Tissue stretching

Abstract

An instrument for extending a fibrous length of tissue, the instrument comprising: a first group of cutting tools, the first group of cutting tools comprising a plurality of cutting tools spaced across the width of the instrument to form an interleaved set of cutting and non-cutting widths; and a second group of cutting tools, the second group of cutting tools comprising a plurality of cutting tools spaced across the width of the instrument to form an interleaved set of cutting and non-cutting widths, each cutting tool of the second group of cutting tools positioned to at least partially overlap at least one non-cutting width of the first group of cutting tools. Each group of cutting tools is arranged to form interleaved regions of cut and non-cut, such that when the instrument is used, each group of cutting tools cuts some fibers of the fibrous length of tissue while leaving other fibers uncut. Each group of cutting tools takes a similar approach to the Bellmans technique by making a series of punctures into the fibrous tissue. However, it is more well defined, reliable and reproducible than the individual punctures of the Bellmans technique because each group of cutting tools has a defined relationship and a non-cutting width that separates the cutting tools such that each cutting tool in a group is guaranteed to cut a different fiber of the tissue. Furthermore, by overlapping at least one non-cutting width of the first group, the second group is guaranteed to cut some fibers not cut by the first group.

Description

[Technical field]

[0001] The present invention relates to tissue distraction techniques, and in particular to ligament distraction techniques that may be applied to processes such as ligament balancing in total knee arthroplasty. [Background technology]

[0002] In total knee arthroplasty (TKA) of the varus knee, there is shortening of the medial structures and lengthening of the lateral structures. The varus knee is the most frequent deformity encountered during TKA. Although controversial as the main factor of implant survival, femoro-tibial alignment remains the primary objective in total knee arthroplasty. The bone deformity is addressed by bone cuts perpendicular to the mechanical axis. In the varus knee, bone cuts perpendicular to the mechanical axis induce a trapezoid-shaped articular femoro-tibial gap with a short medial side. Therefore, it is often necessary to balance the medial soft tissues to provide symmetrical relaxation. This can be achieved by sequentially relaxing one or more medial soft tissues until symmetrical relaxation is achieved.

[0003] Ligament balancing is a well-known procedure and is considered a prerequisite for good function and survival in TKA. Ligament balancing can be established by different techniques. These techniques often focus on the lengthening of the medial collateral ligament (MCL). One conventional technique consists in a subperiosteal release at the MCL foot. Another technique, known as the "Bellmans technique", is a well-proven technique that involves multiple needle punctures, in which the medial collateral ligament is punctured multiple times using a 19-gauge needle to allow for a progressive increase in laxity, thus keeping the knee balanced. The technique typically involves anywhere from 5 to 35 punctures with 3-5 mm spacing required to obtain an increased laxity of 2-4 mm in extension and a desired laxity of 2-6 mm in flexion. However, this does not allow for an accurate quantification of the release. The wide range of puncture numbers required to achieve success in the Bellmans technique leads to a lack of reproducibility and reliability. A typical procedure using the Bellmans technique is to puncture the ligament five times and then retest the knee to see how much ligament stretch has been achieved. If more stretch is required, five more punctures are made and the knee is retested. This process continues until sufficient stretch of the ligament is achieved. The number of punctures required for a given stretch cannot be reliably predicted in advance.

[0004] These problems are not unique to ligament stretching in total knee arthroplasty: similar problems can arise in other situations where tissue stretching is desired. Summary of the Invention

[0005] According to a first aspect, the present invention provides an apparatus for increasing fibre length in tissue, the apparatus comprising: a first group of cutting tools, the first group of cutting tools comprising a plurality of cutting tools spaced across a width of the instrument to form an interleaved set of cutting and non-cutting widths; a second group of cutting tools, the second group of cutting tools comprising a plurality of cutting tools spaced across the width of the instrument to form an interleaved set of cutting and non-cutting widths; Each cutting tool of the second group of cutting tools is positioned to at least partially overlap the non-cutting width of at least one of the first group of cutting tools.

[0006] Each group of cutting tools is aligned across the width of the instrument to form alternating regions of cut and non-cut, so that when the instrument is used, each group of cutting tools cuts some fibers of the fibrous length of the tissue while leaving other fibers uncut. This means that each group of cutting tools takes a similar approach to the Bellmans technique by making a series of punctures in the fibrous tissue. However, each group of cutting tools is more clearly defined, reliable, and reproducible than the individual punctures of the Bellmans technique, as they have a non-cutting width that separates the cutting tools such that they have a defined relationship and each cutting tool within a group is guaranteed to cut a different fiber of the tissue. Note that the second group of cutting tools is arranged parallel to the first group of cutting tools (both arranged across the width of the instrument), but overlaps with at least one non-cutting width of the first group, so that the second group of cutting tools is guaranteed to cut some fibers not cut by the first group. Thus, the second group of cutting tools increases the total number of cut fibers in a controlled, well-defined, repeatable manner. Together, the first and second groups of cutting tools form a well-defined cutting pattern that cuts a well-defined number of fibers of the fibrous tissue. This results in a well-defined elongation of the fibrous tissue.

[0007] In the case of ligament balancing (or otherwise extending the length of fibrous tissue), the amount of extension achieved depends on the number of fibers that are cut. The fiber length of a tissue (e.g., a ligament) contains many parallel fibers that share any applied load between them. When a fiber is cut, it no longer contributes to load support, and therefore the load is distributed among the uncut fibers. Because the fibers are elastic, the uncut fibers will elongate under the increased load, thereby achieving the desired extension of the fibrous tissue (e.g., a ligament). A defined arrangement of cutting tools results in a defined pattern of cut fibers in the tissue, which results in a defined, repeatable extension of the length of the fibrous tissue. This makes it much easier for the practitioner to achieve the desired result. For example, in the case of a ligament balancing procedure, a preliminary measurement of the imbalance indicates how much extension is desired. By selecting an instrument with an appropriate arrangement of cutting tools, the desired extension can be achieved in a predictable and repeatable manner in a single cutting action (i.e., a single application of the instrument). It achieves all the advantages of the Bellmans technique, but with the added advantage of a rapid and accurate procedure. Furthermore, the training requirements for applying the technique are reduced, since consistent results can be achieved without the need for extensive practice and experience.

[0008] In some embodiments, the instrument may further comprise at least one additional group of cutting tools, the additional group of cutting tools comprising a plurality of cutting tools spaced across the width of the instrument to form an interleaved set of cutting and non-cutting widths, and for each additional group of cutting tools, each cutting tool of that group is positioned to at least partially overlap at least one non-cutting width of an adjacent group of cutting tools.

[0009] Additional groups of cutting tools increase the number of fibers cut in the same way that a second group of cutting tools increases the number of fibers cut relative to the first group. Each additional group again adds a defined pattern to the overall pattern, each cutting some fibers not cut by an adjacent group. Thus, taken as a whole, the groups provide a consistent amount of cutting. An instrument may have three, four, five, or more groups of cutting tools, each arranged with partial overlap such that each additional group adds an additional amount of cutting and therefore provides an additional amount of stretching of the fibrous tissue. In this way, different instruments may be formed having different numbers of groups and / or different amounts of cutting, but each capable of obtaining a different but clearly defined degree of cutting and therefore a different but clearly defined degree of stretching.

[0010] In addition to overlapping the non-cutting length of at least one adjacent group, in some preferred embodiments, each group, or at least as many groups as possible, also has a respective cutting tool positioned to at least partially overlap at least one non-cutting width of the first group of cutting tools, hi some embodiments, each group has a respective cutting tool positioned to at least partially overlap at least one non-cutting width of each other group.

[0011] The blades of each group of blades do not necessarily need to be precisely aligned with one another across the width of the instrument. However, it is convenient and preferred that each group of blades comprises a row of blades. Arranging the blades in a row means that the individual blades are all positioned at the same location relative to the length of the fibrous tissue, and therefore cut all of the fibers of the fibrous tissue at the same distance along the length of the fibrous tissue. Different groups of blades can then be spaced apart immediately along the length of the tissue to cut the fibers at different points along the length.

[0012] The groups of cutting tools are preferably spaced apart along the length of the instrument. Each group then cuts a different longitudinal portion of the length of the fibrous tissue, thereby spacing the cuts apart along the length of the tissue. This distributes the stress on the remaining fibers along the length of the tissue, which may reduce the impact of the procedure and promote recovery as each cut spreads over a larger area of ​​the tissue. The spacing of the groups of cutting tools does not have to be regular, i.e., the spacing between adjacent groups may vary along the length of the instrument. However, in some preferred embodiments, the groups of cutting tools are regularly spaced apart so that the cuts (and stresses) are evenly spread along the length of the instrument and along the length of the impacted fibrous tissue.

[0013] Within each group of cutting tools, the spacing of the cutting tools does not need to be regular. In fact, each cutting tool need not be the same length as the other cutting tools in the group. Cutting tools of irregular length and spacing (non-cutting widths) may still be used and coordinated with cutting tools in adjacent groups to achieve the desired amount of overlap and cutting. However, in preferred embodiments, each group of cutting tools includes a set of regularly spaced cutting tools. In some embodiments, each cutting tool in a group is the same width as the other cutting tools in that group. Similarly, each non-cutting width in a group may be the same width as the other non-cutting widths in that group. Such a regular arrangement has the advantage of spreading the cut as evenly as possible across the width of the instrument (and thus across the width of the fibrous tissue), thereby distributing the load and trauma across the width of the tissue.

[0014] Each group of cutting tools may have its own distinct arrangement of cutting tools (cutting width) and spaces (non-cutting width). Different groups need not have the same arrangement, but still provide a well-defined cutting width and overlap between the cutting width and the non-cutting width. However, it is convenient and preferred that each group of cutting tools has the same arrangement of cutting tools, and each group of cutting tools is offset in width by the same offset amount from each adjacent group of cutting tools. Having the same arrangement and offset means that each cutting tool in each group has the same relationship to the corresponding cutting tool in the adjacent group, i.e., the offset applies to each and every cutting tool in the group. This ensures that new fibers (i.e., fibers cut by one group that are not cut by an adjacent group) are also uniformly distributed across the width of the instrument and the width of the fibrous tissue, thereby distributing changes in load and stress across the fibrous tissue. If each group has the same pattern of cutting and non-cutting widths, each progressively offset by the same amount in the width direction, and the groups are also evenly spaced lengthwise, then the cutting tools form a slanted or tilted two-dimensional array of cutting tools. If the cutting tools in each group are regularly spaced widthwise, then the two-dimensional arrangement of cutting tools forms a tilted grid of cutting tools. As mentioned above, this distributes stress and trauma as evenly as possible within the instrument area.

[0015] Each group of cutting tools may be considered to have a total cut width, which is the sum of all individual cut widths within the group, and a total uncut width, which is the sum of all individual uncut widths within the group. The ratio of total cut width to total uncut width is approximately the same for each group. By having the same ratio of cut width to uncut width, the instrument can ensure that the same percentage of the width of the fibrous tissue is cut by each row. For example, it may be desirable to have each group of cutting tools cut about 10% or 20% or 30% (or indeed any ratio) of the fibers in the length of the fibrous tissue. Thus, each group cuts the same percentage of fibers, whereby the number of groups and consistent degree of overlap results in a linear progression of fiber cutting as more groups are added to the instrument. The degree of stretching of certain tissues, such as ligaments, and in particular the medial collateral ligament (MCL), has been found to be linear with respect to the number of groups of such cutting tools, whereby the amount of stretching can be easily selected by simply selecting the appropriate number of groups (e.g., rows) of cutting tools in the instrument. A single application of the selected device can then reliably achieve the desired degree of elongation.

[0016] Preferably, each group of cutting tools also has the same total cutting width. Similarly, each group of cutting tools preferably has the same total non-cutting width, i.e., all groups cut the same amount. Or, stated another way, the total cutting width of a first group of cutting tools is the same as the total cutting width of a second group of cutting tools, and each of the further groups of cutting tools has the same total cutting width as the total cutting width of the first group of cutting tools.

[0017] The number of cutting tools in each group may be selected depending on the application. The number of cutting tools, together with the width of each cutting tool, determines the total amount of cutting. A larger number of cutting tools helps to spread the cut across the width of the tissue. In some embodiments, each group has at least five cutting tools, preferably at least six cutting tools, and more preferably at least seven cutting tools. A larger number of cutting tools also allows the instrument to cover a wider range of tissue widths while still providing a reliable cutting ratio for each width of tissue. For example, the width of a particular ligament, such as the MCL, may vary from patient to patient. In humans, the MCL typically ranges in width from about 14 mm to 20 mm (although in some cases it may be wider or narrower). Ideally, the instrument is wide enough to cover a wider target tissue, but has a sufficient number of cutting tools across the width to still distribute the cutting load across several cutting sites when it cuts a narrower target tissue. Note that if the cutting tools are distributed evenly across the width, the cutting ratio may be the same regardless of the width of the target tissue.

[0018] Thus, in some embodiments, each group of cutting tools extends across a width of at least 20 mm, optionally at least 30 mm. In some examples, each group of cutting tools extends across a common width portion of the instrument, the common width portion having a width of at least 20 mm, optionally at least 30 mm. Thus, the common width portion is shared and encompassed by each and every group of cutting tools, although as noted above, the cutting tools may be offset or arranged differently across that common width. The common width may be larger than the target tissue, for example at least 20 mm or at least 30 mm (or, of course, significantly larger or smaller for other tissues).

[0019] The blades of adjacent groups (or indeed, any two selected groups, as desired) may overlap to various degrees. For example, in one extreme embodiment, the blades of such groups may not overlap at all (i.e., each blade lies completely parallel to the uncut width of the adjacent group, or indeed, every other group, as desired). However, in some embodiments, the blades may overlap such that blades from adjacent groups (or any two selected groups) may be aligned with at least some of the same fibers. As a result, the same fibers may be cut twice by different groups of blades. This is not necessarily a problem because the fibers will heal over time in the stretched configuration. Furthermore, although the blades may overlap, individual blades do not necessarily always cut all fibers across their width, and some fibers may slip or slide out of the path of the blade as the blade is applied, so that fibers near the edge of the blade may not actually be cut by the blade. Thus, some degree of overlap does not necessarily result in multiple cuts of the same fiber. Nevertheless, in some embodiments, significant overlap of the cutting tools may be used such that multiple cuts of the same fiber necessarily result from groups with overlapping cutting tools. As noted above, this is not necessarily a problem, but what is important is that each group cuts at least some new fibers, and the number of groups defines a consistent and reliable total number (or percentage) of cut fibers, thereby defining a consistent degree of elongation achieved with the instrument. In some embodiments, the overlap between the cutting tools of one group and the cutting tools of any other group across the width of the instrument is 80% or less, preferably 70% or less. In some embodiments, the overlap may be about two-thirds across the width of the instrument.

[0020] The width of each cutting tool may vary according to the particular operation, for example, according to the tissue to be stretched and the degree of stretching desired. In some examples, each cutting tool has a cutting width of at least 1 mm, preferably at least 1.5 mm. It has been found that cutting tools smaller than about 1 mm do not cut sufficiently to affect certain fibrous tissues, such as certain ligaments. A cutting tool having a cutting width of about 1.6 mm corresponds closely to the cutting width of the cannula used in certain common applications of the Bellmans technique, and is therefore particularly preferred in some embodiments (e.g., for MCL ligament balancing surgery). In some embodiments, each cutting tool is a cannula. The cannula may then correspond exactly to those used in the Bellmans technique, or may at least resemble the same shape and the same cutting operation, even if they have different widths for different cutting amounts or different ratios.

[0021] The instrument can take any of many forms. For example, the tool can take the form of a single rigid structure with cutting tools attached, or, if desired, an elongated structure with cutting tools formed towards one end thereof. The cutting tools may then be applied to a length of fibrous tissue by simply forcing the cutting tools into the tissue. The array of cutting tools creates a corresponding array of cuts in the tissue, and the instrument can then be removed. The instrument may comprise an applicator, and a group of cutting tools may be formed on an insert that is attachable to the applicator. Such an array is particularly useful when the number of cutting tools required for different degrees of elongation varies, for example when different numbers of groups or different arrays of cutting tools within a group provide different amounts of cut. Thus, different arrays of cutting tools may be formed on different inserts so that the practitioner can select the appropriate insert, mount it on the applicator, and then use the applicator to apply the insert to a length of fibrous tissue. The applicator may be the same for all the different forms of inserts. Of course, different sized applicators may be provided for different applications, e.g., different ligaments or different tissues, as desired, however a single applicator may be suitable for a number of different inserts for different operations.

[0022] The applicator may be disposable. Since the same applicator may be used with different inserts, mass production may be achieved at low cost. However, in some embodiments, the applicator may be reusable. Different inserts may be attached and detached so that the applicator may be used again for another procedure with a different insert. Thus, it is preferred that the inserts are replaceable and / or interchangeable. Although the inserts may be reusable, it is preferred that they are disposable after use.

[0023] The applicator may be a gripping device arranged to, in use, force the cutting tool into the fibrous length of tissue. The applicator may be a pliers. A gripping device such as pliers is advantageous as it allows an operator to apply pressure to the cutting tool from a distance, for example using a scissoring action to force the cutting tool into tissue.

[0024] The instrument may include a backplate arranged facing the cutting tool and movable relative to the cutting tool such that the applicator can urge the cutting tool and the backplate toward one another. The backplate may thereby hold a length of fibrous tissue in place so that the cutting tool can be urged therein by the applicator (e.g., by action of a grasping device or pliers handles).

[0025] The instrument may comprise a plate, the plate comprising holes corresponding in position to each cutting tool, the applicator being arranged to apply the cutting tool towards, and optionally into and / or through, the holes after passing through the fibrous length of the tissue. The plate may function as a backplate, as described above. The holes allow for continuous movement of the cutting tool through the tissue so that a complete and reliable cut can be achieved based on the width of the cutting tool and not on the length of the cutting tool, the flatness of the backplate, or the elasticity of the fibers. Different plates may be provided corresponding to different inserts (and therefore corresponding to different arrangements of the cutting tools). The instrument may be fitted with selected inserts of cutting tools and corresponding selected plates with appropriate holes. However, in some preferred embodiments, the plate is part of the applicator and is common to all inserts. Thus, the holes must correspond to all possible arrangements of cutting tools from all possible inserts, i.e., suitable for applications targeting multiple different degrees of elongation. In some embodiments, different inserts (for different stretches) may include groups (e.g., rows) of different numbers of cutting tools, and the plate may then have corresponding groups (e.g., rows) of holes that correspond to all possible groups of cutting tools that may be used. This allows a single instrument to be used with multiple different inserts and for any desired targeted stretch. This greatly simplifies the procedure for the practitioner, since once the desired degree of stretch is determined, the practitioner simply needs to select the appropriate instrument with the appropriate arrangement of cutting tools that corresponds to that degree of stretch, insert it into the applicator, and apply it to the fibrous tissue to effect the cut.

[0026] The instrument preferably includes an alignment device arranged to be positioned relative to the fiber length of the tissue and aligned to align the groups of cutting tools perpendicular to the length of the fiber length of the tissue. The alignment device ensures that each group of cutting tools is properly aligned perpendicular to the fiber length so that the cutting tools cut the appropriate number of fibers. The alignment device may also be aligned to ensure that the instrument extends across the fiber length of the tissue to cover its entire width. For example, the alignment device may be positioned near the pivot axis of a pliers-type instrument, with the cutting tools aligned to extend away from the pivot axis and the alignment device toward the end of the instrument.

[0027] It will be appreciated that the instrument may be designed for many different procedures. For example, the tool may be designed to lengthen the carpal ligament or the lateral collateral ligament (LCL), or for ligaments at other joints and locations. However, in some embodiments, the instrument may be a medial collateral ligament lengthening instrument.

[0028] The cutting tool (eg, the insert) may be made from any suitable material, including metal and / or plastic.

[0029] The insert and / or instrument may be designed with rounded corners to facilitate easy insertion into the joint area without catching on or damaging other tissue.

[0030] According to another aspect of the present invention, there is provided a method of increasing fiber length in a tissue, the method comprising: 1. Use of an instrument to sever a fiber of a length of tissue, the instrument comprising: a first group of cutting tools, the first group of cutting tools comprising a plurality of cutting tools spaced across a width of the instrument to form an interleaved set of cutting and non-cutting widths; a second group of cutting tools, the second group of cutting tools comprising a plurality of cutting tools spaced across a width of the instrument to form an interleaved set of cutting and non-cutting widths; Each cutting tool of the second group of cutting tools is positioned to at least partially overlap the non-cutting width of at least one of the first group of cutting tools.

[0031] The method may include using an apparatus as described in any of the embodiments described above, optionally including any of the preferred or optional features described above. [Brief description of the drawings]

[0032] Certain preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1a] 1 illustrates a top view of an instrument insert according to one embodiment of the present invention. [Figure 1b] 13 shows how the device is aligned with the ligament in use. [Figure 2a] FIG. 2 shows a perspective view of the instrument insertion portion of FIG. 1. [Figure 2b] FIG. 2 shows a perspective view of the instrument insertion portion of FIG. 1. [Figure 3a] 1 shows a cross-sectional view of a pliers-type applicator instrument. [Figure 3b] 1 shows the head of a pliers-type applicator instrument. [Figure 4] 1 illustrates an alternative forceps-type applicator instrument. [Diagram 5] 1 shows an image of a porcine ligament after application of a device according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The following description is of a preferred embodiment of the invention.

[0034] FIG. 1a shows a top view of an instrument according to an embodiment of the present invention. The instrument is for cutting the fibers of a fibrous length of tissue, such as a ligament, with the purpose of causing a stretching or elongation of the fiber length. One common application of such stretching is for ligament balancing of the medial collateral ligament (MCL) after total knee replacement surgery. The application of the present invention is described herein in the context of such a ligament balancing procedure on the MCL, but it will be understood that the instrument and techniques are applicable in other applications as well. For example, the instrument may be used in any other application in which a ligament is stretched, such as surgery involving ligaments of other joints, such as the knee (e.g., the lateral collateral ligament), hip, elbow, etc. The instrument may also be used to stretch ligaments, such as the carpal ligament. The mechanical principles by which the instrument operates are generally the same across these various procedures.

[0035] Figure 1 shows an instrument 100 designed for use in an MCL ligament balancing procedure. The instrument 100 is shown from above in Figure 1 and also in two perspective views in Figures 2a and 2b.

[0036] The instrument 100 is formed from a base 101 with a number of cutting tools 102 extending from one side of the base 101. The cutting tools 102 are arranged in a pattern of five groups 103a-103e of cutting tools 102. Each group 103a-103e is offset progressively further across the width of the instrument 100 such that the cutting tools 102 in each group 103 cut different fibers of the ligament. Together, the five groups 103a-103e of cutting tools 102 form a slanted or angled grid of cutting tools.

[0037] The present instrument 100 performs the punctures of the Bellmans technique for ligament balancing by puncturing the tissue in multiple separate locations, with each puncture (or cut) cutting a small number of fibers of the ligament. However, the advantage of the present instrument over current applications of the Bellmans technique is that the punctures (or cuts) are all performed simultaneously and in a pre-arranged pattern, thereby cutting a predictable and repeatable number of fibers, thereby achieving a predictable and repeatable stretch of the ligament. Note that because the instrument 100 has a predetermined pattern of cutting tools 102, the risk of complete separation (or cut) of the ligament is also reduced, but this predetermined pattern can be designed to ensure that the cuts are spread out over an area of ​​the ligament, leaving the ligament with sufficient strength.

[0038] Each group 103a-103e of cutting tools 102 includes a set of seven cutting tools 102. The cutting tools 102 in each group 103a-103e are regularly spaced such that the cutting tools 102 form a cutting width (i.e., the portion of the instrument's width that cuts the ligament fibers) and the spaces 104 between the cutting tools 102 form a non-cutting width (i.e., the portion of the instrument's width that does not cut the ligament fibers). All five groups 103a-103e are offset by different amounts along the instrument's width, so that each group of cutting tools cuts a different set of ligament fibers. Comparing two adjacent groups of cutting tools, i.e., groups 103a and 103b, it can be seen that there is an overlap between corresponding cutting tools in adjacent groups. For example, cutting tool 113 of group 103b partially overlaps cutting space 114 of group 103a as well as cutting tool 112 of group 103a. The portions of the cutting tools 113 that overlap the non-cutting space 114 cut the fibers of the ligament that were not cut by any of the cutting tools of the group 103a as the fibers pass through the non-cutting space 114. This can be seen from FIG. 1b, which shows diagrammatically how the instrument is aligned with the fibers 121 of the ligament 120 in use. Each of the fibers 121 extends across the length of the ligament 120, and the fibers 121 are arranged in parallel across the width of the ligament 120. The instrument 100 is arranged such that the instrument width is parallel to the width of the ligament 120, i.e., each group 103a-103e of cutting tools 102 extends across the width of the ligament 120, thereby cutting some of the fibers 121 but not other portions of the fibers 121. In FIG. 1b, the length direction is indicated by arrow L and the width direction is indicated by arrow W.

[0039] In FIG. 1a, each of the five groups 103a-103e is offset to the right along the width of the instrument 100 by a different amount. Each of the second through fifth groups 103b-103e is offset by a multiple of the 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-103e has the same offset between those two groups 103a-103e. Thus, each group 103b-103e has a cutting tool 102 positioned to overlap the uncut space 104 of the previous group 103a-103d. Thus, each additional group 103b-103e beyond the first group 103a cuts a new set of fibers that were not cut by the previous group. In this case, each additional group increases the total number of fibers 121 cut by the instrument 100 as a whole. As more fibers 121 of the ligament 120 are severed, the load on the ligament is shared by fewer fibers, and therefore the ligament stretches under that load. Thus, by carefully selecting the number of groups 103a-103e of cutting tools 102 in the instrument 100, the total amount of cutting, and therefore the total amount of stretching, can be selected. For example, an instrument 100 having only the first two rows 103a-103b of FIG. 1a will cut a certain amount of fibers 121, resulting in some stretching. In comparison, an instrument 100 having the first three rows 103a-103c of FIG. 1a will cut a greater amount of fibers 121, resulting in a greater degree of stretching. It has been found that in certain circumstances, a substantially linear relationship exists between the number of fibers 121 cut and the degree of stretching of the ligament 120. This is the case for MCLs. Thus, different instruments 100 can be easily made with different numbers of groups 103a-103e of cutting tools 102, each corresponding to a different degree of stretch of the target tissue (e.g., ligament). This greatly simplifies the procedure and promotes efficiency by eliminating the repetitive portion of Bellman's process, which requires repeated puncturing and re-measuring until the desired stretch is reached.

[0040] Within each group 103a-103e of cutting tools 102, each cutting tool 102 in the group 103a-103e may be the same or may be of a different size / width. However, when the widths of all cutting tools 102 are added together, they provide the total cutting width for that group 103a-103e. If all cutting tools 102 in a group 103a-103e are the same, then the total cutting width is simply the width of one cutting tool 102 multiplied by the number of cutting tools 102 in the group 103a-103e. A similar calculation may be performed for the total non-cutting widths of the groups 103a-103e. Again, the majority of the non-cutting widths may be the same in some embodiments (although they may also be irregular, with the cutting tools 102 irregularly spaced). However, there is also a non-cutting width at each end of each group 103a-103e, which typically varies between groups 103a-103e as the offsets are different. If the number of cutting tools 102 in each group 103a-103e is the same and the instrument 100 is rectangular (or at least has sides parallel to the cutting area), then the total cutting width plus total non-cutting width of each group 103a-103e is constant.

[0041] In the embodiment shown in Figures 1a, 2a, and 2b, the cutting tools 102 in each group 103a-103e are arranged in a linear row, although it will be understood that this is not strictly necessary to achieve the desired amount of cutting, so long as the correct number of fibers 121 are cut by the groups 103a-103e as a whole.

[0042] As best seen in the perspective views of Figures 2a and 2b, the cutting tools 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 the tissue as it is forced into the tissue parallel to the axis of the tube. The cannula 202 is used in this embodiment as it is used as the cutting device in the standard application of the Vellmans technique for ligament balancing, thereby puncturing the tissue in a similar manner as the Vellmans technique, thereby achieving similar results. However, it will be appreciated that other types of cutting tools may also be used. For example, a sharp scalpel blade may be used instead to incise the tissue in much the same manner.

[0043] In the particular embodiment shown in Figures 1, 2a, and 2b, the cannulas 202 are 1.6 mm diameter cannulas. The cannulas 202 in each group 103a-103e are spaced 3 mm apart on their centers. This leaves an uncut width of 1.4 mm between each adjacent pair of cannulas 202 in one group 103a-103e. Each cannula 202 may cut fibers 121 across its entire 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 fibers 121 out of the way, i.e., to the side, rather than cutting them. This may result in an effective cutting width that is slightly smaller than the diameter of the cannulas 202. This may be taken into consideration when designing the instrument 100, particularly the amount of overlap between cutting tools 102 of adjacent groups 103a-103e, as this affects how many new fibers 121 are cut in each new group 103a-103e, as well as how many fibers 121 may be cut a second time by overlapping cutting tools 102.

[0044] The diameter of the cannula 202 (or other width of the cutting tool 102) can, of course, be varied for different applications and to achieve different degrees of cutting and different degrees of overlap.

[0045] As mentioned above, in the instrument 100 shown in Figures 1a, 2a and 2b, the groups 103a-103e are offset progressively further in width according to their position in the length direction. This forms a slanted grid of cutting tools 102. In the particular embodiment shown in these figures, the angle of slanting is 11.7 degrees, but it will be understood that this is only one example and many other angles are possible. The angle, together with the cutting width and the longitudinal spacing between the groups 103a-103e, determines the amount of overlap between the cutting tools and therefore the number of new fibers cut by each row. For a cannula of 1.6 mm diameter area with 3 mm center spacing (both in width and length), the optimal angle of grid slanting has been found to be between 5 and 25 degrees for a medial collateral ligament balancing procedure. Angles less than 5 degrees result in more double cutting of the ligament with a regular size cannula and not enough additional fibers 121 to be cut with each new group 103a-103e. Angles greater than 25 degrees simply make the instrument 100 wider without adding much benefit. With typical sizes and spacing of the cutting tools, such larger angles also tend to increase the amount of overlap, or double cutting, of the cutting tools. In the embodiment shown in Figures 1a, 2a, and 2b, each row 103a-103e is offset by 0.6 mm from the previous row 103a-103e, i.e., the offsets are 0.6 mm, 1.2 mm, 1.8 mm, and 2.4 mm.

[0046] The device 100 also has two mounting holes 130 that can be used to secure the device 100 to an applicator, such as that of Figures 3 and 4. In this manner, the device 100 becomes a removable insert for a larger device 300.

[0047] Figure 3a shows an applicator 300 in the form of a pliers-type instrument. The applicator 300 has handles 310 which, when squeezed together, bring together a body 320 and a backplate 330. Attached to the body 320 is an insert 340. The insert 340 may be the instrument 100 as shown in Figures 1a, 2a and 2b and may be attached to the body 320 via a fastening device 350 (e.g., a screw or clip) passing through the mounting hole 130.

[0048] The backplate 330 has holes 360 formed therein, one hole corresponding to each cutting tool in the insert 340, and arranged such that when the handles 310 are fully squeezed together, the cutting tools 102 in the insert 340 pass through the holes 360 as the body 320 moves completely. The insert 340 may be removable and replaceable, and disposable so that a new insert may be used for each procedure. The backplate 330 may be removable, replaceable, and disposable as well, but in this embodiment is a permanent part of the applicator 300. Because the backplate 330 is a permanent feature of the applicator 300, it must have holes 360 corresponding to any cutting tools 102 that may be present on any insert 340 that may be used with the applicator 300. As noted above, different instruments 100 (and thus different inserts 340) may have different numbers of groups 103a-103e of cutting tools 102 depending on the desired degree of elongation of the ligament that the instrument 100 is designed to achieve. Since increasing the amount of elongation simply involves adding additional groups 103a-103e of cutting tools 102, an instrument 100 for longer elongations would ideally include at least some groups 103a-103e of cutting tools 102 that are also used in instruments 100 for shorter elongations. In this manner, the backplate 330 may have holes 360 corresponding to each possible group 103a-103e of cutting tools 102 such that the holes 360 are present regardless of whether a cutting tool 102 is present on a particular insert 340.

[0049] 3b shows the head of the applicator instrument 300, but not in cross section. This view shows that the side plate 370 of the applicator 300 is formed with an alignment surface 380 that is parallel to the cutting direction (i.e., the direction in which the cutting tools 102 are driven into the ligament) and perpendicular to the back plate 330. In use, the alignment surface 380 is forced up against the edge of the ligament (or other tissue) to align the insert 340 in a defined orientation relative to the fibers. This ensures that the selected pattern of cutting tools 102 is applied in the correct orientation relative to the fibers 121, thereby ensuring that the correct cutting ratio and therefore the desired elongation is achieved.

[0050] 4 shows an alternative form of applicator 300, in this case in the form of a forceps, with a backplate 330 and cutting instrument 100 at one end and an operating handle 310 at the other end. The cutting instrument 100 may be removable, similar to the pliers of FIG. 3, but may also be a permanent feature of the applicator 300. The applicator 300 may be reusable, and different applicators 300 (with suitably designed instrument 100) may be provided for each desired elongation of the target tissue. For example, different applicators 300 may be provided with two, three, four and five rows of cutting tools, each of which corresponds to a different degree of elongation of the ligament.

[0051] The use of the applicator 300 in an MCL ligament balancing procedure may be as follows: First, the knee ligament balance is tested as a standard to determine the degree of stretch desired. Then, according to the degree of stretch desired, an appropriate insert 340 is selected. The insert 340 may be easily recognized by the number of groups (or rows) 103a-103e present on the insert 340. For example, if each row of cutting tools provides (purely by way of example) approximately 1 mm of stretch and 4 mm of stretch is desired, then the insert 340 may have 4 rows of cutting tools and thus be easily recognized and visually identified. The insert 340 may be attached to the applicator 300 through the mounting holes 130 to secure the device 350. The applicator 300 is then positioned so that the edges of the ligament are in contact with both alignment surfaces 380, such that the MCL is between the cutting tool 102 of the insert 340 and the backplate 330, and such that the cutting tool 102 is properly positioned relative to the ligament fibers 121. The handles 310 are squeezed together completely such that the cutting tool 102 passes through the holes 360 in the ligament 120 and backplate 330, thereby cutting the fibers 121 of the ligament 120 in a predetermined amount and pattern. The handles 310 are then again separated and the applicator 300 is removed from the ligament 120. The positioning of the punctures in the ligament in a predetermined amount and pattern can be expected to reliably provide the desired degree of stretching.

[0052] 5 is a photograph of a porcine medial collateral ligament that has been punctured with an instrument as described above. The holes 500 in the ligament set can be clearly seen. Each hole 500 is here made by the cannula cutting tool 202, and it can be seen that each row 510 of holes 500 is offset from the other rows 510 so as to cut different fibers of the ligament (the ligament fibers extending approximately perpendicular to the arrows 510 in the figure).

Claims

1. 1. A device for increasing fiber length in tissue, said device comprising: a first group of cutting tools, the first group of cutting tools comprising a plurality of cutting tools spaced across the width of the instrument to form an interleaved set of cutting and non-cutting widths; a second group of cutting tools, the second group of cutting tools comprising a plurality of cutting tools spaced across the width of the instrument to form an interleaved set of cutting and non-cutting widths; wherein each cutting tool of the second group of cutting tools is positioned to at least partially overlap the non-cutting width of at least one of the first group of cutting tools.

2. at least one additional group of cutting tools, the additional group of cutting tools comprising a plurality of cutting tools spaced across the width of the instrument to form an interleaved set of cutting and non-cutting widths; The tool of claim 1 , wherein for each additional group of cutting tools, each cutting tool of that group is positioned to at least partially overlap the non-cutting width of at least one of the adjacent groups of cutting tools.

3. The tool of claim 1 , wherein each group of cutting tools comprises a row of cutting tools.

4. The instrument of claim 1 , wherein the groups of cutting tools are spaced apart along the length of the instrument.

5. 10. The tool of claim 1, wherein each group of cutting tools comprises a set of regularly spaced cutting tools.

6. 10. The tool of claim 1, wherein each group of cutting tools has the same arrangement of cutting tools, and each group of cutting tools is offset in the width direction by the same offset amount from each adjacent group of cutting tools.

7. each group of cutting tools has a total cutting width that is the sum of all individual cutting widths in the group and a total non-cutting width that is the sum of all individual non-cutting widths in the group; A tool according to any one of claims 1 to 6, wherein the ratio of total cut width to total uncut width is approximately the same for each group.

8. A tool according to any one of the preceding claims, wherein each group has at least five cutting tools, preferably at least six cutting tools, more preferably at least seven cutting tools.

9. 7. An instrument according to any one of claims 1 to 6, wherein the overlap between the cutting tools of one group and the cutting tools of any other group in the width direction of the instrument is no more than 80%, preferably no more than 70%.

10. An instrument according to any preceding claim, wherein each group of cutting tools extends over a width of at least 20mm, optionally at least 30mm.

11. 11. An instrument according to claim 10, wherein each group of cutting tools extends across a common width portion of the instrument, the common width portion having a width of at least 20mm, optionally at least 30mm.

12. An instrument according to any one of the preceding claims, wherein each cutting tool has a cutting width of at least 1 mm, preferably at least 1.5 mm.

13. The device of any one of claims 1 to 6, wherein each cutting tool is a cannula.

14. The device of any one of claims 1 to 6, wherein the device comprises an applicator, and the group of cutting tools is formed on an insert attachable to the applicator.

15. 15. The device of claim 14, wherein the insert is replaceable and / or interchangeable.

16. An apparatus according to any preceding claim, wherein the applicator is a grasping device arranged to, in use, force the cutting tool into the fibrous length of tissue.

17. The device of claim 16, wherein the applicator is a pliers.

18. 15. The instrument of claim 14, wherein the instrument further comprises a plate having holes positionally corresponding to each cutting tool, the plate being arranged such that the applicator applies the cutting tools towards, and optionally into and / or through, the holes after passing through the fibrous length of tissue.

19. 7. The instrument of claim 1, further comprising an alignment device arranged to be positioned relative to the length of the tissue fibers and to align the group of cutting tools perpendicular to the length of the tissue fibers.

20. The device of any one of claims 1 to 6, wherein the device is a medial collateral ligament lengthening device.

21. 1. A method of increasing fiber length in tissue, the method comprising:

1. Using an instrument to cut fibers of a length of tissue, the instrument comprising: a first group of cutting tools, the first group of cutting tools comprising a plurality of cutting tools spaced across the width of the instrument to form an interleaved set of cutting and non-cutting widths; a second group of cutting tools, the second group of cutting tools comprising a plurality of cutting tools spaced across the width of the instrument to form an interleaved set of cutting and non-cutting widths; using a tool wherein each cutting tool of the second group of cutting tools is positioned to at least partially overlap a non-cutting width of at least one of the first group of cutting tools.

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