U.S. patent application number 10/473998 was filed with the patent office on 2004-08-05 for system for intervertebral disk prostheses.
Invention is credited to Keller, Arnold.
Application Number | 20040153157 10/473998 |
Document ID | / |
Family ID | 8177058 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040153157 |
Kind Code |
A1 |
Keller, Arnold |
August 5, 2004 |
System for intervertebral disk prostheses
Abstract
System of intervertebral disc prostheses which includes standard
prostheses and corrective prostheses. The corrective prostheses
serve to compensate for a ventro-dorsal offset. They are
characterized in that, on one of their cover plates (15), the
surface (4') via which it cooperates in a matching manner with the
prosthesis core (3') is offset ventrodorsally relative to the
contact surface (7) by comparison with the standard prostheses.
Inventors: |
Keller, Arnold; (Kayhude,
DE) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
1177 AVENUE OF THE AMERICAS (6TH AVENUE)
41 ST FL.
NEW YORK
NY
10036-2714
US
|
Family ID: |
8177058 |
Appl. No.: |
10/473998 |
Filed: |
April 2, 2004 |
PCT Filed: |
March 20, 2002 |
PCT NO: |
PCT/EP02/03132 |
Current U.S.
Class: |
623/17.14 |
Current CPC
Class: |
A61F 2002/30841
20130101; A61F 2002/30662 20130101; A61F 2/4425 20130101; A61F
2002/30604 20130101; A61F 2002/30616 20130101; A61F 2002/443
20130101; A61F 2310/00017 20130101; A61F 2310/00179 20130101 |
Class at
Publication: |
623/017.14 |
International
Class: |
A61F 002/44 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 5, 2001 |
EP |
01108607.1 |
Claims
1. System of intervertebral disc prostheses which includes standard
prostheses and corrective prostheses, the standard prostheses in at
least one size category being identical to each other and
consisting of a prosthesis core (3, 3', 23, 23') and of at least
one cover plate (1, 1', 2, 2', 21, 21', 22, 22') which has a
core-matching surface (4, 4', 24, 26) cooperating with the
prosthesis core (3, 3', 23, 23') and a contact surface (7) intended
to adjoin a vertebral body (9), characterized in that the
corrective prostheses (14) have a corrective cover plate (15, 20,
29) whose core-matching surface (4', 28, 26) is offset
ventrodorsally relative to the contact surface (7) by comparison
with the standard prostheses.
2. System according to claim 1, characterized in that a dorsal side
is distinguishable on the corrective cover plates (15, 20, 29), and
the core-matching surface (4', 26, 28) is offset dorsally relative
to the contact surface (7).
3. System according to claim 1 or 2, characterized in that the
diameter (12') of the core-matching surface (4', 26, 28) of the
corrective cover plates (15, 20, 29) is smaller than that of the
standard cover plates.
4. System according to claim 3, characterized in that it includes a
first size category with standard cover plates (1, 2, 21, 22) whose
core-matching surfaces (4, 24) have a first diameter (12), and a
second size category with standard cover plates (1', 2', 21', 22')
whose core-matching surfaces (4', 24', 26) have a second diameter
(12') which is smaller than the first diameter (12), and in that
the first size category includes corrective cover plates (15, 20,
29) whose core-matching surface diameters (12') are identical to
the core-matching surface diameter (12') of the standard cover
plates (1', 2', 21', 22') of the second size category.
5. System according to one of claims 1 to 4, characterized in that
it includes corrective prostheses which consist of two corrective
cover plates (15), arranged in opposite directions relative to each
other, and of a prosthesis core (3').
6. System according to one of claims 1 to 5, characterized in that
the core-matching surfaces (4, 24, 4', 24') are spherical
articulation surfaces.
7. System according to one of claims 4 to 6, characterized in that
it includes corrective cover plates (15) whose width in the
mediolateral direction (10) is equal to the width of the standard
cover plates (1, 2, 21, 22) in the same size category and whose
dimension in the ventrodorsal direction (11) is smaller than that
of the standard cover plates (1, 2, 21, 22) in the same size
category.
Description
[0001] It is known to replace damaged intervertebral discs with
prostheses which consist of two cover plates, each to be connected
to an adjacent vertebral body, and of a prosthesis core, said
prosthesis core cooperating with one or both cover plates via
complementary spherical surfaces of articulation (EP-B 298 233).
The cover plates have contact surfaces by means of which they are
connected to the adjacent vertebral bodies. It is desired that the
centre of articulation of the prostheses be arranged in such a way
that the movements permitted by the prosthesis are as far as
possible identical to the natural ones and that forces can be
transmitted uniformly between the vertebral bodies and the
prosthesis. In known prostheses, this objective is approached by
arranging the centre of articulation in a predetermined spatial
relationship to the contact surfaces of the cover plates and by
providing the cover plates with an edge which bears on the ventral
margin of the associated vertebral body and thereby determines the
relative position of the cover plate to the vertebral body (EP-B
560 140), or by using an implantation instrument which has a limit
stop on the vertebral body (EP-B 333 990). This ensures an at all
times identical position of the centre of articulation of the
prosthesis in relation to the ventral edge of the vertebral bodies.
It is also known (EP-A 955 021), in a system of intervertebral disc
prostheses including several categories of different sizes, to
provide corrective prostheses which belong on one side to one size
category and on the other side to another size category.
[0002] By means of the abovementioned predetermined spatial
relationship of the centre of articulation to the contact surfaces
of the prostheses, the desired spatial relationship to the
vertebral bodies is achieved only if the anatomical conditions
correspond to the normal conditions assumed upon construction of
the prosthesis. If, however, for example for anatomical reasons, a
centre of articulation is by way of exception to have another
position, the prosthesis in question or a cover plate of this
prosthesis must be implanted so as to deviate from the normal
spatial relationship to the vertebral body, which is difficult and
risky.
[0003] Starting from the prior art last mentioned above, it is
therefore an object of the invention to make the implantation of
the prosthesis easier and safer for these cases. This is achieved
by the features of claim 1 and preferably by the features of the
subclaims.
[0004] A system of intervertebral disc prostheses is assumed which
includes standard prostheses and corrective prostheses. The
standard prostheses in each size category are identical to each
other. A plurality of size categories are normally available,
although this is not absolutely necessary. The prostheses consist
of a prosthesis core and of at least one cover plate. The
prosthesis core cooperates with at least one cover plate via
articulation surfaces. The prosthesis core preferably has two
articulation surfaces on opposite sides via which it cooperates
with complementary articulation surfaces of two cover plates.
However, it is also possible for one of the cover plates to
cooperate in a non-articulating manner with the prosthesis core via
retaining surfaces. Articulation surfaces and retaining surfaces
are combined below and in the claims under the term core-matching
surfaces. The cover plates have a contact surface to adjoin a
vertebral body. In this connection, the invention provides for the
corrective prostheses to have at least one corrective cover plate
whose core-matching surface is offset ventrodorsally relative to
the contact surface by comparison with the standard prostheses.
[0005] In this way, it is ensured that the centre of articulation
of a prosthesis relative to the vertebral body on whose side the
corrective cover plate is fitted is offset ventrodorsally compared
to the standard prostheses. The offset can be in the ventral
direction or the dorsal direction depending on the type and
direction of insertion of the cover plate. If the contact surfaces
of the corrective cover plates are of symmetrical configuration in
relation to their mediolateral centre line, they can either be used
with the centre offset in the ventral direction or in the dorsal
direction. Since the offset in question is predominantly in the
dorsal direction, an essential embodiment of the corrective rective
plate according to the invention is distinguished by the fact that
the centre of articulation is offset dorsally, provided that the
dorsal side can be distinguished on the cover plate.
[0006] Cases arise in which the intervertebral disc prosthesis
tends to be offset in an undesired manner because of considerable
curvature of the spinal column or because of high ventrodorsal
forces acting between the vertebrae concerned. This is true in
particular of those prostheses in which the prosthesis core
cooperates with both cover plates via spherical articulation
surfaces. In this type of prosthesis, the cover plates are able to
move slightly in translation relative to each other in an angular
position of the prosthesis core under relative lateral forces. The
use of the invention is particularly advantageous in this type of
prosthesis because the corrective plates make it possible to
arrange the centre of articulation of one cover plate so that it is
displaced relative to the centre of articulation of the other cover
plate, as a result of which said offset is compensated.
[0007] The diameter of the articulation surfaces can be chosen as
large as possible within the limits of the cover plate in order to
keep the surface pressure low. In known prostheses, the
articulation surface formed on the cover surface has an only
slightly smaller ventrodorsal extent than the cover plate. In these
cases the offset of the articulation surface relative to the
contact surface can take place only under the proviso that a
smaller diameter is chosen for the articulation surface. If the
radius of curvature of the articulation surface is left unchanged,
the depth of the articulation surface provided in the cover plate
decreases as the diameter decreases and thus its ability to
transmit forces acting laterally (parallel to the plane of the
cover plate). This may be acceptable in some cases, so that this
embodiment of the invention is not excluded. However, an embodiment
is preferred in which the diameter and the radius of curvature of
the articulation surface of the corrective cover plate are chosen
to complement the articulation surfaces which belong to another,
smaller size category. In the smaller size category, not only is
the diameter of the articulation surfaces chosen smaller, but also
the radius of curvature. The depth of these smaller articulation
surfaces is therefore greater than the depth of an articulation
surface of the larger size category, in which only the diameter was
reduced, but not the radius of curvature.
[0008] Choosing an articulation surface (or other core-matching
surface) admittedly rules out using the corrective cover plate
together with prosthesis parts which belong to the same size
category. However, instead of this, prosthesis parts can be used
which belong to the smaller size category, on whose basis the
articulation surface of the corrective cover plate was chosen. The
prosthesis core is preferably in all cases a standard prosthesis
core. The second cover plate belonging to the prosthesis is
likewise preferably a standard cover plate. However, if a
particularly large offset of the two contact surfaces of the
prostheses relative to each other is wanted, the second cover plate
can also be a corrective cover plate, which is, however, rotated
though 180.degree. in relation to the first one so that the offset
amounts of both plates are added to each other. It is only if, for
some reason, the centre of articulation of the prosthesis is to be
displaced ventrally or dorsally in relation to both adjacent
vertebrae that corrective cover plates are used in the same
orientation on both sides.
[0009] In the case of the corrective cover plates, as a result of
the offset arrangement of the core-matching surface relative to the
contact surface, on one side of the core-matching surface there is
a distance between this and the plate edge. If this part of the
surface is not needed in order to make available as large a contact
surface as possible, the plate can be shortened on this side. The
contact surface is then the same width in the mediolateral
direction as the standard cover plates of the same size category,
but its dimension in the ventrodorsal direction is smaller and can
correspond to the smaller size category. This can afford advantages
in terms of adjustment in cases where the vertebral bodies are
wider in the mediolateral direction and narrower in the
ventrodorsal direction.
[0010] The invention is explained in more detail below with
reference to the drawing which depicts advantageous illustrative
embodiments and in which:
[0011] FIG. 1 shows a medial section through a standard prosthesis
of a first size category,
[0012] FIG. 2 shows a view of the inside of a cover plate of a
standard prosthesis of the first size category,
[0013] FIG. 3 shows a medial section through a standard prosthesis
of a second size category,
[0014] FIG. 4 shows a view of the inside of a cover plate of the
standard prosthesis according to FIG. 3,
[0015] FIG. 5 shows a first embodiment of a corrective prosthesis
in medial section,
[0016] FIG. 6 shows a view of the inside of the associated
corrective cover plate,
[0017] FIG. 7 shows a second embodiment of the corrective
prosthesis in medial section,
[0018] FIGS. 8, 9 show medial sections through standard prostheses
of different size categories in a modified embodiment, and
[0019] FIGS. 10, 11 show two corrective prostheses for the modified
embodiment.
[0020] The standard prostheses according to FIGS. 1 to 4 consist of
a lower cover plate 1, an upper cover plate 2 and a prosthesis core
3. The cover plates form spherical, concave articulation surfaces
4, and the prosthesis core 3 forms two identical convex, spherical
articulation surfaces 5 which lie opposite each other and which are
designed to complement those of the cover plates. All dimensions of
the first size category (FIGS. 1 and 2) are greater than those of
the second size category (FIGS. 3 and 4). In addition to the two
size categories shown, further size categories can be present
within the system.
[0021] The components of the prosthesis can be made of materials
which have proven suitable for endoprostheses, for example metal,
ceramic, polyethylene, with the cover plates 1, 2 preferably being
made of rigid material (for example metal) and the prosthesis core
preferably being made of polyethylene.
[0022] The cover plates 1, 2 have a contact surface 7 which is
intended for connection to the end face of a vertebral body. It can
be equipped with means (not shown) for fixed connection to the
bone, for example teeth. It is more extensive in the mediolateral
direction, which is indicated by the line 10 in FIG. 2, than it is
in the ventrodorsal direction 11. The diameter 12 of the.
articulation surface 4 in the standard prostheses is as large as is
permitted by the dimension of the cover plate in the direction 11.
These explanations concerning FIGS. 1 and 2 apply likewise to the
second size category according to FIGS. 3 and 4.
[0023] As is known, such prostheses are able to transmit from
vertebra to vertebra the forces extending in the direction of the
spinal column, and to a certain extent also the forces extending
transverse to the latter, and at the same time they permit swivel
movements. If they are implanted between vertebrae between which
strong transverse forces act, or between which a substantial
directional change takes place, as is often the case for example
between the last lumbar vertebra and the sacrum, a displacement of
the cover plates and of the vertebrae may occur. This can be
compensated for by using a corrective prosthesis 14. It is
constructed, for example, as is shown in FIG. 5 or FIG. 7.
[0024] According to FIG. 5, the corrective prosthesis has an upper
cover plate 15 which is designed as a corrective cover plate. The
external dimensions of its contact surface 7 and thus the overall
surface dimensions are equal to those of the standard cover plate 2
of the first size category. The centre 16 of the articulation
surface 4' provided on its inside is displaced dorsally in relation
to the centre line 10 by an amount 17. If one were to use the
articulation surface 4 of the standard cover plate for this, it
would assume the position 4" indicated by the broken line in FIG.
2. As this is partially extending out beyond the edge of the
standard prosthesis, the latter would have to be provided at this
location with a projection or a widening, or the articulation
surface would have to be shortened to correspond to the standard
edge contour. Both of these options are within the scope of the
invention but are not generally expedient. The embodiment according
to FIG. 6 is thus preferred, in which use is made of that
articulation surface 4' of the second size category whose diameter
12' is correspondingly smaller and can therefore be accommodated
within the edge of the standard format of the corrective cover
plate 15. Matching this articulation surface 4', the corrective
cover plate 15 is combined with a prosthesis core 3' and a lower
cover plate 1' of the second size category, as is indicated in FIG.
5. If, in this corrective prosthesis, the position of the
articulation centre line 16 is compared with the position of the
contact surface 7 of the corrective cover plate 15, it can be seen
that, unlike in the standard prosthesis, these do not coincide but
instead are offset in relation to one another by the amount 17.
[0025] Instead of being connected to a standard cover plate 1' of
the second size category (FIG. 5), a corrective cover plate 15
turned through 180.degree. can also be used as lower cover plate in
the corrective prosthesis (FIG. 7). The offset 17 obtained on the
lower cover plate is added to the offset 17 on the upper cover
plate with the result that the corrective prosthesis according to
FIG. 7 provides twice the offset of that according to FIG. 5.
[0026] As has been stated, the invention is especially suitable for
the prosthesis type shown in FIGS. 1 to 7 in which the prosthesis
core 3 has two articulation surfaces 5 opposite each other.
However, the invention can also be used in prostheses of the
prosthesis type shown in FIGS. 8 to 11. FIGS. 8 and 9 show medial
sections through prostheses of different size categories. They
consist of a lower cover plate 21, 21', an upper cover plate 22,
22' and a prosthesis core 23, 23'. The upper cover plate 22, 22'
and the top of the prosthesis core 23, 23' are identical to those
of the illustrative embodiment discussed above. They afford a
possibility of articulated movement along the pair of articulation
surfaces 24, 25. The underside of the prosthesis core 23 is made
flat. The lower cover plate 21, 21' and its core-matching surface
26 with edge 27 is designed solely to hold the prosthesis core 23,
23'.
[0027] According to FIG. 10, the upper cover plate 20 is designed
as a corrective cover plate according to the explanations given for
FIGS. 5 and 6. It belongs to the first, larger size category. It is
combined with a prosthesis core 23' and a lower cover plate 21' of
the second, smaller size category.
[0028] Instead of this, it is also possible according to FIG. 11 to
use the lower cover plate 29 as corrective plate. It belongs to the
first size category and is combined with a prosthesis core 23' and
an upper cover plate 22' of the second size category. As in the
examples discussed above, this therefore results in an offset 17 of
the centre of articulation relative to the contact surface of the
corrective cover plate.
[0029] For the sake of simplicity, the offset mentioned in the
explanations has been described relative to the contact surface's
centre point which, in the standard prostheses, coincides with the
centre of articulation of the prosthesis. It goes without saying,
however, that the offset can be determined relative to any desired
point of the contact surface, in which case its relative position
to the articulation centre is to be compared, on the one hand, in a
standard cover plate and, on the other hand, upon use of a
corrective cover plate.
[0030] As can be seen in FIG. 6, the edge strip 30 of the
corrective cover plate 15 is not needed for accommodating the
articulation surface 4'. If it is also not needed with respect to a
desired size of the contact surface 7, it can be dispensed with.
The cover plate 15 and its contact surface 7 are then delimited for
example according to the broken line 31.
* * * * *