U.S. patent application number 11/759609 was filed with the patent office on 2007-12-27 for artificial intervertebral disc.
Invention is credited to Evgeny Rivin.
Application Number | 20070299524 11/759609 |
Document ID | / |
Family ID | 34742577 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070299524 |
Kind Code |
A1 |
Rivin; Evgeny |
December 27, 2007 |
ARTIFICIAL INTERVERTEBRAL DISC
Abstract
The instant invention proposes an artificial intervertebral disc
providing for angular displacements between adjacent vertebrae
wherein these displacements are accommodated by internal shear in
an elastomeric layered element residing between the upper and lower
bases attached, respectively, to the upper and lower adjacent
vertebrae, without sliding.
Inventors: |
Rivin; Evgeny; (West
Bloomfield, MI) |
Correspondence
Address: |
GIFFORD, KRASS, SPRINKLE,ANDERSON & CITKOWSKI, P.C
PO BOX 7021
TROY
MI
48007-7021
US
|
Family ID: |
34742577 |
Appl. No.: |
11/759609 |
Filed: |
June 7, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11037629 |
Jan 12, 2005 |
7235103 |
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11759609 |
Jun 7, 2007 |
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60535741 |
Jan 13, 2004 |
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Current U.S.
Class: |
623/17.13 ;
623/17.14; 623/17.15; 623/17.16 |
Current CPC
Class: |
A61F 2002/30014
20130101; A61F 2/4425 20130101; A61F 2002/30433 20130101; A61F
2220/005 20130101; A61F 2002/30362 20130101; A61F 2002/30448
20130101; A61F 2250/0018 20130101; A61F 2220/0041 20130101; A61F
2002/30685 20130101; A61F 2002/30649 20130101; A61F 2002/30971
20130101; A61F 2220/0033 20130101; A61F 2002/30929 20130101 |
Class at
Publication: |
623/017.13 ;
623/017.14; 623/017.15; 623/017.16 |
International
Class: |
A61F 2/44 20060101
A61F002/44 |
Claims
1. An artificial intervertebral disc, comprising: lower and upper
bases, each made from a rigid material and each attached,
respectively, to the lower and upper adjacent vertebras, said lower
and upper bases having relative mobilities in three angular
coordinate directions, with all these relative mobilities resulting
from shear deformations within at least one elastomeric layered
element attached to said lower and upper bases, wherein both of
said rigid lower and upper bases have co-axial concave spherical
sockets, and an intermediate rigid element is inserted between said
lower and upper bases, said intermediate rigid element having on
its opposing lower and upper sides, respectively adjacent to said
lower and upper bases, convex co-axial spherical protrusions, these
protrusions being co-axial with the concave spherical sockets on
the lower and upper bases, with center points of said spherical
protrusion on the upper side of said intermediate rigid element and
said spherical socket on the upper base approximately coinciding,
with center points of said spherical protrusion on the lower side
of said intermediate rigid element and said spherical socket on the
lower base approximately coinciding, with the lower part of
elastomeric layered element residing between and attached to said
concave spherical socket on said lower base and said convex
spherical protrusion on the upper side of said intermediate
element, and with the upper part of elastomeric layered element
residing between and attached to said concave spherical socket on
the upper base and said convex spherical protrusion on the upper
side of said intermediate element.
2. The artificial intervertebral disc of claim 1, wherein both of
said rigid lower and upper bases have co-axial convex spherical
protrusions, and an intermediate rigid element is inserted between
said lower and upper bases, said intermediate rigid element having
on its opposing lower and upper sides, respectively adjacent to
said lower and upper bases, concave co-axial spherical sockets,
these sockets being co-axial with the convex spherical protrusions
on the lower and upper bases, with center points of said spherical
socket on the upper side of said intermediate rigid element and
said spherical protrusion on the upper base approximately
coinciding, with center points of said spherical socket on the
lower side of said intermediate rigid element and said spherical
protrusion on the lower base approximately coinciding, with the
lower part of elastomeric layered element residing between and
attached to said spherical protrusion on said lower base and said
spherical socket on the upper side of said intermediate element,
and with the upper part of the elastomeric layered element residing
between and attached to said spherical protrusion on the upper base
and said spherical socket on the upper side of said intermediate
element.
3. The artificial intervertebral disc of claim 1, wherein each of
said upper and lower elastomeric layered elements comprise one
layer of an elastomeric material.
4. The artificial intervertebral disc of claim 2, wherein each of
said upper and lower elastomeric layered elements comprise one
layer of an elastomeric material.
5. The artificial intervertebral disc of claim 1, wherein said
upper and lower elastomeric layered elements are preloaded in
compression before insertion between the vertebras.
6. The artificial intervertebral disc of claim 2, wherein said
upper and lower elastomeric layered elements are preloaded in
compression before insertion between the vertebras.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a divisional of U.S. patent
application Ser. No. 11/037,629 filed Jan. 12, 2005, which claims
priority of U.S. Provisional Application Ser. No. 60/535,741 filed
Jan. 13, 2004.
FIELD OF THE INVENTION
[0002] The invention relates to designs of artificial
intervertebral discs for prosthetic and dummy applications.
BACKGROUND OF THE INVENTION
[0003] Intervertebral disc prosthetics must comply with several
requirements, often contradicting each other. These requirements
are derived from studies on natural intervertebral discs. The
prosthetic artificial disc should provide angular mobilities with
specified ranges and stiffness values (two bending mobilities,
fore-and-aft and side-to-side, and torsional around the axis of the
spine), while accommodating large and varying axial (vertical)
loading; it is desirable that the stiffness values are not
significantly influenced by the changing vertical loads. Dummies
are mock-ups of human bodies designed to simulate behavior of human
bodies in extreme circumstances, e.g. crash dummies. Dummies are
not, usually, equipped with all individual vertebras simulating the
human spinal column but have structural elements rather crudely
simulating the human spine. These structural elements will also be
called "vertebras" in this specification. Maintaining the
structural characteristics of artificial intervertebral discs in
close similarity to the natural discs is very important in order to
adequately simulate behavior of the human bodies in the course of
the dummy-based experiments.
[0004] There are various proposed designs of artificial
intervertebral discs attempting to simulate structural
characteristics, especially stiffness values and ranges of motion
of the natural discs. The most widely used designs comprise
spherical joints generated by a concave spherical socket engaged
with a fitting convex spherical protrusion. Both surfaces are
usually made from a low friction plastic capable of sliding without
lubrication. While providing mobility in various angular directions
and capable of accommodating axial loads, these designs have
several shortcomings.
[0005] These artificial discs do not have elastic characteristics
resident in the discs of the natural spinal column in any of the
three angular directions. The natural elastic resistances to the
motions approximately proportional to the deformation angle are
replaced in these prosthetic or artificial discs by frictional
resistances, practically independent on the motion magnitude.
[0006] Secondly, the motion resistances in all three directions
(the friction forces) are increasing with the increasing axial
force in the spinal column (which varies in the wide range). This
also results in some unnatural feelings, since the elastic
resistance forces in the natural spinal column are not
significantly dependent on the axial force.
[0007] Another shortcoming of the state-of-the-art prosthetics is
an unavoidable difference between static and dynamic friction
coefficients in spherical joint. This makes the motion resistance
different in the beginning of the movement and in the process of
movement, since the static friction coefficient is greater than the
dynamic friction coefficient.
[0008] Yet another shortcoming, which is also a result of
frictional interaction in the spherical joint, is inevitable wear
of the sliding connection. The wear is enhanced by sometimes high
axial pressures in the spinal column which are too high for sliding
plastic contacts. The wear process creates worn-out particles which
are contaminating the area around the disc and may increase the
friction forces if accumulated in the sliding connection.
[0009] The subject invention eliminates the listed
shortcomings.
SUMMARY OF THE INVENTION
[0010] The instant invention proposes an artificial intervertebral
disc providing for angular displacements between adjacent vertebrae
wherein these displacements are accommodated by internal shear in
an elastomeric layered element residing between the upper and lower
adjacent vertebrae, without sliding.
[0011] The preferred embodiment of the invention has upper and
lower rigid bases attached, respectively, to the upper and lower
adjacent vertebrae. One of the bases has a spherical convex
protrusion and another has a coaxial concave spherical socket, with
these two spherical surfaces having the common center. The
elastomeric layered element is placed between and attached to these
convex and concave spherical surfaces.
[0012] In another embodiment of the proposed artificial
intervertebral disc, both upper and lower bases have concave
spherical sockets and an intermediate rigid element has two coaxial
convex spherical protrusions on its upper and lower sides, with the
upper protrusion being coaxial with and having the common center
with the concave spherical socket on the upper base, with the lower
protrusion being coaxial with and having the common center with the
convex spherical socket on the lower base, and the elastomeric
layered element consists of two elastomeric layers, one of which is
placed between and attached to the two upper spherical surfaces and
another is placed between and attached to the two lower spherical
surfaces.
[0013] In another embodiment of the proposed artificial
intervertebral disc, both upper and lower bases have convex
spherical protrusions and an intermediate rigid element has two
coaxial concave spherical sockets on its upper and lower sides,
with the upper socket being coaxial with and having the common
center with the convex spherical protrusion on the upper base, with
the lower socket being coaxial with and having the common center
with the convex spherical protrusion on the lower base, and the
elastomeric layered element consists of two elastomeric layers, one
of which is placed between and attached to the two upper spherical
surfaces and another is placed between and attached to the two
lower spherical surfaces.
[0014] Yet another embodiment of the proposed artificial
intervertebral disc is characterized by having means for preloading
the elastomeric layered element in compression.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 shows a correlation between elastomer (rubber)
hardness measured by standard measuring tool--Shore Durometer at
its "A" scale and Young's modulus of the elastomer.
[0016] FIG. 2 shows a cross section of the proposed artificial
intervertebral disc with elastomeric layered element placed between
the spherical socket in the upper base and the spherical protrusion
in the lower base.
[0017] FIG. 3 gives a cross section of spherical elastomeric
element constructed as a laminate with two layers of rubber and one
intermediate layer of a rigid material.
[0018] FIG. 4 shows a plan view of the elastomeric element shaped
for providing a relatively high angular stiffness of the artificial
disc around the spinal axis as compared with its bending angular
stiffness values.
[0019] FIG. 5 shows a plan view of the elastomeric element shaped
for providing a relatively low angular stiffness of the artificial
disc around the spinal axis as compared with its angular bending
stiffness values.
[0020] FIG. 6 depicts the axial cross section of the artificial
spinal disc having an intermediate double-convex element
interacting with the lower and upper bases via elastomeric layered
element.
[0021] FIG. 7 depicts the axial cross section of the artificial
spinal disc having an intermediate double-concave element
interacting with the lower and upper bases via elastomeric
layers.
[0022] FIG. 8 illustrates modification of artificial discs with
intermediate elements, as shown in FIGS. 6 and 7, which can be
axially preloaded before insertion.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] A "rigid" component in this specification means a component
having significantly lesser deformations than the elastomeric
element(s) connecting these components. Specifically, "rigid" is
defined here as having the Young's modulus at least ten times
greater than the Young's modulus E.sub.0 of an elastomer having
hardness H60 on scale A of Shore Durometer. This corresponds, in
accordance with the industry-accepted correlation shown in FIG. 1,
to the Young's modulus E.apprxeq.G>10E.sub.0=.sup.-40 MPa, where
G is the shear modulus.
[0024] Four embodiments of the proposed disc design are shown in
FIGS. 2, 6, 7, and 8.
[0025] FIG. 2 shows an artificial disc comprising lower base 1 and
upper base 2, both made of a metal, plastic, or other rigid
material. One of the bases has a convex spherical protrusion 3
(shown on the lower base 1), while another base (top base 2 in FIG.
2) has a concave spherical socket 4 coaxial with protrusion 3.
Bases 1 and 2 do not have a direct contact, and the space between
protrusion 3 and socket 4 is filled with elastomeric element 5
which constitutes a layer or a laminate (see below) of uniform
thickness, attached by known means (bonded, glued, mechanically
attached, etc.) to both convex and concave spherical surfaces of
protrusion 3 and socket 4. Elastomeric element 5 is shown in FIG. 2
as a "solid" rubber layer, contacting with the full surface area of
socket 4 and protrusion 3. However, it can be designed with smaller
area, as shown in FIGS. 4, 5 below. While an elastomeric element
comprising one layer of rubber is shown in FIG. 2, it can be
embodied as a rubber-metal laminate. Such a laminate comprising two
layers 6 and 7 of rubber with thin layer 8 made of metal or other
material rigid in extension, such as strong fabric, between the
layers of rubber is shown in FIG. 3.
[0026] Bases 1 and 2 in FIG. 2 are attached, respectively, to the
lower and upper adjacent vertebrae (not shown). It is preferable
that the centers of both convex and concave spherical surfaces
coincide at one point, thus minimizing the resistance forces for
angular displacements between the connected vertebras. Spherical
elastomeric layer or laminate 5 is conforming spherical surfaces of
protrusion 3 and socket 4, and can have a shape providing for
desirable stiffness values in different directions. For example,
layers 5a and 5b of the same spherical radius shown in FIGS. 4 and
5, respectively, in the plan views are shown to have the same
surface area, but different shapes, annular in FIG. 4 and solid of
a small diameter in FIG. 5. As a result, they have the same angular
(shear) stiffness in two bending directions shown as .alpha. and
.beta., but layer 5a, FIG. 4, has significantly higher stiffness
than layer 5b, FIG. 5, in y direction (torsional stiffness,
rotation about the spine axis). Other shapes of elastomeric element
5 in FIG. 2 may be beneficial in special cases.
[0027] While the artificial intervertebral disc shown in FIG. 2 has
the convex spherical protrusion on the lower base and the concave
spherical socket on the upper base, this arrangement can be
reversed and the socket can be part of the lower base, while the
spherical protrusion is made on the upper base.
[0028] If the artificial disc is intended to be used as a
prosthetic device, then bases 1 and 2 as well as elastomeric
element 5 must be made of bio-compatible materials.
[0029] In operation, an angular bending displacement between the
adjacent vertebras in .alpha. and/or .beta. directions would induce
the same angular displacement between lower 1 and upper 2 bases
attached to these vertebras. The relative angular displacement in
.alpha. and/or .beta. directions between bases 1 and 2 having,
respectively, convex and concave spherical surfaces centered at the
same point and separated by elastomeric layered element 5, will be
accommodated by a shear deformation of element 5. The shear
resistance associated with this deformation will be of an elastic
nature characteristic for elastomeric (rubberlike) materials and is
approximately proportional to magnitude of the shear deformation
and to shear modulus G=E.sub.0/3 of the elastomeric material. Axial
forces in the spinal column cause compression deformation of the
layered elastomeric element.
[0030] Numerous experiments have shown that the compression forces
cause only a slight increase in the shear resistance, especially
for thin layers of the elastomeric materials.
[0031] Since there is no direct sliding contact between the upper
and lower bases, there is no friction and no wear in the proposed
artificial disc system, which operates in a close similarity to the
natural intervertebral disc.
[0032] FIG. 6 illustrates another embodiment of the proposed
prosthesis, comprising lower base 11 and top base 12 attached to
the respective adjacent vertebrae. Each base has socket 13, 14,
respectively, each socket having concave spherical surface.
Intermediate element 15 has two convex spherical protrusions 16 and
17 with all four spherical surfaces being coaxial in the undeformed
(initial) condition of the artificial disc. The elastomeric element
comprises two elastomeric layers (shown) or laminates as presented
in FIG. 3. The space between protrusion 16 and socket 13 is filled
with elastomeric layer/laminate 18 of uniform thickness, attached
(bonded, glued, etc.) to both convex and concave spherical surfaces
of protrusion 16 and socket 13. The space between protrusion 17 and
socket 14 is filled with a elastomeric layer/laminate 19 of uniform
thickness, attached (bonded, glued, etc.) to both convex and
concave spherical surfaces of protrusion 17 and socket 14.
[0033] FIG. 7 illustrates yet another embodiment of the proposed
artificial intervertebral disc, comprising lower base 21 and top
base 22 attached to the respective adjacent vertebrae. Each base
has spherical protrusion 23, 24, respectively, each protrusion
having convex spherical surface. Intermediate element 25 has two
concave spherical sockets 26 and 27 with all four spherical
surfaces being coaxial in the undeformed (initial) condition. The
elastomeric element comprises two elastomeric layers (shown) or
laminates as presented in FIG. 3. The space between socket 26 and
protrusion 23 is filled with elastomeric layer/laminate 28 of
uniform thickness, attached (bonded, glued, etc.) to both concave
and convex spherical surfaces of socket 26 and protrusion 23. The
space between socket 27 and protrusion 24 is filled with an
elastomeric layer/laminate 29 of uniform thickness, attached
(bonded, glued, etc.) to both concave and convex spherical surfaces
of socket 27 and protrusion 24.
[0034] FIG. 8 shows an embodiment of the proposed prosthesis
similar to the embodiment shown in FIG. 6 wherein the spherical
joint is preloaded (and held captive) by means of preloading member
20 (a bolt is shown but other known designs of preloading elements
can be employed). The preloading element 20 is attached to lower
base 11a and top base 12a, but does not have a contact with
intermediate element 15a. The artificial disc can be preloaded with
a specified load before insertion into the spinal column, resulting
in modification of the axial stiffness.
[0035] A similar preloading system can be applied to the embodiment
shown in FIG. 7.
[0036] It is readily apparent that the components of the artificial
intervertebral disc disclosed herein may take a variety of
configurations. Thus, the embodiments and exemplifications shown
and described herein are meant for illustrative purposes only and
are not intended to limit the scope of the present invention, the
true scope of which is limited solely by the claims appended
thereto.
* * * * *