Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-06-09
2003-06-24
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S020240
Reexamination Certificate
active
06582469
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the field of improvements in total knee prostheses which comprise, as is customary, a femoral element and a tibial plateau. The femoral element is used to replace the destroyed condyles of the femur, while the tibial plateau replaces the defective upper part of the tibia.
2. Discussion of Background Information
Prostheses of this type are already available. They are essentially sliding prostheses, with or without preservation of the posterior cruciate ligament, and in which the femoral element moves over a small surface area in relation to the tibial plateau.
Document GB-A-2 067 412 describes a knee prosthesis in which the femoral element is fitted between its two condyles with a passage which terminates in a convex cam. The tibial plateau of the present prosthesis has recesses to hold the condyles and a concave ramp rising up toward the femoral element and stretching widely between both its condyles.
When the cam is engaged with the ramp, and the free angle is shifted, a very tight fit is created because of the large lever arm formed by attachment of the tibial plateau to the upper part of the tibia.
Moreover, the broad elongation of the ramp of the tibial plateau considerably restricts the amplitude of tibial rotation in relation to the femur.
Finally, the height of the ramp of the tibial plateau requires considerable resection of the femoral epiphysis, which clearly leads to a considerable reduction of its resistance.
These drawbacks have been overcome in Applicant's European patent No. 0 294 298. The total knee prosthesis described in this document includes a femoral element fitted with two asymmetrical condyles and a convex cam which is placed between the two condyles and fashioned as a third condyle.
The tibial plateau consists of a horizontal track which holds the convex cam of the femoral element which is situated below the level of the recesses on which the condyles of the femoral element move. Between the recesses, and aligned with the track, the tibial plateau includes a concave ramp which has the shape of a curved abutment holding the cam at a slight distance from the tibial plateau for the entire length of the course in which both elements are in contact: this reduces as much as possible any forces working on the tibial plateau.
Because of the low-lying position of the cam or third condyle, the lever arm created by its action on the ramp or tibial plateau abutment is reduced as much as possible, so that any forces transmitted to the tibia are minimal.
Total prostheses of the knee as described above have certain drawbacks: it is impossible to retain the posterior cruciate ligament because of the central placement of the convex cam between the two condyles.
The femur of a healthy knee is composed of two distal/posterior condyles which are separated by a space allowing passage of the posterior cruciate ligament which stabilizes the joint in the posterior position.
Improvements made to the knee prosthesis in accordance with the present invention aim to preserve passage of the posterior cruciate ligament while retaining the advantages of the convex cam as described in European patent No. 0 294 298.
SUMMARY OF THE INVENTION
The total prosthesis of the knee according to the present invention comprises a femoral element fitted with two condyles, one external, the other internal, at least one of which is integral on one of its sides with a convex cam ensuring posterior stability. A tibial plateau comprises two custom-made recesses to hold the condyles and at least one track placed in the immediate vicinity of the recess holding the condyle integral with the convex cam. The track is circumscribed by at least one curved abutment and at least one horizontal recess
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between the plateau provison posterior and anterior extremities of the tibial is made between the two condyles of the femoral element and the two recesses of the tibial plateau for a free space and a notch for the passage of the posterior cruciate ligament of the knee, respectively.
The total prosthesis of the knee according to the present invention has, on the internal side of one condyle of the femoral element, a convex cam fashioned as a third condyle in a manner limiting the dimensions of the free space communicating with the notch of the tibial plateau through which the posterior cruciate ligament of the knee passes, while the convex cam works with a track situated between and below the level of the recesses holding the said condyles.
The total prosthesis of the knee has, on the external side of one condyle of the femoral element, a convex cam fashioned as a third condyle in a manner limiting the free space between the external and internal condyles communicating with the notch of the tibial plateau through which the posterior cruciate ligament of the knee passes, while the convex cam works with a track situated on the outside and below the level of the recess holding the condyle.
The total prosthesis of the knee according to the present invention has, on the internal sides of each condyle of the femoral element, a convex cam fashioned as a third condyle in a manner limiting between the cams installed on opposite sides of it, the dimensions of the free space communicating with the notch of the tibial plateau through which the posterior cruciate ligament of the knee passes, while each convex cam works with a track situated between and below the level of the recesses holding the condyles.
The total prosthesis of the knee according to the present invention has a tibial plateau fitted with at least one track holding the convex cam connected to the femoral element and which includes at the side of the posterior extremity of the plateau a horizontal recess situated below the level of the custom-made recesses holding the condyle, the recess extending toward the anterior extremity of the plateau via a curved abutment which is raised against the tibia.
The total prosthesis of the knee according to the present invention has a tibial plateau fitted with at least one track holding the convex cam connected to the femoral element and which includes, at the side of the posterior extremity of the plateau, a first curved abutment rising slightly above the custom-made recesses holding the condyles, the first abutment extending toward the anterior extremity of the plateau via a second curved abutment which is raised against the tibia.
The total prosthesis of the knee according to the present invention has a tibial plateau fitted with at least one track holding the convex cam connected to the femoral element and which includes, at the side of the posterior extremity of the plateau, a curved abutment rising slightly above the recesses provided for holding the condyles, the abutment extending toward the anterior extremity of the plateau via a horizontal recess situated below the level of the recesses.
The total prosthesis of the knee according the present invention has a cam with a curved shape extending from the camber to the anterior wing of the femoral element.
The total prosthesis of the knee according to the present invention has a cam, a portion of which is torus shaped.
The total prosthesis of the knee according to the present invention has a cam which is less wide than the planned width of the external and internal condyles.
According to the invention, total prosthesis of a knee comprises a femoral element fitted with two condyles, a first of the condyles being external, a second of the condyles being internal, and a tibial plateau fitted with custom-made recesses to hold the condyles, wherein at least one of the condyles is integral on one of its sides with a convex cam ensuring posterior stability of the prosthesis, the tibial plateau having at least one track placed in the immediate vicinity of the recess holding the condyle integral with the cam. The at least one track is circumscribed by at least one curved abutment and at least one horizontal recess between posterior and anterior extremities of the tibial plateau, p
Greenblum & Bernstein P.L.C.
Isabella David J.
Tornier S.A.
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