PERFORATOR

Abstract

A perforator for drilling bone tissue has: a drive shaft with a rotational axis A; an inner cutting head with the same rotational axis A; a drive surface provided on the drive shaft; and a connector provided on the inner cutting head. The inner cutting head is displaceable with respect to the drive shaft along the rotational axis between a distal position, in which the inner cutting head is not driveable by the drive shaft, and a proximal position, in which the drive surface abuts the connector to transmit rotational motion from the drive shaft to the inner cutting head. The drive surface is inclined relative to the rotational axis A.

Claims

1-25. (canceled)

26. A perforator for drilling bone tissue, comprising: a drive shaft with a rotational axis A; an inner cutting head with the same rotational axis A; a drive surface provided on the drive shaft; and a connector provided on the inner cutting head; in which the inner cutting head is displaceable with respect to the drive shaft along the rotational axis between a distal position in which the inner cutting head is not driveable by the drive shaft, and a proximal position, in which the drive surface abuts the connector to transmit rotational motion from the drive shaft to the inner cutting head, in which the drive surface is inclined relative to the rotational axis A.

27. The perforator according to claim 26, in which the drive surface is flat and inclined relative to the rotational axis A.

28. The perforator according to claim 26, in which the sloped drive surface extends radially outwards from the rotational axis A, such that the drive surface lies on a virtual helical surface extending around the rotational axis A.

29. The perforator according to claim 26, in which the drive surface is sloped at an angle of between 5° and 30°, preferably between 8° and 20°, particularly preferably between 10° and 15° with respect to the rotational axis A.

30. The perforator according to claim 26, in which a distal end of the drive surface is connected to a flat distal end surface of the drive shaft, the drive surface being configured so that the angle between the flat distal end surface and the drive surface is greater than 90°, preferably at least 95°, particularly preferably 100° or more, for example 105° or 110°.

31. The perforator according to claim 26, in which the connector is configured to engage with the drive surface by abutting the drive surface along a single line of contact when the inner cutting head is in the proximal position; and optionally in which the connector and the drive surface are configured so that the line of contact is spaced from the distal end of the drive surface, preferably in which the line of contact is spaced at least 0.2 mm, or 0.3 mm, or 0.4 mm from the distal end of the drive shaft.

32. The perforator according to claim 26, in which the connector comprises a curved surface, having a radius of curvature R, configured to abut the drive surface when the inner cutting head is in the proximal position, so that the curved surface contacts the inclined drive surface along a single line of contact.

33. The perforator according to claim 26, in which the connector is a pin, preferably a cylindrical pin having a radius R.

34. The perforator according to claim 32, in which the drive surface has a length that is greater than the radius R of the connector, so that when the connector is in the proximal position the line of contact between the connector and the drive surface is spaced from the distal end of drive shaft.

35. The perforator according to claim 26, in which the drive surface forms a first sloped side of a groove formed radially in the distal end of the drive shaft, and in which the second side of the groove is sloped in the opposite direction relative to the rotational axis A; and optionally in which the second side of the groove is sloped at a greater angle than the drive surface, relative to the rotational axis A.

36. The perforator according to claim 35, in which the second side of the groove is sloped at an angle of between 45° and 85°, preferably between 60° and 80°, particularly preferably between 70° and 80° with respect to the rotational axis A.

37. The perforator according to claim 35, in which the sloped second side of the groove extends over an angular distance of between 30° and 156° around the circumference of the drive shaft, preferably between 110° and 156°, particularly preferably between 130° and 156° around the circumference of the drive shaft.

38. The perforator according to claim 35, in which the drive surface is configured so that the second side of the groove is connected to the drive surface by a continuously curved section with a radius of curvature r; optionally in which r<R, so when the connector is engaged with the groove, a proximal portion of the connector abuts the base of the groove at a first contact point to prevent further proximal translation of the connector, and a side portion of the connector abuts the drive surface at a line of contact through which rotational force is transmitted from the drive shaft to the connector; and further optionally in which the radius R of the connector surface is between 10% and 35% greater than the radius r of curvature of the groove, preferably between 15% and 30% greater, particularly preferably between 20% and 25% greater.

39. The perforator according to claim 26, in which the perforator comprises an outer cutting head arranged coaxially around the inner cutting head; and in which a coupling means is provided between the inner cutting head and the outer cutting head, the outer cutting head comprising an outer coupling portion configured to couple with an inner coupling portion provided on the inner cutting head when the inner cutting head is in the proximal position, so that rotational motion is transmitted from the inner cutting head to the outer cutting head, wherein the coupling means is configured to transform relative rotation of the inner and outer cutting heads around the rotational axis A into translational displacement of the inner cutting head along the rotational axis.

40. The perforator according to claim 39, in which one of the inner or outer coupling portions comprises an angled edge configured to transform relative rotation of the inner and outer cutting heads into translational displacement of the inner cutting head along the rotational axis; and optionally in which the inner coupling portion is a pin, and the outer coupling portion is a groove or opening in a wall of the outer cutting head, the groove or opening having a proximal end for receiving the pin in its proximal position and an angled edge for guiding the pin towards its distal position in response to relative rotation of the inner and outer cutting heads.

41. The perforator according to claim 40, in which the angled edge has an angle of between 10° and 45°, preferably between 15° and 30° with respect to the rotational axis A.

42. The perforator according to claim 40, in which the drive surface is inclined at an angle of between 5° and 15°, preferably 10°, relative to the rotational axis A, and the angled edge of the outer coupling portion is inclined in the opposite direction to the drive surface and has an angle of between 10° and 30° relative to the rotational axis.

43. The perforator according to claim 40, in which the angular separation of the drive surface and the angled edge of the outer coupling portion is between 15° and 60°, preferably between 20° and 40°, particularly preferably between 25° and 30°.

44. The perforator according to claim 39, in which the inner coupling portion is the connector, the connector comprising a cylindrical pin which extends radially out of the inner cutting head.

45. The perforator according to claim 26, in which the connector is formed from a material having a hardness that is equal to or greater than the hardness of the drive surface and/or an angled edge of the coupling means, preferably in which the connector and the drive surface are formed from the same material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Specific embodiments of the invention will now be described with reference to the figures, in which:

[0074] FIG. 1 is a cross-section taken along the rotational axis A of a perforator, for example a perforator according to the prior art;

[0075] FIG. 2 is a side-on view of the distal end of a prior art drive shaft;

[0076] FIG. 3 is a close-up side-on view of the prior art drive shaft of FIG. 2 engaged with a connector pin;

[0077] FIG. 4 is a semi-transparent view of an assembled prior art perforator without its cylindrical housing in position;

[0078] FIG. 5A is a side-on view of a drive shaft of a perforator according to the present invention;

[0079] FIG. 5B is a cross-section of the drive shaft of FIG. 5A, taken along the rotational axis A;

[0080] FIG. 5C is an enlarged cross-section of the distal end of the drive shaft of FIG. 5B;

[0081] FIG. 5D is an end-on view of the distal end of the drive shaft of FIGS. 5A-5C;

[0082] FIG. 6 is a side-on view of the distal end of the drive shaft of a perforator according to the present invention;

[0083] FIG. 7 is a close-up cross-sectional view of the distal end of the drive shaft of FIG. 6 engaged with a connector pin;

[0084] FIG. 8 is an enlarged view of a portion of an assembled perforator according to the present invention, with no housing in position; and

[0085] FIG. 9 illustrates a variety of possible drive surface profiles usable in the perforator of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0086] FIGS. 1 to 3 illustrate the parts of a prior art perforator design similar to the perforator disclosed in U.S. Pat. No. 4,456,010, but with a semi-circular drive shaft slot instead of the square slot of U.S. Pat. No. 4,456,010.

[0087] In FIG. 1, the perforator 10 comprises an inner cutting head 12, a hollow outer cutting head 14 arranged coaxially around the inner cutting head, and a drive shaft 16, all rotatable about the same axis of rotation A. The drive shaft has a distal end 15 and a proximal end 17 which is connectable to a hand-held drill housing a motor, for example.

[0088] The distal end of the perforator 10 terminates in the distal tip 20 of the inner cutting head, which contacts bone in use, and is shown positioned at the bottom of FIG. 1. The proximal end of the perforator 10 terminates in the proximal portion 17 of the drive shaft, which is shown at the top in FIG. 1.

[0089] The inner cutting head 12 is movable along the rotational axis A between two positions: a distal position, in which the inner cutting head is not connected to the drive shaft 16, and a proximal position, in which the inner cutting head 12 is connected to the drive shaft 16. The inner cutting head is biased away from the drive shaft 16 and into the distal position by a spring 18, so that the inner cutting head only moves into the proximal position when the distal tip 20 of the inner cutting head is pressed against a surface, such as bone to be drilled.

[0090] When there is no pressure applied to the distal tip 20 of the inner cutting head, the cutting head 12 and the drive shaft 16 are disconnected, and neither of the inner or outer cutting heads 12, 14 rotates even when the drive shaft 16 is rotating. A cylindrical housing 22 is arranged coaxially around the outer cutting head 14.

[0091] Connection of the inner cutting head and the drive shaft 16 is achieved using a slot-and-pin type clutch that comprises a slot 24 (not visible in FIG. 1, as the cross-section is taken along the slot) in the distal end 15 of the drive shaft, and a corresponding connector pin 28 which extends diametrically through the inner cutting head near its proximal end.

[0092] The outer cutting head 14 is not translatable along the rotational axis A, and comprises two triangular-shaped openings 30 through which the two opposite ends of the connector pin 28 extend. The triangular openings 30 are arranged so that the apex of each triangular opening 30 points towards the proximal end of the perforator. Thus, translation of the inner cutting head 12 towards the proximal position moves the connector pin 28 towards the apex of the triangular opening 30.

[0093] As the distal tip 20 of the inner cutting head 12 is pressed against bone in use, a force is applied which moves the inner cutting head 12 against the biasing spring 18 until the connector pin 28 engages with the slot 24 in the rotating drive shaft 16. In this proximal position, the connector pin 28 also engages with the side or apex of the triangular openings 30, so that rotational force is transmitted from the inner cutting head 12 to the outer cutting head 14, and both cutting heads rotate together. As long as force is applied to the tip 20 of the inner cutting head to keep the connector pin 28 engaged with the slot 24, the rotating drive shaft transmits rotational force to the cutting heads so that both cutting heads rotate and the perforator drills through the bone. As soon as the distal tip 20 of the inner cutting head perforates the bone (for example the inner surface of the cranium), however, the force longer applied to the inner cutting head by the bone is greatly reduced, so the biasing spring 18 urges the pin 28 out of the slot 24 in the drive shaft. Both the inner and outer cutting heads should then cease to rotate immediately, to prevent damage to the dura mater.

[0094] As illustrated in FIGS. 2 and 3, the slot 24 in this prior art design takes the form of a semi-circular groove or slot 24 in the flat distal end surface 36 of the drive shaft, where the radius of the groove is chosen to be a perfect fit for the cylindrical connector pin 28. This was intended to have the advantage of providing a close fit for the pin 28 once it is located in the groove, and supporting the connector pin across a large contact area to hold the pin as the drive shaft 16 rotates. In this design, the entire surface of the semi-circular groove is in contact with the pin, around half of the connector pin's circumference, so the trailing half of the slot acts as a drive surface that transmits rotational force to the connector pin. In this design the drive surface therefore takes the form of a quarter-cylindrical surface 32 that abuts the connector pin 28 over a quarter of the pin's circumference.

[0095] The present inventors have found, however, that in this prior art design it cannot be guaranteed that the connector pin always separates from the groove in time. Occasionally the pin can get stuck at the sharp 90° edge 34 of the slot when it is released. This can cause damage to the pin or the groove edge, which is disadvantageous for further drilling and in the worst case can result in the coupling not being released in time. This sharp edge of the groove therefore means that it is difficult to ensure safe uncoupling of the driver portion from the cutting portions. Furthermore, the narrow shape of the semi-circular groove delays engagement at the start of drilling. As the groove 24 extends diametrically across the distal end of the drive shaft 16, the coupling can only take place at 0° or 180°. Only with increasing axial pressure does the pin 28 engage in the groove 24 of the drive shaft, by which time the drive has already picked up speed. Coupling in this form has two disadvantages: (i) the user feels an unpleasant chattering as the connector engages the drive shaft; and (ii) the release mechanism can be damaged at the start of drilling as the pin 28 passes over the sharp groove edge 34.

[0096] FIG. 4 is a semi-transparent view of the perforator 10 in an assembled state with the housing 22 removed, with the connector pin 28 in its proximal position so that the connector pin 28 is located in the semi-circular groove 24. As the drive shaft 16 rotates, rotational motion is transmitted to the connector 28 and the inner cutting head 12 through which the connector pin extends. As the connector pin rotates and contacts the side of the triangular opening 30, the rotational motion is also transmitted to the outer cutting head 14, so that both cutting heads rotate together about the rotational axis A. When the force is removed from the distal tip (not shown in FIG. 4) of the inner cutting head 12, the spring 18 biases the connector pin 28 out of the slot 24 so that the drive shaft 16 no longer drives the inner and outer cutting heads.

[0097] FIGS. 5A-5D, 6, 7 and 8 illustrate a drive shaft 116 and a perforator 100 according to a preferred embodiment of the present invention. In this preferred embodiment, the components of the perforator 100 are generally the same as those of perforator 10 described above, apart from the design of the drive shaft 116 and in particular the drive surface 132.

[0098] As shown in FIGS. 5A-5D, 6 and 7, instead of a semi-circular groove, in perforator 100 the distal end 115 of the drive shaft 116 comprises two asymmetrical grooves 124 spaced evenly around the circumference of the drive shaft. Each asymmetrical groove 124 has a first sloped side which acts as a drive surface 132 and extends from the flat distal end surface 136 of the drive shaft to the base of the groove 138, and a second sloped side 140 which extends from the base of the groove 138 to the flat distal end surface 136 of the drive shaft at a much shallower angle than that of the drive surface.

[0099] The drive surface 132 is positioned on the side of the groove that is the trailing edge when the drive shaft 116 is rotating around the rotational axis A in the desired direction of rotation, so that when the connector pin 128 abuts the drive surface, the drive surface pushes the connector pin around the rotational axis.

[0100] The second sloped side 140 of the groove is positioned on the side of the groove that forms the leading edge as the drive shaft rotates. When the drive shaft 116 is rotating and the connector pin 128 is forced into the distal position, the second sloped side 140 therefore acts as a gradual ramped lead-in to the base of the groove 138, increasing the chance of the connector pin locating successfully in the groove 124 immediately.

[0101] In the embodiment shown, the second sloped side 140 of the groove 124 extends at an angle of 78° relative to the rotational axis A (or 12° relative to the flat distal end of the drive shaft), and extends an angular distance of 135° around the perimeter of the drive shaft 116.

[0102] Unlike the “vertical” slot walls of U.S. Pat. No. 4,456,010, and the semi-circular slot walls of FIGS. 1-3, in the present invention the drive surface is inclined, or sloped, relative to the rotational axis A. In the embodiment shown, the drive surface 132 extends at an angle of 10° relative to the rotational axis A. In other words, the drive surface 132 extends at an angle of 100° relative to the flat distal end 136 of the drive shaft.

[0103] The inclined drive surface 132 can take a variety of forms, as shown in FIG. 8, and need necessarily not be flat as long as the drive surface is inclined at the position which abuts the connector. It is particularly preferable for the drive surface to be flat, or at least to have a different curvature from the connector pin, so that the connector pin 128 abuts the drive surface 132 along a single line of contact when the connector pin is in the proximal position.

[0104] As shown in FIG. 9, as long as the portion of the drive surface that abuts and drives the connector is inclined, the profile of the drive surface could take a variety of forms. For example, the drive surface may be flat and inclined, or could follow an exponential curve for example. It would be possible for the profile of the drive surface to be a curve which is very steep on the bottom and therefore provides a good angle for driving the connector pin, but which changes to a flatter curve with increasing height.

[0105] The depth of the groove 124, from the flat distal end 136 of the drive shaft to the base of the groove 138 is advantageously greater than the radius R of the connector pin 128, so that the connector pin contacts the inclined drive surface 132 below the edge 134 of the groove. This ensures that the power transmission from the drive shaft 116 to the connector pin 128 always runs through the drive surface, and never along the edge 134. In the embodiment shown, the connector pin contacts the inclined drive surface 0.36 mm proximal to the edge 134.

[0106] At the base of the groove 138, the sloped second side 140 is connected to the drive surface 132 by a continuously curved portion 142 that has a radius of curvature r. The radius of curvature r is selected to be smaller than the radius R of the connector pin 128, which ensures that the connector pin cannot contact the groove over a large contact surface as it does in FIG. 3, for example. In the embodiment shown, the connector pin 128 has a radius R of 1.25 mm, while the radius r of the curved portion 142 of the groove is 1 mm. This difference in radii means that when the connector pin 128 is in the proximal position and located in the groove 124, as shown in FIG. 7, the connector pin 128 only contacts the base of the groove 138 along a first line of contact 144, and the drive surface 132 along a second line of contact 146.

[0107] When the force on the distal tip of the inner cutting head 12 is reduced and the connector 128 begins to move towards its distal position, the slope of the drive surface 132 assists this translational motion, as a vector of the rotational force from the drive shaft is transformed into an axial vector which urges the connector towards the distal position. This means that, as the connector disengages, the connector pin 128 slides down the inclined drive surface 132. The connector pin 128 must pass over the edge 134 of the groove to fully disengage, but due to the larger 100° angle of the edge, there is less chance of the connector becoming caught on, or damaged by, this edge during disengagement.

[0108] The triangular opening 130 in the outer cutting head 14 also helps with the disengagement of the connector pin 128 from the groove 124, as like the inclined drive shaft, the angled edge 148 of the triangular opening also urges the connector pin in a distal direction. In the present invention, the angle of this angled edge 148 is carefully chosen to be complementary to the angle of the drive surface 132, as together these angles contribute to the release point of the connector pin 128 from the groove 124. In the embodiments shown, the angled edge 148 of the triangular openings 130 extends at 15° relative to the rotational axis A. The 15° angle of the angled edge 148 and the 10° angle of the drive surface therefore gives these two surfaces an effective angular separation of 25°. As the connector pin 128 is pinched between these two surfaces when it is in the proximal position and being driven by the drive shaft, the angular separation of these surfaces determines the vector of rotational force that urges the connector pin in the distal direction, which thus impacts the release point at which the connector will disengage from the groove 124.

[0109] The triangular openings may alternatively be provided in different forms, as long as the angled edge 148 is provided. Also, rather than abutting the connector pin 128 itself, a separate coupling pin may be used to interact with the angled edge 148.

[0110] In the present invention, the connector pin 128 is formed from a material having a hardness that is equal to the hardness of the drive surface and the angled edge of the coupling means. While prior art connector pins typically had a hardness of 47 HRC, the connector pin 128 in the present invention has a hardness of to 54 HRC, which is the same hardness as the drive shaft and the outer cutting head. This may advantageously ensure that the connector is not easily damaged during engagement and disengagement, and avoid potential problems caused by damage to the connection mechanism. This harder connector pin also allows the use of a 15° angle of the angled edge 148, rather than a larger angle, as the harder connector pin grinds less against the angled surface and therefore slides more smoothly despite the steep angled edge.