Electrosurgical instrument

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ELECTROSURGICAL INSTRUMENT

BACKGROUND OF THE INVENTION

This invention relates to an electrosurgical instrument for the treatment of tissue in the presence of an electrically 5 conductive fluid medium, to electrosurgical apparatus including such an instrument, and to an electrode unit for use in such an instrument.

Endoscopic electrosurgery is useful for treating tissue in cavities of the body, and is normally performed in the 10 presence of a distension medium. When the distension medium is a liquid, this is commonly referred to as underwater electrosurgery, this term denoting electrosurgery in which living tissue is treated using an electrosurgical instrument with a treatment electrode or electrodes immersed in ^ liquid at the operation site. A gaseous medium is commonly employed when endoscopic surgery is performed in a distensible body cavity of larger potential volume in which a liquid medium would be unsuitable, as is often the case in laparoscopic or gastroenterological surgery. 20

Underwater surgery is commonly performed using endoscopic techniques, in which the endoscope itself may provide a conduit (commonly referred to as a working channel) for the passage of an electrode. Alternatively, the endoscope may be specifically adapted (as a resectoscope) to include 25 means for mounting an electrode, or the electrode may be introduced into a body cavity via a separate access means at an angle with respect to the endoscope—a technique commonly referred to as triangulation. These variations in technique can be subdivided by surgical speciality, where one or 30 other of the techniques has particular advantages given the access route to the specific body cavity. Endoscopes with integral working channels, or those characterised as resectoscopes, are generally employed when the body cavity may be accessed through a natural body opening - such as 35 the cervical canal to access the endometrial cavity of the uterus, or the urethra to access the prostate gland and the bladder. Endoscopes specifically designed for use in the endometrial cavity are referred to as hysterocopes, and those designed for use in the urinary tract include cystoscopes, 40 urethroscopes and resectoscopes. The procedures of transurethal resection or vaporisation of the prostrate gland are known as TURP and EVAP respectively. When there is no natural body opening through which an endoscope may be passed, the technique of triangulation is commonly 45 employed. Triangulation is commonly used during underwater endoscopic surgery on joint cavities such as the knee and the shoulder. The endoscope used in these procedures is commonly referred to an as arthroscope.

Electrosurgery is usually carried out using either a 50 monopolar instrument or a bipolar instrument. With monopolar electrosurgery, an active electrode is used in the operating region, and a conductive return plate is secured to the patient's skin. With this arrangement, current passes from the active electrode through the patient's tissues to the 55 external return plate. Since the patient represents a significant portion of the circuit, input power levels have to be high (typically 150 to 250 watts), to compensate for the resistive current limiting of the patient's tissues and, in the case of underwater electrosurgery, power losses due to the fluid 60 medium which is rendered partially conductive by the presence of blood or other body fluids. Using high power with a monopolar arrangement is also hazardous, due to the tissue heating that occurs at the return plate, which can cause severe skin burns. There is also the risk of capacitive 65 coupling between the instrument and patient tissues at the entry point into the body cavity.

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With bipolar electrosurgery, a pair of electrodes (an active electrode and a return electrode) are used together at the tissue application site. This arrangement has advantages from the safety standpoint, due to the relative proximity of the two electrodes so that radio frequency currents are limited to the region between the electrodes. However, the depth of effect is directly related to the distance between the two electrodes; and, in applications requiring very small electrodes, the inter-electrode spacing becomes very small, thereby limiting tissue effect and the output power. Spacing the electrodes further apart would often obscure vision of the application site, and would require a modification in surgical technique to ensure correct contact of both electrodes with the tissue.

There are a number of variations to the basic design of the bipolar probe. For example, U.S. Pat. No. 4,706,667 describes one of the fundamentals of the design, namely that the ratio of the contact areas of the return electrode and of the active electrode is greater than 7:1 and smaller than 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 may be reduced to approximately 1:1 to avoid differential electrical stresses occurring at the contact between the tissue and the electrodes.

The electrical junction between the return electrode and tissue can be supported by wetting of the tissue by a conductive solution such as normal saline. This ensures that the surgical effect is limited to the needle or active electrode, with the electric 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 enable the return electrode to complete the circuit. Another problem is one of the orientation: even a relatively small change in application angle from the ideal perpendicular contact with respect to the tissue surface, will change the contact area ratio, so that a surgical effect can occur in the tissue in contact with the return electrode.

Cavity distension provides space for gaining access to the operation site, to improve visualisation, and to allow for manipulation of instruments. In low volume body cavities, particularly where it is desirable to distend the cavity under higher pressure, liquid rather than gas is more commonly used due to better optical characteristics, and because it washes blood away from the operative site.

Conventional underwater electrosurgery has been performed using a non-conductive liquid (such as 1.5% glycine) as an irrigant, or as a distension medium to eliminate electrical conduction losses. Glycine is used in isotonic concentrations to prevent osmotic changes in the blood when intra-vascular absorption occurs. In the course of an operation, veins may be severed, with resultant infusion of the liquid into the circulation, which could cause, among other things, a dilution of serum sodium which can lead to a condition known as water intoxication.

The applicants have found that it is possible to use a conductive liquid medium, such as normal saline, in underwater endoscopic electrosurgery in place of non-conductive, electrolyte-free solutions. Normal saline is the preferred distension medium in underwater endoscopic surgery when electrosurgery is not contemplated, or a non-electrical tissue effect such as laser treatment is being used. Although normal saline (0.9% w/v; 150 mmol/1) has an electrical conductivity somewhat greater than that of most body tissue, it has the advantage that displacement by absorption or extravasation from the operative site produces little physiological effect, 3

and the so-called water intoxication effects of nonconductive, electrolyte-free solutions are avoided.

The applicants have developed a bipolar instrument suitable for underwater electrosurgery using a conductive liquid or gaseous medium. This electrosurgical instrument for the 5 treatment of tissue in the presence of a fluid medium, comprises an instrument body having a handpiece and an instrument shaft and an electrode assembly, at one end of the shaft. The electrode assembly comprises a tissue treatment electrode which is exposed at the extreme distal end of the 10 instrument, and a return electrode which is electrically insulated from the tissue treatment electrode and has a fluid contact surface spaced proximally from the exposed part of the tissue treatment electrode. In use of the instrument, the tissue treatment electrode is applied to the tissue to be 15 treated whilst the return electrode, being spaced proximally from the exposed part of the tissue treatment electrode, is normally spaced from the tissue and serves to complete an electrosurgical current loop from the tissue treatment electrode through the tissue and the fluid medium. This electro- 20 surgical instrument is described in the specification of the applicants' co-pending International Patent Application No. PCT/GB96/01473, the contents of which are incorporated in this application by reference.

The electrode structure of this instrument, in combination 25 with an electrically conductive fluid medium largely avoids the problems experienced with monopolar or bipolar electrosurgery. In particular, input power levels are much lower than those generally necessary with a monopolar arrangement (typically 100 watts). Moreover, because of the rela- 30 tively large spacing between its electrodes, an improved depth of effect is obtained compared with a conventional bipolar arrangement.

FIG. 1 illustrates the use of this type of instrument for tissue removal by vaporisation. The electrode assembly 12 35 of this instrument comprises a tissue treatment (active) electrode 14 which is exposed at the distal end of the instrument, and a return electrode which is spaced from the exposed part of the tissue treatment electrode by an insulation sleeve 16. This electrode assembly is powered to create 40 a sufficiently high energy density at the tissue treatment electrode 14 to vaporise tissue 22, and to create a vapour pocket 24 surrounding the active tip. The formation of the vapour pocket 24 creates about a 10-fold increase in contact impedance, with a consequent increase in output voltage. 45 Arcs 26 are created in the vapour pocket 24 to complete the circuit to the return electrode 18. Tissue 22 which contacts the vapour pocket 24 will represent a path of least electrical resistance to complete the circuit. The closer the tissue 22 comes to the electrode 14 the more energy is concentrated to 50 the tissue, to the extent that the cells explode as they are struck by the arcs 26, because the return path through the conductive fluid (saline in this case) is blocked by the high impedance barrier of the vapour pocket 24. The saline solution also acts to dissolve the solid products of vapori- 55 sation.

The power threshold required to reach vaporisation is an important parameter of this type of instrument, and it is the aim of the invention to provide a bipolar electrosurgical instrument having improved vaporisation power threshold 60 properties.

SUMMARY OF THE INVENTION

In its broadest aspect, the invention provides an electrosurgical instrument having an electrode which is so con- 65 structed as to have a better vaporisation power threshold than known electrodes.

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Thus, according to a first aspect, the present invention provides an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid, the instrument comprising an instrument shaft, and a tissue treatment electrode at one end of the shaft, the tissue treatment electrode being constructed to define a plurality of pockets for trapping electrically-conductive fluid and vapour.

In use, the tissue treatment electrode traps electricallyconductive fluid, the trapped fluid thereby absorbing more electrical power for conversion to vapour than would otherwise be the case. This leads to a reduction in the power threshold for vaporisation at the tissue treatment electrode.

The electrically conductive fluid trapped within the irregularities (pockets) of the tissue treatment electrode progressively absorbs more power as it becomes hotter and is not refreshed by fluid from the surrounding environment. As the fluid approaches boiling point, vapour pockets begin to form on the surface of the electrode. The vapour pockets effectively insulate regions of the electrode from the conductive fluid; and, as a result, power becomes concentrated at regions of the electrode not enveloped in vapour. Fluid adjacent to these exposed regions then rapidly reaches a point of vaporisation such that the whole tissue treatment electrode becomes coated in vapour. The vapour is entrapped by the irregular form of the active electrode such that, if an area of the electrode becomes exposed to the fluid medium during use, then the vapour pocket is rapidly reestablished with minimal power dissipation to the surrounding fluid. This leads to a reduction in the power threshold required both to initiate and sustain the vapour pocket during use.

In a preferred embodiment, the tissue treatment electrode is constituted by a plurality of interlaced strands of electrically-conductive material. In this case, the pockets are defined by the interlacing of the strands. Each strand may be formed as a helix, the helices preferably having a common central axis, and being of equal diameter and equal pitch. They may be so interlaced that the pockets formed between them take the form of helical apertures providing fluid communication between an axially-extending space within the helices and the space outside the helices. In another variant, the helices may be tightly wound together, so that each helix lies against other helices and the abovementioned pockets are simply helical recesses between neighbouring helices, little or no communication being available between an interior space and the outside of the electrode. It is possible to achieve a similar function to the tightly-wound, interlaced strand variant with a single piece of conductive material with helical ridges about its outer surface, either created by moulding, machining, or by twisting the piece of material about its longitudinal axis, with the twisting causing helical ridges about the outer surface of the material.

Alternatively, the tissue treatment electrode is constituted by a generally helical coil made of electrically-conductive material. Here, the pockets are formed between adjacent turns of the helical coil. Again, the turns of the coil may be spaced apart to allow communication between the interior of the coil and the outside, or they may be tightly abutting with the pockets comprising a single helical recess on the outer surface of the electrode.

The tissue treatment electrode may also be constituted by a plurality of filaments made of an electrically-conductive material. In this case, the spaces between the filaments define the pockets.

In any of these cases, the instrument may further comprise an insulating shroud which extends along, and partially surrounds, the tissue treatment electrode. The shroud traps electrically-conductive fluid and vapour against the tissue treatment electrode, thereby enhancing its power absorption capabilities.

In another preferred embodiment, the tissue treatment electrode is constituted by a spherical member made of electrically-conductive material, the spherical member being mounted on the shaft of the instrument by means of an electrically-conductive support member, the instrument further comprising an insulating shroud which partially surrounds the spherical member.

Advantageously, the tissue treatment electrode is made of tungsten, a noble metal such as platinum, or of a platinum alloy such as platinum/iridium, platinum/tungsten or platinum/cobalt.

Preferably, the instrument further comprises a return electrode which is electrically insulated from the tissue treatment electrode by means of an insulation member, the tissue treatment electrode being exposed at the extreme distal end of the instrument, and the return electrode having a fluid contact surface spaced proximally from the exposed end of the tissue treatment electrode by the insulation member. Conveniently, the fluid contact surface of the return electrode is a smooth polished surface.

According to a second aspect, the present invention provides an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid, the instrument comprising an instrument shaft, and a tissue treatment electrode at one end of the shaft, the tissue treatment electrode being made from an electricallyconductive material and being coated with a resistive inert material which is effective to increase the local power density within the tissue treatment electrode.

Preferably, the resistive inert material is constituted by a conductive ceramic material.

According to a third aspect, the present mention provides an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid, the instrument comprising an instrument shaft, and an electrode assembly at one end of the shaft, the electrode assembly comprising a tissue treatment electrode and a return electrode which is electrically insulated from the tissue treatment electrode by means of an insulation member, the tissue treatment electrode being exposed at the extreme distal end of the instrument, and the return electrode having a smooth, polished, fluid contact surface spaced proximally from the exposed end of the tissue treatment electrode by the insulation member.

In this case the instrument may further comprise means for feeding electrically-conductive fluid over the fluid contact surface of the return electrode.

The electrosurgical instrument of the invention is useful for dissection, resection, vaporisation, desiccation and coagulation of tissue and combinations of these functions with particular application in hysteroscopic surgical procedures. Hysteroscopic operative procedures may include: removal of submucosal fibroids, polyps and malignant neoplasms; resection of congenital uterine anomalys such as a septum or subseptum; division of synechiae (adhesiolys is); ablation of diseased or hypertrophic endometrial tissue; and haemostasis.

The instrument of the invention is also useful for dissection, resection, vaporisation, desiccation and coagulation of tissue and combinations of these functions with

particular application in arthroscopic surgery as it pertains to endoscopic and percutaneous procedures performed on joints of the body including, but not limited to, such techniques as they apply to the spine and other non-synovial joints. Arthroscopic operative procedures may include: partial or complete meniscectomy of the knee joint including meniscal cystectomy; lateral retinacular release of the knee joint; removal of anterior and posterior cruciate ligaments or remnants thereof; labral tear resection, acromioplasty, bursectomy and subacromial decompression of the shoulder joint; anterior release of the temperomandibular joint; synovectomy, cartilage debridement, chondroplasty, division of intra-articular adhesions, fracture and tendon debridement as applied to any of the synovial joints of the body; inducing thermal shrinkage of joint capsules as a treatment for recurrent dislocation, subluxation or repetitive stress injury to any articulated joint of the body; discectomy either in the treatment of 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 haemostasis.

The instrument of the invention is also useful for dissection, resection, vaporisation, desiccation and coagulation of tissue and combinations of these functions with particular application in urological endoscopic (urethroscopy, cystoscopy, ureteroscopy and nephroscopy) and percutaneous surgery. Urological procedures may include: electro-vaporisation of the prostrate gland (EVAP) and other variants of the procedure commonly referred to as transurethral resection of the prostate (TURP) including, but not limited to, interstitial ablation of the prostate gland by a percutaneous or perurethral route whether performed for benign or malignant disease; transurethral or percutaneous resection of urinary tract tumours as they may arise as primary or secondary neoplasms, and further as they may arise anywhere in the urological tract from the calyces of the kidney to the external urethral meatus; division of strictures as they may arise at the pelviureteric junction (PUJ), ureter, ureteral orifice, bladder neck or urethra; correction of ureterocoele shrinkage of bladder diverticular, cystoplasty procedures as they pertain to corrections of voiding dysfunction; thermally induced shrinkage of the pelvic floor as a corrective treatment for bladder neck descent; excision of diseased tissue; and haemostasis.

Surgical procedures using the instrument of the invention include introducing the electrode assembly to the surgical site whether through an artificial conduit (a cannula), or through a natural conduit which may be in an anatomical body cavity or space or one created surgically. The cavity or space may be distended during the procedure using a fluid, or may be naturally held open by anatomical structures. 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 visualisation means.

The invention also provides an electrode unit for an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid medium, the electrode unit comprising a shaft having at one end means for connection to an instrument handpiece, and, mounted on the other end of the shaft, a tissue treatment electrode, the tissue treatment electrode being constructed to define pockets for trapping electrically-conductive fluid and vapour.

The invention further provides an electrode unit for an electrosurgical instrument for the treatment of tissue in the presence of an electrically-conductive fluid medium, the