GB2184025A

GB2184025A - Replacement joint

Info

Publication number: GB2184025A
Application number: GB08629774A
Authority: GB
Inventors: Terry Andrew
Original assignee: VIRGIN PHILIP
Current assignee: VIRGIN PHILIP
Priority date: 1985-12-12
Filing date: 1986-12-12
Publication date: 1987-06-17
Also published as: GB8629774D0; DE3642576A1; GB8530609D0; DE3642576C2; GB2184025B

Abstract

A replacement joint for a knee comprises a tibial component 10 having a spigot 13 depending from its undersurface and an upper surface having an intermediate surface portion 14 and outer raised surface portions 15, 16. The division walls between the surface portion 14 and the surface portions 15, 16 are arcuate when viewed in plan and the meniscal component 11 has a complementary under surface shape. The gaps between the edges of the division walls are such as to allow the meniscal component to be passed through and then moved angularly to its fitted position. The division walls of the two components are provided with tongue and groove connections. <IMAGE>

Description

SPECIFICATION Replacement Joints This invention relates to a method of retaining the meniscal component relative to the tibial component of a three component replacement knee joint of the non-ligament retaining type.

In a known form of joint of the above type the tibial component defines a flat surface upon which rests a flat surface of the meniscal component. The tibial component also defines a tapered hollow spigot by which means it is in use anchored into the tibia. The meniscal component is provided with a peg extending from said flat surface, the peg being shaped in a complementary manner to the interior of the spigot so that in use, the meniscal component can move angularly about the axis of the spigot.

In the operation of fitting the replacement joint, the femur and tibia are shaped to receive the respective components of the joint which are then located in position. The meniscal component is then inserted between the femural and tibial components, a meniscal component of the desired thickness being selected for this purpose. Once the joint has been fitted it is checked to ensure that a meniscal component of the correct thickness has been chosen. In the event that a meniscal component of the incorrect thickness has been fitted it is of course necessary to extract the fitted component and replace it with one of appropriate size. Extracting the meniscal component once it has been located in position, is not easy because of the peg which requires that some separation of the femural and tibial components be effected before the meniscal component can be removed.

The object of the present invention is to provide a three component replacement knee joint of the type specified in a simple and convenient form.

According to the invention in a three component replacement knee joint of the non-ligament retaining type, the tibial component comprises a platform having a lower surface which in the use of the joint is presented to the tibia, and an upper surface which in use is engaged by a complementary surface of the meniscal component, said upper surface being divided into three portions, the first being an intermediate portion and the second and third portions lying at opposite ends of the intermediate portion, the second and third portions of the surface lying above said intermediate portion of the surface, the division walls of the platform extending between the first and the second and third portions being substantially normal to the surfaces and being of arcuate form, and the distance between the outer edge of one wall and the corresponding outer edge of the other wall being at least equal to the maximum width of the meniscal component whereby in the process of fitting the meniscal component it can be slid into position between the tibial and femural component, and then moved angularly to its fitted position.

An example of a replacement knee joint in accordance with the invention will now be described with reference to the accompanying drawings in which:~ Figure 1 is a side elevation of the assembled tibial and meniscal components of the joint, Figure 2 is a plan view of the tibial component with the meniscal component removed, and Figure 3 is a plan view of the meniscal component shown in the position relative to the tibial component of Figure 2, for assembly to the tibial component.

Referring to the drawings it will be appreciated that the femural component of the joint has not been illustrated but this follows the usual form defining a pair of spaced rounded surfaces corresponding generally to the condyles of the normal femur. The joint includes a tibial component generally indicated at 10 and a meniscal component generally indicated at 11. The tibial component comprises a platform 12 from the undersurface of which extends a spigot 13 whereby the component can be secured in the prepared end of the tibia. The spigot is conveniently of oval tapering section.

The upper surface of the platform 12 defines three surface portions 14, 15, 16. The surface portions 15, 16 being located opposite each other at the outer ends of the intermediate surface portion 14. The surface portion 14 is recessed below the surface portions 15, 16 and forms the bearing surface for the meniscal component as will be explained. The platform 12 has curved end walls 17 and contoured side walls. The surface portions 14, 15 and 16 are disposed in parallel relationship and division walls 18 extend between the surface portions 14and 15, and 14 and 16, the division walls being generally normal to the surface portions but in plan view, being of arcuate form with their centres coincident with the axis of the spigot 13.

In plan view the meniscal component 11 is of substantially identical overall shape to the platform 12 of the tibial component and its upper surface 19 is shaped to receive and locate the aforesaid spaced rounded surfaces of the femural component.

The under surface of the meniscal component is divided into three sections which in general, are complementary to the surface portions 14, 15 and 16 respectively of the tibial component. The width of the under surface of the meniscal component is such that when the component is turned through 900 as shown in Figure 2 it can pass between the gaps defined between the presented ends of the division walls 18. However, in order to prevent the meniscal component being pushed too far during such movement one of the gaps is made slightly smaller as indicated by the dotted lines in Figure 2.

Moreover, in order to be able to reduce the widths of the gaps one side wall of the projecting portions of the undersurface is recessed as indicated at 20.

It is thus a simple matter when fitting the joint, to firstly insert the meniscal component since it is only necessaryto displace the tibial andfemural components by a small distance, and if the incorrect size of meniscal component has been selected, to remove the meniscal component and replace it with another component of the appropriate thickness. In the assembled joint the meniscal component is able to rotate about the axis of the spigot as in the existing joints.

In order to prevent separation of the surfaces of the tibial component and the complementary surfaces of the meniscal component, the arcuate division walls 18 of the tibial component and the corresponding walls of the meniscal component, are provided with tongue and groove connections, in the particular example, the grooves 21 being formed in the walls 18. Moreover, in order to facilitate the fixing of the spigot within the prepared tibia, the undersurface of the platform 12 and the surface of the adjacent portion of the spigot are treated to facilitate cement adhesion or biological fixation.

Claims

1. Athree component replacement knee joint of the non-ligament retaining type in which the tibial componentcomprisesa platform having a lower surface which in the use of the joint is presented to the tibia, and an upper surface which in use is engaged by a complementary surface of the meniscal component, said upper surface being divided into three portions, the first being an intermediate portion and the second and third portions lying at opposite ends of the intermediate portion, the second and third portions of the surface lying above said intermediate portion of the surface, the division walls of the platform extending between the first and the second and third portions being substantially normal to the surfaces and being of arcuate form, and the distance between the outer edge of one wall and the corresponding outer edge of the other wall being at least equal to the maximum width of the meniscal component whereby in the process of fitting the meniscal component it can be slid into position between the tibial and femural component, and then moved angularly to its fitted position.

2. A joint according to Claim 1 in which the division walls of the platform and the corresponding walls of the meniscal component are provided with tongue and groove connections to prevent separation of the co-operating surfaces of the tibial and meniscal components.

3. A joint according to Claim 1 or Claim 2 in which the distance between the other outer edge of the one wall and the corresponding outer edge of the other wall is too small to allow the meniscal component to pass therethrough.

4. A joint according to any one of the preceding claims in which the lower surface of the platform is provided with a spigot of non circular section.

5. A joint according to Claim 4 in which the under surface of the platform and a portion of the surface of said spigot are treated to facilitate cement adhesion or biological fixation.

6. A three component replacement knee joint of the non-ligament retaining type comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.