Implant having a sheath with a motion-limiting attribute
A surgical implant containing two opposing shells, a central body disposed between the shells, and a flexible sheath extending between edges of the opposing shells. The sheath provides for resisting at least one predetermined type of relative directional motion.
1 . A surgical implant comprising:
two opposing shells, each having
an outer surface adapted to engage the surfaces of the bones of a joint in such a way that movement of the shell relative to the bone surface is resisted by friction between the outer surface and the surface of the bone;
an inner surface that is smoother than the outer surface; and
an edge between the outer surface and the inner surface;
a central body disposed between the inner surfaces of the shells comprising an outer surface, at least a portion of which has a shape that complements and articulates with the shape of the inner surface of one or both opposing shells; and
a sheath extending between edges of the opposing shells, having a motion-limiting attribute to resist movement outside a constrained range of motion, and an inner surface that, together with the inner surfaces of the shells, defines a cavity containing the central body.
2 . The surgical implant of claim 1 wherein the motion-limiting attribute comprises an anterior aspect of the sheath that is greater in height than the posterior aspect of the sheath.
3 . The surgical implant of claim 1 wherein the sheath is made from an elastomeric polymeric material.
4 . The surgical implant of claim 3 wherein the elastomeric polymeric material is selected from the group consisting of polyurethane, polyethylene, poly carbonates and polyethers.
5 . The surgical implant of claim 3 wherein the elastomeric polymeric material is a copolymer selected from the group consisting of polyurethane-containing elastomeric copolymers and polyether-polyurethane elastomeric copolymers.
6 . The surgical implant of claim 1 , further comprising:
a liquid lubricant, which occupies at least a portion of the cavity.
7 . The surgical implant of claim 1 further comprising:
a motion-limiting device disposed on the inner surface of at least one of the opposing shells.
8 . The surgical implant of claim 7 , wherein the motion limiting device comprises an extension formed on the inner surface.
9 . The surgical implant of claim 8 , wherein the extension is located at the edge of the shell, and extends toward the central body.
10 . The surgical implant of claim 7 , wherein the surface of the central body comprises a motion limiting device disposed thereon, which contacts the motion limiting device of the shell when the implant reaches the end of an acceptable range of motion.
11 . The surgical implant of claim 10 , wherein the motion limiting device on the central body comprises a shoulder.
12 . The surgical implant of claim 7 , wherein the motion limiting device comprises a post extending toward the central body, and wherein the outer surface of the central body further comprises at least one opening adapted to receive the post.
13 . The surgical implant of claim 1 , wherein the edge of at least one of the opposing shells comprises a tab extending axially away from the central body.
14 . The surgical implant of claim 13 , wherein the tab is adapted to releasably receive a tool for manipulating, inserting or removing the implant.
15 . The surgical implant of claim 14 , wherein the edges of both opposing shells comprise a tab.
16 . The surgical implant of claim 1 , wherein the outer surface of each opposing shell is coated with a biocompatible porous coating.
17 . The surgical implant of claim 1 wherein at least one of the opposing shells further comprises a closable passage between its outer surface and its inner surface.
18 . The surgical implant of claim 17 , wherein the closable passage comprises a hole that is closable by insertion of a correspondingly sized plug.
19 . The surgical implant of claim 1 wherein the edge between the outer surface and the inner surface of the rigid opposing shells comprises a circumferential groove adapted to receive a retaining ring.
20 . The surgical implant of claim 19 , wherein the sheath overlaps the circumferential groove and is held against the edge of the opposing shells by the retaining ring.
21 . A system comprising an implant adapted for insertion between adjacent vertebrae, which implant comprises two opposing shells, a central body, and means for encapsulating the central body between the opposing shells, which means also limits movement of the vertebrae adjacent to the implant to a constrained range.
22 . The system of claim 19 wherein the means limits at least one of anterior-posterior flexion, anterior-posterior extension and anterior-posterior translation.
23 . A method comprising:
inserting an implant between adjacent vertebrae, which implant comprises two opposing shells, each shell having an outer surface, an inner surface that is smoother than the outer surface; and an edge between the outer surface and the inner surface; a central body disposed between the inner surfaces of the shells, the central body comprising an outer surface, at least a portion of which has a shape that complements and articulates with the shape of the inner surface of one or both opposing shells; and a sheath extending between edges of the opposing shells, having a motion-limiting attribute; and
limiting movement of the vertebrae adjacent to the implant to a constrained range, which limiting of motion is caused at least in part by the motion-limiting attribute of the flexible sheath.
24 . The method of claim 23 wherein the motion-limiting attribute comprises an anterior aspect of the sheath that is greater in height than the posterior aspect of the sheath.
25 . The method of claim 23 wherein the motion-limiting attribute limits at least one of anterior-posterior flexion, anterior-posterior extension and anterior-posterior translation.