Arthroscopic devices and methods

A medical device includes an elongated sleeve having a longitudinal axis, a proximal end and a distal end. A cutting member having a plurality of sharp edges is formed from a wear-resistant ceramic material is carried at the distal end of the elongated sleeve. A motor drive is coupled to the proximal end of the elongated sleeve to rotate the sleeve at cutting member at high RPMs to cut bone and other hard tissue. An electrode is carried in a distal portion of ceramic cutting member for RF ablation of tissue when the sleeve and cutting member are is a stationary position. In methods of use, (i) the ceramic member can be engaged against bone and then rotated at high speed to cut bone tissue, and (ii) the ceramic member can be held in a stationary (non-rotating) position to engage tissue and RF energy can be delivered to the electrode to create a plasma that ablates tissue.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to arthroscopic tissue cutting and removal devices by which anatomical tissues may be cut and removed from a joint or other site. More specifically, this invention relates to instruments configured for cutting and removing bone or other hard tissue and having a ceramic cutting member.

2. Description of the Background Art

In several surgical procedures including subacromial decompression, anterior cruciate ligament reconstruction involving notchplasty, and arthroscopic resection of the acromioclavicular joint, there is a need for cutting and removal of bone and soft tissue. Currently, surgeons use arthroscopic shavers and burrs having rotational cutting surfaces to remove tissue for such procedures. A typical arthroscopic shaver or burr comprises a metal cutting member carried at the distal end of a metal sleeve that rotates within an open-ended metal shaft. A suction pathway for removal of bone fragments or other tissues is provided through a window proximal to the metal cutting member that communicates with a lumen in the sleeve.

When metal shavers and burrs “wear” during a procedure, which occurs very rapidly when cutting bone, the wear can be accompanied by loss of micro-particles from fracture and particle release which occurs along with dulling due to metal deformation. In such surgical applications, even very small amounts of such foreign particles that are not recovered from a treatment site can lead to detrimental effects on the patient health, with inflammation being typical. In some cases, the foreign particles can result in joint failure due to osteolysis, a term used to define inflammation due to presence of such foreign particles. A recent article describing such foreign particle induced inflammation is Pedowitz, et al. (2013) Arthroscopic surgical tools: “A source of metal particles and possible joint damage”, Arthroscopy—The Journal of Arthroscopic and Related Surgery, 29(9), 1559-1565. In addition to causing inflammation, the presence of metal particles in a joint or other treatment site can cause serious problems for future MRIs. Typically, the MRI images will be blurred by agitation of the metal particles caused by the magnetic field used in the imaging, making assessments of the treatment difficult.

Another problem with the currently available metal shavers/burrs relates to manufacturing limitations in combination with the rapid dulling of metal cutting edges. Typically, a metal cutter is manufactured by machining the cutting surfaces and flutes into a burr or abrader surface. The flute shape and geometry can be limited since it is dictated by the machining process, and burr size and shape limitations may direct usage toward more coarse bone removal applications. Further, when operated in a rotational or oscillatory mode, the cutting edges adapted for coarse bone removal may have a kickback effect as the flutes first make contact with bone, which is aggravated by rapid dulling of the machined cutting edges.

Therefore, the need exists for arthroscopic burrs and/or shavers that can operate to cut and remove bone without the release of fractured particles and micro-particles into the treatment site. Further, there is a need for burrs/cutters that do not wear rapidly and that can have cutting edges not limited by metal machining techniques.

As an alternative to such arthroscopic cutters and shavers, another class of tissue removal tools relies on radiofrequency (RF) ablation to remove the soft tissue. Tools such as those described in U.S. Pat. No. 6,149,620 and U.S. Pat. No. 7,678,069 can be highly effective in volumetric removal of soft tissue in the knee and elsewhere but are ineffective in resecting bone.

Therefore, the need exists for tools that can effectively remove both bone and soft tissue and which can combine the advantages of both cutter-based hard tissue resection and RF-based soft tissue ablation. At least some of these objectives will be met by the inventions described below.

SUMMARY OF THE INVENTION

The present invention provides a variety of improved tissue removal devices and methods, including devices and methods which can remove tissue by cutting (resection) and/or by radiofrequency (RF) ablation.

In a first specific aspect of the present invention, a medical device for removing tissue includes an elongated sleeve having a longitudinal axis, a proximal end, and a distal end. A ceramic cutting member with at least one cutting edge extends distally from the distal end of the elongated sleeve, and an electrode is carried by the cutting member. A motor drive is configured to couple to the proximal end of elongated sleeve to rotate the cutting member. In some embodiments, the elongated sleeve is an inner sleeve and is coaxially and rotatably disposed in an outer sleeve, where the outer sleeve may have a cut-out to expose the ceramic cutting member and the electrode.

The cutting edge of medical device for removing tissue will have a radially outward rotational periphery which is at least as great as an outward rotational periphery of the electrode, and the dielectric material typically comprises a wear-resistant ceramic material, usually consisting exclusively of the wear-resistant ceramic material. Exemplary wear-resistant ceramic materials are selected from the group consisting of yttria-stabilized zirconia, magnesia-stabilized zirconia, ceria-stabilized zirconia, zirconia toughened alumina and silicon nitride. The medical device will typically further comprise an RF source connected to the electrode and a controller operatively connectable to the motor drive, the RF source, and a negative pressure source.

The cutting member of the medical device will often have at least one window in a side thereof which communicates with an interior channel of the elongated (inner) sleeve which is configured to be connected to a negative pressure source. The window is typically adjacent to the electrode so that material released by resection and/or ablation can be aspirated through said window. The window optionally can be used for fluid infusion for use in electrosurgery. In some instances, the window is proximal to the electrode and/or proximal to the cutting edges, an/or at least partly intermediate the cutting edges. The cutting member may have from 1 to 100 cutting edges, a diameter ranging between 2 mm and 10 mm, and may extend over an axial length ranging between 1 mm and 10 mm. The cutting edges may be arranged in a pattern selected from at least one of helical, angled and straight relative to said axis.

In a second specific aspect of the present invention, a medical system for removing tissue includes an elongated rotatable shaft with a distal tip comprising (or composed of) a ceramic material. A motor drive is configured to rotate the shaft and the distal tip, and an electrode is carried by the distal tip. The electrode is coupled to an RF source, and a controller is operatively connected to the motor drive and to the RF source. The controller is configured to stop rotation of the shaft in a selected position, such as a position that will expose the electrode in a position that allows it to be used for ablative or other tissue treatment.

The medical device may further include a sensor configured to sense a rotational position of the shaft and to send signals to the controller indicating said rotational position. The controller may be configured to stop rotation of the shaft in the selected or other position, for example when a portion of distal tip such as the electrode or cutter element is properly oriented to perform a desired ablation, resection, or other treatment. The sensor is usually a Hall sensor. The controller may be further configured to control delivery of RF energy to the electrode when the shaft in said selected position. The distal tip of the rotatable shaft may have at least one window in a side thereof that opens to an interior channel in the shaft where the channel is configured to communicate with a negative pressure source. The window may be adjacent the electrode and/or may be at least partly proximal to the electrode. The distal tip may comprise or consist entirely of a wear-resistant ceramic material, such as those listed elsewhere herein.

In a third specific aspect of the present invention, a medical device for removing tissue includes an elongated shaft with a distal tip having a ceramic member. A window in the ceramic member connects to an interior channel in the shaft, and an electrode in the ceramic member is positioned adjacent to a distal end of the window. The interior channel is configured to be coupled to a negative pressure source.

The electrode may have a width equal to at least 50% of a width of the window, sometimes being at least 80% of the width of the window, and sometimes being at least 100% of the width of the window, or greater. At least one side of the window may have a sharp edge, and the electrode may at least partly encircle the distal end of the window. The ceramic member may have at least one sharp edge for cutting tissue, and a radially outward surface of the ceramic member usually defines a cylindrical periphery with an outward surface of the electrode being within said cylindrical periphery. The ceramic member will usually have at least one and more usually a plurality of sharp edges for cutting tissue.

In a fourth specific aspect of the present invention, a method for electrosurgical tissue ablation comprises providing an elongated shaft with a working end including an active electrode carried adjacent to a window that opens to an interior channel in the shaft. The channel is connected to a negative pressure source, and the active electrode and window are positioned in contact with target tissue in a fluid-filled space. The negative pressure source may be activated to suction the target tissue into the window, and the active electrode is activated (typically to deliver RF energy) to ablate tissue while translating the working end relative to the targeted tissue.

In specific aspects of the methods, a motor drive rotates the shaft and the distal tip (typically at at least 3,000 rpm), and a controller operatively connects the interior channel to the negative pressure source and an RF source to the electrode. The ceramic member is a wear-resistant material, typically as noted previously herein. Tissue debris is aspirated through the interior channel, and the working end is translated to remove a surface portion of the targeted tissue. and/or to undercut the targeted tissue to thereby remove chips of tissue.

In still further aspects, the present invention provides a high-speed rotating cutter or burr that is fabricated entirely of a ceramic material. In one variation, the ceramic is a molded monolith with sharp cutting edges and is adapted to be motor driven at speeds ranging from 3,000 rpm to 20,000 rpm. The ceramic cutting member is coupled to an elongate inner sleeve that is configured to rotate within a metal, ceramic or composite outer sleeve. The ceramic material is exceptionally hard and durable and will not fracture and thus not leave foreign particles in a treatment site. In one aspect, the ceramic has a hardness of at least 8 GPa (kg/mm2) and a fracture toughness of at least 2 MPam1/2. The “hardness” value is measured on a Vickers scale and “fracture toughness” is measured in MPam1/2. Fracture toughness refers to a property which describes the ability of a material containing a flaw to resist further fracture and expresses a material's resistance to such fracture. In another aspect, it has been found that materials suitable for the cutting member of the invention have a certain hardness-to-fracture toughness ratio, which is a ratio of at least 0.5 to 1

While the cutting assembly and ceramic cutting member of the invention have been designed for arthroscopic procedures, such devices can be fabricated in various cross-sections and lengths and can be use in other procedures for cutting bone, cartilage and soft tissue such as in ENT procedures, spine and disc procedures and plastic surgeries.

In another aspect, the present invention provides a medical device that includes an elongated sleeve having a longitudinal axis, a proximal end and a distal end. A cutting member extends distally from the distal end of the elongated sleeve, and has sharp cutting edges. The cutting head is formed from a wear-resistant ceramic material, and a motor coupled to the proximal end of elongated sleeve rotates the cutting member. The cutter may be engaged against bone and rotated to cut bone tissue without leaving any foreign particles in the site.

The wear-resistant ceramic material may comprise any one or combination of (1) zirconia, (2) a material selected from the group of yttria-stabilized zirconia, magnesia-stabilized zirconia and zirconia toughened alumina, or (3) silicon nitride. The cutting member typically has from 2 to 100 cutting edges, a cylindrical periphery, and is usually rounded in the distal direction. The cutting member will typically have diameter ranging from 2 mm to 10 mm, and the cutting edges will typically extend over an axial length ranging between 1 mm and 10 mm. The cutting edges may be any one of helical, angled or straight relative to said axis, and flutes between the cutting edges usually have a depth ranging from 0.10 mm to 2.5 mm. An aspiration tube may be configured to connect to a negative pressure source, where the cutting member has at least one window in a side thereof which opens to a hollow interior. In these embodiments, the hollow interior is open to a central passage of the elongated member which is connected to the aspiration tube.

In a further aspect, the present invention provides a medical device for treating bone including an elongated shaft having a longitudinal axis, a proximal end, and a distal end. A monolithic cutting member fabricated of a material having a hardness of at least 8 GPa (kg/mm2) is coupled to the distal end of the elongated shaft, and a motor is operatively connected to the proximal end of the shaft, said motor being configured to rotate the shaft at at least 3,000 rpm.

The material usually has a fracture toughness of at least 2 MPam1/2, and further usually has a coefficient of thermal expansion of less than 10 (1×106/° C.). The material typically comprises a ceramic selected from the group of yttria-stabilized zirconia, magnesia-stabilized zirconia, ceria-stabilized zirconia, zirconia toughened alumina and silicon nitride, and the cutting member typically has a cylindrical periphery and an at least partly rounded periphery in an axial direction.

In a still further aspect, the present invention provides a medical device for treating bone comprising a monolithic cutting member fabricated of a material having a hardness-to-fracture toughness ratio of at least 0.5:1, usually at least 0.8:1, and often at least 1:1.

In yet another aspect, the present invention provides a medical device for cutting tissue including a motor-driven shaft having a longitudinal axis, a proximal end, a distal end, and a lumen extending therebetween. A rotatable cutting member is fabricated entirely of a ceramic material and is operatively coupled to the distal end of the motor-driven shaft. At least one window in the cutting member communicates with the lumen in the shaft, and a negative pressure source is in communication with the lumen to remove cut tissue from an operative site.

The ceramic material typically has a hardness of at least 8 GPa (kg/mm2) and a fracture toughness of at least 2 MPam1/2. Additionally, the ceramic material will usually have a coefficient of thermal expansion of less than 10 (1×106/° C.). Exemplary ceramic materials are selected from the group consisting of yttria-stabilized zirconia, magnesia-stabilized zirconia, ceria-stabilized zirconia, zirconia toughened alumina and silicon nitride, and the cutting member usually has cutting edges where the at least one window is proximate to the cutting edges, and the at least one window is in at least one flute between the cutting edges.

In another aspect, the present invention provides a method for preventing foreign particle induced inflammation at a bone treatment site. A rotatable cutter fabricated of a ceramic material having a hardness of at least 8 GPa (kg/mm2) and a fracture toughness of at least 2 MPam1/2is engaged against bone and rotated to cut bone tissue without leaving any foreign particles in the site.

The ceramic material is usually selected from the group consisting of yttria-stabilized zirconia, magnesia-stabilized zirconia, ceria-stabilized zirconia, zirconia toughened alumina and silicon nitride, and the cutter is typically rotated at 10,000 rpm or greater. Cut bone tissue is removed from the bone treatment site through a channel in the cutter, typically by aspirating the cut bone tissue through the channel.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to bone cutting and removal devices and related methods of use. Several variations of the invention will now be described to provide an overall understanding of the principles of the form, function and methods of use of the devices disclosed herein. In general, the present disclosure provides for an arthroscopic cutter or burr assembly for cutting or abrading bone that is disposable and is configured for detachable coupling to a non-disposable handle and motor drive component. This description of the general principles of this invention is not meant to limit the inventive concepts in the appended claims.

In general, the present invention provides a high-speed rotating ceramic cutter or burr that is configured for use in many arthroscopic surgical applications, including but not limited to treating bone in shoulders, knees, hips, wrists, ankles and the spine. More in particular, the device includes a cutting member that is fabricated entirely of a ceramic material that is extremely hard and durable, as described in detail below. A motor drive is operatively coupled to the ceramic cutter to rotate the burr edges at speeds ranging from 3,000 rpm to 20,000 rpm.

In one variation shown inFIGS. 1-2, an arthroscopic cutter or burr assembly100is provided for cutting and removing hard tissue, which operates in an manner similar to commercially available metals shavers and burrs.FIG. 1shows disposable burr assembly100that is adapted for detachable coupling to a handle104and motor drive unit105therein as shown inFIG. 3.

The cutter assembly100has a shaft110extending along longitudinal axis115that comprises an outer sleeve120and an inner sleeve122rotatably disposed therein with the inner sleeve122carrying a distal ceramic cutting member125. The shaft110extends from a proximal hub assembly128wherein the outer sleeve120is coupled in a fixed manner to an outer hub140A which can be an injection molded plastic, for example, with the outer sleeve120insert molded therein. The inner sleeve122is coupled to an inner hub140B (phantom view) that is configured for coupling to the motor drive unit105(FIG. 3). The outer and inner sleeves120ands122typically can be a thin wall stainless steel tube, but other materials can be used such as ceramics, metals, plastics or combinations thereof.

Referring toFIG. 2, the outer sleeve120extends to distal sleeve region142that has an open end and cut-out144that is adapted to expose a window145in the ceramic cutting member125extending distally from the inner sleeve122during a portion of the inner sleeve's rotation. Referring toFIGS. 1 and 3, the proximal hub128of the burr assembly100is configured with a J-lock, snap-fit feature, screw thread or other suitable feature for detachably locking the hub assembly128into the handle104(FIG. 3). As can be seen inFIG. 1, the outer hub140A includes a projecting key146that is adapted to mate with a receiving J-lock slot148in the handle104(seeFIG. 3).

InFIG. 3, it can be seen that the handle104is operatively coupled by electrical cable152to a controller155which controls the motor drive unit105. Actuator buttons156a,156bor156con the handle104can be used to select operating modes, such as various rotational modes for the ceramic cutting member. In one variation, a joystick158is moved forward and backward to adjust the rotational speed of the ceramic cutting member125. The rotational speed of the cutter can continuously adjustable, or can be adjusted in increments up to 20,000 rpm.FIG. 3further shows that negative pressure source160is coupled to aspiration tubing162which communicates with a flow channel in the handle104and lumen165in inner sleeve122which extends to window145in the ceramic cutting member125(FIG. 2).

Now referring toFIGS. 2 and 4, the cutting member125comprises a ceramic body or monolith that is fabricated entirely of a technical ceramic material that has a very high hardness rating and a high fracture toughness rating, where “hardness” is measured on a Vickers scale and “fracture toughness” is measured in MPam1/2. Fracture toughness refers to a property which describes the ability of a material containing a flaw or crack to resist further fracture and expresses a material's resistance to brittle fracture. The occurrence of flaws is not completely avoidable in the fabrication and processing of any components.

The authors evaluated technical ceramic materials and tested prototypes to determine which ceramics are best suited for the non-metal cutting member125. When comparing the material hardness of the ceramic cutters of the invention to prior art metal cutters, it can easily be understood why typical stainless steel bone burrs are not optimal. Types 304 and 316 stainless steel have hardness ratings of 1.7 and 2.1, respectively, which is low and a fracture toughness ratings of 228 and 278, respectively, which is very high. Human bone has a hardness rating of 0.8, so a stainless steel cutter is only about 2.5 times harder than bone. The high fracture toughness of stainless steel provides ductile behavior which results in rapid cleaving and wear on sharp edges of a stainless steel cutting member. In contrast, technical ceramic materials have a hardness ranging from approximately 10 to 15, which is five to six times greater than stainless steel and which is 10 to 15 times harder than cortical bone. As a result, the sharp cutting edges of a ceramic remain sharp and will not become dull when cutting bone. The fracture toughness of suitable ceramics ranges from about 5 to 13 which is sufficient to prevent any fracturing or chipping of the ceramic cutting edges. The authors determined that a hardness-to-fracture toughness ratio (“hardness-toughness ratio”) is a useful term for characterizing ceramic materials that are suitable for the invention as can be understood form the Chart A below, which lists hardness and fracture toughness of cortical bone, a 304 stainless steel, and several technical ceramic materials.

As can be seen in Chart A, the hardness-toughness ratio for the listed ceramic materials ranges from 98× to 250× greater than the hardness-toughness ratio for stainless steel 304. In one aspect of the invention, a ceramic cutter for cutting hard tissue is provided that has a hardness-toughness ratio of at least 0.5:1, 0.8:1 or 1:1.

In one variation, the ceramic cutting member125is a form of zirconia. Zirconia-based ceramics have been widely used in dentistry and such materials were derived from structural ceramics used in aerospace and military armor. Such ceramics were modified to meet the additional requirements of biocompatibility and are doped with stabilizers to achieve high strength and fracture toughness. The types of ceramics used in the current invention have been used in dental implants, and technical details of such zirconia-based ceramics can be found in Volpato, et al., “Application of Zirconia in Dentistry: Biological, Mechanical and Optical Considerations”, Chapter 17 inAdvances in Ceramics—Electric and Magnetic Ceramics, Bioceramics, Ceramics and Environment(2011).

In one variation, the ceramic cutting member125is fabricated of an yttria-stabilized zirconia as is known in the field of technical ceramics, and can be provided by CoorsTek Inc., 16000 Table Mountain Pkwy., Golden, Colo. 80403 or Superior Technical Ceramics Corp., 600 Industrial Park Rd., St. Albans City, Vt. 05478. Other technical ceramics that may be used consist of magnesia-stabilized zirconia, ceria-stabilized zirconia, zirconia toughened alumina and silicon nitride. In general, in one aspect of the invention, the monolithic ceramic cutting member125has a hardness rating of at least 8 GPa (kg/mm2). In another aspect of the invention, the ceramic cutting member125has a fracture toughness of at least 2 MPam1/2.

The fabrication of such ceramics or monoblock components are known in the art of technical ceramics, but have not been used in the field of arthroscopic or endoscopic cutting or resecting devices. Ceramic part fabrication includes molding, sintering and then heating the molded part at high temperatures over precise time intervals to transform a compressed ceramic powder into a ceramic monoblock which can provide the hardness range and fracture toughness range as described above. In one variation, the molded ceramic member part can have additional strengthening through hot isostatic pressing of the part. Following the ceramic fabrication process, a subsequent grinding process optionally may be used to sharpen the cutting edges175of the burr (seeFIGS. 2 and 4).

InFIG. 4, it can be seen that in one variation, the proximal shaft portion176of cutting member125includes projecting elements177which are engaged by receiving openings178in a stainless steel split collar180shown in phantom view. The split collar180can be attached around the shaft portion176and projecting elements177and then laser welded along weld line182. Thereafter, proximal end184of collar180can be laser welded to the distal end186of stainless steel inner sleeve122to mechanically couple the ceramic body125to the metal inner sleeve122. In another aspect of the invention, the ceramic material is selected to have a coefficient of thermal expansion between is less than 10 (1×106/° C.) which can be close enough to the coefficient of thermal expansion of the metal sleeve122so that thermal stresses will be reduced in the mechanical coupling of the ceramic member125and sleeve122as just described. In another variation, a ceramic cutting member can be coupled to metal sleeve122by brazing, adhesives, threads or a combination thereof.

Referring toFIGS. 1 and 4, the ceramic cutting member125has window145therein which can extend over a radial angle of about 10° to 90° of the cutting member's shaft. In the variation ofFIG. 1, the window is positioned proximally to the cutting edges175, but in other variations, one or more windows or openings can be provided and such openings can extend in the flutes190(seeFIG. 6) intermediate the cutting edges175or around a rounded distal nose of the ceramic cutting member125. The length L of window145can range from 2 mm to 10 mm depending on the diameter and design of the ceramic member125, with a width W of 1 mm to 10 mm.

FIGS. 1 and 4shows the ceramic burr or cutting member125with a plurality of sharp cutting edges175which can extend helically, axially, longitudinally or in a cross-hatched configuration around the cutting member, or any combination thereof. The number of cutting edges175ands intermediate flutes190can range from 2 to 100 with a flute depth ranging from 0.10 mm to 2.5 mm. In the variation shown inFIGS. 2 and 4, the outer surface or periphery of the cutting edges175is cylindrical, but such a surface or periphery can be angled relative to axis115or rounded as shown inFIGS. 6 and 7. The axial length AL of the cutting edges can range between 1 mm and 10 mm. While the cutting edges175as depicted inFIG. 4are configured for optimal bone cutting or abrading in a single direction of rotation, it should be appreciated the that the controller155and motor drive105can be adapted to rotate the ceramic cutting member125in either rotational direction, or oscillate the cutting member back and forth in opposing rotational directions.

FIGS. 5A-5Billustrate a sectional view of the window145and shaft portion176of a ceramic cutting member125′ that is very similar to the ceramic member125ofFIGS. 2 and 4. In this variation, the ceramic cutting member has window145with one or both lateral sides configured with sharp cutting edges202aand202bwhich are adapted to resect tissue when rotated or oscillated within close proximity, or in scissor-like contact with, the lateral edges204aand204bof the sleeve walls in the cut-out portion144of the distal end of outer sleeve120(seeFIG. 2). Thus, in general, the sharp edges of window145can function as a cutter or shaver for resecting soft tissue rather than hard tissue or bone. In this variation, there is effectively no open gap G between the sharp edges202aand202bof the ceramic cutting member125′ and the sharp lateral edges204a,204bof the sleeve120. In another variation, the gap G between the window cutting edges202a,202band the sleeve edges204a,204bis less than about 0.020″, or less than 0.010″.

FIG. 6illustrates another variation of ceramic cutting member225coupled to an inner sleeve122in phantom view. The ceramic cutting member again has a plurality of sharp cutting edges175and flutes190therebetween. The outer sleeve120and its distal opening and cut-out shape144are also shown in phantom view. In this variation, a plurality of windows or opening245are formed within the flutes190and communicate with the interior aspiration channel165in the ceramic member as described previously.

FIG. 7illustrates another variation of ceramic cutting member250coupled to an inner sleeve122(phantom view) with the outer sleeve not shown. The ceramic cutting member250is very similar to the ceramic cutter125ofFIGS. 1, 2 and 4, and again has a plurality of sharp cutting edges175and flutes190therebetween. In this variation, a plurality of windows or opening255are formed in the flutes190intermediate the cutting edges175and another window145is provided in a shaft portion176of ceramic member225as described previously. The openings255and window145communicate with the interior aspiration channel165in the ceramic member as described above.

It can be understood that the ceramic cutting members can eliminate the possibility of leaving metal particles in a treatment site. In one aspect of the invention, a method of preventing foreign particle induced inflammation in a bone treatment site comprises providing a rotatable cutter fabricated of a ceramic material having a hardness of at least 8 GPa (kg/mm2) and/or a fracture toughness of at least 2 MPam1/2and rotating the cutter to cut bone without leaving any foreign particles in the treatment site. The method includes removing the cut bone tissue from the treatment site through an aspiration channel in a cutting assembly.

FIG. 8illustrates variation of an outer sleeve assembly with the rotating ceramic cutter and inner sleeve not shown. In the previous variations, such as inFIGS. 1, 2 and 6, shaft portion176of the ceramic cutter125rotates in a metal outer sleeve120.FIG. 8illustrates another variation in which a ceramic cutter (not shown) would rotate in a ceramic housing280. In this variation, the shaft or a ceramic cutter would thus rotate is a similar ceramic body which may be advantageous when operating a ceramic cutter at high rotational speeds. As can be seen inFIG. 8, a metal distal metal housing282is welded to the outer sleeve120along weld line288. The distal metal housing282is shaped to support and provide strength to the inner ceramic housing282.

FIGS. 9-11are views of an alternative tissue resecting assembly or working end400that includes a ceramic or other dielectric member405with cutting edges410in a form similar to that described previously.FIG. 9illustrates the monolithic ceramic member405carried as a distal tip of a shaft or inner sleeve412as described in previous embodiments. The ceramic member405again has a window415that communicates with aspiration channel420in shaft412that is connected to negative pressure source160as described previously. The inner sleeve412is operatively coupled to a motor drive105and rotates in an outer sleeve422of the type shown inFIG. 2. The outer sleeve422is shown inFIG. 10.

In the variation illustrated inFIG. 9, the ceramic member405carries an electrode arrangement425, or active electrode, having a single polarity that is operatively connected to an RF source440. A return electrode, or second polarity electrode430, is provided on the outer sleeve422as shown inFIG. 10. In one variation, the outer sleeve422can comprise an electrically conductive material such as stainless steel to thereby function as return electrode445, with a distal portion of outer sleeve422is optionally covered by a thin insulative layer448such as parylene, to space apart the active electrode425from the return electrode430.

The active electrode arrangement425can consist of a single conductive metal element or a plurality of metal elements as shown inFIGS. 9 and 10. In one variation shown inFIG. 9, the plurality of electrode elements450a,450band450cextend transverse to the longitudinal axis115of ceramic member405and inner sleeve412and are slightly spaced apart in the ceramic member. In one variation shown inFIGS. 9 and 10, the active electrode425is spaced distance D from the distal edge452of window415which is less than 5 mm and often less than 2 mm for reasons described below. The width W and length L of window415can be the same as described in a previous embodiment with reference toFIG. 4.

As can be seen inFIGS. 9 and 11, the electrode arrangement425is carried intermediate the cutting edges410of the ceramic member405in a flattened region454where the cutting edges410have been removed. As can be best understood fromFIG. 11, the outer periphery455of active electrode425is within the cylindrical or rotational periphery of the cutting edges410when they rotate. InFIG. 11, the rotational periphery of the cutting edges is indicated at460. The purpose of the electrode's outer periphery455being equal to, or inward from, the cutting edge periphery460during rotation is to allow the cutting edges410to rotate at high RPMs to engage and cut bone or other hard tissue without the surface or the electrode425contacting the targeted tissue.

FIG. 9further illustrates a method of fabricating the ceramic member405with the electrode arrangement425carried therein. The molded ceramic member405is fabricated with slots462that receive the electrode elements450a-450c, with the electrode elements fabricated from stainless steel, tungsten or a similar conductive material. Each electrode element450a-450chas a bore464extending therethrough for receiving an elongated wire electrode element465. As can be seen inFIG. 9, and the elongated wire electrode465can be inserted from the distal end of the ceramic member405through a channel in the ceramic member405and through the bores464in the electrode elements450a-450c. The wire electrode465can extend through the shaft412and is coupled to the RF source440. The wire electrode element465thus can be used as a means of mechanically locking the electrode elements450a-450cin slots462and also as a means to deliver RF energy to the electrode425.

Another aspect of the invention is illustrated inFIGS. 9-10wherein it can be seen that the electrode arrangement425has a transverse dimension TD relative to axis115that is substantial in comparison to the window width W as depicted inFIG. 10. In one variation, the electrode's transverse dimension TD is at least 50% of the window width W, or the transverse dimension TD is at least 80% of the window width W. In the variation ofFIGS. 9-10, the electrode transverse dimension TD is 100% or more of the window width W. It has been found that tissue debris and byproducts from RF ablation are better captured and extracted by a window415that is wide when compared to the width of the RF plasma ablation being performed.

In general, the tissue resecting system comprises an elongated shaft with a distal tip comprising a ceramic member, a window in the ceramic member connected to an interior channel in the shaft and an electrode arrangement in the ceramic member positioned distal to the window and having a width that is at least 50% of the width W of the window, usually at least 80% of the width W of the window, and often at least 100% of the width W of the window, or greater. Further, the system includes a negative pressure source160in communication with the interior channel420.

Now turning toFIGS. 12A-12C, a method of use of the resecting assembly400ofFIG. 9can be explained. InFIG. 12A, the system and a controller is operated to stop rotation of the ceramic member405in a selected position were the window415is exposed in the cut-out482of the open end of outer sleeve422shown in phantom view. In one variation, a controller algorithm can be adapted to stop the rotation of the ceramic member405that uses a Hall sensor484ain the handle104(seeFIG. 3) that senses the rotation of a magnet484bcarried by inner sleeve hub140B as shown inFIG. 2. The controller algorithm can receive signals from the Hall sensor which indicates a rotational position of the inner sleeve412and ceramic member405relative to the outer sleeve422. The magnet484b(FIG. 3) can be positioned in the hub140B (FIG. 2) so that when sensed by the Hall sensor, the controller algorithm can de-activate the motor drive105so as to stop the rotation of the inner sleeve in any selected position, e.g. with the window415and cut-out482aligned.

Under endoscopic vision, referring toFIG. 12B, the physician then can position the electrode arrangement425in contact with tissue targeted T for ablation and removal in a working space filled with fluid486, such as a saline solution which enables RF plasma creation about the electrode. The negative pressure source160is activated prior to or contemporaneously with the step of delivering RF energy to electrode425. Still referring toFIG. 12B, when the ceramic member405is positioned in contact with tissue and translated in the direction of arrow Z, the negative pressure source160suctions the targeted tissue into the window415. At the same time, RF energy delivered to electrode arrangement425creates a plasma P as is known in the art to thereby ablate tissue. The ablation then will be very close to the window415so that tissue debris, fragments, detritus and byproducts will be aspirated along with fluid486through the window415and outwardly through the interior extraction channel420to a collection reservoir. In one method shown schematically inFIG. 12B, a light movement or translation of electrode arrangement425over the targeted tissue will ablate a surface layer of the tissue and aspirate away the tissue detritus.

FIG. 12Cschematically illustrates a variation of a method which is of particular interest. It has been found if suitable downward pressure on the working end400is provided, then axial translation of working end400in the direction arrow Z inFIG. 12C, together with suitable negative pressure and the RF energy delivery will cause the plasma P to undercut the targeted tissue along line L that is suctioned into window415and then cut and scoop out a tissue chips indicated at488. In effect, the working end400then can function more as a high volume tissue resecting device instead of, or in addition to, its ability to function as a surface ablation tool. In this method, the cutting or scooping of such tissue chips488would allow the chips to be entrained in outflows of fluid486and aspirated through the extraction channel420. It has been found that this system with an outer shaft diameter of 7.5 mm, can perform a method of the invention can ablate, resect and remove tissue at a rate greater than 15 grams/min, often greater than 20 grams/min, and sometimes greater than 25 grams/min.

In general, a method corresponding to the invention includes providing an elongated shaft with a working end400comprising an active electrode425carried adjacent to a window415that opens to an interior channel in the shaft which is connected to a negative pressure source, positioning the active electrode and window in contact with targeted tissue in a fluid-filled space, activating the negative pressure source to thereby suction targeted tissue into the window and delivering RF energy to the active electrode to ablate tissue while translating the working end across the targeted tissue. The method further comprises aspirating tissue debris through the interior channel420. In a method, the working end400is translated to remove a surface portion of the targeted tissue. In a variation of the method, the working end400is translated to undercut the targeted tissue to thereby remove chips488of tissue.

Now turning toFIGS. 13A-13C, other distal ceramic tips of cutting assemblies are illustrated that are similar to that ofFIGS. 9-11, except the electrode configurations carried by the ceramic members405are varied. InFIG. 13A, the electrode490A comprises one or more electrode elements extending generally axially distally from the window415.FIG. 13Billustrates an electrode490B that comprises a plurality of wire-like elements492projecting outwardly from surface454.FIG. 13Cshows electrode490C that comprises a ring-like element that is partly recessed in a groove494in the ceramic body. All of these variations can produce an RF plasma that is effective for surface ablation of tissue, and are positioned adjacent to window415to allow aspiration of tissue detritus from the site.

FIG. 14illustrates another variation of a distal ceramic tip500of an inner sleeve512that is similar to that ofFIG. 9except that the window515has a distal portion518that extends distally between the cutting edges520, which is useful for aspirating tissue debris cut by high speed rotation of the cutting edges520. Further, in the variation ofFIG. 14, the electrode525encircles a distal portion518of window515which may be useful for removing tissue debris that is ablated by the electrode when the ceramic tip500is not rotated but translated over the targeted tissue as described above in relation toFIG. 12B. In another variation, a distal tip500as shown inFIG. 14can be energized for RF ablation at the same time that the motor drive rotates back and forth (or oscillates) the ceramic member500in a radial arc ranging from 1° to 180° and more often from 10° to 90°.

FIGS. 15A-15Billustrate other distal ceramic tips540and540′ that are similar to that ofFIG. 14except the electrode configurations differ. InFIG. 15A, the window515has a distal portion518that again extends distally between the cutting edges520, with electrode530comprising a plurality of projecting electrode elements that extend partly around the window515.FIG. 15Bshows a ceramic tip540′ with window515having a distal portion518that again extends distally between the cutting edges520. In this variation, the electrode545comprises a single blade element that extends transverse to axis115and is in close proximity to the distal end548of window515.

FIG. 16illustrates another variation of distal ceramic tip550of an inner sleeve552that is configured without the sharp cutting edges410of the embodiment ofFIGS. 9-11. In other respects, the arrangement of the window555and the electrode560is the same as described previously. Further, the outer periphery of the electrode is similar to the outward surface of the ceramic tip550. In the variation ofFIG. 16, the window555has at least one sharp edge565for cutting soft tissue when the assembly is rotated at a suitable speed from 500 to 5,000 rpm. When the ceramic tip member550is maintained in a stationary position and translated over targeted tissue, the electrode560can be used to ablate surface layers of tissue as described above.

FIG. 17depicts another variation of distal ceramic tip580coupled to an inner sleeve582that again has sharp burr edges or cutting edges590as in the embodiment ofFIGS. 9-11. In this variation, the ceramic monolith has only 4 sharp edges590which has been found to work well for cutting bone at high RPMs, for example from 8,000 RPM to 20,000 RPM. In this variation, the arrangement of window595and electrode600is the same as described previously. Again, the outer periphery of electrode595is similar to the outward surface of the cutting edges590.