Intervertebral disk prosthesis
The intervertebral disk prosthesis comprises first and second parts ( 2, 3 ) intended to be attached respectively to two adjacent vertebrae, an intermediate part ( 4 ) inserted between the first and second parts ( 2, 3 ) and comprising articular surfaces ( 9, 10 ) that cooperate with respective articular surfaces ( 6, 8 ) of the first and second parts ( 2, 3 ), and means ( 11, 12 ) for coupling the first part ( 2 ) and the intermediate part ( 4 ). The coupling means ( 11, 12 ) are arranged to leave the intermediate part ( 4 ) free relative to the first part ( 2 ) during a first phase of a tilting movement of the first part ( 2 ) relative to the second part ( 3 ), but to displace the intermediate part ( 4 ) toward an end (E 2 ) of the prosthesis that is opposite to an end (E 1 ) toward which the first part ( 2 ) is displaced by tilting relative to the second part ( 3 ), during a second phase of the tilting movement of the first part ( 2 ).
1. An intervertebral disk prosthesis comprising:
first and second parts intended to be attached respectively to two adjacent vertebrae,
an intermediate part inserted between the first and second parts and comprising articular surfaces that cooperate with respective articular surfaces of the first and second parts, and
means for coupling the first part and the intermediate part,
wherein the coupling means are arranged to leave the intermediate part free relative to the first part during a first phase of a tilting movement of the first part relative to the second part, such that the intermediate part is displaced toward an end of the prosthesis that is opposite to an end toward which the first part is displaced by tilting relative to the second part, and to drive the intermediate part with the first part during a second phase of the tilting movement, said tilting movement being in the same direction in the second phase as in the first phase,
wherein the first and second parts when placed in the vertebrae are not in abutment during said second phase.
2. The intervertebral disk prosthesis according to claim 1 , wherein said coupling means comprise at least one projecting portion provided on one of the first part and intermediate part and at least one cavity formed in the other of the first part and intermediate part, whereby this cavity receives the projecting portion and has a larger section than that of the projecting portion.
3. The intervertebral disk prosthesis according to claim 2 , wherein said coupling means comprise a single projecting portion provided on a peripheral portion of the first part or the intermediate part and located in a sagittal plane.
4. The intervertebral disk prosthesis according to claim 2 , wherein said coupling means comprise first and second projecting portions provided on the first part or the intermediate part and located in a sagittal plane, on both sides of the axis of the prosthesis, and first and second corresponding cavities formed in the intermediate part or the first part respectively.
5. The intervertebral disk prosthesis according to claim 1 , further comprising means for coupling the intermediate part and the second part, whereby these coupling means limit the relative movements in axial rotation of said intermediate part and second part.
6. The intervertebral disk prosthesis according to claim 5 , wherein said means for coupling the intermediate part and the second part comprise a rail extending in a sagittal direction on one of the second part and intermediate part and a groove formed in the other of the second part and intermediate part and cooperating with this rail.
7. The intervertebral disk prosthesis according to claim 6 , wherein the rail and the groove define respective inclined support surfaces that cooperate during flexion movements of the prosthesis to slightly raise the center of gravity of the intermediate part.
8. The intervertebral disk prosthesis according to claim 5 , wherein said means for coupling the intermediate part and the second part comprise a first groove formed in the second part and oriented in a sagittal direction, a second groove formed in the intermediate part and oriented in a frontal direction, and a mobile guide part cooperating with the first and second grooves.
9. The intervertebral disk prosthesis according to claim 8 , wherein a play is provided between the guide part and at least one of the first and second grooves, allowing axial-rotation travel of the intermediate part relative to the second part.
10. The intervertebral disk prosthesis according to claim 5 , wherein said means for coupling the intermediate part and the second part comprise first and second studs provided on the second part or the intermediate part and located in a frontal plane, on both sides of the axis of the prosthesis, and first and second cavities formed in the intermediate part or the second part, respectively, and receiving the studs.
11. The intervertebral disk prosthesis according to claim 1 , wherein the first phase of the tilting movement corresponds to about 40 to 60% of the maximum tilting angle of the first part relative to the second part, and the second phase corresponds to the remaining 60 to 40%.
12. The intervertebral disk prosthesis according to claim 1 , wherein the first phase of the tilting movement corresponds to an angular tilting range of the first part relative to the second part of about 4 to 8°, and the second phase of the tilting movement corresponds to an angular tilting range of the first part relative to the second part of about 3 to 7°.
13. The intervertebral disk prosthesis according to claim 1 , wherein the first phase of the tilting movement corresponds to an angular tilting range of the first part relative to the second part of about 5 to 7°, and the second phase of the tilting movement corresponds to an angular tilting range of the first part relative to the second part of about 4 to 6°.
14. The intervertebral disk prosthesis according to claim 1 , wherein said articular surfaces of the intermediate part are convex, and said respective articular surfaces of the first and second parts are concave.
15. The intervertebral disk prosthesis according to claim 1 , wherein the articular surface of the first part and the corresponding articular surface of the intermediate part are spherical portions of radius R 1 , and the articular surface of the second part and the corresponding articular surface of the intermediate part are spherical portions of radius R 2 .
16. The intervertebral disk prosthesis according to claim 15 , wherein the first part is an upper part, the second part is a lower part, and the radius R 1 is less than the radius R 2 .
17. The intervertebral disk prosthesis according to claim 1 , wherein the first part is a lower part, the second part is an upper part and the means for coupling the first part and the intermediate part comprise first and second projecting portions provided on the first part or the intermediate part and located in a sagittal plane on both sides of the axis of the prosthesis and first and second corresponding cavities formed in the intermediate part or in the first part respectively, the prosthesis further comprising second coupling means for coupling the second part and the intermediate part, these second coupling means comprising a first groove formed in the second part and oriented in a sagittal direction, a second groove formed in the intermediate part and oriented in a frontal direction, and a mobile guide part cooperating with the first and second grooves.
18. The intervertebral disk prosthesis according to claim 17 , wherein the articular surface of the first part and the corresponding articular surface of the intermediate part are spherical portions of radius R 1 , and the articular surface of the second part and the corresponding articular surface of the intermediate part are spherical portions of radius R 2 , whereby the radius R 2 is less than the radius R 1 .