Abstract:
A tool arrangement including a powered surgical handpiece and an attachment for use therewith which supports a surgical cutting accessory. The attachment includes an arrangement which automatically axially positions the cutting accessory relative to the attachment upon coupling the attachment to the handpiece. A sleeve arrangement is also provided in the attachment which protects bearings, which are provided for rotatably supporting the cutting accessory, from contamination.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention generally relates to a surgical tool arrangement, and more particularly to a surgical tool arrangement including a powered handpiece and an improved attachment usable therewith which supports and accurately positions a surgical cutting accessory driven by the handpiece.  
       BACKGROUND OF THE INVENTION  
       [0002]     Powered surgical tools are utilized extensively in modern surgery. Typically, this tool includes the handpiece which houses a motor. A cutting accessory is secured to the handpiece for accomplishing a specific medical task. More specifically, some powered surgical tools are provided with drills or burrs for cutting bores into bone or hard tissue or for selectively removing portions thereof. Still other powered surgical tools are provided with cutting accessories such as saw blades for separating large sections of hard tissue. The ability to use powered surgical tools has lessened the physical strain on physicians and other personnel when performing medical procedures on a patient. Moreover, most surgical procedures can be performed more quickly and more accurately with powered surgical tools than with the manual equivalents that preceded them.  
         [0003]     Handpieces of the type described above are often utilized with complementary attachments which define the distal head of the handpiece. These attachments function in various ways depending upon the mode in which the handpiece is to be used. For example, some attachments include linkages which transfer the motive power from the handpiece motor to the cutting accessory. Other attachments position the cutting accessory at an angle relative to the longitudinal axis of the handpiece to provide the surgeon with alternative access to the surgical site. Further, some attachments translate the rotary motion of the handpiece rotor into a reciprocating motion, for example when a saw blade is to be used with the handpiece as the cutting accessory. Still other attachments function to provide physical support for a cutting accessory which rotates along with the handpiece rotor, to prevent the shaft of the cutting accessory from bending when exposed to significant loads during surgery. The instant invention generally relates to this latter type of attachment.  
         [0004]     In some instances, it is necessary to cut through and remove parts of a skull of a patient, and in this situation a special attachment, typically referred to as a duraguard, is often utilized with a powered handpiece which assists in this procedure and also protects the dura mater or the dura (the thick and fibrous membrane that lines the interior of the skull) from the tip of the cutting accessory during cutting of the skull. This type of attachment incorporates a distally-located foot which is oriented transversely relative to the longitudinal axis of the handpiece and attachment so as to extend over the free distal end of the cutting accessory which projects from the attachment. The foot is typically utilized by the surgeon to peel the dura away from the skull, and at the same time shields the dura from the moving end of the cutting accessory.  
         [0005]     When a powered handpiece is utilized with an attachment of the above type, it is important that the cutting accessory be correctly axially positioned relative to the attachment foot. More specifically, the terminal distal or working end of the cutting accessory should be spaced proximally or rearwardly from the foot so as to avoid contact therewith and allow the shaft of the cutting accessory to spin freely. In this regard, if the cutting tip is positioned too far in the forward or distal direction so that the cutting tip makes contact with the foot, the cutting tip could cause fragmenting or separation of the foot from the attachment and/or could cause the foot to become heated due to friction with the tip, either of which is non-desirable. Oppositely, if the cutting tip is positioned too far from the foot in the rearward or proximal direction, then the cutting accessory may not cut through the entire depth or thickness of the skull, resulting in an inadequate cut.  
         [0006]     In order to address the above problems, a known duraguard attachment manufactured by the instant assignee incorporates therein a ball-detent arrangement for axially positioning the cutting accessory. This arrangement includes a cutting accessory defining therein a concave annular groove which cooperates with balls located in the attachment in surrounding relation with the cutting accessory. A collar is provided on the attachment which is manipulated by the user to load and unload the cutting accessory. With this attachment, the collar is set to the “run” position, and the cutting accessory is inserted into the attachment until the balls seat within or “find” the accessory groove. The attachment and cutting accessory are then installed on the handpiece by manipulating a collar provided on the handpiece. The attachment is removed from the handpiece by again manipulating the handpiece collar, and then the cutting accessory is removed from the attachment by setting the attachment collar to the “unlock” position. A disadvantage of this arrangement is that the user must manually manipulate two collars during assembly. That is, one collar must be used to lock the attachment to the handpiece, and another collar must be used to position the cutting accessory relative to the attachment.  
         [0007]     The present invention prevents or at least minimizes the above shortcomings of the known arrangement, in that the attachment and cutting accessory according to the invention cooperate to automatically set the axial position or depth of the cutting accessory relative to the attachment, without the need for a separate collar on the attachment. More specifically, the user simply inserts the cutting accessory either into the attachment or alternatively inserts the cutting accessory directly into the distal end of the handpiece, and then secures the attachment to the handpiece. The attachment incorporates therein a positioning arrangement which engages the accessory shaft and cooperates therewith to maintain the shaft in a predetermined axial position relative to the attachment when same is coupled to the handpiece. The arrangement according to the invention correctly sets the depth of the cutting accessory relative to the foot of the attachment, without the surgeon having to manually manipulate a separate collar.  
         [0008]     In addition, the attachment according to the invention incorporates therein an improved bearing arrangement, wherein the bearings within the attachment which support the cutting accessory are shielded by a sleeve-like component interposed between the shaft of the cutting accessory and the bearings. In the arrangement disclosed in U.S. Pat. No. 5,888,200 owned by the assignee hereof, the bearings located in the attachment are in direct contact with the cutting accessory. This known arrangement allows saline and other surgical debris to make contact with the bearings, which can effectively shorten the life thereof. The improved bearing arrangement according to the invention, however, routes fluid and other surgical debris through the attachment and away from the bearings, which results in longer-life bearings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a perspective view of the surgical tool arrangement according to the invention;  
         [0010]      FIG. 2  is a partially exploded perspective view of the surgical tool arrangement of  FIG. 1 ;  
         [0011]      FIG. 3  is an enlarged, longitudinal cross-sectional and fragmentary view of the distal end of the surgical tool arrangement illustrating same in an assembled tool “run” state;  
         [0012]      FIG. 4  is an enlarged, longitudinal cross-sectional view of the attachment;  
         [0013]      FIG. 5  is view similar to  FIG. 4 , but showing the cutting accessory positioned within the attachment;  
         [0014]      FIG. 6  is an enlarged front view of the foot as seen along line  6 - 6  in  FIG. 5 ;  
         [0015]      FIG. 7  is an enlarged and fragmentary side view of the arm and foot of  FIG. 5 ;  
         [0016]      FIG. 8  is an exploded perspective view of the attachment of  FIG. 4 ;  
         [0017]      FIG. 9  is an enlarged side view of the cutting accessory;  
         [0018]      FIG. 10  is an enlarged, cross-sectional view of the cutting accessory of  FIG. 9 , taken substantially along line  10 - 10  in  FIG. 9 ;  
         [0019]      FIG. 11  is an enlarged view of the distal end of the cutting accessory of  FIG. 9 ;  
         [0020]      FIG. 12  is an enlarged, cross-sectional view of a second embodiment of an attachment which may be utilized in the surgical tool arrangement according to the invention;  
         [0021]      FIG. 13  is an exploded perspective view of the attachment of  FIG. 12 ;  
         [0022]      FIG. 14  is an enlarged fragmentary view of the foot of the attachment in a use position;  
         [0023]      FIG. 15  is an enlarged, cross-sectional view of a third embodiment of an attachment which may be utilized in the surgical tool arrangement according to the invention;  
         [0024]      FIG. 16  is an exploded perspective view of the attachment of  FIG. 15 ;  
         [0025]      FIG. 17  is an enlarged and fragmentary perspective view of a second embodiment of a cutting accessory which may be utilized in the surgical tool arrangement according to the invention;  
         [0026]      FIG. 18  is an enlarged and fragmentary perspective view of a third embodiment of a cutting accessory which may be utilized in the surgical tool arrangement according to the invention; and  
         [0027]      FIG. 19  is an enlarged and fragmentary perspective view of a fourth embodiment of a cutting accessory which may be utilized in the surgical tool arrangement according to the invention. 
     
    
       [0028]     Certain terminology will be used in the following description for convenience in reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the tool arrangement and designated parts thereof. The words “forwardly” and “distally” will refer to the direction toward the end of the tool arrangement which is closest to the patient, and the words “rearwardly” and “proximally” will refer to the direction away from the end of the tool arrangement which is furthest from the patient. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.  
       DETAILED DESCRIPTION  
       [0029]      FIGS. 1-3  illustrate the surgical tool arrangement  10  according to the invention. Arrangement  10  includes the handpiece  11  in which a motor is housed. In the illustrated embodiment, handpiece  11  includes an electric motor  12  having a rotor or rotor shaft  12 A, although the handpiece  11  may instead include a pneumatic motor, or indeed any other convenient type of motive power source. Thus, the term “rotor” as used herein in association with the handpiece motor is not to be considered to be limited solely to a rotor or rotating element of an electric motor. The motor  12  is energized with power supplied to the handpiece  11  via a cable  13  coupled to a proximal or base end  14  of the handpiece  11 .  
         [0030]     The arrangement  10  additionally includes an attachment  17  which is coupled to a distal or head end  18  of the handpiece  11 . Attachment  17  includes a housing  19  which is physically coupled to the handpiece  11 , and a cap or guard  20  coupled to housing  19  and defining the distal end of the arrangement  10 . Housing  19  and cap  20  together define a bore  21  ( FIG. 4 ) which extends throughout the entire longitudinal extent of the attachment  17  and during operation is occupied by a cutting accessory  22 . In the illustrated embodiment, the cutting accessory  22  is a router which is coupled to rotor  12 A of motor  12  of handpiece  11 . It will be appreciated that other cutting accessories may be utilized, and that accessory/router  22  is only an example of one type of accessory which may be utilized in accordance with the invention.  
         [0031]     The structure and operation of handpiece  11  illustrated in  FIGS. 1-3  and its cooperation with a conventional attachment is disclosed in detail in U.S. Pat. No. 5,888,200 (herein “the &#39;200 patent”), which is incorporated by reference herein in its entirety. Accordingly, the structure and functioning of the handpiece  11  will be only briefly described herein in relation to the attachment  17 , following the description of the attachment  17 .  
         [0032]     With reference to  FIGS. 4, 5  and  8 , housing  19  of attachment  17  is defined by a generally cylindrical base  26 . Base  26  includes a cylindrical part  27  which defines a bore  28  of a constant diameter. Cylindrical part  27  defines thereon an outwardly projecting annular flange  29 , which is tapered on its distal side and at its proximal side defines a shoulder  31  which is oriented generally perpendicularly relative to the outer surface of part  27 .  
         [0033]     A retainer ring  33  is fixed to the proximal end of base  26 . Retainer ring  33  is defined by a cylindrical sleeve  34  and an annular lip  35  which projects inwardly from a proximal end of sleeve  34  and is generally perpendicular thereto. Lip  35  defines a plurality of inwardly projecting teeth  36  which are spaced uniformly and circumferentially about lip  35 . As shown in  FIGS. 4 and 5 , retainer ring  33  is fixed to the proximal end of base  26 . More specifically, ring  33  is disposed in surrounding relationship with an end  38  of cylindrical part  27  located proximally of flange  29 , and a terminal distal end face  37  of ring  33  is seated against shoulder  31  of part  27 .  
         [0034]     With continued reference to  FIGS. 4, 5  and  8 , cylindrical part  27  includes an angled section  39  which tapers inwardly as same projects distally and adjoins a cylindrical neck  40 . Neck  40  defines thereon a distally facing annular shoulder  41  which adjoins an elongate sleeve-shaped portion  42  of a reduced outer diameter than neck  40 . Sleeve-shaped portion  42 , adjacent neck  40 , defines thereon an externally threaded section  43 , and terminates at a generally cylindrically-shaped distal end section  44 .  
         [0035]     Tapered section  39  of base  26  includes an inner surface which defines a frustoconically-shaped first bore  48  and a cylindrically-shaped second bore  49 . Bore  48  is located at the distal end of and communicates with bore  28  of cylindrical part  27 , and bore  49  is located distally of and communicates with bore  48 . Tapered section  39  also defines an inner and forwardly facing annular surface  50  which adjoins in a perpendicular manner an inner annular surface  51  of neck  40 . Neck  40  additionally defines an annular shoulder  53  which faces distally and generally perpendicularly adjoins annular surface  51 . Sleeve-shaped portion  42  of base  26  defines therein a longitudinal bore  54  of a constant diameter. Bore  54  is located distally of and communicates with bores  48 ,  49  and the space defined by surface  51  of neck  40 .  
         [0036]     Attachment  17  additionally includes a rear bearing sleeve  58  which is disposed in bore  54  of sleeve-shaped portion  42 . Rear bearing sleeve  58  is defined by a cylindrical wall  59  having an outer surface  60 , and a flange  61  which projects outwardly from the proximal end of wall  59  and is generally perpendicular relative to outer surface  60  thereof. A distally-facing surface of flange  61  perpendicularly joins outer surface  60  and defines a shoulder  62  of rear bearing sleeve  58 . Rear bearing sleeve  58  defines therein a bore  64  which extends completely therethrough.  
         [0037]     An elongated front bearing sleeve  66  is also disposed in bore  54  of sleeve-shaped portion  42 , forwardly of rear bearing sleeve  58 . Front bearing sleeve  66  is defined by a cylindrical wall  67  having outer and inner generally parallel surfaces  68  and  69 . Inner surface  69  defines a bore  70  which extends completely through sleeve  66  and has a constant diameter therealong which is similar in dimension to that of bore  64  of rear bearing sleeve  58 . As shown in  FIGS. 4, 5  and  8 , front bearing sleeve  66  has an annular spacer  72  which projects outwardly and perpendicularly from outer surface  68 , part-way between the proximal and distal ends of sleeve  66 .  
         [0038]     A first annular ball bearing  75  is disposed within bore  54  of sleeve-shaped portion  42  of base  26 , and radially between sleeve-shaped portion  42  and front and rear bearing sleeves  66  and  58 . In the illustrated embodiment, bearing  75  and rear bearing sleeve  58  are press-fit together so as to define an integrated bearing for ease of assembly, while the inner diameter of bearing  75  slip-fits over the proximal end of front bearing sleeve  68 .  
         [0039]     A second annular ball bearing  79  substantially identical to ball bearing  75  is disposed within bore  54 , radially between sleeve shaped portion  42  and front bearing sleeve  68 . Second ball bearing  79  is axially spaced from first ball bearing  75  by a biasing member, which in the illustrated embodiment is a coil spring  81 . A pair of washers  82  are provided at the respective ends of the bearings  75  and  79  which face one another, and spring  81  is disposed between the respective washers  82 . In the illustrated embodiment, the inner diameter of bearing  79  slip-fits over the front bearing sleeve  68 .  
         [0040]     A third annular ball bearing  84  substantially identical to bearings  75  and  79  is located forwardly of second ball bearing  79 , radially between the distal end of sleeve-shaped portion  42  and front bearing sleeve  66 . Third bearing  84  is separated from second bearing  79  by spacer  72  of front bearing sleeve  66 . Bearing  84 , in the illustrated embodiment, is press-fit over the distal end of front bearing sleeve  68 .  
         [0041]     With continued reference to  FIGS. 4, 5  and  8 , cap  20  of attachment  17  will now be described. In the illustrated embodiment, cap  20  is configured as a guard which is usable to separate the dura from the skull and also to protect the dura during a cutting procedure.  
         [0042]     Cap  20  includes a generally cylindrically-shaped annular sleeve-like portion  88  which defines the proximal terminal end of cap  20 . Sleeve-like portion  88  defines internal threads which are engageable with the threads of section  43  of base  26  to secure cap  20  on base  26 . Sleeve-like portion  88  is joined to a further sleeve part  89  by a transitional section  90  which tapers inwardly as same projects distally. Transitional section  90  and sleeve part  89  together define a cylindrical bore of a constant diameter in which the distal end section  44  of sleeve-shaped portion  42  is disposed.  
         [0043]     Cap  20  additionally includes a nose  95  having an inner cylindrically-shaped surface  96  which defines a bore  97  of a constant diameter, and in which the terminal front end of front bearing sleeve  66  is disposed. Nose  95  defines thereon a lip  99  which projects inwardly and perpendicularly relative to inner surface  96  and terminates at an edge which defines a bore  100  which opens outwardly. Bore  100  communicates with bore  97  and is of a reduced diameter as compared to bore  97 . Nose  95  additionally defines a shoulder  101  which is generally parallel to and spaced forwardly from shoulder  53  of neck  40 .  
         [0044]     With reference to  FIGS. 4-7 , an elongate arm  102  projects distally from lip  99  of nose  95 , and at its most distal end is fixed to a foot  103  which is generally perpendicularly oriented relative to arm  102 . Foot  103  has an outer wall  104  which has a generally flat exterior surface  104 A defining the distal-most extent of cap  20 , a pair of side walls  105  which adjoin outer wall  104  through respective rounded edge surfaces, and an end wall  107  which adjoins outer and side walls  104  and  105  through respective rounded edge surfaces. Outer, side and end walls  104 ,  105  and  107  of foot  103  together define a pocket or recess  108  which opens proximally.  
         [0045]     Turning now to cutting accessory  22 , and with reference to  FIGS. 9-11 , same includes a terminal proximal or butt end  115  which is normally seated within the handpiece  11  and rotates along with rotor  12 A of motor  12  as discussed below. Cutting accessory  22  includes a shaft-locking section  116  disposed distally of butt end  115 . The shaft locking section  116  is identical to the shaft-locking section illustrated in  FIGS. 13A and 13B  of the &#39;200 patent and cooperates with the handpiece  11  in the same manner as described therein. Thus, this portion of the accessory  22  will be only briefly described.  
         [0046]     Shaft-locking section  116  defines thereon a plurality of flat faces  119  which are recessed inwardly relative to the outer diameter of the adjacent butt end  115  and the remainder of the cutting accessory  22 . These faces  119  interact with a locking mechanism of handpiece  11  as discussed below which transfers the rotational motion of rotor  12 A associated with motor  12  to the accessory  22 .  
         [0047]     Cutting accessory  22  additionally includes a solid cylindrical portion  122  which extends distally from locking section  116  and has approximately the same diameter as butt end  115 . A solid cylindrical portion  123  is located distally of cylindrical portion  122 . Portion  123  is formed to have a slightly lesser diameter than portion  122 , such that a distally facing shoulder  126  is defined therebetween. Shoulder  126  defines the terminal distal end of portion  122 , and has a surface which is perpendicular to a longitudinal axis of  127  of accessory  22 . In the illustrated embodiment, for ease of manufacture, accessory  22  includes a transitional section  128  which tapers outwardly as same projects distally away from shoulder  126 . However, it will be appreciated that shoulder  126  may instead be formed by forming an annular and circumferentially-extending groove between portions  122  and  123 , wherein the groove has a bottom parallel to the longitudinal axis  127  of accessory  22 .  
         [0048]     As shown in  FIGS. 9 and 10 , accessory  22  includes cutting tip  131  extending distally from cylindrical portion  123 . Tip  131  defines thereon a plurality of longitudinally extending cutting edges  132 , which, when the accessory  22  undergoes a sideward motion transverse to the longitudinal axis  127 , allows the accessory to be used as a mill. Tip  131  also includes a plurality of cutting edges  133  located at the terminal distal end thereof, as best shown in  FIG. 11 . These cutting edges  133  allow the accessory  22  to be used as a boring tool or drill when the accessory  22  is advanced toward the bone or hard tissue in a direction along the longitudinal axis  127 , for example when accessory  22  is used with attachments other than attachment  17  which are open or non-obstructed at the distal free end thereof.  
         [0049]      FIGS. 12 and 13  illustrate a second embodiment of an attachment which is usable in the surgical tool arrangement according to the invention. More specifically, these figures illustrate an attachment  139  which is identical to attachment  17 , except for the configuration of the cap. Accordingly, components of attachment  139  which are similar or identical components of attachment  17  are identified in  FIGS. 12 and 13  with the same references numbers, plus an “A”.  
         [0050]     Cap  142  of attachment  139  is identical to cap  20  of attachment  17 , except that the nose  95 A thereof does not include an arm (such as arm  102 ) cantilevered outwardly therefrom. Instead, flange  99 A of nose  95 A defines a generally flat or planar distally-facing end surface  148 .  
         [0051]     The assembly of a conventional attachment to handpiece  11  is described in detail in the &#39;200 patent, and attachments  17  and  139  are assembled in a similar manner. Accordingly, the mounting of the attachments  17 ,  139  to handpiece  11  will only be described briefly herebelow.  
         [0052]     With reference to  FIGS. 1-3  and  5 , to assemble the attachment  17  to the handpiece  11 , cutting accessory  22  is first inserted through attachment  17  until shoulder  126  abuts the rearwardly facing surface of flange  61  of rear bearing sleeve  58 , so that the accessory  22  is loosely fitted within attachment  17 . An actuating collar  150  of handpiece  11  is rotated to the “load” position. The attachment  17  is then seated over the head end  18  of handpiece  11 , and specifically over drill housings  151  and  152  thereof, so that the butt end  115  of accessory  22  inserted into a preload plunger  152 A of handpiece  11  and into the drill housings  151  and  152 . The attachment  17  is positioned over rear drill housing  151  so that the teeth  36  of retaining ring  33  are engaged within corresponding slots  153  of rear drill housing  151 . With attachment housing  19  in this position, locking tabs  154  of a leaf spring  155  (which seats over rear drill housing  151 ) seat over two opposed lock ring teeth  36  of retainer ring  33  and lock the attachment housing  19  in position relative to the handpiece  11 .  
         [0053]     It will be appreciated that in the alternative, cutting accessory  22  can first be inserted into the drill housings  151  and  152  of handpiece  11  (after the collar  150  is rotated to the “load” position), and the attachment  17  then assembled to handpiece  11  over the accessory  22  and the head end  18  of handpiece  11 .  
         [0054]     The actuating collar  150  of handpiece  11  is then rotated to the “run” position. In this regard, the handpiece  11  includes a collet housing  158  which is coupled to the rotor  12 A for rotation therewith and includes a collet  160  which couples to the cutting accessory to cause rotation thereof along with rotor  12 A. Collet housing  158  defines therein an accessory-receiving space  157  and an axially fixed, distally-facing surface  157 A which defines the proximal terminal end of space  157 . In the “run” position, the butt end  115  of cutting accessory  22  is seated in space  157  of collet housing  158 , and the accessory  22  is rotationally locked to the collet housing  158  by the action of a plurality of collet feet  159  (only one of which is shown in  FIG. 3 ) of collet  160  bearing against three of the faces  119  formed in the shaft locking section  116 . The collet  160 , firmly couples the accessory  22  to the rotor  12 A such that the motor-induced rotation of rotor  12 A is transferred to the accessory  22  to rotate same.  
         [0055]     While the collet  160  as discussed above can be utilized to firmly axially hold or lock a cutting accessory within handpiece  11  as disclosed in the &#39;200 patent, the collet  160  in accordance with the invention is only utilized to transfer rotational motion of rotor  12 A to the cutting accessory, since the cooperation between the shoulder  126  of accessory  22  and the attachment  17  as discussed below serves to axially lock the accessory  12  within handpiece  11 .  
         [0056]     Attachment  17  with cap  20  as described above may be used to remove a section of the skull  162 , as shown in  FIG. 14 . More specifically, first a bore is formed in the skull of the patient of a size sufficient to allow passage of the arm  102  and foot  103  into the skull  162 . The handpiece  11  is then energized to rotate the cutting accessory  22 , and the handpiece  11  is moved transversely along the skull  162  to cut with side or lateral cutting edges  132 . During cutting, the surgeon normally applies upward pressure to the handpiece  11  so that the foot  103  is moved along and is positioned closely adjacent the inwardly directed side of the skull  162 , which effectively peels or separates the dura  163  away from the skull  162 . The foot  103  is located above or outside the dura  163  and protects same from damage by the tip  131  of the cutting accessory  22 . The rounded outer surface of foot  103  also helps to prevent damage or trauma to the dura.  
         [0057]     During cutting, it is of great importance that the tip  131  of the accessory  22  be correctly axially positioned within the pocket  108  defined in foot  103 . For example, if during cutting the tip  131  bottoms out in the pocket  108 , this could cause binding of the accessory  22  or other damage to the arrangement. Further, if the tip  131  is positioned too far from or out of the pocket  108  of foot  103 , then the tip  131  will likely not cut through the entire thickness of the skull  162 . The attachment  17  according to the invention prevents or at least significantly minimizes the possibility that any of the above will occur as discussed below.  
         [0058]     When the attachment  17  is not installed on the handpiece  11  as shown in  FIG. 4 , the spring  81  exerts a distally directed force on second bearing  79 , causing bearing  79  to exert a distally directed force on spacer  72  of front bearing sleeve  66 , which in turn causes spacer  72  to exert a distally directed force on third bearing  84  and abut same against shoulder  101  of cap  20 . At the same time, spring  81  exerts a proximally directed force on first bearing  75  to abut same against shoulder  53  of base  26 , and positions rear bearing sleeve  58  a short axial distance forwardly from forwardly facing surface  50  of base  26 . In this unassembled configuration of the handpiece  11  and attachment  17 , the rear bearing sleeve  58  and the proximal end of the front bearing sleeve  66  are axially spaced from one another to define a gap G therebetween.  
         [0059]     When the attachment  17  and accessory  22  are installed on the handpiece  11  as described above and as shown in  FIGS. 3 and 5 , the axially fixed surface  157 A of collet housing  157  serves as a back-stop for the butt end  115  of accessory  22 , and thus forces cutting accessory  22  forwardly a short distance, which in turn causes the shoulder  126  thereof to force rear bearing sleeve  58  and bearing  75  forwardly, which in turn compresses spring  81  against second bearing  79 . This abutment of shoulder  126  against rear bearing sleeve  58  substantially eliminates the gap G between front and rear bearing sleeves  66  and  58  as shown in  FIG. 5 , and advances the cutting accessory  22  and thus the tip  131  thereof forwardly into the correct axial position relative to foot  103  of attachment  17 , wherein the tip  131  is positioned within the pocket  108  of foot  103 , but is not in contact with any inner surfaces of foot  103 . Maintaining the tip  131  in this axial position relative to the attachment  17  effectively covers the distal-most end of tip  131  and cutting edges  133  thereof to protect the dura  163 , so that only the lateral or side cutting edges  132  of accessory  22  are used.  
         [0060]     The configuration of attachment  17  and shoulder  126  of accessory  22  as described above automatically positions the cutting accessory  22  in the optimum predetermined axial location relative to the foot  103  when the attachment  17  is secured to handpiece  11  by rearwardly biasing the butt end  115  of accessory  22  against the axially-fixed collet housing surface  157 A of handpiece  11 . Once the cutting accessory  22  and attachment  17  are installed on handpiece  11 , as is shown in  FIG. 5 , a slight gap exists between the front and rear bearing sleeves  66  and  58 . This gap is provided to compensate for manufacturing tolerances. However, if for some reason the cutting accessory  22  is pushed axially forwardly from its position shown on  FIG. 5 , the rear bearing sleeve  58  will axially abut the proximal face of front bearing sleeve  66 . Since front bearing sleeve  66  is biased forwardly and thus is axially fixed by spring  81  relative to surface  101 , further forward advancement of the cutting accessory  22  is prevented. Thus, the axial abutment of bearing sleeves  58  and  66  will prevent significant forward advancement of cutting accessory  22  relative to foot  103 . The above configuration of attachment  17  also positions the cutting accessory  22  at the optimum rearward position within the pocket  108  of foot  103 . That is, if the tip  131  of cutting accessory  22  is positioned out of or spaced to far rearwardly of pocket  108 , the cutting accessory  22  will not cut through the entire transverse thickness of the skull  162 .  
         [0061]     Another aspect of the improved attachment according to the invention is that the front and rear bearing sleeves  66  and  58  are positioned radially between the cutting accessory  22  and the bearings  75 ,  79  and  84 . One known arrangement, such as that disclosed in the &#39;200 patent, allows for direct contact between the bearings and the rotating cutting accessory or shaft, which allows saline solution and other surgical debris to contaminate the bearings. The sleeves  66  and  58  according to the invention effectively protect the bearings  75 ,  79  and  84  from surgical debris, and route fluid through the attachment  17  and away from the bearings  75 ,  79  and  84 , resulting in longer-life bearings.  
         [0062]     To change or replace the attachment  17 , such as with drill attachment  139  (for example, when a bore must be formed in the skull  162 , such as prior to use of attachment  17  as discussed above), actuating collar  150  is rotated in the reverse direction from the “run” position past the “load” position and into the “eject” position, which forces the leaf spring locking tabs  154  inwardly, and the attachment  17  is forced in a direction away from the handpiece  11  through the action of the preload plunger  152 A bearing against the inner surface of attachment base  26  which defines bore  48 . The attachment  17  is removed from the handpiece  11 , and actuating collar  150  is automatically returned to the “load” position (as described in the &#39;200 patent). Attachment  139  is then secured into position on rear drill housing  151  of handpiece  11  in the same manner as attachment  17  as discussed above. If the same accessory  22  is to be used with attachment  139 , then the accessory  22  can remain in the handpiece  11  while the attachment  17  is removed and the attachment  139  is installed on the handpiece  11 .  
         [0063]     Attachment  139  is typically used when cutting accessory  22  is to be utilized as a drill, wherein the end cutting surfaces or edges  133  of cutting accessory  22  are utilized to bore an opening into bone. As mentioned above, the same cutting accessory  22  is usable with both attachments  17  and  139 , wherein the attachment  17  with its arm  102  and foot  103  effectively prevents usage of the end cutting surfaces  133 , while the attachment  139  allows use of both cutting edges  133  and  132  of cutting accessory  22 .  
         [0064]      FIGS. 15 and 16  illustrate an additional attachment  169  which may be utilized with handpiece  11  according to the invention. Attachment  169  is similar to attachment  17 , and similar or identical components will accordingly be referenced with the same reference numbers, plus a “B”.  
         [0065]     Attachment  169  includes a cylindrical base  26 B which is similar to base  26  of attachment  17 , with the exception of its proximal end configuration. More specifically, base  26 B is defined by a cylindrical part  27 B which has a substantially constant outer diameter along the longitudinal extent thereof. An annular flange or lip  175  is cantilevered outwardly from the most proximal end of cylindrical part  27 B, and is oriented generally perpendicularly relative to the outer surface thereof.  
         [0066]     A retainer ring  33 B is disposed at the proximal end of base  26 B. Retainer ring  33 B has a distally-located and sleeve-shaped terminal end  176  with an inner surface  177  defining a bore with a diameter greater than the outer diameter of cylindrical part  27 B, and a proximally-located sleeve-shaped terminal end  178  joined to end  176 . Sleeve-shaped end  178  defines stepped inner surfaces  179  and  180 , wherein surface  180  defines a bore of a diameter greater than a bore defined by surface  179 , but less than the diameter of surface  177 . Further, terminal end  178  includes an inwardly projecting annular lip  35 B defining a plurality of inwardly projecting teeth  36 B which cooperate with the distal end of handpiece  11  to lock attachment  169  thereto.  
         [0067]     An annular collar  186  is disposed in surrounding relation with the cylindrical part  27 B adjacent flange  175 . Collar  186  defines thereon an outwardly projecting and annular rib  187  at the distal end thereof, and a proximally-facing surface  188  at the opposite end thereof.  
         [0068]     Retainer ring  33 B is attached to base  27 B, with the collar  186  interposed therebetween. More specifically, collar  186  is press-fitted into the bore defined by surface  177  of end  176  so as to be fixed to ring  33 B, and ring  33 B and collar  186  are slip-fitted onto base  27 B. Flange  175  of base  27 B is seated within the bore defined by proximal surface  180  of ring  33 B with some radial clearance. An annular washer  190  is disposed between end surface  188  of collar  186  and a distally-facing surface of flange  175  of sleeve  27 B. In the illustrated embodiment, washer  190  is a teflon washer.  
         [0069]     In this embodiment, the base  27 B is rotationally movable or pivotable relative to retainer ring  33 B, collar  186  and handpiece  11 , which allows the surgeon to “steer” the base  27 B during surgery. The washer  190  reduces the rotational drag while providing some frictional resistance. More specifically, the surgeon can hold the handpiece  11  in one hand and use the fingers of the opposite hand to pivot or rotate the base  27 B (and thus the foot  103 B) relative to the ring  33 B, collar  186  and handpiece  11 . The attachment  169  is used in a manner similar to the attachment  17 , and is attached and detached from the handpiece  11  in manner similar to attachment  17 .  
         [0070]      FIGS. 17-19  illustrate additional embodiments of cutting accessories which may be utilized in accordance with the invention. The cutting accessories shown in these figures are essentially identical to cutting accessory  22  described above, but show additional examples of how a shoulder or abutment may be formed on an intermediate part of the accessory for cooperation with attachments  17 ,  139  and  169 . Accordingly, similar or identical components will accordingly be referenced with the same reference numbers, plus a “B”. It will be appreciated that the cutting accessories shown in  FIGS. 17-19  all include a shaft locking section at their proximal end portion identical to shaft locking section  116  of accessory  22 , although same are not shown for purposes of simplicity.  
         [0071]     Cutting accessory  200  shown in  FIG. 17  is initially a two-part assembly, including an elongated proximal and solid cylindrical part  201  which extends distally from the locking section (not shown), and an elongated distal and solid cylindrical part  202  extending forwardly from proximal part  201 . Parts  201  and  202  are press-fit to one another, for example by inserting the proximal end of part  202  into a suitably-sized opening defined at the distal end of part  201 . The proximal and distal parts  201  and  202  are of differing diameters. That is, distal part  202  is of a lesser diameter than proximal part  201 , so that when the parts are joined, a shoulder or abutment  126 B is formed, which is defined by the distal-most terminal end of proximal part  201 . Alternatively, parts  201  and  202  can joined by welding, or by providing a threaded end on one part and a threaded opening on the other part.  
         [0072]     Cutting accessory  210  shown in  FIG. 18  includes an elongated and solid cylindrical portion  211  which extends proximally from cutting tip  131 B. Cylindrical portion  211  has a constant diameter along the length thereof. A ring  212  is press-fit onto the outer diameter of the cylindrical portion  201  to a set height. A forwardly facing surface of the ring  212  defines a shoulder  126 B.  
         [0073]     Cutting accessory  215  shown in  FIG. 19  includes an elongated and solid cylindrical portion  216  which extends proximally from cutting tip  131 B. Portion  216  has a constant diameter except at an area intermediate the ends of accessory  215 , wherein an annular and shallow groove is defined about the circumference of portion  216 . A spring-like retaining ring  217  is positioned within the groove, and a forwardly facing surface thereof defines a shoulder  126 B.  
         [0074]     It will be appreciated the shoulders  126 ,  126 B defined on the cutting accessories described above all include an axially unobstructed, forwardly or distally facing surface which projects radially beyond the diameter of the portion of the cutting accessory defined on the distal side of the respective shoulder (i.e. parts  123  and  202  of  FIGS. 9 and 17 ), or alternatively beyond both portions of the cutting accessory located on both the proximal and distal sides of the respective shoulder ( FIGS. 18 and 19 ).  
         [0075]     Although a particular preferred embodiment of the invention is disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.