Patent Abstract:
A bone cutter for use within the intramedullary canal is described. The bone cutter comprises a frusto-conical cutting head that extends to a barrel portion for attachment to a drive shaft. The cutting head comprises a plurality of spaced apart blades having a tissue cutting edge that extends radially from the exterior surface of the cutting head. The plurality of blades are arranged at prescribed angular relationships that are designed to increase cutting efficiency and debris removal, thereby reducing reactive torque, axial loading, and head pressure during a surgical procedure.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 62/294,642, filed Feb. 12, 2016. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the art of orthopedic reamers, and more particularly, to cutting heads used for intramedullary reaming. 
       BACKGROUND 
       [0003]    Reamers are tools used in orthopedic procedures to cut bone and associated tissue matter. Specifically, the cutting head of the present invention are designed to cut and bore into the intramedullary space or inner canal of a long bone such as a femur, tibia or humerus. Typically, the intramedullary space of a long bone is reamed to clean and create a space for an implant. As such, these reamers are required to be sterile and sharp. Using a dull reamer generates heat that typically leads to tissue necrosis and results in undesirable patient outcomes. A non-sterile reamer blade typically results in an infected and damaged intramedullary space that may lead to other problems for the patient. 
         [0004]    Reamers are often used in trauma procedures. In one such procedure, a prosthetic implant is inserted into the intramedullary space to help mend a fractured bone. In the procedure, a flexible reamer is first inserted into the intramedullary space of the fractured bone. Using the intramedullary reamer, a cavity space is then formed for insertion of the implant into the fractured bone. 
         [0005]    The preparation of the bone generally consists of removing the interior contents of the bone along its entire length so that a space is created allowing for insertion of the intramedullary nail. The removal of the interior contents occurs in steps, where a cutting head having a relatively small cutting diameter is used to initiate a pilot hole and removal of the medullary contents. A series of cutting heads having progressively larger cutting diameters is then used to further increase the diameter of the intramedullary space and remove more bone and tissue material. The surgeon typically continues to use reamer cutting heads of increasing diameter until the appropriately sized space is created. After the appropriate sized space is created, an intramedullary nail is typically installed within the space to assist in the healing of the traumatized bone. 
         [0006]    However, prior art cutting heads have an inefficient blade design which tends to become increasingly dull, particularly when reaming large portions of bone material within a long bone, such as a femur. Furthermore, because of their high cost, traditional cutter heads are typically reused multiple times. Over time, as these reamer heads are used and reused, the cutting blades become dull. As a result, these less efficient prior art cutting heads tend to promote an increase in “head pressure” within the intramedullary canal. “Head pressure” is the pressure that forms ahead of the reaming bone cutter within the intramedullary canal. Increasing head pressure within the intramedullary canal may result in the occurrence of a “fat” embolism. A fat embolism occurs when fat becomes lodged within a blood vessel and obstructs blood flow. The occurrence of a fat embolism may result in a stroke or even death to the patient. 
         [0007]    The intramedullary cutting head of the present invention, therefore, is designed to cut bone and tissue more efficiently than the cutting heads of the prior art. In contrast to the prior art, the cutting head blades are designed to reduce reactive torque and axial load while cutting, thus reducing trauma to the bone while cutting within the intramedullary space. In addition, the cutting head of the present invention is designed to efficiently remove cut material and debris so that the debris unobstructedly flows over the cutting head. Thus “head pressure” and the possibility of producing a fat embolism within the intramedullary canal is reduced. 
         [0008]    Unfortunately, there is no simple way to evaluate cutting efficiency after these reamer tools have been used and reused. Many times it isn&#39;t until the surgeon has reused the reamer numerous times that he becomes aware that the reamer is cutting incorrectly. In many cases, an ineffective, dull, or contaminated reamer tool is not detected until well into the reaming procedure or even after the procedure is complete. Good surgical outcomes are largely dependent on the use of a sharp, sterile reamer that is in optimal condition. Poor surgical outcomes such as a damaged intramedullary space can occur as a result of using dull or contaminated reamers. 
         [0009]    Accordingly, the present invention provides an embodiment of a cutting head having a novel blade and assembly design that improves cutting efficiency within the intramedullary space. The enhanced reaming efficiencies of the present invention decrease procedural times and minimize patient trauma. Furthermore, the intramedullary cutting head of the present invention ensures sharpness and cleanliness that promotes optimal patient outcomes. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides an embodiment of a bone cutter for use with an intramedullary reamer. The bone cutter of the present invention is of a unitary body construction that comprises a cutting head having a compound frusto-conical body extending from a proximal barrel portion. The barrel portion comprises a cavity therewithin that is configured to receive a drive shaft. 
         [0011]    The cutting head comprises a plurality of cutting blades, each having a tissue cutting edge that extends radially from the compound frusto-conical body. The blades are positioned about the cutting head in a spaced apart manner and designed to increase cutting efficiency and debris removal, thereby reducing reactive torque, axial loading, and head pressure during a surgical procedure. The cutting blades are of a unique compound angle construction that improves cutting efficiency. The cutting blades are oriented at an offset angle with respect to a longitudinal axis of the cutting head. In addition, the tissue cutting edge that extends along each blade is oriented at a cutting angle that is different from the blade offset angle. The angled tissue cutting edge is oriented such that it follows an efficient helical curve as it cuts through bone and tissue. 
         [0012]    Moreover, each blade is positioned about the exterior surface of the frusto-conical body at an optimum separation distance between adjacent blades. This optimal separation distance allows for unobstructed removal of intramedullary debris over the cutting head body. The unique blade design of the present invention thus results in increased blade stability, cutting efficiency, and reduced head pressure. 
         [0013]    A lumen extends lengthwise along the longitudinal axis through the cutting head. The lumen provides an opening through which debris may be removed from within the intramedullary canal. In addition, the lumen provides an opening through which a guidewire may be positioned therethrough. 
         [0014]    In addition, the bone cutter of the present invention may comprise a shaft attachment interface that allows for keyed attachment of the cutting head to a drive shaft. In an embodiment, the shaft attachment interface comprises a drive shaft having an outwardly extending projection. This projection is detachably mated with a proximal cutout portion. The shaft projection is received and mated with the cutout portion of the bone cutter in a keyed relationship. The shaft attachment interface can be provided with a removable interference fit, a locking junction, a dovetail junction or it can be designed as an integral portion of the cutting head and shaft assembly. 
         [0015]    Furthermore, a protective sleeve may be removably attached to the proximal end of the cutting head barrel portion. The sleeve provides an alternative means in which to secure a drive shaft to the cutting head. In addition, the sleeve provides a protective covering that minimizes potential disengagement of the shaft from the cutting head. In an embodiment, the sleeve comprises a tapered collar that surrounds the drive shaft and attaches to the barrel portion proximal end. 
         [0016]    In an embodiment, the bone cutter of the present invention may be manufactured by a metal injection molding process. In an injection molding process, the bone cutter is fabricated by injecting a composite mixture comprising a powered metal and a binder. The metal injection molding process forms the cutting head and barrel portion having a unitary body construction. Metal injection molding provides a low-cost production process that reduces manufacturing time. In addition, the metal injection molding process avoids the need for expensive grinding operations and assembly of individual blade component pieces. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of an embodiment of the cutting head of the present invention. 
           [0018]      FIG. 2  is an alternate perspective view of the embodiment of the cutting head shown in  FIG. 1 . 
           [0019]      FIG. 3  illustrates a perspective view of the embodiment of the cutting head shown in  FIG. 1  taken from the proximal end. 
           [0020]      FIG. 4  is a cross-sectional view of the embodiment of the cutting head shown in  FIG. 1  taken along longitudinal axis A-A. 
           [0021]      FIG. 5  is a side view of the embodiment of the cutting head shown in  FIG. 1 . 
           [0022]      FIG. 6  illustrates a side view of the embodiment of the cutting head shown in  FIG. 1 . 
           [0023]      FIGS. 6A-6F  are cross-sectional views taken along the longitudinal axis A-A of the cutting head shown in  FIG. 1 . 
           [0024]      FIG. 7  is a magnified side view of the embodiment of the cutting head shown in  FIG. 1 . 
           [0025]      FIG. 8  illustrates an embodiment of a sleeve attached to the cutting head shown in  FIG. 1 . 
           [0026]      FIG. 9  shows an embodiment of a sleeve that may be attached to the cutting head shown in  FIG. 1 . 
           [0027]      FIG. 9A  shows a top view of the embodiment of the sleeve shown in  FIG. 9 . 
           [0028]      FIG. 9B  is a cross-sectional view of the embodiment of the sleeve shown in  FIG. 9  taken along longitudinal axis A-A. 
           [0029]      FIGS. 10 and 11  illustrate an embodiment of a shaft attachment interface that may be used to attach a drive shaft to the cutting head shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Now turning to the figures,  FIGS. 1-3, 4, 5, and 6  illustrate an embodiment of a bone cutter comprising a cutting head  10  of the present invention. As shown, the cutting head  10  comprises a frusto-conical body  12  that extends lengthwise along a longitudinal axis A-A from a cutting head distal end  14  to a cutting head proximal end  16 . In an embodiment, a barrel portion  18  extends in a proximal direction along longitudinal axis A-A from a barrel portion distal end at the cutting head proximal end  16  to a barrel proximal end  20 . In an embodiment, the cutting head  10  comprises a distal end wall  22  having an end wall surface  24 . In an embodiment, the end wall surface  24  is oriented perpendicular to longitudinal axis A-A. The cutting head  10  provides for the cutting and removal of bone and tissue from a bone during a surgical procedure, for example, during reaming of an intramedullary canal in a femur. The barrel portion  18  provides for the attachment of the cutting head  10  to a drive shaft  26  ( FIG. 1 ). 
         [0031]    As shown in  FIGS. 2, 3, and 4 , a cavity  28 , dimensioned to receive the drive shaft  26 , extends longitudinally within the barrel portion  18  from the barrel portion proximal end  20  to the cutting head proximal end  16 . In an embodiment, the cavity  28  is dimensioned to provide an interference fit with the drive shaft  26 . In a preferred embodiment, the cavity  28  has a length  30  that may range from about 0.5 cm to about 2 cm and a diameter ( FIG. 2 ) that ranges from about 0.5 cm to about 1 cm. A plurality of spaced apart ribs  34  may extend longitudinally along the length of the barrel exterior surface. 
         [0032]    In addition, a lumen  36  extends along the longitudinal axis A-A through the bone cutting head  10 . As illustrated in  FIGS. 1 and 3 , the lumen  36  extends through the cutting head distal end wall  22 , forming a lumen opening  38  therethrough. The lumen  36  extends longitudinally through the cutting head  10  and meets the cavity  28  within the barrel portion  18 . The lumen  36  provides a channel for removal of cut bone and tissue from, for example, the intramedullary canal during a surgical procedure. In addition, the lumen  36  provides an opening for a guidewire (not shown) to extend therethrough. The guidewire may be used to help to control movement and positioning of the cutting head  10  within the intramedullary canal. In a preferred embodiment, the lumen  36  has a diameter  40  that ranges from about 0.1 cm to about 1 cm and a length  42  that ranges from about 0.1 cm to about 1 cm. 
         [0033]    As illustrated in  FIGS. 1-4, 4A, 5, and 6 , a plurality of spaced apart blades  44  extend radially from an exterior surface  46  of the frusto-conical body  12 . Each of the blades  44  has a distal frusto-conical section  48  that provides for coarse cutting and is delineated by a frusto-conical transition line  50  from a proximal frusto-conical section  52  that provides for fine cutting. As illustrated in  FIG. 1 , five spaced apart blades  44  are shown. However, the cutting head  10  may be designed with at least two spaced apart blades  44  that extend outwardly from the exterior surface  46  of the frusto-conical body  12 . The proximal frusto-conical section  52  extends from the frusto-conical transition line  50  in a proximal direction toward a tail blade segment  54 . The proximal frusto-conical section  52  and the tail blade segment  54  meet at a tail blade segment transition line  56  that is positioned proximal of the frusto-conical transition line  50 . The tail blade segment  54  extends from the tail blade segment transition line  56  to the cutting head proximal end  16 . 
         [0034]    As illustrated, each of the blades  44  comprises a cutting sidewall  58  having opposed leading and trailing blade sidewall surfaces  60 ,  62  that extend outwardly from the exterior surface  46  of the body  12 . (The leading sidewall surface  60  will also be referred to hereinafter as the “compound cutting surface  60 ”.) In an embodiment, the outwardly extending leading and trailing surfaces  60 ,  62  define a blade width  64  therebetween. In a preferred embodiment, the blade width  64  may range from about 0.1 cm to about 0.5 cm. Furthermore, as illustrated, the outwardly extending leading and trailing sidewall surfaces  60 ,  62  meet at a blade relief surface  66  that extends therebetween. The relief surface  66  extends from the cutting head distal end  14  to the cutting head proximal end  16  along the distal frusto-conical section  48 , proximal frusto-conical section  52 , and tail blade segments  54 . 
         [0035]    A tissue cutting edge  68  is formed at the intersection of the leading sidewall surface  60  and the relief surface  66 . In an embodiment, the tissue cutting edge  68  extends from the end wall surface  24 , along the distal and proximal frusto-conical sections  48 ,  52  to the tail blade transition line  56 . In an embodiment, the cutting head  10  is rotated about the longitudinal axis A-A in either a clockwise or counterclockwise direction. In a preferred embodiment, the cutting head  10  is rotated in a clockwise direction so that the tissue cutting edge  68  leads the trailing sidewall surface  62  as the cutting head  10  is rotated within the intramedullary canal. 
         [0036]    In an embodiment, the blades  44  are oriented so that the leading surface  60  of one blade  44  faces the trailing surface  62  of an adjacent blade  44 . A gap  70  ( FIGS. 6A-6F ), forming a clearance space therebetween, resides between two adjacently positioned blades  44 . In an embodiment, the gap  70  resides between the leading and trailing sidewall surfaces  60 ,  62  that are immediately adjacent to each other. In an embodiment, the gap  70  is dimensioned to provide space for the removal of cut bone and tissue during a surgical procedure. In an embodiment, the gap  70  may range from about 0.3 cm to about 2 cm. 
         [0037]    Furthermore, the proximal frusto-conical section  52  comprises a height  72  that extends from the exterior surface  46  of the frusto-conical body  12  to the relief surface  66  that extends along the proximal frusto-conical section  52 . In an embodiment, the height  72  of the proximal frusto-conical section  52  determines the diameter of the reamed opening created by the cutting head  10  within the intramedullary canal. In an embodiment, the proximal frusto-conical section height  72  may range from about 0.5 cm to about 1 cm. 
         [0038]    In an embodiment, the distal frusto-conical section  48  is designed to initially bore into bone, for example, the intramedullary space. The positively sloping relief surface  66  along the distal frusto-conical section  48  is designed to coarsely cut the intramedullary material and move it to the tissue cutting edge  68  along the proximal frusto-conical section  52 , which in turn, cuts the intramedullary tissue matter into more finely comminuted matter. The cut material flows over the exterior surface of the cutting head  10  between the gaps  70 . 
         [0039]    As illustrated in  FIG. 4 , the tissue cutting edge  68  that extends along the distal frusto-conical section  48  is oriented at a distal frusto-conical section lead-in angle φ. The distal frusto-conical section lead-in angle is defined with respect to imaginary plane B-B that is coincident end wall surface  24  and oriented perpendicular to longitudinal axis A-A. In an embodiment, the distal frusto-conical section lead-in angle φ extends between imaginary line C-C that is coincident with the tissue cutting edge  68  along the distal frusto-conical section  48 , and imaginary plane B-B that is positioned perpendicular to longitudinal axis A-A. In an embodiment, the distal frusto-conical lead-in angle φ may range from about 10° to about 80°. In a preferred embodiment, the distal frusto-conical lead-in angle φ may range from about 40° to about 70°. 
         [0040]    As illustrated in  FIG. 6 , the tail segment  54  of each blade  44  of the cutting head  10  further extends distally to the proximal frusto-conical section  52  meeting the distal frusto-conical section  48 . The tail segment extends distally from the cutting head proximal end  16 . The maximum diameter of the cutting head  10  is at the junction of a distal end of the tail segment  54  and a proximal end of the proximal frusto-conical section  52 . 
         [0041]    In that manner, the cutting edge  68  in the proximal frusto-conical section  52  extends distally and downwardly toward the longitudinal axis A-A to a frusto-conical transition point  80 , which resides along the frusto-conical transition line  50 . At this point  80 , the incline of the cutting edge  68  in the distal frusto-conical section  48  extends distally and downwardly toward the longitudinal axis A-A at a greater rate than the incline of the cutting edge  68  in the proximal frusto-conical section  52 . 
         [0042]    Referring back to the drawings, for each cutting blade  44  there is an infinite number of cross-sections from the end wall surface  24  to the frusto-conical transition point  80  of the blade sidewall  58 , and then from the transition point  80  to the proximal end of the proximal frusto-conical section  52 ,  FIGS. 6A to 6F  being just a few of them. In the cross-sections, an imaginary line D-D extends along the blade relief surface  66 . Another imaginary line E-E intersects the longitudinal axis A-A and the outermost endpoint of the cutting edge  68 , it being understood that the outermost endpoint of edge  68  is a point in each cross-section. A third imaginary line F-F aligned perpendicular to line E-E extends through the outermost endpoint of the cutting edge  68 . A relief angle α is then defined between lines D-D and F-F. 
         [0043]    As shown in  FIG. 6A , adjacent to, but spaced somewhat proximal the end wall surface  24 , the relief angle α is about 35°.  FIG. 6B  is a cross-section taken about half-way between the end wall surface  24  and the frusto-conical transition point  80  where the relief angle α is about 32°.  FIG. 6C  is a cross-section taken adjacent to but spaced somewhat distal the frusto-conical transition point  80  where the relief angle is about 28°. Thus, the relief angle α for each of the plurality of cutting blades  44  in the distal frusto-conical section  48  ranges from about 40° at the end wall surface  24  to about 30° at the frusto-conical transition point  80 . Furthermore, the average slope of the relief angle within the distal frusto-conical section  48  is about −3.01°/mm from the distal end wall surface  24  to the frusto-conical transition point  80 . It is understood that each of the plurality of blades  44  has a similar relief angle at the same cross-section. 
         [0044]    Referring now to the proximal frusto-conical section  52  for each blade  44 , the relief angle α is measured in a similar manner as shown in  FIGS. 6A to 6C  for the relief angle in the distal frusto-conical section  48 . In  FIG. 6D , the relief angle, again defined as the angle between the imaginary line D-D extending along the blade relief surface  66  and imaginary line F-F aligned perpendicular to line E-E extending through axis A-A and the outermost endpoint of the cutting edge  68 , is about 26°. In the cross-section of  FIG. 6E , the relief angle is about 21.5°. In  FIG. 6F  the relief angle is about 14.5°. Thus, the relief angle α gradually declines from a maximum of about 40° at the distal end surface  24  to a minimum of about 21° at the proximal end of the proximal frusto-conical section  52 . Furthermore, the average slope of the relief angle α within the proximal frusto-conical section  52  is about −2.22°/mm extending from the frusto-conical transition point  80  to the proximal end of the proximal frusto-conical section  52 . 
         [0045]      FIGS. 6A to 6F  further show that the sidewall  58  for each blade  44  has a leading or partially curved, partially planar compound cutting surface  60  extending proximally from the distal end surface  24  to the proximal end of the proximal frusto-conical section  52 . Beginning at the cross-section of the distal end surface  24  and extending proximally, the compound cutting surface  60  gradually changing from a predominantly curved surface to a mostly planar surface. Thus, with respect to an orientation extending outwardly along any cross-section that is normal to the longitudinal axis and that intersects the outermost endpoint of the cutting edge  68 , and moving axially from the distal end surface  24  to the proximal end of the proximal frusto-conical section  52 , the compound cutting surface  60  of sidewall  58  is mostly first curved and then becomes gradually more planar. Thus, a line along a cross-section coinciding with the distal end surface  24  and intersecting the curvature of the curved portion of the cutting surface  60  at a tangent point has the tangent point coinciding with the outermost endpoint of the cutting edge  68 , which as defined below equates to a rake angle of 0°. The distal end surface cross-section is the only cross-section in which the line is tangent to the curved portion of the cutting surface  60  of sidewall  58  and coincides with the outermost endpoint of the cutting edge  68 . 
         [0046]    Moving proximally, the compound cutting surface  60  of sidewall  58  has an increasingly larger planer surface portion immediately adjacent to the outermost endpoint of the cutting edge  68 . This means that along any one cross-section there is a planar surface portion meeting a curved surface portion at a transition point with this transition point being spaced at greater and greater distances from the outermost endpoint of the cutting edge  68  as the cross-sections are taken more and more proximally. In other words, moving proximally, the transition point between the planar portion of the compound cutting surface  60  and the curved portion of that cutting surface moves closer and closer toward the longitudinal axis and further and further away from the outermost endpoint of the cutting edge  68  until there is substantially no curvature to the cutting surface  60  of the sidewall  58 . Instead, the cutting surface  60  of sidewall  58  is generally a planar surface at the proximal end of the proximal frusto-conical section  52 . 
         [0047]    This is illustrated in  FIG. 6A  in the distal frusto-conical section  48  where imaginary line G-G intersects at a point where an outer planar portion meets a curved portion of the cutting surface  60  of sidewall  58 , this point being spaced from the outermost endpoint of the cutting edge  68 . A rake angle β is then defined between line E-E (intersecting the longitudinal axis A-A and the outermost endpoint of the cutting edge  68 ) and line G-G. In  FIG. 6A , the rake angle β is about 5°. In  FIG. 6B , which is a cross-section taken about half-way between the end wall surface  24  and the frusto-conical transition point  80 , the rake angle β is about 8°. Moving proximally to cross-section  FIG. 6C , which is taken adjacent to, but spaced somewhat distal the frusto-conical transition point  80 , the rake angle β between line G-G and line E-E is about 12°. Thus, the rake angle β for the cutting surface  60  for each of the plurality of cutting blades  44  in the distal frusto-conical section  48  ranges from about 0° at the end wall surface  24  to about 12° at the frusto-conical transition point  80  of the cutting edge  68 . Furthermore, the average slope of the rake angle β, within the distal frusto-conical section  48  is about 2.08°/mm. Again, it is understood that each of the plurality of blades  44  has a similar rake angle at the same cross-section. 
         [0048]    Regarding the rake angle β, in the proximal frusto-conical section  52 , this angle is measured in a similar manner as shown in  FIGS. 6B and 6C  for the rake angle in the distal frusto-conical section  48 . In  FIG. 6D , the rake angle between line E-E (intersecting the longitudinal axis A-A and the outermost endpoint of the cutting edge  68 ) and line G-G coincident to the planar surface portion of the sidewall  58 , is about 13.5°. In  FIG. 6E  the rake angle is about 18.5°. In  FIG. 6F  the rake angle is about 22°. Thus, the rake angle β, gradually increases from a minimum of about 0° at the distal end wall surface  24  to a maximum of about 22° at the blade tail transition line  56  within the tail segment  54 . It is noted that the average slope of the rake angle β, within the proximal frusto-conical section  52  is about 2.11°/mm. 
         [0049]    In an embodiment, the blade tail segment  54  has a curved blade relief surface  66  that extends from the blade tail transition line  56  to the exterior surface  46  of the frusto-conical body  12 . Unlike the distal and proximal frusto-conical sections  48 ,  52 , the tail segment  54  is not intended to cut tissue or bone. As illustrated, the proximal blade relief surface  66  is constructed such that it curves downward and away from the tissue cutting edge  68  of the proximal frusto-conical section  52 . In an embodiment, the tail segment  54  helps to stabilize the cutting head blade  44  as it reams within the intramedullary canal. The sloping surface of the tail relief surface  66  also enables the reamer to traverse the cut canal when the reamer is extracted. 
         [0050]      FIG. 7  illustrates a magnified side view of an embodiment of the cutting head  10  of the present invention. As shown, imaginary plane H-H is aligned perpendicular to longitudinal axis A-A. In an embodiment, each blade  44  of the cutting head  10  comprises a blade deflection angle η in which the leading surface  60  of the proximal frusto-conical section  52  deflects at an angle from the leading sidewall surface  60  of the distal frusto-conical section  48  at the frusto-conical transition point  80 . As illustrated, the blade deflection angle η is defined as the angle that extends between imaginary plane H-H, that lies perpendicular to longitudinal axis A-A and imaginary line I-I that is coincident with the leading sidewall surface  60  of the proximal frusto-conical section  52 . In an embodiment, the blade deflection angle η may range from about 70° to about 90°. 
         [0051]    In an embodiment, the cutting head  10  and barrel portion  18  may be formed having a unitary body construction. In a preferred embodiment, the cutting head  10  and barrel portion  18  may be formed using a metal injection molding process in which powdered metal such as 17-4 stainless steel mixed with a binder material is injected into a mold that defines the cutting head and barrel portion shape. After the shape of the cutting head and barrel portion are formed within the mold, the molded part is them heat treated at a temperature ranging from about 100° C. to about 1,400° C. While 17-4 stainless steel is a preferred material from which the bone cutter is formed, the bone cutter may also be formed from other metallic material such as, but not limited to, ferrous alloys, aluminum, precious metals, titanium alloys, nickel, nickel-base super alloys, molybdenum, molybdenum-copper, tungsten alloys, cobalt-chromium, carbides, ceramic, and cermets such as Fe—TiC. In addition, the cutting head  10  and barrel portion  18  may also be formed from polymeric material materials, such as but are not limited to, polyetheretherketone (PEEK), polyacrylamide (PARA) and acrylonitrile butadiene styrene (ABS). 
         [0052]      FIGS. 8, 9, 9A, and 9B  illustrate an embodiment of an optional sleeve  84  having spaced apart distal and proximal sleeve ends  86 ,  88 . The sleeve distal end  86  may be removably attached to the proximal end of the cutting head  10 . In an embodiment, the sleeve  84  forms a transition between the barrel portion proximal end  20  and the drive shaft  26 . The sleeve  84  is constructed to provide an improved seal between the drive shaft  26  and the cutting head  10 . Furthermore, the sleeve  84  is designed to minimize the possibility that the junction between the cutting head  10  and drive shaft  26  at the barrel proximal end  20  may obstruct insertion or removal of the cutting head  10  within the intramedullary canal. 
         [0053]    In an embodiment, the sleeve  84  comprises a collar  90  that extends to a tube portion  92 . The collar  90  has a tapered construction comprising a distal end outer diameter  98  that is greater than a proximal end outer diameter  100 . As shown, the tube portion  92  comprising a tube outer diameter  102  and a tube inner diameter  104  that extends along longitudinal axis A-A from the collar proximal end  96 . The collar distal end  94  is dimensioned to receive the barrel proximal end  20 . In an embodiment, the collar  90  may comprise a chamfer  106  that is formed within the collar interior at the collar distal end  94 . In an embodiment, the chamfer  106  extends annularly about the interior of the collar distal end  94 . In an embodiment, the chamfer  106  forms a surface that is configured to physically contact the proximal end of the barrel portion  18 . An adhesive positioned along the chamfer surface may be used to connect the barrel portion  18  to the sleeve  84 . 
         [0054]    In an embodiment, the collar proximal end outer diameter  100  is greater than the tube portion outer diameter  102 . This preferred relationship between the two diameters of the collar and tube portions allows for an annular ledge  108  to be formed at the collar proximal end  96 . In addition, a plurality of spaced apart collar ribs  110  may extend longitudinally along the collar exterior surface. These collar ribs  110  are dimensioned similarly to the exterior ribs that extend along the barrel portion exterior surface. In an embodiment, a ring  112 , such as a ring of shrink wrap or other compression material, may be positioned around the tube outer diameter  102 . As such, the ring  112  is designed to constrict the tube portion  92  around the shaft  24  positioned within the tube  92 , thereby forming an interference fit therebetween. 
         [0055]      FIGS. 10 and 11  illustrate an embodiment of a shaft attachment interface  114  which may be used to attach the shaft  24  to the cutting head  10 . As illustrated, the shaft attachment interface  114  may comprise a cutout portion  116  that is designed to receive a projection  118  having a corresponding cross-sectional shape in a keyed mated interface. In an embodiment, the projection  118 , constructed at the shaft distal end, is designed to be received within the cutout portion  116  having a corresponding cross-sectional shape, within a portion of the barrel  18 . The projection  118  may be received within the cutout portion  116  in a dovetail relationship. In the embodiment shown in  FIG. 11 , the cutout portion  116  may comprise at least one groove  120  that is formed within the sidewall of the barrel  18  and that extends perpendicular to the longitudinal axis. A ridge  122  that corresponds to the dimension of the groove  120  extends outwardly from the shaft distal end. As shown in FIG.  10 , the ridge  122  formed at the distal end of the drive shaft is received within the groove  120  formed within the barrel sidewall in a mated dovetail relationship. 
         [0056]    In an embodiment, the cutout portion  116  and the corresponding shaped projection  118  are not limited to the embodiment illustrated in  FIGS. 10 and 11 . It is further contemplated that the cutout portion  116  formed within the barrel portion  18  may be constructed of a plurality of non-limiting shapes such that the shaft distal end is formed of a corresponding shape that is capable of being received in a mated relationship therewithin. For example, the cutout portion  116  may be of a cross-sectional shape having a curved geometry, a rectangle geometry, triangular geometry or star geometry. It is also contemplated that that cutout portion  116  may be formed within the shaft distal end and the corresponding shaped projection  118  is formed extending from the barrel proximal end  20 . 
         [0057]    Thus, it has been shown that the reamer cutting head of the present invention provides for a low cost flexible single use intramedullary cutting tool. The present invention does not require additional grinding or re-sharpening procedures which ensures optimal sharpness and sterilization. The features of the present invention provide for an efficient intramedullary cutting tool with an optimized cutting design that enhances reaming efficiency and effectiveness.

Technology Classification (CPC): 0