WO2008061711A2 - Surgical bur with anti-chatter flute geometry including a pair of symmetric flutes that emerge from the distal end tip of the bur head - Google Patents

Surgical bur with anti-chatter flute geometry including a pair of symmetric flutes that emerge from the distal end tip of the bur head Download PDF

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Publication number
WO2008061711A2
WO2008061711A2 PCT/EP2007/010048 EP2007010048W WO2008061711A2 WO 2008061711 A2 WO2008061711 A2 WO 2008061711A2 EP 2007010048 W EP2007010048 W EP 2007010048W WO 2008061711 A2 WO2008061711 A2 WO 2008061711A2
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WO
WIPO (PCT)
Prior art keywords
flutes
bur
distal end
chamfer
flute
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Application number
PCT/EP2007/010048
Other languages
French (fr)
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WO2008061711A3 (en
Inventor
Denis F. O'sullivan
Original Assignee
Stryker Ireland, Ltd.
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Filing date
Publication date
Application filed by Stryker Ireland, Ltd. filed Critical Stryker Ireland, Ltd.
Publication of WO2008061711A2 publication Critical patent/WO2008061711A2/en
Publication of WO2008061711A3 publication Critical patent/WO2008061711A3/en

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Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B17/00Surgical instruments, devices or methods, e.g. tourniquets
    • A61B17/16Bone cutting, breaking or removal means other than saws, e.g. Osteoclasts; Drills or chisels for bones; Trepans
    • A61B17/1613Component parts
    • A61B17/1615Drill bits, i.e. rotating tools extending from a handpiece to contact the worked material
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C3/00Dental tools or instruments
    • A61C3/02Tooth drilling or cutting instruments; Instruments acting like a sandblast machine
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B17/00Surgical instruments, devices or methods, e.g. tourniquets
    • A61B17/32Surgical cutting instruments
    • A61B17/320016Endoscopic cutting instruments, e.g. arthroscopes, resectoscopes
    • A61B17/32002Endoscopic cutting instruments, e.g. arthroscopes, resectoscopes with continuously rotating, oscillating or reciprocating cutting instruments

Definitions

  • This invention is generally related to surgical burs. More particularly, this invention is related to a surgical bur with a bur head geometry that substantially reduces chatter when the bur is applied to a surgical site.
  • a bur is a tool used to perform a surgical procedure.
  • a bur generally consists of a head formed from rigid material, typically metal, shaped to have a number of flutes. The flutes are formed to define tissue cutting edges.
  • a shaft extends rearwardly from the head of the bur. The free end of the shaft has a feature that facilitates locking the shaft to a powered handpiece. The actuation of the handpiece results in the rotation of the bur.
  • the bur head is placed against a surgical site where a section of tissue is to be removed.
  • the rotating cutting edges excise tissue away from the surgical site. Burs of various shapes and sizes are used in procedures such as orthopedic surgery, neuro and spinal surgery, ear nose and throat surgery and in other surgical procedures in which a sub-procedure is to selectively remove a section of tissue.
  • Burs work well for the purposes for which they are designed. Nevertheless, a problem associated with some burs is chatter. Chatter is the back and forth vibration of a bur head against the surface to which the bur head is applied. Chatter occurs as a result of the bur's individual cutting edges repeatedly being forced against the tissue against which the bur head is applied. Generally, there are three reasons a bur may start to chatter.
  • a bur starts to chatter is because it receives an input of energy due to a process known as regeneration of waviness .
  • This process is due to the fact that, when a cutting edge passes across a section of tissue, it leaves a specific wavy (essentially sinusoidal) profile along the surface of the tissue. If two adjacent cutting edges cut in phase, the second cutting edge excises tissue along a surface profile identical to that along which in was excised by the first flute. In practice, due to the invariable movements of the bur head and the tissue, this does not happen. When any two successive cutting edges pass over the same tissue section, the second flute cutting edge removes tissue on a path that does not overlap the tissue wave excised by the first cutting edge.
  • the debris chips cut by the second cutting edge have variable thickness. This means, during the process in which the second cutting edge excises the chip from the tissue, the cutting edge and its flute are subjected to variable forces. Over time, the repetitive exposure of the bur flutes to these variable forces causes the bur to undergo forced vibration.
  • a second reason a bur may chatter is that it is rotated at its resonant frequency. If this occurs, the repetitive force against the flutes self-excites the bur to move back and forth through a continually increasing range of motion.
  • the third reason a bur may chatter is due to the depth of the cut in the tissue against which the bur head is applied. If a bur head is pressed against the tissue so as to make only a relatively shallow cut, the overall time any two adjacent flutes are exposed to the tissue being cut is relatively small. The time in which the two adjacent flutes, as well as the spatial gap between the flutes, are exposed to the open environment is relatively high. During these relatively long time periods, tissue cut from the bur that is entrained in this gap is able to be discharged away from the bur head. This gap is then relatively debris-free the next time it rotates against the in-place tissue. Additional newly excised tissue fills this gap.
  • the bur of this invention is directed to the design of a new and useful surgical bur.
  • the bur of this invention is provided with cutting edges positioned to reduce, if not eliminate, chatter that occurs during the use of the bur.
  • the bur of this invention has a plurality of arcuately spaced flutes. Each flute defines a cutting edge, an edge that removes tissue from the surgical site to which the bur is applied.
  • a first set of flutes comprises two symmetrical flutes that emerge from the fluteless distal end tip of the bur.
  • There is a second set of flutes that are arranged so that there is at least one second set flute on each side of one of the flutes from the first set.
  • the flutes in a second set of flutes are shaped to have cutting edges that emerge from the bur head at various proximal locations from the distal end tip of the bur.
  • Chamfer surfaces of different lengths and sizes are formed on the intermediate set of flutes. These flutes essentially cascade the cutting edges in a progressive fashion at the surgical site; thus, decreasing or eliminating the amount of chatter the bur experiences under load.
  • An exemplary eight flute bur is used to describe the present invention.
  • other exemplary embodiments include bur heads with cascading cutting edges with 4, 6, 8, 10, 12, or more flutes.
  • “Cascading” means the cutting edges emerge from the bur head at various proximal locations from the distal end tip of the bur on the intermediate set of flutes .
  • Figure 1 is a side view of a basic surgical bur constructed in accordance with this invention,- [00015]
  • Figure 2 is an isometric view of the bur head of Figure 1.
  • Figure 3 is a front view of the bur head showing respective flute chamfers and cutting edges;
  • Figure 4 is a side view of a bur head shaped in accordance with this invention.
  • Figure 5 is a side view of a bur head shaped in accordance with this invention, rotated along the axis of ⁇ the bur;
  • Figure 6 is a cross sectional view of the bur head of Figure 2 ;
  • Figure 7 is a side view of a bur head shaped in accordance with this invention, rotated along the axis of the bur, showing the pitch angles of the chamfer surfaces;
  • Figure 8 is a side view of a bur head shaped in accordance with this invention showing the pitch angles of the chamfer surfaces .
  • FIG 1 illustrates a surgical bur 20 constructed in accordance with this invention.
  • Bur 20 has a head 22 that forms the distal end of the bur.
  • “Distal” it shall be understood, means towards the surgical site to which the bur is applied.
  • "Proximal” means away from the surgical site.
  • Bur head 22 has a distal end tip 23 that is the most forward portion of the bur 20.
  • a shaft 24 extends proximally rearward from the bur head 22.
  • the proximal end of the shaft 24 is provided with coupling features 26, illustrated simply as box in Figure 1.
  • the coupling features 26 comprises of geometric features that facilitate the removable engagement of the shaft 24 to a coupling assembly integral with the rotating shaft of a powered surgical tool with which bur 20 is used (tool not illustrated.)
  • the coupling features 26 may be a set of planar faces recessed relative to the outer diameter of the shaft 24, which is not illustrated.
  • One such geometry is described and illustrated in U.S. Patent No. 5,888,200, issued 30 March 1999, Multi-Purpose Surgical Tool System, the contents of which is incorporated herein by reference.
  • An alternative geometry for coupling features 26 in the form of linearly aligned opposed concave surfaces is illustrated in U.S. Patent No.
  • coupling features 26 may constitute as tabs, not illustrated, that project outwardly from the outer surface of shaft 24. These tabs, like any other coupling feature, function as the coupling features 26.
  • the exact geometry of the coupling feature 26 is not pertinent to the subject of the invention and is only meant to explanatorily show how a surgical bur is typically coupled to a surgical power tool .
  • Bur head 22 is formed with a number of arcuately spaced flutes 30-44.
  • Each flute 30-44 is formed by a rake surface 50 and a clearance surface 52.
  • Rake surface 50 extends approximately radially from the longitudinal axis of the center core of the bur head 22. It should be understood that, as the outer diameter of the bur changes along the length of the bur, the outer diameter of the center core changes.
  • Each clearance surface 52 extends generally tangentially from the outer perimeter of the bur head center core. More specifically, each clearance surface 52 extends approximately tangentially away from the base of the rake surface 50 of the flute adjacent the flute formed by the clearance surface.
  • the clearance surface 52 of flute 30 extends from the position along the perimeter of the bur head core from which rake surface 50 of flute 32 extends.
  • the rake surface 50 and clearance surface 52 that form an individual flute meet to form a cutting edge 54.
  • the bur cutting edges 54 are the edges of the bur head 22 that perform the cutting when the bur 20 is applied to a surgical surface.
  • bur head 22 of this invention first set of two flutes, flutes 30 and 38, are formed so that their rake and clearance surfaces 50 and 52, respectively, meet to form cutting edges 54 at a location that start relatively close to the distal end tip 23 of the bur head. More specifically, at the bur head distal end tip 23 can be considered to be a land at which no flutes are present. Flutes 30 and 32, and their cutting edges 54, emerge outwardly from the perimeter of this land. Flutes 30 and 38 are also symmetrical to one another, 180° apart. Since flutes 30 and 38 start from very close to the distal end tip 23 of the bur head, they can be considered full flutes .
  • each arcuate section of the bur head between flutes 30 and 38 there are plural additional flutes.
  • flutes 32, 34 and 36 In one section there are flutes 32, 34 and 36.
  • the second arcuate section contains flutes 40, 42 and 44.
  • These intermediate sets of flutes 32-36 and 40-44 are formed with chamfers surfaces. These chamfer surfaces effectively "cutoff" the cutting edges of flutes 32-36 and 40-44 so that their cutting edges 54 emerge from the bur head at locations spaced from the land at the bur head distal end tip 23. Given the spacing of flutes 32-36 and 40-44 from the distal end tip of the bur head, these flutes can be considered truncated flutes.
  • each of the chamfer surfaces 56 forms the common distal end face of one of the intermediate flute sets, flute set 32-36 and flute set 40-46.
  • Each chamfer surface 56 starts at the perimeter of the land at the bur head distal end tip 23.
  • Chamfer surfaces 56, relative to the cutting edges 54 of flutes 30 and 38 are angled closer to the proximal end of the bur shaft.
  • the presence of chamfer surfaces 56 means that the cutting edges of flutes 32-36 and 40-46 emerge from the bur head at distances that are spaced proximal to the distal end tip of the bur head.
  • Symmetrically opposed flutes 36 and 44 each have a chamfer surface 60.
  • Each chamfer surface 60 emerges from the perimeter of the land at the bur head distal end tip 23. Thus each chamfer surface 60 forms an edge with an adjacent chamfer surface 56.
  • Each chamfer surface 60 also abuts the distal end rake surface 50 of one of the flutes 30 or 38.
  • Each chamfer surface 60 has an angle from the longitudinal axis of the bur shaft than the angle of the adjacent chamfer surface 56.
  • Each flute 36 and 44 is formed with a second chamfer surface, chamfer surface 62.
  • Each chamfer surface 62 extends distally rearward from the point where the abutting chamfer surfaces 56 and 60 move apart from each other. Thus, each chamfer surface 62 extends between the rake and clearance surfaces 50 and 52, respectively, of the associated flute 36 or 44.
  • Each chamfer surface 62 extends proximally rearward along the bur head further than the associated chamfer surface 56. Thus owing to the presence of chamfer surfaces 62, the cutting edges 54 of flutes 36 and 44 emerge from the bur head at position proximal to those where cutting edges 54 of flutes 34 and 42 emerge. [00032]
  • Each flute 32 and 40 is formed with its own chamfer surface 64. Each chamfer surface 64 starts at a point a short distance proximally rearward from the distal end tip of the bur head. Each chamfer surface 64 extends between the rake and clearance surfaces 50 and 52, respectively, of the associated flute 32 or 40. The distal portion of each chamfer surface 64 intersects the adjacent chamfer surface 56.
  • Each chamfer surface 64 extends rearward along the associated flute 32 or 40 a distance approximately equal to the distance along which chamfer surfaces 62 extend. (These distances being from the distal end tip of the bur head.) Thus, owing to the presence of chamfer surfaces 64, cutting edges 54 of flutes 32 and 40 emerge from the bur head at the approximately the same position at which the cutting edges 54 of flutes 36 and 44 emerge.
  • position is understood to be a location along the longitudinal axis of the bur head 22 relative to the distal end tip 23.
  • each chamfer surface 56, 60, 62, and 64 each have chamfer edges that define the perimeter of each chamfer surface .
  • Chamfer surfaces 56 each have two chamfer edges 70 and 72. Starting at the most proximal location of each chamfer surface 56, cutting edge chamfer edge 70 intersects the cutting edge 54 and clearance surface 52 of flutes 34 and 42. At a more distal location from the most proximal location of chamfer surface 56, chamfer edge 70 arcuately curves to intersect, or abut, each respective chamfer surface 64 present on flutes 32 and 40. More specifically, chamfer edge 70 intersects with the perimeter of chamfer surface 64. Distally forward of this intersection, chamfer edge 70 the reverses in curvature. The distal end terminus of chamfer edge 70 is the perimeter of the land around distal end tip 23.
  • edge 72 The land at distal end tip is also the distal end terminus for chamfer edge 72. Extending proximally from this location, edge 72 initially curves away from edge 70. Edge 70 then forms the boundary first between chamfer surfaces 56 and 60 and then between surfaces 56 and 62. Proximal to where chamfer edge 72 forms this last boundary, this edge reverses the direction of curvature so as to curve toward the linear portion of edge 70. Edges 70 and 72 meet to define the proximal top of chamfer surface 56.
  • Each chamfer surface 60 has two additional edges that create the chamfer surface perimeter; a chamfer edge 74 and a radial chamfer edge 76.
  • Chamfer edge 74 extends from the point surfaces 56, 60 and 62 intersect. Edge 74 then defines the intersection between surfaces 60 and 62.
  • Chamfer edge 74 then intersects with the radial chamfer edge 76 and clearance surface 52 of flutes 36 and 44 of which where it stops.
  • the radial chamfer edge 76 intersects the rake surface 50 of respective flutes 30 and 38 and the chamfer edge 72; as well as meeting with each respective chamfer surfaces 62. Proximally located to where chamfer edge 74 meets with chamfer surface 56, lies the radial chamfer edge 76.
  • Two additional chamfer edges define the perimeter of each chamfer surface 62; chamfer edges 78 and 80.
  • Chamfer edge 80 starts at the point where chamfer edges 74 and 76 intersect.
  • Chamfer edge 80 then extends proximally in an arcuate sweep so as to form the border between the clearance surface 52 of flute 36 (or 44) and the chamfer surface 62.
  • Chamfer edge 80 then terminates where the edge intersects with the distal terminus of the cutting edge of flute 36 (or 44) .
  • Chamfer edge 78 starts proximally further from the distal end tip 23 than does chamfer edge 80.
  • Chamfer edge is generally linear in shape and extends proximally rearward.
  • Chamfer edge 78 extends to the point where for the flute 36 (or 44) the cutting edge 54 meets the chamfer edge 80. Cutting edge 54 of flute 36 (or 44) extends proximally away, in an arcuate fashion, from the most proximal point at which the two chamfer edges 78 and 80 intersect .
  • the chamfer surface 64 includes two chamfer edges 82 and 84.
  • Chamfer edge 82 emerges from the distal end tip 23 and extends along a generally linear path.
  • Chamfer edge 82 thus forms the boundary between rake surface 50 and chamfer surface 64 of flute 32 (or 40) .
  • Chamfer edge 84 starts at the point where rake surface 52 of flute 32 (or 40) and the adjacent chamfer surfaces 56 and 64 meet.
  • Chamfer edge 84 initially extends proximally and linearly away from this point.
  • Chamfer edge 84 then curves towards edge 82.
  • Edge 84 then intersects the proximal end terminus of the complementary chamfer edge 82.
  • each chamfer surface 56, 60, 62, and 64 is not limited to the described version of the invention. It is purely a product of machining and chamfer surface size whether or not chamfer edges are shared or intersect one another. It is within the scope of the present invention to have chamfer surfaces that share fewer edges. Alternatively, one chamfer surface could extend radially around the entire surface of the bur head 22 in a fashion where small chamfer surfaces extend proximal to the large circumferential chamfer surface.
  • each chamfer surface 56, 60, 62, and 64 is not perfectly flat and is arcuate in nature. Therefore, extending a line tangentially to each chamfer surface yields an approximate particular angle relative to the distal end tip 23. It is to be noted, that though chamfer surface 56 looks flat, it is indeed curved. The radius of chamfer surface 56 is so large in nature that when such a small portion of the radius is looked at, the surface visually looks flat.
  • both chamfer surfaces 62 and 64 have the same angles relative to the longitudinal center axis, LCA, of bur head 22.
  • ⁇ l equals ⁇ 4.
  • Tangent line Tl extends tangentially from the chamfer surface 62 intersecting the longitudinal center axis LCA to create angle ⁇ l therebetween.
  • tangent line T4 extends tangentially from the surface of chamfer surface 64 intersecting the longitudinal center axis LCA to create angle ⁇ 2 therebetween. Since ⁇ l equals ⁇ ?4, the chamfer surfaces 62 and 64 have the same angle, or pitch, on bur head 22.
  • FIG 7 shows the relationship between ⁇ l, ⁇ 2, ⁇ 3 , ⁇ 4 , and ⁇ 5 ; though it does not show ⁇ 4 , it has already- been shown that ⁇ l is equivalent to ⁇ 4.
  • each chamfer surface 56, 60, and 62 has a respective line T3 , T2 and Tl, respectively, that corresponds to the approximate chamfer pitch or cutting edge pitch.
  • Each tangential line Tl, T2 and T3 intersects the longitudinal center axis LCA creating an angle ⁇ l, ⁇ 2 and ⁇ 3, respectively, therebetween. It can be seen that ⁇ l is greater than ⁇ 2, which is greater than ⁇ 3 ; which in turn is greater than ⁇ 5.
  • Bur head 22 may be formed by first shaping the head to provide eight (8) identical flutes that extend the full length of the head from the distal end tip to the shaft. Then, portions of flutes 34 and 42 are selectively removed to form chamfer surfaces 56. Similarly, portions of flutes 32, 36, 40, and 44 are selectively removed to form chamfer surfaces 58. Grinding, electro-discharge machining or laser cutting or other machining methods may be employed to excise the material from flutes 32-36 and 40-44 to form their respective chamfer surfaces 56. [00043] Alternatively formed, the bur head 22 may be formed by casting the bur head and grinding down the desired edges to form a cutting edge. By casting the bur head, the chamfer surfaces do not need to be grinded down due to the design of the cast.
  • TPF [RPM X No. of CE] /60
  • RPM revolutions per minute of the bur 20.
  • Variable CE is the number of bur head 22 cutting edges at the position along the bur head at which the bur head is being applied to the tissue to be excised.
  • the tooth passing frequency at the distal end locations is less than the tooth passing frequency at the more proximal locations along the length of the bur head.
  • This reduction in distal end tooth passing frequency further reduces the chatter of bur 20 of this invention. This is because a further means of reducing chatter is to operate the bur at a speed so that the tooth passing frequency as closely as possible matches the chatter frequency.
  • Bur head 22 of bur 20 has what is referred to as an acorn style head.
  • This invention may be incorporated into bur heads having alternative shapes.
  • the bur head 22 of this version of the invention may comprise of a round or spherical shape or a shape that offers a relatively small distal end tip 23 diameter that then tapers proximally outward from the distal end tip creating a larger diameter the further away from the distal end tip of the bur head.
  • the bur heads may have alternative shapes including barrel head, conical, egg, pear or drum shaped. Again, it should be understood that this list is not limiting.
  • the flutes with the short length cutting edges or also accurately described as having the longest chamfer distance, alternate with the flutes having the longer length cutting edges. This feature of the invention need not be incorporated in all versions of the invention.
  • a bur head may be arranged so that two or more long length cutting edges are followed by one or more flutes with shorter length cutting edges.
  • the truncate flute sets need not be limited to three flutes between the flutes 30 and 38 with full cutting edges 54.
  • the number of flutes in each intermediate set of flutes may be less than or equal to three flutes or greater than or equal to three flutes.
  • a bur head could easily have four or six flutes with the aforementioned cutting edge progression created by chamfer surfaces 56, 60, 62, and 64.
  • chamfer surfaces 56, 60, 62, and 64 Just as easily, one could have a bur with 8, 10, 12, 14, 16 or more flutes with the same cutting edge progression.
  • the number of different sized chamfers is also not meant to be limiting.
  • chamfer surfaces For instance, one could easily change the geometry, or surface area, of the preferred embodiment chamfer surfaces to create an equivalent bur head with only two or three different sized chamfers.
  • the chamfers need not intersect or create a common edge with one another, thus creating a need for less chamfer surfaces to provide the same outcome of progressive cutting edges.
  • the bur head of the disclosed preferred embodiment could do with or without chamfer surfaces 60 as well as have more narrow chamfer surfaces 56 if a couple of changes were made.
  • Chamfer surfaces 56 could be narrowed as to take away the need to have intersecting chamfer surfaces.
  • chamfer surfaces 62 and 64 could be the same size in length and width, both starting at the distal end tip of the bur. Effectively creating a bur that is equivalent to the preferred embodiment of the invention, except with different chamfer geometry that yields no chamfer surface intersection, or shared edges, and only two three different size chamfer surfaces, depending whether or not chamfer surface 60 is included.
  • angle and depth of each chamfer are variables to which are not meant to be limiting. It is well within the scope of the present invention to change each of the aforementioned variables to produce the same desired effect of flute cutting edge progression with chamfer angles and depths each correlating to the performance of the excise tissue in a manner that decreases or eliminates chatter.
  • Chamfer length refers to the longitudinal distance from the distal end tip of the bur to a location longitudinally proximal to the distal end tip.
  • Chamfer length is a product of the necessitation to progressively increase the cutting edges on the intermediate flutes. Accordingly, the chamfer length is yet another variable that is not meant to be limiting.
  • the lengths of each chamfer can be changed to alter the length of the overall flute cutting edge progression of the bur. This change could prove to increase or decrease the distance from the distal end tip of the bur where two symmetrical full flute cutting edges are prevalent to a location of which all flute cutting edges are prevalent (absence of chamfers) .
  • a decrease in the aforementioned distance from the distal end tip to the location on the bur head to which each cutting edge of each flute is prevalent would prove to decrease the amount of time the bur head requires to engage all cutting edges of each flute to excise tissue.
  • an increase in this distance would prove to increase the amount of time the bur head require to engage all cutting of each flute to excise tissue; this is of course assuming, for comparison reasons, that the load on the bur head stays the same.
  • the flutes with the shorter length cutting edges may have shorter length cutting edges by virtue of the cutting edges terminating at a position along the bur head spaced distally from the locations along which other cutting edges terminate.
  • Some versions of the invention may be constructed so that, between flutes with cutting edges that extend the full length of the bur head, there are flutes with cutting edges that start a position proximal to the bur head distal end tip and terminate at a position distal to the proximal terminus of the bur head.
  • other versions of this invention may have different flute arrangements and flute shapes to provide the same structural features. Also, flutes of different shapes may be provided on a single bur.
  • the shaft structure is not limited to what has been disclosed.
  • the bur of this invention may have a tubular shaft.
  • the shaft typically has an opening immediately proximal to the bur head.
  • the opening functions as a port through which irrigating fluid is discharged or a suction is drawn.
  • the coupling feature of the bur is often a hub attached to the proximal open end of the shaft .
  • the hub has both geometric features that facilitate the coupling of the bur to a drive handpiece and a port to establish fluid communication to a suction device or from a source of irrigating fluid.
  • the disclosed acorn shaped bur head shape is exemplary, not limiting.
  • the bur heads may have alternative shapes including barrel head, conical, egg, pear or drum shaped.
  • the distal end tips of the bur heads may have profiles different than the curved convex profile of the illustrated embodiments.

Abstract

A surgical bur (20) having a shaft (24) with a bur head (22) at the distal end. A number of flutes are formed on the bur head. Each flute has a cutting edge (54). Two flutes (30, 38) are arcuately symmetrically spaced from one another having cutting edges that start at or approximately, close to the distal end tip (23).and have intermediate sets of flutes (32, 34, 36, 40, 42, 44) therebetween. The intermediate sets of flutes have chamfers (56, 60, 62, 64) so as to progressively engage flute cutting edges into the tissue that is to be excised. The cutting edge progression during the use of the bur decreases or eliminates chatter.

Description

SURGICAL BUR WITH ANTI-CHATTER FLUTE GEOMETRY
INCLUDING A PAIR OF SYMMETRIC FLUTES THAT EMERGE
FROM THE DISTAL END TIP OF THE BUR HEAD
FIELD OF THE INVENTION
[0001] This invention is generally related to surgical burs. More particularly, this invention is related to a surgical bur with a bur head geometry that substantially reduces chatter when the bur is applied to a surgical site.
BACKGROUND OF THE INVENTION
[0002] A bur is a tool used to perform a surgical procedure. A bur generally consists of a head formed from rigid material, typically metal, shaped to have a number of flutes. The flutes are formed to define tissue cutting edges. A shaft extends rearwardly from the head of the bur. The free end of the shaft has a feature that facilitates locking the shaft to a powered handpiece. The actuation of the handpiece results in the rotation of the bur. During a surgical procedure, the bur head is placed against a surgical site where a section of tissue is to be removed. The rotating cutting edges excise tissue away from the surgical site. Burs of various shapes and sizes are used in procedures such as orthopedic surgery, neuro and spinal surgery, ear nose and throat surgery and in other surgical procedures in which a sub-procedure is to selectively remove a section of tissue.
[0003] Burs work well for the purposes for which they are designed. Nevertheless, a problem associated with some burs is chatter. Chatter is the back and forth vibration of a bur head against the surface to which the bur head is applied. Chatter occurs as a result of the bur's individual cutting edges repeatedly being forced against the tissue against which the bur head is applied. Generally, there are three reasons a bur may start to chatter.
[0004] One reason a bur starts to chatter is because it receives an input of energy due to a process known as regeneration of waviness . This process is due to the fact that, when a cutting edge passes across a section of tissue, it leaves a specific wavy (essentially sinusoidal) profile along the surface of the tissue. If two adjacent cutting edges cut in phase, the second cutting edge excises tissue along a surface profile identical to that along which in was excised by the first flute. In practice, due to the invariable movements of the bur head and the tissue, this does not happen. When any two successive cutting edges pass over the same tissue section, the second flute cutting edge removes tissue on a path that does not overlap the tissue wave excised by the first cutting edge. Consequently, the debris chips cut by the second cutting edge have variable thickness. This means, during the process in which the second cutting edge excises the chip from the tissue, the cutting edge and its flute are subjected to variable forces. Over time, the repetitive exposure of the bur flutes to these variable forces causes the bur to undergo forced vibration.
[0005] A second reason a bur may chatter is that it is rotated at its resonant frequency. If this occurs, the repetitive force against the flutes self-excites the bur to move back and forth through a continually increasing range of motion.
[0006] The third reason a bur may chatter is due to the depth of the cut in the tissue against which the bur head is applied. If a bur head is pressed against the tissue so as to make only a relatively shallow cut, the overall time any two adjacent flutes are exposed to the tissue being cut is relatively small. The time in which the two adjacent flutes, as well as the spatial gap between the flutes, are exposed to the open environment is relatively high. During these relatively long time periods, tissue cut from the bur that is entrained in this gap is able to be discharged away from the bur head. This gap is then relatively debris-free the next time it rotates against the in-place tissue. Additional newly excised tissue fills this gap. However, if the bur head is pressed against the tissue to make a deep cut, the time in which the spatial gap between any two flutes is located against the in-place tissue increases. The time this gap is exposed to the open environment drops. Consequently, there may not be enough time for tissue entrained in this gap to be discharged. Consequently, these gaps between the flutes clog. This clogging, in turn, is believed to cause a forced vibration and the resultant chatter.
[0007] The Applicant's Assignee's PCT Application No. PCT/IB2006/002118, titled SURGICAL BUR WITH ANTI-CHATTER FLUTE GEOMETRY, PCT Pub. No. WO 2007/010389 Al, the contents of which are incorporated herein by reference, discloses one flute geometry that, to some extent minimizes chatter. Specifically, the flutes of the bur of this document are constructed so that, at the distal end tip of the bur, less than all of the flutes are present. Then, extending proximally along the length of the bur, additional flutes emerge from the bur head. These emerging flutes are located between the flutes that extend from the distal end tip. Burs with these flutes that emerge from the bur head at different points along the body of the head are less prone to chatter than conventional burs.
[0008] Nevertheless, even these burs can undergo chatter- inducing vibrations. SUMMARY OF THIS INVENTION
[0009] This invention is directed to the design of a new and useful surgical bur. The bur of this invention is provided with cutting edges positioned to reduce, if not eliminate, chatter that occurs during the use of the bur. [00010] The bur of this invention has a plurality of arcuately spaced flutes. Each flute defines a cutting edge, an edge that removes tissue from the surgical site to which the bur is applied. A first set of flutes, comprises two symmetrical flutes that emerge from the fluteless distal end tip of the bur. There is a second set of flutes that are arranged so that there is at least one second set flute on each side of one of the flutes from the first set. The flutes in a second set of flutes are shaped to have cutting edges that emerge from the bur head at various proximal locations from the distal end tip of the bur. [00011] Chamfer surfaces of different lengths and sizes are formed on the intermediate set of flutes. These flutes essentially cascade the cutting edges in a progressive fashion at the surgical site; thus, decreasing or eliminating the amount of chatter the bur experiences under load.
[00012] An exemplary eight flute bur is used to describe the present invention. However, other exemplary embodiments include bur heads with cascading cutting edges with 4, 6, 8, 10, 12, or more flutes. "Cascading" means the cutting edges emerge from the bur head at various proximal locations from the distal end tip of the bur on the intermediate set of flutes . BRIEF DESCRIPTION OF THE DRAWINGS
[00013] The invention is pointed out with particularity in the claims. The above and further features of this invention may be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings in which:
[00014] Figure 1 is a side view of a basic surgical bur constructed in accordance with this invention,- [00015] Figure 2 is an isometric view of the bur head of Figure 1.
[00016] Figure 3 is a front view of the bur head showing respective flute chamfers and cutting edges; [00017] Figure 4 is a side view of a bur head shaped in accordance with this invention;
[00018] Figure 5 is a side view of a bur head shaped in accordance with this invention, rotated along the axis of the bur;
[00019] Figure 6 is a cross sectional view of the bur head of Figure 2 ;
[00020] Figure 7 is a side view of a bur head shaped in accordance with this invention, rotated along the axis of the bur, showing the pitch angles of the chamfer surfaces; and,
[00021] Figure 8 is a side view of a bur head shaped in accordance with this invention showing the pitch angles of the chamfer surfaces .
DETAILED DESCRIPTION
[00022] Figure 1 illustrates a surgical bur 20 constructed in accordance with this invention. Bur 20 has a head 22 that forms the distal end of the bur. ("Distal" it shall be understood, means towards the surgical site to which the bur is applied. "Proximal" means away from the surgical site.) Bur head 22 has a distal end tip 23 that is the most forward portion of the bur 20. A shaft 24 extends proximally rearward from the bur head 22.
[00023] The proximal end of the shaft 24 is provided with coupling features 26, illustrated simply as box in Figure 1. The coupling features 26 comprises of geometric features that facilitate the removable engagement of the shaft 24 to a coupling assembly integral with the rotating shaft of a powered surgical tool with which bur 20 is used (tool not illustrated.) The coupling features 26 may be a set of planar faces recessed relative to the outer diameter of the shaft 24, which is not illustrated. One such geometry is described and illustrated in U.S. Patent No. 5,888,200, issued 30 March 1999, Multi-Purpose Surgical Tool System, the contents of which is incorporated herein by reference. An alternative geometry for coupling features 26 in the form of linearly aligned opposed concave surfaces is illustrated in U.S. Patent No. 6,562,055, issued 13 May 2003, Cutting Attachment For A Surgical Handpiece Designed To Be Selectively Coupled To The Handpiece, the contents of which are incorporated herein by reference . It should be appreciated that these two geometries of coupling features are exemplary and not meant to be limiting. In alternative versions of the invention, the coupling features 26 may constitute as tabs, not illustrated, that project outwardly from the outer surface of shaft 24. These tabs, like any other coupling feature, function as the coupling features 26. The exact geometry of the coupling feature 26 is not pertinent to the subject of the invention and is only meant to explanatorily show how a surgical bur is typically coupled to a surgical power tool . [00024] Bur head 22, as seen best in Figures 2 and 3 is formed with a number of arcuately spaced flutes 30-44. Each flute 30-44, as seen by the front view of flute 30 in Figure 3, is formed by a rake surface 50 and a clearance surface 52. Rake surface 50 extends approximately radially from the longitudinal axis of the center core of the bur head 22. It should be understood that, as the outer diameter of the bur changes along the length of the bur, the outer diameter of the center core changes. Each clearance surface 52 extends generally tangentially from the outer perimeter of the bur head center core. More specifically, each clearance surface 52 extends approximately tangentially away from the base of the rake surface 50 of the flute adjacent the flute formed by the clearance surface. Thus, the clearance surface 52 of flute 30 extends from the position along the perimeter of the bur head core from which rake surface 50 of flute 32 extends.
[00025] The rake surface 50 and clearance surface 52 that form an individual flute meet to form a cutting edge 54. The bur cutting edges 54 are the edges of the bur head 22 that perform the cutting when the bur 20 is applied to a surgical surface.
[00026] As seen best in Figure 3, bur head 22 of this invention, first set of two flutes, flutes 30 and 38, are formed so that their rake and clearance surfaces 50 and 52, respectively, meet to form cutting edges 54 at a location that start relatively close to the distal end tip 23 of the bur head. More specifically, at the bur head distal end tip 23 can be considered to be a land at which no flutes are present. Flutes 30 and 32, and their cutting edges 54, emerge outwardly from the perimeter of this land. Flutes 30 and 38 are also symmetrical to one another, 180° apart. Since flutes 30 and 38 start from very close to the distal end tip 23 of the bur head, they can be considered full flutes .
[00027] Within each arcuate section of the bur head between flutes 30 and 38 there are plural additional flutes. In one section there are flutes 32, 34 and 36. The second arcuate section contains flutes 40, 42 and 44. These intermediate sets of flutes 32-36 and 40-44 are formed with chamfers surfaces. These chamfer surfaces effectively "cutoff" the cutting edges of flutes 32-36 and 40-44 so that their cutting edges 54 emerge from the bur head at locations spaced from the land at the bur head distal end tip 23. Given the spacing of flutes 32-36 and 40-44 from the distal end tip of the bur head, these flutes can be considered truncated flutes.
[00028] Specifically, there is a common chamfer surface, surface 56 over each set of flutes 32-36 and 40-46. Thus each of the chamfer surfaces 56 forms the common distal end face of one of the intermediate flute sets, flute set 32-36 and flute set 40-46. Each chamfer surface 56 starts at the perimeter of the land at the bur head distal end tip 23. Chamfer surfaces 56, relative to the cutting edges 54 of flutes 30 and 38 are angled closer to the proximal end of the bur shaft. Thus, the presence of chamfer surfaces 56 means that the cutting edges of flutes 32-36 and 40-46 emerge from the bur head at distances that are spaced proximal to the distal end tip of the bur head. [00029] Symmetrically opposed flutes 36 and 44 each have a chamfer surface 60. Each chamfer surface 60 emerges from the perimeter of the land at the bur head distal end tip 23. Thus each chamfer surface 60 forms an edge with an adjacent chamfer surface 56. Each chamfer surface 60 also abuts the distal end rake surface 50 of one of the flutes 30 or 38. Each chamfer surface 60 has an angle from the longitudinal axis of the bur shaft than the angle of the adjacent chamfer surface 56.
[00030] Each flute 36 and 44 is formed with a second chamfer surface, chamfer surface 62. Each chamfer surface 62 extends distally rearward from the point where the abutting chamfer surfaces 56 and 60 move apart from each other. Thus, each chamfer surface 62 extends between the rake and clearance surfaces 50 and 52, respectively, of the associated flute 36 or 44.
[00031] Each chamfer surface 62 extends proximally rearward along the bur head further than the associated chamfer surface 56. Thus owing to the presence of chamfer surfaces 62, the cutting edges 54 of flutes 36 and 44 emerge from the bur head at position proximal to those where cutting edges 54 of flutes 34 and 42 emerge. [00032] Each flute 32 and 40 is formed with its own chamfer surface 64. Each chamfer surface 64 starts at a point a short distance proximally rearward from the distal end tip of the bur head. Each chamfer surface 64 extends between the rake and clearance surfaces 50 and 52, respectively, of the associated flute 32 or 40. The distal portion of each chamfer surface 64 intersects the adjacent chamfer surface 56.
[00033] Each chamfer surface 64 extends rearward along the associated flute 32 or 40 a distance approximately equal to the distance along which chamfer surfaces 62 extend. (These distances being from the distal end tip of the bur head.) Thus, owing to the presence of chamfer surfaces 64, cutting edges 54 of flutes 32 and 40 emerge from the bur head at the approximately the same position at which the cutting edges 54 of flutes 36 and 44 emerge. Here "position" is understood to be a location along the longitudinal axis of the bur head 22 relative to the distal end tip 23. [00034] Moreover, each chamfer surface 56, 60, 62, and 64 each have chamfer edges that define the perimeter of each chamfer surface .
[00035] Chamfer surfaces 56 each have two chamfer edges 70 and 72. Starting at the most proximal location of each chamfer surface 56, cutting edge chamfer edge 70 intersects the cutting edge 54 and clearance surface 52 of flutes 34 and 42. At a more distal location from the most proximal location of chamfer surface 56, chamfer edge 70 arcuately curves to intersect, or abut, each respective chamfer surface 64 present on flutes 32 and 40. More specifically, chamfer edge 70 intersects with the perimeter of chamfer surface 64. Distally forward of this intersection, chamfer edge 70 the reverses in curvature. The distal end terminus of chamfer edge 70 is the perimeter of the land around distal end tip 23. The land at distal end tip is also the distal end terminus for chamfer edge 72. Extending proximally from this location, edge 72 initially curves away from edge 70. Edge 70 then forms the boundary first between chamfer surfaces 56 and 60 and then between surfaces 56 and 62. Proximal to where chamfer edge 72 forms this last boundary, this edge reverses the direction of curvature so as to curve toward the linear portion of edge 70. Edges 70 and 72 meet to define the proximal top of chamfer surface 56.
[00036] Each chamfer surface 60 has two additional edges that create the chamfer surface perimeter; a chamfer edge 74 and a radial chamfer edge 76. Chamfer edge 74 extends from the point surfaces 56, 60 and 62 intersect. Edge 74 then defines the intersection between surfaces 60 and 62. Chamfer edge 74 then intersects with the radial chamfer edge 76 and clearance surface 52 of flutes 36 and 44 of which where it stops. The radial chamfer edge 76 intersects the rake surface 50 of respective flutes 30 and 38 and the chamfer edge 72; as well as meeting with each respective chamfer surfaces 62. Proximally located to where chamfer edge 74 meets with chamfer surface 56, lies the radial chamfer edge 76.
[00037] Two additional chamfer edges define the perimeter of each chamfer surface 62; chamfer edges 78 and 80. Chamfer edge 80 starts at the point where chamfer edges 74 and 76 intersect. Chamfer edge 80 then extends proximally in an arcuate sweep so as to form the border between the clearance surface 52 of flute 36 (or 44) and the chamfer surface 62. Chamfer edge 80 then terminates where the edge intersects with the distal terminus of the cutting edge of flute 36 (or 44) . Chamfer edge 78 starts proximally further from the distal end tip 23 than does chamfer edge 80. Chamfer edge is generally linear in shape and extends proximally rearward. Chamfer edge 78 extends to the point where for the flute 36 (or 44) the cutting edge 54 meets the chamfer edge 80. Cutting edge 54 of flute 36 (or 44) extends proximally away, in an arcuate fashion, from the most proximal point at which the two chamfer edges 78 and 80 intersect .
[00038] Lastly, the chamfer surface 64 includes two chamfer edges 82 and 84. Chamfer edge 82 emerges from the distal end tip 23 and extends along a generally linear path. Chamfer edge 82 thus forms the boundary between rake surface 50 and chamfer surface 64 of flute 32 (or 40) . Chamfer edge 84 starts at the point where rake surface 52 of flute 32 (or 40) and the adjacent chamfer surfaces 56 and 64 meet. Chamfer edge 84 initially extends proximally and linearly away from this point. Chamfer edge 84 then curves towards edge 82. Edge 84 then intersects the proximal end terminus of the complementary chamfer edge 82. [00039] The chamfer edge geometry of each chamfer surface 56, 60, 62, and 64 is not limited to the described version of the invention. It is purely a product of machining and chamfer surface size whether or not chamfer edges are shared or intersect one another. It is within the scope of the present invention to have chamfer surfaces that share fewer edges. Alternatively, one chamfer surface could extend radially around the entire surface of the bur head 22 in a fashion where small chamfer surfaces extend proximal to the large circumferential chamfer surface.
[00040] Yet another unique variable to the disclosed invention relates to the particular angles of each chamfer surface 56, 60, 62, and 64 relative to the longitudinal center axis of the bur head 22. For the most part, each chamfer surface is not perfectly flat and is arcuate in nature. Therefore, extending a line tangentially to each chamfer surface yields an approximate particular angle relative to the distal end tip 23. It is to be noted, that though chamfer surface 56 looks flat, it is indeed curved. The radius of chamfer surface 56 is so large in nature that when such a small portion of the radius is looked at, the surface visually looks flat. As can be seen in Figure 8, both chamfer surfaces 62 and 64 have the same angles relative to the longitudinal center axis, LCA, of bur head 22. Thus, αl equals α4. Tangent line Tl extends tangentially from the chamfer surface 62 intersecting the longitudinal center axis LCA to create angle αl therebetween. Likewise, tangent line T4 extends tangentially from the surface of chamfer surface 64 intersecting the longitudinal center axis LCA to create angle α2 therebetween. Since αl equals α?4, the chamfer surfaces 62 and 64 have the same angle, or pitch, on bur head 22. [00041] Figure 7 shows the relationship between αl, α2, α3 , α4 , and α5 ; though it does not show α4 , it has already- been shown that αl is equivalent to α4. Like Figure 8 , each chamfer surface 56, 60, and 62 has a respective line T3 , T2 and Tl, respectively, that corresponds to the approximate chamfer pitch or cutting edge pitch. Each tangential line Tl, T2 and T3 intersects the longitudinal center axis LCA creating an angle αl, α2 and α3, respectively, therebetween. It can be seen that αl is greater than α2, which is greater than α3 ; which in turn is greater than α5. Since the obtuse angle between the lines Tl, T2 and T3 and longitudinal center axis lines were used, the relationship between angles and chamfer pitch or cutting edge pitch are inversed in relationship to the longitudinal center axis line LCA. Following the corollary relationship between angles, chamfer surface 62 has less of a pitch in relationship to the longitudinal center axis of the bur head 22 than chamfer surface 60, which in turn has less of a pitch than chamfer surface 56. The pitch of the cutting edges of flutes 30 and 38 are represented by the line T5 and angle α5. Angle α5 has the greatest pitch at the distal end tip 23 as compared to the pitches of each chamfer surface 56, 60, 62, and 64. [00042] Bur head 22 may be formed by first shaping the head to provide eight (8) identical flutes that extend the full length of the head from the distal end tip to the shaft. Then, portions of flutes 34 and 42 are selectively removed to form chamfer surfaces 56. Similarly, portions of flutes 32, 36, 40, and 44 are selectively removed to form chamfer surfaces 58. Grinding, electro-discharge machining or laser cutting or other machining methods may be employed to excise the material from flutes 32-36 and 40-44 to form their respective chamfer surfaces 56. [00043] Alternatively formed, the bur head 22 may be formed by casting the bur head and grinding down the desired edges to form a cutting edge. By casting the bur head, the chamfer surfaces do not need to be grinded down due to the design of the cast.
[00044] When a surgeon applies a bur 20 to a surgical site, often the section of the bur adjacent the distal end tip 23 is the section of the bur head 22 that is pressed against the tissue to be excised. It is at this time the above-described geometry of the bur of this invention becomes advantageous. There are a reduced number of cutting edges 54 at the distal end tip 23, two that are symmetrical to one another in the preferred embodiment of an eight flute bur. This reduces the extent to which forces generated as a result of regeneration of waviness excite the bur into chatter vibration. Moreover, since there is a reduced number of cutting edges 54 at the most distal section of the bur head 22, the interstitial gap between cutting edges 54 is wider than it would be otherwise. The relatively large size of these gaps minimizes the extent to which excised tissue is trapped in these spaces. This reduces the extent to which tissue entrained in the inter-flute gaps imposes addition vibration-causing force on the bur head 22. [00045] The reduction of the number of cutting edges also reduces the tooth passing frequency at the distal tip of the bur 20. This is the frequency at the cutting edges 54 press against the tissue being excised. This frequency, TPF, is calculated according to the formula:
TPF = [RPM X No. of CE] /60
Here, RPM is the revolutions per minute of the bur 20. Variable CE is the number of bur head 22 cutting edges at the position along the bur head at which the bur head is being applied to the tissue to be excised. With bur head 22 of this invention, since there are fewer cutting edges at the distal end of the bur head 22 than at more proximal locations, the tooth passing frequency at the distal end locations is less than the tooth passing frequency at the more proximal locations along the length of the bur head. [00046] This reduction in distal end tooth passing frequency further reduces the chatter of bur 20 of this invention. This is because a further means of reducing chatter is to operate the bur at a speed so that the tooth passing frequency as closely as possible matches the chatter frequency. This frequency matching assists in the nulling of bur chatter vibration. By reducing the number of flute cutting edges 54 at the distal end of the bur head 22, it is more likely that when, this end of the bur head is pressed against tissue, the tooth passing frequency will more closely approximate the chatter vibration frequency. [00047] Bur head 22 of bur 20 has what is referred to as an acorn style head. This invention may be incorporated into bur heads having alternative shapes. Specifically, the bur head 22 of this version of the invention may comprise of a round or spherical shape or a shape that offers a relatively small distal end tip 23 diameter that then tapers proximally outward from the distal end tip creating a larger diameter the further away from the distal end tip of the bur head. In alternative versions of the invention, the bur heads may have alternative shapes including barrel head, conical, egg, pear or drum shaped. Again, it should be understood that this list is not limiting. [00048] It should be recognized that other alternative versions of the invention may have features different from what has been described. For example, in the disclosed version of the invention, the flutes with the short length cutting edges, or also accurately described as having the longest chamfer distance, alternate with the flutes having the longer length cutting edges. This feature of the invention need not be incorporated in all versions of the invention. Thus, in some versions of the invention a bur head may be arranged so that two or more long length cutting edges are followed by one or more flutes with shorter length cutting edges.
[00049] In alternative embodiments of the invention, the truncate flute sets need not be limited to three flutes between the flutes 30 and 38 with full cutting edges 54. As described herein, the number of flutes in each intermediate set of flutes may be less than or equal to three flutes or greater than or equal to three flutes. Thus allowing for progressive fluting geometry on a multitude of different bur head sizes. For example, a bur head could easily have four or six flutes with the aforementioned cutting edge progression created by chamfer surfaces 56, 60, 62, and 64. Just as easily, one could have a bur with 8, 10, 12, 14, 16 or more flutes with the same cutting edge progression. [00050] The number of different sized chamfers is also not meant to be limiting. In alternative embodiments of the invention, one could have only 1, 2, or 3 chamfer surfaces, such as one might have on a four or six flute bur. Accordingly, one could also have fluting geometry that has more that four chamfer surfaces (surfaces 56, 60, 62, and 64) and instead have 5-6 different chamfer sizes and lengths for a bur with 12 or 16 flutes. Like the number of flutes in each intermediate section; the number of chamfers may be less than or equal to four chamfer surfaces or greater than or equal to four chamfer surfaces, as long as the desired outcome is the same. That is, flute cutting edge progression that yields two symmetrical arcuately arranged flutes with intermediate flute sets therebetween. [00051] For instance, one could easily change the geometry, or surface area, of the preferred embodiment chamfer surfaces to create an equivalent bur head with only two or three different sized chamfers. Here, the chamfers need not intersect or create a common edge with one another, thus creating a need for less chamfer surfaces to provide the same outcome of progressive cutting edges. For instance, the bur head of the disclosed preferred embodiment could do with or without chamfer surfaces 60 as well as have more narrow chamfer surfaces 56 if a couple of changes were made. Chamfer surfaces 56 could be narrowed as to take away the need to have intersecting chamfer surfaces. Accordingly, chamfer surfaces 62 and 64 could be the same size in length and width, both starting at the distal end tip of the bur. Effectively creating a bur that is equivalent to the preferred embodiment of the invention, except with different chamfer geometry that yields no chamfer surface intersection, or shared edges, and only two three different size chamfer surfaces, depending whether or not chamfer surface 60 is included.
[00052] It is also to be appreciated that angle and depth of each chamfer are variables to which are not meant to be limiting. It is well within the scope of the present invention to change each of the aforementioned variables to produce the same desired effect of flute cutting edge progression with chamfer angles and depths each correlating to the performance of the excise tissue in a manner that decreases or eliminates chatter.
[00053] Chamfer length, discussed herein, refers to the longitudinal distance from the distal end tip of the bur to a location longitudinally proximal to the distal end tip. Chamfer length is a product of the necessitation to progressively increase the cutting edges on the intermediate flutes. Accordingly, the chamfer length is yet another variable that is not meant to be limiting. The lengths of each chamfer can be changed to alter the length of the overall flute cutting edge progression of the bur. This change could prove to increase or decrease the distance from the distal end tip of the bur where two symmetrical full flute cutting edges are prevalent to a location of which all flute cutting edges are prevalent (absence of chamfers) . Accordingly, a decrease in the aforementioned distance from the distal end tip to the location on the bur head to which each cutting edge of each flute is prevalent would prove to decrease the amount of time the bur head requires to engage all cutting edges of each flute to excise tissue. Alternatively, an increase in this distance would prove to increase the amount of time the bur head require to engage all cutting of each flute to excise tissue; this is of course assuming, for comparison reasons, that the load on the bur head stays the same.
[00054] Likewise, there is no requirement that, in all versions of the invention, the shorter length cutting edges emerge at the location where the bur heads reach their maximum diameter.
[00055] Also, in some versions of the invention, the flutes with the shorter length cutting edges may have shorter length cutting edges by virtue of the cutting edges terminating at a position along the bur head spaced distally from the locations along which other cutting edges terminate. Some versions of the invention may be constructed so that, between flutes with cutting edges that extend the full length of the bur head, there are flutes with cutting edges that start a position proximal to the bur head distal end tip and terminate at a position distal to the proximal terminus of the bur head. [00056] Further, while two means of shaping the bur to provide cutting edges of different lengths have been described, other versions of this invention may have different flute arrangements and flute shapes to provide the same structural features. Also, flutes of different shapes may be provided on a single bur.
[00057] It is likewise understood that the shaft structure is not limited to what has been disclosed. The bur of this invention may have a tubular shaft. In these versions of the invention the shaft typically has an opening immediately proximal to the bur head. The opening functions as a port through which irrigating fluid is discharged or a suction is drawn. In these versions of the invention, the coupling feature of the bur is often a hub attached to the proximal open end of the shaft . The hub has both geometric features that facilitate the coupling of the bur to a drive handpiece and a port to establish fluid communication to a suction device or from a source of irrigating fluid. [00058] It should likewise be appreciated that the disclosed acorn shaped bur head shape is exemplary, not limiting. In alternative versions of the invention, the bur heads may have alternative shapes including barrel head, conical, egg, pear or drum shaped. Thus, there in some versions of the invention, the distal end tips of the bur heads may have profiles different than the curved convex profile of the illustrated embodiments. [00059]
[00060] Thus, it is an object of the appended claims to cover all such variations and modifications that come within the true spirit and scope of this invention.

Claims

What is claimed is:
1. A surgical bur comprising: an elongated shaft (24) having opposed proximal and distal ends,- a coupling feature (26) associated with the proximal end of the shaft, the coupling feature shaped to engage a drive unit of a surgical handpiece so that the handpiece can rotate the shaft; a bur head (22) attached to the distal end of the shaft, the bur head having a body and a distal end tip (23) and a plurality of arcuately spaced apart flutes (30-44), each flute having a cutting edge (54) , wherein at the distal end tip there is a flute-free land and the flutes emerge from the perimeter of the flute- free land, characterized in that, a single pair of full flutes (30, 38) emerge from land at the distal end tip (23) such that the cutting edges of the full flutes emerges from the land and the full flutes are symmetrical relative to the bur head distal end tip,- and at least one truncated flute (32, 34, 36, 40, 42, 44) is located in each arcuate space between the said single pair of full flutes, said truncated flutes each having a cutting edge that has a starting point that is spaced proximally from the land at the distal end tip.
2. The surgical bur of Claim 1, wherein: in each of the arcuate spaces between said full flutes there at least three truncated flutes (32, 34, 36 and 40, 42, 44) so that on either side of each said full flute there is at least one close truncated flute (32, 36, 40, 44) and at least one arcuately spaced truncated flute (34, 42) ; and said truncated flutes are further formed so that said truncated flutes close to the said full flutes each have a cutting edge that emerges from the distal end of the bur head a first distance proximal to the distal end tip and said truncated flutes spaced from the said full flutes emerge from the distal end of the bur head a second distal proximal to the distal end tip, the second distance being less than the first distance.
3. The surgical bur of Claim 2, wherein: each said truncated flute arcuately spaced from said full flutes (34, 42) is formed to have a first chamfer surface (56) that extends proximally from said distal end tip land such that the cutting edges of said arcuately spaced flutes terminate at the associated said first chamfer surfaces; and each said truncated flute arcuately close to one of said full flutes (32, 36, 40, 44) is formed to have a second chamfer surface (62, 64) that extends proximally from an adjacent first chamfer surface such that the cutting edges of the said arcuately close flutes terminate at the associated second chamfer surfaces .
4. The surgical bur of Claim 3, wherein: the bur head has a longitudinal axis: said first chamfer surfaces (56) define a tangent line that intersects the bur head longitudinal axis at a first pitch angle; and said second chamfer surfaces (62, 64) define a tangent line that intersects the bur head longitudinal axis at a second pitch angle, the second pitch angle being less than the first pitch angle.
5. The surgical bur of Claims 1 or 2, wherein said truncated flutes are formed to define chamfer surfaces (56, 60, 62, 64) that extend from the rake surfaces towards the bur head distal end tip so that said truncated flutes do not have cutting edges along the sections therefore where the chamfered surfaces are present .
6. The surgical bur of Claims 1 or 2 , wherein: in each of the arcuate spaces between said full flutes there at least two truncated flutes (32, 34, 36 and 40, 42, 44) ; and the truncated flutes in each of the arcuate spaces between said full flutes are formed to have a common chamfer surface 56) that extends proximally from the distal end tip land over said truncated flutes so that said truncated flutes do not have cutting edges forward of said chamfered surfaces .
PCT/EP2007/010048 2006-11-21 2007-11-20 Surgical bur with anti-chatter flute geometry including a pair of symmetric flutes that emerge from the distal end tip of the bur head WO2008061711A2 (en)

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