IE44801B1

IE44801B1 - Prosthetic knee joint

Info

Publication number: IE44801B1
Application number: IE64977A
Authority: IE
Original assignee: Nat Res Dev
Priority date: 1977-03-28
Filing date: 1977-03-28
Publication date: 1982-04-07

Description

- Prosthetic joints fall broadly into two types, namely the so-called constrained and unconstrained types. In each case such a joint comprises two pieces which are secured to respective bones of the natural joint in question and have mutually articulatory bearing surfaces. In a joint of the contrained type the pieces are mechanically linked, such as by a hinge pin, to retain the surfaces in articulatory engagement. In contrast, the pieces of a joint of the unconstrained type are not so linked but are held in engagement by only the ligaments and other elements of the natural joint.

According to one aspect of the present invention, there ίελprovided a prosthetic knee joint of the unconstrained type as hereinbefore defined, comprising a tibial piece having a substantially circular-cylindrical, proximal end surface whereof the axis extends laterally, and a femoral piece having a substantially circular-cylindrical, distal end surface whereof the axis extends laterally and which is complementary to said proximal end surface for sliding on the latter, said femoral piece being formed with a posterior notch for receiving a posterior ligament. 44SQi In order that the invention may he clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:Figure 1 is an anterior or posterior elevation of a tibial piece of an unconstrained prosthetic right knee joint, Figure 2 is a lateral elevation of the tibial piece, Figure 3 is a proximal end view of the tibial piece, Figure 4 shows a posterior elevation of a femoral piece of the joint, Figure 5 shows a lateral elevation of the femoral piece, Figure 6 shows an anterior elevation of the femoral piece,. Figure 7 shows a distal end view of the femoral piece.

Figure 8 is an anterior or posterior elevation of a modified version of the tibial piece, and Figure 9 shows a lateral elevation of this modified version, but with a stem removed therefrom and a plug inserted therein.

Referring to Figures 1 to 3, the tibial piece comprises a circular-cylindrical stem 1 integral with a proximal end head 2.

The proximal end surface 3 of tbe tibial piece is of concave circular-cylindrical form, whereof the axis is the axis A of the joint. The axis B of the stem 1 and the head 2 is 90°to the axis A. The stem · 1 is more than 2 inches long, in order to penetrate deeply into the canal of the tibia. Formed between the stem 1 and the head 2 is a small annular groove 4, whilst a small bore 5 is formed substantially horizontally through -the head 2.

The groove 4 and the bore 5 serve to· receive a radiographic marker in the form of ,a metal wire. The tibial piece is made of high-density polyethylene. 44®0i Referring to Figures 4 to 7, the femoral piece comprir.ec c spike-form stem 10 integral with a distal end head 1Ϊ. The distal end surface 12 of the femoral piece is of a convex circular-, cylindrical form v/ith the axis A. The surface 12 is complementary to the surface 5 for sliding on the surface 5. The stem 10 is of a shape to follow the route of the femoral canal. For this reason, it has a distal section 15 which is generally of oval cross-section, an intermediate section 14 which is generally of rounded, square cross-section, and a proximal, posteriorly bent tip 15. Moreover, the general longitudinal axis G thereof is at slightly less than a right angle, in the present case at 85°, to the axis A. The stem 10 is more than 4 inches long. Posteriorly, the surface 12 is formed with a central notch 16 for receiving the posterior ligament. The section 15 is formed with respective opi^osite notches 17 for keying the femoral piece into cement. The femoral piece is made of cobalt-chrome-molybdenum alloy.

In insertion, the shapes and. orientations of the stems 1 and 10 help to ensure that the joint is located in an anatomically correct position. The tibial and femoral pieces are cemented into the bones.

Referring to Figure .8, the tibial piece shown differs from, that shown in Figures 1 to 5 in that the- proximal end head 2 has formed therethrough co-axially with its axis B a bore 6 which at its proximal end region is formed with screwthreading 7 and which has.inserted therein a stem 8 in the form of a plain rod. - 4 I In use of the prosthesis of Figure 8, the rod-like stem 6 is inserted along the medullary cavity of the tibia and thus serves to act as a guide, particularly maintaining the proper alignment of the joint part 2 while cement for anchoring the joint part 2 is setting. After the cement has set, the stem 8 is withdrawn from the associated joint part, and then an externally screwthreaded plug is screwed into the proximal end region of the bore 6, in order to close off the bore. Such a plug is referenced 9 in 'Figure 9, from which it will be seen that the plug 9 has a screwdriver slot 9'. The plug can be of plastics or metal Alternatively, the proximal end region of the bore 6 could be plugged with cement.

The joint shown has the advantage that it is easy to insert at precisely the correct angle in the anterior posterior plane, thus ensuring correct alignment of the leg at the knee joint. The cruciate ligaments are not preserved, stability of the hinge being maintained by the shape of the new joint interface together with the posterior ligament and the two lateral ligsnents and the. normal muscles which move the knee.

The cylindrical shape of the new femoral surface provided by. the joint presents a smooth and regular bearing to the patella throughout the range of movement in the knee.

For a left knee, the tibial piece is identical to that shown, but the femoral piece is, as it were, a mirror image of the femoral piece shown.

Claims

CLAIMS:

1. A prosthetic knee joint of the unconstrained type as hereinbefore defined, comprising a tibial piece having a substantially circular-cylindrical, proximal end surface 5 whereof the axis extends'laterally, and a femoral piece having a substantially circular-cylindrical, distal end surface whefeof the axis extends laterally and which is complementary to said proximal end surface for sliding on the latter, said femoral piece being formed with a posterior » 10 notch for receiving a posterior ligament.

2. A joint as claimed in claim 1, wherein said femoral piece includes a stem which extends proximally away from said distal end surface in a direction which is at-slightly less than a right-angle to the axis of said distal end 15 surface.

3. _A joint as claimed in claim 1 or 2, wherein said I I . ' tibial piece includes a stem which extends substantially radially o£ the axis of said proximal end surface distally away from said proximal end surface. 20

4. A joint as claimed in claim 1 or 2, wherein said tibial piece has means for receiving an intramedullary stem for extending along the cavity of the tibia and removing from said cavity and said tibial piece following anchoring of said tibial piece to said tibia. 25 5. A joint as claimed in claim 4, wherein said means comprises a bore through said tibial piece. - 6 I ' J 48Ql 6. A prosthetic knee joint of the unconstrained type as hereinbefore defined, substantially as hereinbefore described with reference to Figures 1 to 7, or Figures 1 to 7 as modified by Figures 8 and 9 of the accompanying

5. Drawings.