Intervertebral Prosthesis
An intervertebral prosthesis for insertion between adjacent vertebrae includes upper and lower prosthesis plates locatable against respective vertebrae and having opposing, concavely curved recesses therein, and a core located between the plates. The core has opposed, convexly curved surfaces received in the recesses of the plates to allow the plates to slide in articulated manner over the core. The opposed surfaces of the core and the recesses of the plates have cooperating spherical curvatures. The recess of each plate surrounds a locating peg projecting centrally from the base of the recess and is bounded by an annular rim, such that the annular rims of the plates are arranged to contact one another at a predetermined limit of sliding movement of the plates over the core. The peg locates loosely in an opening located centrally in a curved surface of the core, whereby the plates can slide over the core in all directions while the peg holds the core captive.
1 . A method of determining the location of a mobile core of an intervertebral prosthesis during a post-operative X-ray examination, the method comprising:
implanting an intervertebral prosthesis in a patient, the intervertebral prosthesis comprising:
upper and lower prosthesis plates locatable against respective vertebrae and having bearing surfaces thereon;
a rigid core located between the plates, the core having opposed bearing surfaces configured to cooperate with the bearing surfaces of the plates to allow the plates to slide in articulated manner over the core, wherein the core is transparent to X-radiation and is includes one or more radial passages and one or more pins serving as radiographic markers is located within the preformed passages.
determining a position of the X-ray transparent core post-operatively by locating the radiographic markers in an X-ray image.
2 . The method according to claim 1 , wherein the one or more pins comprise a plurality of angularly spaced pins.
3 . The method according to claim 1 , wherein the upper and lower prosthesis plates are formed of metal and the core is formed of a low friction plastics material.
4 . A method of making an intervertebral prosthesis, the method comprising:
forming a core of a rigid, X-ray transparent material, the core including opposed, top and bottom bearing surfaces and a peripheral surface between the top and bottom surfaces;
forming at least one passage in the core extending radially inward from the peripheral surface; and
inserting at least one radiopaque pin into said at least one passage.
5 . A method according to claim 4 , wherein:
forming at least one passage comprises forming a plurality of radial passages; and
inserting comprises inserting at least one radiopaque pin into each of the plurality of passages.
6 . A method according to claim 5 , wherein forming a plurality of passages comprises forming a plurality of equally circumferentially spaced passages.
7 . A method according to claim 4 , further comprising:
forming upper and lower prosthesis plates each having a bearing surface configured to cooperate with one of the top and bottom bearing surfaces of the core, to allow the plates to slide in an articulated manner over the core.
8 . A method according to claim 4 , wherein forming a core comprises forming a core of a low friction plastic.
9 . A method according to claim 4 , wherein inserting at least one radiopaque pin comprises inserting at least one titanium pin.
10 . A method according to claim 4 , wherein forming at least one passage in the core comprises forming at least one blind bore in the core.