Tibial tray for an artificial knee joint

ES 2 182 015 T3

DESCRIPTION

Tibia platform for an artificial knee joint.

The invention deals with a tibial platform for an artificial knee joint, with a metallic lower part that can be anchored in the tibia, with a support part made of plaostic material that presents sliding surfaces for two condyles of femur, which are can rotate around a posterior open joint at the bottom, and that at a distance "l" from the articulation towards the anterior part by means of a ratchet it can be fixed in a projection of the lower part.

A tibia platform of this kind is presented in the patent application EP-A-0 738 504. In this case, a ratchet, made in one piece with the support part, fits during assembly under the shoulder of the part. lower. This kind of abutment is often made of a plastic material, for example polyethylene, in order to achieve a favorable sliding match with respect to metalic femoral condyles. The plastics used offer the advantage that with their structure and resistance they avoid high point loads. This means that in the case of a hitch, these piastics have limits.

In the forces that acted on the supporting part and on the lower part of the tibia platform, the direction and the maximum magnitudes depend remarkably on how intact the set of ligaments is still intact. The smaller the number of ligaments that are still effective, the more it will become necessary to guide the condyles of the femur by means of a central conducting nerve in the form of an artificial eminence, and the more extreme will be the loads attacking in the supporting part.

Another locking of a tibia platform with a bearing part is described in US patent specification 5,330,534. Projections protrude posterior and anteriorly from a flat surface of the platform in the center. On the back side, the supporting part is secured with an open hinge that prevents it from getting up. In the front part, two protruding pins are provided, which carry transverse recesses that allow the support part to be secured avoiding the previous lifting, by means of a latch that passes through the support part and through these recesses. The latch itself is secured by a spring that prevents it from falling. The latch and protruding dowels are metallic, but must be able to mount loosely to each other. The forces that are transmitted from the bearing part to the latch and then to the protruding pins necessarily give rise to micro movements and metal erosion between the latch and the pins. All transverse forces between the support part and the platform are transmitted in the area of ​​the rear and front ribs. Another drawback is that due to the anterior locking mechanism located on the outside of the support part, there are additional corners and edges that give rise to contusions of parts of the tissue if the user of this prosthesis hits the front on knee.

The aim of the invention is to create for these cases an efficient and durable anchoring of the support part in the lower part. This objective is solved with the characteristics of independent claim 1.

The set offers the advantage that the varus and valgus positions of the knee joint can also be supported, the ligamentous apparatus being weak. Another advantage is that in the case of a lower part already inserted in the tibia, it is possible to implant the support part from anteriorly, saving space, despite the protruding eminence. The support part can be slid into the open joint with a very flat angle from anteriorly, while the auxiliary means for anchoring the metal ratchet in the support part can be placed from above and anteriorly. Another advantage is that for an already implanted lower part, support parts with and without marked guide ribs and with different spacing between the support surface and the lower part can be placed as a mechanism. After implanting the lower part, the operator can decide on a suitable support part, according to the state of the ligamentous apparatus.

Further advantageous developments of the invention are described in claims 2 to 6. The invention is described below by means of an exemplary embodiment.

In the figures you can see:

Fig. 6a. schematically a section in the sagittal direction through a lower part and a support part, which are joined together by means of a metal ratchet on the periphery of a turning bolt anchored in the support part;

Fig. 6b. schematically a view of the support part and of the rotating bolt of figure 6a.

The figures show a tibia platform with a metallic inner part 1 and with various support parts 2, made of plaostic material, which can be anchored to each other at the back by means of an open joint 4. The support part 2 carries a guiding nerve 6 to guide the condyles of the femur, and protruding at least 15 mm upwards above the lowest point 7 of the sliding surfaces 3. Due to the fact that in a horizontal projection 5 of the lower part 1 and at a distance "l" from the articulation 4 it grips an independent metal ratchet 8, located movable with respect to the support part 2, and that by means of the auxiliary elements 9 can be permanently positioned on the shoulder 5 in an interlocking position, by forced movement, large lateral forces can be supported, as they appear in the upper guide nerves 6 and in varus / valgus positions of the knee.

In Figures 6a, 6b in the anchoring part 2 and in a vertical direction a rotating bolt 23 is anchored, which at the bottom widens to form a disk, and which is secured from above by means of a lip 32 that prevents it from out. The bolt

The swivel ES 2 182 015 T3 ends in an internal hexagon into which a key can be inserted through a through hole 26, from above. The ratchet 8 is formed as an eccentric projection on the periphery of the rotating bolt 23, and to effect the engagement it can be turned with the key until below the projection 5. A self-braking effect of the pawl 8 is achieved, for example, by the fact that along its periphery it rises slightly, to cradle itself only under the projection 5.