IE41751B1

IE41751B1 - Prosthetic knee joints

Info

Publication number: IE41751B1
Application number: IE222975A
Authority: IE
Original assignee: Atomic Energy Authority Uk
Priority date: 1974-10-14
Filing date: 1975-10-13
Publication date: 1980-03-12
Also published as: GB1507309A; FR2287895B3; JPS5164794A; FR2287895A1; JPS5834138B2; AU499481B2; DE7532545U; IE41751L; AU8569875A; DE2545821A1

Abstract

1507309 Prosthetic knee joints UNITED KINGDOM ATOMIC ENERGY AUTHORITY 1 Oct 1975 [14 Oct 1974] 44456/74 Heading A5R An artificial knee joint comprises a femoral component 1, an intermediate component 2, and a tibial component 3, the intermediate component 2 having a stem 9 rotatably mounted in a blind socket in a stem 5 of the tibial component, a contoured upper surface 8 for sliding engagement with a complementary shaped surface of the femoral component, and an upward projection 14 which is located in a slot of the femoral component, the intermediate component and the femoral component being interconnected by a pin 17. The tibial component is made of high density polyethylene as is the femoral component, the intermediate component being of stainless steel. The stem 5 of the tibial component is externally fluted. and the surfaces of the femoral component can be provided with recesses or keyways to assist is cementation thereof to the bone. The femoral component may have a stem 16.

Description

The present invention concerns artificial knee joints (prostheses).

A known type of existing prosthesis comprises a simple pivot in the form of a pair of hinged pins or stems. The stems are bonded with bone cement within surgically prepared sockets in the femur and tibia respectively and the pivot axis is located as closely as possible to the natural pivot axis of the knee. With such a prosthesis it is not possible for relative rotation to occur between the femur and tibia in contrast with the natural knee which can accommodate such rotational movement.

Other types of existing prostheses employ spherical load bearing surfaces. These are expensive to produce and can result in problems of stability and location.

Any artificial joint must function geometrically closely to the natural joint so as to avoid compromising the ligaments. In addition account must be taken of a number of factors including, the loading pattern applied to the joint; the compatibility of the materials of the artificial joint with human tissue and the surgical ease of installation in the body.

• The present invention seeks to provide an artificial knee joint which will closely reproduce the movements of a natural knee and which can be fitted without excessive surgical removal of bone. - 2 41751 According to the present invention an artificial knee joint comprises a femoral component, a tibial component and an intermediate component rotatably mounted on the tibial component, the femoral component and the intermediate component having co-operating contoured surfaces to enable smooth uninterrupted sliding motion therebetween through an angular arch characteristic of a natural knee joint, the femoral component having a base to seat on the intermediate component and opposed limbs engageable with the anterior and posterior surfaces of the femur, a bridge piece on the base extending centrally between the limbs with a profiled slot in the bridge piece to accommodate a projection of corresponding profile formed integrally with the intermediate component and a hinge connection between the femoral component and the intermediate component to prevent dislocation of the femoral component from the intermediate component. Since the intermediate portion is rotatably mounted on the tibial component, relative rotation of the femur about its anatomical axis is permitted with respect to the tibia. This not only accommodates the natural rotation which occurs in the knee during flexure but also means that it is not important for the tibial and femoral components to be located in precise positions rotationally about the anatomical axis, thus alleviating the need for precision in surgery.

The components are formed from materials which are compatible with human tissue and which will not produce electrolytic voltages. Certain grades of stainless steel, cobalt-chromium-tungsten alloys, and high density polyethylene are considered to be acceptable materials but the choice is not necessarily restricted to these examples.

The invention will be described further, by way of example, and with reference to the accompanying drawings, in which:Figure 1 illustrates a knee, with a prosthesis installed, in a fully extended position with approximately 6° hyperextension; Figure 2 shows the knee with installed prosthesis when flexed through approximately 65°; - 3 41751 Figure 3 shows the knee with installed prosthesis when flexed through approximately 125°; Figure 4 shows the knee with installed prosthesis when flexed through approximately 165° (maximum flexion) from the Figure 1 position; Figure 5 is a pictorial view of one component part of the prosthesis; Figure 6 is a pictorial view of another component part of the prosthesis; and Figure 7 shows a detail, not to scale, in the assembly of the prosthesis. An artificial knee joint comprises three basic components, namely a femoral component 1, an intermediate component 2 and a tibial component 3. As shown on the drawings the femoral component is bonded to the femur 4 while the tibial component has a stem 5 which is inserted in a recess or socket 6 formed in the tibia 7. The intermediate component 2 forms a seat 8 for the femoral component and is rotatably supported and located on the tibial component 3 by means of an integral shank 9 which engages in a blind-ended bore in the stem 5 of the tibial component.

The femoral component 1 comprises a cap 10, having a base adapted to seat on the intermediate component and two opposed limbs 21 and 22 which extend along the resected anterior and posterior surfaces respectively of the femur. The anterior limb provides a surface 11 for the patella 12 to slide on during flexing of the knee, the surface 11 being suitably profiled to cooperate with the corresponding surface of the patella. A bridge piece 13 is centrally and fixedly, located on the base between the opposed limbs. The bridge piece 13 is received in a channel cut between the femoral condyles and serves to position the femoral component on the femur. A slot is provided centrally in the femoral component to accommodate a projection 14 which is an integral part of the intermediate component. Conveniently, the femoral - 4 41751 component is formed in one piece from a plastics material, preferably a high density polyethylene.

The projection 14 engages in the slot and provides lateral location of the femoral and tibial components. The profile of the projection has a corresponding profile to that of the slot. The profiles of the slot and the projection 14 are shown in dotted outline in Figure 2 at which position the leading edges of each have separated and likewise the cap has pivoted through an angle of approximately 65° on the intermediate component.

The intermediate component 2 is conveniently formed from a stainless 10 steel. As seen from Figure 5 the intermediate component 2 has on its upper surface on each side of the projection 14 a curved profile 15 which provides a sliding bearing surface for the posterior of the femoral component, which latter is of matching radius. The integral shank 9 projects from the intermediate component into the blind-ended socket in the tibial portion and the stem is substantially coaxial with the intramedullary axis of the tibia.

The tibial component 3 is conveniently formed from a plastics material such as a high density polyethylene. As seen from Figure 6 the stem 5 of the tibial component 3 is capped by an integral platform 23 which serves as a support for the intermediate component 2. The stem 5 is shaped, as by flutings 24 over an upper portion of its length, so as to obtain a firm hold in the tibia using a bonding cement while retaining sufficient bone structure about the stem to provide adequate support.

The surfaces of the femoral component engaging the femur can be provided with recesses or keyways for embedment of a bonding cement to assist in fixing to the femur. Additionally, the femoral component can be provided with a stem 16 (as shown in dotted outline in Figure 1) which can be inserted in a corresponding socket formed in the femur.

Figure 7 shows the mounting of the femoral component 1 on the intermediate component. A pin 17 can be located in a bore 25 in the femoral component on an axis corresponding to the centre of rotation. The pin passes through a corresponding bore 26 in the projection 14 and serves to prevent dislocation of the femoral component from the intermediate component.

The fitting of the pin 17, which is preferably formed from stainless steel, can depend upon the condition of the ligaments, in particular the patella ligament.

Conveniently, the pin 17 is retained in position by means of two retainers 18, arranged one abutting each end of the pin 17. Each retainer 18 is provided with a peg 19 projecting substantially normal to the axis of the retainer and each peg 19 is received and accommodated firmly in a corresponding bore 20 formed in the femoral component. The retainers 18 are preferably formed from a plastics material, such as high density polyethylene. In Fig. 7, the left hand retainer is not in abutting engagement with the corresponding end of the pin 17 in order to show the peg 19 and the bore 20 in the femoral component.

Figures 1 to 4 of the drawings illustrate different attitudes of the knee. Figure 1 depicts normal stance with 6° hyperextension. Figure 2 typifies the maximum flexion that might arise during walking. Figure 3 is an example of flexion that results when seated or climbing stairs.

Figure 4 shows the maximum possible flexion through an angle of approximately 165° from the Figure 1 position.

Claims

1. An artificial knee joint comprising a femoral component, a tibial component and an intermediate component rotatably mounted on the tibial component, the femoral component and the intermediate component having co-operating contoured surfaces to enable smooth uninterrupted sliding motion therebetween through an angular arch characteristic of a natural knee joint, the femoral component having a base to seat on the intermediate component and opposed limbs engageable with the anterior and posterior surfaces of the femur, a bridge piece on the base - 6 41751 extending centrally between the limbs with a profiled slot in the bridge piece to accommodate a projection of corresponding profile formed integrally with the intermediate component and a hinge connection between the femoral component and the intermediate component to prevent dislocation of the femoral component from the intermediate component.

2. An artificial knee joint as claimed in Claim 1 in which the intermediate component comprises an integral shank rotatably engaged in a blind-ended socket in the tibial component.

3. An artificial knee joint as claimed in Claim 1 or 2 in which the tibial component comprises a platform and an integral stem having flutings to achieve a firm bonded hold in the tibia.

4. An artificial knee joint as claimed in Claim 1, 2 or 3 in which the hinge connection comprises a pin accommodated in a bore in the femoral component and an aligned bore in the projection on the intermediate component.

5. An artificial knee joint substantially as herein described with reference to and as illustrated in the accompanying drawings.