US20160120639A1 - Ligament fixing and a method of attaching a ligament - Google Patents

Abstract

An artificial ligament is provided having an elongate body and two ends, with a loop being provided at least one of the ends and a loop liner being provided within the loop. A kit of artificial ligaments is also provided with each ligament in the kit having a different fixed length. Also provided are methods for determining a length of artificial ligament to be used within a prosthetic knee joint, selecting a ligament from a range or kit of ligaments, and implanting a prosthetic knee joint assembly comprising an artificial ligament.

Description

CLAIM OF PRIORITY
• This application claims the benefit of priority under 35 U.S.C. to United Kingdom Application No. 1419469.0, filed on 31 Oct. 2014, which application is incorporated herein by reference in its entirety.
TECHNICAL FIELD
• This invention relates to artificial knee ligaments and methods for implanting an artificially knee ligament, and is particularly, although not exclusively, concerned with artificial ligaments having looped ends.
BACKGROUND
• The statements in this section merely provide a background to the present disclosure and may not constitute prior art.
• Prosthetic knee joints replace one or more of the articulate surfaces of a patient's knee joint, and are employed to improve the strength and/or mobility of the joint or reduce pain of the patient. Sections of the bones being replaced may be diseased, injured, deteriorated or some combination of the three.
• In many cases the surgeon performing knee replacement surgery will take steps to preserve the ligaments of the knee which connect the bones of the knee across the joint. In some cases the ligaments themselves may be diseased or damaged, or the resection necessary to remove diseased portions of the bones may disrupt the integrity of the ligaments. If the ligaments are removed as part of the surgery and cannot be reattached, a prosthetic knee joint is required which places greater constraints on the movement of the knee joint. This can be achieved through the use of an artificial knee ligament joining the two sides of the joint.
• In one proposed artificial knee joint, artificial ligaments are attached to the prosthetic components by looping or tying the ends of the ligament over bosses or bollards provided on the prosthetic components. As the knee joint moves, the ligament is able to articulate around the body of the bollard as required. Whilst this articulation of the ligament prevents the ligament from being bent or kinked, over time the loops of the ligament can become worn.
• Artificial knee ligaments are not required to be tensioned when installed, however it is undesirable for ligaments to be excessively long or loose as this could reduce the stability of the joint. For similar reasons, it is not desirable for an artificial ligament to be flexible. In one possible surgical procedure, both prosthetic components are first implanted before alternative length ligaments are offered up by the surgeon and one can be selected which the surgeon judges will have suitably laxity when fitted. In order to fit the ligament, the knee must be overflexed to provide the necessary access to the ligament fixings on each side of the joint. This also has the effect of separating the bones of the knee and hence excess force is required to attach the ligament. A device may be required to pull or lever the ligament onto a fixing and there is a significant risk of damaging the artificial ligament in the process.
• In order to avoid this excessive manipulation of the knee joint and potential damage to the ligament, artificial ligaments have been designed with loops which are formed at the operative site, allowing the length of a ligament to be adjusted subsequently to its attachment to both sides of the joint.
• WO 2011/1502538 discloses a prosthetic knee joint assembly with an artificial ligament link. The ligament link extends between first and second ends and includes an outer wall defining an interior longitudinal passage portion. First and second apertures extend through the wall. The first end extends through the first and second apertures and the longitudinal passage portion to define a first adjustable loop, and the second end extends through the first and second apertures and the longitudinal passage portion to define a second adjustable loop.
• It is speculated that ligaments with preformed loops are still more reliable with less chance of becoming loose or failing after implantation. Hence, using a ligament with fixed loops is desirable in some cases.
• The present disclosure relates to a method for implanting an artificial ligament of fixed length without requiring the knee joint to be overflexed, or excessive force being applied to the ligament. An artificial ligament particularly suited for this use is also provided.
STATEMENTS OF INVENTION
• According to an aspect of the present invention there is provided an artificial knee ligament substantially formed of a first material, comprising an elongate body of fixed length and two ends, wherein a loop is provided at each of the ends and a portion of a second material is provided on at least one loop.
• According to another aspect of the present invention there is provided an artificial knee ligament comprising an elongate body and two ends, wherein a loop is provided at at least one of the ends; and a loop liner provided within the loop.
• The length of the ligament and/or the size of the loop may be fixed. The ligament may be configured to couple to a fixing provided on either a femoral or tibial component of a prosthetic knee joint.
• The loop liner may be provided in the area of the loop which contacts the fixing of the prosthetic component. In this way, the loop liner may be provided covering an inside face of the loop. The loop liner may be formed from a different material to the body of the ligament. The loop liner may be formed from polyethylene. The loop liner may be shaped to sit between the fixing of the prosthetic knee component, and the ligament loop. The loop liner may be moulded onto the loop of the ligament or alternatively, the loop liner may comprise a thimble which is trapped within the eye of the loop. Other forms of loop liner may also be possible.
• The loop liner may be resilient and may be elastically deformable to allow the ligament loop to be pushed over an enlarged head of the fixing of the prosthetic component.
• According to another aspect of the present invention there is provided a method of implanting a prosthetic joint assembly, comprising a first component for attaching to a first bone (of the joint), a second component for attachment to a second bone (of the joint) and an artificial ligament, comprising the steps of: implanting the first prosthetic component into a patient;
• coupling the preformed artificial ligament to the prosthetic components; and
• implanting the second prosthetic component into the patient.
• According to another aspect of the present invention there is provided a method of implanting a prosthetic knee joint assembly, comprising a tibial component, a femoral component and an artificial knee ligament, comprising the steps of: implanting the tibial component or the femoral component into a patient; coupling a preformed artificial ligament to the prosthetic components; implanting the other component into the patient.
• The tibial component may be implanted before the femoral component or alternatively, the femoral component may be implanted before the tibial component. The first prosthetic component may be implanted in a temporary manner.
• The method may further comprise the step of determining an appropriate length for a replacement knee ligament to link the tibial and femoral components of the prosthetic knee joint. This step may be completed prior to the step of coupling the preformed artificial ligament to the prosthetic components.
• Additionally or alternatively, the method may further comprise the step of selecting a preformed artificial ligament of a suitable length from a set of artificial ligaments. This step may be completed prior to the step of coupling the preformed artificial ligament to the prosthetic components.
• The step of installing a final meniscal bearing may be performed prior to the step of implanting the second prosthetic component into the patient. Alternatively the step of installing a temporary meniscal spacer may be performed instead and a final meniscal component may be installed between the tibial and femoral components of the prosthetic knee joint in an additional step which may be performed subsequently to the step of implanting the second prosthetic component into the patient.
• The tibial prosthetic component may comprise a fixed knee bearing.
• The method may be performed using the artificial ligament provided by a previously mentioned aspect of the invention.
• According to another aspect of the present invention there is provided a method of determining a suitable length for an artificial ligament for use in a prosthetic joint assembly comprising a first prosthetic component for attaching to a first bone and a second prosthetic component connected to a second bone. The method comprising the steps of:
• coupling a trial first component to the first bone of a patient in a temporary manner;
• creating a trial ligament using an elongate element extended around a fixing on the trial first component and a second fixing on a previously implanted second component to form a continuous band;
• cutting the band and removing the trial ligament from the surgical site; and measuring the reassembled band.
• According to another aspect of the present invention there is provided a method of determining a suitable length for an artificial knee ligament comprising the steps of:
• coupling first and second prosthetic components to a patient in a temporary manner;
• creating a trial ligament using an elongate element extended around a first fixing on the first prosthetic component and a second fixing on the second component to form a continuous band;
• cutting the band and removing the trial ligament from the surgical site; and
• measuring the length of the reassembled band.
• The first and/or second prosthetic components may be trial prosthetic components. Alternatively or additionally, either or both of the prosthetic components may be the final prosthetic components. The fixings provided on the femoral and tibial components may be bollards.
• The method may further comprise the step of installing a trial meniscal component between the tibial and femoral components of the prosthetic knee joint. This step may be performed prior to the step of creating a trial ligament. The trial meniscal component may also be the final meniscal component.
• The elongate element used in the method may comprise a trial ligament with one looped end and one open end which can be tied. Alternatively the elongate element may be a zip tie or any other elongate element suitable for being selectively formed into a continuous band.
• A pin may be used to mark the required length of elongate element whilst fitted to the patient. Alternatively or additionally, the elongate element may comprise markings allowing the length of the band to be determined from the markings on the elongate element.
• The method according to this aspect of the present invention may be used to determine an appropriate length for a replacement knee ligament to link the tibial and femoral components as described in any preceding aspect of the invention.
• According to another aspect of the present invention there is provided an artificial knee joint assembly comprising a tibial component, a femoral component and an artificial knee ligament which may be the artificial ligament as described in any preceding aspect of the invention.
• According to another aspect of the present invention there is provided a kit of artificial knee ligaments wherein each ligament within the kit has a different fixed length. The ligaments in the kit may be as described in any preceding aspect of the invention.
• According to another aspect of the present invention there is provided instrumentation for measuring between first and second ligament fixings of prosthetic components comprising: an elongate body, an arcuate portion provided at or towards one end of the elongate body and a slideable jaw, configured to slide along the elongate body. The arcuate portion may be configured to closely engage the first fixing. The slideable jaw may be configured to engage the second fixing.
• The position of the slideable jaw may be selectively fixable relative to the elongate body. The jaw and the elongate body may be provided with cooperating formations and the jaw may fixed by rotating a portion of the jaw to engage the cooperating formations.
• The elongate body may further comprise a measurement scale. The measurement scale may indicate the size of artificial ligament required to link the first and second fixings.
• According to another aspect of the present invention, there is provided instrumentation for measuring between fixings of prosthetic components comprising: an elongate body with first and second ends; wherein the first end is configured to couple with a first fixing on a first prosthetic component; and the second end comprises a measurement scale. The scale allows the distance from the first fixing to a second fixing on a second prosthetic component to be measured. The scale may indicate the size of artificial ligament required to link the first and second fixings.
• The instrumentation may further comprise a jaw which may be axially slideable along the measurement scale of the elongate body. The jaw may be selectively lockable relative to the elongate body. The jaw and the elongate body may be provided with cooperating features and the jaw may be locked by rotating a portion of the jaw to engage the cooperating features. Alternatively or additionally, the jaw may be configured to engage a second fixing on a second prosthetic component.
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:
• FIG. 1 shows a full knee replacement prosthetic knee joint comprising an artificial ligament according to an example of the present invention.
• FIG. 2 is a sectional view of a full knee replacement prosthetic knee joint comprising an artificial ligament according to an example of the present invention.
• FIG. 3 shows an artificial knee ligament according to one example of the present invention.
• FIG. 4 shows an artificial knee ligament according to a second example of the present invention.
• FIG. 5 is a sectional view showing an example implementation of a biasing element and tension element used to provide the desired stiffness to an artificial ligament according to the present invention.
• FIG. 6 shows an implanted trial prosthetic knee joint assembly according to an example of the present invention, including a trial tibial component and a trial artificial ligament.
• FIG. 7 shows instrumentation for measuring the required length of a ligament.
DETAILED DESCRIPTION
• Referring toFIG. 1, aknee prosthesis2 comprises atibial component4 having atibial tray6 integrally formed with astem8, afemoral component10 and a pair of bearingcomponents12,13. The bearingcomponents12,13 separate thetibial component4 and thefemoral component10 and are formed with proximal and distal bearing surfaces which engage corresponding bearing surfaces14,15,16 on thetibial tray6 and on thefemoral component10. These various bearing surfaces enable thetibial component4 to rotate and translate relative to thefemoral component10. The bearingcomponents12,13 may be meniscal bearing components, rotational platform bearing components, or may be fixed bearing components. The combination of the bearing surfaces14,15,16 and the bearingcomponents12,13 allows the knee prosthesis to achieve a similar range of movements to an anatomical knee joint.
• Anartificial knee ligament20 is provided within theknee prosthesis2 to restrict undesirable movements of the knee prosthesis, improving the stability of the joint in use, as well as reducing the risk of dislocation of the bearingcomponents12,13. Theligament20 is elongate in form and constructed substantially of a first biocompatible material which has high tensile strength and stiffness.
• With reference toFIG. 2, theligament20 is terminated at the proximal end by aproximal loop22 and at the distal end by adistal loop24, both loops having a fixed size. In the embodiment shown, the loops are formed by looping back the material at each end of the ligament to form the loops, and gluing the free ends of the ligament back to itself to secure the loop. Alternatively, another method for securing the loop could be used, for example the individual fibres of the ligament could be separated, then woven back in to the ligament to secure the loop or the ligament could be passed through a washer looped on one side of the washer then the individual fibres of the ligament could be fed back though holes in the washer to secure the loop.
• Thedistal loop24 is connected to a fixing provided on thetibial component4 which may comprise atibial bollard26 and theproximal loop22 is connected to a fixing provided on thefemoral component10 which may comprise afemoral bollard28. Thebollards26,28 comprise a neck portion and a head portion, with the neck portion being narrower in form than the head portion. When theligament20 is fitted to theknee prosthesis2, theloops22,24 rest on the neck portions of the bollards and are prevented from sliding or working themselves off the bollard by the wider head portion.
• With reference toFIG. 3, awear portion30, is provided on the inside of the proximal anddistal loops22,24. In the embodiment shown inFIG. 3, thewear portion30 is moulded into the loop to form a single component. Thewear portion30 is located in the area of eachloop22,24 where the loop contacts the neck of the tibial or femoral bollard when the ligament is fitted. The wear portion may be shaped or dipped to rest against the fixing in use. Thewear portion30 may be formed in a second biocompatible material, such as polyethylene, which has a greater resistance to abrasive wear than the first biocompatible material which forms the ligament. Thewear portion30 may comprise a resilient ring of material and may be configured to pull the loop towards a closed or partially closed configuration. Thewear portion30 may thus be configured to grip thebollard26,28 when fitted, further reducing the possibility of the ligament becoming disconnected. Thewear portion30 may be elastically deformable allowing theloops22,24 to become substantially circular in an open configuration. In the open configuration, as shown inFIG. 3, the loops can be fitted over the head portion of thebollards26,28.
• With reference toFIG. 4, theloops22,24 of theartificial ligament20 may be further secured by the use offerrules32. In the embodiment shown inFIG. 4 thewear portions30 comprise thimbles which are formed as separate loops which are trapped within the eyes of theligament loops22,24. The thimbles are resilient and may be configured hold the loops in the closed condition when not fitted to the bollards, as shown inFIG. 4.
• With reference toFIG. 5, a biasingelement538 may be provided between thetibial bollard26 and thetibial component4. The biasingelement538 is provided within abore508 of thestem8 of thetibial component4. Thetibial bollard26 may also be received within thebore508. Thebore508 opens onto the bearingsurface14 of thetibial tray6. Theartificial ligament20 extends into thebore508 through aspace516 between the bearingcomponents12,13, so that theartificial ligament20 substantially does not interfere with the bearingcomponents12,13 during normal articulation of the prosthesis.
• The biasingelement538 comprises a resilient element40. In the illustrated embodiment, the resilient element40 is a coiled compression spring42 and the bearing element44 is a plate46. However, the resilient element40 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 or may be omitted if not required.
• With continued reference toFIG. 5, the knee prosthesis also comprises atensioning element518. Thetensioning element518 is mounted in thestem8 of thetibial component4. Thetensioning element518 is cylindrical and formed with anexternal thread520 which engages with aninternal thread522 formed in thebore508. Thetensioning element518 acts between the biasingelement538 and thetibial component4. Thetensioning element518 is adjustable, to allow the tension in theligament20 to be set to appropriately.
• In the embodiment shown, theresilient element538 and thetensioning element518 are both provided on thetibial component4 of theknee prosthesis2. It is equally envisaged that both could be provided on thefemoral component10, or one could be provided on each of the prosthetic components. Alternatively one or both could be omitted.
• With reference toFIG. 6, in order to determine a suitable length ofartificial ligament20 to be fitted to theknee prosthesis2, atrial ligament620 may be created. When the trial ligament is created, thetibial component4 of theknee prosthesis2 may not have been implanted and hence atrial tibial component604 may be used temporarily within the knee joint assembly. Thetrial tibial component604 also comprises atibial tray606, a stem608 and atibial bollard626. The connection between thetrial tibial component604 and thetrial ligament620 is substantially the same as the connection between thetibial component4 and theligament20 as shown inFIG. 1. Similarly, thefinal bearing components12,13 may not be fitted, and trial bearing components612,613 may be temporarily used in the assembly when creating thetrial ligament620. Thetrial ligament620 can be formed by tying a length of surgical string around thefemoral bollard28 and the trialtibial bollard626. Alternatively the trial ligament could be formed from a zip tie or any other suitable elongate element which is selectively connectable to form a continuous band. In some cases, thetrial tibial component604 may be thefinal tibial component4 which has been fitted in a temporary manner.
• In order to address the shortcomings recognised in a method for implanting a prosthetic knee joint, as presented in the background section above, improved methods of implanting theprosthesis2 are herein described.
• In one method of implanting theprosthesis2, thefemoral component10 is implanted into the distal end of afemur650; thetrial tibial component604 is fitted temporarily to the proximal end of atibia652 such that thetibial tray606 rests of the resected proximal end of thetibia652. Trial bearing components612,613 are placed between thefemoral component10 and thetrial tibial component604. Thetrial ligament620 is then created by tying off a length of surgical string after it has been tightened around thefemoral bollard28 and the trialtibial bollard626. Thetrial ligament620 is then cut away and removed from the operative site. Thetrial ligament620 can then be reassembled into a closed loop and the length of the loop measured to determine the length ofartificial ligament20 required to be fitted into theknee prosthesis2.
• In an alternative method (not shown), thetrial ligament620 could comprises a tie which is colour coded, such that the length of ligament required can be determined by the colour of thetrial ligament620 at the position it has been tied. Alternatively, thetrial ligament620 could comprise a zip tie with a ratchet head and rather than being tied, the zip tie could be tightened around the bollards using the ratchet head, the colour of the tie at the position of the head could be noted and the tie could then be undone and removed from the operative site. Alternatively, rather than being colour coded, the tie could be marked with numbers or letters, denoting the length of tie used.
• Once the length oftrial ligament620 has been determined, anartificial ligament20 of a suitable length may be selected from a range or kit of artificial ligaments available.
• With reference toFIG. 7, aligament gauge700 can alternatively be used to determine the length of ligament required. Theligament gauge700 comprises ahook702, which is configured to couple with afemoral bollard28, and anelongate shaft portion704. Aslider706 is configured to be axially movable along theshaft704. The slider comprises abody708, ajaw710 and alocking component712. Thelocking component712 can be rotated relative to theslider body708 andshaft704 to lock the slider axially with respect to theshaft704.Measurement markings714 are provided on the shaft for the required length of ligament to be read off. In use, thehook702 is coupled to thefemoral bollard28 of a prosthetic component implanted on to the femur of a patient. The slider is moved along the shaft until thejaw710 engages with thetibial bollard26. The locking component is then rotated to lock the position of the slider. The locking action may be achieved through the use of tabs (not shown) provided on the inside of thelocking component712 which engage with grooves in theshaft704. The shaft may be configured such that the tabs on thelocking component712 do not engage theshaft704 in the unlocked position. Theligament gauge700 can be rotated about thefemoral bollard28 to disengage thejaw710 from thetibial bollard26. Thehook702 can then be unhooked from thefemoral bollard28 and the gauge can be removed. In this way, the measurement recorded on theligament gauge700 can be read after the gauge has been removed from the operative site.
• Once a suitableartificial ligament20 has been selected, thetrial tibial component604 is removed from the joint. Thedistal loop24 of theartificial ligament20 is attached to thetibial bollard26 of thefinal tibial component4. Theproximal loop22 of theartificial ligament20 is then attached to thefemoral bollard28 of thefemoral component10. By attaching the artificial ligament to both thetibial component4 and thefemoral component10 before thetibial component4 is finally implanted, the problem highlighted in the current methods is avoided.
• At this stage the trial bearing components612,613 may be removed, and thefinal bearing components12,13 may be inserted between thetibial tray6 and the bearing surfaces15,16 of thefemoral component10. Alternatively, if desirable, a meniscal spacer (not shown) which is slightly thinner than thefinal bearing components12,13 can be fitted to the prosthetic joint2 to reduce loading of theligament20 during the final stages of the implantation. Thetibial component4 is then implanted into the proximal end of thetibia652.
• If the meniscal spacer or the trial bearing components612,613 are still present within the joint, they are now removed and thefinal bearing components12,13 are fitted to theknee prosthesis2.
• Although in the example shown, the finalfemoral component10 is implanted first, and thetibial component4 of the knee prosthesis is then fitted loosely or a suitable trialtibial component604 is fitted to allow the required length of theartificial ligament20 to be determined, it is equally envisaged that thefinal tibial component4 could be implanted first, and thefemoral component10 or a suitable trial femoral component (not shown) could be fitted thereafter to allow the required artificial ligament length to be determined. It is also considered, that both the femoral and tibial components could be trial components and could be fitted temporarily whilst thetrial ligament620 is formed.

Claims (35)

What we claim is:

1. An artificial knee ligament comprising an elongate body and two ends, wherein a loop is provided at at least one of the ends; and

a loop liner provided within the loop.

2. The artificial knee ligament ofclaim 1, wherein the loop liner is formed from a different material from the body of the ligament.

3. The artificial knee ligament ofclaim 1, wherein the length of the ligament is fixed.

4. The artificial knee ligament ofclaim 1, wherein the loop is configured to couple to a fixing provided on either a femoral or tibial component of a prosthetic knee joint.

5. The artificial knee ligament ofclaim 1, wherein the loop liner covers an inside face of the loop.

6. The artificial knee ligament ofclaim 4, wherein the loop liner is shaped to sit between the fixing of the prosthetic knee component, and the ligament loop.

7. The artificial knee ligament ofclaim 1, wherein the loop liner is resilient and can be deformed elastically to allow the ligament loop to be pushed over an enlarged head of the fixing of the prosthetic component.

8. The artificial knee ligament ofclaim 1, wherein the loop liner is moulded onto the loop of the ligament.

9. The artificial knee ligament ofclaim 1, wherein the loop liner comprises a thimble.

10. The artificial knee ligament ofclaim 1, wherein the loop liner is made from polyethylene.

11. A method of implanting a prosthetic knee joint assembly, comprising a tibial component, a femoral component and an artificial knee ligament, comprising the steps of:

implanting the tibial component or the femoral component into a patient;

coupling a preformed artificial ligament to the prosthetic components;

implanting the other component into the patient.

12. The method ofclaim 11, wherein the first prosthetic component is implanted in a temporary manner.

13. The method ofclaim 11, wherein the tibial component is implanted before the femoral component.

14. The method ofclaim 11, further comprising the step of

determining an appropriate length for a replacement knee ligament to link the tibial and femoral components of the prosthetic knee joint, this step being

completed prior to the step of coupling the preformed artificial ligament to the prosthetic components.

15. The method ofclaim 11, further comprising the step of

selecting a preformed artificial ligament of a suitable length from a set of artificial ligaments, this step being

completed prior to the step of coupling the preformed artificial ligament to the prosthetic components.

16. The method ofclaim 11, further comprising the step of installing a final meniscal bearing, this step being performed prior to the step of implanting the second prosthetic component into the patient.

17. The method ofclaim 11, further comprising the steps of

installing a temporary meniscal spacer, this step being performed prior to the step of implanting the second prosthetic component into the patient; and

installing a final meniscal component between the tibial and femoral components of the prosthetic knee joint, this step being performed subsequently to the step of implanting the second prosthetic component into the patient.

18. The method ofclaim 11, wherein the tibial prosthetic component comprises a fixed knee bearing.

19. A method of determining a suitable length for an artificial knee ligament comprising the steps of:

coupling first and second prosthetic components to a patient in a temporary manner;

creating a trial ligament using an elongate element extended around a first fixing on the first prosthetic component and a second fixing on the second component to form a continuous band;

cutting the band and removing the trial ligament from the surgical site; and

measuring the length of the reassembled band.

20. The method ofclaim 19, wherein the first and/or second prosthetic component is a trial prosthetic component.

21. The method ofclaim 19, wherein the first and/or second prosthetic component is a final prosthetic component

22. The method ofclaim 19, wherein the fixings comprise bollards provided on the femoral and tibial prosthetic components.

23. The method ofclaim 19, further comprising the step of

installing a trial meniscal component between the tibial and femoral components of the prosthetic knee joint, this step being

performed prior to the step of creating a trial ligament.

24. The method ofclaim 23, wherein the trial meniscal component is also the final meniscal component.

25. The method ofclaim 19, wherein the elongate element comprises a trial ligament with one looped end and one open end which can be tied.

26. The method ofclaim 19, wherein a pin is used to mark the required length of elongate element whilst fitted to the patient.

27. The method ofclaim 19, wherein the elongate element comprises a zip tie.

28. The method ofclaim 19, wherein the elongate element comprises markings allowing the length of the band to be determined from the markings on the elongate element.

29. Instrumentation for measuring between first and second ligament fixings of prosthetic components comprising:

an elongate body,

an arcuate portion provided at or towards one end of the elongate body and

a slideable jaw, configured to slide along the elongate body.

30. The instrumentation ofclaim 29, wherein the elongate body further comprises a measurement scale.

31. The instrumentation ofclaim 29, wherein the arcuate portion is configured to closely engage the first fixing.

32. The instrumentation ofclaim 29, wherein the slideable jaw is configured to engage the second fixing.

33. The instrumentation ofclaim 29, wherein the position of the slideable jaw can be selectively fixed relative to the elongate body.

34. The instrumentation ofclaim 33, wherein the jaw and the elongate body are provided with cooperating formations and the jaw is fixed by rotating a portion of the jaw to engage the cooperating formations.

35. The instrumentation ofclaim 30, wherein the measurement scale indicates the size of artificial ligament required to link the first and second fixings.

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