Motion preserving spinal total disc replacement apparatus, method and related systems

A device comprising:

• a. a top endplate comprising a top surface for engaging with the underside of a superior vertebral body and a bottom surface engaged in a ball and socket configuration with a top dome portion of a resilient nucleus to form a first joint of defined, and mechanically constrained, ranges of motion inherently enforced by the joint structure;
• b. the nucleus comprising a top convexly curvate dome portion, a core portion connecting said curvate top dome portion to a substantially planar bottom foot portion, wherein said nucleus including its dome, core and foot, are either unitary or are connected to each other to form a unitary nucleus and wherein said dome of said nucleus is retained in contact with a mating curvate top endplate undersurface, such that said first joint is a closed-profile joint;
• and
• c. a bottom endplate translationally engaged with said bottom foot portion of said nucleus to form a second joint of defined, and mechanically constrained, ranges of motion, wherein said foot of said nucleus is retained within a cavity in said bottom endplate in connection with which it is translationally engaged, such that said second joint is a closed profile joint, wherein said first joint and said second joint, in concert, when implanted into an intervertebral space, comprise a closed profile of two joints which are constrained by the resulting mechanical structure to facilitate substantially physiologically acceptable rotational, lateral and flexural motions, when compared with a biological disc in the spine of a recipient which said device is implanted to replace;
• wherein said first joint and said second joint each comprises a nucleus retention mechanism providing defined, and mechanically constrained, degrees of motion of said top endplate about the top dome portion of said nucleus and said bottom endplate in relation to the bottom foot portion of said nucleus such that each said mechanism sustains, restrains, constrains, stabilizes, or guides the larger motions required to preserve normal mechanical motion of a spinal joint, while at the same time, said nucleus provides a flexion component to guide and restrain or constrain the finer motions reached at the extremes set by mechanical motion preservation components.

The device according to claim 1 wherein:

• a. the device is assembled by either a snap-fit or a non-snap-fit method for associating device components to each other;
• b. the device further comprises a sheath surrounding said nucleus;
• c. said first joint comprises said top endplate which comprises a Ring-Joint-Stop (RJS) unitary with or assembled to become unitary with said top endplate, wherein said Ring-Joint-Stop either:
• i. comprises an orifice and a raceway, such that said top dome portion of said nucleus snap-fits through said orifice for rotational retention within said raceway;
• or
• ii. an orifice and raceway are defined about the core portion of said nucleus and, once assembled thereabout, retains said dome portion from traversing through said orifice for rotational retention within said raceway;
• d. said bottom endplate comprises a nucleus bottom foot portion retention plate unitary with or assembled to become unitary with said bottom endplate, wherein said retention plate either:
• i. comprises an orifice through which said nucleus bottom foot portion is snap-fit for retention within a cavity defined within said bottom endplate;
• or
• ii. is assembled about a core portion of said nucleus to comprise an orifice with sufficiently small diameter that the bottom foot portion of said nucleus cannot traverse through said orifice;
• e. at least one cushion ring which interacts with the Ring-Joint-Stop to protect the RJS and retainer plate from impingement damage that would be caused by rotations exceeding their Range-of-Motion (ROM), by resisting further motion once the RJS contacts a cushion ring;
• or
• f. said nucleus top dome portion comprises a substantially convex top surface shaped to lubriciously mate with the underside of said top endplate and a bottom surface shaped to lubriciously and translationally mate with said bottom endplate such that said top and bottom endplates, once mated with said resilient nucleus, requires super-physiologic force to disengage from each other.

A method of making a device comprising:

• a. manufacturing a top endplate for engagement with a top dome portion of a nucleus, such that said top endplate is engaged in a ball and socket configuration with said top dome portion of a nucleus to form a first joint of defined, and mechanically constrained, ranges of motion;
• b. manufacturing a nucleus comprising a top dome portion, a core portion, and a bottom foot portion;
• c. manufacturing a bottom endplate translationally engaged with said bottom foot portion of said nucleus to form a second joint of defined ranges of motion;
• and
• d. assembling said top endplate with said nucleus and assembling said bottom endplate with said nucleus such that, following assembly, super-physiological force is required to disassemble said device;
• wherein said top endplate comprises a nucleus retaining mechanism providing defined, and mechanically constrained, degrees of rotational motion of said top endplate about the top surface of said nucleus when said top endplate and said nucleus are engaged with each other in a ball and socket configuration.