U.S. patent application number 13/356431 was filed with the patent office on 2012-09-20 for anchoring element for use in spine or bone surgery, methods for use and production thereof.
Invention is credited to Lutz Biedermann, Jurgen Harms.
Application Number | 20120239091 13/356431 |
Document ID | / |
Family ID | 32731147 |
Filed Date | 2012-09-20 |
United States Patent
Application |
20120239091 |
Kind Code |
A1 |
Biedermann; Lutz ; et
al. |
September 20, 2012 |
ANCHORING ELEMENT FOR USE IN SPINE OR BONE SURGERY, METHODS FOR USE
AND PRODUCTION THEREOF
Abstract
A shaft for anchoring in a vertebra or bone section is connected
to a receiving part which serves to connect to a rod having a
pre-determined diameter (D). The receiving part provides a U-shaped
recess, forming a channel for the reception of the rod, and two
legs. The legs are free on their ends and have a thread that
cooperates with a securing element to fix the rod in the receiving
part. When inserted into the receiving part, the rod surface facing
an end surface is at a pre-determined distance (A) in an axial
direction from the end surface. The thread of the legs extends from
the end surface a distance that is smaller than or equal to the
pre-determined distance (A). Also, an undercut is provided adjacent
to the thread whose edge farthest away from the thread is located
at a distance (B) from the end surface.
Inventors: |
Biedermann; Lutz;
(VS-Villingen, DE) ; Harms; Jurgen; (Karlsruhe,
DE) |
Family ID: |
32731147 |
Appl. No.: |
13/356431 |
Filed: |
January 23, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10799143 |
Mar 11, 2004 |
8123784 |
|
|
13356431 |
|
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Current U.S.
Class: |
606/278 ; 470/8;
606/279; 606/308 |
Current CPC
Class: |
A61B 17/7037 20130101;
A61B 17/56 20130101; A61B 17/7032 20130101 |
Class at
Publication: |
606/278 ;
606/308; 606/279; 470/8 |
International
Class: |
A61B 17/86 20060101
A61B017/86; B21H 3/02 20060101 B21H003/02; A61B 17/88 20060101
A61B017/88 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2003 |
DE |
103 10 540.9 |
Claims
1. An anchoring element for use in spinal or bone surgery; said
anchoring element comprising: a shaft for anchoring in a vertebra
or bone section; a receiving part, which is connected to the shaft,
is structured and arranged to connect to a rod having a
pre-determined diameter (D) and an outer surface, the receiving
part having a longitudinal axis and comprising a U-shaped recess
forming a channel for the reception of the red and two legs having
free ends, the legs comprising a first thread, the legs further
providing an exterior end surface of the receiving part; and a
securing element comprising a second thread that engages and
cooperates with the first thread; whereby a first distance between
the exterior end surface ur the receiving part and a closest
portion of the outer surface of the rod in an axial direction is a
pre-determined distance (A); the first thread extends front the
exterior end surface of the receiving part to a second distance
that is smaller than or equal to the pre-determined distance (A);
and the receiving part further comprising an undercut adjacent to
the first thread, the undercut having an edge farthest away from
the first thread, the edge being located at a third distance (B)
from the exterior end surface, the distance (B) being larger than
the pre-determined distance (A).
2. The anchoring element according to claim 1, wherein the undercut
has a depth that corresponds at least to the depth of the
thread.
3. The anchoring element according to claim 1, wherein the first
thread comprises a first internal thread and the securing element
comprises a screw member having a first external thread that
cooperates with the first internal thread.
4. The anchoring element according to claim 1, wherein the first
thread is a find external thread and the securing element comprises
a screw nut leaving a first internal thread that cooperates with
the first external thread.
5. The anchoring element according to claim 1, wherein the
receiving part comprises a first internal thread and the anchoring
element comprises a first securing member comprising a screw member
having a first external thread that cooperates with the first
internal thread; and wherein the receiving part further comprises a
second external thread and the anchoring element further comprises
a screw nut having a second internal thread that cooperates with
the second external thread.
6. The anchoring element according to claim 1, wherein the first
and second threads each are a thread selected from a metric thread,
a buttress thread, a flat thread or a thread with a negative
load-bearing angle.
7. The anchoring element according to claim 1, wherein the
connection between the shaft and the receiving part is structured
and arranged to be a monoaxial Connection.
8. The anchoring element according to claim 1, wherein the shaft
and the receiving part are an integral part.
9. The anchoring element according to Claim I, wherein the
connection between the shaft and the receiving part is structured
and arranged to be polyaxial.
10. An anchoring element for use in spinal or bone surgery; said
anchoring element comprising: a screw member comprising a spherical
segment-shaped head and a shaft with a bone thread; a receiving
part comprising a longitudinal axis, a first bore in axially
symmetrical alignment therewith and having a first diameter of
sufficient size to permit the bone thread of the shaft to pass
through but not to permit the head to pass through, and a second
bore coaxial with the first bore and having a second diameter of
sufficient size to permit the head to pass through, the receiving
part further comprising a U-shaped recess forming a channel for the
reception of a rod and two legs having free ends, the legs
comprising a first thread, the legs further providing an exterior
end surface of the receiving part, the rod having a pre-determined
diameter (D) and an outer surface; a cylindrical pressure element
having an outer diameter of a size capable of being inserted into
the receiving part. having first side shaped to engage the head of
the screw element and a second side opposite the first side shaped
to receive a rod inserted into the V-shaped recess; and a securing
element comprising a second thread that engages and cooperates with
the first thread; whereby a first distance between the exterior end
surface of the receiving part and a closest portion of the outer
surface of the rod in an axial direction is a pre-determined
distance (A); the first thread extends from the exterior end
surface of the receiving part to a second distance that is smaller
than or equal to the pre-determined distance (A); and the receiving
part further comprising en undercut adjacent to the first thread,
the undercut having an edge farthest away from the first thread,
the edge being located at a thud distance (B) from the exterior end
surface, the distance (B) being larger than the pre-determined
distance (A).
11. The anchoring element according to claim 10, wherein the
undercut has a depth that corresponds at least to the depth of the
thread.
12. The anchoring element according to claim 10, wherein the first
thread comprises a first internal thread and the securing element
comprises a screw member having a fuel external thread that
cooperates with the first internal thread.
13. The anchoring element according to claim 10, wherein the first
thread is a first external thread and the securing element
comprises a screw nut having a first internal thread that
cooperates with the first external thread.
14. The anchoring element according to claim 10, wherein the
receiving part comprises a first internal thread and the anchoring
element comprises a first securing member comprising a screw member
having a Brat external thread that cooperates with the first
internal thread; and wherein the receiving part further comprises a
second external thread and the anchoring element further comprises
a screw nut having a second internal thread that cooperates with
the second external thread.
15. The anchoring element according to claim 10, wherein the first
and (second threads each are a thread selected from a metric
thread, a buttress thread, a flat thread or a thread with a
negative load-bearing angle.
16. A method for the manufacture of an anchoring element comprising
a shaft for anchoring in a vertebra or bone section and a receiving
part, the method comprising providing an undercut in the surface of
the receiving element prior to cutting a thread on the surface from
an end of the receiving element to the undercut.
17. A method for performing spinal or bone surgery, the method
comprising: providing a bone anchoring element comprising: a shaft
for anchoring in a vertebra or bone section; a receiving part,
which is connected to the shaft, is structured and arranged to
connect to a rod having a pre-determined diameter (D) and an outer
surface, the receiving part having a longitudinal axis and
comprising a U-shaped recess forming a channel for the reception of
the rod and two legs having free ends, the legs comprising a first
thread, the legs further providing an exterior end surface of the
receiving part; and a securing element comprising a second thread
that engages and cooperates with the first thread; whereby a first
distance between the exterior end surface of the receiving part and
a closest portion of the outer surface of the rod in an axial
direction is a pre-determined distance (A); the first thread
extends from the exterior end surface of the receiving part to a
second distance that is smaller than or equal to the pre-determined
distance (A); and the receiving part further comprising an undercut
adjacent to the first thread, the undercut having an edge farthest
away from the first thread, the edge being located at a third
distance (B) from the exterior end surface, the distance (B) being
larger than the pre-determined distance (A); screwing the shaft
into a vertebra or bone section; positioning a rod into the
U-shaped recess; and fixing the rod in the bone anchoring element
with the securing element.
18. The method according to claim 17, further comprising screwing a
shaft of a plurality of bone anchoring elements into various sites
of a vertebra or bone section, positioning the rod into the
plurality of anchoring elements, and fixing the rod in the
plurality of bone anchoring elements.
19. A method for performing spinal, or bone surgery, the method
comprising: providing a bone anchoring element comprising: a screw
member comprising a spherical segment-shaped head and a shaft with
a bone thread; a receiving part comprising a longitudinal axis, a.
first bore in axially symmetrical alignment therewith and having a
first diameter of sufficient size to permit the bone thread of the
shaft to pass through but not to permit the heed to pass through,
and a second bore coaxial with the first bore and having a second
diameter of sufficient size to permit the head to pass through, the
receiving part further comprising a U-shaped recess forming a
channel for the reception of a. rod and two legs having free ends,
the legs comprising a first thread, the legs further providing an
exterior end surface of the receiving part, the rod having a
pre-determined diameter (D) and an outer surface; a cylindrical
pressure element having an outer diameter of a size capable of
being inserted into the receiving part, having a first aide shaped
to engage the head of the screw element and a second side opposite
the first side shaped to receive a rod inserted into the U-shaped
recess; and a securing element comprising a second thread that
engages and cooperates with the first thread; whereby a first
distance between the exterior end surface of the receiving part and
a closest portion of the outer surface of the rod in an axial
direction is a pre-determined distance (A); the first thread
extends from the exterior end surface of the receiving part to a
second distance that is smaller than or equal to the pre-determined
distance (A); and the receiving part further comprising an undercut
adjacent to the first thread, the undercut having an edge farthest
away front the first thread, the edge being located at a third
distance (B) from the exterior end surface, the distance (B) being
larger than the pre-determined distance (A); screwing the screw
member of a pre-assembled receiving part, screw member and
cylindrical pressure element into a vertebra or bone section;
positioning a rod into the U shaped recess; adjusting the angular
orientation of the receiving part relative to the screw member; and
fixing the rod in the bone anchoring element with the securing
element.
20. The method according to chain 19, further comprising screwing a
screw member of a. plurality of bone anchoring elements into
various sites of a vertebra or bone section, positioning the rod
into the plurality of anchoring elements, adjusting the angular
orientation of the receiving part. relative to the screw member in
each of the plurality of bone anchoring members and fixing the rod
in the plurality of bone anchoring elements.
21. An anchoring element for use in spinal or bone surgery; said
anchoring element comprising: a shaft for anchoring in a vertebra
or bone section; a receiving part winch is connected to the shaft,
is structured in the range to connect to a rod having a
pre-determined diameter (D) and an outer surface, the receiving
part having a longitudinal axis and comprising a U-shaped recess
forming a channel for the reception of the rod and two legs having
free ends, the legs comprising a first thread, the legs further
providing an exterior end surface of the receiving part; and a
securing element comprising a second thread that engages and
cooperates with the first thread; whereby a first distance between
the exterior end surface of the receiving part and a closest
portion of the outer surface of the rod in an axial direction is a
pre-determined distance (A); the first thread extends from the
vicinity of the exterior end surface of the receiving part to a
second distance that is smaller than or equal to the pre-determined
distance (A); and the receiving part further comprising an undercut
adjacent to the first thread, the undercut having an edge farthest
away from the first thread, the edge being located at the third
distance (B) from the exterior end surface, the distance (B) being
larger than the pre-determined distance (A).
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of allowed U.S. patent
application Ser. No. 10/799,143, filed Mar. 11, 2004, which claims
the priority of German Patent Application No. 103 10 540.9, filed
Mar. 11, 2003 the disclosures of which are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an anchoring element for
use in spinal or bone surgery and to methods for the manufacture
and use thereof. The anchoring element typically has (i) a shaft
for anchoring in a vertebra or bone section, (ii) an essentially
cylindrical receiving part which is connected to the shaft and
serves to connect to a rod of a pre-determined diameter (D), and
(iii) a securing element comprising a thread. The receiving part
comprises an U-shaped recess with a channel for the reception of
the rod and forming two legs which are free on their ends. The legs
comprise a thread for cooperating with the securing element.
BACKGROUND OF THE INVENTION
[0003] An anchoring element in the form of a monoaxial bone screw
is described in U.S. Pat. No. 5,005,562 and in the form of a
polyaxial bone screw is described in DE 43 07 576 C1. Typically
such anchoring elements comprise a receiving part for the reception
of a rod connecting several anchoring elements of this type, a bone
anchoring screw element that is monoaxially or polyaxially
connected to the receiving part, and an internal screw that is to
be screwed in between the legs of the receiving part and serves for
the fixation of the rod. The receiving part according to DE 43 07
576 C1 further comprises an external screw nut that can be screwed
onto the receiving part for additional fixation.
[0004] In such anchoring elements, the internal thread or external
thread of the receiving part has incorporated a thread runout.
Further, the distance between the rod support within the receiving
part and the thread runout is smaller than the diameter of the rod
to be received. This ensures that the internal screw or the
external screw nut can exert a sufficient clamping force on the
rod.
[0005] For a given rod diameter, the length of the free legs of the
receiving part and, thus, the overall height of the anchoring
element from the rod support generally is determined by the
distance over which the internal and/or external thread is provided
to ensure reliable fixation. In the area of the thread runout,
which may include more than one thread tooth, the depth of the
thread diminishes and the profile of the thread tooth is poorly
defined. In order to provide for sufficiently firm attachment of
the internal screw or external screw nut, it must be ensured that a
sufficient number of turns of thread with a deep profile are
present. Therefore, it is necessary either to place the thread
runout sufficiently far down in the direction of the rod support or
a corresponding number of turns of thread with a deep profile must
be provided upwards in the direction of the free end of the legs
which increases the overall height.
[0006] Moreover, the manufacture of the thread with a thread runout
is resource-consuming from the point of view of manufacturing
technology.
[0007] Thus, it is desirable to have an improved anchoring element
of the type described above which is easy to manufacture and has a
reduced overall height, but provides the same degree of safety
against the rod becoming loose as is provided by the conventional
anchoring elements.
SUMMARY OF THE INVENTION
[0008] The present invention provides an anchoring element along
with a method for manufacturing the same. In accord with the
present invention, an anchoring element for use with a rod having a
pre-determined diameter (D) in spinal or bone surgery comprises a
shaft for anchoring in a vertebra or bone section, a receiving part
with a longitudinal axis which is connected to the shaft and serves
to connect to the rod, the receiving part comprising a U-shaped
recess forming a channel for the reception of the rod and two legs
each having a free end, the two legs further having a first thread,
and a securing element comprising a second thread that cooperates
with the first thread, wherein the legs have a length such that,
when the rod is inserted in the recess, a surface of the rod facing
the free end is at a pre-determined distance (A) from the free ends
in an axial direction, wherein the first thread, when viewed from
the free end of a leg, extends from the free end to a distance that
is smaller than or equal to the pre-determined distance (A), the
receiving part further comprising an undercut adjacent to the first
thread having an edge farthest away from the first thread at a
distance (B) from the free end, the distance (B) being larger than
the pre-determined distance (A).
[0009] Preferably, the anchoring element is manufactured such that
the undercut is provided in the receiving part before the first
thread is provided therein.
[0010] In certain embodiments of the invention, the depth of the
undercut corresponds to the depth of the thread.
[0011] In various embodiments of the invention the first thread is
an internal thread and the securing element is implemented as an
internal screw. Alternatively, the first thread can be an external
thread and the securing element can be implemented as a screw nut.
The first thread can take any known form, for example, it can be
implemented as a metric thread, buttress thread, flat thread or as
a thread with a negative load-bearing angle.
[0012] In certain embodiments of the invention, the connection
between the shaft and the receiving part is implemented to be
monoaxial. In other embodiments, the connection between the shaft
and the receiving part is implemented to be polyaxial.
[0013] The new anchoring element described herein is advantageous
in that it is cheaper to manufacture, because the cutting of the
thread in the receiver part in accordance with the present
invention is less resource-consuming from the point of view of
manufacturing technology. Moreover, the height of the receiving
part of the anchoring element of the invention is reduced from
conventional receiving parts having the poorly defined runout
thread teeth.
[0014] The invention also provides a method for performing spinal
or bone surgery, the method comprising providing a bone anchoring
element as described above, screwing the shaft into a vertebra or
bone section, positioning a rod into the U-shaped recess and fixing
the rod in the bone anchoring element with the securing element.
Preferably, a plurality of bone anchoring elements are positioned
into various sites of a vertebra or bone section, and the rod is
fixed into the plurality of anchoring elements. When a polyaxial
bone anchoring element is used, the method also includes adjusting
the angular orientation of the receiving part relative to the screw
member.
[0015] Additional features and characteristics of the present
invention are evident from the description of embodiments in view
of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows a side view partially in section of the upper
portion of one embodiment of an anchoring element in accord with
the present invention;
[0017] FIG. 2 shows a side view partially in section of the upper
portion of a second embodiment of an anchoring element in accord
with the present invention; and
[0018] FIG. 3 shows a side view partially in section of a third
embodiment of an anchoring element in accord with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] A monoaxial bone screw is illustrated in FIG. 1 as a first
embodiment of a bone anchoring element in accord with the present
invention. The bone screw comprises a shaft 1 with a bone thread
section and an essentially cylindrical receiving part 2 which is
rigidly connected to the shaft and serves to receive a rod 100 of a
given diameter D which connects the bone screw to additional bone
screws. For this purpose, the receiving part 2 comprises a recess 3
forming a channel having a U-shaped cross section. The recess is
dimensioned just large enough for rod 100 to be inserted and held
by the channel formed by the base 4 of the recess and its side
walls. The U-shaped recess 3 forms two legs 5, 6 which extend from
the base 4 forming the side walls and having free ends that form
the upper end 7 of the receiving part. When the rod is inserted
into the channel and abuts on base 4 of the U-shaped recess, the
topmost surface of the rod is at a pre-determined distance A from
the upper end 7 of the receiving part.
[0020] An internal thread 8 extends from the upper end 7 along legs
5, 6 over a distance, which is equal to the pre-determined distance
A, as illustrated in FIG. 1. In the embodiment shown, the internal
thread is provided as a metric thread. On the inner surface of the
legs 5, 6 adjacent to the internal thread is a recess or an
undercut 9 which extends in a circumferential direction. The lower
edge 10 of the undercut 9 farthest away from the thread 8 is
located at a distance B from upper end 7. The distance B is larger
than the pre-determined distance A. Thus, the lower edge 10 of the
undercut 9 is located at a distance from base 4 of the recess that
is smaller than the rod diameter D. In the embodiment shown, the
upper edge 11 of the undercut closest to the upper end 7 resides at
the level of the rod topmost surface and, thus, is located at a
distance A from the free end. It is preferred that the depth of the
undercut at least be equal to the depth of thread 8. The
cross-section of undercut 9 is formed to be essentially
rectangular.
[0021] A securing element in the form of an internal screw 12 with
an outer thread engaging and cooperating with the internal thread
is provided for the fixation of the rod in the receiving part.
[0022] In operation, the bone screw is screwed into the bone first
followed by the insertion of the rod. Subsequently, the internal
screw 11 is screwed in until its bottom side facing the rod presses
onto the rod and fixes the rod in its position. The manufacture of
the bone screw preferably proceeds such that the undercut 9 in the
receiving part is produced in a first step of the procedure and the
thread 8 is produced in a second step of the procedure. The
manufacturing process for making this anchoring element involves a
smaller number of turns of thread as compared to the conventional
anchoring elements with thread runout. In contrast, these fewer
turns of thread possess a well-defined profile and, thus, high
load-bearing capacity. Consequently, the entire thread 8 can be
shifted downwards in the direction of base 4 by the length of the
weak runout thread teeth present in conventional anchoring elements
with thread runout. As a result, the overall height of the
receiving part is reduced as compared to the conventional anchoring
elements. Moreover, the manufacture is cheaper, because the cutting
of the thread is less work-intensive due to elimination of the
thread runout.
[0023] Alternatively, the internal thread 8 extends from the upper
end 7 over a distance that is smaller than the pre-determined
distance A, such that the upper edge 11 of the undercut 9 is
located above the rod topmost surface when viewed in direction to
the upper end 7, when the rod 100 is positioned in the recess 3.
Modifications of the geometry of the undercut 9 can be made by
those skilled in the art without departing from the spirit of the
invention. For example, the undercut 9 can be formed to have
rounded corners or the upper and lower edge of the undercut can be
beveled.
[0024] The thread also can be provided in alternative forms. For
example, the internal thread can be provided in the form of a
buttress thread or saw teeth thread and, particularly, in the form
of a buttress thread with a horizontal load-bearing flank, or in
the form of a flat thread with two horizontal flanks, or in the
form of a thread with a negative load-bearing flank angle rather
than in the form of a metric thread. In any case, the internal
screw 12 comprises a corresponding external thread for cooperation
with the internal thread 8. Further, the threads can be provided in
the form of right-hand or left-hand threads.
[0025] In the embodiment shown in FIG. 2, an additional external
thread 13 is provided on the legs 5, 6. Preferably, the external
thread 13 extends to a pre-determined distance from the upper end 7
at least equal to distance A of the rod topmost surface, as shown.
Also, preferably, undercut 14 is provided adjacent to the external
thread 13, with the lower edge 15 of said undercut, closest to base
4, located at a distance B' from the upper end 7, wherein B' is
larger than the pre-determined distance A. Preferably, the depth of
the undercut at least is equal to the depth of the external thread.
In this embodiment. an additional securing element is provided in
the form of an external screw nut 16 which comprises an internal
thread that engages and cooperates with the external thread 13.
[0026] The operation of this embodiment is similar to that of the
first embodiment except for the additional step, in which the
external screw nut is screwed on as an additional securing
element.
[0027] Compared to the first embodiment, the manufacture of the
anchoring element of this embodiment includes the additional steps
of forming the external undercut 14 and the external thread 13. As
in the previously described procedure for the internal undercut and
thread, preferably, the undercut is provided first and the external
thread, subsequently.
[0028] Alternatively, the distance for which the internal thread 8
is provided on legs 5, 6 can differ from the distance for which the
external thread 13 is provided. It is very important for making
anchoring elements that properly incorporate the teachings of this
invention that neither the internal thread nor the external thread
extend from the upper end 7 further than to the level of the rod
topmost surface and that the lower edge of the undercut 9 or 13 is
positioned always below the rod topmost surface. However, other
dimensions such as, for example, the heights (i.e., length along
the longitudinal axis) and depths of the undercuts may vary.
[0029] In a further embodiment of the invention, the receiving part
of the anchoring element has no internal thread or adjacent
internal undercut and an internal screw is not used as the securing
element. Instead, in this embodiment, there is only an external
thread and an adjacent external undercut provided. The rod is
secured using an external cap and a pressure element, which may be
part of or separate from the cap.
[0030] As an alternative to the embodiment illustrated in FIG. 2,
an undercut can be provided adjacent to only one of the two
threads, i.e., either the internal thread or the external
thread.
[0031] It should be understood that all modifications described
herein are applicable to the embodiment of the invention having
suitable structure for the modification.
[0032] An embodiment illustrating the use of a polyaxial bone screw
for an anchoring element in accord with the present invention is
illustrated in FIG. 3. The polyaxial bone anchoring element
comprises a screw element having a shaft 20 with a bone thread and
a spherical segment-shaped head 21, which is connected to a
receiving part 22. On one of its ends, receiving part 22 is
provided with a first bore 23 in an axially symmetrical alignment,
whose diameter is larger than that of the thread section of thread
shaft 20 and smaller than that of head 21. Moreover, receiving part
22 is provided with a coaxial second bore 24 which is open on its
end opposite from the first bore 23 and whose diameter is
sufficiently large for the thread shaft of the screw element to be
guided through the first bore 23 and for the head 21 to be guided
through to the base of the first bore 23. A small coaxial section
25 is provided between the first bore and the second bore, said
small coaxial section 25 being adjacent to the first bore 23 and
being of spherical shape to receive and cooperate with the
spherical segment-shaped head 21 of the screw element.
[0033] Receiving part 22 further comprises a U-shaped recess 26
which is arranged symmetrically with regard to the longitudinal
axis of the receiving part and serves for the insertion of the rod
100. The base of the recess 26 is directed towards the first bore
23 and the recess forms two free legs 27, 28, whose ends form the
upper end 29 of the receiving part.
[0034] An internal thread 30 and, preferably, an external thread 31
are provided on legs 27, 28 adjacent to the upper end 29 with the
threads extending over a pre-determined distance from upper end 29.
Moreover, adjacent to the internal thread 30 and to the external
thread 31 there are provided undercuts 33, 34 on the side of the
thread facing away from the upper end 29.
[0035] A cylindrical pressure element 35 is provided whose outer
diameter is selected such that the pressure element can be inserted
in the receiving part from the upper end 29 positioned within bore
24 adjacent the head 21. The end of the pressure element facing
head 21 comprises a spherical segment-shaped recess 36 which widens
towards that end and whose spherical radius is selected to
cooperate with head 21 such that the pressure element surrounds
head 21 from above when it is inserted in the receiving part and
can fix the head 21 to achieve a desired angular position of the
shaft 20 relative to the longitudinal axis of the receiving part.
The opposite end of the pressure element comprises a U-shaped
recess 37 whose dimensions are such that the rod 100 can be
inserted and is held therein. When the pressure element 35 is
inserted into the receiving part 22, the U-shaped recess 37 of
pressure element 35 forms a channel having a base in which the rod
is supported. In the embodiment shown, the side walls of the
U-shaped recess 37 of the pressure element do not protrude beyond
the inserted rod. Moreover, the pressure element has a central bore
38 through which a screwing tool can be inserted to allow the screw
element to be screwed in. Thus, the screw element can be
pre-assembled with the receiving part 22 and pressure element 35
loosely holding the screw element therein.
[0036] An internal screw pressure member is provided for the
fixation of both the head in its angular position and the rod in
the recess 37. Turning the internal screw pressure element into the
recess 37 until it exerts pressure on the topmost surface of the
rod fixes the rod and transmits pressure through the rod to
pressure element 35 to fix the orientation of head 21. Preferably,
an external screw nut also is provided for additional fixation.
[0037] In the assembled state of the anchoring element with the rod
inserted and pressure element 35 pressing on the head 21, the
topmost surface of the rod resides at a distance A from upper end
29 of the receiving part. In the embodiment shown, the internal
thread 30 and the external thread 31 are dimensioned such that they
extend from the upper end 29 to a distance that is smaller than
distance A. The lower edge of the undercuts 33, 34 closest to the
base of the U-shaped recess 37 of pressure element 35 are located
at a distance B from upper end 29 that is larger than distance A
between the rod topmost surface and the upper end.
[0038] In operation, the screw element is inserted in the receiving
part in known fashion, then, the internal pressure screw member is
inserted and the screw is screwed into the bone. Thus, the screw
element and receiving part can be conveniently pre-assembled prior
to screwing the bone screw element into the bone. Subsequently, the
rod is inserted, the angular arrangement of the receiving part with
respect to the screw element is adjusted, and the rod is positioned
and, then, the angular arrangement and the rod are fixed by
screwing in the internal pressure screw member. Finally, the
external screw nut is applied in known fashion.
[0039] The manufacture of this anchoring element, with regard to
the cutting of the threads and undercuts of the receiving part, is
identical to the procedure of the embodiments described
previously.
[0040] As stated above, the internal thread and external thread can
differ and vary in length and/or the undercuts can differ and vary
in depth and height. Again, all modifications or alternatives
described previously are equally applicable to this polyaxial
embodiment.
[0041] The manufacture of the anchoring element of this embodiment
proceeds such that the undercuts 33, 34 in the receiving part are
produced first and the corresponding threads 30, 31 are produced in
a subsequent step of the procedure. As with the monoaxial
embodiments, the manufacturing process for making this anchoring
element involves a smaller number of turns of thread as compared to
the conventional anchoring elements with thread runout. In
contrast, these fewer turns of thread possess a well-defined
profile and, thus, high load-bearing capacity. Consequently, the
overall height of the receiving part is reduced as compared to the
conventional anchoring elements. Moreover, the manufacture is
cheaper, because the cutting of the thread is less work-intensive
due to elimination of the thread runout.
[0042] The invention has been described in detail including the
preferred embodiments thereof However, it will be appreciated that
those skilled in the art, upon consideration of the description and
drawings, may make modifications and improvements within the spirit
and scope of the invention.
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