U.S. patent application number 14/691452 was filed with the patent office on 2015-11-12 for bone anchoring device.
The applicant listed for this patent is Biedermann Technologies GmbH & Co. KG. Invention is credited to Lutz Biedermann, Jurgen Harms, Wilfried Matthis.
Application Number | 20150320467 14/691452 |
Document ID | / |
Family ID | 35426950 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150320467 |
Kind Code |
A1 |
Matthis; Wilfried ; et
al. |
November 12, 2015 |
BONE ANCHORING DEVICE
Abstract
A bone anchoring device has an anchoring element, a receiving
portion, and a pressure element. The anchoring element includes a
shank to be anchored in a bone or a vertebra and a head, the head
having an exterior surface with a spherical segment-shaped portion.
The shank and the head are separate parts. The receiving portion
includes a first end, a second end opposite to the first end, a
longitudinal axis passing through the two ends, a bore coaxial with
the longitudinal axis, and a first region adjacent to the second
end for receiving a spherical segment-shaped section of the head.
The pressure element exerts pressure on the head to lock the head
in the receiving portion. The head has a hollow inner portion to
receive a free end portion of the shank and wherein the head and
the end portion are formed such that the end portion can be
elastically clamped by the head.
Inventors: |
Matthis; Wilfried;
(Weisweil, DE) ; Biedermann; Lutz; (VS-Villingen,
DE) ; Harms; Jurgen; (Karlsruhe, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Biedermann Technologies GmbH & Co. KG |
Donaueschingen |
|
DE |
|
|
Family ID: |
35426950 |
Appl. No.: |
14/691452 |
Filed: |
April 20, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14059196 |
Oct 21, 2013 |
9034021 |
|
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14691452 |
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13252007 |
Oct 3, 2011 |
8591558 |
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14059196 |
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|
12556515 |
Sep 9, 2009 |
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13252007 |
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11482395 |
Jul 7, 2006 |
8034089 |
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12556515 |
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60697670 |
Jul 8, 2005 |
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Current U.S.
Class: |
606/306 ;
606/86A |
Current CPC
Class: |
A61B 17/8605 20130101;
A61B 17/8875 20130101; A61B 17/8685 20130101; A61B 17/7032
20130101; A61B 17/7037 20130101; A61B 17/7085 20130101; A61B
17/7076 20130101; A61B 17/861 20130101; A61B 17/7067 20130101 |
International
Class: |
A61B 17/86 20060101
A61B017/86; A61B 17/70 20060101 A61B017/70 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 2005 |
EP |
05014840.2 |
Claims
1. A bone anchoring device comprising: an anchoring element
comprising a shank to be anchored in a bone or a vertebra and a
head, the head having an exterior surface with a spherical
segment-shaped portion, wherein said shank and said head are
separate parts; a receiving portion comprising a first end, a
second end opposite to the first end, a longitudinal axis passing
through the two ends, a bore coaxial with the longitudinal axis,
and a first region adjacent to the second end for receiving the
spherical segment-shaped section of said head; and a pressure
element which exerts pressure on said head to lock said head in the
receiving portion, the pressure element being of cylindrical
construction and having a spherical recess on a side facing the
head, which cooperates with the head when pressure is exerted;
wherein said head has a hollow inner portion to receive a free end
portion of said shank, wherein said head and said end portion are
formed such that the end portion is elastically clamped by said
head while the head and end portion are located in the receiving
portion and the head and the receiving portion are unlocked to each
other, and wherein said end portion is conically shaped, the
diameter increasing towards a free end of the shank opposite a
second end of the shank.
2. The bone anchoring device of claim 1, wherein the hollow inner
portion has a mating shape corresponding to the conically shaped
end portion
3. The bone anchoring device of claim 1, wherein said conical shape
is a truncated cone.
4. The bone anchoring device of claim 1, wherein a cone angle of
the conically shaped end portion is selected such that a
self-locking occurs between the head and the end portion.
5. The bone anchoring device of claim 4, wherein said angle is
between about 2 and 10 degrees.
6. The bone anchoring device according to claim 1, wherein the head
comprises a spring-like edge facing towards the end portion of the
shank.
7. The bone anchoring device of claim 1, wherein the head comprises
one or more slits which are directed substantially parallel to the
rotational axis of the head and are open on a side facing the end
portion of the shank.
8. The bone anchoring device of claim 1, wherein the hollow inner
portion of the head which receives the end portion of the shank
forms an abutment for the free end of the end portion.
9. The bone anchoring device of claim 1, wherein the hollow inner
portion is shaped as a hollow truncated cone and extends from one
end of the head to an opposite end.
10. The bone anchoring device of claim 1, wherein said receiving
portion has a U-shaped recess extending from the first end in the
direction of the second end which forms a channel to receive a
rod.
11. A tool for use with an anchoring element the anchoring element
comprising a shank to be anchored in a bone or a vertebra and a
head, the head having an exterior surface with a spherical
segment-shaped portion, wherein said shank and said head are
separate parts; and a receiving portion comprising a first end, a
second end opposite to the first end, a longitudinal axis passing
through the two ends, a bore coaxial with the longitudinal axis,
and a first region adjacent to the second end for receiving the
spherical segment-shaped section of said head; the tool comprising
a longitudinal member, a first arm extending from the longitudinal
member, the first arm having a fixed position on the longitudinal
member, and a second arm extending from the longitudinal member,
the second arm being positionable relative to the first arm in a
longitudinal direction of the longitudinal member.
12. The tool of claim 11, wherein said second arm is slidingly
mounted on said longitudinal member.
13. The tool of claim 11, wherein said second arm or said first arm
is fork-shaped.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/059,196, filed Oct. 21, 2013, which is a continuation of
U.S. application Ser. No. 13/252,007, filed Oct. 3, 2011, now U.S.
Pat. No. 8,591,558, which is a continuation of U.S. application
Ser. No. 12/556,515, filed Sep. 9, 2009, which is a continuation of
U.S. application Ser. No. 11/482,395, filed Jul. 7, 2006, now U.S.
Pat. No. 8,034,089, which claims the benefit of U.S. Provisional
Application No. 60/697,670, filed Jul. 8, 2005, and claims priority
from European Patent Application No. EP 05 014 840.2, filed Jul. 8,
2005, the disclosures of which are incorporated by reference
herein.
BACKGROUND
[0002] The present disclosure relates to a bone anchoring device
comprising an anchoring element which has a shank to be anchored in
a bone and a head having an exterior surface with a spherical
segment-shaped portion, a receiving portion to receive said head
and an element which exerts pressure on said head, wherein said
shank and said head are separate parts.
[0003] A bone anchoring device of this type is known from U.S. Pat.
No. 6,835,196 B2. The shank of the anchoring element has a
cylindrical end portion which is received in a corresponding bore
in the head which has a spring-yielding edge to clamp said end
portion of the shank when pressure is exerted on the head. In
another embodiment the end portion of the shank has an outer thread
which cooperates with an inner thread of the bore in the head
receiving said end portion. With this bone anchoring device it is
possible to first screw in the shank, adjusting the length of the
shank, if necessary, and then connecting it with the receiving
portion containing the head.
[0004] U.S. Pat. No. 6,074,391 discloses a bone anchoring device
comprising a bone screw having a threaded shank with a spherical
section forming a free end of the shank. The bone anchoring device
further comprises a receiving part having on the inner side a
conically shaped annular surface converging downwardly. A slotted
cage provided in the receiving part encompasses the spherical
section and has an outer conically shaped surface which cooperates
with the conical surface of the receiver part. The slots in the
cage allow for the spherical section of the shank being clamped
when pressure is exerted onto said cage.
[0005] WO 94/00066 discloses an osteosynthetic fixation device
consisting of a securing component having a conical head section
and an adjoining anchoring component designed for fixing in the
bone and a spherical segment-shaped slotted clamping component with
a conical bore to receive the conical head section to clamp inside
a connecting component having a spherical segment-shaped bore. The
clamping component has an outer surface with a spherical
segment-shaped portion. The fixation of the securing component
inside the connecting component is achieved by pulling the conical
head section into the clamping component such that the clamping
component is spread to press against the spherical segment-shaped
bore of the connecting component.
[0006] U.S. Pat. No. 6,063,090 discloses a device for the
connection of a rod with a pedicle screw which allows to first
screw a screw element with a spherical head into the bone and
thereafter to click a retainer head to be connected with the rod
onto the spherical head. To fix the angular position of the screw
element relative to the retainer head the spherical head is clamped
by a conical spring chuck.
SUMMARY
[0007] A bone anchoring device according to one or more embodiments
of the present disclosure includes a head and a shank as separate
parts which facilitates pre-assembling of the device and which
additionally provides an enhanced fixation when final tightening of
the screw to the rod occurs.
[0008] The bone anchoring element according to one or more
embodiments of the present invention has the advantage that it
allows to combine shanks of different size with the separate head
and receiving portion according to the needs in a specific
situation during or before surgery.
[0009] With the bone anchoring element according to one or more
embodiments of the present invention it is possible to first anchor
the shank into the bone and thereafter to mount the receiving
portion including the spherical segment-shaped head onto the shank.
Due to the conical shape of the end portion of the shank and the
cooperating recess of the head a pre-fixation of the head relative
to the shank is achieved even if the head is not yet locked in its
final polyaxial position.
[0010] If the cone angle of the end portion of the shank and the
recess of the head is in a certain range of about 2 degrees to 10
degrees it is possible to achieve a self-locking connection between
the spherical segment-shaped head and the shank which ensures that
the head cannot fall off or cannot be separated from the shank
unintentionally.
[0011] The bone anchoring device further has the advantage that in
one or more embodiments of the present invention it is compact as
an outer ring or nut is not required.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Further features and advantages of the invention will become
apparent from the description of embodiment in conjunction with the
accompanying figures.
[0013] FIG. 1 shows a cross-sectional view of the bone anchoring
device according to one embodiment of the invention.
[0014] FIG. 2 shows an exploded view of the bone anchoring device
according to FIG. 1.
[0015] FIG. 3 shows a perspective view of the head of the bone
anchoring element which is part of the bone anchoring device
according to FIG. 1.
[0016] FIG. 4 shows a schematic sectional view of the head and the
end portion of the shank of the bone anchoring element of FIGS. 1
to 3.
[0017] FIGS. 5a to 5c show modifications of the shank of the
anchoring element.
[0018] FIG. 6 shows a schematic sectional view of a modification of
the head connected to the shank.
[0019] FIG. 7 shows a schematic side view of a tool to be used with
the head of FIG. 6.
[0020] FIGS. 8a to 8d show schematically steps of in situ removal
of the head and receiving portion according to FIGS. 1 to 4
together with a tool.
[0021] FIG. 9 shows a bottom view of the tool used for the steps
according to FIGS. 8a to 8d.
DETAILED DESCRIPTION
[0022] As shown in FIGS. 1 to 3, the bone anchoring device
comprises a receiving portion 1 which is substantially cylindrical
and has a first end 2 and a second end 3 opposite to the first end.
The two ends are perpendicular to a longitudinal axis 4. Coaxially
with the longitudinal axis 4, a coaxial bore 5 is provided which
extends from the first end 2 to a predetermined distance from the
second end 3. At the second end 3 an opening 6 is provided the
diameter of which is smaller than the diameter of the bore 5. The
coaxial bore 5 tapers towards the opening 6. In the embodiment
shown it tapers in the form of a spherically shaped section 7.
[0023] The receiving portion 1 further has an U-shaped recess 8
which starts from the first end 2 and extends in the direction of
the second end 3 to a predetermined distance from said second end
3. By means of the U-shaped recess two free legs 9, 10 are formed
ending towards the first end 2. Adjacent to the first end 2 the
receiving portion 1 comprises an internal thread 11 at said legs 9,
10.
[0024] The bone anchoring element 13 comprises a shank 14 with a
bone thread and a head 15 which is formed as a separate part and
which is connected to the shank in the assembled state shown in
FIG. 1. The head 15 has a spherical segment-shaped outer surface
portion 16. The radius of this portion of the head 15 is such that
when the head 15 is received in the receiving portion 1, the
spherical outer surface 16 of the head 15 is supported by the
spherical section 7 adjacent to the opening 6 at the second end 3
or is supported by the edge of the opening 6 such that a portion
15a of the head 15 projects from the opening 6. If pressure is not
yet exerted on the head 15, the head 15 is pivotably held in the
spherical region 7 similar to a ball and socket joint.
[0025] A pressure element 17 is provided which has a cylindrical
construction with an outer diameter which is only slightly smaller
than the inner diameter of the bore 5 to allow the pressure element
to be introduced into the bore 5 of the receiving portion 1 and to
be moved in the axial direction. On its lower side facing towards
the second end 3, the pressure element 17 comprises a spherical
recess 18, the radius of which corresponds to the radius of the
spherical portion 16 of the head 15. On the opposite side the
pressure element 17 has a U-shaped recess 19 which extends
transversely to the longitudinal axis 4. The lateral diameter of
this U-shaped recess is selected such that a rod 20 which is to be
received in the receiving portion can be inserted in the recess 19
and guided laterally therein. The depth of the spherical recess 19
is selected such that in an assembled state when the rod is
inserted and pressed against the bottom of the U-shaped recess, the
pressure element 17 exerts a pressure on the head 15.
[0026] The bone anchoring device further comprises an inner screw
21 which can be screwed in between the legs 9, 10 to fix the rod 20
and to exert a pressure via the pressure element 17 on the head 15.
The internal thread 11 and the cooperation thread of the inner
screw 21 can have any known thread shape. A flat thread or a
negative angle thread, however, brings about the advantage that a
splaying of the legs 9, 10 does not occur which makes it
unnecessary to use an outer nut or ring to prevent the splaying of
the legs 9, 10.
[0027] Details of the shank 14 and the head 15 will now be
described. The shank 14 comprises an end portion 22 to be received
in the head 15. The end portion 22 has the shape of a truncated
cone widening towards the free end 23 which has a diameter ds. The
cone angle .alpha. of the conical end portion 22 of the shank is
preferably selected such that a self-locking connection can be
achieved when the shank is connected to the head. As can be seen in
particular in FIGS. 2 and 3, the head 15 has the contour of a
flattened sphere and comprises at its end facing towards the first
end 2 a bore 24 which is coaxial with the longitudinal axis 4 of
the receiving portion and has a diameter slightly larger than the
largest diameter ds of the free end 23 of the conical end portion
22. The bore 24 allows for guiding through the free end 23 of the
conical end portion 22 such that the conical, end portion 22
projects from the head 15 when it is fully inserted, as shown in
FIG. 1. On its side directed towards the second end 3 of the
receiving portion, the head 15 has a recess 25 shaped as a hollow
truncated cone, the dimensions of which are such as to mate with
the dimensions of the conical end portion 22 of the shank when the
shank is inserted into the head 15. The angle .alpha.' of the
conical recess 25 preferably corresponds to the angle .alpha. of
the end portion 22 or is larger than the angle .alpha.. The lower
opening 26 formed by the recess 25 has a diameter db which is
smaller than the largest diameter ds of the free end 23 of the
conical end portion 22 of the shank.
[0028] As shown in FIGS. 2 and 3, the head 15 has a plurality of
longitudinal slits 27 which extend from an outer surface of the
head 15 to the recess 25. The slits 27 extend to the end facing the
end portion 22 of the shank and are arranged equidistantly in a
circumferential direction. The slits 27, are of sufficient size to
allow a spreading of the recess 25 to an extent that the lower
opening 26 widens to allow insertion of the conical end portion 22
and to elastically clamp the end portion after insertion 22.
[0029] As shown in FIG. 4, the free end 23 of the conical end
portion 22 can have a chamfer 28 for facilitating the insertion
into the head 15. The chamfer 28 can be curved so as to mate with
the curvature of the recess 18 of the pressure element 17 (see FIG.
2). The conically shaped recess 25 can also extend throughout the
head 15.
[0030] Preferably, the cone angle .alpha.' of the recess 25 of the
head 15 corresponds to the cone angle .alpha. of the end portion 22
and is selected to achieve a self-locking connection when the
conical end portion 22 is inserted into the recess 25 of the head.
Once a self-locking connection is established, an additional force
is required to remove the conical end portion out of the recess 25
which is greater than the force necessary to insert the conical end
portion into the recess 25. The cone angle to achieve a
self-locking effect is preferably between approximately 2 degrees
to 10 degrees, more preferably about 4 degrees.
[0031] In a first mode of operation, a suitable shank 14 is
selected and connected with its end portion 22 to the head 15. The
introduction of the conical end portion 22 into the head 15 through
the lower opening 26 is facilitated by the chamfer 28. By inserting
the end portion 22, the lower opening 26 is widened and the conical
recess 25 is spread due to the slits 27 so as to allow for the
introduction of the whole conical end portion 22. If the angle
.alpha. is selected such that a self-locking connection is
established when the shank is introduced into the head, the head
cannot fall off or be removed unintentionally once the shank is
inserted into the head.
[0032] With reference to FIGS. 1 and 2, the bone anchoring element
13 consisting of the shank 14 with the mounted head 15 is
introduced into the receiving portion 1 from the first end 2 with
the threaded shank 14 being guided through the opening 6 of the
receiving portion until the head 15 rests against the edge of the
opening 6. Thereafter, the pressure element 17 is introduced and
the threaded shank screwed into the bone. Then, the angular
position of the receiving portion 1 relative to the anchoring
element 13 is adjusted and the rod 20 is inserted. The rod is then
fixed by screwing in the inner screw 21. The inner screw 21 exerts
a pressure onto the rod 20 which presses down the pressure element
17. The pressure element 17 forms an abutment for the free end 23
of the end portion 22 of the shank (see FIG. 4). In this manner,
the head 15 is pressed against the spherical region 7 or the edge
of the opening 6. Consequently, the edge of the opening 6
compresses the head 15, which narrows the recess 25 due to the
slits 27, and which causes the head 15 to clamp the end portion 22
of the shank. In addition, the pressure element 17 presses onto the
free end 23 of the end portion 22 and thus presses the conically
shaped end portion 22 into the conical recess 25 of the head
whereby a firm connection between the head and the shank is
achieved and simultaneously the head is locked in its rotational
position.
[0033] The parts of the bone anchoring device described above are
preferably made of a body-compatible material, such as, for
example, titanium.
[0034] In a second mode of operation, first the threaded shank 14
is screwed into the bone or into a vertebra. For this purpose the
shank 14 has at its free end known engagement possibilities for a
screwdriver, such as a hexagon-shaped recess 30, as shown in FIG.
1. Then the receiving portion 1 together with the loosely
preassembled head 15 and pressure element 17 is pressed onto the
conical end portion 22 of the shank 14 projecting out of the bone.
To accomplish this a certain pressure force is necessary to click
the head 15 onto the conical end portion, i.e. the head 15 is
spread due to the slits 27 and snaps onto the conical end portion
22. The pressing force required to place the head onto the shank
depends on the cone angle and/or the elasticity provided by the
slits. In this state the head is still pivotable in the receiving
portion while the shank is clamped by the head. Next, the rod 20 is
inserted and the angular position of the receiving portion 1
relative to the head 15 is adjusted. Thereafter, the inner screw 21
is screwed in between the legs 9, 10 until it presses on the rod
20, which thereby exerts pressure on the head 15.
[0035] Due to the pressure exerted by the pressure element on the
head 15, the slotted head 15 is firmly connected or clamped to the
shank 14, preventing movement and, at the same time, the head 15 is
locked in its rotational position.
[0036] If necessary, the receiving portion 1 together with the head
15 can be separated from the shank in situ with a tool as shown in
FIGS. 8a to 8d and 9. First, the inner screw 21 and the rod 20 are
removed as shown in FIG. 8a. In this state, the head 15 is unlocked
in the receiving portion 1 but it still clamps the end portion 22
of the shank. Next, as shown in FIG. 8b, a tool 100 is used to push
the head 15 into the receiving portion 1 so that it no longer
projects from the lower opening 6 of the receiving portion.
[0037] The tool 100 comprises a longitudinal bar 101 from which two
arms 102, 103 extend in a perpendicular direction. One of the arms
is fixed at a certain distance from a free end 104 of the bar 101
such that a section 105 of the bar projects above the arm 103 to
facilitate gripping. In the embodiment shown it is the upper aim
103 when the tool is in use. The other arm 102 is slidingly mounted
on the longitudinal bar 101 and can be variably fixed between an
end position at the other end 106 and a desired position in a
direction towards the upper arm 103 so as to vary the distance
between the arms. At least the lower arm 102 is fork shaped so as
to be able to encompass the shank 14. The distance between the arms
when the lower arm 102 is located at the end 106 of the bar is
greater than the height of the receiving portion 1.
[0038] In use, the tool is applied to the receiving portion with
the lower arm 102 at its end position as shown in FIG. 8b. Then,
the lower arm 102 is shifted and pressed against the second end 3
of the receiving portion 1, thus shifting the receiving portion 1
relative to the head 15 until the head 15 is completely within the
receiving portion, as shown in FIG. 8c. In this state the head has
space to widen so that the end portion 22 of the shank can be
pulled out when pulling the tool together with the receiving
portion and the head away from the shank as shown in FIG. 8d.
[0039] Modifications are possible. For example, the upper arm 103
can be slidable instead of the lower arm. The slidable arm need not
be fixed at the bar but can be pressed manually against the
receiving portion.
[0040] The dimensions of the end portion 22, the head 15 and the
receiving portion 1 are selected such that the force which is
required overcome the frictional force of the self-locking
connection between the end portion 22 and the head 15 is tolerable
during surgery.
[0041] FIGS. 5a to 5c show modifications of the shank 14. In FIG.
5a the diameter d of the shank 14 is smaller than the smallest
diameter of the conical portion 22. In FIG. 5b the diameter d of
the shank 14 is larger than the smallest diameter of the conical
end portion 22. In FIG. 5c the shank comprises a threaded section
140 adjacent to the tip 141 and a section 142 without a bone
thread. In all modifications the conical end portion 22 is shaped
so as to be receivable in the recess 25 of the head 15.
[0042] FIG. 6 shows a schematic view of a modification of the head.
The head 15' has the recess 25 shaped as a truncated cone as in the
embodiment shown in FIGS. 1 to 4. However the coaxial bore 24' has
a diameter which is smaller than the diameter of the end 23 of the
conical end portion of the shank. Thus, the upper wall of the
recess 25 forms a ring-shaped abutment 28 for the end portion 22.
The diameter of the bore 24' is sufficiently large to provide
access to the end portion 22 for a screwing-in tool. To allow for
an in situ separation of the head 15' together with the receiving
portion 1 from the shank 14, the head has engagement means for
engagement with a tool which holds the head so that it cannot be
drawn against the opening 6 when the receiving portion 1 is pulled
away from the shank. FIG. 7 shows an example of a tool 30 which
consists of a handle 31 and a bar 32 extending from the handle and
having a threaded end portion 33, sometimes called a threaded tip.
In this case the bore 24' comprises an inner thread for engagement
with the threaded end portion 33. In use, after removal of the
inner screw 21 and the rod 20 (see FIG. 1), and thus relieving the
pressure on the head 15', the head is held with the tool 30 by
screwing in the threaded end portion 33 into the threaded bore 24'
and simultaneously the receiving portion is manually pulled away
from the shank. According to this manner, the end portion 22 of the
shank is drawn out of the head 15.
[0043] The invention is not limited to the embodiments described
above. Further modifications are conceivable. For example, the
invention is not limited to an anchoring element having a threaded
shank, but can also be applied to an anchoring element consisting
of a hook. In this case, the free end of the hook has the conical
end portion 22.
[0044] Furthermore, the shape and diameter of the shank 14 can be
varied and the length of the bone thread can be varied, too. For
example, the modification of FIG. 5c where a shank has a
thread-free section can also be applied to the shank shown in FIG.
5a or 5b.
[0045] The cone angle of the conical end portion 22 and the recess
25 of the shape of a hollow truncated cone can be selected such
that there is no self-locking effect. In this case, the number and
the shape of the slits 27 in the head 15 have to be selected such
that it is possible to snap the head 15 onto the conical end
portion 22.
[0046] Instead of several slits in the head 15, it is possible to
have only one continuing slit, which extends in a longitudinal
direction through the whole wall from one end to the other end of
the head. It is also possible to have the continuing slit in
addition to the slits shown in FIG. 3. Additional slits may be
provided which are open towards the end opposite to the lower
opening 26. Further, it is also possible that the recess 25 shaped
as a hollow truncated cone extends through a whole head 15, thus,
omitting the bore 24 or 24'.
[0047] In a further modification, the head is formed of a material
providing elasticity, for example, of a suitable plastic material.
In this case, the slits may be omitted.
[0048] The receiving portion can be modified, too. The radius of
the spherical portion 7 can be larger than the radius of the head,
as long as the opening 6 is small enough that the head 15 cannot
fall out. Instead of the spherical section 7 a section with another
shape, for example a conical shape is possible.
[0049] Furthermore, the pressure element 17 may have a different
shape. The length of the pressure element in a longitudinal
direction can be as large that the legs being generated by the
U-shaped recess 19 project above the rod when the rod is inserted.
In this case it is possible to separately fix the head 15 via the
pressure element with an inner nut to be screwed in between the
legs 9, 10 and separately fix the rod by an inner screw to be
screwed into the nut.
[0050] The receiving portion can be part of a bone plate. In this
case, the receiving portion does not have a U-shaped recess and
pressure onto the head 15 can be generated by, for example, an
inner screw solely.
[0051] Various other modifications to these embodiments will be
readily apparent to those skilled in the art, and the generic
principles defined herein may be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
the present invention is not intended to be limited to the
embodiments shown herein but is to be accorded the widest scope
consistent with the principles and novel features disclosed
herein.
* * * * *