AU3022397A

AU3022397A - Device for connection of a longitudinal rod with a pedicle screw

Info

Publication number: AU3022397A
Application number: AU30223/97A
Authority: AU
Inventors: Martin Hess; Fridolin Schlapfer
Original assignee: Synthes AG Chur
Current assignee: Synthes GmbH
Priority date: 1997-05-17
Filing date: 1997-06-16
Publication date: 1998-12-11
Anticipated expiration: 2017-06-16
Also published as: KR20010012715A; PT984730E; AU723894B2; JP2001525707A; DK0984730T3; CA2289629C; ES2203807T3; DE19720782B4; HK1023710A1; DE59710520D1; JP4072201B2; CN1254266A; EP0984730B1; KR100509375B1; WO1998052482A1; DE19720782A1; ATE245947T1; EP0984730A1; ZA984064B; TW409048B

Abstract

The invention relates to a device for connecting a longitudinal support (1) to a bone anchorage element inside a spinal fixation system. This device consists of the following: a connecting segment (10, 30) having a central axis (4) and a through-opening (11) perpendicular to the central axis (4) for accommodating a longitudinal support (1); a tensioning-screw (23) which can be screwed in from the top end (28) of the connecting segment (10, 30); and a cylindrical hollow spring chuck (7) which is fitted coaxially in the connecting segment (10, 30) and has an open through-cavity (15) in the direction of the central axis (4) for elastically accommodating the head (5) of a bone anchorage element (30). The spring chuck (7) rests axially in the bore hole (6), in the direction of the bottom end (29) and near the bottom end (29) of the connecting segment (10, 30), without this impeding the radial mobility of the spring chuck (7). The device also comprises an insert (9) which can slide coaxially in the bore hole (6) of the connecting segment (10, 30). Said insert (9) has a bore hole (14) which is complementary to the outer surface (32) of the spring chuck (7).

Description

1 1600/AU 7.5.98 English translation of the International Application PCT/CH97/00236 "Device for the connection of a longitudinal rod with a pedicle {crew" in the name of Synthes AG Chur (Schilpfer) Device for the connection of a longitudinal rod with a pedicle screw The invention relates to a device for the connection of a longitudinal rod with a bone anchoring element according to the definition of claim 1. From prior art pedicle screws to the fixation of vertebral column are known which show the advantage that the longitudinal rod may be inserted afterwards from topside and the angle between 'pedicle screw and longitudinal rod is variably adjustable. Such pedicle screws are known among others from the patents EP-B 0 330 881 SHERMAN and EP-B 0441 729 VIGNAUD. The disadvantage of these known pedicle screws is that in spite of the degree of freedom between pedicle screw and longitudinal rod the latter must often be bent three dimensionally because of the anatomical conditions. In case of other pedicle screws as for instance according to the DE-C 195 09 332 HARMS this disadvantage has been eliminated. Thanks to the spatial movability of the screw head respective to the screw part the longitudinal rod must be bent up to three pedicle screws per longitudinal rod only in one plane when mounted. The disadvantages of this known pedicle screw consist therein that the head part and the threaded part are not apt to be separated, the head part and the longitudinal rod are not apt to be fastened separately with respect to the threaded part, the reachable solidity is low because of the one-sided alignment of the longitudinal slots in the pressure element according to the DE-C 195 09 332 and it is difficult to remobilise the head part once it is fastened. The separability of the head part and the threaded part is a necessity to use different head parts according to the need and that the view is not impeded through the head part during the screwing in of the screw part into the bone. A separate fastening of the head part and the longitudinal rod and a high solidity 2 between head part and threaded part enable the application of distraction and compression without a loss of angle between the pedicle screw and the ngitudinal rod and the conservation of the anatomical bending of the stabilized -vertebral segments. Remobilization i especially important in case of explantation or'new adjustment of the fixation. A further such connection device is disclosed in WO 97/02786 ERRICO which allows in a simple manner to connect a pedicle screw or more generally a bone anchoring element with a longitudinal rod and which permits a great freedom regarding the angle between the two elements. In case of this known connection device the disadvantage consists therein that the spring chuck is part of the connection element and therefore consists of the same material impairing the choice and pairing of the material with the bone screw to improve the solidity. Here, the invention shall offer remedy. The object of the invention lies therein to provide a device for the connection of a longitudinal rod with a pedicle screw having the following qualities: - simple handling; - screwing io the threaded part of the device even without the - connection part; - possible later snap-on of the connection part; - depending on fhe situation and the preference of the surgeon the free choice of or combination of sidewardly open, upwardly open or closed connection parts. For instance an upwardly open connection part facilitates the insertion of the longitudinal rod while a sideward opening enables sideward corrections and thanks to the possibility of the sideward removing of the connection part each pedicle screw may any time be fastened at the longitudinal rod or be removed again without the necessity of demounting the whole fixation system. The invention solves the posed aim with a device providing the features of claim 1. The device according to the invention consists of a connection part accepting the longitudinal rod wherein a pedicle screw having a preferably spherical head may 3 afterwards be snapped-on and fastened. The connection part may be simply snapped-on in the desired number and variant onto the pedicle screws already implanted in the vertebral bodies so that a primary connection between longitudinal rod and pedicle screw is produced. Via the screw-in of the tension means into the fixation device the longitudinal rod is axially and rotatively fastened and simultaneously the device is fastened at a stable angle. Thereby the adjusting screw serving as a tension means presses on the longitudinal rod inserted in the device, this one presses on hollow cylinder which encompasses a hollow truncated cone which is alternatingly slotted and radially not fastened and which is itself compressed because of its conically shaped outer surface and wedging the preferably spherical head of the pedicle screw. The device according to the invention such offers the advantage compared to the known devices that the pedicle screws are not only fastenable exactly perpendicularly to the longitudinal rod but allows an angle of up to ± 250 and because of the distance between the rotating center of the connection part and the axis of the longitudinal rod sideward deviations between longitudinal rod and pedicle screw may be compensated to a certain degree depending on the thickness of the longitudinal rod having an amount of between 4 to 10 mm. This qualities enable the application of longitudinal rods standardizedly prebent at the production site what causes serious difficulties by the mounting of conventional systems. A further advantage of a variant of the device according to the invention consists therein that depending on the embodiment of the hollow cylinder and the tension means respectively on the embodiment of the device the longitudinal rod and the preferably spherical head of the bone screw may be fastened separately. The angular stability may be improved such that the head of the screw consists of a relatively hard material (e.g. Titanium-Aluminium-Niobium-alloy) and the alternately slotted hollow truncated cone consists of a relatively soft material (e.g. Titanium in its soft state). Another possibility for the improvement of the angular stability consists therein to provide the preferably spherical head of the pedicle screw and/or the complementary 4 cavity in the hollow truncated cone with a three dimensional structure e.g. in the shape of grooves. Therewith the structure attached at the head of the screw consisting of a relatively hard material is pressed into the relatively soft material of the hollow truncated cone. A change of the hardness of the materials is possible at least in the contact area, too. The difference of hardness may also be obtained through different cold forming or different crystallization of the same material and whereby the harder material is preferably highly trained steel 1.4441 and the soft material is hot treated steel 1.4441. Apart from this the difference of hardness may be obtained via surface treatment as coating or ion implantation. To be able to screw in the pedicle screws into the bone they are provided at the spherical head preferably with a hexagon socket. If the head apt to be snapped-on is also drilled through optionally only the pedicle screw or the whole device may be screwed in at once. The latter has the advantage above all that at any time the device may be farther screwed in or screwed reverse to obtain a compensation in height. A further embodiment of the invention consists therein that the angles of the cones of the spring chuck and of the insert compressing the spring chuck are different and form a not self-locking cone joining. Other embodiments of the device according to the invention enable a subsequent insertion of the longitudinal rod from the side or from above. Through the screw in of the tension screw into the fixation device simultaneously the longitudinal rod is fastened axially and rotatively within the device and the device is fastened at a stable angle. Thereby the tension screw presses onto the longitudinal rod inserted in the device, this one presses onto the insert of the fixation device and this insert wedges the springable contact studs of the spring chuck via a preferably conical shaped inner surface and a corresponding likewise conical shaped outer surface of the spring chuck on the preferably spherical head of the pedicle screw.

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5 The invention and further embodiments of the invention are discussed in more detail in the following section by means of the partially schematic representations of several embodiments. The figures show: Fig. 1 a longitudinal cut through the connection part of a variant of the device according to the invention together with a longitudinal rod and a pedicle screw having a spherical head; Fig. 2 a perspectival representation of a variant of the device according to the invention; Fig. 3 a longitudinal cut through a modified device according to the invention having qualities as disclosed in fig. I but with the difference that the longitudinal rod is accepted via a sidewardly open channel in the connectionpart; Fig. 4 a longitudinal cut through a modified device according to the invention having qualities as disclosed in fig. 1 but with the difference that the longitudinal rod is accepted in an oval channel in the connection part; Fig. 5 a perspectival representation of a variant of the device according to the invention; Fig. 6 a perspectival representation of a further variant of the device according to the invention; Fig. 7 a perspectival representation of a further variant of the device according to the invention; Fig. 8 a perspectival representation of a further variant of the device according to the invention; and 6 Fig. 9 a perspectival representation of a further variant of the device according to the invention. The variant of the device according to the invention shown in fig. 1 essentially consists of a hollow cylindrical sleeve 10 which is provided with a channel 11 open towards the upper end 28 for the acceptance of the longitudinal rod 1. If required the channel 11 may also be open towards the side (fig. 3) or be formed as an oval bore hole (fig. 4). At the lower end 29 of the sleeve 10 a preferably ring shaped channel 17 is provided wherein the flange 18 of the spring chuck 7 inserted in the bore hole 6 of the sleeve 10 is attachable. Such the spring chuck 7 is fastened against displacement along the central axis 4 of the sleeve 10 but not radially fastened. The spring chuck 7 is provided in its inside with a cavity 15 preferably shaped as a hollow sphere. Slots, wherefrom alternately a first number run into the upper base area 8 and another number run into the lower base area 13 of the spring chuck 7 enable a homogeneous expansion and compression of the spring chuck 7. Thanks to the radial freedom of the spring chuck 7 in the channel 17 the head 5 of the pedicle screw 2 may at any time be snapped into respectively out of the spring chuck 7 as long as the device is not fastened through tightening the tension screw 23. Outside the spring chuck 7 is shaped tapering conically towards its upper end 8. A hollow cylindrical insert 9 which is shaped complementarily conical to the cone at the spring chuck 7 at its lower end may slide within the bore hole 6 of the sleeve 10 and depending on the effect of force radially compress the spring chuck 7 via the conical joining 14 and therewith fasten the head 5 of the pedicle screw 2 being inside of the cavity 15. This connection is also loosenable what is facilitated through the attachment of a shoulder 16 in the insert 9. Longitudinal rod I and pedicle screw 2 are fastened by means of a tension screw 23 which is screwed in coaxially into an insert screw 21 being at the upper end 28 of the sleeve 10. The tension screw 23 presses when being tightened onto the longitudinal rod 1 which itself presses onto the insert 9 and therewith causes the closure of the spring chuck 7 through pushing into one another the cones 14. The function of the insert screw consists therein to alter the thread 19 in the sleeve 10 interrupted by the channel 11 into a closed thread wherein the tension screw 23 may run unhindered.

7 Since the through hole 11 according to the variant of the device according to the invention shown in fig. I is formed as a channel open at the upper end 28 of the sleeve 10 and thus the sleeve 10 is weakened at this part a swivel ring 22 is mounted that prevents the widening of the sleeve 10 when the tension screw 23 is tightened. A further variant of the device according to the invention is shown in fig. 2. The main difference between the embodiment according to fig. 1 and the one according to fig. 2 consists in the sideward dislocation of the channel 52 to the acceptance of the longitudinal rod 1 with respect to the bore hole 6 with the central axis 4. Thus it is possible to separately fasten the longitudinal rod 1 and the pedicle screw 2. From the lower end 29 of the connection part 30 a bone anchoring element 40 may be inserted and be fastened analogously to the variant shown in fig. 1 by means of a spring chuck 7, an insert 9 and a tension means 50. Thereby the tension means 50 according to the variant shown in fig. 2 presses directly onto the insert 9. A channel 52 running transversely to the central axis 4 without contacting the bore hole 6 which may again be optionally sidewardly open, open towards the upper end 28 or be realized as a bore hole serves to the acceptance of the longitudinal rod 1. The fastening of the longitudinal rod 1 is done by means of a separate screw 51. The variant of the device according to the invention shown in fig. 3 differentiates from the variant shown in fig. I only by that means that the sidewardly open through opening 26 in the sleeve 10 accepts the longitudinal rod 1. The insert 9 is lower at this side, too. Thus, the longitudinal rod 1 may be subsequently inserted into the device as in case of the variant shown in fig. 1. The variant of the device according to the invention shown in fig. 4 differentiates from the variant shown in fig. 1 only by that means that a closed oval through opening 27 within the sleeve 10 accepts the longitudinal rod 1. The variant of the device according to the invention shown in fig. 5 differentiates from the variant shown in fig. I only by that means that a nut 42 is employed as a tension means 50. Thereto the sleeve 10 is provided with an exterior thread 41 whereon the nut 42 is screwed. When tightened the nut 42 presses onto the longitudinal

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8 rod 1 which itself presses onto the insert 9 by what means the spring chuck 7 is radially compressed and such the head 5 of the pedicle screw 2 and the longitudinal rod 1 are simultaneously fastened. A collapse of the channel 11 may be prevented by forming the thread 41 as buttress thread or by inserting a cylindrical element 47 into the bore hole 6. In fig. 6 another variant of the device according to the invention is shown. This one differentiates from the variant shown in fig. 1 only by that means that a locking screw 43 serves as a tension means 50. The widening of the channel 11 is prevented by forming the thread 19 as a buttress thread. Also the variant shown in fig. 7 differentiates from the variant shown in fig. 1 only through the construction of the tension means 50. The sleeve 10 is provided with an exterior thread 41 whereon the threaded sleeve 44 is screwed. The fastening of the longitudinal rod 1 and pedicle screw 2 happens by means of a tension screw 23 which is screwed into the threaded sleeve 44. The threaded sleeve 44 thus has the same function as the threaded insert 21 shown in fig. 1. Thanks to the threaded sleeve 44 inserted between the slotted thread 41 and the tension screw 23 the tension screw 23 runs within an uninterrupted thread. Also another variant of the device according to the invention is shown in fig. 8. This variant accentuates by that means that the longitudinal rod 1 and the pedicle screw 2 may be fastened separately. To this purpose the sleeve 10 is provided at its upper end 28 with an interior thread 19 and an exterior thread 41. The channel 12 of the insert 9 is shaped such that the longitudinal rod 1 always lies on the lower edge of the through opening 11 during its fastening by means of the nut 42. When the tension screw 23 which presses directly on the insert 9 extending over the longitudinal rod 1 is tightened the spring chuck 7 is compressed thus fastening the pedicle screw 2. Furthermore, the variant of the device according to the invention shown in fig. 9 enables a separate fastening of the longitudinal rod 1 and the pedicle screw 2. The trough opening 11 and the channel 12 are shaped such that the longitudinal rod 1 always lies on the channel 12 when fastened. The longitudinal rod 1 is fastened by means of a stud bolt 45 which is screwed into an interior thread 46 in the insert 9. The 9 tension screw 23 serves to fasten the pedicle screw 2 whereby the tension screw 23 presses onto the insert 9 whereby this one is sliding over the spring chuck 7 thus radially compressing it. The widening of the channel 11 may also be prevented either by shaping the threads 19 and 46 as buttress threads or by using a sleeve 22 as shown in fig. 1. RAL Ul

Claims

1. Device for the connection of a longitudinal rod (1) with a bone anchoring element (40) within a vertebral fixation system, with . , A) a connection part (10;30) with an upper end (28), a lower end (29) and a bore hole (6) open towards the lower end (29) having a central axis (4) and a through hole (11) running transversely to the central axis (4) for the acceptance of a longitudinal rod (1), B) a tension means (50) for the fixation of the bone anchoring element (40) insertable from the upper end (28) and C) a radially compressible spring chuck (7) arranged within the connection part (10;30) coaxial to the central axis (4) with an upper end (8) and a lower end (13) which is provided in its inside with a cavity (15) downwardly and in the direction of the central axis (4) open for the springlike acceptance of the head (5) of a bone anchoring element (40), characterized in that D) the spring chuck (7) is axially supported in the direction towards the lower end (29) in the bore hole (6) close to the lower end (29) of the connection part (10;30) without impeding the spring chuck (7) in its radial movability therewith; and E) an insert (9) is provided coaxially slidable in the bore hole (6) of the connection.,, part (10;30) having a bore (14) complementary to the outer surface (32) of the spring chuck (7).

2. Device according to claim 1, characterized in that the spring chuck (7) is axially secured by means of a shoulder (31) preferably in the shape of a ring groove running perpendicular to the central axis (4) in the bore hole (6).

3. Device according to one of the claims 1 or 2, characterized in that the connection part (10) is a hollow cylindrical sleeve (10).

4. Device according to one of the claims 1 to 3, characterized in that the outer surface (32) of the spring chuck (7) is conically shaped.

5. Device according to one of the claims 1 to 4, characterized in that the bore (14) is shaped conically widening downwardly.

6. Device according to claim 4 or 5, characterized in that the anglekof the cone of the conically shaped outer surface (32) of the spring chuck (7) and the ang) e of the cone of the conically shaped bore (14) in the insert (9) is greater than 100 and anmounts preferably between 120 and 160.

7. Device according to one of the claims I to 6, characterized in that the angle of the cone of the conically shaped outer surface (32) of the spring chuck (7) and the angle of the cone of the conically shaped bore (14) in the insert (9) provide a difference that is preferably smaller than 1*.

8. Device according to claim 7, characterized in that the difference is greater than 10 and amounts preferably between 40 and 60.

9. Device according to one of the claims I to 8, characterized in that a sidewardly open through hole (26) in the connection part (10;30) serves to the acceptance of the longitudinal rod (1).

10. Device according to one of the claims 1 to 8, characterized in that an oval through hole (27) in the connection part (10;30) serves to the acceptance of the longitudinal rod (1).

11. Device according to one of the claims 1 to 10, characterized in that the interior thread (19) in the connection part (10;30) and the external thread (20) of the insert screw (21) are formed as buttress threads whereby the flat sides of the profile of the interior thread, (19) are directed towards the spring chuck (7) and provide an angle to the central axis (4) amounting between 870 and 930.

12. Device accrdirtto one of the claims 1 to 11, characterized in that a pedicle screw (2) serves as bone anchoring element (40) whereby the diameter of the threaded shaft (3) may conically taper towards its terminal free section, preferably with an angle of thecone with an amount of 30 - 40*. 12

13. Device according to one of the claims 1 to 12, characterized in that the bope anchoring element (40) is provided with a turned groove (53) below the spherical head (5).

14. Device according to one of the claims 1 to 13, characterized in that the hollow space (14) in the insert (9) is convexly shaped in, the area of the contact zone between insert (9) and spring chuck (7).

15. Device according to one of the claims 1 'to 14, characterized in that the spring chuck (7) is convexly preferably spherically shaped, in the area of the contact zone between insert (9) arid spring ch ck (7).

16. Device according to one of the claims 1 to 15, characterized in that the insert (9) provides an anchoring means preferably a shoulder (16) in the upper area.

17. Device according to one 'of the claims 1 to 16, characterized in that the insert is circular cylindrical.

18. Device according to one of the claims 1 to 16, characterized in that the insert (9) provides a polygon like cross section transversely to the central axis (4).

19. Device according to one of the claims I to 18, characterized)n that the insert (9) is also open on the inside towards the top.

20. Device according to one of the claims 1 to 19, characterized in that the insert (9) provides a channel (12) in the upper section.

21. Device- according to one of the claims 1 to 20, characterized in that the bore hole (6) and the through hole (11) are connected to each other.

22. Device according to one of the claims I to 21, characterized in that the tension means (50) enables a simultaneous fixation of the longitudinal rod (1) and the head (5) of the bone anchoring element (40). 13

23. Device according to one of the claims 1 to 22, characterized in that A) the tension means (50) presses directly on the longitudinal rod (1); and B) the motion of the longitudinal rod (1) is not impeded during the tensioning action through the through hole (11) in the sleeve (10).

24. Device according~to claim 23, characterized in that the upper end (28) of the sleeve (10) provides an external thread (41) whereon a nut is screwed as tension means (50).

25. Device according to claim 23, characterized in that the upper end (28) of the sleeve (10) provides an internal thread (19) wherein a locking screw (43) is screwed as tension mean (50).

26. Device according to one of the claims 1 to 25, characterized in that the tension means (50) is multipiece.

27. Device according to claim 23, characterized in that an insert screw (21) with integrated tension screw (23) serves as tension means (50).

28. Device according to claim 23, characterized in that a threaded sleeve (44) with integrated tension screw (23) serves as tension means (50).

29. Device according to one of the claims I to 22, characterized in that the upper end (28) of the sleeve (10) provides an external thread (41) whereon a nut (42) is screwed to the fiation of the longitudinal rod (1).

30. Device according to one of the claims 1 to 29, characterized in that A) a nut presses directly on the longitudinal rod (1); and B) the motion of the longitudinal rod (1) is not impeded during the tensioning action through the channel (12).

31. Device according to claim 30, characterized in that A) the upper end (28) of the sleeve (10) provides an internal thread (19) and B) the insert (9) extends over the longitudinal rod (1) so that in case of tightening the 14 tension screw (23) the insert (9) is moved downwards without pressing on the longitudinal rod (1).

32. Device according to one of the claims 1 to 22, characterized in that the i sert (9) provides an internal thread (46) topside.

33. Device according to claim 32, characterized in that A) a stud bolt (45) presses on the longitudinal rod (1); and B) the motion of the longitudinal rod (1) is not impeded during the tensioning action through the through hole (11).

34. Device according to one of the claims I to 33, characterized in that the spring chuck (7) is provided on its inside with a cavity (15) having the form of a hollow sphere to the acceptance of the preferably spherical head (5) of the bone anchoring element (40).

35. Device according to one of the claims 1 to 34, characterized in that the spring chuck (7) provides at least four slots whereof a number run into the front side at the lower end (13).

36. Device according to one of the claims I to 34, characterized in that the spring chuck (7) provides at least four slots whereof a number run into the front side at the upper end (8).

37. Device according to one of the claims to 34, characterized in that the spring chuck (7) provides at least four slots which run alternately into the front side at the lower end (13) and into the front side at the upper end (8).

38. Device according to one of the claims 1 to 23, 25 to 27 and 32 to 37, characterized in that a swivel ring (22) at the upper end (28) of the sleeve (10) impedes spreading of the sleeve (10).

39. Device according to claim 38, characterized in that the swivel ring (22) may be attached at the sleeve (10) by means of an insert screw (21). 15

40. Device according to one of the claims I to 39, characterized in that A) the channel (11) at the sleeve (10) is open towards the upper endf28); B) the threads (19;41) at the upper end (28) of the sleeve (10) and the co plemontary threads of the respective tension means (50) are provided as butt ess threads whereby the flat sides of the profile are directed such that in case of tightening the tension means (50) no spreading of the sleeve (10) appears; and C) the flat side of the profile provides an angle having an amount between 870 and 930 to the central axis (4).

41. Device according to one of the claims I to 21- and 33 to 37, characterized in that p channel (52) in the connection part (30) running transverse to the central axis (4) and dislocated beside the bore hole (6) serves to the acceptance of the longitudinal rod (1) and a screw (51) serves to the fixation of the longitudinal rod (1).

42. Device according to one of the claims I to 41, characterized in that the cavity (15) within the spring chuck (7) and/or the head (5) of the bone anchoring element (40) is provided with a structure preferably in the form of transverse grooves respectively transverse ribs.

43. Device accoFding to 'one of the claims 1 to 42, characterized in that the spring chuck (7) and the head (5) of the bone anchoring element (40) consist at least in the contact area of materials with different hardness.

44. Device according to claim 43, characterized in that the harder material is preferably Titanium-Aluminium-Niobium and the soft material is preferably pure Titanium.

45. Device according to one of the claims 1 to 42, characterized in that the spring chuck (7) and, the head (5) of the bone anchoring element (40) provide at least in the contact @ea a different hardness whereby this difference of hardness is obtained via different cold forming or different crystallization of the same material and whereby the harder material is preferably highly trained steel 1.4441 and the soft material is hot-treated steel 1.4441. 16

46. Device according to one of the claims 1 to 42, characterized in that the spring chuck (7) and the head (5) of the bone anchoring element (40) provide at least in the contact area a different hardness, whereby this difference of hardness is obtained via surface treatment as coating or ion implantation.

47. Device according to one of the claims 1 to 46, characterized in that the spring chuck (7) is axially secured towards the lower end (28) by means of a shoulder (31) within the bore hole (6) running orthogonal to the central axis (4).

48. Device according k one of the claims 1 to 47, characterized in that the spring chuck (7) is supported axially stable within the bore hole (6).