MXPA98010741A - Treatment under the a - Google Patents

Abstract

An electrosurgical instrument, for the treatment of tissue in the presence of an electrically conductive fluid medium, comprises an instrument arrow (10), and an electrode assembly (12) at one end of the arrow. The electrode assembly (12) comprises a tissue treatment electrode (14) and a return electrode (18) which is electrically isolated from the tissue treatment electrode by means of an insulating member (16). The tissue treatment electrode (14) has an exposed end (14a) extending laterally through a cut-out (16a) provided in the insulating member (16). The return electrode (18) has a contact surface with the fluid (18a) is separated from the tissue treatment electrode (814) in such a way as to define, in use, a conductive fluid path that contemplates an electrical circuit between the electrode of treatment and the return electrode

Description

TREATMENTS UNDER THE WATER This invention relates to an electrosurgical instrument for the treatment of tissue in the presence of a fluid electrically conductive medium, with an electrosurgical apparatus including such an instrument, and with an electrode unit for use in such an instrument. Endoscopic electrosurgery is useful for treating tissue in body cavities, and is usually performed in the presence of a distention medium. When the distension medium is a liquid, this is commonly known as underwater electrosurgery, this term denotes electrosurgery in which the living tissue is treated using an electrosurgical instrument with an electrode or treatment electrodes submerged in liquid at the site of the operation. A gaseous medium is commonly used when performing endoscopic surgery in a body cavity that can be distended of a larger potential volume in which a liquid medium would be inconvenient, as is often the case in laparoscopic or gastroenterological surgery. Underwater surgery is commonly carried out using endoscopic techniques, in which the same endoscope can provide a conduit (commonly known as a working channel) for the passage of an electrode. Alternatively, the endoscope can be specifically adapted (as in a reeectoscope) to include means for mounting an electrode, or the electrode can be introduced into a body cavity via a separate access means at an angle to the endoscope - a technique commonly known as triangulation These variations in technique can be subdivided by surgical specialty, when one or other of the techniques has particular advantages given the access route to the specific body cavity. Endoscopes with integral working channels, or those characterized as resectoscopes, are generally used when the body cavity can be accessed through a natural opening of the body - such as the cervical canal to access the endometrial cavity of the uterus, or the urethra to have access to the prostate gland and the bladder. Endoscopes specifically designed for use in the endometrial cavity are known as hysteroscopes, and those designed for use in the urinary tract include cystoscopes, urethroscopes and resectoscopes. Procedures for transurethral resection or vaporization of the prostate gland are known as TURP and EVAP, respectively. When there is no natural bodily opening through which an endoscope can be passed, the triangulation technique is commonly used. Triangulation is commonly used during underwater endoscopic surgery in joint cavities such as the knee and shoulder. The endoscope used in these procedures is commonly known as an arthroscope. Electrosurgery is usually carried out using either a monopolar instrument or a bipolar instrument. With monopolar electrosurgery, an active electrode is used in the region of operation, and a conductive return plate is secured to the patient's skin. With this arrangement, the current passes from the active electrode through the patient's tissues to the external return plate. Since the patient represents a significant portion of the circuit, the input energy levels have to be high (typically 150 to 250 watts), to compensate for the limiting resistive current of the patient's tissues and, in the case of electrosurgery under the water, the energy is lost due to the fluid medium which becomes partially conductive due to the presence of blood or other bodily fluids. Using high energy with a monopolar array is also risky due to heating of the tissue that occurs in the return plate, which causes severe skin burns. There is also the risk of capacitive coupling between the instrument and the patient's tissues at the point of entry into the body cavity. With bipolar electrosurgery, a pair of electrodes (an active electrode and a return electrode) are used together at the site of the application of the tissue. This arrangement has advantages from the point of view of safety, due to the relative proximity of the two electrodes so that the radiofrequency currents are limited to the region between the electrodes. However, the depth of the effect is directly related to the distance between the two electrodes; and in applications that require very small electrodes, the space between electrodes becomes very small, thereby limiting the tissue effect and the output energy. Further separating the electrodes would often obscure the vision of the application site, and would require a modification in the surgical technique to ensure direct contact of both electrodes with the tissue. There are numerous variations of the basic design of the bipolar probe. For example, U.S. Patent Specification No. 4706667 describes one of the design fundamentals, namely, the ratio of contact areas of the return electrode and active electrode is greater than 7: 1 and less that 20: 1 for cutting purposes. This range relates only to cutting electrode configurations. When a bipolar instrument is used for desiccation or coagulation, the ratio of the contact areas of the two electrodes can be reduced to approximately 1: 1 to avoid the electrical differential voltages that occur at the contact between the tissue and the electrode. The electrical connection between the return electrode and the tissue can be supported by moistening the tissue by a conductive solution such as normal saline. This ensures that the surgical effect is limited to the needle or the active electrode, the electrical circuit between the two electrodes being completed by the tissue. One of the obvious limitations with the design is that the needle must be completely buried in the tissue to allow the return electrode to complete the circuit. Another problem is the orientation: even a relatively small change in the angle of application from the ideal perpendicular contact with respect to the surface of the tissue, the proportion of the contact area will change, so that a surgical effect can occur in the tissue in contact with the return electrode. The distention of the cavity provides space to gain access to the operation site, to improve visualization, and to allow the manipulation of instruments. In low volume body cavities, particularly when it is desirable to distend the cavity under higher pressure, liquid is commonly used instead of gas due to better optical characteristics, and because it washes the blood away from the operating site. Conventional underwater electrosurgery has been carried out using a non-conductive liquid (such as 1.5 percent glycine) as an irrigator, or as a distention medium to eliminate electrical conduction losses. Glycine is used in isotonic concentrations to avoid osmotic changes in the blood when intra-vascular absorption occurs. In the course of an operation, the veins can be cut, with the resulting infusion of the fluid in the circulation, which could cause, among other things, a dilution of serum sodium that can lead to a condition known as water intoxication. Applicants have found that it is possible to use a conductive liquid medium, such as normal saline, in endoscopic electrosurgery under water instead of non-conducting solutions, without electrolytes. Normal saline is the preferred distention medium in endoscopic underwater surgery when electrosurgery is not contemplated, or a non-electrical tissue effect such as laser treatment is being used. Although normal saline solution (0.9 percent weight / volume, 150 mmol / liter) has a slightly higher electrical conductivity than most body tissue, has the advantage that the displacement by absorption or extravasation of the operative site produces little physiological effect, and the effects of the so-called water intoxication of non-conductive solutions, without electrolytes, are avoided. Applicants have developed a convenient bipolar instrument for underwater electrosurgery using a liquid or gaseous conductive medium. This electrosurgical instrument for treating tissue in the presence of a fluid medium, comprises an instrument body having an instrument handle and arrow, and an electrode assembly at one end of the shaft. The electrode assembly comprises a tissue treatment electrode which is exposed at the distal end furthest from the instrument, and a return electrode which is electrically isolated from the tissue treatment electrode and has a contact surface with the separated fluid proximally of the exposed part of the tissue treatment electrode. In use of the instrument, the tissue treatment electrode is applied to the tissue to be treated while the return electrode, being proximally separated from the exposed portion of the tissue treatment electrode, is normally separated from the tissue and serves to complete a cycle of electrosurgical current from the tissue treatment electrode through the tissue and the fluid medium. This electrosurgical instrument is described in the specification of our European Patent Application 96918786.1. The electrode structure of this instrument, in combination with a fluid electrically conductive medium, largely avoids the problems experienced with monopolar or bipolar electrosurgery. In particular, the input power levels are much lower than those generally needed with a monopolar array (typically 100 watts). Moreover, due to the relatively large separation between their electrodes, an improved depth of effect is obtained compared to conventional bipolar arrays. An arthroscope electrode can be characterized as short (100 to 140 millimeters), and rigid with a working diameter of up to 5 millimeters. It can be introduced through a small incision in a joint cavity (with or without a cannula) using the triangulation technique. This electrode is operated with a movement that moves the electrode between the clock positions from 9 o'clock and 3 o'clock on the arthroscopic image. As a result, the tissue to be treated usually approaches a shallow working angle with respect to the axis of the electrode. Such an arthroscopic electrode needs to have a consistent effect with this form of angled approach to the tissue. The tissue to be treated, such as meniscal cartilage, is commonly dense and high in electrical impedance. An arthroscope electrode requires fixations of the output and voltage energy that reflect the type of tissue being treated, the size of the electrode, and the fact that arthroscopists are looking for a speed of effect comparable to that of mechanical shaving devices. that they currently use, although with an electrode of smaller dimensions than a shaver knife for improved access. Joint spaces are commonly small (articulation spaces in the knee are typically 60 to 100 milliliters under fluid distension), and tissue often needs mechanical manipulation. Known monopolar arthroscopic electrode configurations, therefore, are rigid construction, having angled hook or probe type configurations to produce high impedance tissue cutting, and to connect it to an ergonomic handle to aid in tissue manipulation. The object of the invention is to provide an improved electrosurgical instrument of this type. The present invention provides an electrosurgical instrument for the treatment of tissue in the presence of a fluid electrically conductive medium, the instrument comprising an instrument arrow and an electrode assembly at one end of the arrow, the electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically isolated from the tissue treatment electrode by a member insulator, the treatment electrode having an exposed end extending laterally through a cutout provided in the insulating member in the distal end portion of the instrument, and the return electrode having a surface in contact with the fluid that overlaps the insulating member in the region of the cutout, the contact surface of the fluid being separated from the tissue treatment electrode so as to define, in use, a conductive fluid path that completes an electrical circuit between the tissue treatment electrode and the electrode return. The invention also provides an electrosurgical instrument for the treatment of tissue in the presence of a fluid electrically conductive medium, the instrument comprising an instrument arrow, and an electrode assembly at one end of the shaft, the electrode assembly comprising a treatment electrode. of tissue and a return electrode which is electrically isolated from the tissue treatment electrode by means of an insulating member, the tissue treatment electrode having an exposed end extending laterally through a cutout provided in the insulating member, wherein the return electrode has a distal end portion with a fluid contacting surface that overlaps the insulating member in the region of the cutout and faces laterally in a first direction and wherein the insulating member projects laterally outwardly between the distal end portion and the treatment electrode of tissue, the tissue treatment electrode facing laterally in a second direction opposite to the first direction. The laterally projecting part of the insulating member increases the length of the conductive fluid path from the tissue treatment electrode to the return electrode, and forces the electric field outward, thereby avoiding the preferential arcing between the return electrode and the nearest part of the tissue treatment electrode, and promoting the arching between the tissue treatment electrode and the tissue in the vicinity. The return electrode is separated from the tissue treatment electrode so that, in use, it does not contact the tissue to be treated, and thus the electrical circuit is always completed by the conductive fluid, and not simply by arching between the electrodes Undoubtedly, the arrangement is such that arching between adjacent parts of the electrode assembly is avoided, thereby ensuring that the tissue treatment electrode can be wrapped in a vapor pocket so that the tissue entering the steam bag the preferred path for the current to flow back to the return electrode via the conductive fluid becomes. The electrosurgical instrument of the invention is useful for tissue dissection, resection, vaporization, desiccation and coagulation, as well as for combinations of these functions. It has particular application in arthroscopic surgery since it deals with endoscopic and percutaneous procedures performed on joints of the body that include, but are not limited to, techniques such as applied to the spine and other non-synovial joints. Arthroscopic operative procedures may include: partial or complete meniscosectomy of the knee joint including meniscus cystectomy, lateral retinacular release of the knee joint; removal of anterior and posterior cruciate ligaments or remnants thereof; tear resection of the labium articulare, acromioplasty, bursectomy and subacromial decompression of the shoulder joint, anterior release of the temporomandibular joint, synovectomy, debridement of the cartilage, chondroplasty, division of intra-articular adhesions, fracture and debridement of the tendon applied to anyone of the synovial joints of the body; inducing thermal shrinkage of the joint capsules as a treatment for recurrent dislocation, subluxation or repetitive stress damage to any articulated joint in the body; discosectomy either a treatment of a disc prolapse or as part of a spinal fusion via a posterior or anterior approach to the cervical, thoracic and lumbar spine or any other fibrous joint for similar purposes excision of diseased tissue, and hemostasis. The instrument of the invention is also useful for tissue dissection, resection, vaporization, drying and coagulation, as well as combinations of these functions, with particular application in urological endoscopic surgery (urethroscopy, cystoscopy, ureteroscopy and nephroscopy) and percutaneous surgery. Urological procedures may include: electro-vaporization of the prostate gland (EVAP) and other variants of the procedure commonly known as transurethral resection of the prostate (TURP) including, but not limited to, interstitial ablation of the prostate gland by a percutaneous route or Perurethral either performed for benign or malignant disease, transurethral or percutaneous resection of tumors of the urinary tract that may arise as primary or secondary neoplasms, and also as they may arise anywhere in the urological tract from the calyces of the kidney to the urethral meatus external, division of strictures as they may arise in the pelviuretic union (PUJ), ureter, ureteral orifice, neck of the bladder or urethra; ureterocoelus correction, - diverticular bladder shrinkage; cystoplasty procedures in regard to correction of voiding dysfunction, thermally induced shrinkage of the pelvic floor as a corrective treatment for the descent of the bladder neck, excision of diseased tissue, and hemostasis. Surgical procedures using the electrosurgical instrument of the invention may also include introducing the electrode assembly to the surgical site, either through an artificial conduit (a cannula) or a natural conduit, which may be in an anatomical cavity or body space, or one created surgically. The cavity or space may be distended during the procedure using a fluid, or it may be kept naturally open by anatomical structures. The surgical site may be bathed in a continuous flow of conductive fluid such as saline either to fill and distend the cavity, or to create a locally irrigated environment around the tip of the electrode assembly in a gas-filled cavity. The irrigating fluid can be aspirated from the surgical site to remove products created by the application of radiofrequency energy, tissue or blood remnants. The procedures may include simultaneous viewing of the site via an endoscope or using an indirect display means. An irrigated bipolar electrosurgical instrument is described in the specification of our International Patent Application GB96 / 01472. Advantageously, the exposed end of the tissue treatment electrode is constituted by a plurality of filamentary tissue contacting members made of an electrically conductive material, the filamentary members being electrically connected to a common electrical supply conductor. In a preferred embodiment, a single rolled filament constitutes the filamentary member, the rolls of a filament constituting the filamentary members. The filament can have a diameter that is in the range of from 0.05 millimeters to 0.5 millimeters. In another preferred embodiment, a plurality of separate, separate filaments constitute the filamentary members. The filaments can each have a length that lies in the range from 0.5 millimeters to 5 millimeters, and a diameter that is within the range of 0.05 millimeters to 0.5 millimeters. Preferably, the filamentary members are made of tungsten, or of a tungsten or platinum alloy. Alternatively, the exposed end of the contact electrode with the fabric is constituted by a mesh. Preferably, the instrument further comprises suction means for applying a subatmospheric pressure to the interior of the insulating member, whereby the vapor bubbles produced in the region of the tissue treatment electrode are evacuated via the interior of the instrument. Advantageously, the cutout is formed on the lateral surface of the insulating member adjacent the distal end thereof. In this case, the instrument can be used as a side effect instrument. Alternatively, the cutout is formed obliquely across the face of the distal end of the insulating member, whereby the exposed end of the tissue treatment electrode has both an axially facing tissue contact portion and a contact portion of the tissue. tissue facing laterally. In this case the instrument can be used as both an extreme effect instrument and a side effect instrument.

Advantageously, the dimensions and configuration of the tissue treatment electrode, the fluid contact surface and the insulating member are such that, when the electrode assembly is immersed in a conductive fluid medium, the ratio of (i) the length of the shortest conductive path through the fluid medium between the contact surface with the fluid and that part of the tissue treatment electrode which is farthest from the fluid contact surface, a (ii) the length of the shortest driving path through the fluid medium between the contact surface with the fluid and the tissue treatment electrode is at most 2 a l. Preferably, the laterally projecting portion of the insulating member defines an insulating barrier for dividing the flow of electrical current through the fluid medium thereby increasing the length of the shortest path of travel between the contact surface with the fluid and the tissue treatment electrode. The first address can define a treatment axis, and the two shorter conductor paths can be in a common plane containing the treatment axis. The invention also provides an electrode unit for an electrosurgical instrument for treating tissue in the presence of a fluid electrically conductive medium, the electrode unit comprising an arrow having at one end means for connection to an instrument handle, and, mounted on the other end of the arrow, an electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically isolated from the tissue treatment electrode by means of an insulating member. The tissue treatment electrode has an exposed end that extends laterally through a cutout provided in the insulating member in the distal end portion of the instrument, the return electrode having a contact surface with the fluid which overlaps the insulating member in the region of the cutout, and the radiofrequency generator having a bipolar output connected to the electrodes, the contact surface with the fluid being separated from the tissue treatment electrode so as to define, in use, a fluid path A conductor that completes an electrical circuit between the tissue treatment electrode such that it defines, in use, a conductive fluid path that completes an electrical circuit between the tissue treatment electrode and the return electrode. Advantageously, the radio frequency generator includes control means for varying the output energy delivered to the electrodes. The control means may be such that they provide output power in a first and second output ranges, the first output range being to energize the electrosurgical instrument for drying the tissue and the second output range is to energize the instrument electrosurgical for the removal of tissue by cutting or vaporization. Conveniently, the first output range is from about 150 volts to 200 volts, and the second output range is from about 250 volts to 600 volts, the voltages are peak voltages. Preferably, the control means is such that it alternates the output energy between the first and second energies in the first and second output ranges. Alternatively, the control means is such that it drives the output energy at an energy within the second output range. The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 is a diagram showing an electrosurgical apparatus constructed in accordance with the invention. Figures 2 through 6 are diagrammatic side elevations of the electrode assemblies of five electrode unit shapes constructed in accordance with the invention, - Figure 7 is a perspective view of a modified form of the electrode assembly of the electrode assembly. Figure 3, - Figure 8 is a perspective view of part of the assembly of Figure 7; and Figure 9 is a cross-section taken on the lines AA of Figure 7. Each of the electrode units described below is intended to be used with a conductive distension means such as normal saline solution, and each unit has a structure of dual electrode, the conductive medium acting as a conductor between the tissue being treated and one of the electrodes, later called the return electrode. The other electrode is applied directly to the tissue, and is called later in the present (active) tissue treatment electrode. In many cases, the use of a liquid distension means is preferable, since it avoids the excessive temperature of the electrode in many circumstances, and largely eliminates sticking of the tissue. Referring to the drawings, Figure 1 shows the electrosurgical apparatus including a generator 1 having an output socket 2 providing a radiofrequency (RF) output for an instrument in the form of a handle 3 via a connecting cord 4. The activation of the generator 1 can be carried out from the handle 3 via a control connection on the cord 4, or by a pedal switch unit 5, as shown, connected separately to the rear part of the generator 1 by a foot switch connecting cord 6. In the illustrated embodiment, the foot switch unit 5 has two foot switches 5a and 5b for selecting a desiccation mode and a vaporization mode of the generator 1 respectively. The front panel of the generator has pressure buttons 7a and 7b to respectively set the drying and vaporization energy levels, which are indicated in the visual display 8. The pressure buttons 9a are provided as an alternative means for selection between the modes of desiccation and vaporization. The handle 3 mounts a detachable electrode unit E, such as the electrode units El to E5 which will be described later. Figure 2 shows the first form of an electrode unit El for detachable attachment to the handle of the electrosurgical instrument 3, the electrode unit comprising an arrow 10, which is constituted by a semi-flexible tube made of stainless steel or electroplated finox in copper or gold, with an assembly of electrodes 12 at the distal end thereof. At the other end (not shown) of the arrow 10, means are provided for connecting the electrode unit El to the handle 3 both mechanically and electrically. The radio frequency generator 1 (not shown in the Figure 2) administers an electrosurgical current to the electrode assembly 12. The generator includes means to vary the output energy delivered to satisfy different electrosurgical requirements. The generator can be as described in the specification of our European Patent Application 96304558.8. The electrode unit El includes an active electrode 14 which is constituted by a plurality of filaments made of tungsten or a tungsten or platinum alloy. The active electrode (brush) 14 is connected to the radio frequency generator 1 via an isolated central copper conductor (not shown). A ceramic insulating sleeve 16 surrounds the central conductor, the filaments 14a of the brush electrode pass along the insulating sleeve and extend laterally therefrom through a cut-out 16a. A return electrode 18, which is constituted by the distal end of the arrow of the instrument, surrounds the closest end of the sleeve 16. An outer insulating coating 20 (which could be polyvinylidene fluoride, a polyimide, polytetrafluoroethylene, a polyolefin, a polyester or ethylene tetrafluoroethylene) surrounds the proximal portion of the arrow adjacent the return electrode 18. The return electrode 18 is formed with a cap-like extension 18a extending over the surface of the sleeve 16 which is opposite to cut 16a. The electrode unit El can, thus, provide maximum embedding of tissue for shallow working angle applications, and is known as a side effect electrode. This electrosurgical instrument is particularly useful for rapid tissue demassing. One of the problems that could be encountered when the tissue is rapidly demasked using an arthroscopic electrode configuration, particularly when working in small joint spaces, is the production of vapor bubbles generated as a final product of tissue vaporization. These bubbles obscure vision, and can melt at the site of the tissue application, so that the electrical circuit between the active and return electrodes becomes compromised by the absence of conductive fluid. Irregular active electrodes having filamentary, mesh or coiled spring forms go some way to solve this problem, since they reduce the vaporization thresholds as described in the specification of our International Patent Application GB97 / 00065. Another advantage of these electrode shapes is that the bubbles generated by vaporization are smaller than those formed by solid electrodes. Since the brush electrode 14 of this electrosurgical instrument is irregular in shape, it also has the advantage of producing relatively small vapor bubbles as the product of tissue vaporization. The production of vapor bubbles, however, is further reduced as a result of the lower vaporization threshold that results from the use of the electrode unit El. This improvement results from the extension as a cap 18a of the return electrode 18 which is extends over the back of the active electrode 14. This reduces the separation between the active electrode 14 and the return electrode 18, thereby reducing the electric field and the vaporizing threshold energy of the active electrode. This improves the vaporization rate of the tissue at a lower power than would otherwise be required for the given area of active electrode, and therefore reduces the formation of vapor bubbles. Since the extension as a cap 18a extends along the entire length of the active electrode 14, a large active electrode size can be supported, despite the reduction in electrode spacing. The robustness of the electrode assembly 12 is also important in arthroscopic surgery, both because of the tendency of surgeons to use an electrode assembly and a cold manipulator, as due to the rigid nature of the tissue to be treated - particularly bone and cartilage. The cap-like extension 18a adds mechanical strength to the electrode assembly 12, as it extends over the ceramic insulating sleeve 16, thereby reducing the risk of ceramic fracture and potential deterioration of the insulation. The electrode unit El is intended primarily for use in arthroscopic surgery that requires rapid tissue demassing by vaporization. In use, the electrosurgical instrument is manipulated to introduce the electrode assembly 12 at a selected operating site (e.g., within the joint space of a knee), so that the brush electrode 14 makes contact with the tissue that It will be treated, and with the tissue and electrode assembly submerged in saline. The pedal switch 5b (or the pressure button 7b) is then operated to set the energy level required for vaporization. The generator 1 then provides sufficient radiofrequency energy for the assembly of electrodes 12 to vaporize the saline solution surrounding the brush electrode 14, and to maintain a vapor pocket surrounding the electrode. Using a brushing technique, with firm pressure against the surface of the tissue, the rapid desmasification of the tissue is achieved. Touching the tissue gently will reduce the effect, and can be used to sculpt and smooth the residual tissue surface. Due to its demassing rate and lateral effect configuration, the El electrode unit also has advantages in urological surgery as a vaporization technique for use in conjunction with a resectoscope. A resectoscope electrode unit is inserted very differently, because it is mounted on an endoscope before the passage of the assembled instrument through a working sheath inserted via the urethra. The proximal end of the electrode unit is connected to a trigger assembly and an electrical contact that is integrated with the resectoscope. By this means, the electrode unit can be moved back and forth through a defined range of motion by operating the trigger mechanism. Since the electrode unit is assembled before the introduction, the size of the tip is not restricted by the dimensions of the working channel, but by the diameter of the working sheath that can be up to 10 millimeters. Part of this diameter is occupied by the support wires for the electrode unit, these wires commonly bend at an angle downwards, with respect to the endoscopic image, towards the working tip, so that they do not interfere with the visualization nor with its operation. The brush electrode 14 can have a length that is within the range of from 3 millimeters to 4 millimeters and a width that is in the range of from 2 millimeters to 3 millimeters, and this size is necessary for urological surgery since, in average, an average of 20-30 grams of tissue from the prostate should be removed. Due to the urinary bladder vessel effect, and the mounting of the endoscope to see the tip of the active electrode from eibajo, the generation of bubbles during vaporization gives fewer problems during endoscopic urology, since the bubbles flow away from the endoscope to accumulate in the bladder. However, the use of the electrode unit El substantially reduces the possibility of generating bubbles that cause problems.

Although the electrode unit El is intended primarily for use in vaporizing the tissue, it can also be used for desiccation, particularly of synovial membranes or for separating muscle junctions. In this case, as soon as the electrode assembly 12 has been introduced into a selected operating site, the radio frequency generator 1 is activated using the foot switch 5a or the push button 7a to establish the energy level required for the drying . The generator will then provide sufficient radiofrequency energy for the assembly of electrodes 12 to maintain the saline solution adjacent the brush electrode 14 substantially at its boiling point without creating a vapor pocket around that electrode. The instrument can then be manipulated by moving the brush electrode 14 through the surface of the fabric to be treated in a "sweep" from side to side. The electrode unit El can also be used for mixing fabric. Thus, by automatically alternating the output of the radio frequency generator 1 between the energy levels of desiccation and vaporization, then it is possible to produce more hemostasis in the vaporization mode. As a consequence, the speed of tissue demassing can be reduced, which is useful when cutting or demassing vascular tissue structures. Alternatively, the output of the radiofrequency generator 1 can be driven to the level of vaporization energy, and cycled activation of the desiccation mode. This produces less aggressive tissue vaporization than that which occurs in the vaporization mode, with a consequent reduction in both the formation of bubbles and the risk of carbonizing the tissue. Figures 3 to 6 show electrode units E2 to E5 which are modified versions of the electrode unit El. In accordance with the above, equal reference numerals will be used for equal parts, and only the modifications will be described in detail. Thus, the active electrode 14 of the electrode unit E2 is a wound spring electrode mounted within the cutout 16a. The wound spring electrode 14 is made of tungsten or a tungsten or platinum alloy, and its proximal end is connected to the radio frequency generator via an insulated central copper conductor (not shown). The electrode unit E3 of Figure 4 is of "sputnik" shape, having an active electrode 14 constituted by a plurality of protuberances as needles 14a extending from a thin metal base plate 14b mounted within the cut-out 16a in the insulating sleeve 16. Both the base plate 14b and the protuberances 14a are made of tungsten or a tungsten or platinum alloy. The needle-like protuberances 14a are connected to the radiofrequency generator 1 via a common insulated central copper conductor (not shown). This E3 unit is less difficult to manufacture compared to the brush type shape of the El unit, and will produce similar effects. Moreover, it allows variations in the density of the needle-like protuberances 14a over the area of the base plate 14b. Figure 5 shows the electrode unit E4 having an active electrode 14 which is constituted by a mesh made of tungsten or a tungsten or platinum alloy. This electrode unit E4 may be provided with a suction pump (not shown) that can remove steam bubbles via the arrow of the instrument through the active electrode 14. This improves the elimination of vapor bubbles from an operating site, which is particularly advantageous during the aggressive demassing of tissue. The suction pump must be controlled so that the flow of bubbles through the electrode 14 is balanced for the output characteristics of the radiofrequency generator 1 to prevent excessive cooling of the active electrode and a resulting increase in its vaporization energy threshold . The thermal mass of the 14 mesh active electrode is less than that of a solid electrode active and this helps to quickly restore the vapor pocket around the active electrode if this collapse follows excessive cooling. The control means for the suction pump may involve the use of an intermittent suction technique.

Figure 6 shows the electrode unit E5 having an active electrode 14 of the coiled spring type. Here, however, the cutout 16a is formed obliquely (at 45 °) through the distal end face of the insulation sleeve 16, so that the exposed end of the active electrode 14 has both a tissue contact portion that is faces axially as a contact portion with the tissue facing laterally. The tip of the wound electrode 14 also has an angle at 45 degrees from the axis of the instrument, so that this electrode unit is either a final effect electrode or a side effect electrode. The main advantage of this E5 electrode unit is that it can be used in conjunction with endoscopic surgery techniques that require the introduction of a working channel. Figures 7 to 9 show a modified form of the electrode unit E2 of Figure 3. This electrode unit E2 'has an active electrode 14' in the form of a wound spring electrode mounted within a cutout 16a 'in the member insulation 16 '. The wound spring electrode 14 'is made of tungsten or a tungsten or platinum alloy, and its proximal end is connected to the radiofrequency generator by an insulated central copper conductor (not shown). As shown in Figure 8, the insulating member 16 'is formed with a recess 16b' which receives the return electrode 18 'and its extension 18a' (not shown in Figures 7 and 8). As shown in Figure 9, the active electrode 14 'has a distal end portion that is exposed to the distal end of the instrument to come into contact with the tissue. This embodiment has advantages over the above embodiments, particularly when access to the remote areas of a joint cavity is needed, the extension of the insulating member 16 of each of the embodiments of Figures 2 to 5 can prevent the associated active electrode 14 have access to these areas. Figure 9 illustrates the manner in which the insulating member 16 'projects laterally in the region between the active electrode 14' and the extension 18a 'of the return electrode 18'. This laterally projecting part of the insulating member 16 'increases the length of the path of the conductive fluid from the active electrode 14' to the return electrode 18 ', and forces the electric field outwards, thereby avoiding the preferential tonnage between the return electrode and the nearest part of the active electrode, and promoting the arc between the active electrode and the tissue of the neighborhood. The return electrode 18 'is separated from the active electrode 14' so that, in use, it does not contact the tissue to be treated, and so that the electrical circuit is always completed by the saline solution, and not simply arching between the electrodes. Undoubtedly, the arrangement is such that arching between adjacent parts of the electrode assembly is prevented, thereby ensuring that the active electrode 14 'can be wrapped in a vapor pocket, so that the tissue entering the steam bag the preferred path for the current to flow back to the return electrode 18 'via the conductive fluid becomes. To consider the operation of the electrode unit E2 'in more detail, when operating in a tissue cutting or vaporizing mode, a vapor bubble is formed around the tip 14a' of the active electrode 14 '. This tip 14 'a constitutes an active electrode treatment portion. This bubble is held arching within it. The greater the applied voltage, the greater the size of the bubble. The energy dissipated by each arc has impedance limited by the remaining fluid in the conduction path and by the source impedance of the generator. However, an arc behaves as a negative impedance because, if the energy in the arc is sufficiently high, an ionized path of very low impedance is formed. This can lead to an unstable impedance of ionized path always decreasing unless the impedance of the fluid between the bubble and the return electrode 18 'is sufficient to act as a limit on the dissipated energy. It is also possible for the vapor pocket around the treatment portion of the active electrode 14 'to invade the return electrode 18'. Under these circumstances, the arc energy is limited only by the impedance of the generator source, but this energy limitation is poor and can not be adjusted according to the size of the electrode. For these reasons, the dimensions and configuration of the insulating member 16 should be such that they define a minimum path length of 1 millimeter between the treatment portion of the active electrode 14 'and the contact surface with the fluid of the return electrode 18 '. This minimum path length is, in the case of the embodiment shown in Figure 9, the arc length of an insulating member 16 'plus the step dimension c of the laterally projecting part of the insulating member. Another consideration is the possibility of a vapor bag that is formed on only a portion of the exposed treatment portion 14 'a of the active electrode 14'. When the applied voltage and energy are sufficiently high, a vapor pocket will form around the exposed active electrode treatment portion 14 'a. Preferably, the bag is formed uniformly over the entire length of the treatment portion. In this situation, the load impedance presented to the generator can change by as much as a factor of 20. However, when there are significant differences in the length of the conduction path between the fluid contact surface of the return electrode 18a 'and different parts of the treatment portion of the exposed active electrode 14 'a, a voltage gradient is established over the length of each electrode. With some insulating member and active electrode configuration, the voltage gradient may be large enough to allow the formation of a vapor pocket only on that part of the exposed treatment portion still in contact with the conductive fluid. Thus, the voltage gradient within the conductive fluid is established where the edge of the vapor pocket intersects the surface of the treatment portion of the active electrode 14 'a. The electrical behavior of this partially wrapped active electrode treatment portion 14 'a is very different from that of a fully wrapped treatment portion. In terms of controlling the output of the generator by picking up the peak voltage, the behavior of the electrode assembly is no longer bistable. However, the energy demand is considerably higher as a result of the vaporization voltage presented through the wet low impedance region of the active electrode treatment portion 14 'a. The clinical effect is not only the required vaporization, but also an undesirable thermal damaging effect resulting from the increased dissipation of energy. The partial wrapping of the active electrode treatment portion 14 'can be largely prevented by ensuring that the ratio of the length b of the conductive path between the point furthest from the treatment portion of the active electrode and the length of the path shorter conductive between the treatment portion of the active electrode and the contact surface with the fluid is when more 2: 1, ie b / (a + c) <; 2. The laterally projecting portion of the insulating member 16 'defines an insulating barrier for directing the flow of electrical current through the fluid medium, thereby increasing the shortest conductive path between the contact surface with the fluid 18' and the 14 'active electrode. It will be noted from Figure 9 that the downward extension of the active electrode treatment portion, i.e. the distance d by which the active electrode projects beyond the cover portions of the insulating member 16 'on each side, is at least half the width of the treatment portion exposed in a transverse plane. This allows the instrument to rotate around the axis of its arrow to some degree without losing the surgical effect required. Figure 9 also shows that the active electrode 14 'has an exposed end (the tip 14' a) which extends laterally through the cutout 16 'a in a first direction which is opposite to the direction in which the contact surface with fluid 18a '. This first direction defines a treatment axis that is in a common plane with the two shorter conductive paths referred to above. The electrode units of the embodiments of Figures 2 to 6 also include this feature. It should be noted that the insulating member 16 of each of the embodiments of Figures 2 to 6 also has a laterally projecting part which increases the length of the conductive fluid path from the active electrode 14 to the return electrode 18. These units of electrode are also such that the ratio of the length of the conductive path between the point furthest from the treatment portion of the active electrode and the contact surface with the fluid of the return electrode, and the length of the shorter conductive path between the active electrode treatment portion and the contact surface with the fluid is when more than 2: 1. In order to further improve access to the remote areas of the joint cavities, the distal portion of the electrode shaft of each of the embodiments described above could be angled, say between 15 ° and 30 °, with respect to the main portion of the arrow of the instrument. In another modification, titanium could be used as the material for each of the active electrodes. It will be apparent that modifications could be made to the modalities described above. For example, the modalities of Figures 1 through 4 and 6 could each be provided with a suction pump to remove the vapor bubbles via the arrow of the instrument through the active electrode. It would also be possible to make the insulation sleeve 16 of each of the embodiments of a silicone rubber (such as silicone polyurethane), glass, a polyimide or a thermoplastic material.

Claims (30)

1. An electrosurgical instrument for the treatment of tissue in the presence of a fluid electrically conductive medium, the instrument comprising an instrument arrow, and an electrode assembly at one end of the shaft, the electrode assembly comprising a tissue treatment electrode and a return electrode that is electrically isolated from the tissue treatment electrode by means of an insulating member; the tissue treatment electrode has an exposed end which extends laterally through a cutout provided in the insulating member at the distal end portion of the instrument, and a return electrode having a surface in contact with the fluid which overlaps to the insulating member in the region of the cutout, said fluid contacting surface is separated from the tissue treatment electrode such that it defines, in use, a conductive fluid path that completes an electrical circuit between the tissue treatment electrode and the return electrode.

An electrosurgical instrument as claimed in claim 1, wherein the contact surface with the fluid of the return electrode is provided at the distal end portion thereof, the fluid contact surface faces laterally in a first direction , and wherein the insulating member projects laterally outwardly between the distal end portion and the tissue treatment electrode, laterally facing the tissue treatment electrode in a second direction opposite the first direction.

An electrosurgical instrument as claimed in claim 1 or claim 2, wherein the exposed end of the tissue treatment electrode is constituted by a plurality of filamentary tissue contacting members made of an electrically conductive material, the electrically connected filamentary members to a common electrical supply conductor.

4. An electrosurgical instrument as claimed in claim 3, wherein a single rolled filament constitutes the filamentary members, the filament rolls constituting the filamentary members.

5. An electrosurgical instrument as claimed in claim 4, wherein the filament has a diameter that is in the range of from 0.05 millimeters to 0.5 millimeters.

6. An electrosurgical instrument as claimed in claim 3, wherein a plurality of separate, separate filaments constitute the filamentary members.

7. An electrosurgical instrument as claimed in claim 6, wherein each of the filaments has a length that is within the range of 0.5 millimeters to 5 millimeters.

8. An electrosurgical instrument as claimed in claim 6 or claim 7, wherein each of the filaments has a diameter that is within the range of 0.05 millimeters to 0.5 millimeters.

9. An electrosurgical instrument as claimed in any of claims 3 to 8, wherein the filamentary members are made of tungsten.

10. An electrosurgical instrument as claimed in any of claims 3 to 8, wherein the filamentary members are made of a tungsten or platinum alloy.

11. An electrosurgical instrument as claimed in claim 1 or claim 2, wherein the exposed end of the tissue contact electrode is constituted by a mesh.

An electrosurgical instrument as claimed in any of claims 1 to 11, further comprising suction means for applying a subatmospheric pressure to the interior of the insulating member, whereby vapor bubbles produced in the region of the treatment electrode are evacuated. of tissue via the interior of the instrument.

13. An electrosurgical instrument as claimed in any of claims 1 to 12, wherein the cutout is formed on a lateral surface of the insulating member adjacent the distal end thereof.

An electrosurgical instrument as claimed in any one of claims 1 to 12, wherein the cutout is formed obliquely through the face of the distal end of the insulating member, whereby the exposed end of the tissue treatment electrode has both a tissue contact portion facing axially as a laterally facing tissue contact portion.

15. An electrosurgical instrument as claimed in any of claims 14, wherein the dimensions and configuration of the tissue treatment electrode, the fluid contact surface and the insulating member are such that, when the electrode assembly is immersed in a conductive fluid medium, the ratio of (i) the length of the shortest conductive path through the fluid medium between the contact surface with the fluid and the part of the tissue treatment electrode that is the furthest from the surface of contact with the fluid, a (ii) the length of the shortest conductive path through the fluid medium between the contact surface with the fluid and the tissue treatment electrode is at most 2 to 1.

16. A electrosurgical instrument as claimed in claim 15, wherein the proportion of (i) the length of the shortest conductive path through the fluid medium between the sup contact surface with the fluid and the part of the treatment electrode of the tissue that is furthest away from the fluid contact surface, a (ii) the length of the shortest conductive path through the fluid medium between the surface of the contact with the fluid and the tissue treatment electrode is greater than or equal to 1.25.

An electrosurgical instrument as claimed in claim 15, when dependent on claim 2, wherein the laterally projecting portion of the insulating member defines an insulating barrier for dividing the flow of electrical current through the fluid medium by means of which the length of the shortest path of travel between the contact surface with the fluid and the tissue treatment electrode is increased.

18. An electrosurgical instrument as claimed in claim 17, wherein the first direction defines a treatment axis and the two shorter conduction paths are in a common plane containing the treatment axes. 1 .

An electrosurgical instrument as claimed in any of claims 1 to 18, wherein at least one transverse plane extending in the first direction, the tissue treatment electrode is projected beyond the insulating member in the first direction by a distance which is at least half the transverse width of the projecting part of the tissue treatment electrode.

An electrosurgical instrument as claimed in any of claims 1 to 19, wherein the dimensions and configuration of the tissue treatment electrode, the fluid contact surface and the insulating member are such that, when the assembly of electrodes are immersed in a conductive fluid medium, the length of the shortest path of conduction through the fluid medium between the contact surface with the fluid and the tissue treatment electrode is at least 1 millimeter.

21. An electrosurgical instrument as claimed in any one of claims 1 to 20, wherein the return electrode has the form of a cylindrical conductive sleeve with an exposed surface portion having a length and a diameter, the length of the portion of exposed surface at least as large as the diameter, and where, when the electrode assembly is immersed in a conductive fluid medium, the proportion of (i) the shortest conduction path through the fluid medium between the contact surface with the fluid and that part of the tissue treatment electrode that is furthest from the fluid contact surface, (ii) the diameter of the exposed surface portion of the return electrode is at most 4.5 to 1.

22. An electrode unit for an electrosurgical instrument for treating a tissue in the presence of an electrically conductive fluid medium, the electrode unit comprising an arrow having at one end means for connection to an instrument handle, and, mounted on the other end of the arrow, an electrode assembly comprising a tissue treatment electrode and a return electrode on the which is electrically isolated from the tissue treatment electrode by means of an insulating member, the tissue treatment electrode having an exposed end extending the Aterally through a cutout provided in the insulating member, and the return electrode having a contact surface with the fluid that is superimposed on the insulating member in the region of the cutout, the contact surface with the fluid is separated from the treatment electrode. of tissue such that it defines, in use, a conductive fluid path that completes an electrical circuit between the tissue treatment electrode and the return electrode.

23. An electrode unit as claimed in claim 22, wherein the contact surface with the fluid of the return electrode is provided at the distal end portion thereof, laterally facing the contact surface with the fluid in a first direction, and wherein the insulating member projects laterally outwardly between the distal end portion and the tissue treatment electrode, laterally facing the tissue treatment electrode in a second direction opposite to the first direction.

An electrosurgical apparatus comprising a radiofrequency generator and an electrosurgical instrument for the treatment of tissue in the presence of a fluid electrically conductive medium, the instrument comprising an instrument arrow, and an electrode assembly at one end of the arrow, comprising the electrode assembly a tissue treatment electrode and a return electrode which is electrically isolated from the tissue treatment electrode by means of an insulating member, the tissue treatment electrode having an exposed end extending laterally through a cut-out provided in the insulating member in the distal end portion of the instrument, the return electrode having a contact surface with the fluid that overlaps the insulating member in the region of the cutout, and the radio frequency generator has a bipolar output connected to the electrodes, the contact surface with the fluid or is separated from the tissue treatment electrode so that it defines, in use, a conductive fluid path that completes an electrical circuit between the tissue treatment electrode and the return electrode.

An electrosurgical apparatus as claimed in claim 24, wherein the contact surface with the fluid of the return electrode is provided in the distal end portion thereof, the fluid contact surface faces laterally in a first direction , and wherein the insulating member projects laterally outwardly between the distal end portion and the tissue treatment electrode, laterally facing the tissue treatment electrode in a second direction opposite the first direction.

26. Apparatus as claimed in claim 24 or claim 25, wherein the radiofrequency generator includes control means for varying the output energy delivered to the electrodes.

27. Apparatus as claimed in claim 26, wherein the control element is such as to provide output energy in the first and second output ranges, the first output range being to energize the electrosurgical instrument for drying the tissue, and being the second output range to give energy to the electrosurgical instrument for the removal of tissue by cutting or vaporization.

28. Apparatus as claimed in claim 27, wherein the first output range is from about 140 volts at 200 volts, and the second output range is from approximately 250 volts to 600 volts, the voltages are peak voltages.

29. Apparatus as claimed in any of claims 26 to 28, wherein the control means is the one that alternates the output energy between the first and second energies in the first and second output range.

30. Apparatus as claimed in any of claims 26 to 28, wherein the control means is such as to drive the output power to a power within the second output range.