Artificial intervertebral disc
An artificial intervertebral disc for implantation between two adjacent vertebrae includes superior and inferior shells connected in a ball and socket arrangement. The inferior shell preferably incorporating a convex portion that cooperates with a concave portion on the superior shell. A resilient nucleus is provided within an enclosure defined by the opposing inner surfaces of the shells and biases the shells against each other. The ball portion can be provided in either fixed or slidable arrangement. The artificial disc of the invention includes various resistance means for restricting and limiting the range of rotational and translational motion between the shells.
1. An artificial intervertebral disc for implantation between adjacent superior and inferior vertebrae of a spine, the disc comprising:
a superior shell, an inferior shell, and a resilient nucleus, wherein the nucleus is a unitary and generally “U” shaped body;
the superior and inferior shells being movable with respect to each other;
the inferior shell having a superior surface, the superior surface including an integral convex portion and a generally “U” shaped well, the convex portion being posteriorly positioned on the superior surface of the inferior shell;
the superior shell having an inferior surface opposing the superior surface of said inferior shell, the inferior surface including an integral concave portion and a generally “U” shaped recess, the concave portion being posteriorly positioned on said inferior surface, wherein the concave portion is opposite to said convex portion and the recess is opposite the well when the inferior shell and superior shell are aligned;
the well and recess combining to form an enclosure to contain said nucleus;
the convex portion of the inferior shell and concave portion of the superior shell being in articulating cooperation to form a ball and socket joint
wherein said superior shell includes a first wall and said inferior shell includes a second wall, said first and second walls being positioned at an anterior end of the disc, at least a portion of said walls being overlapped wherein said first wall extends downward and said second wall extends upward and is positioned posteriorly of said first wall; and,
wherein said inferior shell includes an anteriorly extending lip for limiting anterior movement of said first wall.
2. The artificial disc of claim 1 wherein said nucleus applies a biasing force to elastically separate the inferior and superior shells.
3. The artificial disc of claim 1 wherein said nucleus is provided at least in an anterior section of the disc.
4. The artificial disc of claim 1 further comprising one or more motion regulating means to limit or prevent relative movement between the superior and inferior shells in one or more planes.
5. The artificial disc of claim 1 wherein one of the superior or inferior shells includes one or more inferiorly depending tabs on lateral sides thereof and the other of the superior or inferior shells includes slots for receiving said tabs.
6. The artificial disc of claim 5 wherein said tabs are provided on the superior shell and said slots are provided on the inferior shell.
7. The artificial disc of claim 1 wherein said second wall prevents posterior movement of said first wall whereby extension motion of the disc is limited.