The present invention relates to a disposable perforator for perforating bone tissue.

The perforator is a medical device which can be used to perform trepanation on the crane i.e. drill a hole therein, and in particular to perform craniotomy after the trepanation. During the trepanation of the crane it is a problem, that substantial pressure has to be applied for advancing the drill head, however, the advancing of the drill head needs to be stopped immediately after perforation of the bone in order to prevent the drill head from penetrating and damaging the dura mater. In order to carry out surgical closure successfully it is a prerequisite that the dura mater must stay undamaged to be able to create fluid (liquor) sealing seam thereon.

The above problem is overcome by a perforator disclosed in patent application WO2015/150844A1 , the content of which is incorporated herein by reference.

The perforator according to WO2015/150844A1 comprises a drive shaft having a rotation axis, a drill head having the same rotation axis, and a chipping head arranged coaxially around the drill head. The objective of the present invention is to improve the external connection between the drive shaft and the chipping head of such perforators. An objective of the invention is to provide a non-releasable connection, which guarantees that the parts of the perforator cannot be disassembled whereby it cannot occur that somebody takes the perforator apart, attempts to clean it (which can never be fully accomplished due to the spring disengagement mechanism) and then reassembles it and it is reused. A further objective of the invention is to stabilise the connection while the drive shaft and the drill head are rotating together and once the rotation is stopped.

These objects are achieved by a perforator according to claim 1.

Further advantageous embodiments of the invention are defined in the attached dependent claims.

Further details of the invention will be explained by way of exemplary embodiments with reference to the figures.

Fig. 1 is a partially cut-away side view of a perforator according to the invention.

Fig. 2a is a side view of a drive shaft of the perforator according to Fig. 1.

Fig. 2b is a side view of the drive shaft of the perforator according to Fig. 1 in a position rotated by 90 degrees.

Fig. 2c is a plan view of the drive shaft of the perforator according to Fig. 1 taken from the direction of its distal end.

Fig. 2d is a perspective view of the drive shaft of the perforator according to Fig. 1

Fig. 3a is a side view of a drill head of the perforator according to Fig. 1.

Fig. 3b is a side view of the drill head of the perforator according to Fig. 1 in a position rotated by 90 degrees.

Fig. 3c is a plan view of the drill head of the perforator according to Fig. 1 taken from the direction of its proximal end.

Fig. 3d is a perspective view of the drill head of the perforator according to Fig. 1.

Fig. 4a is a side view of a chipping head of the perforator according to Fig.

1.

Fig. 4b is a side view of the chipping head of the perforator according to Fig.

1 in a position rotated by 90 degrees.

Fig. 4c is a cross sectional view taken along line A-A of Fig. 4b.

Fig. 4d is a perspective view of the chipping head of the perforator according to Fig. 1.

Fig. 5b is a top view of a securing ring of the perforator according to Fig. 1.

Fig. 5a is a side view of the securing ring of the perforator according to Fig.

1.

Fig. 6 is a side view of the ring stop of the perforator according to Fig. 1.

Fig. 7a is a side view of a slide ring of the perforator according to Fig. 1.

Fig. 7b is a cross sectional view taken along line A-A of Fig. 7a.

Fig 1 shows the main components of an exemplary embodiment of a perforator 10 according to the invention in an assembled state. The main components are as follows: a drive shaft 12 having a rotation axis t, a drill head 14 having the same rotation axis t and a chipping head 16 arranged coaxially therewith, and a securing ring 90 connecting the drive shaft 12 with the chipping head 16.

The present invention is directed to the connection between the drive shaft 12 and the chipping head 16. The drive shaft 12 and the chipping head 16 are secured to each other by the securing ring 90, which also ensures non-releasable connection after assembly. A proximal portion 161 of a proximal wall 42 of the chipping head 16 extends beyond the drill head 14 which is arranged within the chipping head 16, and overlaps a distal portion 121 of the drive shaft 12. Grooves 122 and 162 are provided along the external circumference of the distal portion 121 of the drive shaft 12 and along the internal circumference of the proximal portion 161 of the chipping head 16, respectively, which together define a ring shaped nest 92 when the distal portion 121 of the drive shaft 12 and the proximal portion 161 of the chipping head 16 are inserted into one another and the two grooves 122, 162 are facing each other

The securing ring 90 is shown separately in Figs. 5a and 5b. The dimensions of the ring 90 in it relaxed (non-stressed) state is chosen such that in the assembled state of the perforator 10 the securing ring 90 extends into both grooves 122, 162 forming the ring shaped nest 92 in order to prevent displacement of the grooves 122, 162 and thereby displacement of the drive shaft 12 and the chipping head 16 along the rotation axis t with respect to each other. The securing ring 90 is partially cut and its material allows for changing its circumference by elastic deformation, whereby the securing ring 90 can be slid over the distal portion 121 of the drive shaft 12, and can be positioned above the groove 122 and in this position the proximal portion 161 of the wall 42 of the chipping head 16 can be slid over the securing ring 90.

According to the present embodiment driving the drill head 14 and the chipping head 16 with the drive shaft 12 and automatic decoupling therefrom is achieved with a similar structure as disclosed in the patent application WO2015/150844A1 , hence this will be explained more briefly here. It should be appreciated that other type of known driving and decoupling mechanism can also be applied inside the perforator 10 of the present invention.

The drive shaft 12 may be connected to a revolution reducer, so-called TREAPAN adapter, coupled with a drive motor (not shown), and may be formed for example as a Hudson cone as better seen in Figs. 2a - 2d. The drill head 14 and the chipping head 16 each comprise a distal cutting edge 15 and 17 respectively, and the distal cutting edge 15 of the drill head 14 extends beyond the distal cutting edge 17 of the chipping head 16.

According to the present embodiment first connecting profile 20 is provided on a proximal end 18 of the drill head 14 (see Figs. 3a - 3d), while a second connecting profile 24 is provided on a distal end 22 of the drive shaft 12 (see Figs. 2a - 2d). The drill head 14 is arranged so as to be displaceable along the rotation axis t with respect to the chipping head 16 (and with respect to the drive shaft 12 at the same time) between a proximal position and a distal position. In the proximal position the second connecting profile 24 on the distal end 22 of the drive shaft 12 engages the first connecting profile 20 and cooperates therewith such as to transmit rotational motion from the drive shaft 12 to the drill head 14. In the distal position the first connecting profile 20 on the proximal end 18 of the drill head 14 and the second connecting profile 24 on the distal end 22 of the drive shaft 12 are disengaged, whereby the driving torque ceases.

The first connecting profile 20 formed on the drill head 14 comprises at least one, but according to the present embodiment two abutting surfaces 26.

The second connecting profile 24 on the drive shaft 12 also comprises at least one driving surface 28. Preferably, the same number of driving surfaces 28 are provided as abutting surfaces 26.

According to the present invention the two abutting surfaces 26 and the two driving surfaces 28 each delimit a projection 30 and 32. The projections 32 of the drive shaft 12 are formed with a wedge surface 34 on their side opposite the driving surface 28. The length of the wedge surfaces 34 is preferably such that a clearance 35 is provided between the wedge surface 34 and the neighbouring driving surface 28 for receiving the rectangular projections 30 of the first connecting profile 20 of the drill head 14. Naturally, an inverted design is also conceivable, wherein the drive shaft 12 is provided with rectangular projections and the drill head 14 is provided with projections arranged between wedge surfaces and clearances.

Preferably, the projections 30 of the first connecting profile 20 of the drill head 14 and the projections 32 of the second connecting profile 24 of the drive shaft 12 are formed rotation-symmetrically with respect to the rotational axis t (i.e. formed evenly spaced around the circumference of a circle), whereby the proximal end 18 of the drill head 14 may engage the distal end 22 of the drive shaft 12 in more than one position. Engagement is understood to describe the situation wherein the projections 30 of the drill head 14 are received in the clearances 35 of the drive shaft 12 and the abutting surfaces 26 and the driving surfaces 28 abut each other.

In case of the present embodiment the two projections 30 of the connecting profile 20 are rotated with respect to each other by 180 degrees around the rotational axis t, however this angle depends on the number of the projections 30. For example, in case of three projections 30, those are preferably evenly spaced along the circumference of the proximal end 18, being in positions rotated by 120 degrees with respect to each other. In case a number of n projections 30 are provided those are preferably rotated by 360/n degrees with respect to the neighbouring projection 30. The connecting profile 24 of the distal end 22 of the drive shaft 12 is designed to correspond to the number and arrangement of the abutting surfaces 26 and the projections 30; accordingly, the projections 32 of the drive shaft 12 are preferably also formed rotation-symmetrically and evenly spaced along the circumference of the distal end 22.

When the connecting profile 20 of the drill head 12 engages the connecting profile 24 of the drive shaft 14 the abutting surface 26 and the driving surface 28 abutting each other overlap in the direction of the rotational axis t and contact each other along a given connection length. If the length of the abutting surface 26 and of the driving surface 28 is the same along the rotational axis t then the overlapping is complete, otherwise the shorter element determines the connection length. The connection length determines the distance by which the proximal end 18 of the drill head 14 must be displaced from the distal end 22 of the drive shaft 12 in order to terminate the torque transmission connection between the two. Preferably, the connection length is between 0.4 to 1 mm, preferably 0.6 to 0.9 mm, more preferably approximately 0.7 mm. The drill head 14 may be displaced along the rotational axis t by a distance corresponding to the connection length before the drive mechanism is disengaged.

Disengagement of the drive mechanism can be ensured by providing a connection between the drill head 14 and the chipping head 16, which transforms relative rotation of the drill head 14 and the chipping head 16 around the rotational axis t into relative displacement along the rotational axis t. According to an exemplary embodiment this connection is ensured such that the drill head 14 comprises a bore hole 40 extending through an external surface 38 of the drill head 14, and an inwardly opening groove 46 with a proximal helical edge 44 corresponding to the driving direction is provided in a cylindrical wall 42 of the chipping head 16. An angle a between the helical edge 44 and the rotational axis t is preferably 40 to 50 degrees. In case of the embodiment depicted in Figs. 4a and 4b this groove 46 is a triangular groove formed through the wall 42, one edge of the triangle forming the helical edge 44. However, grooves 46 with other shapes may be applied as well, which have a suitable proximal helical edge 44. The connection between the drill head 14 and the chipping head 16 is ensured by a bolt pin 48 arranged in the bore hole 40 of the drill head 14 and extending into the groove 46 of the chipping head 16, which bolt pin 48 is guided by the proximal helical edge 44. The helical edge 44 is formed such that its elevation 49 is greater than the connection length in order to provide for disengagement of the first connection profile 20 of the proximal end 18 of the drill head 14 from the second connection profile 24 of the of the distal end 22 of the drive shaft 12 such as to terminate the torque transmission connection between the two when the bolt pin 48 is guided from the proximal position defined by one end of the edge 44 to the distal position defined by an opposite end of the edge 44 along the trajectory defined by the edge 44.

The perforator 10 is preferably provided with a mechanism for biasing the proximal end 18 of the drill head 14 from the distal end 22 of the drive shaft 12 when the perforator 10 is not being used. This can be achieved for example by providing nests 50 and 52 in the proximal end 18 of the drill head 14 and in the distal end 22 of the drive shaft 12 respectively, which nests 50, 52 open into one another when the drill head 14 and the drive shaft 12 are engaged and wherein a spring 54 is arranged. The spring 54 is compressed by the two nests 50, 52 along the rotational axis t when the drill head 14 and the drive shaft 12 are engaged, consequently, the spring 54 forces the drill head 14 into the distal position which is defined by the bolt pin 48 extending into the groove 46 of the chipping head 16 and traversing the bore hole 40 of the drill head 14, meaning that the spring 54 helps to disengage the drill head 14 from the drive shaft 12.

Preferably a spring stop 53 is also applied, which is shown separately in Fig. 6. In this case the spring stop 53 is applied on an end of the spring 54 and it serves to prevent the spring 54 from catching the bottom of the nest 50 formed in the proximal end 18 of the drill head 14 after the drive shaft 12 and the drill head 14 have been disengaged during use which could otherwise cause further rotation of the drill head 14. The spring stop 53 is preferably made of copper or a copper alloy.

The middle portion of the perforator 10, which is shown in a sectional view, is preferably encased by a cylindrical case 55 which also seals the openings 46 formed in the wall 42 of the chipping head 16, thus preventing any contamination from entering and hindering the displacement of the pin bolt 48. According to the present embodiment the proximal end 55a of the case 55 abuts the collar 58 of the drive shaft 12 as shown in Fig. 1 . The distal end 55b of the case 55 abuts a flange 43 protruding from the wall 42 of the chipping head 16. The case 55 is preferably made of plastic, e.g. such ABS material that can be gamma sterilized but is unsuitable for sterilization in an autoclave, whereby the case 55 cannot be desterilized in an autoclave which is a further measure to prevent re-use of the disposable perforator.

The proximal portion 161 of the wall 42 of the chipping head 16 extends beyond the drill head 14 and preferably a slide ring 64 is arranged between the drive shaft 12 and an end portion 163 of the proximally extending proximal portion 161 which end portion 163 has an increased inner diameter. The slide ring 64 is shown separately in Figs. 7a and 7b. In the assembled state of the perforator 10 a rim 64a of the slide ring 64 tightly fits between the collar 58 of the drive shaft 12 and the proximal end 164 of the chipping head 16 as can be seen in Fig. 1 . The slide ring 64 serves as a bearing and is preferably made of a soft plastic material, copper or a copper alloy or any material of similar property in order to prevent wearing between the drive shaft 12, which is preferably made of metal, in particular of stainless steel, and the wall 42 of the chipping head 16 when rotating and in order to prevent the components from getting stuck or sticking to each other which would hinder the disengagement during use.

Preferably an inwardly facing side 64b of the rim 64a of the slide ring 64 and an outwardly facing side 90a of the distal end of the securing ring 90 are formed conically in order to facilitate sliding the slide ring 64 onto the securing ring 90 as will be explained later on. According to the preferred embodiment illustrated in Fig. 1 the perforator 10 is further provided with a security spring 80 which counteracts the effect of the ring 54 assisting the disengagement of the drill head 14. The security ring 80 is arranged between an external wall 14a of the drill head 14 and an internal wall 17a of the chipping head 16, within a ring shaped nest 82 defined by a proximal external circumferential flange 14b of the drill head 14 and a distal internal circumferential flange 17b of the chipping head 16. The length of the security spring 80 is determined from one direction by the position of the external circumferential flange 14b of the drill head 14 and from the other direction by the internal circumferential flange 16b of the chipping head 16. In the proximal position of the drill head 14, i.e. when the proximal end 18 of the drill head 14 abuts the distal end 22 of the drive shaft 12 and the first and second connection profiles 20, 24 engage with each other, the security spring 80 is slightly biased (compressed). The spring 54 and the security spring 80 are preferably dimensioned such that in the proximal position of the drill head 14, the spring force is greater in the spring 54 arranged in the nest 52 of the drive shaft 12 and in the nest 50 of the drill head 14, than the spring force of the security spring 80. Preferably, such a spring 54 is used which has a greater spring constant than the spring constant of the security spring 80.

In case of drilling a cranial bone, at the end of the drilling, when the distally extending cutting edge 15 of the drill head 14 has cut through the spongiosa of the bone tissue and starts to penetrate the internal bone plate of the bone tissue, the counter force acting on the drill head 14 drastically decreases while the cutting edge 17 of the chipping head 16 lying in the distal direction is still inside the external bone structure - or having drilled there through, it is still in the spongiosa - requiring substantial driving torque to be rotated therein. The drill head 14 exerts torque on the chipping head 16 by way of the bolt pin 48. Due to the decreasing resistance the drill head 14 begins to rotate more rapidly together with the bolt pin 48 as compared to the rotation of the chipping head 16, which is allowed by the helical proximal edge 44 of the groove 46 receiving the bolt pin 48 and at the same time the helical proximal edge 44 guides the bolt pin 48 and the drill head 14 therewith until the bolt pin 48 and the drill head 14 reaches the distal position.

Since the case 55 and the securing ring 90 holds the drive shaft 12 at a constant distance from the chipping head 16, thus the drill head 14 is not only displaced relative to the chipping head 16 but is also displaced relative the drive shaft 12. Consequently, the abutting surfaces 26 of the first connecting profile 20 of the drill head 14 are gradually shifted along the driving surfaces 28 of the second connecting profile 24 of the drive shaft 12. As long as the extent of shifting is less then the connection length, the drill head 14 is still driven by the drive shaft 12, accordingly, by suitable dimensioning of the connection length it is possible to achieve that the drill head 14 cuts partially or wholly through the internal bone plate while shifting in the distal direction. When the extent of the shifting exceeds the connection length 36, the abutting surfaces 26 of the first connecting profile 20 of the drill head 14 disengage the driving surfaces 28 of the second connecting profile 24 of the drive shaft 12, whereby the driving torque ceases to act on the drill head 14, and together with it, on the chipping head 16. In absence of a driving torque the chipping head 16 and the drill head 14 connected therewith by the bolt pin 48 come to a halt, whereby the perforator 10 only just cuts through the internal bone plate of the bone tissue, and automatically stops thereafter.

Releasing of the driving mechanism is further facilitated by the compressed spring 54 which is arranged in the nests 50, 52 of the drive shaft 12 and of the drill head 14 respectively, opening into each other, since the spring 54 biasis the drill head 14 in the direction of the disengaged position.

During use the first spring 54 and the security spring 80 act in the opposite sense: in the proximal position of the drill head 14 the first spring 54 is more compressed, it exerts greater spring force which forces the drill head 14 in the distal direction, while the security ring 80 is less compressed, thus exerting a smaller spring force and forcing the drill head 14 in the proximal direction to a less extent. In the distal position of the drill head 14, however, the first spring 54 is less compressed, whereby the distal spring force decreases, while the security spring 80 becomes more compressed, thus the proximal spring force increases. Consequently, the spring 54 and the security spring 80 counterbalance each other's effect, which results in a more steady motion of the drill head 14, rendering the cutting motion more balanced.

Assembling the perforator 10 according to the invention may be carried out as follows. The steps are not necessarily performed in the order disclosed herein. The securing ring 90 is placed around the distal portion 121 of the drive shaft 12 from the direction of the distal end 22 such that it is positioned around the groove 122 encircling the distal portion 121 of the drive shaft 12. The securing ring 90 is made of a resilient material (e.g. plastic such as ABS) and its not closed (that is it is partially cut open, whereby it can also be pushed over the part of the drive shaft 12, which has a larger diameter than the groove 122 when it is in a somewhat opened state which is achieved by the resilient deformation of the securing ring 90. Once the securing ring 90 is positioned around the groove 122 the slide ring 64 is pulled over the distal portion 121 of the drive shaft 12 and also over the securing ring 90 which is facilitated by the conic sides 64b and 90a of the slide ring 64 and of the securing ring 90, respectively, which are facing each other. As a result of this the securing ring 90 is forced inside the groove 122 and assumes a compressed state also by way of elastic deformation. The slide ring 64 is only displaced along the distal portion 121 of the drive shaft 12 in the proximal direction until it does not come off the securing ring 90 in order to keep it inside the groove 122.

Preferably the spring stop 53 is also applied. In this case the spring stop 53 is inserted into one end of the spring 54 after which the spring 54 and the spring stop 53 are placed inside the nest 52 formed in the distal end 22 of the drive shaft 12.

The security spring 80 is arranged inside the chipping head 16 on the flange 16b then the drill head 14 is guided through the security spring 80 and rotated to a position within the chipping head 16 where the bolt pin 48 can be pushed through the bore hole 40 and the opening 46 so as to traverse both the drill head 14 and the chipping head 16. Thereby the bolt pin 48 secures the chipping head 16, the drill head 14 and the security spring 80.

The case 55 is pulled over the exterior of the chipping head 16 such that the distal end 55b abuts the flange 43 of the chipping head 16 whereby the case 55 retains the bolt pin 48.

The components held together by the case are then pushed over the distal end 22 of the drive shaft 12. The end portion 163 of the chipping head 16 having a wider inner diameter slides onto the slide ring 64 until the proximal end 164 of the chipping head 16 abuts the rim 64a formed at the proximal end of the slide ring 64 and then pushes the slide ring 64 further along the drive shaft 12 up to its collar 58. Meanwhile, the slide ring 64 slides off the securing ring 90, which partially snaps out from the groove 122 when the internal groove 162 of the chipping head is moved thereover. The internal groove 162 is formed such as to partially receive the securing ring 90 therein as can be seen in Fig. 1 , thus the securing ring 90 is positioned partly inside the groove 122 provided on the external side of the drive shaft 12 and partly inside the groove 162 provided on the internal side of the chipping head 16, thereby preventing any further displacement of the chipping head 16 and the drive shaft 12 with respect to each other in both directions along the rotation axis t. Consequently, the assembled chipping head 16 can no longer be pulled off the drive shaft 12.

The non-releasable connection guarantees that the components of the perforator 10 cannot be disassembled whereby it cannot occur that somebody takes the perforator 10 apart, attempts to clean it (which can never be fully accomplished due to the spring disengagement mechanism) and then reassembles it and it is reused.

The novel connection does not hinder disengagement of the drive shaft 12 and the drill head 14 because the lateral displacement of the drill head 14 along the rotation axis t is determined by dimensions of the openings 46 provided on the chipping head 16 since the drill head 14 can only be displaced together with the bolt pin 48 reaching into the openings 46.

Various modifications to the above disclosed embodiments will be apparent to a person skilled in the art without departing from the scope of protection determined by the attached claims.