Prosthetic Knee Device

Abstract

A first prosthetic fixture has a head portion with a fixation stem extending therefrom which is fitted into a prepared cavity in a femur and cemented thereto. A second prosthetic fixture has a head portion with a fixation stem extending therefrom which is fitted into a prepared cavity formed in the end of a tibia and cemented thereto. The head of the femur fixture includes a shaft therein which is rotatably supported for single axis rotation on a pair of bearings to provide torsional stability to the joint along with a high load handling capability. The head of the tibia fixture has a slot formed therein which engages the rotatable shaft for rotation therewith, this slotted portion being fitted between side faces of the bearing fitted into the femur fixture head so as to retain the tibia fixture against major lateral movement. The tibia fixture is fitted with a set of bearing blocks which ride on the outer surfaces of the femoral fixture to provide a large diameter bearing surface concentric with the center shaft to carry the normal axial load and to provide for minor lateral stability associated with standing and walking. The two head members may be joined together after the fixtures are set in their respective associated bone portions to form an articulated joint rotatable about a single axis and stabilized against lateral and torsional movements.

Description

This invention relates to prosthetic devices, and more particularly to a prosthetic knee capable of articulation about a single axis.

In situations where severe articular cartilage degeneration has taken place, such as rheumatoid arthristis, osteoarthritis, or when there is severe bone damage to a knee, a prosthetic knee is often called for. Prosthetic devices of the prior art for use as knee joints often involve simple hinge arrangements staked or cemented into the bone or runners and guides set into the respective surfaces of the joint. Such hinge devices have the shortcomings of pivoting about a point near the surface rather than about a center which is the average of the instantaneous rotation centers, of not providing low friction bearing surfaces compatible with prior hip joint prosthetic art, and providing poor translation of leg torsional loads into the adjoining bone structure in the vicinity of the device. The runner-guide type joints have the shortcoming of not providing the needed lateral and torsional support, which in the case of the natural knee is provided by the ligaments, and have limited bearing surface. It is to be noted along these lines that the ligaments are often damaged so that they are no longer able to adequately perform these functions. Without such lateral and torsional support, the knee joint is unable to perform satisfactorily a number of functions involving sidewise and torsional loads, as for example, in climbing stairs.

It is further to be noted that in case of the runner-guide type prosthetic devices, the respective pieces are cemented directly into the bones, making the replacement of bearing members, should they become worn, difficult or impossible.

The device of this invention overcomes the shortcomings of the prior art in providing a prosthetic joint suitable for use as a knee, having full lateral and torsional stability using low friction, low wear bearings which are replaceable in a relatively simple surgical procedure, and which rotates about the average center of the instantaneous rotation centers. Further, the device of the invention utilizes double bearings providing an improved load handling capability as compared with single bearing devices of the prior art. The aforementioned features of the invention are provided in a device having a relatively simple and reliable mechanical configuration which utilizes low friction bearings which generate a minimal amount of debris with wear.

It is therefore an object of this invention to provide an improved prosthetic device capable of handling sidewise and torsional loading and which affords rotation on a large surface area, compatible with large loadings as encountered in stair climbing.

It is another object of this invention to provide a prosthetic device which provides a better translation of torsional and lateral loads into the surrounding bone structure.

It is a further object of this invention to provide a prosthetic device in which the bearings can be readily replaced without removing the implanted elements.

Other objects of this invention will become apparent as the description proceeds in connection with the accompanying drawings, of which:

FIG. 1 is an elevational view illustrating a preferred embodiment of the invention installed in place;

FIG. 2 is a cross-sectional view taken along the plane indicated by 2--2 in FIG. 1;

FIG. 3 is an elevational view of the preferred embodiment;

FIG. 4 is a cross-sectional view taken along the plane indicated by 4--4 in FI. 3;

FIG. 5 is a view taken along the plane indicated by 5--5 in FIG. 3;

FIG. 6 is an elevational view of a second embodiment of the invention;

FIG. 7 is a cross-sectional view taken along the plane indicated by 7--7 in FIG. 6; ane

FIG. 8 is a cross-sectional view taken along the plane indicated by 8--8 in FIG. 6.

Briefly described, the device of the invention is as follows: A first fixture for attachment to the femur bone has a head portion with a fixation stem extending therefrom, this fixation stem and head portion both being inserted in a cavity formed in the femur and cemented to the femur. A fixture for attachment to the tibia bone has a head portion with a fixation stem extending therefrom, a part of the head portion and the fixation stem being inserted in a cavity formed in the tibia and cemented to this bone. A shaft is rotatably mounted in the head portion of the femur fixture, this shaft being supported on removable bearing members mounted on oppositely facing members of the head portion. The head portion of the tibia fixture has a slot formed therein which engages the shaft and which fits between the oppositely facing members. Low friction bearing surfaces are further provided on the head of the tibia portion, these bearing surfaces riding on opposing surfaces of the head portion of the femur fixture.

Referring now to the drawings, a preferred embodiment of the invention is illustrated. Tibia fixture 11 which may be made of a metal such as stainless steel on a chromium cobalt alloy, has a head portion 12 and a fixation stem 13 which extends from the head portion. Fixation stem 13 and part of the head 12b are inserted into a cavity formed in the tibia plateau and attached to tibia 14 by suitable means such as cementing thereto, after the tibia has been properly cut and broached. Head portion 12 has a slotted arm 12a which extends from a flat plate portion 12b. Removably mounted on plate portion 12b of the head are a pair of bearing blocks 16. These blocks are press-fitted into slots 12c formed in the head portion, there further being a finger 16a extending from each of the blocks which fits into a corresponding aperture in plate portion 12b. Bearing blocks 16 have arcuate bearing surfaces 16b which mate with the arcuate surface 27a on the head portion of the femur fixture. Bearing blocks 16 are preferably made of a low-wear low-friction material, such as polypropylene or ultra high density polyethylene.

Femur fixture 19 has a head portion 20 with a fixation stem 22 extending therefrom, this head portion and fixation stem being fitted into a cavity formed in femur 25 and joined to the femur as by cementing. Head portion 20 has a pair of oppositely positioned members 27 which have arcuate bearing surfaces 27a on which the bearing surfaces 16b of bearing blocks 16 ride. Members 27 further have apertures formed therethrough into which bearing members 30 are press-fitted from the inside. Bearing members 30 are preferably made of a low-friction low-wear material, which may as for the bearing blocks be polypropylene or ultra high density polyethylene. Head portion 20 has, rotatably mounted in bearings 30, a shaft 35 which at its central portion has a square cross-section. The shaft is retained in the bearing by means of disc shaped side caps 38 which are press-fitted into the apertures formed in members 27. It is to be noted that in order to avoid metal to metal contact at the interfaces between shaft 35 and head portion 12 and thus to minimize the possibilities of wear of the metal surfaces and corrosion thereof that an insert of plastic material such as polypropylene or ultra high density polyethylene may be placed between the shaft and head portions. Such an insert can be press fitted into the slotted pair of head portion 12.

In installing the device of the invention, the two fixtures 11 and 19 are first each implanted in the tibia and femur respectively, as shown in FIG. 1 with the entire head portion 20 of fixture 19 implanted in the femur and the flat plate portion 12b of fixture 11 implanted in the tibia. After such installation has been completed, the slotted end portion 12a of the tibia fixture is placed over the square central portion of shaft 35 in mating engagement therewith, with bearing surfaces 16b riding on surfaces 27a and with the slotted end portion of head retained against sidewise movement by the flange portion of the bearing 30 pressing against the members 27. The installation of the prosthetic device is facilitated in that the two separate fixtures can be firmly installed in their associated bone portions individually, and the slotted portion of head 12 then engaged with the square part of the shaft 35 of the other head portion.

It is further to be noted that in the event of malfunction or damaging wear of the bearing members 30 and 16, they can be replaced without removing the structures from their installed positions in the bones. As already noted, the bearing members 30 and 16 are preferably made of a low-friction durable material which produces a minimal amount of debris with wear so as to afford long-time trouble-free operation.

Referring now to FIGS. 6-8, a second embodiment of the invention is illustrated. This embodiment is the same as the first except for the means used to interconnect the heads of the two fixtures. Head portion 12, which as for the first embodiment has a fixation stem 13 which is fitted into the tibia, has a six-sided arm portion 12a with a cylindrical pin 12d extending from the end thereof. Pin 12d fits into cylindrical aperture 35a formed in shaft 35 for axial rotation therein. This rotation is limited by virtue of the abutment of the side faces of portion 12a against the side faces 35a of slot 35c formed in shaft 35. The bearing surfaces 16b of bearing blocks 16, and the bearing surfaces 27a are made similarly spherical to permit rotational movement therebetween. This second embodiment is otherwise identical to that first described. The second embodiment thus permits some rotational play at the junction between the two fixtures, this being advantageous in situations where the patient's ligaments are still able to control such movement.

The device of this invention is particularly useful for cases where cruciate ligament damage exists and the prosthetic device needs to supply both the running surface and stability to the joint. Further, the use of replaceable bearings facilitates repair, should the operation of the joint become impaired due to wear.

While the device of the invention has been described and illustrated in detail, it is to be clearly understood that this is intended by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the following claims.

Claims

We claim:

1. A prosthetic device for providing an articulated joint between a pair of human or animal bones comprising:

a first prosthetic fixture having a head portion and a fixation stem extending therefrom, said fixation stem and at least a part of the head portion of the first fixture being adapted to be fitted into one of said bones and fixedly attached thereto,

the head portion of said first fixture comprising a shaft, bearing means for supporting said shaft for rotation about a single axis, and oppositely facing members between which the central portion of said shaft is positioned, and

a second prosthetic fixture having a head portion and a fixation stem, said fixation stem and at least a part of the head portion of the second fixture being adapted to be fitted into the other of said bones and fixedly attached thereto,

the head portion of the second fixture being removably fitted between the oppositely facing members of the head portion of the first fixture in engagement with the shaft for movement therewith, said second fixture head including means removably engaging said shaft for easy detachment therefrom while said central portion of the shaft remains positioned between said oppositely facing members.

2. The prosthetic device of claim 1 wherein the head portions and stems of said first and second fixtures are shaped and sized for fitting cavities formed in the central portions of the femur and tibia bones.

3. The prosthetic device of claim 1 wherein the heat portion of the second fixture comprises a slotted part which engages said shaft.

4. The prosthetic device of claim 3 wherein said shaft has a right angled cross section, said slotted part being right angled to fit over said shaft in mating engagement therewith.

5. The prosthetic device of claim 1 wherein said bearing means for supporting the shaft comprises a pair of bearing members, said bearing members being removably supported on the oppositely facing members of the head portion of the first fixture.

6. The prosthetic device of claim 5 wherein said bearing members are of a low-friction low-wear material.

7. The prosthetic device of claim 1 wherein the members of the head portion of the first fixture have arcuate outer surfaces, and further including a pair of bearing blocks attached to said second fixture having arcuate bearing surfaces which mate with the arcuate surfaces of said members and ride thereon.

8. The prosthetic device of claim 7 wherein said bearing blocks are removably attached to said second fixture.

9. The prosthetic device of claim 1 wherein the head portion of the second fixture comprises an arm with a pin extending therefrom, said shaft having an aperture formed therein for receiving said pin for axial rotational movement therein, said arm having freedom of limited axial rotational movement between the opoositely facing members of the head portion of said first fixture.