GB2491997A

GB2491997A - Linked meniscal bearings for a prosthetic knee joint

Info

Publication number: GB2491997A
Application number: GB1216476.0A
Authority: GB
Inventors: David Wolfson; Russell Lloyd; John Joseph O'connor; David Murray; Christopher Alexander Dodd; John Goodfellow
Original assignee: Biomet UK Ltd
Current assignee: Biomet UK Ltd
Priority date: 2008-04-01
Filing date: 2008-04-01
Publication date: 2012-12-19
Anticipated expiration: 2028-04-01
Also published as: GB201216476D0; GB2491997B

Abstract

A bearing assembly for a prosthetic joint has two bearing elements 4,6 connected by an integral linking element 8. The assembly is moulded as a block and then material is removed from between the bearings to create the linking element. Alternatively, a separate linking element may have its ends compression moulded into the bearing elements. Preferably, the linking element is flexible but resilient; it may be made from polyethylene or may be a fabric or polyester cord. A retaining bridge 50 may restrain movement of the linking element to prevent dislocation of the joint. Preferably the bearing assembly sits on a tibial plate 30 as part of a prosthetic knee joint.

Description

I

BEARING COMPONENT

The present invention relates to a bearing component for a prosthesis and particularly, but not exclusively, relates to a bearing component for a total knee replacement prosthesis.

Background

Joint replacement prostheses commonly comprise two bone engaging components that articulate via a bearing component. In a total knee replacement prosthesis, the bone engaging components are a femoral component, comprising an anterior surface with patella track and two femoral condyles, and a tibial component, comprising a substantially planar surface or tray and a post, keel or other stabilising feature. The femoral and tibial components articulate via a bearing component mounted on the tray of the tibial component. The bearing component may be fully or partially fixed with respect to the tibial component, and commonly comprises a single piece of high density polyethylene.

In order to more closely replicate the natural kinematics of the knee, it is desirable for a total knee replacement prosthesis to facilitate a combination of rolling, rotational and translational movement between the femoral and tibial components of the prosthesis.

This can be achieved in part by employing a "mobile" bearing component, having some freedom of movement relative to the tibial component on which it is supported. In addition, it has been shown that mobile bearing components exhibit more favourable wear characteristics than so called "fixed" meniscal bearings. However, experience, particularly with uni-compartmental knee replacements, indicates that mobile bearings are associated with a higher risk of dislocation in the event of joint distraction, in either the medial or lateral compartments, when compared with fixed meniscal bearings.

Summary of Invention

According to a first aspect of the present invention, there is provided a bearing component for a joint replacement prosthesis, the component comprising: a first bearing element; a second bearing element, and a linking element, operatively connecting the first and second bearing elements and permitting relative motion there between.

The linking element provides a physical connection between the two bearing elements while still allowing relative motion between the two bearing elements. The linking element thus prevents dislocation of either bearing element in the event of distraction in either compartment of the prosthesis in which the bearing element is employed.

The linking element may be flexible and may be elastic or resilient. Such a linking element thus affords a greater range of relative motion between the two bearing elements The first and second bearing elements and the linking element may be integrally formed. The linking element may comprise a polyethylene membrane.

Alternatively, the linking element may comprise a fabric or polyester cord.

Respective ends of the linking element may be moulded into the first and second bearing elements. The linking element may extend into and through bores that may extend at least partially through the bearing elements.

According to another aspect of the present invention, there is provided a joint replacement prosthesis comprising first and second bone engaging components that articulate via the bearing component of the first aspect of the invention.

The prosthesis may be a knee replacement prosthesis, the first bone engaging component comprising a femoral component and the second bone engaging component comprising a tibial component.

The bearing component may be supported on the tibial component such that relative motion between the tibial component and first and second bearing elements is enabled.

The articulation between the femoral component and the first and second bearing elements may be at least partially spherical.

The tibial component may comprise at least one tray, on which the bearing component is supported, and a retaining element that extends across the tray, between the first and second bearing elements, passing over the linking element. The retaining element may thus prevent dislocation of the entire bearing component in the event of bilateral distraction.

The retaining element may comprise a bridge, under which the linking element of the bearing component passes, such that the bridge limits the extent of relative motion possible between the linking element and the tibial tray.

The retaining element may be removably connected to the tibial tray, thus facilitating assembly of the prosthesis.

The joint replacement prosthesis may further comprise an artificial ligament.

The artificial ligament may extend between and be connected to the tibial and femoral components.

The tibia! component of the joint replacement prosthesis may comprise first and second bearing surfaces, operable to articulate with the first and second bearing elements of the bearing component, the first bearing surface being convex and the second bearing surface being non con-convex.

The second bearing surface may be concave. The convex and concave bearing surfaces may be at least partially spherical.

According to another aspect of the present invention, there is provided a method of making a bearing component of the present invention comprising direct compression moulding ends of the linking element into the first and second bearing elements.

According to another aspect of the present invention, there is provided a method of making a bearing component of the present invention comprising moulding the first and second bearing elements as a single piece and removing material from the area between the first and second bearing components to define the linking element.

According to another aspect of the present invention, there is provided a flexible linking element for use in preventing dislocation of mobile bearings in a total knee replacement prosthesis.

The flexible linking element may connect first and second mobile bearing elements.

Movement of the flexible linking element may be at least partially constrained by a retaining element.

According to another aspect of the present invention, there is disclosed use of a flexible linking element to prevent disbcation of mobile bearings in a total knee replacement prosthesis.

According to another aspect of the present invention, there is provided a tibial component for a knee replacement prosthesis, the component comprising a lateral compartment having a convex bearing surface and a medial compartment having a non-convex bearing surface. The convex lateral bearing surface provides increased stability to the lateral compartment of the joint, when the tibial component is assembled in a knee replacement prosthesis.

The bearing surface of the medial compartment may be concave. Such a concave medial compartment provides greater stability and facilitates in replicating the natural motion of the knee when the tibial component is assembled in a knee replacement prosthesis, primarily by reducing motion in the medial compartment of the knee.

Combining a convex lateral compartment with a concave medial compartment facilitates restoration of the natural motion of the knee.

Alternatively, the bearing surface of the medial compartment may be planar.

The lateral and medial bearing surfaces may be part spherical and the radii of curvature of the lateral and medial bearing surfaces may be substantially the same.

The centre of curvature of each bearing surface may be anterior of the anterior/posterior centre line of the bearing surface and on the medial/lateral centre line of the bearing surface.

The lateral and/or medial bearing surfaces may comprise modular surface components, operable to be connected to a tray component to form the tibial component. The modular surface components and tray component may comprise cooperating fittings to facilitate connection and removal of the modular surface components.

According to another aspect of the present invention, there is provided a kit of parts for a tibial component of a knee prosthesis, the kit comprising a tibial tray and a plurality of surface components, operable to be removably connected to the tray, the surface components each comprising a bearing surface, at least one surface component comprising a convex bearing surface and at least one surface component comprising a concave bearing surface.

According to another aspect of the present invention, there is provided a knee replacement prosthesis comprising the bearing component of the first aspect of the present invention and the tibial component of the above aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-Figure 1 is a plan view of a bearing component Figure 2 is a plan view of an alternative bearing component Figure 3 is a plan view of a tibial tray component Figure 4 is a perspective view of the tibia I tray component of Figure 3 Figure 5 is a perspective view of the bearing component and the tibial tray component Figure 6 is a perspective view of a partially assembled knee replacement prosthesis Figure 7 is a plan view of an embodiment of a tibial component Figure 8 is a sectional view along the anterior/posterior centre line XX of the component of Figure 7.

Figure 9 is a sectional view along the medial/Lateral centre line (V of the lateral compartment of the component of Figure 7.

Figure 10 is a sectional view along the medial/lateral centre line ZZ of the medial compartment of the component of Figure 7.

Figure 11 is a perspective view of an embodiment of a tibial component Figure 12 is a sectional view of another embodiment of a tibial component Figure 13 is a sectional view of the component of Figure 12 in an alternative arrangement Figure 14 is a sectional view of an embodiment of a bearing component

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to Figures 1 and 2, a bearing component 2 comprises first and second bearing elements 4, 6 and a flexible linking element 8. Bearing component 2 is suitable for use as a meniscal bearing component of a total knee prosthesis, the prosthesis comprising a tibial component, a femoral component and the bearing component 2.

Bearing elements 4, 6 of the bearing component are formed of moulded high density polyethylene and each comprise a distal bearing surface (not shown), that is shaped to articulate with a tibial tray, and a proximal bearing surface 10, 12, that is shaped to articulate with an associated condyle of a femoral prosthesis. The proximal bearing surfaces 10, 12 may have any suitable shape appropriate for the chosen femoral component with which the bearing component is to articulate.

The linking element 8 may be a separate cord 14, connected to the bearing elements 4, 6, as illustrated in Figure 1. The cord 14 may be of any appropriate shape or material. For example, it may comprise a woven flexible fabric or polyester cord. The cord 14 passes through appropriately dimensioned bores 18, 20 that extend across the width of the bearing elements 4, 6 such that ends of the cord 14 extend out of opposite sides of each bearing element 4, 6. A knot 22 is tied in each end of the cord 14 to prevent the cord 14 passing back through the bores 18, 20. The two bearing elements 4, 6 are thus connected together. Relative movement between the bearing elements 4, 6 is possible, as the cord 14 is flexible. In alternative embodiments, the knot 22 may be replaced by a ball or other protruding feature that prevents passage of the ends of the cord back through the bores 18, 20. In another embodiment, as illustrated for example in Figures 5 and 6, the cord 14 may be moulded into the bearing elements at the time of manufacture.

In an alternative embodiment, the linking element 8 may be an integral component 16 of the bearing elements 4, 6, as illustrated in Figure 2. The linking element may for example comprise a thin polyethylene membrane 16 that connects the bearing elements 4, 6 while permitting relative motion there between. The membrane 16 may be moulded into the bearing elements 4, 6 or may be formed during manufacture of the bearing elements by forming the bearing component 2 as a single component and then removing material from the component so as to define the two bearing elements 4, 6, leaving only the thin membrane of material 16 connecting the two elements together.

With reference to Figures 3 to 6, a tibial component suitable for use with the bearing component 2 comprises a tray 30 and a bridge element 50. The bridge element 50 is omitted in Figures 3 to 5 for clarity. The tray 30 is formed of a suitable biocompatible metal, such as stainless steel or cobalt chromium molybdenum. The tray comprises a distal surface 32, which engages a resected tibial bone surface, and may comprise a keel or other stabilising feature (not shown). The tray 30 further comprises a proximal surface 34 that articulates with the distal surfaces of the bearing elements 4, 6 of the bearing component 2, when the bearing component 2 and tibiat component are assembled. The tibial component comprises a lateral compartment 36 and a medial compartment 38. The lateral and medial compartments may each comprise bearing surfaces 40, 42 with which the bearing elements 4, 6 of the bearing component 2 articulate. The bearing surfaces 40, 42 may be planar, and the articulation may comprise sliding articulation.

With reference particularly to Figure 6, the bridge element 50 comprises a beam 52 and two supporting legs 54, 56. The beam 52 extends substantially parallel to the proximal surface 34 of the tibial tray 30 in an anterior/posterior direction and spans substantially the entire width of the tray 30. The supporting legs 54, 56 are positioned proximate the anterior and posterior edges of the tray, substantially equidistant of the medial and lateral edges of the tray 30. The bridge element 50 thus divides the tray 30 into its lateral and medial compartments 36, 38 and defines a passage 60 there between. A proximal surface of the beam 52 may comprise a threaded blind bore and cooperating screw (not shown), suitable for attaching one end of an artificial ligament (not shown) to the bridge element 50. Alternative means of connecting an artificial ligament may also be used.

The bridge element 50 is formed of any suitable biocompatible metal and may be formed integrally with the tibial tray 30. Alternatively, the bridge element may be connected to the tray 30 in any appropriate manner. Preferably, the bridge element 50 is removably connected to the tray 30, facilitating assembly of the final prosthesis.

Alternatively, the bridge element 50 may be fixedly connected to the tray 30 at the time of manufacture.

The bearing component 2 and tibial tray 30 may be assembled at the time of manufacture or immediately prior to implantation. When the bearing component 2 and tibial tray 30 are assembled, as illustrated in Figure 5, the bearing elements 4, 6 of the bearing component 2 each rest on a respective bearing surface 40, 42 of the tray 30.

The linking element 8 of the bearing component 2 connects the bearing elements 4, 6 together. When the bridge element 50 is assembled with the tray 30 to form the tibial component, as illustrated in Figure 6, the linking element 8 of the bearing component extends under the beam 52 of the bridge element, through the passage 60 to connect the bearing element 4, 6. If the bridge element 50 is integrally formed with the tibial tray 30, the tray 30, bridge element 50 and bearing component 2 may be assembled at the time of manufacture. Alternatively, if the bridge element 50 is not integrally formed with the tray 30 but may be connected to the tray after manufacture, then the tray 30, bridge element 50 and bearing component 2 may be assembled at any time prior to implantation.

In use, the tibial tray 30, bridge element 50 and bearing component 2 are assembled and implanted by mounting the tibial component onto a resected proximal surface of a tibia. A femoral component is attached to a distal surface of a femur and the resurfaced joint is assembled. The bearing elements 4, 6 cushion the articulation between the tibial tray and the condyles of the femoral component. The bearing elements 4, 6 are mobile but are retained safely within the joint by the combined action of the linking element 8 and the bridge element 52. In the event of distraction of the joint in either the lateral or medial compartments, the bearing element in the distracted compartment is held within the joint by its connection to the other bearing element via the linking element 8. In the event of bilateral distraction, the bearing component 2 is held within the joint space by the bridge 52. The passage 60 defined by the bridge element 50 is not sufficiently large to allow passage of either of the bearing elements 4, 6, so dislocation of the bearing component 2 is prevented.

With reference to Figures 7 to 11, a tibial component 100 of a knee prosthesis comprises a distal surface 102, that is operable to engage a resected surface of a tibia, and a proximal surface 104, that is operable to engage one or more bearing components (not shown). The component may further comprise a post, keel or other stabilising feature (not shown) that extends from the distal surface and provides stability to the component 100 when implanted. The component comprises a lateral compartment 106, including a lateral portion of the proximal and distal surfaces 102, 104, and a medial compartment 108, including a medial portion of the proximal and distal surfaces 102, 104. The lateral and medial compartments are separated by a central region 114.

Each of the lateral and medial compartments comprises a proximal bearing surface 110, 112. The lateral proximal bearing surface 110 is convex or domed, having a part spherical surface with a radius of curvature R1. The centre of curvature of the lateral bearing surface 110 is just anterior of the anterior/posterior centre line XX of the tibial component 100, and is approximately on the medial/lateral centreline YY of the lateral compartment 106 of the tibial component 100. The medial proximal bearing surface 112 is concave or dished, having a part spherical surface with a radius of curvature Rm, which is preferably of a similar length to the lateral bearing surface radius of curvature R1. The centre of curvature of the medial bearing surface 112 is also just anterior of the anterior/posterior centre line)O( of the tibial component 100, and is approximately on the medial/lateral centreline ZZ of the medial compartment 108 of the tibial component 100.

Kinematic analysis of a patient may be employed to determine the height hm, h1 of each compartment of the tibial component 100. Alternatively, the heights h, hm of the lateral and medial compartments may be selected according to the natural positions of the lateral and medial bearing surfaces of the healthy tibia.

With reference to Figures 12 and 13, another embodiment of tibial component 200 comprises a tibial tray 270 and at least three modular surface components 280, 282, 284. The tibial tray 270 comprises a distal surface 202, that is operable to engage a resected surface of a tibia, and a proximal surface 204, that is operable to engage one or more modular surface components. The proximal surface 204 comprises lateral and medial support surfaces 208, 210, each of which may comprise a connection feature, for example a recess 212, operable to cooperate with a corresponding connection feature on a corresponding modular surface component, as described below.

The at least three modular surface components comprise a domed lateral surface component 280, having a convex part spherical proximal bearing surface 210 as described above with respect to tibial component 100, a dished medial surface component 282, having a concave part spherical proximal bearing surface 212 as described above with respect to tibial component 100, and a planar medial surface component 284, having a planar proximal bearing surface 213. The tibial component may also comprise a lateral planar surface component having a planar proximal bearing surface (not shown). Each modular surface component 280, 282, 284 comprises a distal bearing surface that articulates with a corresponding support surface 208, 210 of the tibial tray 270. The distal bearing surfaces of the modular surface components 280, 282, 284 each comprise a connection feature, for example a lug 290, operable to cooperate with the corresponding connection feature on the corresponding tibia I support surface 208, 210.

The tibial component 200 may be provided as a kit of parts comprising a tibial tray 270 and a selection of modular surface components 280, 282, 284, enabling a surgeon to select an appropriate combination of domed, dished and planar bearing surfaces to suit a particular patient.

Both embodiments of tibial component 100, 200 are operable to be used in combination with appropriately shaped bearings (not shown). The bearings preferably comprise individual medial and lateral bearings, each having a proximal femoral bearing surface that is shaped to articulate with a femoral component of a knee prosthesis, and a distal tibial bearing surface that is shaped to articulate with the appropriate one of the lateral or medial bearing surfaces of the tibial component 100, 200. A combination of domed lateral and dished medial bearing surfaces on the tibial component 100, 200 provides increased stability to individual meniscal bearings, and facilitates in recreating the natural motion of the knee.

The tibial components 100, 200 described with reference to figures 7 to 13, may used in combination with the bearing component 2 described with reference to Figures 1 to 6. A bridge element 50 as described above with respect to Figure 6 may be mounted in the central region 114 of the tibial component 100, 200 of Figures 7 to 13. if the bearing component 2 is to be used in connection with a tibial component 100, 200 as described with reference to Figures 7 to 13, the distal bearing surfaces of the bearing elements 4, 6 of the bearing component 2 are shaped to articulate with, for example, the convex and concave bearing surfaces 210, 212 of the fibial component 200. An example of a bearing component 102 for use with either of the tibial components 100, of Figures 7 to 13 is illustrated in sectional view in Figure 14. The bearing component 102 comprises lateral and medial bearing elements 106, 104, each of which comprises a proximal bearing surface 110, 112, shaped to articulate with an associated femoral condyle. The bearing elements 104, 106 further comprise distal bearing surfaces 113, 111, each of which is shaped to articulate with a corresponding proximal tibial bearing surface 210, 212. Thus, the distal bearing surface 113 of the lateral bearing element 106 is part spherical concave, having a radius of curvature substantially equal to the radius of curvature R1 of the lateral bearing surface 210 of the tibial component. Similarly, the distal bearing surface 111 of the medial bearing element 104 is part spherical convex, having a radius of curvature substantially equal to the radius of curvature Rm of the medial bearing surface 212 of the tibiaE component.

Additional Statements of Invention

Statement 1. A bearing component for a joint replacement prosthesis, the component comprising: a first bearing element; a second bearing element, and a linking element, operatively connecting the first and second bearing elements and permitting relative motion there between.

Statement 2. The bearing component of statement 1, wherein the linking element is flexible.

Statement 3. The bearing component of statement 1 or 2, wherein the linking element is elastic/resilient.

Statement 4. The bearing component of any of the preceding statements, wherein the first and second bearing elements and the linking element are integrally formed.

Statement 5. The bearing component of any of the preceding statements, wherein the linking element comprises a polyethylene membrane.

Statement 6. The bearing component of any of statements I to 3, wherein the linking element comprises a fabric or polyester cord.

Statement 7. The bearing component of statement 6, wherein respective ends of the linking element are moulded into the first and second bearing elements.

Statement 8. A joint replacement prosthesis comprising first and second bone engaging components that articulate via a bearing component of any of statements I to 7.

Statement 9. The joint replacement prosthesis of statement 8, wherein the prosthesis is a knee replacement prosthesis, the first bone engaging component comprising a femoral component and the second bone engaging component comprising a tibial component.

Statement 10. The joint replacement prosthesis of statement 9, wherein the bearing component is supported on the tibia! component such that relative motion between the tibial component and first and second bearing elements is enabled.

Statement 11. The joint replacement prosthesis of statement 9 or 10, wherein the articulation between the femoral component and the first and second bearing elements is at least partially spherical.

Statement 12. The joint replacement prosthesis of any of statements 9 to 11, wherein the tibial component comprises at least one tray, on which the bearing component is supported, and a retaining element that extends across the tray, between the first and second bearing elements, passing over the linking element.

Statement 13. The joint replacement prosthesis of statement 12, wherein the retaining element comprises a bridge, under which the linking element of the bearing component passes, such that the bridge limits the extent of relative motion possible between the linking element and the tibial tray.

Statement 14. The joint replacement prosthesis of statement 12 or 13, wherein the retaining element is removably connected to the tibial tray.

Statement 15. The joint replacement prosthesis of any of statements 9 to 14, further comprising an artificial ligament.

Statement 16. The joint replacement prosthesis of statement 15, wherein the artificial ligament extends between and is connected to the tibial and femoral components.

Statement 17. The joint replacement prosthesis of any of statements 9 to 16, wherein the tibial component comprises first and second bearing surfaces, operable to articulate with the first and second bearing elements of the bearing component, the first bearing surface being convex and the second bearing surface being non con-convex.

Statement 18. The joint replacement prosthesis of statement 17, wherein the second bearing surface is concave.

Statement 19. The joint replacement prosthesis of statement 17 or 18, wherein the convex and concave bearing surfaces are at least partially spherical.

Statement 20. A method of making a bearing component of statement 1, comprising direct compression moulding ends of the linking element into the first and second bearing elements.

Statement 21. A method of making a bearing component of statement 1, comprising moulding the first and second bearing elements as a single piece and removing material from the area between the first and second bearing components to define the linking element.

Statement 22. A flexible linking element for use in preventing dislocation of mobile bearings in a total knee replacement prosthesis.

Statement 23. The flexible linking element of statement 22, wherein the flexible linking element connects first and second mobile bearing elements.

Statement 24. The flexible linking element of statement 22 or 23, wherein movement of the flexible linking element is at least partially constrained by a retaining element.

Statement 25. Use of a flexible linking element to prevent dislocation of mobile bearings in a total knee replacement prosthesis.

Statement 26. Use of a flexible linking element of statement 25, wherein the flexible linking element connects first and second mobile bearing elements.

Statement 27. Use of a flexible linking element of statement 25 or 26, wherein movement of the flexible linking element is at least partially constrained by a retaining element.

It will be understood by one skilled in the art that any aspect of any of the embodiments described herein may be used in combination with any other aspect of any of the embodiments described herein.

Claims

CLAIMS1 A method of making a bearing component comprising a first bearing element, a second bearing element, and a linking element operatively connecting the first and second bearing elements, the method comprising moulding the first and second bearing elements as a single piece and removing material from the area between the first and second bearing elements to define the linking element.
2 A method as claimed in claim 1, wherein the linking element is flexible.
3 A method as claimed in claim I or 2, wherein the linking element is elastic/resilient.
4 A method as claimed in any preceding claim, wherein material is removed until the linking element comprises a membrane.
A method as claimed in any preceding claim, wherein the linking element is formed from polyethylene.
6 A method of making a bearing component comprising a first bearing element, a second bearing element, and a linking element operatively connecting the first and second bearing elements, the method comprising direct compression moulding ends of the linking element into the first and second bearing elements.
7 A method as claimed in claim 6, wherein the linking element comprises a fabric or polyester cord.
8 A method as claimed in any preceding claim, wherein the bearing component comprises the meniscal component of a knee replacement prosthesis.