U.S. patent application number 12/706405 was filed with the patent office on 2010-07-01 for intervertebral connecting device.
This patent application is currently assigned to WARSAW ORTHOPEDIC, INC.. Invention is credited to Henry Graf.
Application Number | 20100168797 12/706405 |
Document ID | / |
Family ID | 26212506 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100168797 |
Kind Code |
A1 |
Graf; Henry |
July 1, 2010 |
Intervertebral Connecting Device
Abstract
The invention concerns a device comprising at least a fixed
element (2), secured to a vertebra, at least a mobile element (10),
capable of moving relative to the or each fixed element, and at
least an intermediate element (22) for articulating the mobile
element relative to the fixed element. The intermediate element
(22) is received in an internal volume of the mobile element, (10),
and the fixed element (2) is received at least partly in an
internal volume (26) of the intermediate element (22). Means are
provided for securing, at least in translation, said intermediate
element (22) to the fixed element (2), comprising the periphery of
the substantially rigid outlet of the internal volume of the
intermediate element.
Inventors: |
Graf; Henry; (Lyons,
FR) |
Correspondence
Address: |
MEDTRONIC;Attn: Noreen Johnson - IP Legal Department
2600 Sofamor Danek Drive
MEMPHIS
TN
38132
US
|
Assignee: |
WARSAW ORTHOPEDIC, INC.
Warsaw
IN
|
Family ID: |
26212506 |
Appl. No.: |
12/706405 |
Filed: |
February 16, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10330722 |
Dec 27, 2002 |
7691131 |
|
|
12706405 |
|
|
|
|
Current U.S.
Class: |
606/264 ;
606/278 |
Current CPC
Class: |
A61B 17/7041 20130101;
A61B 17/7058 20130101; A61B 17/7007 20130101; A61B 17/8047
20130101; A61B 17/8605 20130101; A61B 17/7035 20130101; A61B
17/7011 20130101; A61B 17/701 20130101 |
Class at
Publication: |
606/264 ;
606/278 |
International
Class: |
A61B 17/70 20060101
A61B017/70 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2000 |
FR |
00/08522 |
Aug 1, 2000 |
FR |
00/10155 |
Jun 29, 2001 |
FR |
PCT/FR01/02098 |
Claims
1. An intervertebral connecting device, which is intended to
connect at least two vertebrae together, this device being
characterized in that it includes: at least one stationary element
(2; 2'; 2''; 2'''; 52, 53; 152, 153), connected with a vertebra or
the sacrum, at least one mobile connecting element (10; 10'; 10'';
10'''; 60; 110; 165; 215; 265; 315) capable of moving with respect
to the stationary element or each stationary element, as well as at
least one intermediate element (22; 22'; 22''; 22'''; 72; 172,
172') allowing the articulation of the mobile element or each
mobile element with respect to the stationary element or each
stationary element, in that the intermediate element or each
intermediate element is received in interior volume (16; 16'; 116;
167, 169; 217, 227; 327) of said mobile element (10; 10'; 10'',
10'''; 110; 165; 215; 265; 315) or of said stationary element (52,
53), in that stationary element (2; 2'; 2''; 2'''; 152, 153) or
mobile element (60) is received at least partially in interior
volume (26; 26') of the intermediate element, and in that it is
provided with some means allowing the connection, at least in
translation, of said element (2; 2', 2''; 2'''; 152, 153) or of
said mobile element (60) with respect to said intermediate element,
these means of connection in translation including the periphery of
outlet (27), which is essentially rigid, of interior volume (26) of
intermediate element (22).
2. A device according to claim 1, characterized in that
intermediate element or each intermediate element (22; 22'; 22'';
172, 172') is received in an interior volume of mobile element (10;
10'; 10''; 10''', 110; 165; 215; 265; 315), in that stationary
element (2; 2', 2''; 2'''; 152, 153) is received at least partially
in an interior volume of the intermediate element, and in that
[text missing in source document] are provided [text missing] of
the stationary element with respect to the intermediate
element.
3. A device according to claim 2, characterized in that said
intermediate element (22; 22'; 22''; 22'''; 172) is connected in
translation with respect to said mobile element (10; 10', 10'';
10'''; 110; 165; 215).
4. A device according to claim 3, characterized in that outlet
(16') of interior volume (16) of mobile element (10) has an
essentially rigid periphery, capable of connecting in translation
the intermediate element with respect to the mobile element.
5. A device according to claim 3 or 4, characterized in that said
intermediate element (22; 22'; 22''; 22'') has truncated spherical
exterior surface (24) and cooperates with corresponding spherical
interior surface (18) with which said mobile element (10; 10';
10''; 10'') is provided.
6. A device according to claim 5, characterized in that stationary
element (2') has head (4') which is received in the interior volume
of intermediate element (22'), and in that said head, the
intermediate element and the interior volume of said mobile element
(10') are concentric.
7. A device according to claim 3, characterized in that said
intermediate element (172') is also connected in rotation with
respect to mobile element (165; 215; 265; 315).
8. A device according to claim 2, characterized in that
intermediate element (22) has at least one degree of freedom, at
least in translation, with respect to said first mobile element
(110).
9. A device according to claim 8, characterized in that said mobile
element (110) has tubular portion (112), along which said
intermediate element (22) is capable of sliding.
10. A device according to one claims 2 to 9, characterized in that
said mobile element (10; 10'; 10''; 10'''; 110) has notch (20; 120)
for introduction of intermediate element (22; 22'; 22''; 22''') in
interior volume (16; 116) of this mobile element.
11. A device according to one of claims 2 to 10, characterized in
that said stationary element (2; 2'; 2'') has at least one degree
of freedom in rotation with respect to intermediate element (22;
22'; 22'').
12. A device according to claim 11, characterized in that said
stationary element (2; 2'; 2'') has a spherical exterior surface
which is capable of cooperating with corresponding spherical
interior surface (28) of intermediate element (22; 22'; 22'').
13. A device according to claim 12, characterized in that the
spherical exterior surface of said stationary element is provided
with equatorial flat part (6; 6') for introduction of said
stationary element (2; 2'; 2'') into the interior volume of
intermediate element (22; 22'; 22'').
14. A device according to claim 13, characterized in that said
stationary element (2) is provided with stop component (32), which
is removable in particular, making it possible to limit the
pivoting of intermediate element (22) with respect to stationary
element (2).
15. A device according to any one of claims 1 to 10, characterized
in that in operation, stationary element (2''') is connected with
intermediate element (22''') both in translation and in
rotation.
16. A device according to claim 15, characterized in that the
stationary element has threaded end (3''') capable of cooperating
with threaded opening (23''') of intermediate element (22''').
17. A device according to claim 1, characterized in that
intermediate element or each intermediate element (72) is received
in an interior volume of stationary element (52, 53), in that
mobile element (60) is received at least partially in an interior
volume of the intermediate element, and in that some means are
provided allowing the connection, at least in translation, of the
mobile element with respect to the intermediate element.
18. A device according to any one of the preceding claims,
characterized in that the stationary element is pedicle screw (2;
2'; 2''; 2'''; 52, 152).
19. A device according to any one of the preceding claims,
characterized in that the stationary element is plate (53, 153)
which can be attached on the sacrum.
Description
[0001] The present invention relates to an intervertebral
connecting device.
[0002] A known device of this type exists, which has at least two
pedicle screws, each of which has a first end connected with a
corresponding vertebral body, a swollen intermediate portion, as
well as a second threaded end. Auxiliary components, provided with
a bow for attachment of a rod extending between the vertebrae, are
arranged on each of the aforementioned swollen portions. A bolt,
which cooperates with the threaded end of each screw, makes
possible the immobilization of each auxiliary component, once the
latter is positioned in the appropriate manner.
[0003] This known device nevertheless has certain disadvantages, in
that it involves a relatively delicate assembly process.
Furthermore, once implanted, it offers no degree of freedom between
the different elements of which it consists. Thus, when forces are
exerted on the vertebral bodies, this absence of degree of freedom
induces a transmission of these forces over the whole device, so
that the latter has a tendency to become disconnected from the
vertebrae which it connects and furthermore induces malfunctionings
with regard to the whole vertebral chain.
[0004] In order to palliate these different disadvantages, the
present invention proposes the execution of a device whose
structure is simple, the assembly of which is easy and which is
implanted in a reliable manner in the vertebrae which it
connects.
[0005] To this effect, it relates to an intervertebral connecting
device, which is intended to connect at least two vertebrae
together, this device being characterized in that it includes:
[0006] at least one stationary element, connected with a vertebra
or with the sacrum, [0007] at least one mobile connecting element
capable of moving with respect to the stationary element or each
stationary element, [0008] as well as at least one intermediate
element allowing the articulation of the mobile element or each
mobile element with respect to the stationary element or each
stationary element, [0009] in that the intermediate element or each
intermediate element is received in an interior volume of said
mobile element, [0010] in that the stationary clement or the mobile
element is received at least partially in an interior volume of the
intermediate element, [0011] and in that it is provided with some
means allowing the connection, at least in translation, of said
stationary element or of said mobile element with respect to said
intermediate element, these means of connection in translation
including the periphery of the outlet, which is essentially rigid,
of the interior volume of the intermediate element.
[0012] The invention will be described below in reference to the
appended drawings given only as non-limiting examples and in
which:
[0013] FIG. 1 is a view in longitudinal section, illustrating the
different elements constituting an intervertebral connecting device
according to a first embodiment of the invention;
[0014] FIGS. 2, 2A and 2B are views similar to FIG. 1, illustrating
three steps of the assembly of an intermediate element of the
device of FIG. 1, in the interior volume of a mobile element of
this device;
[0015] FIGS. 3 and 3A are views similar to FIG. 1, illustrating the
introduction of a stationary element of the device of FIG. 1 into
the interior volume of its intermediate element;
[0016] FIGS. 4 to 6 are views similar to FIG. 3A, illustrating
embodiment variants of the device according to the invention;
[0017] FIGS. 7 and 8 are respectively views in longitudinal and
cross section of a device according to an additional embodiment of
the invention,
[0018] FIGS. 9 and 10 are views in longitudinal section,
illustrating two additional embodiment variants of the
invention;
[0019] FIG. 11 is a perspective view, illustrating the different
elements of a device according to an additional variant of the
invention;
[0020] FIG. 12 is a view in longitudinal section of the device of
FIG. 11, once assembled; and
[0021] FIGS. 13 to 15 are perspective views, similar to FIG. 11,
illustrating three additional embodiment variants of the
invention.
[0022] FIG. 1 illustrates a first embodiment of the connecting
device according to the invention, which includes pedicle screw 2,
which is intended to be connected in a vertebral body which is not
represented. This pedicle screw, which thus constitutes a
stationary element, is provided with spherical head 4 which has
equatorial flat part 6 extending in an inclined manner, in the
sense that it is not perpendicular to main axis A of screw 2. Head
4 is furthermore hollowed with blind hole 8, intended for receiving
a maneuvering component, in particular the end of a screwdriver
which is not represented.
[0023] The device represented in FIG. 1 also includes a mobile
element, which is illustrated partially and designated overall by
the reference 10. This mobile element has body 12 which extends
between the two vertebrae connected by the device of the invention
and which is ended by two hollow ends, a single one of which, 14,
is represented.
[0024] Each end defines housing 16, forming an interior volume of
element 10, which is bordered by walls 18 forming a truncated
sphere. These walls have notch 20 making it possible to locally
widen the section of passage of housing 16 so as to allow
introduction of the intermediate element, as will be described
subsequently. Furthermore, the transverse dimension 1 of outlet 16'
of housing 16 is less than the diameter L of this housing.
[0025] The device of FIG. 1 finally includes intermediate element
22, whose exterior surface 24 forms a portion of a sphere, whose
diameter is identical to that L of housing 16. Intermediate element
22 is hollowed with an opening passing through, which defines
housing 26, forming an interior volume bordered by truncated
spherical walls, whose diameter D is identical to that of head 4.
Housing 26 connects with chamber 30 allowing passage of the
aforementioned maneuvering component, in the direction of blind
hole 8.
[0026] The assembly of the device illustrated in FIG. 1 will be
described in reference to FIGS. 2 and 3.
[0027] In a first step, it is a matter of introducing intermediate
element 22 into interior volume 16 of mobile element 10. To this
effect, this intermediate element 22 is arranged so that its
spherical exterior surface 24 is in the vicinity of outlet 16'.
Then, intermediate element 22 and mobile element 10 are axially
brought together. The intermediate element and the mobile element
are not connected in rotation or in translation in this position of
introduction.
[0028] Intermediate element 22 is then pivoted around its axis so
that its exterior surface 24 extends in the vicinity of interior
walls 18, as shown in FIG. 2C. Once these operations are completed,
intermediate element 22 has no degree of freedom in translation
with respect to the mobile element, in this position of use. In
effect, the transverse dimension 1 of outlet 16' is less than the
exterior diameter of intermediate element 22. On the other hand,
the latter has three degrees of freedom in rotation with respect to
mobile element 10.
[0029] Then, as shown in FIG. 3, it is a matter of introducing
spherical head 4 of pedicle screw 2 into housing 26 of intermediate
element 22. To this effect, this screw 2 is first of all inclined
so that flat part 6 extends horizontally in this FIG. 3, namely
perpendicularly to the main axis of intermediate element 22.
[0030] This intermediate element 22 is then brought toward screw 2,
according to a translation parallel to the main axis of this
intermediate element 22. Given that the transverse dimension d of
the flat part is equal to, or slightly less than, the transverse
dimension d' of outlet 27 of housing 26, this allows free
introduction of head 4 into this housing 26, which is illustrated
in FIG. 3.
[0031] The periphery of outlet 27 is essentially rigid, that is to
say non-deformable. To this effect, intermediate element 22 can be
produced entirely out of a rigid material, metallic in particular.
As a variant, this intermediate element can be produced out of a
deformable material, such as polyethylene, a rigid ring then being
connected in the vicinity of this outlet.
[0032] Then, head 4 is pivoted inside of the housing so that flat
part 6 is inclined again, that is to say that it is no longer
facing the aforementioned outlet 27. Head 4 is then free to pivot
with respect to this housing 26 but has no degree of freedom in
translation with respect to intermediate element 22, given that
diameter D of head 4 is greater than the transverse dimension of
outlet 27 of housing 26.
[0033] Once the device is put in the configuration illustrated in
FIG. 3A, it is a matter of attaching pedicle screw 2 in a
corresponding vertebral body, by means of a maneuvering component
cooperating with blind hole 8 of this pedicle screw 2.
[0034] As an assembly variant, it is possible to first of all
attach each pedicle screw in a corresponding vertebral body. Then,
each intermediate element 22 is introduced into interior volume 16
of mobile element 10, as explained in reference to FIG. 2.
[0035] The stationary element and the mobile element are then
mutually brought together, intermediate element 22 is tilted within
its housing 6. Then one brings closer intermediate element 22 thus
tilted, with respect to pedicle screw 2, so that flat part 6
cooperates with the periphery of outlet 27, as illustrated in FIG.
3.
[0036] Once the device of the invention is placed in the
configuration of this FIG. 3A, it is possible to connect, on flat
part 6, a stop means which is advantageously removable, such as
screw 32. The latter, by limiting the pivoting of head 4 with
respect to intermediate element 22, keeps this head from regaining
its position in FIG. 3, which prevents any disconnection between
intermediate element 22 and pedicle screw 2.
[0037] FIG. 4 illustrates an embodiment variant of the invention,
in which pedicle screw 2' is provided with spherical head 4' which
is itself provided with inclined equatorial flat part 6'. This head
4' is introduced, in a manner similar to that described in the
preceding, into intermediate element 22' provided with interior
volume 26'.
[0038] It should be noted that, contrary to the example described
in reference to FIGS. 1 to 3, spherical head 4' and interior volume
26' are concentric. In other respects, intermediate element 22' is
received in interior volume 16' of mobile element 10' in a manner
similar to that described above.
[0039] FIGS. 5 and 5A illustrate embodiment variants in which
removable attachment means are provided, allowing one to connect
pedicle screw 2'' either with mobile element 10'' or with
intermediate element 22''. To this effect, head 4'' of the pedicle
screw is provided with threading 5'', cooperating with threaded rod
32 of attachment element 34. The latter also has dome 36 in the
shape of a mushroom, which rests on the walls of end 14'' of mobile
element 10''.
[0040] In the embodiment of FIG. 5A, dome 36' of attachment element
34' also rests on the end of intermediate element 22'', while
threaded rod 32' is connected with spherical head 4'' of the
pedicle screw.
[0041] FIG. 6 illustrates an additional variant of the invention,
in which intermediate element 22'' is hollowed with threading 23''.
The latter cooperates with threaded end 3''' of pedicle screw 2'',
which has no spherical head. Intermediate element 22'' is in other
respects received, in the manner of a ball and socket joint, in
mobile element 10'' as in the preceding examples.
[0042] As a variant, it is possible to replace the pedicle screw
described above by a rod extending from a sacral plate, namely a
plate which is intended to be screwed on the sacrum.
[0043] FIGS. 7 and 8 illustrate another embodiment of the
invention, which uses at least two pedicle screws 2, as well as at
least two intermediate elements 22, identical to those described in
reference to FIGS. 1 to 3.
[0044] Mobile element 110 has tubular body 112 which is ended by
two closed ends 114 and is hollowed with first longitudinal notch
120 whose periphery is essentially rigid, allowing each
intermediate element 22 to be introduced into interior volume 116
of mobile element 110.
[0045] This introduction is carried out in a manner similar to that
described in reference to FIGS. 2, 2A and 2B, by pivoting, of the
intermediate element a quarter turn. Provided furthermore is a
second longitudinal notch 120' diametrically opposite the one 120,
allowing passage of a maneuvering component, for the purpose of
attachment of each screw 2 in the corresponding vertebrae.
[0046] This embodiment gives three degrees of freedom in rotation
to intermediate element 22 with respect to mobile element 110; and
also allows axial sliding of this intermediate element along
cylindrical body 112. As a variant, head 4 of each screw can be
concentric with respect to the intermediate element, as in the
embodiment example described in reference to FIG. 4.
[0047] FIG. 9 illustrates a device allowing one to connect three
neighboring vertebrae.
[0048] This device includes two end screws 2', similar to those of
FIG. 4. Each screw has head 4' provided with flat part 6',
cooperating with intermediate element 22'. The latter is received
in interior volume 16' of mobile element 10', which is ended,
opposite from its end which receives intermediate element 22', by
spherical head 15'.
[0049] Provided furthermore is additional screw 3', placed in
middle position. It has elongated head 5', in which two housings 7'
are arranged, of which the truncated spherical walls extend
according to an angular sector greater than 180.degree..
[0050] These two housings are open on opposite sides from one
another, in a manner roughly perpendicular to the main axis of this
screw 3'. The transverse dimension of the outlet of each housing 7'
is less than the diameter of its spherical walls. Spherical head
15' of each mobile element 10', which is provided with inclined
equatorial flat part 17', cooperates with one of housings 7' of
middle screw 3'.
[0051] For the purpose of assembling the prosthesis, it is first of
all a matter of introducing each spherical head 15' into the
interior volume of a corresponding housing 7', as described in the
preceding for the introduction of head 4 of screw 2 in the interior
volume of intermediate element 22'.
[0052] Then, each intermediate element 22' is introduced into the
interior volume of mobile element 10'. Finally, head 4' of each end
screw 2' is introduced into the interior volume of a corresponding
intermediate element 22'.
[0053] FIG. 10 illustrates a device allowing one to connect two
neighboring vertebrae, as well as the sacrum.
[0054] Two similar mobile elements 60 are provided, each of which
includes rod 61. The latter is ended, at its two ends, by spherical
head 65 provided with inclined flat parts 67.
[0055] Middle screw 53' similar to that 3' of FIG. 9 is furthermore
provided. Each spherical head 65 is received in corresponding
housing 57' belonging to this middle screw 53'.
[0056] Furthermore, two stationary end elements are provided,
namely pedicle screw 52, as well as plate 53, attached on the
sacrum. At its opposite end from middle screw 53', each mobile
element 60 is received in intermediate element 72, similar to those
22, 22', 22'' and 22'''' described above.
[0057] Furthermore, this intermediate element 72 is received in the
interior volume of head 54, 55, respectively belonging to pedicle
screw 52 or to sacral plate 53.
[0058] The mutual connection between head 65, intermediate element
72, and screw 52 or plate 53 is similar to that existing between,
for example, head 4 of screw 2, intermediate element 22 and mobile
element 10.
[0059] In other words, in this FIG. 10, head 65 is substituted for
head 4, the interior volume of screw 52 or plate 53 is substituted
for the interior volume of mobile element 10, while intermediate
element 72 ensures the articulation of mobile element 60 and of
screw 52, just as intermediate element 22 ensures the articulation
of screw 2 and of mobile element 10.
[0060] FIGS. 11 and 12 illustrate a device allowing one to mutually
connect two lumbar vertebrae, as well as the sacrum.
[0061] This device has upper pedicle screw 152, ended by spherical
head 154 provided with inclined flat part 156. Provided furthermore
is sacral plate 153, ended by spherical head 155 provided with
inclined flat part 157. This device also has middle screw 159 ended
by spherical head 161 provided with inclined equatorial flat part
163.
[0062] Also provided is elongated plate 165, of which each end is
hollowed with corresponding cavity 167. Each cavity is similar to
housing 16 represented in FIG. 1. This elongated plate 165 is
furthermore hollowed with oblong opening 169.
[0063] Head 154, 155 of end screw 152 or of plate 153 is received
in corresponding cavity 167, with insertion of intermediate element
172, similar in particular to that 22. Head 161 of middle screw 159
is received in the interior volume of intermediate element 172',
which differs from that 172, in the sense that it is provided,
opposite from its outlet, with threaded rod 173', which is capable
of cooperating with nut 174'.
[0064] The assembly of the device of FIGS. 11 and 12 will now be
explained.
[0065] It is first of all a matter of introducing each intermediate
element 172 into corresponding cavity 167, as described in
reference to FIGS. 2 to 2B. Then, elongated plate 165 is brought
towards screw 152 and sacral plate 153.
[0066] Heads 154, 155 are then introduced into the interior volume
of each intermediate element 172. For this purpose, it can be wise
to pivot these intermediate elements without moving in translation
elongated plate 165, with respect to screw 152 and plate 153. This
can be done by the intermediary of compression device 175, whose
end passes through the opening of cavity 167 opposite from the
vertebrae.
[0067] It should be noted that before elongated plate 165 is moved
towards the vertebrae, intermediate element 172' has been placed on
spherical head 161 of middle screw 159. Rod 173' of this
intermediate element then passes through opening 169 of the plate.
It is thus possible, by screwing of nut 174' on threaded rod 173',
to move, with respect to elongated plate 165, middle screw 159
according to arrow F. This is particularly advantageous inasmuch as
it allows one to induce a movement of the last lumbar vertebra
according to this arrow F, that is to say "to pull" this
vertebra.
[0068] FIG. 13 illustrates an additional embodiment variant of the
invention, in which elongated plate 165 is replaced by connecting
component 215, which has rod 219 ended by two disks 221, each of
which is provided with cavity 217, similar to those 167.
[0069] Provided furthermore is intermediate disk 223 which can be
attached on rod 219 by collar 225. This disk 223 is hollowed with
middle opening 227.
[0070] Each end disk 221 is capable of cooperating, with insertion
of intermediate element 172, with screw 152 or sacral plate 153.
Furthermore, threaded rod 173' of intermediate element 172' is
capable of passing through opening 227 of intermediate disk 223, in
a manner similar to oblong opening 169.
[0071] FIG. 14 illustrates an additional variant of the invention.
Three pedicle screws 152, sacral plate 153, as well as elongated
connecting plate 265 are provided. The spherical head of each screw
152 or of plate 153 is received in the interior volume of
corresponding intermediate element 172'.
[0072] Furthermore, each threaded rod 173' of corresponding
intermediate element 172' is capable of penetrating into opening
269 of plate 265; in such a way as to cooperate with corresponding
nut 174'.
[0073] FIG. 15 illustrates a last embodiment variant of the
invention.
[0074] Connecting component 315 is provided, which has rod 319 on
which disks 323 are arranged, which can be attached by means of
collars 325.
[0075] Opening 327 of each disk 323 is capable of receiving
threaded rod 173' of intermediate element 172', which cooperates
with the spherical head of screw 152, or else of sacral plate 153.
Each rod 173' is furthermore capable of receiving nut 174'.
[0076] The invention allows one to accomplish the objectives
mentioned in the preceding.
[0077] In effect, the different elements constituting the
intervertebral connecting device of the invention have a relatively
simple structure.
[0078] The assembly of these elements is particularly and can be
done by a surgeon without his having to use great physical
force.
[0079] The assembly of the different elements of the connecting
device of the invention furthermore induces almost no deformation
of these elements, which is advantageous in terms of mechanical
reliability.
[0080] It should be noted that the presence of the intermediate
element allows mutual assembly of the stationary element and the
mobile element, even when there is practically no clearance in
terms of rotation between these two elements.
[0081] Finally, once the intervertebral connecting device of the
invention is assembled, it has a great resistance with regard to
mechanical stresses, exerted in traction in particular. In effect,
the presence of the intermediate element allows the possible forces
to which the connecting device according to the invention is
subjected to be transmitted only to a very slight degree.
* * * * *