Abstract:
Systems and methods for securing a screen-type active electrode to the distal tip of an electrosurgical device used for selectively applying electrical energy to a target location within or on a patient&#39;s body. A securing electrode is disposed through the screen electrode and mechanically joined to an insulative support body while also creating an electrical connection and mechanical enagement with the screen electrode. The electrosurgical device and related methods are provided for resecting, cutting, partially ablating, aspirating or otherwise removing tissue from a target site, and ablating the tissue in situ. The present methods and systems are particularly useful for removing tissue within joints, e.g., synovial tissue, meniscus, articular cartilage and the like.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. application Ser. No. 12/190,752, filed Aug. 13, 2008, and entitled “Systems and Methods for Screen Electrode Securement,” hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to the field of electrosurgery, and more particularly to apparatus and methods for applying high frequency voltage to ablate tissue. More particularly, the present invention relates to apparatus and methods for securing a substantially flat screen-type active electrode to the distal tip of the shaft of an electrosurgical instrument. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventional electrosurgical methods are widely used since they generally achieve hemostasis and reduce patient bleeding associated with tissue cutting operations while improving the surgeon&#39;s visibility of the treatment area. Many of the electrosurgical devices used in electrosurgery make use of a screen-type active electrode which is typically cut, or etched, from a sheet of conductive material. These electrosurgical devices and procedures, however, suffer from a number of disadvantages. For example, screen-type active electrodes typically require some method of securement to an insulative body and furthermore to the distal tip of the device itself. Failure to adequately secure the screen electrode to the insulative body may result in improper device function and possible patient harm during the electrosurgical procedure. 
         [0004]    Prior attempts to secure the screen active electrode to the insulative body have involved mechanical, thermal, and chemical means or various combinations thereof. Numerous mechanical forms of securement have been utilized, while adhesives have been used as a chemical form of joining, and welding the screen may provide one thermal method of joining These mechanical joining methods may also include the use of plastic, or non-recoverable, deformations of the materials being used for securement. However, even in combination with other joining methods, the above-listed methods for fixation provide only marginally effective solutions that typically are challenged over extended periods of use. 
         [0005]    Accordingly, devices and methods which allow for the securement of flat screen active electrodes to the insulative body of an electrosurgical instrument while maintaining electrical connections through the insulative body are desired. In particular, mechanical methods for providing reasonable and durable securement of an electrically connected screen active electrode to the insulative body at the distal tip of an electrosurgical device while providing enhanced electrosurgical operating parameters are desired. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides systems, apparatus and methods for mechanically securing a screen type active electrode to the insulative body at the distal tip of an electrosurgical device. In particular, methods and apparatus are provided for reliably securing the screen electrode over extended periods of use. Further, the methods and systems of the present invention are particularly useful for providing expanded and enhanced electrosurgical operating parameters. 
         [0007]    In one aspect of the invention, the method of securement comprises inserting a securing electrode through a channel or slot in both the screen electrode and insulative body. In a configuration where the screen electrode is supported by the insulative body, the securing electrode functions to mechanically couple the screen electrode to the insulative body, and also functions to electrically couple the screen electrode to a high frequency power supply via electrical connectors. The securing electrode may be characterized by extended leg portions having tabs at one end that engage or interfere with the channel in the insulative body, thereby preventing axial movement of the securing electrode. Thus, the securing electrode provides a mechanical method of joining the screen electrode to the insulative body while also providing an electrical connection to transmit RF energy through the insulative body to the screen electrode. 
         [0008]    Another configuration of the electrosurgical device according to the present disclosure comprises an active screen electrode having at least two bilateral channels therethrough. At least two bilateral securing electrodes are provided and are respectively inserted through the channels of the screen electrode. Additionally, the device comprises an insulative support member having at least two bilateral channels correspondingly positioned with regard to the screen electrode channels. The bilateral securing electrodes are inserted through the support member and screen electrode channels and may be oriented symmetrically to thereby allow for creation of a zone for RF ablation between the two securing electrodes. Further, the bilateral screen electrodes each have a leg portion with a tab at one end, wherein the tab slides into a locked position within the support member to secure the screen electrode in place. 
         [0009]    In certain configurations, the securing electrodes may be characterized by a saw tooth pattern on a superior surface. Additionally, the securing electrodes may be formed in the shape of a staple or bridge, thereby allowing for the creation of another zone of RF ablation in a space between the staple securing electrode and the screen electrode. The added edges formed on the securing electrode in these configurations may result in increased current density and thus promote the formation of improved zones of RF ablation. 
         [0010]    In yet another configuration, the active electrode comprises a conductive screen having a single aperture and is positioned over the insulative body at the distal tip of an electrosurgical device in relation to the distal opening of an aspiration lumen. In the representative embodiment, the screen electrode is supported by the insulating support member such that the single aperture on the screen is aligned with the aspiration lumen opening, thereby allowing for the aspiration of unwanted tissue and electrosurgery byproducts from the target site. Additionally, the screen and the distal opening of the aspiration lumen may be positioned on a lateral side of the instrument (i.e., facing 90 degrees from the instrument axis). 
         [0011]    In open procedures, the system may further include a fluid delivery element for delivering electrically conducting fluid to the active electrode(s) and the target site. The fluid delivery element may be located on the instrument, e.g., a fluid lumen or tube, or it may be part of a separate instrument. Alternatively, an electrically conducting gel or spray, such as a saline electrolyte or other conductive gel, may be applied to the tissue. In addition, in arthroscopic procedures, the target site will typically already be immersed in a conductive irrigant, i.e., saline. In these embodiments, the apparatus may not have a fluid delivery element. In both embodiments, the electrically conducting fluid will preferably provide a current flow path between the active electrode terminal(s) and the return electrode(s). In an exemplary embodiment, a return electrode is located on the instrument and spaced a sufficient distance from the active electrode terminal(s) to substantially avoid or minimize current shorting therebetween and to isolate the return electrode from tissue at the target site. 
         [0012]    In another aspect of the invention, a method comprises positioning one or more active electrode(s) (which may include an active screen electrode and securing electrode) at the target site within a patient&#39;s body and applying a suction force to a tissue structure to draw the tissue structure to the active electrode(s). High frequency voltage is then applied between the active electrode(s) and one or more return electrode(s) to ablate the tissue structure. Typically, the tissue structure comprises a flexible or elastic connective tissue, such as synovial tissue. This type of tissue is typically difficult to remove with conventional mechanical and electrosurgery techniques because the tissue moves away from the instrument and/or becomes clogged in the rotating cutting tip of the mechanical shaver or microdebrider. The present invention, by contrast, draws the elastic tissue towards the active electrodes, and then ablates this tissue with the mechanisms described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of an electrosurgical system incorporating a power supply and an electrosurgical probe; 
           [0014]      FIG. 2  is a perspective view of another electrosurgical system incorporating a power supply, an electrosurgical probe and a supply of electrically conductive fluid for delivering the fluid to the target site; 
           [0015]      FIG. 3  is a side view of an electrosurgical probe for ablating and removing tissue; 
           [0016]      FIG. 4  is a cross-sectional view of the electrosurgical probe of  FIG. 3 ; 
           [0017]      FIG. 5  illustrates a detailed view illustrating ablation of tissue; 
           [0018]      FIG. 6  is an enlarged detailed view of the distal end portion of an embodiment of the probe of  FIG. 3 ; 
           [0019]      FIGS. 7A and 7B  are detailed view of the securing electrode and screen electrode utilized in the electrosurgical probe of  FIG. 6 ; 
           [0020]      FIG. 8  is an exploded view of the distal end portion of the probe of  FIG. 6 ; 
           [0021]      FIG. 9  is a perspective view of the distal end portion of the probe of  FIG. 6 ; 
           [0022]      FIG. 10  is a perspective view of the securing electrodes and screen electrode; 
           [0023]      FIG. 11A  is a perspective view of a single aperture screen electrode on the distal end portion of an electrosurgical probe in accordance with at least some embodiments; 
           [0024]      FIG. 11B  is a perspective view of a circular shape aperture screen electrode; and 
           [0025]      FIGS. 12A-H  illustrate screen electrodes with suction apertures in accordance with at least some embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    The present invention provides systems and methods for selectively applying electrical energy to a target location within or on a patient&#39;s body. The present invention is particularly useful in procedures where the tissue site is flooded or submerged with an electrically conducting fluid, such as arthroscopic surgery of the knee, shoulder, ankle, hip, elbow, hand or foot. In other procedures, the present invention may be useful for collagen shrinkage, ablation and/or hemostasis in procedures for treating target tissue alone or in combination with the volumetric removal of tissue. More specifically, the embodiments described herein provide for electrosurgical devices characterized by a substantially flat screen active electrode disposed at the distal tip of the device. Additionally, the present embodiments include apparatus and methods for the mechanical securement of the screen electrode to the insulative body located at the distal tip of the device. Such methods of mechanical securement of the screen electrode may extend the operating period of the electrosurgical device by providing a more secure method of attachment. 
         [0027]    Before the present invention is described in detail, it is to be understood that this invention is not limited to particular variations set forth herein as various changes or modifications may be made to the invention described and equivalents may be substituted without departing from the spirit and scope of the invention. As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the objective(s), spirit or scope of the present invention. All such modifications are intended to be within the scope of the claims made herein. 
         [0028]    Methods recited herein may be carried out in any order of the recited events which is logically possible, as well as the recited order of events. Furthermore, where a range of values is provided, it is understood that every intervening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the invention. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. 
         [0029]    All existing subject matter mentioned herein (e.g., publications, patents, patent applications and hardware) is incorporated by reference herein in its entirety except insofar as the subject matter may conflict with that of the present invention (in which case what is present herein shall prevail). The referenced items are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such material by virtue of prior invention. 
         [0030]    Reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms “a,” “an,” “said” and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Last, it is to be appreciated that unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. 
         [0031]    The electrosurgical device of the present embodiments may have a variety of configurations as described above. However, at least one variation of the embodiments described herein employs a treatment device using Coblation® technology. 
         [0032]    As stated above, the assignee of the present invention developed Coblation® technology. Coblation® technology involves the application of a high frequency voltage difference between one or more active electrode(s) and one or more return electrode(s) to develop high electric field intensities in the vicinity of the target tissue. 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 tip of the active electrode(s) and the target tissue. The electrically conductive fluid may be a liquid or gas, such as isotonic saline, blood, extracelluar or intracellular fluid, delivered to, or already present at, the target site, or a viscous fluid, such as a gel, applied to the target site. 
         [0033]    When the conductive fluid is heated enough such that atoms vaporize off the surface faster than they recondense, a gas is formed. When the gas is sufficiently heated such that the atoms collide with each other causing a release of electrons in the process, an ionized gas or plasma is formed (the so-called “fourth state of matter”). Generally speaking, plasmas may be formed by heating a gas and ionizing the gas by driving an electric current through it, or by shining radio waves into the gas. These methods of plasma formation give energy to free electrons in the plasma directly, and then electron-atom collisions liberate more electrons, and the process cascades until the desired degree of ionization is achieved. A more complete description of plasma can be found in Plasma Physics, by R. J. Goldston and P. H. Rutherford of the Plasma Physics Laboratory of Princeton University (1995), the complete disclosure of which is incorporated herein by reference. 
         [0034]    As the density of the plasma or vapor layer becomes sufficiently low (i.e., less than approximately 1020 atoms/cm3 for aqueous solutions), the electron mean free path increases to enable subsequently injected electrons to cause impact ionization within the vapor layer. Once the ionic particles in the plasma layer have sufficient energy, they accelerate towards the target tissue. Energy evolved by the energetic electrons (e.g., 3.5 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. Often, the electrons carry the electrical current or absorb the radio waves and, therefore, are hotter than the ions. Thus, the electrons, which are carried away from the tissue towards the return electrode, carry most of the plasma&#39;s heat with them, allowing the ions to break apart the tissue molecules in a substantially non-thermal manner. 
         [0035]    By means of this molecular dissociation (rather than thermal evaporation or carbonization), the target tissue structure is volumetrically removed through molecular disintegration of larger organic molecules into smaller molecules and/or atoms, such as hydrogen, oxygen, 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. A more detailed description of these phenomena can be found in commonly assigned U.S. Pat. No. 5,697,882 the complete disclosure of which is incorporated herein by reference. 
         [0036]    In some applications of the Coblation® technology, high frequency (RF) electrical energy is applied in an electrically conducting media environment to shrink or remove (i.e., resect, cut, or ablate) a tissue structure and to seal transected vessels within the region of the target tissue. Coblation® technology is also useful for sealing larger arterial vessels, e.g., on the order of about 1 mm in diameter. In such applications, 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 heat, shrink, and/or achieve hemostasis of severed vessels within the tissue. 
         [0037]    The amount of energy produced by the Coblation® device 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 Coblation® device may be configured to produce energy sufficient to break the molecular bonds of certain tissue but insufficient to break the molecular bonds of other tissue. For example, fatty tissue (e.g., adipose) has double bonds that require an energy level substantially higher than 4 eV to 5 eV (typically on the order of about 8 eV) to break. Accordingly, the Coblation® technology generally does not ablate or remove such fatty tissue; however, it 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 also be broken in a similar fashion as the single bonds (e.g., increasing voltage or changing the electrode configuration to increase the current density at the electrode tips). A more complete description of these phenomena can be found in commonly assigned U.S. Pat. Nos. 6,355,032, 6,149,120 and 6,296,136, the complete disclosures of which are incorporated herein by reference. 
         [0038]    The active electrode(s) of a Coblation® device may be supported within or by an inorganic insulating support member positioned near the distal end of the instrument shaft. The return electrode may be located on the instrument shaft, on another instrument or on the external surface of the patient (i.e., a dispersive pad). The proximal end of the instrument(s) will include the appropriate electrical connections for coupling the return electrode(s) and the active electrode(s) to a high frequency power supply, such as an electrosurgical generator. 
         [0039]    Further discussion of applications and devices using Coblation® technology may be found as follows. Issued U.S. Pat. Nos. 6,296,638; and 7,241,293 both of which are incorporated by reference. Pending U.S. application Ser. No. 11/612,995 filed Dec. 19, 2006, which is incorporated by reference. 
         [0040]    In one example of a Coblation® device for use with the presently-described embodiments, the return electrode of the device is typically spaced proximally from the active electrode(s) a suitable distance to avoid electrical shorting between the active and return electrodes in the presence of electrically conductive fluid. In many cases, the distal edge of the exposed surface of the return electrode is spaced about 0.5 mm to 25 mm from the proximal edge of the exposed surface of the active electrode(s), preferably about 1.0 mm to 5.0 mm. Of course, this distance may vary with different voltage ranges, conductive fluids, and depending on the proximity of tissue structures to active and return electrodes. The return electrode will typically have an exposed length in the range of about 1 mm to 20 mm. 
         [0041]    A Coblation® treatment device for use according to the present descriptions may use a single active electrode or an array of active electrodes spaced around the distal surface of a catheter or 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 fluids, such as blood, normal saline, and the like. The active electrodes may be independently current-limited by isolating the terminals from each other and connecting each terminal 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 catheter to form a single wire that couples to a power source. 
         [0042]    In certain configurations, each individual active electrode in the electrode array may be electrically insulated from all other active electrodes in the array within the instrument 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 instrument, connectors, cable, controller, or along the conductive path from the controller to the distal tip of the instrument. 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). 
         [0043]    The Coblation® device is not limited to electrically isolated active electrodes, or even to a plurality of active electrodes. For example, in certain embodiments the array of active electrodes may be connected to a single lead that extends through the catheter shaft to a power source of high frequency current. 
         [0044]    The voltage difference applied between the return electrode(s) and the active electrode(s) 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, often less than 350 kHz, and often between about 100 kHz and 200 kHz. In some applications, applicant has found that a frequency of about 100 kHz is useful because the tissue impedance is much greater at this frequency. In other applications, such as procedures in or around the heart or head and neck, higher frequencies may be desirable (e.g., 400-600 kHz) to minimize low frequency current flow into the heart or the nerves of the head and neck. 
         [0045]    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, often between about 150 volts to 400 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, cutting or ablation). 
         [0046]    Typically, the peak-to-peak voltage for ablation or cutting with a square wave form will be in the range of 10 volts to 2000 volts and preferably in the range of 100 volts to 1800 volts and more preferably in the range of about 300 volts to 1500 volts, often in the range of about 300 volts to 800 volts peak to peak (again, depending on the electrode size, number of electrons, the operating frequency and the operation mode). Lower peak-to-peak voltages will be used for tissue coagulation, thermal heating of tissue, or collagen contraction and will typically be in the range from 50 to 1500, preferably 100 to 1000 and more preferably 120 to 400 volts peak-to-peak (again, these values are computed using a square wave form). Higher peak-to-peak voltages, e.g., greater than about 800 volts peak-to-peak, may be desirable for ablation of harder material, such as bone, depending on other factors, such as the electrode geometries and the composition of the conductive fluid. 
         [0047]    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%. 
         [0048]    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 treated, and/or the maximum allowed temperature selected for the instrument tip. The power source allows the user to select the voltage level according to the specific requirements of a particular neurosurgery procedure, cardiac surgery, arthroscopic surgery, dermatological procedure, ophthalmic procedures, open surgery or other endoscopic surgery procedure. For cardiac procedures and potentially for neurosurgery, the power source may have an additional filter, for filtering leakage voltages at frequencies below 100 kHz, particularly voltages around 60 kHz. Alternatively, a power source having a higher operating frequency, e.g., 300 kHz to 600 kHz may be used in certain procedures in which stray low frequency currents may be problematic. A description of one suitable power source can be found in commonly assigned U.S. Pat. Nos. 6,142,992 and 6,235,020, the complete disclosure of both patents are incorporated herein by reference for all purposes. 
         [0049]    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 U.S. Pat. No. 5,697,909, 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 blood), the resistance of the current limiting resistor increases significantly, thereby minimizing the power delivery from said active electrode into the low resistance medium (e.g., saline irrigant or blood). 
         [0050]    Referring now to  FIG. 1 , an exemplary electrosurgical system for resection, ablation, coagulation and/or contraction of tissue will now be described in detail. As shown, certain embodiments of the electrosurgical system generally include an electrosurgical probe  20  connected to a power supply  10  for providing high frequency voltage to one or more electrode terminals on probe  20 . Probe  20  includes a connector housing  44  at its proximal end, which can be removably connected to a probe receptacle  32  of a probe cable  22 . The proximal portion of cable  22  has a connector  34  to couple probe  20  to power supply  10  at receptacle  36 . Power supply  10  has an operator controllable voltage level adjustment  38  to change the applied voltage level, which is observable at a voltage level display  40 . Power supply  10  also includes one or more foot pedals  24  and a cable  26  which is removably coupled to a receptacle  30  with a cable connector  28 . The foot pedal  24  may also include a second pedal (not shown) for remotely adjusting the energy level applied to electrode terminals  42 , and a third pedal (also not shown) for switching between an ablation mode and a coagulation mode. 
         [0051]    Referring now to  FIG. 2 , an exemplary electrosurgical system  211  for treatment of tissue in ‘dry fields’ will now be described in detail. Of course, system  211  may also be used in ‘wet field’, i.e., the target site is immersed in electrically conductive fluid. However, this system is particularly useful in ‘dry fields’ where the fluid is preferably delivered through electrosurgical probe to the target site. As shown, electrosurgical system  211  generally comprises an electrosurgical handpiece or probe  210  connected to a power supply  228  for providing high frequency voltage to a target site and a fluid source  221  for supplying electrically conducting fluid  250  to probe  210 . The system  211  may also include a vacuum source (not shown) for coupling to a suction lumen disposed in probe  210  (not shown) via a connection tube (not shown) on probe  210  for aspirating the target site, as discussed below in more detail. 
         [0052]    As shown, probe  210  generally includes a proximal handle  219  and an elongate shaft  218  having an array  212  of electrode terminals  258  at its distal end. A connecting cable  234  has a connector  226  for electrically coupling the electrode terminals  258  to power supply  228 . The electrode terminals  258  are electrically isolated from each other and each of the terminals  258  is connected to an active or passive control network within power supply  228  by means of a plurality of individually insulated conductors (not shown). A fluid supply tube  215  is connected to a fluid tube  214  of probe  210  for supplying electrically conducting fluid  250  to the target site. 
         [0053]    Similar to the above embodiment shown in  FIG. 1 , power supply  228  has an operator controllable voltage level adjustment  230  to change the applied voltage level, which is observable at a voltage level display  232 . Power supply  228  also includes first, second and third foot pedals  237 ,  238 ,  239  and a cable  236  which is removably coupled to power supply  228 . The foot pedals  237 ,  238 ,  239  allow the surgeon to remotely adjust the energy level applied to electrode terminals  258 . In an exemplary embodiment, first foot pedal  237  is used to place the power supply into the “ablation” mode and second foot pedal  238  places power supply  228  into the “coagulation” mode. The third foot pedal  239  allows the user to adjust the voltage level within the “ablation” mode. In the ablation mode, a sufficient voltage is applied to the electrode terminals to establish the requisite conditions for molecular dissociation of the tissue (i.e., vaporizing a portion of the electrically conductive fluid, ionizing charged particles within the vapor layer and accelerating these charged particles against the tissue). As discussed above, the requisite voltage level for ablation will vary depending on the number, size, shape and spacing of the electrodes, the distance in which the electrodes extend from the support member, etc. Once the surgeon places the power supply in the “ablation” mode, voltage level adjustment  230  or third foot pedal  239  may be used to adjust the voltage level to adjust the degree or aggressiveness of the ablation. 
         [0054]    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. 
         [0055]    In the coagulation mode, the power supply  228  applies a low enough voltage to the electrode terminals (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 pedals  237 ,  238 , 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 soft tissue in the ablation mode, the probe typically will simultaneously seal and/or coagulation 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 pedal  238 , 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 pedal  237 . 
         [0056]    Now referring to  FIGS. 3 and 4 , an exemplary electrosurgical probe  300  incorporating an active screen electrode  302  is illustrated. Probe  300  may include an elongated shaft  304  which may be flexible or rigid, a handle  306  coupled to the proximal end of shaft  304  and an electrode support member  308  coupled to the distal end of shaft  304 . Probe  300  further includes active screen electrode  302  and securing electrode  303 . Return electrode  310  is spaced proximally from screen electrode  302  and provides a method for completing the current path between screen electrode  302  and securing electrode  303 . As shown, return electrode  310  preferably comprises an annular exposed region of shaft  304  slightly proximal of insulative support member  308 , typically about 0.5 to 10 mm and more preferably about 1 to 10 mm. Securing electrode  303  and return electrode  310  are each coupled to respective connectors  328  disposed in handle  306  (as illustrated in  FIG. 4 ) that extend to the proximal end of probe  300 , where connectors  328  are suitably electrically connected to a power supply (e.g., power supply  10  in  FIG. 1  or power supply  228  in  FIG. 2 ). As shown in  FIG. 4 , handle  306  defines an inner cavity  326  that houses the electrical connectors  328 , and provides a suitable interface for connection to an electrical connecting cable (e.g., cable  22  in  FIG. 1  or cable  234  in  FIG. 2 ). 
         [0057]    Still referencing  FIGS. 3 and 4 , in certain embodiments screen electrode  302 , securing electrode  303  and insulative support member  308  are configured such that screen electrode  302  and securing electrode  303  are positioned on a lateral side of the shaft  304  (e.g., 90 degrees from the shaft axis) to allow the physician to access tissue that is offset from the axis of the portal or arthroscopic opening into the joint cavity in which the shaft  304  passes during the procedure. To accomplish this, probe  300  may include an electrically insulating cap  320  coupled to the distal end of shaft  304  and having a lateral opening  322  for receiving support member  308 , screen electrode  302 , and securing electrode  303 . 
         [0058]    Shaft  304  preferably comprises an electrically conducting material, usually metal, which is selected from the group consisting of tungsten, stainless steel alloys, platinum or its alloys, titanium or its alloys, molybdenum or its alloys, and nickel or its alloys. Shaft  304  may include an electrically insulating jacket  309 , which is typically formed as one or more electrically insulating sheaths or coatings, such as polytetrafluoroethylene, polyimide, and the like. The provision of the electrically insulating jacket over 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 and an exposed electrode could result in unwanted heating and necrosis of the structure at the point of contact causing necrosis. 
         [0059]    The probe  300  further includes a suction connection tube  314  for coupling to a source of vacuum, and an inner suction lumen  312  ( FIG. 4 ) for aspirating excess fluids, tissue fragments, and/or products of ablation (e.g., bubbles) from the target site. Preferably, connection tube  314  and suction lumen  312  are fluidly connected, thereby providing the ability to create a suction pressure in lumen  312  that allows the surgeon to draw loose tissue, e.g., synovial tissue, towards the screen electrode  302 . Typically, the vacuum source is a standard hospital pump that provides suction pressure to connection tube  314  and lumen  312 . As shown in  FIGS. 3 and 4 , internal suction lumen  312 , which preferably comprises peek tubing, extends from connection tube  314  in handle  306 , through shaft  304  to an axial opening  316  in support member  308 , through support member  308  to a lateral opening  318  in support member  308 . Lateral opening  318  is positioned adjacent to screen electrode  302 , which further includes a suction port (not shown) disposed on the surface of screen electrode  302  and fluidly connected to lateral opening  318  for allowing aspiration therethrough, as discussed below in more detail. 
         [0060]      FIG. 5  representatively illustrates in more detail the removal of a target tissue by use of an embodiment of electrosurgical probe  50  according to the present disclosure. As shown, the high frequency voltage is sufficient to convert the electrically conductive fluid (not shown) between the target tissue  502  and active electrode terminal(s)  504  into an ionized vapor layer  512  or plasma. As a result of the applied voltage difference between electrode terminal(s)  504  and the target tissue  502  (i.e., the voltage gradient across the plasma layer  512 ), charged particles  515  in the plasma are accelerated. At sufficiently high voltage differences, these charged particles  515  gain sufficient energy to cause dissociation of the molecular bonds within tissue structures in contact with the plasma field. This molecular dissociation is accompanied by the volumetric removal (i.e., ablative sublimation) of tissue and the production of low molecular weight gases  514 , such as oxygen, nitrogen, carbon dioxide, hydrogen and methane. The short range of the accelerated charged particles  515  within the tissue confines the molecular dissociation process to the surface layer to minimize damage and necrosis to the underlying tissue  520 . 
         [0061]    During the process, the gases  514  will be aspirated through a suction opening and suction lumen to a vacuum source (not shown). In addition, excess electrically conductive fluid, and other fluids (e.g., blood) will be aspirated from the target site  500  to facilitate the surgeon&#39;s view. During ablation of the tissue, the residual heat generated by the current flux lines  510  (typically less than 150° C.) between electrode terminals  504  and return electrode  511  will usually be sufficient to coagulate any severed blood vessels at the site. If not, the surgeon may switch the power supply (not shown) into 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&#39;s ability to perform the procedure. Once the blockage has been removed, aeration and drainage are reestablished to allow the sinuses to heal and return to their normal function. 
         [0062]    Now referring to  FIG. 6 , the distal end portion of a preferred embodiment of an electrosurgical probe according to present disclosure is shown. Electrosurgical probe  600  comprises active screen electrode  602  mounted to insulative support member  604  disposed at a distal end of elongate shaft  601 . Probe  600  also includes electrically insulating cap  612  coupled to the end of shaft  601  and configured to receive screen electrode  602  and support member  604 . In preferred embodiments, securing electrode  606  extends through screen electrode  602  and support member  604  to mechanically secure screen electrode  602  to support member  604  and electrically insulating cap  612 . In certain configurations, securing electrodes  606  may be characterized by head  607 , leg  608 , and tab  610 . Preferably, head  607  contacts or engages the superior surface of screen electrode  602 , thereby providing an electrical means for the transmission of RF energy between securing electrode  606  and screen electrode  602 . Support member  604  may be characterized by channel  609  and slot  611 , wherein channel  609  is oriented perpendicularly with respect to the axis of shaft  601  and slot  611  is oriented axially with respect to the axis of shaft  601 . Wire  613  extends proximally from slot  611 , and is electrically connected to the electrical connectors disposed in the handle of the probe (as discussed above). Return electrode  614  is spaced proximally from screen electrode  602 . As discussed above, in this embodiment screen electrode  602  and support member  604  are configured such that screen electrode  602  is positioned on the lateral side of shaft  601  (e.g., 90 degrees from the shaft axis) to allow the physician to access tissue that is offset from the axis of the port or arthroscopic opening into the joint cavity in which shaft  601  passes during the procedure. 
         [0063]    Referring now to  FIG. 7A , an embodiment of securing electrode  606  is shown. Securing electrode  606  may be formed with a conductive material such as tungsten, and the shape and profile of securing electrode  606  may be manufactured via etching, laser cutting, or injection molding. In certain configurations, securing electrode  606  may be characterized by saw tooth pattern  615  on the superior plasma forming surface of securing electrode  606 . The added edges formed on securing electrodes  606  by saw tooth pattern  615  in this configuration may result in increased current density and thus promote the formation of improved zones for plasma formation and RF ablation. 
         [0064]    Referring now to  FIG. 7B , screen electrode  602  will comprise a conductive material, such as tungsten, titanium, molybdenum, stainless steel, aluminum, gold, copper or the like. Screen electrode  602  will usually have a diameter in the range of about 0.5 to 8 mm, preferably about 1 to 4 mm, and a thickness of about 0.05 to about 2.5 mm, preferably about 0.1 to 1 mm. Screen electrode  602  may have a variety of different shapes, such as the shape shown in  FIG. 7B . Screen electrode may have slots  616  therethrough, and may comprise suction opening  618  having sizes and configurations that may vary depending on the particular application. The exposed surface of screen electrode  602  is preferably generally planar, with no projections extending from the surface of screen electrode  602  or from an area associated with suction opening  618 . Suction opening  618  will typically be large enough to allow ablated tissue fragments to pass through into suction lumen port  620  (see  FIG. 8 ), typically being about 2 to 30 mils in diameter, preferably about 5 to 20 mils in diameter. In some applications, it may be desirable to only aspirate fluid and the gaseous products of ablation (e.g., bubbles) so that the holes may be much smaller, e.g., on the order of less than 10 mils, often less than 5 mils. In certain configurations, suction opening  618  may be formed in the shape of a zigzag or lightning bolt. 
         [0065]    Suction opening  618  is preferably formed in a design such as a zigzag or lightning bolt shape that affords for increased edge surface exposure around along the boundary of suction opening  618  in combination with a sufficiently opening area to allow material desired to be aspirated to enter the suction lumen via the suction lumen port. Consistent with any variation of selected aperture shape, suction opening  618  is characterized by an opening perimeter  619  and an opening area  620 . Opening perimeter  619  may be the sum of the length of the exposed edge surfaces bounding suction opening  618 , and opening area  620  may be the two-dimensional size of the region bounded by the closed opening perimeter  619 . Alternatively, the opening area  620  may be the total area of the exposed surface of a projected three-dimensional solid corresponding in shape to that of suction opening  618 . As is discussed below in more detail, it is preferred that the ratio of opening perimeter  619  to opening area  620  be greater than the ratio of a corresponding circular opening perimeter to a circular opening area where the suction opening is formed in a generally circular shape. 
         [0066]    Referring now to  FIG. 8 , insulative electrode support member  604  preferably comprises an inorganic material, such as glass, ceramic, silicon nitride, alumina or the like, that has been formed with lateral and axial suction lumen openings  620 ,  622 , and with one or more lateral axial passages  624  for receiving electrical wires  613 . Wires  613  extend from electrical connectors (i.e., electrical connectors  328  in  FIG. 4 ), through shaft  601  and passages  624  in support member  604 , terminating in proximity to slots  611  and tabs  610  of securing electrodes  606 . Wires  613  are electrically connected to securing electrodes  606  (e.g., by a laser welding process) thereby electrically coupling securing electrodes  606  and screen electrode  602  to a high frequency power supply. Referring to  FIGS. 6 ,  7 B, and  8 , legs  608  may extend through slots  616  of screen electrode  602  and channels  609  of support member  604 , and tabs  610  may be inserted into slots  611  of support member  604  such that tabs  610  interfere or engage with a portion of support member  604 . The placement of securing electrodes  606  such that tabs  610  are inserted into slots  611  creates a mechanical method of joining securing electrodes  606  to support member  604  and thereby prevents securing electrodes  606  from moving axially with respect to shaft  601  and support member  604 . Additionally, the method of mechanical securement results in the capture of screen electrode  602  between securing electrodes  606  and support member  604 . Further, as described above the contact between heads  607  of securing electrodes  606  and screen electrode  602  provides a method to electrically transmit RF energy through support member  604  to screen electrode  602 . 
         [0067]    In additional embodiments, the mechanical method of joining may comprise complementary helical threads cut in channels  609  of support member  604  and respectively in legs  608  of securing electrodes  606 , wherein legs  608  of securing electrodes  606  are operable to threadingly engage channels  609  of support member  604 . Additional embodiments of the present disclosure may include configurations where tabs  610  are formed in a barb or arrowhead shape and are disposed in interference with support member  604 . Moreover, in additional embodiments tabs  610  may be completely enclosed within support member  604 , and may be further secured to support member  604  by epoxy. 
         [0068]    Referring now to  FIGS. 9 and 10 , the distal end portion of representative probe  600  is shown with at least two bilateral securing electrodes  606  thereon. In this configuration, securing electrodes  606  may be oriented symmetrically about the central axis of shaft  601 , and may thereby allow for creation of a zone for RF ablation or plasma chamber  1000  between the symmetrically oriented bilateral securing electrodes  606  as well as between securing electrodes  606  and screen electrode  602  (see i.e.,  FIG. 10 ). Incorporation of symmetrical securing electrodes  606  may allow for the creation of a three dimensional zone represented by plasma zone  1000  for carrying out RF ablation. 
         [0069]    Referring now to  FIG. 11A , an alternative screen electrode configuration is shown in accordance with at least some embodiments. Electrosurgical probe  1100  comprises active screen electrode  1102  mounted to insulative support member  1104  disposed at a distal end of elongate shaft  1101 . Probe  1100  also includes electrically insulating cap  1112  coupled to the end of shaft  1101  and configured to receive screen electrode  1102  and support member  1104 . In certain embodiments, at least one securing electrode  1106  extends through screen electrode  1102  and support member  1104  to mechanically secure screen electrode  1102  to support member  1104  and electrically insulating cap  1112 . Return electrode  1114  is spaced proximally from screen electrode  1102 . As discussed above, in this embodiment screen electrode  1102  and support member  1104  are configured such that screen electrode  1102  is positioned on the lateral side of shaft  1101  (e.g., 90 degrees from the shaft axis) to allow the physician to access tissue that is offset from the axis of the port or arthroscopic opening into the joint cavity in which shaft  1101  passes during the procedure. 
         [0070]    In certain embodiments, screen electrode  1102  may comprise a conductive material, such as tungsten, titanium, molybdenum, stainless steel, aluminum, gold, copper or the like. Screen electrode  1102  may have a variety of different shapes and sizes, i.e., comparable to the shapes and sizes of the screen electrode embodiment(s) shown herein in  FIGS. 7B and 9 . In the present embodiment, screen electrode may comprise a suction opening  1118  (or suction aperture  1118 ) having sizes and configurations that may vary depending on the particular application. The exposed surface of screen electrode  1102  is preferably generally planar, with no projections extending from the surface of screen electrode  1102  or from an area associated with suction aperture  1118 . Suction aperture  1118  will typically be large enough to allow ablated tissue fragments to pass through into a suction/aspiration lumen port and suction/aspiration lumen (not shown) integrated into shaft  1101  of probe  1100 . 
         [0071]    In configurations according to the present embodiments, suction aperture  1118  is preferably formed in a design that provides for increased aperture edge surface exposure in combination with a sufficient aperture area large enough to allow material desired to be aspirated to enter the suction lumen via the suction lumen port. For example, suction aperture  1118  may preferably be formed in the shape of a star, an asterisk, a lightning bolt, or the like. Consistent with the selected size and shape of the suction opening in screen electrode  1102 , suction aperture  1118  is characterized by an aperture perimeter  1119  and an aperture area  1120 . In the configurations described in accordance with at least some embodiments, aperture perimeter  1119  may be the sum of the length of the exposed edge surfaces bounding suction aperture  1118 , and aperture area  1120  may be the two-dimensional size of the region bounded by the closed aperture perimeter  1119 . Alternatively, the aperture area  1120  may be expressed as the total area of the exposed surface of a projected three-dimensional solid corresponding in shape to that of suction aperture  1118 . 
         [0072]    In comparison and by way of example to further describe the present screen electrode aperture design providing increased edge surface in combination with sufficient area for materials desired to be aspirated to enter the suction lumen, a corresponding and comparative suction aperture  1118 ′ configured in the shape of a circle having a circular perimeter  1119 ′ corresponding to an aperture area  1120 ′ is illustrated in  FIG. 11B . Suction aperture  1118 ′ may be further defined by radius R, such that aperture area  1120 ′ has a value of π·R 2  and circular perimeter  1119 ′ has a value of 2 π·R. Accordingly, the ratio of circular perimeter  1119 ′ to aperture area  1120 ′ may be expressed as 2/R. 
         [0073]    Referring both to  FIGS. 11A and 11B , the present disclosure is directed to designs of active screen electrodes with a single, non-circular aperture for aspirating electrosurgical byproducts. Therefore, in order to provide for such a screen electrode suction aperture design having increased aperture edge surface exposure in combination with a sufficient aperture area large enough to allow materials to enter the suction lumen, in preferred embodiments suction aperture  1118  is configured such that aperture perimeter  1119  has a value substantially greater than a corresponding circular perimeter  1119 ′ if the related aperture area  1120 ′ is characterized by a circular shape. Accordingly, it is preferred that the shape of suction aperture  1118  be characterized such that the ratio of aperture perimeter  1119  to aperture area  1120  for at least the useful life of screen electrode  1102  is greater than 2/R as compared to a corresponding suction aperture  1118 ′ having a generally circular shape with circular perimeter  1119 ′ with a value of 2 π·R and related to an aperture area  1120 ′ with a value of π·R 2 . 
         [0074]    Referring now to  FIGS. 12A-H , additional variations of suction aperture configurations are shown by way of example and without limitation to the subject matter of the present claims and disclosure. Designs of suction aperture shapes in accordance with at least some embodiments may have any combination of arcs, angles, projections, or the like defining the exposed edge surfaces of the suction aperture and the aperture perimeter. It is preferred in all embodiments that the exposed screen electrode surface is generally planar, with no projections extending from the surface of screen electrode or from an area associated with the suction aperture. For example,  FIG. 12A  illustrates screen electrode  1202 A having suction aperture  1218 A formed in the shape of a “block S.” Suction aperture  1218 A may be bounded by an aperture perimeter  1219 A that defines an aperture area  1220 A.  FIG. 12B  illustrates screen electrode  1202 B having suction aperture  1218 B formed in the shape of a “multi-S curve.” Suction aperture  1218 B may be bounded by an aperture perimeter  1219 B that defines an aperture area  1220 B.  FIG. 12C  illustrates screen electrode  1202 C having suction aperture  1218 C formed in the shape of a “four-point arched star.” Suction aperture  1218 C may be bounded by an aperture perimeter  1219 C that defines an aperture area  1220 C.  FIG. 12D  illustrates screen electrode  1202 D having suction aperture  1218 D formed in the shape of a “double asterisk.” Suction aperture  1218 D may be bounded by an aperture perimeter  1219 D that defines an aperture area  1220 D. 
         [0075]      FIG. 12E  illustrates screen electrode  1202 E having suction aperture  1218 E formed in the shape of a “four leaf clover.” Suction aperture  1218 E may be bounded by an aperture perimeter  1219 E that defines an aperture area  1220 E.  FIG. 12F  illustrates screen electrode  1202 F having suction aperture  1218 F formed in the shape of a “multi-point star.” Suction aperture  1218 F may be bounded by an aperture perimeter  1219 F that defines an aperture area  1220 F.  FIG. 12G  illustrates screen electrode  1202 G having suction aperture  1218 G formed in the shape of “conjoined repeating alternating arcs.” Suction aperture  1218 G may be bounded by an aperture perimeter  1219 G that defines an aperture area  1220 G.  FIG. 12H  illustrates screen electrode  1202 H having suction aperture  1218 H formed in the shape of a “block X.” Suction aperture  1218 H may be bounded by an aperture perimeter  1219 H that defines an aperture area  1220 H. 
         [0076]    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 electrode terminals. 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 electrode terminal may be sufficient to contract collagen tissue, ablate tissue, or the like. 
         [0077]    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 electrode terminals. 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. 
         [0078]    While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching herein. The embodiments described herein are exemplary only and are not limiting. Because many varying and different embodiments may be made within the scope of the present teachings, including equivalent structures or materials hereafter thought of, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.