Abstract:
There is disclosed an apparatus and method of manufacture relating to a pre-sutured, high-strength allograft tendon construct. One embodiment of the allograft tendon construct includes first and second tendon lengths that are positioned longitudinally in parallel to one another. A whip stitched pattern secures the first and second tendon lengths at a free end, forming a stitched end portion that abuts an unstitched middle portion. The whip stitched pattern includes a plurality of sutures that originate adjacent to the free end and progress or advance inward toward the unstitched middle portion. A multiple knot bundle is applied immediately prior to a final suture, such that the final suture loops about the multiple knot bundle and locks the multiple knot bundle in place beneath the final suture. Other embodiments are also disclosed.

Description:
BACKGROUND 
     An allograft includes bone, tendon, skin, or other types of tissue transplanted from one person to another. Allografts are used in a variety of medical treatments, such as knee replacements, bone grafts, spinal fusions, eye surgery, and skin grafts for the severely burned. Allografts come from voluntarily donated human tissue obtained from donor-derived, living-related, or living-unrelated donors and can help patients regain mobility, restore function, enjoy a better quality of life, and even save lives. 
     When a ligament or tendon becomes detached from the bone, surgery is usually required to re-secure the ligament or tendon. Often, a substitute allograft ligament or tendon (hereinafter an “allograft construct” or “allograft tendon construct”) is attached to the bone to facilitate regrowth and permanent attachment. The reattachment procedure involves drilling a bone tunnel between two bones such as, for example, the tibia and the femur, and securing the allograft construct within the tunnel. To demonstrate this technique, Prior Art  FIG. 1  shows an exemplary prior art allograft construct  50  secured within femoral and tibial tunnels  52 ,  54 , each formed in femur and tibia  56 ,  58 , respectively. 
     An allograft construct must be properly tensioned within the bone tunnel to achieve optimal results. That is, the tension or the “fit” of the allograft construct within the bone tunnel prior to being anchored to the bone must be sufficient to achieve stability, but not so excessive that it captures the joint. One variable in achieving optimal tension of the allograft construct within the bone tunnel involves preparing an allograft construct having the proper cross-sectional diameter. Preparing a construct with the requisite cross-sectional diameter typically involves folding a single tendon strand in half, which results two abutting tendon lengths having in a common middle region bounded by a folded end and a free end. The free end may then be whip stitched together. Alternatively, two separate tendon strands may be associated with one another, or “doubled up,” before one or both free ends are whip stitched together. 
     Prior Art  FIG. 2  illustrates a partial perspective view of an unstitched middle region  59  and a free end  60  of prior art allograft construct  50 , in which free end  60  has been whip stitched using a flexible strand to form a stitched pattern  62 . Notably, the whip stitched pattern  62  of prior art allograft construct  50  originates inward toward unstitched middle region  59 , from where a number of sutures  64   1-5  progress or advance outward toward free end  60  along arrow A. As a result, final suture  64   5  is located adjacent to free end  60 , and pulling forces applied to the flexible strand along arrow B are transferred to final suture  64   5  at free end  60 . 
     Prior art stitch pattern  62  is often applied to a folded allograft tendon, and discussed above. Alternatively, it is applied to two independent tendon strands that are stitched together at one or both of their ends using a similar whip stitching technique. 
     Traditionally, surgeons have been responsible for tendon graft preparation, individually preparing appropriately cross-sectioned, whip stitched grafts for each patient and/or circumstance. Recently, pre-sutured allograft constructs have become available from third-part providers, such as, for example, allograft processing centers, thereby allowing surgeons to order high quality, consistent, strong, and sterile tendon allografts, either individually or as part of a larger “kit” carrying a variety of sizes. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended for use as an aid in determining the scope of the claimed subject matter. 
     One embodiment provides a method of tendon reconstruction. The method includes (1) positioning a first tendon length and a second tendon length longitudinally in parallel to one another; (2) threading a flexible strand through and about a first free end of the first and second tendon lengths to form an allograft construct having a stitched end portion that abuts an unstitched middle portion, where the threading comprises forming a plurality of sutures by advancing the flexible strand away from a first suture located adjacent to the first free end and toward a final suture located adjacent to the unstitched middle portion; and (3) after forming the final suture, stringing the flexible strand through a space between the first and second tendon lengths and out the first free end of the stitched end portion. 
     Another embodiment provides an allograft construct. The allograft construct includes a first tendon length and a second tendon length, where the first and second tendon lengths are positioned longitudinally in parallel to one another. The allograft construct also includes a whip stitched pattern that secures together the first and second tendon lengths at a fee end, thereby forming a stitched end portion that abuts an unstitched middle portion. The whip stitched pattern includes a plurality of sutures that originate adjacent to the free end and progress inward toward the unstitched middle portion. 
     Yet another embodiment provides a substitute tendon having at least a stitched end portion and an unstitched middle portion and including a continuous flexible strand forming a whip stitched pattern and an anchor. The whip stitched pattern comprises a plurality of sutures that secure a common free end of two longitudinally abutting tendon lengths, the plurality of sutures originating with a first suture located adjacent to the free end and progressing toward a final suture located adjacent to the unstitched middle portion. The anchor originates at the final suture and threads through a space between the tendon lengths and out the common free end of the stitched end portion. 
     Other embodiments are also disclosed. 
     Additional objects, advantages and novel features of the technology will be set forth in part in the description which follows, and in part will become more apparent to those skilled in the art upon examination of the following, or may be learned from practice of the technology. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention, including the preferred embodiment, are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. Illustrative embodiments of the invention are illustrated in the drawings, in which: 
         FIG. 1  illustrates a perspective view of a prior art allograft construct affixed within femoral and tibial bone tunnels of a patient; 
         FIG. 2  illustrates a partial-perspective view of the prior art allograft construct of  FIG. 1 ; 
         FIG. 3  illustrates a partial-perspective view of one embodiment of a high-strength, pre-sutured allograft tendon construct; 
         FIGS. 4A-4C  illustrate respective partial-side, end, and partial-perspective views of first and second tendon lengths of the allograft construct of  FIG. 3 ; 
         FIG. 4D  illustrates a perspective view of one embodiment of a folded-over tendon strand forming the first and second tendon lengths of FIGS.  4 A- 4 C; 
         FIGS. 5A-5C  illustrate respective partial-side, end, and partial-perspective views of the first and second tendon lengths of  FIGS. 4A-4C , including a first suture applied adjacent to a free end; 
         FIGS. 6A-6C  illustrate respective partial-side, end, and partial-perspective views of the first and second tendon lengths of  FIGS. 4A-4C , including a first suture located adjacent to a free end and a second suture applied in a direction progressing inward toward an unstitched middle portion; 
         FIGS. 7A-7C  illustrate respective partial-side, end, and partial-perspective views of the first and second tendon lengths of  FIGS. 4A-4C , including first through fourth sutures that originate adjacent to a free end and progress inward toward an unstitched middle portion; 
         FIGS. 8A-8C  illustrate respective partial-side, end, and partial-perspective views of the first and second tendon lengths and sutures of  FIGS. 7A-7C , including a Duncan Loop knot applied after the fourth suture; 
         FIG. 9  illustrates a partial-side view of the first and second tendon lengths, sutures, and Duncan loop knot of  FIGS. 8A-8C , including three Reverse-Half-Hitch-Alternating-Post knots applied after the Duncan loop knot; 
         FIG. 10  illustrates a partial-side view of the first and second tendon lengths, sutures, and knots of  FIG. 9 , where the knots are tightened into a multiple knot bundle; 
         FIGS. 11A-11C  illustrate respective partial-side, end, and partial-perspective views of the first and second tendon lengths, sutures, and multiple knot bundle of  FIG. 10 , including an initiated fifth suture; 
         FIGS. 12A-12C  illustrate respective partial-side, end, and partial-perspective views of the first and second tendon lengths, sutures, and multiple knot bundle of  FIGS. 11A-11C , with an anchor threaded through a space between the tendon lengths and out a free end; 
         FIG. 13  illustrates a partial-perspective view of the high-strength, pre-sutured allograft tendon construct of  FIG. 3 , including indications of a direction of suture progression and directions of force application and force transfer; and 
         FIG. 14  illustrates a flow chart depicting an exemplary method of manufacturing the high-strength, pre-sutured allograft tendon construct of  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments are described more fully below in sufficient detail to enable those skilled in the art to practice the system and method. However, embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. The following detailed description is, therefore, not to be taken in a limiting sense. 
     Various embodiments of the systems and methods described herein relate to a pre-sutured, high-strength allograft construct that may be pre-ordered and made available for a surgeon to position and affix in place within a target bone tunnel(s) of a patient. The allograft construct features a whip stitched suture pattern that outperforms current methods of suturing tendons and ligaments for use in tendon replacement surgeries (e.g., ACL replacement surgeries). One embodiment provides an allograft tendon construct having a whip stitched pattern that originates at an outermost end of the allograft construct and progresses inward. The new suture pattern results in a stronger final product that increases the maximum force that can be applied to a pre-sutured tendon construct without risking suture pull-out and/or slippage. This unique pattern also prevents deformation of the allograft tendon construct when subjected to the type of excessive tensile forces that are often applied to the suture pattern after surgery and in use. 
       FIG. 3  illustrates a partial perspective view of one embodiment of a high-strength allograft construct  100 . In this embodiment, allograft construct  100  may include first and second tendon lengths  102   1 ,  102   2  that have been whip stitched together at a stitched end portion  104 . Stitched end portion  104  may secure a common free end  112  with a whip stitched pattern  108 , which, in this embodiment, may include five sutures  114   1-5 , and an anchor  109 . Stitched end portion  104  may abut an unstitched middle portion  110 . 
     Whip stitched pattern  108  may be needle-threaded through and about first and second tendon lengths  102   1 ,  102   2 . Pattern  108  and anchor  109  may be formed of any appropriate and continuous flexible strand  113 , including suture material of rope or wire that is formed of natural or manmade materials that do not react negatively with human tissue. 
       FIGS. 4-13  detail the intricacies of whip stitched pattern  108  and anchor  109  to demonstrate how high-strength allograft construct  100  resists maximum pull-out force, while also resisting suture deformation and slippage. Specifically,  FIGS. 4A-4C  illustrate side-partial, end, and perspective-partial views of first tendon length  102   1  and second tendon length  102   2  positioned in parallel along a longitudinal axis, X. Each of first and second tendon lengths  102   1 ,  102   2  may be formed of separate tendon or ligament strands. Alternatively, and as shown in  FIG. 4D , first and second tendon lengths  102   1 ,  102   2  may be formed of first and second halves of a single tendon or ligament strand that has been folded over or doubled. In either alternative, first and second tendon lengths  102   1 ,  102   2  may meet at a common free end  112  ( FIGS. 4B-4C ). 
       FIGS. 5A-5C and 6A-6C  illustrate side-partial, end, and perspective-partial views of first and second sutures  114   1 ,  114   2 , respectively, as applied to free end  112  of first and second tendon lengths  102   1 ,  102   2 . As shown in  FIGS. 5A-5C , first suture  114   1  threads flexible strand  113  both through and about free end  112 , securing both tendon lengths  102   1 ,  102   2  relative to one another. Second suture  114   2 , added in  FIGS. 6A-6C , repeats the loop. Notably, first suture  114   1  originates at a location adjacent to free end  112 . As a result, additional sutures  114   2-n  progress or advance inward toward unstitched middle portion  110  ( FIG. 3 ). 
       FIGS. 7A-7C  illustrate side-partial, end, and perspective-partial views of first through fourth sutures  114   1-4 , as applied to free end  112  of first and second tendon lengths  102   1 ,  102   2 . In this embodiment, fourth suture  114   4  is the fourth of five total sutures  114   1-5 . That is, suture  114   4  is the second-to-last suture, and, therefore, suture  114   4  may differ slightly from sutures  114   1-3  in that flexible strand  113  may exit the loop prior to completion at a space or junction  116  between first and second tendon lengths  102   1 ,  102   2 , as shown in  FIG. 7B . Once flexible strand  113  has exited suture  114   4 , a Duncan loop Knot  118  may be applied, as shown in  FIGS. 8A-8C , and tightened. In this embodiment, Duncan loop Knot  118  may be followed by three Reverse-Alternating-Post-Half-Hitch knots  120 , shown in  FIG. 9 . Duncan Loop Knot  118 , along with Reverse-Alternating-Post-Half-Hitch knots  120  may then be tightened to form a multiple knot bundle  122 , shown in  FIG. 10 . 
       FIGS. 11A-11C and 12A-12C  illustrate side-partial, end, and perspective-partial views of an initiation and completion of fifth and final suture  114   5 , respectively. As shown in  FIGS. 11A-11C and 12A-12C , final suture  114   5  may loop about first and second tendon lengths  102   1 ,  102   2  in a manner that locks-in multiple knot bundle  122 , or that secures multiple knot bundle  122  beneath the flexible strand  113  of final suture  114   5 . This configuration ensures that multiple knot bundle  122  is protected or safeguarded beneath the suture that experiences the highest pull-out forces during use, or beneath final suture  114   5 . As force is applied, final suture  114   5  cinches about multiple knot bundle  122  and tendon lengths  102   1 ,  102   2 , which further stabilizes multiple knot bundle  122  to resist pull-out of the knots. 
     The completion of final suture  114   5  completes whip stitched pattern  108 . Any trailing flexible strand  113  may, in this embodiment, form anchor  109  that is strung or threaded back through the center space  116  between first and second tendon lengths  102   1 ,  102   2  and out free end  112  of stitched end portion  104 . Anchor  109  may then be used to anchor or affix allograft construct  100  within a target bone tunnel (not shown) of a patient. 
       FIG. 13  illustrates a partial perspective view of completed allograft construct  100 , featuring the whip stitched pattern  108 . In this embodiment, as discussed above, first suture  114   1  is located adjacent to free end  112 . The remaining sutures  114   2-5  progress inward along arrow C toward unstitched middle section  110 , such that final suture  114   5  is placed at the farthest point from free end  112 . As a result, tensile force applied to anchor  109  along arrow D is transferred directly to final suture  114   5  at the innermost area of stitched end  104 , causing final suture  114   5  to cinch/lock about tendon lengths  102   1 ,  102   2  upon the application of force. Excess force is then translated to the previous suture, or fourth suture  114   4 , then to suture  114   3 , then to suture  114   2 , and finally to suture  114   1 , causing whip stitched pattern  108  to tighten along arrow E like a noose when under stress. 
     In use, the highest force is always experienced by final suture  114   5 , which is farthest from the edge of construct  100 . The least amount of force is transferred to the most vulnerable first suture  114   1 , located closest to the edge of construct  100 . This configuration allows allograft construct  100  with whip stitched pattern  108  to resist much higher applied forces than prior art constructs (e.g., prior art construct  50  of  FIG. 2 ) without experiencing suture pull-out and/or deformation because far more tendon material separates the most highly stressed suture from the edge of the construct. 
     As discussed above in the Background section, prior art whip stitched patterns typically place the first suture at an inward location toward the unstitched middle portion of the construct and progress the remaining sutures outward toward the open end/edge of the construct. As a result, the final suture in the prior art commonly resides adjacent to the free end. Thus, the highest force applied to the prior art anchor is transferred directly to the final suture, located closest to the end of the construct, which often results in suture pull-out and/or deformation. 
     Allograft construct  100  also serves to prevent knot pull-out because multiple knot bundle  122  ( FIGS. 10 and 11A ) is applied immediately prior to the final suture, or between the second-to-final suture (here, fourth suture  114   4 ) and the final suture (here, final suture  114   5 ). This positioning allows the final suture to “lock-in” the multiple knot bundle, or to tighten about the multiple knot bundle upon the application of force, thereby preventing knot pull-out. 
     Plane strain tensile (PST) testing was performed on six sample allograft constructs, including three prior art constructs (labeled “Old” or “O”) and three constructs featuring whip stitched pattern  108  (labeled “New” or “N”). The results are shown in Table 1, below. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Deformation of Construct &gt;1 cm or Suture Failure 
               
             
          
           
               
                   
                   
                 Deformation 
                   
                 Whip Stitch Suture 
               
               
                   
                   
                 of &gt;1 cm 
                 Suture yield 
                 Technique 
               
               
                   
                 Sample 
                 (lbs) 
                 (lbs) 
                 Old OR New 
               
               
                   
               
               
                   
                 A 
                 na 
                 64.5 
                 N 
               
               
                   
                 B 
                 6.8 
                 na 
                 O 
               
               
                   
                 C 
                 na 
                 63.4 
                 N 
               
               
                   
                 D 
                 na 
                 67.3 
                 N 
               
               
                   
                 E 
                 5.6 
                 na 
                 O 
               
               
                   
                 F 
                 4.5 
                 na 
                 O 
               
               
                   
               
             
          
         
       
     
     Testing criteria was set to “fail” at the point where elongation of the construct exceeded 1 cm. The force required to reach the point of failure, as well as the force at which the suture failed, were recorded to demonstrate the integrity of each suture. As shown in Table 1, none of the prior art samples maintained tissue integrity until suture yield (i.e., the construct deformed beyond 1 cm or the sutures pulled out prior to the point of suture breakage), while all of the constructs featuring stitched pattern  108  maintained tissue integrity until the suture broke at its expected value above 60 pounds of force. Constructs featuring stitching pattern  108  experienced no deformation throughout the tensile strength of the suture, while all of the prior art constructs experienced deformation of the construct beyond the allowable 1 cm and did not exhibit tensile strength beyond 6.8 lbs. 
       FIG. 14  provides a flow chart illustrating an exemplary method  200  of manufacturing one embodiment of high-strength allograft construct  100 . Method  200  initiates with the positioning ( 202 ) of first tendon length  102   1  and second tendon length  102   2  longitudinally in parallel to one another. As discussed above, this positioning may include placing independent tendon strands side-by-side or by folding over a single tendon strand to form two distinct lengths  102   1 ,  102   2 , as shown in  FIG. 4D . Method  200  continues with the threading ( 204 ) of flexible strand  113  through and about free end  112  to form first suture  114   1  located adjacent to free end  112  of combined tendon lengths  102   1 ,  102   2 . After the placement of first suture  114   1 , method  200  may continue with the threading of additional sutures ( 206 ), such as sutures  114   2-4 , which progress inward toward unstitched middle portion  110 . Additional sutures may be threaded through to the second-to-final suture, or, in this embodiment, fourth suture  114   4 . After placing the second-to-final suture and immediately prior to placing the final suture, flexible strand  113  may be knotted ( 208 ). In one embodiment, knotting flexible strand  113  ( 208 ) may involve applying a Duncan Loop Knot  118 , followed by three Reverse Half-Hitch-Alternating-Post Knots  120  ( 210 ) to form multiple knot bundle  122 . After knotting ( 208 ) flexible strand  113 , method  200  may continue with the threading of a final suture ( 212 ) (e.g., final suture  114   5 ) to complete whip stitched pattern  108 . Final suture  114   5  may be looped about multiple knot bundle  122  to guard against knot pull-out, as discussed above. Once the final knot has been applied ( 212 ), flexible strand  113  may be threaded through center space/junction  116  between first and second tendon lengths  102   1 ,  102   2  and out free end  112  to form anchor  109  ( 214 ), which may be affixed within a target bone tunnel of a patient. 
     While method  200  discusses whip stitched pattern as having a total of five suture, it should be understood that any appropriate number of sutures may apply. 
     Although the above embodiments have been described in language that is specific to certain structures, elements, compositions, and methodological steps, it is to be understood that the technology defined in the appended claims is not necessarily limited to the specific structures, elements, compositions and/or steps described. Rather, the specific aspects and steps are described as forms of implementing the claimed technology. Since many embodiments of the technology can be practiced without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.