Abstract:
Methods for resecting a portion of a knee joint are described herein. While the described methods can comprise any suitable step, in some implementations, the methods include cutting a cylindrically-shaped hole in a portion of the knee joint selected from at least one of a distal portion of a femur and a proximal portion of a tibia in the knee joint; and using a depth of the cylindrically-shaped hole as a reference point to resect bone around the cylindrically-shaped hole to a depth substantially matching the depth of the cylindrically-shaped hole. Other implementations are described.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/726,386 (Attorney Docket No. 7782.32) filed Dec. 24, 2012, entitled “SYSTEMS AND METHODS FOR PROVIDING A BONE MILLING DEVICE”, which is a continuation of U.S. patent application Ser. No. 12/191,217 (Attorney Docket No. 7782.9) filed Aug. 13, 2008, entitled “SYSTEMS AND METHODS FOR PROVIDING A BONE MILLING DEVICE” (now U.S. Pat. No. 8,337,498), the entire disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is related to the use of instruments for guiding preparation of a knee for resection, as well as for guiding preparation of a knee for installation of an implant during an arthroplasty procedure. In particular, the present invention is related to a system for guiding a milling tool along a specific axis to provide an aperture of a desired depth, prior to resection. 
         [0004]    2. Description of Related Art 
         [0005]    During a knee arthroplasty, a surgeon typically must gain access to the knee joint in order to perform resections of existing bone and cartilage so as to shape the tibia and femur to fit mating surfaces of the implant. This shaping is initiated by making resection cuts to the knee joint either by referencing off the femur or off the tibia. The accuracy and precision of the resection cuts greatly affects the quality of the arthroplasty procedure. Therefore, extreme caution is used in planning executing the resection cuts based on the chosen reference. 
         [0006]    Femoral cuts are typically easier to make in surgery because the femur is easily exposed and accessible. Also, many techniques exist to open the knee and expose the femur in a relatively non-invasive manner. Once the femoral cuts have been made, the tibia is better exposed and accessible for the tibial cuts. 
         [0007]    While preparing the femur first is more convenient and relatively non-invasive, ideal femoral cuts are referenced off a prepared tibia. However, complete preparation of the tibia is hindered by overlapping portions of the femur. With the knee in flexion, there is always access to the central part of the tibia; however this exposure is insufficient to completely prepare the tibia. 
         [0008]    It would therefore be advantageous to have instrumentation for sufficiently preparing the tibia for use as a reference to make the femoral resections. It would be further advantageous if the instrumentation was capable of interchangeable use with other necessary instrumentation. Finally, it would be advantageous to have instrumentation that could access and sufficiently prepare the tibia in a relatively non-evasive manner. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The present invention is related to the use of instruments for guiding preparation of a knee for resection, as well as for guiding preparation of a knee for installation of an implant during an arthroplasty. In particular, the present invention is related to a system for guiding a milling tool along a specific axis to provide an aperture of a desired depth, prior to resection. 
         [0010]    An implementation of the present invention includes a bone milling system having a milling tool member and a guide rod. The guide rod is partially deposited within the intramedullary (IM) canal of the bone, and a portion of the guide rod extends outwardly from the IM canal along a desired axis. The exposed portion of the guide rod is adapted to rotatably insert within a cavity of the milling tool member. As such, the milling tool member is guided along the desired axis by the exposed portion of the guide rod. 
         [0011]    The milling tool member includes a cutting head portion and a shaft. The cutting head potion includes a blade having a cutting edge and a window. The cutting edge cuts the aperture into the bone, and the window provides an escape route for the removed bits of bone debris. A cavity is also provided running through the shaft and cutting head portion. The cavity is generally tube shaped having an open end and a closed end. The open end is in fluid communication with an opening in the blade. The closed end includes a shank for coupling the milling tool member to a drill or other device for rotating the member. 
         [0012]    Following creation of the aperture, a resection block is combined with the bone milling system to resect the bone. In some embodiments, the aperture is first made in the tibia and then used as a reference point and/or mounting surface for tensioning the knee and making resections to the exposed femur. In other embodiments, the aperture is first made in the tibia and then used as a reference point and/or mounting surface for positioning a resection block to resect the tibia. Other embodiments of the present invention include a bone milling device that incorporates a guide rod, a cutting surface and a shank into a singular unit. 
         [0013]    While the methods and processes of the present invention have proven to be particularly useful in the area orthopedics, those skilled in the art can appreciate that the methods and processes can be used in a variety of different applications and in a variety of different areas of manufacture to yield functionally equivalent results. 
         [0014]    These and other features and advantages of the present invention will be set forth or will become more fully apparent in the description that follows and in the appended claims. The features and advantages may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. Furthermore, the features and advantages of the invention may be learned by the practice of the invention or will be obvious from the description, as set forth hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0015]    In order that the manner in which the above recited and other features and advantages of the present invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. Understanding that the drawings depict only typical embodiments of the present invention and are not, therefore, to be considered as limiting the scope of the invention, the present invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0016]      FIG. 1  is a perspective view of a representative embodiment of the present system as incorporated into a knee, shown in phantom; 
           [0017]      FIG. 2  is a cross-sectioned view of a representative embodiment of the present system prior to formation of an aperture; 
           [0018]      FIG. 3  is a cross-sectioned view of a representative embodiment of the present system following formation of an aperture, demonstrating use of a depth gauge; 
           [0019]      FIG. 4  is a cross-sectioned view of a representative embodiment of the present system following formation of an aperture; 
           [0020]      FIG. 5  is a cross-sectioned view of a representative embodiment of the present system incorporating a resection block; 
           [0021]      FIG. 5A  is a perspective view of a representative embodiment of a resection block having a plurality of adjustments and apertures; 
           [0022]      FIG. 5B  is a cross-sectioned view of a representative embodiment of a resection block system coupled to a portion of the guide rod; 
           [0023]      FIG. 6  is a perspective view of a representative embodiment of the milling bit; 
           [0024]      FIG. 7  is a perspective view of a representative embodiment of the milling bit; and 
           [0025]      FIG. 8  is a perspective view of a representative embodiment of the bone milling device as embodied in a singular unit. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    The present invention is related to the use of instruments for guiding preparation of a knee for resection, as well as for guiding preparation of a knee for installation of an implant during an arthroplasty. In particular, the present invention is related to a system for guiding a milling tool along a specific axis to provide an aperture of a desired depth. 
         [0027]    Referring now to  FIG. 1 , a perspective view of an implementation of the current invention is shown as positioned within a knee  12  in flexion, shown in phantom. The bone milling device  10  comprises a milling bit  20  and a guide rod  40 . The bone milling device  10  generally comprises surgical metal materials that are compatible with surgical applications, such as surgical steel, titanium, aluminum, and alloys thereof. However, one of skill in the art will appreciate that other non-metallic materials, such as Teflon and nylon, may be incorporated into the current invention within the scope of the present disclosure. For example, in one embodiment a Teflon coating is applied to opposing surfaces of the bone milling device  10  to reduce friction. 
         [0028]    Referring now to  FIGS. 1-3 , the milling bit  20  comprises a cutting head portion  22  and a shaft portion  24 . The cutting head portion  22  is generally bell-shaped having a wider base  26  and a narrower, tapered top  28  that joins the shaft portion  24 . In some implementations of the current invention, a ledge or stepped surface  30  is interposed between the cutting head portion  22  and the shaft portion  24  to support a depth gauge  60 , as shown in  FIG. 3 . The shaft portion  24  further comprises a shank  66  for coupling the milling bit  20  to a drill or other device for rotating the bit  20 . 
         [0029]    The cutting head portion  22  further comprises a removable blade  32 . The removable blade  32  is generally disk shaped having a cutting edge  34  and a window  36 . The cutting edge  34  is provided to cut through the bone to create the aperture  50 , while the window  36  is provided to remove the cut bone debris from the aperture  50 . In this manner, the aperture  50  is both cut and cleared by the milling bit  20 . The cutting head portion  22  further includes a window  38  that aligns with the window  36  of the removable blade  32 . As such, bone debris is entirely removed from the cutting head portion  22  of the milling bit  20  and does not interfere with the ability of the milling bit  20  to form the aperture  50 . 
         [0030]    The milling bit  20  further comprises a cavity  52  extending through the central core of the shaft portion  24  and the cutting head portion  22 . The cavity  52  is closed on one end and includes an opening  54  in the cutting head portion  22  of the bit  20 . The cavity  52  comprises a diameter that is adapted to rotatably receive a portion of the guide rod  40 . The tolerance between the cavity  52  and the guide rod  40  permits the bit  20  to freely rotate around the guide rod  40  yet controls and limits the movement of the bit  20  relative to the axis of the guide rod  40 . As such, the interaction between the cavity  52  and the guide rod  40  ensures that the angle of the aperture  50  is parallel to the angle of the guide rod  40 . 
         [0031]    The guide rod  40  is inserted or anchored within a portion of the bone  14  that is to receive the aperture  50 . Typically, the bone  14  is predrilled to provide an access or opening  46  into the intramedullary (IM) canal  48  of the bone. The pre-drilling procedure is common to the area of orthopedic medicine. Following this procedure, a first end  44  of the guide rod  40  is inserted into the opening  46  and positioned within the IM canal  48  such that a portion of the second end  42  of the guide rod  40  extends outwardly from the opening  46 . 
         [0032]    In one embodiment, the first and second ends  44  and  42  of the guide rod  40  are threadedly coupled to form the guide rod  40 . As such, the first end  44  of the guide rod  40  may threadedly receive a plurality of compatible surgical devices. For example, in one embodiment the second end  42  of the guide rod  40  is removed, following creation of the aperture  50 , and replaced with another surgical instrument needed to complete the arthroplasty procedure. 
         [0033]    The second half  42  of the guide rod  40  comprises a post portion  56  and a base  58 . The base  58  is threadedly coupled to the first end  44  and generally comprises the same diameter as the first end  44 . The post portion  56  extends outwardly from the base  58  and is substantially positioned exterior to the IM canal  48 . As previously discussed, the diameter of the post portion  56  is selected and adapted to rotatably insert within the cavity  52  of the milling bit  20 . In one embodiment the diameter of the base  58  is made greater than the diameter of the post portion  56  so as to increase the surface area of the guide rod  40  in contact with the IM canal, yet still provide the post portion  56  with a diameter compatible with the cavity  52 . In another embodiment, the base  58  and the first end  44  further include fluted outer surfaces to enhance contact with the IM canal  48  and prevent rotation of the guide rod  40  within the IM canal  48 . 
         [0034]    The depth and positioning of the guide rod  40  within the IM canal is selected to permit the milling bit  20  to precisely cut the aperture  50  to a desired depth. The accuracy of the depth of the aperture  50  is a crucial element of any arthroplasty procedure. As such, the milling device  10  further comprises means for accurately determining the depth of the aperture  50 . For example, in one embodiment the outer surface of the shaft portion  24  comprises a plurality of annular reference marks  68 . The reference marks  68  provide a visual indication of the depth of the removable blade  32  relative to various physiological references on the bone being cut. In an embodiment where the aperture  50  is being cut into the tibia  14 , the required depth of the aperture  50  is either 2 mm below the normal level  70  of the bone, 13 mm below the tibial spines 72, or 10 mm below the lateral side  74 . Thus, the reference marks  68  are observed relative to the physiological references  70 ,  72  and  74  to determine the depth of the aperture  50 . Where the aperture is being cut into another bone, such as the femur  16 , other honey references are used, as known in the art. 
         [0035]    In another embodiment, a depth gauge  60  is placed over the shaft portion  24  of the bit  20  and supported by the stepped surface  30 . The depth gauge  60  includes a base  62 , an arm  64  and a pin  66 . The base  62  further includes an aperture having a diameter to rotatably receive the shaft portion  24  of the bit  20 . The arm  64  extends outwardly from the base  62  so as to position the pin  66  beyond the aperture  50 . In one embodiment, the arm  64  further comprises a joint to adjust the length of the arm  64 . In another embodiment, the arm  64  further comprises a set screw to adjust and lock the pin  66  to a desired position relative to the arm  64 . In yet another embodiment, a plurality of depth gauges  60  is provided to accommodate various physiological references on the bone being cut. 
         [0036]    The depth gauge  60  provides a physical indication of the depth of the removable blade  32  relative to the various physiological references, as previously discussed. In one embodiment, the depth gauge  60  is seated against the stepped surface  30  and the arm  64  and the pin  66  are adjusted to be in alignment with the desired physiological reference  74 . Additionally, the height of the pin  66  is set relative to the physiological reference to produce an aperture  50  of a desired depth. Thereafter, the depth gauge  60  is held in place and prevented from rotating while the bit  20  is rotated to form the aperture  50 . Once the pin  66  touches the physiological reference  74 , the bit  20  is removed from the aperture  50 , having achieved the desired depth. 
         [0037]    Referring now to  FIG. 4 , another method for accurately cutting the aperture  50  to a desired depth is shown. In this method, the desired aperture  50  depth is attained by cutting into the bone  14  until the cutting bit  20  contacts the base  58  of the guide rod  40 . This method requires that the base  58  of the guide rod  40  be accurately positioned within the IM canal  48  relative to the cutting edge  34  of the blade  32 . Therefore, the blade  32  cuts and descends into the bone  14  along the guide rod  40  until the point at which the cutting head  22  contacts the base  58 . Once contact between the cutting head  22  and the base  58  occurs the milling bit  20  is removed from the aperture  50 . In one embodiment, the cutting head portion  22  of the milling bit comprises a recessed compartment  80  having a diameter adapted to compatibly and rotatably receive the base  58  of the post portion  56 . Thus, in this embodiment the depth of the base  58  is set within the IM canal  48  such that when the base  58  fully engages the recessed compartment  80 , the cutting edge  34  of the blade  32  is positioned accurately at the desired depth of the aperture  50 . While several different methods have been discussed, one of skill in the art will appreciate that various other methods and apparatuses may be successfully combined with the milling device  10  to achieve the desired results. 
         [0038]    Referring now to  FIG. 5 , the tibia  14  is shown following formation of the aperture  50  and prior to resection. Once the aperture  50  is provided, the guide rod  40  may be further utilized to assist in completing the arthroplasty procedure. For example, in one embodiment a resection block  90  is positioned over the guide rod  40 , via a channel  102 , and seated within the aperture  50 . The resection block  90  comprises a base  92 , an arm  94 , and a cutting guide block  96 . The base further comprises a flange portion  100  having a diameter equal to the diameter of the aperture  50 . Additionally, the base  92  includes a channel  102  having contours and dimensions adapted to compatibly engage the post portion  56  and the base  58  of the guide rod  40 . As such, the resection block  90  accurately seats within the aperture  50  and is steadied by the interposing and complimentary surfaces of the guide rod  40 . 
         [0039]    The arm  94  of the resection block  90  is attached to the base  92  at a height equal to the lateral side  74  of the bone  14 . As such, the arm  94  clears the surface of the bone  14  and extends laterally from the base  92  beyond the aperture  50 . In one embodiment, the resection block  190  further includes a plurality of adjustments  108  to position the arm  94  relative to the depth and location of the aperture  50  as required by the individual, physiological features of the bone  14  undergoing the arthroplasty, as shown in  FIG. 5A . Thus, one resection block  90  may be infinitely adjusted and adapted for use with any procedure as required. 
         [0040]    The cutting guide block  96  is attached to the end of the arm  94  opposite the base  92 . The cutting guide block  96  is positioned such that a saw blade (not shown) may be inserted through the slot  104  to resect the bone  14  to the depth of the aperture  50 . In one embodiment, the resection block  90  further includes a plurality of adjustments  112  to position the cutting block guide  96  relative to the depth and location of the aperture  50  as required by the individual, physiological features of the bone portions  70 ,  72  and  74  undergoing resection, as shown in  FIG. 5A . In some implementations of the current invention, the cutting block guide  96  further comprises a plurality of apertures for attaching the cutting block guide  96  to the bone  14  via fasteners. In other implementations, a plurality of adjustments permits removal of the cutting block guide  96  from the arm  94 . Therefore, in one embodiment the cutting block guide  96  is first positioned on and attached to the bone  14  with fasteners to ensure accurate positioning. Following attachment, the cutting block guide  96  is then removed from the remainder of the resection block  90  and the resections are made. As such, the resections are made accurately and efficiently with minimal componentry. 
         [0041]    In another embodiment, instrumentation for performing the femoral cuts is inserted into and/or referenced from the final depth of the aperture  50 . Since the depth of the aperture  50  is the final level for the tibial cuts, all femoral cuts may be accurately referenced from the depth of the aperture  50 . As such, the aperture  50  provides a sufficient and relatively non-invasive reference point for the tibia  14 . Once the femoral cuts are made, the remaining uncut portions of the tibia  14  are then exposed and easily accessible for resection. In another embodiment, tensioning devices are combined with the guide rod  40 , the resection block  90 , and the aperture  40  to tension the knee  12  as part of the resection procedure. Tensioning devices and procedures as taught in U.S. patent application Ser. No. 11/349,772, entitled GUIDE ASSEMBLY FOR GUIDING CUTS TO A FEMUR AND TIBIA DURING A KNEE ARTHROPLASTY, filed Feb. 8, 2006 (now U.S. Pat. No. 7,927,336), and U.S. patent application Ser. No. 12/191,245, entitled SYSTEMS AND METHODS FOR GUIDING CUTS TO A FEMUR AND TIBIA DURING A KNEE ARTHROPLASTY, filed Aug. 13, 2008 (now U.S. Pat. No. 8,303,597), may be easily combined with the present device  10 , and are incorporated herein by reference, in their entirety. Modifications to the instrumentation and bone  14  are discussed in connection with  FIG. 5B , below. 
         [0042]    Referring now to  FIG. 5B , an implementation of a resection block is shown as combined with the first end  44  of the guide rod  40 . In this embodiment, the post portion or the second end  42  of the guide rod  40  is removed from the first end  44  and replaced with a resection block system  140 . The resection block system  140  includes an integrated base  142  and arm  144 , as well as a sled-style cutting guide block  150 . The base  142  is disk-shaped having a diameter slightly less than the diameter of the aperture  50 . The arm  144  extends laterally outward from the base  142  in the same plane as the base  142 . As such, a portion  160  of the bone  14  must be removed to provide a pathway for the arm  144 . In one embodiment, a rongeur or other surgical device is used to remove the bone portion  160  to create the pathway. Once the bone portion  160  is removed, the first end  44  of the guide rod  40 , with the attached system  140 , is repositioned within the IM canal  48 . The cutting guide block  150  is then slid over the distal end  146  of the arm  144  and positioned against the bone  14 . At this point, the cutting guide block  150  is securely attached to the bone via fasteners and the required resections are made via the slot  104 . In one embodiment, the cutting guide block  150  further includes means for releasing the guide block  150  from the arm  144  while the guide block  150  is fastened to the bone  14 . For example, an upper portion  152  of the guide block  150  may be adapted to be removable thereby releasing the lower, fastened half of the block  150  from the remainder of the system  140 . 
         [0043]    In an alternate embodiment, the cutting guide block  150  is first slid over the distal end  146  of the arm  144  so that the slot  104  of the guide block  150  aligns with femur  16  rather than with the tibia  14 . In this configuration, the guide block  150  is positioned, relative to the depth of the aperture  50 , to make the femoral cuts. Thus, the aperture  50  of the tibia  14  acts as a reference point to accurately make the femoral cuts. Once the femoral cuts have been made, the guide block  150  is removed and repositioned to make the tibial cuts, as previously discussed. 
         [0044]    Referring now to  FIGS. 6 and 7 , various perspective views of implementations of the milling bit  20  are shown. Of particular note are the various configurations of removable blades  32 . The removable blade  32  is attached to the cutting head portion  22  via a set of screws  110 . As such, the blade  32  is easily removed from the bit  20  to allow sharpening and/or replacement of the blade  32 . As shown in  FIG. 6 , some implementations of the removable blade  32  include a single window  36  and a single cutting edge  34 . As shown in  FIG. 7 , some implementations of the removable blade  32  include multiple windows  36  and multiple cutting edges  34 . 
         [0045]    Referring now to  FIG. 8 , an implementation of a bone milling device  120  is shown. Unlike the previously discussed bone milling device  10 , the present device  120  combines all of the elements of the bone milling device  10  into a singular unit  120 . The bone milling device  120  comprises a guide rod  122 , a cutting head portion  124 , and a shank  126 . The guide rod  122  is sized and adapted to rotatably insert within the opening  46  of the bone  16 . The guide rod  122  thereby aligns and directs the cutting head portion  124  into the opening  46  of the bone  46 . The shank  126 , as previously discussed, couples the milling device  120  to a drill (not shown) or other means for rotating the milling device  120 . 
         [0046]    The cutting head portion  124  includes a plurality of annularly situated cutting teeth  130 . Unlike the cutting edge  34  of the previous embodiments, the cutting teeth  130  provide a corrugated surface of sharpened edges that extend radially outward from the guide rod  122 . Thus, the cutting teeth  130  contact and grind the adjacent surfaces of the opening  46  to level or knock down any inconsistent features or ridges of the bone  16  surface. As such, the cutting teeth  130  provide a uniform surface having a diameter equal to the diameter of the cutting head portion  124 . The milling device  120  is useful where a level and consistent bone surface is required adjacent to the opening  46 . In some implementations of the milling device  120 , the cutting head portion  124  includes a plurality of cutting edges and windows to form an aperture in the bone  16 . 
         [0047]    Thus, as discussed herein, the embodiments of the present invention embrace technologies and methods for accurately milling a bone preparatory to an arthroplasty procedure. As will be appreciated by one of skill in the art, the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. For example, in some embodiments the present invention is modified for use in a unicompartmental knee arthroplasty procedure. In another embodiment, the present invention is modified for use in a total knee arthroplasty procedure. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.