FR2884706A1 - PROTHETIC KNIT FOR SUPPORT IMPLANTS - Google Patents

Abstract

The present invention relates to a perforated prosthetic knit (1) for the treatment of urinary incontinence and / or prolapse, based on a thread arrangement of a biocompatible polymer material comprising at least a first ply defining a first armor chain, characterized in that said son arrangement further comprises at least two non-meshing plies, partial weft, the number of warp threads of said chain armor ranging from 6 to 12. The invention also relates to a support implant for the treatment of stress urinary incontinence and / or prolapse obtained from this knit, as well as on the method of manufacturing such a knit.

Description

The present invention relates to a perforated prosthetic knit for

  treatment of urinary incontinence and / or prolapse, in particular for the manufacture of urethral support strips or strips in the treatment of stress incontinence in women, as well as in the treatment of urinary incontinence

  pelvic static disorders mainly in women in general, also called prolapse.

  The surgical treatment of stress incontinence in women generally involves the use of reinforcements in the form of strips placed under the middle urethra. The central part of the implant is disposed at this body and can be in contact with the latter to support it while the lateral parts of the implant are attached to stable anatomical elements such as for example the abdominal wall, the posterior surface of the pubis, or the obturator membrane, for example by means of staples, sutures or by simple tissue anchoring.

  With regard to the treatment of prolapse, the implant is disposed on the one hand at or near the organ to be supported and on the other hand at the level of stable anatomical elements such as, for example, the abdominal wall, the posterior face of the pubis, the obturator membrane, the promontory of the sacrum, sacro-sciatic ligaments, for example by means of staples, sutures or by simple tissue anchoring.

  In known manner, such a support implant must meet many constraints, and in particular have a suitable mechanical strength, particularly in the longitudinal direction, be biocompatible and flexible, These support implants must also be macroporous so as to integrate intimately and quickly into the tissues of the recipient while respecting the hollow viscera in contact with which they are implanted. These implants are advantageously made from monofil of biocompatible material so as to develop a minimal area potentially unfavorable for bacterial colonization. These support implants can be suturable. These implants may also advantageously be slightly longitudinally extensible so as to be easily towed in sometimes tortuous anatomical paths. Finally, it is desirable that these support implants be adapted to the anatomy and the morphology of the patient in both width and length.

  An essential property of these implants is their mechanical strength, which is particularly important for supporting the organs to be treated.

  To increase this resistance, it has been proposed to increase the amount of material constituting these implants, for example by using thicker son, and therefore more resistant, or by making a more dense mesh.

  However, since such implants are intended to remain permanently in the body of the patient, the increase in material entrained by these solutions is undesirable because contrary to the current criteria of tolerance and tissue integration of the implants of support and reinforcements.

  Another problem presented by the support strip is their tiling. For the purposes of the present application, the term "curling" means the spontaneous winding of the strip on itself, around its longitudinal axis, under tension stress along its length. These implants must retain in this form mechanical properties, especially in strength, sufficient, while limiting as much as possible the release of particles, that is to say son ends, when they are under stress and allow tissue anchoring mechanically stable.

  Thus, there is the need for a knit, in particular macroporous and made from monofilament, which would make support implants, particularly in the form of strips, having both an optimal mechanical strength and a mass per unit area. the weakest possible.

  The present invention aims to remedy this need by proposing a knit having an arrangement of particular threads, in particular having at least one mesh ply and at least two non-meshing plies, making it possible to produce support strips which are particularly mechanically strong and particularly light and stable.

  The present invention relates to a perforated prosthetic knit for the treatment of urinary incontinence and / or prolapse, based on a son arrangement of a biocompatible polymer material comprising at least a first ply defining a first chain armor, characterized in that said son arrangement further comprises at least two non-meshing, partial weft webs, the number of warp threads of said chain armor ranging from 6 to 12.

  The present invention also relates to the use of a prosthetic knit as above to obtain a prosthetic product for surgical use, in particular to obtain a support implant for the treatment of stress urinary incontinence and / or prolapse.

  The knit according to the invention can be used directly as a support implant for the treatment of stress urinary incontinence and / or prolapse or it can be cut transversely to obtain such an implant.

  Another object of the invention is a support implant for the treatment of stress urinary incontinence and / or prolapse, characterized in that it is obtained by transverse cutting of a prosthetic knit such as above. .

  The present invention also relates to a method of making a perforated prosthetic knit as above characterized in that it comprises the following steps: a) a knitted structure is manufactured on a warp or Rachel loom according to a first ply continuously threaded or available and being obtained from a first guide bar, the scale followed for knitting the son of said first ply leading to the formation of a chain, and at least a first non-meshing ply and a second non-meshing ply, said non-meshing plies being threaded continuously or at disposal, each of said non-meshing plies being obtained from a guide bar, the scale followed for the knitting of the threads of each non-spunlace ply being such that for all n yarns (A) of the warp armor, n ranging from 6 to 12, any yarn of said meshing plies approaching the n + 1 chain yarn (Al, A11, Al2) makes a half turn at said n + 1 chain yarn, said n + 1 chain yarn being called free chain yarn, b) said free chain yarns are stripped along the length of the knitted structure obtained at step a) and eliminating said free warp threads to obtain knits with a number of warp threads ranging from 6 to 12.

  The knit or implant according to the invention has an excellent mechanical strength, in particular an excellent tensile strength, can be inelastic, and is thus quite suitable for the manufacture of a support implant for the treatment of the urinary stress incontinence and prolapse, without the need for a protective sheath.

  Moreover, thanks to the arrangement of specific threads that it comprises, in particular because of the presence of two non-meshing plies, the knit or implant according to the invention is particularly light, while having a sufficient mechanical strength to support the organs to be treated. Thus, the knit or implant according to the invention comprises a minimum amount of yarn and therefore of material and nevertheless has the adequate strength to support the organs to be treated.

  In particular, the presence of two non-meshing plies, in particular two intermeshing non-meshing plies, that is to say whose respective guide bars move symmetrically with respect to one another and staggered one by relationship to the other in the direction of the manufacture of the knitted structure on the knitting machine, provides knits and / or strips and / or implants with very good resistance to lateral compression. Thus, when one compresses, for example between two fingers, the two opposite longitudinal edges of a knit, strip and / or implant according to the invention obtained from said knitted structure, this knit, band and / or implant keeps significantly the same width. Preferably, the width loss of a knit, strip and / or implant according to the invention under the effect of the compression of its two opposite longitudinal edges between two fingers is less than 10%. The knit, tape and / or implant according to the invention is therefore particularly stable in handling, in passing through possible ancillaries (needle eye, cannula, etc.) and in the tissues of the patient (limitation of the rope effect ).

  Because of its particular son arrangement, the knit tape and / or implant according to the invention therefore has no risk of unraveling.

  Furthermore, because of its manufacturing process, this knit has atraumatic and stable edges, that is to say without risk of fraying or releasing particles, allowing its introduction into the fabrics without protective sheath. Finally, all knits, strips or implants obtained from the same knitted structure have a homogeneous thermofixation and are easily manipulated.

  In the present application, prosthetic knit means a knit intended to be implanted in the human or animal body in the form of a prosthesis or of any other part shaped at least in part with said knit.

  In the present application, openwork knit means a knit whose armor or armor determine cells or voids in the thickness of the knit, these cells or voids may constitute channels opening on either side of the knit . Such openwork knit, also called macroporous, allows better tissue integration.

  By mesh ply is meant according to the present application, a sheet of son for which the scale followed for the knitting son leads to the formation of meshes. In known manner, a chain-weave web is a mesh web, while partial weft webs are non-mesh webs.

  In the present application, the term "free warp thread" is understood to mean a warp thread traversed by no weft yarn, in other words a warp thread for which any weft thread approaching this warp thread makes a half-turn at this thread. chain yarn, and this over the entire longitudinal dimension of the knitted structure.

  In the present application, the basis weight of a knit is measured according to ISO 3801, the breaking force of a knit in the longitudinal direction and in the transverse direction is measured according to ISO 13934-1, the elongation under 2 daN in the longitudinal direction is measured according to ISO 13934-1.

  Preferably, the number of warp yarns of the knit according to the invention ranges from 8 to 11, preferably from 9. Such a number of warp threads makes it possible to obtain a knit having a good mechanical strength in the direction of the length and good longitudinal and transverse stability.

  Preferably, the knit is made from yarns, monofilaments or multifilaments, a biocompatible polymer material selected from polypropylene, polyester, polyamide and mixtures thereof. Advantageously, said biocompatible polymer material is polypropylene.

  In another embodiment, the knit according to the invention is made from yarns, monofilaments or multifilaments, of a biocompatible and bioabsorbable polymer material.

  In yet another embodiment, the knit according to the invention can be made from a mixture of bioabsorbable bioabsorbable yarns and nonabsorbable biocompatible yarns. Thus, it is possible to realize temporarily reinforced implants whose skeleton is to remain permanently in the body of the patient for a minimum permanent support.

  Preferably, the knit according to the invention is made from monofilament yarns having a diameter ranging from 0.05 mm to 0.15 mm, preferably from approximately 0.10 mm.

  Such a diameter, associated with the particular arrangement of yarns of the knit 5 according to the invention makes it possible to obtain an excellent mechanical strength without having to add the quantity of material by means of thick threads.

  Preferably, the knit according to the invention has a thickness ranging from 0.20 mm to 0.40 mm, preferably around 0.30 mm.

  In a preferred embodiment of the invention, the knit 10 comprises cells having a diameter ranging from 0.3 to 1.5 mm, preferably from 0.3 to 0.9 mm. Such a structure allows improved tissue anchoring.

  Preferably, the knit according to the invention has a width ranging from 0.6 cm to 1.5 cm.

  Preferably, the knit according to the invention has a weight per unit area of from 40 to 75 g / m 2, preferably from 50 to 60 g / m 2.

  Advantageously, the breaking force of the knit according to the invention in the longitudinal and transverse direction, measured according to ISO 13934-1, ranges from 40 to 90N, preferably from 55 to 75 N, more preferably from 60 to 70 N. Thus, the knit or implant according to the invention has both excellent mechanical strength, or breaking strength, and a low mass per unit area while being inelastic and insensitive to changes related to the conditions of use such as tiling, stringing or deformation in the transverse direction, release of particles. Such an implant is advantageous because it provides effective support organs to treat while minimizing the mass of foreign body implanted.

  Preferably, the knit according to the invention has an elongation under 2 daN in the longitudinal direction, measured according to ISO 13934-1, less than or equal to 15%, more preferably less than or equal to 10%.

  Preferably, the knit according to the invention comprises a first non-meshing web and a second non-meshing web, said first non-meshing web having the table 1-1 / 3-3 / 2-2 / 0-0 //, said second web non-meshing tablecloth showing the scale 3-3 / 2-2 / 0-0 / 1-1 //.

  Such scales are particularly advantageous because they make it possible to obtain a better maintenance of the warp threads as well as an excellent transverse and longitudinal mechanical resistance while retaining the widest possible cells and without addition of material. Preferably, the knit according to the invention is heat set.

  In one embodiment of the invention, the knit according to the invention has a length ranging from 10 to 50 cm and constitutes a support implant for the treatment of stress urinary incontinence and / or prolapse.

  In another embodiment of the invention, an implant according to the invention is obtained by transverse cutting of the knit according to the invention. Preferably, the implant according to the invention has a length ranging from 10 to 50 cm. The knit according to the invention is preferably manufactured according to a process comprising the following epates: -a) a knitted structure is manufactured on a warp loom or Rachel according to a first sheet continuously threaded or available and being obtained from a first guide bar, the scale followed for the knitting son of said first sheet leading to the formation of a chain, and at least a first non-meshing ply and a second non-meshing ply, said non-meshing plies being threaded continuously or at disposal, each of said non-meshing plies being obtained from a guide bar, the scale followed for knitting the yarns of each ply not meshing being such that for all the n yarns (A) of the chain armor, n ranging from 6 to 12, any yarn of said meshing mats approaching the n + 1 chain yarn (A1, A11, Al2) makes a half-turn at said n + 1 chain yarn, said n + 1 chain yarn being called free chain yarn, - b) said free chain yarns are cut to length of the knitted structure obtained in step a) and eliminating said free warp threads to obtain knits with a number of warp threads ranging from 6 to 12.

  Preferably, n is from 8 to 11, and more preferably n is 9.

  In a preferred embodiment of the method according to the invention, the son of the first tablecloth in chain weave are knitted according to a scale 1-0 / 0-1 //, the son of the first non-meshing ply are knitted according to a scale 1-1 / 3-3 / 2-2 / 0-0 //, the yarns of the second non-meshing ply are knitted according to a scale 3-3 / 2-2 / 0-0 / 1-1 //.

  Preferably, the guide bar of the first ply according to chain weave is threaded continuously solid, the guide bar of the first non-weaving ply is threaded continuously 1 full, 1 empty, 3 full, 1 empty, 1 full, 3 empty, and the guide bar of the second non-meshing web is threaded continuously 1 full, 1 empty.

  Advantageously, the two guide bars of the two non-meshing plies move in partial weft under three needles, symmetrically relative to each other, offset with respect to each other in the direction of manufacture of the knitted structure. Such a knitting, with the weft bars moving symmetrically relative to one another and thus crossing between them, makes it possible to obtain a better maintenance of the chains and thus a better resistance to the lateral compression of knits, implants and / or strips according to the invention obtained from this knitted structure.

  Preferably, the knitted structure is subjected to a thermofixation operation between step a) and step b). The knitted structure is thus easily handled, in particular for the demaling step. Moreover, all the knits and implants according to the invention obtained from the same knitted structure heat-set have a homogeneous heat-setting which makes it possible to better guarantee the homogeneity of the physico-mechanical properties of one strip to the other after demagnage .

  The invention will be better understood from the following description with reference to the accompanying drawings.

  FIG. 1 represents a simplified schematic drawing of a knitted structure comprising a first warp armor ply and two non-knit plies making it possible to obtain the knit according to the invention; FIG. 2 represents a knitted structure making it possible to obtain knits according to the invention, of which two free warp threads are partially unraveled; - FIG. 3 is a scanning electron microscopic Itashi S 800, magnification X20, of unbraiding a free warp thread of a knitted structure to obtain knits according to the invention, - Figure 4 is a scanning electron micrograph Itashi S 800, magnification X20, the heart of a knit or implant according to the invention.

  In FIG. 1, for a knitted structure that makes it possible to obtain a knit according to the invention, EE 'represents the direction or transverse dimension of the knit, by FF' the direction or longitudinal dimension of the knit and by GG 'the direction or diagonal dimension of the knitting.

  This figure shows the movements of the warp yarns and weft yarns for a knitted structure for obtaining a knit according to the invention, having a chain ply and two non-meshing plies. The wires A and Al of the chain armor are represented in solid lines. The wire Al is a free-chain thread within the meaning of the present invention. The yarns of the first non-meshing ply are represented in fine solid lines: they are the B yarns. The yarns of the second non-meshing ply are represented by a dashed line: these are the C yarns. In this example, the first bar with shelves, corresponding to the armor chain is threaded continuously full. The second guide bar, corresponding to the first non-meshing sheet and son B, is threaded continuously 1 full, 1 empty, 3 full, 1 empty, 1 full, 3 empty. The third guide bar, corresponding to the second non-meshing web and son C, is threaded continuously 1 full, 1 empty.

  The knitting scales for these three plies are as follows: the chain ply (yarns A and A1): 1-0 / 0-111, the first non-meshing ply (yarns B): 1-1 / 3-3 / 2-2 / 0-0 //.

  the second non-meshing sheet (thread C): 3-3 / 2-2 / 0-0 / 1-1 //.

  Thus, the warp yarn Al, as it appears in FIG. 1, is completely traversed by no weft yarn, or in other words, any weft yarn, that is to say any yarn B or C, approaching said yarn. Chain yarn Al makes a half-turn at this chain yarn Al.

  The free warp thread A1 can thus be demilled without any consequences on the neighboring warp threads and thus without destructuring the knit on either side of this thread Al. By pulling on the warp thread A1, the part of the knit is separated. located to the left of this wire Al of the part located to the right of this wire Al without unraveling these two parts.

  On the other hand, because any weft yarn approaching the yarn Al makes a half-turn at this yarn Al, the edges of the separated parts only have one yarn B or C making a half-turn and are therefore made smooth.

No fraying occurs.

  Such unraveling of a free warp thread A1 of a knitted structure making it possible to obtain a knit according to the invention is visible in FIG. 3, which is a photograph, taken with an Itashi S 800 scanning electron microscope, magnification X20. , a demagnetizing zone of such a knitted structure according to Figure 1 and Example 1 of the present application. In the upper part of the figure, the Al wire is demaillé and the knit portions on either side of this Al wire are not destructured. Their edges are smooth: only a wire C performs a half-turn. No knitting yarn is cut or frayed. In this figure, the Al wire is being unmaked. Thus, at the bottom of the figure, the wire Al 5 is still meshed with the son C approaching him.

  At the end of the unraveling, that is to say when the yarn Al has been peeled over the entire length of the knitted structure, the yarn Al is removed from said knitted structure and the two parts of the knitted fabric from else of this wire Al are completely separated. By unraveling in the same manner a second free warp thread, a strip of said knitted structure is completely separated, this band constituting the knit according to the invention. The distribution of the son Al allows to predetermine with great precision the width of each strip.

  In Figure 2 is shown schematically a knitted structure 2 for obtaining knits 1 according to the invention. Two of the free warp threads, the Al1 and Al2 wires, are partially unraveled. Thus, by completely unraveling these free warp threads Al 1 and Al 2, a knit 1 according to the invention is obtained, namely a strip that can be used in the treatment of stress urinary incontinence in women. Such strips may also be used in the treatment of prolapse.

  The heart of a knit, tape or implant according to the invention is shown in Figure 4, which is a photograph, taken with Itashi S 800 scanning electron microscope, X20 magnification. The knit or implant according to the invention corresponds to a zone of said knitted structure 2 between two consecutive free-knit threads. Thus, the knit or implant itself does not include free warp threads. It does not present any risk of unraveling.

EXAMPLE:

  A knitted structure was produced which made it possible to obtain a knit according to the invention from a polypropylene monofilament yarn, with a diameter of 0.10 mm, on a Rachel loom, with a chain ply and two non-meshing plies, according to the following scales for the different plies: - the chain ply: 1-0 / 0-1 //, - the first non-meshing ply: 1-1 / 33 / 2-2 / 0-0 //, - the second ply not Mesillante: 3-3 / 2-2 / 0-0 / 1-1 //.

  The first guide bar, corresponding to the chain armor was threaded continuously full. The second guide bar, corresponding to the first non-meshing web, of partial weft, was threaded continuously 1 full, 1 empty, 3 full, 1 empty, 1 full, 3 empty. The third guide bar, corresponding to the second non-meshing nonwoven web, was threaded continuously 1 full, 1 empty. The threading of the two partial wefts was carried out so as to move under nine warp threads, this finally obtaining strips separated by about 1 cm in width each. Thus, in this example, 1 out of every 10 threads was a free warp thread within the meaning of the invention.

  The gauge used was 24 needles.

  The guide bars of the two non-meshing plies moved in partial weft under three needles, symmetrically relative to each other, shifted relative to each other in the direction of manufacture of the knitted structure.

  This knitted structure corresponds to the weave shown in FIG. 1 of the present application.

  On leaving the trade, the knitted structure was subjected to a heat-setting operation.

  From this knitted structure, knits or strips were obtained by unraveling at least two consecutive free-knit threads. The knits or strips had the following characteristics: - thickness: about 0.3 mm - diameter of the cells: about 1 mm.

- width: about 1 cm.

  - area weight: about 50 g / m2.

  - breaking force measured according to ISO 13934-1 method on a strip of 1 cm wide and 20 cm long: 66 N. The knit or strip obtained by unraveling at least two free warp threads, Preferably, these knitted structures have excellent tensile strength and are therefore very suitable for use as, or in the manufacture of, a support implant for the treatment of stress urinary incontinence and prolapse.

  For example, an implant 20 cm in length, or 30 cm in length or 40 cm in length can be prepared from this strip. Such an implant has a particularly low surface mass. Thus a minimum of material is implanted in the body of the patient to be treated.

  Moreover, because of its manufacturing process, this implant is not elastic and has edges, including longitudinal, atraumatic allowing its implantation without protective sheath. Finally, all knits, strips or implants obtained from the same knitted structure have a homofixation homogeneous and are easily manipulated.

Claims (25)

  1. Prosthetic knit (1) perforated for the treatment of urinary incontinence and / or prolapse, based on a son arrangement of a biocompatible polymer material comprising at least a first ply defining a first chain armor, characterized in that said yarn arrangement further comprises at least two non-meshing, partial weft webs, the number of warp yarns of said chain armor ranging from 6 to 12.   2. Knit (1) according to claim 1, characterized in that the number of chain son is 8 to 11, preferably 9.   3. Knit (1) according to any one of the preceding claims, characterized in that it is made based son, monofilaments or multifilament, a biocompatible polymer material selected from polypropylene, polyester, polyamide and their mixtures.   4. Knit (1) according to claim 3, characterized in that said biocompatible polymer material is polypropylene.   5. Knit (1) according to one of claims 1 to 4, characterized in that it is made from a mixture of biocompatible son bioabsorbable and biocompatible son non-bioabsorbable.   6. Knit (1) according to any one of the preceding claims, characterized in that it is made based monofilament son having a diameter of 0.05 mm to 0.15 mm, preferably about 0, 10 mm.   7. Knit (1) according to any one of the preceding claims, characterized in that it has a thickness ranging from 0.20 mm to 0.40 mm, preferably about 0.30 mm.   8. Knit (1) according to any one of the preceding claims, characterized in that it comprises cells having a diameter ranging from 0.3 to 1.5 mm, preferably from 0.3 to 0.9 mm .   9. Knit (1) any one of the preceding claims, characterized in that it has a width ranging from 0.6 cm to 1.5 cm.   10. Knit (1) any one of the preceding claims, characterized in that its basis weight ranges from 40 to 75 g / m2, preferably from 50 to 60 g / m2.   11. Knit (1) any one of the preceding claims, characterized in that its breaking force in the longitudinal and transverse direction, measured according to ISO 13934-1, is 40 to 90N, preferably 55 at 75 N, more preferably from 60 to 70 N. Knit (1) any one of the preceding claims, characterized in that it has an elongation under 2 daN in the longitudinal direction, measured according to ISO 13934-1, less than or equal to 15%, of still preferably less than or equal to 10%.   13. Knit (1) according to any one of the preceding claims, characterized in that it comprises a first non-meshing web and a second non-meshing web, said first non-meshing web having the scale 1-1 / 3-3 / 2-2 / 0-0 //, said second non-meshing web having the scale 3-3 / 2-2 / 0-0 / 1-1 //.   14. Knit (1) according to any one of the preceding claims, characterized in that it is heat set.   15. Knit (1) according to any one of the preceding claims, characterized in that it has a length ranging from 10 to 50 cm and is a support implant for the treatment of stress urinary incontinence and / or prolapse.   16. Use of a prosthetic knit (1) according to any one of claims 1 to 15 for obtaining a prosthetic product for surgical use, in particular for obtaining a support implant for the treatment of stress urinary incontinence and / or prolapse.   17. Supporting implant for the treatment of stress urinary incontinence and / or prolapse, characterized in that it is obtained by transverse cutting of a prosthetic knit (1) according to any one of claims 1 at 15.   18. Implant according to claim 17, characterized in that it has a length ranging from 10 to 50 cm.   19. A method of manufacturing a knit (1) prosthetic according to claim 1, characterized in that it comprises the following steps: a) a knitted structure (2) is manufactured on a loom chain or Rachel according to a first threaded sheet continuously or available and being obtained from a first guide bar, the scale followed for the knitting of the son of said first ply leading to the formation of a chain, and at least a first non-meshing ply and a second non-meshing ply, said non-meshing plies being threaded continuously or at disposal, each of said non-meshing plies being obtained from a guide bar, the scale followed for the knitting of the threads of each non-spunlace ply being such that for all the n yarns (A) of the chain armor, n ranging from 6 to 12, any yarn of said meshing mats approaching the n + 1 chain yarn (Al, A11, Al2) performs a half-turn at the cedit level. n + 1 chain yarn, said n + 1 chain yarn being called free chain yarn; b) said free chain yarns are demilled along the length of the knitted structure obtained in step a) and said yarns are eliminated; of free chain to obtain knits (1) whose number of warp threads ranges from 6 to 12. de8à11. 9.   20. The method of claim 19, characterized in that n va 21. Method according to claim 20, characterized in that n is 22. The method of claim 21, characterized in that the son of the first ply chain weave are knitted according to a scale 1-0 / 01/1, the son of the first non-meshing ply are knitted according to a scale 1-1 / 3-3 / 2-2 / 0-0 //, the yarns of the second non-meshing ply are knitted according to a scale 3-3 / 2-2 / 0-0 / 1-1 //.   23. A method according to claim 22, characterized in that the guide bar of the first ply in chain weave is threaded continuously full, the guide bar of the first non-meshing ply is threaded continuously 1 full, 1 empty, 3 full, 1 empty, 1 full, 3 empty, and the guide bar of the second non-meshing web is threaded continuously 1 full, 1 empty.   24. The method of claim 23, characterized in that the two guide bars of the two non-meshing plies move in partial frame under three needles, symmetrically relative to each other, offset with respect to the other in the direction of knitting.   25. A method according to any one of claims 19 to 24, characterized in that the knitted structure (2) is subjected to a thermofixation operation between step a) and step b).