SURGICAL DRILL BIT

Abstract

A drill bit (1) for creating a tubular hole in a bone (9), comprises: a longitudinal body (2) extending along an axis (21) and having a proximal end and a distal end (22); a main cutting edge (3) formed at the distal end (22) of the body (2); a main cutting face (4) extending from the main cutting edge (3) and defining a rake angle (); and a spiral flute (5) formed around the body (2) and extending from the main cutting face (4) along the axis (21) of the body (2). The main cutting edge (3) is the only single main cutting edge (3) of the drill bit (1). The spiral flute (5) is the only single spiral flute (5) of the drill bit. The rake angle () is at least 25. The drill bit (1) according to the invention drill bit allows for minimizing heat production when drilling a hole into the bone.

Claims

1. Drill bit (1) for creating a tubular hole in a bone (9), comprising a longitudinal body (2) extending along an axis (21) and having a proximal end and a distal end (22), a main cutting edge (3) formed at the distal end (22) of the body (2), a main cutting face (4) extending from the main cutting edge (3) and defining a rake angle (), and a spiral flute (5) formed around the body (2) and extending from the main cutting face (4) along the axis (21) of the body (2), characterized in that the main cutting edge (3) is the only single main cutting edge (3) of the drill bit (1), the spiral flute (5) is the only single spiral flute (5) of the drill bit (1), and the rake angle () is at least 25.

2. Drill bit (1) according to claim 1, wherein the rake angle () is smaller than 40.

3. Drill bit (1) according to claim 1 or 2, wherein the rake angle () is defined between an intended new surface (91) of the bone (9) to be generated by the drill bit (1) and the main cutting face (4) of the drill bit (1) less 90.

4. Drill bit (1) according to claim 3, wherein the intended new surface (91) of the bone (9) is an inner surface of the tubular hole.

5. Drill bit (1) according to any one of the preceding claims, wherein the spiral flute (5) defines a helix angle () which is smaller than the rake angle ().

6. Drill bit (1) according to claim 5, wherein the helix angle () is defined between a land (51) of the spiral flute (5) and the axis (21) of the longitudinal body (2).

7. Drill bit (1) according to any one of the preceding claims, wherein the main cutting face (4) passes over into the spiral flute (5).

8. Drill bit (1) according to any one of the preceding claims, wherein the distal end (22) of the body (2) has a front profile (221) orthogonal to the axis (21) of the body (2) and the main cutting edge (3) extends across the front profile (221) of the distal end (22) of the body (2).

9. Drill bit (1) according to any one of the preceding claims, wherein the distal end (22) of the body (2) has a point (223) located on the axis (21) of the body (2).

10. Drill bit (1) according to claims 8 and 9, wherein the main cutting edge (3) is offset from the point (223) of the body (2).

11. Drill bit (1) according to claim 10, wherein a conical chisel face (225) is arranged between the point (223) of the body (2) and the main cutting edge (3).

12. Drill bit (1) according to any one of claims 9 to 11, wherein the point (223) defines a point angle (6) in a range of about 70 to about 140.

13. Drill bit (1) according to any one of the preceding claims, wherein the body (2) comprises a shaft (71) extending from the proximal end along the axis (21).

14. Drill bit (1) according to claim 13, wherein the body (2) comprises a transition portion (72) between the spiral flute (5) and the shaft (71) in which the spiral flute (5) continuously passes over into the shaft (71).

15. Drill bit (1) according to any one of the preceding claims, wherein the spiral flute (5) has a distal end adjacent to the main cutting face (4) and a shallow proximal end (52).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drill bit according to the invention is described in more detail herein below by way of an exemplary embodiment and with reference to the attached drawings, in which:

[0027] FIG. 1 shows a schematic front view of an embodiment of the drill bit according to the invention;

[0028] FIG. 2 shows a schematic side view of the drill bit of FIG. 1;

[0029] FIG. 3 shows a schematic cross sectional view of the drill bit of FIG. 1 along the line Z-Z of FIG. 2 in operation;

[0030] FIG. 4 shows temperature results of a test comparison between a standard drill bit and a custom drill bit as a further embodiment of the drill bit according to the invention;

[0031] FIG. 5 shows thrust force results of the test comparison of FIG. 4; and

[0032] FIG. 6 shows torque results of the test comparison of FIG. 4.

DESCRIPTION OF EMBODIMENTS

[0033] In the following description certain terms are used for reasons of convenience and are not intended to limit the invention. The terms right, left, up, down, under and above refer to directions in the figures. The terminology comprises the explicitly mentioned terms as well as their derivations and terms with a similar meaning. Also, spatially relative terms, such as beneath, below, lower, above, upper, proximal, distal, and the like, may be used to describe one element's or feature's relationship to another element or feature as illustrated in the figures. These spatially relative terms are intended to encompass different positions and orientations of the devices in use or operation in addition to the position and orientation shown in the figures. For example, if a device in the figures is turned over, elements described as below or beneath other elements or features would then be above or over the other elements or features. Thus, the exemplary term below can encompass both positions and orientations of above and below. The devices may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein interpreted accordingly. Likewise, descriptions of movement along and around various axes include various special device positions and orientations.

[0034] To avoid repetition in the figures and the descriptions of the various aspects and illustrative embodiments, it should be understood that many features are common to many aspects and embodiments. Omission of an aspect from a description or figure does not imply that the aspect is missing from embodiments that incorporate that aspect. Instead, the aspect may have been omitted for clarity and to avoid prolix description. In this context, the following applies to the rest of this description: If, in order to clarify the drawings, a figure contains reference signs which are not explained in the directly associated part of the description, then it is referred to previous or following description sections. Further, for reason of lucidity, if in a drawing not all features of a part are provided with reference signs it is referred to other drawings showing the same part. Like numbers in two or more figures represent the same or similar elements.

[0035] FIG. 1 shows a view on a distal end 22 of a body 2 of a drill bit 1 according to the invention. Thereby, a front profile 221 of the distal end 22 is visible wherein the front profile 221 extends orthogonally to an axis (not visible in FIG. 1) of the body 2. The drill bit 1 has a diameter which is constant over its whole length. For example, the diameter can be in a range from about 1.5 mm to about 4 mm or from about 2 mm to about 3 mm or it can be about 2.5 mm.

[0036] The drill bit 1 has a curved main cutting edge 3 or cutting lip which extends across the front profile 221 of the distal end 22 of the body 2 and which can be a sharp edge or a rounded edge. In particular, the main cutting edge 3 runs from one side of a periphery of the front profile 221 to an opposite side of the periphery of the front profile 221. Thereby, the main cutting edge 3 crosses the periphery of the front profile 221 at two different locations such that a peripheral cutting edge offset 222 of about 135 is defined.

[0037] Centrally or at the end of the axis (not visible in FIG. 1) the distal end 22 of the body 2 has a point 223. The main cutting edge 3 passes besides the point 223 across the front profile 221 such that a point offset 224 is defined as the closest distance between the point 224 and the main cutting edge 3. The point offset 224 is comparably small. For example, for a drill bit 1 with a diameter of about 2.5 mm it is in a range from about 0.03 mm to about 0.1 mm or about 0.04 to about 0.08 or it can be 0.05 mm. The range might vary for other diameters.

[0038] Between the point 223 of the body 2 and the cutting edge 3 a conical chisel face 225 is formed. The conus of the chisel face 225 is comparably steep such that the point 223 is comparably sharp. The drill bit 1 further comprises a flank portion 6 and one single spiral flute 5 or helix portion which enables evacuation of cut bone or chips. The design of the drill bit 1 allows minimizing a diameter of the chisel face 225 and comprises of a minimal asymmetry. Radially from two opposite sides of the flank portion 6 two corresponding margins 8 extend. The margins 8 can have a thickness in a range from about 0.1 mm to 0.5 mm. The margins 8 reduce the contact surface of outer drill bit diameter and a drilled hole. The drill bit 1 can also have less or more than two margins.

[0039] As can be seen in FIG. 2, the point 223 defines a point angle which is important for centering the drill bit 1 particularly on oblique surfaces. The axis 21 of the body 2 extends longitudinally along and centrally through the body 2. Between a land 51 of the spiral flute 5, which lies at the outer diameter of the drill bit 1, and the axis 21 of the body 2 a helix angle is defined. The helix angle is in a range from about 15 to about 35 which is comparably small. The helix angle defines how the spiral flute 5 winds around the axis 21 of the drill bit 1. It influences chip evacuation.

[0040] Starting at the main cutting edge 3 the drill bit 1 comprises a main cutting face 4 which passes over into the spiral flute 5. The distance of the cutting face 4 passing over into the spiral flute 5 can be in a range from about 1 mm to about 5 mm.

[0041] Towards a proximal end the body 2 of the drill bit 1 has shaft 71. Between the shaft 71 and a proximal helix end 52 of the spiral flute 5 a transition portion 72 is formed. In the transition portion 72 the spiral flute 5 smoothly passes over into the shaft 71. The transition portion 72 is designed with a radius to reduce vibration and fracture risk. The helix end 52 is designed with a smoothly transitioned shallow ending. The shaft 71 is dimensioned to fit a connection means of a drill. More particularly, it has a desirable length, diameter and design to allow coupling to a desired manual or electronic device, i.e. the drill device. This device can be set to any desirable parameter such as rotational speed, feed rate and the like.

[0042] In FIG. 3 the drill bit 1 is schematically shown while being applied to a bone 9. The bone 9 has an original or old surface 93 which is the surface where the drill bit 1 has not acted on and a new surface 92 which is the surface where the drill bit 1 already did act on. In one plane with the new surface 92 lies an intended new surface 91 which is the surface to be generated by the drill bit 1 when being further applied. The main cutting face 4 upwardly from the main cutting edge 3 cuts the bone 9. Thereby, chips 94 are created of the bone 9 which are forwarded through the spiral flute 5.

[0043] The drill bit 1 has a rake angle which is defined between the intended new surface 91 of the bone 9 and the main cutting face 4 less 90. Or in other words, the rake angle is defined between a plane normal to the intended new surface 91 of the bone 9 and the main cutting face 4. The rake angle is in a range of about 25 to about 35 which is comparably large. By dimensioning the rake angle in such a range it can be achieved that the drill bit 1 cross sectional wedge forming the cutting face 4 is sufficiently firm and still an appropriate clearance between the drill bit 1 and the bone 9 is provided. In particular, in the cross sectional view of FIG. 3 the wedge can define a wedge angle . Furthermore, the clearance is formed by the flank portion 6 being angled with a clearance angle . The clearance angle avoids scratching of the material with elevated feed rate. The sum of the rake angle , the wedge angle and the clearance angle amounts to 90. The clearance angle is in range from about 15 to about 25. Since the rake angle is comparably high the point angle is comparably small such that the point 223 is comparably sharp.

[0044] In the following, an exemplary investigation is described in which a standard surgical drill bit was compared to custom drill bit as a further embodiment of a drill bit according to the invention. Both drill bits had a diameter of 2.5 mm. The custom drill bit was designed in accordance with the invention to generate less heat than the standard drill bit manufactured by Synthes, Johnson & Johnson, USA. A new experimental setup was developed to measure drilling forces and torques as well as the two dimensional (2D) temperature field at any depth at a distance of 0.5 mm to drilled hole using a high resolution thermal camera. The rotational speed was set to 1000 rounds per minute (RPM) and the feed rate to 0.5 mm/s. The drilling depth was 25 mm and external irrigation rate was set to 30 ml/min. The drilled material was freshly frozen cortical bone from a 4 year old cow. Continuous intervals of 0.5 mm were drilled with an extraction of the drill bit in-between the intervals to allow intermittent cooling of the bone. The experiments were repeated 8 times and maximal elevation of temperature, force and torque of each interval was extracted over the whole drilling depth.

[0045] FIG. 4 shows the maximal temperature elevation (y=Temperature [ C.]) for the standard drill bit (x=1) and the custom drill bit (x=2). Experiments were conducted at room temperature (24 C.) and temperature elevations were extracted for each interval over the whole drilling depth. The maximal temperature elevation of the custom drill bit is significantly lower (>10 C.) compared to the standard drill bit. This is important, because it limits the overall temperature rise to 34 C. (T10 C. from room temperature). This can be converted to body temperature 37 C.+10 C.=47 C. which is the threshold of tissue damage. Therefore it is possible to drill with the custom drill bit without damaging the surrounding bone or other vulnerable structures such as nerves and the like. This is not possible with the standard drill bit.

[0046] In FIG. 5 the maximal axial thrust force (y=Force [N]) of the standard (x=1) and the custom drill bit (x=2) is shown. It can be seen that the force elevation of the custom drill bit is below the thrust forces of the standard drill bit.

[0047] FIG. 6 shows the maximal torque (y=Torque [Nm]) of the standard (x=1) and the custom drill bit (x=2). The torque of the custom drill bit is around half the value of the standard drill bit. Therefore, the custom drill bit is able to cut the material much more efficiently than the standard drill bit which explains the significantly lower temperature elevation.

[0048] This description and the accompanying drawings that illustrate aspects and embodiments of the present invention should not be taken as limiting-the claims defining the protected invention. In other words, while the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Various mechanical, compositional, structural, electrical, and operational changes may be made without departing from the spirit and scope of this description and the claims. In some instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the invention. Thus, it will be understood that changes and modifications may be made by those of ordinary skill within the scope and spirit of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below.

[0049] The disclosure also covers all further features shown in the Figs. individually although they may not have been described in the afore or following description. Also, single alternatives of the embodiments described in the figures and the description and single alternatives of features thereof can be disclaimed from the subject matter of the invention or from disclosed subject matter. The disclosure comprises subject matter consisting of the features defined in the claims or the exemplary embodiments as well as subject matter comprising said features.

[0050] Furthermore, in the claims the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. A single unit or step may fulfil the functions of several features recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The terms essentially, about, approximately and the like in connection with an attribute or a value particularly also define exactly the attribute or exactly the value, respectively. The term about in the context of a given numerate value or range refers to a value or range that is, e.g., within 20%, within 10%, within 5%, or within 2% of the given value or range. Components described as coupled or connected may be electrically or mechanically directly coupled or the like, or they may be indirectly coupled via one or more intermediate components. Any reference signs in the claims should not be construed as limiting the scope.