Abstract:
A method and apparatus for grinding bone for use in orthopaedic procedures includes a bone shoot for receiving bone segments which are fed into a grinding assembly rotatable about an axis such that a plurality of cutting plates rotate about such axis to grind bone into uniform and desirable sized portions suitable for use in cementing of bone implants.

Description:
RELATED APPLICATION 
     This application claims priority from U.S. Provisional Patent Application No. 60/170,006 filed on Dec. 9, 1999. The entire disclosure of the provisional application is considered to be part of the disclosure of the accompanying application and is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to a method and apparatus for grinding bone for use in orthopaedic procedures. 
     BACKGROUND OF THE INVENTION 
     Various bone grinding devices are known in the art utilizing a variety of mechanisms in order to achieve a desired particle size of bone. Many of such devices are powered with a motor whereas others are manually driven by a hand crank. The size, expense and weight of available bone grinders, however, limit their practical application. Moreover, many of such bone grinders do not consistently produce bone particles of a uniform size which is deemed necessary in order to achieve desired tissue growth once the ground bone particles are placed adjacent to a surgical implant. Other prior art devices are prone to jam during cutting and grinding operations and motorized devices are often too heavy and cumbersome to provide easy access by a surgeon in an operating room environment. Still other bone grinding devices suffer from the fact that the grinding operation destroys bone cells such that a significant portion of the ground bone fraction is unusable for its intended purpose of promoting additional bone growth around surgical implants. 
     There is therefore a long-felt, but unsolved need in the industry to provide a method and system for grinding bone in a fashion that generates bone fragments of a desired size such that such bone fragments can be used in the regeneration of bone tissue surrounding surgical implants. Preferably, such a device would be relatively lightweight, be manually operated to facilitate use in various operating environments and would have a grinding mechanism that permits easy cleaning/autoclaving in order to ensure the requisite sterile nature of surgical instruments. 
     SUMMARY OF THE INVENTION 
     The present invention is a novel bone grinder for use in orthopaedic procedures such as in surgical procedures where bones are removed from one portion of a patient&#39;s body, and subsequently ground so that the resulting bone fragments may be utilized to augment or repair defects in other areas of the patent&#39;s skeletal system. The bone grinder of the present invention provides bone fragments of a preferred size, wherein substantially 100% of the bone segments provided to the present invention are transformed into appropriately sized bone fragments. Moreover, the present invention performs such uniform grinding on substantially all sizes and types of bone using a novel arrangement and configuration of bone cutting teeth on a rotatable bone grinding assembly, wherein the cranking force for rotating the grinding assembly effectively to grind bones input into the present invention can be readily manually applied by even petite medical professionals. 
     The novel bone grinding assembly of the present invention has a configuration of novel bone cutting teeth that is particularly useful in grinding bones via a manual cranking operation. In particular, the grinding assembly includes a plurality of bone cutting plates, each having a plurality of teeth on their outer circumference, wherein the cutting plates are positioned in contacting fixed alignment to one another on a rotatable shaft of the grinding assembly. Moreover, the configuration of cutting teeth on a fully assembled grinding assembly is such that there is: (a) relatively small amount of the total number of teeth contacting and cutting the input bone segments at any one time during operation, and (b) the arrangement of cutting teeth on immediately adjacent cutting plates is such that the teeth are offset circumferentially around the rotatable grinding shaft whereby each tooth is able to take advantage of a preceding cut made into a bone segment by an immediately adjacent tooth. That is, since each tooth both cuts into the bone segments as well as shears the bone segments along the tooth sides perpendicular to the tooth&#39;s cutting edge, and since the cutting teeth are both offset radially around the grinding shaft and have immediately adjacent cutting paths, substantially every tooth upon contacting the bone segments already has one tooth side that has been sheared by a preceding adjacent tooth. Thus, each tooth substantially shears (unassisted by adjacent teeth) the bone from the bone segments on at most a single side of the cutting tooth. Moreover, the configuration of the cutting teeth are such that each cutting tooth cuts (along its cutting edge) and shears (along a tooth side) bone fragments having substantially the desired size without fracturing these bone fragments into unacceptably small sizes. 
     It is also an aspect of the present invention that the bone grinding assembly, as well as all other bone contacting portions of the present invention, may be manufactured and assembled without any welds coming in contact with bone matter. In fact, it is an aspect of at least some embodiments of the present invention that it can be manufactured without any welds whatsoever. Note that this lack of welds is advantageous in that bone matter or other contaminants from, e.g., a previous use of the present invention can become entrapped in or about such welds and thereby in a subsequent operation, compromise the purity of the bone fragments produced by the present invention. 
     It is a further aspect of the present invention that the cutting plates, and indeed the entire grinding assembly, can be easily removed from the bone grinder of the present invention. In particular, each of the cutting plates of a grinder assembly have a central opening therethrough for sliding uniquely and fixedly onto the grinding shaft. Thus, since the adjacent side-to-side contact of the cutting plates extends substantially the entire width of the grinding chamber residing within the bone chute, the cutting plates remain in proper alignment without the use of welds or other techniques for fixing the position of cutting plates within the bone grinding assembly. Further note that each collection of cutting plates used together in an assembled grinding assembly may be slightably replaced upon the grinding shaft by a different such collection of cutting plates for providing a different size of resulting bone fragments, and/or easily replacing a dulled or chipped collection or any cutting plates within a collection. 
     It is a further aspect of the present invention that a gear box is provided thereon for increasing the cutting force that is applied by, for example, a manual crank for the present invention. In particular, the Applicant has discovered that the present invention effectively grinds bones, via a manual cranking operation, by utilizing a gear reduction of approximately 2.4 to 1. 
     It is a further aspect of the present bone grinder that it is sufficiently lightweight (approximately less than 20 lbs and preferably less than about 15 lbs, in one embodiment approximately 14 lbs), and compact in size so that the entire device can be sterilized in, e.g., an autoclave. Moreover, such repeated sterilization will not affect the performance of the bone grinder in that there are no parts that are subject to degrading during harsh sterilization techniques, and the bone grinder of the present invention neither requires nor uses any lubricants. 
     It is a further aspect of the present invention that the plunger used to force bone segments toward and into contact with the bone grinding assembly is connected, via a linkage  102  assembly, to an ergonomically designed handle that allows an operator to maintain uniform pressure on the bone segments within the bone chute by lightly squeezing a trigger-like handle oriented at approximately 30° to 60° from horizontal. Thus, even petite operators may easily maintain an effective pressure on the bone segments within the bone chute with one hand while operating a manual crank of the present invention with the other hand for thereby producing appropriately sized bone fragments. Moreover, a hand held bone grinding (sub)assembly of the bone grinder is removable from a base upon which the hand held assembly may be mounted. Accordingly, the hand held assembly of the present invention as capable of being used both on the base as well as when detached from the base. 
     It is a further aspect of the present invention that once bone fragments have been cut away from the input bone segments, such bone fragments readily exit the bone grinder and thereby do not clog the grinding assembly or the bone fragment exiting portion of the bone chute. In particular, the exiting portion of the bone chute is vertical and short in length (e.g., in the range of 1 inch to 4 inches, preferably less than about 2 inches). Moreover, the bone cutting teeth of the grinding assembly, even though configured to scoop an appropriate volume of bone material from the bone segments, has a relatively shallow convex leading face so that the reduced surface area and the centrifugal force from the rotating of the grinding assembly tends to eject the bone fragments vertically downward and through the short bone fragment exiting portion of the bone chute without sticking to the interior of the bone grinder. The grinding teeth are preferably made of hardened steel and are honed until very sharp. 
    
    
     Other features and benefits of the present invention will become evidence from the accompanying drawings and detailed description. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the present invention showing a cross section through the grinding house  56  for illustrating the bone chute  60  and the grinding assembly  64 . 
     FIG. 2 is a side view from the opposite side from that of FIG. 1, wherein only the hand held assembly  14  is shown. 
     FIG. 3 is a cut away view of the grinding house  56  as indicated by labels “ 3 ” in FIG.  2 . FIG. 3 shows the input portion  110  of the bone chute  60 , and the grinding assembly  64  within the bone chute. 
     FIG. 4 is a cross section of the grinding shaft  150  showing the key portion  166 . 
     FIG. 5 is a cut away view of the grinding housing  56  as indicated by the labels “ 5 ” in FIG.  2 . 
     FIG. 6 is a side view of a cutting plate  154 . 
     FIG. 7 is an edge view of the cutting plate  154  shown in FIG.  6 . 
     FIG. 8 is an alternative embodiment of a cutting plate  154  having cutting teeth  210  and  210   a  facing in opposite directions of rotation of the cutting plate. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1 a side view of the bone grinder  10  of the present invention is shown. The bone grinder  10  includes a hand held bone grinding assembly  14  which is attached to a base  22 , wherein the base has a base plate  26  and a mount  18  attached to the base plate. The hand held assembly  14  (a view of its opposite side also being shown in FIG. 2) is detachable from the mount  18  by, e.g., unthreading a threaded shaft  30  having a hand turnable head  34  so that the shaft  30  only resides in the mount  18  and does not enter corresponding threaded bore within the hand held assembly  14 . 
     The base  22 , in one embodiment, is made of stainless steel, wherein the base plate  26  has substantially planar bottom and top sides  40  and  44  respectively. Further, each of the bottom and top sides  40  and  44  may be rectangular in shape having, e.g., a length L of approximately 9 inches, and a width (not shown) of approximately 6 inches. Thus, as can be ascertained from FIG. 1, the bone grinder  10  of the present invention is relatively small in size (having a height of approximately 8 inches), and additionally, can be easily hand carried between operating rooms and/or sterilization devices, such as an autoclave, wherein the entire bone grinder  10  may be provided for sterilizing. Additionally note that the base plate  26  can provide a suitable platform for positioning a receptacle  48 , wherein bone fragments of a desired size exit the hand held assembly  14  via the bone fragment exit  52 . 
     The hand held assembly  14  includes a grinding housing  56  having a bone chute  60  therein for receiving bone segments to be ground by a rotatable grinding assembly  64  also provided within the housing  56 . Referring to FIGS. 1 and 2, the housing  56  has attached thereto a crank assembly  68  that in at least one embodiment, can be manually operated to rotate the grinding assembly  64  for grinding bone. The crank assembly  68  includes a gear box  72  having a crank attachment  74  protruding therefrom upon which an end of the crank arm  76  is attached for rotating the crank attachment  74 . The crank attachment, in operation, is used to rotate the grinding assembly  64  via a series of reduction gears within the gear box  72  such that gear reductions in the range of 2:1 to 4:1 are provided therein. In particular, the Applicant has discovered that such gear reduction ratios for grinding bone with the present invention provides properly sized bone fragments from substantially any type of bone by exerting approximately 3 to 5 lbs at the free end of the crank arm  76  wherein the crank arm is approximately 5 to 6 inches in length. Accordingly, an effective amount of properly sized bone fragments can be produced in approximately 1 to 5 minutes by an operator manually rotating the crank arm  76  at approximately 60 revolutions per minute. 
     The grinding housing  56  is also attached to a hand grip assembly  90  which, in turn, is attached to the mount  18  via the threaded shaft  30 . The hand grip assembly  90  includes a grip  94  extending at an angle of approximately 30° to 60° from the horizontal from its attachment to the mount  18 . Additionally, the assembly  90  also includes a lever  98  and a linkage assembly  102  for a slidable moving a plunger  106  within the bone chute  60 , wherein this plunger is shaped and sized to substantially entirely fill a cross section of the input portion  110  of the bone chute  60 . Thus, the plunger  106  is able to apply pressure to the bone segments between the plunger and the grinding assembly  64  for maintaining the bone segments in contact with the grinding assembly. The lever  98  is pivotally mounted on pivot pin  120 , wherein the finger grip portion  124  pivots in the directions of arrow  128  between a first position (labeled position A) and a second position (labeled position B). Note that the lever  98  pivots about pivot pin  120  within a slot (not shown) of the hand grip assembly  90 , wherein the slot substantially encloses, within the hand grip assembly  90 , the finger grip  124  when the finger grip is in position B. Accordingly, the portion of the lever  98  extending from the finger grip  124  to the pivot pin  120  pivots from: (a) being fully enclosed within the slot of the hand grip assembly  90  (corresponding to position B of the finger grip) to (b) being only partially enclosed within the grip  94  as, e.g., when the finger grip  124  is in position A. 
     The portion of the lever  98  on the opposite side of the pivot pin  120  from that of the finger grip  124  is pivotally connected at pivot pin  140  (shown in FIG. 1 in two positions corresponding to positions A and B of the lever  98 ) for connecting to the plunger linkage  102 , wherein this linkage in combination with the pivotal movement of the lever  98  causes the plunger  106  to slide within the input portion  110  of the bone chute  60  without binding therein. 
     FIG. 3 shows a cross section of the grinding housing  56  according to the sectioning plane  3  as indicated in FIG.  2 . In particular, FIG. 3 shows a fully assembled grinding assembly  64  provided within the grinding housing  56 . The grinding assembly  64  includes a grinding shaft  150  that extends through the grinding housing  56 , and upon which a plurality of bone cutting plates  154  are provided in fixed alignment to one another. The grinding shaft  150  includes a plate stop  158  substantially adjacent end  178  of the grinding shaft  150 , wherein the plate stop contacts an end cutting plate  154  of the series of vertically aligned and mutually contacting (i.e., contiguous) cutting plates. Note that the grinding shaft  150  also includes a keyed portion  166  thereon, wherein the grinding shaft is substantially cylindrical with the exception of a keyed portion  166 . Accordingly, since the keyed portion  166  may be flattened or recessed, a central opening  198  (FIG. 6) piercing the center portion of each of the cutting plates  154  matches a cross section of the grinding shaft  150  traverse to the grinding shaft axis  170  (such as at the cross sectioning plane indicated by the label “ 4 ” in the present figure and shown face on in FIG.  4 ). Accordingly during assembly, the cutting plates  154  sequentially slide onto the grinding shaft  150  through their central openings  198  thereby assuring that each cutting plate must rotate in unison with the rotation of the grinding shaft  150  in that the mated keyed portion  166  and the central openings prevent the cutting plates from rotational slippage when the grinding shaft  150  rotates. Additionally, the cutting plates  154  can be slidably removed from the grinding shaft  150  for replacement and/or repair. 
     Further note that during assembly of the bone grinder  10 , the grinding shaft  150  with the plurality of grinding plates  154  thereon may be inserted into the grinding housing  56  via an opening  174  into a chamber  176  (FIGS. 3 and 5) that is substantially cylindrical and traverses through the bone chute  60  wherein the shaft end  178  of the grinding shaft  150  is inserted into a compound bore  182  within the grinding housing  156  such that this compound bore substantially mates with the shaft end  178  and the plate stop  158 . Thus, the sequentially contiguous cutting plates  154  substantially entirely fill the cylindrical portion of the chamber  176  that extends across an end of the input portion  110  of the bone chute  60 . Moreover, during assembly, the opening  174  is snugly sealed with an annular insert portion  190  (FIG. 5) of the gear box  72 , wherein the insert portion has an outer diameter substantially equal to the diameter of the opening  174  and an inner opening therethrough that is of sufficient diameter to fit over the grinding shaft  150  such that the grinding shaft can readily rotate when the shaft end  186  mates with a recess within a driving gear  194  (FIG. 5) of the gear box  72  such that the keyed portion  166  extends into the mating portion of the driving gear. 
     Returning now to the contiguous series of cutting plates  154  as shown in FIGS. 3 and 5, each cutting plate  154  substantially resembles, in at least one embodiment, the cutting plate  154  shown in FIGS. 6 and 7. Accordingly, each such cutting plate  154  has a central opening  198  therethrough which is a silhouette of the grinding shaft  150  cross section as shown in FIG.  4 . Each cutting plate  154  also has a plurality of bone cutting teeth  210  on an outer rim  234 , wherein each such tooth has a leading face  214 , a trailing face  218 , and a cutting edge  222  facing generally in the direction of cutting blade  154  rotation (i.e., in the direction of arrow  226 ). In the cutting plate  154  embodiment of FIGS. 6 and 7, there are six such cutting teeth  210  evenly spaced upon the outer rim  234  of the cutting plate  154 . However, a fewer or greater number of teeth  210  may be dispersed about the outer rim  234  of such cutting plates  154 . Moreover, the number of teeth  210  per cutting plate  154  can be depend upon the diameter of such cutting plates, which in the embodiment of FIGS. 6 and 7 is 1.25 inches. Moreover, note that at least some of the cutting edges  222  are shown on the cutting plates  154  of FIGS. 3 and 5. 
     It is believed that the general configuration of each cutting tooth  210  is an important feature of the present invention in allowing a manual cranking force to cut through substantially any type of bone without chipping the teeth, and without clogging the front face  214  area with bone matter during operation of the bone grinder  10 . In particular, Applicant has discovered that a shallow concave curve in the leading face  214  of, e.g., approximately 0.046 inches for the embodiment shown in FIGS. 6 and 7 produces a leading face to which bone matter does not excessively adhere, and therefore will readily detach from the leading face when gravity and the centrifugal of the rotating grinding assembly  64  combine to urge such bone matter downwardly through the bone fragment exit  52  (FIG.  1 ). More generally, it is believed that if the concave curve of the leading face  214  causes substantially no portion of this leading face to be on a trailing side of a radius from the center point  238  to the tooth edge  222  (FIG.  6 ), then there is a reduced likelihood of the teeth  210  becoming clogged with bone matter during operation. Additionally, it is believed that a slight convex rim contour just preceding each leading face  114  (according to the rotation of the cutting plate  154  as indicated by the direction of arrow  226  of FIG. 6) both facilitates the strengthening of the teeth  210  as well as assists in reducing clogging of the leading faces  214 . Such a slight convex contour is illustrated in FIG. 6 as having a curvature corresponding to a radius of 0.55 inches in, e.g., a convex region  230  along the rim  234 . In particular, each convex region  230  smoothly blends into the concave curve of the leading face  214  of the immediately trailing tooth  210 , and at the opposite (leading) end of the convex region, it smoothly blends into a substantially straight region corresponding to the trailing face  218  of the immediately leading tooth. 
     Of course, the dimensions provided for the cutting plates  154  hereinabove are merely representative of a particular embodiment of the cutting plates  154 . Such dimensions may be changed as one skilled in the art will appreciate according to, e.g., the diameter of such cutting plates  154 , and the size of the bone fragments desired from the bone grinder  10 . The dimensions provided hereinabove correspond with a tooth height (along a radius from the center point  238  to a tooth edge  222 ) of approximately ⅛ of an inch between the tooth edge  222  and the area where the corresponding leading face  214  merges into the corresponding convex region  230 . Additionally, as shown in FIG. 7, the thickness of the cutting plate  154  is approximately 0.1326 inches which is only slightly larger than ⅛ of an inch. Thus, it is believed that the present dimensions of the embodiment of cutting plates  154  as shown in FIGS. 6 and 7 function within the bone grinder  10  to cuttingly scoop from the input bone segments, bone fragments that are approximately one-eighth inch in size since the cutting teeth  210  cut into the input bone segments a depth of approximately one-eighth of an inch and the width of the cut along the cutting edge  222  is just greater than one-eighth of an inch. Additionally, since the cutting edges  222  on different cutting plates  154  of a grinding assembly  64  are staggered, it is believed that the bone segments input to the grinding assembly  64  are substantially prohibited from both tumbling and shifting during a grinding operation. For example, pressure applied via the plunger  106  reduces a tumbling of the bone segments radially away from grinding shaft axis  170 , and the staggered tooth configuration on the contiguous cutting blades  154  reduce lateral movement of the bone segments away from each cutting edge path through the bone segments. That is, regarding such lateral movement, it is believed that since the input bone segments are of sufficient size so that more than one cutting edge  222  may be simultaneously cutting through a bone segment, the bone segment is substantially prohibited from lateral movement away from the cutting and shearing performed by the teeth  210 . Accordingly, each tooth  210  is substantially able to gouge or cut out a bone fragment from a substantially immobile input bone material, wherein such fragments are a substantially uniform in size (e.g., one-eighth of an inch). 
     One skilled in the art will readily understand that the configuration described hereinabove for the cutting plates  154  can be embodied using different dimensions than those cited above for providing a different size of bone fragments. In particular, by changing the height of the teeth  210  and the edge  234  thickness, coarser or finer bone fragments can be generated by the present invention. For example, by replacing a first collection of contiguous cutting plates  154  on the grinding shaft  150  with a second collection of cutting plates having teeth  210  twice as high (e.g., approximately one-quarter of an inch instead of one-eighth of an inch), wherein the thickness of each cutting plate in the second collection is approximately one-quarter of an inch thick, bone fragments of approximately one-quarter of an inch in size may be provided by the present invention. Alternatively, finer bone fragments may be provided by reducing the height of the teeth  210  and narrowing the thickness of the cutting plates  154 . 
     It is a further aspect of the present invention that the cutting plates  154  should have a hardness corresponding to the range of 52 through 56 Rockwell. In particular, one embodiment of the cutting plates  154  are composed of  4-40 C stainless steel that has been double drawn. However, it is within the scope of the present invention to utilize other materials such as ceramics for the cutting blades. 
     Further, note that in operation, the embodiments of the bone grinder  10  shown hereinabove are such that the cutting plates  154  rotate in a clockwise direction when viewed from the side of the bone grinder  10  shown in FIG. 1, and accordingly, the cutting edges  222  generally point in a clockwise direction in FIG.  1 . However, as shown in FIG. 8, it is also within the scope of the present invention that additional cutting teeth  210   a  may be provided on the cutting plates  154 , wherein the additional teeth are for cutting in the opposite direction of rotation. Thus, if such additional teeth have a different tooth height (from where their leading faces  214   a  merges into the corresponding convex region  230   a ) than the original teeth  210 , then an operator may vary the size of generated bone fragments according to the direction that the crank arm  76  is cranked. For example, ⅛ inch bone fragments may be generated when the crank arm  76  is rotated in the counterclockwise direction, and bone fragments of {fraction (1/16)} inch in size may be provided when the crank arm is rotated in the clockwise direction. 
     Moreover, in some embodiments of the present invention, the shape at the teeth  210  ( 210   a ) may be different from that described above. In particular, teeth with straight or planar leading and trailing faces may be used. 
     It is also within the scope of the present invention that the pattern of cutting teeth  222  distributed about the grinding assembly  64  may have other configurations than those shown in the figures discussed hereinabove. In particular, the cutting edges  222  may be disbursed in a manner so that no two cutting edges  222  align with one another in the direction of the grinding shaft axis  170 . Additionally, such cutting edges  222  may be angled with respect to the grinding shaft axis  170 . Moreover, in some embodiments of the present invention, the configuration of cutting edges  222  may be helical on the grinding assembly  64 . Further, other embodiments of the present invention may include multiple input portions  110  having different sizes (e.g., diameters) for different sized bone segments. In such an embodiment, a single grinding assembly  64  may be utilized as in the figures described hereinabove, or, the grinding assembly  64  may have two collections of contiguous cutting plates  154  thereon wherein a first of the collections produces bone fragments from a first size of bone segments, and the second collection produces bone fragment from a different second size of bone segments. 
     In use, the bone grinder of the present invention is placed in or near the operation arena. Bone tissue from a patient, for example, from a patient&#39;s rib, is excised from the patient and is then immediately conveyed to the bone shoot of the present device. As the excised bone is fed into the bone shoot, the grinding assembly is operated through the use of a hand crank such that the plurality of cutting plates is set in rotational movement. As the bone comes into contact with such cutting plates, the bone is sliced into appropriately sized particles and/or segments. Such bone particles/segments are collected and are then used by the physician as a type of living mortar to anchor surgical implants into a patient&#39;s bone. 
     The foregoing discussion of the invention has been presented for purposes of illustration and description. Further, the description is not intended to limit the invention to the form disclosed herein. Consequently, variation and modification commensurate with the above teachings, within the skill and knowledge of the relevant art, are within the scope of the present invention. The embodiment described hereinabove is further intended to explain the best mode presently known of practicing the invention and to enable others skilled in the art to utilize the invention as such, or in other embodiments, and with the various modifications required by their particular application or uses of the invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.