Electrode for electrosurgical coagulation of tissue

An electrosurgical electrode, comprising a metal conductor having a first external surface area and having a convex body, a flat face on the body, and a connector for attaching the body to an electrosurgical probe handle, and an insulating layer covering the first external surface of the metal conductor except at a selected second area of one of the convex body and the flat face, the second area being positioned on the metal conductor so that a line from a geometric center of the second area and substantially perpendicular to the second area intersects at an angle an axis formed by a probe handle and the metal conductor upon attachment of a probe handle to the connector, wherein the second area does not intersect the axis along the probe handle. Also disclosed are methods of manufacture and similar off-axis electrodes useful in endoscopic electrosurgery.

TECHNICAL FIELD 
 This invention is directed to electrodes used in electrosurgical 
 procedures. 
 BACKGROUND 
 Numerous patents and patent applications exist in the field of 
 electrosurgical methods and apparatuses that describe electrode shapes 
 used to modify tissue in vivo. Early devices, including the design of 
 their electrodes, were crude, and advances in surgical techniques over the
 years, especially the development of surgery using endoscopes 
 (arthroscopic surgery), have continually led to new designs of electrodes 
 as new uses call for the design of an apparatus specifically designed for 
 that new use. Arthroscopic surgery is becoming increasingly popular, 
 because it generally does less damage than open procedures, produces less 
 scarring in and around joints, and results in faster healing and return of
 the patient to full productivity. 
 Nevertheless, arthroscopic surgery has its limitations. The surgeon must 
 operate through a narrow tube formed in the body on which surgery is being
 carried out, which is awkward. Only one probe can be used at a time for 
 many operations. Often the viewing camera is positioned at an angle 
 different from the surgeon's normal gaze. This contrasts with "open 
 surgery" where the surgeon has relative ease of viewing the surgical site 
 and can freely move both hands, even utilizing the hands of colleagues. 
 In view of such difficulties of arthroscopic surgery, it is understandable 
 that radio-frequency (RF) probes which simultaneously cut and coagulate 
 are preferred. However, current RF probes are poorly adapted to certain 
 activities, such as smoothing surfaces located at an angle to the axis of 
 entry of an arthroscopic probe. 
 Current probes have convex, pointed and/or flat tips and are generally 
 oriented so that the ablation process occurs substantially along the axis 
 of the elongated probe being used for the operation. U.S. Pat. No. 
 5,308,311 (issued May 3, 1994 to Eggers and Shaw) is exemplary in that it 
 has a pointed tip with a convex side. With current probes, the surgeon has
 poor ability to ablate tissue in directions off the axis of insertion of 
 the probe and little control when attempting to ablate a tough substrate, 
 such as cartilage. Thus, there are certain procedures that surgeons still 
 prefer to perform in the "open." Unfortunately, this often results in 
 bigger scars, longer convalescence, and more irritation of an already 
 irritated joint. 
 What is needed is a probe that can direct ablation of tissue at an angle to
 the principal axis of the probe, as well as a technique for easy 
 manufacture of such an apparatus. Some procedures which have been 
 considered too awkward or difficult to perform by arthroscopy can then be 
 performed efficiently by arthroscopy. 
 SUMMARY OF THE INVENTION 
 It is an object of the invention to provide an electrode for an 
 electrosurgical apparatus capable of superior performance in ablating 
 collagen, including collagen present in cartilage, relative to existing 
 electrodes. 
 It is a further object of the invention to provide an electrode for an 
 electrosurgical apparatus that can ablate tissue at an angle to the 
 principal axis of the probe on which it is used without requiring a bend 
 in the probe itself. 
 It is another object of the invention to provide an electrode for an 
 electrosurgical apparatus that can be adapted to multiple end uses by a 
 single selection of a mechanical operation on different locations on the 
 electrode surface during manufacture of the electrode. 
 These and other objects of the invention as will hereinafter become more 
 readily apparent have been accomplished by providing an electrosurgical 
 electrode, comprising a metal conductor having a first external surface 
 area and having a convex body, a flat face on the body, and a connector 
 for attaching the body to an electrosurgical probe handle, and an 
 insulating layer covering the first external surface of the metal 
 conductor except at a selected second area of one of the convex body and 
 the flat face, the second area being positioned on the metal conductor so 
 that a line from a geometric center of the second area and substantially 
 perpendicular to the second area intersects at an angle an axis formed by 
 a probe handle and the metal conductor upon attachment of a probe handle 
 to the connector, wherein the second area is less than 30% of the first 
 area. 
 The electrode is used in preferred embodiments in an electrosurgical probe,
 comprising a handle, an elongated probe neck connected to the handle and 
 having a terminus distal to the handle, and the electrode of the invention
 located at the terminus of the elongated probe neck. The electrosurgical 
 probe so formed is preferably used as part of an electrosurgical system, 
 comprising an electrical power supply, a first electrode adapted to 
 contact and electrically ground a living body, the first electrode being 
 electrically connected to the power supply, and an electrosurgical probe, 
 the probe comprising a handle, an elongated probe neck connected to the 
 handle and having a terminus at a distal end from the handle, and a second
 electrode, the second electrode being the electrode of the invention and 
 being located at the terminus of the elongated probe neck, the probe being
 adapted to contact the body and complete an electrical circuit, the second
 electrode being electrically connected to the power supply. 
 Also provided is a general method of manufacturing off-axis electrosurgical
 electrodes, by preparing a metal conductor having a first external surface
 area and having a first body shape and a connector for attaching the body 
 to an electrosurgical probe handle, applying an insulating layer to cover 
 all of the first external surface of the metal conductor, and removing a 
 portion of the insulating layer at a selected second area of the body 
 shape, the second area being positioned on the metal conductor so that a 
 line from a geometric center of the second area and substantially 
 perpendicular to the second area intersects the principal axis of the 
 probe at an angle, the axis being defined by the probe handle and the 
 metal conductor upon attachment of a probe handle to the connector, 
 generally through an elongated linear neck. Any electrode so formed is 
 also part of the present invention. 
 In another embodiment of the invention a surgical instrument is disclosed. 
 The surgical instrument includes a handle, an elongated probe and at least
 one electrode. The elongated probe is connected to the handle. The 
 elongated probe has a terminus distal to the handle. The electrode 
 includes an electrode surface positioned on the terminus so that a line 
 from a geometric center of the electrode surface and subtantially 
 perpendicular to the electrode surface intersects at an angle a 
 longitudional axis formed by the elongated probe. The conductor attaches 
 the electrode to the handle.

DESCRIPTION OF SPECIFIC EMBODIMENTS 
 The invention comprises improved electrodes used for electrosurgical 
 operations, any apparatus incorporating such electrodes, and a general 
 method for making an off-axis electrode useful for arthroscopic surgery. 
 The electrosurgical electrode, in its preferred embodiments, comprises a 
 metal conductor having a first external surface area and having a convex 
 body, a flat face on the body, and a connector for attaching the body to 
 an electrosurgical probe handle. This preferred electrode shape will be 
 used to describe preparation of an electrode of the invention, but those 
 skilled in the arts of making and manipulating solid metal bodies will 
 recognize that other shapes can be manufactured in a similar manner. The 
 preferred electrode bodies can readily be formed from a spherical metal 
 body blank by grinding one region with a flat grinding element to produce 
 a flat face, before or after drilling (or otherwise providing) a location 
 to attach the electrode to an elongated probe. 
 Instead of providing a pencil-eraser-like electrode at the terminus of the 
 probe, so that cutting or ablation operations occur primarily at the tip 
 of and collinearly with the principal axis of the probe, an insulating 
 layer covering the first external surface of the metal conductor is 
 provided except at a selected second area of one of the convex body and 
 the flat face. The area is positioned on the metal conductor so that a 
 line from the geometric center of the second area and substantially 
 perpendicular to the second area intersects at an angle an axis defined by
 a line between a probe handle and the metal conductor upon attachment of a
 probe handle to the connector. In preferred embodiments, the angle is 
 greater than 60.degree.; in more preferred embodiments, greater than 
 80.degree.. The second area is sufficiently small so that none of the 
 second area is intersected by the principal axis of the probe. Typically, 
 the second area is less than 30% of the first area, preferably less than 
 20%. 
 Selection of materials to use in manufacturing an electrode of the 
 invention (which are primarily the metal used in the body of the electrode
 and the insulator used to cover the metal) can be made from any of the 
 materials normally used in the art of electrosurgical electrode 
 manufacture. Biocompatibility and stability in the presence of heat are 
 primary factors in the choice of both metals and insulating layers. For 
 preferred embodiments of the invention, metals include stainless steel, 
 gold, silver, and platinum; insulating materials include 
 polytetrafluoroethylene (e.g., Teflon) and nylon. A typical electrode will
 be prepared from a metal electrode having a tensile strength of 25 to 400 
 ksi, a thermal conductivity of 0.025 to 1.0 cal/cm.sub.2 /cm/s/.degree. 
 C., a resistivity of 80 to 1500 n.OMEGA.m, and an EMF of -0.44 to +1.5 V. 
 For indications in which high power output through the electrode is 
 desired, such as in the ablation of cartilage, small active electrode 
 areas are desired in order to have high current densities. For such uses, 
 the exposed electrode area typically has a surface area of from 0.005 to 
 0.150 square inches, preferably from 0.010 to 0.080 square inches for 
 treatment of chondromalacia, and from 0.015 to 0.020 square inches for 
 ablation. For exposed electrode areas of these sizes, a 50-watt RF power 
 supply provides satisfactory cartilage ablation. 
 Probes containing electrodes of the invention can have any of the features 
 present in other probes, such as thermocouples or other sensing devices 
 for use in feedback control of the power supply. Electrodes in which the 
 body has a hollow interior (to allow room for such thermocouples, for 
 example) are preferred when appropriate for the intended end use of the 
 electrode. 
 An electrosurgical probe of the invention will have a handle, an elongated 
 probe neck connected to the handle and having a terminus distal to the 
 handle, and the electrode of the invention located at the terminus of the 
 elongated probe neck. Any other device incorporating an electrode of the 
 invention falls within the scope of the invention. For example, an 
 electrosurgical system of the invention will have an electrical power 
 supply, a first electrode adapted to contact and electrically ground a 
 living body, the first electrode being electrically connected to the power
 supply, and an electrosurgical probe of the invention, which will in turn 
 incorporate the electrode of the invention, that electrode being 
 electrically connected to the power supply to complete the circuit. 
 Preferred are radio frequency energy power supplies, although the 
 electrodes of the invention can be used with other power supplies, such as
 microwave power supplies. Systems in which the power supply is operably 
 connected to a temperature-sensitive feedback monitor located in the probe
 are preferred, such as those described in U.S. applications Ser. Nos. 
 08/637,095 and 08/714,987. These applications also contain many details 
 related to other components that can be used with the electrodes of the 
 present invention. 
 In all of these operations, current and voltage are used to calculate 
 impedance. An operator-set level of power and/or temperature may be 
 determined, and this level can be maintained manually or automatically if 
 desired. The amount of RF energy delivered controls the amount of power. 
 Feedback can be the measurement of impedance or temperature and occurs 
 either at the controller or at the RF source if it incorporates a 
 controller. Impedance measurement can be achieved by supplying a small 
 amount of non-therapeutic RF energy. Voltage and current are then measured
 to confirm electrical contact. Accordingly, it is well within the skill of
 the art to determine satisfactory optimum operating conditions for 
 electrodes of the invention having different active electrode areas from 
 those exemplified herein. Circuitry, software and feedback to a controller
 result in full process control and are used to change (i) power 
 (modulate)--including RF, incoherent light, microwave, ultrasound and the 
 like, (ii) the duty cycle (on-off and wattage), (iii) monopolar or bipolar
 energy delivery, (iv) fluid (electrolytic solution delivery, flow rate and
 pressure and (v) determine when ablation is completed through time, 
 temperature and/or impedance. 
 The present invention provides a general method of manufacturing off-axis 
 electrosurgical electrodes, by preparing a metal conductor having a first 
 external surface area and having a first body shape and a connector for 
 attaching the body to an electrosurgical probe handle, applying an 
 insulating layer to cover all of the first external surface of the metal 
 conductor, and removing a portion of the insulating layer at a selected 
 second area of body shape, the second area being positioned on the metal 
 conductor so that a line from a geometric center of the second area and 
 substantially perpendicular to the second area intersects the principal 
 axis of the probe at an angle, the axis being defined by the probe handle 
 and the metal conductor upon attachment of a probe handle to the 
 connector, generally through an elongated linear neck. Since the body of 
 the electrode is formed from metal that is harder than the insulators 
 commonly used in such electrodes, a grinding process can be used to remove
 a selected portion of an initially applied layer that covers the entire 
 external surface of the electrode body. Care may need to be taken with 
 softer metals if their original shape is to be maintained, but selection 
 of grinding conditions based on the harness of the material being removed 
 are well known in the grinding art. In an embodiment of the invention 
 insulating material on a flat surface is readily removed using a grinding 
 disk; if desired a flat face can be formed on the electrode at the same 
 time by using a grinding material harder than both the insulator and the 
 metal used in the disk. Such a technique is particularly useful with 
 softer metals, such as gold. Insulating material on a convex surface can 
 be removed by a wire brush or a specially shaped grinding wheel. In an 
 another embodiment the probe surface can be masked in the tip region 
 Insulation material can then be applied to the probe. The mask is then 
 removed exposing the conductive tip. Any electrode formed by the 
 manufacturing process described here is also part of the present 
 invention. 
 Turning now to the drawings, FIGS. 1A-C, 2A-C show alternate embodiments of
 a detachable tip with an off-axis electrode. In the embodiments shown in 
 FIGS. 1A-C the detachable tip may be made from a generally insulating 
 material. In the embodiment shown in FIGS. 2A-C the detachable tip may be 
 made from a generally conductive material. FIGS. 1A-C show, respectively, 
 a cross-sectional elevation, an end view and an exterior view of the 
 detachable tip. As shown in FIG. 1A, the detachable tip 100 includes a 
 tapered shaft 108A connected to an arcuate extension 104A. A flat 
 electrode surface 120A is defined at the terminus of the arcuate 
 extension. The electrode's surface is located about a normal axis which is
 orthogonal to the axis of the tapered shaft 108A. As shown in FIG. 1A, an 
 annular cavity 102A is defined by both the tapered shaft and arcuate 
 extension. The flat surface 120A defines a through hole 114 which connects
 to the annular cavity 102A. A conductive material 106 fills the through 
 hole. In an embodiment of the invention the conductive material comprises 
 silver solder, or conductive powdered metal. RF power is provided to the 
 tip through a wire 110B which is joined at 110A to the conductive material
 106. To provide feedback for control of RF power, a thermal couple 112A is
 also bonded to the conductive material. Lead wires 112B extend from the 
 thermal couple to an exit point at a proximal end of the tapered shaft. 
 FIGS. 2A-C show an alternate embodiment of the detachable tip to that 
 discussed above in connection with FIGS. 1A-C. In this embodiment the 
 entire detachable tip 200 may be comprised of a conductive material. An 
 annular cavity 102B is defined within both the tapered shaft 108B and the 
 arcuate extension 104B of the detachable tip. At a terminus of the arcuate
 extension a flat surface 120B is defined. Portions of the arcuate 
 extension are covered with insulator 260 so as to localize the RF 
 generation to flat surface 120B. Within the annular cavity 102B of the 
 generally conducting detachable tip 200, both the RF and thermal couple 
 connections are made. Because the detachable tip is generally conducting, 
 no through hold to the flat surface 120B is required. Instead, thermal 
 couple 112A is bonded to an interior surface of the annular cavity and 
 wires 112B to that thermal couple extend from the distal end of the 
 tapered shaft 108B. The RF wire 110B terminates in a bond 110A to the 
 interior surface of the annular cavity. 
 In the embodiments shown the electrode portion of the detachable tip 
 provides monopolar RF delivery which induces tissue heating by a 
 combination of molecular friction and conduction. A complete electrical 
 circuit for monopolar RF delivery includes a return current pad in 
 electrically conductive contact with the patient's body. The pad in turn 
 is connected to the RF generator to complete an electrical circuit from 
 the RF delivery 110 within the detachable tip through the conductive 
 tissue to the return pad. 
 This will be obvious to those skilled in the art. Bipolar delivery can be 
 implemented using the teachings of the current invention by providing at 
 least two distinct electrodes on the tip, each connected to outgoing and 
 return electrical paths from the RF power supply. Monopolar heating has 
 the advantage that tissue, rather than the surgical instrument itself, is 
 heated. In bipolar delivery, energy follows the path of least resistance 
 through conductive irrigating solution in the body tissue, causing 
 superficial surface heating with minimal tissue penetration. 
 FIGS. 3A-B show the detachable tip assembled with a surgical instrument 
 350. FIG. 3A shows the surgical instrument to include a handle 354, an 
 extended probe or shaft 352 and the detachable tip 200 at a distal end of 
 the probe 352. The handle is attached to the proximal end of the probe. 
 FIG. 3B shows the detachable tip 200 frictionally affixed within the 
 distal end of probe 352. Probe 352 is tubular in cross-section and has an 
 interior annular surface dimensioned to press fit with the exterior 
 surface of tapered shaft 108B. Thus, the detachable tip is fastened to the
 distal end of probe 352. In alternate embodiments the tip can be fastened 
 to the shaft by press fit, by mechanical fastener, by an interlocking 
 action, by an adhesive compound, a bonding compound, by braising or by 
 welding, for example. Electrical connections to both the RF and thermal 
 couple connections discussed above in connection with FIGS. 2A-C extend 
 the length of the probe to power and control connections within the handle
 354. 
 FIGS. 4A-E show an alternate embodiment for the off-axis RF tip of the 
 current invention. The tip in these embodiments is integrated with the 
 probe 352. The probe has a distal end 400 on which various embodiments of 
 arcuate extensions 404B-E are shown in, respectively, FIGS. 4B-E. These 
 arcuate extensions can be formed on the distal end of the probe through 
 fabrication steps such as swaging, rotoforming, bending, etc. The probe 
 may be solid or tubular in cross-section. In embodiments where the probe 
 is solid, it may be made of a conductive material coated with an insulator
 460B-E. At the terminus of the probe the insulating covering 420B-E ceases
 and an exposed portion of the probe forms a conductive electrode on the 
 tip. Planar electrode surfaces 420B-E are shown in, respectively, FIGS. 
 4B-E. RF connection can be made to the probe within the handle. The 
 electric current will be carried the length of the conductive probe and 
 will radiate from the flat surfaces 420 at the exposed probe tip 406B-E 
 also shown respectively in FIGS. 4B-E. In an alternate embodiment of the 
 current invention the probe is annular in cross-section and may be made 
 from an insulating or conductive material. In the event the probe is made 
 from an insulating material, the probe tip 406B-E shown in, respectively, 
 FIGS. 4B-E may be comprised of a conductive material such as silver solder
 or conductive metallic powder. RF and thermal couple connections may be 
 made to this conductive material 406 through wires extending from the 
 handle through the annular opening within the probe 352 to the conductive 
 tip material 406. The flat surfaces 420B-E may be formed on the tip by 
 grinding and allow radiation of RF energy from an electrode surface whose 
 normal axis is off the longitudinal axis about which the probe 352 is 
 defined. 
 FIGS. 5A-B show cross-sectional views of the integrated off-axis tip 
 discussed above in connection with FIGS. 4A-E. FIG. 5A shown an embodiment
 in which the probe 352A is fabricated from a conductive material. FIG. 5B 
 shows an embodiment in which probe 352B may be fabricated from an 
 insulating material. The conductive probe 562A shown in FIG. 5A is covered
 with an insulating material 560. This material covers all portions of the 
 probe with the exception of the distal end. The probe has an arcuate 
 extension 404E. The probe may have an annular cavity 564 in cross-section.
 In alternate embodiments the probe may be solid in cross-section. At the 
 distal end of the probe, a conductive material 406E fills the annular 
 opening and defines a flat electrode surface 420E. A normal to this 
 surface is in the embodiment shown off-axis or in the embodiment shown 
 orthogonal to the longitudinal axis of the probe 352A. RF power is 
 supplied to the conductive material 406E via the conductive probe 562A 
 from an RF attachment in the handle 354. An RF junction 510A to an RF 
 delivery wire 510B is made to the proximal end of the probe where it joins
 to handle 354. 
 In FIG. 5B the probe 562B defines an annular cavity 564 extending from the 
 proximal to the distal end of the probe. At the distal end of the probe an
 arcuate extension 404E is defined. At the terminus of the probe a 
 conductive material 406E fills the annular opening and defines a flat 
 electrode surface 420E. Because the probe is generally insulating, a 
 connection is made between RF delivery wire 510B, which extends the length
 of the annular cavity of the probe and forms a junction 510A with the 
 conductive material 406E. Either embodiment shown in FIG. 5A or 5B can 
 additionally include a thermal couple to provide temperature feedback to 
 an RF power source. 
 Although, each of the above mentioned embodiments disclose an electrode 
 surface which is flat it will be obvious to those skilled in the art that 
 other surface profiles including concave and convex may also be utilized 
 for the off-axis electrodes. Choice of surface profile will depend on the 
 surgical environment. For example, in joints a flat electrode surface 
 allows a probe with a low form factor. Additionally, a flat surface allows
 a larger contact area between the electrode and the surgical site. A 
 concave surface may have the further advantage of isolating the surgical 
 site from surrounding saline solution. The isolation of the concave design
 allows better thermal conductivity and therefore reduced thermal 
 fluctuation. 
 Embodiments intended for use in the treatment of chondromalacia preferably 
 have a convex surface with a radius of curvature of from 0.010 to 0.25 
 inches, preferably from 0.040 to 0.060 inches. For this indication, an 
 electrode formed from a metal body so that the first external surface area
 described above is essentially the surface of a sphere with one flat face 
 is preferred. 
 FIGS. 6 and 7A-B show an alternate embodiment to the probes shown in FIGS. 
 1-5. In these embodiments, the tip itself is formed from the distal end of
 the probe via machining operations such as swaging, thermal forming, 
 bending, etc. No conductive material is required and no 
 attachable/detachable tip is required. Instead, the terminus of the probe 
 is formed into an off-axis tip. In the embodiment shown in FIG. 6, the 
 probe 652 is made from a conductive material 662 about which an insulating
 shell 660 is formed. The insulating shell can be formed in a variety of 
 fashions. In one embodiment the insulating shell can be formed by heat 
 shrink tubing which is slipped over the conductive probe and to which heat
 is applied to cause it to conform to the exterior of the probe. In an 
 alternate embodiment, the probe itself after being formed can be dipped in
 an insulating solution. In still another embodiment, the probe can be 
 coated with a powdered insulator which is activated by temperature to 
 conform to the exterior surface of the probe. (In one such embodiment, 
 Corvel.RTM. nylon coating may be used and is available from Morton Powder 
 Coatings, P.O. Box 15240, Reading, Pa. 19612-5240, (800) 367-3318). In 
 FIG. 6 arcuate surfaces 604B-C are formed on opposing sides of the distal 
 end of the probe. As shown in cross-sectional view, A--A an arcuate 
 extension 604A is also formed at the terminus of the probe, thereby 
 positioning the tip of the probe 620 so as to form a surface the normal to
 which is off the longitudinal axis about which the probe itself is 
 defined. The tip itself is further formed to pinch or close the opening of
 annular cavity 664. This has the advantage of forming a longitudinal 
 electrode surface 620 which may, with appropriate shaping operations such 
 as grinding, offer a cutting surface or scraping surface which can be 
 utilized in conjunction with the cutting or cauterizing capability of RF 
 alone. 
 FIG. 7A shows an alternate embodiment to that shown in FIG. 6 in which a 
 distal end of a probe is formed into an off-axis electrode 720 having a 
 longitudinal electrode surface the normal to which is orthogonal to a 
 longitudinal axis about which the probe is defined. Additionally, in 
 contrast to the embodiment shown in FIG. 6, the electrode surface 720 is 
 rectangular in cross-section and the longitudinal axis of that surface is 
 also orthogonal to the longitudinal probe axis. Appropriate shaping of 
 this surface allows chiseling or scraping of a mechanical nature to 
 complement the RF surgical process. All portions of the probe except for 
 the exposed tip are wrapped in an insulating shell 760. The probe 752 is 
 fabricated with opposing arcuate surfaces 704B-C and an arcuate extension 
 704A which positions the electrode tip 720 in the manner described and 
 discussed above. The probe may be annular or solid in cross section. 
 All publications and patent applications mentioned in this specification 
 are herein incorporated by reference to the same extent as if each 
 individual publication or patent application was specifically and 
 individually indicated to be incorporated by reference. 
 The invention now being filly described, it will be apparent to one of 
 ordinary skill in the art that many changes and modifications can be made 
 thereto without departing from the spirit or scope of the appended claims.