U.S. patent application number 14/635633 was filed with the patent office on 2015-08-27 for elastic element for the use in a stabilization device for bones and vertebrae and method for the manufacture of such elastic element.
This patent application is currently assigned to Biedermann Technologies GmbH & Co. KG. The applicant listed for this patent is Biedermann Technologies GmbH & Co. KG. Invention is credited to Lutz Biedermann, Jurgen Harms, Wilfried Matthis.
Application Number | 20150238232 14/635633 |
Document ID | / |
Family ID | 34935100 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150238232 |
Kind Code |
A1 |
Biedermann; Lutz ; et
al. |
August 27, 2015 |
ELASTIC ELEMENT FOR THE USE IN A STABILIZATION DEVICE FOR BONES AND
VERTEBRAE AND METHOD FOR THE MANUFACTURE OF SUCH ELASTIC
ELEMENT
Abstract
A stabilization device for bones or vertebrae comprises a
substantially cylindrical elastic element. The elastic element has
a first end and a second end opposite to the first end. An elastic
section extends between the first end and the second end. The
elastic section includes at least first and second helical coils.
The first and second helical coils are arranged coaxially so that
the first helical coil extends at least in a portion between the
second helical coil. The elastic element may form, for example, a
portion of a rod, bone anchoring element, or plate.
Inventors: |
Biedermann; Lutz;
(VS-Villingen, DE) ; Harms; Jurgen; (Karlsruhe,
DE) ; Matthis; Wilfried; (Weisweil, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Biedermann Technologies GmbH & Co. KG |
Donaueschingen |
|
DE |
|
|
Assignee: |
Biedermann Technologies GmbH &
Co. KG
|
Family ID: |
34935100 |
Appl. No.: |
14/635633 |
Filed: |
March 2, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13856987 |
Apr 4, 2013 |
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14635633 |
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12882392 |
Sep 15, 2010 |
8449574 |
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13856987 |
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11102247 |
Apr 8, 2005 |
7833256 |
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12882392 |
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60563241 |
Apr 16, 2004 |
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Current U.S.
Class: |
606/257 |
Current CPC
Class: |
A61B 17/7002 20130101;
A61B 17/866 20130101; A61B 2017/00862 20130101; Y10T 409/303752
20150115; B23P 13/02 20130101; A61B 17/7037 20130101; A61B 17/7004
20130101; Y10T 29/49995 20150115; F16F 1/04 20130101; A61B
2017/00526 20130101; F16F 1/043 20130101; B23H 7/02 20130101; A61B
17/8625 20130101; A61B 17/7032 20130101; B23C 3/32 20130101; A61B
17/7062 20130101; A61B 17/7059 20130101; A61F 2/4455 20130101; A61B
17/7028 20130101 |
International
Class: |
A61B 17/70 20060101
A61B017/70 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2004 |
DE |
102004018621.9 |
Claims
1-25. (canceled)
26. A bone anchoring element for bones or vertebrae, comprising: a
shaft with a free end; a receiving portion opposite to the free end
along a longitudinal axis of the shaft, the receiving portion
having a U-shaped recess opening in a direction away from the free
end of the shaft and forming two legs for accommodation of a rod
therebetween; and a locking element configured to secure to the
receiving portion to lock the rod in the U-shaped recess; wherein a
first section of the shaft has a first end and a second end spaced
apart along the longitudinal axis, the first section being
cylindrical and having an exterior surface that is entirely
threadless from the first end to the second end and an interior
surface defining a coaxial bore extending from the first end of the
first section to a portion of the shaft between the second end of
the first section and the free end of the shaft; and wherein the
first section of the shaft further defines at least two recesses
each extending through a wall of the first section and forming an
opening on the exterior surface of the first section, wherein the
exterior surface of the first section completely separates the
respective openings of the at least two recesses from one another
along an entire length of the cylindrical section from the first
end to the second end.
27. The bone anchoring element of claim 26, wherein the shaft
further comprises a second section having an exterior surface that
is threaded.
28. The bone anchoring element of claim 26, wherein the first
section of the shaft comprises first and second helical coil
segments arranged coaxially around the coaxial bore and separated
from one another in a circumferential direction by the at least two
recesses.
29. The bone anchoring element of claim 28, wherein the first and
second helical coils are substantially identical to one
another.
30. The bone anchoring element of claim 28, wherein each of the
first and second helical coils extends along an entire length of
the cylindrical section from the first end to the second end.
31. The bone anchoring element of claim 28, wherein the first
helical coil is rotated approximately 180 degrees with respect to
the second helical coil.
32. The bone anchoring element of claim 28, wherein the first and
second helical coils each has a pitch, and wherein the pitches of
the first and second helical coils are identical.
33. The bone anchoring element of claim 26, wherein the first
section of the shaft is elastic.
34. The bone anchoring element of claim 26, wherein the bone
anchoring element comprises a bio-compatible material.
35. The bone anchoring element of claim 26, wherein at least one of
the first end and the second end of the first section of the shaft
is provided with internal threads.
36. The bone anchoring element of claim 26, wherein at least one of
the first end and the second end of the first section of the shaft
is provided with a cylindrical projection having an external
thread.
37. The bone anchoring element of claim 26, wherein the each of the
recesses extends in a radial direction relative to the longitudinal
axis through the wall of the first section of the shaft.
38. The bone anchoring element of claim 26, wherein the shaft and
the head are monoaxially connected.
39. The bone anchoring element of claim 26, wherein the shaft has a
spherical segment-shaped head at an end of the shaft opposite the
free end, and wherein the receiving portion is a separate part
which is provided with a seat for pivotably holding the head.
40. The bone anchoring element of claim 39, further comprising a
pressure element configured to lock the head against the seat.
41. The bone anchoring element of claim 26, wherein the coaxial
bore extends partially through the shaft and ends at the portion of
the shaft between the second end of the first section and the free
end of the shaft.
Description
REFERENCE TO EARLIER FILED APPLICATIONS
[0001] The present invention claims the benefit of the filing date
under 35 U.S.C. .sctn.119(e) of U.S. Provisional Patent Application
Ser. No. 60/563,241, filed Apr. 16, 2004, which is hereby
incorporated by reference. The present application also claims
foreign priority benefits pursuant to 35 U.S.C. .sctn.119(a-d) for
German Patent Application Number 10 2004 018 621.9, filed Apr. 16,
2004 in Germany.
BACKGROUND
[0002] The present invention relates to an elastic element for use
in a bone anchoring element, a connecting element, a rod, and a
stabilization device and a method for manufacturing the same.
[0003] It is known to use fixation and stabilization devices to fix
fractures and stabilize spinal columns. These fixation and
stabilization devices commonly comprise at least two bone anchoring
elements or bone screws. Each of the bone anchoring elements is
anchored in a bone or vertebra and is connected by a rigid plate or
a rod. These types of fixation and stabilization devices generally
do not allow any movement of the bones or vertebrae relative to
each other.
[0004] In some instances, however, it is desirable to stabilize the
bones or vertebrae so that the bones or vertebrae can carry out
limited, controlled motion relative to each other. This is known as
dynamic stabilization. Dynamic stabilization devices commonly
comprise an elastic element instead of a rigid plate or rod that
connects each of the bone anchoring elements.
[0005] One example of a dynamic stabilization device for vertebra
is disclosed in United States Patent Application Publication No.
2003/0109880 A1. The dynamic stabilization device comprises first
and second screws that are each anchored in a vertebra. Each of the
screws has a receiving member for insertion of a spring which
thereby connects the screws. The spring is provided in the form of
a helical spring having closely neighboring coils like a tension
spring. The spring is fixed in the receiving members by clamping
screws. In this arrangement, however, because the spring is
flexible, the spring can evade the pressure of the clamping screw
and therefore become unfixed from the bone screw. Furthermore, both
the elasticity and the flexural strength of the spring depend on
the length of the spring. Thus, in applications requiring a spring
with a short length, the elasticity and flexural strength of the
spring is relatively small.
[0006] Another example of a dynamic stabilization device for a
joint such as a wrist or knee joint is disclosed in U.S. Pat. No.
6,162,223. The dynamic stabilization device comprises a rod having
a proximal rod section and a distal rod section connected to bone
pins. The proximal rod section and the distal rod section are
connected to each other by a flexible spring. The proximal rod
section, the distal rod section, and the flexible spring are
arranged outside of the body. The proximal rod section and the
distal rod section are not fixedly connected to the flexible
spring, but can move freely along a bore therein. In this
arrangement, the flexible spring must be formed to have a diameter
larger than a diameter of the rod. Additionally, the flexible
spring must be large in order to have a high flexural strength.
This dynamic stabilization device therefore has a complicated and
voluminous structure, which prevents the dynamic stabilization
device from being used inside the body on spinal columns.
BRIEF SUMMARY
[0007] The invention relates to an elastic element for use in a
stabilization device for bones or vertebrae. The elastic element
comprises a substantially cylindrical member having a first end, a
second end opposite to the first end, and an elastic section
between the first end and the second end. The elastic section
includes at least first and second helical coils. The first and
second helical coils are arranged coaxially so that the first
helical coil extends at least in a portion between the second
helical coil.
[0008] The invention further relates to a stabilization device for
bones or vertebrae comprising a substantially cylindrical elastic
element. The elastic element has a first end and a second end
opposite to the first end. At least one of the first and second
ends has threads. An elastic section extends between the first end
and the second end. The elastic section includes at least first and
second helical coils. The first and second helical coils are
arranged coaxially so that the first helical coil extends at least
in a portion between the second helical coil.
[0009] The invention still further relates to a method of
manufacturing an elastic element for a stabilization device for
bones or vertebrae. The method includes providing a substantially
cylindrical body and forming first and second helical recess in the
cylindrical body from an outside so that the first helical recesses
are formed at least in a portion between the second helical
recesses.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is an elevational view of an elastic element
according to a first embodiment;
[0011] FIG. 2a is an elevational view of a double helical spring of
the elastic element of FIG. 1;
[0012] FIG. 2b is an exploded view of the double helical spring of
the elastic element of FIG. 1;
[0013] FIG. 3 is an elevational view of an elastic element
according to a second embodiment;
[0014] FIG. 4a is an elevational view of an elastic element
according to a third embodiment;
[0015] FIG. 4b is a partial exploded view of the elastic element of
FIG. 4a;
[0016] FIG. 5a is an elastic element with a double helical coil
section according to a fourth embodiment of the invention;
[0017] FIG. 5b is a sectional view of the elastic element of FIG.
5a;
[0018] FIG. 6 is a sectional view of an elastic element having a
double helical coil section according to a fifth embodiment of the
invention;
[0019] FIG. 7a is an elastic element having a double helical coil
section according to a sixth embodiment of the invention;
[0020] FIG. 7b is a sectional view of the elastic element of FIG.
7a
[0021] FIG. 8a is a elevational view of a rod comprising the
elastic element of FIG. 1;
[0022] FIG. 8b is a partial sectional exploded view of a polyaxial
bone screw comprising the elastic element of FIG. 1;
[0023] FIG. 8c is a partial sectional view of a monoaxial screw
comprising the elastic element of FIG. 1;
[0024] FIG. 8d is a plan view of a connecting element comprising
the elastic element of FIG. 1;
[0025] FIG. 8e is a sectional view taken along line A-A of FIG.
5d;
[0026] FIG. 9 is a partial sectional view of a stabilization device
comprising several of the elastic elements of FIG. 1;
[0027] FIG. 10a is a schematic illustration of a method of
manufacturing the elastic element of FIG. 1;
[0028] FIG. 10b is a schematic illustration of a method of
manufacturing the elastic element of FIG. 1;
[0029] FIG. 10c is a schematic illustration of a method of
manufacturing the elastic element of FIG. 1; and
[0030] FIG. 11 is a schematic illustration of a method of
manufacturing the elastic element of FIG. 1.
DETAILED DESCRIPTION OF THE DRAWINGS AND PRESENTLY PREFERRED
EMBODIMENTS
[0031] Various embodiments of the invention are illustrated in
FIGS. 1-11 and described herein. Elements of the various
embodiments that are substantially identical will be referred to
with the reference numerals.
[0032] FIGS. 1-2b show an elastic element 1 according to a first
embodiment of the invention. The elastic element 1 may be made, for
example, from a bio-compatible material, such as titanium. Examples
of other bio-compatible materials include stainless steel, titanium
alloys, nickel-titanium alloys, nitinol, chrome alloy, cobalt
chrome alloys, shape memory alloys, materials with super elastic
properties, carbon reinforced composites, silicone, polyurethane,
polyester, polyether, polyalkene, polyethylene, polyamide,
poly(vinyl)fluoride, polyetheretherketone (PEEK),
polytetrafluoroethylene (PTFE) and shape memory materials or
alloys, such as nickel titanium or nitinol. As shown in FIG. 1, the
elastic element 1 is a substantially hollow Cylindrical member with
an outer wall and a continuous coaxial bore 2. The coaxial bore 2
extends from a first end 9 to a second end 9' of the elastic
element 1 and has a diameter D1. A first helical recess 3 is formed
in the outer wall in a direction of a central axis M of the
cylindrical member. The first helical recess 3 has a height H and
opens into the coaxial bore 2 in a radial direction. The first
helical recess 3 is formed at a predetermined angle a and extends
over a predetermined length L of the outer wall. A second helical
recess 4 is formed in the outer wall in-between the first helical
recess 3 in the direction of the central axis M of the cylindrical
member. The second helical recess 4 is formed at substantially the
same angle a and extends over substantially the same length L of
the outer wall as the first helical recess 3. The second helical
recess 4 opens into the coaxial bore 2 in the radial direction.
[0033] First and second internal threads 5, 5' are formed at the
first and second ends 9, 9', respectively, of the elastic element
1. The first and second internal threads 5, 5' extend over a
predetermined length in an axial direction. The lira and second
internal threads 5, 5' do not overlap or extend into the first and
second helical recesses 3, 4 formed in the outer wall. The elastic
element 1 has an outer diameter, which is selected according to the
desired use thereof. The length L of the first and second helical
recesses 3, 4 in the direction of the central axis M of the
cylindrical member, the height H of the first and second recesses
3, 4, the angle a of the helices along which the first and second
helical recesses 3, 4 are formed, and the diameter D1 of the
coaxial bore 2 is selected to provide a desired stiffness to the
elastic element 1 with respect to axial forces F.sub.ax, bending
forces F.sub.B and torsional forces F.sub.T acting on the elastic
element 1.
[0034] As shown in FIGS. 2a-2b, a double helical spring or elastic
section 6 consisting of a first helical coil 7 and a second helical
coil 8 is formed by the first and second helical recesses 3, 4.
Coils of the first helical coil 7 extend between coils of the
second helical coil 8. The first and second helical coils 7, 8 are
substantially identical and have substantially the same angle a.
The coils of the first helical coil 7 are rotated approximately 180
degrees with respect to the coils of the second helical coil 8
around the central axis M, which is common to both the first and
second helical coils 6, 7, so that the first and second helical
recesses 3, 4 oppose each other. The coils of the first helical
coil 7 therefore run midway between the coils of the second helical
coil 8 and vice versa. It will be appreciated by those skilled in
the art that the elastic member 1 may additionally comprise more
than two of the helical coils, wherein coils of each of the helical
coils extend in-between coils of adjacent helical coils.
[0035] In order to obtain optimal elastic properties in an elastic
element (not shown) with a single helical spring (not shown) having
a predetermined length, the angle of the helices of the single
helical spring (not shown) must be formed to have at least one
whole turn. In the double helical spring 6 shown in FIGS. 2a-2b,
however, the first helical coil 7 and the second helical coil 8
require less than one whole turn to obtain optimal elastic
properties even though the double helical spring 6 has the same
predetermined length as the single helical spring (not shown).
Unlike the angle of the helices of the single helical spring (not
shown), the angle a of the helices of the double helical spring 6
may therefore be increased to increase the flexural strength of the
elastic element 1. Additionally, the elastic element 1 may be
formed, for example, to have an ovular cross-section or to be
waisted such that the elastic element 1 has a flexural strength
which is dependent on direction. The elastic element 1 therefore
has a high flexural strength and a short length such that the
elastic element 1 may be handled easily while at the same time
providing a high operational reliability. Additionally, the elastic
element 1 may be combined with other elements in various different
ways to be a dynamic stabilization device for vertebrae or
bones.
[0036] FIG. 3 shows an elastic element 11 according to a second
embodiment of the invention. The elastic element 11 is a
substantially hollow cylindrical member having first and second
helical recesses 13, 14 formed in an outer wall thereof to form a
double helical spring or elastic section. The double helical spring
is formed in a similar fashion to the first embodiment. The elastic
element 11 of the second embodiment differs from the first
embodiment in that the elastic element 11 has a coaxial bore 12
that extends partially through the cylindrical member. The coaxial
bore 12 extends from a first end 17 over the length L of the double
helical spring and is coaxial with the central axis M of the
cylindrical member. Internal threads 15 are provided in the coaxial
bore 12 adjacent to the first end 17. At a second end 17', which
opposes the first end 17, the elastic element 11 is provided with a
cylindrical projection 16. The cylindrical projection 16 has
external threads. Alternatively, the coaxial bore 12 may have a
diameter smaller than an outer diameter of the cylindrical
projection 16 and may extend through the entire cylindrical
member.
[0037] FIGS. 4a-4b show an elastic element 21 according to a third
embodiment of the invention. The elastic element 21 is a
substantially cylindrical member having first and second helical
recesses 24, 25 formed in an outer wall thereof to form a double
helical spring or elastic section consisting of a first helical
coil 26 and a second helical coil 27. The double helical spring is
formed similar to the first and second embodiments. The elastic
element 21 of the third embodiment differs from the first and
second embodiments in that the elastic element 21 does not have a
bore coaxial with the central axis M of the cylindrical member. The
elastic member 21 has a first end 22 and a second end 22'. The
first and second ends 22, 22' have first and second cylindrical
projections 23, 23', respectively. The first and second cylindrical
projections 23, 23' have external threads.
[0038] An elastic element according to a fourth embodiment is shown
in FIG. 5a. FIG. 5b is a sectional view of the elastic element of
FIG. 5a. The elastic element 30 according to the fourth embodiment
differs from the elastic element according to the first embodiment
in that the pitch a of the recesses 31, 32 which form the double
helical coil is not constant but varies over the length L of the
double helical coil of the elastic element 30. The pitch a varies
in such a way that the distance) L of the recesses 31, 32 increases
from the free ends of the elastic element 30 towards the middle.
Accordingly, the bending stiffness of the elastic element 30 varies
and increases with increasing distance L of the recesses 31, 32. By
varying the pitch of the recesses along the central axis of the
elastic element, it is possible to achieve a particular stiffness
at a particular position. Similar to the elastic element of the
first embodiment, the elastic element 30 according to the fourth
embodiment has coaxial bore 34 having an inner diameter D1 and
inner threads 33, 33' extending a predetermined length from the
free end, respectively. FIG. 6 shows sectional view of an elastic
element according to a fifth embodiment.
[0039] The elastic element according to the fifth embodiment
differs from the elastic element 30 according to the fourth
embodiment in that the inner diameter D1 of the continuous coaxial
bore 42 is not constant but varies of the length L' of the elastic
element 40. The inner diameter D1 of the bore 42 varies in such
away that it decreases from the free ends towards the middle of the
elastic element 40. Accordingly, the final stiffness of the elastic
element 40 varies and increases with decreasing inner diameter D1.
By varying the inner diameter of the coaxial bore, the stiffness of
the elastic element 40 can be varied at different positions.
[0040] Similar to the fourth embodiment the elastic element 40
includes a section with an inner thread 41, 41' having a
predetermined length adjacent to each of its free end,
respectively.
[0041] In FIG. 7a an elastic element according to a sixth
embodiment is shown. FIG. 7b is a sectional view of the elastic
element of FIG. 7a.
[0042] The elastic element 35 according to the sixth embodiment
differs from that of the fifth embodiment in that the outer
diameter D2 of the elastic element 35 is not constant but varies
over the length L' of the elastic element 35. The outer diameter D2
varies in such a way that it increases from the free ends towards
the middle of the elastic element 35. Accordingly, the bending
stiffness of the elastic element 35 varies and increases with
increasing outer diameter. Therefore, a position with a desired
bending stiffness can be obtained by adjusting the outer diameter
of the elastic element.
[0043] Similar to the fourth embodiment the elastic element 35 has
adjacent to its free ends a section with an inner thread 36, 36' of
a predetermined length, respectively, and a continuous coaxial bore
37 with an inner diameter D1. Recesses 38 and 39 to form the double
helical coil are formed like in the other embodiments.
[0044] In the fourth to sixth embodiments of the instant invention,
the bending stiffness of the elastic element increases from the
free ends towards the middle of the elastic element. However, by
appropriate selection of the pitch a of the recesses, the outer
diameter D2 of the elastic element and the inner diameter D1 of the
coaxial bore, the bending stiffness can be adjusted to have a
desired stiffness at a particular position along the length L, L'
of the double helical coil of the elastic element.
[0045] FIG. 8a illustrates a first example of an application of the
elastic element 1. As shown in FIG. 8a, the elastic element 1 may
form a portion of a rod 50, which may be used, for example, to
connect pedicle screws (not shown) at a spinal column (not shown).
The rod 50 in the illustrated embodiment consists of the elastic
element 1 and first and second end portions 51, 51'. The first and
second end portions 51, 51' each have a cylindrical projection (not
shown) with external threads (not shown) that cooperates with the
first and second internal threads 5, 5', respectively, of the
elastic element 1, shown in FIG. 1. Alternatively, an external nut
(not shown) or other attachment member may be used to fix the
elastic element 1 to the first and second end portions 51, 51'. In
the illustrated embodiment, the first and second end portions 51,
51' and the elastic element 1 have approximately the same outer
diameter. The first and second end portions 51, 51' have a length
that may be selected independently from the length L of the elastic
element 1, which is shown in FIG. 1. The length of the first and
second end portions 51, 51' and the length L of the elastic element
1 selected depends on a desired end application. Because the rod 50
is formed with the elastic element 1, the rod 50 can absorb
compression forces, extension forces, bending forces and torsional
forces to a predetermined extent by means of the elastic properties
of the elastic element 1.
[0046] FIG. 8b illustrates a second example of an application of
the elastic element 1. As shown in FIG. 8b, the elastic element 1
may form a portion of a bone anchoring element, such as a polyaxial
bone screw 60. The polyaxial bone screw 60 in the illustrated
embodiment includes a screw 61 with a shaft 62 and a head 63. The
shaft 62 has a tip (not shown) and includes bone threads 64 for
screwing into a bone (not shown) and. A cylindrical projection (not
shown) extends from the shaft 62 on a side opposite from the tip
(not shown) and has external threads (not shown) that cooperate
with the internal threads 5 of the elastic element 1, which are
shown in FIG. 1. As shown in FIG. 8b, the head 63 has a cylindrical
section 65 adjacent thereto. A cylindrical projection (not shown)
extends from the cylindrical section 65 and has external threads
(not shown) that cooperate with the internal threads 5' of the
spring element 1, which are shown in FIG. 1.
[0047] As shown in FIG. 8b, the screw 61 is pivotally held in a
receiving member 66 in an unloaded state. The receiving member 66
is substantially cylindrical and has a first receiving member bore
67 and a second receiving member bore 68. The first receiving
member bore 67 is provided at a first end of the receiving member
66. The first receiving member bore 67 is substantially axially
symmetrical and has a diameter larger than a diameter of the shaft
62 but smaller than a diameter of the head 63. The second receiving
member bore 68 is substantially coaxial and opens at a second end
of the receiving member 66 opposite the first end. The second
receiving member bore 68 has a diameter large enough that the shaft
62 of the screw 61 may be guided through the second end and the
second receiving member bore 68 until the head 63 abuts an edge of
the first receiving member bore 67. The receiving member 66 has a
substantially U-shaped recess 69, which extends from the second end
towards the first end. The substantially U-shaped recess 69 forms
first and second legs 70, 70' with free ends. In a region adjacent
to the free ends, the first and second legs 70, 70' have internal
threads, which cooperate with corresponding external threads of a
securing element 71 that fixes a rod 72 in the receiving member
66.
[0048] A pressure element 73 that is provided for fixation of the
head 63 in the receiving member 66 has a concave recess 74 on a
side facing the head 63. The concave recess 74 has a radius
substantially identical to a radius of the head 63. The pressure
element 73 has an outer diameter selected so that the pressure
element 73 can be inserted into the receiving member 66 and can
slide towards the head 63. The pressure element 73 has a coaxial
pressure element bore 75 for providing access to a tool receiving
recess (not shown) in the head 63.
[0049] During assembly, the cylindrical projection (not shown) of
the shaft 62 is screwed into the internal threads 5 of the elastic
element 1 and the cylindrical projection (not shown) of the
cylindrical section 65 of the head 63 is screwed into the internal
threads 5' of the elastic element 1 to form the screw 61. The shaft
62 of the screw 61 is then inserted into the second end of the
receiving member 66 and guided through the second receiving member
bore 68 until the head 63 abuts the edge of the first receiving
member bore 67. The pressure element 73 is inserted into the second
receiving member bore 68 so that the concave recess 74 is
positioned adjacent to the head 63. The screw 61 is screwed into a
bone (not shown) or vertebra (not shown). The rod 72 is inserted
into the receiving member 66 and is arranged between the first and
second legs 70, 70'. The angular position of the screw 61 relative
to the receiving member 66 is then adjusted and fixed with the
securing element 71.
[0050] Because the screw 61 is formed with the elastic element 1,
the screw 61 may be diverted from the angular position by a limited
extent. Additionally, if the elastic element 1 protrudes at least
partially above a surface of the bone (not shown), the elastic
element 1 can absorb compression forces, extension forces, bending
forces and torsional forces because of the elastic properties of
the elastic element 1. If the elastic element 1 does not at least
partially protrude above the surface of the bone (not shown), the
screw 61 can still slightly yield, when the bone (not shown) or
vertebra (not shown) moves such that the occurrence of unfavorable
stress is avoided.
[0051] FIG. 8c illustrates a third example of an application of the
elastic element 1. As shown in FIG. 8c, the elastic element 1 may
form a portion of a bone anchoring element, such as a monoaxial
screw 80. The monoaxial screw 80 in the illustrated embodiment
consists of a head formed as a receiving member 81 and a shaft 86.
The receiving member 81 has a substantially U-shaped recess 83
formed at a first end thereof. First and second legs 84, 84' are
formed by the U-shaped recess 83. The first and second legs 84, 84'
receive a rod 82 therebetween. Internal threads (not shown) that
correspond to external threads on securing member 85 are formed on
inside surfaces of the first and second legs 84, 84'. The rod 82 is
clamped between a bottom surface of the U-shaped recess 83 and the
securing member 85 when the securing member 85 is engaged with the
internal threads (not shown). A cylindrical projection (not shown)
extends from a second end of the receiving member 81 opposite from
the first end. The cylindrical projection (not shown) has external
threads (not shown) that correspond to the internal threads 5' of
the elastic element 1, which are shown in FIG. 1. The shaft 86 is
similar to the shaft 62 previously described and has a cylindrical
projection (not shown) extending therefrom with external threads
(not shown) that corresponds to the internal threads 5 of the
elastic element 1, which are shown in FIG. 1.
[0052] During assembly, the cylindrical projection (not shown) of
the shaft 86 is screwed into the internal threads 5 of the elastic
element 1 and the cylindrical projection (not shown) of the
receiving member 81 is screwed into the internal threads 5' of the
elastic element 1 to form the monoaxial screw 80. The monoaxial
screw 80 is screwed into a bone (not shown) or vertebra (not
shown). The U-shaped recess 83 is aligned and the rod 82 is
inserted into the receiving member 81 and is arranged between the
first and second legs 84, 84''. The rod 82 is then fixed by the
securing member 85.
[0053] FIGS. 8d-8e illustrate a fourth example of an application of
the elastic element 1. As shown in FIG. 8d, the elastic element 1
may form a portion of a connecting element 90. The connecting
element 90 in the illustrated embodiment consists of a rod 91 and a
plate 92. The rod 91 has a cylindrical,projection (not shown) with
external threads that correspond to the internal threads 5 of the
elastic element 1, which are shown in FIG. 1. A cylindrical
projection (not shown) extends from the plate 92 and has external
threads (not shown) corresponding to the internal threads 5' of the
elastic element 1, which are shown in FIG. 1. As shown in FIG. 8d,
the plate 92 has a first section 93 and a second section 93'
connected by a bridge 94. The first and second sections 93, 93' are
substantially circular from a top view. The bridge 94 has a width B
smaller than a diameter D of the first and second sections 93, 93'.
The first and second sections 93, 93' each have a screw receiving
bore 95, 95', respectively, formed coaxially with the first and
second sections 93, 93'. The screw receiving bores 95, 95' have a
shape adapted for the reception of countersunk screws (not shown).
As shown in FIG. 8e, a first side 96 of the plate 92 has a convex
curvature and a second side 97 of the plate 92 has a concave
curvature for abutting a surface of a bone (not shown). Due to the
different curvatures of the first and second sides 96, 97, the
plate 92 tapers towards lateral edges 98, 98'. The plate 92 is,
therefore, stable and compact.
[0054] Modifications of the rod 50, the polyaxial bone screw 60,
the monoaxial screw 80, and the connecting element 90, shown in
FIGS. 8a-8e are also possible. For example, the elastic element 1
in the rod 50, the polyaxial bone screw 60, the monoaxial screw 80,
and the connecting element 90 is illustrated as being a separate
element that requires connection therewith. Alternatively, the
elastic element 1 may be integrally formed with the polyaxial bone
screw 60, the monoaxial screw 80, and the connecting element 90 or
press-fit thereto.
[0055] FIG. 9 illustrates a fifth example of an application of the
elastic element 1. As shown in FIG. 9, the elastic element 1 may
form a portion of a stabilization device 100 that is used, for
example, in spinal columns. The stabilization device 100 in the
illustrated embodiment consists of first and second bone anchoring
elements 101, 101', respectively, connected by a rod 103. Each of
the first and second bone anchoring elements 101, 101' has a screw
102, 102', respectively, formed with an elastic element 1. The rod
103 is also formed with an elastic element 1. Each of the screws
102, 102' is screwed into a vertebra 104, 104' so that a dynamic
stabilization is established between the vertebrae 104, 104' and
the stabilization device 100. Because the rod 103 and the screws
102, 102' are made of several elements, the stabilization device
100 has various properties by the combination of only a few basic
elements. The stabilization device 100 is not limited to the
embodiment illustrated and depending on a desired application
thereof, it is possible, for example, to provide only the rod 103
with the elastic element 1.
[0056] A method of manufacturing the elastic element 1 by wire
electrical discharge machining (EDM) is shown in FIGS. 10a-10c. As
shown in FIG. 10a, a first bore 110 is formed in a solid cylinder
112 of a biocompatible material, such as titanium, perpendicular to
a central axis M' of the cylinder 112. The first bore 110 extends
through the whole cylinder 112. A second bore 111 is formed coaxial
with the central axis M' of the cylinder 112 so that the cylinder
112 is made hollow. The order of forming the first and second bores
110, 111 is arbitrary and may be varied according to a desired
manufacturing process. A wire 113 for wire EDM is guided through
the first bore 110 in a direction indicated by arrow P.
[0057] As shown in FIG. 10b, wire EDM is performed by moving the
cylinder 112 in a direction indicated by arrow X along the central
axis M'. The cylinder 112 is moved at a constant feed rate relative
to the wire 113 and is simultaneously rotated around the central
axis M' in a direction indicated by arrow R with a constant angular
velocity. Only relative movement of the wire 113 relative to the
cylinder 112 is relevant. Accordingly, either the wire 113 or the
cylinder 112 may be fixed during the wire EDM. As the cylinder 112
is rotated, first and second helical recesses 114, 115 are
formed.
[0058] As shown in FIG. 10c, after the first and second helical
recesses 114, 115 have been formed over a predetermined length of
the cylinder 112 along the central axis M', the rotation of the
cylinder 112 is stopped. FIG. 10c shows the elastic element 1
shortly before completion of the wire EDM. The wire EDM thereby
simultaneously forms in the outer wall of the cylinder 112, first
and second helical recesses 114, 115 having approximately identical
angles, which open in a radial direction into the second bore
111.
[0059] As shown in FIG. 11, a first run-out 120 may be formed at a
beginning of the wire EDM and at a second run-out 120' may be
formed at an end of the wire EDM. The first and second run-outs 120
and 120' have a configuration by which load peaks can be minimized
in the material at a transition from the elastic section to the
rigid section during operation. The first and second run-outs 120,
120' may have, for example, a semi-circular configuration. The
first and second run-outs 120, 120' advantageously may be made in
one common manufacturing step. Additionally, unlike during the
manufacture of a single helical spring (not shown), during the
manufacture of the elastic element 1, switching between each axis
of the wire EDM machine is not necessary. Internal threads are then
formed along the central axis M' in end sections of the second bore
111 adjacent to the first and second ends.
[0060] Alternatively, the elastic element 1 may be milled. A first
helical recess is milled along a first helix of a central axis of a
solid cylinder formed of a bio-compatible material, such as
titanium, having a predetermined outer diameter. The first helical
recess is formed collinear with the central axis of the cylinder by
a side mill. A second helical recess is milled along a second helix
of the central axis such that coils of the second helical recess
run between coils of the first helix. A bore is formed along the
central axis of the cylinder over the whole length of the cylinder
so that the first and second helical recesses communicate with the
bore. The first and second helical recesses have first and second
run-outs, respectively. The first and second run-outs of the first
and second helical recesses at a transition between the first and
second helices and end sections of the cylinder have a large
influence on the stability of the elastic element 1. The first and
second run-outs of the first and second helixes at both of the end
sections are reworked by an end mill so that Sharp edges on an
internal surface of the bore are removed. The first and second
run-outs are milled by the end mill at an angle that is tangential
relative to a helical line. The part is then chamfered on an inside
and on an outside. Internal threads are then formed along the
central axis in the end sections of the bore adjacent to first and
second ends of the cylinder.
[0061] Further alternative methods for manufacturing the elastic
element 1 are, for example, laser milling or hydro milling. These
methods are performed similar to the wire EDM method, but instead
of simultaneously forming the first and second helical recesses by
a wire, a laser beam or a water beam is used. Additionally, instead
of forming at least one of the internal threads, a cylindrical
projection with external threads may be formed at a beginning of
any one of the manufacturing methods by a lathe. In this instance,
the bore has a diameter smaller than a diameter of the cylindrical
projection. The spring element 1 may also be formed without the
bore.
[0062] The embodiments described above and shown herein are
illustrative and not restrictive. The scope of the invention is
indicated by the claims, including all equivalents, rather than by
the foregoing description and attached drawings. The invention may
be embodied in other specific forms without departing from the
spirit and scope of the invention.
* * * * *