The present invention relates to an implantable surgical cord formed from overlapping yarn strands.
Because connective tissues are mostly avascular they have a poor capacity for healing and so their injuries are often repairable only via surgical procedures in which implantable connecting devices are used to reconnect or reattach torn tissue to its original anchor site.
An important consideration with connective devices such as sutures and tapes is the strength of repair. The repair strength is governed by the strength of the device and also its resistance to being pulled through the tissue when under load, whereby the suture might slip or cut through the tissue. Sutures have small diameters and flat tapes sharp edges which lead to such devices pulling, or cutting, through tissue. A surgical implantable connective device which resists tissue pull through would have improved function for numerous surgical applications.
The present invention provides a surgical cord in which the yarn strands are arranged to provide strength and resistance to stretch in response to the application of a tensile loading force. The surgical cord is also configured so as not to present sharp edges that would otherwise lead to tissue pull through when the implant is loaded post surgical implantation, while providing end regions that are easy to thread through eyelets of needles and easy for a surgeon to grasp, manipulate and apply tension so as to aid surgical implantation.
According to a first aspect of the present invention there is provided a surgical cord comprising: a plurality of overlapping yarn strands forming the walls of a substantially tubular region extending over a length of the cord.
The tubular region of the device may comprise a substantially circular, elliptical, or oval hollow cross sectional profile whilst the bordering substantially flat regions comprise a reduced cross sectional profile relative to the tubular region and are not hollow.
The structure of the device may be braided, woven or knitted, and formed from bundles of fibres that may be twisted together extend parallel and/or are crimped together. Preferably the structure is woven. However, it may comprise a combination of the aforementioned structures.
The yarn strands may be constructed from individual filaments. Each filament may be individually twisted, but preferably they are parallel and not twisted. These filaments may be braided, woven or twisted together to form the yarn. Preferably the filaments are twisted together. Additionally, the filaments may be crimped. Where the surgical cord comprises a woven pattern having warps, aligned substantially parallel to the longitudinal axis of the cord and wefts aligned transverse to the longitudinal axis, the warps and wefts may comprise the same or different yarn configurations comprising woven, braided, twisted and/or crimped filaments.
Discrete regions or sections along the length of the tube may comprise yarns made from different materials having different physical and/or mechanical properties. These regions of different materials may be formed as annular bands to give the cord different mechanical and/or physical properties along its length. A first region along the length may exhibit greater extensibility than a second region whilst the second region may exhibit greater stiffness and abrasion resistance. Alternatively or in addition, the different physical and/or mechanical properties of the cord at these discrete regions along its length may be provided by changing the relative thickness of the yarn strands, the overlap configuration including variation of the overlap pattern (e.g. braiding, intertwining, plaiting, linking, knotting, weaving, plying or twisting), porosity, density of the mesh/braid and the thickness and/or cross sectional profile of the yarn strands, a coating, manufacturing process that affects the bulk material (for example heat treatment) or surface treatment (for example gas plasma treatment). In particular, where the cord is woven, the number of warps and/or wefts at each of these specific regions may be different.
When the surgical cord is utilized, for example, as a prosthetic ligament, it could pass through regions of soft tissue such as tendon and regions of hard tissue such as bone. It is advantageous for the cord to exhibit different mechanical and/or physical properties along its length to correspond with such variations in the tissue through which the cord could pass. In particular, the filaments which lie in the direction of the longitudinal axis of the device at the end portions of the device which would locate adjacent to bone may be composed from a first material that exhibits abrasion resistance and a high resistance to extension. While the central section that is adjacent to tendon is composed from a second material that is more extensible than the first material. This would provide a device with relative inextensible extremities such that when the device is loaded the motion between the device and bone is reduced which would aid bone ingrowth into the device and hence provide enhanced fixation to the hard bone. Their abrasion resistance would further provide protection against potential sharp edges of bone which can lead to cutting of and rupture of the cord. The central tubular section would have properties to match the soft tissue that is being reconstructed.
The structure may be constructed from a variety of biocompatible materials including but not confined to surgical gut, silk, cotton, polyamide (Nylon), polyethylene terepthelate (polyester), polyethylene (PE), ultrahigh molecular weight polyethylene (UHMWPE), polypropylene (PP), polydioxanone, polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), polyaramid, or bioabsorbable materials. The device may be composed of a combination of the aforementioned materials. Preferably the device is constructed wholly from polyester.
In one alternative embodiment of the invention, where the cord is woven, the first material forming the warp yarns is a material such as UHMWPE or polyester and the second material forming the wefts is a bioabsorbable such as polyglycolic acid (PGA), polylactic acid (PLA) or co-polymer of such materials. This provides a device which retains its strength over time since all the load transmitting fibres are permanently implanted. This device has the advantage that it would gradually reduce in bulk as the non load bearing fibres resorb over time. The resorption of the non load bearing fibres has the advantage that further space is created for unrestricted tissue ingrowth. Moreover, fibres of differing resorption rates could be utilized so that the amount of space made available to the encroaching tissue ingrowth can be governed over time.
Such a structure could be manufactured by forming yarns which are composed of interlinking loops of different materials. Many configurations of interlinking loops can be used. Materials may also be linked by air entanglement or air splicing. The distinction between adjacent sectors of materials may be abrupt, or a gradual change may be incorporated.
The cord may comprise multiple regions along its length in which the yarn strands comprise the same or different material. In particular, regions or bands of the cord that are intended to be secured to bone may comprise a material that is inextensible, inflexible and exhibits abrasion resistance. Such materials include stainless steel, titanium or synthetic polymers optionally with or without coatings to enhance stiffness. Conversely, the sections of the cord along its length that are configured to simulate biological tissue at a joint region may be made from a flexible extensible material. This type of configuration involving multiple changes of material along the length of the cord may be provided by interlinked loops of yarn strands formed from twisted filaments.
In one alternative embodiment of the invention, the first material is a material such as UHMWPE or polyester and the second material is a bioabsorbable which incorporates a drug, a growth factor, or other biologically active substance. This material may be formed by impregnating the substance within the bioabsorbable material. Alternatively, the substance may be coated on the bioabsorbable material. Alternatively, the bioabsorbable material may be coated in the substance. Alternatively the substance and the polymer may be combined prior to or during fibre spinning. The change in material may be within the filaments/yarn strands which lie in the perpendicular direction of the longitudinal axis of the device (wefts where the cord is a woven mesh structure). This provides a device which retains its strength over time since all the load transmitting fibres are permanently implanted. This device has the advantage that the non-load bearing filaments perpendicular to the longitudinal axis would gradually resorb and release a substance. Moreover, fibres of differing resorption rates could be utilized to provide a timed substance release delivery system. By way of example, the filaments in the second material may comprise three fibres, each of different absorption rates. This would provide a system whereby the first would be a quickly absorbing fibre that would release a substance soon after implantation, the second fibre would resorb three months after implantation to provide a further or different dose of a substance, and the third fibre would resorb six months after implantation to provide another or different dose.
In one alternative embodiment of the invention the material in the sector of the device which lies adjacent to the bone tunnels would be one which is permanent or bioabsorbable which incorporates a drug, growth factor, surface treatment or a substance which is oseoinductive or osteoconductive, so promoting bone in growth into the device to provide fixation. Materials typically include tricalcium phosphate, hydroxyapatite or poly lactide carbonate. The material in the sector of the device which lies between bone anchor sites may be one that incorporates a drug, growth factor, surface treatment or a substance to enhance cell adherence and proliferation to encourage tissue ingrowth to reconstruct the soft tissue, for example a ligament or tendon.
Alternatively, or in addition to incorporating different materials, the amount of material may change along the cord length to affect its physical and/or mechanical properties. This may increase or reduce the bulk or diameter of the material at various sections of the cord. This increase in material may provide protection from external objects or edges, changes in properties such as strength or extension, or provide a means of fixation by using a stepped bone tunnel so that the increased diameter section of the device wedges against the smaller section. The increase in diameter may be provided by using yarns created by linking loops together, where one of the loops contains more material than adjacent loops. Materials may also be added by air entanglement or air splicing.
Optionally, the yarn strands and in particular at least one of the filaments/yarn strands that lie in the perpendicular direction of the longitudinal axis of the device is made from a material that is radio opaque. This filament is configured to form an identifiable trace on an X-ray. Since the filament would spiral through the wall thickness, when assembled as a woven structure or braid for example, it would identify the entire outer diameter or bulk of the ligament and hence the surgeon can determine on a post operative X-ray whether the device has been implanted in the correct position.
Preferably, the cord comprises one or more fibres of contrasting colors. This may be provided by dying fibres of polyester or polyamide (Nylon), or a monofilament of colour extruded polypropylene or polydioxanone. These high visibility fibres would be used to identify the transitions between different materials or changes in structural properties in a device with a composite structure. These coloured fibres could also mark the apertures, so enabling the surgeon to easily identify the holes in the device through which the tissue can be threaded and consequently ease the surgical procedure. Without such coloured marking fibres identification between the adjacent sectors of UHMWPE fibres and PET fibres would be difficult as both materials are typically white or translucent. Each feature could be identified by a fibre of a different colour; by way of example a blue fibre could be used to identify the apertures, while a black fibre used to identify material changes.
Optionally, at least one of the fibres that lie in the direction of the longitudinal axis of the device is coloured. This coloured fibre forms an identifiable trace along the length of the device to enhance visibility during surgery.
According to a second aspect of the present invention there is provided a woven surgical cord comprising: a plurality of yarn strands having warps aligned with the longitudinal axis of said cord that overlap wefts aligned transverse to the longitudinal axis of said cord; said yarn strands at a first region extending over a portion of the length of the cord comprising a first material and; said yarn strands at a second region extending over a portion of the length of the cord comprising a second material.
According a third aspect of the present invention there is provided a braided surgical cord comprising: a plurality of yarn strands overlapping to form a braided pattern; said yarn strands at a first region extending over a portion of the length of the cord comprising a first material and; said yarn strands at a second region extending over a portion of the length of the cord comprising a second material.
According to a fourth aspect of the present invention there is provided a knitted surgical cord comprising: a plurality of yarn strands overlapping to form a knitted pattern; said yarn strands at a first region extending over a portion of the length of the cord comprising a first material and; said yarn strands at a second region extending over a portion of the length of the cord comprising a second material.
Optionally, the cord being either a woven, knitted or braided structure may comprise regions along its length having a different overlapping weave pattern selected from any one or a combination of a woven, knitted or braided structure. The different overlapping pattern may be formed integrally with the main length of the cord or may be supplementary to the overlapping yarn strands that extend over the main length of the cord. That is, the additional woven, knitted or braided pattern may be overlaid on top of the yarn strands upon which the cord is formed.
Further details of the present invention will now be described by way of example only with reference to the accompanying drawings in which:
Referring to
Referring to
According to further specific implementations, material 201 may be overlaid on top of material 200. These discrete regions along the length of the cord provide sections exhibiting different mechanical and/or physical properties such as extensibility, stiffness, and abrasion resistance, for example.
Changes in material along the length of the cord may be provided at any point along the cord length and in particular at the region of the interface 106 between end regions 102 and main length 101.
Referring to
Referring to
As illustrated in (b) the change in cross sectional profile along the length of the cord may be used as a means to anchor the cord in position. For example, when inserted within a bone tunnel comprising a first diameter 706 and a reduced diameter 707, the larger cross sectional profile portion 701 would abut the constriction 708 formed by the change in diameters 706, 707 within bone 705. This would prevent the cord from completely pulling through bone 705.
Referring to the embodiments of
According to the further embodiments of
The examples referred to in
Number | Date | Country | Kind |
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0819912.7 | Oct 2008 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/GB2009/051459 | 10/29/2009 | WO | 00 | 7/19/2011 |