US2009210059A1PendingUtilityA1
Vertebral Disc Prosthesis
Est. expiryApr 6, 2025(expired)· nominal 20-yr term from priority
A61B 2034/108A61F 2/4425A61F 2002/3065A61B 34/10A61F 2002/30662A61F 2/44A61F 2002/30884A61F 2/08A61F 2002/30943A61F 2002/443A61F 2002/30663A61F 2002/30654
47
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Claims
Abstract
A prosthesis for a vertebral column has an upper part ( 10 ) for attachment to an upper vertebrae, a lower part ( 12 ) for attachment to a lower vertebrae and a middle part ( 11 ) located between the upper and the lower parts, wherein the upper part has a lower surface portion with a first radius of curvature, the middle part has an upper surface portion with a second radius of curvature and a lower surface with a third radius of curvature and the lower part has an upper surface with a fourth radius of curvature. The centre of the radius of curvature for at least two surfaces is offset rearwardly with respect to a central vertical axis ( 13 ) through the upper and lower vertebrae and/or the upper and lower parts. Also defined is device for linking bones, in the form of a band with attachment portions having a number of filaments that provide zones conducive to cellular growth as well as a method of modelling a prosthesis and a process for analysing performance of a prosthesis.
Claims
exact text as granted — not AI-modified1 . A prosthesis for a vertebral column comprising an upper part for attachment to an upper vertebrae, a lower part for attachment to a lower vertebrae and a middle part located between the upper and lower parts, wherein the upper part has a lower surface portion with a first radius of curvature, the middle part has an upper surface portion with a second radius of curvature and a lower surface portion with a third radius of curvature and the lower part has an upper surface portion with a fourth radius of curvature, wherein the center of the radius of curvature for at least two surfaces is offset rearwardly with respect to a central vertical axis through the upper and lower vertebrae and/or the upper and lower parts.
2 . The prosthesis as claimed in claim 1 wherein at least one of the fourth radius of curvature and the first radius of curvature is offset rearwardly of the central vertical axis.
3 . The apparatus as claimed in claim 1 wherein the center of radius of curvature of each of the surfaces is offset rearwardly with respect to the central vertical axis.
4 . The prosthesis as claimed in claim 1 wherein the center of the radius of curvature for each of the surfaces is located in the posterior third of the prosthesis.
5 . The prosthesis as claimed in claim 1 wherein the middle part has a minor central axis and a major central axis, the minor central axis being located through the center of the radius of curvature of the second and third surfaces.
6 . The prosthesis as claimed in claim 5 wherein the minor central axis is inclined with respect to the vertical central axis.
7 . The prosthesis as claimed in claim 5 wherein the major axis is located through the center of the posterior and anterior ends of the middle part.
8 . The apparatus as claimed in claim 1 wherein the middle part has a convex upper surface and a concave lower surface.
9 . The prosthesis as claimed in claim 1 wherein the upper surface of the middle part is concave and the lower surface of the middle part is concave.
10 . The prosthesis as claimed in claim 8 wherein the radius of curvature of the upper surface of the middle part is greater than the radius of curvature of the lower surface.
11 . The prosthesis as claimed in claim 8 wherein the lower surface first radius of curvature is substantially the same as the radius of curvature of the second radius of curvature.
12 . The prosthesis as claimed in claim 8 wherein the third radius of curvature is substantially the same as the fourth radius of curvature.
13 . The prosthesis as claimed in claim 1 wherein the first, second, third and fourth radius of curvature are centered on a vertical axis rearwardly offset from the central vertical axis through the upper part and lower part.
14 . The prosthesis as claimed in claim 1 wherein the upper part has a lower surface front portion which is substantially flat.
15 . The prosthesis as claimed in claim 1 wherein the lower part has an upper surface front portion which is substantially flat.
16 . The prosthesis as claimed in claim 1 wherein the lower part has an upper surface comprising a rear surface portion and a front surface portion, wherein the rear surface portion comprises a convex portion symmetrical about a vertical central axis through the middle part.
17 . The prosthesis as claimed in claim 16 wherein the upper surface rear portion of the lower part comprises recessed portions on either side of the convex portion.
18 . The prosthesis as claimed in claim 1 wherein the middle part has an upper convex surface and a lower convex surface with the radius of curvature of each of the upper and lower surfaces of the middle part being configured whereby movement of the middle part relative to the upper part or lower part, within a predetermined range results in the middle part being urged to a position of equilibrium located substantially along a central axis of the prosthesis.
19 . The prosthesis as claimed in claim 1 wherein the middle part has an upper concave surface and a lower concave surface with the radius of curvature of each of the upper and lower surfaces of the middle part being configured whereby movement of the middle part relative to the upper part or lower part, within a predetermined range results in the middle part being urged to a position of equilibrium located substantially along a central axis of the prosthesis.
20 . The prosthesis as claimed in claim 18 wherein the second radius of curvature is greater than the third radius of curvature.
21 . The prosthesis as claimed in claim 20 wherein the ratio of the second radius of curvature compared to the third radius of curvature is between 3:1 to 10:1.
22 . (canceled)
23 . The prosthesis as claimed in claim 1 wherein the center of rotation of the upper part, middle part and lower part is rearwardly offset with respect to a central vertical axis through the prosthesis.
24 . The prosthesis as claimed in claim 23 wherein the radius of curvature of each surface is configured whereby movement of any one or more parts within a predetermined range results in the middle part being urged to a position of equilibrium located substantially along a central vertical axis of the prosthesis.
25 . The prosthesis as claimed in claim 1 wherein the prosthesis has a center of rotation corresponding to a position of equilibrium for the middle part.
26 . The prosthesis as claimed in claim 1 wherein a major portion of the middle part is configured to be located forward of the anatomical center of rotation of a vertebral column when the upper and lower vertebrae are substantially vertically aligned.
27 . The prosthesis as claimed in claim 1 wherein the prosthesis includes a stopping means located behind and in front of the middle part when the prosthesis is located in a vertebral column.
28 . The prosthesis as claimed in claim 27 wherein the stopping means includes end portions of the upper and lower parts.
29 . The prosthesis as claimed in claim 1 wherein the middle part has a position of equilibrium defined by:
δ
l
δ
α
=
o
δ
l
δ
β
=
o
and
δ
2
l
δ
β
2
=
+
ve
and
δ
2
l
δ
β
2
=
+
ve
wherein α is the angular displacement of the upper part relative to the middle part
β is the angular displacement of the middle part relative to the lower part; and
l is the length of a ligature joining a part of the upper part with the center of rotation of the skeletal structure when in use and wherein:
l (α,β)=√{square root over ( x (α,β) 2 +y (α,β) 2 )}{square root over ( x (α,β) 2 +y (α,β) 2 )}
where x(α,β) and y(α,β) are different functions.
30 . The prosthesis as claimed in claim 1 wherein the middle part is configured with an upper surface and a lower surface with a position of equilibrium relative to the upper and lower parts being defined by:
δ
l
δ
α
=
o
δ
l
δ
β
=
o
and
δ
2
l
δ
β
2
=
+
ve
and
δ
2
l
δ
β
2
=
+
ve
wherein α is the angular displacement of the upper part relative to the middle part
β is the angular displacement of the middle part relative to the lower part; and
l is the length of a ligature joining a part of the upper part with the center of rotation of the skeletal structure when in use and wherein:
l (α,β)=√{square root over ( x (α,β) 2 +y (α,β) 2 )}{square root over ( x (α,β) 2 +y (α,β) 2 )}
where x(α,β) and y(α,β) are different functions;
wherein small changes in the length l relative to small changes in either the angle α or β is a minimum and either side of the position of equilibrium the length l increases if the middle part moves away from the position of equilibrium.
31 . The prosthesis as claimed in claim 30 wherein each of the variables α, β or l are determined relative to the center of rotation of the prosthesis.
32 . The prosthesis as claimed in claim 1 wherein the upper part, middle part and lower part are configured whereby the prosthesis has a position of equilibrium aligned with a central vertical axis offset from an anatomical central axis and is configured with a self-centering means which tends to cause the prosthesis to align with the equilibrium position if there is movement of any one of the parts to move away from the position of equilibrium.
33 . The prosthesis as claimed in claim 32 wherein the self-centering means comprises a predetermined surface configuration for the first, second, third and fourth radius of curvature respectively which results in a tendency for the prosthesis to self-center about the position of equilibrium whenever the upper part and/or middle part move away from the position of equilibrium.
34 . The prosthesis as claimed in claim 1 wherein the upper part, middle and lower part have a stable equilibrium position.
35 . The prosthesis as claimed in claim 34 wherein the equilibrium position is offset with respect to a vertical central axis through the prosthesis.
36 . The prosthesis as claimed in claim 34 wherein the first, second, third and fourth radius of curvature are configured to urge the prosthesis to the stable equilibrium position if there is relative movement between any of the upper part, middle part and lower part.
37 . The prosthesis as claimed in claim 1 wherein the upper part when the prosthesis is attached to upper and lower vertebrae, closely simulates rotational and translational movements possible with an invertebral disk.
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