Abstract:
A single use bone cutter comprised of a plate with a plurality of insert blade enclosures is described. The insert blade enclosures are arranged in a spiral pattern about the plate and are further positioned at varying height intervals through the thickness of the plate. The bone cutter provides a means whereby the insert blades can be easily positioned within the plurality of blade enclosures to provide a wide array of cutting diameters.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 61/353,699, filed Jun. 11, 2010. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention, relates to the art of orthopedic cutting tools, and more particularly, to a disposable cutter used for shaping and preparing the femoral bone for implant insertion. 
       PRIOR ART 
       [0003]    Cutting tools used in orthopedic procedures are designed to cut bone and associated tissue matter. Specifically, cutters of the present invention are designed to cut and shape the end of a long bone such as a femur or humerus. Typically, the end of the long bone is cut and shaped for insertion of an implant. As such, these cutters are required to be sterile and sharp. Using a dull cutter generates heat that typically leads to tissue necrosis and results in undesirable patient outcomes. A non-sterile cutter blade typically results in an infected and damaged bone that may lead to other problems for the patient. 
         [0004]    Depicted in  FIG. 1  is an image of a prior art bone cutter  10  designed to cut and shape the femoral head  12  of the femur  14 . As shown in the figure, the prior art cutter  10  is similar to that of a “hole saw” drill. These prior devices  10  generally comprise a hollow cylinder in which a series of fixed cutting teeth slots  16  are formed within the cylinder wall thickness  18 . Specifically, these prior art cutters  10  are designed with a fixed, predetermined diameter. As such, these prior art cutters  10  cannot be easily modified to accommodate a wide range of bone diameters. 
         [0005]    In addition, traditional bone cutters are typically reused multiple times. That is because of their high cost. Such multiple reuses require that the cutter be cleaned and sterilized before each use. Furthermore, over time, as these cutters are used and reused, they become dull, thus requiring resharpening. Therefore the blades of the cutter are required to be resharpened, cleaned and sterilized. However, these resharpening and sterilization processes add additional costs and increase the possibility of infection. In addition, resharpening tends to deform the dimensions of the cutter. These dimensional changes could adversely impact the optimal fit and function of the implant. Furthermore, there is a high likelihood that the cleaning and sterilization process may not remove all possible infection agents such as bacteria, machining lubricants, and the like. 
         [0006]    Accordingly, the present invention provides a cost effective single use bone cutter with a novel blade and assembly design. These design features provide for a bone cutter that is easily adaptable to cut and shape an array of bone diameters. In addition to ensuring proper cutter sharpness and cleanliness that promotes optimal patient outcomes, the enhanced bone cutting features of the present invention ensure proper implant fit and reduced implant wear, 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a disposable bone cutter device comprising a cutter housing assembly, insert blades and guide-rod for orthopedic surgical applications. Specifically, the cutter device of the present invention is designed to re-shape the head of a femur for joint revision surgeries. 
         [0008]    The cutter of the present invention is designed with a plurality of discreet insert blade enclosures within which an insert blade resides. These blade enclosures are further oriented in a “step wise” spiral formation which allows for the creation of customizable cutting diameters. Therefore, unlike the prior art, the bone cutter of the present invention allows for a cutting diameter that can be finely tuned to match the diameter of an implant. 
         [0009]    In a preferred embodiment of the bone cutter of the present invention, the blade enclosures are positioned such that they are equidistant about a central longitudinal axis. This design aspect provides for precise concentric circular cutting of the bone. 
         [0010]    The cutter housing assembly further comprises insert blades which can be easily inserted into their respective blade enclosures. Each insert blade comprises a blade cutting surface and a chamferred region which minimizes interference of the cut through the bone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a cross-sectional view of the prior art bone cutter and bone. 
           [0012]      FIG. 2  is a perspective view of the bone cutter and guide-rod of the present invention. 
           [0013]      FIG. 3  is a perspective view of an embodiment of the bone cutter of the present invention taken from the distal end. 
           [0014]      FIG. 4  is a perspective view of an embodiment of the bone cutter of the present invention taken from the perspective end. 
           [0015]      FIG. 5A  is a top view of the embodiment of the bone cutter shown in  FIGS. 3 and 4 . 
           [0016]      FIG. 5B  is a cross-sectional view of the bone cutter taken along cross-sectional line  5 B- 5 B of  FIG. 5A . 
           [0017]      FIG. 6  is a perspective view of an embodiment of the cutter housing assembly of the present invention. 
           [0018]      FIG. 7  is a side view illustrating the cutter housing assembly of the present invention. 
           [0019]      FIG. 8A  is a bottom view illustrating a preferred embodiment of the housing assembly of the present invention. 
           [0020]      FIG. 8B  is a cross-sectional view of the housing assembly taken along cross-sectional line  8 B- 8 B of  FIG. 8A . 
           [0021]      FIG. 9  is a perspective view of an embodiment of the insert blade of the present invention. 
           [0022]      FIG. 10  is a magnified side view of the distal end region of the insert blade of the present invention shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    Now turning to the figures,  FIGS. 2-10  illustrate embodiments of the disposable bone cutter  30  of the present invention. As illustrated in  FIG. 2 , the bone cutter  30  comprises a cutter housing assembly  32 , a plurality of insert blades  34  and a guide rod  36 . As shown in  FIGS. 3 ,  4 ,  5 A,  6 ,  7  and  8 , the cutter housing assembly  32  further comprises a plate  38 , having a planar top surface  40 , a planar bottom surface  42 , a plate thickness  44  therebetween and a central longitudinal axis A-A therethrough. 
         [0024]    As illustrated in  FIGS. 3 ,  4 ,  5 A,  6 , and  8 A the plate  38  preferably has a curved edge  46 . More preferably, the plate  38  is generally of a spiral form. It is contemplated however, that the general shape of the plate  38  is non-limiting and may be of a rectangular, square, circular, oval, or triangular shape. 
         [0025]    A plurality of blade enclosures  48  is positioned through the thickness  44  of the plate  38  such that the central axis A-A is parallel to a blade enclosure longitudinal axis B-B as shown in  FIGS. 3 and 4 . It should be noted that although longitudinal axis B-B is illustrated through different examples of the plurality of blade enclosures  48  in  FIGS. 3 and 4 , each of the plurality of blade enclosures  48  has a longitudinal axis B-B that is parallel to central axis A-A. 
         [0026]    In addition, each enclosure  48  has an enclosure width  50 , an enclosure length  52 , and an enclosure depth  54  that extends along enclosure longitudinal axis B-B. Furthermore, each blade enclosure  48  comprises a proximal end region  56  and a distal end region  58 . 
         [0027]    In a preferred embodiment, the width  50  of the blade enclosure  48  ranges from about 5 mm to about 20 mm, the length  52  of the blade enclosure  48  ranges from about 10 mm to about 50 mm and the depth  54  of the blade enclosure  48  ranges from about 2 mm to about 10 mm. 
         [0028]    As illustrated in  FIGS. 3 ,  5 A,  6 , and  8 A, each enclosure  48  further comprises an opening  60  therewithin. This opening  60  allows for the insertion of the insert blade  34 . Each blade enclosure opening  60  comprises an opening width  62 , an opening length  64  and an opening depth  66  that extends from the distal end  72  of the blade enclosure  48  to a position within the proximal end region  70  thereof. An enclosure wall with a wall thickness ranging from about 0.5 mm to about 5 mm, surrounds the opening  60  of the enclosure  48 . In a preferred embodiment, the opening width  62  ranges from about 2 mm to about 20 mm, the opening length  64  ranges from about 10 mm to about 45 mm and the opening depth  66  ranges from about 0.5 mm to about 5 mm. 
         [0029]    As illustrated in  FIG. 4 , it is preferred that the proximal end  56  of the blade enclosure  48  is closed. However, it is contemplated that the proximal end  70  of the blade enclosure  48  may have an opening, thereby creating a throughbore (not shown) that extends through both the proximal and distal ends  70 ,  68  of the blade enclosure  48 . 
         [0030]    In a preferred embodiment, the opening  60  of the blade enclosure  48  is tapered. More specifically, the width  62  of the opening  60  of the blade enclosure  48  at the distal end  58  is greater than at the proximal end  56 . This preferred tapered opening  60  embodiment is designed to provide the insert blade  34  with a snug fit. In an alternate embodiment, the blade enclosure  48  is tapered such that its width at the distal end  68  is greater than at the proximal end  70 . 
         [0031]    In a preferred embodiment, the plurality of blade enclosures  48  are aligned such that the distal end region  58  of each of the blade enclosures  48  is directed towards the distal end region  72  of the housing assembly  48 . Furthermore, each of the individual blade enclosures  48  is positioned such that their longitudinal axes B-B are parallel to the central longitudinal axis A-A of the housing assembly  32 . 
         [0032]    In a preferred embodiment of the present invention, the plurality of the blade enclosures  48  are arranged in a spiral orientation about a central through bore  74  of the housing assembly  32 , as shown in  FIGS. 4 ,  5 A,  6  and  8 A. Furthermore, it is preferred that for each of the plurality of blade enclosures  48 , there is a corresponding blade enclosure  48  positioned directly across and equidistant from the central longitudinal axis A-A of the assembly  32 . In other words, the central longitudinal axis A-A of the housing assembly  32  is similar to that of a “mirror plane” in that there are “paired” blade enclosures  48 . As shown in  FIGS. 3 ,  5 A,  6  and  8 A, these “paired” blade enclosures  48  are designated as  48 A and A′,  48 B and B′,  480  and C′,  48 D and D′,  48 E and E′,  48 F and F′,  48 G and G′. The enclosures  48  pairs face each other with there being an equal distance between the central axis A-A and the blade enclosure longitudinal axis B-B of each of the “paired” blade enclosures  48 . For example, the distance between the central axis A-A and  48 A is equal to the distance between the central axis A-A and the longitudinal axis B-B of A′. In a preferred embodiment, this distance can range from about 10 mm to about 40 mm. 
         [0033]    In addition, it is further preferred that the plurality of blade enclosures  48  are positioned at varying height intervals  76  below the bottom surface  42  of the plate  38 . A height interval  76  is herein defined as the distance between the distal end  68  of the blade enclosure  48  and the bottom surface  42  of the plate  38 , as shown in  FIGS. 3 ,  6  and  7 . In a preferred embodiment, the height interval  76  ranges from about 0 cm, i.e. flush with the bottom surface  42  of the plate  38 , to about 20 mm. It is further preferred that each “paired” enclosure  48 A/ 48 A′ to  48 G/ 48 G′ ( FIGS. 3 and 6 ), have a similar height interval  76 . 
         [0034]    In a preferred embodiment shown in  FIGS. 3 ,  4 ,  5 A,  6  and  8 A, the housing assembly  32  has a boss  78  that is positioned within the central through-bore  74  of the assembly  32 . More specifically, the boss  78  is centrally positioned within the through-bore  74  of the housing assembly  32  and is co-axial with the central longitudinal axis A-A. In a preferred embodiment, the boss  78  comprises a bore  80 . 
         [0035]    A plurality of bars  82 , secure the boss  78  within the central through-bore  74  of the assembly  32 . The bars  82  have a length  88  from about 5 mm to about 30 mm and a thickness  90  from about 5 mm to about 10 mm, and fluidly extend from the interior wall surface  84  of the through-bore  74  of the assembly  32  to the exterior wall surface  86  of the boss  78 . It is preferred that a plurality of at least two bars  82  connect the boss  78  within the through-bore  74  of the assembly  32 . Although it is preferred that these bars  82  have a round cross-section, as illustrated in  FIGS. 3 ,  4 ,  5 A,  6 , and  8 A, they may be designed with a multitude of non-limiting cross-section shapes such as rectangular, square, triangular and the like. 
         [0036]    In a preferred embodiment, illustrated in  FIGS. 3 and 6 , the boss  78  is constructed with a distal planar edge  92 . This distal planar edge  92  is designed to act as a “stop” to prevent further advancement of the cutter  30  into the end  12  of the bone  14 . The boss  78  is preferably positioned within the central through-bore  74  of the plate  38  such that a cut depth  94 , defined between the distal planar edge  92  of the boss  78  and the distal end surface  96  of the insert blade  34  is created. It is contemplated that this distal planar edge  92  can be positioned anywhere within the central through-bore  74  of the plate  38  to establish an optimal cut depth  94  for a particular implant (not shown). In a preferred embodiment, the cut depth  94  ranges from about 20 mm to about 100 mm. 
         [0037]    It is preferred that the housing assembly  32  be composed of a biocompatible material. In a preferred embodiment, the assembly  32  is composed of a biocompatible thermoplastic such as, but not limited to, Acrylonitrile Butadiene Styrene (ABS), Polyarylamide (PAA), or Polyetheretherketone (PEEK). 
         [0038]      FIGS. 9 and 10  illustrate preferred embodiments of the insert blade  34  of the present invention. The insert blade  34  is preferably made from a biocompatible metal such as stainless steel, MP35N, titanium, and combinations thereof. Each insert blade  34  comprises a proximal blade region  98 , a distal blade region  100  and a blade length  102  therebetween. 
         [0039]    In a preferred embodiment, the proximal blade region  98  comprises a tapered proximal end blade width  104  with a roughened surface  106 . The proximal end  98  of the blade  34  is designed and dimensioned to be inserted into the blade enclosure  48 . The roughened surface  106  provides for an interference fit within the blade enclosure  48 . 
         [0040]    As illustrated in  FIGS. 9 and 10 , a groove  110  is preferably formed within the surface  112  of the distal end region  100  of the insert blade  34 . In a preferred embodiment, the groove  110  has a “V” shape. The groove  110  is designed to establish a rake angle θ of the insert blade  34 . The rake angle θ is defined as the intersection between the distal surface  114  of the groove  110  and a line E-E perpendicular to the cutting edge surface  116 , as shown in  FIG. 10 . It is preferred that rake angle θ range from about 4° to about 30°. 
         [0041]    A relief angle Ø, as illustrated in  FIG. 10 , is formed between the intersection of the distal end surface  96  of the blade  34  and a cut surface  118 . The cut surface  118  is herein defined as the surface  118  that is cut by the cutter  30  of the present invention, such as the surface of a femur bone  14 . It is preferred that the relief angle Ø range from about 4° to about 20°. 
         [0042]    In a preferred embodiment, the distal region  100  of the insert blade  34  has a chamfered portion  120 . More specifically, the chamfered portion  120  of the insert blade  34  is characterized by a region of the blade  34  that has been removed as illustrated in  FIGS. 9 and 10 . In a more preferred embodiment, the chamfered portion  120  has a chamfer angle β that ranges from about 5° to about 45°. The chamfer angle β is measured between the distal edge  124  of the proximal region  98  of the insert blade  34  and the proximal edge  126  of the chamfer portion  120 , as shown in  FIG. 9 . The chamfered portion  120  is designed such that the cutting edge  116  of the blade  34  is wider than the trailing edge  128  of the blade  34 . The chamfered portion  120  ensures that the trailing edge  128  does not interfere with the cut of the blade  34  as it is rotated about the end  12  of the bone  14 . 
         [0043]    In a preferred embodiment, each of the insert blades  34  are secured in the blade enclosure  48  via an induction bonding process. In this preferred embodiment, electromagnetic current heats the metal of the insert blade  34 , thereby causing the polymeric body of the blade enclosure  48  to melt, solidifying a bond between the blade  34  and enclosure  48 . In an equally preferred embodiment, a snap fit engagement of the insert blade  34  and blade enclosure  48  may also be designed. It is also contemplated that adhesives, cross pinned engagements, direct insert molding or ultrasonic insertion may also be used to secure and/or strengthen the bonding of the blade  34  within the enclosure  48 . 
         [0044]    Now, it is therefore apparent that the present invention has many features and benefits among which are promoting proper implant fit, decreased procedural times and minimized patient trauma. While embodiments of the present invention have been described in detail, that is for the purpose of illustration, not limitation.