Abstract:
A surgical instrument and method according to which at least a portion of a collet housing is inserted into a motor case. A locking element locks the collet housing to the motor case and includes a circumferentially-extending channel formed therein and into which a distal portion of the motor case extends.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to a surgical instrument and in particular to a surgical instrument with a locking element, and to a method of assembling same.  
       BACKGROUND  
       [0002]     Many conventional surgical instruments include components that are connected to each other using a locking element. For example, a cylindrical structure, such as a collet for receiving a shaft, may be inserted into a tubular member, such as a motor case for housing a motor to rotate the shaft. An externally-threaded locking element is often used that threadably engages the motor case to lock the collet to the motor case. To maintain the threaded engagement, the locking element may be torqued to a predetermined value and a thread-locking adhesive may be applied to the threads.  
         [0003]     However, problems may arise during the operation of a surgical instrument having a locking element configuration that includes one or more threaded engagements. For example, during normal operation, the surgical instrument may experience vibratory loading to such a degree that the locking element disengages from the motor case, increasing the risk of harm to the patient and/or the instrument operator. Also, the surgical instrument may be cleaned and sterilized in an autoclave, resulting in the surgical instrument being subjected to high-temperature cycling that could degrade the thread-locking adhesive so that the adhesive fails to hold the threaded engagement.  
                                         TABLE 1                       United States Patent   Publication       Appl. Ser.       Publication No.   Date   Inventor   No.                   2002/0151902   Feb. 17, 2002   Riedel et al.   10/102,762       2002/0165549   Nov. 07, 2002   Owusu-Akyaw et al.   10/135,608       2003/0023256   Jan. 30, 2003   Estes et al.   10/200,683       2003/0163134   Aug. 28, 2003   Riedel et al.   10/164,867       2003/0229351   Dec. 11, 2003   Tidwell et al.   10/164,880       2004/0122460   Jun. 24, 2004   Shores et al.   10/326,178            N/A (Copending Application -   Shores et al.   N/A       Attorney Docket No. 31849.52/P-       21133.00US)                  
 
         [0004]     All references listed in Table 1 are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and Claims set forth below, many of the devices and methods disclosed in the references of Table 1 may be modified advantageously by using the teachings of the present invention.  
       SUMMARY OF THE INVENTION  
       [0005]     In order to overcome one or more of the above-described problems, and according to an embodiment of the present invention, a surgical instrument is provided that includes a collet housing, at least a portion of which is inserted into a motor case. A locking element locks the collet housing to the motor case. The locking element includes a circumferentially-extending channel formed therein and into which a distal portion of the motor case extends. Thus, the integrity of the connection between the locking element and the motor case is not solely dependent upon one or more threaded engagements.  
         [0006]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It is understood that various embodiments of the present invention may overcome one or more of the above-described problems. It is further understood that the detailed description is intended for the purpose of illustration only and is not intended to limit the scope of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is an exploded view of a surgical instrument according to an embodiment of the invention.  
         [0008]      FIG. 2  is an exploded view of a portion of the surgical instrument of  FIG. 1 .  
         [0009]      FIG. 3  is a perspective view of a component of the surgical instrument of  FIG. 2 .  
         [0010]      FIG. 4  is a perspective view of the portion of the surgical instrument of  FIG. 2 .  
         [0011]      FIG. 5  is a sectional view of the portion of the surgical instrument shown in  FIG. 4  taken along the line  5 - 5 , but having the viewing angle rotated approximately 135 degrees clockwise from the horizontal viewing angle associated with the line  5 - 5 .  
         [0012]      FIG. 6A  is an enlarged view of a portion of the sectional view shown in  FIG. 5 , but depicting two components of the surgical instrument in a partially-assembled condition.  
         [0013]      FIG. 6B  is a view similar to that of  FIG. 6A , but depicting another partially-assembled condition between the two components.  
         [0014]      FIG. 6C  is a view similar to that of  FIG. 6B , but depicting a fully-assembled condition between the two components. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring to  FIG. 1 , the reference numeral  10  refers, in general, to a surgical instrument such as, for example, a dissection tool assembly used to dissect human bone or other tissue. A pneumatic motor  12  having a motor case  14  is connected to a hose assembly  15  that supplies pressurized air to the motor and vents low-pressure exhaust air away from the surgical area. A collet  16  is connected to the distal end of the motor  12 , and includes a distal portion  18  and segments  20  and  22 . An attachment  24  having a housing  24   a  is connected to the collet  16  so that the distal portion  18  and the segments  20  and  22  are disposed in the housing. The motor  12 , the hose assembly  15 , the collet  16  and the attachment  24  are disclosed in detail in co-pending patent application Ser. No. 10/164,880, filed Jun. 7, 2002 (pub. No. 2003/0229351), the disclosure of which is incorporated by reference.  
         [0016]     A dissection tool  26  includes a shaft  28  and a surgical element such as a dissection head  30  connected to the distal end of the shaft. The shaft  28  is disposed through the attachment  24  and inserted into and coupled to the collet  16 . This coupling of the shaft  28  to the collet  16  is disclosed in detail in co-pending patent application Ser. No. 10/200,683, filed Jul. 22, 2002 (pub. No. 2003/0023256, the disclosure of which is incorporated by reference.  
         [0017]     Referring to  FIGS. 2 through 3 , with continuing reference to  FIG. 1 , the motor case  14  includes a distal portion  14   a  having an undercut  14   b  formed in the inner wall of the housing. An internal threaded portion  14   c  is also formed in the inner wall of the motor case  14  adjacent the undercut  14   b . It is understood that the motor case  14 , and particularly the distal portion  14   a , may be made out of a material having a relatively low material hardness such as, for example, an aluminum alloy.  
         [0018]     The collet  16  further includes a collet housing  32  having a reduced-diameter externally-threaded end portion  32   a , and a raised-diameter end portion  32   b  having a shoulder  32   c . Opposed axially-extending slots  32   d  and  32   e  are formed in the raised-diameter end portion  32   b  and receive pins  34   a  and  34   b , respectively.  
         [0019]     A cylindrical locking element  36  includes a bore  36   a  and an external threaded portion  36   b . A radially-extending through-opening  36   c  is formed in the locking element  36  and a ring  36   d  extends around the locking element between the through-opening and the threaded portion  36   b . As more clearly shown in  FIG. 3 , a channel  36   e  extends around the locking element  36 . The channel  36   e  is formed in a side wall of the ring  36   d  and extends in an angular direction towards the bore  36   a  and away from the threaded portion  36   b  to define a camming surface  36   f  for reasons to be described. It is understood that the locking element  36  may be made out of a material having a relatively high material hardness such as, for example, heat treated stainless steel, and that this material hardness may be higher than the material hardness of the motor case  14   a.    
         [0020]     When the collet  16  is assembled with the motor  12 , as shown in  FIGS. 4 and 5 , the raised-diameter end portion  32   b  of the collet housing  32  is inserted into the motor case  14  and the collet housing extends through the bore  36   a  of the locking element  36 . Although not shown for clarity purposes, it is understood that the collet housing  32  also extends through the segments  20  and  22  ( FIG. 1 ), and that the externally-threaded end portion  32   a  is threadably engaged with the distal portion  18 , as disclosed in the above-incorporated co-pending patent application Ser. No. 10/200,683. It is further understood that the housing  24   a  of the attachment  24  extends over the distal portion  18 , the segments  20  and  22 , and the locking element  36 , and abuts the ring  36   d.    
         [0021]     As shown in  FIG. 5 , opposed axially-extending slots  14   d  and  14   e  are formed in the inner wall of the motor case  14  and are circumferentially aligned with the slots  32   d  and  32   e , respectively, so that portions of the pins  34   a  and  34   b  extend into the slots  14   d  and  14   e , respectively. An radially-extending inner wall  14   f  is formed in the motor case  14  and is contacted by the proximal end of the collet housing  32 .  
         [0022]     The locking element  36  is threadably engaged with the motor case  14  via the threaded portions  36   b  and  14   c , respectively. It is understood that an adhesive, such as Loctite® threadlocker adhesive, may be applied to the threaded portions  36   b  and  14   c . The distal portion  14   a  is crimped or deformed and extends into the channel  36   e . It is understood that the channel  36   e  may also be filled with adhesive. The distal portion  14   a , and the portion of the motor case  14  immediately adjacent the distal portion, are twisted or torqued for reasons to be described in detail below.  
         [0023]     It is understood that the collet  16  is represented only by the collet housing  32  for clarity purposes, and that the collet may include additional components such as, for example, components disclosed in detail in the above-incorporated co-pending patent application Ser. No. 10/164,880.  
         [0024]     During assembly, and referring to  FIGS. 6A through 6C  with continuing reference to  FIGS. 1 through 5 , the distal portion  14   a  of the motor case  14  is initially in an uncrimped or undeformed condition so that the distal portion has a continuous profile and cross-section, tapering to the distal end of the motor case, as shown in  FIG. 6A . The pins  34   a  and  34   b  are held in place in the slots  32   d  and  32   e , respectively, and the raised-diameter end portion  32   b  of the collet housing  32  is inserted into the motor case  14  so that the pins  34   a  and  34   b  extend into the slots  14   d  and  14   e , respectively.  
         [0025]     The locking element  36  is slid over the outer surface of the collet housing  32  so that the collet housing extends through the bore  36   a . The locking element  36  is inserted into the motor case  14 , passing under the undercut  14   b  until the threaded portion  36   b  is able to engage the threaded portion  14   c . The locking element  36  is then rotated to threadably engage the threaded portions  36   b  and  14   c , thereby moving the locking element in a longitudinal direction, relative to the motor case  14  and towards the shoulder  32   c . Rotation may be facilitated by inserting a portion of a tool, such as a torque wrench, into the hole  36   c  and manipulating the tool to rotate the locking element  36 .  
         [0026]     As the locking element  36  moves closer to the shoulder  32   c , the distal end of the motor case  14  engages the camming surface  36   f  so that the distal portion  14   a  is forced downwards and begins to deform and extend into the channel  36   e , as shown in  FIG. 6B , thereby locking the motor case to the locking element. The relatively thin wall of the motor case  14 , corresponding to the location of the undercut  14   b , facilitates the plastic deformation of the distal portion  14   a  into the channel  36   e . The difference between the above-described material hardnesses of the motor case  14  and the locking element  36  also facilitates the deformation of the distal portion  14   a.    
         [0027]     As the locking element  36  continues to be rotated, the distal portion  14   a  further deforms and extends into the channel  36   e  so that the distal end of the motor case  14  (or the distal end of the distal portion  14   a ) is radially offset from the engagement of the threaded portions  36   b  and  14   c . The rotation of the locking element  36  also causes the walls of the channel  36   e  to torque the distal portion  14   a  so that the distal portion is twisted about the longitudinal axis of the motor case  14 . Rotation of the locking element  36  is continued until the threaded portion  36   b  bottoms out, that is, until the threaded portions  36   b  and  14   c  are fully engaged, and/or until the proximal end of the locking element contacts the shoulder  32   c  and the distal end of the collet housing  32  contacts the wall  14   f , as shown in  FIG. 6C .  
         [0028]     The locking element  36  may be threadably engaged with the motor case  14  in the above-described manner with or without a torque wrench. If a torque wrench is used, the torque reading provided by the torque wrench during the assembly and locking of the cylindrical housing  32  to the motor case  14  provides feedback as to the relative conditions of the locking element  36  and the distal portion  14   a  during the assembly. The torque reading shows an initial torque spike when the distal portion  14   a  is bent beyond the yield strength of the motor case material, indicating that the distal portion is plastically deforming while being forced into the channel  36   e.    
         [0029]     The torque reading is relatively constant as the distal portion  14   a  continues to be forced into the channel  36   e  and torqued about the longitudinal axis of the motor case  14 , indicating that further threaded engagement between the portions  36   b  and  14   c  is possible and desired to further lock the motor case  14  to the locking element  36 . The torque reading begins to appreciably increase after the threaded portion  36   b  bottoms out, that is, after the threaded portions  36   b  and  14   c  are fully engaged. At this point, rotation of the locking element  36  is stopped. Thus, the torque reading provides feedback as to the degree of threaded engagement between the locking element  36  and the motor case  14 , and as to when rotation of the locking element  36  should cease. It is understood that this feedback may be a substitute for specifying a value to which the locking element  36  may be torqued.  
         [0030]     If a torque wrench is not used during the above-described operation, the resistance to rotation provides tactile feedback as to the relative conditions of the locking element  36  and the distal portion  14   a  during the assembly. That is, the initial plastic deformation of the distal portion  14   a  into the channel  36   e  will be felt by the assembler/operator of the surgical instrument. After continued rotation of the locking element  36 , the subsequent bottomed-out condition of the threaded portions  36   b  and  14   c  will be felt due to the appreciable increase in the resistance to further rotation. Thus, this tactile feedback indicates the degree of threaded engagement between the locking element  36  and the motor case  14 .  
         [0031]     In operation, the motor  12  receives high-pressure air via the hose assembly  15  to rotate a rotor shaft (not shown) that is coupled with the shaft  28  of the surgical instrument  10 , as disclosed in detail in the above-incorporated co-pending patent application Ser. No. 10/200,683. Due to this coupling, the shaft  22  rotates, thereby rotating the dissection head  24 , which may be applied against bone or other human tissue to cut or dissect the bone or tissue. Low-pressure exhaust air exits the motor  12  through an exhaust passage in the hose assembly  15 .  
         [0032]     While the surgical instrument  10  is dissecting the bone or other tissue, the instrument is subjected to a variety of static and/or dynamic (shock or vibrating) loads in a variety of directions. The collet housing  32  is prevented from rotating relative to the motor case  14 , and vice versa, due to the contact between the pins  34   a  and  34   b  and the substantially aligned walls defined by the slots  32   d  and  14   d , and  32   e  and  14   e , respectively.  
         [0033]     The collet housing  32  is prevented from sliding out of the distal end of the motor case  14   a , in a direction away the motor  12 , due to the contact between the shoulder  32   c  and the proximal end of the locking element  36 . The locking element  36  is able to so hold the collet housing  32  because, inter alia, the adhesive applied to the threaded portions  14   c  and  36   b  prevents the locking element from disengaging from the motor case  14 , especially when the surgical instrument is undergoing vibratory loading. The extension of the distal portion  14   a  into the channel  36   e  also prevents the locking element  36  from disengaging from the motor case  14  due to the contact between the distal portion and the walls of the channel. The radial offset between the distal end of the motor case  14  (or the distal end of the distal portion  14   a ) and the engagement of the threaded portions  36   b  and  14   c , relative to the longitudinal axis of the motor case, further promotes resistance to disengagement. Thus, the locking element  36  is locked to the motor case  14  and, as a result, the collet housing  32  is locked to the motor case.  
         [0034]     It is understood that the distal portion  14   a  operates to prevent disengagement between the threaded portions  14   c  and  36   b , and therefore between the collet housing  32  and the motor case  14 , even if the adhesive applied to the threaded portions has weakened or undergone performance degradation for any reason. Such reasons may include the repeated operation of the surgical instrument  10  for long periods of time, or the sterilization of the surgical instrument in an autoclave, during which time the adhesive is subjected to high-temperature cycling. Thus, due to the extension of the distal portion  14   a  into the channel  36   e , the connection between the motor case  14  and the locking element  36  is more resistant to disengagement.  
         [0035]     During disassembly, a predetermined amount of torque is applied to the locking element  36  to untwist and bend the distal portion  14   a  back to or near its initial condition so that the locking element and the collet housing  32  may be disengaged from the motor case  14 . The motor case  14  may be a disposable article, that is, it may be discarded and a new motor case may be used when re-assembling the surgical instrument  10 .  
       Variations  
       [0036]     It is understood that variations may be made in the foregoing without departing from the scope of the disclosure. These variations include the following:  
         [0037]     1. The locking element  36  may be used to lock any type of cylindrical structure to any type of tubular member. For example, the cylindrical structure could extend through the locking element  36  and be inserted into the tubular member. The locking element  36  could be threadably engaged with internal threads formed in the inner wall of the tubular member, thereby locking the cylindrical structure to the tubular member.  
         [0038]     2. The distal portion  14   a  may be a separate component from and connected to the remaining portion of the motor case  14 . Thus, after the distal portion  14   a  has been bent back and the locking element  36  has been disengaged from the motor case  14 , the distal portion may be disconnected from the rest of the motor case and a new distal portion may be used with the motor case when re-assembling the surgical instrument  10 .  
         [0039]     3. The motor case  14  and/or the distal portion  14   a  may be designed for reuse, that is, the components could accommodate the repeated assembly and disassembly of the locking element  36  to the distal portion. Further, the locking element  36  and the motor case  14  could be modified so that the distal portion  14   a  only elastically deforms. It is understood that reuse of the motor case  14  would be facilitated with such a modification.  
         [0040]     4. The distal portion  14   a  could be designed to break when a predetermined amount of torque is applied to the locking element  36  to remove the locking element from the motor case  14 .  
         [0041]     5. The ring  36   d  and the channel  36   e  could be modified so that the channel  36   e  extends in a different angular direction. For example, the angular direction of the channel  36   e  could be modified so that the distal portion  14   a  is forced radially outwards, that is, flares out away from the bore  36   a , when the locking element  36  threadably engages the motor case  14 .  
         [0042]     6. In addition to the pneumatic motor  12 , other types of motors using electricity or other motive forces may be used with the surgical instrument  10 . If other types of motors are employed, it is understood that the hose assembly  15  may be removed from the surgical instrument  10 .  
         [0043]     7. Any foregoing spatial references, such as “upper,” “between,” “front,” “right side,” “side,”  37  above,” “beneath,” etc., are for the purpose of illustration only and do not limit the specific spatial orientation of the structure described above.  
         [0044]     The preceding specific embodiments are illustrative of the practice of the invention. It is to be understood, therefore, that other expedients known to those skilled in the art or disclosed herein, may be employed without departing from the invention or the scope of the appended claims. For example, the present invention is not limited to instruments and methods for connecting different components of a dissection tool assembly. The present invention is also not limited to instruments and associated methods for dissecting bone or other tissue per se, but may find further application in other surgical instruments used in other operations such as, for example, dental procedures. The present invention further includes within its scope the methods of making, assembling and using the surgical instrument  10  described hereinabove.  
         [0045]     It is intended that the scope of the disclosure be defined by the claims appended hereto and their equivalents. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts a nail and a screw are equivalent structures.