Patent Publication Number: US-7588572-B2

Title: Connector for domed cutting tool

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/359,605, filed Feb. 7, 2003, now U.S. Pat. No. 7,048,740, which is a continuation of U.S. patent application Ser. No. 09/671,234, filed Sep. 19, 2000, now abandoned, which is the U.S. national stage of international patent application No. PCT/US99/05951, filed Mar. 18, 1999, which claims priority to U.S. patent application Ser. No. 09/040,861, filed Mar. 18, 1998, now U.S. Pat. No. 5,976,144. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to surgical devices, and more particularly concerns a rotatable surgical cutting tool for shaping a joint socket in preparation for receiving a joint prosthetic device. 
     BACKGROUND OF THE INVENTION 
     It is now common practice in the treatment of severe cases of arthritic and other forms of degenerative joint diseases, especially the hip, to shape the hip joint socket by removing diseased and eroded bone and cartilage to conform with the shape of a prosthetic device to be implanted. Prior to installing a hip joint prosthesis, for example, articular cartilage and bone is commonly removed from the socket to reshape the acetabulum to accurately match the dimensions of the prosthetic device to be implanted. In the past, the tissue and debris removed from the hip socket was discarded; however, more recently, it has become important to capture the debris for preservation and use later in the procedure. 
     It is generally desirable for milling devices and reamers used in preparing a joint socket for a prosthesis to have cutting edges that can cut through a wide variety of tissue, such as joint cartilage and bone tissue, ranging in density from the soft or porous tissue to the denser bone. The surgical tools with hollow cutting heads are more widely used than other more open designs, because hollow head devices allow tissue and other debris to be captured within the cutting head. 
     Two distinct types of hollow dome cutting tools are currently available that capture the debris. One type employs a slotted dome with adjacent blades that are shaped to generate a socket, when rotated, conforming to the shape and dimensions of the prosthesis to be implanted. The debris cut by the blades falls through slots in the dome. 
     In another type of surgical milling tool, commonly called a “grater” reamer, the milling cutters are formed on the body by upsetting the body around openings in the body, and sharpening selected edges of the upset portions of the body. The surgical milling tool has a body with a hemispherically-shaped outer surface, an internal cavity, and milling cutters formed out of the perforations in the body at spaced-apart locations on the outer surface. The tool can be rotated in a joint socket to mill the tissues of the joint socket, such as for preparation of the joint socket for a prosthesis. The perforations in the body communicate with the internal cavity which receives the debris. The milling cutters of the milling tool are formed as cup-shaped projections extending above the perforations that face in a direction of rotation, and are arranged in a series of arcs extending circumferentially around the body. The outer wall of the milling tool forming the cup-shaped cutting edge projections is relatively thin, resulting in reduced cutting accuracy. The milling tool and cutting edge projections are formed of sheet steel, which can become dull relatively rapidly during use. Typically, if the cutting surfaces are formed integrally with the shell, such as with raised cutting edges formed directly in the shell, the manufacturing of the devices becomes very costly. In addition, once the projections forming the cutting edges of the milling tool are dull, the entire milling tool is typically discarded. 
     An example of a grater type of reamer is shown in U.S. Pat. No. 5,658,290 to Lechot, which further provides radial rods on the underside of the reamer cap that join up at the center of the cap and are integral. A reamer spindle has a shank with a head equipped with a bayonet having a locking mechanism for securing the reamer. The center of the bayonet is recessed to receive the radial rods and serve as a cavity for debris. 
     It would be desirable to provide a reaming tool fabricated from heat treated machined metal components to provide greater cutting accuracy, and at lower manufacturing costs than conventional surgical cutters. In this regard it would be desirable to form the cutters of a hardened cutting material to provide superior cutting edges. In addition, it would be desirable to provide a reaming tool with replaceable cutting edges, so that once the cutting edges become dull, they can be removed, resharpened, and replaced, for improved economy of use and maintenance. The present invention meets these needs. 
     It would be further desirable to provide a reaming tool that not only captures debris passing through the teeth, but one that also allows easier removal and use of the debris collected within the tool, versus currently available tools. The present invention is also an improved means for meeting this need. 
     SUMMARY OF THE INVENTION 
     Briefly, and in general terms, the present invention provides for an improved reaming tool that is fabricated from machined metal components to provide greater cutting accuracy, and at lower manufacturing costs than conventional cutters. The reaming tool has a multiplicity of cutters that can be formed of heat treated tool steel, to provide superior cutting edges. In addition, once the individual cutters become dull, they can readily be removed, replaced, and can even be resharpened and used again, for improved economy of use and maintenance. 
     The present invention accordingly provides for a rotary surgical reamer for removing bone and tissue from a joint to facilitate the installation of a prosthetic device. The rotary surgical reamer comprises a hollow reamer body, the hollow reamer body having a base portion, a wall with a surface defining a central cavity and a plurality of spaced apart apertures through the wall at a plurality of spaced apart locations on the wall defining cutting sites. Means are provided for connecting the hollow reamer body to a source of rotary power, and a plurality of teeth are removably disposed in the apertures. Each of the teeth have a tooth body having a base portion and a raised cutting edge, and the tooth body includes means for holding the tooth in a fixed position at one of the cutting sites. The tooth body also has a surface defining a passageway communicating between the external surface of the wall and the central cavity for passage of removed bone and tissue through the wall into the central cavity. In a currently preferred embodiment, the tooth body includes a flange for spacing the cutting edge a desired distance beyond the external surface of the wall of the reamer body. In one presently preferred embodiment, the teeth have a generally tubular shape. 
     The hollow reamer body preferably has a shape with a central axis of rotation about which perpendicular cross-sectional cutting patterns are generated during rotation of the hollow reamer body, allowing the hollow reamer body to be rotated without wobbling. In one presently preferred embodiment, the external surface of the hollow reamer body has a three-dimensional contour that is generally hemispherical, although the hollow reamer body may also have a three-dimensional contour selected from the group consisting of generally spherical, oblate spheroid, generally cylindrical, generally polygonal, or combinations thereof. Means for connecting the hollow reamer body to a source of rotary power is carried on the base portion of the hollow reamer body. 
     In one presently preferred embodiment, the external surface of the hollow reamer body has a three-dimensional contour having an apex, and the plurality of cutting sites are spaced apart in an arcuate array extending from a site adjacent the apex toward the base portion of the hollow reamer body, forming a helical pattern. In another presently preferred embodiment, the cutting sites are arranged in a plurality of arcs extending from a site adjacent to an apex of the hollow reamer body to the base portion. 
     In another preferred aspect of the invention, the rotary surgical reamer includes closure means adapted to be secured to the base portion of the hollow reamer body. In a presently preferred embodiment, the closure means comprises a base plate removably disposed on the base portion of the hollow reamer body and means for securing the base plate to the base portion of the hollow reamer body for closure of the central cavity of the hollow reamer body. The internal surface of the central cavity preferably defines at least one inner annular groove, and the means for securing the base plate to the base portion of the hollow reamer body comprises a retaining spring having first and second ends and having a relaxed bent configuration and a compressed configuration in which the ends of the retaining spring can be extended into the inner annular groove of the base portion of the hollow reamer body. 
     A drive shaft is also provided for transmitting torque for rotation of the hollow reamer body, the retaining spring having a surface defining a central aperture for receiving the drive shaft, and the base plate having a surface defining a central aperture for receiving the drive shaft for transmitting torque for rotation of the hollow reamer body. The drive shaft has a terminal end that is press fit into the central aperture in the base plate, and the terminal end of the drive shaft has a transverse aperture in the shaft, and a retaining pin adapted to be received in the transverse aperture that when received in the transverse aperture extends above the surface of the shaft, for securing the drive shaft to the base plate. 
     In one currently preferred embodiment, the means for securing the base plate to the base portion of the hollow reamer body includes a retaining spring having a relaxed bent configuration and a compressed, substantially flat configuration in which the terminal ends of the retaining spring can be extended into the inner annular groove of the base portion of the hollow reamer body. The retaining spring also preferably has a central aperture with a notch to allow the drive shaft to pass through the retaining spring. 
     A tubular collar is provided for securing the retaining spring in the compressed configuration. The tubular collar is provided with a keyway for receiving a retaining pin inserted in the shaft, such that the tubular collar can be placed over the shaft and pressed against the retaining spring and rotated to lock the pin in the collar in a position pressing against the retaining spring, so that the retaining spring is locked in the flattened configuration. 
     In an alternate preferred embodiment, the hollow reamer body comprises a hollow can having a base portion, a wall with a top surface and an internal surface defining a central cavity and a plurality of spaced apart cutting sites on the wall. The hollow can has a central axis of rotation about which perpendicular cross-section cutting patterns are generated upon rotation of the hollow can, allowing the hollow can to be rotated without wobbling. The base portion of the hollow can also preferably includes means for connecting the hollow can to a source of rotary power. In this embodiment, the plurality of cutting sites comprises a site located adjacent to the axis of the can, with a plurality of sites arrayed in a plurality of arcs extending on the top surface of the can from the axis of the can to the edge of the top surface. 
     In another general aspect of the invention, a rotary surgical reamer comprises a hollow reamer body having a wall with an external surface and a periphery, the wall defining a central cavity and a plurality of spaced apart apertures through the wall at a plurality of spaced apart locations on the wall defining cutting sites. The cutting sites define passageways communicating between the external surface of the wall and the central cavity for passage of removed bone and tissue through the wall into the central cavity. A single mounting bar extends diametrically across and is affixed to a back side of the periphery, the mounting bar having means for attaching a powered rotary driver thereto. 
     In yet another general aspect of the invention, a rotary surgical reamer comprises a hollow reamer body having a wall with an external surface and a periphery, the wall defining a central cavity and a plurality of spaced apart apertures through the wall at a plurality of spaced apart locations on the wall defining cutting sites. The cutting sites define passageways communicating between the external surface of the wall and the central cavity for passage of removed bone and tissue through the wall into the central cavity. A pair of parallel mounting bars extend chordally across and are affixed to a back side of the periphery, the mounting bars having means for attaching a powered rotary driver thereto. 
     In still another general aspect of the invention, a rotary surgical reamer comprises a hollow reamer body having a wall with an external surface and a periphery, the wall defining a central cavity and a plurality of spaced apart apertures through the wall at a plurality of spaced apart locations on the wall defining cutting sites. The cutting sites define passageways communicating between the external surface of the wall and the central cavity for passage of removed bone and tissue through the wall into the central cavity. Removable teeth are located at substantially all of the cutting sites. An array of three radial mounting bars extend inwardly from and are affixed to a back side of the periphery, the mounting bars having means for attaching a powered rotary driver thereto. 
     These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an hollow dome reamer with removable, replaceable cutters according to the present invention; 
         FIG. 2  is a top plan view of the hollow dome reamer of  FIG. 1 ; 
         FIG. 3  is a side elevational view of the hollow dome reamer of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view of the hollow dome reamer taken along line  4 — 4  of  FIG. 2 ; 
         FIG. 5  is a bottom plan view of the hollow dome reamer of  FIG. 1 ; 
         FIG. 6  is a side elevational view of a portion of the hollow dome reamer taken along line  6 — 6  of  FIG. 4 ; 
         FIG. 7  is a schematic diagram of a pattern of placement of the cutters of the hollow dome reamer; 
         FIG. 8  is a schematic diagram of an alternate pattern of placement of the cutters of the hollow dome reamer; 
         FIG. 9  is a side elevational view of a cutter of the hollow dome reamer of  FIG. 1  according to the invention; 
         FIG. 10  is a bottom plan view of the cutter of  FIG. 9 ; 
         FIG. 11  is a perspective view of the cutter of  FIG. 9 ; 
         FIG. 12  is a bottom plan view of the base plate and drive shaft of the hollow dome reamer of  FIG. 1  according to the invention; 
         FIG. 13  is a side elevational view of the base plate of  FIG. 12 , shown without the drive shaft, for the sake of simplicity; 
         FIG. 14  is a side elevational view of a portion of the base plate taken along line  14 — 14  of  FIG. 12 , showing a key flange corresponding to the notches in the dome; 
         FIG. 15  is another side elevational view of the base plate and drive shaft of the hollow dome reamer of  FIG. 1  showing the placement of a retaining pin according to the invention; 
         FIG. 16  is a side elevational view of a retaining collar for compressing the retaining spring to engage the inner annular groove of the dome, according to the invention; 
         FIG. 17  is another side elevational view of the base plate and drive shaft of the hollow dome reamer of  FIG. 1  showing the placement of a retaining spring over the drive shaft and retaining pin according to the invention; 
         FIG. 18  is a plan view of the retaining spring of  FIG. 17  according to the invention; 
         FIG. 19 , is a plan view of a ring lock spring adapted to be received on the annular groove of the drive shaft; 
         FIG. 20  is a partial view of a hollow drive rod adapted to fit over the drive shaft and ring lock spring; 
         FIG. 21  is a sectional view of an alternate embodiment of a hollow reamer body of the hollow dome reamer of the invention having a shape for use as a glenoid reamer; 
         FIG. 22  is a sectional view of another alternate embodiment of a hollow reamer body of the hollow dome reamer of the invention having an inverted curved shape for use as a femur or glenoid reamer; 
         FIG. 23  is a sectional view of another alternate embodiment of a hollow reamer body of the hollow dome reamer of the invention having a tiered shape with flattened shoulders for use as a patella recessing tool; 
         FIG. 24  is a top plan view of the hollow reamer body of  FIG. 23  showing the pattern of the cutting teeth; 
         FIG. 25  is an external perspective view of the underside of a reamer having a single peripherally emanating mounting bar, according to the invention; 
         FIG. 26  is a bottom view of the reamer of  FIG. 25 ; 
         FIG. 27  is a bottom view of the underside of a reamer having a pair of peripherally emanating parallel mounting bars, according to the invention; 
         FIG. 28  is a bottom view of the underside of a reamer having a triangular array of peripherally emanating radial mounting bars, according to the invention; 
         FIG. 29  is a bottom view of the underside of a reamer having an alternative triangular array of peripherally emanating mounting bars of the invention; 
         FIG. 30  is a side view of a preferred driver of the invention, shown with the reamer of  FIGS. 25-26  prior to assembly; 
         FIG. 31  is a perspective view of  FIG. 30 ; and 
         FIG. 32  is an enlarged perspective view of the driver and reamer dome of  FIG. 30 , shown assembled with one another. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     During surgery for preparation of a joint for installation of a joint prosthesis, it has become important to capture and preserve the tissue and debris removed from a joint for later use. However, conventional surgical tools with hollow cutting heads that are typically used for this type of surgery commonly have cup-shaped cutting edge projections that are relatively thin, become dull relatively rapidly during use, and are not readily sharpened or replaced, so that once the cutting edges of the surgical tool become dull, the surgical tool is useless. 
     As is illustrated in the drawings, the invention is accordingly embodied in a hollow dome reamer that provides greater cutting accuracy, with removable teeth having superior cutting edges. The removable teeth can readily be replaced, and resharpened for repeated usage. Referring to  FIGS. 1 through 11 , the hollow dome reamer  20  is preferably a rotary surgical reamer having a plurality of inserted modular teeth  22  or cutters that are removably disposed in a hollow reamer body or dome  24  having a plurality of apertures  26  formed therein spaced apart at various locations around the dome. In one presently preferred embodiment, the dome has a hemispherical shape, although other three dimensional geometrical shapes may also be desirable and suitable for different applications, and in general the dome may be shaped to be generally spherical, an oblate spheroid, generally cylindrical, generally polygonal, and combinations thereof. The dome is also advantageously shaped to have a central axis of rotation about which perpendicular cross-sectional cutting patterns are generated during rotation of the hollow reamer body, allowing the hollow reamer body to be rotated without wobbling. In a presently preferred embodiment, the teeth are tubular, and the apertures are correspondingly cylindrical to accept the tubular teeth, but other geometrical shapes of the teeth and the apertures may also be suitable. The apertures of the dome and the tubular teeth are currently preferably dimensioned so that the tubular teeth can be press fit into the apertures in the dome; although threading the tubular teeth and the apertures to have corresponding threads to allow the tubular teeth to be threadedly secured in the dome, and other similar ways of securing the tubular teeth in the cylindrical apertures of the dome may also be suitable. 
     As can best be seen in  FIGS. 2 ,  3 ,  5 ,  7  and  8 , the apertures are preferably arranged in a plurality of arcs  28  extending from an apex  30  of the dome to the base portion  32  of the dome. In one presently preferred embodiment illustrated in  FIGS. 1 to 5  and  7 , a tubular cutter or tooth is provided in an apex aperture located off-center at the apex of the dome, with tubular teeth being provided in a series of three equally spaced arcs of spaced apart apertures, each of the arcs commencing at the center of the apex aperture and extending to the periphery of the base portion, with the apertures in the arcs being regularly spaced apart at pre-determined distances along the arcs. In this embodiment, there are currently preferably three equally spaced arcs, with three regularly spaced apertures in each arc, but greater numbers of arcs may also be suitable. 
     In an alternative preferred embodiment illustrated in  FIG. 8 , a tubular tooth is provided in an apex aperture located adjacent to the apex of the dome, with tubular teeth being provided in an arcuate, generally helical path of spaced apart apertures, the arc commencing generally at the apex of the dome and extending to the periphery of the base portion. The apertures in the helical arc are preferably spaced apart at pre-determined distances along the arcs such that all of the apertures fall on a spiral line extending from the apex aperture of the dome to the periphery of the base portion. 
     Referring to  FIGS. 4 and 5 , the dome has an inner central cavity  34  or chamber, a hemispherical external surface  36 , and an outer wall  38  having a thickness that is sufficient to provide adequate support for a plurality of the tubular teeth disposed in the apertures of the dome. Each tubular tooth preferably also has an interior passageway  39 , so that when the teeth are inserted in the apertures of the dome, the hollow tubular teeth provide communication between the external and internal areas of the dome through the wall. As explained above, while the teeth are currently preferably tubular, and the apertures are cylindrical, other cross-sectional shapes of the teeth and apertures may also be suitable as long as an interior passageway is provided in the teeth, and the teeth can be removably disposed in the apertures of the dome. 
     The base portion of the dome preferably has at least one inner annular groove  40  that can be seen in  FIG. 4 , for receiving the terminal ends  42  of a retaining spring  44  of the base plate, and a plurality of notches  46  adapted to receive corresponding key flanges  48  of the base plate, described below. In one presently preferred embodiment, the base portion of the dome has two diametrically opposed notches adapted to receive corresponding key flanges of the base plate. The dome is currently preferably formed from metal, such as steel, such as stainless steel or tool steel for example, titanium alloy, aluminum, aluminum alloy, nitinol, and molybdenum, although the dome can be made of other suitable materials, such as ceramic or plastic, for example. 
     As can best be seen in  FIGS. 9 and 11 , the tubular teeth each have a raised cutting edge  50 , a tubular base portion  51 , and a flange  52  or shoulder that is aligned with the hemispherical external surface of the dome to position the cutting edges of the teeth at a specific desired distance above or beyond the hemispherical external surface of the dome. The teeth are currently preferably fabricated of heat treated tool steel, although the teeth can also be formed from other suitable materials, such as stainless steel, ceramic, plastic, titanium alloy, aluminum alloy, nitinol, and molybdenum. Each cylindrical, tubular tooth insert is preferably formed by cutting a tube formed of tool steel into segments, and grinding down a portion of one end of a segment to form the flange or shoulder, and leaving the raised portion of the end of the segment as the cutting edge. The cylindrical, tubular tooth insert is then press fit in an aperture of the dome, oriented so that the flange is flush with the external surface of the dome and facing in a direction of rotation  54  of the dome, so that when the dome is rotated in the specified direction, the raised circular cutting edge section will perform the cutting of bone and other tissue, which will then be extruded through the central hole or passageway  39  in the tooth and into the central cavity of the dome. 
     With reference to  FIGS. 12 to 14 , the hollow dome reamer also includes a circular base plate  56  with a plurality of key flanges  48  adapted to be received in the corresponding notches  46  of the base portion of the dome. The base plate is removably disposed on the base portion of the dome, and achieves closure of the central cavity of the dome. In a currently preferred embodiment, the circular base plate has a pair of diametrically opposed key flanges, and means  58  for securing the base plate to the base portion of the dome. 
     In a currently preferred embodiment, the means for securing the base plate to the base portion of the dome comprises a leaf spring retaining spring  44  shown in  FIGS. 17 and 18  that has a compressed, considerably flattened configuration in which the terminal ends of the retaining spring can be extended into the inner annular groove  40  of the base portion of the dome, and a relaxed, slightly bent configuration illustrated in  FIG. 17  in which the terminal ends of the retaining spring do not extend into the inner annular groove of the base portion of the dome. The retaining spring preferably has a central aperture  66  to allow passage of a drive shaft, shown in  FIGS. 15 and 17 , through the retaining spring, and the circular base plate also has a central aperture  68  for receiving the drive shaft. The drive shaft  70  is provided for transmitting torque for rotation of the dome. The drive shaft has a terminal end  72  that is press fit into the aperture  68  in the base plate. The terminal end  72  of the shaft also has an aperture  74  for receiving a retaining pin  76  that, when received in the aperture of the terminal end of the drive shaft, extends above the surface of the drive shaft, for securing the drive shaft to the base plate. The retaining spring central aperture also includes a notch  77  to allow the retaining spring to slide over the retaining pin  76  of the drive shaft. 
     Referring to  FIGS. 16 and 17 , a tubular collar  78  having a keyway  80  for receiving the pin of the shaft is also provided that fits over the drive shaft. The collar can be pressed against the retaining spring to flatten it, and then rotated to lock the pin in the keyway of the collar, so that the retaining is locked in a flattened configuration. 
     With reference to  FIGS. 15 and 19 , the proximal end  82  of the drive shaft also preferably has an annular groove  84  for receiving an annular spring lock  86  shown in  FIG. 19 . The spring lock comprises a main loop  88  that is received in the annular groove of the drive shaft, an arm  90  extending generally perpendicular to the curve of the loop, and a ball tip  92  at the distal end of the arm. Referring to  FIG. 20 , the arm and ball tip of the spring lock are adapted to be received in a slot  94  of a slotted collar  96  of a hollow drive rod  98 , adapted to be connected to a source of rotary drive power, such as an electric drill motor. 
       FIG. 21  illustrates a first variant of the shape of the hollow reamer body illustrated in  FIGS. 1-8 , adapted for use as a glenoid reamer. In this variant, the shape of the external cutting surface of the hollow reamer body can be generally convex. but not necessarily hemispherical, and is similar in many respects to the embodiment illustrated in  FIGS. 1-8 , so that elements of the first variant that are similar to those of the first embodiment described above are described with similar reference numbers. The convex hollow dome glenoid reamer  120  preferably has a plurality of inserted modular teeth  122  that are removably disposed in the hollow reamer body or dome  124  having a plurality of apertures  126  formed therein spaced apart at various locations around the dome. The dome of the glenoid reamer is shaped to have a central axis of rotation about which perpendicular cross-sectional cutting patterns are generated during rotation of the hollow reamer body, allowing the hollow reamer body to be rotated without wobbling. 
     As was illustrated in  FIGS. 1-5  and  7 - 8  in connection with the first embodiment, in the glenoid variant of the hollow dome reamer, the apertures are preferably arranged in a plurality of arcs extending from an apex of the dome to the base of the dome. Alternatively, a tubular tooth can be provided in an apex aperture located adjacent to the apex of the dome, with tubular teeth being provided in an arcuate, generally helical path of spaced apart apertures, the arc commencing generally at the apex of the dome and extending to the periphery of the base portion. 
     The hollow reamer body or dome has an inner central cavity  134  or chamber, an external surface  136 , and an outer wall  138  having a thickness that is sufficient to provide adequate support for a plurality of the tubular teeth disposed in the apertures of the dome. The cutting teeth are as described hereinabove. As explained above, while the teeth are currently preferably tubular, and the apertures are cylindrical, other cross-sectional shapes of the teeth and apertures may also be suitable as long as an interior passageway is provided in the teeth, and the teeth can be removably disposed in the apertures of the dome. The base portion  132  of the dome preferably has an integral base plate  140  having an aperture for receiving a drive shaft for supplying rotary power to the reamer. 
     In another presently preferred variant of the hollow reamer body illustrated in  FIG. 22 , the shape of the hollow reamer body is adapted for use as a femur or glenoid reamer. In this second variant, the shape of the external cutting surface of the hollow reamer body can be generally concave, but not necessarily hemispherical, and is similar in many respects to the embodiment illustrated in  FIG. 21 , so that elements of this second variant that are similar to those described above are described with similar reference numbers. The hollow dome glenoid reamer  220  preferably has a plurality of inserted teeth  222  that are removably disposed in the hollow reamer body or dome  224  having a plurality of apertures  226  formed therein spaced apart at various locations around the dome. The dome of the concave femur or glenoid reamer is shaped to have a central axis of rotation about which perpendicular cross-sectional cutting patterns are generated during rotation of the hollow reamer body, allowing the hollow reamer body to be rotated without wobbling. 
     As was illustrated in  FIGS. 1-5  and  7 - 8  in connection with the first embodiment, in the glenoid variant of the hollow dome reamer, the apertures are preferably arranged in a plurality of arcs extending from an apex of the dome to the base of the dome. Alternatively, a tubular tooth can be provided in an apex aperture located adjacent to the apex of the dome, with tubular teeth being provided in an arcuate, generally helical path of spaced apart apertures, the arc commencing generally at the apex of the dome and extending to the periphery of the base portion. 
     The hollow reamer body or dome has an inner central cavity  234  or chamber, an external surface  236 , and an outer wall  238  having a thickness that is sufficient to provide adequate support for a plurality of the tubular teeth disposed in the apertures of the dome. The cutting teeth are as described hereinabove. As explained above, while the teeth are currently preferably tubular, and the apertures are cylindrical, other cross-sectional shapes of the teeth and apertures may also be suitable as long as an interior passageway is provided in the teeth, and the teeth can be removably disposed in the apertures of the dome. The base portion  232  of the dome preferably has an integral base plate  240  having an aperture for receiving a drive shaft for supplying rotary power to the reamer. 
     In another presently preferred variant of the hollow reamer body illustrated in  FIGS. 23 and 24 , the shape of the hollow reamer body is adapted for use as a patella recessing tool. In this third variant, the shape of the external cutting surface of the hollow reamer body can be generally tiered to have two or three tiers for example. Referring to the specific embodiment shown in  FIGS. 23 and 24 , the patella recessing reamer provides a generally flat raised first inner tier  316 , and a generally flat lower second tier  318 . This embodiment is similar in many respects to the embodiments illustrated in  FIGS. 21 and 22 , so that elements of this third variant that are similar to those described above are described with similar reference numbers. The hollow dome patella recessing reamer  320  preferably has a plurality of inserted teeth  322  that are removably disposed in the hollow reamer body or dome  324  having a plurality of apertures  326  formed therein spaced apart at various locations around the dome. The dome of the tiered patella recessing reamer is shaped to have a central axis of rotation about which perpendicular cross-sectional cutting patterns are generated during rotation of the hollow reamer body, allowing the hollow reamer body to be rotated without wobbling. 
     As is shown in  FIG. 24 , in the patella recessing variant of the hollow dome reamer, the apertures are preferably arranged in a plurality of arcs extending from an apex of the dome to the base of the dome. Alternatively, a tubular tooth can be provided in an apex aperture located adjacent to the apex of the dome, with tubular teeth being provided in an arcuate, generally helical path of spaced apart apertures, the arc commencing generally at the apex of the dome and extending to the periphery of the base portion. 
     The hollow reamer body or dome has an inner central cavity  334  or chamber, an external surface  336 , and an outer wall  338  having a thickness that is sufficient to provide adequate support for a plurality of the tubular teeth disposed in the apertures of the dome. 
     The cutting teeth are as described hereinabove. As explained above, while the teeth are currently preferably tubular, and the apertures are cylindrical, other cross-sectional shapes of the teeth and apertures may also be suitable as long as an interior passageway is provided in the teeth, and the teeth can be removably disposed in the apertures of the dome. The base portion  332  of the dome preferably has an integral base plate  340  having an aperture for receiving a drive shaft for supplying rotary power to the reamer. 
     It has thus been demonstrated that the present invention provides for a reaming tool that provides greater cutting accuracy, with tubular teeth superior cutting edges that can readily be removed, replaced, and resharpened for repeated usage. The tubular teeth can be simply and inexpensively manufactured from hardened tool steel. The present invention thus provides for an improved hollow dome reamer providing for improved economy of use and maintenance, and at lower manufacturing costs than other conventional hollow dome reamers. 
     It should be recognized that other patterns of the teeth on the dome may also be suitable, such as a random scattering of locations of the teeth on the dome, or a symmetrical balancing of locations of the teeth on the dome so that forces exerted on the dome would be generally balanced. Other suitable closure means also may alternatively be provided, such as by simply providing the circular base plate with peripheral threads adapted to interfit with corresponding threads on the inner base portion of the dome, with the direction of the threading being such that the base plate can be secured to the dome by rotating the base plate in the direction of rotation of the dome. 
       FIGS. 25-32  portray still other, general aspects of the invention. Specifically,  FIGS. 25-26  and  30 - 32  show one of such embodiments, i.e., a rotary surgical reamer  420  comprises a hollow reamer body  24  having a domed shape with an apex  424 , a wall  38  with an external surface  436  and a peripheral base  432 , the wall defining a central cavity  434  and a plurality of spaced apart apertures  426  through the wall  38  at a plurality of spaced apart locations on the wall  38  defining cutting sites. The cutting sites define passageways  439  communicating between the external surface  436  of the wall and the central cavity  434  for passage of removed bone and tissue through the wall  38  into the central cavity. A single mounting bar/retaining member  440  extends diametrically across and is affixed to a back side of the peripheral base  432 , the mounting bar/retaining member  440  having a centering structure  443  with radiused sides  445  centered on the mounting bar/retaining member  440 . Portions of the radiused sides  445  extend beyond parallel side surfaces  447  of the retaining member  440 , and are adapted for centering a powered rotary driver thereto via a corresponding centering structure  443 ′. For example, an aperture  442  and interfacing cylindrical surface of a shaft  464  represent a suitable centering structure and corresponding structure  443 ′ combination, with the purpose of facilitating a bayonet-type connection between the reamer  420  and driver in a manner described below. Mourning bar/retaining member  440  may be molded with base  432 , as shown by armatures  441  or the like which further aid in the connection mechanism. 
     Yet another general aspect of the invention is depicted in  FIG. 27 , where a pair of parallel mounting bars  440   a - b  extend chordally across and are affixed to a back side of the peripheral base, the mounting bars having means in the form of complementary notches  442   a ,  442   b  for centering a powered rotary driver (not shown) for connection to the reamer  420  in a manner that will be appreciated by those in the art from a discussion of  FIGS. 30-32 . 
     Still another general aspect of the invention is shown in  FIG. 28 , where an array of three radial mounting bars  440   a - c  extend inwardly from and are affixed to a back side of the peripheral base  432 , the mounting bars  440   a - c  respectively having central termini  442   a - c  spaced from one another which functions as a means for centering a powered rotary driver (not shown) during connection to the reamer. 
     As shown in  FIG. 29 , the mounting bars  440   a - c  may alternatively meet centrally, as where a recessed driver connection is desired, as explained below. 
     It will be appreciated that, although the various mounting bar configurations described above in  FIGS. 25-29  are depicted without the removable cutting teeth  422  shown in  FIGS. 30-32  below, it is preferred that the apertures  426  which define the cutting sites have the removable teeth of the present invention. 
     The driver  444  represented in  FIGS. 30-32  comprises a shank  446  with a shoulder  448 , and a spindle head generally indicated at  450 . Head  450  further comprises a slide  452  mounted about a shaft  454 , one end  456  of which is fixed to the shank  446  and the other end of which is provided with a flange  458  having a diameter greater than that of the shaft  454 . The slide  452  is pushed on the shaft  454  axially in the direction of arrow  460  by a spring (not shown) which applies it against the upper flange  462  of the shaft. The upper flange  458  serves as bayonet, preferably having a protrusion  464  at its center thus forming a collar shape. Formed in this collar are four L-shaped bayonet catches  466  which are intended to receive the mounting bar  440  of the reamer. The slide  452  is provided with four studs  468  which are parallel to the shaft  454  and to which there correspond four holes  470  ( FIG. 32 ) in the flange  462 , the studs passing through these holes in order to close the catches  446  of the bayonet and thus lock the mounting bar  440  of the reamer in the head  450  of the spindle shaft  454 . In order to unlock the mounting bar  440 , slide  452  is moved in a direction away from the flange  462  (opposite the direction of arrow  460 ) so that mounting bar  440  is no longer blocked in the catches  446  of the bayonet by the studs  470 . This allows the driver  444  to be disassembled from the reamer  420 . 
     As shown in  FIGS. 27-29 , greater number and a different array of mounting bars can be provided as described above, in which case the number and location of the bayonet catches would need to be correspondingly structured and arrayed so as to accommodate the particular choice of design, respectively. Those skilled in the art will appreciate the manner in which the catches could be provided to adapt them to receive whatever number and array is intended by the user, according to the teachings of the present invention. 
     Protrusion  464  could be stationary or spring-loaded, however, in use with a reamer  420  of the type shown in either  FIGS. 25-28  the protrusion functions as a centering means allowing for greater ease of effecting the bayonet connection between driver  444  and reamer  420 . In the case where protrusion  464  functions as a centering means, for example, in conjunction with the single mounting bar  440  having aperture  442  within which it is received ( FIGS. 30-32 ), the user experiences less effort and time finding the correct orientation needed for making the bayonet connection. This is important in minimizing the surgeon&#39;s time in performing the bone preparation steps of the given implantation procedure. The single mounting bar  440  ( FIGS. 25-26  and  30 - 32 ) may be captured by the bayonet connection in any opposed pair of the (four) catches  466  due to its relatively simple orientation requirements. Where the protrusion is spring-loaded (not shown), this allows use of the same driver with the mounting bars  440   a - c  of  FIG. 29  which meet centrally and require a recessed structure of the area between catches  466  internally of upper flange  462 , as will be appreciated by those skilled in the art. Alternatively, where centrally meeting mounting bars  440   a - c  are employed, as in  FIG. 29 , the protrusion  464  could be eliminated altogether. 
     The structure of those reamers  420  shown by  FIGS. 25-29  yield further improvements in the ease and speed by which removed bone matter can, in turn, be emptied from the cavity  434  within which it has been captured, for later reuse by the surgeon in the implantation procedure. This is because the underside of the base  432  of reamer  420  is more open and thus accessible to the surgeon&#39;s extrication. 
     The entire reamer  420 , exclusive of removable and replaceable teeth  422 , can be cast, molded or stamped. Where a molding operation is used, the mounting bar  440  and armatures  441  ( FIGS. 25-26 ) can be molded in the same operation as the wall of reamer  420 , thus reducing the number of components and steps needed to fabricate the reamer. 
     It will be apparent from the foregoing that while particular forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.