Abstract:
A high strength abrasion resistant surgical suture material with industry standard knot tying characteristics and color marking characteristics includes a core formed of a plurality of twisted fibers of a first material, surrounded by a braided cover made from fibers of a second material different than the first material. The first material is preferably ultrahigh molecular weight polyethylene and the second material is preferably a polymeric material having good knot-tying characteristics.

Description:
[0001]     This application claims the benefit of U.S. provisional patent application No. 60/455,843, filed on Mar. 18, 2003, the entire disclosure of which is incorporated herein by this specific reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to high strength surgical suture materials, and more particularly to braided suture blends of ultrahigh molecular weight polyethylene and polyester. The composite sutures have high tensile strength as well as excellent knot tying characteristics.  
       DESCRIPTION OF THE RELATED ART  
       [0003]     Strength, particularly tensile strength, is an important consideration in any surgical suture material. One of the strongest materials currently formed into elongated strands is an ultrahigh molecular weight long chain polyethylene (UHMWPE), typically used for fishing line and the like, which is sold under the trade names such as Dyneema® or Spectra®. However, this material, while much stronger than ordinary surgical suture, does not have acceptable knot tying characteristics for use in surgical applications because of its low frictional coefficient. Additionally, this material only comes in one color, making multiple suture distinction difficult, especially arthroscopically.  
         [0004]     Current braided suture technology allows for acceptable knot tying characteristics through use of the material properties afforded by silicone-coated polyester. Polyester also comes in a variety of colors making it easy for the manufacturer to assemble many color patterns and color schemes to assist the surgeon in sorting out the many sutures used in a procedure.  
         [0005]     Suture knot holding characteristics are a function of the suture&#39;s ability to frictionally lock to itself within the knot. The magnitude of this friction is determined by the coefficient of friction of the material used to form the suture, as well as the geometry of the suture-to-suture interface within the knot. Polyester&#39;s relatively high coefficient of friction has made it the material of choice within the industry, while the standard interface in the industry is woven braid upon woven braid. The individual elements of the braid in this crossed up interplay leave small round elements laying lo across each other, producing point contacts between the elements. Point contacts result in relatively low friction, and thus result in less than optimum knot tying abilities.  
         [0006]     Accordingly, there exists a need for improved suture materials having high strength and excellent knot tying characteristics.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention advantageously provides a suture strand having high tensile strength as well as clinically acceptable knot-tying characteristics. Briefly, the suture strand comprises a core formed of a plurality of core fibers of a first material, surrounded by a cover including a plurality of cover fibers made of a second material different than the first material. Preferably, the first material is a high tensile strength, high tenacity material such as ultrahigh molecular weight long chain polyethylene, and the second material is a material having good knot-tying characteristics, such as a polymer selected, for instance, from the group consisting of PET, polyester, coated urethanes, and mixtures thereof.  
         [0008]     The core may consist of a single core element comprising a plurality of core fibers that have been twisted together to form a bundle. Each fiber within the bundle itself comprises of a plurality of core filaments of the first material. The number of fibers in a bundle, as well as the cross-sectional shape of the bundle, may be varied to form different embodiments of the invention.  
         [0009]     Alternatively, the core may comprise a sub-core surrounded by an outer ring. The sub-core may consist of a single core fiber, or it may comprises a plurality of core fibers arranged in a twisted bundle. The outer ring comprises an annular woven braid of core fibers. The number and cross-sectional shape of the core fibers in the sub-core may be varied to form different embodiments of the invention.  
         [0010]     Advantageously, the filaments in both the core fibers and the cover fibers are circular in cross-section. The core filaments are preferably larger in diameter than the cover filaments. In embodiments having a sub-core and an outer ring, the filaments in the sub-core may be larger than or the same size as the filaments in the outer ring.  
         [0011]     More particularly, in one aspect of the invention there is provided a suture strand suitable for use as a suture or ligature, which comprises a core including a plurality of core fibers made of a first material, and a cover surrounding the core, wherein the cover includes a plurality of cover fibers made of a second material different than the first material.  
         [0012]     In another aspect of the invention, there is provided a suture strand suitable for use as a suture or ligature, which comprises a core including a plurality of core fibers consisting solely of a first material, and a cover surrounding the core, wherein the cover includes a plurality of cover fibers consisting solely of a second material different than the first material.  
         [0013]     Additional aspects and advantages of the present invention are set forth in the following description and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a cross-sectional view of a suture strand according to the present invention;  
         [0015]      FIG. 2  is a cross-sectional view of a suture strand according to an alternate embodiment of the invention;  
         [0016]      FIG. 3  is a perspective view, partially broken away, of the suture strand of  FIG. 1 ;  
         [0017]      FIG. 4  is a perspective view, partially broken away, of the suture strand of  FIG. 2 ;  
         [0018]      FIG. 5  is a cross-sectional view of a suture strand according to another embodiment of the invention;  
         [0019]      FIG. 5  is a cross-sectional view of a suture strand according to yet another embodiment of the invention;  
         [0020]      FIG. 7  is a perspective view, partially broken away, of the suture strand of  FIG. 5 ;  
         [0021]      FIG. 8  is a perspective view, partially broken away, of the suture strand of  FIG. 6 ;  
         [0022]      FIG. 9  is a cross-sectional view of a suture strand according to still another embodiment of the invention;  
         [0023]      FIG. 10 a  cross-sectional view of a suture strand according to yet still another embodiment of the invention;  
         [0024]      FIG. 11  is a perspective view, partially broken away, of the suture strand of  FIG. 9 ; and  
         [0025]      FIG. 12  is a perspective view, partially broken away, of the suture strand of  FIG. 10 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     Referring now to  FIGS. 1 and 3 , a suture strand  10  according to the present invention comprises a core  12  and a cover  14 . The core  12  comprises three core fibers  16  twisted together to form a single core element. Each core fiber  16  itself comprises a bundle of core filaments  18  of a first material. The cover  14  comprises an annular woven braid including eighteen cover fibers  20  surrounding the core  12 . Each cover fiber  20  comprises a bundle of cover filaments  22  of a second material. Both the core filaments  18  and the cover filaments  22  are substantially circular in cross section, the core filaments  18  having larger diameters than the cover filaments  22 . In addition, both the core fibers  16  and the cover fibers  20  are substantially circular in cross-section, the core fibers  16  having larger diameters than the cover fibers  20 .  
         [0027]     The first material, i.e. the material used to form the core filaments  18 , is preferably a high strength, high molecular weight, high tenacity material such as ultrahigh molecular weight long chain polyethylene. The second material, i.e. the material used to form the cover filaments  24 , is preferably a material having clinically acceptable knot tying characteristics. Preferably the second material is also opaque and available in a wide variety of colors. This allows the cover fibers  20  to be woven into a wide variety of visually distinguishable patterns, so the correct sutures can easily be identified in a multi-suture application. Acceptable materials having the proper combination of knot-tying ability and color selection include PET, polyester, coated urethanes, and mixtures thereof.  
         [0028]     The size of the core  12  is selected according to the suture strength desired. An appropriately sized core  12  can increase the composite suture strength of a suture  10  having the construction of a standard # 2  suture to that of a standard # 5  suture.  
         [0029]      FIGS. 2 and 4  show a suture strand  10   a  according to an alternate embodiment of the invention. The core  12   a  comprises four core UHMWPE fibers  16   a  twisted together to form a single core element. The cover  14   a  comprises eighteen polyester cover fibers  20   a  woven together to form an annular braid around the core  12   a.  Each of the core fibers  16   a  is substantially wedge-shaped and has a length L that is greater than the diameter of each of the cover fibers  20   a.  The size of the core  12   a  is preferably selected to increase the increase the composite suture strength of a suture  10   a  having the construction of a standard # 2  suture to that of a standard # 5  suture.  
         [0030]      FIGS. 5 and 7  show a suture strand  10   b  according to another embodiment of the invention. The core  12   b  comprises five core UHMWPE fibers  16   b  twisted together to form a single core element. The cover  14   b  comprises eighteen polyester cover fibers  20   b  woven together to form an annular braid around the core  12   b.  Each of the core fibers  16   b  is substantially wedge-shaped and has a length L that is greater than the diameter of the cover fibers  20   b.  The size of the core  12   b  is preferably selected to increase the increase the composite suture strength of a suture  10   b  having the construction of a standard # 2  suture to that of a standard # 5  suture.  
         [0031]      FIGS. 6 and 8  show a suture strand  10   c  according to still another embodiment of the invention. The core  12   c  comprises a sub-core  13  consisting of a single, centrally located UHMWPE sub-core fiber, surrounded by six UHMWPE core fibers  15  that have been woven or braided together to form an outer ring  17  around the sub-core  13 . The cover  14   c  comprises eighteen polyester cover fibers  20   c  woven together to form an annular braid around the core  12   c.  This is a particularly flexible embodiment of the invention, having knot-tying characteristics similar to those of a standard # 2  suture.  
         [0032]      FIGS. 9 and 11  show a suture strand  10   d  according to yet another embodiment of the invention. The core  12   d  comprises a sub-core  13   d  consisting of three UHMWPE sub-core fibers  19  arranged in a twisted bundle, surrounded by twelve UHMWPE core fibers  21  that have been woven or braided together to form an outer ring  15   d  around the sub-core  13 . The cover  14   d  comprises twenty eight polyester cover fibers  20   d  woven together to form an annular braid around the core  12   d.  The sub-core fibers  19 , core fibers  21 , and cover fibers  20   d  are all substantially circular in cross-section, the core fibers  21  in the outer ring  15   d  having diameters smaller than the diameters of the sub-core fibers  19  and larger than the diameters of the cover fibers  20   d.  In addition, the diameter of each core filament  23  within each core fiber  21  of the outer ring  15   d  is smaller than the diameter of each sub-core filament  25  within each sub-core fiber  19  and larger than the diameter of each cover filament  27  within each cover fiber  20   d.  This embodiment of the invention exhibits knot-tying characteristics identical to that of a standard # 2  suture.  
         [0033]      FIGS. 10 and 12  show a suture strand  10   e  according to yet another embodiment of the invention. The core  12   e  comprises a sub-core  13   e  consisting of three UHMWPE sub-core fibers  19   e  arranged in a twisted bundle, surrounded by twelve UHMWPE core fibers  21   e  that have been woven or braided together to form an outer ring  15   e  around the sub-core  13   e.  The cover  14   e  comprises fourteen polyester cover fibers  20   e  woven together to form an annular braid around the core  12   e.  The sub-core fibers  19   e,  core fibers  21   e,  and cover fibers  20   e  are all substantially circular in cross-section, the core fibers  21   e  in the outer ring  15   e  having diameters smaller than the diameters of the sub-core fibers  19   e  and larger than the diameters of the cover fibers  20   e.  In addition, the diameter of each core filament  23   e  within each core fiber  21   e  of the outer ring  15   d  is smaller than the diameter of each sub-core filament  25   e  within each sub-core fiber  19   e  and larger than the diameter of each cover filament  27   e  within each cover fiber  20   e.  This embodiment of the invention, like the previous embodiment, exhibits knot-tying characteristics identical to that of a standard # 2  suture. Furthermore, the looser weave of the cover  14   e  increases the suture&#39;s coefficient of fiction, resulting in better knot-holding characteristics than the standard suture.  
         [0034]     The suture of the present invention, which can be attached to a suture anchor or curved needle, is ideally suited for a wide variety of surgical procedures and in particular, most orthopedic procedures, including rotator cuff repair, Achilles tendon repair, patellar tendon repair, ACL/PCL reconstruction, hip and shoulder reconstruction procedures, and replacement of suture in anchors.  
         [0035]     While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.