Patent Description:
The disclosure relates to a surgical systems for bone cutting or shaping, and more particularly to surgical burs.

Surgical burs need sharp and durable cutting edges in order to efficiently dissect, cut and/or shape bone during a surgical procedure. Human anatomy tends to locate sensitive soft tissue structures, such as nerves and blood vessels, near bones for protection. These structures can include the dura mater. Dura mater, or dura, refers to the outermost layer of protective soft tissue surrounding the brain and spinal column of a patient. During cranial and spinal procedures, the distal end of a bur can come in contact with dura mater. The term "distal" means furthest away from a medical practitioner holding a surgical tool with a rotating bur. The term "proximal" means towards the medical practitioner and away from the patient.

It is desirable for the surgical burs to provide stability while drilling in an axial direction and to be able to efficiently cut while being moved in a radial direction. The axial direction may be, for example, a direction parallel to, along, and/or in line with a longitudinal axis of the surgical bur. The radial direction may be, for example, a direction away from and not parallel to the longitudinal axis of the surgical bur. The radial direction may be a direction away from and/or perpendicular to the longitudinal axis.

Document <CIT> discloses a surgical dissection tool having a cutting head with a plurality of flutes. Each flute has a rake surface intersecting an outer surface to form a cutting edge.

A surgical bur as defined in claim <NUM> is provided and includes flutes and lands. Each of the flutes includes a cutting edge, rake surfaces, and a clearance surface. The rake surfaces of one of the flutes are decoupled from each other. The rake surfaces of each of the flutes may be decoupled from each other. Each of the lands is disposed between a pair of the flutes.

Alternatively or in addition, the rake surfaces of one of the flutes includes (i) a first rake surface having a first rake angle, and (ii) a second rake surface having a second rake angle. Each of the flutes may have multiple rake surfaces with respective rake angles. The second rake angle is decoupled from the first rake angle.

<FIG> show side and perspective views of a predicate dissection tool <NUM> including a surgical bur <NUM>. The surgical bur <NUM> includes three convex lands <NUM> and three flutes <NUM>. Each of the flutes <NUM> is located between the lands <NUM> and has a corresponding chip space <NUM>. The lands <NUM> are equally spaced about a longitudinal axis <NUM> of the surgical bur <NUM>. Distal portions <NUM> of the lands <NUM> are referred to as axial relief surfaces, which are convex-shaped. The axial relief surfaces <NUM> are not distinct from the lands <NUM> because: the lands <NUM> and the axial relief surfaces <NUM> are both convex-shaped (or have the same type of surface); and the axial relief surfaces <NUM> are continuous with the lands <NUM> without transitional surfaces or borders between the axial relief surfaces <NUM> and the lands <NUM>.

The flutes <NUM> are also equally spaced about the longitudinal axis <NUM>. Each of the flutes <NUM> has a single rake face <NUM> with a cutting edge <NUM> and a clearance surface <NUM>. Each of the clearance surfaces <NUM> includes a distal portion (or surface) and a proximal portion (or surface). The distal portions of the clearance surfaces <NUM> are identified by numerical designator <NUM>. The proximal portions of the clearance surfaces <NUM> are identified by numerical designator <NUM>.

The efficiencies and stability of surgical bur <NUM> are constrained by the single rake surface <NUM> found on each flute. The placement of the rake surface <NUM> influences the entirety of the flute and the corresponding cutting edge <NUM>. As manifested, the rake surface <NUM> is parallel to the longitudinal axis <NUM> and past a center point <NUM> (to the left of and not in alignment with the longitudinal axis as viewed from the distal end of the surgical bur <NUM>). As a result, the surgical bur <NUM> has a neutral axial rake angle and a positive radial rake angle.

Surgical burs may have rake surfaces with (i) axial rake angles that are positive or negative, and (ii) radial rake angles that vary along cutting edges of corresponding flutes relative to locations along the cutting edges. The radial rake angle of a rake surface may be neutral (i.e. <NUM>°) at a point where the rake surface crosses a plane through a longitudinal axis of the corresponding surgical bur. Examples of surgical burs having flutes that each includes multiple axial and radial rake angles are disclosed below.

The following description discloses rotatable surgical burs (referred to below as the surgical burs). The surgical burs include decoupled rake surfaces (may be referred to as rake faces) per flute and corresponding axial rake angles and radial rake angles. A negative axial rake angle may improve drilling stability of the surgical burs. A positive radial rake angle may increase cutting efficiency of the surgical burs.

<FIG> shows a surgical dissection cutter assembly <NUM> incorporating a rotating surgical bur in use on a patient <NUM>. The patient is undergoing a neurological operation. Access to the brain or other neurological structures often requires delicate dissection of bone and other tissues. <FIG> is provided for example purposes only, the surgical burs disclosed herein may be used in different tools and/or cutter assemblies and may be used for other procedures and/or operations. The dissection cutter assembly <NUM> includes a dissection tool driver <NUM>, which is being utilized to dissect a portion of bone and adjacent tissue of the patient <NUM> in the surgical access site <NUM>.

<FIG> is a perspective view of the surgical dissection cutter assembly <NUM>. The dissection tool driver <NUM> includes a motor housing <NUM> connected to a hose or cable assembly <NUM>. The hose assembly <NUM> supplies external power and control for the motor housing <NUM>. The dissection tool driver <NUM> further includes an attachment housing <NUM> that connects to a dissection tool <NUM>. A distal end of the dissection tool <NUM> includes a surgical bur <NUM>. Examples of dissection tools that may be used in replacement of the dissection tool <NUM> are shown and described below with reference to <FIG>.

<FIG> is a perspective view of a portion <NUM> of a surgical bur. The portion <NUM> includes a rake face <NUM> with a cutting edge <NUM> and a relief surface <NUM>. The cutting edge <NUM> may be at a distal end of the surgical bur and adjacent to the relief surface <NUM>. <FIG> is provided as an example and may be used to describe, for (i) an axial rake angle and axial relief surface of a cutting edge of a first rake surface, or (ii) a radial rake angle and a radial relief surface of a cutting edge of a second rake surface. The first rake surface may be the same or different than the second rake surface. Depending upon whether the surgical bur is being used for axial drilling or radial side cutting, the surgical bur may be in a different orientation relative to a cutting surface. A first orientation may be used for axial drilling and a second orientation may be used for radial side cutting.

If <FIG> is used to show the first orientation, an axial rake angle and an axial relief surface, a rake angle <NUM> (may be referred to as an axial rake angle for the first orientation) of the rake face <NUM> may be between (i) a line (or plane) <NUM> on the rake face <NUM> and a plane perpendicular to the cutting edge <NUM> and (ii) a line (or plane) <NUM> extending perpendicular to a surface <NUM> of a bone <NUM> into which the surgical bur is cutting and extending in a direction of the cut and/or a line (or plane) <NUM> perpendicular to line <NUM>. A relief angle <NUM> (may be referred to as an axial relief angle for the first orientation) may be between (i) a line (or plane) <NUM> on the relief surface <NUM> (or axial relief surface <NUM> for the first orientation) and a plane perpendicular to the cutting edge <NUM> and (ii) the line <NUM>. The cutting edge <NUM> may be on a plane perpendicular to the line <NUM> for the first orientation. The rotational axis of the surgical bur is parallel to line <NUM> for the first orientation.

If <FIG> is used to show the second orientation, a radial rake angle and a radial relief surface, the line <NUM> may be perpendicular to the longitudinal axis of the surgical bur. The cutting edge <NUM> may be in a plane that passes through the longitudinal axis. For the second orientation, the cutting edge <NUM> may be the same or a different cutting edge than the cutting edge referred to above for the first orientation. The relief surface <NUM> may be referred to as a radial relief surface for the second orientation. The rake angle <NUM> may be referred to as a radial rake angle for the second orientation. The relief angle <NUM> may be referred to as an axial relief angle for the second orientation.

Although the following surgical burs are shown as having a particular number of flutes, rake surfaces per flute, rake angles per flute, clearance surfaces per flute, lands, axial relief surfaces, clearance surfaces, etc., the surgical burs may have other quantities of each of these items.

<FIG> show side and perspective views of a dissection tool <NUM>. The dissection tool <NUM> may be used as part of the assembly <NUM> of <FIG> and replace the dissection tool <NUM> of <FIG>. The dissection tool <NUM> includes a shaft <NUM> and a surgical bur <NUM>. The surgical bur <NUM> has a "match head" design and includes a body <NUM>. The surgical bur <NUM> may be referred to as a "neuro" or "matchstick" bur. The body <NUM> has two convex lands <NUM> and two flutes <NUM>. Each of the flutes <NUM> is located between the lands <NUM> and has a corresponding chip space <NUM>. The lands <NUM> are convex-shaped and/or rounded and may be in respective <NUM>° locations about a longitudinal axis <NUM> of the dissection tool <NUM>, the shaft <NUM>, and/or the surgical bur <NUM>. The surgical bur is rotated about the longitudinal axis <NUM>. The flutes <NUM> may also be in respective <NUM>° locations about the longitudinal axis <NUM>. Each of the flutes <NUM> has two or more rake surfaces (two rake surfaces <NUM>, <NUM> per flute <NUM> are shown) with a cutting edge <NUM> and corresponding clearance surfaces <NUM> with distal portions (or distal clearance surfaces) <NUM> and proximal portions (or proximal clearance surfaces) <NUM>. The clearance surfaces <NUM> are on distal portions of the flutes <NUM>. The clearance surfaces <NUM> are on proximal portions of the flutes <NUM>.

In the example shown, first portions <NUM> of the cutting edges <NUM> extend from a center point <NUM> or bridge <NUM> at a distal end of the surgical bur <NUM>, radially away from the longitudinal axis <NUM>, and towards second portions <NUM> of the cutting edges <NUM>. The bridge <NUM> extends over the center point <NUM> and connects axial relief surfaces <NUM> on respective ones of the lands <NUM>.

The second portions <NUM> of the cutting edges <NUM> extend from proximal ends of the first portions <NUM> and axially along the longitudinal axis <NUM>. The first portions <NUM> of the cutting edges <NUM> have negative axial rake angles. The left-hand (or negative) axial angle α shown and creates the negative axial rake angle. As an example, a negative axial rake angle may be -<NUM>° or other suitable negative axial rake angle. The second portions <NUM> of the cutting edges <NUM> have positive radial rake angles proximal from point <NUM>. An example right-hand (or positive) axial angle β is shown and creates the radial rake angles when manifested with location of point <NUM>. As an example, a right-hand axial angle may be <NUM>° or other suitable axial angle. As an example, the radial rake angles may vary from -<NUM>° at point <NUM> to <NUM>° at the proximal end of the second portions <NUM>.

Axial rake angles affect cutting performance when drilling in a distal direction. The portion <NUM> is primarily used when drilling in the distal direction. The axial rake angles, of concern when drilling in a distal direction, are measured between a plane perpendicular to the longitudinal axis <NUM> and a plane on the distal rake face <NUM> and when viewed from a side of the surgical bur, as shown in <FIG>. Radial rake angles affect cutting performance in a lateral direction. Some of the portion <NUM> and/or some of the portion <NUM> may be used when cutting in a lateral direction. A lateral direction refers to a direction away from the longitudinal axis <NUM>. The lateral direction may not necessarily be a direction perpendicular to the longitudinal axis. The radial rake angles are measured between the longitudinal axis <NUM> and the respective portions <NUM>, <NUM> of the cutting edges <NUM>. The radial rake angles may be measured from a respective side of the surgical bur <NUM> and in a direction perpendicular to the longitudinal axis <NUM> and passing through a point on the cutting edges <NUM>. The radial rake angles may also be measured from a distal end of the surgical bur <NUM> and/or at lateral cross-sectional planes of the surgical bur. The lateral cross-sectional planes of the surgical bur <NUM> being at points along the longitudinal axis <NUM> and the cutting edges <NUM>. An example of a radial rake angle as measured from a distal end of a surgical bur is shown in <FIG>.

The radial rake angle at a point on the cutting edges <NUM> may be described as being negative when that point is before (or to the right of) the longitudinal axis <NUM>, as depicted in <FIG>. The radial rake angle is neutral at points <NUM> where the second portions <NUM> cross the longitudinal axis <NUM>. The radial rake angle at a point on the cutting edges <NUM> may be described as being positive when that point is after (or to the left of) the longitudinal axis <NUM>, as depicted in <FIG>. The first portions <NUM> and the second portions <NUM> of the cutting edges <NUM> may each be in a respective plane.

The axial and radial rake angles of the rake surfaces <NUM>, <NUM> of each of the flutes <NUM> are decoupled. This is because: the axial rake angles of the rake surfaces <NUM>, <NUM> of each of the flutes <NUM> are different and have different vertices; and/or the radial rake angles of the rake surfaces <NUM>, <NUM> of each of the flutes <NUM> are different and have different vertices. The radial rake angles of each of the rake surfaces <NUM>, <NUM> of each of the flutes <NUM> may not be constant along a corresponding cutting edge. In one implementation, each of the rake surfaces <NUM>, <NUM> may have one or more (or a set) of radial rake angles. As an example, each of the rake surfaces <NUM>, <NUM>, corresponding to the portions <NUM> and located between a proximal end of the surgical bur <NUM> and second points <NUM>, has multiple radial rake angles including a negative radial rake angle distal of the point <NUM>, a neutral radial rake angle at the point <NUM>, and a positive radial rake angle proximal of the point <NUM>.

The first portions <NUM> of the cutting edges <NUM> may begin at or near the center point <NUM> and end at first points <NUM> proximal to the second points <NUM>. The first points <NUM> refer to where distal ends of the first rake surfaces <NUM> and distal ends of the clearance surfaces <NUM> meet. When the surgical bur <NUM> is viewed from the side as shown and as described above, each of the first points <NUM> is on a corresponding first side of the longitudinal axis <NUM>. The second points <NUM> refer to locations at which the first portions <NUM> of the cutting edges <NUM> meet the second portions <NUM> of the cutting edges <NUM>. When the surgical bur <NUM> is viewed from the side as shown and as described above, each of the second portions <NUM> of the cutting edges <NUM> begins at a respective one of the second points <NUM> on the respective first side of the longitudinal axis <NUM> and extends across the longitudinal axis <NUM> to a respective second side of the longitudinal axis <NUM>.

The cutting edges <NUM> provide a combination of right-hand axial and left-hand axial aspects with respect to the longitudinal axis <NUM>. The first portions <NUM> of the cutting edges <NUM> are shown as providing left-hand axial aspects. For this reason, distal portions of the flutes <NUM> are referred to as left-hand portions. The second portions <NUM> of the cutting edges <NUM> are shown as providing right-hand axial aspects. For this reason, proximal portions of the flutes <NUM> are referred to as right-hand portions. The left-hand and right-hand axial aspects are provided for a surgical bur designed to be rotated in a clockwise direction about a longitudinal axis, as viewed from a proximal end of the surgical bur, to drill and/or cut. For a surgical bur designed to be rotated in a counter clockwise direction about a longitudinal axis, as viewed from a proximal end of the surgical bur, to drill and/or cut, (i) the first portions <NUM> may be opposite that shown and provide right-hand axial aspects, and (ii) the second portions <NUM> may be opposite that shown and provide left-hand axial aspects.

The clearance surfaces <NUM>, <NUM> may each be flat (or planar), as shown, or may be curved. A transition edge <NUM> may extend laterally between the clearance surfaces <NUM>, <NUM> of each of the flutes <NUM> and away from a corresponding one of the second rake surfaces <NUM>. The clearance surfaces <NUM>, <NUM> are at different angles relative to the longitudinal axis <NUM> and are in contact with each other at the transition edge <NUM>. Each of the transition edges <NUM> borders and provides a transition between the corresponding clearance surfaces <NUM>, <NUM>.

For each of the flutes <NUM>, the rake surfaces <NUM>, <NUM> are decoupled and as a result are not continuous with each other. The rake surfaces <NUM>, <NUM> of each of the flutes <NUM> may be distinct planar surfaces and are not parallel to each other. Due to the decoupling of the rake surfaces <NUM>, <NUM>, each of the clearance surfaces <NUM> includes a decoupling area <NUM> located between two of the corresponding rake surfaces <NUM>, <NUM>. The decoupling areas <NUM> extend axially and/or generally along the longitudinal axis <NUM> from the second points <NUM> to distal ends of the second clearance surfaces <NUM>. Distal ends of the decoupling areas <NUM> are laterally in alignment with the decoupling edges <NUM>. The first rake surfaces <NUM> meet the second rake surfaces <NUM> at the second points <NUM>. The decoupling areas <NUM> separate proximal ends of the first rake surfaces <NUM> from distal ends of the second rake surfaces <NUM>.

Depths (i.e. distances between the first portions <NUM> of the cutting edges to the clearance surfaces <NUM>) of the first rake surfaces <NUM> may increase from distal ends of the first rake surfaces <NUM> to the corresponding points <NUM>. Depths of the first rake surfaces <NUM> may decrease from the points <NUM> to the points <NUM>. Depths (i.e. distances between the second portions <NUM> of the cutting edges to the clearance surfaces <NUM>) of the second rake surfaces <NUM> may increase from distal ends of the second rake surfaces <NUM> and/or the points <NUM> to an equator (a planar second of the surgical bur <NUM> shown by a dashed line <NUM>) and/or proximal ends of the second rake surfaces <NUM>.

The equator <NUM> may refer to planar portion of the surgical bur <NUM> that is perpendicular to the longitudinal axis <NUM> and may be where a diameter of the surgical bur <NUM> is at a maximum. If the surgical bur has a constant diameter for an extended portion of the surgical bur, as in the example shown, the equator may be at the most distal portion of the surgical bur, which has the maximum diameter. The equator <NUM> may be (i) distal to the points <NUM> at which the second portions <NUM> of the cutting edges <NUM> cross the longitudinal axis <NUM>, and (ii) proximal to the first points <NUM>.

The rake surfaces <NUM>, <NUM> and the respective portions <NUM>, <NUM> of the cutting edges <NUM> decouple the rake angles of the portions <NUM>, <NUM> and have respective functions. The first portions <NUM> of the cutting edges <NUM> are at distal ends of the flutes <NUM> to provide stability during drilling. Due to the decoupling of the rake surfaces <NUM>, <NUM>, the first portions <NUM> of the cutting edges <NUM> minimally or do not negatively affect side cutting or shaving when using the second portions <NUM> of the cutting edges <NUM>. The second portions <NUM> of the cutting edges <NUM> extend along sides of the body <NUM> and in distal and proximal directions away from the equator <NUM>. The second portions <NUM> of the cutting edges <NUM> provide efficient side cutting or shaving. Due to the decoupling of the rake surfaces <NUM>, <NUM>, the second portions <NUM> of the cutting edges <NUM> minimally or do not negatively affect drilling when using the first portions <NUM> of the cutting edges <NUM>.

The surgical bur <NUM> includes a drill point <NUM> at a distal end of the surgical bur <NUM>. The drill point <NUM> may include the center point <NUM> and the axial relief surfaces <NUM>. The longitudinal axis <NUM> passes through the center point <NUM>. The axial relief surfaces <NUM> are at ends of the flutes <NUM> and may be continuous with the lands <NUM> or may be distinct from the lands <NUM>, as shown. The axial relief surfaces <NUM>, as shown, are distinct from the lands <NUM> because: the axial relief surfaces <NUM> are a different type of surface than the lands (e.g., the lands <NUM> may be convex-shaped and the axial relief surfaces <NUM> may be planar-shaped); and there are transitional surfaces or edges (referred to as borders) between the axial relief surfaces <NUM> and the lands <NUM>. In another embodiment, the axial relief surfaces <NUM> may be convex-shaped and/or provide a non-transitional (or continuous surface) with the lands <NUM>.

Each of the axial relief surfaces <NUM> are bordered by (i) one of the first portions <NUM> of one of the cutting edges <NUM>, (ii) a distal end portion <NUM> of one of the lands <NUM>, and (iii) one of the clearance surfaces <NUM>. The axial relief surfaces <NUM> may be flat (or planar) surfaces, as shown. Each of the axial relief surfaces <NUM> may have two nominally straight edges (the first portions <NUM> and the distal edges of the clearance surfaces <NUM>) connected by a respective circular edge (one of the curved edges is identified by numerical designator <NUM>). The curved edges <NUM> of the axial relief surfaces <NUM> border respectively the lands <NUM>.

The clearance (or distal) surfaces <NUM> have corresponding gash angles. Each of the gash angles refers to an angle between (i) a line (or plane) extending parallel to and on one of the distal surfaces <NUM> and away from the center point <NUM> and/or the longitudinal axis <NUM> and (ii) a line (or plane) extending perpendicular to the longitudinal axis <NUM>.

<FIG> show side and perspective views of a dissection tool <NUM>. <FIG> shows a lateral side view of the dissection tool <NUM> taken from a left side when looking at <FIG> shows a lateral side (or top) view of the dissection tool <NUM> taken from above the dissection tool when looking at <FIG>. The dissection tool <NUM> may be used as part of the assembly <NUM> of <FIG> and replace the dissection tool <NUM> of <FIG>. The dissection tool <NUM> includes a shaft <NUM> and a spherically-shaped surgical bur <NUM>. The surgical bur <NUM> includes a body <NUM>. The body <NUM> has three convex-shaped lands <NUM> and three flutes <NUM>. Each of the flutes <NUM> is located between a pair of the lands <NUM> and has a corresponding chip space <NUM>. The lands <NUM> are convex-shaped and/or rounded and may be in respective <NUM>° locations about a longitudinal axis <NUM> of the dissection tool <NUM>, the shaft <NUM>, and/or the surgical bur <NUM>. The surgical bur is rotated about the longitudinal axis <NUM>. The flutes <NUM> may also be in respective <NUM>° locations about the longitudinal axis <NUM>. Each of the flutes <NUM> has distal and proximal rake surfaces (or faces) <NUM>, <NUM> with a cutting edge <NUM> and clearance surfaces <NUM>. The clearance surfaces <NUM> include distal portions (or distal clearance surfaces) <NUM> and proximal portions (or proximal clearance surfaces) <NUM>. The clearance surfaces <NUM> are on distal portions of the flutes <NUM>. The clearance surfaces <NUM> are on proximal portions of the flutes <NUM>.

The surgical bur <NUM> includes a drill point <NUM> at a distal end of the surgical bur <NUM>. The drill point <NUM> may include a center point <NUM> and three axial relief surfaces <NUM>. The longitudinal axis <NUM> passes through the center point <NUM>. The axial relief surfaces <NUM> are at ends of the flutes <NUM> and may be distinct from the lands <NUM>. The axial relief surfaces <NUM> may be distinct from the lands <NUM> because: the axial relief surfaces <NUM> are a different type of surface than the lands (e.g., the lands <NUM> may be convex-shaped and the axial relief surfaces <NUM> may be planar-shaped); and there are transitional surfaces (or borders) between the axial relief surfaces <NUM> and the lands <NUM>. In another embodiment, the axial relief surfaces <NUM> may be convex-shaped and/or provide a non-transitional (or continuous surface) with the lands <NUM>.

Each of the axial relief surfaces <NUM> are bordered by (i) a respective distal end (or first) portion <NUM> of one of the cutting edges <NUM>, (ii) a distal end portion <NUM> of one of the lands <NUM>, and (iii) a distal end of one of the clearance surfaces <NUM>. The axial relief surfaces <NUM> may be flat (or planar) surfaces, as shown. Each of the axial relief surfaces <NUM> are triangular-shaped with two nominally straight edges (two of the nominally straight edges are identified by numerical designator <NUM>) and a curved edge (one of the curved edges is identified by numerical designator <NUM>). The curved edges <NUM> of the axial relief surfaces <NUM> border respectively the lands <NUM>.

In the example shown, the first portions <NUM> of the cutting edges <NUM> extend from the center point <NUM> at a distal end of the surgical bur <NUM>, radially away from the longitudinal axis <NUM>, and towards second portions <NUM> of the cutting edges <NUM>. The second portions <NUM> of the cutting edges <NUM> extend from proximal ends of the first portions <NUM> and axially along the longitudinal axis <NUM>. The first portions <NUM> of the cutting edges <NUM> have negative axial rake angles. An example left-hand axial angle α is shown and creates the negative axial rake angle. As an example, a negative axial rake angle may be -<NUM>° or other suitable negative axial rake angle. The second portions <NUM> of the cutting edges <NUM> have positive radial rake angles proximal from point <NUM>. An example axial angle β is shown and creates the radial rake angles when manifested with location of point <NUM>. As an example, a right-hand axial angle may be <NUM>° or other suitable axial angle. As an example, the radial rake angles may vary from -<NUM>° near point <NUM> to <NUM>° at the proximal end of the second portions <NUM>.

The axial rake angles are measured between a plane perpendicular to the longitudinal axis <NUM> and a plane on the distal rake face. The radial rake angles are measured between the longitudinal axis <NUM> and the respective portions <NUM>, <NUM> of the cutting edges <NUM>. These measurements are taken from a respective side of the surgical bur <NUM> and in a direction perpendicular to the longitudinal axis <NUM> and passing through a point on the cutting edges <NUM>. The first portions <NUM> and the second portions <NUM> of the cutting edges <NUM> may each be in a respective plane.

The rake angles of each of the flutes <NUM> are decoupled since the rake angles are different, have different vertices, and are associated with different rake surfaces. The vertices of the axial rake angles may be at the same point (e.g., the center point <NUM>). The vertices of the radial rake angles are different and refer to points (e.g., the point <NUM>) where the second portions <NUM> of the cutting edges <NUM> cross the longitudinal axis <NUM>.

The first portions <NUM> of the cutting edges <NUM> may begin at or near the center point <NUM> and end at first points <NUM> proximal to second points <NUM>. The first points <NUM> refer to where distal ends of the first rake surfaces <NUM> and distal ends of the clearance surfaces <NUM> meet. When the surgical bur <NUM> is viewed from the side as shown and as described above, each of the first points <NUM> is on a corresponding first side of the longitudinal line <NUM>. The second points <NUM> refer to locations at which the first portions <NUM> of the cutting edges <NUM> meet the second portions <NUM> of the cutting edges <NUM>. When the surgical bur <NUM> is viewed from the side as shown and as described above, each of the second portions <NUM> of the cutting edges <NUM> begins at a respective one of the second points <NUM> on the respective first side of the longitudinal axis <NUM> and extends across the longitudinal axis <NUM> to a respective second side of the longitudinal axis <NUM>.

The cutting edges <NUM> provide a combination of right-hand axial and left-hand axial aspects with respect to the longitudinal axis <NUM>. When viewed from the side (as shown in <FIG>), the cutting edges <NUM> extend along the longitudinal axis <NUM>, from above the longitudinal axis <NUM> at a proximal end of the surgical bur <NUM>, to the second points <NUM> at locations below the longitudinal axis <NUM>, and generally back up to the longitudinal axis <NUM> at the center point <NUM>. The first portions <NUM> of the cutting edges <NUM> are shown as providing left-hand axial aspects. For this reason, distal portions of the flutes <NUM> are referred to as left-hand portions. The second portions <NUM> of the cutting edges <NUM> are shown as providing right-hand axial aspects. For this reason, proximal portions of the flutes <NUM> are referred to as right-hand portions. The left-hand and right-hand axial aspects are provided for a surgical bur designed to be rotated in a clockwise direction about a longitudinal axis, as viewed from a proximal end of the surgical bur, to drill and/or cut. For a surgical bur designed to be rotated in a counter clockwise direction about a longitudinal axis, as viewed from a proximal end of the surgical bur, to drill and/or cut, (i) the first portions <NUM> may be opposite that shown and provide right-hand axial aspects, and (ii) the second portions <NUM> may be opposite that shown and provide left-hand axial aspects.

The clearance surfaces <NUM>, <NUM> may each be flat (or planar), as shown, or may be curved. A transition edge <NUM> may extend laterally between the clearance surfaces <NUM>, <NUM> of each of the flutes <NUM> and away from a corresponding one of the second rake surfaces <NUM>. The clearance surfaces <NUM>, <NUM> are at different angles relative to the longitudinal axis <NUM> and are in contact with each other at the decoupling edge <NUM>. Each of the transition edges <NUM> borders and provides a transition between the corresponding clearance surfaces <NUM>, <NUM>.

For each of the flutes <NUM>, the rake surfaces <NUM>, <NUM> are decoupled and as a result are not continuous with each other. The rake surfaces <NUM>, <NUM> of each of the flutes <NUM> may be distinct planar surfaces and are not parallel to each other. Due to the decoupling of the rake surfaces <NUM>, <NUM>, each of the clearance surfaces <NUM>, <NUM> includes a decoupling area <NUM> located between two of the corresponding rake surfaces <NUM>, <NUM>. The decoupling areas <NUM> extend axially and/or generally along the longitudinal axis <NUM> from the second points <NUM> to distal ends of the clearance surfaces <NUM>. Distal ends of the decoupling areas <NUM> are laterally in alignment with the transition edges <NUM>. The first rake surfaces <NUM> meet the second rake surfaces <NUM> at the second points <NUM>. The decoupling areas <NUM> separate proximal ends of the first rake surfaces <NUM> from distal ends of the second rake surfaces <NUM>.

Depths (i.e. distances between the first portions <NUM> of the cutting edges <NUM> to the clearance surfaces <NUM>) of the first rake surfaces <NUM> may increase from distal ends of the first rake surfaces <NUM> to the corresponding points <NUM>. Depths of the first rake surfaces <NUM> may decrease from the points <NUM> to the points <NUM>. Depths (i.e. distances between the second portions <NUM> of the cutting edges <NUM> to the clearance surfaces <NUM>) of the second rake surfaces <NUM> may increase from distal ends of the second rake surfaces <NUM> and/or the points <NUM> to an equator (a midline or planar section of the surgical bur <NUM> shown by a dashed line <NUM>) and/or proximal ends of the second rake surfaces <NUM>.

The equator <NUM> may refer to planar portion of the surgical bur <NUM> that is perpendicular to the longitudinal axis <NUM> and may be where a diameter of the surgical bur <NUM> is at a maximum. The equator <NUM> is (i) proximal to the points <NUM> at which the second portions <NUM> of the cutting edges <NUM> cross the longitudinal axis <NUM>, and (ii) proximal to the first points <NUM>.

Each of the rake surfaces <NUM> has a corresponding radial rake angle <NUM>. A radial rake angle <NUM> refers to an angle between (i) a line (or plane) <NUM> parallel to one of the rake surfaces <NUM> and (ii) a line (or plane) <NUM> passing through the second portions <NUM> of the cutting edge <NUM> and the longitudinal axis <NUM>. Radial rake angles <NUM> of the rake surfaces <NUM> may be associated with a left-hand helix with respect to the longitudinal axis <NUM> corresponding to the left-hand axial aspects of the rake surfaces <NUM>.

The above-disclosed implementations include surgical bur configurations designed to drill, cut and shape bone efficiently while allowing contact with sensitive soft tissue structures (e.g., nerves, blood vessels, membranes, etc.) without tearing the soft tissue structures. This is especially applicable in neurological and spinal procedures where the dura mater can be exposed to a distal portion of a bur.

In certain implementations, rake angles of the surgical burs may also be within predetermined ranges and based on the application of use.

Claim 1:
A surgical bur (<NUM>) comprising:
a plurality of flutes (<NUM>), wherein each of the plurality of flutes comprises a cutting edge (<NUM>), a plurality of rake surfaces (<NUM>, <NUM>) and a clearance surface (<NUM>),
wherein
the plurality of rake surfaces of one of the plurality of flutes includes at least a first rake surface (<NUM>) and a second rake surface (<NUM>),
the first rake surface has a first distinct surface,
the second rake surface has a second distinct surface,
the first rake surface and the second rake surface are distinct from the clearance surface; and
a plurality of lands (<NUM>), each of the plurality of lands is disposed between a pair of the plurality of flutes;
characterised in that
a) the first rake surface (<NUM>) and the second rake surface (<NUM>) are decoupled from each other or b) a second rake angle of the second rake surface is decoupled from a first rake angle of the first rake surface or c) the first rake surface and the second rake surface are decoupled from each other and a second rake angle of the second rake surface is decoupled from a first rake angle of the first rake surface; and in that
the one of the plurality of flutes comprises a decoupling area (<NUM>); and
the decoupling area is located between the first rake surface and the second rake surface of the one of the plurality of flutes.