TISSUE EXTENSION

Abstract

A tool for elongating a fibrous length of tissue, the tool comprising: a first group of cutters, the first group of cutters comprising a plurality of cutters spaced apart across a width of the tool so as to form an interleaved set of cutting widths and non-cutting widths; a second group of cutters, the second group of cutters comprising a plurality of cutters spaced apart across the width of the tool so as to from an interleaved set of cutting widths and non-cutting widths; and wherein each cutter of the second group is positioned so as to at least partially overlap at least one non-cutting width of the first group. As each group of cutters is arranged to form interleaved areas of cutting and non-cutting, when the tool is used, each group of cutters will cut some fibres of the fibrous length of tissue while leaving other fibres uncut.

Claims

1. A tool for elongating a fibrous length of tissue, the tool comprising: a first group of cutters, the first group of cutters comprising a plurality of cutters spaced apart across a width of the tool so as to form an interleaved set of cutting widths and non-cutting widths; a second group of cutters, the second group of cutters comprising a plurality of cutters spaced apart across the width of the tool so as to from an interleaved set of cutting widths and non-cutting widths; and, wherein each cutter of the second group of cutters is positioned so as to at least partially overlap at least one non-cutting width of the first group of cutters.

2. The tool as claimed in claim 1, further comprising: at least one further group of cutters, the further group of cutters comprising a plurality of cutters spaced apart across the width of the tool so as to form an interleaved set of cutting widths and non-cutting widths; and, wherein for each further group of cutters, each cutter of that group is positioned so as to at least partially overlap at least one non-cutting width of an adjacent group of cutters.

3. The tool as claimed in claim 1, wherein each group of cutters comprises a row of cutters.

4. The tool as claimed in claim 1, wherein the groups of cutters are spaced apart along the length of the tool.

5. The tool as claimed in claim 1, wherein each group of cutters comprises a regularly spaced set of cutters.

6. The tool as claimed in claim 1, wherein each group of cutters has the same arrangement of cutters and wherein each group of cutters is offset, in a width direction, from each adjacent group of cutters by a same offset amount.

7. The tool as claimed in claim 1, wherein each group of cutters has a combined cutting width, being a sum of all individual cutting widths in the group; and a combined non-cutting width, being a sum of all individual non-cutting widths in the group; and, wherein a ratio of combined cutting width to combined non-cutting width is approximately the same for each group.

8. The tool as claimed in claim 1, wherein each group has at least five cutters; preferably at least six cutters; more preferably at least seven cutters.

9. The tool as claimed in claim 1, wherein the overlap, in a width direction of the tool, between the cutters of one group and any other group is no more than 80%, preferably no more than 70%.

10. The tool as claimed in claim 1, wherein each group of cutters extends across a width of at least 20 mm, optionally at least 30 mm.

11. The tool as claimed in claim 10, wherein each group of cutters extends across a common width portion of the tool, the common width portion having a width of at least 20 mm, optionally at least 30 mm.

12. The tool as claimed in claim 1, wherein each cutter has a cutting width of at least 1 mm, preferably at least 1.5 mm.

13. The tool as claimed in claim 1, wherein each cutter is a cannula.

14. The tool as claimed in claim 1, wherein the tool comprises an applicator and wherein the groups of cutters are formed on an insert which is mountable to the applicator.

15. The tool as claimed in claim 14, wherein the insert is replaceable and/or interchangeable.

16. The tool as claimed in claim 1, wherein the applicator is a gripping device arranged, in use, to press the cutters into the fibrous length of tissue.

17. The tool as claimed in claim 14, wherein the applicator is pliers.

18. The tool as claimed in claim 14, wherein the tool further comprises a plate, the plate comprising a hole corresponding positionally to each cutter, and wherein the applicator is arranged to apply the cutters towards and optionally into and/or through the holes after passing through the fibrous length of tissue.

19. The tool as claimed in claim 1, wherein the tool comprises an alignment device arranged for placement against the fibrous length of tissue and arranged to align the groups of cutters perpendicular to a length direction of the fibrous length of tissue.

20. The tool as claimed in claim 1, wherein the tool is a medial collateral ligament lengthening tool.

21. A method of elongating a fibrous length of tissue, the method comprising: using a tool to cut fibres of the fibrous length of tissue, the tool comprising: a first group of cutters, the first group of cutters comprising a plurality of cutters spaced apart across a width of the tool so as to form an interleaved set of cutting widths and non-cutting widths; and, a second group of cutters, the second group of cutters comprising a plurality of cutters spaced apart across the width of the tool so as to from an interleaved set of cutting widths and non-cutting widths; and. wherein each cutter of the second group of cutters is positioned so as to at least partially overlap at least one non-cutting width of the first group of cutters.

Description

[0039] Certain preferred embodiments of the invention will now be described by way of example only, and with reference to the accompanying drawings in which:

[0040] FIG. 1a shows a view from above of a tool insert according to an embodiment of the invention;

[0041] FIG. 1b shows how the tool is aligned with a ligament in use;

[0042] FIGS. 2a and 2b show perspective views of the tool insert of FIG. 1;

[0043] FIG. 3a shows a cross-section of a pliers-type applicator tool;

[0044] FIG. 3b shows a head of a pliers-type applicator tool

[0045] FIG. 4 shows an alternative forceps-type applicator tool; and

[0046] FIG. 5 shows an image of a porcine ligament after application of a tool according to the invention.

[0047] The following description is of preferred embodiments of the invention

[0048] FIG. 1a shows a view from above of a tool according to an embodiment of the invention. The tool is for cutting the fibres of a fibrous length of tissue such as a ligament with the aim of causing extension or elongation of that length of tissue. One common application of such elongation is for ligament balancing of the medial collateral ligament (MCL) after total knee arthroplasty operations. The application of this invention is described here in the context of such ligament balancing operations on the MCL, but it will be appreciated that the tool and the technique is applicable in other applications too. For example, the tool may be used in any other application where ligaments are to be elongated such as operations involving ligaments in other joints in the knee (e.g. lateral collateral ligament), hip, elbow, etc. The tool may also be used for lengthening of ligaments such as the carpal ligament. The mechanical principles upon which the tool operates are broadly the same across these various procedures.

[0049] FIG. 1 shows a tool 100 designed for use in MCL ligament balancing procedures. The tool 100 is shown from above in FIG. 1 and is also shown in two perspective views in FIGS. 2a and 2b.

[0050] The tool 100 is formed from a base 101, with a number of cutters 102 extending from one side of the base 101. The cutters 102 are arranged in a pattern which is made up of five groups 103a-103e of cutters 102. Each group 103a-103e is progressively offset further in a width direction of the tool 100 so that the cutters 102 of each group 103 cut different fibres of the ligament. Together the five groups 103a-e of cutters 102 form a tilted or slanted grid of cutters.

[0051] This tool 100 effects the puncturing of Bellemans' technique for ligament balancing by puncturing the tissue in multiple separate places, each puncture (or cut) severing a small number of fibres of the ligament. However, the advantage of this tool over the current application of Bellemans' technique is that the punctures (or cuts) are all made simultaneously and in a pre-arranged pattern so that a predictable and repeatable number of fibres will be cut, thereby achieving a predictable and repeatable extension of the ligament. In addition, the risk of complete detachment (or severing) of the ligament is also reduced, as the tool 100 has a predetermined pattern of cutters 102 which can be designed to ensure that the cuts are spread across the area of the ligament, leaving enough strength left in the ligament.

[0052] Each group 103a-e of cutters 102 comprises a set of seven cutters 102. The cutters 102 within each group 103a-e are regularly spaced so that the cutters 102 form cutting widths (i.e. portions of the width of the tool that will cut fibres of the ligament) and the spaces 104 between cutters 102 form non-cutting widths (i.e. portions of the width of the tool that will not cut fibres of the ligament). As the five groups 103a-e are all offset along the width of the tool by different amounts, each group of cutters causes different sets of fibres of the ligament to be cut. Comparing two adjacent groups of cutters, namely groups 103a and 103b, it can be seen that there is an overlap between corresponding cutters in the adjacent groups. For example, cutter 113 of group 103b is partially overlapped with cutter 112 of group 103a as well as being partially overlapped with non-cutting space 114 of group 103a. The part of cutter 113 that overlaps the non-cutting space 114 will cut fibres of the ligament that were not cut by any cutters of group 103a as those fibres passed through the non-cutting space 114. This can be seen from FIG. 1b which shows schematically how the tool is aligned, in use, with the fibres 121 of a ligament 120. The fibres 121 each extend the length of the ligament 120 and the fibres 121 are arranged in parallel across the width of the ligament 120. The tool 100 is arranged so that the tool width is parallel to the width of the ligament 120, i.e. so that each group 103a-e of cutters 102 extends across the width of the ligament 120 such that it will cut some of the fibres 121 but will not cut others of the fibres 121. In FIG. 1b, the length direction is indicated by arrow L and the width direction by arrow W.

[0053] In FIG. 1a, each of the five groups 103a-e is offset to the right, along the width of the tool 100 by a different amount. Each of the second to fifth groups 103b-e is offset by a multiple of a base offset amount. The base offset amount is the offset of the second group 103b relative to the first group 103a. Thus any pair of adjacent groups 103a-e has the same offset between those two groups 103a-e. Each group 103b-e therefore has cutters 102 positioned to overlap a non-cutting space 104 of the group 103a-d above. Thus each additional group 103b-e beyond the first group 103a cuts a new set of fibres that were not cut by the group above. In this one, each additional group adds to the total number of fibres 121 that are cut by the tool 100 as a whole. As more fibres 121 of the ligament 120 are cut, the load on the ligament is shared by fewer fibres and thus it elongates under that load. Thus, but carefully selecting the number of groups 103a-e of cutters 102 in the tool 100, the total amount of cutting, and hence the total amount of lengthening can be selected. For example, a tool 100 with only the first two rows 103a-b of FIG. 1a will cut a certain quantity of fibres 121 and will result in a certain degree of lengthening. By comparison, a tool 100 with the first three rows 103a-c of FIG. 1a will cut a greater quantity of fibres 121 and will result in a greater degree of lengthening. It has been found that in certain situations, there is a substantially linear relationship between the number of cut fibres 121 and the degree of lengthening of the ligament 120. This is the case with the MCL. Accordingly, different tools 100 can readily be made with different numbers of groups 103a-e of cutters 102, each of those tools 100 corresponding to a different degree of lengthening of the target tissue (e.g. ligament). This greatly simplifies and speed up the procedure as it removes the iterative part of Bellemans' process in which repeated puncturing and re-measuring is required until the desired lengthening is achieved.

[0054] Within each group 103a-e of cutters 102, each cutter 102 in the group 103a-e may be identical or they may be of different sizes/widths. However, when the widths of all cutters 102 are added together, they provide a total cutting width for that group 103a-e. In the case where all cutters 102 of a group 103a-e are identical then the total cutting width with simply be the width of one cutter 102 multiplied by the number of cutters 102 in the group 103a-e. A similar calculation may be performed for the total non-cutting width of the group 103a-e. Again, the majority of non-cutting widths may in some embodiments be the same (although they could also be irregular with irregularly spaced cutters 102). However, there are also non-cutting widths at each end of each group 103a-e which will typically vary between groups 103a-e as the offsets are different. If the number of cutters 102 in each group 103a-e is the same and the tool 100 is rectangular (or at least has parallel sides in the cutting region) then the total cutting width plus the total non-cutting width for each group 103a-e will be constant.

[0055] In the embodiment shown in FIGS. 1a, 2a and 2b, the cutters 102 in each group 103a-e are arranged in a straight row, although it will be appreciated that this is not strictly necessary to achieve the desired amounts of cutting, so long as the right number of fibres 121 are cut by the group 103a-e as a whole.

[0056] As can best be seen from the perspective views of FIGS. 2a and 2b, the cutters 102 in this embodiment are cannulas 202. Each cannula 202 is a hollow tube with a tapered tip 203 that tapers to a point 204. The tapered tip 203 is sharp and acts as a cutting blade, slicing through tissue as it is pressed into the tissue parallel to the axis of the tube. Cannulas 202 are used in this embodiment as they are used as the cutting device in the standard application of Bellemans' technique for ligament balancing, thereby making punctures in the tissue in a similar manner to Bellemans' technique and thereby achieving similar results. However, it will be appreciated that other types of cutters may also be used. For example, a pointed scalpel blade may be used instead to make an incision in the tissue in much the same manner.

[0057] In the specific embodiment shown in FIGS. 1, 2a and 2b, the cannulas 202 are 1.6 mm diameter cannulas. The cannulas 202 in each group 103a-e have their centres spaced 3 mm apart. This leaves a 1.4 mm non-cutting width between each adjacent pair of cannulas 202 of one group 103a-e. Each cannula 202 may cut fibres 121 across its whole diameter (e.g. across a width of 1.6 mm for a 1.6 mm diameter cannula), but due to the cylindrical shape of the cannulas 202, they may also push some fibres 121 out of the way, i.e. to the sides, rather than cut them. This can result in an effective cutting width that is slightly smaller than the diameter of the cannula 202. This may be taken into account when designing the tool 100, in particular the amount of overlap between cutters 102 of adjacent groups 103a-e as this will affect how many new fibres 121 are cut with each new group 103a-e as well as how many fibres 121 may be cut twice by overlapped cutters 102.

[0058] The diameter of cannula 202 (or width of other cutter 102) can of course be different for different applications and in order to achieve different degrees of cutting and different degrees of overlap.

[0059] As noted above, in the tool 100 shown in FIGS. 1a, 2a and 2b, the groups 103a-e get progressively further offset in the width direction according to their position in the length direction. This forms a slanted grid of cutters 102. In the particular example shown in these figures, the angle of the slant is 11.7 degrees, although it will be appreciated that this is just one example and that many other angles are possible. The angle, together with the cutting widths and the lengthwise spacing between groups 103a-e determines the amount of overlap between cutters and therefore determines the number of new fibres cut by each row. For cannulas in the region of 1.6 mm diameter, with centre spacings of 3 mm (in both width and length directions), an optimal angle for the slant of the grid has been found to be between 5 degrees and 25 degrees for medial collateral ligament balancing procedures. An angle of less than 5 degrees leads to more double-cutting of ligaments with normal sized cannulas and does not result in enough additional fibres 121 being cut with each new group 103a-e. An angle greater than 25 degrees just makes the tool 100 wider without adding much benefit. With common sizes and spacings of cutters, such large angles also tend to increase the overlap of cutters, i.e. the amount of double-cutting. In the example shown in FIGS. 1a, 2a and 2b, each row 103a-e is offset from the previous row 103a-e by 0.6 mm, i.e. offsets are at 0.6 mm, 1.2 mm, 1.8 mm and 2.4 mm.

[0060] The tool 100 also has two mounting holes 130 that may be used to fix it to an applicator such as those of FIGS. 3 and 4. In this way the tool 100 becomes a removable insert to a larger tool 300.

[0061] FIG. 3a shows an applicator 300 in the form of a pliers-type tool. The applicator 300 has handles 310 which, when squeezed together, bring a body 320 and a back plate 330 together. An insert 340 is mounted to the body 320. The insert 340 may be the tool 100 as shown in FIGS. 1a, 2a and 2b and can be mounted to the body 320 via fixing devices 350 (e.g. screws or clips) passed through the mounting holes 130.

[0062] The back plate 330 has holes 360 formed therein, with one hole corresponding to each cutter in the insert 340 and arranged so that the cutters 102 in the insert 340 will pass through the holes 360 upon a full travel of the body 320 when the handles 310 are squeezed fully together. The insert 340 is removable and replaceable and may be disposable so that a new insert can be used for each procedure. The back plate 330 may similarly by removable, replaceable and disposable, but in this embodiment it is a permanent part of the applicator 300. As the back plate 330 is a permanent feature of the applicator 300, it needs to have holes 360 which correspond to any cutters 102 that may be present on any insert 340 that may be used with the applicator 300. As discussed above, different tools 100 (and therefore different inserts 340) may have different numbers of groups 103a-e of cutters 102 depending on the desired degree of lengthening of the ligament that the tool 100 is designed to achieve. As increasing the amount of lengthening simply involves adding additional groups 103a-e of cutters 102, tools 100 for longer elongations can ideally include at least some groups 103a-e of cutters 102 that are also used on tools 100 for shorter elongations. In this way, the back plate 330 can have holes 360 corresponding to each possible group 103a-e of cutters 102 so that the holes 360 are present regardless of whether or not the cutters 102 are present on the particular insert 340.

[0063] FIG. 3b shows the head of the applicator tool 300, but not in cross-section. This figure shows that side plates 370 of the applicator 300 are formed with an alignment surface 380 parallel with the cutting direction (i.e. the direction in which the cutters 102 are pressed into the ligament) and perpendicular to the back plate 330. The alignment surfaces 380 are, in use, pressed up to the edge of the ligament (or other tissue) so as to align the insert 340 in a defined orientation relative to the fibres. This ensures that the selected pattern of cutters 102 is applied at the correct orientation relative to the fibres 121, thereby ensuring that the correct cutting ratios are achieved and hence that the desired lengthening is achieved reliably.

[0064] FIG. 4 shows an alternative form of applicator 300, this time in the form of forceps with a back plate 330 and cutting tool 100 provided at one end and operating handles 310 at the other end. The cutting tool 100 may be removable as with the pliers of FIG. 3, but may also be a permanent feature of the applicator 300. The applicator 300 may be reusable and a different applicator 300 (with suitably designed tool 100) may be provided for each desired elongation of the target tissue. For example, different applicators 300 may be provided with two rows, three rows, four rows and five rows of cutters, each of these corresponding to different degrees of lengthening of a ligament.

[0065] Using the applicator 300 in an MCL ligament balancing procedure may be as follows. First the balance of the knee ligaments is tested as normal to determine the desired degree of lengthening. Next an appropriate insert 340 is selected according to the desired degree of lengthening. The insert 340 may be readily recognised by the number of groups (or rows) 103a-e present on the insert 340. For example, if each row of cutters gives approximately 1 mm of lengthening (purely by way of example) and a 4 mm lengthening is desired, then the insert 340 may have four rows of cutters and is thus easily recognised and verified by eye. The insert 340 is attached to the applicator 300 may fixing devices 350 through mounting holes 130. The applicator 300 is then positioned such that the MCL is between the cutters 102 of the insert 340 and the back plate 330 and such that the edge of the ligament is in contact with both alignment surfaces 380 so that the cutters 102 are appropriately positioned relative to the ligament fibres 121. The handles 310 are squeezed fully together so that the cutters 102 pass through the ligament 120 and through the holes 360 in the back plate 330, thereby cutting fibres 121 of the ligament 120 is a predetermined amount and pattern. The handles 310 are then separated once again and the applicator 300 is removed from the ligament 120. The placement of the punctures in the ligament in the predetermined amount and pattern can be expected to provide the desired degree of lengthening reliably.

[0066] FIG. 5 is a photograph of a porcine medial collateral ligament which has been punctured with a tool as discussed above. The holes 500 in the ligament tissue can clearly be seen. Each hole 500 here has been made by a cannula cutter 202 and it can be seen that each row 510 of holes 500 is offset from the other rows 510 such that it cuts different fibres of the ligament (the ligament fibres running approximately perpendicular to the arrows 510 in the figure).