Abstract:
A high efficiency electrosurgical electrode with an advanced electrically conductive tip and aspiration port, and a method of conducting an electrosurgical procedure with such electrode. The electrosurgical electrode comprises an electrically conductive body portion of various geometries, an electrically conductive tip and a dielectric insulator adjacent the metallic body portion. The electrically conductive tip comprises a plurality of protuberances of various forms and geometries that define a plurality of recesses. The aspirating member includes a wall surrounding the aspirating port, to separate the aspirating port from adjacent recesses and prevent the flow of fluid from the recesses directly into the aspirating port.

Description:
The present application claims the benefit of U.S. Provisional Application Ser. No. 60/681,124, filed on May 13, 2005, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to electrosurgical devices for use in a conductive fluid environment and, more specifically, to electrosurgical devices for bulk vaporization of tissue in a conductive fluid environment which have increased efficiency through the minimization of process heat loss. 
     BACKGROUND OF THE INVENTION 
     Least invasive surgical techniques have gained significant popularity because of their ability to accomplish outcomes with reduced patient pain and accelerated return of the patient to normal activities. Arthroscopic surgery, in which the intra-articular space is filled with fluid, allows orthopedic surgeons to efficiently perform procedures using special purpose instruments designed specifically for arthroscopists. Among these special purpose tools are various manual graspers and biters, powered shaver blades and burs, and electrosurgical devices. During the last several years, specialized arthroscopic electrosurgical electrodes called ablation electrodes or ablators have been developed. Exemplary of these instruments are ArthroWands manufactured by Arthrocare (Sunnyvale, Calif.), VAPR electrodes manufactured by DePuy Mitek, a subsidiary of Johnson &amp; Johnson (Westwood, Mass.) and electrodes by Smith and Nephew, Inc. (Andover, Mass.). These ablation electrodes differ from conventional arthroscopic electrosurgical electrodes in that they are designed for the bulk removal of tissue by vaporization, rather than the cutting of tissue or coagulation of bleeding vessels. While standard electrodes are capable of ablation, their geometries are not efficient for accomplishing this task. The tissue removal rates of ablation electrodes are lower than those of arthroscopic shaver blades, however, electrosurgical ablation electrodes or “ablators” are used because they achieve hemostasis (stop bleeding) during use and are able to efficiently remove tissue from bony surfaces. Ablation electrodes are used in an environment filled with electrically conductive fluid. 
     During ablation, current flow from the ablator into the conductive fluid heats the fluid to its boiling point. Heating of the conductive fluid is proportional to the density of electrical current flowing from the electrode into the fluid. Regions of high current density will experience higher rates of heating as compared to regions of low current density. Such regions of high current density typically arise at the corners and edges of the electrode. Steam bubbles form first at the edges of an ablator but eventually cover virtually the entire surface of the electrode. When a steam bubble reaches a critical size, arcing occurs within the bubble. If the bubble intersects with tissue, arcing occurs between the electrode and the tissue thereby vaporizing a portion of the tissue. A train of sparks often occurs within the bubble with the train ending when the bubble grows too large or the tissue enclosed in the bubble is evaporated, at which point conditions within the bubble become unfavorable for sparking. 
     During ablation, water within the target tissue is vaporized. Because volumes of tissue are vaporized rather than discretely cut out and removed from the surgical site, the power requirements for ablation electrodes are generally higher than those of other arthroscopic electrosurgical electrodes. The efficiency of the electrode design and the characteristics of the Radio Frequency (RF) power supplied to the electrode also affect the amount of power required for ablation. Electrodes with inefficient designs and/or powered by RF energy with poorly suited characteristics will require higher power levels than those with efficient designs and appropriate generators. Because of these factors, the ablation power levels of devices produced by different manufacturers vary widely with some requiring power levels significantly higher than those commonly used by arthroscopists. For example, ablation electrode systems from some manufacturers may use up to 280 Watts, significantly higher than the 30 to 70 Watt range generally required by other arthroscopic electrosurgical electrodes. 
     During artroscopic electrosurgery, all of the RF energy supplied to the electrode becomes heat, thereby raising the temperature of the fluid within the joint and the temperature of adjacent tissue. And, until the introduction of ablation electrodes, the temperature of the fluid within the joint was not of concern to the surgeon. However, fluid temperature is a primary concern during the use of ablation electrodes due to the higher power levels at which they generally operate and the longer periods of time that they are energized. Standard arthroscopic electrosurgical electrodes are usually energized for only brief periods, generally measured in seconds, while specific tissue is resected or modified, or a bleeder coagulated. In contrast, ablation electrodes are energized for longer periods of time, often measured in minutes, while volumes of tissue are vaporized. 
     The temperature of the fluid within the joint is critical since cell death occurs at 45° C., a temperature easily reached with high-powered ablators if fluid flow through the surgical site is insufficient. Patient injury can result and such injuries have been documented. 
     The likelihood of thermal injury is strongly affected by the amount of power supplied to the ablator. This, in turn, is determined by the efficiency of the ablator and the speed with which the surgeon desires to remove tissue. A highly efficient ablator will allow the surgeon to remove tissue at desirably high rates, while requiring low levels of power input. Under these conditions the likelihood of thermal injuries is reduced significantly. 
     Ablation electrodes are produced in a variety of sizes and configurations to suit a variety of procedures. For example, ablators for use in ankle, wrist or elbow arthroscopy, are smaller than those used in the knee or shoulder. In each of these sizes, a variety of configurations are produced to facilitate access to various structures within the joint being treated. These configurations differ in the working length of the electrode (i.e., the maximum distance that an electrode can be inserted into a joint), in the size and shape of their ablating surfaces and in the angle between the ablating face and the axis of the electrode shaft. Electrodes are typically designated by the angle between a normal to the ablating surface and the axis of the electrode shaft, and by the size of their ablating surface and any associated insulator. 
     Primary considerations of surgeons when choosing a particular configuration of ablator for a specific procedure include its convenience of use (i.e., the ease with which the instrument is able to access certain structures) and the speed with which the ablator will be able to complete the required tasks. When choosing between two configurations capable of accomplishing a task, surgeons will generally choose the ablator with the larger ablating surface so as to remove tissue more quickly. This is particularly true for procedures during which large volumes of tissue must be removed. One such procedure is acromioplasty, the reshaping of the acromion. The underside of the acromion is covered with highly vascular tissue which may bleed profusely when removed by a conventional powered cutting instrument such as an arthroscopic shaver blade. Ablation electrodes are used extensively during this procedure since they are able to remove tissue without the associated bleeding which can obscures the surgeon&#39;s view of the site. Ablation in the area under the acromion is most efficiently accomplished using an electrode on which a line normal to the ablating surface is approximately perpendicular to the axis of the ablator shaft. Such an electrode is designated as a “90 Degree Ablator” or a “side effect” ablator. Exemplary of such electrodes are the “3.2 mm 90 Degree Three-Rib UltrAblator” by Linvatec Corporation (Largo, Fla.), the “90 Degree Ablator” and “90 Degree High Profile Ablator” by Smith and Nephew (Andover, Mass.), the “Side Effect VAPR Electrode” by DePuy Mitek, a subsidiary of Johnson and Johnson, and the “3.5 mm 90 Degree Arthrowand,” “3.6 mm 90 Degree Lo Pro Arthrowand,” and “4.5 mm 90 Deg. Eliminator Arthrowand” by Arthrocare Corporation. 
     A recent improvement to ablation electrodes is the addition of means of aspiration to remove bubbles and debris from the surgical site. During electrosurgery in a conductive fluid environment, tissue is vaporized, thereby producing steam bubbles which may obscure the view of the surgeon or displace saline from the area of the intra-articular space which the surgeon wishes to affect. In the case of ablation (bulk vaporization of tissue), the number and volume of bubbles produced is even greater than when using other electrodes since fluid is continually boiling at the active electrode during use. Ideally, flow through the joint carries these bubbles away; however, in certain procedures this flow is frequently insufficient to remove all of the bubbles. The aspiration means on an aspirating ablator removes some bubbles as they are formed by the ablation process, and others after they have collected in pockets within the joint. The ablator aspiration means is connected to an external vacuum source which provides suction for bubble evacuation. 
     The aspiration means on currently available ablator products may be divided into two categories according to their level of flow. High-flow ablators have an aspiration tube, the axis of which is coaxial with the axis of the ablator rod or tube, which draws in bubbles and fluid through its distal opening and/or openings cut into the tube wall near its distal tip. High-flow ablators may decrease the average joint fluid temperature by removing heated saline (waste heat since it is an undesirable biproduct of the process) from the general area in which ablation is occurring. The effectiveness of the aspiration, both for removal of bubbles and for removal of waste heat, will be affected by the distance between the opening through which aspiration is accomplished and the active electrode. The distal tip of the aspiration tube is generally several millimeters distant proximally from the active electrode so as to not to obstruct the surgeon&#39;s view of the electrode during use. Decreasing this distance is desirable since doing so will increase the effectiveness of the aspiration. However, this must be accomplished without limiting the surgeon&#39;s view or decreasing the ablator&#39;s ability to access certain structures during use. Examples of high-flow aspirating ablators systems include the Three Rib-Aspirating ablators by Linvatec Corporation and the 2.3 mm and 3.5 mm Suction Sheaths for the VAPR system by DePuy Mitek, the sheaths being used with standard VAPR ablation probes. 
     Arthrex, Inc. (Naples, Fla.) markets aspirating ablators having an aspiration means wherein the aspiration port is in the distal-most surface of the device, and the aspiration path is through the device. These devices have higher flow rates than low-flow ablators, though less than the high-flow models previously herein described. 
     Low-flow ablators are those which aspirate bubbles and fluid through gaps in the ablating surfaces of the active electrode and convey them from the surgical site via means in the elongated distal portion of the device. Current low-flow ablators require increased power to operate as effectively as a nonaspirating or high-flow aspirating ablators because the low-flow aspiration is drawing hot saline from the active site of a thermal process. In the case of low-flow ablators, the heat removed is necessary process heat rather than the waste heat removed by high-flow ablators. Because of this, aspirating ablators of the low-flow type generally require higher power levels to operate than other ablators thereby generating more waste heat and increasing undesirable heating of the fluid within the joint. Typical of low-flow aspirating ablators are those produced by Arthrocare and Smith and Nephew. 
     Each of these types of aspirating ablation electrodes has its drawbacks. In the case of high-flow aspirating ablators, the aspiration tube increases the diameter of the device thereby necessitating the use of larger cannulae, which, in turn, results in an increase in wound size and often an increase in patient pain and recovery time. In the case of low-flow aspirating ablators, the devices decrease the efficiency of the probes since process heat is removed from a thermal process. This decreased efficiency results in decreased rates of tissue removal for a given power level. This results in increased procedure times or necessitates the use of higher power levels to achieve satisfactory tissue removal rates. High power levels are undesirable as they cause increased heating of the fluid at the site and thereby increase the likelihood of thermal injury to the patient. 
     It is an object of this invention to produce an electrosurgical ablation electrode which aspirates through the ablating portion of the active electrode and has increased ablation efficiency as compared to existing ablation electrodes which aspirate through the active electrode. 
     SUMMARY OF THE INVENTION 
     The present invention provides an aspirating electrosurgical ablator for use in a conductive fluid environment, and which has a means for directing aspiration flow so that the loss of process heat is minimized. In one embodiment, the means for directing aspiration flow comprises a tubular member which draws fluid preferentially from the region distal to (above) the active electrode, and which reduces fluid flow through the spaces between protuberances of the active electrode adjacent the tubular member. The tubular member may be integral with the active electrode or provided as a separate component. 
     The present invention also provides an electrosurgical ablator with increased efficiency in an electrosurgical procedure. The method comprises the steps of: (i) positioning an electrosurgical probe adjacent a target tissue, the electrosurgical probe comprising a means for directing aspiration flow to minimize the loss of process heat; and (ii) either submerging the target tissue in an electrical conducting fluid or (iii) directing an electrically conducting fluid to the target tissue to ablate tissue in the region adjacent the means for directing aspiration flow. 
     These and other features and advantages of the present invention will become more fully apparent from the following description of the invention which refers to the accompanying drawings. However, it is to be understood that both the foregoing summary of the invention and the following detailed description are of illustrative and preferred embodiments, and should not be construed as restrictive of the present invention or other alternate embodiments. For example, although the present invention is described herein in the context of arthroscopy, the invention is not so limited. Rather, the present invention is equally applicable to other procedures that involve the application of high frequency electrical power to cut, vaporize, ablate, coagulate and/or treat a body tissue, cavity or vessel in a conductive fluid environment. Furthermore, in addition to the ablative procedures discussed in detail herein, the electrosurgical devices of the present invention also find utility in the context of thermal treatments, lesion formation, tissue sculpting and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of the electrosurgical system according to the principles of this invention. 
         FIG. 2  is a plan view of an electrosurgical ablator constructed in accordance with the principles of this invention. 
         FIG. 3  is a perspective view of the objects of  FIG. 2 . 
         FIG. 4  is a plan view of the mandrel component of the object of  FIG. 2 . 
         FIG. 5  is a side elevational view of the object of  FIG. 4 . 
         FIG. 6  is a perspective view of the object of  FIG. 4 . 
         FIG. 7  is a side elevational sectional view of the object of  FIG. 2  at location A-A of  FIG. 2 . 
         FIG. 8  is a plan view of the active electrode component of the object of  FIG. 2 . 
         FIG. 9  is a side elevational view of the object of  FIG. 8 . 
         FIG. 10  is a perspective view of the object of  FIG. 8 . 
         FIG. 11  is a side elevational sectional view of the object of  FIG. 8  at location B-B of  FIG. 8 . 
         FIG. 12  is a proximal axial view of the object of  FIG. 8 . 
         FIG. 13  is a plan view of the aspiration tube component of the object of  FIG. 2 . 
         FIG. 14  is a side elevational view of the object of  FIG. 13 . 
         FIG. 15  is a plan view of the insulator component of the object of  FIG. 2 . 
         FIG. 16  is a side elevational view of the object of  FIG. 15 . 
         FIG. 17  is a plan view of the distal end assembly of the object of  FIG. 2 . 
         FIG. 18  is a side elevational sectional view of the objects of  FIG. 17  at location A-A of  FIG. 17 . 
         FIG. 19  is a side elevational view of the objects of  FIG. 17 . 
         FIG. 20  is a perspective view of the objects of  FIG. 17 . 
         FIG. 21  is an axial sectional view of the objects of  FIG. 17  at location B-B of  FIG. 17 . 
         FIG. 22  is an expanded perspective view of the ablating surface of the active electrode showing aspiration flow. 
         FIG. 23  is an expanded side elevational view of the distal portion of the objects of  FIG. 16  during use showing bubble formation. 
         FIG. 24  is an expanded plan view of the distal portion of a prior art device. 
         FIG. 25  is a side elevational sectional view of the objects of  FIG. 24  at location A-A of  FIG. 24 . 
         FIG. 26  is an expanded perspective view of the ablating surface of the objects of  FIG. 24  during use showing the aspiration flow. 
         FIG. 27  is an expanded side elevational view of the distal portion of the objects of  FIG. 24  during use showing bubble formation. 
         FIG. 28  is an expanded perspective view of the distal portion of the distal assembly of an alternate embodiment. 
         FIG. 29  is an expanded side elevational sectional view of the distal portion of the distal assembly of an alternate embodiment. 
         FIG. 30  is an expanded plan view of the distal portion of an alternate embodiment formed in accordance with the principles of this invention. 
         FIG. 31  is a side elevational sectional view of the objects of  FIG. 30  at location A-A of  FIG. 30 . 
         FIG. 32  is a perspective view of the objects of  FIG. 30 . 
         FIG. 33  is a schematic cross-sectional view of a knee joint undergoing an electrosurgical procedure employing an electrosurgical electrode of the present invention. 
         FIGS. 34 and 35  depict an expanded plan view of the distal portion of alternate embodiments formed in accordance with the principles of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides an electrosurgical probe with an electrosurgical electrode having means for directing aspiration flow so that the loss of process heat is minimized and being capable of achieving high ablation rates at low RF power levels. 
     Referring now to the drawings, where like elements are designated by like reference numerals,  FIG. 1  depicts an electrosurgery system constructed in accordance with the principles of this invention. Ablation electrode  100  is connected by electrical cable  108  to electrosurgical generator  10 , and by tube  120  to an external vacuum source  12 . A return electrode (not shown) is connected to the electrosurgical generator to provide a return path for the RF energy. The return electrode may be a dispersive pad attached to the patient at a site remote from the surgical site, or may be in proximity to the active electrode in contact with tissue or the conductive liquid. 
     Reference is now made to  FIGS. 2 and 3 , which illustrate an electrosurgical instrument  100  constructed in accordance with the principles of this invention. Instrument  100 , also called an ablation electrode, “ablator” or “probe,” has a proximal portion  102  forming a handle and an elongated distal portion  104 . Handle  102  has passing from its proximal end  106  electrical cable  108  which is connected to electrosurgical generator  10 , and flexible tube  110  which is connected to tube  120  and thereby to external vacuum source  12 . Near distal end  112  of handle  102 , first activation button  114  labeled “ablate” and second activation button  116  labeled “coagulate,” protrude from top surface  118  of handle  102 . Elongated distal portion  104  has a proximal end  120  which is mounted to distal end  112  of handle  102 , and a distal end  122 . 
     Referring now to  FIGS. 4 through 7 , mandrel  126  has a proximal portion  130  of diameter  131 , a mid-portion  132  and a distal portion  134  of diameter  135 , and a lumen having a proximal portion  136  extending through proximal portion  130  and mid-portion  132 , and a distal lumen portion  138  within distal portion  134  of mandrel  126 . Passage  139  extends from outer surface  144  of distal portion  134  to distal lumen portion  138 . Mandrel  126  is made from a suitable metallic material, examples of which include, but are not limited to, stainless steel, nickel, titanium or tungsten, and equivalents thereof. 
     As seen in  FIGS. 8 through 12 , electrode piece  150  has an upper portion  156  of diameter  158 , with an upper surface  160  in which are formed a series of elevated protuberances or ribs  162  that define a plurality of corresponding recessed grooves or channels  163 , and a mid-portion  159  of diameter  161 . Piece  150  also has a lower portion  164  (a body region) of diameter  166  in which is formed cylindrical radial passage  168  of diameter  170  and depth  172 . Lumen  174 , coaxial with upper portion  156  and lower portion  164 , has an upper portion  176  of diameter  178  and a lower portion  180  of diameter  182 . Lower portion  180  intersects radial passage  168 . Top surface  184  of lower portion  164  forms a shelf. Beveled surfaces  186  are parallel to axis  188  of passage  168 . Diameter  170  of radial passage  168  is slightly less than diameter  135  of distal portion  134  of mandrel  126  ( FIG. 7 ). 
     Electrode piece  150  may be made from a suitable electrically conductive material, examples of which include, but not limited to, metals such as stainless steel, nickel, titanium and tungsten, among many others, or an electrically conductive ceramic. The body region of the electrode piece  150  may have various cross-sectional shapes and geometries, including, but not limited to, cylindrical, rectangular, or ellipsoidal, among many others. When viewed in side elevation as in  FIGS. 9 and 11 , protuberances or ribs  162  and corresponding recessed grooves  163  may also have various geometries and/or shapes and various cross-sections, including, but not limited to, rectangular trapezoidal, triangular, square, hexagonal, round, and ellipsoidal, among many others. 
       FIGS. 13 and 14  depict aspiration means  190  of length  192 . In an exemplary embodiment, the aspiration means  190  is an aspiration tube having an outer diameter  194  and a lumen  195  of diameter  196 . The wall thickness  197  of aspiration tube  190  is preferably between about 0.08 mm to about 1.5 mm, and more preferably between about 0.1 mm to about 0.6 mm. Diameter  194  is slightly larger than diameter  178  of upper portion  176  of lumen  174  of electrode piece  150  ( FIG. 11 ). 
     Aspiration tube  190  may be made from a suitable electrically conductive material including, but not limited to, metallic material such as, for example, stainless steel, nickel, titanium or tungsten, or alternatively from a ceramic materials such as alumina or zirconia. In yet other embodiments, the aspiration tube  190  may comprise a combination of at least a metallic material and at least a ceramic material. Although reference to the aspiration means is made in this application as to an “aspiration tube,” the invention contemplates any aspirating member having various shapes and different cross-sections when viewed in plan view. For example, lumen  195  may be round ( FIG. 13 ), but the outer shape may have a rectangular cross-section, a square, a hexagonal, or an ellipsoidal shape, among many others. The wall thickness  197  of the aspiration member may be constant (as for aspiration tube  190 ), or may vary depending on the lumen and outer shape cross-sections. As noted above, the thickness  197  of aspiration tube  190  is preferably between about 0.08 mm to about 1.5 mm, and more preferably between about 0.1 mm to about 0.6 mm. In exemplary embodiments, the aspiration member may be provided as a separate component, or constructed integral with the active electrode (as a one-piece assembly, for example). 
     As seen in  FIGS. 15 and 16 , insulator  200  of height  202  and outer diameter  204  has a cylindrical inner lumen of diameter  206 . Diameter  206  is slightly larger than diameter  161  of mid-portion  159  of electrode piece  150  ( FIG. 9 ). Insulator  200  has a bottom surface  201 . Insulator  200  is made from a suitable dielectric material such as alumina or zirconia, or a high-temperature polymeric material. 
     Referring to  FIGS. 17 through 21  showing distal end assembly  210 , aspiration tube  190  is provided as a component separate from the electrode piece  150 . According to an exemplary embodiment, aspiration tube  190  is pressed into upper portion  176  of lumen  174  ( FIG. 11 ) such that top end surface  191  of tube  190  is coplanar with surface  160  of electrode piece  150 . Electrode piece  150  is assembled to mandrel  126 , distal portion  134  of mandrel  126  being pressed into radial passage  168  of electrode  150  ( FIG. 11 ) such that passage  139  of mandrel  126  is aligned with lower portion  180  of lumen  174  of piece  150 . Proximal portion  130  of mandrel  126  ( FIG. 7 ) is assembled to distal end  212  of tube  214 , tube  214  extending proximally from assembly  210  to handle  102 . Insulator  200  is assembled to electrode piece  150 , bottom surface  201  of insulator  200  ( FIG. 16 ) resting on shelf  184  of piece  150  ( FIGS. 10 and 11 ), and mid-portion  159  of piece  150  being within lumen  206  of insulator  200  so that insulator  200  is coaxial with upper portion  156  of electrode piece  150 . A dielectric coating (not shown) covers elongated distal portion  104  from handle  102  to line  220  at a distance  222  above shelf  184  and bottom surface  201  of insulator  200 . 
     Lumen  195  of aspiration tube  190 , lumen  174  of electrode piece  150 , passage  139 , distal lumen portion  138  and proximal lumen portion  136  of mandrel  126 , and lumen  226  of tube  214  together form a flow path in communication via means within handle  102  with flexible tube  110  which is connected to external vacuum source  12 . During use, with the probe distal end  122  submerged in conductive liquid and with a vacuum applied to the flow path, liquid  300  is aspirated from the from the site as shown in  FIG. 22 , particularly from the region distal to (above) surface  160  of electrode  150 , and surface  191  of aspiration tube  190 . 
     Referring now to  FIG. 23 , radio frequency (RF) energy is supplied to active electrode  150  creating an electric field in the conductive fluid. Current flows into the conductive fluid from the portion of active electrode upper portion  156  protruding above insulator  200 . Current flowing through the liquid heats the fluid, making it more conductive, which in turn causes more current to flow through the heated region. Heating of the conductive liquid in this region causes it to boil so as to form bubbles at active electrode  150 . These bubbles form at surface  160  of ribs  162 , and in grooves  163 . Bubbles filling grooves  163  insulate the surfaces of the grooves thereby decreasing current flow from these surfaces. 
     Bubbles forming at surface  160  and in portions of the ribs adjacent thereto grow to a critical size whereupon arcing occurs within some of these bubbles. When distal end  122  of ablator  100  is brought into close proximity to tissue, some of the bubbles intersect the tissue and arcing occurs between active electrode  150  and the tissue resulting in vaporization (ablation) of tissue. 
     The beneficial effect of aspiration tube  190  is best understood by considering the operation of a prior art ablation electrode  500  similar to ablator  100 , with the exception that aspiration tube  190  is absent. Referring now to  FIGS. 24 and 25  which depict the distal portion of prior art device  500 , active electrode piece  150  has a lumen  502  of the same diameter as lumen  195  of aspiration tube  190  ( FIG. 13 ). Lumen  502  intersects medial grooves  504 . Lumen  502 , lumen  174  of electrode piece  150 , passage  139 , distal lumen portion  138  and proximal lumen portion  136  of mandrel  126 , and lumen  226  of tube  214  together form a flow path in communication via means within handle  102  with flexible tube  110  which is connected to external vacuum source  12 . During use, with the probe distal end  122  submerged in conductive liquid and with a vacuum applied to the flow path, liquid  300  is aspirated from the site as shown in  FIG. 26 , from the region distal to (above) surface  160  of electrode  150 , and (referring to flow paths  510 ) from medial grooves  504 . 
     Radio Frequency (RF) energy is supplied to active electrode  150  creating an electric field in the conductive fluid. Current flows into the conductive fluid from the portion of active electrode upper portion  156  protruding above insulator  200 . Current flowing through the liquid heats the fluid, making it more conductive, which in turn causes more current to flow through the heated region. Referring to  FIG. 27 , heating of the conductive liquid in this region causes it to boil forming bubbles at active electrode  150 . These bubbles form at surface  160  of ribs  162 , and in lateral grooves  512 . Flow  510  in medial grooves  504  carries the heat away from these regions thereby preventing fluid therein from boiling. Because medial grooves  504  do not fill with bubbles so as to insulate the grooves&#39; surfaces, current flows from the surfaces to the conductive fluid in contact therewith so as to heat the fluid which is then aspirated from the region providing no clinical benefit to the patient. Ribs  514  adjacent to medial ribs  504  are also cooled by flow  510  which decreases bubble production on these ribs. Accordingly, the number of bubbles produced by the ablator, and therefore the number of bubbles which grow to critical size, create arcing and vaporize tissue is decreased. This, in turn, results in decreased efficiency. The power applied to the electrode must be increased to achieve tissue removal rates comparable to those of an ablator produced in accordance with the principles of this invention. 
     The principles of this invention may be advantageously applied to ablator electrodes having active electrodes with ablating surfaces which are not ribbed but rather include protuberances of other shapes. That is, the present invention contemplates the addition of an aspirating member according to the principles of this invention of any ablation electrode so as to minimize cooling flow around the active elements and thereby increase the efficiency of the probe. For instance, aspirating ablating electrode  600 , the distal portion of which is shown in  FIG. 28 , is similar in construction to the previous embodiment, except that electrode  150  has an upper portion  602  which forms cylindrical protuberances  604  which protrude through passages in ceramic insulator  605 , to a height  606  above surface  608  of insulator  605 . These elevated protuberances define a plurality of recessed “channels” therebetween, such “channels” being analogous to the linear “grooves” of previous embodiments. Aspiration tube  190  protrudes above surface  608  of insulator  605  approximately distance  606 . As with the previous embodiment, aspiration tube  190  causes fluid aspiration primarily from the region distal to (above) distal ends  610  of protuberances  604 . Protuberances  604  have a circular shape when viewed in a plan view. In other embodiments, protuberances  604  may have other shapes when viewed in a plan view including ellipsoidal, for example, or regularly or irregularly polygonal, or a combination of such regularly or irregularly polygonal shapes. The cross-sections may be constant or alternatively, may vary with height. 
     The increase in efficiency of an ablator electrode through the incorporation of an aspirating member according to the principles of this invention is determined by the degree of reduction of the flow between protuberances of the active electrode. This, in turn, is determined by the height of the aspirating member relative to the height of the protuberances. In embodiments described above, the height of aspirating member  190  is about equal to the height of the protuberances on the active electrode face. In other embodiments contemplated by the present invention, member  190  may have a height that is less than the height of the protuberances. In these exemplary embodiments, the cooling flow between the protuberances will be reduced but not eliminated, as in previous embodiments having aspirating members equal in height to the protuberances. This reduced flow will increase the efficiency of the ablator since the removal of process heat is decreased compared to the same aspirating electrode without an aspirating member of the present invention. It may be desirable in some embodiments to aspirate liquid from regions farther removed distally from the ablating surface of the active electrode. Referring to  FIG. 29  showing the distal portion of an ablator  700 , aspirating tube  190  protrudes beyond surface  160  of active electrode  150  by a distance  702 . The distance or height  702  is preferably between about 0.1 mm to about 3 mm, and more preferably between about 0.1 mm to about 2 mm. 
     In yet another embodiment, at least one circular groove is formed in the ablating surface, the at least one groove being concentric with the aspiration port. Referring now to  FIGS. 30 through 32 , showing the distal portion of an ablator  800 , groove  802  is concentric with aspirating lumen  195 . As shown in  FIG. 31 , tubular portion  804  of active electrode  150  has replaced aspiration tube  190  of previous embodiments. Surface  808  of portion  804  protrudes distance  806  beyond surface  160  of active electrode  150 . Because groove  802  does not intersect lumen  195 , cooling of adjacent rib surfaces by aspiration flow is prevented. Tubular portion  804  of active electrode  150  protrudes beyond surface  160  of electrode  150  so as to increase the efficiency of ablator  800  by decreasing cooling caused by liquid flow across surfaces  160 . In other embodiments, surface  808  of portion  804  is coplanar with surface  160 . In yet other embodiments having larger diameter ablating surfaces, additional circular grooves  802  are formed in active electrode  150 . 
       FIG. 34  depicts an alternate embodiment in which the grooves are angularly oriented to each other so as to form a tubular portion around the aspirating port, the tubular portion having an outer surface that forms a regular polygon. Ablator  900  has grooves  163  are that are angulary oriented to one-another so as to form tubular portion  904  around aspiration port  195 . Portion  904  forms a regular polygon when viewed in a plan view. 
       FIG. 35  depicts an alternate embodiment in which the grooves are angularly oriented to each other so as to form a tubular portion around the aspirating port, the tubular portion having an outer surface that forms an irregular polygon. Ablator  940  has grooves  163  that are angulary oriented to one-another so as to form tubular portion  904  around aspiration port  195 . Portion  904  forms an irregular polygon when viewed in a plan view. 
     Other groove configurations may also be used in accordance with the present invention. For example, the grooves may have a curvilinear path so that the tubular portion formed has an irregular shape, the sides of the shape being curvilinear or linear, or a combination of linear and curvilinear. Any configuration which forms a tubular portion having a minimum wall thickness in the preferred range, and a maximum wall thickness in the preferred range may be used. 
     The high efficiency electrosurgical ablator  100 ,  600 ,  700 ,  800  of the present invention illustrated and described above may be employed in a variety of surgical medical procedures in the presence of an electrically conductive fluid to remove and/or modify a particular target tissue. Accordingly, the electrosurgical ablator  100 ,  600 ,  700 ,  800  of the present invention may be used in a conventional open surgery environment or in other, less invasive, techniques that use cannulas or various port access devices if conductive fluid is present. The present invention has also applications in surgical procedures where the target tissue is flooded with, or submerged in, an electrically conductive fluid such as in many arthroscopic procedures for ablation, coagulation, shaping and cutting of various body parts such as the knee, shoulder, hip, ankle, elbow, hand or foot. 
     The present invention has also equal applicability to surgical procedures where the target tissue is flooded with a natural conductive fluid of the human body, such as blood or lymphatic plasma, for example, which act as electrically conductive fluids. Nevertheless, an electrically conductive fluid introduced into the patient&#39;s body is preferred over blood because blood tends to coagulate at certain temperatures. In addition, the patient&#39;s blood or plasma may lack the necessary conductivity to adequately carry out the particular electrosurgical procedure desired. 
     Surgical procedures using the electrosurgical ablator  100 ,  600 ,  700 ,  800  of the invention include introducing the electrode assembly in close proximity to the surgical site through an artificial conduit or a cannula, or through a natural conduit which may be in an anatomical body cavity or space or one created surgically. For the purposes of the present invention, the terms “close proximity” and “proximity” are defined as “in contact with” or “at a distance of about 0.1 to about 10 millimeters.” The cavity or space may be distended during the procedure using a fluid or may be naturally held open by anatomical structures. In addition, the surgical site may be bathed in a continuous flow of conductive fluid, such as saline solution, to fill and distend the cavity. The procedures may include simultaneous viewing of the site via an endoscope or using an indirect visualization means. 
     To better illustrate an exemplary surgical procedure conducted with the electrosurgical ablator  100  of the present invention, reference is now made to  FIG. 33 , which illustrates a schematic cross-sectional view of a knee joint region  95 . The knee joint region  95  of  FIG. 33  may undergo an arthroscopic procedure, for example, with electrosurgical ablator  100  fabricated according to the present invention. As known in the art, an endoscope (not shown) may be provided at one end with the distal active electrode piece  150  having aspiration tube  190 , and then introduced into knee cavity  92  ( FIG. 33 ) containing electrically conductive fluid  91  ( FIG. 33 ) and in close proximity to target tissue  99  ( FIG. 33 ). If the target tissue  99  of the knee joint region  95  is a damaged meniscus, for example, then target tissue  99  may undergo a partial or complete electrosurgical meniscectomy using active electrode  150 . Alternatively, the endoscope may be introduced separately from the electrosurgical electrode, via separate access means in a surgical technique commonly known as triangulation. In any event, knee cavity  92  may be distended during the arthroscopic procedure using electrically conductive fluid  91 , so that target tissue  99  may be bathed in a continuous flow of conductive fluid  91 , which may be preferably a saline solution. 
     Once distal active electrode  150  is positioned in the proximity of the target tissue  99  and the target tissue  99  is submerged in the electrically conductive fluid  91 , the electrosurgical probe is energized by the electrosurgery power supply. The power supply delivers radio frequency energy, typically in the range of 100 kHz to 3 MHz, through a cable system to the electrosurgical electrode  100  and further to the distal active electrode  150 . 
     The above description and drawings illustrate preferred embodiments which achieve the objects, features and advantages of the present invention. It is not intended that the present invention be limited to the illustrated embodiments. Any modification of the present invention which comes within the spirit and scope of the following claims should be considered part of the present invention.