Abstract:
A disposable reamer designed to improve bone and tissue removal efficiency is described. The reamer device comprises a reamer body shell, a series of reamer blades and a reamer shaft interface. The reamer body shell has a hemispherical structure having a concave interior surface and a convex outer surface. The series of reamer blades have a cutting portion comprised of a series of discrete cutting edges that is bent at an angle from the planar portion of the blade. The reamer blades are positioned along the curved concave interior surface of the hemispherical shell or along the curved convex outer surface of the shell. The reamer blades are positioned along the hemispherical shell such that their leading edges lie parallel to and tangent a bisecting plane.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application Ser. No. 61/434,839, filed Jan. 21, 2011. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the art of orthopedic reamers, and more particularly, to a disposable reamer used for cutting a concave or convex surface of a bone. 
     PRIOR ART 
     Reamers are tools used in orthopedic procedures to cut bone and associated tissue matter. In particular, the present invention is focused on disposable cutting tools for orthopedic surgical applications. Specifically, the present invention is utilized to preferably cut hemispherical surfaces of bone and/or tissue matter. Bones that require an exterior rounding of a convex hemispherical surface, typically include the femur or the ends of the phalanges of the hand or foot. Such a reaming process is often rendered following arthroplasty, which typically results from the condition of rheumatoid arthritis. 
     An example of producing a concave hemispherical surface includes reshaping of the acetabulum of the pelvis. In a surgical procedure, the acetabulum is reshaped to accept a cup prosthesis during hip arthroplasty. That is following the destruction of cartilage and bone, generally due to arthritis. 
     Most prior art acetabular reamers used in surgeries are of the geometry stated in U.S. Pat. No. 4,811,632 to Salyer. The reamer disclosed in the &#39;632 patent has a hemispherical shell with a plurality of perforated holes that act as cutting edges. Each hole is surrounded by a margin of the hemispherical shell. A portion of the margin of the shell is generally deformed outwardly to form the cutting edge raised above the surface of the shell. This type of prior art reamer requires complex manufacturing methods and costly materials to produce, therefore necessitating that the device be reused multiple times. In the case of cup arthroplasty in either a hip replacement or hip revision surgery, a set of acetabular reamers may consist of reamers with diameters ranging from about 37 mm to about 68 mm in 1 mm step increments, thus totaling over 30 sizes. Over time, as these reamers are used and reused, the cutting blades become dull. Therefore, the reamer cutting blades are required to be resharpened and sterilized before each reuse. However, this resharpening and sterilization process adds additional cost and increases the possibility of infection. There is a high likelihood that the sterilization process may not remove all possible infection agents such as bacteria, machining lubricants, and the like. 
     The geometry of the cutting edges also are known to affect the efficiency of the cutting tool. Preferably, the cutting edge of any surgical tool should be able to cut through a wide variety of tissue and bone. Examples of tissue and bone include cartilage, muscle and bone material ranging from porous cancellous bone to denser, harder cortical bone. Surgical to which merely scrape or “tear off” tissue work well on hard bone but tend to be less effective with less dense porous bone. Such scraping instruments are described in U.S. Pat. Nos. 3,630,204 and 3,633,583, both to Fishbein. In U.S. Pat. No. 3,630,204, Fishbein describes a bone cutting tool blade that is rotatable about an axis wherein the axis intersects the cutting blade at the cutting edge midpoint. At this intersection, the cutting edge reverses orientation to accommodate approaching bone and tissue that is being cut. The cutting edge is segmented to reduce the amount of contact with the surface being cut, thus reducing the cutting forces on the blade. The cutting segments on one side of the midpoint correspond with gaps or notches on the opposite side of the mipoint, thus allowing the cutting edge of the blade to contact a full hemispherical surface when rotated about the axis. 
     In U.S. Pat. No. 3,633,583, Fishbein describes a surgical device incorporating cutting blades similar to the construction of the blade described in the &#39;204 patent. The blades disclosed in the &#39;583 patent, however, do not have notches as specified in the &#39;204 patent. Instead, the blades are positioned on the tool such that their cutting edges lie within a plane that includes the axis of rotation of the device. Thus, the geometry, position and construction of the cutting edge of the blades of the tools described in the Fishbein &#39;204 and &#39;583 patents are mainly suited for a scraping method of tissue and bone removal. The Fishbein blades, however, are not capable of efficient cutting of bone and/or tissue. 
     In U.S. Pat. No. 4,621,637 to Fishbein, an attempt is made to address the scraping method of tissue and bone removal. In the &#39;637 patent, Fishbein incorporates a blade where the underside of the cutting surface is ground to effectively produce a cutting edge with a positive, non-zero rake angle. The geometry of this cutting edge insures that a skiving or cutting method of tissue and bone removal is employed. The blades of the &#39;637 patent are designed such that they are separate from the shell. Fishbein contends that this particular design yields a more cost effective method of manufacture when the cutting edge is incorporated within the shell. However, such a design does not produce a reamer with the cutting efficies afforded to by the present invention. 
     Such is also the case with U.S. Pat. No. 4,131,116 to Hedrick for creating a concave hemispherical shape. Hedrich incorporates radial slots in a formed hemispherical shell where the trailing edge of each radial slot is formed as a cutting edge and raised slightly above the surface of the hemispherical shell. Salyer also utilizes radial slots formed in a hemispherical shell in U.S. Pat. No. 5,116,165. However, Salyer&#39;s reamer design is different than Hendrick&#39;s in that Salyer utilizes radial slots that are shorter in length than those described in U.S. Pat. No. 4,131,116. In addition, the Salyer radial slots are positioned over the surface of the shell in a spiral arrangement. In the &#39;116 patent, Hendrick contends that the position of the cutting edges parallel to the hemispherical shell produce a more precise cut. Additionally, the short lengths of the slots in the &#39;116 patent are claimed to reduce chipping and produce a more desirable cut surface finish. 
     Finally, U.S. Pat. No. 5,203,653 to Kudla, U.S. Pat. No. 5,376,092 to Hein and Utley and U.S. Pat. No. 6,764,490 to Szabo all make use of a formed shell with helical slots cut into the shell in which the trailing edge of the slots serve as the cutting edge. In all cases, the method of incorporating the cutting edge into the hemispherical shell requires the use of costly materials and manufacturing methods. The present invention, unlike the prior art, incorporates a series of discrete cutting teeth with cutting edges that are strategically positioned at an offset distance. The position of these discrete cutting teeth in the design of the present invention, produces a reamer with increased cutting efficiencies in comparison to those of the prior art. Such increases in cutting efficiency minimizes drive motor torque, which allows for increased cutting precision and minimized patient trauma. 
     Accordingly, the present invention provides a cost effective single use reamer with a novel blade and assembly design that improves cutting efficiency. The enhanced reaming efficiencies of the present invention decrease procedural times and minimize patient trauma. The hemispherical reamer of the present invention ensures sharpness and cleanliness that promotes optimal patient outcomes. 
     SUMMARY OF THE INVENTION 
     The present invention provides a disposable reamer for shaping either concave or convex surfaces. The reamer of the present invention comprises a reamer body and a plurality of blades that are incorporated along a curved surface of the body. 
     The reamer body of the present invention is generally of a semi-hemispherical form, similar to that of a cup or a shell. Accordingly, the reamer body comprises a concave interior portion and a convex outer portion. In one embodiment, the plurality of reamer blades is incorporated along the curved interior surface within the concave portion of the body. In a preferred embodiment, the blades are aligned along the curved concave surface of the body such that the respective cutting edges face away toward the interior region of the shell in the direction of rotation. 
     In a second embodiment, the plurality of reamer blades is aligned with the curved outer surface of the convex portion of the reamer body shell. In this embodiment, the blades are positioned along the outer convex surface of the reamer body such that the blade cutting edges are facing outwards and in the direction of rotation. 
     In a featured embodiment of the present invention, the reamer blades are comprised of a series of discrete cutting teeth that are aligned in a linear row. The linear row of blades is further positioned along the curved surface of the body shell of the reamer. The series of discrete cutting teeth may be positioned along the curved concave interior surface of the body shell or alternatively, may be positioned along the curved convex outer surface of the shell. In either case, the reamer blades are preferably composed of a metallic material such as stainless steel, MP35N, titanium, and the like. 
     In a preferred embodiment, the reamer of the present invention comprises four linear rows of blades. Each of the rows is positioned such that they reside along the curved surface of the concave or convex portions of the sidewall of the reamer shell. Each of the four rows of blades lies within a quadrant of the concave or convex portion of the body. Specifically, each of the four linear rows of blades is positioned parallel to one of two imaginary planes perpendicular to each other that bisect the shell of the reamer. Furthermore, each of the rows of blades is aligned such that they are offset a distance from the imaginary bisecting plane. The offset position and parallel orientation with respect to the bisecting plane produces a reamer capable of efficient bone cutting action. 
     Each of the reamer blades has a cutting portion that fluidly extends from a planar portion. A gap separates each of the cutting surfaces that comprise the cutting portion of the reamer blade thus creating a series of discreet cutting teeth. The planar portion of the blade is designed to mate along the curved concave surface of the body or is positioned such that it resides along the contour of the curved convex surface of the body. Alternatively, the linear series of blades may be bonded within a slot that is formed within the curved sidewall surface of the body. The opposing, cutting edge portion of a blade is bent at an angle away from the planar surface of the blade. The cutting edge is further angled from the planar surface of the blade in the direction of rotation of the reamer. It is the series of angled discrete cutting edges in combination with the offset distance that increases the cutting efficiency of the reamer of the present invention. 
     The reamer body is designed with a perpendicular axis that is coincident with the axis of rotation of the device. This feature enables the reamer body and accompanying reamer blades to rotate in a controlled manner about the bone or tissue that is to be cut. The reamer body is preferably composed of a polymeric material, such as polyetherether ketone (PEEK) or acrylonitrile butadiene styrene (ABS). The reamer body may also comprise a series of openings that extend through the wall of the frame. These openings are designed to facilitate removal of bone and tissue. 
     During the manufacturing process, each linear row of blades is aligned along the curved concave surface of the reamer body either in direct contact with the curved surface of the sidewall of the body or residing within respective blade slots. Once positioned along the curved surface of the reamer frame, the blades are bonded thereto via an induction heating process. During this induction heating process, the reamer assembly is subjected to a heat source that melts the surrounding material of the reamer frame. The melted material flows covering the surface of the blade attachment portion. The flowing molten material then penetrates through the blade engagement openings, creating a fluid connection between the frame and the insert reamer blade, thereby bonding each blade to the frame. This low cost production process avoids the need for expensive grinding operations and can use simple stamping or chemical etching to form the reamer blades. Alternatively, an adhesive material may be used to bond the reamer blades to the surface of the reamer body. 
     In addition, a reamer connector shaft may also be provided. The reamer shaft can be removably attached to the interface portion of the reamer. Alternatively, the shaft may be provided with an interference fit, a locking junction, or can be designed as an integral portion of the reamer. In either case, the opposite end of the shaft is designed to connect to a motor to provide rotational torque to the reamer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of an embodiment of the reamer of the present invention. 
         FIG. 1A  shows a perspective view of an alternative embodiment of the reamer shown in  FIG. 1 . 
         FIG. 2  illustrates a perspective view of an embodiment of the reamer body and reamer blades shown in  FIG. 1 . 
         FIG. 3  shows a perspective view of an embodiment of a reamer body. 
         FIGS. 4A and 4B  illustrate an embodiment of the offset of the reamer blade within the reamer body. 
         FIG. 5  shows a perspective view of reamer body and attachment portion. 
         FIG. 6  illustrates a perspective view of an embodiment of a reamer blade. 
         FIG. 7  shows a side view of the reamer blade shown in  FIG. 6 . 
         FIG. 8  illustrates a magnified cross-section view of an embodiment of a reamer tooth. 
         FIG. 9  illustrates an alternative embodiment of the reamer of the present invention. 
         FIG. 10  shows a perspective view of the components comprising the reamer shown in  FIG. 9 . 
         FIG. 11  illustrates a perspective view of an alternative embodiment of a reamer body. 
         FIG. 12  shows a top view of the reamer body shown in  FIG. 11 . 
         FIG. 13  shows a magnified perspective view of an embodiment of a reamer blade shown in  FIG. 10 . 
         FIGS. 14 and 15  illustrate different embodiments of a shaft engagement portion. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now turning to the figures,  FIGS. 1-2  and  5  illustrate an embodiment of an orthopedic reamer  10  of the present invention. As shown, reamer  10  comprises a reamer body portion  12 , a shaft engagement portion  14  ( FIG. 2 ) and a series of reamer blades  16  that are incorporated with the body portion  12 . The reamer body  12  of the present invention is generally of a semi-hemispherical form, similar to that of a cup or shell. Accordingly, the body  12  comprises a curved interior sidewall surface  18  and a curved outer sidewall surface  20 . In a first embodiment of the reamer  10  of the present invention, the reamer blade  16  of a concave embodiment is positioned lengthwise along the curved interior sidewall surface  18  of the body  12 . In a second embodiment of the reamer  22  ( FIG. 9 ) of the present invention, a reamer blade  24  of a convex embodiment is positioned lengthwise along the curved outer surface of the body. 
     With regards to the first embodiment of the reamer  10  of the present invention, the reamer body portion  12  preferably comprises a curved sidewall  26  that encompasses an interior region  28 . As shown in  FIGS. 1 and 3 , the sidewall  26  has a curved interior surface  18 . More specifically, the body portion  12  is of a generally semi-hemispherical shell form such that the interior sidewall surface  18  of the sidewall  26  is concave. The reamer body  12  further comprises a body base portion  30  with a lower edge  32 . Preferably the shell is half of a hemisphere with the lower edge  32  residing along an imaginary equatorial plane. In a preferred embodiment, the hemispherical shell curves upwards from the lower edge  32  of the base portion  30  to an apex  34  that is located about the center of the hemispherical shell. An opening  36  is positioned through the sidewall  26  at the apex  34 . As shown, a perpendicular axis A-A extends through the apex opening  36  of the shell body  12 . Axis A-A defines a rotational axis of the reamer  10  during use. 
     In a preferred embodiment, the base portion  30  has a diameter  38  ranging from about 1 cm to about 10 cm and a body height  40  ranging from about 1 cm to about 10 cm. The sidewall  26  of the body  12  has a thickness ranging from about 1 mm to about 5 mm. The reamer body  12  is designed such that the diameter of the base  30  is greater than the opening  36  at the apex  34 . Furthermore, the body portion  12  is preferably composed of a polymeric material, such as acroylonitrile butadiene styrene (ABS), polyarylamide, polyetheretherketone (PEEK), or the like. 
     As shown in  FIGS. 1 and 3 , a series of slots  42  may be positioned along the curved interior surface of the body shell  12 . As shown, each slot  42  has opposing slot sidewalls  44 A,  44 B, that extend along the interior surface  18  of the sidewall  26 . A slot groove  46  resides between the opposing sidewalls  44 A,  44 B. Each slot  42  is preferably designed such that a concave reamer blade  16  is positioned therewithin. In a preferred embodiment, there are four slots  42 A,  42 B,  42 C,  42 D, ( FIG. 1 ) each of the slots having opposing slot sidewalls  44 A,  44 B, that extend lengthwise from the apex  34  to the lower edge  32  of the base  30  of the body  12 . Thus, each of the concave reamer blades  16  preferably extends lengthwise from the apex to the lower edge  32  of the base  30 . Alternatively, the slots  42  may be designed such that they reside within a portion of the thickness of the interior sidewall surface  18 . 
     As shown in  FIGS. 1 ,  3 ,  4 A, and  4 B, the slots  42  are preferably positioned along the curved interior surface of the body  12  such that they extend lengthwise about parallel to an imaginary plane  48  that bisects the body shell  12 . In addition, the slots  42  are positioned such that there is an offset distance  50  separating the lengthwise oriented slot  42  from its respective bisecting plane  48  ( FIG. 4B ). More specifically, each slot  42  is positioned along the curved interior surface  18  of the sidewall  26  of the body  12  such that the length of the slot  42  lies about parallel to, and is offset a distance from, the imaginary plane  48  that bisects the hemispherical shell. As shown in  FIG. 3 , there are two imaginary bisecting planes  48 ,  52 . The bisecting planes  48 ,  52  are perpendicular to each other and intersect along the perpendicular axis A-A. A bisecting plane is herein defined as an imaginary plane that extends through the semi-hemispherical shell dividing the shell into two equal parts. For example, slot  42 A is positioned lengthwise parallel to imaginary plane  52 , and slot  42 D is positioned lengthwise parallel to imaginary plane  48 . 
     The offset is defined herein as the distance measured from the center or midline of the slot groove  46  to the imaginary bisecting plane  48 ,  52  that extends about parallel to the slot  42 . Thus, when the reamer blade  16  is positioned within the slot, the offset distance is measured from the centerline of the length of the blade to the bisecting plane  48 ,  52  that extends about parallel to the length of the blade  16 . In a preferred embodiment, the length of the offset distance  50  ranges from about 0.5 mm to about 5 mm. The offset design of the reamer blades  16  enables the reamer  10  to cut in an efficient hemispherical path once it begins rotation about its rotational axis  54 . 
       FIGS. 2 ,  6 ,  7  and  13  illustrate embodiments of the concave and convex reamer blades  16 ,  24  of the present invention. In a preferred embodiment, the blades are composed of a biocompatible material such as stainless steel, 316-stainless steel, titanium, MP35N, or combinations thereof. 
     As shown, the blade  16  comprises a cutting portion  56  that fluidly extends from a planar blade portion  58 . The cutting portion  56  is positioned along the curved, concave side of the blade  16 . It should be noted that both concave and convex embodiment blades  16 ,  24  comprise a cutting portion  56  that extends from a planar portion  58 . The difference between the concave and convex blades  16 ,  24  resides in the position of the cutting portion  56  along the curvature of the blade. The cutting portion  56  for concave blade  16  lies along the concave blade bend whereas the cutting portion  56  for convex blade  24  lies along the convex blade bend as shown in  FIGS. 6 ,  7  and  13 . In the case of concave blade  16 , the planar portion  58  is preferably positioned within the groove  46  of the slot  42  of the reamer body  17 . As illustrated in  FIG. 1 , the curved convex side edge of the planar portion  58  of blade  16  is positioned within the groove  46  of the slot  42 . 
     Alternatively, blade  16  may be positioned directly along the interior surface of the body shell  12 . In this alternative embodiment (not shown), the convex side edge surface of the planar portion  58  of the blade is directly adhered to the interior concave shell surface  18  of the body  12 . As shown in  FIG. 1A , the convex side edge surface of the planar portion  58  of blade  16  resides within a recessed groove or slot  25  partially extending within the interior surface  18  of the body  12 . In these embodiments, the blade  16  is positioned lengthwise such that it is parallel to, and offset from, bisecting plane  48 ,  52 , similar to the position of the blade slot  42  as previously discussed. 
     In a preferred embodiment, the cutting portion  56  comprises a series of discrete cutting teeth  50 , each of them comprising a cutting edge  62 . In a preferred embodiment, the cutting teeth  60  are separated from each other by a gap  64 . As shown in  FIGS. 6-7  and  13 , each of the gaps  64  extends through the cutting portion and partially into the planar portion  58  thereby creating discrete reamer teeth  60 . These gaps  64  are strategically positioned between each tooth of the blade  16 ,  24 . That&#39;s to minimize contact of the cutting edge  62  with the surface being cut, thereby reducing the force required to cut the surface. 
       FIG. 8  shows a detailed view of the section profile of the concave blade  16 . The leading surface of the cutting edge  62  and the bisecting plane  48 ,  58  define a rake angle α at the point where the hemispherical surface to be cut. In a preferred embodiment, the rake angle α may range from about 0° to about 30°. A positive rake angle α is beneficial in that it encourages a more direct cutting motion of the blade and avoids a scraping method of cutting. It is, therefore, apparent that by bending the cutting teeth  60  and offsetting the blade from its bisecting plane, a non-zero, positive rake angle can be created. In a preferred embodiment, the leading edge of the blade cutting edge  62  lies within the bisecting plane  48 ,  52 . This embodiment helps ensure that a complete 180 hemispherical cut is achieved. Furthermore, both concave and convex reamer blade embodiments  16 ,  24  comprise a cutting edge as embodied in  FIG. 8 . Regardless of the orientation of the cutting teeth  60  of the present invention, whether the blade is a concave style blade or a convex style blade, the design and orientation of the cutting teeth  60 , illustrated in  FIG. 8 , applies to both blade embodiments. 
     In a preferred embodiment, the cutting edge  62  of each of the teeth  60  is angled in a direction facing the desired direction of rotation. In addition, the rake angle α allows the cutting edge  62  of the blade to remove both hard and soft bone and tissue using a skiving or cutting method. The cutting edge  62  is thus curved to precisely follow the contour of the intended surface being cut. As shown in  FIG. 8 , a relief surface  66  is provided at the trailing surface behind the cutting edge  62 . That&#39;s so as to not interfere in any way with the surface being cut. Moreover, the cutting teeth  62  from one blade to the next are staggered so that a gap between adjacent teeth of one blade is cut by a tooth  62  of a following blade. That way, a smooth cut surface is formed, such as a smooth semi-hemispherical cut surface without ridges or a rough contour. 
     As shown in  FIG. 5 , an embodiment of the shaft engagement portion  14  is positioned on the convex side of the reamer body  12 . As shown in the illustrated embodiment, the shaft engagement portion  14  comprises a shaft engagement annular sidewall  68  that is raised from the surface of the body  12 . The sidewall  68  is centered over the apex opening  36  of the body  12 . A cross bar  70  is positioned within the opening of the annular sidewall  68 . The ends of the bars forming the cross  70  are directly connected to an inner surface of the sidewall  68 . Preferably, the sidewall  68  has lobes  68 A where the cross bar ends connect. The engagement portion  14  is constructed such that a reamer shaft (not shown) may be releasably connected to the cross bar  70 . A motor (not shown) may then be attached to the shaft to provide rotation to the reamer. 
       FIGS. 9-12  illustrate the second alternate embodiment of the reamer  22  of the present invention. Similar to the first reamer  10  shown in  FIGS. 1 and 2 , reamer  22  comprises a body portion  72 , a series of reamer blades  24  and a shaft attachment portion  74 . Also, similar to the reamer body  12  of the first embodiment, the reamer body illustrated in  FIGS. 9-11  of the present invention, is generally of a semi-hemispherical form, like that of a cup or shell. Preferably the shell is half of a hemisphere with the lower edge  81  residing along an imaginary equatorial plane. The reamer body  72 , shown in  FIG. 11 , comprises a curved inner surface  76  and a curved outer surface  78 . More specifically, the reamer body  72  of reamer  22  comprises a concave interior region and a convex outer surface  78 . However, unlike the reamer  10  of the first embodiment, as previously discussed, convex reamer blades  24  are positioned within the body  72 . More specifically, the convex blades  24  are positioned such that the cutting portion  56  of the blade  24  protrudes though a series of corresponding slits  80 . These series of slits  80  extend through the thickness of the curved exterior sidewall of the body  72 . 
     As illustrated in  FIGS. 9 and 10 , the reamer  22  is designed with the series of cutting teeth  60  extending through their respective slit opening  80 . Similar to the blade slots  42  of reamer  10 , as previously described, the blade slit openings  80  are positioned parallel and offset from a corresponding bisecting plane. Like the reamer of the first embodiment, the orientation of the slit openings  80  positions the cutting portion  56  of the convex reamer blade  24  to enable a cut in an efficient hemispherical path about its rotational axis  54 . 
     As shown in  FIGS. 10 and 13 , the convex reamer blades  24  are constructed such that the cutting portion  56  and cutting teeth  60  are positioned about the outward curvature of the blade  24 . The outward curvature defined by a reamer blade radius is of curvature that ranges from about 1 cm to about 10 cm. In a preferred embodiment, the convex blades  24  are composed of a biocompatible material such as stainless steel, more preferably, 316-stainless steel. Other biocompatible metals such as titanium, MP35N, and combinations thereof may also be used. 
     Similar to the concave reamer blade  16  of the previous embodiment, the convex reamer blade  24  comprises a planar blade portion  58  spaced from a cutting portion  56 . A tab  82  portion extends from the end of the planar portion as shown in  FIG. 13 . When correctly positioned within the reamer body  72 , the cutting portion  56  is positioned within the slit  80  of the reamer body  72 . The planar portion  58  is preferably anchored within the reamer body  72  with the tab portion  82  extending past the base of the reamer body  72  extending through opening  83 . 
     Similar to the concave reamer blade  16 , the cutting portion  56  of the convex reamer blade  24  comprises a series of discrete cutting teeth  60 , each of the cutting teeth  60  are separated from each other by a gap  64 . These gaps  64  are strategically positioned between each tooth of the blade  60  to minimize contact of the cutting edge  62  with the surface being cut, thereby, reducing the forces required to cut the surface. In addition, each of the teeth  60  of the convex blade  24  comprises a cutting edge  62  has an associated rake angle and is positioned a skew from the planar portion  58  of the blade  24 . The cutting portion  56  is also angled in a direction towards the desired direction of rotation. Moreover, the cutting teeth  62  from one blade to the next are staggered so that a gap between adjacent teeth of one blade is cut by a tooth  62  of a following blade. That way, a smooth cut surface is formed, such as a smooth semi-hemispherical cut surface without ridges or a rough contour. 
     As illustrated in  FIGS. 9 ,  10 ,  14 - 15 , connected to the base portion of the reamer body  72 , is positioned a convex reamer adapter  74 . The adapter  74  comprises an annular adapter sidewall  84  with perpendicular cross bars positioned therewithin. Alternatively, as shown in  FIG. 15 , the convex adapter  74  may comprise a boss plate  86  instead of the cross bars  70  as illustrated in  FIG. 14 . The boss plate  86  comprises a retaining bar  85  with spaced apart first and second retaining bar sides  85 A,  85 B extending to the base periphery and located on opposite sides of the longitudinal axis of the retaining bar  85  and a central retaining bar structure  87  substantially centered between where the opposed ends of the retaining bar attach to the base periphery, the central retaining bar structure having opposed first and second radiused sides  87 A,  87 B extending beyond respective planes of the first and second retaining bar sides, the opposed first and second radiused sides being aligned with each other along a perpendicular axis bisecting the longitudinal axis of the retaining bar. A more detailed description of the boss plate embodiment adapter is given in U.S. Pat. No. 7,588,572, to White et al., which is assigned to the assignee of the present invention and incorporated herein by reference. In either embodiment, the adapter  74  has a series of adapter slots  88  within which the convex blade tabs  82  reside therewithin. 
     As shown in Table 1 below, the embodiments of the reamer  10 ,  22  of the present invention were tested against reamers that are commercially available from Acumed® USA of Hillsboro, Oreg. As shown below, an Acumed® 24 mm cup and cone style reamer were tested against the respective first and second embodiments of the reamer  10 ,  22  of the present invention. In the comparison, all reamers were set to a rotation speed of about 1,600 RPM and were used to cut samples of a urethane test material to simulate the cutting of bone. As the reamers cut the test material, their respective torque values were recorded. 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                 Reamer 
                 Trial 1 
                 Trial 2 
                 Trial 3 
                 Average 
               
               
                   
               
             
             
               
                 Acumed ® Cup 
                 3.4 Nm 
                 2.5 Nm 
                 2.7 Nm 
                 2.87 Nm 
               
               
                 Acumed ® Cone 
                 3.2 Nm 
                 3.0 Nm 
                 2.9 Nm 
                 3.03 Nm 
               
               
                 Embodiment 1 
                 1.4 Nm 
                 0.8 Nm 
                 1.2 Nm 
                 1.13 Nm 
               
               
                 Embodiment 2 
                 2.3 Nm 
                 2.0 Nm 
                 1.7 Nm 
                 2.00 Nm 
               
               
                   
               
             
          
         
       
     
     As shown in the results table above, the average measured torque value for the reamer of embodiment 1 was 1.13 Nm. In comparison, the measured average torque value for the Acumed® Cup style reamer was 2.87 Nm. Per the test results above, the reamer  10  of the first embodiment of the present invention achieved an average lower measured torque value of 1.74 Nm in comparison to the Acumed® cup style reamer. This is an improvement of about 61 percent of increased torque efficiency as compared to the Acumed® model. Likewise, the reamer  22  of the second embodiment of the present invention achieved a measured torque value of 2.00 Nm. In comparison, the Acumed® cone style reamer achieved an average measured torque value of 3.03 Nm. Thus, an improvement of about 1.03 Nm, equally about a 34 percent increase in torque efficiency was achieved in comparison to the Acumed® Cone style reamer. 
     Thus the design features of the reamer  10 ,  22  of the present invention enables efficient removal of both hard and soft bone and tissue using a skiving or cutting method. The cutting edge  62  is thus curved to precisely follow the contour of the surface being cut. The offset blade design, in combination with the use of the cutting teeth rake angle, provides a reamer capable of more efficient hemispherical cutting of both tissue and bone. 
     Accordingly, the invention is not limited, except by the appended claims.