MEDICAL INSTRUMENT AND METHOD FOR THE MANUFACTURE OF A MEDICAL INSTRUMENT

Abstract

A medical instrument has a first part connected to a second part with a connecting element. The first and second parts are pivotable relative to one another about a pivot axis defined by a longitudinal axis of the connecting element. The first part has a first bearing area, and the second part has a second bearing area. The first bearing area and second bearing area face each other. In a mounted state, a biasing element is arranged between the first and second bearing areas. The biasing element, in the mounted state, is held in a compressed state between the first and second bearing areas by the connecting element so as to exert a biasing force on the first and second bearing areas to keep them biased away from one another.

Claims

1. A medical instrument comprising: a first part; a second part; a connecting element; and a biasing element, the connecting element connecting the first part to the second part so that the first part and the second part are pivotable relative to one another about a pivot axis defined by a longitudinal axis of the connecting element, the first part comprising at least one first bearing area, the second part comprising at least one second bearing area, the at least one first bearing area and the at least one second bearing area facing each other, the biasing element, in a mounted state, being arranged between the at least one first bearing area and the at least one second bearing area, the biasing element, in the mounted state, being held in a compressed state between the at least one first bearing area and the at least one second bearing area by the connecting element so as to exert a biasing force on the at least one first bearing area and the at least one second bearing area for keeping the at least one first bearing area and the at least one second bearing area biased away from one another.

2. The medical instrument according to claim 1, wherein: the biasing element comprises a spring washer having a central opening for receiving the connecting element, and the biasing element surrounds the pivot axis.

3. The medical instrument according to claim 2, wherein the spring washer is a wave washer.

4. The medical instrument according to claim 3, wherein the wave washer has a wavelike shape defining at least one wave trough and at least one wave crest.

5. The medical instrument according to claim 4, wherein the at least one wave trough comprises a plurality of wave troughs, and at least one wave crest comprises a plurality of wave crests.

6. The medical instrument according to claim 5, wherein the wave washer comprises a first surface and a second surface, the first surface and the second surface facing in opposite directions, wherein the first surface defines a first contact plane of the plurality of wave crests, and wherein the second surface defines a second contact plane of the plurality of wave troughs.

7. The medical instrument according to claim 6, wherein the first contact plane and the second contact plane extend parallel to one another.

8. The medical instrument according to claim 7, wherein the first contact plane and the second contact plane extend parallel to one another in an initial state and/or in a mounted state.

9. The medical instrument according to claim 8, wherein: the first contact plane and the second contact plane define a first distance from one another in the initial state, the first contact plane and the second contact plane define a second distance from one another in the mounted state, in which the biasing element is mounted between the at least one first bearing area and the at least one second bearing area, and the first distance is greater than the second distance.

10. The medical instrument according to claim 9, wherein: a) in the mounted state, the second distance has a maximum value of about 1.2 times a thickness of the wave washer; and/or b) in the initial state, the first distance has a value in a range from about 2 times the thickness of the wave washer to about 10 times the thickness of the wave washer.

11. The medical instrument according to claim 3, wherein the wave washer has a constant thickness.

12. The medical instrument according to claim 3, wherein the wave washer undulates: a) in a circumferential direction with respect to the pivot axis; or b) in a radial direction with respect to the pivot axis.

13. The medical instrument according to claim 3, wherein the wave washer comprises a cutting line extending in a radial or circumferential direction with respect to the pivot axis, the cutting line having at least two points of inflection.

14. The medical instrument according to claim 1 further comprising a connecting device, the connecting device comprising an applied connecting device, the at least one first bearing area comprising one single first bearing area, the at least one second bearing area comprising one single second bearing area, the applied connecting device comprising the one single first bearing area and the one single second bearing area, wherein the first part comprises the one single first bearing area, the first part being applied to the one single second bearing area with the biasing element arranged between the first part and the one single second bearing area.

15. The medical instrument according to claim 14, wherein the connecting device comprises a box-type connecting device, wherein the first part has a female connecting portion with a through opening, wherein the second part has a male connecting portion, and wherein the male connecting portion extends through the through opening in the mounted state.

16. The medical instrument according to claim 15, wherein the female connecting portion has two first bearing areas facing each other, and wherein the male connecting portion has two second bearing areas facing away from one another.

17. A method for manufacturing a medical instrument having a first part and a second part, the first part having at least one first bearing area, the second part having at least one second bearing area, the method comprising the steps of: arranging the at least one first bearing area and the at least one second bearing area such that the at least one first bearing area and the at least one second bearing area face each other; connecting the first part and the second part to one another with a connecting element such that the first part and the second part are pivotable relative to one another about a pivot axis defined by a longitudinal axis of the connecting element; arranging a biasing element between the at least one first bearing area and the at least one second bearing area before connecting the first part and the second part to one another; compressing the biasing element with the first part and the second part in a compressed state; and maintaining the compressed state by adjusting the connecting element such that the biasing element exerts a biasing force on the at least one first bearing area and the at least one second bearing area to keep the at least one first bearing area and the at least one second bearing area biased away from one another.

18. The method for manufacturing a medical instrument according to claim 17, wherein the biasing element comprises a wave washer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The following description of preferred embodiments serves, in conjunction with the drawing figures, for a more detailed explanation of the present disclosure.

[0038] FIG. 1 shows a schematic exploded view of an embodiment of a medical instrument;

[0039] FIG. 2 shows an enlarged partial view of a distal end of the instrument depicted in FIG. 1;

[0040] FIG. 3 shows a partially broken view of the arrangement in FIG. 2 before adjusting the connecting element, i.e. with the biasing element in the initial state;

[0041] FIG. 4 shows a partially broken view of the arrangement in FIG. 3 in the mounted state, i.e. with the biasing element in the compressed state;

[0042] FIG. 5 shows a partially broken plan view of the arrangement in FIG. 4 in the region of the connecting device;

[0043] FIG. 6 shows a sectional view taken along line 6-6 in FIG. 5 before adjusting the instrument;

[0044] FIG. 7 shows a view similar to the arrangement in FIG. 6 with the biasing element in the mounted state, i.e. compressed;

[0045] FIG. 8 shows a perspective view of the embodiment of a biasing element shown in FIGS. 1 to 7;

[0046] FIG. 9 shows a side view of the embodiment of the biasing element in FIG. 8;

[0047] FIG. 10 shows a top view of the biasing element shown in FIGS. 8 and 9;

[0048] FIG. 11 shows a perspective view of a further embodiment of a wave washer;

[0049] FIG. 12 shows a side view of the wave washer depicted in FIG. 11;

[0050] FIG. 13 shows a top view of the wave washer depicted in FIGS. 11 and 12;

[0051] FIG. 14 shows a perspective view of a further embodiment of a wave washer;

[0052] FIG. 15 shows a side view of the wave washer depicted in FIG. 14;

[0053] FIG. 16 shows a top view of the wave washer depicted in FIGS. 14 and 15;

[0054] FIG. 17 shows a perspective view of a further embodiment of a wave washer;

[0055] FIG. 18 shows a side view of the wave washer depicted in FIG. 17;

[0056] FIG. 19 shows a top view of the wave washer depicted in FIGS. 17 and 18;

[0057] FIG. 20 shows a perspective view of a further embodiment of a wave washer;

[0058] FIG. 21 shows a side view of the wave washer depicted in FIG. 20;

[0059] FIG. 22 shows a top view of the wave washer depicted in FIGS. 20 and 21;

[0060] FIG. 23 shows a partially broken view of a portion of a further embodiment of a medical instrument with a box-type connecting device in the mounted state; and

[0061] FIG. 24 shows a sectional view taken along line 24-24 in FIG. 23.

DETAILED DESCRIPTION

[0062] FIG. 1 shows a first embodiment of a medical instrument 10 in an exploded view. The instrument 10 comprises a first part 12 and a second part 14. The exploded view in FIG. 1 shows the instrument 10 during assembly.

[0063] The first part 12 has a first distal end 16 and a first proximal end 18. A first tool element 20 is formed or arranged on the first distal end 12. Further, a first holding element 22 is formed or arranged on the first proximal end 18.

[0064] In a similar manner as described in connection with the first part 12, the second part 14 has a second distal end 24 and a second proximal end 26. A second tool element 28 configured for cooperating with the first tool element 20 is formed or arranged on the second distal end 24. Moreover, a second holding element 30 is formed or arranged on the second proximal end 26.

[0065] The first tool element and the second tool element 28 form or define a medical tool 32.

[0066] In the embodiment of the medical instrument 10 shown in FIGS. 1 to 7, the first and second tool elements 20, 28 are configured in the form of clamping jaws 34, 36 so that the medical instrument 10 as a whole is configured in the form of a medical clamp 36.

[0067] The first and second holding elements 22, 30 are configured in the form of rings 40, 42 commonly used with such standard medical instruments for an easy handling by a surgeon or another user.

[0068] In alternative embodiments not shown in the drawing figures, the first and second tool elements 20 are made in the form of cooperating cutting edges so that the medical tool 32 is configured in the form of a pair of scissors.

[0069] In a further embodiment not depicted in the drawing figures, the medical tool 32 is configured in the form of a needle holder which has structured gripping phases.

[0070] The first and second parts 12, 14 are connected to one another in a connecting region 44 by a connecting element 46. The embodiment of the medical instrument 10 shown in FIG. 1 has elongated arms 48, 50, also called branches, which extend between the connecting region 44 and the respective proximal ends 18, 26.

[0071] Further, the first part 12 has a first bearing area 52. The second part 14 has a second bearing area 54. As shown in FIGS. 1 to 7, the first bearing area 52 and the second bearing area 54 are arranged so as to face each other.

[0072] In a standard medical instrument, the two parts 12 and 14 would be assembled so that the first and second bearing areas 52 and 54 would directly contact each other. The two parts 12 and 14 would be connected with a connecting element in the form of a screw or rivet so as to pivotably connect the two parts 12 and 14 to one another.

[0073] The main difference between the medical instrument 10 shown in FIGS. 1 to 7 and the described standard medical instrument is that the first and second bearing areas 52 and 54 are not in direct contact with one another. Rather, a biasing element 56 is arranged between the first and second bearing areas 52, 54.

[0074] The connecting region 44 comprises, in particular, the first and second bearing areas 52 and 54 and the connecting element 46, which together define a so-called connecting device 58. The connecting element 46 serves the purpose of pivotably connecting the first and second parts 12, 14 to one another so as to be pivotable about a pivot axis 60 defined by a longitudinal axis 62 of the connecting element 46.

[0075] The biasing element 56 is configured in the form of a spring washer 64 having a central opening 66 for receiving the connecting element 46. The configuration of the spring washer 64 further allows for the arrangement of the biasing element 56 so as to surround the pivot axis 60 as depicted, in particular, in FIGS. 5 and 6.

[0076] FIGS. 1 to 10 show an embodiment of a spring washer 64 in the form of a so-called wave washer 68. The wave washer 68 has a wavelike shape as shown, in particular, in FIGS. 8 to 10. Theses drawing figures show an initial state of the wave washer 68, in which it is separate from the first and second parts 12, 14. The wave washer 68 does not exert any spring force in this initial state.

[0077] The wavelike shape of the wave washer 68 defines several wave troughs 70 and several wave crests 72.

[0078] Further, the wave washer 68 of the embodiment depicted in drawing FIGS. 1 to 10 has a constant or substantially constant thickness 74.

[0079] The wave washer 68 depicted in the drawing FIGS. 1 to 10 undulates in a circumferential direction with respect to the pivot axis 60. This means that the curvature of the wave washer 68 changes in an alternating manner from a convex to a concave curvature and vice versa.

[0080] The wave washer 68 has a first surface 76 and a second surface 78. The first and second surfaces 76, 78 face in opposite directions. As depicted in FIG. 9, the first surface 76 defines a first contact plane 80 of the wave crests 72. The second surface 78 defines a second contact plane 82 of the wave troughs 70.

[0081] The first and second contact planes 80, 82 extend in parallel or substantially in parallel to one another. This is the case in the initial state as depicted in FIG. 9. It is also the case in the mounted state as described further below.

[0082] A cutting line 84 of the wave washer 68 in a circumferential direction defines several points of inflection 86 and 88, which are defined alternatingly along the circumference of the cutting line 84. With respect to the first surface 76 and with reference to FIGS. 8 to 10, adjacent points of inflection 86 and 88 define either a wave crest 72 or a wave trough 70 between them.

[0083] Looking at FIG. 10, moving along the cutting line 84 along its circumference in a clockwise direction 90 and starting at any point of inflection 86 follows a concave curvature of the wave washer 68 pointing away from the first surface 76 until the adjacent point of inflection 88 is reached, where the curvature changes from concave to convex with respect to the first surface 76. Further following the cutting line 84 in the clockwise direction 90 to the next point of inflection 86, the curvature remains substantially convex until the point of inflection 86 is reached. The described change of curvature of the cutting line 84 continues along its circumference. The described configuration results from the wave washer's shape undulating in a circumferential direction with respect to the pivot axis 60.

[0084] As already mentioned, FIG. 1 schematically shows the assembly of the medical instrument 10. The second part comprises a bore 92 with an enlarged region 94. Bore 92 is adapted to receive an unthreaded shaft portion 96 of the connecting element 46, which is configured in the form of a connecting screw 98. The region 94 is configured to receive a screw head 100 of the connecting screw 98.

[0085] A threaded shaft portion 102 extends between shaft portion 96 and a free end 104 opposite the screw head 100 of the connecting screw 98.

[0086] A bore 106 with inner threads 108 is provided on the first part 12 for receiving the threaded shaft portion 102.

[0087] For the assembly of the medical instrument 10, the connecting screw 98 is introduced with its free end 104 through bore 92 so that threaded shaft portion 102 projects beyond the second bearing area 54 as shown in FIG. 1.

[0088] The wave washer 68 is then placed over the threaded shaft portion 102 so that the second surface 78 contacts the second bearing area 54 as shown in FIG. 1.

[0089] Next, the first part 12 is brought into engagement with the connecting screw 98 by screwing the threaded shaft portion 102 into bore 106 with its inner threads 108, which correspond to the threaded shaft portion 102.

[0090] FIG. 6 shows a state during the assembly in which the wave washer 68 is still in the initial state, i.e. it does not exert any spring force as it is not deformed with respect to its initial state shown in FIGS. 8 to 10. However, the first surface 76 with the wave crests 72 is now in contact with the first bearing area 52.

[0091] In the initial state, the first contact plane 80 and the second contact plane 82 define a first distance 110 from one another. The distance 110 corresponds to the gap between the first and second bearing areas 52, 54 as shown in FIG. 6 as long as the wave washer 68 is in the initial state.

[0092] For adjusting the instrument 10, the connecting screw 98 is further screwed into bore 106, thereby compressing the wave washer 68 and transferring the same from the initial state to a compressed state. FIG. 7 shows a compressed state of the wave washer 68 in the mounted or assembled state of the medical instrument 10.

[0093] In this mounted state, the first contact plane 80 and the second contact plane 82 define a second distance 112 corresponding to the reduced gap between the first and second bearing areas 52, 54. As can be seen in FIGS. 6 and 7, the first distance 110 is greater than the second distance 112.

[0094] Further, the wave washer 68, i.e. the biasing element 56, is arranged between the first and second bearing areas 52, 54 in the mounted state, and it is held in the compressed state between them by the connecting element 46. Since the biasing element 56 is held compressed by the arrangement of the connecting device 58, it exerts a biasing force on the first and second bearing areas 52, 54 for keeping them biased away from one another.

[0095] The spring force exerted by the wave washer 68 on the parts 12 and 14 depends on its compression. The more it is compressed, the greater the spring force becomes. This allows for an individual adjustment of a motion force of the medical instrument 10 when the two parts 12, 14 are pivoted relative to one another about the pivot axis 60. The motion force is related to the friction between the parts 12 and 14 on the one hand and the biasing element 56 on the other hand.

[0096] In order to improve the cleanability of the medical instrument 10, it is preferably adjusted such that, in the mounted state, the second distance 112 has a maximum value of about 1.2 times the thickness 74 of the wave washer 68. In order to reduce recesses between the bearing areas 52 and 54 defined by the wave troughs 70 and the wave crests 72, the connecting screw 98 is adjusted such that the maximum value of the second distance 112 is about 1.1 times the thickness 74 of the wave washer 68.

[0097] Referring to FIG. 9, the first distance 110 in the initial state has a value in a range of about two times the thickness 74 of the wave washer 68 to about ten times the thickness 74. The embodiment shown in FIG. 9 has a ratio of about 5:1 between the first distance 110 and the thickness 74. This means that the first distance 110 has a value in a range from about two times to about five times the thickness 74 of the wave washer 68.

[0098] The medical instrument 10 depicted in FIGS. 1 to 7 has a connecting device 58 which is configured in the form of an applied connecting device 114. The applied connecting device 114 comprises one single first bearing area 52 and one single second bearing area 54. It is further configured such that the first part 12 with the single first bearing area 52 is applied to the single second bearing area 54 with the biasing element 56 arranged therebetween.

[0099] The embodiment of the wave washer 68 depicted in FIGS. 1 to 10 has five wave troughs 70 and five wave crests 72 and a corresponding number of five points of inflection 86 and five points of inflection 88 along the cutting line 84 as described above.

[0100] FIGS. 11 to 13 show a further embodiment of a wave washer 68. The configuration of the wave washer 68 shown in FIGS. 11 to 13 is similar to the wave washer 68 depicted in FIGS. 1 to 10. Therefore, the same reference numerals are used for denoting identical or similar elements.

[0101] The main difference between the wave washer 68 depicted in FIGS. 11 to 13 and the wave washer 68 depicted in FIGS. 1 to 10 is the number of wave troughs 70 and wave crests 72. The embodiment shown in FIGS. 11 to 13 has only three wave troughs 70 and three wave crests 72. This leads to a corresponding number of points of inflection 86 and 88 along the cutting line 84, namely three points of inflection 86 and 88 each.

[0102] A further embodiment of a wave washer 68 is shown in FIGS. 14 to 16. Again, the same reference numerals are used for denoting identical or similar elements as for the embodiments shown in FIGS. 1 to 13.

[0103] The embodiment of the wave washer shown in FIGS. 14 to 16 differs from the embodiments described above again in the number of wave troughs 70 and wave crests 72. The embodiment shown in FIGS. 14 to 16 has ten wave troughs 70 and ten wave crests 72. This results in a corresponding number of ten points of inflection 86 and ten points of inflection 88 along cutting line 90 as described above.

[0104] FIGS. 17 to 19 show a further embodiment of a spring washer 68. The configuration of this spring washer 68 differs from the previously described spring washers in that the spring washer 68 undulates in a radial direction with respect to pivot axis 60. This results in a cutting line 84 in a radial direction 116 with respect to the pivot axis 60 having two points of inflection 86, 88. Starting from the pivot axis 60, a wave trough 70 is defined by an inner rim of the wave washer 68 surrounding the central opening 66. The concave curvature of wave trough 70 changes to a convex curvature at the point of inflection 88. Moving further away from the pivot axis 60 results in reaching the wave crest 72, and further moving from the wave crest 72 to the outer rim of the wave washer 68 defining a second wave trough 70 results in passing a second point of inflection 86 where the convex curvature changes to a concave curvature.

[0105] Moreover, a further embodiment of a wave washer 68 is depicted in FIGS. 20 to 22. Again, reference numerals used for denoting identical or similar elements are used with respect to FIGS. 20 to 22 as in FIGS. 17 to 19.

[0106] This embodiment generally corresponds to the embodiment shown in FIGS. 17 to 19. This means that this wave washer 68 undulates in the radial direction 116 with respect to the pivot axis 60. This embodiment has three wave troughs 70 and two wave crests 72 starting with a wave trough 70 defined by an inner rim delimiting the central opening 86. An outer rim of the wave washer 68 defines a further wave trough 70.

[0107] FIGS. 23 and 24 show a further embodiment of a medical instrument 10, namely a distal end region thereof. This instrument 10 is configured in the form of a needle holder 118. The tool elements 20 and 28 are curved with respect to a reference plane extending perpendicularly to the pivot axis 60.

[0108] The instrument 10 depicted in FIGS. 23 and 24 differs from the medical instrument depicted in FIGS. 1 to 7, in particular, in the different configuration of the connecting device 58. The instrument 10 shown in FIGS. 23 and 24 has a connecting device 58 which is configured in the form of a box-type connecting device 120.

[0109] The box-type connecting device 120 is characterized by the first part 12 having a female connecting portion 122 with a through opening 124. The second part 14 has a male connecting portion 126 which extends through the through opening 124 in the mounted state as shown in FIGS. 23 and 24. Due to this configuration, the female connecting portion 122 has two first bearing areas 52 facing each other. The male connecting portion 126 has two second bearing areas 54 facing away from one another. However, each first bearing area 52 faces a second bearing area 54.

[0110] Arranged between the respective first and second bearing areas 52, 54 is a biasing element 56. FIG. 24 shows the two biasing elements 56 in the compressed state, i.e. in the mounted or assembled state of the instrument 10.

[0111] The second part 14 is provided with a bore 106 coaxial with the pivot axis 60 and provided with inner threads 108.

[0112] Two connecting elements 46 in the form of connecting screws 98 are provided for connecting the first and second parts 12, 14 to one another. In an alternative embodiment, a rivet is provided for connecting the first and second parts 12, 14 to one another so as to form a so-called riveted boxlock with biasing elements 56.

[0113] The first part 12 comprises two bridges 128 delimiting the through opening 124 on both sides. Each bridge 128 is provided with a bore 92, which broadens away from the male connection portion 126 for receiving a screw head 100 of a connecting screw 98.

[0114] An unthreaded shaft portion 96 extends through the bore 92. A threaded shaft portion 102 extending between the shaft portion 96 and a free end 104 of the connecting screw 98 is provided with outer threads corresponding to the inner threads 108 of bore 106. This allows for screwing the connecting screws 98 into inner threads 108 of bore 106 with their respected shaft portion 102.

[0115] The described configuration of the connecting device 58 allows for individually compressing both biasing elements 56 between the respective first and second bearing areas 52, 54.

[0116] The medical instruments 10 described in connection with FIGS. 1 to 7 on the one hand and in connection with FIGS. 23 and 24 on the other hand can be provided with any of the above-described biasing elements 56 in the form of spring washers 64. Any of the described embodiments of wave washers 68 is suited to be placed between the first and second bearing area 52, 54 of the described instruments 10.

[0117] The described spring washers have a preferred thickness 74 in the range of about 0.05 mm to about 0.2 mm. As the instruments 10 have to be cleanable and sterilizable, the spring washers 64 are preferably made from stainless spring steel.

[0118] The biasing elements 65 described above can optionally be coated or provided with a hardened surface by an appropriate treatment, for example by diffusion hardening or blasting for obtaining an additional hardness to improve dry running properties of the biasing element 56.

[0119] As described above, the gaps defined by the wave troughs 70 and the wave crests 72 are closed or almost closed in the course of the assembly of the instrument 10 due to the compression of the biasing element so that the influence on the cleanability of the instrument 10 is rather limited.

[0120] Further, for avoiding increased friction between the first and second parts 12, 14 on the one hand and the biasing element 56 on the other hand, the biasing element 56 is preferably made from a material with an increased hardness or a reduced hardness compared to the material from which the first and second parts 12, 14 are made, so that there is a difference between the respective hardness of the first and second parts 12, 14 on the one hand and the biasing element 56 on the other hand.

[0121] The embodiments of the medical instruments 10 described above have, in particular, the advantageous property of maintaining a perceptible motion force, which is regarded as pleasant by surgeons, over their entire lifetime. Readjusting such instruments 10 is generally not necessary as the biasing element 56 maintains the motion force as desired even if the medical instrument 10 is subject to wear in the region of the connecting device 58.

[0122] Further, if the instrument 10 is damaged and requires repair and/or service, the biasing element 56 can easily be exchanged and the running surfaces do not require reworking, e.g. milling, grinding or polishing.

REFERENCE NUMERALS

[0123] 10 medical instrument [0124] 12 first part [0125] 14 second part [0126] 16 first distal end [0127] 18 first proximal end [0128] 20 first tool element [0129] 22 first holding element [0130] 24 second distal end [0131] 26 second proximal end [0132] 28 second tool element [0133] 30 second holding element [0134] 32 medical tool [0135] 34 clamping jaw [0136] 36 clamping jaw [0137] 38 clamp [0138] 40 ring [0139] 42 ring [0140] 44 connecting region [0141] 46 connecting element [0142] 48 arm [0143] 50 arm [0144] 52 first bearing area [0145] 54 second bearing area [0146] 56 biasing element [0147] 58 connecting device [0148] 60 pivot axis [0149] 62 longitudinal axis [0150] 64 spring washer [0151] 66 central opening [0152] 68 wave washer [0153] 70 wave trough [0154] 72 wave crest [0155] 74 thickness [0156] 76 first surface [0157] 78 second surface [0158] 80 first contact plane [0159] 82 second contact plane [0160] 84 cutting line [0161] 86 point of inflection [0162] 88 point of inflection [0163] 90 clockwise direction [0164] 92 bore [0165] 94 region [0166] 96 shaft portion [0167] 98 connecting screw [0168] 100 screw head [0169] 102 shaft portion [0170] 104 end [0171] 106 bore [0172] 108 inner threads [0173] 110 first distance [0174] 112 second distance [0175] 114 applied connecting device [0176] 116 radial direction [0177] 118 needle holder [0178] 120 box-type connecting device [0179] 122 female connecting portion [0180] 124 through opening [0181] 126 male connecting portion [0182] 128 bridge