Abstract:
An adapter unit for a mechanical tissue cutting implement such as a shaver, morcellator or the like includes a mounting block from which an electrically insulating sheath extends. The sheath fits over the cannula or shaft of the cutting implement, and is secured in alignment and attached so that the cutting tip, for example, the tool and its window in the cannula tip, are exposed through the sheath. A conductor, which may be a conductive layer, extends along the length of the sheath and is exposed to form a distal electrode at the tip in close proximity to the opening, constituting one electrode of a bipolar electrode arrangement at the exposed tool. The other electrode is provided by electrical connection to the implement itself, so that a high current density path is formed through tissue in the cutting region. Preferably both output connections of an electrosurgical generator are coupled through a matching transformer to the mounting block by a plug, socket, cable or fixed cord arrangement, and the mounting block may, for example, be formed of plastic, preferably having an alignment feature such as a notch to fasten to the implement so that the sheath opening aligns with the cutter. Electrical connection to the implement may be effected via a conductive bushing, fastening bolt or the like which contacts one of the supply leads through a wire, spring or other conductive path. The adapter may also provide a sheath opening and distal electrode about a non-apertured region of the cannula, for example on the rear surface of the cannula opposed to the cutting tool aperture, to form a hemostasis element that may be rotated into position to coagulate bleeding. In this case the bipolar electrode geometry may be configured for high energy density delivery that does not vary with tool rotation. The adapter may also convert a monopolar device to bipolar operation, providing a single additional electrode positioned by the sheath at the cutting aperture.

Description:
GOVERNMENT RIGHTS 
     Not applicable. 
     CROSS REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     Rotating surgical instruments that mechanically cut, shave, abrade and drill hard or soft tissue are well known in the art and have proven, over time, to be quite useful. Such tools can be used in open or closed surgical procedures to remove affected tissue. Typical rotating instruments used in these procedures include surgical drilling instruments, such as bone drills, and other rotating mechanical cutting and shaving devices, such as morcellators and power shavers. 
     Conventional power shavers include an inner rotatable drive shaft having an abrading element at a distal end. The drive shaft seats within a central lumen of the shaver housing such that the abrading element is exposed at the distal end. The drive shaft couples to a motor which imparts rotary movement to the shaft. The power shaver mechanically cuts or shaves affected tissue by the direct mechanical contact of the abrading element with the tissue. 
     One drawback of such devices is that the abrading edge of the instrument must be extremely sharp to enable effective mechanical cutting of the tissue. During the course of the surgical procedure, however, the abrading or cutting edge of the rotating tool tends to dull, thereby decreasing the cutting performance of the tool. When this occurs, the cutting tool must be replaced. The need for frequent replacement of the abrading portion of the device increases the overall time necessary to conduct the surgical procedure while concomitantly increasing the cost of delivering the medical services and in stocking the replacement components for the medical device. 
     There thus exists a need in the art for rotary surgical devices that are able to provide effective cutting and abrading of tissue while minimizing or eliminating the need to replace selected components, such as the abrading element, of the device. In particular, it would be useful to provide an adapter device to convert such mechanical surgical tools to electrosurgical tools. 
     The use of mechanical surgical devices can sometimes lead to undesirable bleeding, which must often be controlled using a separate device. It would also be useful to provide a device that enables a mechanical surgical tool to be used in a manner that it can provide a hemostasis effect. 
     SUMMARY OF THE INVENTION 
     The present invention pertains to an electrosurgical adapter assembly to convert a mechanical apparatus that includes a rotary, tissue affecting device in the form of one or more rotating blades, a rotating drill, or a rotating shaving/abrading device, so that its tissue-cutting end serves as one electrode of a bipolar electrosurgical tool. The bipolar electrode action effectively cuts tissue at the surgical site without relying solely upon the mechanical cutting action of the tissue affecting device. The rotary surgical device can be in a form such that it is suitable for use in open or closed surgery. The term “closed surgery” is intended to include arthroscopic, endoscopic, hysteroscopic, laparoscopic, and resectoscopic surgical techniques. Closed surgical techniques typically utilize elongated instruments which are inserted into the patient&#39;s body through a small incision or a natural orifice, to allow a secondary instrument easy access to the surgical site. A variety of such surgical devices are well known in the art and are well described in the patent literature. Representative devices are described in U.S. Pat. No. 4,842,578 (Johnson et al.), U.S. Pat. No. 5,411,514 (Fucci et al.) and U.S. Pat. No. 5,492,527 (Glowa et al.). 
     In its basic configuration, the electrosurgical adapter device of the present invention attaches to a rotating, tissue affecting device having a distal, tissue contacting end which serves as an active, mechanically-operated implement for cutting tissue, and provides a mounting block and a sheath extension assembly which are operative to interconnect a pair of electrosurgical energy contacts or leads to energize, on the one hand, the mechanical cutting tool, and on the other hand, an electrode band which is included in the sheath extension and positioned proximal to or surrounding an exposed region of the distal end of the cutting tool. The actual shape and structure of the mechanical cutting device will depend upon the purpose for which the device is to be used. For example, rotating cutting devices and arthroscopic shaving devices are well known in the art and the structure of such devices can be assumed. The rotating, tissue affecting device also includes a proximal end, usually in the form of an elongate drive shaft, which fits within an outer cannula. The cannula and drive shaft typically form co-acting portions of the cutter, and may constitute a disposable assembly. The cannula can form part of an arthroscope, endoscope, hysteroscope, laparoscope, or resectoscope surgical tool as is well known in the art. The adapter device has a shape corresponding to the cannula/cutter shape of the basic mechanical surgical tool. 
     The adapter includes electrical contacts that electrically connect at one end to outputs of a remote electrosurgical generator and at their other end connect, respectively, to a conductive body portion of the tissue affecting device, and to an electrode extension carried in the adapter sheath fitted over the outer cannula assembly of the tissue affecting device. The contacts energize the mechanical cutting assembly and thus the distal abrading end by transferring cutting energy from the electrosurgical generator to the drive shaft or cannula, on the one hand, and to a distal electrode which is maintained electrically insulated therefrom and is exposed for a small area proximal to or surrounding the cutter at the distal end. 
     The adapter of the present invention thus converts a simple mechanical tissue cutting device to a bipolar electrosurgical device, or may be used to convert a monopolar electrosurgical device to bipolar operation. When applied to a simple mechanical cutting device, bipolar operation is achieved between the distal end of the rotating, tissue affecting device and/or its surrounding cannula which serves as one energy delivering electrode, and a second electrode carried in an insulating sheath that fits over the cannula. When applied to adapt a monopolar cutting device to bipolar operation, the adapter adds a second electrode carried in an insulating sheath that insulates the electrode from the cannula and positions it so a current path is formed through tissue in a band surrounding an exposed region at the distal end of the cannula. 
     During closed surgical procedures it is sometimes necessary to supply a fluid to a surgical site in order to distend the surgical area and to improve visibility for the surgeon. The present system converts cutting tools to bipolar electrosurgical operation, allowing use of an isotonic solution (e.g., saline or Ringer&#39;s solution) to distend the surgical site, rather than a non-ionic solution. The patient, therefore, is not exposed to potentially dangerous electrolytic imbalances associated with absorption of non-ionic solution into the patient&#39;s bloodstream, and the localization of current paths at the cutting locus prevents the ionic solution from degrading the electrosurgical current paths. 
     A preferred adapter construction readily configured to convert diverse mechanical cutting instruments includes a mounting block that is adapted to mount to the instrument, for example with a sliding bushing or clamp that connects over the existing cannula and establishes electrical connection to the instrument body. An insulated sheath is carried by the mounting block and extends over the cannula to provide an electrical barrier. The sheath contains a further conductor, which may be a conductive layer extending in or on the sheath, that is exposed at its distal end to form a second electrosurgical electrode for defining current paths in a small region of tissue at the cutting end of the tool. Preferably, the mounting block holds an RF plug, socket, or cable to which the electrosurgical energy source is applied, and connects the two outputs to the instrument body and the further conductor, respectively. The sheath and block form a single unit that fits over the existing cannula, insulating the assembly without substantially increasing the diameter of its shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be more fully understood from the following detailed description in combination with the drawings in which: 
     FIG. 1 is a top view of an adapter device for converting a mechanical cutting device to an electrosurgical cutting device; 
     FIG. 2 is a cross-section front view of the adapter device of FIG.  1 . 
     FIG. 2A is an enlarged view of the proximal portion of the adapter device shown in FIG. 2; 
     FIG. 3 is an enlarged view of portion A of a distal end of the adapter device of FIG. 1; 
     FIG. 3A is an enlarged view of an alternative construction of a distal portion of the adapter device; 
     FIG. 3B is an enlarged view of another alternative construction of a distal portion of the adapter device; 
     FIG. 4 is a cross-sectional view taken along lines  4 — 4  of FIG. 1; 
     FIG. 5 is a front view of an alternative embodiment of the adapter device of the present invention mounted upon a mechanical surgical shaver tool; 
     FIG. 6 is an enlarged top view of the distal end of the adapter device of FIG. 5; 
     FIG. 6A is an enlarged bottom view of the distal end of the adapter device shown in FIG. 5; 
     FIG. 7 is an exploded view of the adapter device of FIG.  1  and mechanical shaver device; 
     FIG. 8 is an assembled front view of the device of FIG. 7; 
     FIG. 9 is a block diagram of an adapter device coupled to an electrosurgical generator through an impedance transformer; and 
     FIG. 10 is a sectional view of another embodiment of the adapter device of the present invention having a fixed cord assembly and spring contact mounted on a mechanical shaver device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The adapter device of the present invention is an electrical connecting and electrode-forming adapter that attaches to an existing surgical tool, such as a purely mechanical, or even a monopolar, shaver or morcellator, and converts it to bipolar electrosurgical operation. As such, it allows the use of isotonic inflation or irrigation fluids for endoscopic electrosurgical procedures, and allows the existing tool to operate while performing hemostasis, and also to operate with increased tool lifetime, or greater effectiveness that may be realized, for example, by electrosurgical treatment of tissue at the cutting or shaving region. 
     According to the present invention, illustrated in FIGS. 1-10, there is provided an adapter assembly that converts a mechanical surgical tool, e.g., a cutting or shaving device, to a bipolar electrosurgical device. For purposes of illustration the adapter device is described with reference to use with an endoscopic shaving device, but it is understood that the adapter may be used with other endoscopic surgical instruments that perform functions other than shaving of tissue. 
     Referring now to FIGS. 1-4, in which like elements are provided having like reference designations throughout the several views, an adapter device or sheath  200  includes a mounting region mounting block  202  which, in an exemplary embodiment, may be provided as a plastic block having a first end  202   a , with metal bushing  205   a  disposed therein, and a second end  202   b  with a metal bushing  205   b  disposed therein. A bore extends from the first end  202   a  to the second end  202   b  of the block  202 . The first end  202   a  of the mounting block  202  may include an alignment mechanism such as a key  203  which provides a means for mechanically aligning and coupling the adapter device  200  with a compatible surgical tool, such as an endoscopic cutting device or shaver. The key  203  is here provided as an alignment notch or opening in the mounting block  202  but it should be understood that the key  203  may alternatively be provided as a pin or other member (e.g., a boss) projecting from a surface of the mounting block  202 . The bushing  205   a  provides an electrical signal path having a relatively low impedance characteristic between the surgical tool and a first pin  224 . The bushing  205   b  provides an electrical signal path having a relatively low impedance characteristic between a conductive portion of the sheath body  204  and a second pin  223 . 
     Alternatively, the relatively low impedance signal path between the adapter device  200  and the surgical tool  150  may also be provided from a side-loaded spring  234  which is compressed by coupling the sheath  200  to a surgical tool  150 , for example, and forcing the spring to contact conductive regions of both the bushing  205   a  and the surgical tool, as shown in FIG.  10 . Alternatively, still, a wide variety of means including, but not limited to, brushes and bushings, can be used to provide the desired electrical contact. 
     It should be noted that although the mounting block  202  is here provided as a plastic member, other adapter devices  200  may be provided having other types of mounting blocks  202 . The mounting region is preferably provided as a high quality, reliable, relatively low cost mounting structure which allows the adapter device  200  to be firmly and accurately affixed to the surgical tool in a rapid and relatively simple manner to provide or facilitate an electrical connection between the surgical tool and the adapter device  200 . The particular type of mounting block  202  used in any particular application is selected in accordance with a variety of factors including, but not limited to, compatibility with the particular surgical tool to which the adapter device  200  is to be coupled, ease of coupling the mounting block to the surgical tool, ease of manufacture of the particular type of mounting block, cost of manufacture of the mounting block including the cost of the mounting block  202  relative to the cost of the entire adapter device  200 , and ease of assembly of the mounting block and sheath body (in the event the mounting block and sheath body are manufactured as separate pieces). 
     The adapter device  200  further includes a sheath body  204  which is carried by and projects distally from the mounting block  202 . The sheath body  204  has a first or proximal end  204   a  which extends at least part way into the bore of the mounting block  202  and is secured within the mounting block  202  using any suitable fastening technique known to those of ordinary skill in the art. A second portion of the sheath  204 , including a second or distal end  204   b , projects distally away from the mounting block  202 , and preferably extends at least as far as the windowed cutting aperture of the tool to which the assembly attaches. 
     FIG. 4 illustrates an exemplary configuration of sheath body  204 . As illustrated, the innermost layer is a first, nonconductive substrate  212  having a thickness (T1) that is in the range of about 0.15 mm to 0.8 mm. A conductive layer  208  is disposed immediately adjacent an outer surface of the nonconductive substrate  212 . Conductive layer  208  can be formed on the outer surface of nonconductive substrate  212  by techniques such as coating, plating, or bonding. The thickness (T2) of conductive layer  208  is in the range of about 0.02 to 0.15 mm. An insulative layer  210  is disposed immediately adjacent the outer surface of the conductive layer  208 . The thickness (T3) of the insulative layer  210  is in the range of about 0.025 mm to 0.1 mm. The nonconductive substrate  212  defines a substantially circular opening  206  in the sheath  204  within which a portion of the endoscopic surgical tool  150  such as the outer cannula  152 , as shown in FIG. 7, may be disposed. 
     One of ordinary skill in the art will appreciate that the various layers that make up the sheath body  204  can be made from a variety of suitable materials. The nonconductive substrate  212 , for example, is to be made from a material which is biocompatible and which has good dielectric properties, sufficient to provide a nonconductive barrier between the conductive portion of the sheath and the outer cannula of the device. In addition, the substrate  212  should be made from a material with sufficient strength and manufacturing tolerances to allow the sheath body  204  to accept a portion of a surgical tool without an interference fit or excessive tightness. Exemplary materials include, but are not limited to, polymers such as polycarbonate, polyvinyl chloride, and polysulfones. 
     The conductive layer  208  should likewise be a biocompatible material that is able to be adhered to substrate  212 . Exemplary materials may be gold, silver and stainless steel, although a lesser conductive material may be used in buried or coated regions, with only exposed regions being formed of such biocompatible metal. Further, the conductive layer  208  can be formed from conductive paints and inks. 
     The insulative layer  210  should be formed from a biocompatible material that provides good dielectric properties so as to provide electrical insulation. One of ordinary skill in the art can readily ascertain suitable materials for insulative layer  210 . Exemplary materials include polyester shrink tubing and Kynar coatings. 
     The particular materials and techniques for manufacturing each of the layers  208 ,  210  and  212  of sheath body  204  are selected in part such that tolerances can be controlled to provide a snug fit of the surgical device within the sheath  204 . This mininizes the overall diameter of the assembled device. 
     Referring again to each of the several views, and in particular to FIG. 2, a connecting assembly  222  projects from the mounting block  202  and provides an electrical signal path from a power source such as an electrosurgical generator to the conductive layer  208  of the sheath body  204  and to a conductive portion of the tissue affecting device. In the illustrated embodiment, the connecting assembly  222  includes a pair of connecting pins  223 ,  224  disposed through the mounting block  202 . The first pin  224  makes an electrical contact to the conductive bushing  205   a . The second pin  223  has a surface in electrical contact with the conductive layer  208  of sheath body  204  via bushing  205   b  and thus provides an electrical signal path to the conductive layer  208 . This configuration enables the entire assembly to mount on a standard surgical tool, such as an endoscopic shaver, so that its cutting assembly is energized with an RF output via pin  224  and bushing  205   a  while an exposed conductive area of the sheath forms the second electrode and is connected to the second generator output via pin  223 , bushing  205   b , and conductive layer  208 . 
     It should be appreciated that alternatively the connecting assembly  222  may be replaced by a fixed cord assembly  230  (see FIG. 10) thus allowing the adapter device  200  to be efficiently manufactured, and eliminating one field assembly step. 
     As shown in FIGS. 2-4, the conductive layer  208  extends along the length of the sheath, and is exposed for a distance L (FIG. 3) proximally from the furthermost edge of distal end  204   b  of sheath  204 . The distance L is typically in the range of about 10 mm to 15 mm. The remaining portions of the outer surface of the sheath body  204  are covered by the nonconductive material  210 . The conductive portion  208  extends proximally beyond a second end of the aperture  214  by a distance L1 which is typically in the range of about 1 mm to 4 mm. The exposed electrode area may extend for a greater length without impairing its operation, and a larger exposed conductive layer  208  may be desirable for ease of manufacturing. However, in general a band extending for about one to four times (and preferably about three times) the width of non-conductive region  215  is appropriate to achieve effective hemostasis. 
     In operation, when the adapter device  200  is disposed over a mechanical surgical tool, such as a shaver, the cutting portion  154  of the surgical tool  150  is exposed through the aperture  214  and its tool is energized via the proximal end signal connector pin  224 . Thus, RF current effective for coagulation or local hemostasis flows in a region at the moving tool end through a small region of tissue extending near the entire non-conductive region  215  when the leads or pins  223 ,  224  are energized. Thus, when the cutting portion moves with either rotational or translational movement, the movement of the cutting tool tip proximate the exposed conductive region  208  at the distal end  204   b  of sheath body  204  effectively results in mechanical cutting proceeding simultaneously with local hemostasis. 
     The conductive layer  208  provides a conductive path to the second active electrode signal pin  223  which is electrically coupled to an electrosurgical generator. In this manner, bulk hemostasis takes place about the entire periphery of the cutting area defined by the aperture  214 . The ability to provide bulk hemostasis in the cutting area during movement of the cutting device (for example, movement of a blade in a rotational or nibbling movement) in combination with the close physical proximity of conductive layer  208  to the conductive portion of the cutting element effectively provides tissue sealing limited to the localized region of cutting. 
     By providing a system in which the hemostasis takes place in the cutting area, it is not necessary for the operator to stop using the cutting device to provide the hemostasis function. Thus, the adapter assembly  200  provides a separately-mountable RF connector and electrode set that converts a mechanical cutting device into an electrosurgical cutting device to simultaneously provide hemostasis in conjunction with its function of cutting, shaving, or otherwise affecting tissue. As shown in FIG. 3, the distal end  204   b  of sheath body  204  includes the aperture  214  which is defined by a nonconductive perimeter band  215 . The size and shape of the aperture  214  is selected to allow proper operation of the cutting device exposed in the aperture. Thus, while the aperture  214  is here shown having an oval shape with a major axis typically of about 10 mm and a minor axis typically of about 5 mm, it should be appreciated that in other embodiments it may be desirable to provide aperture  214  having other sizes and shapes including but not limited to a square shape, a rectangular shape, a triangular shape, or an irregular shape. The particular size and shape of aperture  214  is typically selected to accommodate the size and shape of a particular cutting device and may be positioned asymmetrically about the cutting opening. It should be noted that to accommodate a cutting device, the aperture  214  need not have the same shape as the cutting device. In general, the shape may also depend upon the firmness of the tissue to which the cutting tool is directed, with the aperture being sized to allow a sufficient, but not excessive, amount of tissue to enter the cutting path of the tool moving internally within the aperture. 
     The nonconductive area  215  can be provided by a masking step during conductor fabrication, or by removing or otherwise preventing the conductive layer  208  from covering the sheath body substrate  212  in a predetermined region corresponding to the desired non-conductive area. Here, the nonconductive perimeter area  215  is provided having an oval shape. It may further be a beveled surface, or have such a step or relief as may be appropriate for achieving the desired rake angle and tissue entry penetration for effective operation of the moving cutter blade inside. 
     The width of the area  215  is selected to prevent an excitation voltage signal provided by the electrosurgical RF signal generator from short circuiting between conductive region  208  and the cutting tool assembly. It is preferable to provide the band  215  having the minimum width possible while still being able to maintain electrical insulation at the applied excitation voltage. By keeping the width of the band of insulating material small, surrounding tissue is better able to maintain firm physical contact against the conductive electrode area  208  to provide dependable electrical contact. In one embodiment, for operation with an electrosurgical generator setting of up to about 70 watts (W), the band  215  is provided having a width typically of about 0.8 mm. FIG. 8 illustrates the adapter assembly of the present invention affixed to a mechanical shaver or other tissue-affecting device  150 . As shown, the mounting block  202  provides a connection for the signal source, and positions the exposed electrode  208  at the aperture  214  about the cutter  154  which has been energized at the proximal end by the electrode connection  223  of the mounting block. 
     In operation, the hemostasis takes place at the cutting area and thus it is not necessary to cease cutting in order to provide hemostasis. Thus, with the present invention one can provide hemostasis in conjunction with cutting simultaneously. If bleeding nonetheless occurs, the operator may suspend the mechanical cutting while maintaining the electrosurgical energy. Since no repositioning of the cutter is needed, such operation is quick, accurate, and does not disrupt the direction or area of cutting. Thus, the provision of a conductive electrode region  208  closely surrounding the entire cutting aperture assures effective coagulation during routine operation and facilitates continuity of the cutting procedure. The exposed electrode area  208  may be positioned quite close to the cutting tool and be limited in overall surface area to assure that bulk hemostasis takes place all along the periphery of the cutting area. 
     The foregoing embodiment may be fabricated using a sheath body  204  formed of a polycarbonate substrate having appropriate coatings disposed thereon. In another embodiment the sheath body  204  may be fabricated of stainless steel tubing, a so-called hypotube, which then has an insulative coating disposed over the internal surfaces thereof and over selected portions of external surfaces thereof. The assembly may even be fabricated integrally with the cannula of a replaceable cannula/cutter assembly, in which case it would preferably be supplied as a kit complete with matched cutting tool. As one of ordinary skill in the art will appreciate, the hypotube may be an annealed stainless steel so as to be useful with bendable shaver devices. 
     FIGS. 3A and 3B illustrate alternative configurations for the distal portion  204   b  of sheath body  204 , in which elements corresponding to like elements in FIGS. 1-4 are provided having like reference designations. With particular reference to FIG. 3A, the distal portion  204   b  of sheath body  204  includes the aperture  214  and the conductive region  208 . In this particular embodiment, the conductor extends ahead of the aperture over a distance L3 to the distal extremity of the sheath  204  and the conductive portion  208  surrounds all sides of the aperture  214 . The conductive portion  208  also extends before the aperture  214  along a length L4. 
     FIG. 3B illustrates another configuration for the distal portion  204   b  of sheath body  204 . In FIG. 3B, the distal portion  204   b  of sheath body  204  includes the aperture  214  and the conductive region  208 . In this particular embodiment, the distal end of sheath  204  is provided having a square or rectangular shape. The conductive portion  208  is disposed around the aperture  214 , outside of the non-conductive band  215 . 
     With reference to FIGS. 3-3B, the overall length of aperture  214  is generally in the range of about 5-10 mm. The dimension (L1 and L4) by which the conductive portion  208  extends proximally from non-conductive region  215  is about 1 to 4 mm. In the embodiment of FIG. 3A, the length (L3) is about 1 to 4 mm. 
     A further embodiment of adapter device  200 , which is useful to extend the achievable hemostatic control, is described below with reference to FIGS. 5-6A, in which elements corresponding to like elements in FIGS. 1-4 are provided having like reference designations. With particular reference to FIG. 5, the distal portion  204   b  is shaped to provide a pair of apertures  214   a ,  214   b . When the sheath body  204  is mounted on its cutting tool, a blade may cut tissue through one of the apertures  214   a  while the other aperture  214   b  is configured to provide hemostasis only. This second aperture  214   b  is provided with an electrode structure that does not rely on the cutting blade as its electrode, and thus provides a high level of hemostasis that does not vary with blade position when the cutter is stopped. For example, aperture  214   b  may extend through the sheath to expose a solid, non-apertured, region of the underlying conductive cannula  152 , so that the cannula surface, rather than a cutting blade, acts as the second electrode surface. 
     As can be clearly seen in FIGS. 6 and 6A, the conductive portion  208  provides a conductive electrode disposed around each of the apertures  214   a ,  214   b . Thus, hemostasis is provided in each of the areas defined by apertures  214   a ,  214   b . It should be noted that although the apertures  214   a ,  214   b  are here shown located in a particular portion of the sheath at the distal end of the cutting device and having an oval shape, it should be appreciated that the apertures and distal end  204   b  of the sheath  204  may be provided having a variety of shapes and may be located in a variety of different locations including any of the locations described above in conjunction with FIGS. 3-3B. Advantageously, however, in this embodiment the hemostasis aperture  214   b  is aligned opposite the cutting aperture, and thus may be conveniently positioned on the exact site being cut by operator with the cutting/hemostasis tool aperture  214   a , by performing a simple axial rotation around the shaft axis of the device, without otherwise shifting the cutting position, realigning or withdrawing the implement. The second electroded aperture thus provides the benefits of a separate electrosurgical sealing tool without the positioning drawbacks that would be introduced by a separate hemostasis instrument. 
     FIGS. 7 and 8 illustrate the relationship of the adapter device  200  of the present invention to a conventional mechanical surgical tool  150 . As illustrated, the adapter  200  has a mounting block  202  and a distally extending sheath body  204 . 
     For purposes of illustration the mechanical surgical tool  150  is an endoscopic shaver device having an outer cannula  152  within which is mounted an inner, tissue-affecting element  153 . The tissue-affecting element  153  may be rotatable or translatable such that a distal, cutting portion  154  thereof is able to cut or abrade tissue. The distal end of the outer cannula  152  has an aperture through which at least part of the cutting portion  154  may project. 
     The mechanical cutting tool is assembled by placing the tissue-affecting element  153  within the outer cannula  152 . This tool  150  may be converted to a bipolar surgical tool by sliding the adapter device  200  over outer cannula  152 . 
     Referring now to FIG. 9, an adapter device  250  for converting a mechanical cutting device to an electrosurgical cutting device is coupled to a first port of an impedance transformer  252 . The adapter device  250  may be similar to the adapter device  200  described above. A second port of the impedance transformer  252  is coupled to an output port of an electrosurgical generator  254 , e.g., to the bipolar output port of the generator. 
     In operation, the electrosurgical generator  254  provides a drive signal having a predetermined or controlled signal energy to a signal port having a predetermined impedance characteristic. For example, a typical electrosurgical generator may provide a bipolar output with power settings of between twenty and one hundred watts, and provide a voltage-limited signal or otherwise control the signal energy at the port to achieve the selected power delivery. While these generators work well with many bipolar devices, the adapter of the present invention presents a novel situation in which a sheath presents an electrode  208  that is positioned in proximity to, but curving sharply away from, a second electrode which has been defined by the pre-existing cutting tool and aperture of the device on which the adapter  250  is fitted. Such pre-existing cutting tool has dimensions determined by purely mechanical considerations, without reference to operation as an electrode. Thus, the standard output of the generator  254  may be poorly adapted to effectively transfer power to tissue near the cutting tool. The drive voltage may be excessive, leading to arcing or charring near the tool, and causing irregular current flow and heat distribution in the target tissue. To provide an efficient energy transfer between the signal port of the electrosurgical generator  254  and the adapter device  250 , the adapter device  250  would ideally be provided having a predetermined impedance characteristic selected to maximize the efficiency of the power or energy transfer. In practice, however, the adapter device  250  has exposed electrodes of small size, and may operate with a particular instrument, or to cut a specific tissue having its own characteristic conduction properties. The adapter device  250  therefore typically has an impedance characteristic which would not result in an efficient application of the energy from the electrosurgical generator  254  to the tissue path contacted by the electrodes formed with the adapter device  250 . 
     Thus, in accordance with this aspect of the invention, the impedance transformer  252  is configured with input and output sides that are impedance-matched to the generator  254  and to the adapter  250 , respectively. Transformer  252  has a first port having an impedance characteristic selected to provide an efficient power transfer from the electrosurgical generator  254  and a second port having an impedance characteristic which is selected to provide an efficient power transfer to the adapter device  250 . For example, the transformer may be configured to produce an output voltage across the tissue electrodes, that is high enough to drive the applied power across the tissue in contact therewith but is below a breakdown or charring level. For example, where the sheath is to deliver up to seventy watts of power, the transformer  252  may be wound to match the respective generator and adapter/tissue impedances while reducing the voltage appearing at the generator port by a factor of about two, to a level which heats tissue more effectively and controllably. For other instrument diameters, aperture size and tool configurations, proper matching may involve increasing the voltage. In this way, a controlled and predetermined amount of signal power as indicated or measured by the electrosurgical generator  254  is effectively transferred from the signal generator  254  to and applied by the adapter device  250 . 
     Although the impedance transformer  252  is here shown as a piece separate from the adapter device  250 , it is to be understood that in some embodiments, the transformer  252  may advantageously be provided as an integral component or subassembly of the adapter device  250  or the generator  254 . 
     FIG. 10 illustrates yet another embodiment of the adapter of the present invention. In this embodiment a fixed power cord assembly  230  attaches to the mounting block  202 . As further shown in that FIG. a flex spring  234  or conductive elastic seal ring  234  acts as a contact to interconnect one side of the power source directly to the conductive cannula of the  10  mechanical tool via a bushing or collar similar to bushing  205   a  of FIG.  1 . 
     The foregoing electrosurgical tissue cutting devices and sheaths are adapted for use in surgical procedures including, but not limited to, arthroscopic, endoscopic, hysteroscopic, laparoscopic, or resectoscopic surgical procedures. 
     Having described preferred embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating the concepts herein disclosed may be used. It is felt, therefore, that these concepts should not be limited to disclosed embodiments but rather should be limited only by the spirit and scope of the appended claims. The contents of all cited references are expressly incorporated herein in their entirety.