Cutting blade assembly for an arthroscopic surgical instrument drive system
This application is a continuation of application Ser. No. 07/437,270 filed Dec. 4, 1989, now U.S. Pat. No. 5,269,794 which is a division of application Ser. No. 07/016,140, filed Feb. 18, 1987, now U.S. Pat. No. 5,217,478. The entire disclosures from those applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to surgical instruments and, more particularly, to instruments having rotatable motor-driven arthroscopic cutting blades capable of removing fibrous tissue lying between articulate surfaces in and around joints of the body. In addition, the instrument of the present invention can be used to balance meniscal rims and to evacuate excised tissue. 
     2. Discussion of the Prior Art 
     A typical prior art arthroscopic surgical instrument is disclosed in U.S. Pat. Nos. 4,203,444 (Bonnell et al) and 4,274,414 (Johnson et al). The disclosed instruments are elongated handpieces serving as a housing for a motor which rotatably drives a cutting blade projecting longitudinally from the forward end of the handpiece. The blade is disposed in an apertured sheath or outer tube through which excised tissue material is aspirated via suction applied through the handpiece. Controls for the motor (i.e., on/off, speed control, etc.) are located at a console and connected to the motor via a cable interconnecting the console with the handpiece. 
     Surgical instruments of the type described must be fabricated of material capable of withstanding autoclave temperatures (i.e., in excess of 270 degrees Fahrenheit) so that the instrument may be sterilized between surgical procedures. It is recognized in the prior art that cutting blades may be designed to be disposable (i.e., the blades are used for a single procedure and then discarded) so as to avoid the requirement of blade sterilization between procedures. However, the handpiece and the components housed therein must be repeatedly sterilized. On the other hand, the control console, which houses electrical circuitry and controls, is not required to be sterilized between uses. As a consequence, a surgeon cannot operate the console controls during a surgical procedure and must rely on an assistant to do so. 
     It is also recognized in the prior art that certain cutting blades, designed for specific types of surgical procedures, operate optimally within specified ranges of rotational speed. In some commercially-available systems a switch is provided on the control console to permit the operator to select a speed range that is consistent with the cutting blade to be used. A further control at the console permits the operator to select the desired speed within the selected range. A more recent development (made commercially available by Dyonics, Inc., of Andover, Mass. as the &#34;Advanced Arthroscopic Surgical System&#34;) automatically sets the speed range appropriate for the selected cutting blade. This is achieved by providing three different cutting blade adapters (i.e., one adapter for each of the possible speed ranges) by which the cutting blade may be operably engaged with the handpiece. The adapters are coded for the desired speed range by means of one or more magnets at specified locations in the adapters. Reed switches in the handpiece are actuated by respective magnets and transmit the speed range control code information to the console to establish the correct speed range. A manual control at the console permits selection of particular speeds within the established range. 
     As noted above, prior art instruments of the type described have controls at the console which cannot be operated by the surgeon during a procedure without compromising sterilization. It is desirable, therefore, to provide all of the controls on the handpiece. However, there are a number of obstacles which have precluded placing the controls on the handpiece. Specifically, the entire handpiece must be capable of withstanding the temperatures experienced in an autoclave during sterilization In addition, the controls should not increase the bulk of the handpiece, particularly in its transverse dimension, since increased bulk renders the handpiece unwieldy to manipulate during surgical procedures. Finally, the controls must be located in a convenient manner so as to permit the surgeon to quickly and easily operate each control, preferably with the one hand that holds the handpiece. Prior to the present invention, the prior art has been unable to overcome this combination of obstacles. 
     In addition, although it is desirable to provide for automatic setting of speed ranges to optimize specific blade operation, the prior art approach has certain disadvantages. In particular, the coded adapter is an additional part of the system which must be capable of withstanding autoclaving temperatures. Consequently, the adapter is relatively heavy and adds significantly to the overall weight of the handpiece. This adversely affects manipulability of the handpiece during surgical procedures. It is desirable, therefore, to provide for automatic speed range selection while eliminating the extra adapter part. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a surgical instrument of the type described wherein controls are provided at the handpiece to permit the entire operation of the instrument to be controlled from the handpiece without adding significant weight or volume to the handpiece. 
     It is another object of the present invention to provide a surgical instrument of the type described which includes automatic speed range selection without requiring a separate adapter part for connecting the cutting blade to the handpiece. 
     A further object of the invention is to provide a disposable cutting blade for a surgical instrument of the type described, which blade can be used with both the handpiece of the present invention and with the above-described prior art instruments having speed range adapters for connecting the blade to the handpiece. 
     It is yet another object of the present invention to provide a switch cluster on a handpiece of an arthroscopic surgical instrument wherein the cluster does not project transversely significantly beyond the contour of the handpiece, wherein the individual switches in the cluster are oriented to be easily accessed by the surgeon&#39;s hand in which the handpiece is held, and wherein the switch cluster and associated circuit in the handpiece are capable of withstanding autoclave temperatures. 
     A still further object of the present invention is to provide a surgical instrument of the type described wherein automatic setting of the optimal speed range for each disposable cutting blade is achieved by coding the disposable cutting blades themselves rather than by employing a separate coded and reusable adapter part for connecting the cutting blade to the handpiece. 
     In accordance with the present invention an arthroscopic surgical instrument can be controlled from a switch cluster located proximate the forward end of a handpiece. The switch cluster includes a plurality of pushbutton switches and is arrayed arcuately to correspond to the curvature of the handpiece periphery. An arcuate printed circuit board is disposed within the handpiece and closely spaced from the switch cluster so that actuation of each switch bridges a corresponding pair of printed circuit contacts. Both the arcuate switch cluster and the arcuate printed circuit board are constructed to withstand autoclave temperatures to which the entire handpiece assembly is subjected when sterilized. Importantly, the small radius of curvature required for the printed circuit board renders the choice of material of paramount importance in order to prevent the board from becoming brittle when exposed to autoclaving temperatures. 
     The switch cluster includes four pushbuttons for: (1) controlling motor direction; (2) increasing motor speed; (3) decreasing motor speed; and (4) actuating and deactuating the motor (i.e., on/off). In the optimum arrangement, switches (1), (2) and (3) are disposed proximate the forward end of the handpiece and are aligned along an arcuate path extending along the handpiece circumference. The on/off switch (4) is disposed immediately longitudinally behind the other three switches and is elongated arcuately. The surgeon can actuate each of the switches using a single finger of the hand in which the handpiece is supported. The arcuately elongated on/off switch permits the motor to be rapidly deactuated with minimal movement of the surgeon&#39;s actuation finger. 
     In order to automatically select the optimal motor speed range for each cutting blade, mutually interactive coding and decoding elements are disposed directly in the cutting blade and the handpiece, respectively. In the preferred embodiment, magnets are disposed in the cutting blade and reed switches are disposed in the handpiece to effect automatic speed range control in a manner similar to the prior art described above; however, and importantly, control is effected without the need for an extra adapter part. An advantage of the magnet and reed switch arrangement is that it permits the cutting blades to be usable with the handpiece of the present invention while also mechanically fitting into the adapter of the prior art handpiece. However, other cutting blade-handpiece coding arrangements may be employed, such as: mechanical projections on the cutting blade hubs positioned to actuate respective pressure-sealed switches in the handpiece; projections on the blade hubs blocking respective light paths in light-actuated circuits in the handpiece; etc. Whichever coding arrangement is used, the sensing components in the handpiece must be sealed so as not to be damaged during autoclaving. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of a specific embodiment thereof, especially when taken in conjunction with the accompanying drawings wherein like reference numerals in the various figures are utilized to designate like components, and wherein: 
     FIG. 1 is a view in perspective of a control console and handpiece unit of a preferred embodiment of the present invention; 
     FIG. 2 is a view in elevation of the front panel of the control console of FIG. 1; 
     FIG. 3 is a side view in elevation of the handpiece unit of FIG. 1; 
     FIG. 4 is a top view in plan of the handpiece unit of FIG. 3; 
     FIG. 5 is an end view in elevation of the handpiece unit of FIG. 3; 
     FIG. 6 is a view in longitudinal section taken along lines 6--6 of FIG. 5; 
     FIG. 6A is a view in transverse section taken along lines FIG. 6A--6A of FIG. 3; 
     FIG. 7 is a view of the rearward-facing surface of the locking ring secured to the handpiece unit as viewed along lines 7--7 of FIG. 6; 
     FIG. 8 is a view in section of the locking ring taken along lines 8--8 of FIG. 7; 
     FIG. 9 is an exploded side view in elevation and partial section of a cutting blade assembly employed in conjunction with the handpiece unit of FIG. 6; 
     FIG. 10 is a diagramatic illustration of the manner in which the speed range coding of a cutting blade is detected by the handpiece unit in accordance with the principles of the present invention; 
     FIG. 11 is a view in longitudinal section of a reed switch employed in the handpiece unit to detect magnetic speed range coding present in cutting blade assemblies inserted into the handpiece; 
     FIG. 12 is a top view in plan of the control switch cluster provided on the handpiece unit of the present invention; 
     FIG. 13 is a view in transverse section taken along lines 13--13 of FIG. 12 and showing three of the control switches provided as part of the control switch cluster; 
     FIG. 14 is a view in perspective of the printed circuit board employed as part of the switch cluster assembly in the handpiece; 
     FIG. 15 is a view in transverse section taken along lines 15--15 of FIG. 12 and showing a fourth switch provided as part of the handpiece switch cluster; 
     FIG. 16 is a view in section of the cutting blade assembly taken along lines 16--16 of FIG. 9; 
     FIG. 17 is a view similar to that of FIG. 16 for a different cutting blade assembly coded to have a different optimal operating speed than the cutting blade assembly illustrated in FIG. 16; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring specifically to FIG. 1 of the accompanying drawings, a surgical instrument constructed according to the present invention includes a control console 10 electrically interconnected to a surgical handpiece 11 via a flexible drive unit cable 12. Cable 12 terminates at one end in a plural-conductor connector (not shown) that is received in a receptacle (not shown) secured at the rear or side of console 10. The other end of cable 12 terminates in an end cap 13 located at the proximal or rearward end of the handpiece 11. Also extending from the handpiece end cap 13 is a suction tube 14 that communicates with the handpiece interior and serves, in a conventional manner, to conduct fluid from the handpiece to a vacuum source (not shown). Typically, a control valve is disposed in the suction line intermediate tube 14 and the vacuum source to provide control over the aspiration of fluid from the surgical site and through the handpiece interior. A cutting blade 15 projects from a locking ring 16 disposed at the forward or distal end of the handpiece 11. The handpiece is generally cylindrical and the cutting blade is oriented to project substantially coaxially along the central longitudinal axis of the locking ring 16. A cluster 17 of control switches is disposed in an arcuate array proximate the forward end of the handpiece 11, the cluster being curved to correspond to the circumferential profile of the handpiece. 
     As illustrated in greater detail in FIG. 2, control console 10 has a front panel 20 with a number of controls and indicators. Specifically, a mains power switch 21 of the rocker type permits application and removal of primary power to and from the system. Lighted switches 22 and 23 actuate the blade drive motor in the handpiece 11. If the continuous switch 22 is pressed and released, the drive motor rotates and the switch lights; if the switch is pressed and released again, the motor stops and the switch light is turned off. If the touch switch 23 is held depressed, the motor rotates and the switch lights; release of the switch stops the motor and turns off the switch light. 
     The blade rotation switches 24 and 25 control the rotation direction of the motor. When the OSC switch 24 is pressed and released, the motor changes rotation directions at pre-set intervals and the switch is lighted; the NORM switch 25 is unlighted. When the NORM switch 25 is pressed and released, the motor rotates in the direction selected at switch cluster 17 in the handpiece (as described below) and the switch is lighted; the OSC switch 26 remains unlighted. 
     The drive mode indicators 26, 27 and 28 are lighted to indicate when a respective motor speed range has been automatically established by the particular cutting blade 15 inserted into the handpiece (in the manner described below). The high indicator 26 lights when a high speed burr blade is inserted into the handpiece. The medium indicator 27 lights when a medium speed blade is inserted into the handpiece. The low indicator 26 lights when no blade or a low speed blade is inserted into the handpiece. In the preferred embodiment disclosed herein, the high speed range extends between 1500 and 2500 rpm; the medium range extends between 500 and 900 rpm; and the low speed range extends between 75 and 400 rpm. Indicators 26, 27 and 28 are preferably bordered in different colors corresponding to the color of the blade resulting in the automatic selection of the indicated range. 
     The maximum speed display 29 is a four-digit light-emitting diode (LED) display for the upper limit of the speed range currently in force. The minimum speed display 31 is a four-digit LED display for the lower limit of the speed range currently in force. The RPM range LED bar display 30 indicates the relative motor speed between the displayed minimum and maximum limits and is in the form of a lighted bar having a vertical dimension which increases with increasing motor speed. The maximum and minimum displays 29 and 31 are vertically spaced, and the range display 30 is disposed therebetween to present the range indication in a position permitting an observer to easily estimate, from the bar display, the location of the actual speed within the selected operating range. An RPM digital display 32 is a four-digit LED display of the actual motor speed. It must be noted that the word &#34;actual&#34; employed above to describe the speed display on bar display 30 and by digital display 32 is a misnomer. The information from which these displays are derived is the control input information originating at the console 10 and applied, by electrical signal, to the motor in the handpiece 11. In other words, the display does not reflect the measured rotational speed of the motor. However, the response of the motor to the control signal is known with sufficient accuracy to permit the control information to serve as the source of the motor speed display within the precision requirements of the system. 
     Indicators 33, 34 and 35 are individually illuminated status indicators. The reverse indicator 33 is illuminated when the reverse motor direction is selected at switch cluster 17 at handpiece 11; this indicator flashes on and off when the motor is rotating in reverse direction. The forward indicator 34 is illuminated when the forward motor direction is selected at switch cluster 17; this indicator also flashes when the motor is rotating in the forward direction. The footswitch indicator is illuminated when a separate foot-controlled switch (not shown) is connected to console 10. When the footswitch is so connected, the on/off, forward and reverse control switches at switch cluster 17 at the handpiece are inhibited. 
     Handpiece 11 is illustrated in detail in FIGS. 3-8 to which specific reference is now made. Handpiece unit 11 includes an integrally formed lightweight metal body member 40 of generally cylindrical configuration. Body member 40 is sealed at its rearward end by end cap 13 and at its forward end by locking ring 16. A slightly radially enlarged flange 42 terminates the rearward end of body member 40 as best illustrated in FIGS. 6 and 6a. The forward portion 41 of body member 40 occupies approximately twenty percent of the length of that member and is cylindrical with a somewhat larger outer-diameter than the remainder of the length of body member 40. Typically, for a body member 40 having a length of 6.57 inches, the outer diameter of forward section 41 would be 13/8 inches, while the outer diameter of the remainder of the body member 40 would be 1.2 inches. However, forward section 41 is not disposed coaxially with respect to the remainder of body member 40. In this regard, it is helpful to consider body member 40 as having a top side and a bottom side. The top side (which is seen in plan in FIG. 4 and appears as extending along the top of the body member in FIGS. 3 and 6), is considered to be angularly centered on the line which divides switch cluster 17 into two equal transverse halves and extends longitudinally along the outside of member 40. The bottom side of body member 40 is located diametrically opposed to the top side. As best illustrated in FIGS. 3 and 6, the top side of forward section 41 is longitudinally continuous (i.e., forming a straight line) with the top side of the remainder of body member 40. At all other angular positions about the body member, forward section 41 is transversely larger than the rest of the body member 40. The transverse dimensional difference between forward section 41 and the rest of body member 40 increases with angular displacement from the top side of the bottom member to a maximum difference occurring at the bottom side of the member. The transition between forward section 41 and the rest of body member 40 takes the form of a chamfered surface 43 subtending an angle of approximately 45° with the longitudinal dimension of body member 40. The overall effect of the enlarged forward section 41 is a barrelled-out portion of the body member at its forward end. 
     As best illustrated in FIG. 6, a longitudinally-extending cylindrical bore 44, having a series of sections of different diameter, is defined entirely through body member 40. Bore 44 is concentrically disposed within forward section 41 but is displaced closer to the bottom of the remainder of body member 40. A rearward section 45 of bore 44 serves to house the drive motor for the unit and, in the described embodiment, is typically 4.475 inches long and has a diameter of 0.805 inches. Immediately forward of bore section 45 is a shorter section 46 of smaller diameter in which the motor drive shaft engages the cutting blade. Bore section 46, in the disclosed embodiment, is typically 0.805 inches long with a diameter of 0.565 inches. The next forward bore section 47 serves as an aspirator communication compartment and, in the disclosed embodiment, is typically 0.500 inches long and 0.750 inches in diameter. A short section 48 (i.e., typically 0.060 inches long, 0.565 inches in diameter) separates the aspiration communication chamber 47 from a housing section for an O-ring 49. The O-ring housing section is typically 0.110 inches long and 0.750 inches in diameter. Finally, the forward-most bore section 50 serves to receive the hub of the cutting blade. Bore section 50 is typically 0.620 inches long and 0.565 inches in diameter. The transitions between all bore sections are annular shoulders. 
     The motor assembly includes a cylindrical motor 51 disposed in bore section 45 and from which a rotatably driven pin 52 projects longitudinally in a forward direction into a hollow cylindrical spacer 55. Spacer 55 remains stationary and has a hollow cylindrical drive tube 56 disposed concentrically therein. Drive tube 56 is welded, tightly fit, or otherwise secured about driven pin 52 in radially spaced relation to spacer 55. Driven pin 52 has a generally rectangular transverse cross-section and is engaged in a bifurcated rearward end 53 of a drive shaft 54 which is also received in and secured to drive tube 56. Thus, when the motor is actuated, driven pin 52 is rotated and rotatably drives the drive tube 56 and drive shaft 54. A stationary bearing housing 57 is disposed immediately forward of spacer 55 to provide a bearing support for the rotatable drive shaft extending therethrough. A plurality of O-rings 58, 59 are disposed about bearing housing 57 and serve as pressure seals in a longitudinal direction in bore section 45. Additional pressure sealing is provided by a gasket 60 disposed adjacent the annular shoulder demarcating the transition between bore sections 45 and 46 and adjacent which the forward-facing end of bearing housing 57 is forcefully urged. In this regard, the housing for motor 51 is provided with a pair of diametrically opposed apertures 61 proximate the rearward end of the motor so that pins (not shown) can be inserted transversely through suitably provided openings in the handpiece body member 40 to lock the motor assembly in place against gasket 60. 
     The forward end of drive shaft 54 projects into bore section 46 wherein it receives a drive tang 72, projecting from the rearward end of the cutting blade, in rotatably drivable engagement. The cutting blade assembly is illustrated in greater detail in FIGS. 9, 16 and 17 to which specific reference is now made. The cutting blade assembly includes an outer member 70 and an inner member 71. The inner member includes a tube 74 with a distal cutting end 73 which, in the illustrated embodiment, is an arthroplasty burr, although other blade types (such as meniscal open end, meniscal side cutter, end cutter, trimmer, meniscus cutter, synovial resector, and full radius resector) may be employed. Each cutting blade tube 74 is hollow and has an opening 75 proximate the distal end 73 to admit excised tissue aspirated from the surgical site in response to suction applied at the proximal end of the tube. The proximal end 76 of tube 74 is disposed in a molded member having a frusto-conical forward section 78, a hollow intermediate section 77 and a rearward section comprising the drive tang 72. A bore extends transversely through the intermediate section 77 which is recessed to a reduced radial dimension at the bore openings 79. The proximal end 76 of the hollow cutting blade tube 74 communicates with this bore so that aspirated material received in tube 74 can flow out of the cutting blade through bore openings 79. Drive tang 72 is received in a cup-like spring retainer member 80 that is open at both ends. Spring retainer member 80 has an annular lip projecting radially inward at its forward end and adapted to engage a radially outward projecting lip on the rearward section of the molded member from which drive tang 72 extends. The molded member, including sections 78, 77 and 72, and spring retainer 80 are preferably made of plastic so that the spring retainer can be forced into place on the molded member into a position whereby the two lips prevent mutual disengagement. A helical spring 81 is disposed inside spring retainer 80 to surround the drive tang 72 and serve to bias the rearward end of the spring retainer away from the blade. In this manner, spring 81 urges the two annular lips axially against one another in the absence of any axial force in opposition to the spring. Whereas tube 74 and burr 73 are made of metal (preferably stainless steel), the remainder of the inner member 71 is preferably made of plastic. 
     Outer member 70 includes a hollow metal (preferably stainless steel) tube 82 having an inside diameter which is larger than the outside diameter of tube 74 in inner member 71. The length of tube 82 is such that the distal end of tube 74, including the cutting blade 73 and opening 75, project through, the open distal end of tube 82 when inner member 71 is inserted into and through inner member 70 in the manner described below. In this regard, the inner and outer members are conventional. Tube 82 extends through a hollow hub preferably made of plastic material and having a short hollow frusto-conical forward end 83 formed integrally with a cylindrical section 84 having an annular rearward-facing surface that is ultrasonically welded or otherwise sealingly disposed against a fixed forward-facing annular surface 85 of a hollow cylindrical section 86. Immediately rearward of hollow section 86 is a hollow cylindrical section 87 of reduced outer diameter. A proximal end section 88 of the hub takes the form of a hollow cylinder with an outer diameter corresponding to that of sections 86 and 84. A central bore 89 extends longitudinally through the integrally formed molded plastic sections 86, 87 and 88 and is generally cylindrical except at its proximal end where it has a frusto-conical contour 90 to receive the frusto-conical section 78 of the inner member 71. Bore 89 is sized to permit tube 74 to extend therethrough, and through a similar aligned bore in sections 83 and 84, into tube 82. The cutting blade, when thusly assembled, has the forward-facing annular shoulder of section 77 of the inner member 71 disposed proximate the rearward-facing proximal end of rearward section 88 of outer member 70. The arrangement permits the inner member 70 to rotate within outer member 70 about the axis of tube 74. 
     As best illustrated in FIGS. 16 and 17, one or more cylindrical recesses 91 are defined in hub section 86 at the forward-facing surface 85. The number of such recesses 91 provided for any given cutting blade depends upon the optimal rotational speed range for that blade. Specifically, there are three possible speed ranges in the system of the preferred embodiment, although it will be apparent that any number of speed ranges may be designed into the system. For low speed blades, hub section 86 has no recesses defined in surface 85. For medium speed blades, hub section 86 has one recess 91 defined therein at a location radially spaced from the central bore 89 (as illustrated in FIG. 16). For high speed blades, hub 86 has two recesses 91 disposed symmetrically on opposite sides of the central bore 89 (as illustrated in FIGS. 17). Each recess 91 receives a magnet 92 that serves as a coding element for the blade. The material from which the hub is fabricated must be such as to permit the magnetic field of magnets 92 to be sensed in handpiece 11 when the cutting blade is inserted therein (in the manner described below). In order to assure proper orientation of magnet 92 in the handpiece, hub section 86 is formed with a locator stub 93 projecting a short distance radially outward from section 86 at a prescribed annular location on the hub circumference. Specifically, stub 93 is displaced 90° from each of the two possible angular orientations of recesses 91. 
     Referring again to FIGS. 3-8, locking ring 16 is provided with a central aperture 101 extending longitudinally therethrough and aligned with bore section 50 in body member 40. The diameters of aperture 101 and bore section 50 are slightly greater than the diameter of hub sections 86 and 88 and spring retainer 80. Locator stub 93 in hub sections 86, however, projects radially beyond the boundary of aperture 101 and bore section 50. In order to permit the cutting blade assembly to be accommodated into the handpiece through aperture 101, a radially-extending slot 102 is defined in locking ring 16 at the periphery of aperture 101. A corresponding radially-extending slot 103 is disposed at the periphery of bore section 50 and is sized to permit locator stub 93 to be received therein when the cutting blade assembly is inserted into the handpiece in the manner described below. 
     As best illustrated in FIG. 10, the forward-facing end surface 104 of body member 40 is provided with two generally cylindrically recesses 105, 106 disposed on diametrically opposite sides of bore section 50 and radially spaced from that bore section. Recesses 105 and 106 are spaced on opposite sides and 90° from slot 103, and each has a generally cylindrical reed switch assembly 107 disposed therein. Reed switch assembly 107, which is illustrated in greater detail in FIG. 11, includes a pair of normally open switch contacts 108, 109 embedded in a glass capsule 12 or potting compound, along with respective lead wires 110, 111 which are insulated and extend from the rearward end of the capsule. The reed switches are oriented to sense the presence of respective magnets 93 in the blade assembly hub so as to register the coded information from the inserted blade. This information, in the form of open/closed conditions of contacts 108, 109, is transmitted to the control circuity in the console 10 via wires 110, 111. The insulated wires 110, 111 at the rear of the reed switch assembly pass into respective recesses 105, 106 and through respective obliquely oriented wire-conducting channels 113, 114. These channels terminate in a generally rectangular recessed space 115 in the top side of forward section 41, immediately below the switch cluster 17 and its associated printed circuit board 116. The rear wall of recess 115 opens to a channel 117 that runs rearwardly for the remaining length of body member 40. Channel 117 conducts reed switch wires 110, 111 and wires from printed circuit board 116 to the rearward end of body member 40 where the wires form part of cable 12 along with the wires connected to motor 51. The wires in cable 12 conduct signals to and from the circuitry in the control console. 
     A bore 118 extends from the forward end of surface 104 of body member 40 into recess 115. Bore 118 is used during assembly of the handpiece unit as an access opening for potting compound. Once sufficient potting compound has been delivered into the handpiece, bore 118 is sealed by a set screw 119 and additional compound. 
     Referring again to FIG. 6, an aspiration path for excised tissue material flowing through hollow tube 74 FIGS. 5 and 9 and out through bore openings 79 in the cutting blade is provided via widened bore section 47. Specifically, when the cutting blade assembly is properly inserted into the handpiece, section 77 of the molded part of the inner blade member 71 is disposed within bore section 44. Openings 79 are clear from the bore walls to permit aspirated material to flow into bore section 47 and through an oblique channel 120 extending both rearwardly and toward the top side of body member 40 until terminating in a suction channel 121. This suction channel extends rearwardly in parallel spaced relation to wire channel 117 until reaching the rearward end of body member 40 where it communicates, via end cap 13, with suction tube 14. As described above, the suction tube 14 communicates with a source of suction pressure (not shown) via a control valve (not shown) to permit selective aspiration from the surgical site. The O-ring 49 disposed in bore section 48 surrounds hub section 86 of the cutting blade assembly to provide a pressure seal forwardly of the aspiration chamber formed by bore section 44. Gasket 60 and O-rings 58, 59 provide pressure seals rearwardly of the aspiration chamber. 
     Locking ring 16 is a generally cylindrical member having an exposed forward-facing surface 130 and a rearward-facing surface 131 abutting surface 104 of body member 40. The locking ring is made of metal and includes a raised annular lip surrounding surface 131 and extending over a short length of the body member 40. A circular recess 132 in surface 130 is disposed concentrically about aperture 101. Arcuate channels 133, 134 are defined through the locking ring within recess 132. Channels 133 and 134 are equally spaced from slot 102 and are disposed symmetrically about aperture 101. Each channel subtends approximately 90° of arc at a constant radial distance from the center of aperture 101. A disc-shaped spacer 135 is disposed in recess 132 and is provided with a central aperture 140, aligned with aperture 101, and with two screw holes spaced by 180° and aligned with corresponding tapped bores in forward end surface 104 of body member 40. Screws 136, 137 pass through the screw holes and are threadedly engaged in the tapped bores to secure spacer 135 to body member 40. These screws pass through respective channels 134, 133 to permit locking ring 16 to be rotated relative to spacer 135 and body member 40. Such rotation is limited by the lengths of the channels 133, 134 (i.e., 90°). Spacer 135 also has a slot 138 defined therethrough to extend radially from central aperture 140. When slot 138 is rotatably aligned with slot 102 in locking ring 16, and with slot 103 in bore section 50, locator stub 93 on the cutting blade assembly can freely pass into and out of the body member 40. 
     The rearward-facing side of the locking ring 16, as seen in FIGS. 7 and 8, includes an arcuate ramp surface 141 extending approximately 140° from slot 102 along the outer edge of aperture 101 and the inner edge of arcuate slot 134. Ramp surface 141 serves as a camming surface for inserting the cutting blade into the handpiece. Specifically, in one extreme rotational position of locking ring 16, slot 102 is aligned with slot 138 in spacer 135 and with slot 103 in bore section 50. It is to be noted that slots 138 and 103 are permanently aligned but that slot 102 can be misaligned as a function of the rotation of the locking ring. When all the slots are aligned, the cutting blade assembly may be inserted through the locking ring as far as possible. The open rearward end of the spring retainer member slides over the forward end of the motor drive shaft 54 (as best illustrated in FIG. 6) until the edge of the opening in member 84 abuts the frusto-conical surface of the drive shaft immediately rearward of the forward end of the drive shaft. In this position the locator stub 93 on the cutting blade hub is disposed substantially entirely in slot 103 in bore section 50 with just a small portion of the stub projecting partially into slot 102 of the locking ring. If the locking ring is then rotated 90° to its other extreme position, the camming surface 141 gradually forces stub 93, and with it the cutting blade assembly, rearwardly. This pushes the drive tang 72, in opposition to the bias force of spring 81, further rearward in spring retainer 80 and into more positive engagement with the drive shaft 54. Thus, in the installed position of the blade assembly, spring 81 is axially compressed as camming surface 141 forces locator stub fully into the slot 103 in bore section 50. 
     In order to remove the cutting blade assembly, the locking ring is rotated 90° in the opposite direction to its initial extreme position, thereby gradually releasing the compression force on spring 81. When slot 102 becomes aligned with slots 138 and 103, spring 81 forces the cutting blade assembly slightly forward so that a portion of stub 93 extends into slot 102. The blade assembly may then be easily removed and replaced by another blade. 
     The two extreme positions of the locking ring are maintained by means of a detent ball 143 and spring 144 located in a recess in forward-facing surface 104 of body member 40. The detent ball and spring cooperate with two dimples 145, 146 formed at 90° spaced locations in the rearward-facing surface of the locking ring to provide stops at the two extreme rotational positions of the locking ring. Dimples 145 and 146 are configured as spherical segments to match the configuration of ball 143. The locking ring 16 is retained in fixed axial or longitudinal position between the spacer 135 and body member 40 by means of screws 136, 137, but is free to rotate with respect to the spacer and body member by virtue of the 90° channels 133 and 134 that slide about the screws. 
     An important feature of the present invention is the switch cluster 17 located on the top side of body member 40 in forward section 41. Specifically, and referring to FIG. 6, a printed circuit board 116 is contoured to fit into a shallow recess in forward section 41 of body member 40. This shallow recess surrounds the deeper recess 115 so that lead wires from the printed circuit board can pass into the recess 115 and through wire conducting channel 117 to the cable assembly. The printed circuit board 116 is illustrated in greater detail in FIG. 14 and is transversely arcuate to match a segment of the circumference of forward section 41 of body member 40. Typically, the printed circuit board 116 is made from a rectangular blank or sheet of decarburized steel having a length (i.e., longitudinally of body member 40) of 0.998 inches, a width (i.e., along the circumference of forward section 41) of 1.294 inches and a thickness of 0.013 inches. The sheet is bent to be curved about its longitudinal center line with a radius of curvature of approximately 0.656 inches and so as to subtend an arc of 113° It is to be understood that these dimensions are by way of example only are and not to be construed as limiting on the scope of the invention, except for the considerations set forth below. A layer of porcelain is deposited on each surface of the sheet, and the metal circuit elements are deposited, dr otherwise formed, on the top porcelain surface. A pair of flaps 187, 188 at the center of the sheet are bent downwardly into recess 115 to provide access for lead wires running from the deposited circuitry on the top surface of the board to the handpiece cable via channel 117. The particular materials used in fabricating the printed circuit board 116 are important since the board must withstand autoclave temperatures without becoming brittle and breaking. This becomes a particularly important consideration where, as here, the printed circuit board must be curved at a relatively small radius of curvature. Typically, in order for the printed circuit board to conform to the curvature of the handpiece circumference, the radius of curvature is on the order of 0.6 to 0.7 inches, and usually is in the narrower range of 0.64 to 0.66 inches. Although the decarburized steel sheet with porcelain coatings on both sides is suitable for the printed circuit board of the present invention, I have found that other materials are also suitable. For example, the printed circuit board may be a sheet of aluminum on which a thick film process is employed to form a layer of epoxy with gold silk screening to define the circuit elements. Alternatively, the board may be a thin film TEFLON (polytetrafluorethylene) weave board with copper laminate used to form the circuit elements. Another alternative is a fiberglass epoxy substrate with copper laminate forming the circuit elements. 
     Referring to FIGS. 12, 13, and 15, an integral electrically non-conductive silicone rubber sheet 150, having a Durometer on the order of seventy, is disposed atop the printed circuit board 116. A plurality of resilient push button switches 151, 152, 153 and 154 are defined in sheet 150. Each of pushbutton switches 151, 152 and 153 includes a resilient dome-like member 155 tapering from an open end facing the printed circuit board 116 to a closed end 156 remote from the printed circuit board. The closed end 156 encompasses a smaller area and has a smaller periphery than the open end. An electrically conductive member 157 is secured to the underside of the closed end 156. The electrically conductive member of each of pushbuttons 151, 152 and 153 is normally disposed in spaced alignment between a respective pair of contacts on the printed circuit board so that, when the pushbutton is depressed, those contacts are electrically bridged by the conductive member 157. Pushbutton switch 151 has a square-shaped closed end 156 and serves as the forward/reverse control switch. Pushbutton switches 152 and 153 are circular and serve as the decrease speed and increase speed control switches, respectively, for the motor. Pushbutton switches 151, 152 and 153 are disposed in transversely aligned spaced relation along the circumference of the handpiece. 
     Pushbutton switch 154 is the on/off control switch for the motor and is generally oval-shaped. In this regard pushbutton switch 154 is slightly rearward of the aligned switches 151-153 and has a length along the circumference of the handpiece which corresponds approximately to the total spaced length of the aligned switches 151-153. In this manner the on/off switch 154 is immediately proximate any of the other three switches and can be quickly actuated to turn the motor on or off. Pushbutton switch 154 is also formed as a dome-like member 158 with a closed small end 159 and an open larger end. Three electrically conductive members 160, 161, 162 are secured in transversely spaced relation (i.e., in the same spaced relation as pushbutton switches 151, 152 and 153) to the underside of closed end 159 and are positioned opposite three respective pairs of contacts on the printed circuit board 116. These printed circuit board contacts are connected electrically parallel to one another so that bridging of any one or more of the contact pairs effects the same on/off function. In the preferred embodiment, electrically conductive member 160 is longitudinally aligned with electrically conductive member 157 of switch 151; electrically conductive member 161 is longitudinally aligned with electrically conductive member 157 of switch 152; and electrically conductive member 162 is longitudinally aligned with electrically conductive member 157 of switch 153. The transverse spacing of conductive members 160, 161 and 162 assure that substantially any location along the transverse dimension of switch 154 can be depressed to effect actuation of the on/off function. In this regard, the transverse spacing between successive electrically conductive members 160, 161 and 162 is only slightly greater than the transverse dimension of each of these individual electrically conductive members. For the given Durometer of sheet 150, effective actuation of switch 154 may be achieved from anywhere along the transverse dimension of that switch. 
     The circuitry on printed circuit board 116 is illustrated in FIG. 14 to which specific reference is now made. All contact pairs for all four switches 151, 152, 153 and 154 include one contact associated with a common lead 170 serving as a circuit ground in the system control circuitry. In this regard, lead 170 surrounds the other leads on three sides and includes six contacts 171, 172, 173, 174, 175 and 176 at spaced locations along its length. A second lead 177 is associated only with on/off switch 154 and includes three contacts 178, 179 and 180 along its length. Contacts 176 and 178 are closely spaced from one another and are positioned under electrically conductive member 162 to be electrically bridged by that member when it is pressed against the printed circuit board 116. In a similar manner contacts 175 and 179 are positioned to be selectively bridged by conductive member 161, and contacts 174 and 180 are positioned to be selectively bridged by electrically conductive member 160. 
     A third lead 181 has a single contact 182 positioned adjacent but spaced from ground contact 173 so that these two contacts can be selectively bridged by the electrically conductive member 157 of the forward/reverse switch 151. A fourth lead 183 has a single contact 184 positioned adjacent but spaced from ground contact 172 so that these two contacts can be selectively bridged by the electrically conductive member 157 of the decrease speed switch 152. A fifth lead 185 has a single contact 186 positioned adjacent but spaced from ground contact 171 so that these two contacts can be selectively bridged by the electrically conductive member 157 of the increase speed switch 153. 
     All five leads 170, 177, 181, 183 and 185 extend along one or the other of the centrally located and downwardly bent flaps 187, 188 to connect to appropriate wires in recess 115. As noted above, such wires are conducted through channel 117 to the cable assembly at the rearward end of the handpiece. 
     A metal cover plate or bezel 190 is disposed over sheet 150 and is apertured to permit pushbuttons 151, 152, 153 and 154 to project therethrough. A plurality of screw holes disposed about the border of plate 190 are aligned with respective holes in sheet 150 and with edge notches in printed circuit board 116 in order to secure these elements together and to body member 40 via respective screws threadedly engaging respective tapped bores in the shallow body member recess in which printed circuit board 116 resides. 
     All of the components of the handpiece 11 are made of materials that are capable of withstanding the high temperatures to which they are exposed when the handpiece is sterilized by autoclaving or the like. A potting compound or epoxy is used to protect the electrical components from damage during autoclaving. 
     With brief reference to FIG. 9, the forward section 84 of the hub member for the cutting blade may be colored in a manner to match the border of one of the indicators 26, 27, 28 so as to provide a color-coded indication on the cutting blade of the speed range corresponding to the correspondingly color coded indicator border. 
     The body member 40 is made of lightweight material and is balanced to facilitate small joint arthroscopy. Longitudinally-extending fluting along the length of the body member facilitates handling. The body member houses a powerful brushless motor providing the necessary torque and speed for all types of powered arthroscopic procedures. The location of switch cluster 17 on the handpiece greatly facilitates operation by the surgeon. Automatic speed range is provided without the need for heavy adapters which must be sterilized after each surgical procedure. Although the motor may be completely controlled from the handpiece, a footswitch is provided to permit control over forward and reverse rotation while allowing the surgeon to select the proper speed from the handpiece. The entire handpiece and cord may be immersed and soaked in a sterilized solution without corroding. In addition, the unit may be flashed, steamed autoclaved or gas sterilized. The use of disposable, single-use cutting blades assures factory-fresh sharpness with every surgical procedure and eliminates the expense and time delay involved in sharpening and re-sharpening blades. 
     It is to be understood that the various specific dimensions presented by way of example herein are intended to be only exemplary unless otherwise stated. 
     From the foregoing description it will be appreciated that the invention makes available a novel drive system for an arthroscopic surgical instrument wherein the drive motor may be entirely controlled from the handpiece and wherein automatic speed range control is effected by directly coding the cutting blade assembly and thereby eliminating the need for an intermediate adapter. The unique arcuate printed circuit board, serving as part of the handpiece control switch cluster, permits that cluster to be contoured to fit generally within the contour of the handpiece so that the handpiece itself may be more easily manipulated and so that the individual switches in the switch cluster may be quickly and accurately accessed. 
     Having described a preferred embodiment of a new and improved electrosurgical instrument constructed in accordance with the present invention, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the techniques set forth herein. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the scope of the present invention as defined in the appended claims. ##SPC1##