GB2474394A

GB2474394A - Artificial ligament with spring biasing and tension adjustment

Info

Publication number: GB2474394A
Application number: GB1101112A
Authority: GB
Inventors: David Wolfson; Russell Lloyd; Mohammed Imran Khan; John O'connor; David Wycliffe Murray; Christopher Dodd; John Goodfellow
Original assignee: Biomet UK Ltd
Current assignee: Biomet UK Ltd
Priority date: 2007-11-02
Filing date: 2007-11-02
Publication date: 2011-04-13
Anticipated expiration: 2027-11-02
Also published as: GB201001643D0; GB0721610D0; GB201101112D0; GB2454251A; GB2464639A; GB2454251B; GB2464639B; GB2474394B

Abstract

An artificial ligament 318 has a biasing element such as a spring 340 at one end to control its effective stiffness. It may also have a tensioning device such as a screw threaded adjuster collar 320. Alternatively, the ligament may have only the tension adjuster. A hollow stem 302 may be inserted into a bone and the tensioning and biasing means mounted within it. The artificial ligament may be secured by a knot 335 which prevents it from pulling through an aperture 350 in the biasing means. Also disclosed is a prosthesis (figure 7) incorporating an artificial ligament and a ligament support (70, figure 7) that influences the line of action of the ligament by causing it to bend.

Description

PROSTHESIS COMPRISING AN ARTIFICIAL LIGAMENT

This invention relates to a prosthesis comprising an artificial ligament.

It is known to implant an artificial ligament to replace a natural ligament which has become damaged. Conventional artificial ligaments are formed from strands or bundles of artificial fibres which may be woven and/or aligned to form a flexible member which is substantially uniform in size and is resilient along its length.

A natural ligament exhibits high strength, toughness and resilience and retains these properties for many years. To date, it has been impossible to match these properties using artificial fibres.

When implanted, artificial ligaments may be attached to existing bone tissue, provided the tissue at the attachment site is relatively intact. However, if surrounding bone tissue is diseased or damaged, it may be necessary to remove both the natural ligament and the adjacent bone tissue and replace them with prosthetic components.

Joint replacement operations commonly result in removal of at least one ligament. The functionality of the ligament is replicated as closely as possible by one or more features of the replacement prosthesis (as for example in the case of a cooperating cam and post in a total knee replacement). However, it has proved extremely difficult to replicate the natural kinematics of a joint without the presence of naturally functioning ligaments. This is particularly evident in the case of the knee joint, which exhibits a complex movement that is highly dependent upon the interaction of ligaments with the articulating areas of bone.

According to an aspect of the present invention, there is provided a prosthesis comprising an artificial ligament, which is adapted to replace a human or animal ligament, and a biasing element operatively coupled to the artificial ligament to control the effective stiffness of the artificial ligament.

The biasing element enables an effective stiffness of the artificial ligament to be achieved that more closely approximates the stiffness of a natural ligament.

The biasing element may be operatively coupled to the ligament at or near one end only of the ligament.

The biasing element may comprise an elastic element.

The biasing element may comprise a spring or springs or an elastomeric member.

The biasing element may engage the ligament via a bearing component.

The biasing element may have a stiffness approximating that of a natural ligament that is to be replaced. In this manner, the biasing element may assist in replicating the natural characteristics of the joint. The biasing element may have linear or non-linear stiffness characteristics which may be achieved by methods known in the art.

According to another aspect of the present invention there is provided a prosthesis comprising an artificial ligament, which is adapted to replace a human or animal ligament, and a tensioning element operatively coupled to the ligament for applying tension to the ligament.

The tensioning element may be operatively coupled to the ligament at or near one end only of the ligament.

The prosthesis may further comprise a biasing element, which may comprise an elastic element. The biasing element may act between the tensioning element and the ligament. The tensioning element may be coupled to the ligament via the biasing element. The biasing element may engage the ligament via a bearing element.

The biasing element may comprise a spring, which may be a compression spring. The spring may be of any form. For example it may comprise a coil spring, a leaf spring or a Belleville washer.

Alternatively, the biasing element may comprise an elastomeric member.

The biasing element may have a stiffness approximating that of a natural ligament that is to be replaced. The biasing element may have a linear stiffness characteristic.

Alternatively, the biasing element may have a non-linear stiffness characteristic.

The ligament may be coupled to the tensioning element via an attachment means. The attachment means may comprise an enlarged portion that is formed on the ligament and engages the tensioning element. For example, the enlarged portion may comprise a knot tied in the artificial ligament.

The prosthesis may further comprise a bone engaging element for attachment to a bone. The tensioning element may act between the bone engaging element and the artificial ligament.

The tensioning element may be at least partially housed within the bone engaging element. The bone engaging element may comprise a stem, and the tensioning element may be at least partially housed within the stem.

The tensioning element may be adjustable and may be operable to adjust the tension within the ligament. The adjustable tensioning element therefore enables the tension in the ligament to be adjusted in a controlled manner, independently and controllably altering the characteristics of the ligament.

The prosthesis may further comprise adjustment means operable to adjust the tension in the ligament. The tension may be adjusted by adjusting the position of the tensioning element relative to the bone engaging element. Thus tension in the ligament may be altered even after both ligament and bone engaging element have been implanted into a patient.

The adjustment means may comprise a threaded connection between the tensioning element and the bone engaging element. The tensioning element may comprise an external thread and the stem may comprise a corresponding internally threaded bore within which the tensioning element is received.

The tensioning element may be configured to be screwed into or out of the bore to adjust the tension in the ligament.

The tensioning element may be accessed through an opening formed in the bone engaging element.

The prosthesis may comprise at least part of a joint replacement prosthesis, which may be a knee replacement prosthesis.

The prosthesis may comprise at least part of a knee replacement prosthesis in which the bone engaging element comprises a tibial component and the artificial ligament comprises a replacement anterior cruciate ligament (AOL).

According to another aspect of the present invention, there is provided a prosthesis comprising a bone engaging element having a stem which is adapted to project into a bone, and an artificial ligament, an end of the ligament extending into and being secured within the stem.

The ligament may be secured within the stem of the bone engaging element via a tensioning element, the tensioning element being at least partially housed within the bone engaging element.

The ligament may be secured within the stem of the bone engaging element via a biasing element, the biasing element being at least partially housed within the bone engaging element.

The ligament may be secured within the stem of the bone engaging element via both a tensioning element and a biasing element, the tensioning element and the biasing element being at least partially housed within the bone engaging element.

According to another aspect of the present invention, there is provided a prosthesis comprising a bone engaging element and an artificial ligament, an end of the artificial ligament being secured to the body of the bone engaging element, the prosthesis further comprising a ligament support, the ligament support at least partially determining the line of action of the ligament.

The artificial ligament may be secured within a recess formed in the body of the bone engaging element, and the ligament support may comprise the mouth of the recess.

The mouth of the recess may be radiused or chamfered.

The ligament support may project from a surface of the bone engaging element.

The artificial ligament may be secured to a surface of the bone engaging element.

The prosthesis may comprise at least part of a knee replacement prosthesis.

According to another aspect of the present invention, there is provided a method of implanting a prosthesis comprising first and second bone engaging elements, an artificial ligament and a biasing element, comprising: (a) operatively coupling the biasing element to a first end of the artificial ligament; (b) operatively coupling the biasing element to the first bone engaging element; (c) implanting the first and second bone engaging elements into bone tissue; (d) connecting a second end of the artificial ligament to the second bone engaging element, (e) balancing tension within the artificial ligament.

According to another aspect of the present invention, there is provided a method of implanting a prosthesis comprising first and second bone engaging elements, an artificial ligament and an adjustable tensioning element operatively coupled to a first end of the artificial ligament and to the first bone engaging element, the method comprising: (a) assembling the first bone engaging element, adjustable tensioning element and artificial ligament; (b) implanting the first and second bone engaging elements into bone tissue; (c) connecting a second end of the artificial ligament to the second bone engaging element; (d) adjusting the position of the adjustable tensioning element until a predetermined tension within the artificial ligament is achieved.

For a better understanding of the present invention, and to show 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 perspective view of a knee prosthesis having an artificial ligament.

Figure 2 is a partially sectioned side view of a first embodiment of knee prosthesis having an artificial ligament secured via a biasing element.

Figure 3 is a partial sectional view of the first embodiment of knee prosthesis.

Figure 4 is a partially sectioned side view of a second embodiment of knee prosthesis having an artificial ligament secured via a tensioning device.

Figure 5 is a partial sectional view of the second embodiment of knee prosthesis.

Figure 6 is a partial sectional view of a third embodiment of knee prosthesis having an artificial ligament secured via a tensioning device and a biasing device.

Figure 7 is a partial sectional view of another embodiment of knee prosthesis having and artificial ligament and a ligament support.

Referring to Figure 1, a knee prosthesis 2 comprises a tibial component 4 having a tibial tray 6 integrally formed with a stem 8, a femoral component 10 and a pair of bearing components 12, 13. The bearing components 12, 13 separate the tibial component 4 and femoral component 10, and are formed with proximal and distal bearing surfaces which engage corresponding bearing surfaces 14, 15, 16 on the tibial tray 6 and on the femoral component 10. These various bearing surfaces enable the tibial component 4 to rotate and translate relative to the femoral component 10. The bearing components 12, 13 may be meniscal bearing components, rotational platform bearing components, or may be fixed bearing components.

Referring to Figure 2, in a first embodiment of prosthesis 102, an artificial ligament 118 is connected at one end 121 to the femoral component 110, and at the other end 123 to a biasing element 140 mounted in the stem 108 of the tibial component 104. The biasing element 140 engages the ligament 118 via a bearing element 144. The biasing element 140 and bearing element 144 are both received within a bore 126 formed in the stem 108. The bore 126 opens onto the bearing surface 114 of the tibial tray 106 at a mouth 130. The mouth 130 extends partially into the bore 126 to define an internal annular shoulder 154 having an annular bearing surface 156. The mouth 130 is smooth, widening to accommodate the artificial ligament 118 with some play. The mouth may be radiused or chamfered. The artificial ligament 118 extends into the bore 126 through a space 127, defined between the bearing components 112, 113, so that the artificial ligament 118 substantially does not interfere with the bearing components 112 during normal articulation of the prosthesis.

Any convenient means of connection of the end 121 of the ligament 118 to the femoral component 110 is contemplated. For example, a boss or peg 119 may be formed on the femoral component for attachment of the ligament 118. The end 121 of the ligament 118 may be folded over and glued, sewn or otherwise fixed to form a loop (not shown). Alternatively, a hole or eye may be formed in the end 121 of the ligament 118.

The artificial ligament may then be secured to the boss 119 by passing the loop or eye over the boss 119. The boss 119 may have an enlarged head and narrower stem to encourage stable fixation of the ligament once attached to the boss 119.

With reference also to Figure 3, the other end 123 of the artificial ligament 118 is attached to the biasing element 140 via the bearing element 144. Any convenient means of connection between the end 123 of the ligament 118 and the bearing element 144 is contemplated. For example, the end 123 of the ligament 118 may pass wholly or substantially through the bearing element 144 and be prevented from passing back through the bearing element 144 by a stop 134. The stop 134 may take the form of an enlarged body, for example a spherical body (as illustrated in Figure 2), a cylinder, or any other appropriate form. Alternatively, the stop may comprise a knot formed in the end 123 of the ligament 118 (as illustrated in Figure 3). In an alternative embodiment (not shown) the end 123 of the ligament 118 may be attached directly to the bearing element 144 without passing through the body of the bearing element 144.

The biasing element 140 comprises a resilient element 142. In the illustrated embodiment, the resilient element 142 is a coiled compression spring 146 and the bearing element 144 is a plate 148. However, the resilient element may consist of or comprise any appropriate spring or springs, for example a Belleville washer or an elastomeric member. An appropriate bearing element may be selected according to the choice of resilient element.

As illustrated particularly in Figure 3, the spring 146 and bearing plate 148 are received within the bore 126 of the stem 108. The artificial ligament 118 extends into the mouth of the bore 126, through the coil spring 146 and through a passage 150 formed in the bearing plate 148. A stop 134 or knot 136 prevents the ligament 118 passing back through the passage 150 as described above. When tensile forces are applied to the ligament 118, the knot 135 or stop 134 bears against an adjacent surface of the plate 148, forcing an opposite surface of the plate 148 to engage and compress the spring 146 against the annular bearing surface 152 of the shoulder 150.

The spring 146 assists in replicating the natural stiffness of the ligament that is to be replaced. The characteristics of the spring are therefore selected to be similar to those of the natural AOL.

Referring to Figures 4 and 5, in a second embodiment of prosthesis 202, an artificial ligament 218 is connected at one end 221 to the femoral component 210, and at the other end 223 to a tensioning element 220 mounted in the stem 208 of the tibial component 204. The tensioning element 220 is cylindrical and formed with an external thread 222 which engages an internal thread 224 formed in a bore 226 in the stem 208.

As in the first embodiment, any convenient means of connection of the end 221 of the ligament 218 to the femoral component 210 is contemplated. For example, a boss or peg 219 may be formed on the femoral component for attachment of the ligament 218.

The end 221 of the ligament 218 may be folded over and glued, sewn or otherwise fixed to form a loop (not shown). Alternatively, a hole or eye may be formed in the end 221 of the ligament 218. The artificial ligament may then be secured to the boss 219 by passing the loop or eye over the boss 219. The boss 219 may have an enlarged head and narrower stem to encourage stable fixation of the ligament once attached to the boss 219.

The other end 223 of the artificial ligament 218 is attached to the tensioning element 220. Again, as in the first embodiment, any convenient means of connection between the end 223 of the ligament 218 and the tensioning element 220 is contemplated. For example, the end 223 of the ligament 218 may pass wholly or substantially through the tensioning element 220 and be prevented from passing back through the tensioning element 220 by a stop 234. The stop 234 may take the form of an enlarged body, for example a spherical body (as illustrated in Figure 4), a cylinder, or any other appropriate form. Alternatively, the stop may comprise a knot 235 formed in the end 223 of the ligament 218 (as illustrated in Figure 5). In an alternative embodiment (not shown) the end 223 of the ligament 218 may be attached directly to the tensioning element 220 without passing through the body of the tensioning element 220.

The bore 226 in which the tensioning element 220 is received opens onto the bearing surface 214 of the tibial tray 206 at a mouth 230. The mouth 230 is smooth, widening to accommodate the artificial ligament 218 with some play. The mouth may be radiused or chamfered. The artificial ligament 218 extends into the bore 226 through a space 227, defined between the bearing components 212, 213, so that the artificial ligament 218 substantially does not interfere with the bearing components 212 during normal articulation of the prosthesis. In the case of a monoblock bearing component (not shown) a suitable opening is formed to allow passage of the artificial ligament and to minimise wear or abrasion of the ligament 218 during movement.

As illustrated in Figure 4, the tensioning element 220 may have a substantially spherical recess 229 in its end 231 closest to the free end 228 of the stem 28. A passage 232 extends from a base of the recess through the tensioning element towards the mouth 230 in the tibial tray. The passage 232 is large enough to receive the loop, eye or other fixation feature at the end 221 of the ligament 218, but is too small to allow the stop 234 to pass through. Alternatively, as illustrated in Figure 5, the tensioning element may simply comprise a passage 232, the stop or knot 234, 235 engaging against a surface 237 of the tensioning element 220.

With reference to Figure 6, a third embodiment of knee prosthesis combines features of the first and second embodiments. The prosthesis 302 comprises a tensioning element 320, substantially as described with reference to the second embodiment, and a biasing element 340, substantially as described with reference to the first embodiment. The biasing element 340 acts between the ligament 318 and the tensioning element 320, as opposed to the shoulder 350 of the first embodiment. The biasing element 340 comprises a resilient element 342, which engages the ligament 318 via a bearing element 344. In the illustrated embodiment, the resilient element 342 is a coiled compression spring 346 and the bearing element 344 is a plate 348.

However, the resilient element may be any appropriate spring or springs, for example a Belleville washer or an elastomeric member. An appropriate bearing element may be selected according to the choice of resilient element.

As illustrated in Figure 6, the spring 346 and bearing plate 348 are received within the bore 326 of the stem 308 beneath the tensioning element 320. The artificial ligament 318 extends through the passage 332 in the tensioning element, through the coil spring 346 and through a passage 350 formed in the bearing plate 348. A stop 334 or knot 336 is formed on the end 323 of the ligament 318 as described above. The knot 335 or stop 334 prevents the ligament 318 passing back through the passage 350. When tensile forces are applied to the ligament 318, the knot 335 or stop 334 bears against an adjacent surface of the plate 348, forcing an opposite surface of the plate 348 to engage and compress the spring 346 against the adjacent surface of the tensioning element 320.

The spring assists in replicating the natural stiffness of a ligament. The characteristics of the spring are selected accordingly to be similar to those of the natural AOL.

Implantation of the prosthesis of the present invention will be described with reference to the third embodiment, as illustrated in Figure 6. However, it will be understood that corresponding techniques may be employed for all embodiments disclosed herein.

In use of the prosthesis 302, the femoral component 310 is implanted into a distal end of a femur (not shown) and the tibial component 304 is implanted into a proximal end of a tibia (not shown), such that the stem 308 is located in the intramedulary canal of the tibia, and the tibial tray 306 rests on the resected proximal end of the tibia. The appropriate bearing component(s) are placed between the femoral component 310 and the tibial component 304.

The artificial ligament 318, compression spring 346 and bearing plate 348, tensioning element 320 and tibial component 304 are preassembled prior to implantation. The ligament 318 is connected to the tensioning element 320 by passing the end 321 of the ligament 318 through the passage 332 via the passage 350 in the bearing plate 348 and the spring 346 and feeding the ligament 318 through the passage 332 until the stop 334 or knot 335 engages a surface of the bearing plate 348. The tensioning element 320 is then screwed to an appropriate depth into the bore 326 in the tibial component 304 to achieve initial tensioning of the ligament 318 when fully connected.

The femoral and tibial components 310, 304 are then implanted using standard techniques. Once the tibial component 304 is implanted, the free end 321 of the ligament 318 projects through the mouth 330 in the tibial tray towards the femoral component 310. The appropriate bearing components are then placed between the femoral component 310 and the tibial component 304 in a known manner.

The end 21 of the ligament 18 is then attached to the femoral component 10 by passing the loop or eye over the boss 19.

The joint is then examined to determine whether the tension in the artificial ligament 318 is balanced with the tension in the retained posterior cruciate ligament (PCL). If the tension in the artificial ligament 318 is balanced with that in the PCL, the implantation procedure is complete. If the tension in the artificial ligament 318 is not balanced with that in the PCL, the position of the tensioning element 320 within the bore 26 is adjusted, so as to increase or reduce the tension applied to the ligament 318. A tool (not shown) is inserted through the mouth 330 to engage a drive formation (not shown) formed on the tensioning element 320. By rotating the tool, the tensioning element 320 is rotated and moves axially along the internal thread in the bore 326, thereby adjusting the tension in the artificial ligament 318.

With reference to Figures 1 to 7, the embodiments of the present invention may further comprise a ligament support 60 that is operable to change the line of action of the artificial ligament 18. The ligament support may comprise a section of the mouth 30 of the bore 26 in the tibial component 4. Alternatively, as shown in Figure 7, the ligament support may comprise a lug 70 that projects from the surface 14 of the tibial tray 6.

It is contemplated that any feature or features of a particular embodiment of the invention may be used with or applied to any other embodiment of the invention.

The present application is a divisional application of GB 0721610.4. The original claims of GB 0721610.4 are presented as statements below.

1. A prosthesis comprising an artificial ligament, which is adapted to replace a human or animal ligament, and a biasing element operatively coupled to the artificial ligament.

2. A prosthesis according to statement 1, wherein the biasing element is operatively coupled to the ligament at or near one end only of the ligament.

3. A prosthesis according to statement 1 or 2, wherein the biasing element comprises an elastic element.

4. A prosthesis according to any one of the preceding statements, wherein the biasing element comprises a spring.

5. A prosthesis according to any one of statements 1 to 3, wherein the biasing element comprises an elastomeric member.

6. A prosthesis according to any one of the preceding statements, wherein the biasing element engages the ligament via a bearing component.

7. A prosthesis comprising an artificial ligament, which is adapted to replace a human or animal ligament, and a tensioning element operatively coupled to the ligament for applying tension to the ligament.

8. A prosthesis according to statement 7, wherein the tensioning element is operatively coupled to the ligament at or near one end only of the ligament.

9. A prosthesis according to statement 7 or 8, wherein the prosthesis further comprises a biasing element.

10. A prosthesis according to statement 9, wherein the biasing element comprises an elastic element.

11. A prosthesis according to statement 9 or 10, wherein the biasing element acts between the tensioning element and the ligament.

12. A prosthesis according to statement 11, wherein the tensioning element is coupled to the ligament via the biasing element.

13. A prosthesis according to statement 11 or 12, wherein the biasing element engages the ligament via a bearing element.

14. A prosthesis according to any one of statements 9 to 12, wherein the biasing element comprises a spring.

15. A prosthesis according to any one of statements 9 to 12, wherein the biasing element comprises an elastomeric member.

16. A prosthesis according to any one of statements 9 to 15, wherein the biasing element has a stiffness approximating that of a natural ligament that is to be replaced.

17. A prosthesis according to any one of statements 9 to 16, wherein the biasing element has a linear stiffness characteristic.

18. A prosthesis according to any one of statements 9 to 16, wherein the biasing element has a non-linear stiffness characteristic.

19. A prosthesis according to any one of statements 7 to 18, wherein the ligament is coupled to the tensioning element via an attachment means.

20. A prosthesis according to statement 19, wherein the attachment means comprises an enlarged portion that is formed on the ligament and engages the tensioning element.

21. A prosthesis according to statement 20, wherein the enlarged portion comprises a knot tied in the artificial ligament.

22. A prosthesis according to any one of statements 7 to 21, further comprising a bone engaging element for attachment to a bone.

23. A prosthesis according to statement 22, wherein the tensioning element acts between the bone engaging element and the artificial ligament.

24. A prosthesis according to statement 22 or 23, wherein the tensioning element is at least partially housed within the bone engaging element.

25. A prosthesis according to any one of statements 22 to 24, wherein the bone engaging element comprises a stem, and the tensioning element is at least partially housed within the stem.

26. A prosthesis according to any one of the preceding statements, wherein the tensioning element is adjustable and is operable to adjust the tension within the ligament.

27. A prosthesis according to any one of the preceding statements, further comprising adjustment means operable to adjust the tension in the ligament.

28. A prosthesis according to statement 26 or 27, when dependent on any one of statements 22 to 25, wherein the tension in the ligament is adjusted by adjusting the position of the tensioning element relative to the bone engaging element 29. A prosthesis according to statement 27, when dependent on any one of statements 22 to 25, wherein the adjustment means comprises a threaded connection between the tensioning element and the bone engaging element.

30. A prosthesis according to statement 25, wherein the tensioning element comprises an external thread and the stem comprises a corresponding internally threaded bore within which the tensioning element is received.

31. A prosthesis according to statement 30, wherein the tensioning element is configured to be screwed into or out of the bore to adjust the tension in the ligament.

32. A prosthesis according to statement 31, wherein the tensioning element is accessed through an opening formed in the bone engaging element.

33. A prosthesis according to any one of the preceding statements, wherein the prosthesis comprises at least part of a joint replacement prosthesis.

34. A prosthesis according to any one of the preceding statements, wherein the prosthesis comprises at least part of a knee replacement prosthesis.

35. A prosthesis according to any one of statements 22 to 34, wherein the prosthesis comprises at least part of a knee replacement prosthesis, the bone engaging element comprising a tibial component and the artificial ligament comprising a replacement anterior cruciate ligament.

36. A prosthesis comprising a bone engaging element having a stem which is adapted to project into a bone, and an artificial ligament, an end of the ligament extending at least partially into and being secured at least partially within the stem.

37. A prosthesis according to statement 36, wherein the prosthesis comprises at least part of a joint replacement prosthesis.

38. A prosthesis according to statement 36, wherein the prosthesis comprises at least part of a knee replacement prosthesis.

39. A prosthesis according to statement 36, wherein the prosthesis comprises at least part of a knee replacement prosthesis, the bone engaging element comprising a tibial component and the artificial ligament comprising a replacement anterior cruciate ligament.

40. A prosthesis according to any one of statements 36 to 39, wherein the ligament is secured within the stem of the bone engaging element via a tensioning element.

41. A prosthesis according to any one of statements 36 to 39, wherein the ligament is secured within the stem of the bone engaging element via a biasing element.

42. A prosthesis according to any one of statements 36 to 39, wherein the ligament is secured within the stem of the bone engaging element via both a tensioning element and a biasing element.

43. A prosthesis comprising a bone engaging element and an artificial ligament, an end of the artificial ligament being secured to the body of the bone engaging element, the prosthesis further comprising a ligament support, the ligament support causing a deflection of the line of action of the ligament.

44. A prosthesis according to statement 43, wherein the artificial ligament is secured within a recess formed in the body of the bone engaging element and the ligament support comprises the mouth of the recess.

45. A prosthesis according to statement 44, wherein the mouth of the recess is chamfered.

46. A prosthesis according to statement 43, wherein the ligament support projects from a surface of the bone engaging element.

47. A prosthesis according to statement 46, wherein the artificial ligament is secured to a surface of the bone engaging element.

48. A prosthesis according to any one of statements 43 to 47, wherein the prosthesis comprises at least part of a knee replacement prosthesis.

49. A method of implanting a prosthesis comprising first and second bone engaging elements, an artificial ligament and an adjustable tensioning element operatively coupled to a first end of the artificial ligament and to the first bone engaging element, the method comprising: a) assembling the first bone engaging element, adjustable tensioning element and artificial ligament; b) implanting the first and second bone engaging elements into bone tissue; c) connecting a second end of the artificial ligament to the second bone engaging element; d) adjusting the position of the adjustable tensioning element until a predetermined tension within the artificial ligament is achieved.

50. A prosthesis substantially as described herein, with reference to and as shown in the accompanying drawings.

51. A method of implanting a prosthesis substantially as described herein, with reference to and as shown in the accompanying drawings.

Claims

CLAIMS: 1. A prosthesis comprising first and second bone engaging elements, an artificial ligament and a biasing element, the biasing element being operatively coupled to a first end of the artificial ligament and to the first bone engaging element, and a second end of the artificial ligament being connected to the second bone engaging element.
2. A prosthesis as claimed in claim 1, wherein the biasing element comprises an elastic element.
3. A prosthesis as claimed in claim 1 or 2, wherein the biasing element comprises a spring.
4. A prosthesis as claimed in claim 1 or 2, wherein the biasing element comprises an elastomeric member.
5. A prosthesis as claimed in any one of the preceding claims, wherein the biasing element is operatively coupled to the ligament via a bearing component.
6. A prosthesis as claimed in any one of the preceding claims, wherein the biasing element has a stiffness approximating that of a natural ligament that is to be replaced.
7. A prosthesis as claimed in any one of the preceding claims, wherein the biasing element has a linear stiffness characteristic.
8. A prosthesis as claimed in any one of claims 1 to 6, wherein the biasing element has a non-linear stiffness characteristic.
9. A prosthesis as claimed in any one of the preceding claims, further comprising a tensioning element operatively coupled to the first end of the ligament.
10. A prosthesis as claimed in claim 9, wherein the biasing element acts between the tensioning element and the ligament.
11. A prosthesis as claimed in claim 9 or 10, wherein the tensioning element is coupled to the ligament via the biasing element.
12. A prosthesis as claimed in any one of claims 9 to 11, wherein the ligament is coupled to the tensioning element via an attachment means.
13. A prosthesis as claimed in claim 12, wherein the attachment means comprises an enlarged portion that is formed on the ligament and engages the tensioning element.
14. A prosthesis as claimed in claim 13, wherein the enlarged portion comprises a knot tied in the artificial ligament.
15. A prosthesis as claimed in any one of claims 9 to 14, wherein the tensioning element is at least partially housed within the bone engaging element.
16. A prosthesis as claimed in any one of claims 9 to 15, wherein the tensioning element is adjustable and is operable to adjust the tension within the ligament.
17. A prosthesis as claimed in any one of claims 9 to 16, further comprising adjustment means operable to adjust the tension in the ligament.
18. A prosthesis as claimed in claim 16 or 17, wherein the tension in the ligament is adjusted by adjusting the position of the tensioning element relative to the bone engaging element
19. A prosthesis as claimed in claim 17 or 18, wherein the adjustment means comprises a threaded connection between the tensioning element and the bone engaging element.
20. A prosthesis comprising first and second bone engaging elements and an artificial ligament, a first end of the artificial ligament being secured to the body of the first bone engaging element and a second end of the artificial ligament being connected to the second bone engaging element, the prosthesis further comprising a ligament support, the ligament support at least partially determining the line of action of the ligament.
21. A prosthesis as claimed in claim 20, wherein the artificial ligament is secured within a recess formed in the body of the first bone engaging element and the ligament support comprises the mouth of the recess.
22. A prosthesis as claimed in claim 21, wherein the mouth of the recess is chamfered.
23. A prosthesis as claimed in claim 20, wherein the ligament support projects from a surface of the first bone engaging element.
24. A prosthesis as claimed in claim 23, wherein the artificial ligament is secured to a surface of the first bone engaging element.
25. A prosthesis comprising a bone engaging element and an artificial ligament, an end of the artificial ligament being secured within a recess formed in the body of the bone engaging element, a mouth of the recess comprising a ligament support which at least partially determines the line of action of the ligament.
26. A prosthesis as claimed in claim 25, wherein the mouth of the recess is chamfered.