Patent Description:
In several surgical procedures including subacromial decompression, anterior cruciate ligament reconstruction involving notchplasty and arthroscopic resection of the acromioclavicular j oint, 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 characterized 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 <NPL>. 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, such 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. Additionally, there is a need for efficient methods and apparatus for manufacturing such improved arthroscopic burrs and/or shavers. At least some of these needs will be met by the inventions described below.

Description of the Background Art. Relevant commonly owned patent publications include: <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>.

<CIT> describes an arthroscopic system including a re-useable sterilizable handle integrated with a single umbilical cable or conduit that carries electrical power from a power and/or control console to the handle for operating both a motor drive unit within the handle and delivering RF power to a disposable RF probe or cutter which may be detachably attached to the handle. The cutter is a ceramic cutter.

<CIT> describes a ZrO<NUM>-Al<NUM>O<NUM> composite ceramic material. This ceramic material includes a first phase of ZrO<NUM> grains having an average grain size of <NUM> to <NUM> and containing <NUM> to <NUM> mol % of CeO<NUM> and <NUM> mol % to less than <NUM> mol % of Y<NUM>O<NUM>, and a second phase of Al<NUM>O<NUM> grains having an average grain size of <NUM> to <NUM>. The ZrO<NUM> grains is composed of <NUM> vol % or more of tetragonal ZrO<NUM>, and a content of the second phase in the composite ceramic material is in a range of <NUM> to <NUM> vol %, and preferably <NUM> to <NUM> vol %.

A paper entitled "ZTA-<NUM> Zirconia Toughened Alumina Ceramic" describes an alumina ceramic which is <NUM>% alumina and <NUM>% zirconia with a grain size of <NUM> micrometers.

<CIT> describes a rotating instrument made of a ceramic material and comprising a shaft and a working member which is secured to the shaft or can be detachably secured to the shaft, wherein at least part of the working member is made from a ceramic material having a surface roughness of <NUM> to <NUM>.

The present disclosure provides a high-speed rotating cutter or cutting member 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 <NUM>,<NUM> RPM to <NUM>,<NUM> 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 of the cutting member 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 <NUM> Gpa (kg/mm<NUM>) and a fracture toughness of at least <NUM> MPam<NUM>/<NUM>. The "hardness" value is measured on a Vickers scale and "fracture toughness" is measured in MPam<NUM>/<NUM>. 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 <NUM> to <NUM>.

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 or soft tissue.

In particular, the present invention provides methods and apparatus for molding improved arthroscopic and other cutters and burrs, typically by molding ceramic materials.

In a first aspect, the present invention provides a method of fabricating a ceramic surgical cutting member of a type including a ceramic body having an outer surface, a longitudinal axis, a distal cutting portion with cutting edges, and a proximal shaft portion with a window that opens to an interior channel. The method comprises providing an injection mold with a mold cavity configured to form the outer surface of the cutting member, a first core pin which is configured to form the window of the cutting member, and a second core pin which is configured to form the interior channel. A flowable ceramic material is injected into the mold cavity to form the outer surface of the ceramic body. The first core pin is then removed from the mold to leave a void in the ceramic body which forms the window in the cutter body. The second core pin is removed from the mold to leave a void in the ceramic body which forms the interior channel of the cutter body. The at least first and second components of the mold components are then separated to allow release of the cutting member body from the mold cavity.

In particular embodiments of the methods, the cutting member body may be sintered after it has been released from the mold cavity to provide a hardened ceramic cutting member. Such sintered cutting members will typically have a hardness of at least <NUM> Gpa (kg/mm<NUM>) and a fracture toughness of at least <NUM> MPam<NUM>/<NUM>.

In other particular embodiments of the methods, the first core pin may be removed in a direction orthogonal to said longitudinal axis to form the window or the first core pin may be removed in a direction angled to said longitudinal axis to form the window. The second core pin may be removed in a direction aligned with said longitudinal axis to form the interior channel, and the at least first and second mold components may be separated in a direction orthogonal to the longitudinal axis of the cutter body. Alternatively, the at least first and second mold components may be separated in a direction aligned with the longitudinal axis of the cutter body. In still further embodiments of the methods of the preset invention, an additional mold component which forms helical cutting threads on the cutter body may be used and be separated by helical rotation of said mold component relative to the cutter body.

The mold cavity and mold components may be dimensioned and configured to provide cutter bodies which are particularly suitable for arthroscopic cutting. For example, the mold cavities may be configured and dimensioned to form a proximal shaft portion having a diameter ranging between <NUM> inch (<NUM>) and <NUM> inch (<NUM>), to form a distal cutting portion having an outer diameter ranging between <NUM> inch (<NUM>) and <NUM> inch (<NUM>), to form non-helical cutting edges, to form cutting edges aligned with the longitudinal axis, to form cutting edges with a radial rake angle ranging between <NUM>° and <NUM>°, to form cutting edges having a length ranging <NUM> inch (<NUM>) to <NUM> inch (<NUM>), to form a window with an area ranging from <NUM> in<NUM> (<NUM><NUM>) to <NUM> in<NUM> (<NUM><NUM>), to form an interior channel with a mean cross-sectional width ranging from <NUM> inch (<NUM>) to <NUM> inch (<NUM>), to form a window with edges having a sharp apex, to form a window with edges having a positive radial rake angle, and/or to form a window with edges having a radial rake angle greater than <NUM>°.

In a second aspect, the present invention provides a mold assembly for fabricating a ceramic surgical cutting member of the type including a ceramic body having an outer surface, a longitudinal axis, a distal cutting portion with cutting edges, and a proximal shaft portion with a window that opens to an interior channel. The mold assembly comprises a main body mold component having (<NUM>) an internal mold cavity configured to receive a flowable material comprising a ceramic to form the outer surface of the cutting member, (<NUM>) a window aperture, and (<NUM>) an interior passage aperture. A first core pin is configured to pass through the widow aperture in the mold component to form the window of the cutting member, and a second core pin which is configured to pass through the interior channel aperture in the mold to form the interior channel of the cutting member. The interior channel aperture is oriented to align the second core pin axially through the mold component, and the window aperture is oriented to align the first core pin laterally through the mold component so that a distal end of the first core pin engages a side of the second core pin to connect the window of the cutting member to the interior passage of the cutting member so that tissue may be drawn through the window into the interior passage of a cutting member formed by the mold assembly.

In other particular embodiments of the mold assemblies, the main body mold component may include at least first and second subcomponents which are separable to allow release of the cutting member body from the main body mold component cavity. The mold assembly may further comprise an end cap component having an end mold cavity which aligns with the interior passage of the main body mold component to form the distal cutting portion with cutting edges of the cutting member. The first core pin may be oriented in an orthogonal direction relative to said longitudinal axis to form the window. Alternatively, the first core pin may oriented in an angled direction relative to said longitudinal axis to form the window. The second core pin may be oriented in a direction aligned with said longitudinal axis to form the interior channel, and the at least first and second subcomponents may be configured to separate in a direction orthogonal to the longitudinal axis of the cutter body. The end cap may be configured to separate in a direction aligned with the longitudinal axis of the cutter body, and the end cap component may form helical cutting threads on the cutter body and be configured to separate from the mold assembly by helical rotation od said end cap relative to the cutter body. Alternatively, the end cap may be configured to form non-helical cutting edges on the cutter body.

In a first aspect, the present disclosure comprises a cutting member for use in a rotational cutting device. The cutting member comprises a ceramic body having cutting edges and being formed of a ceramic composite which includes alumina and zirconia. The alumina has a grain size ranging between <NUM> micrometer <NUM> micrometers, and the zirconia has a grain size ranging between <NUM> micrometer <NUM> micrometer.

In preferred embodiments, the ceramic body will further comprise at least one of the following eight additional characteristics, often further comprising at least two, more often comprising at least three, frequently comprising at least four, sometimes comprising at least five, sometimes comprising at least six, sometimes comprising at least seven, and in exemplary instances comprising all eight of the additional characteristics: (<NUM>) the alumina grain shape and zirconia grain shape are non-elongated; (<NUM>) the alumina grain shape and zirconia grain shape are each substantially round; (<NUM>) the ceramic has a fracture toughness of at least <NUM> MPam<NUM>/<NUM>; (<NUM>) a thermal expansion coefficient ranging from <NUM> ppm/°C to <NUM> ppm/°C; (<NUM>) a bulk density ranging from <NUM> to <NUM>; (<NUM>) comprising at least <NUM> wt% alumina; (<NUM>) comprising at least <NUM> wt% zirconia; and (<NUM>) comprising <NUM> wt% cerium or less, typically from <NUM> wt% cerium to <NUM> wt% cerium.

The present disclosure further provides medical devices for cutting bone and soft tissue, such as arthroscopic and other endoscopic tissue cutters. The medical devices comprise a shaft including a rotating component having a working end. A cutting member as described above is carried on the working end of the rotating component. Typically, an electrode is also carried on the working end of the shaft. For example, the electrode may be disposed between cutting edges of the cutting member. In many instances, the cutting member has at least one window therein which opens to an interior channel in the shaft, and the interior channel is configured to removably connect to a negative pressure source. In still other examples, the device further comprises a motor configured to detachably couple to the proximal end of the shaft to rotate the cutting member.

In a second aspect, the present disclosure comprises a medical device for cutting bone and soft tissue. The medical device comprises an elongated shaft having a longitudinal axis, a proximal end, and a distal end. A cutting member with cutting edges is rotatably attached to and extends distally from the distal end of the elongated sleeve. The cutting member is formed of a ceramic composite including alumina and zirconia, and a motor configured to couple to the proximal end of the sleeve to rotate the cutting member. The alumina has a grain shape which is substantially round with a diameter ranging between <NUM> micrometer- <NUM> micrometers, and the zirconia has a grain shape which is substantially round with a diameter ranging between <NUM> micrometer- <NUM> micrometer.

In specific examples of this medical device, the ceramic composite has at least <NUM> wt% of alumina, at least <NUM> wt% of zirconia, and has less than <NUM> wt% of cerium, typically from <NUM> wt% cerium to <NUM> wt% cerium. In other examples, the ceramic composite has a fracture toughness of at least <NUM> MPam<NUM>/<NUM>. In still other examples, the ceramic composite has a thermal expansion coefficient ranging from <NUM> ppm/°C to <NUM> ppm/°C. In yet additional examples, the ceramic composite has a bulk density ranging from <NUM> to <NUM>.

In specific instances, the cutting member carries an electrode, typically with the electrode disposed between the cutting edges of the cutting member.

Various embodiments of the present invention will now be discussed with reference to the appended drawings. It should be appreciated that the drawings depict only typical embodiments of the invention and are therefore not to be considered limiting in scope.

The present disclosure relates to bone and cutting and removal devices and related methods of use. Variations of a ceramic cutter will 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 for cutting 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 o is not meant to limit the inventive concepts in the appended claims.

In general, the present disclosure 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 <NUM>,<NUM> RPM to <NUM>,<NUM> RPM. As will be described further below, in a variation, the ceramic cutter is operated at <NUM>,<NUM> RPM for cutting bone.

In one variation shown in <FIG>, an arthroscopic cutter or cutter assembly <NUM> is provided for cutting and removing hard tissue, which operates in an manner similar to commercially available metals shavers and burrs. <FIG> shows disposable cutter assembly <NUM> that is adapted for detachable coupling to a handle <NUM> and motor drive unit <NUM> therein as shown in <FIG>.

The cutter assembly <NUM> of <FIG> has a shaft <NUM> extending along longitudinal axis <NUM> that comprises an outer sleeve <NUM> and an inner sleeve <NUM> rotatably disposed therein with the inner sleeve <NUM> carrying a distal ceramic cutting member <NUM> having an interior channel <NUM> therein that communicates with lumen <NUM> in the inner sleeve <NUM>. The shaft <NUM> extends from a proximal hub assembly <NUM> wherein the outer sleeve <NUM> is coupled in a fixed manner to an outer hub 140A which can be an injection molded plastic, for example, with the outer sleeve <NUM> insert molded therein. The inner sleeve <NUM> is coupled to an inner hub 140B (phantom view) that is configured for coupling to the motor drive unit <NUM> (<FIG>). The outer and inner sleeves <NUM> ands <NUM> typically can be a thin wall stainless steel tube, but other materials can be used such as ceramics, metals, plastics or combinations thereof.

Referring to <FIG>, the outer sleeve <NUM> extends to distal sleeve region <NUM> that has an open end and cut-out <NUM> that is adapted to expose a window <NUM> in the ceramic cutting member <NUM> during a portion of the inner sleeve's rotation. The window <NUM> communicates with interior channel <NUM> in the cutting member <NUM>. Referring to <FIG> and <FIG>, the proximal hub <NUM> of the cutter assembly <NUM> is configured with a J-lock, snap-fit feature, screw thread or other suitable feature for detachably locking the hub assembly <NUM> into the handle <NUM>. As can be seen in <FIG>, the outer hub 140A includes a projecting key <NUM> that is adapted to mate with a receiving J-lock slot in the handle <NUM> (see <FIG>).

In <FIG>, it can be seen that the handle <NUM> is operatively coupled by electrical cable <NUM> to a controller <NUM> which controls the motor drive unit <NUM>. Actuator buttons 156a, 156b or 156c on the handle <NUM> can be used to select operating modes, such as various rotational modes for the ceramic cutting member. In one variation, a joystick <NUM> be moved forward and backward to adjust the rotational speed of the ceramic cutting member <NUM>. The rotational speed of the cutter can continuously adjustable, or can be adjusted in increments up to <NUM>,<NUM> RPM. <FIG> further shows that negative pressure source <NUM> is coupled to aspiration connector <NUM> which communicates with a flow channel <NUM> in the handle <NUM> and through the shaver hub <NUM> (<FIG>) to the lumen <NUM> in inner sleeve <NUM> which extends to window <NUM> in the ceramic cutting member <NUM> (<FIG>).

Now referring to <FIG> and <FIG>, the cutting member <NUM> comprises 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 MPam<NUM>/<NUM>. 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 member <NUM>. 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 <NUM> and <NUM> stainless steel have hardness ratings of <NUM> and <NUM>, respectively, which is low and a fracture toughness ratings of <NUM> and <NUM>, respectively, which is very high. Human bone has a hardness rating of <NUM>, so a stainless steel cutter is only about <NUM> times harder than bone. The high fracture toughness of stainless steel provides ductile behavior which causes rapid cleaving and wear on sharp edges of a stainless steel cutting member. In contrast, technical ceramics materials have a hardness ranging from approximately <NUM> to <NUM>, which is five to six times greater than stainless steel and which is <NUM> to <NUM> 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 <NUM> to <NUM> 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 <NUM> 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 98X to 250X greater than the hardness-toughness ratio for stainless steel <NUM>. In one aspect, a ceramic cutter for cutting hard tissue is provided that has a hardness-toughness ratio of at least <NUM>:<NUM>, <NUM>:<NUM> or <NUM>:<NUM>.

In one variation, the ceramic cutting member <NUM> of <FIG> is 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 <NPL>).

In one variation, the ceramic cutting member <NUM> of <FIG> is fabricated of an yttria-stabilized zirconia as is known in the field of technical ceramics, and can be provided by CoorsTek Inc. , <NUM> Table Mountain Pkwy. , Golden, CO <NUM> or Superior Technical Ceramics Corp. , <NUM> Industrial Park Rd. Albans City, VT <NUM>. Other technical ceramics that may be uses consist of magnesia-stabilized zirconia, ceria-stabilized zirconia, zirconia toughened alumina and silicon nitride. In general, in one aspect, the monolithic ceramic cutting member <NUM> has a hardness rating of at least <NUM> Gpa (kg/mm<NUM>). In another aspect, the ceramic cutting member <NUM> has a fracture toughness of at least <NUM> MPam<NUM>/<NUM>.

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 cutting or resecting devices. Ceramic part fabrication includes molding a part such as a cutting member <NUM> which is called "green" after release from a mold, then sintering or "firing" the molded green part at high temperatures over precise time intervals to transform the compressed ceramic powder into a ceramic monoblock which can provide the hardness range and fracture toughness range as described above. Injection molds for fabricating such ceramic cutting members are described in more detail below.

In <FIG>, one variation of ceramic cutter <NUM> is shown which has a proximal shaft portion <NUM> and distal portion <NUM> which has cutting edges <NUM> extending radially outward from the outer surface OS of the cutting member. The shaft portion <NUM> has a reduced diameter section <NUM> that includes projecting elements <NUM> which engage receiving openings in the inner sleeve <NUM> for locking the cutting member <NUM> to the inner sleeve <NUM> (phantom view). A thin-wall polymeric sleeve <NUM>, for example, heat shrink tubing is shown in phantom view in <FIG> extending over the inner sleeve <NUM> and the reduced diameter section <NUM> shaft portion <NUM> to provide a lubricious, dielectric outer layer covering the inner sleeve <NUM>. In other variations, a ceramic cutting member <NUM> can be coupled to metal sleeve <NUM> by brazing, adhesives, threads or a combination thereof. Still referring to <FIG>, the window <NUM> in the ceramic cutting member <NUM> can extend over a radial angle ranging between about <NUM>° to <NUM>° of the shaft portion <NUM>. In a variation, the window <NUM> is provided with sharp outer edges 185A and 185B with a high radial rake angle for capturing bone chips and cutting soft tissue as will be described further below. Further, the bone chips or the resected soft tissue are moved or suctioned by the negative pressure source <NUM> through the window <NUM> and interior channel <NUM> (with diameter C) in the ceramic member <NUM> and thereafter into the increased diameter lumen <NUM> of the inner sleeve <NUM> (see <FIG>). The increase in diameter from channel <NUM> to inner sleeve lumen <NUM> is advantageous for providing a clog-free outflow pathway as any removed tissue that passes through the interior channel <NUM> in the ceramic cutting member <NUM> will be then entrained in fluid outflows in inner sleeve lumen <NUM>.

As will be described next, a ceramic cutting member <NUM> of <FIG> corresponding to the invention has many unique features for functional purposes that distinguish its shape and configuration from prior art metal burrs or blades. After extensive testing, it has been found that an optimized ceramic cutting member <NUM> differs from typical metal burrs (see <FIG>) in several ways, including (i) the number of cutting edges, (ii) the height of the cutting edges, (iii) the thickness of the cutting edges (iv) the length and surface area of the cutting edges, and (v) the dimensions, configuration and location of the window in the cutting member. Further, the system uses higher rotational speeds than prior art systems for optimizing use of a ceramic cutter in cutting bone.

In the variation shown in <FIG> and <FIG>, the ceramic cutting member or cutter body has three cutting edges <NUM> and three flutes <NUM> with the outer diameter or cutting edge periphery P being cylindrical and tapered or rounded in the distal direction. Metal shaver blades typically have six, eight or more cutting edges. <FIG> show a prior art metal shaver blade or burr <NUM> with eight cutting edges <NUM>' and eight intermediate flutes <NUM>'.

As can be seen in <FIG> and <FIG>, the cutting edges <NUM> in ceramic cutting member <NUM> are typically non-helical or straight and aligned with longitudinal axis <NUM> to facilitate injection molding as will be described below. <FIG> shows the a cutting edge <NUM> as being defined as the hatched area that extends radially outward from the outer surface OS. In one aspect, it has been found that the ceramic cutter <NUM> (<FIG> and <FIG>) with fewer cutting edges <NUM> than a metal burr is optimal for bone cutting. Further, an optimal ceramic cutter has cutting edges with a height A which is much less than a cutting edge height in a typical metal burr (see <FIG>). The ceramic cutting member <NUM> in <FIG>, for example, is configured with three cutting edges <NUM>. The reduced cutting edge height A allows for a smoother cutting, less chattering, and improved tactile feedback to the user's hand during the bone cutting process. In addition, a ceramic cutting member with fewer cutting edges <NUM> and reduced cutting edge height A can be combined with higher rotational speeds than prior art metal burrs to cut bone at a faster rate (in terms of grams/min). The system of <FIG> and <FIG> corresponding to the invention operates at up to <NUM>,<NUM> RPM and in one variation operates at <NUM>,<NUM> RPM for bone cutting. Commercially available metal burrs typically operate at a maximum of <NUM>,<NUM> RPM. If commercially available metal burrs were operated at higher RPMs, the metal edges would become dull much more rapidly.

Referring to <FIG>, a variation of ceramic cutting member <NUM> has three cutting edges <NUM>, however other variations for bone cutting can have from <NUM> to <NUM> cutting edges. In another aspectrelating to the cutting edges <NUM>, the reduced number of cutting edges allows for much higher strength cutting edges in a ceramic body. It has been found that ceramic cutting edges <NUM> benefit from substantial bulk or thickness B (see <FIG>) behind the cutting faces <NUM> which can prevent a potential fracture in the ceramic, for example, along line <NUM> indicated in <FIG>. <FIG> shows a prior art metal cutting edge <NUM>' which has relatively little bulk or thickness B' compared to the ceramic cutting edge thickness B of <FIG>. Referring to <FIG>, an appropriate manner of characterizing the thickness or bulk of a cutting edge <NUM> is to define the cutting edge thickness B as a dimension along a tangent T to a diameter D at a midpoint MP from a cutting face <NUM> to the back side <NUM> of the cutting edge <NUM> which is a surface of the adjacent flute <NUM>. As can be seen in the prior art metal cutter of <FIG>, the prior art thickness B' of the cutting edge <NUM>' along tangent T' of diameter D' at midpoint MP' of the cutting edge is small in relation to height A' of the cutting edge due to the ductile, high fracture resistance of metal as opposed to a ceramic (see Chart A above). <FIG> illustrates a hypothetical cutting member <NUM>' that fabricated of a ceramic with the cutting edge height A and thickness B of a prior art metal burr as in <FIG>. In such a ceramic cutter <NUM>' as depicted in <FIG>, the cutting edges <NUM> would fracture along line <NUM>' due to the lack of cutting edge thickness B which equates with strength or fracture resistance. Referring back to the prior art metal burr embodiment of <FIG>, the ratio of edge thickness B' to edge height A' in the is much less than <NUM>:<NUM>. In the cutting member <NUM> in <FIG>, such a ceramic cutting member has a cutting edge thickness B to height A ratio of greater than <NUM>, and more often greater than <NUM>:<NUM>.

In general, an arthroscopic cutter corresponding to the disclosure comprises a ceramic body with a plurality of cutting edges <NUM> and intermediate flutes <NUM> wherein each cutting edge defines a cutting edge height A measured from an outer cutting edge diameter P to a flute bottom or surface OS, where the ratio of the cutting edge thickness to the cutting edge height is at least <NUM>:<NUM> when the cutting edge thickness is measured along a tangent to a midpoint of the cutting face <NUM> to the adjacent flute. In another variation, the ratio of the cutting edge thickness to the cutting face height is at least <NUM>:<NUM>.

In another aspect, the cutting edge height A relative to the outer cutting edge diameter P is small compared to prior art metal burrs such as illustrated in <FIG>. In the variation shown in <FIG> and <FIG>, the cutting edge height A is <NUM> inch (<NUM>) which is less than <NUM>% of the outer periphery diameter P of the cutting member. In general, the ratio of the cutting edge height A to the periphery diameter P is <NUM>:<NUM> or less, or often such a ratio is <NUM>:<NUM> or less.

Another way to define the bulk or thickness of the cutting edges <NUM> of ceramic cutter <NUM> (<FIG>) compared to a prior art metal burr as in <FIG> is to consider the primary relief angle of the cutting edges. Referring to <FIG>, in standard nomenclature for rotary cutters, the primary relief angle E is the angle of the outer surface just behind the apex X of the cutting edge <NUM>'. In metal burrs, there is typically a relief angle of a <NUM>° to <NUM>°, which allows the apex X to engage targeted material even after the apex X becomes dull. It can be easily understood that as an apex X of a metal cutting edge becomes dull, a relief angle is needed. Otherwise, the rotating cutter could simply ride on the backside of the cutting edge <NUM>' over the targeted tissue. In contrast, turning to <FIG>, the cutting edges <NUM> of the ceramic cutter <NUM> of <FIG>, <FIG> and <FIG> have no primary relief angle at all. Of particular interest, it has been found that since the ceramic cutting edges <NUM> do not become dull, there is no need (or performance gain) by providing a primary relief angle. Instead, in a ceramic cutter <NUM> corresponding to the disclosure, the lands <NUM> have a lands width LW at the outer periphery diameter P than extends over a radial angle of greater than <NUM>°, and in the variation of <FIG> and <FIG>, greater than <NUM>°. The scope of the disclosure includes the option of providing some primary clearance, for example a clearance angle of up to <NUM>°. Alternatively, the amount of clearance can be better defined by the "radial" depth of the clearance, as in a percentage of the periphery diameter P of the ceramic cutter <NUM>. In general, referring to <FIG>, an arthroscopic cutter corresponding to the disclosure comprises a ceramic body with a plurality of cutting edges <NUM> and intermediate flutes <NUM> wherein each cutting edge <NUM> has lands <NUM> with a clearance of less than <NUM>% of the outer periphery diameter P at a radial angle of <NUM>° behind the apex X of the cutting edge <NUM>.

In another aspect of the disclosure referring to <FIG>, the ceramic cutter <NUM> has cutting edges <NUM> with a <NUM>° radial rake angle RA whereas metal burrs always have a substantial positive radial rake angle. The radial rake angle RA' of a prior art metal burr of <FIG> can range from about <NUM>° to <NUM>°. Positive rake angles are needed in metal burrs or cutters to make such cutters function somewhat effectively as the apex X of the cutting edge dulls rapidly. Of particular interest, referring to <FIG>, it has been found that an optimal radial rake angle RA of a ceramic cutter <NUM> is <NUM>°. In other variations, the radial rake angle RA of a ceramic cutter <NUM> can range from about -<NUM>° up to about +<NUM>°.

In another aspect of the disclosure as described above referring to <FIG> and <FIG>, the ceramic cutter <NUM> has cutting edges <NUM> that are non-helical and aligned with the longitudinal axis <NUM> of the cutting member <NUM>. In contrast, typical prior art metal burrs as shown in <FIG> have helical cutting edges. This aspect of the ceramic cutting member <NUM> of <FIG> that relates to non-helical cutting edges facilitates a method of injection molding the ceramic body <NUM> with a three-component parting mold <NUM> as shown in <FIG>. <FIG> is a schematic sectional view of a parting mold with three parting mold components M1, M2 and M3 and two core pins CP1 and CP2. The mold <NUM> parts along lines <NUM> and <NUM> as can be seen in <FIG> and <FIG>. <FIG> schematically depicts several steps of releasing the green ceramic cutting member <NUM> from mold <NUM>. Of particular interest, the mold component M1 is adapted to part from the other components M2 and M3 by axial movement away form distal portion <NUM> and cutting edges <NUM> of ceramic cutting member <NUM> aligned with the longitudinal axis <NUM> as can be understood from <FIG> and <FIG>. It is for this reason that cutting edges <NUM> are straight and aligned with the ceramic body's longitudinal axis <NUM>. In other words, the axially-aligned cutting edges <NUM> are aligned with the parting direction (the longitudinal axis <NUM>) of mold component M1 (<FIG>). As can be understood from the <FIG>, the cutting edges <NUM> can also have a positive rake angle of up to <NUM>° or more (see <FIG>) and the mold component M1 then can still release from the molded green cutting member body <NUM>.

<FIG> further shows other steps of the mold release which includes withdrawal of core pin CP1 in a direction orthogonal to axis <NUM> to provide the window <NUM> in the ceramic cutter <NUM>. This design of the mold <NUM> and core pin CP1 is configured to form the window edges 185A and 185B with high positive radial rake angles (see <FIG> and <FIG>) as will be discussed further below. Also, <FIG> shows withdrawal of core pin CP2 in the axial direction to provide axial inner channel <NUM> in the ceramic cutting member <NUM>.

<FIG> shows another step of the mold release wherein the mold component M2 is moved away from the shaft portion <NUM> of cutting member <NUM> in a direction orthogonal to the longitudinal axis. Further, the mold component M3 is moved relative to the shaft portion <NUM> of the cutting member to thereby release green cutting member <NUM> from the mold <NUM>. A typical mold <NUM> will also have ejector pins for pushing the green ceramic cutting member <NUM> from the mold. Such ejector pins are not shown in the drawings for convenience.

In another aspect of the disclosure referring to <FIG>, a multi-cavity ceramic injection mold <NUM>' can be fabricated to mold a plurality of cutting members <NUM>. The multi-cavity mold incorporates the mold release parting lines and release directions described above as shown in <FIG>. It can be seen that <FIG> show the single-cavity mold <NUM> in a "side view" relative to the cutting member <NUM> whereas <FIG> show the mold <NUM>' in a "top view" with respect to the green cutting members <NUM>. <FIG> is a sectional view through an exemplary four-cavity mold <NUM>' although such a mold can have from <NUM> to <NUM> or more mold cavities. In <FIG>, the mold component M2 and core pin CP1 (see <FIG>) are removed so the surface <NUM> of mold component M3 is shown with a sectional view of mold component M1. <FIG> shows core pins CP2 in sectional view with the cutting member <NUM> in an elevational top view. <FIG> shows how mold component M1 can be moved axially in alignment with the axis <NUM> of the cutting members <NUM> to release the mold component from the distal portion <NUM> of a plurality of ceramic cutting members <NUM> as described previously. Core pins CP2 are shown in a retracted position in <FIG>.

In general, an arthroscopic cutting member configured for ceramic injection molding comprises a cutting member <NUM> having a longitudinal axis <NUM> and a plurality of cutting edges <NUM> extending radially outwardly from an outer surface OS, wherein the cutting member is formed from a wear-resistant ceramic material and wherein each cutting edge is non-helical and aligned with the longitudinal axis to enable ceramic injection molding with a multi-component parting mold (see <FIG>, <FIG> and <FIG>).

Now referring to <FIG>, it can be seen that the cutting edge height A (<FIG>) and the cutting face surface area SA (see hatched area in <FIG> and <FIG>) relative to the cutter periphery diameter P is substantially less than that of the prior art metal burr as shown in <FIG>. As described above, the reduced height A of a ceramic cutting edge <NUM> (<FIG>) when combined with the non-dulling aspect of the ceramic edge <NUM> and the higher rotational speed allows for cutting bone at a faster rate than prior art metal burrs. As can be understood intuitively, the cutting edge height A and surface area SA (<FIG> and <FIG>) are the key factors that determine the size of bone chips and the cutting rate. In general, referring to <FIG>, the size of bone chips <NUM> typically is no larger in cross-section than the height A of cutting edge <NUM> as the elongated cutting surface does not result in elongated bone chips. Rather, the cross-sectional dimensions of bone chips <NUM> are essentially limited to the potential cutting depth (edge height A). Any elongated cut bone chips will fracture into smaller chips as schematically depicted in <FIG>. Since the non-dulling ceramic cutter <NUM> cuts bone at a very fast rate, there is a complementary need for fast, efficient bone chip evacuation through the window <NUM>. As outlined above, bone chips <NUM> are evacuated through window <NUM> into interior channel <NUM> of ceramic cutting member <NUM> (<FIG>) and the lumen <NUM> of the inner sleeve <NUM> (<FIG>) that communicates with negative pressure source <NUM>. The bone chips <NUM> are collected in a collection reservoir <NUM> (see <FIG>).

In one aspect of the disclosure, referring to <FIG>, <FIG> and <FIG>, the width WW of the window <NUM> is critically important for the efficient extraction of bone chips, with the window length WL being a suitable length, for example, at least equal to the window width WW. With the cutting member <NUM> rotating at <NUM>,<NUM> RPM, it has been found that window width WW is most critical in capturing and then suctioning bone chips <NUM> away from the treatment site. In the variation shown in <FIG> and <FIG>, the ratio between the width WW of window <NUM> relative to the cutting edge height A is at least <NUM>:<NUM> and often greater than <NUM>:<NUM>. This allows for bone chips to be rapidly suctioned into and through the window <NUM> and through interior passageway <NUM> of cutting member <NUM> in response to the negative pressure source <NUM>. Further, the diameter C of interior channel is large relative to the cutting edge height A (<FIG>) as will be described further below.

In another aspect of the disclosure, referring to <FIG> and <FIG>, the volume of bone chips <NUM> resulting from rotation of the cutting member <NUM> is a function of both the height A and length L of the cutting edges <NUM>. In other words, the surface area SA of a cutting edge face <NUM> or faces and the rotational speed are directly correlated to the cutting rate in grams/minute of bone removal. It can be easily understood that it is the cutting edge surface area SA that interfaces with bone and thus cuts a corresponding volume of bone chips. In this regard, the window area WA relative to a cutting edge surface area SA is an important functional metric for a ceramic cutter, and in the variation of <FIG>, the ratio of the window area WA to a cutting edge surface area SA is greater than <NUM>:<NUM>. In a typical prior art metal burr as shown in <FIG>, the window to edge surface area ratio is much less, for example about <NUM>:<NUM>. In another metric, if the aggregate surface area of all cutting edges were considered, a ceramic cutter with only <NUM> or <NUM> cutting edges would have a far higher ratio of window to cutting surface than that of a typical metal burr with <NUM> to <NUM> or more cutting edges.

Referring to <FIG> and <FIG>, in another aspect of the disclosure relating to extracting bone chips <NUM> from the treatment site, it can be seen that the diameter C of the interior channel <NUM> in the ceramic cutting member <NUM> is substantially larger than height A of the cutting edge <NUM>. In one variation of <FIG>, the ratio of the inner channel diameter C to the cutting edge height A is about <NUM>:<NUM>, and the scope of the disclosure includes such a ratio being at least <NUM>:<NUM>, at least <NUM>:<NUM> or at least <NUM>:<NUM>. In general, the cutting member comprises a wear resistant ceramic body carried by an elongate shaft, wherein the ceramic body has a plurality of cutting edges and flutes intermediate the cutting edges, and a window <NUM> in the cutting member open to an interior channel <NUM> that communicates with a lumen <NUM> in the shaft <NUM> wherein the ratio of the diameter C of the interior channel to the height A of the cutting faces is at least <NUM>:<NUM>. In this variation, each cutting edge <NUM> defines a cutting edge height A or face height measured from an outer cutting edge periphery diameter P to a flute bottom diameter or outer surface OS.

Referring to <FIG>, <FIG>, in another aspect of the disclosure, the diameter C of the interior channel <NUM> of the cutting member <NUM> is large relative to the outer periphery diameter P. The ratio of the interior channel diameter C to the outer periphery diameter P of the cutting edges <NUM> is at least <NUM>:<NUM>. In the variation of <FIG>, <FIG>, the ratio is <NUM>:<NUM>. In general, a ceramic cutter differs from a metal burr in that the height A of the cutting edges is small relative to the outer periphery diameter P and the interior channel diameter C for extracting bone chips is large relative to the outer periphery P. Thus, in one aspect of the disclosure, a cutting member has a longitudinal axis and a plurality of cutting edges extending radially outwardly from an outer surface OS thereof, a window <NUM> through the outer surface OS communicating with a longitudinal interior channel <NUM> therein, wherein the ratio of the outer surface diameter OS to the outer periphery diameter P of the cutting edges <NUM> is at least <NUM>:<NUM>, and wherein the ratio of the channel diameter C to the outer diameter P of the cutting edges <NUM> is at least <NUM>:<NUM>.

In another aspect of the disclosure, referring to <FIG>, the window <NUM> is configured to assist in the extraction of bone chips <NUM> during high-speed rotation in the cut-out <NUM> region of outer sleeve <NUM>. As can be seen in <FIG>, each window edge 185A, 185B has a sharp apex <NUM> and more importantly has a radial window rake angle WRA is non-zero and positive, (see <FIG>) and typically ranges from about <NUM>° to <NUM>° to capture bone chips <NUM> as the shaft portion <NUM> and window <NUM> rotate. In <FIG>, the high radial rake angle WRA (see <FIG>) of the window edge 185A and apex <NUM> are shown in assisting in the capture bone chips <NUM> in window <NUM> under the negative pressure in the window <NUM> provided by the negative pressure source <NUM>. In <FIG>, the sectional view schematically depicts that the outer edge or apex <NUM> of the window <NUM> can strike and deflect bone chips <NUM> inwardly into the interior channel <NUM>. In contrast, <FIG> illustrates a sectional view of the metal burr window <NUM>' of <FIG> under high-speed rotation. The prior art metal burr of <FIG> does not have a positive window radial rake angle, and in fact has a negative radial rate angle WRA' (<FIG>), so that bone chips <NUM> are struck by the window face <NUM> instead of a sharp outer edge with a positive rake angle as in the ceramic cutter <NUM> of <FIG>. In the prior art metal burr of <FIG> and <FIG>, the substantially negative radial rake angle of window face <NUM> is fabricated simply by grinding flat faces on the metal sleeve <NUM> in which the window <NUM> is formed.

In another aspect of the disclosure, the ceramic cutting member <NUM> of <FIG>, <FIG>, <FIG> and <FIG> has the distal edge of the window <NUM> positioned very close to the proximal end of the cutting edges <NUM>, for example less than <NUM> inch (<NUM>) or less than <NUM> inch (<NUM>). In prior metal burrs such as in the burr <NUM> of <FIG>, the aspiration window <NUM>' is necessarily positioned axially away from the cutting edges <NUM>' since the metal sleeve <NUM> need a distal portion configured for welding to the portion carrying the cutting edges.

Chart B below describes the various dimensions and ratios of the ceramic cutter <NUM> of <FIG>, <FIG>, <FIG> that were described above. This is one variation of a ceramic cutter <NUM> that has been tested extensively and operated at <NUM>,<NUM> RPM to cut bone.

As described above with reference to <FIG>, the three component ceramic injection mold <NUM> with multiple cavities can be used to fabricate the green ceramic cutting members <NUM> which then after being released from the mold can be sintered to provide the final product. In other variations of a ceramic injection mold, <FIG> show two component injection molds that can be used to mold the ceramic cutting member that can have from <NUM> to <NUM> non-helical cutting edges. <FIG> first illustrate a two component mold <NUM> that is configured to mold the ceramic cutting member <NUM> that has two cutting edges <NUM>. The cutting member <NUM> of <FIG> is very similar to the cutting member <NUM> of <FIG> above except for the number of cutting edges. As can be seen in <FIG>, the mold parting line <NUM> is on the centerline of the cutting member <NUM> so that each half of the mold (250A and 250B) can from both the shaft portion and distal cutting portion of the cutting member (cf. In this variation, there are no undercuts in the mold <NUM> so that a simple parting mold is possible. The core pins for the window and interior channel can be identical to those shown in <FIG>. An ejector pin for ejecting the green cutting member <NUM> from the mold <NUM> can be provided, but is not shown for convenience.

<FIG> show another two component injection mold <NUM> that can be used to mold a ceramic cutting member <NUM> with <NUM> cutting edges <NUM> that is virtually identical to the <NUM>-edge cutting member <NUM> of <FIG>, <FIG> and <FIG> above. This variation thus illustrates that a <NUM>-edge cutting member <NUM> can be made with a simple two component (one parting line) mold rather than the more complex three component (two parting lines) mold of <FIG>. As can be seen in <FIG>, it is necessary to configure the cutting member <NUM> with flat surfaces 288a and 288b so that there are no undercuts in the mold <NUM>. The parting line <NUM> is then can off-center. In <FIG>, it can be understood that the sides of the shaft portion with such flat surfaces 288a and 288b allow an upper mold component 295A to be released vertically as shown in <FIG> which would not be possible if the outer surface OS was not configured with the flat surfaces 288a and 288b. As shown in <FIG>, this variation of mold <NUM> allows the cutting member <NUM> having cutting edges <NUM> with zero radial rake angle to be released from the lower mold component 295B with a vertical and slight rotational movement indicated by the arrows. An ejector pin (not shown) for ejecting the green cutting member from the mold can be provided at an appropriate angle relative to the parting line <NUM> to push the green cutting member from the mold. This mold embodiment <NUM> can have core pins CP1 and CP2 as described in <FIG> to form the window <NUM> and the interior channel <NUM>. It can be further understood from <FIG> that a two component parting mold with a parting line on the center of the cutting member can be used to mold a four-edge cutting member.

As described above, several variations of ceramic cutter <NUM> have non-helical cutting edges. The non-helical edges allow for simplified ceramic injection molding. In another variation, a different type of injection mold <NUM> shown in <FIG> can be fabricated to allow for molding a cutting member <NUM> with helical cutting edges <NUM> and helical flutes <NUM>. <FIG> shows an injection mold <NUM> with three components that is similar to that of <FIG>. In this embodiment, the first and second mold components 315A and 315B are adapted to part as described previously around shaft portion <NUM> of the cutting members <NUM>. The third mold components indicated at 320A-320D are adapted to release from the green ceramic cutting members <NUM> by moving axially and rotationally (see <FIG>). In other words, the mold components 320A-320D are moved helically or effectively unscrewed from the cutting members <NUM>. This mold <NUM> has core pins CP1 and CP2 as described previously to form the window <NUM> and the interior channel <NUM> in the cutting members.

In general a method of the disclosure for fabricating a surgical cutting member of a ceramic material, comprises (i) providing an injection mold with a mold cavity defining outer surfaces of a cutting member having a longitudinal axis, a distal cutting portion with cutting edges, a proximal shaft portion with a window that opens to an interior channel in the ceramic member, (ii) injecting a flowable material comprising a ceramic into the mold cavity to provide a molded ceramic member, (iii) removing a first core pin which is configured to form the window, (iv) removing a second core pin which is configured to form the interior channel and (v) parting at least first and second mold components that define the outer surfaces of the cutting member to there by release the green cutting member from the mold. The method of fabrication further comprises sintering the released cutting member to provide a hardened cutting member.

In the method of fabrication described above, the first core pin is removed in a direction orthogonal to said longitudinal axis to form the window and the second core pin is removed in a direction aligned with said longitudinal axis to form the interior channel. Of particular interest, the core pin that forms the window is configured to provides window edges that have a sharp apex <NUM> and have a high positive window radial rake angle WRA, for example greater than <NUM>°. Typically, the window radial rake angle in the range of <NUM>° to <NUM>°, and extends from the outer surface OS to the open diameter C of the interior channel <NUM>, which dimension in one variation can be determined from Chart B above.

In the method of fabrication described above, one mold component is moved in a direction relative to the cutter body that is orthogonal to said longitudinal axis to release the cutter body. In a variation, another mold component may be moved in a direction relative to the cutter body that is aligned with said longitudinal axis thereof to release the cutting member body. In another variation, a mold component may be moved in a direction relative to the cutting member body that is helical to release the cutting member.

A further method of fabricating the cutting member includes the mold cavity forming a proximal shaft portion having a diameter ranging between <NUM> inch (<NUM>) and <NUM> inch (<NUM>). Another method of fabrication includes the mold cavity forming a distal cutting portion having an outer diameter ranging between <NUM> inch (<NUM>) and <NUM> inch (<NUM>). Another method of fabrication includes the mold cavity forming non-helical cutting edges. Another method of fabrication includes the mold cavity forming cutting edges aligned with the longitudinal axis of the cutting member. Another method of fabrication includes the mold cavity forming cutting edges with a radial rake angle ranging between <NUM>° and <NUM>°. Another method of fabrication includes the mold cavity forming cutting edges having a length ranging <NUM> inch (<NUM>) to <NUM> inch (<NUM>). Another method of fabrication includes a core pin forming the window with an area ranging from <NUM> sq. (<NUM><NUM>) to <NUM> sq. in (<NUM><NUM>). Another method of fabrication includes a core pin forming the interior channel with a mean cross-sectional width ranging from <NUM> inch (<NUM>) to <NUM> inch (<NUM>).

<FIG> is a schematic cross-sectional view of another mold <NUM> with two parting components 352A and 352B to form cutting member <NUM> and further showing a core pin <NUM> partially removed from the upper mold component 352B. The core pin <NUM> is configured with non-parallel side portions 358A and 358b that can be used to form window edges with a range of positive window radial rake angles WRA depending on the angle of the side portions 358a and 358b.

<FIG> is a schematic view of another mold <NUM> with two parting components 362A and 362B that shows a core pin <NUM> that extends through the ceramic cutting member <NUM> to provide windows 368A and 368B in both sides of the cutting member.

<FIG> is a longitudinal sectional view of another mold <NUM> with two parting components 372A and 372B configured to form cutting member <NUM>. In this a core pin is provided for forming a window <NUM> that is angled longitudinally relative to the axis <NUM> of the cutting member. Core pin <NUM> is configured for forming the interior channel in the cutting member.

<FIG> is a schematic top view of another mold <NUM> similar to those described above showing a ceramic cutting member <NUM> with a window <NUM> having non-parallel sides 388a and 388b which can be formed by a similarly shaped core pin. In this variation, the angled cutting edges 388a and 388b provide the advantage of shearing soft tissue captured in the window in a scissor-like manner as the angled window edges 388a and 338b progressively sweep past the lateral edges of the cut-out <NUM> in the outer sleeve <NUM> (see <FIG>).

<FIG> show another variation of ceramic cutting member <NUM> that is intentionally designed with rotational weight asymmetry in the distal cutting portion <NUM> thereof. As can be understood from <FIG>, the proximal shaft portion <NUM> of the cutter is asymmetric in cross-section due to the window <NUM> and thus does not have rotational weight symmetry. At high-speed rotation, for example <NUM>,<NUM> RPM or more, the weight asymmetry may cause a slight vibration or wobbling sensation in the handle by the operator's hand. To overcome the weight asymmetry in the proximal shaft portion <NUM>, the variation of <FIG> is configured with counter-balancing weight asymmetry in the distal cutting portion <NUM>. In one variation, the core pin CP1 as shown in <FIG> can be used to provide an off-center void <NUM> in the interior channel <NUM> within the distal cutting portion <NUM> as can be seen in <FIG>. In another variation of cutting member <NUM>' shown in <FIG>, the interior channel <NUM> can be off center through the proximal shaft portion <NUM> and the distal cutting portion to balance the cutting member <NUM>' relative to the central axis <NUM> of the overall cutting member.

Alternatively, another variation (not shown) can have a concavity or in the exterior surface, such as deeper flutes, in the ceramic body to provide the weight asymmetry in distal cutting portion to counter-balance the weight asymmetry in the proximal shaft portion caused by the window. In another variation (not shown), the cutting edges can be formed in various asymmetric radial positions to provide the desired weight asymmetry or the cutting edges thicknesses can vary to provide the desired weight asymmetry. In another variation, more than one of the features described above may be used to achieve the targeted weight asymmetry.

Now turning to <FIG>, another variation of an arthroscopic probe and ceramic cutter <NUM> is shown wherein the proximal probe hub and shaft are similar to the embodiment of <FIG>. In this variation, ceramic cutter <NUM> can be similar to that of <FIG> and <FIG>, except that the ceramic cutter also carries an active electrode <NUM> (<FIG>) which is similar to the embodiments described in commonly-owned <CIT> titled "Arthroscopic Devices and Methods". <FIG> shows the outer sleeve <NUM> with an inner sleeve <NUM> that carries the ceramic cutter <NUM>. The ceramic cutter <NUM> in this variation has three cutting edges <NUM>. A window <NUM> is provided in the ceramic cutter <NUM> that communicates with a aspiration channel <NUM> in the cutter and probe. <FIG> shows the inner sleeve <NUM> in the ceramic cutter <NUM> rotated <NUM>° which shows active electrode <NUM> disposed between two cutting edges <NUM>.

The inner sleeve <NUM> can comprise conductive metal that carries current to the electrode <NUM>. The outer sleeve <NUM> carries a return electrode indicated at <NUM>. In use, RF current delivery flows from the active electrode <NUM> to the return electrode <NUM> and is adapted to ignite plasma around the active electrode <NUM>. It can be understood that when electrode arrangement is energized while submerged in a conductive fluid (e.g., saline), a plasma will be ignited and reach very high temperatures about the active electrode <NUM>.

As described above, in order for the ceramic cutter <NUM> to perform both soft tissue cutting and bone cutting, it is critical that the ceramic material have superior hardness and fracture toughness characteristics. When using an RF electrode carried by the ceramic cutter <NUM> to provide an ablation mode in addition to soft and hard tissue cutting, it has been found that additional stresses, particularly thermal stresses, are put upon the ceramic cutter <NUM>. It can be understood that when the active RF electrode is energized in an ablation mode, a plasma is ignited about the electrode <NUM> in a close interface with the ceramic material wherein the plasma can be very hot. The fact that the probe working end and ceramic cutter <NUM> are submerged in a saline is not a factor as the plasma occurs as the saline is vaporized. In conventional RF devices, there are known common, ceramic material that can withstand high temperatures associated with RF plasma. However, it has been found such common ceramics do not provide the hardness and fracture toughness characteristics needed for cutting edges in an arthroscopic tools. Thus, new ceramic formulations have been evaluated and developed to meet the requirements of (i) fracture toughness to hardness for soft and hard tissue cutting, and (ii) resisting thermal stresses caused by RF plasma formation that interfaces with a surface of a ceramic cutter <NUM> as shown in <FIG>.

In one variation, it has been found that a ceramic formulation of ATZ (alumina-toughened zirconia) can be meet the above stated requirements, but only if very specific properties of the ceramic material are tightly controlled in the fabrication of the ceramic powder constituents and thereafter in molding the ceramic cutter.

In a first aspect, it has been found that the ceramic composition must have a very small grain size, and further, that the grain shape cannot be rod-like or elongated. Rather, the grain shape must be rounded. In the general ceramic types described above in Chart A, the grain size and shape was not specified. It was found that such general ceramic types are typically formulated with elongated or rod-like grain shapes which are believed to enhance fracture toughness. However, it has been found that such elongated grain shapes are a negative factor for resisting thermal stresses on the molded ceramic.

In one specific ceramic formulation , the ATZ or ceramic composite includes alumina and zirconia, wherein the alumina has a grain size ranging between <NUM>-<NUM> micrometers and the zirconia has a grain size ranging between <NUM>-<NUM> micrometer. Further, the grain shape of both the alumina and zirconia is not elongated or rod-like. The grain shapes are round or rounded particles with a mean cross-sectional dimension that is similar in all directions. In general, a medical device corresponding to the disclosure comprises an elongated sleeve having a longitudinal axis, a proximal end and a distal end, a cutting member with cutting edges extending distally from the distal end of the elongated sleeve, said cutting member formed of a ceramic composite including alumina and zirconia, wherein the alumina has a grain size ranging between <NUM>-<NUM> micrometers and the zirconia has a grain size ranging between <NUM>-<NUM> micrometer, and a motor configured to couple to the proximal end of the sleeve to rotate the cutting member <NUM> as depicted in <FIG>. Further, the ceramic cutting member <NUM> can carry an active electrode that is coupled to an RF source.

In another specific aspect, ceramic composite material of the cutter body has a fracture toughness of at least <NUM> MPam<NUM>/<NUM>. In another aspect, the ceramic composite has a thermal expansion coefficient ranging from <NUM> to <NUM> ppm/°C.

In another specific variation, the ceramic composite has at least <NUM> wt% of alumina. In another variation, the ceramic composite has at least <NUM> wt% of zirconia. In yet another variation, the ceramic composite has less than <NUM> wt% of cerium. In another specific variation, the ceramic composite has a bulk density ranging from <NUM> to <NUM>. Further, the ceramic composite has a flexural strength the least <NUM>,<NUM> MPa.

The key parameters of one variation of suitable ATZ are found in Chart C below.

Referring back to <FIG>, it can be seen that the electrode is disposed between cutting edges of the cutting member <NUM>. Further, the cutting member <NUM> has at least one window <NUM> therein as described previously which opens to an interior extraction or aspiration channel <NUM> extending through the probe shaft to a negative pressure source.

In general, an arthroscopic probe corresponding to the disclosure comprises an elongated sleeve <NUM> having a longitudinal axis, a proximal end and a distal end a cutting member <NUM> with cutting edges extending distally from the distal end of the elongated sleeve, the cutting member <NUM> being formed of a ceramic composite including alumina and zirconia wherein the grain shape of the alumina is substantially round with a diameter ranging between <NUM>-<NUM> micrometers wherein the grain shape of the zirconia is substantially round with a diameter ranging between <NUM>-<NUM> micrometer, and a motor configured to couple to the proximal end of the sleeve <NUM> to rotate the cutting member <NUM>. Further, the ceramic composite comprises <NUM>-<NUM> wt% of alumina, <NUM>-<NUM> wt% of zirconia and less than <NUM> wt% of cerium.

Although particular embodiments of the present invention have been described above in detail, it will be understood that this description is merely for purposes of illustration and the above description is not exhaustive. Specific features of the invention are shown in some drawings and not in others, and this is for convenience only and any feature may be combined with another in accordance with the invention. A number of variations and alternatives will be apparent to one having ordinary skills in the art. Such alternatives and variations are intended to be included within the scope of the claims. Particular features that are presented in dependent claims can be combined and fall within the scope of the invention. The invention also encompasses embodiments as if dependent claims were alternatively written in a multiple dependent claim format with reference to other independent claims.

The use of the terms "a" and "an" and "the" and similar referents in the context of the present disclosure (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The term "connected" is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate embodiments of the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the claimed invention.

Claim 1:
A cutting member for use in a rotational arthroscopic cutting device, said cutting member comprising:
a ceramic body (<NUM>; <NUM>; <NUM>) having cutting edges (<NUM>; 388a and 388b; <NUM>), said cutting body (<NUM>; <NUM>; <NUM>) formed of a ceramic composite including alumina and zirconia characterized in that the alumina has a grain size ranging between <NUM> micrometer- <NUM> micrometers and the zirconia has a grain size ranging between <NUM> micrometer- <NUM> micrometer, and that the ceramic composite comprises <NUM>-<NUM> wt% of alumina, <NUM>-<NUM> wt% of zirconia and less than <NUM> wt% of cerium.