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 which engages a vertebra, and
an inner bearing surface; and
a core comprising upper and lower surfaces configured to engage the inner bearing surfaces of the upper and lower supports,
wherein the core is formed as a unitary member with at least one lateral cut positioned between the upper and lower surfaces to allow the upper and lower surfaces of the core to move resiliently toward and away from each other, and
wherein the core comprises an annular groove extending about a periphery of the core, the annular groove configured to align with a peripheral restraining structure of the upper or lower support so as to retain the core between the upper and lower supports during flexure of the disc.
2 . The disc of claim 1 , wherein the at least one lateral cut of the core comprises a plurality of lateral cuts in oriented in different directions.
3 . The disc of claim 2 , wherein the plurality of lateral cuts overlay each other in a vertical plane.
4 . The disc of claim 2 , wherein the plurality of lateral cuts include at least three lateral cuts extending 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 plurality of lateral cuts is formed in a staggered arrangement with the cuts substantially evenly spaced around a periphery of the core.
6 . 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.
7 . The disc of claim 1 , wherein the lower surface of the core is capable of attachment to the lower support plate.
8 . 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.
9 . The disc of claim 1 , wherein the at least one lateral cut divides 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.
10 . The disc of claim 2 , wherein the plurality of lateral cuts are of uneven depth to create a core with a preferential deflection direction.
11 . The disc of claim 1 , wherein the at least one lateral cut has a tapering cross section to provide increasing stiffness with progressive compression.
12 . The disc of claim 1 , wherein the at least one lateral cut is a spiral shaped cut.
13 . The disc of claim 1 , wherein the at least one lateral cut comprises a plurality of spiral cuts.
14 . The disc of claim 13 , wherein the plurality of spiral cuts is in at least two different directions.
15 . The disc of claim 1 , wherein the core has a maximum compression of about 1 mm or less.
16 . The disc of claim 1 , wherein the core has a minimum compression of about 0.01 mm.
17 . The disc of claim 1 , wherein the core comprises a NiTi alloy.
18 . 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.
19 . The disc of claim 1 , wherein the core is movable between the upper and lower supports after implantation of the disc in a patient.
20 . The disc of claim 1 , wherein the inner bearing surfaces of the upper and lower supports are concave and the upper and lower surfaces of the core are convex, and wherein when implanted the core is movable laterally between the upper and lower supports to provide a movable center of rotation.
21 . 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.
22 . 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.
23 . The disc of claim 1 , wherein the peripheral restraining structure comprises an inwardly directed flange coupled to the upper or lower support, wherein the flange is configured to engage the annular groove of the core during flexure of the disc so as to ensure that the core is held captive between the upper and lower supports.