Patent Description:
This section provides background information related to the present disclosure.

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.

Damage to the dura mater can increase risks of infections (e.g., meningitis) and/or result in surgical complications (e.g., swelling of the brain). Thus, in order to preserve the integrity of the dura mater, it is desirable for surgical burs, intended for dissection of bone, to have a high-level of control (minimal flail or chatter) and have a geometry not predisposed to dissect soft tissue.

<CIT>, <CIT>, <CIT> and <CIT> all teach surgical burs.

A surgical bur is provided as defined by claim <NUM>.

In other features, a surgical bur is provided and includes a body and a drill point. The body includes flutes and lands. Each of the flutes includes a cutting edge and a clearance surface. Each of the lands is disposed between a pair of the flutes. The drill point includes axial relief surfaces. Each of the axial relief surfaces is distinct from the lands and borders (i) a distal portion of one of the cutting edges, (ii) one of the lands, and (iii) one of the clearance surfaces. At least one axial relief angle of the axial relief surfaces is within a predetermined range.

In other features, a surgical bur is provided and includes a body and a drill point. The body includes flutes and lands. Each of the flutes includes a cutting edge and a clearance surface. Each of the lands is disposed between a pair of the flutes. The drill point includes axial relief surfaces. Each of the axial relief surfaces is distinct from the lands and borders (i) a distal portion of one of the cutting edges, (ii) one of the lands, and (iii) one of the clearance surfaces. The drill point has a drill point angle of greater than or equal to a predetermined angle.

Drill bits for machining naturally occurring and/or engineered materials, such as metal, wood and plastic have drill point geometries for improved cutting efficiency, stability, and feed rates, as well as for minimized thermal energy buildup during machining. In general, drill point angles for machining softer materials are more acute than those for machining harder materials.

<FIG> shows side views of three drill bits <NUM>, <NUM>, <NUM> and corresponding drill point angles <NUM>, <NUM>, <NUM>. A drill point angle refers to an angle between tip cutting edges (e.g., tip cutting edges <NUM>, <NUM>) of a tip (e.g., tip <NUM>) of a drill bit. The tip cutting edges extend radially away from (i) a center (e.g., center <NUM>) of the tip, and (ii) respective ends of a chisel edge (e.g., chisel edge <NUM>) of the drill bit.

The drill bits <NUM>, <NUM>, <NUM> are shaped to work on materials having different hardness characteristics. The drill point angle <NUM> of the first drill bit <NUM> may be, for example, <NUM>° and is for materials having a first hardness. The first drill bit <NUM> has the tip cutting edges <NUM>, <NUM>. The drill point angle <NUM> of the second drill bit <NUM> may be, for example, <NUM>° and is for materials having a second hardness. The second hardness is greater than the first hardness. The second drill bit <NUM> has tip cutting edges <NUM>, <NUM>. The drill point angle <NUM> of the third drill bit <NUM> may be, for example, <NUM>° and is for materials have a third hardness. The third hardness is less than the second hardness and the first hardness. The third drill bit <NUM> has tip cutting edges <NUM>, <NUM>.

The drill bits <NUM>, <NUM>, <NUM> have respective tips <NUM>, <NUM>, <NUM>. Each of the tips <NUM>, <NUM>, <NUM> includes relief surfaces that extend away from the respective cutting edges <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. Although the relief surfaces are distinct surfaces, the relief surfaces are identified by numerical designator <NUM>. The relief surfaces <NUM> are convex-shaped.

Each of the drill bits <NUM>, <NUM>, <NUM> has two helically shaped lands and two flutes. Although the lands are distinct surfaces, the lands are identified by numerical designator <NUM>. Although the flutes are distinct from each other, the flutes are identified by numerical designator <NUM>. The lands <NUM> are not convex-shaped. Each of the flutes <NUM> is located between a pair of the lands <NUM> and has a corresponding chip space <NUM> along and in the flutes. The lands <NUM> are in respective <NUM>° locations about a corresponding longitudinal axis (the longitudinal axes are identified by numerical designator <NUM>). The flutes <NUM> are also in respective <NUM>° locations about a corresponding longitudinal axis.

<FIG> show side and distal end views of a predicate dissection tool <NUM> including a surgical bur <NUM>. The surgical bur <NUM> includes three cam 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 equally spaced about a longitudinal axis <NUM> of the surgical bur <NUM>. The longitudinal axis <NUM> is shown by point <NUM> in <FIG>. Distal portions <NUM> of the lands <NUM> are referred to as axial relief surfaces <NUM>, 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 rake face <NUM> with a cutting edge <NUM> and a clearance surface <NUM>. Each of the clearance surfaces <NUM> includes 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 geometries of the drill bits <NUM>, <NUM>, <NUM> of <FIG> and the surgical bur <NUM> of <FIG> have associated disadvantages. Although the drill bits <NUM>, <NUM>, <NUM> provide cutting efficiency and stability due to the corresponding drill point angles, the geometries of the drill bits <NUM>, <NUM>, <NUM> would be inappropriate for surgical use in certain procedures. This is because the drill bits would likely cut dura mater and can be difficult to use for shaping purposes. The tips <NUM>, <NUM>, <NUM> of the drill bits <NUM>, <NUM>, <NUM> have a minimal amount of contact surface area, which increases chances of cutting dura mater. Although the surgical bur <NUM> is rounded and has a less tendency to cut dura mater than the drill bits <NUM>, <NUM>, <NUM>, the surgical bur <NUM> has an increased tendency to drift due to the geometries of a distal end or tip <NUM> of the surgical bur <NUM>. The surgical bur <NUM> also has a greater amount of contact area, requiring more irrigation to mitigate friction and the concomitant torsional shear forces that may be exerted on an underlying soft tissue structure. For at least these reasons, it is desirable to construct surgical burs (or drilling tools) with geometries including a rounded tip and certain rake, axial relief and drill point angles, such that the surgical burs do not engage soft tissue and/or dura mater.

The following description discloses rotatable surgical burs (referred to below as the surgical burs). The surgical burs have fewer tendencies to cut dura mater and increased tendency to cut bone more efficiently as compared to predicate burs due to the geometries of the surgical burs. The surgical burs also have fewer tendencies to drift into sensitive anatomy. The surgical burs have tips with distal geometries that allow the surgical burs, with adequate irrigation, to glide over the dura mater without engaging and/or tearing the dura mater. The distal geometries include: axial relief surfaces with planar shapes and increased surface area; drill point angles in predetermined ranges; and axial relief angles in predetermined ranges. The distal geometries are set for maximum cutting and stability performance and for minimal tendencies to engage dura mater. The gliding aspect occurs over dura mater as opposed to bone due to the soft flexible nature of dura mater and the balance of surface area, shapes, and angles of the axial relief surfaces. The surgical burs have an increased tendency to cut into bone where the surgical burs are placed without drifting into nearby anatomy.

Although the surgical burs disclosed herein may be used, for example, for cutting and shaping bone, the surgical burs may be used for other dissecting, cutting, and/or shaping purposes. The disclosed implementations include bur configurations that minimize risk for challenges to sensitive anatomy, in particular, dura mater. The surgical burs are constructed with geometry to allow a practitioner to perform a procedure (e.g., a craniotomy) including casual contact atop dura mater. The surgical burs allow the practitioner to create a bore through a bone and/or a lateral path in the bone without tearing dura mater.

<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 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 axial relief surface <NUM>. A rake angle <NUM> 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>. An axial relief angle <NUM> may be between (i) a line (or plane) <NUM> on the axial relief surface <NUM> and a plane perpendicular to the cutting edge <NUM> and (ii) the line <NUM>.

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

<FIG> is a perspective view of a dissection tool <NUM>. The dissection tool <NUM> includes a shaft <NUM> and a surgical bur <NUM>. The surgical bur <NUM> includes a body <NUM>. The body <NUM> has three cam 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 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 flutes <NUM> may also be in respective <NUM>° locations about the longitudinal axis <NUM>. Each of the flutes <NUM> has a 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) <NUM> and a proximal portion (or surface) <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 are distinct from the lands <NUM>. The axial relief surfaces <NUM> are distinct from the lands <NUM> because: the axial relief surfaces <NUM> are a different type of surface than the lands (the lands <NUM> are convex-shaped and the axial relief surfaces <NUM> may be planar shaped); there are transitional surfaces (or borders) between the axial relief surfaces <NUM> and the lands <NUM>; and/or the axial relief surfaces <NUM> do provide a border edge <NUM> with the lands.

Each of the axial relief surfaces <NUM> are bordered by (i) a respective distal end portion <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 distal portions <NUM> 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> wherein a proximal most edge of each of the plurality of axial relief surfaces borders a distal most edge of a respective one of the plurality of lands.

<FIG> shows another side view of the dissection tool <NUM> including the surgical bur <NUM> is shown. The surgical bur <NUM> includes the cutting edges <NUM>. The cutting edges <NUM> may provide a right-hand helix, straight or left-hand helix with respect to the longitudinal axis <NUM>. The cutting edges <NUM> are shown as providing a right-hand helix. When viewed from the side and as shown, the cutting edges <NUM> of the right-hand helix configuration extend along the longitudinal axis <NUM>, generally from above to below, and towards the drill point <NUM>. When viewed from the side, the cutting edges <NUM> of the straight configuration extend towards the drill point <NUM> and parallel with the longitudinal axis <NUM>. When viewed from the side, the cutting edges <NUM> of the left-hand helix configuration extend along the longitudinal axis <NUM>, generally from below to above, and towards the drill point <NUM>.

The surgical bur <NUM> also includes the clearance surfaces <NUM> having the distal surfaces <NUM>. The distal surfaces <NUM> have corresponding gash angles (one gash angle <NUM> is shown). Each of the gash angles refers to an angle between (i) a line (or plane) <NUM> extending parallel to 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) <NUM> extending perpendicular to the longitudinal axis <NUM>.

<FIG> shows another side view of the surgical bur <NUM> orthogonal to the distal end portion <NUM> of one of the cutting edges <NUM>. The surgical bur <NUM> includes the axial relief surfaces <NUM> (one is shown in <FIG>) and the rake faces <NUM> (one is shown in <FIG>) with corresponding cutting edges <NUM> therebetween.

Each of the axial relief surfaces <NUM> has a corresponding axial relief angle (one axial relief angle <NUM> is shown) and axial rake angle (one axial rake angle <NUM> is shown). Each axial relief angle <NUM> can be measured between (i) a first line (or plane) <NUM> on an axial relief surface and observed perpendicular to the distal end portion <NUM> of one of the cutting edges <NUM> and (ii) a second line (or plane) <NUM> perpendicular to the longitudinal axis <NUM>. The second plane <NUM> may also extend across a surface of an object (e.g., a surface of a bone) being cut. Each axial rake angle refers to an angle between (i) a third line (or plane) <NUM> on one of the rake faces <NUM> and observed perpendicular to the distal end portion <NUM> of one of the cutting edges <NUM> and (ii) a fourth line (or plane) extending along, passing through, and/or parallel to the longitudinal axis <NUM>.

Each distal portion <NUM> of the cutting edges <NUM>, along a corresponding one of the axial relief surfaces <NUM>, has a corresponding axial relief surface angle, a drill point angle, and a remainder angle. The axial relief surface angle (e.g., axial relief surface angle <NUM>) refers to an angle between (i) a line (or plane) <NUM> extending along and parallel to one of the axial relief surfaces <NUM> and away from the longitudinal axis <NUM> and/or distal portion <NUM> of one of the cutting edges <NUM>, and (ii) a line (or plane) <NUM> extending perpendicular to the longitudinal axis <NUM> and passing through the center point <NUM>.

A remainder angle (e.g., remainder angle <NUM>) may refer to an angle between (i) a line (or plane) <NUM> on one of the rake faces <NUM> and observed perpendicular to the distal end portion <NUM> of one of the cutting edges <NUM> and (ii) the line (or plane) <NUM> extending along and parallel to one of the axial relief surfaces <NUM> and away from the longitudinal axis <NUM> and/or the distal portion <NUM> of one of the cutting edges <NUM>. The remainder angle <NUM> is shown in <FIG> and <FIG>. The remainder angle <NUM> may be an acute, right, or obtuse angle. In one implementation, the remainder angle <NUM> is an obtuse angle.

A drill point angle is described with respect to <FIG> and an example drill point angle is shown in <FIG>. <FIG> shows a side view of the dissection tool <NUM> including the surgical bur <NUM> is shown. Multiple techniques may be used to determine the drill point angle. A drill point angle DP (not shown in <FIG>) may be equal to <NUM>° minus two times an acute angle (AA) (or DP = <NUM>°-2AA). The acute angle AA refers to an angle between (i) a line (or plane) <NUM> extending perpendicular to the longitudinal axis and tangent to the center point <NUM> and (ii) a line (or plane) <NUM> extending parallel to the distal portion <NUM> of one of the cutting edges <NUM>. When a surgical bur has two flutes and/or opposing cutting edges with distal portions <NUM>° apart and extending away from a center point, a corresponding drill point angle of the surgical bur refers to an angle between distal portions of the cutting edges. An example surgical bur with two flutes is shown in <FIG>.

<FIG> shows a distal end view of the surgical bur <NUM>. The surgical bur <NUM> includes the rake faces <NUM>. Each of the rake faces <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 a rake face and (ii) a line (or plane) <NUM> passing through the cutting edge <NUM> and the longitudinal axis. Radial rake angles <NUM> of the rake faces <NUM> may be associated with a left-hand helix, straight or righted-hand helix with respect to the longitudinal axis <NUM> (shown in previous <FIG>). The rake faces <NUM> of the surgical bur <NUM> as shown provide a right-hand helix.

<FIG> show perspective and distal end views of another dissection tool <NUM> having a surgical bur <NUM>. The surgical bur <NUM> as shown has a straight configuration. The surgical bur <NUM> has a body <NUM> with two flutes <NUM> equally spaced around longitudinal axis <NUM>.

Each of the flutes <NUM> has a rake face <NUM> with a cutting edge <NUM> and a clearance surface <NUM>. Each clearance surface <NUM> may include a proximal portion (or surface) <NUM>, a center portion (or surface) <NUM>, and a distal portion (or surface) <NUM>. A land <NUM> exists between each cutting edge <NUM> and a corresponding clearance surface <NUM>. The lands <NUM> are convex-shaped.

The surgical bur <NUM> also includes a drill point <NUM> with a center point <NUM> and axial relief surfaces <NUM>. The axial relief surfaces <NUM> may be flat (or planar) surfaces. A bridge <NUM> may extend between the axial relief surfaces <NUM> and/or be part of the axial relief surfaces <NUM>. The bridge <NUM> may extend across the center point <NUM> and have a corresponding thickness and/or a chisel edge <NUM>. In one implementation, the bridge <NUM> does not include a chisel edge. The chisel edge <NUM> may extend across the bridge <NUM> between the flutes <NUM>. Each of the axial relief surfaces <NUM> includes two straight edges <NUM> and a curved edge <NUM>. The curved edges <NUM> border respectively the lands <NUM>. Each of the axial relief surfaces <NUM> may include circular areas <NUM>. In one implementation, the circular areas <NUM> are flat (or planar), protrude from the remainder of the axial relief surfaces <NUM>, and do not protrude from (or in a more distal direction than) the bridge <NUM>. In another implementation, the axial relief surfaces <NUM> do not include the circular areas <NUM>.

The rake faces <NUM>: extend parallel to each other; are not in alignment with each other; are offset from each other; and have overlapping portions (i.e. the portions are side-by-side) at the bridge <NUM>. Similarly, the straight edges <NUM>: extend parallel to each other; are not in alignment with each other; are offset from each other; and have overlapping portions (i.e. the portions are side-by-side) at the bridge <NUM>.

<FIG> shows a side view of the surgical bur <NUM>. The surgical bur <NUM> includes the cutting edges <NUM> and axial relief surfaces <NUM>. The distal portions <NUM> of the cutting edges <NUM> have an associated drill point angle <NUM>. The drill point angle <NUM> is an obtuse angle. Acute angles are shown between (i) distal portions <NUM> and (ii) a line (or plane) <NUM>. A sum of the drill point angle <NUM> and the acute angles <NUM>, <NUM> is equal to <NUM>°. The plane <NUM> is perpendicular to a longitudinal axis <NUM> of the surgical bur <NUM>. Lines (or planes) <NUM> tangent to the axial relief surfaces <NUM> are shown.

The above-disclosed implementations include surgical bur configurations designed to 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, drill point angles of surgical burs (e.g., the surgical burs <NUM> and <NUM>) are obtuse angles greater than or equal to a first predetermined angle (e.g., <NUM>°) and/or are within a first predetermined range (e.g., between <NUM>°-<NUM>°). Corresponding axial relief angles of the surgical burs are less than or equal to a second predetermined angle (e.g., <NUM>°) and/or are within a second predetermined range (e.g., between <NUM>°-<NUM>°). An example drill point angle is shown in <FIG>. An example of axial relief angles are shown in <FIG> and <FIG>. These drill point angles and axial relief angles provide stable cutting of hard surfaces (such as surfaces of bone) while allowing the surgical burs to glide over soft surfaces (e.g., surfaces of dura mater). This is further improved by having the axial relief surfaces be planar surfaces. Rake angles of the surgical burs may also be within predetermined ranges and based on the application of use.

As a result, "skating" over hard surfaces is prevented providing improved and consistent drilling control while not challenging (or negatively affecting) integrity of dura mater. Reduced skating improves cutting quality while reducing risk of surgical complications concomitant with dural tears. The geometry of the surgical burs including the drill point angles and axial relief angles are tunable (i.e. can be adjusted) based on the application of use.

Claim 1:
A surgical bur comprising:
a body (<NUM>) extending from a proximal end to a distal end of the surgical bur, wherein the body comprises
a plurality of flutes (<NUM>), wherein each of the plurality of flutes comprises a cutting edge (<NUM>), a rake face (<NUM>), and a clearance surface (<NUM>), and
a plurality of lands (<NUM>) extending from the proximal end toward the distal end of the surgical bur, wherein each of the plurality of lands is convex-shaped along a longitudinal axis of the surgical bur and disposed between a pair of the plurality of flutes; and
a drill point (<NUM>) comprising a plurality of axial relief surfaces (<NUM>), wherein each of the plurality of axial relief surfaces is distinct from the plurality of lands and borders (i) a distal portion of one of the cutting edges, and (ii) one of the plurality of lands,
characterised in that each of the plurality of axial relief surfaces (<NUM>) also borders (iii) one of the clearance surfaces, and in that wherein a proximal most edge (<NUM>) of each of the plurality of axial relief surfaces borders a distal most edge of a respective one of the plurality of lands.