GB2597512A

GB2597512A - Perforator

Info

Publication number: GB2597512A
Application number: GB2011529.1A
Authority: GB
Inventors: Fersterer Johann; Von Zeppelin Fabio
Original assignee: Adeor Medical AG
Current assignee: Adeor Medical AG
Priority date: 2020-07-24
Filing date: 2020-07-24
Publication date: 2022-02-02
Also published as: GB202011529D0

Abstract

A perforator 300 for drilling bone tissue comprising a drive shaft 302, an inner perforator head 314 arranged coaxially with the drive shaft and a ball clutch. The ball clutch comprises one or more balls 310, a first engagement region 305 that may be on the drive shaft for restricting axial and rotational movement of the ball relative to the perforator head or the drive shaft, and a second engagement region that may be on the perforator head. The inner perforator head is axially displaceable along the drive shaft axis A between a distal position in which the inner perforator is not driven (shown), and a proximal cutting position (see figure 4) where the ball couples the engagement regions such that the drive shaft drives the perforator head. The perforator may comprise an outer perforator head 312 with a third engagement region to transmit rotary motion to the outer perforator.

Description

Perforator The present invention relates to a perforator for drilling bone tissue. More particularly, the invention relates to a cranial perforator, or a cranial drill, for use by medical practitioners in operations performed on the skull of a human or animal.

Background

In order to carry out surgical operations inside the cranial cavity, it is necessary to first obtain access to the cranial cavity by drilling one or more holes through the bone of the skull (the cranium). The process of drilling a hole through the skull is called trepanation. Trepanation is a difficult and delicate procedure, as sufficient force must be applied to the drill head to advance through the hard layers of bone tissue, but the drill head must be halted immediately after perforation of the skull in order to avoid the drill head damaging the dura mater or soft tissue inside the cranium.

In order to provide a perforator in which the rotation of the drill head stops as soon as the cranium has been perforated, cranial perforators are provided in the prior art in which the drill head is not permanently coupled to the drive shaft of the drill.

A well-known example of a prior art design is disclosed in US Patent No. 4,456,010. The drill of US 4,456,010 comprises an inner drill head, an outer drill head arranged coaxially around the inner drill head, and a drive shaft, all rotatable about the same axis of rotation. The inner drill head is biased away from the drive shaft with a spring, so that when there is no pressure applied to the tip of the inner drill head, the drill head and the shaft are disconnected, and neither of the inner or outer drill heads rotates even when the drive shaft is rotating. Connection of the inner drill head to the drive shaft is controlled using a slot-and-pin type clutch that comprises a slot in the distal end of the drive shaft, and a corresponding pin in the proximal end of the drill head. The clutch-pin also extends into a triangular slot in the wall of the outer drill head.

As the inner drill head of US 4,456,010 is pressed against bone in use, a force is applied which moves the inner drill head against the biasing spring until the clutch-pin in the inner drill head engages with the slot in the rotating drive shaft. In this position, the clutch-pin also extends into a triangular slot in the wall of the outer drill head and engages with the apex of the triangular slot, so that rotational force is transmitted from the drive shaft via the inner drill head to the outer drill head, and both drill heads rotate together. As long as sufficient force is applied to the tip of the inner drill head to overcome the biasing force of the spring such that the clutch-pin remains engaged with the slot, the rotating drive shaft transmits rotational force to the inner and outer drill heads so that both drill heads rotate and the perforator drills through the bone. As soon as the inner drill head perforates the inner surface of the cranium, however, force is no longer applied to the drill head by the bone, so the biasing spring urges the inner drill head forward and forces the clutch-pin out of the slot in the drive shaft. Both the inner and outer drill heads should then cease to rotate immediately, to prevent damage to the dura mater. 1.

While the clutch-slot in the drive shaft of US 4,456,010 was a square-sided slot, with the slot walls aligned with the axis of rotation, other prior art variations of this design have instead used semi-circular slot profiles to provide a close fit for cylindrical pins. The present inventors have found, however, that a shortfall of both of these designs is that it cannot be guaranteed that the release mechanism in the perforator always separates immediately due to the shapes of the slot and the pin.

In the prior art perforator's, due to the high contact pressure and sliding friction, the pin may get jammed at the edge of the slot when the pressure on the inner drill head ceases and the clutch-pin should be immediately released. This may cause damage to the pin or the slot edge, which is disadvantageous for further drilling and in the worst case may result in the clutch not being released in time. As the inner drill head, which has a plurality of sharp cutting surfaces, penetrates the skull, it may injure the dura mater or soft tissue if the clutch does not immediately disengage.

Furthermore, the slot in the drive shafts of the prior art is typically very narrow, which delays engagement at the start of drilling as it is difficult for the pin to locate the slot. In the design of US 4,456,010, for example, the coupling may only take place at 00 or 1800. Only with increasing axial pressure does the pin engage in the slot 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 driving portion engages; and (ii) the release mechanism may be damaged at the start of drilling as the pin passes over the sharp groove edge.

Other attempts have been made in the prior art to improve the clutch mechanism of the US 4,456,010 perforator.

One such attempt was made in W02015/150844A1, which replaced the slot-and-pin clutch of US 4,456,010 with two square-sided first connecting profiles on the proximal end of the drill head, and two square-sided second connecting profiles on the distal end of the drive shaft. Both the first and second connecting profiles are designed to generate lines that are parallel to the rotational axis of the perforator, so when the drill head engages the drive shaft, the flat connecting profiles are in continuous contact over a connection length determined by the height of the connecting profiles. This creates the result that the drill head does not disconnect from the drive shaft as long as the distal displacement of the drill head does not exceed the connection length. However, the square-sided connection profiles of W02015/150844A1 still retain the sharp trailing edge present on the square slot of the US 4,456,010 design, and therefore are liable to suffer from the same problems described above.

The inventors have appreciated the need for a perforator having a clutch allowing for smooth and fast engagement, and disengagement, in response to pressure being applied on, or released from, a perforator head. The clutch should be less prone to damage and jamming than prior art perforators, in which the high contact pressure and sliding friction cause jamming, leading to inadvertent continued rotation of the cutting heads even once trepanation is complete, or damage to the slot or clutch-pin, which may negatively affect further drilling.

Summary of Invention

The invention provides a perforator as defined in the appended independent claim, to which reference should now be made. Preferred or advantageous features of the invention are set out in dependent subclaims.

In a first aspect, the invention provides a perforator for drilling bone tissue. The perforator comprises a drive shaft having a rotational axis A, an inner perforator head arranged coaxially with the drive shaft, and a ball clutch. The ball clutch comprises a ball, a first engagement region for restricting axial and rotational movement of the ball relative to one of the inner perforator head or the drive shaft, and a second engagement region, wherein the inner perforator head is axially displaceable with respect to the drive shaft between a distal position, in which the inner perforator head is not driveable by the drive shaft, and a proximal cutting position, in which the ball connects the first engagement region and the second engagement region to transmit rotational motion from the drive shaft to the inner perforator head.

The perforator may alternatively be termed a cranial perforator, or a drill, and is preferably attachable to a drill body, for example a hand-held drill, so that the perforator acts as the "drill bit" of a drill for drilling bone tissue, in particular bone tissue of the cranium. The perforator, or drill, may preferably be attachable to the drill body via a standardised connector, such as a Hudson connector.

The inner perforator head is termed generically. The inner perforator head may be a perforator pin, or grating pin, which is configured not to cut bone tissue and thus may functionally differ from an inner cutting head of the prior art. If the inner perforator head is a perforator pin, it may have a smaller relative diameter than an inner cutting head of the prior art.

Alternatively, the inner perforator head may be similar to an inner cutting head in both diameter and function. Alternatively, the inner perforator head may be a unitary cutting head having two cutting diameters, which acts to replace both the inner and outer cutting head of the prior art perforators.

The term "distal" refers herein to portions of the perforator, and portions of individual components of the perforator, positioned towards the drilling tip of the perforator, which in use is intended to contact the bone tissue, while the term "proximal" refers to portions of the perforator that are further from the bone being drilled and closer to, for example, the hand of the user holding the drill.

The term "axially" refers herein to a direction defined by the shared rotational axis A of the drive shaft, perforator pin, and cutting head of the perforator, whereas the term "radially" refers to a direction defined by a radius of the perforator or its components. As such, "radially" refers to any direction perpendicular to the shared rotational axis A. Therefore, "axial movement" is movement in a direction defined by the shared rotational axis A. The term "about" refers herein to an approximate value, the approximate value being within about 10% of the stated value.

The term "rotational" refers herein to rotation about/around the shared rotational axis A. As such, as rotational movement of the ball relative to the first engagement region is restricted, if the first engagement region rotates about/around the shared rotational axis A, the ball rotates along with the first engagement region. As such, the ball may rotate relative to the second engagement region.

Regardless of whether the inner perforator head is a perforator pin configured not to cut bone tissue or an inner cutting head, the coaxial arrangement of the inner perforator head and drive shaft may be generally similarto the perforators of US 4,456,010 and W02015/150844A1. Like the inner cutting head in the prior art designs, the inner perforator head is configured to engage and disengage with the drive shaft in response to a change in pressure on the inner perforator head resulting in translational movement of the inner perforator head along the axis of rotation. The inner perforator head comprises a distal tip which forms the distal end of the entire perforator. The inner perforator head is biased into its distal position by a biasing means such as a spring, so that when no pressure is applied to the distal tip of the inner perforator head, the inner perforator head and outer cutting head are disengaged from the drive shaft.

When pressure is applied to the distal end of the inner perforator head, the inner perforator head is translated along the axis of rotation, towards its proximal cutting position, so that the ball, which is restricted in its axial movement relative to one of the inner perforator head or the drive shaft by a first engagement region, may easily roll into the second engagement region. This allows the ball to engage with both the first and the second engagement region, one each on the inner perforator head and the drive shaft, such that the ball abuts both the inner perforator head and the drive shaft and is confined between them. When the ball connects with both engagement regions, rotational force is transmitted from the rotating drive shaft to the inner cutting head.

In contrast to the prior art perforators, the clutch of the present invention is a ball clutch, wherein engagement and disengagement of the clutch is based on rolling friction rather than sliding friction. When the inner perforator head is in the distal position and the ball clutch is not engaged, the ball is free to rotate relative to the second engagement region, but when the inner perforator head translates into the proximal culling position the ball rolls into the second engagement region to engage the ball clutch. The use of a rolling ball clutch mechanism rather than a sliding slot-and-pin advantageously provides a clutch that can engage and disengage much more smoothly and consistently than the clutches in the prior art.

As soon as the pressure on the distal tip of the inner perforator head is removed, for example when the tip perforates a layer of bone, the pressure maintaining the inner perforator head in its proximal cutting position is removed, and the inner perforator head is biased towards its distal position so that the ball rolls out of the second engagement region. Upon the inner perforator head being in its distal position, the ball may be free to spin, translate in a radial direction, and/or rotate relative to the second engagement region. As such, rotational motion of the drive shaft stops being transmitted from the rotating drive shaft to the inner perforator pin.

The present invention may be applied to perforator embodiments which have only one cutting head. For example, if the inner perforator head is a perforator pin, the perforator may comprise a single outer cutting head, which may simply be termed cutting head, or drill head. Such a cutting head or drill head may be a unitary cutting head having more than one cutting diameter. As such, the unitary cutting head may have two cutting diameters, an inner cutting diameter which is substantially similar to a diameter of a prior art inner cutting head, and an outer cutting diameter, which is substantially similar to a diameter of a prior art outer cutting head. The inner cutting diameter of the unitary cutting head may form a distal end of the unitary cutting head, whereas the outer cutting diameter may be axially spaced from the distal end of the unitary cutting head in a proximal direction.

Alternatively, the inner perforator head may be a unitary inner cutting head having a first and a second cutting diameter, which may simply be termed cutting head, or drill head.

In other embodiments, the inner perforator head may be an inner cutting head and the perforator may comprise a second "outer" cutting head or drill head, arranged coaxially around the inner perforator head, similar to the prior art perforators described above.

In any of these embodiments, the cutting head is preferably configured to cut around the perimeter of a disc of bone when the perforator is in use. The cutting head is preferably configured to cut around a circular disc of bone at a predetermined radius from the axis of rotation.

If the inner perforator head is a perforator pin, it is preferably configured to drill a hole through the bone, and not to cut around a circular disc of bone. In order to do this, the distal end of the perforator pin preferably comprises a point, or a projection, which projects from the perforator along the rotational axis A. The first engagement region and second engagement region are preferably at different axial positions, or "heights", when the inner perforator head is in the distal position, in which one of the first or second engagement portions is positioned distally relative to the other. Movement of the inner perforator head into the proximal cutting position preferably moves the first and second engagement regions into axial alignment (so that the first and second engagement regions are at the same axial "height" in the perforator), so that the ball can couple the two engagement regions of the ball clutch together.

Preferably, the first engagement region and the second engagement region are axially aligned with one another when the inner perforator head is in the proximal cutting position, such that the ball is receivable partially in the first engagement region and partially in the second engagement region upon the inner perforator head being in the proximal cutting position. Advantageously, this allows for the ball to connect the first engagement region and the second engagement region and transmit rotational motion of the drive shaft to the inner perforator head.

The term "axially aligned" refers herein to the first engagement region and the second engagement region being at the same "height" in a direction of the rotational axis A. Preferably one of the first engagement region and the second engagement region is fixed relative to the inner perforator head, and the other of the first engagement region and the second engagement region is provided on the drive shaft. In other words one of the two engagement regions is fixed relative to the inner perforator head, and the other engagement regions is fixed relative to the drive shaft. In preferred embodiments, one of the first engagement region and the second engagement region is provided on the inner perforator head, and the other of the first engagement region and the second engagement region is provided on the drive shaft. This means that movement of the inner perforator head between the distal position and the proximal cutting position changes the relative positioning of the first and second engagement regions, so that movement into the proximal cutting position aligns the first and second engagement regions such that the ball couples the first and second engagement regions together. This allows rotational motion of the drive shaft to be transmitted to the inner perforator head through the ball clutch when the inner perforator head is in the proximal cutting position.

In a preferred embodiment the first engagement region is provided on the drive shaft, and the second engagement region is provided on the inner perforator head. Alternatively, the arrangement of the two engagement regions could be reversed without affecting the function of the ball clutch.

The first engagement region restricts axial and rotational movement of the ball relative to one of the inner perforator head or the drive shaft, i.e. the first engagement region restricts axial and rotational movement of the ball relative to the one of the inner perforator head or the drive shaft which comprises the first engagement region. If the first engagement region is fixed relative to (or provided on) the drive shaft, then the first engagement region restricts axial and rotational movement of the ball relative to the drive shaft. If the first engagement region is fixed relative to (or provided on) the inner perforator head, then the first engagement region restricts axial and rotational movement of the ball relative to the inner perforator head.

Preferably, upon the inner perforator head being in the distal position, the ball is free to rotate around the rotational axis relative to the second engagement region.

The second engagement region is configured to restrict relative rotational movement of the ball only when the inner perforator head is in the proximal cutting position. When the inner perforator head is in the proximal cutting position the ball clutch is engaged, and the second engagement region prevents the ball from rotating relative to the second engagement region. This means that if the drive shaft is rotating, rotational motion is transmitted through the ball clutch so that the first engagement region, the ball, and the second engagement region rotate together.

As the ball does not engage with the second engagement region upon the inner perforator head being in the distal position, it is free to rotate relative to the second engagement region. For example, if the first engagement region is provided on the drive shaft, the ball may rotate together with the drive shaft around the rotational axis, whereas the second engagement region remains substantially inert as long as the inner perforator head is in the distal position. On the other hand, if the first engagement region is provided on the perforator head, the drive shaft may rotate but the ball does not rotate together with the drive shaft.

In preferred embodiments, the perforator is configured so that a portion of the ball is always received in the first engagement region. A portion of the ball is received in the second engagement region upon the inner perforator head being in the proximal cutting position, so that the ball couples the two engagement regions together. Advantageously, this allows the ball to be confined by the first engagement region such that there is no danger of the ball jamming the clutch mechanism or detaching from the first engagement region, while still allowing for the ball to transmit rotational motion of the drive shaft to the cutting head when the ball clutch is engaged.

When the inner perforator head is in the distal position and the ball clutch is not engaged, the ball remains in its position in the first engagement region. When the inner cutting head moves to the proximal cutting position, the ball is then also partially received in the second engagement region, so that the ball is held partially in each of the two engagement regions. In this position, the ball couples the drive shaft and the inner perforator head together, so that the clutch is engaged and rotational motion is transmitted.

Preferably, the first engagement region comprises a receiving region configured to receive a portion of the ball, and the second engagement region comprises a notch arranged in a direction having an axial component, so that upon the inner perforator head being in the distal position, the ball is received in the receiving region and free to rotate relative to the second engagement region, and upon the perforator head being in the proximal cutting position, the ball is held partly in the receiving region and partly in the notch.

The notch of the second engagement region may alternatively be termed a slot, or a channel, and is suitable for receiving a portion of the ball when the ball clutch is engaged. The notch is configured to restrict the rotational movement of the ball relative to the second engagement region, so that when the ball is received in the notch, further rotational movement of the ball is transmitted to the second engagement region so that both rotate together.

The notch is preferably open-ended, so that the ball can roll into the notch through its open end when the inner perforator head moves towards the proximal cutting position. When the inner perforator head moves back towards the distal position, the ball rolls back out of the open end of the notch, and the ball clutch disengages. More preferably, a proximal end of the notch is open-ended.

As described in the background section, in prior art perforators, a slot-and-pin type clutch is used, in which a slot is arranged diametrically across the distal end of the drive shaft. The slot of the clutch in the drive shaft of the prior art perforators is typically very narrow, which delays engagement at the start of drilling as it is difficult for the pin to locate the slot, which may result in unpleasant chattering as the drive portion engages. Further, the release mechanism may be damage at the start of drilling as the pin passes over the sharp groove edge, and upon disengagement, it cannot be guaranteed that the release mechanism in the perforator of the prior art always separates immediately due to the shape of the slot and the pin.

Advantageously, the present invention, which relies on rolling friction rather than sliding friction to transmit rotational movement from the drive shaft to the inner perforator head, uses a ball, which is received in a receiving region of the first engagement region, and may easily roll into an open end of a notch of the second engagement region as the inner perforator head translates into the proximal cutting position. As such, the present invention avoids any unpleasant chattering as the clutch engages and minimises any risk of damage to the release mechanism, as there are no sharp edges. Additionally, as the ball may easily roll out of the open-ended notch of the second engagement region as the inner perforator head is biased back into the distal position, the ball clutch of the present invention disengages immediately and more consistently than the slot-and-pin clutch of the prior art.

The notch is arranged in a direction having an axial component. This advantageously means that the ball can enter and move axially along the notch in response to axial movement of the inner perforator head.

The notch is preferably arranged at an angle relative to the rotational axis A, more preferably at an angle relative to the rotational axis A of between 10° and 70°, yet more preferably between 20° and 60°. If the notch is arranged substantially in an axial direction, i.e. at an angle relative to the rotational axis A of about 0°, upon release of the clutch, the biasing force of the spring acts directly on the perforator pin to urge it distally forward. Having the notch arranged at an angle relative to the rotational axis A allows for the biasing force to be distributed between the spring and the angled notch, allowing for a smoother and more predictable release of the ball clutch.

Whether the notch is angled relative to the rotational axis A in a clockwise direction or in an anticlockwise direction depends on the direction of rotation of the drive shaft. For example, if the drive shaft rotates in a clockwise fashion, the notch is angled relative to the rotational axis A in an anticlockwise direction, and vice versa.

The perforator is preferably configured so that the ball is movable radially in response to axial displacement of the inner perforator head towards the proximal cutting position, from a first radial position in which the ball is free to rotate relative to the second engagement region, to a second radial position in which the ball is confined by the first engagement region and the second engagement region and not rotatable relative to the second engagement region.

Upon the inner perforator head being in its distal position, the ball may be moveable between a first radial position and a second radial position, whereas upon the inner perforator head being in its proximal cutting position, the ball is confined by the first engagement region and the second engagement region in its second radial position.

Advantageously, the ball moving into the second radial position upon axial movement of the inner perforator head into its proximal cutting position allows for the ball to more easily connect or engage the second engagement region, in particular as the engagement region on the drive shaft is in rotational motion.

In preferred embodiments, the second engagement region is positioned axially adjacent to a substantially cylindrical surface (i.e. either distal or proximal to the substantially cylindrical surface), so that upon the inner perforator head being in the distal position, the substantially cylindrical surface is axially aligned with (positioned at the same height as) the first engagement region, and upon the inner perforator head being in the proximal cutting position, the second engagement region is axially aligned with the first engagement region. Advantageously, the ball may easily run circumferentially along the substantially cylindrical surface upon the inner perforator head being in the distal position. The substantially cylindrical surface therefore provides a surface along which the ball may run when the ball clutch is disengaged. Additionally, the ball may also easily run axially along the substantially cylindrical surface upon axial movement of the inner perforator head between the distal position and the proximal cutting position.

The diameter of at least one of the drive shaft and the inner perforator head preferably varies in an axial direction, such that a diameter of the second engagement region differs from a diameter of the substantially cylindrical surface. In particular, if the second engagement region is provided on the inner perforator head, the second engagement region may have a larger diameter than the substantially cylindrical surface, such that, upon the inner perforator head moving towards the proximal cutting position, the second engagement region forces the ball radially outwards, thus trapping, or confining, the ball so as to prevent radial movement of the ball when the clutch is engaged. Alternatively, if the second engagement region is provided on the drive shaft, i.e. on the inner surface of the drive shaft, it may have a smaller diameter than the substantially cylindrical surface, such that, upon the inner perforator head moving towards the proximal cutting position, the second engagement region forces the ball radially inwards, thus trapping, or confining, the ball so as to prevent radial movement. Advantageously, this allows for smooth engagement and disengagement, without jamming, chattering, or damage to the release mechanism.

In preferred embodiments, the drive shaft comprises the first engagement region and the inner perforator head comprises the second engagement region. As described above, in the preferred embodiments, the first engagement region restricts axial and rotational movement of the ball relative to the drive shaft. As such, if the first engagement region is provided on the drive shaft, the ball rotates around the rotational axis A together with the drive shaft. This advantageously means that the ball is in rotation when it engages with the second engagement region on the inner perforator head which is not rotating (but which is moving in an axial direction towards the proximal cutting position), ensuring smooth engagement of the ball with the second engagement region.

In more preferred embodiments, a radial separation between the first engagement region and the inner perforator head is greater upon the inner perforator head being in the distal position than upon the inner perforator head being in the proximal cutting position. This allows for the ball to move radially upon the inner perforator head being in the distal position, but for radial movement of the ball to be restricted upon the inner perforator head being in the proximal cutting position.

In yet more preferred embodiments, upon the inner perforator head being in the distal position, the radial separation between the first engagement region and the inner perforator head is greater than a diameter of the ball so that the ball is rotatable relative to the second engagement region, and wherein upon the inner perforator head being in the proximal cutting position, the radial separation between the first engagement region and the second engagement region is equal to the diameter of the ball so that the ball is held by the first engagement region and the second engagement region. Advantageously, this allows for the ball to be tightly confined by the first engagement region and the second engagement region upon the inner perforator head being in the proximal cutting position, such that transmission of rotational motion from the drive shaft to the inner perforator head is steady, and there is no unevenness or intermittency in the transmission of the motion.

In alternative embodiments, the perforator further comprises an outer perforator head arranged coaxially around the inner perforator head, and a third engagement region configured so that, upon the inner perforator head being in the proximal cutting position, the ball is held between the first, second and third engagement regions to transmit rotational motion from the drive shaft to the inner perforator head and the outer perforator heads. The third engagement region is preferably configured to restrict rotational motion of the ball relative to the outer perforator head when the ball clutch is engaged. Advantageously, this allows for the ball to connect the first, second and third engagement regions to transmit rotational motion from the drive shaft to both the inner perforator head and the outer perforator head.

In some preferred embodiments, the third engagement region is axially aligned with (i.e. positioned at the same height as) the first engagement region. As such, the ball is axially aligned with the third engagement region, as axial and rotational movement of the ball relative to one of the inner perforator head or the drive shaft is restricted by the first engagement region.

Preferably, the first engagement region is disposed radially between the third engagement region and the second engagement region. Advantageously, such an arrangement allows for radial movement of the ball to be confined by the second and third engagement region, while axial movement relative to one of the drive shaft and the inner perforator head is restricted by the first engagement region. In this way, the ball remains within a predefined space between the first, second, and third engagement reason, such that there is no danger of the ball jamming the clutch mechanism.

The first engagement region more preferably comprises an opening in a wall of the drive shaft, the second engagement region comprises a first notch arranged in a direction having an axial component in the inner perforator head, and the third engagement region comprises a second notch in the outer perforator head, in which the perforator is configured so that upon the inner perforator head being in the distal position, the ball is rotatable relative to the inner and outer perforator heads, and upon the inner perforator head being in the proximal cutting position, the ball is held between the first notch, the opening and the second notch.

The outer perforator head yet more preferably is coupled to the inner perforator head only upon the inner perforator head being in the proximal cutting position. Advantageously, this allows for rotational motion to be transmitted to both perforator heads simultaneously and only concurrently.

The ball clutch preferably comprises a plurality of balls. If there is a single ball that connects the first and second engagement regions, the force caused by the rotational friction between the ball, the first engagement region, the second engagement region and, if the perforator comprises a third engagement region, the third engagement region, is concentrated in a single portion of the circumference of the perforator. By providing a plurality of balls, the force may be distributed around the circumference such that the force at each portion of the circumference of the perforator is reduced, which may result in improved durability and reliability of the clutch.

Each ball preferably has an identical radius. This allows for each ball to transmit an equal force when transmitting rotational motion from the drive shaft to the inner perforator head.

The balls are more preferably evenly distributed around the circumference of the perforator. Advantageously, this allows for the force to be transmitted evenly around a circumference of the drive shaft and inner perforator head, which may result in improved durability and reliability of the clutch.

Preferably the ball clutch comprises three balls. Advantageously, three is the minimum number of balls required to evenly distribute force around the circumference of the perforator.

In preferred embodiments, the first engagement region comprises a plurality of openings and axial and rotational movement of each ball relative to one of the inner perforator head or the drive shaft is restricted by one of the plurality of openings. In more preferred embodiments, axial movement of each balls is restricted by a separate one of the plurality of openings.

In yet more preferred embodiments, a number of openings and a number of balls are equal. The number of openings should be no more than required to accommodate each ball, as additional openings may reduce the structural stability of the first engagement region.

Each one of the plurality of openings is preferably axially equidistant to a distal end of the drive shaft. This allows the balls to each engage with and disengage from the second engagement region simultaneously, making engagement and disengagement smooth and even around the circumference of the perforator. This also makes production and assembly of the perforator simpler.

The second engagement region preferably comprises a plurality of first notches arranged in a direction having an axial component, each one of the first notches sized to receive a portion of one of the plurality of balls. The second engagement region preferably comprises more first notches than there are balls in the ball clutch. Advantageously, this allows for the or each ball to more easily roll into the first notches when the inner perforator head translates axially from the distal to the proximal cutting position, thereby ensuring consistent engagement of the ball clutch.

As such, the present invention avoids any unpleasant chattering as the clutch engages and reduces the likelihood of damage to the release mechanism, as the clutch does not comprise sharp edges as described above for prior art perforators. Additionally, as the or each ball may easily roll out of the second engagement region as the inner perforator head translates into the distal position, the ball clutch of the present invention disengages immediately and more consistently than the slot-and-pin clutch of the prior art, such that the inner perforator head, and outer cutting head if present, stop rotating immediately.

The plurality of first notches yet more preferably is spaced evenly around a circumference of the drive shaft or the inner perforator head, and most preferably the first notches cover an entire circumference of the drive shaft or the inner perforator head. Advantageously, maximising the number of notches such that they cover the entire circumference of the drive shaft or the inner perforator head allows for engagement of the ball with the second engagement region to occur quickly, as the or each ball can easily locate one of the notches.

Each of the first notches is preferably arranged at an angle relative to the rotational axis A, more preferably at an angle relative to the rotational axis of between 100 and 70°, yet more preferably between 20° and 60°. If each notch is arranged in an axial direction, i.e. at an angle relative to the rotational axis A of 0°, upon release of the clutch, the biasing force of the spring acts directly on the perforator pin to urge it distally forward. Having each notch arranged at an angle relative to the rotational axis A allows for the biasing force to be distributed between the spring and the angled notches (but only the notch or each notch that is coupled by the or one of the balls), allowing for a smoother and more predictable release of the ball clutch.

The third engagement region, in preferred embodiments, comprises a plurality of second notches, each one of the second notches sized to receive a portion of one of the balls.

More preferably, the third engagement region comprises more second notches than there are balls in the ball clutch. Yet more preferably, the second notches are evenly spaced around a circumference of the outer cutting head. This allows for a ball which is restricted by the first engagement region but may rotate relative to the third engagement region to more easily locate and engage with one of the second notches upon the inner perforator pin moving into the proximal cutting position.

Preferably, the number of second notches is the same as the number of first notches, and more preferably the first notches and the second notches are axially aligned, upon the inner perforator head being in the proximal cutting position, such that each ball connects one of the first notches and a corresponding one of the second notches.

In a particularly preferred embodiment, the ball clutch comprises three balls, a first engagement region comprising three openings through a cylindrical wall of the drive shaft, a second engagement region comprising twelve open-ended first notches positioned on the inner perforator head radially inside the cylindrical drive shaft wall, and a third engagement region arranged on an outer perforator head outside the drive shaft wall, and comprising twelve second notches for receiving a portion of a ball held in one of the openings. When the clutch is engaged, the three balls are held in the openings, the first notches, and the second notches such that the inner perforator head, the drive shaft and the outer perforator head rotate together.

In preferred embodiments, the first notches and the second notches, upon the inner perforator head being in the proximal cutting position, align such that a centre of curvature of each one of the first notches coincides with a centre of curvature of a corresponding one of the second notches.

In more preferred embodiments, a centre of curvature of each one of the plurality of balls, upon the inner perforator head being in the proximal cutting position, coincides with the centres of curvature of one of the first notches and a corresponding one of the second notches. This allows for the or each ball to be held firmly and securely between the first, second, and third engagement regions to transmit rotational motion from the drive shaft to the inner and outer perforator heads.

Preferably, each one of the openings is a hole through a wall of the drive shaft. Advantageously, a hole may easily be drilled into the wall of the drive shaft. More preferably, the holes have a diameter greater than the diameter of the balls. This allows for axial and rotational movement relative to the hole to be restricted but for the ball to easily connect the second and optionally third engagement region(s).

The hardness specifications of the perforator components are given in HRC (Hardness Rockwell C) according to EN ISO 6508-1. In prior art designs, the connector pin of the slot-and-pin clutch had a hardness of 47 HRC. This was 7 HRC less than the hardness of the complementary parts, for example the drive surface. The inventors of the present invention have found that a connector of at least the same hardness as the drive surface and the angled edge of the cutting means is significantly more reliable, as the connector is not deformed or damaged during use.

Similarly, in preferred embodiments of the present invention, the or each ball is formed from a material having a hardness that is equal to or greater than the hardness of the first engagement region and the second engagement region. This ensures that neither the or each ball nor the engagement regions are damaged upon engagement and/or disengagement.

In more preferred embodiments, the or each ball and the first engagement region and the second engagement region are formed from the same material. This ensures that none of the ball, first, and second engagement regions easily become damaged so that the clutch may engage and disengage repeatedly without deterioration in performance.

In particularly preferred embodiments, the ball and the first and second engagement region may have a hardness of up to 54 HRC, which is preferably the same hardness as the drive shaft and the outer cutting head. In yet more preferred embodiments, the third engagement region also has a hardness of up to 54 HRC.

Description of Specific Embodiments of the Invention Specific embodiments of the invention will now be described with reference to the figures, in which: Figure 1 is a partially cut-away side view of a perforator according to the prior art; Figure 2A is a side-on view of the distal end of a prior art drive shaft; Figure 2B is a close-up side-on view of the prior art drive shaft of Figure 2A engaged with a clutch-pin; Figure 2C is a semi-transparent view of an assembled prior art perforator without its cylindrical housing in position; Figure 3 is a cross-section of a perforator according to the present invention taken along the rotational axis A, in which the perforator pin is in a distal position; Figure 4 is a cross-section of the perforator of Figure 3 taken along the rotational axis A, in which the perforator pin is in a proximal cutting position; Figure 5A is an enlarged side-on view of an example of a perforator pin of a perforator; Figure 5B is an enlarged cross-section of the perforator of Figure 4, in which a perforator pin is in a proximal cutting position, taken along plane X-X; Figure 6A is an enlarged side-on view of the distal end of an example of a perforator pin of a perforator; Figure 6B is an enlarged side-on view of the distal end of a perforator having the example of a perforator pin of Figure 6A; Figure 7A is an enlarged perspective view of the distal end of the example perforator pin of Figures 6 A and 6B; Figure 7B is an enlarged perspective view of the distal end of an example perforator having the example perforator pin of Figure 7A.

Specific description

Figure 1 illustrates the parts of a prior art perforator design similar to the perforator disclosed in US Patent No. 4,456,010.

In Figure 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. The proximal end 17 is connectable to a hand-held drill housing a motor, for example. In particular, the proximal end 17 is a standardised connector 17A, such as a Hudson connector.

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 at the bottom of Figure 1. The proximal end of the perforator 10 terminates in the standardised connector 17A of the drive shaft, which is shown at the top in Figure 1.

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 cutting 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 cutting position when the distal tip 20 of the inner cutting head 12 is pressed against a surface, such as bone to be drilled. The force with which the distal tip 20 has to be pressed against the surface to overcome the biasing force of the spring 18 is determined by the spring constant of the spring 18 and the axial separation between the distal position and the proximal cutting position.

When no pressure is applied to the distal tip 20 of the inner cutting head 12, the inner 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.

In the prior art, connection of the inner cutting head 12 and the drive shaft 16 is achieved using a slotand-pin type clutch that comprises a slot 24 (not visible in Figure 1, as the cross-section is taken along the slot, but shown in Figures 2A and 2B) in the distal end 15 of the drive shaft 16, and a corresponding clutch-pin 28 which extends diametrically through the inner cutting head 12 near its proximal end.

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 clutch-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 cutting position moves the clutch-pin 28 towards the apex of the triangular opening 30.

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 clutch-pin 28 engages with the slot 24 in the rotating drive shaft 16. In this proximal cutting position, the clutch-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 clutch-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 at an inner cutting diameter of the inner cutting head 12 and at an outer cutting diameter of the outer cutting head 14.

As soon as the distal tip 20 of the inner cutting head 12 perforates the bone (for example the inner surface of the cranium), however, the force applied to the inner cutting head 12 by the bone is greatly reduced, so that it is exceeded by the force exerted by the biasing spring 18 on the inner cutting head 12, so that the biasing spring 18 urges the clutch-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 as the biasing spring 18 urges the inner cutting head 12 into its distal position.

The present inventors have found, however, that in this prior art design it cannot be guaranteed that the inner cutting head does not damage the dura mater. This is in part because the clutch-pin 28 does not always separate from the slot 24 in time. Occasionally the pin may get stuck at the sharp edge 34 of the slot when it is released. This may cause damage to the pin or the groove edge, which is disadvantageous for further drilling and in the worst case may result in the coupling not being released in time. Furthermore, as the inner cutting head 12 is configured to cut bone tissue, it comprises a number of sharp projections 31 or blades which are configured to cut the bone which the distal tip 20 of the inner cutting head 12 contacts. As the biasing spring 18 is configured to urge the inner cutting head 12 forward when the distal tip 20 perforates the bone, the sharp projections 31 of the inner cutting head 12 may damage the dura mater.

Figure 20 is a semi-transparent view of the perforator 10 in an assembled state with the housing 22 removed, with the clutch-pin 28 in its proximal cutting position so that the clutch-pin 28 is located in the semi-circular groove 24. As the drive shaft 16 rotates, rotational motion is transmitted to the connector or clutch-pin 28 and the inner cutting head 12 through which the clutch-pin 28 extends. As the clutch-pin 28 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 along with the drive shaft 16. When the force is removed from the distal tip (not shown in Figure 20) of the inner cutting head 12, the biasing spring 18 urges the clutch-pin 28 out of the slot 24 so that the drive shaft 16 no longer drives the inner and outer cutting heads.

However, as described above, the clutch-pin 28 may become damaged, or may not disengage from slot 24 and triangular opening 30 in time. As such, the inventors have appreciated the need for a safer perforator in which the release mechanism is more reliable.

Perforator Ball Clutch Figures 3, 4, 5A, and 5B illustrate a perforator 300 according to a preferred embodiment of the present invention. In this preferred embodiment, the components of the perforator 300 are generally similar to those of perforator 10 described above, apart from the design of the clutch and the structure and function of the inner and outer cutting heads 12, 14.

As shown in Figures 3, 4, 5A, and 5B, instead of a slot-and-pin type clutch, the perforator 300 of the present invention comprises a ball clutch. A hollow distal end portion 303 of the drive shaft 302 of the perforator 300 comprises three openings 305 (only one shown in Figures 3 and 4) provided in a cylindrical wall of the drive shaft 302. The three openings 305 are round holes and are spaced evenly around the circumference of the drive shaft. A ball 310 is held in each one of the three openings 305. Each opening 305 is sized to restrict axial movement of the ball (along the rotation axis A) and rotational movement (around the axis of rotation A) relative to the drive shaft 302.

The perforator 300 has a perforator pin 314 which extends along the rotational axis A, and a cutting head 312 which is arranged coaxially around the perforator pin 314.

Although the inner, translatable head of the perforator 300 is shown as a perforator pin 314 having a relative tip diameter significantly smaller than the cutting head 312, the present ball clutch is equally applicable to alternative perforators having an inner cutting head and an outer cutting head, or an inner drill head and outer chipping head, as described in detail above in relation to prior art perforators.

The spring 304 biases perforator pin 314 away from drive shaft 302 into a distal position, as shown in Figure 3. The drive shaft 302 engages with a cylindrical housing 308 of the perforator 300 via two sliding rings 306. The hollow distal end portion 303 of the drive shaft 302 is arranged coaxially around a proximal end of the perforator pin 314. The cutting head 312 is arranged coaxially around both the perforator pin 314 and the distal end portion 303 of the drive shaft 302.

As shown in Figure 3, the or each ball 310 is not only confined by the opening 305 in the drive shaft 302, but also by the perforator pin 314 and cutting head 312. As such, each ball 310 is confined in a predefined space when the perforator pin 314 is in the distal position as shown in Figure 3. Within this space, the or each ball 310 may move at least in a radial direction (i.e. in a direction towards and away from the rotational axis A, along the radius of the perforator). As such, as at least a part of the inner surface of the cutting head 312 is radially spaced apart from the drive shaft 302, even where the inner surface of the cutting head 312 is not adjacent an opening 305 in the wall of the drive shaft 302, there may be a space 307 between the drive shaft 302 and the cutting head 312.

Each ball 310 is free to move in a circumferential direction (i.e. to rotate around the rotational axis A), e.g. in response to rotational motion of the drive shaft 302. As each ball 310 is confined so that movement relative to the drive shaft 302 is restricted, the balls 310 rotate around the rotational axis A together with the drive shaft 302. In other words, the balls 310 are free to rotate relative to the cutting head 312 and the perforator pin 314 when the perforator pin 314 is in the distal position as shown in Figure 3.

Therefore, rotational motion of the drive shaft 302 is not transmitted to the cutting head 312 or perforator pin 314 when the perforator pin 314 is in its distal position.

The perforator pin 314, similarly to the inner cutting head 12 of the prior art perforators of Figures 1, 2A, 2B, and 2C, is movable along the rotational axis A between two positions. In a distal position, the perforator pin 314 is not connected to the drive shaft 302 via the balls 310, and in a proximal cutting position, as shown in Figure 4, the perforator pin 314 is connected to the drive shaft 302 via the or each ball 310. The perforator pin 314 is biased away from the drive shaft 302 and into the distal position by a biasing spring 304, so that the perforator pin 314 only moves into the proximal culling position when the distal tip 500 of the perforator pin 314 is pressed against a surface, such as the bone to be drilled, with sufficient force.

When there is no pressure applied to the distal tip 500 of the perforator pin 314, the perforator pin 314 and cutting head 312 are disconnected from the drive shaft 302 as the ball 310 is not connected to either of the perforator pin 314 and the cutting head 312 and free to rotate relative to the cutting head 312 and the perforator pin 314 along with the drive shaft 302. Therefore, even when the drive shaft 302 is rotating, neither of the perforator pin 314 and the cutting head 312 rotate.

Unlike the perforators of US 4,456,010 and W02015/150844A1, all embodiments of the present invention comprise a ball clutch. The perforators of the prior art comprise slot-and-pin type clutches, which have the disadvantages of chattering upon engagement, damage to the release mechanism from a sharp groove edge, and unreliable disengagement, described in detail above. On the other hand, the ball clutch of the present invention, which relies on rolling friction rather than sliding friction to transmit force/rotational motion from the drive shaft 302 to the cutting head 312 and the perforator pin 314, overcomes these disadvantages. As each ball may easily and smoothly roll into and out of engagement with perforator pin 314 and the cutting head 312, chattering, damage to the release mechanism, and unreliable disengagement are prevented.

As shown in Figure 4, when the perforator pin 314 is in its proximal cutting position, i.e. closer to the standardised connector 317A at the top of the drawing, each ball 310 is confined between the drive shaft 302, the cutting head 312, and the perforator pin 314 such that each ball 310 is no longer free to rotate relative to the perforator pin 314 and the cutting head 312. In this position the or each ball 310 is trapped so that rotational motion of the drive shaft 302 is transmitted to the cutting head 312 and the perforator pin 314 via the balls 310.

Proximally, the perforator pin 314 terminates in a flat end surface 406 configured to engage with the biasing spring 304. The proximal end of the perforator pin 314 has a cylindrical surface 408 which is axially aligned with (i.e. positioned at the same axial height as) each opening 305 in the wall of the drive shaft 302 and each ball 310, upon the perforator pin 314 being in its distal position as shown in Figure 3. When the perforator pin 314 is in the distal position and the drive shaft 302 is rotating, each ball 310 is free to roll against the cylindrical surface 408, as each ball 310 rotates around the rotational axis A together with the drive shaft 302.

When pressure is exerted on the tip of the perforator pin 314, and the perforator pin 314 is urged from the distal position into the proximal cutting position, the cylindrical surface 408 allows for the balls 310 to easily run along the cylindrical surface 408 and into engagement with an engagement region 407 of the perforator pin 314, as shown in Figure 4. The engagement region 407 is positioned on the perforator pin 314, on a distal side of the cylindrical surface 408, so that, as the perforator pin 314 moves into the proximal cutting position, the engagement region 407 becomes axially aligned with (i.e. positioned at the same axial height as) the openings 305 in the wall of the drive shaft 302 and the balls 310, as shown in Figures 4 and 5B.

A diameter of the perforator pin 314 varies in an axial direction. The diameter of the perforator pin 314 along the cylindrical surface 408 is smallerthan the diameter of the perforator pin along the engagement region 407. The transition 404 between the cylindrical surface 408 and the engagement region 407 is not abrupt, but smooth, e.g. rounded. As such, upon axial movement of the perforator pin 314 from the distal position to the proximal cutting position, the balls 310 may easily run along the cylindrical surface 408, past the transition 404, and into engagement with the engagement region 407 of the perforator pin 314, whereupon the variation in diameter of the perforator pin 314 forces the balls 310 radially outward and into engagement with the cutting head 312.

As shown in Figures 5A and 5B, the engagement region 407 of the perforator pin 314 comprises a plurality of first notches 512 configured to receive a portion of the balls 310 when the perforator pin 314 is in its proximal cutting position. The first notches 512 are open-ended notches, i.e. a proximal end of each notch 512 is open, to facilitate engagement of one of the balls 310 with one of the notches 512. The first notches 512 are arranged in a generally axial direction, such that the balls 310 may easily roll into and out of the first notches 512 upon relative axial movement of the perforator pin 314. That is, an axial component of the notches 512 allows for the balls 310 to roll into engagement with the engagement region 407 of the perforator pin 314 upon axial displacement of the perforator pin 314 towards the proximal cutting position.

The first notches 512 are angled relative to the rotational axis A, such that any biasing force of the spring 304, which acts upon the flat end surface 406 of the perforator pin 314 to urge it into a distal direction along rotational axis A, may be distributed between the spring 304 and the angled notches 512 coupled to one of the balls 310.

Similarly, an inner surface of the cutting head 312 comprises a plurality of second notches 514, each of which is configured to receive a portion of the balls 310. As the drive shaft 302 and the cutting head 312 are not movable relative to one another in an axial direction, the plurality of second notches 514 of the cutting head 312 are aligned with the balls 310 and the openings 305 in the wall of the drive shaft 302 irrespective of the position the perforator pin 314. However, as the balls 310 are movable radially upon the perforator pin 314 being in the distal position, the second notches 514 do not necessarily receive a portion of the balls 310 until axial displacement of the perforator pin 314 towards the proximal cutting position.

Unlike first notches 512, second notches 514 may not be arranged in an axial direction and/or may not be open-ended. Second notches 514 may simply be grooves, or cavities, in the inner surface of cutting head 312.

As may be appreciated from Figures 3,4, 5A, and 5B, when the perforator pin 314 is in its distal position, the radial separation between the cutting head 312 and the perforator pin 314 is larger than the diameter of the balls 310. In contrast, when the perforator pin 314 is in its proximal cutting position, the radial separation between the cutting head 312 and the perforator pin 314 is about equal to the diameter of the balls 310. As such, as shown in Figure 5B, when the perforator pin 314 is in its proximal cutting position, each ball 310 is trapped between a first notch 512 in the perforator pin 314 and a second notch 514 in the cutting head 312, such that rotational motion of the drive shaft 302 is transmitted to the perforator pin 314 and the cutting head 312 via the balls 310.

As will be readily appreciated, as the balls 310 are configured to rotate around the rotational axis A along with the drive shaft 302, when the balls 310 are pushed into engagement with the first notches 512 in the perforator pin 314 and the second notches 514 in the cutting head 312, rotational motion of the drive shaft 302 is transmitted to the perforator pin 314 and the cutting head 312. As such, the transmission of rotational motion relies on rotational friction between the balls 310 and the perforator pin 314 and the cutting head 312. In contrast, prior art perforators rely on sliding friction between a clutch-pin and a slot (or between drive surfaces) to transmit rotational motion.

The first notches 512 in the perforator pin 314 are distributed equally around the circumference of the engagement region 407 of the perforator pin 314, and coverthe entire circumference of the engagement region 407 of the perforator pin 314. This facilitates each ball 310 engaging with a notch 512, as it is easier and quicker for the balls 310 to locate one of the notches 512.

Similarly, the second notches 514 in the cutting head 312 are distributed equally around the circumference of the inner surface of the cutting head 312, and cover the entire circumference of the inner surface of the cutting head 312. This facilitates each ball 310 engaging with a notch 514, as it is easier and quicker for the balls 310 to locate the notches 514.

As the preferred embodiment of the present invention comprises three balls 310 (only one ball shown in Figures 3 and 4), which are distributed equally around the circumference of the drive shaft 302, the force of the rotational motion of the drive shaft 302 is transmitted to the inner perforator head/perforator pin 314 and the outer cutting head 312 at three point evenly distributed around the circumference of the drive shaft 302, the perforator pin 314, and the outer cutting head 312. In contrast, in the prior art perforators described above, the force is transmitted at a single or only two points, resulting in a less even distribution of the force and higher forces at each point.

Perforator Pin As shown in Figure 5A, the perforator pin 314 terminates in a distal portion including a distal head 502 having a sharpened distal tip 500, as shown in Figure 5A. The distal tip 500 is configured to penetrate the centre of a disc of bone being cut. However, the distal head 502 and its sharpened distal tip 500 are configured to grate or scrape bone when the perforator is in use rather than to cut it. The perforator pin 314 is pointed to penetrate, or drill, a single continuous hole, rather than to cut around the perimeter of a circular disc of bone. As such, the function and structure of the perforator pin 314 shown in Figure 5A differs significantly from the inner cutting/drill head 12 of the prior art perforators described above.

The distal portion of the perforator pin 314 is further made up of a distal shaft 506, which has a smaller diameter than the distal head 502. As such, the proximal end of the of the distal head 502 connects to the distal shaft 506 forming a lip 504. The lip 504 may hold a disc of bone being cut, which has been penetrated by the distal head 502, in place. As such, the function of the lip 502 may be comparable to the barbs of a barbed arrowhead. This may ensure that a disc of bone being cut is stable during trepanation. Additionally, the lip 504 may restrict movement of the disc of bone relative to the perforator pin 314, so that once trepanation is completed, the disc of bone may be removed with the perforator 300.

The distal shaft 506 terminates proximally in a central shaft 508 having a diameter which is larger than the diameter of the distal shaft 506. The perforator pin 314, at a proximal end of the central shaft 508, has a flange 510 which is configured to engage with a flat inner surface 400 of an inner bore of the culling head 312 upon the perforator pin 314 being in the distal position shown in Figure 3. The flat inner surface 400 is perpendicular to the rotational axis A. As such, the axial position of the flange 510 limits axial movement of the perforator pin 314 distally. Upon the perforator pin 314 being in the proximal cutting position, as shown in Figure 4, the flange 510 is configured to engage with a flat end surface 402 of the drive shaft 302. As such, the axial position of the flange 510 limits axial movement of the perforator pin 314 proximally.

Although the perforator pin 314 shown in the drawings may terminate in a distal portion having a sharpened distal tip 500 which is configured to penetrate the centre of a disc of bone being cut, but not to cut bone, in some embodiments of the present invention the inner perforator head is similar to an inner cutting head or inner drill head of the prior art. Indeed, if the inner perforator head is an inner cutting head or inner drill head, the unitary cutting head 312 shown in the drawings may instead be an outer cutting head or outer chipping head of the prior art. Like the embodiment of the perforator 300 of Figures 3, 4, 5A, and 5B, a perforator according to the present invention having an inner cutting head comprises a ball clutch to selectively transmit radial motion of a drive shaft 302 to the inner perforator head.

The distal head 502 comprises a plurality of rounded cut-outs or recesses 600 as shown in Figure 6A, leaving a distal tip 500 and a plurality of remnants 604, similar to the tip of a twist drill bit for drilling wood, steel, or concrete. The proximal ends 606 of cut-outs 600 are rounded and terminate distally of the proximal end of the distal head 502. As such, at the proximal end of the distal head 502, there remains a smooth circumference 602 having head diameter x.

The rounded cut-outs 600 allow for bone chippings created by the drilling process to be carried away from the distal head 502, while the smooth circumference 602 having head diameterx, which proximally terminates in the lip 504, along with the inner bore in cutting head 312 prevent bone chippings from jamming the perforator pin 314 by entering into the cutting head 312.

As shown in the enlarged side-on view of the distal end of the perforator 300 in Figure 6B, which shows the perforator pin 314 in the proximal cutting position, the distal tip 500 of the distal head 502 of the perforator pin 314 extends distally beyond a distal end 606 of the cutting head 312 upon the perforator pin 314 being in the proximal cutting position. In the embodiment of Figure 6B, the distal tip 500 extends beyond the distal end 606 of the cutting head 312 by about 1.2 mm.

Because the distal tip 500 of the perforator pin 314 extends distally beyond a distal end 606 of the cutting head 312, the perforator pin 314 penetrates the skull before the disc of bone is fully cut around its perimeter. A further advantage of the distal extension of the perforator pin 314 beyond the cutting head 312 is that the distal tip 500 of the perforator pin 314 acts as a centring tip for easier drilling, i.e. by preventing the perforator from slipping.

The cutting head 312 comprises an inner cutting portion 608 having a plurality of projections 609 which are configured to cut at an inner cutting diameter z and an outer cutting portion 610 configured to cut at an outer cutting diameter y. The inner cutting portion 608 extends distally beyond a distal end of the outer cutting portion 610. In use, the cutting head 312 cuts the bone tissue at two diameters, the inner cutting diameter z and the outer cutting diameter y. Because the inner cutting portion 608 extends distally beyond the outer cutting portion 610, the outer cutting portion 610 supports the bone tissue being cut, thereby reducing the risk of a disc of bone being cut breaking off or loosening prematurely.

A radially outward portion 612 of the inner cutting portion 608, e.g. radially outward projections 609, extends distally beyond a central portion 614 of the inner cutting portion 608. In the embodiment of Figure 6B, the radially outward portion 612 extends beyond the central portion 614 by about 0.6 mm.

Figures 7A and 7B show further details of the distal head. The proximal ends 606 of cut-outs 600 are slightly rounded and terminate distally of the proximal end of the distal head 502. As such, at the proximal end of the distal head 502, there remains a smooth circumference 602 having head diameter x. A disc of bone 808 is shown which has a diameter substantially equivalent to the inner cutting diameter of the unitary cutting head 312.

The perforator pin 314 of the exemplary embodiment of Figures 5A, 6A, 7A, and 7B is configured not to cut bone tissue. The rake angle of the perforator pin 314 is negative, preferably between 10° and 50°, more preferably between 20° and 40°, most preferably about 30°. The perforator pin 314 not cutting bone tissue may further be achieved by the perforator pin 314 not creating clearance angles but only raised angles, the perforator pin 314 not being ground free, and a clearance milling of the perforator pin 314 having a negative angle.

Although the perforator pin 314 has been described in detail, the ball clutch of the present invention may be applied in a perforator which is more similar to one of the prior art perforators described above, having an inner cutting head and an outer cutting head.

Claims

Claims 1. A perforator for drilling bone tissue, comprising: a drive shaft having a rotational axis A; an inner perforator head arranged coaxially with the drive shaft; and a ball clutch comprising: a ball; a first engagement region for restricting axial and rotational movement of the ball relative to one of the inner perforator head or the drive shaft; and a second engagement region, wherein the inner perforator head is axially displaceable with respect to the drive shaft between a distal position, in which the inner perforator head is not driveable by the drive shaft, and a proximal cutting position, in which the ball connects the first engagement region and the second engagement region to transmit rotational motion from the drive shaft to the inner perforator head.
2. A perforator according to claim 1, wherein one of the first engagement region and the second engagement region is provided on the inner perforator head, and the other of the first engagement region and the second engagement region is provided on the drive shaft.
3 A perforator according to claim 1 or 2, wherein the first engagement region and the second engagement region are axially aligned with one another when the inner perforator head is in the proximal cutting position, such that the ball is receivable partially in the first engagement region and partially in the second engagement region upon the inner perforator head being in the proximal cutting position.
4. A perforator according to any preceding claim, wherein upon the inner perforator head being in the distal position, the ball is free to rotate around the rotational axis relative to the second engagement region.
A perforator according to any preceding claim, wherein the perforator is configured so that a portion of the ball is always received in the first engagement region and a portion of the ball is received in the second engagement region upon the inner perforator head being in the proximal cutting position.
6. A perforator according to claim 5, wherein the first engagement region comprises a receiving region configured to receive a portion of the ball, and the second engagement region comprises a notch arranged in a direction having an axial component, so that upon the inner perforator head being in the distal position, the ball is received in the receiving region and free to rotate relative to the second engagement region, and upon the perforator head being in the proximal cutting position, the ball is held partly in the receiving region and partly in the notch; preferably wherein a proximal end of the notch is open-ended.
7. A perforator according to any preceding claim, wherein the perforator is configured so that the ball is movable radially in response to axial displacement of the inner perforator head towards the proximal cutting position, from a first radial position in which the ball is free to rotate relative to the second engagement region, to a second radial position in which the ball is confined by the first engagement region and the second engagement region.
8. A perforator according to any preceding claim, wherein the second engagement region is positioned axially adjacent to a substantially cylindrical surface, so that upon the inner perforator head being in the distal position, the substantially cylindrical surface is axially aligned with the first engagement region, and upon the inner perforator head being in the proximal cutting position, the second engagement region is axially aligned with the first engagement region.
9 A perforator according to claim 8, wherein a diameter of at least one of the drive shaft and the inner perforator head varies in an axial direction, such that a diameter of the second engagement region differs from a diameter of the substantially cylindrical surface.
10. A perforator according to any preceding claim, wherein the drive shaft comprises the first engagement region and the inner perforator head comprises the second engagement region.
11. A perforator according to claim 10, wherein a radial separation between the first engagement region and the inner perforator head is greater upon the inner perforator head being in the distal position than upon the inner perforator head being in the proximal cutting position.
12 A perforator according to claim 10 or 11, wherein upon the inner perforator head being in the distal position, the radial separation between the first engagement region and the inner perforator head is greater than a diameter of the ball so that the ball is rotatable relative to the second engagement region, and wherein upon the inner perforator head being in the proximal cutting position, the radial separation between the first engagement region and the second engagement region is equal to the diameter of the ball so that the ball is held by the first engagement region and the second engagement region.
13. A perforator according to any of the preceding claim, further comprising an outer perforator head arranged coaxially around the inner perforator head, and a third engagement region configured so that, upon the inner perforator head being in the proximal cutting position, the ball is held between the first, second and third engagement regions to transmit rotational motion from the drive shaft to the inner perforator head and the outer perforator head; preferably, wherein the third engagement region is axially aligned with the first engagement region.
14 A perforator according to claim 13, wherein the first engagement region is disposed radially between the third engagement region and the second engagement region, and preferably wherein the first engagement region comprises an opening in a wall of the drive shaft, the second engagement region comprises a first notch in the inner perforator head arranged in a direction having an axial component, and the third engagement region comprises a second notch in the outer perforator head, in which the perforator is configured so that upon the inner perforator head being in the distal position, the ball is rotatable relative to the inner and outer perforator heads, and upon the inner perforator head being in the proximal cutting position, the ball is held between the first notch, the opening and the second notch.
15. A perforator according to claim 13 or 14, wherein the outer perforator head is coupled to the inner perforator head only upon the inner perforator head being in the proximal cutting position.
16. A perforator according to any of the preceding claims, wherein the ball clutch comprises a plurality of balls, preferably each ball having an identical radius, yet more preferably the balls are evenly distributed around a circumference of the perforator; most preferably the ball clutch comprises three balls.
17 A perforator according to claim 16, wherein the first engagement region comprises a plurality of openings and wherein axial movement of each one of the balls is restricted by one of the openings; preferably each one of the balls is restricted by a separate opening; more preferably the number of openings and the number of balls are equal.
18. A perforator according to claim 17, wherein each one of the plurality of openings is axially equidistant to a distal end of the drive shaft.
19 A perforator according to any of claims 16, 17, or 18, wherein the second engagement region comprises a plurality of first notches arranged in a direction having an axial component, each first notch being suitable for receiving a portion of one of the balls; preferably wherein each first notch is open-ended; more preferably wherein there are more first notches than there are balls; yet more preferably the first notches are spaced evenly around a circumference of the drive shaft or the inner perforator head; most preferably the first notches cover an entire circumference of the drive shaft or the inner perforator head.
20. A perforator according to claim 19, wherein each first notch is arranged at an angle relative to the rotational axis A; more preferably wherein the angle relative to the rotational axis A is between 100 and 70'; and yet more preferably between 20° and 60°.
21 A perforator according to any one of claims 16 to 20 when dependent on any of claims 13 to 15, wherein the third engagement region comprises a plurality of second notches, each second notch being suitable for receiving a portion of one of the balls; preferably wherein there are more second notches than there are balls; more preferably the second notches are evenly spaced around a circumference of the outer cutting head.
22 A perforator according to claim 21 when dependent on claim 19 or 20, wherein there are the same number of first notches and second notches, and preferably wherein the first notches and the second notches, upon the inner perforator head being in the proximal cutting position, align radially with one another, such that each one of the plurality of balls connects one of the first notches and a corresponding one of the second notches.
23 A perforator according to claim 22, wherein the first notches and the second notches, upon the inner perforator head being in the proximal cutting position, align axially such that a centre of curvature of each one of the first notches coincides with a centre of curvature of a corresponding one of the second notches, and preferably wherein a centre of curvature of each one of the plurality of balls, upon the inner perforator head being in the proximal cutting position, coincides with the centres of curvature of one of the first notches and a corresponding one of the second notches.
24. A perforator according to any one of claims 17 to 23, wherein each opening is a hole through a wall of the drive shaft, and wherein preferably each hole has a diameter greater than the diameter of each ball.A perforator according to any preceding claim, in which the or each ball is formed from a material having a hardness that is equal to or greater than the hardness of the first engagement region and the second engagement region, preferably in which the or each ball and the first engagement region and the second engagement region are formed from the same material.