of which is incorporated herein by reference.

The power source may be current limited or otherwise controlled so that undesired heating of the target tissue or surrounding (non-target) tissue does not occur. In a presently preferred embodiment of the present invention, current limiting inductors are placed in series with each independent active electrode, where the inductance of the inductor is in the range of 10 uH to 50,000 uH, depending on the electrical properties of the target tissue, the desired tissue heating rate and the operating frequency. Alternatively, capacitor-inductor (LC) circuit structures may be employed, as described previously in copending PCT application No. PCT/US94/05168, the complete disclosure of which is incorporated herein by reference. Additionally, current limiting resistors may be selected. Preferably, these resistors will have a large positive temperature coefficient of resistance so that, as the current level begins to rise for any individual active electrode in contact with a low resistance medium (e.g., saline irrigant or conductive gel), the resistance of the current limiting resistor increases significantly, thereby minimizing the power delivery from the active electrode into the low resistance medium (e.g., saline irrigant, a conductive gel, or natural body fluids such as blood).

Referring toFIG. 1, an exemplary electrosurgical system11for treatment of tissue in the spine will now be described in detail. Electrosurgical system11generally comprises an electrosurgical handpiece or probe10connected to a power supply28for providing high frequency voltage to a target site, and a fluid source21for supplying electrically conductive fluid50to probe10. In addition, electrosurgical system11may include an endoscope (not shown) with a fiber optic head light for viewing the surgical site, particularly in endoscopic spine procedures. The endoscope may be integral with probe10, or it may be part of a separate instrument. The system11may also include a vacuum source (not shown) for coupling to a suction lumen or tube211(seeFIG. 2) in the probe10for aspirating the target site.

As shown, probe10generally includes a proximal handle19and an elongate shaft18having an array12of active electrodes58at its distal end. A connecting cable34has a connector26for electrically coupling the active electrodes58to power supply28. The active electrodes58are electrically isolated from each other and each of the electrodes58is connected to an active or passive control network within power supply28by means of a plurality of individually insulated conductors (not shown). A fluid supply tube15is connected to a fluid tube14of probe10for supplying electrically conductive fluid50to the target site.

Power supply28has an operator controllable voltage level adjustment30to change the applied voltage level, which is observable at a voltage level display32. Power supply28also includes first, second and third foot pedals37,38,39and a cable36which is removably coupled to power supply28. The foot pedals37,38,39allow the surgeon to remotely adjust the energy level applied to active electrodes58. In an exemplary embodiment, first foot pedal37is used to place the power supply into the “ablation” mode and second foot pedal38places power supply28into the “coagulation” mode. The third foot pedal39allows the user to adjust the voltage level within the “ablation” mode. In the ablation mode, a sufficient voltage is applied to the active electrodes to establish the requisite conditions for molecular dissociation of the tissue, as described elsewhere herein. As discussed above, the requisite voltage level for ablation will vary depending on the number, size, shape and spacing of the electrodes, the distance to which the electrodes extend from the support member, etc. Once the surgeon places the power supply in the “ablation” mode, voltage level adjustment30or third foot pedal39may be used to adjust the voltage level to adjust the degree or aggressiveness of the ablation.

Of course, it will be recognized that the voltage and modality of the power supply may be controlled by other input devices. However, applicant has found that foot pedals are convenient methods of controlling the power supply while manipulating the probe during a surgical procedure.

In the coagulation mode, the power supply28applies a low enough voltage to the active electrodes (or the coagulation electrode) to avoid vaporization of the electrically conductive fluid and subsequent molecular dissociation of the tissue. The surgeon may automatically toggle the power supply between the ablation and coagulation modes by alternatively stepping on foot pedals37,38, respectively. This allows the surgeon to quickly move between coagulation and ablation in situ, without having to remove his/her concentration from the surgical field or without having to request an assistant to switch the power supply. By way of example, as the surgeon is sculpting or ablating soft tissue in the ablation mode, the probe typically will simultaneously seal and/or coagulate any small severed vessels within the tissue. However, larger vessels, or vessels with high fluid pressures (e.g., arterial vessels) may not be sealed in the ablation mode. Accordingly, the surgeon can simply step on foot pedal38, automatically lowering the voltage level below the threshold level for ablation, and apply sufficient pressure onto the severed vessel for a sufficient period of time to seal and/or coagulate the vessel. After this is completed, the surgeon may quickly move back into the ablation mode by stepping on foot pedal37. A specific design of a suitable power supply for use with the present invention can be found in U.S. Provisional Patent Application No. 60/062,997, entitled “Systems and Methods for Electrosurgical Tissue and Fluid Coagulation,” filed Oct. 23, 1997, which is incorporated herein by reference.

FIGS. 2–5illustrate an exemplary electrosurgical probe20constructed according to the principles of the present invention. As shown inFIG. 2, probe20generally includes an elongated shaft100which may be flexible or rigid, a handle204coupled to the proximal end of shaft100and an electrode support member102coupled to the distal end of shaft100. Shaft100preferably comprises a plastic material that is easily molded into the shape shown inFIG. 2. In an alternative embodiment (not shown), shaft100comprises an electrically conducting material, usually metal, which is selected from the group comprising tungsten, stainless steel alloys, platinum or its alloys, titanium or its alloys, molybdenum or its alloys, and nickel or its alloys. In this embodiment, shaft100includes an electrically insulating jacket108, which is typically formed as one or more electrically insulating sheaths or coatings, such as polytetrafluoroethylene, polyimide, and the like. The provision of electrically insulating jacket108over the shaft prevents direct electrical contact between these metal elements and any adjacent body structure or the surgeon. Such direct electrical contact between a body structure (e.g., tendon) and an exposed electrode could result in unwanted heating of the structure at the point of contact causing necrosis.

Handle204typically comprises a plastic material that is easily molded into a suitable shape for handling by the surgeon. Handle204defines an inner cavity (not shown) that houses the electrical connections250(FIG. 5), and provides a suitable interface for connection to an electrical connecting cable22(seeFIG. 1). Electrode support member102extends from the distal end of shaft100(usually about 1 mm to 20 mm), and provides support for a plurality of electrically isolated active electrodes104(seeFIG. 4). As shown inFIG. 2, a fluid tube233extends through an opening in handle204, and includes a connector235for connection to a fluid supply source, for supplying electrically conductive fluid to the target site. Fluid tube233is coupled to a distal fluid tube239that extends along the outer surface of shaft100to an opening237at the distal end of the probe20, as discussed in detail below. Of course, the invention is not limited to this configuration. For example, fluid tube233may extend through a single lumen (not shown) in shaft100, or it may be coupled to a plurality of lumens (also not shown) that extend through shaft100to a plurality of openings at its distal end. Probe20may also include a valve17(FIG. 1) or equivalent structure for controlling the flow rate of the electrically conductive fluid to the target site.

As shown inFIGS. 3 and 4, electrode support member102has a substantially planar tissue treatment surface212and comprises a suitable insulating material (e.g., ceramic or glass material, such as alumina, zirconia and the like) which could be formed at the time of manufacture in a flat, hemispherical or other shape according to the requirements of a particular procedure. The preferred support member material is alumina, available from Kyocera Industrial Ceramics Corporation, Elkgrove, Ill., because of its high thermal conductivity, good electrically insulative properties, high flexural modulus, resistance to carbon tracking, biocompatibility, and high melting point. The support member102is adhesively joined to a tubular support member (not shown) that extends most or all of the distance between support member102and the proximal end of probe20. The tubular member preferably comprises an electrically insulating material, such as an epoxy or silicone-based material.

In a preferred construction technique, active electrodes104extend through pre-formed openings in the support member102so that they protrude above tissue treatment surface212by the desired distance. The electrodes104are then bonded to the tissue treatment surface212of support member102, typically by an inorganic sealing material. The sealing material is selected to provide effective electrical insulation, and good adhesion to both the alumina member102and the platinum or titanium active electrodes104. The sealing material additionally should have a compatible thermal expansion coefficient and a melting point well below that of platinum or titanium and alumina or zirconia, typically being a glass or glass ceramic.

In the embodiment shown inFIGS. 2–5, probe20includes a return electrode112for completing the current path between active electrodes104and a high frequency power supply28(seeFIG. 1). As shown, return electrode112preferably comprises an annular conductive band coupled to the distal end of shaft100slightly proximal to tissue treatment surface212of electrode support member102, typically about 0.5 mm to 10 mm and more preferably about 1 mm to 10 mm proximal to surface212. Return electrode112is coupled to a connector258(FIG. 5) that extends to the proximal end of probe10, where it is suitably connected to power supply28(FIG. 1).

As shown inFIG. 2, return electrode112is not directly connected to active electrodes104. To complete a current path so that active electrodes104are electrically connected to return electrode112, electrically conductive fluid (e.g., isotonic saline) is caused to flow therebetween. In the representative embodiment, the electrically conductive fluid is delivered through an external fluid tube239to opening237, as described above. Alternatively, the fluid may be delivered by a fluid delivery element (not shown) that is separate from probe20. In some microendoscopic discectomy procedures, for example, the trocar cannula may be flooded with isotonic saline and the probe20will be introduced into this flooded cavity. Electrically conductive fluid will be continually resupplied with a separate instrument to maintain the conduction path between return electrode112and active electrodes104.

In alternative embodiments, the fluid path may be formed in probe20by, for example, an inner lumen or an annular gap between the return electrode and a tubular support member within shaft100(not shown). This annular gap may be formed near the perimeter of the shaft100such that the electrically conductive fluid tends to flow radially inward towards the target site, or it may be formed towards the center of shaft100so that the fluid flows radially outward. In both of these embodiments, a fluid source (e.g., a bag of fluid elevated above the surgical site or having a pumping device), is coupled to probe20via a fluid supply tube (not shown) that may or may not have a controllable valve. A more complete description of an electrosurgical probe incorporating one or more fluid lumen(s) can be found in parent application U.S. Pat. No. 5,697,281, filed on Jun. 7, 1995, the complete disclosure of which is incorporated herein by reference.

Referring toFIG. 4, the electrically isolated active electrodes104are spaced apart over tissue treatment surface212of electrode support member102. The tissue treatment surface and individual active electrodes104will usually have dimensions within the ranges set forth above. In the representative embodiment, the tissue treatment surface212has a circular cross-sectional shape with a diameter in the range of about 1 mm to 30 mm, usually about 2 mm to 20 mm. The individual active electrodes104preferably extend outward from tissue treatment surface212by a distance of about 0.1 mm to 8 mm, usually about 0.2 mm to 4 mm. Applicant has found that this configuration increases the high electric field intensities and associated current densities around active electrodes104to facilitate the ablation of tissue as described in detail above.

In the embodiment ofFIGS. 2–5, the probe includes a single, larger opening209in the center of tissue treatment surface212, and a plurality of active electrodes (e.g., about 3–15 electrodes) around the perimeter of surface212(seeFIG. 3). Alternatively, the probe may include a single, annular, or partially annular, active electrode at the perimeter of the tissue treatment surface. The central opening209is coupled to a suction or aspiration lumen213(seeFIG. 2) within shaft100and a suction tube211(FIG. 2) for aspirating tissue, fluids and/or gases from the target site. In this embodiment, the electrically conductive fluid generally flows from opening237of fluid tube239radially inward past active electrodes104and then back through the central opening209of support member102. Aspirating the electrically conductive fluid during surgery allows the surgeon to see the target site, and it prevents the fluid from flowing into the patient's body, e.g., into the spine, the abdomen or the thoracic cavity. This aspiration should be controlled, however, so that the conductive fluid maintains a conductive path between the active electrode(s) and the return electrode.

Of course, it will be recognized that the distal tip of probe may have a variety of different configurations. For example, the probe may include a plurality of openings209around the outer perimeter of tissue treatment surface212(this embodiment not shown in the drawings). In this embodiment, the active electrodes104extend from the center of tissue treatment surface212radially inward from openings209. The openings are suitably coupled to fluid tube233for delivering electrically conductive fluid to the target site, and aspiration lumen213for aspirating the fluid after it has completed the conductive path between the return electrode112and the active electrodes104.

In some embodiments, the probe20will also include one or more aspiration electrode(s) coupled to the aspiration lumen for inhibiting clogging during aspiration of tissue fragments from the surgical site. As shown inFIG. 6, one or more of the active electrodes104may comprise loop electrodes140that extend across distal opening209of the suction lumen within shaft100. In the representative embodiment, two of the active electrodes104comprise loop electrodes140that cross over the distal opening209. Of course, it will be recognized that a variety of different configurations are possible, such as a single loop electrode, or multiple loop electrodes having different configurations than shown. In addition, the electrodes may have shapes other than loops, such as the coiled configurations shown inFIGS. 6 and 7. Alternatively, the electrodes may be formed within suction lumen proximal to the distal opening209, as shown inFIG. 8. The main function of loop electrodes140is to ablate portions of tissue that are drawn into the suction lumen to prevent clogging of the lumen.

Loop electrodes140are electrically isolated from the other active electrodes104, which can be referred to hereinafter as the ablation electrodes104. Loop electrodes140may or may not be electrically isolated from each other. Loop electrodes140will usually extend only about 0.05 mm to 4 mm, preferably about 0.1 mm to 1 mm from the tissue treatment surface of electrode support member104.

Referring now toFIGS. 7 and 8, alternative embodiments for aspiration electrodes will now be described. As shown inFIG. 7, the aspiration electrodes may comprise a pair of coiled electrodes150that extend across distal opening209of the suction lumen. The larger surface area of the coiled electrodes150usually increases the effectiveness of the electrodes150on tissue fragments passing through opening209. InFIG. 8, the aspiration electrode comprises a single coiled electrode154passing across the distal opening209of suction lumen. This single electrode154may be sufficient to inhibit clogging of the suction lumen. Alternatively, the aspiration electrodes may be positioned within the suction lumen proximal to the distal opening209. Preferably, these electrodes are close to opening209so that tissue does not clog the opening209before it reaches electrode154. In this embodiment, a separate return electrode156may be provided within the suction lumen to confine the electric currents therein.

Referring toFIG. 10, another embodiment of the present invention incorporates an aspiration electrode160within the aspiration lumen162of the probe. As shown, the electrode160is positioned just proximal of distal opening209so that the tissue fragments are ablated as they enter lumen162. In the representative embodiment, the aspiration electrode160comprises a loop electrode that stretches across the aspiration lumen162. However, it will be recognized that many other configurations are possible.

In this embodiment, the return electrode164is located outside of the probe as in the previously described embodiments. Alternatively, the return electrode(s) may be located within the aspiration lumen162with the aspiration electrode160. For example, the inner insulating coating163may be exposed at portions within the lumen162to provide a conductive path between this exposed portion of return electrode164and the aspiration electrode160. The latter embodiment has the advantage of confining the electric currents to within the aspiration lumen. In addition, in dry fields in which the conductive fluid is delivered to the target site, it is usually easier to maintain a conductive fluid path between the active and return electrodes in the latter embodiment because the conductive fluid is aspirated through the aspiration lumen162along with the tissue fragments.

Referring toFIG. 9, another embodiment of the present invention incorporates a wire mesh electrode600extending across the distal portion of aspiration lumen162. As shown, mesh electrode600includes a plurality of openings602to allow fluids and tissue fragments to flow through into aspiration lumen162. The size of the openings602will vary depending on a variety of factors. The mesh electrode may be coupled to the distal or proximal surfaces of ceramic support member102. Wire mesh electrode600comprises a conductive material, such as platinum, titanium, tantalum, steel, stainless steel, tungsten, copper, gold or the like. In the representative embodiment, wire mesh electrode600comprises a different material having a different electric potential than the active electrode(s)104. Preferably, mesh electrode600comprises steel and active electrode(s)104comprises tungsten. Applicant has found that a slight variance in the electrochemical potential of mesh electrode600and active electrode(s)104improves the performance of the device. Of course, it will be recognized that the mesh electrode may be electrically insulated from active electrode(s) as in previous embodiments

Referring now toFIGS. 11A–11C, an alternative embodiment incorporating a metal screen610is illustrated. As shown, metal screen610has a plurality of peripheral openings612for receiving active electrodes104, and a plurality of inner openings614for allowing aspiration of fluid and tissue through opening609of the aspiration lumen. As shown, screen610is press fitted over active electrodes104and then adhered to shaft100of probe20. Similar to the mesh electrode embodiment, metal screen610may comprise a variety of conductive metals, such as platinum, titanium, tantalum, steel, stainless steel, tungsten, copper, gold, or the like. In the representative embodiment, metal screen610is coupled directly to, or integral with, active electrode(s)104. In this embodiment, the active electrode(s)104and the metal screen610are electrically coupled to each other.

FIGS.32A–B and33A–C illustrate alternative embodiments of the mesh and screen aspiration electrodes. As shown inFIGS. 32A and 32B, the probe may include a conductive cage electrode620that extends into the aspiration lumen162(not shown) to increase the effect of the electrode on aspirated tissue.FIGS. 33A–33Cillustrate a dome-shaped screen electrode630that includes one or more anchors632(four in the representative embodiment) for attaching the screen electrode630to a conductive spacer634. Screen electrode630includes a plurality of holes631for allowing fluid and tissue fragments to pass therethrough to aspiration lumen162. Screen electrode630is sized to fit within opening609of aspiration lumen162except for the anchors632which include holes633for receiving active electrodes104. Spacer634includes peripheral holes636for receiving active electrodes104and a central hole638aligned with suction lumen162. Spacer634may further include insulated holes640for electrically isolating screen electrode630from active electrodes104. As shown inFIG. 33C, dome-shaped screen electrode630preferably extends distally from the probe shaft100about the same distance as the active electrodes104. Applicant has found that this configuration enhances the ablation rate for tissue adjacent to active electrodes104, while still maintaining the ability to ablate aspirated tissue fragments passing through screen630.

FIG. 5illustrates the electrical connections250within handle204for coupling active electrodes104and return electrode112to the power supply28. As shown, a plurality of wires252extend through shaft100to couple electrodes104to a plurality of pins254, which are plugged into a connector block256for coupling to a connecting cable22(FIG. 1). Similarly, return electrode112is coupled to connector block256via a wire258and a plug260.

In some embodiments of the present invention, the probe20further includes an identification element that is characteristic of the particular electrode assembly so that the same power supply28can be used for different electrosurgical operations. In one embodiment, for example, the probe20includes a voltage reduction element or a voltage reduction circuit for reducing the voltage applied between the active electrodes104and the return electrode112. The voltage reduction element serves to reduce the voltage applied by the power supply so that the voltage between the active electrodes and the return electrode is low enough to avoid excessive power dissipation into the electrically conducting medium and/or ablation of the soft tissue at the target site. The voltage reduction element primarily allows the electrosurgical probe20to be compatible with various generator or power supply models that are adapted to apply higher voltages for ablation, molecular dissociation, or vaporization of tissue (e.g., generators supplied by ArthroCare Corporation, Sunnyvale, Calif.). For contraction of tissue, for example, the voltage reduction element will serve to reduce a voltage of about 100 to 135 volts rms (which is a setting of 1 on the ArthroCare Model 970 and 980 (i.e., 2000) Generators) to about 45 to 60 volts rms, which is a suitable voltage for contraction of tissue without ablation (e.g., without molecular dissociation) of the tissue.

Of course for some procedures in endoscopic spine surgery, the probe will typically not require a voltage reduction element. Alternatively, the probe may include a voltage increasing element or circuit, if desired.

In the representative embodiment, the voltage reduction element comprises a pair of capacitors forming a bridge divider (not shown) coupled to the power supply and coagulation electrode380. The capacitors usually have a capacitance of about 200 pF to 500 pF (at 500 volts) and preferably about 300 pF to 350 pF (at 500 volts). Of course, the capacitors may be located in other places within the system, such as in, or distributed along the length of, the cable, the generator, the connector, etc. In addition, it will be recognized that other voltage reduction elements, such as diodes, transistors, inductors, resistors, capacitors or combinations thereof, may be used in conjunction with the present invention. For example, the probe350may include a coded resistor (not shown) that is constructed to lower the voltage applied between the return and coagulation electrodes360,380, respectively. In addition, electrical circuits may be employed for this purpose.

Alternatively or additionally, the cable22that couples the power supply28to probe20/90may be used as a voltage reduction element. The cable has an inherent capacitance that can be used to reduce the power supply voltage if the cable is placed into the electrical circuit between the power supply, the active electrodes and the return electrode. In this embodiment, the cable22may be used alone, or in combination with one of the voltage reduction elements discussed above, e.g., a capacitor.

In some embodiments, probe20/90will further include a switch (not shown) or other input that allows the surgeon to couple and decouple the identification element to the rest of the electronics in probe20/90. For example, if the surgeon would like to use the same probe for ablation of tissue and contraction of tissue in the same procedure, this can be accomplished by manipulating the switch. Thus, for ablation of tissue, the surgeon will decouple the voltage reduction element from the electronics so that the full voltage applied by the power source is applied to the electrodes on the probe. When the surgeon desires to reduce the voltage to a suitable level for contraction of tissue, he/she couples the voltage reduction element to the electronics to reduce the voltage applied by the power supply to the active electrodes.

Further, it should be noted that the present invention can be used with a power supply that is adapted to apply a voltage within the selected range for treatment of tissue. In this embodiment, a voltage reduction element or circuitry may not be desired.

The present invention is particularly useful in microendoscopic discectomy procedures, e.g., for decompressing a nerve root with a lumbar discectomy. As shown inFIGS. 12–15, a percutaneous penetration270is made in the patients' back272so that the superior lamina274can be accessed. Typically, a small needle (not shown) is used initially to localize the disc space level, and a guidewire (not shown) is inserted and advanced under lateral fluoroscopy to the inferior edge of the lamina274. Sequential cannulated dilators276are inserted over the guide wire and each other to provide a hole from percutaneous penetration270to the lamina274. The first dilator may be used to “palpate” the lamina274, assuring proper location of its tip between the spinous process and facet complex just above the inferior edge of the lamina274. As shown inFIG. 13, a tubular retractor278is then passed over the largest dilator down to the lamina274. The dilators276are removed, establishing an operating corridor within the tubular retractor278.

As shown inFIG. 13, an endoscope280is then inserted into the tubular retractor278and a ring clamp282is used to secure the endoscope280. Typically, the formation of the operating corridor within retractor278requires the removal of soft tissue, muscle or other types of tissue that were forced into this corridor as the dilators276and retractor278were advanced down to the lamina274. In procedures of the prior art, this tissue has usually been removed with mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders and the like. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, these instruments sever blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon's view of the target site.

According to the present invention, an electrosurgical probe or catheter284as described above is introduced into the operating corridor within the retractor278to remove the soft tissue, muscle and other obstructions from this corridor so that the surgeon can easily access and visualize the lamina274. Once the surgeon has introduced the probe284, electrically conductive fluid285is delivered through tube233and opening237to the tissue (seeFIG. 2). The fluid flows past the return electrode112to the active electrodes104at the distal end of the shaft. The rate of fluid flow is controlled with valve17(FIG. 1) such that the zone between the tissue and electrode support102is constantly immersed in the fluid. The power supply28is then turned on and adjusted such that a high frequency voltage difference is applied between active electrodes104and return electrode112. The electrically conductive fluid provides the conduction path (see current flux lines) between active electrodes104and the return electrode112.

The high frequency voltage is sufficient to convert the electrically conductive fluid (not shown) between the target tissue and active electrode(s)104into an ionized vapor layer or plasma (not shown). As a result of the applied voltage difference between active electrode(s)104and the target tissue (i.e., the voltage gradient across the plasma layer), charged particles in the plasma (e.g., electrons) cause dissociation of the molecular bonds within tissue structures. This molecular dissociation is accompanied by the volumetric removal (i.e., ablative sublimation) of tissue and the production of low molecular weight gases, such as oxygen, nitrogen, carbon dioxide, hydrogen and methane. This process can be precisely controlled to effect the volumetric removal of tissue as thin as 10 microns to 150 microns with minimal heating of, or damage to, underlying tissue structures. A more detailed description of this phenomenon is presented in commonly assigned U.S. Pat. No. 5,697,882, the complete disclosure of which is incorporated herein by reference.

During the process, the gases will be aspirated through opening209and suction tube211to a vacuum source. In addition, excess electrically conductive fluid, and other fluids (e.g., blood) will be aspirated from the operating corridor to facilitate the surgeon's view. During ablation of the tissue, the residual heat generated by the current flux lines (typically less than 150° C.), will usually be sufficient to coagulate any severed blood vessels at the site. If not, the surgeon may switch the power supply28into the coagulation mode by lowering the voltage to a level below the threshold for fluid vaporization, as discussed above. This simultaneous hemostasis results in less bleeding and facilitates the surgeon's ability to perform the procedure.

Another advantage of the present invention is the ability to precisely ablate soft tissue without causing necrosis or thermal damage to the underlying and surrounding tissues, nerves or bone. In addition, the voltage can be controlled so that the energy directed to the target site is insufficient to ablate the lamina274so that the surgeon can literally clean the tissue off the lamina274, without ablating or otherwise effecting significant damage to the lamina.

Referring now toFIGS. 14 and 15, once the operating corridor is sufficiently cleared, a laminotomy and medial facetectomy is accomplished either with conventional techniques (e.g., a Kerrison punch or a high speed drill) or with the electrosurgical probe284as discussed above. After the nerve root is identified, medical retraction can be achieved with a retractor288, or the present invention can be used to ablate with precision the disc. If necessary, epidural veins are cauterized either automatically or with the coagulation mode of the present invention. If an annulotomy is necessary, it can be accomplished with a microknife or the ablation mechanism of the present invention while protecting the nerve root with the retractor288. The herniated disc290is then removed with a pituitary rongeur in a standard fashion, or once again through ablation as described above.

In another embodiment, the electrosurgical probe of the present invention can be used to ablate and/or contract soft tissue within the disc290to allow the annulus292to repair itself to prevent reoccurrence of this procedure. For tissue contraction, a sufficient voltage difference is applied between the active electrodes104and the return electrode112to elevate the tissue temperature from normal body temperatures (e.g., 37° C.) to temperatures in the range of 45° C. to 90° C., preferably in the range from 60° C. to 70° C. This temperature elevation causes contraction of the collagen connective fibers within the disc tissue so that the nucleus pulposus291withdraws into the annulus fibrosus292.

In one method of tissue contraction according to the present invention, an electrically conductive fluid is delivered to the target site as described above, and heated to a sufficient temperature to induce contraction or shrinkage of the collagen fibers in the target tissue. The electrically conductive fluid is heated to a temperature sufficient to substantially irreversibly contract the collagen fibers, which generally requires a tissue temperature in the range of about 45° C. to 90° C., usually about 60° C. to 70° C. The fluid is heated by applying high frequency electrical energy to the active electrode(s) in contact with the electrically conducting fluid. The current emanating from the active electrode(s)104heats the fluid and generates a jet or plume of heated fluid, which is directed towards the target tissue. The heated fluid elevates the temperature of the collagen sufficiently to cause hydrothermal shrinkage of the collagen fibers. The return electrode112draws the electric current away from the tissue site to limit the depth of penetration of the current into the tissue, thereby inhibiting molecular dissociation and breakdown of the collagen tissue and minimizing or completely avoiding damage to surrounding and underlying tissue structures beyond the target tissue site. In an exemplary embodiment, the active electrode(s)104are held away from the tissue a sufficient distance such that the RF current does not pass into the tissue at all, but rather passes through the electrically conductive fluid back to the return electrode. In this embodiment, the primary mechanism for imparting energy to the tissue is the heated fluid, rather than the electric current.

In an alternative embodiment, the active electrode(s)104are brought into contact with, or close proximity to, the target tissue so that the electric current passes directly into the tissue to a selected depth. In this embodiment, the return electrode draws the electric current away from the tissue site to limit its depth of penetration into the tissue. Applicant has discovered that the depth of current penetration can also be varied with the electrosurgical system of the present invention by changing the frequency of the voltage applied to the active electrode and the return electrode. This is because the electrical impedance of tissue is known to decrease with increasing frequency due to the electrical properties of cell membranes which surround electrically conductive cellular fluid. At lower frequencies (e.g., less than 350 kHz), the higher tissue impedance, the presence of the return electrode and the active electrode configuration of the present invention (discussed in detail below) cause the current flux lines to penetrate less deeply resulting in a smaller depth of tissue heating. In an exemplary embodiment, an operating frequency of about 100 to 200 kHz is applied to the active electrode(s) to obtain shallow depths of collagen shrinkage (e.g., usually less than 1.5 mm and preferably less than 0.5 mm).

In another aspect of the invention, the size (e.g., diameter or principal dimension) of the active electrodes employed for treating the tissue are selected according to the intended depth of tissue treatment. As described previously in copending patent application PCT International Application, U.S. National Phase Serial No. PCT/US94/05168, the depth of current penetration into tissue increases with increasing dimensions of an individual active electrode (assuming other factors remain constant, such as the frequency of the electric current, the return electrode configuration, etc.). The depth of current penetration (which refers to the depth at which the current density is sufficient to effect a change in the tissue, such as collagen shrinkage, irreversible necrosis, etc.) is on the order of the active electrode diameter for the bipolar configuration of the present invention and operating at a frequency of about 100 kHz to about 200 kHz. Accordingly, for applications requiring a smaller depth of current penetration, one or more active electrodes of smaller dimensions would be selected. Conversely, for applications requiring a greater depth of current penetration, one or more active electrodes of larger dimensions would be selected.

FIGS. 16–18illustrate an alternative electrosurgical system300specifically configured for endoscopic discectomy procedures, e.g., for treating extruded or non-extruded herniated discs. As shown inFIG. 16system300includes a trocar cannula302for introducing a catheter assembly304through a percutaneous penetration in the patient to a target disc in the patient's spine. As discussed above, the catheter assembly304may be introduced through the thorax in a thoracoscopic procedure, through the abdomen in a laparascopic procedure, or directly through the patient's back. Catheter assembly304includes a catheter body306with a plurality of inner lumens (not shown) and a proximal hub308for receiving the various instruments that will pass through catheter body306to the target site. In this embodiment, assembly304includes an electrosurgical instrument310with a flexible shaft312, an aspiration catheter314, an endoscope316and an illumination fiber shaft318for viewing the target site. As shown inFIGS. 16 and 17, aspiration catheter314includes a distal port320and a proximal fitment322for attaching catheter314to a source of vacuum (not shown). Endoscope316will usually comprise a thin metal tube317with a lens324at the distal end, and an eyepiece (not shown) at the proximal end.

In the exemplary embodiment, electrosurgical instrument310includes a twist locking stop330at a proximal end of the shaft312for controlling the axial travel distance TDof the probe. As discussed in detail below, this configuration allows the surgeon to “set” the distance of ablation within the disc. In addition, instrument310includes a rotational indicator334for displaying the rotational position of the distal portion of instrument310to the surgeon. This rotational indicator334allows the surgeon to view this rotational position without relying on the endoscope316if visualization is difficult, or if an endoscope is not being used in the procedure.

Referring now toFIGS. 17 and 18, a distal portion340of electrosurgical instrument310and catheter body306will now be described. As shown, instrument310comprises a relatively stiff, but deflectable electrically insulating support cannula312and a working end portion348movably coupled to cannula312for rotational and translational movement of working end348. Working end348of electrosurgical instrument310can be rotated and translated to ablate and remove a volume of nucleus pulposus within a disc. Support cannula312extends through an internal lumen344and beyond the distal end346of catheter body306. Alternatively, support cannula312may be separate from instrument310, or even an integral part of catheter body306. The distal portion of working end348includes an exposed return electrode350separated from an active electrode array352by an insulating support member354, such as ceramic. In the representative embodiment, electrode array352is disposed on only one side of ceramic support member354so that its other side is insulating and thus atraumatic to tissue. Instrument310will also include a fluid lumen (not shown) having a distal port360in working end348for delivering electrically conductive fluid to the target site.

In use, trocar cannula302is introduced into a percutaneous penetration suitable for endoscopic delivery to the target disc in the spine. A trephine (not shown) or other conventional instrument may be used to form a channel from the trocar cannula302through the annulus fibrosus292and into the nucleus pulposus. Alternatively, the probe310may be used for this purpose, as discussed above. The working end348of instrument310is then advanced through cannula302a short distance (e.g., about 7 to 10 mm) into the nucleus pulposus291, as shown inFIG. 18. Once the electrode array352is in position, electrically conductive fluid is delivered through distal port360to immerse the active electrode array352in the fluid. The vacuum source may also be activated to ensure a flow of conductive fluid between electrode array352past return electrode350to suction port320, if necessary. In some embodiments, the mechanical stop330may then be set at the proximal end of the instrument310to limit the axial travel distance of working end348. Preferably, this distance will be set to minimize (or completely eliminate) ablation of the surrounding annulus.

The probe is then energized by applying high frequency voltage difference between the electrode array352and return electrode350so that electric current flows through the conductive fluid from the array352to the return electrode350. The electric current causes vaporization of the fluid and ensuing molecular dissociation of the nucleus pulposus tissue as described in detail above. The instrument310may then be translated in an axial direction forwards and backwards to the preset limits. While still energized and translating, the working end348may also be rotated to ablate tissue surrounding the electrode array352. In the representative embodiment, working end348will also include an inflatable gland380opposite electrode array352to allow deflection of working end348relative to support cannula312. As shown inFIG. 18, working end348may be deflected to produce a large diameter bore within the nucleus pulposus, which assures close contact with tissue surfaces to be ablated. Alternatively, the entire catheter body306, or the distal end of catheter body306may be deflected to increase the volume of nucleus pulposus removed.

After the desired volume of nucleus pulposus is removed (based on direct observation through port324, or by kinesthetic feedback from movement of working end348of instrument310), instrument310is withdrawn into catheter body306and the catheter body is removed from the patient. Typically, the preferred volume of removed tissue is about 0.2 cm3to 5.0 cm3.

Referring now toFIGS. 19–28, alternative systems and methods for ablating tissue in confined (e.g., narrow) body spaces will now be described.FIG. 19illustrates an exemplary planar ablation probe400according to the present invention. Similar to the instruments described above, probe400can be incorporated into electrosurgical system11(or other suitable systems) for operation in either the bipolar or monopolar modalities.

Probe400generally includes a support member402, a distal working end404attached to the distal end of support member402and a proximal handle406attached to the proximal end of support member402. As shown inFIG. 19, handle406includes a handpiece408and a power source connector410removably coupled to handpiece408for electrically connecting working end404with power supply28through cable34(seeFIG. 1).

In the embodiment shown inFIG. 19, planar ablation probe400is configured to operate in the bipolar modality. Accordingly, support member402or a portion thereof functions as the return electrode and comprises an electrically conducting material, such as titanium, or alloys containing one or more of nickel, chromium, iron, cobalt, copper, aluminum, platinum, molybdenum, tungsten, tantalum or carbon. In the preferred embodiment, support member402is an austenitic stainless steel alloy, such as stainless steel Type304from MicroGroup, Inc., Medway, Mass. As shown inFIG. 19, support member402is substantially covered by an insulating layer412to prevent electric current from damaging surrounding tissue. An exposed portion414of support member402functions as the return electrode for probe400. Exposed portion414is preferably spaced proximally from active electrodes416by a distance of about 1 mm to 20 mm.

Referring toFIGS. 20 and 21, planar ablation probe400further comprises a plurality of active electrodes416extending from an electrically insulating spacer418at the distal end of support member402. Of course, it will be recognized that probe400may include a single electrode depending on the size of the target tissue to be treated and the accessibility of the treatment site (seeFIG. 26, for example). Insulating spacer418is preferably bonded to support member402with a suitable epoxy adhesive419to form a mechanical bond and a fluid-tight seal. Electrodes416usually extend about 2.0 mm to 20 mm from spacer418, and preferably less than 10 mm. A support tongue420extends from the distal end of support member402to support active electrodes416. Support tongue420and active electrodes416have a substantially low profile to facilitate accessing narrow spaces within the patient's body, such as the spaces between adjacent vertebrae and between articular cartilage and the meniscus in the patient's knee. Accordingly, tongue420and electrodes416have a substantially planar profile, usually having a combined height He of less than 4.0 mm, preferably less than 2.0 mm and more preferably less than 1.0 mm (seeFIG. 25). In the case of ablation of meniscus near articular cartilage, the height He of both the tongue420and electrodes416is preferably between about 0.5 mm to 1.5 mm. The width of electrodes416and support tongue420will usually be less than 10.0 mm and preferably between about 2.0 mm to 4.0 mm.

Support tongue420includes a “non-active” surface422opposing active electrodes416covered with an electrically insulating layer (not shown) to minimize undesirable current flow into adjacent tissue or fluids. Non-active surface422is preferably atraumatic, i.e., having a smooth planar surface with rounded corners, to minimize unwanted injury to tissue or nerves in contact therewith, such as disc tissue or the nearby spinal nerves, as the working end of probe400is introduced into a narrow, confined body space. Non-active surface422of tongue420help to minimize iatrogenic injuries to tissue and nerves so that working end404of probe400can safely access confined spaces within the patient's body.

Referring toFIGS. 21A–B and 22, an electrically insulating support member430is disposed between support tongue420and active electrodes416to inhibit or prevent electric current from flowing into tongue420. Insulating member430and insulating layer412preferably comprise a ceramic, glass or glass ceramic material, such as alumina. Insulating member430is mechanically bonded to support tongue420with a suitable epoxy adhesive to electrically insulate active electrodes416from tongue420. As shown inFIG. 26, insulating member430may overhang support tongue420to increase the electrical path length between the active electrodes416and the insulation covered support tongue420.

As shown inFIGS. 21A–23, active electrodes416are preferably constructed from a hollow, round tube, with at least the distal portion432of electrodes416being filed off to form a semi-cylindrical tube with first and second ends440,442facing away from support tongue420. Preferably, the proximal portion434of electrodes416will remain cylindrical to facilitate the formation of a crimp-type electrical connection between active electrodes416and lead wires450(seeFIG. 23). As shown inFIG. 26, cylindrical proximal portions434of electrodes416extend beyond spacer418by a slight distance of 0.1 mm to 0.4 mm. The semi-cylindrical configuration of distal electrode portion432increases the electric field intensity and associated current density around the edges of ends440,442, as discussed above. Alternatively, active electrodes416may have any of the shapes and configurations described above or other configurations, such as square wires, triangular shaped wires, U-shaped or channel shaped wires and the like. In addition, the surface of active electrodes416may be roughened, e.g., by grit blasting, chemical or electrochemical etching, to further increase the electric field intensity and associated current density around distal portions432of electrodes416.

As shown inFIG. 24, each lead wire450terminates at a connector pin452contained in a pin insulator block454within handpiece408. Lead wires450are covered with an insulation layer (not shown), e.g., Tefzel™, and sealed from the inner portion of support member402with an adhesive seal457(FIG. 22). In the preferred embodiment, each electrode416is coupled to a separate source of voltage within power supply28. To that end, connector pins452are removably coupled to mating receptacles456within connector410to provide electrical communication with active electrodes416and power supply28(FIG. 1). Electrically insulated lead wires458connect receptacles456to the corresponding sources of voltage within power supply28. The electrically conductive wall414of support member402serves as the return electrode, and is suitably coupled to one of the lead wires450.

In an alternative embodiment, adjacent electrodes416may be connected to the opposite polarity of source28so that current flows between adjacent active electrodes416rather than between active electrodes416and return electrode414. By way of example,FIG. 21Billustrates a distal portion of a planar ablation probe400′ in which electrodes416aand416care at one voltage polarity (i.e., positive) and electrodes416band416dare at the opposite voltage polarity (negative). When a high frequency voltage is applied between electrodes416a,416cand electrodes416b,416din the presence of electrically conductive liquid, current flows between electrodes416a,416cand416b,416das illustrated by current flux lines522′. Similar to the above embodiments, the opposite surface420of working end404′ of probe400′ is generally atraumatic and electrically insulated from active electrodes416a,416b,416cand416dto minimize unwanted injury to tissue in contact therewith.

In an exemplary configuration, each source of voltage includes a current limiting element or circuitry (not shown) to provide independent current limiting based on the impedance between each individual electrode416and return electrode414. The current limiting elements may be contained within the power supply28, the lead wires450, cable34, handle406, or within portions of the support member402distal to handle406. By way of example, the current limiting elements may include resistors, capacitors, inductors, or a combination thereof. Alternatively, the current limiting function may be performed by (1) a current sensing circuit which causes the interruption of current flow if the current flow to the electrode exceeds a predetermined value and/or (2) an impedance sensing circuit which causes the interruption of current flow (or reduces the applied voltage to zero) if the measured impedance is below a predetermined value. In another embodiment, two or more of the electrodes416may be connected to a single lead wire450such that all of the electrodes416are always at the same applied voltage relative to return electrode414. Accordingly, any current limiting elements or circuits will modulate the current supplied or the voltage applied to the array of electrodes416, rather than limiting their current individually, as discussed in the previous embodiment.

Referring toFIGS. 25–28, methods for ablating tissue structures with planar ablation probe400according to the present invention will now be described. In particular, exemplary methods for treating a diseased meniscus within the knee (FIGS. 29–31) and for removing soft tissue between adjacent vertebrae in the spine (FIG. 32) will be described. In both procedures, at least the working end404of planar ablation probe400is introduced to a treatment site either by minimally invasive techniques or open surgery. Electrically conductive liquid is delivered to the treatment site, and voltage is applied from power supply28between active electrodes416and return electrode414. The voltage is preferably sufficient to generate electric field intensities near active electrodes that form a vapor layer in the electrically conductive liquid, and induce the discharge of energy from the vapor layer to ablate tissue at the treatment site, as described in detail above.

Referring toFIG. 25, working end404and at least the distal portion of support member402are introduced through a percutaneous penetration500, such as a cannula, into the arthroscopic cavity502. The insertion of probe400is usually guided by an arthroscope (not shown) which includes a light source and a video camera to allow the surgeon to selectively visualize a zone within the knee joint. To maintain a clear field of view and to facilitate the generation of a vapor layer, a transparent, electrically conductive irrigant503, such as isotonic saline, is injected into the treatment site either through a liquid passage in support member402of probe400, or through another instrument. Suitable methods for delivering irrigant to a treatment site are described in commonly assigned U.S. Pat. No. 5,697,281 filed on Jun. 7, 1995, the contents of which are incorporated herein by reference.

In the example shown inFIG. 25, the target tissue is a portion of the meniscus506adjacent to and in close proximity with the articular cartilage510,508which normally covers the end surfaces of the tibia512and the femur514, respectively. The articular cartilage508,510is important to the normal functioning of joints, and once damaged, the body is generally not capable of regenerating this critical lining of the joints. Consequently, it is desirable that the surgeon exercise extreme care when treating the nearby meniscus506to avoid unwanted damage to the articular cartilage508,510. The confined spaces513between articular cartilage508,510and meniscus506within the knee joint are relatively narrow, typically on the order of about 1.0 mm to 5.0 mm. Accordingly, the narrow, low profile working end404of ablation probe400is ideally suited for introduction into these confined spaces513to the treatment site. As mentioned previously, the substantially planar arrangement of electrodes416and support tongue420(typically having a combined height of about 0.5 to 1.5 mm) allows the surgeon to deliver working end404of probe400into the confined spaces513, while minimizing contact with the articular cartilage508,510(seeFIG. 26).

As shown inFIG. 26, active electrodes416are disposed on one face of working end404of probe400. Accordingly, a zone520of high electric field intensity is generated on each electrode416on one face of working end404while the opposite side521of working end404is atraumatic with respect to tissue. In addition, the opposite side521is insulated from electrodes416to minimize electric current from passing through this side521to the tissue (i.e., adjacent articular cartilage508). As shown inFIGS. 26, the bipolar arrangement of active electrodes416and return electrode414causes electric current to flow along flux lines522predominantly through the electrically conducting irrigant503, which envelops the tissue and working end404of ablation probe400and provides an electrically conducting path between electrodes416and return electrode414. As electrodes416are engaged with, or positioned in close proximity to, the target meniscus506, the high electric field present at the electrode edges cause controlled ablation of the tissue by forming a vapor layer and inducing the discharge of energy therefrom. In addition, the motion of electrodes416relative to the meniscus506(as shown by vector523) causes tissue to be removed in a controlled manner. The presence of the irrigant also serves to minimize the increase in the temperature of the meniscus during the ablation process because the irrigant generally comes in contact with the treated tissue shortly after one of the electrodes416has been translated across the surface of the tissue.

Referring now toFIG. 28, an exemplary method for removing soft tissue540from the surfaces of adjacent vertebrae542,544in the spine will now be described. Removal of this soft tissue540is often necessary, for example, in surgical procedures for fusing or joining adjacent vertebrae together. Following the removal of tissue540, the adjacent vertebrae542,544are stabilized to allow for subsequent fusion together to form a single monolithic vertebra. As shown, the low-profile of working end404of probe400(i.e., thickness values as low as 0.2 mm) allows access to and surface preparation of closely spaced vertebrae. In addition, the shaped electrodes416promote substantially high electric field intensities and associated current densities between active electrodes416and return electrode414to allow for the efficient removal of tissue attached to the surface of bone without significantly damaging the underlying bone. The “non-active” insulating side521of working end404also minimizes the generation of electric fields on this side521to reduce ablation of the adjacent vertebra542.

The target tissue is generally not completely immersed in electrically conductive liquid during surgical procedures within the spine, such as the removal of soft tissue described above. Accordingly, electrically conductive liquid will preferably be delivered into the confined spaces513between adjacent vertebrae542,544during this procedure. The fluid may be delivered through a liquid passage (not shown) within support member402of probe400, or through another suitable liquid supply instrument.

Other modifications and variations can be made to disclose embodiments without departing from the subject invention as defined in the following claims. For example, it should be clearly understood that the planar ablation probe400described above may incorporate a single active electrode, rather than a plurality of such active electrodes as described above in the exemplary embodiment.FIG. 27illustrates a portion of a planar ablation probe according to the present invention that incorporates a single active electrode416′ for generating high electric field densities550to ablate a target tissue552. Electrode416′ may extend directly from a proximal support member, as depicted inFIG. 31, or it may be supported on an underlying support tongue (not shown) as described in the previous embodiment. As shown, the representative single active electrode416′ has a semi-cylindrical cross-section, similar to the electrodes416described above. However, the single electrode416′ may also incorporate any of the above described configurations (e.g., square or star shaped solid wire) or other specialized configurations depending on the function of the device.

Referring now toFIGS. 29–31an alternative electrode support member500for a planar ablation probe404will be described in detail. As shown, electrode support member500preferably comprises a multilayer or single layer substrate502comprising a suitable high temperature, electrically insulating material, such as ceramic. The substrate502is a thin or thick film hybrid having conductive strips that are adhered to, e.g., plated onto, the ceramic wafer. The conductive strips typically comprise tungsten, gold, nickel or equivalent materials. In the exemplary embodiment, the conductive strips comprise tungsten, and they are co-fired together with the wafer layers to form an integral package. The conductive strips are coupled to external wire connectors by holes or vias that are drilled through the ceramic layers, and plated or otherwise covered with conductive material.

In the representative embodiment, support member500comprises a single ceramic wafer having a plurality of longitudinal ridges504formed on one side of the wafer502. Typically, the wafer502is green pressed and fired to form the required topography (e.g., ridges504). A conductive material is then adhered to the ridges504to form conductive strips506extending axially over wafer502and spaced from each other. As shown inFIG. 30, the conductive strips506are attached to lead wires508within shaft412of the probe404to electrically couple conductive strips506with the power supply28(FIG. 1). This embodiment provides a relatively low profile working end of probe404that has sufficient mechanical structure to withstand bending forces during a surgical procedure.

FIGS. 34–36illustrate another system and method for treating swollen or herniated intervertebral discs according to the present invention. In this procedure, an electrosurgical probe700comprises a long, thin shaft702(e.g., on the order of about 1 mm or less in diameter) that can be percutaneously introduced posteriorly through the patient's back directly into the spine. The probe shaft702will include one or more active electrode(s)704for applying electrical energy to tissues within the spine. The probe700may include one or more return electrodes706, or the return electrode may be positioned on the patient's back as a dispersive pad (not shown).

As shown inFIG. 34, the distal portion of shaft702is introduced posteriorly through a small percutaneous penetration into the annulus292of the target intervertebral disc290. To facilitate this process, the distal end of shaft702may taper down to a sharper point (e.g., a needle), which can then be retracted to expose active electrode(s)704. Alternatively, the active electrode(s) may be formed around the surface of the tapered distal portion of shaft702(not shown). In either embodiment, the distal end of shaft702is delivered through the annulus292to the target nucleus pulposus291, which may be herniated, extruded, non-extruded, or simply swollen. As shown inFIG. 35, high frequency voltage is applied between active electrode(s)704and return electrode(s)706to heat the surrounding collagen to suitable temperatures for contraction (i.e., typically about 55° C. to about 70° C.). As discussed above, this procedure may be accomplished with a monopolar configuration, as well. However, applicant has found that the bipolar configuration shown inFIGS. 34–36provides enhanced control of the high frequency current, which reduces the risk of spinal nerve damage.

As shown inFIGS. 35 and 36, once the nucleus pulposus291has been sufficiently contracted to retract from impingement on a nerve or nerve root, probe700is removed from the target site. In the representative embodiment, the high frequency voltage is applied between active and return electrode(s)704,706as the probe is withdrawn through the annulus292. This voltage is sufficient to cause contraction of the collagen fibers within the annulus292, which allows the annulus292to contract around the hole formed by probe700, thereby improving the healing of this hole. Thus, the probe700seals its own passage as it is withdrawn from the disc.

FIGS. 37A to 39illustrate systems and methods for treating and ablating intervertebral discs according to the present invention. Electrosurgical probe800generally comprises a shaft802that can be percutaneously introduced posteriorly (through the patient's back) into the spine. The shaft802will include one or more active electrode(s)804for applying electrical energy to the intervertebral disc. The system may include one or more return electrodes806. The return electrode(s)806can be positioned proximal of the active electrode(s)804on the electrosurgical probe or on a separate instrument (not shown). The ablation probe800shown inFIG. 37Ais configured to operate in the bipolar modality. In alternative embodiments, however, the return electrode806may be positioned on the patient's back as a dispersive pad (not shown) so as to operate in a monopolar modality.

In the exemplary embodiment shown inFIGS. 37A and 37B, the distal end of the shaft802is curved or bent to improve access to the disk being treated. The treatment surface808of the electrosurgical probe is usually curved or bent to an angle of about 10 degrees to 90 degrees relative to the longitudinal axis of shaft802, preferably about 15 degrees to 60 degrees and more preferably about 15 degrees. In alternative embodiments, the distal portion of shaft802comprises a flexible material which can be deflected relative to the longitudinal axis of the shaft. Such deflection may be selectively induced by mechanical tension of a pull wire, for example, or by a shape memory wire that expands or contracts by externally applied temperature changes. A more complete description of this embodiment can be found in U.S. Pat. No. 5,697,909, the complete disclosure of which is incorporated herein by reference. Alternatively, the shaft802of the present invention may be bent by the physician to the appropriate angle using a conventional bending tool or the like.

The active electrode(s)804typically extend from an active tissue treatment surface of an electrode support member810of the probe shaft802. Opposite of the active electrodes802is a non-active insulating side812, which has an insulator814that is configured to protect the dura mater816and other non-target tissue, e.g., spinal cord818. The insulator814minimizes the generation of electric fields on the non-active side and reduces the electrical damage to the dura mater816and spinal cord818during disc ablation. While the insulator814is shown opposite the active electrode array804, it will be appreciated that the insulator814can be positioned completely around the probe, be positioned around only portions of the probe, be along the sides of the active electrode array, and the like.

The tissue treatment surface808and individual active electrodes804will usually have dimensions within the ranges set forth above. In some embodiments, the active electrodes804can be disposed within or on an insulating support member810, as described above. In the representative embodiment, the surface of the active electrodes804has a circular cross-sectional shape with a diameter in the range of about 1 mm to 30 mm, usually about 2 mm to 20 mm. The individual active electrodes802preferably extend outward from tissue treatment surface808by a distance of about 0.1 mm to 8 mm, usually about 0.2 mm to 4 mm. Applicant has found that this configuration increases the electric field intensities and associated current densities around active electrodes804to facilitate the ablation of tissue as described in detail above. Of course, it will be recognized that the active electrodes may have a variety of different configurations. For example, instead of an array of active electrodes, a single active electrode may be used.

An exemplary method for ablating and removing at least a portion of the target intervertebral disc290will now be described. Removal of a degenerative or damaged disc is necessary, for example, in surgical procedures during placement of a cage, or the fusing or joining of adjacent vertebrae together. Following the removal of the disc290, the adjacent vertebrae824are stabilized to allow for subsequent fusion together to form a single monolithic vertebra. During such procedures it would be preferable to protect the dura mater816and spinal cord818from damage from the electrosurgical probe800.

In use, the distal end of probe800is introduced into a treatment site either by minimally invasive techniques or open surgery. The distal portion of electrosurgical probe800can be introduced through a percutaneous penetration826e.g., via a camiula, into the body cavity828. The insertion of probe800is usually guided by an endoscope (not shown) which can include a light source and a video camera to allow the surgeon to selectively visualize a zone within the vertebral column. The distal portion of shaft802can be introduced posteriorly through a small percutaneous penetration into the annulus fibrosus292of the target intervertebral disc290(FIGS. 38 and 39).

To maintain a clear field of view and to facilitate the generation of a vapor layer, a transparent, electrically conductive irrigant (not shown), such as isotonic saline, can be injected into the treatment site either through a liquid passage in probe800, or through another instrument. Suitable methods for delivering irrigant to a treatment site are described in commonly assigned, U.S. Pat. No. 5,697,281 filed on Jun. 7, 1995, the contents of which are incorporated herein by reference.

After (or during) introduction of the electrosurgical probe800into the intervertebral disc290, an electrically conductive liquid830can be delivered to the treatment site, and voltage can be applied from power supply28between active electrodes804and return electrode806through the conductive fluid. The voltage is preferably sufficient to generate electric field intensities near active electrodes804that form a vapor layer in the electrically conductive liquid so as to induce a discharge of energy from the vapor layer to ablate tissue at the treatment site, as described in detail above. As shaft802is moved through the spinal disc290, the insulator814can be positioned to engage the dura mater816and protect the dura mater816(and spinal cord818) from damaging electrical current flow.

FIGS. 40 to 41show yet another embodiment of the present invention. The electrosurgical probe800includes an aspiration lumen832for aspirating the target area and a fluid delivery lumen834for directing an electrically conductive fluid830to the target area. In some implementations, the aspiration lumen832and the fluid delivery lumen834are coupled together in an annular pattern along the exterior of the electrosurgical probe. A distal end of the aspiration lumen832typically ends proximal of the return electrode806while the distal end of the fluid delivery lumen834extends to a point adjacent the distal end of the electrosurgical probe800. As shown inFIG. 41, the fluid delivery lumen834preferably occupies a larger portion of the annular region. In one specific embodiment, the fluid delivery lumen834occupies approximately two-thirds of the annular region.

The electrosurgical probe may have a single active electrode804or an electrode array distributed over a contact surface of a probe. In the latter embodiment, the electrode array usually includes a plurality of independently current-limited and/or power-controlled active electrodes to apply electrical energy selectively to the target tissue while limiting the unwanted application of electrical energy to the surrounding tissue and environment. In one specific configuration the electrosurgical probe comprises23active electrodes. Of course, it will be appreciated that the number, size, and configuration of the active electrodes may vary depending on the specific use of the electrosurgical probe (e.g. tissue contraction, tissue ablation, or the like).

The shaft802will usually house a plurality of wires or other conductive elements axially therethrough to permit connection of active electrodes or electrode array804to a connector at the proximal end of the shaft (not shown). Each active electrode of an active electrode array may be connected to a separate power source that is isolated from the other active electrodes. Alternatively, active electrodes804may be connected to each other at either the proximal or distal ends of the probe to form a single wire that couples to a power source.

The active electrode(s)804are typically supported by an electrically insulating electrode support member836that extends from the electrosurgical probe800. Electrode support member836typically extends from the distal end of shaft802about 1 mm to 20 mm. Electrode support member836typically comprises an insulating material (e.g., a silicone, ceramic, or glass material, such as alumina, zirconia and the like) which could be formed at the time of manufacture in a flat, hemispherical or other shape according to the requirements of a particular procedure.

In use, the electrosurgical probe800can be positioned adjacent the target tissue, as described above. When treating an intervertebral disc, the distal end of shaft802is typically delivered through the annulus to the nucleus pulposus291, which may be herniated, extruded, non-extruded, or simply swollen. As shown inFIG. 42, high frequency voltage is applied between active electrode(s)804and return electrode(s)806to heat the surrounding collagen to suitable temperatures for contraction (i.e., typically about 55° C. to about 70° C.) or ablation (i.e. typically less than 150° C.). As discussed above, this procedure may also be performed with a monopolar configuration. However, applicant has found that the bipolar configuration provides enhanced control of the high frequency current, which reduces the risk of spinal nerve damage.

In the exemplary embodiments, an electrically conductive fluid830is delivered through fluid delivery lumen834to the target site. In these embodiments, the high frequency voltage applied to the active electrode(s) is sufficient to vaporize the electrically conductive fluid (e.g., gel or saline) between the active electrode(s) and the tissue. Within the vaporized fluid, an ionized plasma is formed and charged particles (e.g., electrons) are accelerated towards the tissue to cause the molecular breakdown or disintegration of several cell layers of the tissue. This molecular dissociation is accompanied by the volumetric removal of the tissue. Because the aspiration lumen832is placed proximal of the return electrode (and typically outside of the intervertebral disc290), the aspiration lumen832typically removes the air bubbles from the spinal disc and leaves the disc tissue relatively intact. Moreover, because the aspiration lumen834is spaced from the target area, the conductive fluid830is allowed to stay in the target area longer and the plasma can be created more aggressively.

FIGS. 43A to 43Dshow embodiments of the electrosurgical probe of the present invention which have a curved or steerable distal tip for improving navigation of the electrosurgical probe800within the disc. Referring now toFIG. 43A, probe800comprises an electrically conductive shaft802, a handle803coupled to the proximal end of shaft802and an electrically insulating support member836at the distal end of shaft802. Probe800further includes an insulating sleeve838over shaft802, and an exposed portion of shaft802that functions as the return electrode806. In the representative embodiment, probe800comprises a plurality of active electrodes804extending from the distal end of support member836. As shown, return electrode806is spaced a further distance from active electrodes804than in the embodiments described above. In this embodiment, the return electrode806is spaced a distance of about 2.0 mm to 50 mm, preferably about 5 mm to 25 mm. In addition, return electrode806has a larger exposed surface area than in previous embodiments, having a length in the range of about 2.0 mm to 40 mm, preferably about 5 mm to 20 mm. Accordingly, electric current passing from active electrodes804to return electrode806will follow a current flow path840that is further away from shaft802than in the previous embodiments. In some applications, this current flow path840results in a deeper current penetration into the surrounding tissue with the same voltage level, and thus increased thermal heating of the tissue. As discussed above, this increased thermal heating may have advantages in some applications of treating disc or other spinal defects. Typically, it is desired to achieve a tissue temperature in the range of about 60° C. to 100° C. to a depth of about 0.2 mm to 5 mm, usually about 1 mm to 2 mm. The voltage required for this thermal treatment will depend in part on the electrode configuration, the conductivity of the tissue and of the milieu immediately surrounding the electrodes, and the time period during which the voltage is applied. With the electrode configuration described inFIGS. 43A–43D, the voltage level for thermal heating will usually be in the range of about 20 volts rms to 300 volts rms, preferably about 60 volts rms to 200 volts rms. The peak-to-peak voltages for thermal heating with a square wave form having a crest factor of about 2 are typically in the range of about 40 to 600 volts peak-to-peak, preferably about 120 to 400 volts peak-to-peak. The higher the voltage is within this range, the less time required for a given effect. If the voltage is too high, however, the surface tissue may be vaporized, debulked or ablated, which is often undesirable.

As shown by the dotted lines inFIGS. 43A–43D, the distal tip837of the electrosurgical probe800can have a pre-formed curvature or can be steered to a curved configuration so as to approximate the curvature of the inner surface839of the annulus (FIGS. 46A–B). In some embodiments, distal tip837is made of a shape memory material that can be shaped to approximate the inside curvature of the annulus. In other embodiments, distal tip837of the electrosurgical probe800is steerable or deflectable by the user. The flexible shaft and steerable distal tip may be combined with pull wires, shape memory actuators, heat actuated materials, or other conventional or proprietary mechanisms for effecting selective deflection of the distal tip of the shaft to facilitate positioning of the electrode array relative to a target tissue. A user can track the position of the steerable distal tip using fluoroscopy, optical fibers, transducers positioned on the probe, or the like.

In some embodiments, the electrosurgical probe800may include a dispersive return electrode842(FIG. 44) for operating the apparatus in monopolar mode. In this embodiment, the power supply28will typically include a switch, e.g., a foot pedal843, for switching between the monopolar and bipolar modes. The system will switch between an ablation mode, where the dispersive pad842is deactivated and voltage is applied between active and return electrodes804,806, and a subablation or thermal heating mode, where the active electrode(s)804are deactivated and voltage is applied between the dispersive pad842and the return electrode806. In the subablation mode, a lower voltage is typically applied and the return electrode806functions as the active electrode to provide thermal heating and/or coagulation of tissue surrounding return electrode806. A more complete description of the use of the dispersive return electrode is described in co-pending U.S. patent application Ser. No. 09/316,472, filed May 21, 1999, the complete disclosure of which is incorporated herein by reference.

FIG. 43Billustrates yet another embodiment of the present invention. As shown, electrosurgical probe800comprises an electrode assembly having one or more active electrode(s)804and a proximally spaced return electrode806as in previous embodiments. Return electrode806is typically spaced about 0.5 mm to 25 mm, preferably 1.0 mm to 5.0 mm from the active electrode(s)804, and has an exposed length of about 1 mm to 20 mm. In addition, the electrode assembly can include two additional electrodes844,846spaced axially on either side of return electrode806. Electrodes844,846are typically spaced about 0.5 mm to 25 mm, preferably about 1 mm to 5 mm from return electrode806. In the representative embodiment, the additional electrodes844,846are exposed portions of shaft802, and the return electrode806is electrically insulated from shaft802such that a voltage difference may be applied between electrodes844,846and electrode806. In this embodiment, probe800may be used in at least two different modes, an ablation mode and a subablation or thermal heating mode. In the ablation mode, voltage is applied between active electrode(s)804and return electrode806in the presence of electrically conductive fluid, as described above. In the ablation mode, electrodes844,846are deactivated. In the thermal heating or coagulation mode, active electrode(s)804are deactivated and a voltage difference is applied between electrodes844,846and electrode806such that a high frequency current840flows therebetween, as shown inFIG. 43B. In the thermal heating mode, a lower voltage is typically applied such that the voltage is below the threshold for plasma formation and ablation, but sufficient to cause some thermal damage to the tissue immediately surrounding the electrodes without vaporizing or otherwise debulking this tissue so that the current840provides thermal heating and/or coagulation of tissue surrounding electrodes804,844,846.

FIG. 43Cillustrates another embodiment of probe800incorporating an electrode assembly having one or more active electrode(s)804and a proximally spaced return electrode806as in previous embodiments. Return electrode806is typically spaced about 0.5 mm to 25 mm, preferably 1.0 mm to 5.0 mm from the active electrode(s)804, and has an exposed length of about 1 mm to 20 mm. In addition, the electrode assembly includes a second active electrode848separated from return electrode806by an electrically insulating spacer382. In this embodiment, handle803includes a switch850for toggling probe800between at least two different modes, an ablation mode and a subablation or thermal heating mode. In the ablation mode, voltage is applied between active electrode(s)804and return electrode806in the presence of electrically conductive fluid, as described above. In the ablation mode, electrode848is deactivated. In the thermal heating or coagulation mode, active electrode(s)804may be deactivated and a voltage difference is applied between electrode848and electrode806such that a high frequency current840flows therebetween. Alternatively, active electrode(s)804may not be deactivated as the higher resistance of the smaller electrodes (active electrodes804) may automatically send the electric current to electrode848without having to physically decouple electrode(s)804from the circuit. In the thermal heating mode, a lower voltage is typically applied, i.e. a voltage below the threshold for plasma formation and ablation, but sufficient to cause some thermal damage to the tissue immediately surrounding the electrodes without vaporizing or otherwise debulking this tissue so that the current840provides thermal heating and/or coagulation of tissue surrounding electrodes804,848.

FIG. 43Dillustrates yet another embodiment of the invention designed for channeling through tissue and creating lesions therein to treat the interior tissue of intervertebral discs. As shown, probe800is similar to the probe inFIG. 43Chaving a return electrode806and a third, coagulation electrode848spaced proximally from the return electrode806. In this embodiment, active electrode804comprises a single electrode wire extending distally from insulating support member836. Of course, the active electrode804may have a variety of configurations to increase the current densities on its surfaces, e.g., a conical shape tapering to a distal point, a hollow cylinder, loop electrode and the like. This embodiment includes a proximal support member852. In the representative embodiment, support members836and852are constructed of inorganic material, such as a ceramic, a glass, a silicone, and the like. The proximal support member852may also comprise a more conventional organic material as this support member852will generally not be in the presence of a plasma that would otherwise etch or wear away an organic material.

The probe800inFIG. 43Ddoes not include a switching element. In this embodiment, all three electrodes are activated when the power supply is activated. The return electrode806has an opposite polarity from the active and coagulation electrodes804,848such that current840flows from the latter electrodes to the return electrode806as shown. In the preferred embodiment, the electrosurgical system includes a voltage reduction element or a voltage reduction circuit for reducing the voltage applied between the coagulation electrode848and return electrode806. The voltage reduction element allows the power supply28(FIG. 1) to, in effect, apply two different voltages simultaneously to two different electrodes. Thus, for channeling through tissue, the operator may apply a voltage sufficient to provide ablation of the tissue at the tip of the probe (i.e., tissue adjacent to the active electrode804). At the same time, the voltage applied to the coagulation electrode848will be insufficient to ablate tissue. For thermal heating or coagulation of tissue, for example, the voltage reduction element will serve to reduce a voltage from about 100 to 300 volts rms down to about 45 to 90 volts rms, wherein the latter range provides a suitable voltage for coagulation of tissue without ablation (e.g., without molecular dissociation) of the tissue.

In the representative embodiment, the voltage reduction element is a capacitor (not shown) coupled to the power supply and coagulation electrode848. The capacitor usually has a capacitance of about 200 pF to 500 pF (at 500 volts) and preferably about 300 pF to 350 pF (at 500 volts). Of course, the capacitor may be located in other places within the system, such as in, or distributed along the length of, the cable, the generator, the connector, etc. In addition, it will be recognized that other voltage reduction elements, such as diodes, transistors, inductors, resistors, capacitors or combinations thereof, may be used in conjunction with the present invention. For example, the probe800may include a coded resistor (not shown) that is constructed to lower the voltage applied between the return and coagulation electrodes806,848. In addition, electrical circuits may be employed for this purpose.

Of course, for some procedures, the probe will typically not require a voltage reduction element. Alternatively, the probe may include a voltage increasing element or circuit, if desired. Alternatively or additionally, cable22(FIG. 1) that couples power supply28to probe800may be used as a voltage reduction element. The cable has an inherent capacitance that can be used to reduce the power supply voltage if the cable is placed into the electrical circuit between the power supply, the active electrodes and the return electrode. In this embodiment, the cable22may be used alone, or in combination with one of the voltage reduction elements discussed above, e.g., a capacitor. Further, it should be noted that the present invention can be used with a power supply that is adapted to apply two different voltages within the selected range for treatment of tissue. In this embodiment, a voltage reduction element or circuitry may not be desired.

In use, the electrosurgical instruments ofFIGS. 43A–43Dcan be used to treat the tissue within the disc290. In particular, the electrosurgical instrument800can be used to treat damaged discs (e.g., herniated, bulging, fissured, protruding, or the like), denervate selected nerves embedded in the annulus, cauterize granulation tissue that is ingrown into the annulus, seal fissures along the inner surface of the annulus, and the like. Preferably, the electrosurgical probe800can achieve these results in a minimally destructive manner so as to maintain the water content and tissue mass within the disc. Of course, the present invention can also be adapted to ablate tissue, to shrink tissue, to decrease the mass of tissue, or to reduce the water content of the disc.

In preferred embodiments, the electrosurgical probe800minimizes ablation of the nucleus pulposus291by moving along an inner surface of the annulus292. Accordingly, after the distal tip of the electrosurgical probe is inserted into the disc290(FIG. 45), the distal tip837can be steered along the interface between the annulus292and nucleus pulposus291.

Referring now toFIG. 45, in some methods the physician positions active electrode804adjacent to the tissue surface to be treated (e.g., an intervertebral disc). The power supply is activated to provide an ablation voltage between active and return electrodes804,806and a coagulation or thermal heating voltage between coagulation and return electrodes806,848. An electrically conductive fluid can then be provided around active electrode804, and in the junction between the active and return electrodes804,806to provide a current flow path therebetween. This may be accomplished in a variety of manners, as discussed above. The active electrode804is then advanced through the space left by the ablated tissue to form a channel in the disc. During ablation, the electric current between the coagulation and return electrode is typically insufficient to cause any damage to the surface of the tissue as these electrodes pass through the tissue surface into the channel created by active electrode804. Once the physician has formed the channel to the appropriate depth, he or she will cease advancement of the active electrode, and will either hold the instrument in place for approximately 5 seconds to 30 seconds, or can immediately remove the distal tip of the instrument from the channel (see detailed discussion of this below). In either event, when the active electrode is no longer advancing, it will eventually stop ablating tissue.

Prior to entering the channel formed by the active electrode804, an open circuit exists between return and coagulation electrodes806,848. Once coagulation electrode848enters this channel, electric current will flow from coagulation electrode848, through the tissue surrounding the channel, to return electrode806. This electric current will heat the tissue immediately surrounding the channel to coagulate any severed vessels at the surface of the channel. If the physician desires, the instrument may be held within the channel for a period of time to create a lesion around the channel.

In an exemplary embodiment, once the distal tip837of the electrosurgical probe800has channeled through the annulus fibrosus292, the distal tip837can be steered or deflected so as to move along the inner surface of the annulus fibrosus292. As shown inFIGS. 46A and 46B, the electrosurgical device is advanced into an intervertebral disc290, and the physician can simultaneously steer the distal tip237from the proximal end of the electrosurgical device (not shown). As noted above, the distal end of the electrosurgical device preferably is steered or deflected around the inner surface839of the annulus fibrosus292. The physician can use fluoroscopy to monitor the position and movement of the distal end of the probe. Alternatively, the surgeon may insert an imaging device or transducer directly into the disc to monitor the position of electrodes804,806, and848. The imaging device (not shown) can be positioned on the electrosurgical probe or it can be on a separate instrument.

In other embodiments, instead of a steerable distal tip837, the distal tip of the electrosurgical probe800can be composed of a shape-memory material that can be pre-shaped to have the approximate curve of the inner surface of the annulus292. The shape-memory tip can be biased to a pre-bent curved configuration, such that in the absence of a straightening force (e.g., within the annulus, within a tube, or the like) the distal tip will bias to the curved configuration. For example, after an operating corridor has been created to the target site, electrosurgical probe800can be moved adjacent the outer surface of the annulus fibrosus292(FIGS. 12–15). The active electrode804can channel through the tough annulus fibrosus292, as described above. Once the distal tip837enters the nucleus pulposus291, the distal tip will no longer be constrained in the substantially straight configuration by the tough, annulus fibrosus292and the distal tip will bias to its pre-bent curved configuration. As the electrosurgical device is advanced into the disc290, the biased distal tip encourages the electrosurgical instrument to follow the curved inner surface839of the annulus fibrosus292.

As described in detail above, once electrosurgical probe800has been steered to the target position, the high frequency voltage can be delivered between the active electrode(s) and return electrode(s) in a bipolar mode or monopolar mode to treat inner surface839of annulus fibrosus292. In some embodiments, an electrically conductive fluid, such as isotonic saline, can be delivered to the active electrode. As noted above, in procedures requiring ablation of tissue, the tissue is removed by molecular dissociation or disintegration processes. In these embodiments, the high frequency voltage applied to the active electrode(s) is sufficient to vaporize the electrically conductive fluid between the active electrode(s) and the tissue. Within the vaporized fluid, an ionized plasma is formed and charged particles (e.g., electrons) cause the molecular breakdown or disintegration of the tissue to a depth of perhaps several cell layers. This molecular dissociation is accompanied by the volumetric removal of the tissue. The molecular dissociation process can be precisely controlled to target specific tissue structures or layers, thereby minimizing damage and necrosis to non-target tissue. In monopolar embodiments, the conductive fluid need only be sufficient to surround the active electrode and to provide a layer of fluid between the active electrode and the tissue. In bipolar embodiments, the conductive fluid preferably generates a current flow path between the active electrode(s) and the return electrode(s).

Depending on the procedure, the inner surface839of annulus292can be ablated, contracted, coagulated, sealed, or the like. For example, the high frequency voltage can be used to denervate the pain receptors in a fissure in the annulus fibrosus, deactivate the neurotransmitters, deactivate heat-sensitive enzymes, denervate nerves embedded in the wall of the annulus fibrosus, ablate granulation tissue in the annulus fibrosus, shrink collagen in the annulus fibrosus, or the like.

Other modifications and variations can be made to disclose embodiments without departing from the subject invention as defined in the following claims. For example, it should be noted that the invention is not limited to an electrode array comprising a plurality of active electrodes. Certain embodiments of the invention could utilize a plurality of return electrodes, e.g., in a bipolar array or the like. In addition, depending on other conditions, such as the peak-to-peak voltage, electrode diameter, etc., a single active electrode may be sufficient to contract collagen tissue, ablate tissue, or the like.

In addition, the active and return electrodes may both be located on a distal tissue treatment surface adjacent to each other. The active and return electrodes may be located in active/return electrode pairs, or one or more return electrodes may be located on the distal tip together with a plurality of electrically isolated active electrodes. The proximal return electrode may or may not be employed in these embodiments. For example, if it is desired to maintain the current flux lines around the distal tip of the probe, the proximal return electrode will not be desired.

There now follows a description, with reference toFIGS. 47A–50B, of an electrosurgical probe having a curved shaft, according to additional embodiments of the invention.FIG. 47Ais a side view of an electrosurgical probe900, including a shaft902having a distal end portion902aand a proximal end portion902b. An active electrode910is disposed on distal end portion902a. Although only one active electrode is shown inFIG. 26A, embodiments having a plurality of active electrodes are also within the scope of the invention. Probe900further includes a handle904which houses a connection block906for coupling electrodes, e.g. active electrode910, thereto. Connection block906includes a plurality of pins908adapted for coupling probe900to a power supply unit, e.g. power supply28(FIG. 1).FIG. 47Aalso shows a first curve924and a second curve926located at shaft distal end portion902a, wherein second curve926is proximal to first curve924. First curve924and second curve926may be separated by a linear (i.e. straight, or non-curved), or substantially linear, inter-curve portion925of shaft902.

FIG. 47Bis a side view of shaft distal end portion902awithin a representative introducer device or needle928having an inner diameter D. Shaft distal end portion902aincludes first curve924and second curve926separated by inter-curve portion925. In one embodiment, shaft distal end portion902a includes a linear or substantially linear proximal portion901extending from proximal end portion902bto second curve926, a linear or substantially linear inter-curve portion925between first and second curves924,926, and a linear or substantially linear distal portion909between first curve924and the distal tip of shaft902(the distal tip is represented inFIG. 47Bas an electrode head911). When shaft distal end portion902ais located within introducer needle928, first curve924subtends a first angle ∀ to the inner surface of needle928, and second curve926subtends a second angle ∃ to inner surface932of needle928. (In the situation shown inFIG. 47B, needle inner surface932is essentially parallel to the longitudinal axis of shaft proximal end portion902b(FIG. 47A).) In one embodiment, shaft distal end portion902ais designed such that the shaft distal tip occupies a substantially central transverse location within the lumen of introducer needle928when shaft distal end portion902ais translated axially with respect to introducer needle928. Thus, as shaft distal end portion902ais advanced through the distal opening of needle928(FIGS. 30B,31B), and then retracted back into the distal opening, the shaft distal tip will always occupy a transverse location towards the center of introducer needle928(even though the tip may be curved or biased away from the longitudinal axis of shaft902and needle928upon its advancement past the distal opening of introducer needle928). In one embodiment, shaft distal end portion902ais flexible and has a configuration which requires shaft distal end portion902abe distorted in the region of at least second curve926by application of a lateral force imposed by inner wall932of introducer needle928as shaft distal end portion902ais introduced or retracted into needle928. In one embodiment, first curve924and second curve926are in the same plane relative to the longitudinal axis of shaft902, and first and second curves924,926are in opposite directions.

The “S-curve” configuration of shaft902shown inFIGS. 47A–Callows the distal end or tip of a device to be advanced or retracted through needle distal end928aand within the lumen of needle928without the distal end or tip contacting introducer needle928. Accordingly, this design allows a sensitive or delicate component to be located at the distal tip of a device, wherein the distal end or tip is advanced or retracted through a lumen of an introducer instrument comprising a relatively hard material (e.g., an introducer needle comprising stainless steel). This design also allows a component located at a distal end or tip of a device to be constructed from a relatively soft material, and for the component located at the distal end or tip to be passed through an introducer instrument comprising a hard material without risking damage to the component comprising a relatively soft material.

The “S-curve” design of shaft distal end portion902aallows the distal tip (e.g., electrode head911) to be advanced and retracted through the distal opening of needle928while avoiding contact between the distal tip and the edges of the distal opening of needle928. (If, for example, shaft distal end portion902aincluded only a single curve, the distal tip would ordinarily come into contact with needle distal end928aas shaft902is retracted into the lumen of needle928.) In preferred embodiments, the length L2of distal portion909and the angle ∀ between distal portion909and needle inner surface932928, when shaft distal end portion902ais compressed within needle928, are selected such that the distal tip is substantially in the center of the lumen of needle928, as shown inFIG. 47B. Thus, as the length L2increases, the angle ∀ will decrease, and vice versa. The exact values of length L2and angle ∀ will depend on the inner diameter, D of needle928, the inner diameter, d of shaft distal end portion902a, and the size of the shaft distal tip.

The presence of first and second curves,924,926provides a pre-defined bias in shaft902. In addition, in one embodiment shaft distal end portion902ais designed such that at least one of first and second curves924,926are compressed to some extent as shaft distal end portion902ais retracted into the lumen of needle928. Accordingly, the angle of at least one of curves924,926may be changed when distal end portion902ais advanced out through the distal opening of introducer needle928, as compared with the corresponding angle when shaft distal end portion is completely retracted within introducer needle928. For example,FIG. 47Cshows shaft902ofFIG. 47Bfree from introducer needle928, wherein first and second curves924,926are allowed to adopt their natural or uncompressed angles ∀′ and ∃′, respectively, wherein ∃′ is typically equal to or greater than ∃. Angle ∀′ may be greater than, equal to, or less than angle ∀. Angle ∃′ is subtended by inter-curve portion925and proximal portion901. When shaft distal end portion902ais unrestrained by introducer needle928, proximal portion901approximates the longitudinal axis of shaft902. Angle ∀′ is subtended between linear distal portion909and a line drawn parallel to proximal portion901. Electrode head911is omitted fromFIG. 47Cfor the sake of clarity.

The principle described above with reference to shaft902and introducer needle928may equally apply to a range of other medical devices. That is to say, the “S-curve” configuration of the invention may be included as a feature of any medical system or apparatus in which a medical instrument may be axially translated or passed within an introducer device. In particular, the principle of the “S-curve” configuration of the invention may be applied to any apparatus wherein it is desired that the distal end of the medical instrument does not contact or impinge upon the introducer device as the medical instrument is advanced from or retracted into the introducer device. The introducer device may be any apparatus through which a medical instrument is passed. Such medical systems may include, for example, a catheter, a cannula, an endoscope, and the like.

When shaft902is advanced distally through the needle lumen to a point where second curve926is located distal to needle distal end928a, the shaft distal tip is deflected from the longitudinal axis of needle928. The amount of this deflection is determined by the relative size of angles ∃′ and ∀′, and the relative lengths of L1and L2. The amount of this deflection will in turn determine the size of a channel or lesion (depending on the application) formed in a tissue treated by electrode head911when shaft902is rotated circumferentially with respect to the longitudinal axis of probe900.

As a result of the pre-defined bias in shaft902, shaft distal end portion902a will contact a larger volume of tissue than a linear shaft having the same dimensions. In addition, in one embodiment the pre-defined bias of shaft902allows the physician to guide or steer the distal tip of shaft902by a combination of axial movement of needle distal end928aand the inherent curvature at shaft distal end portion902aof probe900.

Shaft902preferably has a length in the range of from about 4 to 30 cm. In one aspect of the invention, probe900is manufactured in a range of sizes having different lengths and/or diameters of shaft902. A shaft of appropriate size can then be selected by the surgeon according to the body structure or tissue to be treated and the age or size of the patient. In this way, patients varying in size from small children to large adults can be accommodated. Similarly, for a patient of a given size, a shaft of appropriate size can be selected by the surgeon depending on the organ or tissue to be treated, for example, whether an intervertebral disc to be treated is in the lumbar spine or the cervical spine. For example, a shaft suitable for treatment of a disc of the cervical spine may be substantially smaller than a shaft for treatment of a lumbar disc. For treatment of a lumbar disc in an adult, shaft902is preferably in the range of from about 15 to 20 cm. For treatment of a cervical disc, shaft902is preferably in the range of from about 4 to about 15 cm.

The diameter of shaft902is preferably in the range of from about 0.5 to about 2.5 mm, and more preferably from about 1 to 1.5 mm. First curve924is characterized by a length L1, while second curve926is characterized by a length L2(FIG. 47B). Inter-curve portion925is characterized by a length L3, while shaft902extends distally from first curve924a length L4. In one embodiment, L2is greater than L1. Length L1may be in the range of from about 0.5 to about 5 mm, while L2may be in the range of from about 1 to about 10 mm. Preferably, L3and L4are each in the range of from about 1 to 6 mm.

FIG. 48Ais a side view of electrosurgical probe900showing details of shaft distal end portion902aincluding an active electrode head911of active electrode910(the latter not shown inFIG. 48A), according to one embodiment of the invention. Distal end portion902aincludes an insulating collar or spacer916proximal to active electrode head911, and a return electrode918proximal to collar916. A first insulating sleeve (FIG. 48B) may be located beneath return electrode918. A second insulating jacket or sleeve920may extend proximally from return electrode918. Second insulating sleeve920serves as an electrical insulator to inhibit current flow into non-target tissue. In a currently preferred embodiment, probe900further includes a shield922extending proximally from second insulating sleeve920. Shield922may be formed from a conductive metal such as stainless steel, and the like. Shield922functions to decrease the amount of leakage current passing from probe900to a patient or a user (e.g., surgeon). In particular, shield922decreases the amount of capacitive coupling between return electrode918and an introducer needle928(FIG. 50A).

In this embodiment, electrode head911includes an apical spike911aand an equatorial cusp911b. Electrode head911exhibits a number of advantages as compared with, for example, an electrosurgical probe having a blunt, globular, or substantially spherical active electrode. In particular, electrode head911provides a high current density at apical spike911aand cusp911b. In turn, high current density in the vicinity of an active electrode is advantageous in the generation of a plasma; and, as is described fully hereinabove, generation of a plasma in the vicinity of an active electrode is fundamental to ablation of tissue with minimal collateral thermal damage according to certain embodiments of the instant invention. Electrode head911provides an additional advantage, in that the sharp edges of cusp911b, and more particularly of apical spike911a, facilitate movement and guiding of head911into fresh tissue during surgical procedures, as described fully hereinbelow. In contrast, an electrosurgical probe having a blunt or rounded apical electrode is more likely to follow a path of least resistance, such as a channel which was previously ablated within nucleus pulposus tissue. Although certain embodiments of the invention depict head911as having a single apical spike, other shapes for the apical portion of active electrode910are also within the scope of the invention.

FIG. 48Bis a longitudinal cross-sectional view of distal end portion902aof shaft902. Apical electrode head911is in communication with a filament912. Filament912typically comprises an electrically conductive wire encased within a first insulating sleeve914. First insulating sleeve914comprises an insulator, such as various synthetic polymeric materials. An exemplary material from which first insulating sleeve914may be constructed is a polyimide. First insulating sleeve914may extend the entire length of shaft902proximal to head911. An insulating collar or spacer916is disposed on the distal end of first insulating sleeve914, adjacent to electrode head911. Collar916preferably comprises a material such as a glass, a ceramic, or silicone. The exposed portion of first insulating sleeve914(i.e., the portion proximal to collar916) is encased within a cylindrical return electrode918. Return electrode918may extend proximally the entire length of shaft902. Return electrode918may comprise an electrically conductive material such as stainless steel, tungsten, platinum or its alloys, titanium or its alloys, molybdenum or its alloys, nickel or its alloys, and the like. A proximal portion of return electrode918is encased within a second insulating sleeve920, so as to provide an exposed band of return electrode918located distal to second sleeve920and proximal to collar916. Second sleeve920provides an insulated portion of shaft920which facilitates handling of probe900by the surgeon during a surgical procedure. A proximal portion of second sleeve920is encased within an electrically conductive shield922. Second sleeve920and shield922may also extend proximally for the entire length of shaft902.

FIG. 49Ashows distal end portion902aof shaft902extended distally from an introducer needle928, according to one embodiment of the invention. Introducer needle928may be used to conveniently introduce shaft902into tissue, such as the nucleus pulposus of an intervertebral disc. In this embodiment, due to the curvature of shaft distal end902a, when shaft902is extended distally beyond introducer needle928, head911is displaced laterally from the longitudinal axis of introducer needle928. However, as shown inFIG. 49B, as shaft902is retracted into introducer needle928, head911assumes a substantially central transverse location within lumen930(see alsoFIG. 50B) of introducer928. Such re-alignment of head911with the longitudinal axis of introducer928is achieved by specific design of the curvature of shaft distal end902a, as accomplished by the instant inventors. In this manner, contact of various components of shaft distal end902a(e.g., electrode head911, collar916, return electrode918) is prevented, thereby not only facilitating extension and retraction of shaft902within introducer928, but also avoiding a potential source of damage to sensitive components of shaft902.

FIG. 50Ashows a side view of shaft902in relation to an inner wall932of introducer needle928upon extension or retraction of electrode head911from, or within, introducer needle928. Shaft902is located within introducer928with head911adjacent to introducer distal end928a(FIG. 50B). Under these circumstances, curvature of shaft902may cause shaft distal end902ato be forced into contact with introducer inner wall932, e.g., at a location of second curve926. Nevertheless, due to the overall curvature of shaft902, and in particular the nature and position of first curve924(FIGS. 47A–B), head911does not contact introducer distal end928a.

FIG. 50Bshows an end view of electrode head911in relation to introducer needle928at a point during extension or retraction of shaft902, wherein head911is adjacent to introducer distal end928a(FIGS. 49B,50B). In this situation, head911occupies a substantially central transverse location within lumen930of introducer928. Therefore, contact between head911and introducer928is avoided, allowing shaft distal end902ato be extended and retracted repeatedly without sustaining any damage to shaft902.

FIG. 51Ashows shaft proximal end portion902bof electrosurgical probe900, wherein shaft902includes a plurality of depth markings903(shown as903a–finFIG. 51A). In other embodiments, other numbers and arrangements of depth markings903may be included on shaft902. For example, in certain embodiments, depth markings may be present along the entire length of shield922, or a single depth marking903may be present at shaft proximal end portion902b. Depth markings serve to indicate to the surgeon the depth of penetration of shaft902into a patient's tissue, organ, or body, during a surgical procedure. Depth markings903may be formed directly in or on shield922, and may comprise the same material as shield922. Alternatively, depth markings903may be formed from a material other than that of shield922. For example, depth markings may be formed from materials which have a different color and/or a different level of radiopacity, as compared with material of shield922. For example, depth markings may comprise a metal, such as tungsten, gold, or platinum oxide (black), having a level of radiopacity different from that of shield922. Such depth markings may be visualized by the surgeon during a procedure performed under fluoroscopy. In one embodiment, the length of introducer needle928and shaft902are selected to limit the range of shaft distal end902abeyond the distal tip of introducer needle928.

FIG. 51Bshows a probe900, wherein shaft902includes a mechanical stop905. Preferably, mechanical stop905is located at shaft proximal end portion902b. Mechanical stop905limits the distance to which shaft distal end902acan be advanced through introducer928by making mechanical contact with a proximal end928bof introducer928. Mechanical stop905may be a rigid material or structure affixed to, or integral with, shaft902. Mechanical stop905also serves to monitor the depth or distance of advancement of shaft distal end902athrough introducer928, and the degree of penetration of distal end902ainto a patient's tissue, organ, or body. In one embodiment, mechanical stop905is movable on shaft902, and stop905includes a stop adjustment unit907for adjusting the position of stop905and for locking stop905at a selected location on shaft902.

FIG. 52Aschematically represents a normal intervertebral disc290in relation to the spinal cord818, the intervertebral disc having an outer annulus fibrosus292enclosing an inner nucleus pulposus291. The nucleus pulposus is a relatively soft tissue comprising proteins and having a relatively high water content, as compared with the harder, more fibrous annulus fibrosus.FIGS. 52B–Deach schematically represent an intervertebral disc having a disorder which can lead to discogenic pain, for example due to compression of a nerve root by a distorted annulus fibrosus. Thus,FIG. 52Bschematically represents an intervertebral disc exhibiting a bulge or protrusion of the nucleus pulposus and a concomitant distortion of the annulus fibrosus. The condition depicted inFIG. 52Bclearly represents a contained herniation, which can result in severe and often debilitating pain.FIG. 52Cschematically represents an intervertebral disc exhibiting a plurality of fissures1106within the annulus fibrosus, again with concomitant distortion of the annulus fibrosus. Such annular fissures may be caused by excessive pressure exerted by the nucleus pulposus on the annulus fibrosus. Excessive pressure within the nucleus pulposus tends to intensify disc disorders associated with the presence of such fissures.FIG. 52Dschematically represents an intervertebral disc exhibiting fragmentation of the nucleus pulposus and a concomitant distortion of the annulus fibrosus. In this situation, over time, errant fragment291′ of the nucleus pulposus tends to dehydrate and to diminish in size, often leading to a decrease in discogenic pain over an extended period of time (e.g., several months). For the sake of clarity, eachFIGS. 52B,52C,52D shows a single disorder. However, in practice more than one of the depicted disorders may occur in the same disc.

Many patients suffer from discogenic pain resulting, for example, from conditions of the type depicted inFIGS. 52B–D. However, only a small percentage of such patients undergo laminotomy or discectomy. Presently, there is a need for interventional treatment for the large group of patients who ultimately do not undergo major spinal surgery, but who sustain significant disability due to various disorders or defects of an intervertebral disc. A common disorder of intervertebral discs is a contained herniation in which the nucleus pulposus does not breach the annulus fibrosus, but a protrusion of the disc causes compression of the exiting nerve root, leading to radicular pain. Typical symptoms are leg pain compatible with sciatica. Such radicular pain may be considered as a particular form of discogenic pain. Most commonly, contained herniations leading to radicular pain are associated with the lumbar spine, and in particular with intervertebral discs at either L4-5or L5-S1. Various disc defects are also encountered in the cervical spine. Methods and apparatus of the invention are applicable to all segments of the spine, including the cervical spine and the lumbar spine.

FIG. 53schematically represents shaft902of probe900inserted within a nucleus pulposus of a disc having at least one fissure in the annulus. Shaft902may be conveniently inserted within the nucleus pulposus via introducer needle928in a minimally invasive percutaneous procedure. In a preferred embodiment, a disc in the lumbar spine may be accessed via a posterior lateral approach, although other approaches are possible and are within the scope of the invention. The preferred length and diameter of shaft902and introducer needle928to be used in a procedure will depend on a number of factors, including the region of the spine (e.g., lumbar, cervical) or other body region to be treated, and the size of the patient. Preferred ranges for shaft902are given elsewhere herein. In one embodiment for treatment of a lumbar disc, introducer needle928preferably has a diameter in the range of from about 50% to 150% the internal diameter of a 17 Gauge needle. In an embodiment for treatment of a cervical disc, introducer needle928preferably has a diameter in the range of from about 50% to 150% the internal diameter of a 20 Gauge needle.

Shaft902includes an active electrode910, as described hereinabove. Shaft902features curvature at distal end902a/902′a, for example, as described with reference toFIGS. 47A–B. By rotating shaft902through approximately 180°, shaft distal end902acan be moved to a position indicated by the dashed lines and labeled as902′a. Thereafter, rotation of shaft902through an additional 180° defines a substantially cylindrical three-dimensional space with a proximal frusto-conical region, the latter represented as a hatched area (shown between902aand902′a). The bi-directional arrow distal to active electrode910indicates translation of shaft902substantially along the longitudinal axis of shaft902. By a combination of axial and rotational movement of shaft902, a much larger volume of the nucleus pulposus can be contacted by electrode910, as compared with a corresponding probe having a linear (non-curved) shaft. Furthermore, the curved nature of shaft902allows the surgeon to change the direction of advancement of shaft902by appropriate rotation thereof, and to guide shaft distal end902ato a particular target site within the nucleus pulposus. In addition, further control may be exerted over which sites or regions within the disc can be accessed by shaft distal end902aby advancing or retracting introducer needle928to change the initiation point from which shaft distal end902amay be guided or steered. Alternatively, selection of an appropriate position from which shaft distal end902amay be advanced, guided, or steered to a target location may make use of an introducer extension tube (FIG. 61A) which acts as an extension of introducer needle928. By changing the location of the introducer needle or the introducer extension tube relative to the disc, different regions of the disc can be accessed by shaft distal end902a.

It is to be understood that according to certain embodiments of the invention, the curvature of shaft902is the same, or substantially the same, both prior to it being used in a surgical procedure and while it is performing ablation during a procedure, e.g., within an intervertebral disc. (One apparent exception to this statement, relates to the stage in a procedure wherein shaft902may be transiently “molded” into a somewhat more linear configuration by the constraints of introducer inner wall932during housing, or passing, of shaft902within introducer928.) In contrast, certain prior art devices, and embodiments of the invention to be described hereinbelow (e.g., with reference toFIGS. 59A,59B), may be linear or lacking a naturally defined configuration prior to use, and then be steered into a selected configuration during a surgical procedure.

While shaft distal end902ais at or adjacent to a target site within the nucleus pulposus, probe900may be used to ablate tissue by application of a first high frequency voltage between active electrode910and return electrode918(e.g.,FIG. 26B), wherein the volume of the nucleus pulposus is decreased, the pressure exerted by the nucleus pulposus on the annulus fibrosus is decreased, and at least one nerve or nerve root is decompressed. Accordingly, discogenic pain experienced by the patient may be alleviated. Preferably, application of the first high frequency voltage results in formation of a plasma in the vicinity of active electrode910, and the plasma causes ablation by breaking down high molecular weight disc tissue components (e.g., proteins) into low molecular weight gaseous materials. Such low molecular weight gaseous materials may be at least partially vented or exhausted from the disc, e.g., by piston action, upon removal of shaft902and introducer928from the disc and the clearance between introducer needle928and shaft902. In addition, by-products of tissue ablation may be removed by an aspiration device (not shown inFIG. 53), as is well known in the art. In this manner, the volume and/or mass of the nucleus pulposus may be decreased.

In order to initiate and/or maintain a plasma in the vicinity of active electrode910, a quantity of an electrically conductive fluid may be applied to shaft902and/or the tissue to ablated. The electrically conductive fluid may be applied to shaft902and/or to the tissue to be ablated, either before or during application of the first high frequency voltage. Examples of electrically conductive fluids are saline (e.g., isotonic saline), and an electrically conductive gel. An electrically conductive fluid may be applied to the tissue to be ablated before or during ablation. A fluid delivery unit or device may be a component of the electrosurgical probe itself, or may comprise a separate device, e.g., ancillary device940(FIG. 57). Alternatively, many body fluids and/or tissues (e.g., the nucleus pulposus, blood) at the site to be ablated are electrically conductive and can participate in initiation or maintenance of a plasma in the vicinity of the active electrode.

In one embodiment, after ablation of nucleus pulposus tissue by the application of the first high frequency voltage and formation of a cavity or channel within the nucleus pulposus, a second high frequency voltage may be applied between active electrode910and return electrode918, wherein application of the second high frequency voltage causes coagulation of nucleus pulposus tissue adjacent to the cavity or channel. Such coagulation of nucleus pulposus tissue may lead to increased stiffness, strength, and/or rigidity within certain regions of the nucleus pulposus, concomitant with an alleviation of discogenic pain. Furthermore, coagulation of tissues may lead to necrotic tissue which is subsequently broken down as part of a natural bodily process and expelled from the body, thereby resulting in de-bulking of the disc. AlthoughFIG. 53depicts a disc having fissures within the annulus fibrosus, it is to be understood that apparatus and methods of the invention discussed with reference toFIG. 53are also applicable to treating other types of disc disorders, including those described with reference toFIGS. 52B,52D.

FIG. 54shows shaft902of electrosurgical probe900within an intervertebral disc, wherein shaft distal end902ais targeted to a specific site within the disc. In the situation depicted inFIG. 54, the target site is occupied by an errant fragment291′ of nucleus pulposus tissue. Shaft distal end902may be guided or directed, at least in part, by appropriate placement of introducer928, such that active electrode910is in the vicinity of fragment291′. Preferably, active electrode910is adjacent to, or in contact with, fragment291′. AlthoughFIG. 54depicts a disc in which a fragment of nucleus pulposus is targeted by shaft902, the invention described with reference toFIG. 54may also be used for targeting other aberrant structures within an intervertebral disc, including annular fissures and contained herniations. In a currently preferred embodiment, shaft902includes at least one curve (not shown inFIG. 54), and other features described herein with reference toFIGS. 26A–35, wherein shaft distal end902amay be precisely guided by an appropriate combination of axial and rotational movement of shaft902. The procedure illustrated inFIG. 54may be performed generally according to the description presented with reference toFIG. 53. That is, shaft902is introduced into the disc via introducer928in a percutaneous procedure. After shaft distal end902ahas been guided to a target site, tissue at or adjacent to that site is ablated by application of a first high frequency voltage. Thereafter, depending on the particular condition of the disc being treated, a second high frequency voltage may optionally be applied in order to locally coagulate tissue within the disc.

FIG. 55schematically represents a series of steps involved in a method of ablating disc tissue according to the present invention; wherein step1200involves advancing an introducer needle towards an intervertebral disc to be treated. The introducer needle has a lumen having a diameter greater than the diameter of the shaft distal end, thereby allowing free passage of the shaft distal end through the lumen of the introducer needle. In one embodiment, the introducer needle preferably has a length in the range of from about 3 cm to about 25 cm, and the lumen of the introducer needle preferably has a diameter in the range of from about 0.5 cm to about 2.5 mm. Preferably, the diameter of the shaft distal end is from about 30% to about 95% of the diameter of the lumen. The introducer needle may be inserted in the intervertebral disc percutaneously, e.g. via a posterior lateral approach. In one embodiment, the introducer needle may have dimensions similar to those of an epidural needle, the latter well known in the art.

Optional step1202involves introducing an electrically conductive fluid, such as saline, into the disc. In one embodiment, in lieu of step1202, the ablation procedure may rely on the electrical conductivity of the nucleus pulposus itself. Step1204involves inserting the shaft of the electrosurgical probe into the disc, e.g., via the introducer needle, wherein the distal end portion of the shaft bears an active electrode and a return electrode. In one embodiment, the shaft includes an outer shield, first and second curves at the distal end portion of the shaft, and an electrode head having an apical spike, generally as described with reference toFIGS. 26A–32.

Step1206involves ablating at least a portion of disc tissue by application of a first high frequency voltage between the active electrode and the return electrode. In particular, ablation of nucleus pulposus tissue according to methods of the invention serves to decrease the volume of the nucleus pulposus, thereby relieving pressure exerted on the annulus fibrosus, with concomitant decompression of a previously compressed nerve root, and alleviation of discogenic pain.

In one embodiment, the introducer needle is advanced towards the intervertebral disc until it penetrates the annulus fibrosus and enters the nucleus pulposus. The shaft distal end in introduced into the nucleus pulposus, and a portion of the nucleus pulposus is ablated. These and other stages of the procedure may be performed under fluoroscopy to allow visualization of the relative location of the introducer needle and shaft relative to the nucleus pulposus of the disc. Additionally or alternatively, the surgeon may introduce the introducer needle into the nucleus pulposus from a first side of the disc, then advance the shaft distal end through the nucleus pulposus until resistance to axial translation of the electrosurgical probe is encountered by the surgeon. Such resistance may be interpreted by the surgeon as the shaft distal end having contacted the annulus fibrosus at the opposite side of the disc. Then, by use of depth markings on the shaft (FIG. 51A), the surgeon can retract the shaft a defined distance in order to position the shaft distal end at a desired location relative to the nucleus pulposus. Once the shaft distal end is suitably positioned, high frequency voltage may be applied to the probe via the power supply unit.

After step1206, optional step1208involves coagulating at least a portion of the disc tissue. In one embodiment, step1206results in the formation of a channel or cavity within the nucleus pulposus. Thereafter, tissue at the surface of the channel may be coagulated during step1208. Coagulation of disc tissue may be performed by application of a second high frequency voltage, as described hereinabove. After step1206or step1208, the shaft may be moved (step1210) such that the shaft distal end contacts fresh tissue of the nucleus pulposus. The shaft may be axially translated (i.e. moved in the direction of its longitudinal axis), may be rotated about its longitudinal axis, or may be moved by a combination of axial and rotational movement. In the latter case, a substantially spiral path is defined by the shaft distal end. After step1210, steps1206and1208may be repeated with respect to the fresh tissue of the nucleus pulposus contacted by the shaft distal end. Alternatively, after step1206or step1208, the shaft may be withdrawn from the disc (step1212). Step1214involves withdrawing the introducer needle from the disc. In one embodiment, the shaft and the needle may be withdrawn from the disc concurrently. Withdrawal of the shaft from the disc may facilitate exhaustion of ablation by-products from the disc. Such ablation by-products include low molecular weight gaseous compounds derived from molecular dissociation of disc tissue components, as described hereinabove.

The above method may be used to treat any disc disorder in which Coblation® and or coagulation of disc tissue is indicated, including contained herniations. In one embodiment, an introducer needle may be introduced generally as described for step1200, and a fluoroscopic fluid may be introduced through the lumen of the introducer needle for the purpose of visualizing and diagnosing a disc defect or disorder. Thereafter, depending on the diagnosis, a treatment procedure may be performed, e.g., according to steps1202through1214, using the same introducer needle as access. In one embodiment, a distal portion, or the entire length, of the introducer needle may have an insulating coating on its external surface. Such an insulating coating on the introducer needle may prevent interference between the electrically conductive introducer needle and electrode(s) on the probe.

The size of the cavity or channel formed in a tissue by a single straight pass of the shaft through the tissue to be ablated is a function of the diameter of the shaft (e.g., the diameter of the shaft distal end and active electrode) and the amount of axial translation of the shaft. (By a “single straight pass” of the shaft is meant one axial translation of the shaft in a distal direction through the tissue, in the absence of rotation of the shaft about the longitudinal axis of the shaft, with the power from the power supply turned on.) In the case of a curved shaft, according to various embodiments of the instant invention, a larger channel can be formed by rotating the shaft as it is advanced through the tissue. The size of a channel formed in a tissue by a single rotational pass of the shaft through the tissue to be ablated is a function of the deflection of the shaft, and the amount of rotation of the shaft about its longitudinal axis, as well as the diameter of the shaft (e.g., the diameter of the shaft distal end and active electrode) and the amount of axial translation of the shaft. (By a “single rotational pass” of the shaft is meant one axial translation of the shaft in a distal direction through the tissue, in the presence of rotation of the shaft about the longitudinal axis of the shaft, with the power from the power supply turned on.) To a large extent, the diameter of a channel formed during a rotational pass of the shaft through tissue can be controlled by the amount of rotation of the shaft, wherein the “amount of rotation” encompasses both the rate of rotation (e.g., the angular velocity of the shaft), and the number of degrees through which the shaft is rotated (e.g. the number of turns) per unit length of axial movement. Typically, according to the invention, the amount of axial translation per pass (for either a straight pass or a rotational pass) is not limited by the length of the shaft. Instead, the amount of axial translation per single pass is preferably determined by the size of the tissue to be ablated. Depending on the size of the disc or other tissue to be treated, and the nature of the treatment, etc., a channel formed by a probe of the instant invention may preferably have a length in the range of from about 2 mm to about 50 mm, and a diameter in the range of from about 0.5 mm to about 7.5 mm. In comparison, a channel formed by a shaft of the instant invention during a single rotational pass may preferably have a diameter in the range of from about 1.5 mm to about 25 mm.

A channel formed by a shaft of the instant invention during a single straight pass may preferably have a volume in the range of from about 1 mm3, or less, to about 2,500 mm3. More preferably, a channel formed by a straight pass of a shaft of the instant invention has a volume in the range of from about 10 mm3to about 2,500 mm3, and more preferably in the range of from about 50 mm3to about 2,500 mm3. In comparison, a channel formed by a shaft of the instant invention during a single rotational pass typically has a volume from about twice to about 15 times the volume of a channel of the same length formed during a single rotational pass, i.e., in the range of from about 2 mm3to about 4,000 mm3, more preferably in the range of from about 50 mm3to about 2,000 mm3. While not being bound by theory, the reduction in volume of a disc having one or more channels therein is a function of the total volume of the one or more channels.

FIG. 56schematically represents a series of steps involved in a method of guiding the distal end of a shaft of an electrosurgical probe to a target site within an intervertebral disc for ablation of specifically targeted disc tissue, wherein steps1300and1302are analogous to steps1200and1204ofFIG. 55. Thereafter step1304involves guiding the shaft distal end to a defined region within the disc. The specific target site may be pre-defined as a result of a previous procedure to visualize the disc and its defect, e.g., via X-ray examination, endoscopically, or fluoroscopically. As an example, a defined target site within a disc may comprise a fragment of the nucleus pulposus that has migrated within the annulus fibrosus (see, e.g.,FIG. 52D) resulting in discogenic pain. However, guiding the shaft to defined sites associated with other types of disc disorders are also possible and is within the scope of the invention. In one embodiment, as a prelude to guiding the shaft distal end to a target site, the shaft distal end may first be introduced into the disc at a selected location within the disc. Such a selected location defines a space within the disc from where the shaft distal end may be advanced in order to reach or access the target site. Preferably, the selected location defines a space in the general vicinity of the target site from where the shaft distal end may readily access the target site. The shaft distal end may be introduced at the selected location within the disc by advancing or retracting the introducer needle within the disc until the introducer needle distal end reaches the selected location. In another embodiment, the shaft distal end may be introduced at the selected location within the disc by advancing or retracting an introducer extension tube within the lumen of the introducer needle until the distal end of the introducer extension tube reaches the selected location (FIGS. 62A–B).

Guiding the shaft distal end to the defined target site may be performed by axial and/or rotational movement of a curved shaft, as described hereinabove. Or the shaft may be steerable, for example, by means of a guide wire, as is well known in the art. Guiding the shaft distal end may be performed during visualization of the location of the shaft relative to the disc, wherein the visualization may be performed endoscopically or via fluoroscopy. Endoscopic examination may employ a fiber optic cable (not shown). The fiber optic cable may be integral with the electrosurgical probe, or be part of a separate instrument (endoscope). Step1306involves ablating disc tissue, and is analogous to step1206(FIG. 55). Before or during step1306, an electrically conductive fluid may be applied to the disc tissue and/or the shaft in order to provide a path for current flow between active and return electrodes on the shaft, and to facilitate and/or maintain a plasma in the vicinity of the distal end portion of the shaft. After the shaft distal end has been guided to a target site and tissue at that site has been ablated, the shaft may be moved locally, e.g., within the same region of the nucleus pulposus, or to a second defined target site within the same disc. The shaft distal end may be moved as described herein (e.g., with reference to step1210,FIG. 55). Or, according to an alternative embodiment, the shaft may be steerable, e.g., by techniques well known in the art. Steps1310and1312are analogous to steps1212and1214, respectively (described with reference toFIG. 55).

It is known in the art that epidural steroid injections can transiently diminish perineural inflammation of an affected nerve root, leading to alleviation of discogenic pain. In one embodiment of the invention, methods for ablation of disc tissue described hereinabove may be conveniently performed in conjunction with an epidural steroid injection. For example, ablation of disc tissue and epidural injection could be carried out as part of a single procedure, by the same surgeon, using equipment common to both procedures (e.g. visualization equipment). Combining Coblation® and epidural injection in a single procedure may provide substantial cost-savings to the healthcare industry, as well as a significant improvement in patient care.

As alluded to hereinabove, methods and apparatus of the present invention can be used to accelerate the healing process of intervertebral discs having fissures and/or contained herniations. In one method, the present invention is useful in microendoscopic discectomy procedures, e.g., for decompressing a nerve root with a lumbar discectomy. For example, as described above in relation toFIGS. 18–20, a percutaneous penetration can be made in the patient's back so that the superior lamina can be accessed. Typically, a small needle is used initially to localize the disc space level, and a guide wire is inserted and advanced under lateral fluoroscopy to the inferior edge of the lamina. Sequential cannulated dilators can be inserted over the guide wire and each other to provide a hole from the incision to the lamina. The first dilator may be used to “palpate” the lamina, assuring proper location of its tip between the spinous process and facet complex just above the inferior edge of the lamina. A tubular retractor can then be passed over the largest dilator down to the lamina. The dilators can then be removed, so as to establish an operating corridor within the tubular retractor. It should be appreciated however, that other conventional or proprietary methods can be used to access the target intervertebral disc. Once the target intervertebral disc has been accessed, an introducer device may be inserted into the intervertebral disc.

With reference toFIG. 57, in one embodiment, both introducer needle928and a second or ancillary introducer938may be inserted into the same disc, to allow introduction of an ancillary device940into the target disc via ancillary introducer938. Ancillary device940may comprise, for example, a fluid delivery device, a return electrode, an aspiration lumen, a second electrosurgical probe, or an endoscope having an optical fiber component. Each of introducer needle928and ancillary introducer938may be advanced through the annulus fibrosus until at least the distal end portion of each introducer928and938, is positioned within the nucleus pulposus. Thereafter, shaft902″ of electrosurgical probe900′ may be inserted through at least one of introducers928,938, to treat the intervertebral disc. Typically, shaft902″ of probe900′ has an outer diameter no larger than about 7 French (1 Fr: 0.33 mm), and preferably between about 6 French and 7 French.

Prior to inserting electrosurgical probe900into the intervertebral disc, an electrically conductive fluid can be delivered into the disk via a fluid delivery assembly (e.g., ancillary device940) in order to facilitate or promote the Coblation® mechanism within the disc following the application of a high frequency voltage via probe900′. By providing a separate device (940) for fluid delivery, the dimensions of electrosurgical probe900′ can be kept to a minimum. Furthermore, when the fluid delivery assembly is positioned within ancillary introducer938, electrically conductive fluid can be conveniently replenished to the interior of the disc at any given time during the procedure. Nevertheless, in other embodiments, the fluid delivery assembly can be physically coupled to electrosurgical probe900′.

In some methods, a radiopaque contrast solution (not shown) may be delivered through a fluid delivery assembly so as to allow the surgeon to visualize the intervertebral disc under fluoroscopy. In some configurations, a tracking device942can be positioned on shaft distal end portion902″a. Additionally or alternatively, shaft902″ can be marked incrementally, e.g., with depth markings903, to indicate to the surgeon how far the active electrode is advanced into the intervertebral disc. In one embodiment, tracking device942includes a radiopaque material that can be visualized under fluoroscopy. Such a tracking device942and depth markings903provide the surgeon with means to track the position of the active electrode910relative to a specific target site within the disc to which active electrode910is to be guided. Such specific target sites may include, for example, an annular fissure, a contained herniation, or a fragment of nucleus pulposus. The surgeon can determine the position of the active electrode910by observing the depth markings903, or by comparing tracking device output, and a fluoroscopic image of the intervertebral disc to a pre-operative fluoroscopic image of the target intervertebral disc.

In other embodiments, an optical fiber (not shown) can be introduced into the disc. The optical fiber may be either integral with probe900′ or may be introduced as part of an ancillary device940via ancillary introducer938. In this manner, the surgeon can visually monitor the interior of the intervertebral disc and the position of active electrode910.

In addition to monitoring the position of the distal portion of electrosurgical probe900′, the surgeon can also monitor whether the probe is in Coblation® mode. In most embodiments, power supply28(e.g.,FIG. 1) includes a controller having an indicator, such as a light, an audible sound, or a liquid crystal display (LCD), to indicate whether probe900′ is generating a plasma within the disc. If it is determined that the Coblation® mechanism is not occurring, (e.g., due to an insufficiency of electrically conductive fluid within the disc), the surgeon can then replenish the supply of the electrically conductive fluid to the disc.

FIG. 58is a side view of an electrosurgical probe900′ including shaft902′ having tracking device942located at distal end portion902″a. Tracking device942may serve as a radiopaque marker adapted for guiding distal end portion902″awithin a disc. Shaft902″ also includes at least one active electrode910disposed on the distal end portion902″a. Preferably, electrically insulating support member or collar916is positioned proximal of active electrode910to insulate active electrode910from at least one return electrode918. In most embodiments, the return electrode918is positioned on the distal end portion of the shaft902″ and proximal of the active electrode910. In other embodiments, however, return electrode918can be omitted from shaft902″, in which case at least one return electrode may be provided on ancillary device940, or the return electrode may be positioned on the patient's body, as a dispersive pad (not shown).

Although active electrode910is shown inFIG. 58as comprising a single apical electrode, other numbers, arrangements, and shapes for active electrode910are within the scope of the invention. For example, active electrode910can include a plurality of isolated electrodes in a variety of shapes. Active electrode910will usually have a smaller exposed surface area than return electrode918, such that the current density is much higher at active electrode910than at return electrode918. Preferably, return electrode918has a relatively large, smooth surfaces extending around shaft902″ in order to reduce current densities in the vicinity of return electrode918, thereby minimizing damage to non-target tissue.

While bipolar delivery of a high frequency energy is the preferred method of debulking the nucleus pulposus, it should be appreciated that other energy sources (i.e., resistive, or the like) can be used, and the energy can be delivered with other methods (i.e., monopolar, conductive, or the like) to debulk the nucleus.

FIG. 59Ashows a steerable electrosurgical probe950including a shaft952, according to another embodiment of the invention. Preferably, shaft952is flexible and may assume a substantially linear configuration as shown. Probe950includes handle904, shaft distal end952a, active electrode910, insulating collar916, and return electrode918. As can be seen inFIG. 59B, under certain circumstances, e.g., upon application of a force to shaft952during guiding or steering probe950during a procedure, shaft distal end952acan adopt a non-linear configuration, designated952′a. The deformable nature of shaft distal end952′aallows active electrode910to be guided to a specific target site within a disc.

FIG. 60shows steerable electrosurgical probe950inserted within the nucleus pulposus of an intervertebral disc. An ancillary device940and ancillary introducer928may also be inserted within the nucleus pulposus of the same disc. To facilitate the debulking of the nucleus pulposus adjacent to a contained herniation, shaft952(FIG. 59A) can be manipulated to a non-linear configuration, represented as952′. Preferably, shaft952/952′ is flexible over at least shaft distal end952aso as to allow steering of active electrode910to a position adjacent to the targeted disc defect. The flexible shaft may be combined with a sliding outer shield, a sliding outer introducer needle, pull wires, shape memory actuators, and other known mechanisms (not shown) for effecting selective deflection of distal end952ato facilitate positioning of active electrode910within a disc. Thus, it can be seen that the embodiment ofFIG. 60may be used for the targeted treatment of annular fissures, or any other disc defect for which Coblation® is indicated.

In one embodiment shaft952has a suitable diameter and length to allow the surgeon to reach the target disc or vertebra by introducing the shaft through the thoracic cavity, the abdomen or the like. Thus, shaft952may have a length in the range of from about 5.0 cm to 30.0 cm, and a diameter in the range of about 0.2 mm to about 20 mm. Alternatively, shaft952may be delivered percutaneously in a posterior lateral approach. Regardless of the approach, shaft952may be introduced via a rigid or flexible endoscope. In addition, it should be noted that the methods described with reference toFIGS. 57 and 60may also be performed in the absence of ancillary introducer938and ancillary device940.

FIG. 61Ashows an electrosurgical apparatus or system including a probe1050in combination with an introducer extension tube1054, according to another aspect of the invention. Probe1050generally includes at least one active electrode910disposed at a shaft distal end1502a, an electrically insulating spacer or support916proximal to active electrode910, and a return electrode918proximal to support916.FIG. 61Ashows shaft distal end1502apositioned within introducer extension tube1054, which is in turn positioned within introducer needle928. Introducer extension tube1054is adapted for passing shaft1052therethrough, and for being passed within introducer needle928. Introducer extension tube1054may be advanced distally from introducer distal end928ato a site targeted for treatment, e.g., to a selected location within an intervertebral disc. In this way, extension tube distal end1054a(FIG. 61B) may define a starting point for advancement of shaft distal end1052ainto the disc tissue, and in some embodiments extension tube distal end1054amay define a starting point from which guiding or steering of shaft distal end1052ais initiated. By selecting a starting point within the disc from which guiding or steering of shaft distal end1052ais initiated, much greater control can be exerted over accessing a given target site, and in addition a much greater range of regions within the disc can be accessed with a given probe (e.g., with a probe having a shaft of a given length and curvature).

FIG. 61Bshows shaft distal end1052aof the probe ofFIG. 61Aextending beyond the distal end of both introducer extension tube1054and introducer needle928, with shaft distal end1052aadopting a curved configuration. Such a curved configuration allows access to a much greater number of regions, or to a much larger volume of tissue, within an intervertebral disc, for example, by rotating shaft1052. Such a curved configuration may be due to a pre-defined bend or curve in shaft1052(e.g.,FIGS. 47A–C), or may be the result of a steering mechanism, the latter well known in the art. In the former situation, a pre-defined curvature in shaft1052may be restrained or compressed while shaft1052is within introducer extension tube1054or introducer needle928. Introducer extension tube1054may be rigid or somewhat flexible. Introducer extension tube1054may be constructed from an electrically conductive material such as stainless steel, and the like. Alternatively, introducer extension tube1054may be constructed from an electrically insulating material, such as various plastics, and the like.

FIG. 62Ashows distal end1054aof introducer extension tube1054advanced to a first position within an intervertebral disc290. Shaft1052lies within introducer extension tube1054, which in turn lies within introducer needle928. Needle distal end928ais introduced within disc290, while extension tube distal end1054ais advanced slightly distal to needle distal end928a. Shaft distal end1052aextends beyond extension tube distal end1054aand adopts a curved configuration to access a first region, R1, of nucleus pulposus291. Curvature of shaft distal end1052amay result from a predefined bias or curve in shaft1052, or shaft distal end1052amay be steerable. Certain other regions of disc290may be accessed by shaft distal end1052aby circumferentially rotating shaft1052about its longitudinal axis prior to shaft distal end1052abeing advanced distally beyond extension tube distal end1054a(i.e., by rotating shaft1052while shaft1052lies within introducer extension tube1054).

FIG. 62Bschematically represents a situation wherein extension tube distal end1054ais advanced to a second position within intervertebral disc290. Much greater control can be exerted over the range of regions within disc290that can be accessed by shaft distal end1052awhen the location of introducer extension tube1054is selected prior to advancing shaft distal end1052ainto the disc tissue. For example, as represented inFIG. 62B, by advancing introducer extension tube1054distally within introducer needle928prior to advancing shaft distal end1052afrom introducer extension tube1054, shaft distal end1052acan readily access a second region R2, wherein R2may be located remote from first region R1(FIG. 62A). In contrast it is more problematic, if not impossible, for shaft distal end1052ato access region R2while introducer extension tube1054is positioned in relation to the disc as shown inFIG. 62A. Similarly, without the use of introducer extension tube1054(i.e., using an introducer needle928alone to advance shaft1052into the disc) it is problematic, if not impossible, for shaft distal end1052ato access region R2. The inclusion of an extension device such as introducer extension tube1054as a component of the instant invention provides major advantages in accessing a target site within an intervertebral disc or other tissues.

Although certain embodiments of the invention have been described primarily with respect to treatment of intervertebral discs, it is to be understood that these methods and apparatus of the invention are also applicable to the treatment of other tissues, organs, and bodily structures. While the exemplary embodiments of the present invention have been described in detail, by way of example and for clarity of understanding, a variety of changes, adaptations, and modifications will be obvious to those of skill in the art. Therefore, the scope of the present invention is limited solely by the appended claims.