U.S. patent application number 11/390972 was filed with the patent office on 2007-03-08 for screw.
This patent application is currently assigned to Biedermann Motech GmbH. Invention is credited to Lutz Biedermann, Jurgen Harms, Dezso Jeszensky, Helmar Rapp.
Application Number | 20070055238 11/390972 |
Document ID | / |
Family ID | 39720082 |
Filed Date | 2007-03-08 |
United States Patent
Application |
20070055238 |
Kind Code |
A1 |
Biedermann; Lutz ; et
al. |
March 8, 2007 |
Screw
Abstract
An element with a thread is created, in which both partial
flanks enclose a negative angle with a plane extending
perpendicular to the screw axis. Further, a screw or a hook for
connecting to a rod, as used in particular in spinal column
surgery, is created, wherein the inner thread of a holder, to which
the rod is connected, and the associated thread of a nut comprise
the thread according to the invention.
Inventors: |
Biedermann; Lutz;
(VS-Villingen, DE) ; Jeszensky; Dezso; (St.
Gallen, CH) ; Harms; Jurgen; (Karlsruhe, DE) ;
Rapp; Helmar; (Deisslingen, DE) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Assignee: |
Biedermann Motech GmbH
|
Family ID: |
39720082 |
Appl. No.: |
11/390972 |
Filed: |
March 27, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10098937 |
Mar 15, 2002 |
7018378 |
|
|
11390972 |
Mar 27, 2006 |
|
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Current U.S.
Class: |
606/308 |
Current CPC
Class: |
A61B 17/7037 20130101;
A61B 17/7032 20130101 |
Class at
Publication: |
606/061 |
International
Class: |
A61F 2/30 20060101
A61F002/30 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 16, 2001 |
EP |
01 106 711.3 |
Claims
1. (canceled)
2. (canceled)
3. A device comprising: a shank; a holding component for engaging
and holding a rod, the holding component comprising a recess having
two legs, a U-shaped cross-section for accommodating the rod, an
open end for receiving the rod into the U-shaped cross-section
between the legs, and an inner thread on the legs; and a screw,
which cooperates with the inner thread and directly or indirectly
acts on the rod when positioned in the recess, the screw having a
central axis; wherein the inner thread comprises an inner thread
base, first and second partial flanks adjacent to one another, and
an internal thread edge between the first and second partial
flanks; wherein the screw has an outer thread for engagement with
the inner thread of the legs, the outer thread comprising an outer
thread base, third and fourth partial flanks adjacent to one
another, and an external thread edge between the third and fourth
partial flanks; the first and third partial flanks, which face away
from the open end, enclose a negative angle .beta..sub.2 with a
plane which extends through the respective thread base and extends
perpendicular to the central axis; the second and fourth partial
flanks, which face toward the open end, enclose a positive angle
.beta..sub.1 with a plane which extends through the respective
thread base and extends perpendicular to the central axis.
4. The device according to claim 3, wherein the internal thread
base is rounded between adjacent first and second partial flanks.
Description
[0001] The invention relates to an element to be used in spinal
column or accident surgery for connecting to a rod.
[0002] From U.S. Pat. No. 5,129,388 a pedicle screw is known which
comprises a head with a U-shaped recess defining two free legs to
accommodate a rod, wherein the legs are provided with an inner
thread to receive a fixing screw for fixing the rod. To prevent
spreading of the legs a cap is provided embracing the legs.
[0003] From U.S. Pat. No. 5,005,562 it is known with a pedicle
screw according to the preamble of Patent claim 1 to construct the
inner thread and the thread of the screw cooperating with it as a
saw-tooth thread, so as in this way to avoid spreading out of the
two flanks by completely eliminating the radial components of the
force during screwing in.
[0004] A saw or else saw-tooth thread of this kind is known from
Meyer's Enzyklopadisches Lexikon, Mannheim, 1974, page 302. From
both the specifications U.S. Pat. Nos. 5,605,458 and 5,607,304,
concerning implants, it is known with implants of this kind to be
introduced into the body, in particular hip implants, also to
construct the saw thread in such a way that the flank bearing the
load is constructed not only at 90.degree. to the thread axis but
even at a negative angle. This is supposed to achieve that the
connection obtained with the thread resists a radial relative
movement of the connected parts and thus guarantees better fixing
of the implant. From EP-A-1 128 773 a pedicle screw is known in
which the inner thread of a head accommodating a rod has a negative
thread and the screw cooperating with it is correspondingly
constructed.
[0005] The object of the invention is to create an element of the
kind initially described, which is suitable for avoiding the above
described disadvantage. In particular bending up of the open ends
of a mount of this kind and therefore loosening of the connection
between screw and rod should be avoided.
[0006] This object is achieved by the element characterised in
Patent claim 1.
[0007] This construction has the advantage that the action of force
between the exposed legs and the inner thread happens in such a way
that the open ends of the holding element are not pressed outwards,
but instead are drawn inwards, so an intensive connection takes
place between the cooperating elements.
[0008] Further features and advantages of the invention emerge from
the description of the embodiment examples using the figures.
[0009] FIG. 1 shows a side view of a monoaxial pedicle screw in a
bisected exploded illustration.
[0010] FIG. 2 shows the head of the pedicle screw shown in FIG. 1
with inserted rod and inserted nut.
[0011] FIG. 3 shows the detail III indicated in FIG. 2 in enlarged
scale.
[0012] FIG. 4 shows a section corresponding to the illustration
chosen in FIG. 2 for a polyaxial screw.
[0013] FIG. 5 shows a schematically illustrated holding element
with inserted rod and loosely screwed in inner screw.
[0014] FIG. 6 shows the detail VI in FIG. 5 in enlarged scale.
[0015] FIG. 7 shows the illustration corresponding to the
illustration shown in FIG. 5 after the inner screw has been
tightened.
[0016] FIG. 8 shows the detail VIII shown in FIG. 7 in enlarged
scale.
[0017] The pedicle screw according to FIG. 1, which can, of course,
also be used generally as a bone screw or constructed as a hook,
has a thread shank 1 and a head 2. The head 2 has a U-shaped recess
4, extending in the direction of the longitudinal axis 3 of the
screw and with a predetermined depth. On the two thereby
constructed legs 5, 6 an inner thread 8 is provided coming from the
open end 7 of the legs. Matched to the inner thread 8, a screw 9 is
provided, the outer thread of which is constructed in such a way
that it cooperates with the inner thread 8.
[0018] In operation a rod 10, to be connected to the screw, is
placed in the U-shaped recess 4 in such a way that the rod comes to
rest on the base of the U-shaped recess. The screw 9 is then
screwed in far enough for it to exert sufficient stopping pressure
on the rod 10 located in the U-shaped recess.
[0019] As can be seen more clearly in FIGS. 2 and 3, the inner
thread in the head 2 and the outer thread of the screw 9 are
constructed in the way of a saw thread. On the surface 11 facing
away from the rod 10 to be fixed the screw 9 has a slit or a
hexagonal recess for the insertion of a screwdriver.
[0020] In the thread in each case two adjacent partial flanks 12,
13 form a thread pitch. The two partial flanks 12, 13 enclose the
flank angle .beta.. The flank side 13 facing the open end 7
encloses a positive angle .beta..sub.1 with a plane 40, extending
perpendicular to the longitudinal axis 3 and intersecting the flank
side 13 on the base 23 of the thread (see FIG. 3). The partial
flank 12 facing away from the open end is inclined in such a way
that in the manner shown in FIG. 3 it encloses a negative angle
.beta..sub.2 with a corresponding plane 40. As can be seen from the
figures the thread of the screw 9 is made correspondingly, so the
pitches of the screw 9 engage appropriately in the inner thread 8.
In screw 9 therefore each flank 26 facing the open end 7 or the
surface 11 forms the negative angle .beta..sub.2, which cooperates
with the corresponding flank 12.
[0021] The embodiment shown in FIG. 4 corresponds identically in
the construction of the inner thread 8 and the screw 9 cooperating
with it and of the rod 10. Corresponding features are characterised
by the same reference numerals.
[0022] By contrast with the first embodiment here there is a
so-called polyaxial screw, in which the thread shank 1 is connected
to a receiving part 15 via a spherical head 14. The receiving part
has on one end an axially symmetrically aligned first bore 16, the
diameter of which is larger than that of the thread section 1 and
smaller than that of the head 14. The receiving part further has a
coaxial second bore 17, which is open on the end located opposite
the first bore and the diameter of which is large enough for the
screw element to be guided through the open end with its thread
section through the first bore and with the head 14 to the base of
the second bore. Between the first and the second bore a small
coaxial section us provided, which directly borders on the first
bore and is constructed as spherical towards the open end, wherein
the radius is substantially identical to the radius of the
ball-segment-shaped section of the head 14. The inner thread 8 is
again provided bordering on the open ends 7 of the legs 5, 6. The
receiving part 15 further has a U-shaped recess 18, arranged
symmetrical to the centre of the part, the base of which is
directed towards the first bore, the two side legs 5, 6 of which
extend towards the open end 7. Further, in the second bore 17 a
pressure element is placed, which is situated on the spherical head
14. In operation the rod 10 is inserted into the U-shaped recess.
Then the screw 9 is turned and screwed, in the same way as shown in
FIG. 2, until it exerts a desired pressure on the pressure element
19 and therefore on the head 14 to stop it.
[0023] Instead of the above described embodiments, in which the
head or the receiving part are connected in each case to a bone
screw, the head or the receiving part can also be connected to a
hook, as used in spinal column surgery for hooking in behind bone
projections of the spinal column.
[0024] When a saw thread is spoken of above this is only supposed
to characterise the direction of the partial flanks. Threads with
rounded tips and rounded base, pointed threads and pointed thread
base and flat thread edges and flat thread base should be also be
included, as is also the case with a triangular thread, round
thread and trapezoidal thread.
[0025] Whereas with known screws with a metric thread, in which the
screw presses on a rod in the way shown in FIG. 2, one force
component acts towards the open side 11 of the screw and a second
force component acts outwards in each case, with the above
described thread according to the invention again one component
acts towards the open end 7, but the second component acts in the
direction of the longitudinal axis 3. The result of this is that
the exposed legs 5, 6 are not pressed outwards, but are drawn
towards the symmetrical axis.
[0026] In FIG. 5, as in FIG. 2, the head of the pedicle screw shown
in FIG. 1 is shown with inserted rod and only initially inserted
inner thread 9. In FIG. 6 section VI from FIG. 5 is illustrated in
larger detail. As emerges from this enlarged illustration, the
inner screw 9 and the outer thread of the legs 5 are dimensioned
relative to one another as follows: radius r.sub.1 from the centre
of the screw coinciding with the longitudinal axis 3 to the base 21
of the thread of the screw 9 is smaller than radius r.sub.2 from
the central axis of the holding element coinciding with the
symmetrical axis 3 to the tip of its spiral 20. Radius r.sub.3 from
the centre of the screw coinciding with the longitudinal axis 3 to
the tip of the spiral 22 of the screw 9 is smaller than radius
r.sub.4 from the central axis of the holding element coinciding
with the longitudinal axis 3 to the base 23 of the thread of its
inner thread.
[0027] As can be seen in particular in FIG. 6, when screw 9 and
exposed legs 5, 6 of the holding element are brought into
engagement without load, when the cooperating flanks 13 of the
inner thread and 24 of the screw, having the positive flank angles,
are adjacent to one another there is a gap 25 between the flanks
12, 26, having a negative flank angle, facing one another in each
case.
[0028] FIG. 7 shows the same object as in FIGS. 5 and 6, wherein
the screw 9 is now screwed inwards far enough for it to press on
the rod 10 and thereby to effect a counter-force, indicated by the
arrow 27, on the screw 9. As a result of this, as can be seen in
FIG. 8, the flanks 12, 26 facing one another in each case thereby
end up on top of one another at a negative flank angle
.beta..sub.2, whereby the spirals 28, 29 of the inner thread are
drawn inwards towards the respective base 21 of the pitches of the
thread of the screw 9 in the manner shown in FIG. 8, with the
result that the exposed legs are biased not outwards but
inwards.
[0029] In a preferred embodiment the difference between the
measurement of radii r.sub.1 and r.sub.2 is about 1 to 5% of the
outer diameter of the thread or 0.1 to 0.5 mm with a screw diameter
of 5 to 12 mm.
* * * * *