INTERVERTEBRAL PROSTHETIC DISC WITH SHOCK ABSORPTION CORE
An artificial intervertebral disc with shock absorption includes upper and lower plates disposed about a shock absorbing movable core. The upper and lower plates have an outer surface which engages a vertebrae and an inner bearing surface. The shock absorbing core includes a unitary member of a rigid material having at least one lateral cut between upper and lower surfaces of the core to allow the upper and lower surfaces to move resiliently toward and away from each other. This allows the core to absorb forces applied to it by the vertebrae.
1 . An artificial intervertebral disc comprising:
upper and lower supports, each support comprising:
an outer surface configured to engage a vertebra, and
an inner bearing surface; and
a core comprising upper and lower surfaces configured to engage and articulate with respect to the inner bearing surfaces of the upper and lower supports,
wherein the core is formed as a unitary member with upper and lower lips formed at the upper and lower surfaces, and at least three lateral cuts positioned between the upper and lower lips to allow the upper and lower surfaces of the core to move resiliently toward and away from each other without affecting articulation of the upper and lower surfaces of the core with respect to the inner bearing surfaces of the upper and lower supports.
2 . The disc of claim 1 , wherein the at least three lateral cuts of the core are evenly spaced between the upper and lower lips.
3 . The disc of claim 2 , wherein the at least three lateral cuts overlay each other in a vertical plane.
4 . The disc of claim 2 , wherein the at least three lateral cuts extend into the core to a depth of at least two thirds of a width of the core.
5 . The disc of claim 2 , wherein the at least three lateral cuts extend into the core to a depth of at least one half and less than three quarters of a width of the core.
6 . The disc of claim 2 , wherein the at least three lateral cuts are formed in a staggered arrangement with the cuts substantially evenly spaced around a periphery of the core.
7 . The disc of claim 1 , wherein the inner bearing surface of the upper support comprises a curved surface and the upper surface of the core comprises a curved surface to slide against the inner bearing surface of the upper support.
8 . The disc of claim 1 , wherein the lower surface of the core is capable of attachment to the lower support plate.
9 . The disc of claim 1 , wherein the lower surface of the core slides against the inner bearing surface of the lower support when the disc is in an implanted configuration.
10 . The disc of claim 1 , wherein the at least three lateral cuts divide the core into portions, and there is no sliding contact between the portions as the upper and lower surfaces of the core move with respect to one another in response to loading.
11 . The disc of claim 2 , wherein the at least three lateral cuts are of uneven depth to create a core with a preferential deflection direction.
12 . The disc of claim 1 , wherein the at least three lateral cuts have tapering cross sections to provide increasing stiffness with progressive compression.
13 . The disc of claim 1 , wherein the core has a maximum compression of about 1 mm or less.
14 . The disc of claim 1 , wherein the core has a minimum compression of about 0.01 mm.
15 . The disc of claim 1 , wherein the core has a maximum angle of inflection when loaded between the upper and lower surfaces of the core of about 6 degrees.
16 . The disc of claim 1 , wherein the core is configured for a cervical application and has a stiffness of about 300 to about 2000 N/mm between the upper and lower surfaces of the core.
17 . The disc of claim 1 , wherein the core is configured for a lumbar application and has a stiffness of about 600 to about 2000 N/mm between the upper and lower surfaces of the core.
18 . The disc of claim 1 , wherein the core is formed of a rigid material.
19 . An artificial intervertebral disc comprising:
upper and lower supports, each support comprising:
an outer surface configured to engage a vertebra, and
an inner bearing surface; and
a core comprising upper and lower surfaces configured to engage and articulate with respect to the inner bearing surfaces of the upper and lower supports,
wherein the core is formed as a unitary member with a lateral spiral shaped cut to allow the upper and lower surfaces of the core to move resiliently toward and away from each other without affecting articulation of the upper and lower surfaces of the core with respect to the inner bearing surfaces of the upper and lower supports.
20 . The disc of claim 19 , wherein the spiral cut comprises a plurality of spiral cuts.
21 . The disc of claim 20 , wherein the plurality of spiral cuts is in at least two different directions.
22 . The disc of claim 19 , wherein the core includes a central bore and the spiral cut intersects the central bore
23 . The disc of claim 19 , wherein the spiral cut and central bore form a continuous spring element which provides compliance to the core.
24 . The disc of claim 19 , wherein the core has a maximum compression of about 1 mm or less.
25 . The disc of claim 19 , wherein the core has a minimum compression of about 0.01 mm.
26 . The disc of claim 19 , wherein the core is configured for a cervical application and has a stiffness of about 300 to about 2000 N/mm between the upper and lower surfaces of the core.