Patent Publication Number: US-2019192171-A1

Title: Thermally Sensitive Retention Mechanism For Orthopedic Cutting Instruments

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application 62/609,469 filed Dec. 22, 2017 which is fully incorporated herein by reference. 
    
    
     FIELD 
     The present invention is directed at a thermally sensitive retention mechanism for orthopedic cutting instruments. More specifically, the present invention incorporates structural engagement features into a rotational orthopedic cutting instrument that transfers torque from a driver to a cutting component and which upon heating result in disengagement of the cutting component from the driver portion. 
     BACKGROUND 
     There have been a variety of reported efforts to provide a disposable medical device with a design that prevents the medical device from being utilized a second time. For example, U.S. Pat. No. 5,569,163 entitled Disposable Surgical Instrument discloses the use of a lens mounting element molded from a material such as a natural or synthetic polymer which is capable of deforming in the presence of a deforming agent such as water, organic solvent, heat, gas, or light. U.S. Pat. No. 5,779,686 is entitled Disposable Medical Instrument and discloses a medical instrument which cannot be reused if it is washed after use, or which makes it possible to judge whether the medical instrument has been washed thereby precluding reuse. U.S. Pat. No. 6,869,392 is entitled Disposable Implement Inserted Into An Endoscope and discloses the use of a disposable implement insertable into an endoscope and comprising at least one zone matched to the shape of the endoscope that is designed to be permanently deformed on account of having been used a first time by the inevitable mechanical, thermal and/or chemical treatment it undergoes in the endoscope. U.S. Pat. No. 8,383,804 is entitled Prevention Of Reuse Of A Medical Device and discloses the use of a clamp that has an element that alters its appearance while being heated over a threshold temperature, thus giving optical or mechanical information that the device should not be used a second time. U.S. Publ. No. 2009/00655565 is entitled System, Method And Apparatus For Preventing Reuse Of Medical Instruments and discloses a circuit embedded in the disposable medical device to identify the device and a circuit for reading the status, such as whether the device has been used. WO98/37819 is entitled Preventing Reuse Of Surgical Devices and discloses a single use ultrasonic surgical device that relies upon the use of a hub coupled to the transmission component and includes a temperature sensitive material that distorts when exposed to heat. 
     Accordingly, there exists a continuing need for surgical instrument designs that will prevent re-use of the instrument, and in particular, re-use of orthopedic cutting instruments, which would then reduce the problems associated with cleanliness and sterility of patients undergoing orthopedic procedures in which articular surfaces are removed, resurfaced and prepared to receive an implant. 
     SUMMARY 
     A cutting instrument comprising a driver component adapted to provide a rotating torque motion including an end portion containing one or a plurality of axial-bearing bosses and optionally one or a plurality of torque-bearing bosses and a cutting component including one or a plurality of holes to engage with said axial bearing bosses and said optional torque-bearing bosses. The axial-bearing bosses comprise a temperature sensitive material which upon exposure to steam sterilization do not allow for engagement of said axial-bearing bosses with said cutting component to thereby prevent reuse of the cutting instrument. 
     In related embodiment the present invention relates to a cutting instrument comprising: a driver component adapted to provide a rotating torque motion including an end portion containing: (i) one or a plurality of axial-bearing bosses having a height in the range of 1.0 mm to 4.0 mm and a diameter of 0.25 mm to 4.0 mm, and (ii) one or a plurality of torque-bearing bosses having a height in the range of 1.0 mm to 4.0 mm and a diameter of 0.25 mm to 4.0 mm. The cutting instrument also includes a cutting component including one or a plurality of holes to engage with said axial bearing bosses and said optional torque-bearing bosses. The axial-bearing bosses comprise a temperature sensitive material which upon exposure to steam sterilization do not allow for engagement of said axial-bearing bosses with said cutting component to thereby prevent reuse of the cutting instrument. 
     In method form, the present invention relates to a method for preventing reuse of an orthopedic cutting instrument comprising: providing a driver component adapted to provide a rotating torque motion including an end portion containing one or a plurality of axial-bearing bosses and optionally one or a plurality of torque-bearing bosses. One then provides a cutting component including one or a plurality of holes to engage with said axial bearing bosses and said optional torque-bearing bosses. This is followed by engaging said axial-bearing bosses to said cutting component wherein said axial-bearing bosses comprise a temperature sensitive material which upon exposure to steam sterilization disengage from said cutting component to thereby prevent reuse of the cutting instrument. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be best understood by reference to the following detailed description of the preferred embodiments when considered in conjunction with the accompany drawings wherein: 
         FIG. 1  illustrates an example of the present invention in the form of an unassembled patella reaming instrument. 
         FIG. 2  illustrates the assembled configuration of the patella reamer illustrated in  FIG. 1 . 
         FIG. 3  illustrates another example of the present invention in the form of an unassembled acetabular reaming instrument. 
         FIG. 4 , illustrates the assembly of the unassembled acetabular reaming instrument shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With attention directed to  FIG. 1 , the present invention is illustrated in the form of an unassembled patella reaming instrument having a cutting component  10  that has the indicated holes  12  preferably along the perimeter  11  of the component. Preferably, the holes are positioned such that they are within 1-10 mm of the perimeter  11 . Also shown is driver interface component  14  which has standing bosses  16 . The standing bosses are positioned on an end portion  15  such that they will align with the holes  12  on the cutting component  10 . The driver interface component is adapted to provide a rotating torque motion to the cutting component  10 . For clarity, the cutting edges are not shown on the cutting component. Reference to a standing boss  16  may be understood as a protruding feature from a surface of the driver that is intended to be located in the corresponding holes  12 . In the broad context of the present invention the total number of standing bosses may preferably fall in the range of 1-10, with a height preferably in the range of 1.0 mm to 4.0 mm, more preferably 2.0 mm to 3.0 mm, and most preferably, a height of 2.5 mm with a +/−0.1 mm tolerance. The standing bosses also may be of any geometrical shape, but are preferably round or oval. The standing bosses preferably have a diameter of 0.25 mm to 4.0 mm, most preferably 1.5 mm to 3.5 mm, and in an even more preferred embodiment, a diameter of 2.0 mm at a +/−0.1 mm tolerance. 
     The standing bosses are preferably of two types and formed from two different materials. That is, a first material which defines the bosses as torque-bearing bosses and a second material that defines the bosses as axial-bearing bosses. The torque bearing bosses are preferably made to protrude and releasably engage through holes  12  and are capable of transferring torque from the driver interface  14  to the cutting component  10 . It should be noted that the torque-bearing bosses are optional, in the sense that it is contemplated herein that the only bosses necessary are the axial-bearing bosses, further described herein. However, to the extent that torque-bearing bosses are utilized, they are preferably present at a level of 1 torque-bearing boss to a plurality of torque bearing bosses, more preferably up to and including 9 torque-bearing bosses. The corresponding number of axial-bearing bosses are preferably present at a minimum level of 1 axial-bearing boss to a plurality of axial bearing bosses, more preferably up to 9 axial bearing bosses. This in turn provide that the total number of bosses, as noted above, is preferably in the range of 1-10 bosses. 
     The torque-bearing bosses that are releasably engaged in through-holes  12  are preferably made of material that does not soften during steam sterilization, as described herein. Accordingly, the torque-bearing bosses are such that they preferably maintain their torque-bearing ability following steam sterilization. Preferred materials for the torque-bearing bosses include both polymeric material and/or metallic material. Polymer material preferably includes polysulfones, such as polyphenylsulfone sold under the tradename Radel® R-5100, available from Solvay. In addition the torque-bearing bosses may be made from a polyarylamide sold under the tradename Ixef® HC-1022 also available from Solvay. 
     The axial-bearing bosses are to be understood as mechanical engaging with the driver and which serve to releasable secure the driver to the cutting component. More specifically, the axial-bearing bosses secure the cutting component to the driver and reduce or prevent movement along the axial or longitudinal axis  18  during a given cutting procedure. Preferably, when the cutting component is assembled to the driver, the axial-bearing bosses are heat-staked such that the boss material melts flush to the surface  20  of the cutting component or below the cutting surface. Heat staking is reference to the general procedure where the bosses  16  are positioned in holes  12  and the bosses are then deformed with heating which mechanical engages the driver  14  to the cutting component  10 . Other contemplated procedures for engaging the axial-bearing bosses to the driver include exposure of the bosses to ultrasonic welding or swaging. Swaging is reference to cold-forming of the axial-bearing boss to the cutting component such that the axial bearing boss is again flush to the surface of the cutting component after joining. 
     Attention is directed to  FIG. 2  which illustrates the assembled configuration of the patella reamer illustrated in  FIG. 1  therein providing a cutting instrument  22  having a cutting component  24  and a driver component  26 . As can be seen, after heat-staking, the two axial-bearing bosses  28  (white) which are directly opposed to one another on the circular cutting component  24 , are flush to the surface  30  of the cutting component  24  after the heat staking procedure. Meanwhile, the six torque bearing bosses  32  (black) are originally designed to be flush to the cutting surface  30 . Accordingly, in this particular preferred example, there are two axial bearing bosses heat-staked to the cutting component, six torque-bearing bosses that are releasably engaged to cutting component  24 , and the total number of bosses is eight. It should be appreciated that while the torque-bearing bosses  32  are present to transfer torque from the driver component  26  to the cutting component  24 , the axial-bearing bosses also serve to transfer torque, but since they preferably made from a relatively lower melting material than the torque-bearing bosses, with a relatively lower flexural modulus, their ability to transfer torque is not as efficient as the torque-bearing bosses. 
     The axial-bearing bosses are therefore preferably made from a temperature sensitive material that will soften and flow during a steam-sterilization protocol such that they no longer remain engaged to the cutting component to prevent reuse of the cutting instrument. Or, stated another way, the axial-bearing bosses are such that upon exposure to steam-sterilization, they convert to a form that will not allow for engagement of the driver component  26  to the cutting component  24 . This in turn will provide that the cutting instrument will not be reused and will be limited to a single use since after steam sterilization, the instrument will not function for a selected cutting procedure as the cutting component  24  will not be secured to the driver  26 . Accordingly, the axial-bearing bosses herein, which as noted soften and flow during steam sterilization, may be understood as providing a reuse inhibiting feature since after steam sterilization, such bosses will no longer engage with the cutting component and assume any axial load and will render the instrument inoperable. This in turn will eliminate the risks to patients of having a dull and potentially unsanitary cutting instrument otherwise suitable for an orthopedic procedure. Stated another way, the surgeon will now receive a cutting instrument herein in a clean and sterile form limited to a one-time use. The surgeon is assured that such instrument will therefore be sharp and suitable for resurfacing of bone material. Once the surgery is complete, the process utilized by hospitals to clean and sterilize the instrument (i.e. steam sterilization) will, as noted, render the instrument unworkable and prevent the surgeon from using the instrument on a second patient. 
     The steam sterilization protocol herein is one in which the device will be exposed to steam and temperatures of preferably 121° C. to 134° C. for a time of 3 minutes to 15 minutes, that is best accomplished in an autoclave. Preferably, the axial-bearing bosses are made from a polymeric material that indicates a melting temperature (Tm) of less than 121° C., or in the range of 60° C. to less than 121° C. Such polymeric material is also one that preferably indicates a melt flow index (MFI) in the range of 5-500, more preferably 25-500. Melt flow index is conveniently determined according to ISO standard 1133-1 (Dec. 1, 2011). Accordingly, upon exposure to such steam-sterilization, as noted above, the axial-bearing bosses will soften as flow. However, it is useful to note that both the axial-bearing bosses and torque-bearing bosses herein are such that they may both be capable of undergoing alternative sterilization procedures prior to initial use of the cutting instruments herein. This would include, but is not limited to sterilization by exposure to gamma radiation or ethylene oxide (ETO) sterilization protocols. 
     Preferably, the axial-bearing bosses are sourced from polycarprolactone, which is available under the trade name CAPA™ and identified as a thermoplastic material available from Perstorp with a reported melting point of around 60° C. The axial-bearing bosses may also be preferably made from an ethylene-co-vinyl-acetate polymer, under the trade name ELVAX™ available from DuPont, with a reported melting point of around 87° C. More specifically, ELVAX™ 250 with a melt flow index of 25, ELVAX™ 410 with a melt flow index of 500 and ELVAX 420 with a melt flow index of 150. 
     Attention is next directed to  FIG. 3 , which illustrates another example of a cutting instrument in the context of the present invention. More specifically,  FIG. 3  identifies an unaassembled acetabular reaming instrument having a driver assembly  34  and a cutting component  36 . The cutting component may have a hemispherical type cutting surface  37 . Again, for clarity, the cutting edges are not shown on the cutting component. The driver again is configured to have standing bosses  38  that extend from the surface  40  of the driver and are designed to be located in corresponding holes  42  on the cutting component  36 . In addition, as can be seen, the holes on the cutting component are provided in the form of tab  43  that may be attached to the cutting component  36  or such tabs may be part of and extend directly from the cutting component  36 . 
     As can be seen in this exemplary embodiment, the standing bosses  38 , which may all be axial-bearing bosses, are shown as a pair of standing bosses located at what may be described as the 0°, 90°, 180° and 270° location about the circular perimeter of the driver assembly  34 . It should therefore be appreciated that in the broad context of the present invention, with respect to a driver having a generally circular configuration, the bosses may be preferably disposed as such relative angular locations, or at only the 0° and 180° location, or only at the 90° and 270° location. Alternatively, if three (3) the bosses herein are utilized, such bosses may be placed at the 0°, 120° and 240° locations. Finally, attention is directed to  FIG. 4 , which illustrates the assembly of the unassembled acetabular reaming instrument shown in  FIG. 3  wherein the driver assembly  34  and a cutting component  36  are jointed and the axial-bearing bosses have been heat-staked to the cutting component. Although not shown, one or more of the axial-bearing bosses may be replaced with a torque-bearing boss. 
     With regards to the standing bosses herein, it should be noted that the use of the axial-bearing bosses alone, or in combination with the torque-bearing bosses, are such that they preferably provide the ability to support a torque load, as between the driver and the rotational cutting surface, in the range of 1 Nm to 40 Nm, more preferably in the range of 5 Nm to 20 Nm. In addition, it should now be appreciated that the use of the coupling system herein that relies upon the axial-bearing bosses, either alone or in combination with the torque-bearing bosses, may be used to couple a driver providing a rotary motion to a rotatory cutting component, in an orthopedic reamer, such as in the above exemplary patella reamer design or acetabular reaming instrument. However, in the broad context of the present invention, such bosses may be utilized in glenoid reamers, intramedullary reamers or calcar reamers.