WO1990002532A1

WO1990002532A1 - Artificial ligaments

Info

Publication number: WO1990002532A1
Application number: PCT/GB1989/001064
Authority: WO
Inventors: Andrew Amis
Original assignee: Imperial College Of Science And Technology
Priority date: 1988-09-09
Filing date: 1989-09-11
Publication date: 1990-03-22
Also published as: GB8821229D0

Abstract

There is disclosed a prosthetic ligament arrangement (1) for implantation across a joint of a human or animal body formed between two adjacent bones (4, 5), in which the ligament arrangement comprises an elongate member composed of individual strands extending alongside each other and having first and second runs (2, 3) each intended to extend between the first and second bones forming the joint, with the first and second runs defining two separate paths across the joint in order to simulate the action of the natural ligament material requiring replacement or repair.

Description

Artificial ligaments

The present invention relates to an improved prosthetic ligament, and particularly though not exclusively to such a ligament intended to replace the natural anterior cruciate ligament connecting the fejjiur and the tibia across the knee joint, and to a method of implantation of such a ligament.

The anterior cruciate ligament (ACL) is the most commonly injured knee ligament, and a number of artificial replacement ligaments are currently available. The natural ACL actually comprises two main bundles of fibres, the antero-medial bundle and a postero-lateral bundle.

Conventional artificial ligaments have only a single elongate element or bundle of fibres. When implanted by the most commonly used technique, in which the implant passes "over the top" of the lateral femoral condyle, it replaces the natural antero-medial fibre bundle of the ACL. Whilst such an implant gives adequate knee stability when the knee is in extension, the absence of the postero-lateral bundle results in reduced stability when the knee is in flexion.

Normal activities such as standing and walking, for which the extended knee must be stable, are not hindered by the lack of a postero-lateral bundle. However, certain problems can arise due to the absence of the postero- lateral bundle for example during sports or when rising from a sitting position. In addition, many animals walk on flexed knees, and thus the existing "single bundle" ligaments are not particularly suitable for veterinary work .

It is therefore the aim of the present invention to provide an improved artificial ligament which overcomes the above-mentioned disadvantages.

According to a first aspect of the present invention there is provided a prosthetic ligament arrangement for implantation across a joint of a human or animal body, the ligament arrangement comprising an elongate member composed of individual strands extending alongside each other and having first and second runs each intended to extend between first and second bones forming a said joint, said first and second runs defining, in the implanted ligament, two separate paths across said joint.

Preferably, when the artificial ligament arrangement is implanted across said joint at least one of said runs is under tension at the extremes of flexion or extension of said joint whilst both of said runs are under tension at intermediate joint positions between said extremes of flexion and/or tension.

In the case where the ligament arrangement is implanted across a knee joint, the provision of two separate ligament runs means that one of the runs simulates the action of the natural antero-medial fibre bundle of the ACL, and the other of the runs simulates the action of the natural postero-lateral fibre bundle of the ACL. thus ^"resulting in much improved stability of the joint in all degrees of flexion.

The first and second runs of the ligament arrangement may comprise two separate elongate members of a suitable implantable artificial ligament material, in which case each run has a first end for fixation to said first bone and a second end for fixation to a second bone. Alternatively, the first and second runs may form part of a single elongate member of suitable ligament material, in which case said elongate member has first and second ends both for attachment to one of the two bones of the joint, and the elongate member is attached to the other of the two bones of the joint at a point approximately midway along its length.

Any suitable fixation means may be used to secure the elongate member or members to the bones, for example a bone staple or equivalent fixation device.

In the case where there are two separate elongate members, the first and second ends of each member may be secured to a respective bone by a separate fixation means, or alternatively a single fixation means may be utilised to secure the ends of both elongate members to one or both of the bones. Clearly, in the case of a single elongate member only one fixation means is required to secure_^the mid point of the ligament to one of the bones whereas either one or two separate fixation means will be required to secure the two ends of the elongate member to the other of the two bones.

According to a second aspect of the present invention there is provided a method of implanting a prosthetic ligament arrangement across the joint of a human or animal body, the method comprising removing the natural ligament if necessary and extending across said joint a ligament arrangement having first and second runs, and fixing each of said first and second runs to the first and second bones forming said joint such that the two runs define separate paths across the joint.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a medial -latera1 (M/L) view of a human knee joint across which there is implanted an artificial ligament arrangement according to the present invention;

Figure 2 is an anterior-posterior (A/P) view of the joint and artificial ligament shown in Figure 1;

Figure 3 is a detailed view of one type of fixation means for securing the ligament arrangement to the bones forming the joint;

Figure 4 is a detailed view of an alternative fixation means :

Figure 5 is a detailed view of a further alternative fixation means: and,

Figure 6 is a schematic and enlarged view showing the strands from which each run of the prosthetic ligament is composed .

Referring to the drawings, an artificial ligament arrangement 1 according to the present invention comprises first and second runs 2,3 of suitable ligament material, both for extending between a first bone which in the illustrated example is a femur 4 and a second bone which is in the illustrated example a tibia 5, such as to replace the natural ACL of the knee joint.

In the embodiment shown in Figures 1 and 2, each run 2,3 of the ligament arrangement comprises a separate length of ligament material each having a first end 2a,3a for fixation to the femur 4 and a second end 2b,3b for fixation to the tibia 5. One of the lengths 2 passes through a bone tunnel 6 in the tibia 5 to be secured at end 2b to the outside of the tibia 5, and also passes through a further bone tunnel 7 in the lateral femoral condyle of the femur 4 to be secured at end 2a to the outside of the femur. The path defined by this length 2 closely approximates to the path defined by the postero-lateral bundle of the natural ACL.

The other length 3 passes through a bone tunnel 8 in the tibia to be secured at end 3b to the outside of the tibia 5. and also passes through the inter-condylar notch and over the top of the lateral femoral condyle to be secured at end 3a^' to the outside of the femur 4. The path defined by this length 3 closely approximates to the path of the antero-medial bundle of the natural ACL.

Suitable fixation means 10.11.12 and 13 are used to secure the two lengths of the ligament arrangement to the respective bone.

In the embodiment shown in Figure 3. the ligament arrangement comprises a single length of ligament material 15 which is secured at each of its ends to the femur 4 in the same mahner as described above, and is secured to the tibia at a point appro imately midway along its length by a suitable fixation means 17. In the example illustrated in Figure 3, the two free ends of the ligament length 15 are secured to the femur with the mid point of the ligament secured to the tibia, but it is also envisaged that the ligament could be implanted such that the two free ends are fixed to the tibia and the ligament is attached at its mid point to the femur.

Figure 4 illustrates an embodiment in which a single fixation means 18 is used to secure both ends of the two separate ligament runs 2,3, and this type of fixation may be used either on one or on both of the two bones. In the case of runs 2,3 having looped ends, the fixation means 18 may take the form of a grommet which is inserted within the looped end, as shown in Figure 4. However, in Figure 5 a bone staple 18a is used to secure the ends of runs 2,3, which are not looped, to the bone. Tests have been conducted using cadaveric knees in which the resulting knee stability was compared to that obtained by a conventional single bundle ligament, and the results showed that the stability was considerably improved by the use of two bundles particularly when the knee is in flexion.

The runs 2 and 3 of the prosthetic ligament are shown only schematically in Figures 1 to 5, and in fact each ligament run is formed of a bundle of strands of any- suitable implantable material which extend alongside and parallel to each other between the ends 2a, 2b and 3a, 3b. The strands in each bundle are not criss-cross linked to each other, but are free to slide longitudinally relative to each other during flexing of the joint in which they are implanted. Also, the individual strands define longitudinal spaces therebetween, into which natural tissue ingrowth can take place over a period of time in order to improve the strength of the joint and the retention in position of the implanted ligament.

Figure 6 of the drawings shows schematically and to an enlarged scale the strand formation of each ligament run. Each run can be formed from a single length of implantable filament material which is taken around any suitable former (not shown) so that successively reversing strands (shown e.g. by references 19 and 20) . extend between opposed looped ends 21 and 22. The looped end formation of the loops 21 and 22 is achieved by application of any suitable ties 23 taken around the ends of the parallel strands adjacent to the looped ends 21 and 22. This provides anchorage holes through which any suitable fixation means can be taken in order to secure the implanted ligament run in posit ion .

Figure 6 shows schematically a single run (2 or 3) which is formed from its own individual continuous length of implantable filament material, to provide individual ligament runs as shown in Figures 1. 2, 4 or 5. However, if both runs are to be formed from a single length of filament, to provide an arrangement as shown in Figure 3, clearly it will only be necessary to lay down the strand formation as shown in Figure 6, but with a longer length between the two looped ends 21 and 22, and then the ends 21 and 22 can be brought towards each other by inward folding at appro imately midway along the length of the parallel strands (19. 20) and a further loop will be formed which can be secured in position by anchoring means 17, as shown in Figure 3. This further loop also may be fixed in position by application of suitable ties (not shown) , if required.

Claims

CLA I MS

1. A prosthetic ligament arrangement for implantation across a joint of a human or animal body, the ligament arrangement comprising an elongate member composed of individual strands extending alongside each other and having first and second runs each intended to extend between first and second bones forming said joint, said first and second runs defining, in the implanted ligament, two separate paths across said joint.

2. A prosthetic ligament arrangement according to Claim 1. in which the first and second runs of the ligament arrangement comprise two separate elongate members of an implantable material, each run having a first end for fixation to said first bone and a second end for fixation to the second bone.

3. A prosthetic ligament arrangement according to Claim 1 , in which the first and second runs are formed as integral parts of a single elongate member of implantable material, said elongate member having first and second ends both intended for attachment to one of the two bones of the joint, and being attachable to the other of the two bones of the joint at a point approximately midway along its length .

4. A prosthetic ligament arrangement according to any one of Claims 1 to 3, and including a fixation device for fixing the ligament runs to the bones.

5. A prosthetic ligament arrangement according to Claim 4, including a separate fixation means for securing the end of each ligament run in position.

6. A method of implanting a prosthetic ligament arrangement across the joint of a human or animal body, the method comprising removing the natural ligament if necessary and extending across said joint a ligament arrangement having first and second runs, and fixing each of said first and second runs to the first and second bones forming said joint such that the two runs define separate paths across the joint.

7. A method according to Claim 6, in which the ligament arrangement comprises an elongate member composed of individual strands extending alongside each other.

8. A method according to Claim 6 or 7, in which the end of each run is anchored in position by fixation means.

9. A method according to Claim 8, in which a common fixation means is used to anchor two adjacent run ends in position .