WO1998031290A1

WO1998031290A1 - Bipolar vaporization apparatus and method for arthroscopy

Info

Publication number: WO1998031290A1
Application number: PCT/US1998/002499
Authority: WO
Inventors: Roger C. Odell; Joe W. Tippett; Lawrence T. Kirwan, Jr.
Original assignee: Electroscope, Inc.
Priority date: 1997-01-15
Filing date: 1998-01-15
Publication date: 1998-07-23
Also published as: AU6274898A

Abstract

A bipolar vaporization probe (10) has a coaxial bipolar arrangement with an elongated outer electrode (20) positioned concentrically over the elongated inner electrode (30) and with an elongated concentric electrical inner insulation layer (40) positioned between the outer electrode (20) and the inner electrode (30). The bipolar probe (10) also has an elongated outer electrical insulation sleeve (44) concentrically over the outer electrode (20) and a proximal end outer housing terminating in a plug with two prongs that are electrically connected in the housing to outer electrode (20) and inner electrode (30). The prongs of the plug are adapted to plug into a suitable receptacle for connection to an RF generator (36).

Description

BIPOLAR VAPORIZATION APPARATUS AND METHOD FOR ARTHROSCOPY

Description

Technical Field

This invention relates to electrosurgical devices and more specifically to a bipolar chondromalacia removal apparatus and method for arthroscopy.

Background Art

Arthroscopic surgery is used to treat: (i) torn menisci, anterior cruciate, posterior cruciate, patella malalignment, synovia! diseases, loose bodies, osteal defects, osteophytes, and damaged articular cartilage (chondromalacia) of the knee; (ii) synovial disorders, labial tears, loose bodies, rotator cuff tears, anterior impingement and degenerative joint disease of the acromioclavicular joint and diseased articular cartilage of the shoulder joint, (iϋ) synovial disorders, loose bodies, osteophytes, and diseased articular cartilage of the elbow joint; (iv) synovial disorder, loose bodies, ligament tears and diseased articular cartilage of the wrist; (v) synovial disorders, loose bodies, labrum tears and diseased articular cartilage in the hip; and (vi) synovial disorders, loose bodies, osteophytes, fractures, and diseased articular cartilage in the ankle. Articular cartilage is the tough, hyaline tissue covering the ends or articular surfaces of bones in shoulder, knee, and other joints.

Chondromalacia of healthy cartilage is usually a result of diseased or traumatic induced changes in hyaline cartilage and may cause pain, stiffness, effusion, and/or grinding in the joint A common arthroscopic treatment of such chondromalacia is to use a motorized rotary shaver to extricate and remove the damaged, worn or diseased articular cartilage tissue. When performing such arthroscopy, it is not unusual for the rotary shaver to remove not only the damaged, worn, or diseased articular cartilage, but also to remove a significant amount of healthy cartilage, which is undesirable. Also, because the rotary shaver tends to grab and tear tissue that is not cut cleanly, the articular cartilage remaining after treatment with the rotary shaver is often left with a rough surface that can slow healing and accelerate the onset of new chondromalacia.

The bipolar coagulator disclosed in U.S. Patent No. 5,089,002, issued in 1992 to Lawrence T. Kirwan, Jr., one of the co-inventors of this invention, and which is incorporated herein by reference, is a bipolar device that was designed for desiccating several microscopic layers of eye tissue, including tiny blood vessels, on the eye before eye surgery in order to reduce bleeding encounters during eye surgery. The result is that the tiny blood vessels near the eye surface, where the surgical incisions are to be made during eye surgery, are necrosed — virtually obliterated or erased — before any incisions are made. A bipolar coagulator similar to that shown and described in U.S. Patent No. 5,089,002, but with an electrical insulation coating around substantially the entire length of the outer conductor or electrode, was also developed by Lawrence T. Kirwan, Jr., for very fine hemotosis in neural endoscopy applications where the insulation coating prevents outer electrode contact with surrounding tissue. However, both of those bipolar coagulators developed by Kirwan are designed for the specific eye surgery and neural endoscopy necrosing applications described above, which are not in fluid-filled environments and which are not effective for treating chondromalacia encountered in the arthroscopy procedures described above. Disclosure of Invention

Accordingly, it is a general object of the present invention to provide an improved method and apparatus for removing chondromalacia in arthroscopy of shoulders, elbows, wrists, hips, knees, and ankles. A more specific object of the present invention is to provide an improved method and apparatus for removing chondromalacia while minimizing damage to and removal of healthy tissue; and

It is another specific object of the present invention to provide an improved method and apparatus for removing chondromalacia without grabbing and tearing of tissue.

Additional objects, advantages, and novel features of the invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following description or may be learned by the practice of the invention. The objects and the advantages may be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims.

To achieve the foregoing and other objects and in accordance with the purposes of the present invention, as embodied and broadly described herein, the bipolar vaporization apparatus of this invention may comprise an elongated co-axial probe including an elongated inner electrode surrounded by an elongated outer electrode with a layer of electrical insulation positioned between the inner electrode and the outer electrode. A sleeve of electrical insulative material surrounds the outer electrode for approximately all of the length of the outer electrode. Distal ends of both the inner electrode and the outer electrode are not covered with electrical insulative material. To achieve the foregoing and other objects and in accordance with the purposes of the present invention, as embodied and broadly described herein, the method of this invention may comprise positioning an end surface of a first electrode into a sterile fluid, preferably a normal saline fluid, and in contact with chondromalacia, positioning a second electrode in the sterile fluid in contact with the chondromalacia, and applying an RF electric current through the first electrode and the second electrode while applying a voltage across the first electrode and the second electrode.

Brief Description of the Drawings

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the preferred embodiments of the present invention, and together with the descriptions serve to explain the principles of the invention. In the Drawings:

Figure 1 is a preoperative view of the bipolar probe of the present invention as it may be used to ablate chondromalacia in a knee;

Figure 2 is a simplified isometric view of the bipolar vaporization probe of the present invention positioned adjacent diseased cartilage or chondromalacia on a section of healthy cartilage and in immersing sterile fluid;

Figure 3 is an isometric diagrammatic view of a prior art rotary shaver positioned adjacent healthy cartilage and chondromalacia and being used to remove chondromalacia to contrast results with the bipolar probe of the present invention;

Figure 4 is an elevation view of the bipolar probe of the present invention as it is being used to ablate chondromalacia to illustrate results contrasted to the prior art rotary shown in Figure 3; Figure 5 is an enlarged cross-sectional view of the bipolar probe of the present invention positioned to ablate strands of chondromalacia and illustrating the current path and ablation results;

Figure 6 is a cross-sectional view similar to Figure 5, but after the strands of chondromalacia are ablated;

Figure 7 illustrates an alternate embodiment of the bipolar probe of the present invention, with a tapered end;

Figure 8 shows another alternate embodiment with a square cross-section; and

Figure 9 shows another alternate embodiment with the electrodes flat and sandwiched. Best Mode for Carrying out the Invention

The bipolar vaporization probe 10 for removing chondromalacia according to the present invention is illustrated in Figure 1 in a typical application of arthroscopy in a knee joint, where chondromalacia can develop, for example, on the lateral femoral condyle 80, the medial femoral condyle 82, the lateral tibial plateau 84, the medial tibial plateau 86, the intracondylian notch 88, and the patella 89. However, the use of this invention is not limited to arthroscopy in the knee, but can also be used as well in removing chondromalacia in shoulders, elbows, wrists, hips, and ankles. Essentially, the chondromalacia 12 comprises frayed strands 15 of diseased cartilage that extend outwardly from the surface 13 of remaining healthy cartilage 14, for example, on the inferior surface 13 of the lateral femoral condyle 80 as illustrated in the enlarged view of the lateral femoral condyle in Figure 2.

In operation, the distal end 18 of the probe 10 is positioned near or on the surface 13 of healthy cartilage 14 and in contact with the diseased cartilage or chondromalacia 12. A sterile and transparent fluid 16, such as normal saline, ringer lactate, glycine, or other fluid suitable for use in arthroscopic surgery is injected into and circulated through the joint to expand the surrounding tissue and make it easier for the surgeon to see and work inside the joint as well as to flush away debris created during the surgical procedure, as is done in conventional arthroscopic procedures. The RF electric power, represented schematically at 36, is turned on, causing RF current to flow through strands 15 of the diseased cartilage or chondromalacia 12 that comes near or into contact with the distal ends 21, 31 of outer electrode 20 and the inner electrode 30, respectively. The strands 15 of chondromalacia 12 that contact or are near the distal end 18 of the probe 10 conduct substantial amounts of electric current and can create virtual electric circuits between the outer electrode 20 and the inner electrode 30, thereby allowing the electric current to flow through the chondromalacia strands 15 between the outer electrode 20 and the inner electrode 30. The electric current flowing through the chondromalacia strands 15 heats the chondromalacia strands 15 to a sufficient extent to vaporize the chondromalacia strands 15, thus causing ablation (separation) of the chondromalacia strands 15 from the healthy cartilage 14, as illustrated in Figure 2 by the vaporized chondromalacia 17 and the path 19 cleared of chondromalacia 12.

An important feature of the bipolar probe 10 and its use in the method of ablating chondromalacia according to the present invention is the biophysics of the operation of the bipolar probe 10 and the vaporization of the chondromalacia 12 while having only minimal, if any, adverse effect on the healthy cartilage 14. Furthermore, the bipolar probe 10 sculpts the surface 13 of the healthy cartilage as the chondromalacia 12 is being removed and, as a result, the surface 13 of the healthy cartilage 14 will be generally smooth.

The sterile fluid solution 16 is preferably a normal saline fluid, so it will conduct electric current, although the sterile fluid 16 can be any fluid suitable for use in arthroscopy. However, strands 15 of the chondromalacia 12, when positioned near or in contact with the outer electrode 20 and the inner electrode 30 of the probe, are usually, but not necessarily, more conductive man the sterile fluid 16. Therefore, since the electric current will find the path of least resistance to flow between the outer electrode 20 and the inner electrode 30, and since the path of least resistance is the best electrical conductor, i.e., usually the chondromalacia 12, and since the outer electrode 20 and inner electrode 30 are both positioned adjacent or in contact with strands 15 of the chondromalacia 12, a substantial proportion of the electric current will flow through those strands 15 of the chondromalacia 12. Therefore, the RF current flowing through the strands 15 of chondromalacia 12 is very concentrated, particularly in comparison with the amount of RF current flowing from the outer electrode 20 to the inner electrode 30 but not through the chondromalacia 12. The electric current flowing through the chondromalacia strands 15 and the voltage level across the chondromalacia strands 15 will cause electric power to be dissipated in the chondromalacia strands 15. Power is the product of the square of the current I times the resistance R, i.e., PR, so that substantial power is dissipated in the chondromalacia strands 15 where the current is concentrated. Power dissipates in the form of heat. Consequently, heat is created by the RF current flowing through the chondromalacia strands 15 sufficient to vaporize the chondromalacia strands 15, as indicated at 17, and thereby effectively remove the chondromalacia strands 15 from the healthy cartilage 14. The heat generated in the strands 15 of chondromalacia 12 will generally vaporize and remove all of such strands 15 from the remaining healthy tissue 14. However, if some portions of some of the strands 15 get ablated but do not get completely vaporized, the remaining unvaporized portions will never-the-less be flushed away by the sterile fluid 16 that is flowing through the joint, as indicated by the flow arrow 59.

To illustrate some of the advantages of this feature as compared to the conventional rotary shaver method of ablating chondromalacia a rotary shaver 50 is shown in Figure 3 positioned adjacent a portion of chondromalacia 12, for example, on the inferior surface of a lateral condyle 80 of a knee joint similar to Figures 2 and 3. The conventional rotary shaver 50 typically has multiple, shaφ-edged blades that are driven by a shaft 54 to rotate about an axis 57, usually in a clockwise angular direction as indicated by the arrows

56. The rotary shaver 50 is usually used by sweeping the rotating blades 52 in a side-to-side pattern, as indicated by the arrow 58, such that the blades 52 cut or "scoop" out the strands 15 of chondromalacia 12, which are either sucked into the interior of the rotary shaver 50 by fluid 16 flowing into the shaver 50, as indicated by arrow 59, or washed or flushed away by a sterile solution, as indicated by flow arrow 59. Chondromalacia strands 15 that are not cut sharply by the rotating blades 52 are often pulled and torn from the surface 13 of healthy cartilage tissue 14, leaving the surface 13 abraded and rough. Therefore, using a rotary shaver 50 to remove chondromalacia 12 has two significant disadvantages. First, the rotary shaver 50 will ablate or remove portions of healthy cartilage 14 in addition to the chondromalacia 12, and, second, the rotary shaver 50 will leave the healthy cartilage 14 with a rough surface 68, which is a problem because such roughened cartilage, which is sometimes called "hayline," does not heal due to its inherent histological properties and will often be the beginning of additional future chondromalacia development in the remaining healthy cartilage.

A typical original, undiseased section of cartilage 14 can have a depth or thickness of, for example, approximately 3.0 millimeters (mm), as illustrated at 60 in Figure 3. Once the original healthy section of cartilage 14 becomes diseased, however, the chondromalacia 12 can extend to a depth of, for example, 1.0 mm into the once healthy tissue 14, as indicated at 61 in Figure 3. Therefore, the remaining healthy cartilage

14 will have a depth or thickness of approximately 2.0 mm, as indicated at 62 in Figure 3. Unfortunately, the rotary shaver 50 will cut into and remove additional portions of the remaining healthy cartilage 14 along with the chondromalacia 12 as shown at 63. For example, the rotary shaver 50 can easily remove up to 0.5 mm or more of the remaining healthy cartilage 14, as indicated at 64 in Figure 3, leaving less than 1.5 mm of healthy cartilage 14 remaining after the surgical procedure, as indicated at 66 in Figure 3. The rotary shaver 50 cannot select between the healthy cartilage 14 and the chondromalacia 12 when the rotary shaver 50 is being swept across the cartilage 14. Furthermore, the weight, size, and mechanical vibration of the rotary shaver 50 make it difficult for the operator to control, thereby limiting the operator's ability to control how much healthy cartilage 14 is removed by the rotary shaver 50 in addition to the chondromalacia 12. As previously discussed above, the second significant disadvantage of the rotary shaver 50 is that the surface 68 on the healthy cartilage remaining 14 is roughened, torn, and not smooth. Therefore, it remains irregular and may have a propensity to deteriorate again due to the roughness. In an ideal arthroscopic surgical procedure to remove chondromalacia 12, the surface of the healthy cartilage 14 left remaining after the procedure would not contain the rough, irregular surface 68 that is common with removal of chondromalacia 12 with a mechanized rotary shaver 50.

Now referring primarily to Figure 4 and 5, a bipolar probe 10 is positioned adjacent a portion of chondromalacia 12 in a joint, such as in a shoulder, knee, or other joint. The bipolar probe 10 is moved preferably, but not necessarily, primarily in the direction indicated by the arrow 70 to vaporize the chondromalacia 12. In contrast to the prior art rotary shaver 50 illustrated in Figure 3 and discussed above, however, the bipolar probe 10 does not cut or scoop out any of the healthy cartilage 14 under the chondromalacia 12, since no blades or edges are used with the bipolar probe 10. Therefore, the amount of healthy cartilage 14 remaining after removal of the chondromalacia 12 with the bipolar probe 10 can easily be as much as 1.7 mm, as indicated by the arrow 72. Since vaporizing the chondromalacia 12 with the bipolar probe 10 produces heat, however, some thermal activity does take place on the surface 13 of the healthy cartilage 14 at the distal end 18 of the probe 10, as indicated at 71, and a very thin layer 73 of cartilage 14 (best seen in Figure 5) will usually be necrosed by the heat generated from the bipolar probe 10. The thickness of the layer of necrosed cartilage 73 on the surface 13 will usually be less than 0.3 mm, as indicated at 74 in Figure 5. The thickness 74 of the layer of necrosed cartilage 73 can be reduced by reducing the amount of time the bipolar probe 10 is kept in one place and increasing the speed with which the bipolar probe 10 is moved through the chondromalacia 12. While the layer of necrosed cartilage 73 reduces slightly the amount of healthy cartilage 71 remaining after the chondromalacia 12 is removed with the bipolar probe 10, the thickness 74 of the layer of necrosed cartilage 73 is much smaller than the depth 63 of healthy tissue removed by the rotary shaver 50 that was illustrated in Figure 3 and described above, and it also actually provides a significant benefit. Specifically, the layer of necrosed cartilage 73 forms a smoother surface 13 on the remaining healthy cartilage 14 than is possible with the rotary shaver 50 discussed previously above. A smooth surface 13 on the healthy cartilage

14 is desirable, because it wears better mechanically and has histiological properties that are more conducive to healing and less conducive to future deterioration than the rough and abraded surface 13 left by the prior art rotary shaver that was discussed above.

The overall structure of the probe 10 is similar to the structure described in U.S. Patent 5,089,002, which is incorporated herein by reference, but with several significant differences. Similar to that structure, the probe 10 of this invention has a coaxial bipolar arrangement with the elongated outer electrode 20 positioned concentrically around the elongated inner electrode 30 and with an elongated concentric electrical inner insulation layer 40 positioned between the outer electrode 20 and the inner electrode 30. A portion of uie distal ends of the outer electrode 20 and the inner insulation layer 40 are shown cut away in Figure 2 and 4 and in cross section in Figure 5 to reveal this structure more clearly. The probe 10 of this invention also has an elongated outer electrical insulation sleeve 42 concentrically around the outer electrode 20, and, as shown in Figure 1, a proximal end outer housing 44 terminating in a plug 46 with two prongs 48, 49 that are electrically connected (not shown) in the housing 44 to outer electrode 20 and inner electrode 30, respectively. The prongs 48, 49 of the plug 46 are adapted to plug into a suitable receptacle indicated only by phantom lines 47 in Figure 1, which will be understood by persons skilled in the art and can be a conventional connection to an RF generator 36, which is denoted only schematically.

The distal ends 21, 41, 31, and 43 of the outer electrode 20, inner insulation layer 40, inner electrode 30, and outer insulation sleeve 42, respectively, can be, but are not required to be, circular. With such a circular configuration, there is no rotationally preferred orientation of the probe 10 with respect to the chondromalacia 12 or the healthy cartilage 14. The distal end 18 of the bipolar probe 10 can be in a plane that is perpendicular to the longitudinal axis 45, as shown in Figure 5, or it can be angled, as best seen in Figure 7, which will increase the exposed surface area of the outer electrode 20 and the inner electrode 30, thereby increasing the amount of chondromalacia 12 that will be adjacent the outer electrode 20 and the inner electrode 30 simultaneously. It should be noted that the distal end 18 of the bipolar probe 10 and, therefore, the distal ends 21, 41, 31, and 43 of the outer electrode 20, inner insulation layer 40, inner electrode 30, and outer insulation sleeve 42, respectively, can have other shapes depending on the preference of the surgeon, the ease of manufacture, or area in which chondromalacia 12 is to be removed. For example, the distal ends 21, 41, 31, 43 of the outer electrode 20, inner insulation layer 40, inner electrode 30, and outer insulation sleeve 42, respectively, can be oval, square, rectangular, or other shapes.

The inner insulation layer 40 and outer insulation sleeve 42 can be any of a variety of high temperature, flexible plastics, such as, for example, polyvinylidene flouride (PVDF), silicone, rubber, tetrafluorethylene (Teflon" , (PEEK), or perfluoralkoxy (PFA), as is understood by persons skilled in the art. For example, as illustrated in Figure 1, respectively, the probe 10 of this invention is particularly suited for use in removing chondromalacia 12 encountered during arthroscopy in the knee, and can also be used to remove chondromalacia in shoulders, elbows, wrists, hips, knees, and ankles. It is preferred, although not essential, that the outer electrode 20 and inner electrode 30 be made of a malleable metal or alloy, for example uminum, which can be easily formed or bent into any desired shape or configuration by the surgeon to enable ready access and optimum positioning of the distal end 18 of the probe 10 in places that are tight or difficult to reach. For example, the probe 10 is shown in Figure 1 bent at 81 and 83 to enhance access and optimal positioning on the three-dimensional surfaces in the knee. Referring now primarily to Figure 5, the distal end 18 of the probe 10 is shown in position with its longitudinal axis 38 generally parallel to the surface 13 of the cartilage 14, so that the respective distal ends 21, 31 o the outer electrode 20 inner electrode 30. When the RF electric power source 36 is turned on and connected to the outer electrode 20 and to the inner electrode 40, electric current flows, as indicated by the electron (e ) symbols in arrow 24, from the distal end 21 of the outer electrode 20, through the chondromalacia strands 15 that are adjacent to the distal end 18 of the probe 10 as well as through the sterile fluid 16 that is adjacent to the distal end 18, and then to the distal end 41 of the inner electrode 40. Actually, the electric current is an RF (radio frequency) alternating current, so it flows in both directions, but the arrow 24, while not strictly technically accurate, does depict in a simplified diagrammatic manner the current path through the chondromalacia strands 15 and sterile fluid 16 between the outer electrode 20 and the inner electrode 30 in a sufficient manner to describe the invention, as will be understood by persons skilled in the art. The electric current flowing through the strands 15, as indicated by arrow 24, heats the strands 15 to a sufficient extent to cause almost instantaneous vaporization of the strands 15, especially where the strands 15 are in contact with, or closest to, one or both of the outer electrode 20 and inner electrode 40.

It is preferred, although not essential, that the outer insulation 42 cover the entire length of the probe 10 so that the distal end 43 of the outer insulation 42 is about flush with the distal end 21 of outer electrode

20 in order to concentrate the current path 24 to the space in front of the distal end 18 of the probe 10 and not allow it to extend significantly into the healthy cartilage tissue 14. If the distal end 21 of the outer electrode 20 would extend longitudinally beyond the distal end 43 of the outer insulation 43, the current path 24 would extend farther into the healthy cartilage 14, which would desiccate and necrose more of the healthy cartilage tissue 14. However, with the distal end 43 of the outer insulation 42 practically flush with the distal end 21 of the outer electrode 42, as described above, such necrosis by desiccation of healthy cartilage 14 occurs only in a very small, confined area 71 of the healthy cartilage 14 and results in only a very thin necrosed layer 73 as described above.

At the same time, a large proportion of the electric current flows through the strands 15, as indicated by the current path arrow 24. The current flow distribution can be modeled as two parallel circuits 90, 92. Circuit 90 has a resistance 94 representing current flow through strands 15, and circuit 92 has a resistance 96 representing current flow through the sterile fluid 16. It is beheved, based on observation of the bipolar probe 10 in operation according to this invention, that the tissue is less resistive to flow of electric current than the sterile fluid 16, or at least not substantially greater. Therefore, it is beheved that initially, there is a higher current concentration in the strand 15 than in the sterile fluid 16, which is sufficient to heat the tissue of the strands 15 to at least about 100° C, where cells explode and vaporize. Regardless of the relative proportions, there is sufficient flow of electric current in the first parallel circuit 90, i.e., in the strands 15, to cause vaporization. There is, of course, also heat produced by the electric currents flowing in the sterile fluid 16 circuit 92, e.g., by resistance 96, even to the point of causing some vaporization of the sterile fluid 16, but the sterile fluid 16 in arthroscopic procedures is kept flowing at a high enough rate through the area where the procedure is being performed, as indicated by flow arrow 59, so that heat produced in the sterile fluid 16 is carried away and dissipated rapidly by the flowing fluid 16 with no appreciable temperature increase at the probe 10.

The result of partial or complete vaporization of the strands 15 that are very close to, or in contact with, the probe 10 is that the current path 24 flows only through the sterile fluid 16 between the outer electrode 20 and the inner electrode 30, as shown in Figure 6, at least until the probe 10 is moved closer to more of the unvaporized chondromalacia. This self-limiting feature, in which the current flow does not vaporize healthy cartilage 14 or even desiccate and necrose more than only a minimal thickness 74 into the healthy tissue 14 and with no carbonation of tissue, but instead reverts to flowing through primarily only the sterile fluid 16, as illustrated by both resistances 94' and 96 in Figure 6, is a significant feature of this invention. To function in this manner, it is important for the purposes of this invention to size and proportion the exposed portions of the outer electrode 20 and inner electrode 30 such that the probe 10 is truly bipolar. For the purposes of this invention, bipolar means that it is possible for both the outer electrode 20 and the inner electrode 30 to be surgically active, even though they might not both always be actually surgically active. Surgically active means that sufficient heat is produced in cells at or immediately adjacent to the electrode to alter cells physically, such as desiccation, coagulation, necrosis, ablation, vaporization, carbonization and the like. Therefore, to be truly bipolar for purposes of this invention, the probe 10 must be capable of causing such surgical activity in tissue or immediately adjacent both the outer electrode 20 and the inner electrode 30.

In dual electrode surgical systems where there is an electrical potential between two electrodes and current passes between the two electrodes, there will tend to be significant heating at or adjacent only one of the electrodes when the ratio of the respective electrode surface areas is about ten to one ( 10:0) or higher. The electrode with the smaller surface area will have proportionately higher current density than the electrode with the larger surface area and will heat to the point that its contact impedance increases dramatically. Therefore, when die ratio of the electrode surface areas of the respective electrodes is about 10: 1 or greater, as mentioned above, it becomes virtually impossible to flow enough current through the electrode with the larger surface area at a current density high enough to heat tissue adjacent the larger electrode to above about 50°C, which is the temperature at which tissue effects or surgical activity begins. At about 100°C, cells explode and vaporize, and carbonization occurs at about 200 °C. Therefore, to be truly bipolar for purposes of this invention, the surface area of either electrode must be less than about ten times as large as the surface area of the other electrode to keep the ratio of the respective surface areas less than about 10: 1. In the surgical probe preferred embodiment 10 of this invention, where the distal ends 21, 31 of outer electrode 20 and inner electrode 30, respectively, are substantially coplanar and the outer insulation 42 covers substantially the entire peripheral surface of the outer electrode 20, leaving only the distal ends 21, 31 of me outer electrode 20 and inner electrode 30 exposed or uninsulated as described above, the surface area of the outer electrode 20 is effectively the uninsulated surface area of the distal end 21 of the outer electrode 20. The surface area of the inner electrode 30 is essentially the uninsulated surface area of the distal end 31 of inner electrode 30. If the distal end 31 of the inner electrode 30 should also extend slightly beyond the inner insulation, which, while not preferred, will work according to this inventory, then the surface area of the inner electrode 30 would also include any additional uninsulated surface area of the periphery of the inner electrode 30 for purposes of the 10: 1 ration of respective surface areas of electrodes described above. Also, if the distal end 21 of the outer electrode 20 is made to extend beyond the distal end 43 of outer insulation 42, the uninsulated portion of the peripheral surface of the outer electrode would be included in the uninsulated surface area of the outer electrode 20.

As also mentioned above, providing effective uninsulated surface areas of outer electrode 20 and inner electrode 30 within the 10:0 ratio described above does no mean that surgical activity occurs at or immediately adjacent both the outer electrode 20 and the inner electrode 30 at all times. For example, in the preferred embodiment and application illustrated in Figure 5, the distal end 31 of the inner electrode 30 is spatially removed from strand 15, so there may not be actual surgical activity strictly at the inner electrode 30, while vaporization of the strand 15 and the slight desiccation and necrosis in the area 71 occurs, as described above. Also, when most or all of the current flow shifts to flow through the fluid 16 in path after vaporization strands 15 and necrosis in the area 71 occurs, as described above, such surgical activity stops also at and near outer electrode 20. Also, if the probe 10 is oriented in such a way as to contact more of the outer electrode 20 surface area to healthy cartilage 14 or even to contact both the outer electrode 20 and the inner electrode 30 with healthy cartilage 14, desiccation and necrosis of the healthy cartilage would only occur to a shallow depth. Then, since desiccated tissue is highly resistive to electric current flow, the current flow would self- limit and either stop or shift back to the fluid 16, thus preventing any deep necrosis or vaporization of healthy cartilage 14.

The diameter of me probe 10 is preferred in the range of 3.0 - 10.0 mm with the inner electrode 30 being about 1 - 2 mm diameter and the outer electrode 20 being about 2.5 - 5.0 mm diameter. The inner insulation 40 is preferably in the range of about 0.2 to 3 mm thick and the outer insulation is preferably in the range of about 0.2-3 mm thick. The length of the probe 10 should be long enough to extend through an incision or cannula to reach any desired location in the shoulder or knee joint, it is also preferred, but not necessary, that the RF current supply is approximately three-hundred (300 KHz) to three megahertz (3 MHz) and, optimally, the RF current supply is approximately five-hundred kilohertz (500 KHz). The power should be in the range of about twenty to one-hundred watts and is preferably in the range between forty and seventy watts into a load impedance in the range of about 25-1000 ohms preferably about 50-250 ohms, for example, 100 ohms to achieve the desired desiccation and shrinking of blood vessels, coagulation of blood, and necrosis of tissue as described above along with the self-selective current paths and self-limiting of surgical activity according to this invention.

In an alternative embodiment illustrated in Figure 7, the distal end 18 of the probe 10 can be tapered at an angle θ from a plane 39 that is perpendicular to the longitudinal axis 38 of the probe 10. This angle θ can be any desired angle, but it has been found that an angle in the range of 10 °-30 degrees works well, and about 20° is preferred, because it provides the most convenient orientation for rotating the probe 10 to reach different cartilage surfaces in the tight spaces where arthroscopic procedures are usually performed.

The cross-section of the probe does not have to be circular, as mentioned above. For example, an alternate probe 300 with a square cross-section fee concentric inner electrode 330, inner insulation 340, outer electrode 320, and outer insulation 342, as shown in Figure 8 can be used according to this invention. Other cross-sectional configurations, such as oval polygonal, or other shapes can also be used. It is also not necessary for the electrodes to be concentric. For example, the probe 400 shown in Figure 9 has an inner electrode 430 sandwiched between two outer electrodes 420, 420^* with respective inner insulation layers 440, 440* intervening. The two outer electrodes 420, 420' can be, but are not necessarily at the same electrical potential as each other. The outer insulation 442 surrounds all of the electrodes. Many other variations of the invention are also possible to provide the bipolar surgical activity within the surface area ratios and exposed outer electrode parameters described above.

The foregoing description is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and process shown and described above. Accordingly, all suitable modifications and equivalents may be resorted to falling within the scope of the invention as defined by the claims which follow.

Claims

ClaimsThe embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Bipolar probe apparatus for removing diseased cartilage or chondromalacia during arthroscopy, comprising: an elongated co-axial probe having an elongated inner electrode surrounded by an elongated outer electrode with electrical insulation positioned between the inner electrode and outer electrode, said probe also having an outer electrical insulation sleeve surrounding the outer electrode, said outer electrode having a distal end that is not covered with electrical insulation and said inner electrode also having a distal end that is not covered with electrical insulation.

2. The bipolar probe apparatus of claim 1 , wherein said distal end of said inner electrode lays in a common plane with the distal end of the outer electrode.

3. The bipolar probe apparatus of claim 2, wherein said elongated co-axial probe has a longitudinal axis and said plane is perpendicular to said longitudinal axis.

4. The bipolar probe apparatus of claim 1, wherein the distal end of the inner electrode protrudes longitudinally beyond said distal end of said outer electrode.

5. The bipolar probe apparatus of claim 1, wherein said outer electrode and said inner electrode both comprise a malleable metal or alloy that is an electrical conductor.

6. The bipolar probe apparatus of claim 5, wherein said outer electrode and said inner electrode both comprise aluminum.

7. The bipolar probe apparatus of claim 2, wherein said distal end of said inner electrode has a non-circular shape.

8. The bipolar probe apparatus of claim 7, wherein said distal end of said inner electrode has an oval shape.

9. The bipolar probe apparatus of claim 7, wherein said distal end of said inner electrode has a rectangular shape.

10. The bipolar probe apparatus of claim 9, wherein said distal end of said inner electrode has a square shape.

11. A method of removing diseased cartilage or chondromalacia during arthroscopy where a sterile fluid immerse exposed surfaces of the diseased cartilage, comprising the steps of: positioning a peripheral surface of a first electrode in the sterile fluid and in contact with the chondromalacia and positioning a second electrode in the sterile fluid adjacent the chondromalacia; and applying an RF current through said first electrode and said second electrode with a voltage across said first electrode and said second electrode.

12. The method of claim 11, including the step of providing said first electrode positioned concentrically around said second electrode with an electric insulator positioned between said first electrode and said second electrode.

13. The method of claim 12, including die steps of providing said first electrode in an elongated shape with a distal end of said first electrode, and providing said second electrode in an elongated shape with a distal end of said second electrode such that said distal end of said second electrode extends as least as far longitudinally as said distal end of said first electrode.

14. The method of claim 13 , including the steps of providing said first electrode with an elongated outer electrical insulation sleeve that covers all of said first electrode.

15. The method of claim 11 , including the step of applying said RF current in the range of about 300-3,000 KHz.

16. The method of claim 15, including the step of applying said RF current at about 500 KHz.

17. The method of claim 11 , including the step of applying said RF current and voltage in the range of about 20-100 watts.

18. The me od of claim 17, wherein said RF current and voltage are applied in a range of about 40-70 watts.

19. The method of claim 11, wherein said sterile fluid is a saline fluid.

20. The method of claim 19, wherein said saline fluid is a normal saline fluid.