DEVICE FOR CONNECTING A LONGITUDINAL SUPPORT WITH A PEDICLE SCREW

DISPOSITIF POUR RELIER UN SUPPORT LONGITUDINAL AVEC UNE VIS PEDONCULAIRE

English Abstract

The invention relates to a device for connecting a rod to a bone anchoring
element. The device includes a connecting member having upper and lower
ends, a bore hole with a central axis, and a through hole positioned
perpendicular to the central axis. The device has a tensioning member
insertable in the upper end of the connecting member for securing the
anchoring
element to the connector at a surgeon selected angle. A radially compressible
spring chuck is arranged within the connecting member and has a cavity for
receiving the head of the anchoring element. An insert slides into the bore
hole
of the connecting member and has a recess with a shape complementary to the
outer surface of the chuck. The chuck is axially supported in the bore hole in
such a fashion that radial movement of the chuck is not affected.

French Abstract

L'invention concerne un dispositif pour relier un support longitudinal (1) à un élément d'ancrage dans l'os à l'intérieur d'un système de fixation spinal. Ce dispositif comporte un adaptateur (10, 30) avec un axe central (4) et une ouverture de passage (11) perpendiculaire à l'axe central (4) pour la réception d'un support longitudinal (1), une vis de tension (23) que l'on peut visser à partir de l'extrémité supérieure (28) de l'adaptateur (10, 30) et une pince de serrage (7) cylindrique creuse disposée coaxialement dans l'adaptateur (10, 30) et formée à l'intérieur avec une cavité ouverte (15) de part en part dans le sens de l'axe central (4) pour loger de façon élastique la tête (5) d'un élément d'ancrage (30) dans l'os. La pince de serrage (7) s'appuie dans la direction de l'extrémité inférieure (29) axialement dans l'orifice (6) proche de l'extrémité inférieure (29) de l'adaptateur (10, 30) sans être entravée dans sa mobilité radiale. Le dispositif comporte également un insert (9) pouvant glisser coaxialement dans l'orifice (6) de l'adaptateur (10, 30) avec un orifice complémentaire (14) à la surface externe (32) de la pince de serrage (7).

Claims

10
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A vertebral fixation system connector for connecting a longitudinal rod
with
a bone-anchoring element, the connector comprising:
a connecting member having upper and lower ends, a bore hole through the
lower end with a central axis, and a through hole running transversely to the
central axis for receiving a longitudinal rod;
a tensioning member configured and dimensioned for insertion in the upper end
of the connecting member for securing a bone-anchoring element, having a head
and a shaft, to the connector at a surgeon-selected angle;
a radially-compressible spring chuck arranged within the connecting member,
coaxial with the central axis and having an upper end and a lower end that
includes a cavity for receiving the head of the bone-anchoring element; and
an insert slidable in the bore hole of the connecting member and having a
recess complementary in shape to an outer surface of the radially compressible
spring chuck;
wherein the spring chuck is axially supported in the bore hole without
impeding
radial movement of the spring chuck therein.
2. The connector of claim 1, wherein the connecting member has a shoulder
for supporting the spring chuck in the bore hole.
3. The connector of claim 2, wherein the shoulder has a ring groove.
4. The connector of claim 1, 2 or 3, wherein the connecting member is a
cylindrical sleeve.

11
5. The connector of any one of claims 1 to 4, wherein the outer surface of
the spring chuck and the recess of the insert each have a conical shape.
6. The connector of claim 5, wherein both the outer surface of the spring
chuck and the recess have conical angles of at least about 10°, with
the angles
differing by less than about 1°.
7. The connector of claim 5, wherein both the outer surface of the spring
chuck and the recess have conical angles of at least about 10°, with
the angles
differing by between about 4° wind 6°.
8. The connector of any one of claims 1 to 7, wherein a sidewall of the
connecting device has an opening for receiving the longitudinal rod.
9. The connector of any one of claims 1 to 8, wherein the through hole has
an oval shape.
10. The connector of any one of claims 1 to 9, wherein the tensioning member
includes an insert screw having an external thread, and wherein the upper end
of
the connecting member has an internal thread.
11. The connector of claim 10, wherein the internal thread and external thread
are buttress threads.
12. The connector of any one of claims 1 to 11, wherein the recess is
convexly shaped in an area of contact between the insert and the spring chuck.

12
13. The connector of any one of claims 1 to 12, wherein the upper end of the
insert has a ridge for compressing against the spring chuck.
14. The connector of any one of claims 1 to 13, wherein the insert has a
cylindrical shape.
15. The connector of any one of claims 1 to 13, wherein a cross-section of the
insert has a polygonal shape.
16. The connector of any one of claims 1 to 15, wherein the bore hole and the
through hole are connected to each other.
17. The connector of any one of claims 1 to 16, wherein the tensioning
member provides for simultaneous fixation of the longitudinal rod and the head
of
the bone anchoring element.
18. The connector of any one of claims 1 to 16, wherein the tensioning
member is configured and dimensioned to press on the longitudinal rod.
19. The connector of claim 18, wherein the tensioning member comprises a
nut, and the upper end of the connecting member has an external thread for
threadably receiving the nut.
20. The connector of claim 18, wherein the tensioning member comprises a
locking screw and the upper end of the connecting member has an internal
thread for threadably receiving the locking screw.

13
21. The connector of any one of claims 1 to 20, wherein at least a portion of
the insert has an internal thread, and wherein a stud bolt having a shaft with
an
external thread is threadably received by the insert to press on the
longitudinal
rod.
22. The connector of any one of claims 1 to 21, wherein the cavity of the
spring chuck has a spherical shape.
23. The connector of any one of claims 1 to 22, wherein the spring chuck has
a plurality of slots for allowing the radial movement of the spring chuck,
with at
least one of the slots extending from the upper end of the spring chuck.
24. A vertebral fixation system comprising:
a longitudinal rod;
a bone anchoring element; and
a connector for connecting the rod to the bone-anchoring element, said
connector comprising:
a connecting member having upper and lower ends, a bore hole
through the lower end with a central axis, and a through hole running
transversely to the central axis for receiving the longitudinal rod;
a tensioning member configured and dimensioned for insertion in the
upper end of the connecting member for securing a bone-anchoring
element, having a head and a shaft, to the connector at a surgeon-
selected angle;
a radially-compressible spring chuck arranged within the connecting
member, coaxial with the central axis and having an upper end and a

14
lower end that includes a cavity for receiving the head of the bone
anchoring element; and
an insert slidable in the bore hole of the connecting member and having
a recess complementary in shape to an outer surface of the radially
compressible spring chuck:
wherein the spring chuck is axially supported in the bore hole without
impeding radial movement of the spring chuck therein.
25. The system of claim 24, wherein the bone-anchoring element is a pedicle
screw.
26. The system of claim 24 or 25, wherein the bone-anchoring element has a
turned groove below the head.
27. The system of claim 24, 25 or 26, wherein the spring chuck and the head
of the bone-anchoring element have different hardnesses in an area of contact
between the head and the spring chuck.
28. The connector of claim 27, wherein the harder material is an alloy of
Titanium, Aluminum, and Niobium, and the softer material is commercially pure
titanium.
29. The connector of claim 27, wherein the head and the spring chuck are
made of the same material and the difference in hardness is obtained by
surface
treatment processing of the material.

Description

CA 02289629 2001-10-09
1
DEVICE FOR THE CONNECTION OF A LONGITUDINAL ROD WITH A
I'EDICLE SCREW
The invention relates to a device for the connection of a longitudinal rod
with a
bone-anchoring element.
From prior art pedicle screws to the fixation of vertebral column are known
which
show the advantage that the longitudinal rod may be inserted afterwards from
topside and the angle between pedicle screw and longitudinal rod is variably
adjustable. Such pedicle screwy are known among others from the patents EP-B
0 330 881 SHERMAN and EP-B 0 441 729 VIGNAUD. The disadvantage of
these known pedicle screws is that in spite of the degree of freedom between
pedicle screw and longitudinal rod the latter must often be bent three
dimensionally because of the anatomical conditions.
In case of other pedicle screws as for instance according to the DE-C 195 09
332
HARMS this disadvantage has been eliminated. Thanks to the spatial movability
of the screw head respective to the screw part the longitudinal rod must be
bent
up to three pedicle screws per longitudinal rod only in one plane when
mounted.
The disadvantages of this known pedicle screw consist therein that the head
part
and the threaded part are nolr apt to be separated, the head part and the
longitudinal rod are not apt to be fastened separately with respect to the
threaded part, the reachable solidity is low because of the one-sided
alignment of
the longitudinal slots in the pressure element according to the DE-C 195 09
332
and it is difficult to remobilise the head part once it is fastened. The
separability
of the head part and the threaded part is a necessity to use different head
parts
according to the need and that the view is not impeded through the head part
during the screwing in of the screw part into the bone. A separate fastening
of
the head part and the longitudinal rod and a high solidity between head part
and
threaded part enable the application of distraction and compression without a
loss of angle between the pedicle screw and the longitudinal rod and the

CA 02289629 2001-10-09
2
conservation of the anatomical bending of the stabilized vertebral segments.
Remobilization is especially important in case of explantation or new
adjustment
of the fixation.
A further such connection device is disclosed in WO 97/02786 ERRICO which
allows in a simple manner to connect a pedicle screw or more generally a bone-
anchoring element with a longitudinal rod and which permits a great freedom
regarding the angle between thE: two elements. In case of this known
connection
device the disadvantage consists therein that the spring chuck is part of the
connection element and therefore consists of the same material impairing the
choice and pairing of the material with the bone screw to improve the
solidity.
Here, the invention shall offer remedy. The object of the invention lies
therein to
provide a device for the connection of a longitudinal rod with a pedicle screw
having the following qualities:
- simple handling;
- screwing in the threaded part of the device even without the connection
part;
- possible later snap-on of the connection part;
- depending on the situation and the preference of the surgeon the free choice
of
or combination of sidewardly open, upwardly open or dosed connection parts.
For instance an upwardly open connection part facilitates the insertion of the
longitudinal rod while a sideward opening enables sideward corrections and
thanks to the possibility of the aideward removing of the connection part each
pedicle screw may any time be fastened at the longitudinal rod or be removed
again without the necessity of de~mounting the whole fixation system.
The invention provides a vertebral fixation system connector for connecting a
longitudinal rod with a bone-anchoring element, the connector comprising a
connecting member having upper and lower ends, a bore hole through the lower
end with a central axis, and a through hole running transversely to the
central
axis for receiving a longitudinal rod, and a tensioning member configured and

CA 02289629 2001-10-09
2a
dimensioned for insertion in the upper end of the connecting member for
securing a bone-anchoring element, having a head and a shaft, to the connector
at a surgeon-selected angle. The connector also comprises a radially-
compressible spring chuck arranged within the connecting member, coaxial with
the central axis and having an upper end and a lower end that includes a
cavity
for receiving the head of the bone-anchoring element, and an insert slidable
in
the bore hole of the connecting member and having a recess complementary in
shape to an outer surface of the radially compressible spring chuck. The
spring
chuck is axially supported in the bore hole without impeding radial movement
of
the spring chuck therein.
The invention also provides a vertebral fixation system comprising a
longitudinal
rod, a bone anchoring element, and a connector for connecting the rod to the
bone-anchoring element. Th~~ connector comprises a connecting member
having upper and lower ends, a bore hole through the lower end with a central
axis, and a through hole running transversely to the central axis for
receiving the
longitudinal rod, and a tensioning member configured and dimensioned for
insertion in the upper end of the connecting member for securing a bone-
anchoring element, having a head and a shaft, to the connector at a surgeon-
selected angle. The connector also comprises a radially-compressible spring
chuck arranged within the connecting member, coaxial with the central axis and
having an upper end and a louver end that includes a cavity for receiving the
head of the bone-anchoring element, and an insert slidable in the bore hole of
the connecting member and having a recess complementary in shape to an outer
surface of the radially compressible spring chuck:. The spring chuck is
axially
supported in the bore hole without impeding radial movement of the spring
chuck
therein.
The device according to the invention consists of a connection part accepting
the
longitudinal rod wherein a pediclE~ screw having a preferably spherical head
may

. CA 02289629 1999-11-09
3
afterwards be snapped-on and fastened. The connection part may be simply
snapped-on in the desired number and variant onto the pedicle screws already
implanted in the vertebral bodies so that a primary connection between
longitudinal
rod and pedicle screw is produced. Via the screw-in of the tension means into
the
fixation device the longitudinal rod is axially and rotatively fastened and
simultaneously the device is fastened at a stable angle. Thereby the adjusting
screw
serving as a tension means presses on the longitudinal rod inserted in the
device,
this one presses on hollow cylinder which encompasses a hollow truncated cone
which
is alternatingly slotted and radially not fastened and which is itself
compressed
because of its sonically shaped outer surface and wedging the preferably
spherical
head of the pedicle screw.
The device according to the invention such offers the advantage compared to
the
known devices that the pedicle screws are not only fastenable exactly
perpendicularly
to the longitudinal rod but allows an angle of up to ~ 25° and because
of the distance
between the rotating center of the connection part and the axis of the
longitudinal rod
sideward deviations between longitudinal rod and pedicle screw may be
compensated
to a certain degree depending on the thickness of the longitudinal rod having
an
amount of between 4 to 10 mm. This qualities enable the application of
longitudinal rods standardizedly prebent at the production site what causes
serious
difficulties by the mounting of conventional systems. A further advantage of a
variant of
the device according to the invention consists therein that depending on the
embodiment of the hollow cylinder and the tension means respectively on the
embodiment of the device the longitudinal rod and the preferably spherical
head of
the bone screw may be fastened separately.
The angular stability may be improved such that the head of the screw consists
of a
relatively hard material (e.g. Titanium-Aluminium-Niobium-alloy) and the
alternately slotted hollow truncated cone consists of a relatively soft
material (e.g.
Titanium in its soft state).
Another possibility for the improvement of the angular stability consists
therein to
provide the preferably spherical head of the pedicle screw and/or the
complementary

CA 02289629 1999-11-09
4
cavity in the hollow truncated cone with a three dimensional structure e.g. in
the
shape of grooves.
Therewith the structure attached at the head of the screw consisting of a
relatively
hard material is pressed into the relatively soft material of the hollow
truncated cone.
A change of the hardness of the materials is possible at least in the contact
area,
too. The difference of hardness may also be obtained through different cold
forming or different crystallization of the same material and whereby the
harder
material is preferably highly trained steel 1.4441 and the soft material is
hot treated
steel 1.4441. Apart from this the difference of hardness may be obtained via
surface
treatment as coating or ion implantation.
To be able to screw in the pedicle screws into the bone they are provided at
the
spherical head preferably with a hexagon socket. If the head apt to be snapped-
on
is also drilled through optionally only the pedicle screw or the whole device
may be
screwed in at once. The latter has the advantage above all that at any time
the device
may be farther screwed in or screwed reverse to obtain a compensation in
height.
A further embodiment of the invention consists therein that the angles of the
cones of
the spring chuck and of the insert compressing the spring chuck are different
and
form a not self locking cone joining.
Other embodiments of the device according to the invention enable a subsequent
insertion of the longitudinal rod from the side or from above. Through the
screw in of
the tension screw into the fixation device simultaneously the longitudinal rod
is
fastened axially and rotatively within the device and the device is fastened
at a stable
angle. Thereby the tension screw presses onto the longitudinal rod inserted in
the
device, this one presses onto the insert of the fixation device and this
insert wedges
the springable contact studs of the spring chuck via a preferably conical
shaped
inner surface and a corresponding likewise conical shaped outer surface of the
spring
chuck on the preferably spherical head of the pedicle screw.

CA 02289629 1999-11-09
The invention and further embodiments of the invention are discussed in more
detail in the following section by means of the partially schematic
representations of
several embodiments.
The figures show:
Fig. 1 a longitudinal cut through the connection part of a variant of the
device
according to the invention together with a longitudinal rod and a pedicle
screw
having a spherical head;
Fig. 2 a perspectival representation of a variant of the device according to
the
invention;
Fig. 3 a longitudinal cut through a modified device according to the invention
having qualities as disclosed in fig. 1 but with the difference that the
longitudinal rod is
accepted via a sidewardly open channel in the connectionpart;
Fig. 4 a longitudinal cut through a modified device according to the invention
having qualities as disclosed in fig. 1 but with the difference that the
longitudinal rod is
accepted in an oval channel in the connection part;
Fig. 5 a perspectival representation of a variant of the device according to
the
invention;
Fig. 6 a perspectival representation of a further variant of the device
according to the
invention;
Fig. 7 a perspectival representation of a further variant of the device
according to the
invention;
Fig. 8 a perspectival representation of a further variant of the device
according to the
invention; and

CA 02289629 1999-11-09
6
Fig. 9 a perspectival representation of a further variant of the device
according to the
invention.
The variant of the device according to the invention shown in fig. 1
essentially
consists of a hollow cylindrical sleeve 10 which is provided with a channel 11
open
towards the upper end 28 for the acceptance of the longitudinal rod 1. If
required the
channel 11 may also be open towards the side (fig. 3) or be formed as an oval
bore
hole (fig. 4). At the tower end 29 of the sleeve 10 a preferably ring shaped
channel
17 is provided wherein the flange 18 of the spring chuck 7 inserted in the
bore hole 6
of the sleeve 10 is attachable. Such the spring chuck 7 is fastened against
displacement along the central axis 4 of the sleeve 10 but not radially
fastened. The
spring chuck 7 is provided in its inside with a cavity 15 preferably shaped as
a hollow
sphere. Slots, wherefrom alternately a first number run into the upper base
area 8 and
another number run into the lower base area 13 of the spring chuck 7 enable a
homogeneous expansion and compression of the spring chuck 7. Thanks to the
radial
freedom of the spring chuck 7 in the channel 17 the head 5 of the pedicle
screw 2
may at any time be snapped into respectively out of the spring chuck 7 as long
as
the device is not fastened through tightening the tension screw 23. Outside
the spring
chuck 7 is shaped tapering sonically towards its upper end 8. A hollow
cylindrical
insert 9 which is shaped complementarily conical to the cone at the spring
chuck 7 at
its lower end may slide within the bore hole 6 of the sleeve 10 and depending
on the
effect of force radially compress the spring chuck 7 via the conical joining
14 and
therewith fasten the head 5 of the pedicle screw 2 being inside of the cavity
15. This
connection is also loosenable what is facilitated through the attachment of a
shoulder
16 in the insert 9. Longitudinal rod 1 and pedicle screw 2 are fastened by
means of a
tension screw 23 which is screwed in coaxially into an insert screw 21 being
at the
upper end 28 of the sleeve 10. The tension screw 23 presses when being
tightened
onto the longitudinal rod 1 which itself presses onto the insert 9 and
therewith causes
the closure of the spring chuck 7 through pushing into one another the cones
14.
The function of the insert screw consists therein to alter the thread 19 in
the sleeve 10
interrupted by the channel 11 into a closed thread wherein the tension screw
23 may
run unhindered.

CA 02289629 1999-11-09
7
Since the through hole 11 according to the variant of the device according to
the
invention shown in fig. 1 is formed as a channel open at the upper end 28 of
the
sleeve 10 and thus the sleeve 10 is weakened at this part a swivel ring 22 is
mounted
that prevents the widening of the sleeve 10 when the tension screw 23 is
tightened.
A further variant of the device according to the invention is shown in fig. 2.
The main difference between the embodiment according to fig. 1 and the one
according to fig. 2 consists in the sideward dislocation of the channel 52 to
the
acceptance of the longitudinal rod 1 with respect to the bore hole 6 with the
central
axis 4. Thus it is possible to separately fasten the longitudinal rod 1 and
the pedicle
screw 2. From the lower end 29 of the connection part 30 a bone anchoring
element
40 may be inserted and be fastened analogously to the variant shown in fig. 1
by
means of a spring chuck 7, an insert 9 and a tension means 50. Thereby the
tension
means 50 according to the variant shown in fig. 2 presses directly onto the
insert 9. A
channel 52 running transversely to the central axis 4 without contacting the
bore hole
6 which may again be optionally sidewardly open, open towards the upper end 28
or
be realized as a bore hole serves to the acceptance of the longitudinal rod 1.
The fastening of the longitudinal rod 1 is done by means of a separate screw
51.
The variant of the device according to the invention shown in fig. 3
differentiates
from the variant shown in fig. 1 only by that means that the sidewardly open
through
opening 2fi in the sleeve 10 accepts the longitudinal rod 1. The insert 9 is
lower at this
side, too. Thus, the longitudinal rod 1 may be subsequently inserted into the
device as in case of the variant shown in fig. 1.
The variant of the device according to the invention shown in fig. 4
differentiates
from the variant shown in fig. 1 only by that means that a closed oval through
opening 27 within the sleeve 10 accepts the longitudinal rod 1.
The variant of the device according to the invention shown in fig. 5
differentiates
from the variant shown in fig. 1 only by that means that a nut 42 is employed
as a
tension means 50. Thereto the sleeve 10 is provided with an exterior thread 41
whereon the nut 42 is screwed. When tightened the nut 42 presses onto the
longitudinal

CA 02289629 1999-11-09
8
rod 1 which itself presses onto the insert 9 by what means the spring chuck 7
is
radially compressed and such the head 5 of the pedicle screw 2 and the
longitudinal
rod 1 are simultaneously fastened. A collapse of the channel 11 may be
prevented by
forming the thread 41 as buttress thread or by inserting a cylindrical element
47 into
the bore hole 6.
In fig. 6 another variant of the device according to the invention is shown.
This
one differentiates from the variant shown in fig. 1 only by that means that a
locking
screw 43 serves as a tension means 50. The widening of the channel 11 is
prevented
by forming the thread 19 as a buttress thread.
Also the variant shown in fig. 7 differentiates from the variant shown in fig.
1 only
through the construction of the tension means 50. The sleeve 10 is provided
with an
exterior thread 41 whereon the threaded sleeve 44 is screwed. The fastening of
the
longitudinal rod 1 and pedicle screw 2 happens by means of a tension screw 23
which is screwed into the threaded sleeve 44. The threaded sleeve 44 thus has
the
same function as the threaded insert 21 shown in fig. 1. Thanks to the
threaded
sleeve 44 inserted between the slotted thread 41 and the tension screw 23 the
tension
screw 23 runs within an uninterrupted thread.
Also another variant of the device according to the invention is shown in fig.
8. This
variant accentuates by that means that the longitudinal rod 1 and the pedicle
screw 2
may be fastened separately. To this purpose the sleeve 10 is provided at its
upper
end 28 with an interior thread 19 and an exterior thread 41. The channel 12 of
the
insert 9 is shaped such that the longitudinal rod 1 always lies on the lower
edge of the
through opening 11 during its fastening by means of the nut 42. When the
tension
screw 23 which presses directly on the insert 9 extending over the
longitudinal
rod 1 is tightened the spring chuck 7 is compressed thus fastening the pedicle
screw 2.
Furthermore, the variant of the device according to the invention shown in
fig. 9
enables a separate fastening of the longitudinal rod 1 and the pedicle screw
2. The
trough opening 11 and the channel 12 are shaped such that the longitudinal rod
1
always lies on the channel 12 when fastened. The longitudinal rod 1 is
fastened by
means of a stud bolt 45 which is screwed into an interior thread 46 in the
insert 9. The

CA 02289629 1999-11-09
9
tension screw 23 serves to fasten the pedicle screw 2 whereby the tension
screw 23
presses onto the insert 9 whereby this one is sliding over the spring chuck 7
thus
radially compressing it. The widening of the channel 11 may also be prevented
either
by shaping the threads 19 and 46 as buttress threads or by using a sleeve 22
as
shown in fig. 1.

Representative Drawing