U.S. patent application number 13/612321 was filed with the patent office on 2013-03-14 for instrument for assembling a bone anchoring device.
This patent application is currently assigned to Biedermann Technologies GmbH & Co. KG. The applicant listed for this patent is Lutz Biedermann, Jurgen Harms, Wilfried Matthis. Invention is credited to Lutz Biedermann, Jurgen Harms, Wilfried Matthis.
Application Number | 20130065698 13/612321 |
Document ID | / |
Family ID | 39629058 |
Filed Date | 2013-03-14 |
United States Patent
Application |
20130065698 |
Kind Code |
A1 |
Biedermann; Lutz ; et
al. |
March 14, 2013 |
INSTRUMENT FOR ASSEMBLING A BONE ANCHORING DEVICE
Abstract
An instrument for assembling a bone anchoring device includes a
shank with a shaft section to be anchored in a bone and a
engagement end, a head being separate from the shank and having a
through bore, and a receiving part having a first end, a second end
and a longitudinal bore extending from the first to the second end,
the head being positionable within the bore at the second end. The
instrument includes a holding portion arranged to hold a pin, which
has a rod section with a length and a diameter suited to fit and
extend at least through the bore of the head, and which has a free
end portion extending from the rod section such as to project from
the bore of the head when the pin is inserted, and configured to
engage with the engagement end of the shank.
Inventors: |
Biedermann; Lutz;
(VS-Villingen, DE) ; Matthis; Wilfried; (Weisweil,
DE) ; Harms; Jurgen; (Karlsruhe, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Biedermann; Lutz
Matthis; Wilfried
Harms; Jurgen |
VS-Villingen
Weisweil
Karlsruhe |
|
DE
DE
DE |
|
|
Assignee: |
Biedermann Technologies GmbH &
Co. KG
|
Family ID: |
39629058 |
Appl. No.: |
13/612321 |
Filed: |
September 12, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12424436 |
Apr 15, 2009 |
8303602 |
|
|
13612321 |
|
|
|
|
61047062 |
Apr 22, 2008 |
|
|
|
Current U.S.
Class: |
470/58 |
Current CPC
Class: |
A61B 17/7076 20130101;
B21K 23/00 20130101; A61B 17/864 20130101; A61B 17/7037
20130101 |
Class at
Publication: |
470/58 |
International
Class: |
B21K 23/00 20060101
B21K023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2008 |
EP |
EP 08007795.1 |
Claims
1. An instrument for assembling a bone anchoring device including a
shank having a longitudinal axis with a shaft section to be
anchored in a bone and a engagement end, a head being separate from
the shank and having a through bore, and a receiving part having a
first end, a second end defining a longitudinal axis and a
longitudinal bore extending from the first to the second end, the
head being positionable within the longitudinal bore at the second
end, the instrument comprising: a holding portion and a pin, the
holding portion configured to hold the pin; the pin comprising: a
rod section having a length and a diameter configured to fit and
extend at least through the bore of the head when the pin is
inserted therein; and a free end portion extending from the rod
section such as to project from the bore of the head, and
configured to engage with the engagement end of the shank and
project past the engagement end of the shank to align the
longitudinal axis of the receiving part with the longitudinal axis
of the shank.
2. The instrument according to claim 1, further comprising: a
spring force device; wherein the pin further comprises: a support
section configured to slideably move with respect the holding
portion along a longitudinal axis of the pin against a resilient
force of the spring force device.
3. An instrument according to claim 2, wherein the spring force
device is a helical spring configured to exert the resilient force
between the holding portion and the pin when the pin engages with
the shank.
4. An instrument according to claim 1, wherein the free end portion
of the pin includes an extended rod section coaxial with the rod
section along the longitudinal axis of the pin, wherein the
extended rod section has a diameter smaller than the diameter of
the rod section.
5. An instrument according to claim 4, wherein the pin comprises a
transition portion between the rod section and the extended rod
section, the transition portion including at least one of a conical
and tapered profile configured to at least one of widen a diameter
of an elastic projection provided in the bore of the head and to
abut on an end face of the engagement end.
6. An instrument according to claim 4, wherein the free end section
further comprises a tip having rounded or tapered profile to
facilitate insertion of the pin.
7. An instrument according to claim 1, wherein the holding portion
includes an outer thread arranged to be screwed into an inner
thread near the first end of the receiving part of the bone
anchoring device for fixing and securing a rod inserted into the
device with a fixation element.
8. An instrument according to claim 2, wherein the holding portion
includes a support bore arranged in the longitudinal direction,
wherein the support bore holds the support section of the pin, and
wherein the support bore is provided with a length such as to
enable a sliding movement of the support section of the pin between
an outer rest position and an inner compressed position.
9-19. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of allowed U.S. patent
application Ser. No. 12/424,436, filed Apr. 15, 2009 which claims
the benefit of U.S. Provisional Patent Application Ser. No.
61/047,062, filed Apr. 22, 2008, the contents of which are hereby
incorporated by reference in their entirety, and claims priority
from European Patent Application EP 08007795.1, filed Apr. 22,
2008, the contents of which are hereby incorporated by reference in
their entirety.
BACKGROUND
[0002] The present application relates to an instrument for
assembling a bone anchoring device, which includes a shank, a head
being separate from the shank, and a receiving part having a first
end, a second end and a longitudinal bore extending from the first
to the second end, the head being positionable within the
longitudinal bore at the second end.
[0003] Such a bone anchoring device is described, for example, in
U.S. Pat. No. 6,835,196 B2, by the same applicant. The device is
arranged to connect a screw with a rod. The shank of the screw and
the head are formed as separate parts. The head is shaped as a
spherical segment thus being adapted to be pivotably held in the
receiving part for allowing a multiaxial arrangement of the device.
On example disclosed relates to the shank which has a cylindrical
shape while the separate head is provided with one or more slits
and further with a cylindrical bore into which the cylindrical end
portion of the shank can be inserted.
[0004] Another example of a bone anchoring device having a screw
with a shank and a spherically segmented head, which is separate
from the head, is disclosed in EP 1741396 A1, by the same
applicant. The shank has a threaded section and an engagement end,
which is of conical shape, wherein the diameter increases towards
the free end. Similarly, the head has a bore which is of conical
shape, wherein the respective cone angles may be the same.
[0005] The head according to EP'396 is also provided with one or
more slits to enable an elastic widening of the diameter at the
bottom opening of the bore, when the engagement end is inserted,
whose end diameter is slightly larger than former diameter of the
head. The widening is facilitated by a chamfer arranged at the
edges of the engagement end. As a result of this configuration, the
head may be clicked onto shank upon assembly wherein the conical
shape allows for enhanced stability, once the head is clamped.
[0006] Another example of a bone anchoring device having a screw
with a separate shank and head is disclosed in European Patent
Application no. 06 024 232 not yet published. The spherically
segmented head has a cylindrical shape similar to the example
disclosed in US'196 described above. However, for example, a ring
opened by a slit is provided as an elastic projection positioned
within a circumferential groove inside the bore of the head. The
engagement end of the shank is also of cylindrical in shape and has
substantially the same diameter as the bore of the head to be
insertable therein. The engagement end has a corresponding
circumferential groove that may receive the projection, which may
thus snap into the groove upon insertion of the engagement end into
the cylindrical bore of the head.
[0007] The separate provision of the shank and the head with
respect to the screw makes it possible to assemble sets of bone
anchoring devices, in which one head may be combined with shanks of
various sizes, structure and material properties. This may reduce
the costs of a set since the heads will generally have to satisfy
strong requirements with regard to accuracy, stress and tension
characteristics, selection of material, etc., while the shanks may
be produced according to the specific needs in large number with
slightly less accuracy. This becomes particularly valid in cases,
where spherically segmented heads are used, which provide for
multi- or polyaxial arrangements of bone anchoring devices.
[0008] Further, simple screwing-in of the bone screw into the bone
may be accomplished followed by easily clicking the preassembled
receiving part including the head onto the engagement end.
[0009] It has been observed, however, that the assembly of bone
anchoring devices as described above may eventually become somewhat
circumstantial, just when multi- or polyaxial arrangements are
involved. For example, the bore of the head positioned inside the
bottom opening of the receiving part may pivot in any direction
away from the engagement end of the shank which can render the
assembly as a difficult procedure.
[0010] Based on the foregoing, there is a need to improve and
facilitate the assembly of bone anchoring devices, in particular
where bone screws are provided which have separate shanks and
heads.
SUMMARY
[0011] The instrument according to the disclosure provides for a
holding portion and pin. The pin is structured to have a rod
section and a free end portion which is adjacent to the rod
section. The rod section and free end portion can be inserted into
a bore of a head which can be preassembled within the longitudinal
bore of a receiving part of a bone anchoring device. Consequently,
the rod section extends through the bore of the head such that the
free end portion may project from the bore of the head and from an
opening of the receiving part. In this case, the bore of the head
is aligned with a longitudinal direction of the pin.
[0012] This configuration, i.e., the instrument holding the
receiving part, can be applied to a shank. According to one aspect,
the holding portion has an external thread that may engage an
internal thread of the receiving part, commonly used for
screwing-in a fixation element, in order to hold the receiving
part.
[0013] The free end portion of the pin engages with the engagement
end of the shank. The receiving part including the head and pin is
preassembled. The pin thereby--according to one specific
embodiment--sits on a spring and is therefore able to move along
the longitudinal axis. The pin's free end portion helps to easily
engage with an engagement end (comprising for example a bore) of
the shank. After contacting the, e.g., planar face of the shank
with the pin, a small compressive force applied to the instrument
and the receiving part results in an axial movement of the pin. In
one embodiment, the pin is supported in the holding portion of the
instrument by a spring force means. When increasing the force a
final end-position is achieved, in which the engagement end of the
shank is locked to the head. This allows to disengage and remove
the instrument.
[0014] The rod section of the pin serves to align the bore of the
head with the longitudinal axis of the shank and, according to one
embodiment, further widens an elastic projection, for example an
elastic ring, in or at the bore of the head, which provides for the
click mechanism designed to protect the shank from falling out. The
projection may be, e.g., an elastic ring as in EP'232, or a slotted
segment of the head providing a conical shape as in EP'396.
[0015] According to the specific embodiment detailed below, due to
the retracting movement of the pin, the engagement end of the shank
may slide into the head without a necessity to repeatedly widen the
projection. Hence the force necessary to apply the preassembled
receiving part to the shank may be considerably reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows an exploded view of a system having an
instrument and a bone anchoring device according to an embodiment
of the invention.
[0017] FIGS. 2A-B show a side view (FIG. 2A) and a sectional
profile (FIG. 2B) of the embodiment shown in FIG. 1 in a state,
where the receiving part is held by the instrument, but the shank
is yet unloaded.
[0018] FIGS. 3A-B show the same as in FIGS. 2A-B, respectively, but
in a state, where the shank is clicked to the receiving part.
[0019] FIG. 4 shows a total side view of the system with the bone
anchoring device being held by the instrument according to the
embodiment shown in FIG. 1.
[0020] FIGS. 5A-D illustrates the steps of loading the shank to the
receiving part according to the invention according to an
embodiment of the method.
[0021] FIGS. 6A-D illustrate the steps of inserting the pin into
the receiving part and the bore of the head according to the
embodiment.
[0022] FIG. 7 shows a modification of the head 3 according to
another embodiment.
DETAILED DESCRIPTION
[0023] One embodiment of the instrument 12 and bone anchoring
device 11 according to the invention is illustrated in the exploded
view shown in FIG. 1. The bone anchoring device includes a shank 2,
a head 3 separate from the shank 2, a partly opened ring 7, a
pressure element 5 and a receiving part 4. Not illustrated in FIG.
1 are a rod and a fixation element (screw), which elements are to
be applied only after the instrument 12 has been removed from the
bone anchoring device 11.
[0024] The shank 2 has a threaded portion 21 intended to be
anchored in a bone (not shown). The shank 2 further includes an
engagement end 22, which in this specific embodiment is of
substantially cylindrical shape, i.e., it has a constant outer
diameter along its entire length except a groove 24 to be described
below.
[0025] The head 3 has a substantially spherical outer surface 31,
wherein a flattened surface may be provided on a top section
thereof (not visible in the Figures). Further, a bore 32 extends
through the head opening towards the top and bottom section
thereof. The bore 32 in this specific embodiment is of cylindrical
shape, the inner diameter of which corresponds to the outer
diameter of the engagement end 22 of the shank 2. Still further, a
slit 33 extends from the inner surface of the bore 32 to the outer
spherical surface segment of the head. The slit 33 supports the
clamping the engagement end 22 when the fixation element is screwed
into the receiving part upon final fixation.
[0026] A circumferential groove 34 is also provided within the
inner surface of the bore 32. The partly opened ring 7 serving as
an elastic projection is provided in the groove 34. If no force is
exerted on this ring 7, its diameter is smaller than the inner
diameter of the bore 32. However, the ring may be widened to at
least the inner diameter of the bore 32 upon exertion of a force
which is directed radially outwards.
[0027] The pressure element 5 has on its bottom side a spherically
shaped surface 51 which corresponds with the spherical outer
surface 31 of the head 3. Due to this configuration, the head 3 is
pivotable with respect to the pressure element in any direction
prior to fixation. The device 11 thus refers to a multi- or
polyaxial bone anchoring device. The pressure element 5 further has
a center bore 52.
[0028] The receiving part 4 has a first end 41 and a second end 42.
A longitudinal bore 48 extends between the first end 41 and the
second end 42. The bore 48 is coaxial with a longitudinal axis of
the receiving part 4 and may taper in a lower region towards the
second end 42. An opening 43 formed at the second end 42 thus has a
reduced diameter with respect to an upper region of the
longitudinal bore 48 in order to position and clamp the head 3
after being inserted in the receiving part 4. The tapered profile
may result in a spherically shaped surface which also corresponds
with the outer spherical surface 31 of the head 3. However, the
disclosure shall not be limited to the specific configuration of
the receiving part.
[0029] The receiving part 4 further has a U-shaped recess 45
arranged to receive a rod (not shown). As a consequence two legs
44, 45 extend towards the first end 41. At the inner surface of the
two legs 44, 45, an internal thread 47 is provided to engage with
an outer thread of the fixation element (not shown)--and notably
also with an outer thread 92 of a holding portion 9 of the
instrument 12.
[0030] The instrument 12 includes the holding portion 9, a pin 8
and a spring force device 10. For example, the spring force device
10 may be a helical spring 101. A complete view of the instrument
12 holding the bone anchoring device 11 in an assembled state is
provided in FIG. 4. The holding portion 9 includes a handle 93 that
may be gripped manually by the surgeon or any other person that
intends to assemble the device. An elongated rigid shaft 94
transfers forces exerted by the attending person to a
pin-and-receiving-part holding section 95.
[0031] Section 95 therefore includes the external thread 92 as
described above and a support bore 91 which receives and slideably
supports a support section 85 of the pin 8.
[0032] The pin 8 may generally be fabricated from stainless steel
or a biocompatible metal such as a Titanium alloy, a carbon filled
PEEK (polymer), etc., and includes the support section 85, a rod
section 81 and a free end portion 82, which herein is formed as an
extended rod section. Portions 85, 81 and 82 are in this specific
embodiment formed adjacent to each other in this order along the
same longitudinal axis of the pin 8. The extended rod section has a
tip 84 including a rounded profile. This profile serves to
facilitate insertion of the pin into the bores 52, 32 of the head 3
and bore 26 of the engagement end 22 of the shank 2. The profile
can also be otherwise tapered.
[0033] The free end portion 82, or extended rod section in this
embodiment, serves to engage with the engagement end of the shank
2.
[0034] The rod section 81 has a diameter larger than that of the
extended rod section. Between the rod section 81 and the extended
rod section there is a transition portion 83 which has a tapered
profile and which connects sections of different diameters. The
angle of the tapered profile is preferably be set to
90.degree..+-.30.degree. with respect to the longitudinal axis of
the pin. As will be described below, the transition portion 83
serves to widen the ring 7, when the pin 8 is inserted in the bore
32 of the head 3, and to abut on the end face 23 of the engagement
end 22 of the shank 2.
[0035] FIGS. 2A-B show in a side view (FIG. 2A) and a sectional
profile (FIG. 2B) a state wherein the receiving part 4 is assembled
with the head 3, the ring 7 and the pressure element 5, and wherein
the pin 8 is inserted into bores 52, 32 of the pressure element 5
and the head 3, respectively, but prior to engagement of the shank
2. The receiving part 4 is thereby held by holding portion 9 of the
instrument 12 via the external thread 92 being screwed into the
internal thread 47. The helical spring 101 abuts on a stop 86 of
the pin 8 and thus presses the pin 8 in axial direction towards the
distal direction. The other end of the spring 101 is supported on a
stop face 97 inside the support bore 91 of the holding portion
9.
[0036] It may be noted that the compression force may also be
generated by any other suitable means such as for example pneumatic
configurations provided inside the holding portion 9. Hence, the
invention shall not be limited to the specific spring configuration
described herein.
[0037] In a rest position shown in FIGS. 2A-B, the pin 8 attains
the lowered end position D1 due to the compression or resilient
force of the spring wherein the rod portion extends through the
bores 52 and 32, and the free end portion 82 projects from the
opening 43 of the receiving part 4. The rod section 81 has a
diameter that in this embodiment corresponds to the inner diameter
of the center bore 52 of the pressure element.
[0038] As a result, when in operation the instrument is first
applied to the receiving part, the pin 8 is advantageously centered
along the longitudinal central axis of the receiving part 4.
Further, the rod section 81 has a diameter that also corresponds to
the inner diameter of the bore 32 of the head 3. As a result, the
bore 32 of the head 3 is advantageously aligned along the
longitudinal central axis of the receiving part 4.
[0039] FIGS. 3A-B show the same configuration as in FIGS. 2A-B,
respectively, but, in a state wherein the shank 2 is loaded to the
receiving part 4. In this state the pin 8 is in the retracted upper
end position D2. Prior to that, the tip 84 and the free end portion
82 may enter longitudinal bore 26 of the shank 2 which opens as an
engagement portion 27 at the engagement end 22. An inner diameter
of the longitudinal bore 26 is equal to or slightly larger than
that of the free end portion, such as to ensure proper alignment of
the shank 2 with the longitudinal direction each of the pin 8 and
the receiving part 4.
[0040] Upon further insertion of the pin 8, the transition portion
83 eventually abuts on the annular shaped end face 23 of the
engagement end 22. As a result, when the attending person further
exerts a pressure force via the handle 93 to the receiving part 4
and the pin 8, the pin 8 starts a retracting movement relative to
the receiving part 4 fixed to the holding portion 9 against the
resilient or compression force of the helical spring 101. This
process is depicted in detail in FIGS. 5A-5D.
[0041] It may be noted that the engagement portion 27 of the shank
2 may simultaneously serve to engage the shank 2 with a hexagonally
shaped screwing tool in order to screw the shank 2 into the bone
prior to the steps described herein. In this case, the bore 26 has
in an upper portion at the engagement end 22 a hexagonal shape.
[0042] The distance of the positions D1 and D2 between which the
pin 8 is slideably moved is indicated in FIGS. 2 and 3. This
distance is at least as large as the length of the bore 32 in order
that the engagement end 22 of the shank 2 may enter the bore when
the pin 8 is further retracted. More specifically, the distance is
at least as large such that the groove 24 foamed in the outer
surface of the engagement end 22 may be snapped by the ring 7
arranged inside the bore 32.
[0043] In operation, assembly of the bone anchoring element 11 is
started by inserting first the spherically segmented head 3 already
including the ring 7 into the receiving part 4, followed by
inserting the pressure element 5. Next, the instrument 12 is
applied to the receiving part 4 from the side of the first end 41
thereof. Initially, the tip 84 and the free end portion 82 enter
the center bore 52 of the pressure element 5. The tip 84 then also
enters the bore 32 of the head 3, which until then may be
misaligned. It is then proceeded with the insertion movement
wherein the tip 84 starts to leave the bore 32 and opening 43,
while the transition portion 83 enters first the bore 52 and then
the bore 32. Both the pressure element 5 and the head 3 are now
aligned with respect to the longitudinal axis of the instrument 12
and the receiving part 4.
[0044] Next, the external thread portion 92 of the holding portion
9 abuts on the legs 44, 45 at the first end 41 of the receiving
part 4. The external thread 92 is then screwed into the internal
thread 47. One then arrives at the situation depicted in FIG. 2 or
5A.
[0045] Subsequently, the receiving part 4 now held by the
instrument 12 is applied to the shank 2. The application may be
performed in situ, i.e., when the shank 2 is already screwed into
the bone, or prior to surgery. However, in case of an in situ
application a particular advantage arises in that since only
moderate forces are applied, stress acting on the bone material can
be relieved using this embodiment of the invention.
[0046] The tip 84 of the free end portion 82 is thereby inserted to
the bore 26 which opens at the engagement end 22 of the shank 2.
Upon further insertion to sufficient depth an alignment of the
shank 2 with the longitudinal axis of the pin 8 is achieved (FIG.
5B).
[0047] Eventually, the transition portion 83 abuts on the end face
23 of the engagement end 22. The pin then moves into the support
bore 91 of the holding portion 9. This results in a compression
force of the helical spring 10 (FIG. 5C). Thereby, the engagement
end 22 of the shank enters the opening 43 of the receiving part 4
and the bore 32 of the head 3. Since the projecting ring 7 has been
widened by the transition portion 83, substantially no widening
force has to be exerted by the engagement end 22 when its end face
23 passes the ring 7, which stays widened until the groove 33
passes into which it then snaps. The shank is now temporarily
locked.
[0048] The external thread 92 may then be unscrewed from the
internal thread portion 47 of the receiving part 4 to remove the
instrument. Thereby the pin returns sliding outwards under the
compression force of the helical spring. Next a rod may be inserted
into the U-shaped recess 46 of the receiving part and secured by a
fixation element.
[0049] FIG. 6A-6D illustrate in detail the steps of aligning the
head 3 with longitudinal axes 401, 801 of the receiving part and
the pin, respectively, with regard to the above described
embodiment. In FIG. 6A, the pin 8 is inserted in the pre-assembled
receiving part 4. In this situation axes 401, 801 of both
components not yet aligned with each other, and the longitudinal
axis 301 of the spherical segmented head is strongly inclined to
both axes 401, 801. In FIG. 6B, the tip of the pin 8 enters the
bore 32 of the head 3. The head 3 starts to be slightly rotated due
to the engagement by the pin 8.
[0050] In FIG. 6C, the transition portion 83 and subsequently the
rod portion 81 enter the center bore of the pressure element and
thereafter also bore 32 of head 3. As a consequence, the head 3 is
centered and its longitudinal axis 301 is aligned with axes 401,
801 (FIG. 6D). In a next step shown in FIGS. 5B-5D, the
longitudinal axis 201 of the shank 2 is also aligned with axes 301,
401, 801, when the free end portion 82 enters the bore at the
engagement end 22 of the shank 2.
[0051] A specific embodiment has been described herein. It becomes
clear to the person skilled in the art that other features yielding
similar functions may be employed instead of those detailed herein.
It also becomes clear that other specific features shown herein may
be omitted, while the desired functions may still be achieved. For
example, the figures show a shank 2 having a radial bore 26, which
is connected to radial bores 25 intended to provide bone cement
into the bone in order to improve bone growth in a vicinity of the
shank. However, the present instrument achieves its functions as
well if the shank merely had a short longitudinal bore 26 having
length corresponding to that of the free end portion 82 of the pin
8, i.e., without necessitating radial bores 25.
[0052] It is noted that the through-hole as set forth in the
appended claims may be represented by a single bore 32 having a
substantially constant diameter over its entire length. The bore 32
of the embodiment described above has a diameter corresponding to
that of a section of the pin 8 and to that of the engagement end 22
of the shank 2 (bone screw). However, this limitation may not be
required according to the invention.
[0053] For example, the through-hole of the head 3 may comprise a
first bore 321 with a first diameter, into which the engagement end
22 of the shank fits, and a second bore 322 coaxial with and
adjacently extending from the first bore 321, into which the pin 8
is inserted prior to entering the second bore. The situation is
schematically depicted in FIG. 7. The engagement end 22 of the
shank according to the modification of the embodiment according to
FIG. 7 may for example abut on a stop face 323, when the elastic
ring simultaneously snaps into the groove.
[0054] Further, the engagement end 22 and the bore 32 of the head
have been described as being cylindrical, wherein a projection and
a groove provide a click mechanism. However, the invention may
similarly be embodied with the engagement end and the bore arranged
in conical shape such as in EP'396.
[0055] Further the head 3 may also comprise a slit (not shown)
which extends along the entire length in the direction of its
longitudinal axis, whereby it elastically opens the head 3 on one
side thereof, reaching from the inner surface of the through-hole
or bore(s) 32 to the outer spherically shaped surface 31 of the
head 3.
[0056] Further, the engagement portion at the engagement end of the
shank, which also serves to be engaged by a screwing-in tool, may
be of any other type than a polygonal or hexagonal bore. For
example, the engagement portion may be of a cross-slot type, etc.
Or a polygonal or hexagonal shaped bore is formed in the free end
portion of the pin while the engagement end has a corresponding
protrusion including a suitable diameter.
* * * * *