A system including a milling head and a base unit for converting bone fragments into bone granules.

Abstract

To provide a bone mill to use for breaking a bone to use for a surgery.SOLUTION: A bone mill 30 includes a base 32 and a mill head 34 that is removably attached to the base. A cutting disc is rotatably disposed in the mill head. When the mill head is attached to the base unit, the cutting disc is rotated by a motor internal to the base unit. A plunger 40 mounted on the mill head urges bone against the cutting disc. The cutting disc and an abutting plate internal to the mill head shear the bone into bone grains. The bone grains are discharged from an opening in the mill head into a catch tray 42 removably attached to the mill head.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention generally relates to a bone mill used for crushing bones used in surgery. More particularly, the present invention generally relates to a system including a removable mill head of the bone mill and a base unit used with the mill head.

Background Art

[0002] As its name indicates, a bone mill is a medical instrument for crushing bone fragments. The crushed bone, which is often in the size of chips, is used as a filler placed adjacent to other areas of bone in surgery. For example, in spinal fusion surgery, it is a well-known technique to place a composite formed from crushed bone around a rod used to hold adjacent vertebrae in alignment. This composite serves as a lattice when the tissue that generates vertebrae grows to form a bone union between these vertebrae. This union minimizes the load applied to the rod. Similarly, in other surgeries such as orthopedic surgery and craniofacial surgery, crushed bone is used as a filler and / or growth formation lattice.

[0003] The reason crushed bone is used as a filler / growth formation lattice in these surgeries is that the material forming the bone, i.e., protein, functions as a supplement that promotes the budding of adjacent living bone cells to generate new bone. Therefore, in surgeries where it is desired to promote the growth of new bone, crushed bone, to which auxiliary materials may be added, is used as a filler within the space where bone growth is desired.

[0004] Crushed bone is formed by collecting large pieces of bone that may occupy a volume of 8 cm 3 or more and crushing the bone into bone granules. Bone granules typically occupy a volume of 0.008 cm 3 or less.

[0005] A bone mill is a device used to break down, or subdivide, large chunks of bone into bone particles. A typical mill has a housing. A blade assembly or mill head is rotatably mounted in the housing. This blade assembly / mill head has cutting surfaces. These cutting surfaces allow for cutting or crushing of the bone pressed against them. There is also a device for driving the blade assembly / mill head. If the bone mill is manually operated, this drive device is often a handle that can rotate the blade assembly / mill. Powered bone mills have a motor that performs this function.

[0006] It should also be understood that bone mills are typically designed for use in the operating room where surgeries requiring bone granules are performed. This is because, in many cases, the bone used to create the granules is harvested from another part of the patient's body. Using the patient's own bone tissue reduces the possibility of rejection by the body. Therefore, the first step in surgery using bone composites often involves harvesting small fragments of bone from another part of the patient's body. This bone will then be broken down into granules to form the composite. Bone harvested from the patient themselves is called autogenous bone graft. Bone obtained from someone other than the patient is called allogeneic bone graft.

[0007] Ideally, surface oxidation of bone nodules that form a composite before implantation should be minimized as much as possible. Surface oxidation can reduce the degree to which the material forming the bone nodules functions as a lattice or raw material that promotes new bone growth. Therefore, even when allografts are crushed to generate bone nodules, this crushing process should be carried out as close as possible to the time when the bone nodule composite is needed.

[0008] Well-known bone mills are not perfect, but are satisfactory. Nevertheless, there are several limitations associated with these devices. For example, some bone mills have reusable blades / mill heads. One drawback of this type of assembly is that it takes time to disassemble it after each use to clean its parts and then reassemble it for subsequent use. Yet another drawback of this type of device is that the blades / mill heads usually have numerous densely packed surfaces, some of which have sharp edges. Care must be taken to sterilize the blades after each use of this device. This process requires considerable time to ensure that the blades are properly sterilized and that the person performing the work does not cut their fingers on the sharp edges.

[0009] Furthermore, over time, reusable mill blades inevitably become dull. This necessitates either replacing the blade set with a new one or sharpening the existing blades again.

[0010] To avoid the problems associated with sterilizing bone mill blades, single-use bone mills, or replaceable mill units, are commercially available. These devices feature a base unit to which the mill unit is detachably mounted. The mill unit comprises a body to which the blade is rotatably mounted. Often, the base unit includes a motor for driving the blade. These devices are designed so that the mill unit is discarded after a single use. The advantage of this type of device is that medical personnel do not need to sterilize the blade, i.e., the sharp metal object.

[0011] Some of these systems are designed so that once the bone has been crushed, a medical professional must use an instrument or their fingers to remove the bone from around the blade. This extra step increases the overall time required to process the bone. Some well-known disposable bone mills are designed so that a medical professional must remove the blade to access the bone fragments. This step in the procedure requires the medical professional to take care not to cut their fingers on the sharp metal object.

[0012] Furthermore, many well-known bone mills are configured so that the blade repeatedly strikes the same surface of the bone or bone granules. The frictional heat generated by such activity can damage the bone-forming material. This damage can negatively affect the ability of the bone granules to function as growth material for new bone.

[0013] Another drawback of some well-known bone mills is that the number of times bone is crushed during the crushing process is not uniform, even within a single crushing process. Some bone undergoes only the intended crushing. The resulting bone particles may be too large to be used in subsequent surgery. In the same crushing operation, other bone may be crushed repeatedly, resulting in extremely small, almost dust-sized particles. These small bone particles are difficult to recover for surgical use.

[0014] Furthermore, a significant portion of the bone crushed by some bone mills may not be easily recovered. This is especially true when generating bone granules using autologous bone grafts, which tend to be moist. As a result, these granules are known to adhere to the surface of the bone mill, including the blades. To ensure that a sufficient amount of granules are available from the newly harvested bone, medical professionals may feel compelled to generate an excess of granules, knowing that some will be unusable. Alternatively, these medical professionals may have to carefully remove any bone that has adhered to the mill's surface, including the surface around the sharp cutting edges of the blades, once the crushing process is complete. [Overview of the project]

[0015] The present invention relates to a novel and useful bone mill. The bone mill of the present invention comprises a base unit and a mill head detachably mounted to the base unit. A motor is located inside the base unit. A rotating cutting disc is located inside the mill head. A movable plunger is mounted to the mill head. A receiving tray is also mounted to the mill head, aligned with the plunger.

[0016] To use the bone mill of the present invention, first, the bone mill head is attached to the base unit. The cutting disc is rotated by the motor. The plunger is pushed down, pressing the bone against the cutting disc. As the cutting disc rotates, it cuts the bone, generating bone granules. The bone granules fall into the receiving tray. The bone granules can then be easily obtained by removing the receiving tray.

[0017] The mill head of the present invention has cutting sections that minimize the extent to which the generated bone granules adhere to the cutting disc and other surfaces of the mill head. Thus, these cutting sections ensure that a substantial portion of the bone granules generated by the mill head enter the receiving tray and are used for surgery.

[0018] Another feature of the bone mill of the present invention is that once a bone granule is removed from the bone, it does not come into contact with the cutting disc again. By minimizing contact with the cutting disc in this way, the possibility of the frictional heat generated by such contact damaging the bone granule can be reduced.

[0019] Furthermore, the base unit and mill head are configured such that the cutting disc automatically engages with the drive spindle, which is integrated with the motor, upon seating of the head on the base unit. This engagement occurs even if the disc is not precisely aligned with the spindle. This feature of the bone mill of the present invention helps to minimize the costs associated with the manufacture of the mill head.

[0020] The present invention is described in detail in the claims. The above and further features and gains of the bone mill of the present invention will be better understood by reading the following detailed description in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0021] [Figure 1] This is a perspective view of the bone mill of the present invention. [Figure 2] This is an exploded view of the mill's base unit. [Figure 3] This is a cross-sectional view of the legs of the base unit. [Figure 4] This is a cross-sectional view of the base unit. [Figure 5] This is a perspective view of the top of the base unit. [Figure 6] This is a cross-sectional view of a retaining arm used to detachably hold a mill head to a base unit. [Figure 7] This is an exploded view of the gear train inside the base unit. [Figure 7A] This is a cross-sectional view of the gear train housing, i.e., the ring gear. [Figure 8] This is a cross-sectional view of a gear train. [Figure 9] It is a cross-sectional view of a drive coupler of a gear train. [Figure 10] It is an exploded view showing the relationship of the spindle to the gear train. [Figure 11] It is an exploded view of the mill head. [Figure 12] It is a perspective view of the upper shell of the mill head housing. [Figure 13] It is a cross-sectional view of the upper shell. [Figure 14] It is a bottom view of the upper shell. [Figure 15] It is a perspective view of the bottom shell, more specifically, the exposed bottom surface of the bottom shell. [Figure 16] It is a plan view of the inside of the bottom shell. [Figure 17] It is a cross-sectional view of the bottom shell along line 17-17 of FIG. 16. [Figure 18] It is a plan view of the cutting disk. [Figure 19] It is a cross-sectional view of one scallop of the cutting disk. [Figure 20] It is a perspective view of the abutment plate. [Figure 21] It is a cross-sectional view of the abutment plate. [Figure 22] It is a perspective view of the plunger. [Figure 23] It is a side view of the plunger. [Figure 24] It is a perspective view of the receiving tray. [Figure 25] It is a plan view looking inside the receiving tray. [Figure 26] It is a side view of the receiving tray.

Mode for Carrying Out the Invention

[0022] [I. Overview] As can be seen with reference to Figure 1, the bone mill 30 of the present invention comprises a base unit 32 to which a mill head 34 is detachably attached. A motor 36 (Figure 2) is located inside the base unit 32. A substantially flat cutting disc 38 (Figure 18) is located inside the mill head 34. A plunger 40 is attached to the upper end of the mill head 34. A detachable receiving tray 42 is located below the plunger 40 and below the bottom surface of the cutting disc 38. When the bone mill 30 is in use, the motor 36 is activated, thereby rotating the disc 38. The plunger 40 is used to press bone against the rotating disc 38, thereby generating bone granules. These bone granules fall into the receiving tray 42 and are used in surgical procedures.

[0023] [II. Base Unit] As shown in Figures 1 and 2, the base unit 32 comprises a circular foot portion 46. A leg portion 48 having a circular cross-section extends upward from the foot portion 46. In the illustrated embodiment of the present invention, the upper end of the foot portion 46 has a truncated conical contour with an inward taper, and the leg portion 48 extends upward from the center of this upper end of the foot portion. The leg portion 48 has a diameter smaller than the diameter of the foot portion 46.

[0024] The leg portion 48 is formed from a metal such as aluminum or stainless steel, or from plastic. In the illustrated embodiment of the present invention, as best shown in Figure 3, the leg portion 48 has a circular cross-sectional contour along its entire length, but the diameter of the leg portion is not constant. Specifically, the diameter of the leg portion 48 gradually decreases in the first 25% region along the leg from the upper end of the foot portion 46. Beyond this point, the diameter of the leg portion 48 gradually increases along the remaining length of the leg portion. In the illustrated embodiment of the present invention, the leg portion 48 has a diameter at its upper end that is somewhat smaller than the diameter of the base. A hole 47 penetrates the leg portion 48 axially. This hole 47 has a number of adjacent regions. Each of these regions has a diameter different from the diameter of the adjacent (one or more) regions. The leg portion 48 is formed to have an annular inward-facing lip 49 at its upper end. The lip 49 defines the upper end opening of the hole 47.

[0025] A base 50 is positioned at the upper end of the leg portion 48. As best shown in Figures 4 and 5, the base 50 has a substantially circular cross-sectional contour. In the illustrated embodiment of the present invention, the base 50 has a bottom surface 52 that tapers outward from the upper end of the leg portion 48. An arc-shaped side wall 54 extends upward from the upper end of the bottom surface 52. In the illustrated embodiment of the present invention, the base unit 32 is formed such that the side wall 54 of the base defines a circle having a diameter smaller than the maximum diameter of the foot portion 46 and larger than the diameter of the maximum diameter portion of the leg portion 48.

[0026] The upper part of the side wall 54 of the base forms part of an arc-shaped lip 56. This lip 56 extends along the perimeter of the base 50 and protrudes upward from the surrounding upper surface 58 of the base. Thus, the lip 56 and the upper surface 58 define a recess 60 above the upper end of the base 50. The recess 60 is a cavity in which the mill head 34 is seated when it is attached to the base unit 32.

[0027] Furthermore, the base 50 is formed to define a through-opening 64 centered on the long axis of the base. In the illustrated embodiment of the present invention, an annular skirt 66 is formed integrally with the base 50, extending downward from the bottom surface of the base. The inner surface of the skirt 66 defines the opening 64. When the base unit 32 is assembled, the skirt 66 of the base is positioned to cover the adjacent inwardly stepped surface 68 (Figure 3) of the leg portion 48. The skirt 66 of the base is press-fitted into this upper end of the leg portion.

[0028] The base 50 is further formed to define a notch 70. The notch 70 protrudes outward from the opening 64 toward the outer circumference of the base 50. The notch 70 is partially defined by two parallel inner surfaces 72 (one surface 72 is shown in Figure 5) within the parallel body. Inside the lip 56, each inner surface 72 terminates at an outer surface 74. The outer surfaces 74 are inclined outward from the associated inner surfaces 72. Thus, these outer surfaces 74 define the outer circumference of the notch 70. Because the opposing outer surfaces 74 flare outward in a trumpet shape, the notch 70 has an inwardly tapered shape where it is adjacent to the outer circumference of the base 50. Inside the outer surfaces 74, the parallel inner surfaces 72 give the notch 70 a rectangular shape.

[0029] The base 50 is further formed to have a number of teeth 80 spaced apart from each other along an arc. These teeth 80 are arranged along the outer circumference of the upper surface 58 of the base and extend upward from the outer circumference. Each tooth 80 is positioned relative to the inner arcuate surface of the lip 56. In some embodiments of the present invention, these teeth 80 are formed integrally with the inner arcuate surface of the lip 56. Each tooth 80 is formed to have an upper end, i.e., a crown. The crown has an upper surface 82 from which two lateral surfaces 84 extend diagonally downward. In the illustrated embodiments of the present invention, semicircular grooves (not part numbered) are formed on both sides of each tooth 80 of the lip 56. These grooves are provided for manufacturing purposes and are not otherwise related to the present invention.

[0030] A pair of retaining arms 88, pivotably mounted to a base 50, removably hold the mill head 34 to the base unit 32. As shown in detail in Figure 6, each retaining arm 88 has a solid base 90 having a substantially polygonal shape. The corners of the base 90 are generally angular, but the inner corner faces 91 of the upper end of the base 90, i.e., the corners that will face the upper end and center of the base, are rounded. Inside the corner faces 91, a hole 92 is formed in the base of the arm. A shelf 93 extends inward from the inside of the base 90 of the arm. The shelf 93 is lower in height than the height of the base 90. The arm 88 is further formed to have a hole 114 extending downward from the upper surface of the shelf 93. A lever 96 extends downward from the bottom surface of the shelf 93 of the arm. Each arm 88 is further formed to have a finger 98 extending upward from the outer upper surface of the base 90. The finger 98 is a hook formed to have an inward-facing tab 102 at the upper end of the finger, which extends a short distance from the upper surface of the base 90 of the arm 88.

[0031] Each retaining arm 88 acts within a notched space 104 defined in the base 50. Part of each notched space 104 is formed by cuts in the bottom surface 52 and side walls 54 of the base (which define individual, continuous spaces on which the base 90 and shelf portion 93 of the arm are seated). Part of each notched space 104 on which the arm fingers 98 are seated is further formed by cuts on the outer circumference of the lip 56 of the base. A notch at the upper end of the lip 54 on which the finger tabs 102 are seated is integrated with the notched space 104 (the notch is not numbered). The tabs 102 of the retaining arms protrude into the upper end of the recess 60 of the base.

[0032] Pivot pins 108 (one shown in Figure 2) rotatably hold each retaining arm 88 to the base pedestal 50. Each pin 108 passes through a hole 92 in the inner upper corner of the associated arm base 90. Both ends of the pin 108 are positioned within holes 109 formed in the pedestal 50. (One opening of the pin holes 109 is shown in Figure 5). Note that each pin hole 109 intersects with a notch space 104.

[0033] A coil spring 112 (Figure 2) attached to the base 50 holds each retaining arm 88 in a permanently locked state. Each coil spring 112 has a first end positioned in a hole 115 formed in the base 50, one end of which is closed and the other is open downwards. Each hole 115 opens into a notch space 104 for the associated arm 88. The other end of each spring 112 is seated in a hole 114 formed in the associated arm 88. Thus, each spring 112 applies force to the associated arm 88, thereby positioning the arm 88 so that the tab 102 is permanently seated at the upper end of the recess 60 of the base. It should be further understood that the biasing of the arm by the spring 112 causes each arm lever 96 to be permanently pointed downwards so as to be almost straight with the base leg 48.

[0034] Here, with reference to Figures 2 and 4, the motor 36 of the base unit will be described. This motor 36 is located within the holes 47 of the leg. In one embodiment of the present invention, the motor 36 is the motor used in the ES6 surgical sagittal saw by the assignor of the present applicant. This motor is a 4-pole / 3-phase motor. This particular motor can achieve a no-load maximum shaft speed of at least 20,000 RPM. The motor 36 is located within the leg 48 so as to be suspended within the leg 48 above the foot 46. The motor 36 has an output shaft (not shown) to which a gear head 122 is attached. A flexible circuit 123 extends downward from the motor 36. The flexible circuit 123 has conductors that selectively connect the motor windings to ground and a voltage source. The flexible circuit 123 also has conductors that output signals from a Hall sensor inside the motor, and conductors that supply 5VD to the motor (Hall) and make a ground connection.

[0035] The outer circumference of the motor 36 is positioned on a ring 126 that is screwed to the inside of the leg portion 48. This ring is screwed into the area 127 of the hole 47 (Figure 3) in the leg portion. The ring 126 has an elongated hole 128 located on its outer circumference. When the base unit 32 is assembled, the flexible circuit 123 extending from the motor 36 will be positioned within the ring 126.

[0036] The gear train 134 is positioned above the motor 36 and is located within the hollow portion of the leg 48. As best shown in Figures 7 and 8, the gear train 134 comprises a set of planetary gear assemblies. These planetary gear assemblies are intended to reduce the rotational motion generated by the motor 36 and increase the torque of that rotational motion. Specifically, the gear train 134 comprises a tubular housing 136, best shown in Figure 7A. The housing 136 functions as a ring gear for the individual planetary gear assemblies. The housing 136 has a smooth outer wall and is designed to slip-fit ​​tightly into the hollow hole of the leg 48. The housing 136 of the gear train is formed such that the lower inner circumferential wall has teeth 138 spaced apart from each other along an arc. Above the teeth 138, the housing 136 is formed to have an inner diameter larger than the inner diameter of the cavity formed by the toothed portion of the housing. Just below the upper end of housing 138, the housing is formed to have a groove 140 that extends circumferentially along the inner wall of the housing. The gear train housing 136 is further formed to have a semicircular groove 142 that extends downward along the outer surface from the upper end of the housing. The groove 142 extends longitudinally along the housing for a distance of approximately 5% of the total length of the housing.

[0037] Two notches 143 are formed at the bottom of the gear train housing 136, facing each other in the diametrical direction. These notches 143 are provided to receive a tool used to facilitate the insertion / removal of the gear train 134 from the leg holes 47. Furthermore, when the base unit 32 is assembled, a motor-integrated tab (not shown) will seat within the notches 143. The engagement of these tabs with the gear train housing 136 prevents the motor 36 from rotating.

[0038] Three planetary gear assemblies are arranged within the gear train housing 136. The first planetary gear assembly includes a carrier disk 146. Three gears 148 (two of which are shown in Figure 7) are rotatably mounted on the bottom surface of the carrier disk 146, with their sides facing the motor 36. The gears 148 are spaced equally apart from each other. The gears 154 and 182 of the second and third planetary gear assemblies are similar, but the gears 148 are mounted on the carrier disk 146 such that their teeth engage with the teeth 138 of the gear housing. When the base unit 32 is installed, the gears 148 will also engage with the gear head 122 of the motor 36. A central gear 150 is fixedly mounted on the upper side of the carrier disk 146. The central gear 150 is coaxial with the disk 146.

[0039] A second carrier disc, namely disc 152, constitutes part of a second planetary gear assembly. Three gears 154 are rotatably mounted on the bottom surface of disc 152, spaced equally apart from each other. The gears 154 are dimensioned and positioned to engage with both the central gear 150 and the teeth 138 of the gear train housing. A tubular stem 156 extends coaxially upward from the top surface of the carrier disc 152. The stem 156 is shaped to define a gear 158 located above the surface of the carrier disc 152.

[0040] The third planetary gear assembly includes a multi-zone drive coupler 162, which will be described in detail with reference to Figure 9. The drive coupler 162 is formed to have a cylindrical base 164. At the bottom end of the base, a small annular step 166 projects radially outward from the periphery of the base. The drive coupler 162 is formed to have an annular groove 167 located a short distance from the upper end of the base 164. The groove 167 extends circumferentially along the outer surface of the base 164. The drive coupler 164 is formed to have a stem 168 formed integrally with the base 164 and extending above the base 164. The stem 168 is concentric with the base 164 but has a smaller diameter than the diameter of the base.

[0041] The drive coupler 162 is further formed to have three coaxial holes that are continuous with each other. These holes are connected at their ends to form a single through-opening centered on the long axis of the coupler. The first hole in Figure 9, namely hole 169, extends from the bottom of the coupler through a thin longitudinal section defined by the step 166 and the area of ​​the base 164 above the step. Just above the open end of hole 169, the drive coupler 164 is formed to define an annular groove 170 on the inner wall defining hole 169. The drive coupler 162 is formed to define a second hole, namely hole 172, which is continuous with hole 169 and located above it. Hole 172 extends upward from hole 169 to just below the upper end of the base 164 of the coupler. Hole 172 has a diameter slightly smaller than the diameter of hole 169. Holes 169 and 172 both have a diameter larger than the diameter of the stem 156, which is integrated with the second planetary gear assembly. Above hole 172, the drive coupler 162 is formed to have a third hole, namely hole 176. Hole 176 extends from hole 172 through the upper end of the coupler base and the entire stem 168. Thus, the open end of hole 176 forms the upper end opening of the drive coupler. Hole 176 has a diameter larger than the diameter of hole 172.

[0042] The drive coupler 162 is further formed to have two elliptical openings 178 that face each other in the diametrical direction. The openings 178 are formed above the portion of the stem 168 that protrudes from the base unit. The openings 178 have a major axis parallel to the major axis of the drive coupler 162. Thus, the openings 178 are continuous with the hole 176.

[0043] The third planetary gear assembly has four planetary gears 182 (three of which are shown in Figure 7). The planetary gears 182 are mounted on the bottom surface of the base 164 of the drive coupler. The planetary gears 182 are dimensioned and positioned to engage with the teeth 158 of the second planetary gear assembly and the teeth 138 of the housing.

[0044] Once the gear train 134 is assembled, the second planetary gear assembly is positioned so that the stem 156 is positioned in the holes 169 and 172 of the drive coupler. The bearing assembly 186 provides a low-friction connection between the stem 156 and the drive coupler 162. The outer ring of the bearing assembly 186 is seated on the outer circumference of the hole 169 of the drive coupler. At least one snap ring 185, positioned in the groove 170 of the drive coupler, holds the bearing assembly 186 in the hole 169. The inner ring of the bearing assembly 186 is positioned above the gear 158, around the outer surface of the stem 156. A sleeve 187, formed from stainless steel, is press-fitted onto the outer circumference of the portion of the stem 156 (above the bearing assembly 186). The sleeve 187 has an (unnumbered) lip that abuts against the exposed upper portion of the inner ring of the bearing assembly 186. Therefore, the sleeve 187 prevents the carrier disc 152 from detaching from the drive coupler 162.

[0045] Two bearing assemblies 188 and 192 rotatably hold the drive coupler 162 in the gear train housing 136. The outer rings of each bearing assembly 188 and 192 are positioned on the smooth inner wall of the gear train housing 136, and the inner rings of each bearing assembly are positioned on the outer circumferential wall of the base 164 of the drive coupler. The first bearing assembly, namely assembly 188, is positioned such that the outer ring of the assembly seats on a step defined by the upper end of the teeth 138 of the housing. The inner ring of bearing assembly 188 seats on the step 166 of the drive coupler.

[0046] A ring-shaped spacer 190 isolates the bearing assemblies 188 and 192. The spacer 190 is positioned on the smooth inner wall of the gear train housing. The spacer is sandwiched between the outer rings of the respective bearing assemblies 188 and 192.

[0047] A retaining ring 196 is snap-fitted into a groove 140 in the housing 134 of the gear train. This retaining ring 196 extends across the entire outer ring of the bearing assembly 192. In this way, the retaining ring 196 holds the bearing assembly 192 and the components located beneath the assembly 192 within the housing 134 of the gear train.

[0048] Here, we will first describe the spindle 202 with reference to Figure 10. This spindle 202 extends from the drive coupler 162 and is configured to transmit the torque generated by the motor 36 to the mill's cutting disc 38. The spindle 202 is formed to have a solid post 204. The post 204 has a diameter that allows it to slide-fit into a hole 176 in the stem 168 of the drive coupler. The post 204 is formed to have a lateral through hole 206.

[0049] Above post 204, the spindle 202 is formed to have a disc-shaped head 208. The spindle 202 is formed such that the head 208 has a diameter approximately equal to the diameter of the base 164 of the drive coupler. A number of different parts extend upward from the top surface of the spindle head 208. One of these parts is the alignment pin 210. The alignment pin 210 is coaxial with the long axis of the spindle 202 and extends upward from the center of the head. The pin 210 is formed such that its lower portion, i.e., the portion extending upward from the spindle head 208, has a cylindrical shape. The upper part of the alignment pin has a conical shape with a flat tip. (The individual parts of the alignment pin 210 are not numbered.)

[0050] Furthermore, four drive teeth 212, spaced equally apart from each other, extend upward from the upper surface of the spindle head 208. These teeth 212 are arranged along the outer circumference of the spindle head 208. The arc-shaped outer surfaces of the teeth 212 are in the same plane as the outer surface of the spindle head 208. Each tooth has a pair of inwardly tapered sides and an arc-shaped inner surface (these surfaces are not numbered). The radius of curvature of the inner surface of each tooth 212 is smaller than the radius of curvature of the outer surface. The teeth 212 do not extend as far upward from the spindle head 208 as the alignment pins 210.

[0051] The spindle 202 is positioned such that the post 204 is slidably mounted within the stem hole 176 of the drive coupler. A pin 214 passes through the spindle hole 206. Both ends of the pin 214 are seated within an elliptical opening 178 formed in the stem 168 of the drive coupler. Thus, the pin 214 holds the spindle 202 in the drive coupler 162, allowing the spindle to rotate with the drive coupler and move longitudinally relative to the drive coupler.

[0052] Spring 216 is positioned below the spindle 202 within the drive coupler 162. Spring 216 is a corrugated spring. One end of spring 216 is seated on an annular step between holes 172 and 176 within the drive coupler. The other end of spring 216 is positioned at the bottom of the spindle post 204. Spring 216 is selected to apply an upward biasing force to the spindle post 204. Thus, a force that can be overcome by applying manual force is constantly biasing the spindle head 208 away from the drive coupler 162.

[0053] When the gear train 134 is installed in the leg portion 48, the anti-rotation pin 218 is seated in a groove 142 formed in the housing 136 of the gear train. The exposed portion of the pin 218 is seated in a complementary groove (not shown) formed in the inner wall of the leg portion 48 (which defines the area of ​​the hole 47 in which the gear train is seated). Thus, the anti-rotation pin 218 prevents the rotational movement of the housing 136 of the gear train.

[0054] In some embodiments of the present invention, the motor 36 and the gear train 134 are arranged in conjunction so that the spindle 202, and therefore the cutting disc 38, can rotate at a speed of 150–500 RPM. In some embodiments of the present invention, the components within the base unit 32 are selected so that the disc can rotate at a speed of 250–350 RPM. It should be understood that these speeds are the load speed of the disc 38 when the bone fragments are pressed against the cutting disc 38.

[0055] Referring to Figure 2, it can be seen that a spring-driven normally open push-button switch 220 is mounted on the outer upper surface of the base unit's foot 46. The switch 220 is mounted on a plate 222, which is located in a recess 224 on the outer surface of the foot 220. A socket 226 is located in an opening in the outer peripheral wall of the foot 46. The socket 226 receives the following for connecting the base unit to the control console (described below) that operates the bone mill 30. The circuit board and conductors within the base unit 32, which provide conductive connections from the motor's flexible circuit 122 and the switch 220 to the pins in the socket 226, are not shown.

[0056] Figures 2 and 4 show a base plate 228 positioned across the entire open end of the foot portion 46 of the base unit. The fasteners holding the plate 228 to the foot portion 46 are not shown.

[0057] [III. Millhead] As shown in Figure 11, the mill head 34 comprises an upper shell 240 and a lower shell 242. When assembled together, these shells 240, 242 form the housing of the mill head 34. The cutting disc 38 is positioned between these shells. A stopper plate 244 is attached to the upper shell 240. The plunger 40 is slidably mounted to the upper shell 240 with its bottom surface facing the cutting disc 38. The receiving tray 42 is mounted to two parallel rails 358, 360 (Figure 15) which are integral to the lower shell 242. The receiving tray 42 is mounted to the mill head 34 so that it is located below the plunger 40. Mounting the receiving tray to the rails allows the tray to be slid radially away from the rest of the mill head 34 and removed.

[0058] Referring to Figures 12, 13, and 14, it can be seen that the upper shell 240 of the mill head is formed from a single piece of plastic. An example of an optimal plastic for the upper shell is MAKROLON RX2530 polycarbonate plastic, commercially available from Bayer Material Science AG in Leverkusen, Germany. It should be understood that the material forming the upper shell 240 of the mill head and the other components constituting the upper shell is a material that can be sufficiently gamma-sterilized.

[0059] The upper shell 240 is formed to have a circular head 250 that is generally disc-shaped. The bottom surface 251 of the head 250 is generally shown as planar. The upper shell 240 is further formed such that the top surface of the head immediately inside the periphery of the head, i.e., the surface 252, is parallel to the bottom surface 251. Inside this circumferential surface 252, a central surface 254 is formed on the head 250 of the upper shell. This central surface 254 is slightly raised such that the center of its apex is located above the circumferential surface 252. The head 250 of the upper shell is further formed to have symmetrically arranged recesses 256. Each of the recesses 256 intersects with the circumferential surface 252. The recesses 256 face each other in the diametrical direction. The head 250 of the upper shell is further formed such that each recess 256 has a lateral distance that is somewhat greater than the width of the base retaining arm 88.

[0060] An arc-shaped outer lip 255 extends downward from the bottom surface of the head 250 of the upper shell. The lip 255 is L-shaped such that a small step 257 is formed on the inside of the lip, parallel to the bottom surface 251 of the head 250 of the upper shell. The head 250 is further formed to have an inner lip 260 that is spaced inward from the outer lip 255 and is concentric with the outer lip 255. The inner lip 260 has a rectangular cross-sectional profile. Specifically, the inner lip 260 extends downward such that its bottom surface is coplanar with the step 257 which is integral to the outer lip 255. Between the outer lip 254 and the inner lip 260, the head 250 defines an annular groove 258. The groove 258 has a base that is recessed relative to the bottom surface 251.

[0061] Inside the inner lip 260, the head 250 of the upper shell is formed to have a circular outer confinement ring 264. The confinement ring 264 protrudes downward from the head 250 and has a rectangular cross-sectional profile. An annular groove 262 is located between the inner lip 260 and the outer confinement ring 264. The base of the groove 262 is in the same plane as the surrounding groove 258.

[0062] Lips 255,260 are curved but not continuous circles. Below the area of ​​the outer circumferential surface where the recess 252 is formed, the upper shell 240 is formed such that two rectangular blocks 268 facing each other in the diametrical direction intersect the grooves 258,262 and the inner lip 260. The upper shell 240 is further formed such that four gaps 272 spaced at equal angles apart divide the outer lip 255 into four sections. Aligned radially with each gap 272 are elongated holes 274. Each elongated hole 274 divides a section of the inner lip 260 and has a base that extends further into the shell head 250 deeper than the base of the section of grooves 258,262 that intersects the elongated hole 274. Each elongated hole 274 defines an arc larger than the arc defined by the gaps 272 of the outer lip adjacent to and continuous with the elongated hole.

[0063] The head 250 of the upper shell is further formed to have a circular inner confinement ring 276 located outside the center of the head. The inner confinement ring 276 has a rectangular cross-sectional contour. From Figure 14, it can be seen that the outer confinement ring 264 and the inner confinement ring 276 define the outer and inner circumferences of the bottom surface 251 of the head, respectively. The head 250 is further formed so that the confinement rings 264 and 276 extend downward by the same distance from the bottom surface 251. Also, the surface of the head 250 within the inner confinement ring 276 is located deeper than the bottom surface 251 with respect to the exposed surface of the ring 276. Furthermore, the head 250 of the upper shell is formed to define a dome-shaped cavity 275 concentric with the head.

[0064] The upper shell 240 is further formed to have an opening 278 in the head 250. The opening 278 extends from the arcuate edge of the head immediately outside the inner confinement ring 276 to the arcuate edge of the head immediately inside the outer confinement ring 264. These arcuate edges are concentric with the central axis of the head 250. The opening 278 is further defined by two parallel side edges within the head 250. Each of these side edges extends between the opposing ends of the associated arcuate inner and outer edges.

[0065] The head 250 of the upper shell is further formed to define a cavity 280 extending inward from the bottom surface 251 adjacent to the opening 278. The cavity 280 is formed by an inner step (the step is not part numbered) provided in the material forming the head 250. The cavity 280 is positioned to be continuous with one side of the opening 278. More specifically, the cavity is adjacent to the side of the opening 278 corresponding to the direction in which the cutting disc 38 rotates when the bone mill 30 is in operation. The upper shell is further formed to define two mounting posts 282 extending from the head into the cavity 280. If Figure 4 is inverted relative to the actual orientation of the upper disc, the posts 282 will project downward into the cavity from the surface defining the upper end of the cavity 280.

[0066] The head 250 of the upper shell also includes three reinforcing ribs 284, 286, and 288 spaced equally apart from each other. Each of the ribs 284-286 extends radially from the inner containment ring 276 toward the outer containment ring 264. Each of the ribs 284-286 also projects downward from the lower surface 251 of the head for a shorter distance than the distance the containment rings 264 and 276 extend downward. Two of these ribs, namely ribs 284 and 286, are centered longitudinally on radial lines projecting from the center of the head 250. The third rib, namely rib 288, has several distinct regions. The inner region projects from the inner ring 276 around the inner edge of the cavity 280. The central region extends around the front edge of the cavity, i.e., the edge away from the opening 278. The third region of rib 288 extends from the central region toward the outer containment ring 264. This third region is centered on a radial line projecting from the center of head 250. The radial lines centered on the outer regions of rib 284, rib 286, and rib 288, i.e., the third region, are spaced equiangled from each other.

[0067] A hollow supply sleeve 292, which is part of the upper shell 240, extends above the head 250 and is positioned around the opening 278. In the illustrated embodiment of the present invention, the sleeve 292 is a structure having four walls. Adjacent to the center of the head 250 is the inner wall 294. The inner wall 294 has three sections: a central section that curves inward and two coplanar outer sections (the individual sections are not numbered). The outer wall 298 has an arcuate contour. The sleeve 292 has two mutually parallel side walls 296. Each side wall 296 extends between one outer edge of the outer section of the inner wall 294 and the adjacent outer edge of the outer wall 298. The hollow section within the sleeve 292, defined by walls 294-298, is not numbered. This hollow section opens into the opening 278 of the head. More specifically, the head 250 of the upper shell is formed to have the same cross-sectional contour as the opening 278 defined by the hollow portion of the sleeve 292.

[0068] Furthermore, the upper shell 240 has reinforcing members formed adjacent to the sleeve 292. Specifically, webs 304 protrude in a coplanar manner with each side wall. Each web 304 extends across the entire central surface 254 of the head on the side opposite to the side from which the sleeve 292 protrudes.

[0069] As shown in Figures 15-17, the bottom shell 242 of the mill head housing is formed to have a substantially circular body 308. The bottom shell 242 may be formed from the same material as the upper shell 240. Having a substantially disc shape, the shell body 308 is further formed to have a through hole 310. The hole 310 is concentric with the long axis of the body 308.

[0070] The shell body 308 is further formed to define an opening 312, which is separated from the hole 310. The opening 312 extends inward from the body from an arc-shaped edge of the body located on the inner side of the outer circumference of the body 308. The opening 312 is further defined by two mutually parallel inner walls that extend inward from the arc-shaped outer edge. One of the side walls, namely wall 314 in Figure 15, is inclined outward so as to extend diagonally outward from the upper end of the opening 312 toward the exposed bottom surface of the shell body 308. Wall 314 also extends upward for a short distance from the upper inner surface of the shell body 308. The side wall opposite wall 314, namely wall 316 (Figure 16), extends perpendicular to the flat top surface of the shell body 308. The shell body 308 is formed so as to extend on both sides of the portion of the body where walls 314 and 316 define the hole 310. The inner wall 318 extends between the side walls 314 and 316, defining the inner circumference of the opening 312. The inner wall 318 has numerous sections (not numbered). Adjacent to each side wall 314 or 316, this inner wall has an outer section that extends inward perpendicularly from the adjacent side wall 314 or 316. The outer section of the inner wall 318 that abuts a side wall, for example, side wall 314, is tapered inward. Between these outer sections, the inner wall 318 has an inwardly curved intermediate section. The portion of the shell body 308 that defines the intermediate section of the inner wall 318 also defines the adjacent arc section of the hole 310.

[0071] A multi-section lip 320 extends upward from the outer circumference of the shell body 308. The lip 320 is formed to define a first outer step 322 and a second outer step 324. The first outer step 322 is the step located furthest from the center of the shell. The second outer step 324 is located immediately inside the first outer step 322. The step 324 is located above the outer step 322. The lip 320 is further formed to define a crown 326 located inside the second outer step 324 and extending above the step 324. The crown 326 is formed to have a pyramidal cross-sectional contour to define a peak 330. The crown 326 also has parallel outer surfaces 328 and inner surfaces 332 located on either side of the peak 330. Thus, the surfaces 328, 332 project upward perpendicular to the plane of the outer step 324. Furthermore, the shell lip 320 is formed to have an inner step 334. The inner step 334 is coplanar with the second outer step 324.

[0072] The upper shell 240 and the lower shell 242 are further formed such that when assembled, the crown 326 of the lower shell fits tightly into the groove 258 of the upper shell. Additionally, the first outer step 322 of the lower shell extends over the entire outermost arcuate surface of the bottom of the outer lip 255 of the upper shell, and has an outer diameter approximately equal to that arcuate surface. Furthermore, when assembled together, the shells 240 and 242 are formed such that the opening 312 of the lower shell defines a region defined by the opening 278 and the adjacent void 280 of the upper shell.

[0073] Four notches 340, spaced equally apart from each other, are formed in the bottom shell 242. The bottom shell 242 is further formed to have fingers 342 extending upward just inside each notch 242. Each finger 342 is formed to have curved inner and outer surfaces (unnumbered). The side-to-side width of each finger 342 is sized so that the finger can seat in one of the elongated holes 274 of the upper shell. Each finger 342 has an inner / outer depth that allows the finger to define an arc region of the bottom shell (the other arc regions of the bottom shell are defined by the inner step 334 of the lip and the adjacent inner surfaces of the shell body 308). Reinforcement tabs 344 are formed integrally with each finger 342 and extend across the entire inner surface of the finger. Similar to the associated fingers 342, each tab 344 extends upward from the adjacent top surface of the shell body.

[0074] Two sections of the lip 320 have discontinuous portions 348 that face each other in the diametrical direction. Each discontinuous portion 348 essentially divides the crown 326 of the associated lip section into two sections. Each discontinuous portion 348 defines an arc-shaped cavity that is dimensioned so that the block 268 of the upper shell seats within the discontinuous portion when the mill head 34 is assembled.

[0075] The bottom shell 242 is formed to define a circular outer confinement ring 350, located inward from the circle defined by the reinforcing tab 344. The confinement ring 350 extends upward from the inner surface of the shell body and has a rectangular cross-sectional profile. The bottom shell 242 is further formed to have an inner confinement ring 352. The inner confinement ring 352 extends upward from the inner surface of the shell body 308 and has a diameter somewhat larger than the diameter of the central hole 310. Like the outer confinement ring 350, the inner confinement ring has a rectangular cross-sectional profile. It should be understood that the inner confinement ring 352 extends across the entire arc region of the shell body 308 that separates the hole 310 and the opening 312. The outer diameter of the inner confinement ring 352 is somewhat smaller than the arc that defines the central region of the opening 312, i.e., the arc that defines the inner wall 318. In the illustrated embodiment of the present invention, for manufacturing purposes, the ring 352 is not circular adjacent to the point where the containment ring and the side wall 318 intersect.

[0076] When the shells 240 and 242 are assembled together to form the housing of the mill head, the entrapment rings 264 and 276 of the upper shell are further configured to overlap the entrapment rings 350 and 352 of the lower shell, respectively. When the mill head 34 is assembled, the shells 240 and 242 are ultrasonically welded to each other.

[0077] As best shown in Figure 16, the reinforcing rib 354 protrudes away from the inner containment ring 352 of the bottom shell 242. The rib 354 extends onto the inner surface of the base 308 of the shell. The rib 354 extends from the ring 352 over the entire portion of the body 308 that defines the area of ​​the inner wall 318 adjacent to the side wall 314. Since the rib 354 has a rectangular cross-sectional contour 354, it is substantially coplanar with the adjacent area of ​​the inner wall 318. At the end of the inner wall 318, the rib is bent at a right angle and extends onto the surface of the shell body adjacent to the upper edge of the side wall 314. The rib 354 extends toward the outer circumference of the base of the shell, but terminates at a point somewhat inward from the outer containment ring 350.

[0078] Two parallel rails 358 and 360 protrude downward from the bottom surface of the shell base 308. The rails 358 and 360 are integral structural members of the mill head housing and slidably hold the receiving tray 42 to the rest of the mill 34. Both rails 358 and 360 are parallel to the opening 312 that defines the side walls 314 and 316. Rail 358 extends downward from a position near the side wall 314 (away from the opening 312) on the bottom surface of the housing body. Rail 358 takes the form of a rectangular structure that extends obliquely toward the opening 312. Rail 360 extends from a position near the side wall 316 (away from the opening 312) on the bottom surface of the shell body 308. Rail 360 generally takes the form of a rectangular structure that extends obliquely toward the opening 312. These rails differ in that rail 360 is longer than rail 358. Additionally, teeth (unnumbered) extend from the body of rail 360. These teeth are formed for manufacturing purposes and are otherwise unrelated to the present invention. Similar teeth may protrude from the side wall 316 of the shell body. These teeth are also provided for manufacturing purposes.

[0079] Additionally, a pair of tabs 364 protrude downward from the bottom surface of the shell body 308. The tabs 364 are located between the outer circumference of the bottom shell 242 and the rails 358 and 360. The first tab 364 is adjacent to the rail 358 and is oriented to extend away from the central long axis of the rail 358, i.e., away from the opening 312. The second tab 364 is adjacent to the rail 360 and is oriented to extend outward relative to the opening 312. The tabs 364 generally take the form of rectangular blocks. Thus, the tabs 364 function as alignment members that facilitate centering the receiving tray 42 between the rails 358 and 360.

[0080] Here, the cutting disc 38 will first be described with reference to Figure 18. The cutting disc 38 is formed from the following material, namely, a material that can be appropriately molded, does not fatigue when used for bone cutting as described below, and can undergo a sterilization process. In some embodiments of the present invention, the cutting disc 38 is formed from stainless steel, for example, 304 stainless steel. Generally, the disc 38 has a circular shape with an upper plane 370 and a bottom plane 372 facing each other. The diameter of the cutting disc 38 is approximately 0.10 cm larger than the outer diameter of the outer containment rings 264, 350 which are integrated with the housing of the mill head. However, the disc 38 is further formed so that there is a gap between it and the reinforcing tab 344 of the bottom shell adjacent to it. This gap allows the disc 38 to move laterally within the mill housing defined by the shells 240, 242.

[0081] The cutting disc 38 is further formed to have a centrally located hole 374. The hole 374 is sized to receive a base spindle 202 and an integral alignment pin 210. The cutting disc 38 is formed to have four openings 376 spaced equally apart from each other around the hole 374. Each opening 376 is formed to receive an individual tooth 212 integral with the spindle 202. Thus, the openings 376 are formed in an arc shape. The circle defined by the outer circumference of these openings 376 is smaller than the inner diameter of the inner confinement rings 276,352 integral with the mill head housing.

[0082] The cutting disc 38 is further formed to have a number of cutting scallops 378. The cutting disc 38 has a through-opening 380 that is integral with each cutting scallop 378 and is aligned axially with the scallop 378 in the longitudinal direction. As shown in Figure 19, each scallop 378 is formed by shaping the cutting disc 38 such that the upper surface 370 and bottom surface 372 of the disc adjacent to the opening 380 are curved upward to form the scallop upper surface 382 and scallop bottom surface 386, respectively. The scallop upper surface 382 is planed so that the upper surface 382 and bottom surface 386 intersect at an edge 384. This edge 384 is the cutting edge of the scallop 378.

[0083] Edge 384 is also the edge of the scallop that defines the perimeter of the associated opening 380. Each opening 380 is substantially rectangular in shape, with a long side extending forward from a scallop 378 that is integral to the opening. Each opening 380 is not precisely rectangular because the sides of the opening, including the sides defined by the edge 384, are curved outward. Furthermore, the corners where the sides of the openings 380 intersect are rounded.

[0084] The cutting disc 38 is formed such that pairs of scallops 378 / openings 380 are spaced apart from each other radially along an arc around the disc. The scallops 378 / openings 380 located closest to the center of the disc are spaced radially away from the center so as to be located outside a circle on the disc having a diameter equal to the outer diameter of the inner confinement rings 276,352. The outermost pairs of scallops 378 / openings 380 are located inside a circle on the disc having a diameter equal to the inner diameter of the outer confinement rings 264,350. The pairs of scallops 378 / openings 380 are further positioned so that the two scallop edges 384 do not lie on the same radial line protruding from the center of the disc 38.

[0085] When the mill head 34 is assembled, the cutting disc is sandwiched between the downward-facing upper confinement rings 264, 276 and the upward-facing lower confinement rings 350, 352. Due to the relative dimensionality of these parts, the thickness between the top surface 370 and the bottom surface 372 of the cutting disc 38 is approximately 0.009 inches (0.23 mm) smaller than the gap between the arranged confinement ring pairs 264-350, 276-352. As a result, the cutting disc 38 can move and float somewhat within the housing of the mill head in three degrees of freedom, namely in the vertical and lateral directions.

[0086] The abutment plate 244 shown in Figures 20 and 21 is formed from a material that is sterilizable and does not break when bone is pressed against it. In some embodiments of the present invention, the abutment plate is formed from stainless steel, for example, 304 stainless steel. The abutment plate 244 generally takes the form of a block having an upper surface 388 and a lower surface 389 facing each other. The plate is dimensioned to seat in a cavity 280 defined within the upper shell 240. In addition, one of the side walls of the abutment plate is curved (the curved side is not numbered). The abutment plate has a front surface 391. This front surface 391 is the longer of the front and rear surfaces of the plate in terms of length. (In Figure 20, the edge of the front surface 391 is not numbered). The abutment plate 244 is further formed to have a bevel 392 extending downward around the upper surface 388 of the plate.

[0087] Two holes 394 penetrate the abutment plate from the top to the bottom. Each hole 394 actually opens from a larger diameter countersunk hole 395 that extends upward from the bottom surface 389 of the plate.

[0088] As the mill head 34 is assembled, the abutment plate 244 is positioned to seat within the cavity 280 of the upper shell. The abutment plate is positioned such that its front surface 391 serves as a surface defining the front of the opening 278. The top surface 388 of the plate will abut against the interior of the shell 240 defining the roof of the cavity. With the abutment plate positioned in this manner, each post 282 will be seated within each pair of holes 394 / countersunk holes 395. The abutment plate is secured to the upper shell 240 by thermally deforming the tips of the posts 282. The molten plastic will form rivets within the countersunk holes 395.

[0089] Figures 22 and 23 show the plunger 40. The plunger 40 can be formed from the same material that forms the upper shell 240. The plunger 40 is formed to have a head 402 from which a rod 404 extends. The rod 404 is formed to have two parallel side panels 406 and a front panel 408 extending between these side panels. A bottom panel 410 extends between the side panels and the front panel and forms the base or bottom of the rod 404. The rod 404 is dimensioned so that the side panels 406, the front panel 408, and the bottom panel 410 slidably fit into the supply sleeve 250 of the housing. Thus, the bottom panel 410 has an exposed edge with an inwardly curved area 412. The curvature of the edge area matches the curvature of the inner wall 294 of the supply sleeve, and is somewhat greater than the curvature of the inner wall.

[0090] The plunger rod 404 also includes an upper plate 414. The plunger 40 is formed such that the upper plate 414 extends over the entire side panel 406 and front panel 408 and protrudes above them. More specifically, the upper plate 414 is dimensioned to define an area larger than the cross-sectional area of ​​the central cavity of the supply sleeve 292 of the housing. Thus, the upper plate 414 limits the extent to which the plunger rod 404 is pushed into the sleeve and the opening 278 directly below the sleeve. In some embodiments of the present invention, the components of the mill head 34 are dimensioned such that the bottom plate 412 is located at least 0.05 cm above the cutting disc 38 when the plunger 40 is fully positioned within the sleeve 292.

[0091] The plunger 40 is further formed such that the head 402 extends diagonally upward from the outer circumference of the rod 404. Numerous webs 416 extend between the upper surface of the upper plate and the head 402. The webs 416 reinforce the strength to prevent bending of the head 402 relative to the upper plate 414.

[0092] As shown in Figures 24-26, the receiving tray 42 is formed to have a front panel 420 and a rear panel 422 facing each other with a side panel 424 in between. A bottom panel 426 extends between the above panels at the base of the tray 42. In the illustrated embodiment of the present invention, the front panel 420 has an arc-shaped contour. For aesthetic reasons, at the upper end of the front panel, this contour has a radius of curvature equal to the diameter of the upper shell 240.

[0093] The rear panel 422 of the tray has several distinct sections. The bottom section 430 extends upward from the bottom plate 426 of the tray. More specifically, the bottom section extends diagonally upward from the panel 426. The bottom section 430 of the panel is substantially planar. The rear panel 422 has an upper section 432 that is continuous with the bottom section and located above the bottom section. Similar to the bottom section, the upper section extends diagonally away from the bottom plate 425. The portion of the upper section 432 directly above the bottom section 430 is tapered outward away from the bottom section. Above this portion of the upper section, the upper section of the rear panel is substantially vertical. Furthermore, the receiving tray 42 is further formed to have a circular recess 436. The recess 436 has a curvature somewhat greater than the curvature of the outer circumference of the arc section of the bottom shell body 308 that isolates the hole 310 from the opening 312.

[0094] The lip 438 extends upward from the upper section 432 of the rear panel of the tray. It can be seen that the lip 438 extends above the side panel 424 of the tray. The lip 438 has the same curvature as the recess 436. Thus, when the tray 42 is mounted to the housing of the mill head, the outer surface of the lip will contact the arc-shaped section of the base 308 of the bottom shell that defines the inner circumference of the opening 312.

[0095] The side panels 424 are planar structures that are parallel to each other. On each side of the receiving tray 42, the individual side panels extend between the opposing side edges of the front panel 420 and the rear panel 424. A flange 440 extends diagonally outward from the upper edge of each side panel 424. The flange 440 is sized to seat on the inner surfaces of the rails 358,360 of the bottom shell.

[0096] [IV.Operation] The bone mill assembly 30 of the present invention is prepared for use by first attaching the mill head 34 to the base unit 32. This is done by positioning the base unit so that the bottom shell 242 seats in the recess 60 of the base. As the first step in this process, the mill head is aligned so that the receiving tray 42 is positioned in the notch 70 of the base. As a result of this arrangement of the parts, the long axis of the mill head 34 is aligned approximately in line with the long axis of the base unit 32. Once the bottom shell 242 of the mill head is seated in the recess 60 of the base, the spindle alignment pin 210 passes through the shell hole 310. More specifically, the alignment pin 210 passes through the hole 310 in the bottom shell and enters the central hole 374 of the cutting disc.

[0097] Since the cutting disc 38 is floating within the housing of the mill head, when the mill 34 is seated further into the base unit, the cutting disc 38 is positioned around the alignment pin 210 of the drive spindle. When the mill head 34 is seated even further into the base unit 32, the teeth 212 of the spindle may, in some cases, align with a complementary opening 376 formed in the disc 36 and seat within the complementary opening 376, or they may not align with the complementary opening 376 and therefore not seat within the complementary opening 376. In either case, the movement of the cutting disc 36 relative to the spindle 202 applies a force that exceeds the force of the spring 216 biasing the spindle upward. Therefore, when the mill head 34 is seated into the recess 60 of the base unit, the spindle 202 is retracted at least somewhat toward the foot portion 46 of the base unit. When the spindle teeth 212 are not seated within the disk opening 376, the spindle 202 is in its most retracted position.

[0098] As part of the process of mounting the mill head 34 to the base, the teeth 80 of the base are seated within the notches 340 of the bottom shell. As a result of the receiving tray 42 of the mill head being fitted into the notches 70 of the base, the teeth 80 of the base are necessarily aligned in a straight line with the complementary notches 340 of the bottom shell. Furthermore, as a result of the mill head 34 being seated within the recesses 60 of the base, each recess 256 of the upper shell of the mill head is positioned adjacent to each individual retaining arm 88.

[0099] Next, the mill head 34 is fixed to the base unit by pivoting the retaining arm 88 upward. This movement of the retaining arm causes the top of the arm finger 98 to seat in the recess 256 of the upper shell 240 of the mill head adjacent to the top. The arm 88 is held in this position by the spring 112.

[0100] As part of the process of preparing the bone mill for use, the base unit 32 is connected to a complementary console that provides a signal to energize the motor 36. One such console is commercially available as the CORE® console from Stryker, Inc. of Kalamazoo, Michigan, USA. The circuitry within this console, usable for the electric motor 36, is described in U.S. Patent Application Publication No. 2006 / 0074405A1. This disclosure is incorporated herein by reference. A cable (not shown) extends from socket 226 of the base unit to a complementary socket integrated with the associated console. The conductors of this cable bring on / off signals to the console, selectively apply energizing signals to the windings in the motor, and return signals from sensors in the motor to the control console. The aforementioned CORE console can operate surgical instruments other than the bone mill 30 of the present invention. In other aspects of the present invention, a console specifically designed to energize the motor 36 may be provided. Accordingly, the exact structure of the console used to supply energizing signals to the motor 36 is not relevant to the present invention.

[0101] In practice, bone fragments, which are either autografts or allografts, are loaded into the supply sleeve 292 of the mill head. Once the bone fragments are loaded in this manner, the plunger 40 is positioned within the supply sleeve.

[0102] By pushing down the plunger 40 and pressing the bone against the cutting disc 38, bone granules are generated by operating this disc. The cutting disc 38 is started by pressing the switch 220, which activates the motor 36 of the base unit. The operation of the motor causes the spindle 202 to rotate.

[0103] As mentioned above, when the mill head is mounted on the base unit, the teeth 212 of the spindle may already be engaged with the opening 376 of the disk. In this case, the rotation of the spindle 202 will immediately cause a similar rotation of the cutting disk. However, it is also possible that the cutting disk 38 and the spindle 202 are not initially aligned in a straight line with each other. In this case, the initial rotation of the spindle will cause the teeth 212 of the spindle to take an arc-shaped path relative to the bottom surface 372 of the disk. The teeth 212 move in this manner relative to the disk until they are aligned with the opening 376 of the disk. Once this alignment occurs, the spring 216, which is applying an upward force to the spindle 202, pushes the spindle upward, causing the teeth 212 to seat in the opening 376 of the disk. At this point, the cutting disk 38 will rotate together with the spindle 202. It should be understood that the disk 38 rotates across the space between the upper opening 278 and the lower opening 312 of the mill housing.

[0104] The rotation of the cutting disc 38 means that the scallop 378 of the disc is rotating toward the abutment plate 244. More specifically, the assembly of the mill head 34 causes the scallop 378 to pass below the opening 278 of the upper shell, and the scallop edge 384 to rotate toward the abutment plate 244. As previously mentioned, simultaneously with the rotation of the cutting disc 38, the plunger 40 presses the bone fragments against the cutting disc 38 through the opening 278. As the disc rotates, the lower portion of the bone fragments is wedge-shaped and pressed between the slap edge 384 and the front surface 391 of the abutment plate 244. As the rotation of the cutting disc continues, the disc edge 384 will shear the bone that is wedge-shaped and pressed between the scallop of the disc and the front surface 391 of the abutment plate. The sheared bone fragments enter the opening 380 of the cutting disc, which is defined by the disc edge that sheared the bone fragments into bone fragments. The bone granules are designed to fall from the opening 380 of the disk through the opening 312 of the bottom shell into the receiving tray 42.

[0105] During the granulation process, some granules may initially adhere to the bottom surface of the disc. These granules are positioned to contact the wall 314 of the bottom shell. Thus, the wall 314 acts as a wiper, preventing the granules from rotating with the disc 38. The granules remain in the area above the opening 312 of the bottom shell, if they are adhered. Here, during the granulation process, the inner containment ring 352, integrated with the bottom shell 242, acts as a barrier, preventing the granules from being ejected through the opening 310. The inner containment ring 276, integrated with the upper shell 240, acts as a barrier, preventing the free material, integrated with the granules, from moving toward the center of the cutting disc (where the free material may be ejected through openings 374, 376).

[0106] In the embodiments of the present invention described herein, the reduction of the rotational motion of the motor shaft by the gear train 134 can significantly increase the stall torque available from the drive spindle 202. Specifically, in some embodiments of the invention, the gear train is configured to reduce the spindle speed to 250–300 RPM. In this speed range, using the aforementioned motor, the spindle can output a torque of at least 75 inches / pound (8.5 Nm), and typically 100 inches / pound (11.3 Nm) or more. Because the spindle can produce such relatively high torque, the possibility of the motor stalling when a bone fragment is pressed against the cutting disc is substantially eliminated.

[0107] The relative dimensions of the mill head 34 components ensure that the upper plate 414 of the plunger acts as a stopper, preventing the bottom of the plunger rod 404 from pressing against the cutting disc 38.

[0108] When a sufficient amount of bone fragments has formed, the motor 36 is stopped. The receiving tray 42 containing the bone fragments is removed from the mill head 34. As a result of sliding the receiving tray 42 away from the housing of the mill head, the tray's lip 438 sweeps the area below the bottom surface 372 of the disc located directly above the opening 312 of the bottom shell. The lip 438 captures any bone fragments that may be adhering to the bottom-facing surface of the cutting disc 38 and the underside of the wall 314. The bone fragments are removed from the receiving tray 42 and used.

[0109] The mill head 34 of the present invention comprises a flat cutting disc 38. Having this geometric shape, the disc 38 is more economical than providing other cutting blades such as cylindrical or curved blades. Minimizing the cost associated with this component helps enable the mill head 34 to be provided as a pre-sterilized, single-use disposable part. Therefore, medical professionals do not need to sterilize the cutting disc 38, which has sharp edges 384, while using the bone mill 30.

[0110] As described above, the bone mill 30 of the present invention is further configured such that the floating cutting disc 38 can be aligned with the drive spindle 202 by seating the mill head 34 on the base unit 32. Accordingly, the need to provide a means to precisely hold the cutting disc in a fixed position and rotate the disc around this position is eliminated. The elimination of the costs associated with providing this subassembly further contributes to the economic aspect of enabling the mill head 34 to be provided as a single-use disposable part.

[0111] Furthermore, while the mill 30 is in operation, the only mill housing surface supporting the cutting disc is the retaining rings 264, 276, which are integrated with the upper shell 240. This essentially eliminates the possibility that the metal-to-plastic motion of the disc could abrade any part of the shell and introduce those abrasive fragments into the granules.

[0112] The fact that the hole 376 functions as a feature connecting the cutting disc 38 to the drive fastener further minimizes costs. Furthermore, the need for additional fasteners to perform this function is eliminated.

[0113] The bone mill 30 of the present invention is designed so that most bone particles are discharged through an opening 380 attached to the scallop 378 from which the bone was removed, as soon as they are removed. From the opening 380, the bone particles typically fall into the receiving tray 42. Thus, substantially all of the bone particles formed in the mill head 34 are removed only once, that is, they pass through either the cutting disc 38 or the stop plate 244 only once. Since the bone particles pass through these parts only once, the amount of frictional heat the bone particles receive as a result of such contact is also kept to a minimum. This reduction in frictional heat of the bone particles similarly minimizes the extent to which such heat damages the material forming the bone particles.

[0114] Another gain obtained from the design feature that each bone fragment is pressed only once against the cutting disc 38 or abutment block 244 is that the bone fragments are not cut to a size smaller than the desired size. Furthermore, when cut, there are almost no bone fragments adhering to the bottom surface 372 of the disc. Substantially all bone fragments are pushed into the receiving tray 42 immediately after they are generated. Thus, the bone fragments generated by the mill 30 are approximately the same size.

[0115] In the assembly 30 of the present invention, the base unit 32 and mill head 34 are configured such that the teeth 80 of the base seat are seated in the recess 340 of the mill, thereby preventing the transmission of rotational motion of the cutting disc 38 to the rest of the mill 34. The effect of these teeth 80 in preventing rotation is that the extent to which the retaining arms 88 perform this function can be minimized. This rotation-stopping effect of the teeth helps to minimize the size and / or number of retaining arms. Thus, in most embodiments of the present invention, at most two retaining arms or other restraining members are required to detachably hold the mill head 34 in the base unit 32.

[0116] Immediately after the mill head of the present invention is used, the receiving tray 42 is removed from the mill head housing. The mill head 34 is detached from the base unit 32 by pivoting the retaining arm 88 away from the upper shell 240 of the mill. The biasing force of the spring 216 displaces the mill somewhat upward from the base unit pedestal 50. Thus, the spring 216 facilitates the separation of the mill head 34 from the base unit 32. Furthermore, after use, the openings 278 and 312 of the mill housing that expose the cutting disc 38 are covered by the plunger 40 and the receiving tray 42, respectively. This reduces the likelihood of a person handling the mill 34 after use accidentally coming into contact with the biological material and sharp disc edges 384 inside the housing. Also, even when the plunger and receiving tray are removed, the presence of the sleeve 296 above the opening 278 and the relatively small opening 312 makes it difficult for fingers to come into contact with the disc 38.

[0117] Another feature of the bone mill 30 of the present invention is that the mill can be used to produce bone fragments of various sizes by changing the mill head 34. More specifically, individual mill heads may be equipped with cutting discs 38 having openings of various sizes. Here, the "size" of the opening is defined by the width across the opening below the cutting edge 384. In one embodiment of the present invention, this width may be 8 mm between the ends. Using a mill head with a disc opening of this size, large and coarse bone fragments can be formed. Using a mill head 34 with a disc 38 having an opening 380 with a width of 5 mm between the ends, medium bone fragments can be formed. Alternatively, a mill head 34 with a cutting disc 38 having an opening with a width of 3 mm between the ends can also be used. Using this particular type of mill head, fine bone fragments can be formed.

[0118] [V. Alternative Embodiments] The above description is limited to a specific embodiment of the bone mill of the present invention. Alternative embodiments are possible. For example, not all embodiments of the present invention are required to possess each of the features described above.

[0119] Alternative forms of the features described above are also possible. Therefore, in all embodiments of the present invention, the cutting member does not need to be the circular disc described above. In some embodiments of the present invention, the cutting member may be a blade-shaped member, which may have a number of blade-shaped arms protruding outward from a central hub.

[0120] Furthermore, while the aforementioned embodiments of the mill head of the present invention have a single-use mill head 34, other forms having more sterilizable and more reusable components may be designed. Accordingly, in one alternative embodiment of the present invention, the mill head has a bottom section integrated with the base unit. The mill head also has a removable top section. In this embodiment of the present invention, the top section of the mill is removed after use. This allows access to the cutting components for sterilization or replacement. By separating the two sections of the mill, the inside of the mill can also be accessed for cleaning.

[0121] In some embodiments of the present invention, complementary geometric features that facilitate the alignment of the cutting member with respect to the drive spindle that rotates the cutting member may differ from those described above. That is, in some embodiments of the present invention, the alignment pin may protrude from the cutting member. In these embodiments of the present invention, the drive spindle has a hole positioned to receive this pin. The hole may have a conical contour such that, when the pin enters the hole, the pin and the entire cutting member are centered with respect to the drive spindle.

[0122] Similarly, the configuration of the complementary coupling between the cutting member and the drive spindle that transmits torque to the cutting member may differ from that described. In some embodiments of the present invention, teeth may protrude from the cutting member. These teeth are configured to engage with complementary elongated holes or openings associated with the drive spindle.

[0123] Similarly, in some embodiments of the present invention, a single feature portion of the cutting member may function as both an alignment portion for positioning the disc and a torque-receiving coupling portion. An example of such a feature portion is a non-circular centralized hole. In these embodiments of the present invention, the mill unit may first have a tapered spindle having a first narrow portion for centering the cutting disc 38. This drive spindle would also have a second wider portion having a surface that engages with the cutting disc to transmit torque to the disc. Thus, in this embodiment of the present invention, a single component of the base 40 would have a feature portion that aligns the cutting disc and transmits torque to the cutting disc.

[0124] The structure of the feature fixed to the base unit 32 and the removable mill 34 to prevent the rotation of the base unit 32 is not limited to that disclosed. For example, small fingers may protrude from the mill. In these embodiments of the invention, the base unit 32 has an elongated hole for receiving the fingers. In some embodiments of the invention, a rotation-preventing pin that prevents the rotation of the gear train housing 136 may be a pin extending into a hole that extends radially within the housing. In some embodiments of the invention, one or both of the plunger 40 and the receiving tray 42 have a structural feature that prevents unintended detachment from the rest of the mill head 34. These feature may be a stopper or a notch for receiving a stopper. If the feature is a stopper, this member will seat in an elongated hole formed in the head 34. If the feature is a notch for receiving a stopper, the stopper is a stationary part located at another complementary position on the head.

[0125] Similarly, an alternative assembly may be provided for detachably securing the mill head 34 to the base unit 32. Such an assembly may include a pair of retaining arms that move in a horizontal plane to engage with and detach from the mill head. In some aspects of the present invention, these detachment arms are attached to the mill head.

[0126] Similarly, some embodiments of the present invention may have various assemblies for detachably holding the mill head 34 to the base unit 32 and preventing the rotation of the mill. For example, in one alternative embodiment of the present invention, either the base unit or the mill is provided with an L-shaped tab. The other of the mill or the base unit is provided with a keyhole-type slot for receiving the tab. Once the mill is seated and rotated, the engagement of the tab into the slot prevents the mill from detaching. In these embodiments of the present invention, retractable teeth integrated with the base may expand and seat in the slot formed in the mill. These teeth prevent the rotation of the mill.

[0127] Alternative structures for the cutting disc are also possible. Although generally not useful, the disc may have only a cutting edge defining a single opening. For certain low-speed precision processes that generate bone fragments, a disc with one or very few openings may be desirable. Furthermore, in some embodiments of the invention, the disc may be formed such that the edge that collides with the bone and severs the bone fragment (defining the opening) is not located above the upper surface of the disc.

[0128] Similarly, in some embodiments of the present invention, the component forming the abutment surface for shearing the bone fragments does not have to be a separate abutment plate. In some embodiments of the present invention, the surface of the housing may perform this function. This area of ​​the housing may be formed from the plastic forming the surrounding area of ​​the housing. Alternatively, this area of ​​the housing may be formed from a fragment area of ​​cured plastic.

[0129] In some embodiments of the present invention, a hand crank is attached to the mill head. This hand crank is connected to the cutting member and is used to rotate the cutting member. The advantage of this embodiment of the present invention is that it eliminates the need for a motor. In some embodiments of this embodiment of the present invention, a gear assembly connects the hand crank to a motor. This configuration allows the user to push the plunger downward with one hand, pressing the bone against the cutting member, while using the other hand to rotate the crank.

[0130] Therefore, the intended purpose of the attached claims is to encompass all such modifications and changes that fall within the true spirit and scope of the invention.

Claims

1. A mill head used with a base unit having a drive spindle to convert bone fragments into bone granules, A housing configured to be detachably attached to the base unit, the housing having an inlet into which bone fragments are introduced, and an outlet positioned at a distance from the inlet, A circular cutting disc rotatably disposed within the housing between the inlet and the outlet, the cutting disc having a connecting portion that engages with the drive spindle when the housing is attached to the base unit, the cutting disc having a plurality of cutting scallops discretely arranged in the radial and rotational directions, each cutting scallop defining an opening and having a scallop top surface and a scallop bottom surface that intersect at the cutting edge of the cutting scallop, A plunger is movably attached to the inlet and presses bone fragments against the cutting disc and discharges bone fragments through the outlet, A stopper plate separate from the housing, which is fixed to the housing adjacent to the inlet, and is positioned such that when the cutting disc rotates, the cutting edge rotates toward the stopper plate, Equipped with, A mill head is configured such that bone fragments introduced through the inlet are pressed against the cutting disc, which is rotated by the drive spindle, causing the lower portion of the bone fragments to be wedged between the cutting edge of the cutting scallop and the stop plate, sheared, and converted into bone granules.

2. The mill head according to claim 1, wherein the plunger is slidably mounted on the upper part of the housing with its bottom surface facing the cutting disc, and comprises an upper plate sized to define an area larger than the cross-sectional area of ​​the inlet.

3. The mill head according to claim 1, further comprising a tray detachably attached adjacent to the discharge port of the housing for receiving bone particles discharged through the discharge port.

4. The mill head according to claim 1, wherein the cutting disc collides with a bone fragment and bone particles are cut from the bone fragment by the cutting edge, and furthermore, each of the cutting edges of the cutting scallop is positioned between the inlet and the outlet in the housing so as to pass through the opening defined by the cutting scallop.

5. The mill head according to claim 1, wherein the cutting disc has a plurality of openings spaced outward from the center of the cutting disc and spaced equally apart from each other around the center of the cutting disc, and the portion of the cutting disc forming the openings is formed to function as the connecting portion.

6. It is a system for converting bone fragments into bone granules. Equipped with a mill head and a base unit, The aforementioned mill head is A housing configured to be detachably attached to the base unit, the housing having an inlet into which bone fragments are introduced, and an outlet positioned at a distance from the inlet, A circular cutting disc rotatably disposed between the inlet and outlet within the housing, having a plurality of cutting scallops discretely arranged in the radial and rotational directions, each cutting scallop defining an opening and having a scallop top surface and a scallop bottom surface that intersect at the cutting edge of the cutting scallop, A plunger is movably attached to the inlet and presses bone fragments against the cutting disc and discharges bone fragments through the outlet, The system comprises a stopper plate separate from the housing, which is fixed to the housing adjacent to the inlet, and is positioned such that when the cutting disc rotates, the cutting edge rotates toward the stopper plate, The base unit comprises a motor and a drive spindle configured to transmit torque generated by the motor to the cutting disc, the drive spindle having a coupling portion that engages with the cutting disc when the housing is attached to the base unit. A system configured such that bone fragments introduced through the inlet are pressed against the cutting disc, which is rotated by the drive spindle, causing the lower portion of the bone fragments to be wedged between the cutting edge of the cutting scallop and the stop plate, thereby being sheared and converted into bone fragments.

7. The system according to claim 6, further comprising a tray detachably attached adjacent to the discharge port of the housing for receiving bone particles discharged through the discharge port.

8. The system according to claim 6, wherein the plunger is slidably mounted on the upper part of the housing with its bottom surface facing the cutting disc, and the plunger comprises an upper plate sized to define an area larger than the cross-sectional area of ​​the inlet.

9. The system according to claim 6, wherein the cutting disc has a plurality of openings spaced outward from the center of the cutting disc and spaced equally apart from each other around the center of the cutting disc, and the portion of the cutting disc forming the openings is formed to function as a connecting portion that engages with the connecting portion of the drive spindle.

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