Abstract:
Self-reinforcing mechanical systems with application to biological fixation of a first tissue (for example, soft tissue) to a second tissue (for example, bone). As a repair construct is stressed, there is a feedback mechanism (self-reinforcing) against failure that is initially triggered by early failure. The construct “detects” its early/impending failure and utilizes the potentially destructive force to reinforce itself.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part of application Ser. No. 11/702,621, filed on Feb. 6, 2007, which is a continuation-in-part of application Ser. No. 11/392,798, filed on Mar. 30, 2006, which claims the benefit of provisional application Ser. No. 60/666,518, filed on Mar. 30, 2005, the entire disclosures of which are incorporated by reference herein. This application also claims the benefit of provisional application Ser. No. 60/913,406 filed on Apr. 23, 2007, the entire disclosure of which is incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to self-reinforcing mechanical systems utilizing potentially destructive forces to reinforce themselves, and in particular, to self-reinforcing surgical fixation of tissue to bone using a chain-like serial suture loop construct. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to self-reinforcing mechanical systems utilizing potentially destructive forces to reinforce themselves. Non-limiting examples are: 1) Chinese finger trap—the harder you pull against it, the tighter it becomes; and 2) airplane door that is rhomboid-shaped—as a plane gains altitude, the pressure differential between the pressurized cabin and the outside becomes greater, wedging the door for a tighter, more secure construct. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention applies the self-reinforcing mechanical system described above to biological fixation of a first tissue (for example, soft tissue) to a second tissue (for example, bone). As a repair construct is stressed, there is a feedback mechanism (self-reinforcing) against failure that is initially triggered by early failure. Simply stated, the construct “detects” its early/impending failure and utilizes the potentially destructive force to reinforce itself. 
         [0005]    Other features and advantages of the present invention will become apparent from the following description of exemplary embodiments of the invention with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  illustrates a double-row repair construct with sutures; 
           [0007]      FIG. 2  illustrates a double-row repair construct with FiberChain; 
           [0008]      FIG. 3  illustrates a schematic view of a construct A (before loading the tendon); 
           [0009]      FIG. 4  illustrates a schematic view of a construct B (after loading the tendon); and 
           [0010]      FIGS. 5(   a )-( d ) illustrate schematic views of the tensile load when the tendon is unloaded, or loaded under different tensile forces (e.g., T 1 , T 2 ). 
           [0011]      FIGS. 6(   a ) and  6 ( b ) show the Suture Bridge™ and SpeedBridge™ fixation techniques. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    The present invention provides self-reinforcing mechanical systems and methods for tissue fixation using serial suture loop constructs. The construct  100  preferably includes at least two loops of suture (FiberChain®) 99, preferably high strength suture, as described in U.S. Appl. Publ. No. 2006/0259076, the disclosure of which is incorporated by reference in its entirety herein. 
         [0013]    As detailed in U.S. Appl. Publ. No. 2006/0259076, each loop of the serial “chain” preferably has a fixed perimeter. The suture can be interlaced or knotted. The loops may all be similar in size. In an exemplary embodiment, high-strength suture is utilized, such as the high strength suture sold by Arthrex, Inc. of Naples, Fla. under the tradename FiberWire®, which is disclosed and claimed in U.S. Pat. No. 6,716,234, the entire disclosure of which is incorporated herein by reference. FiberWire® suture is formed of an advanced, high-strength fiber material, namely ultrahigh molecular weight polyethylene (UHMWPE), sold under the tradenames Spectra® (Honeywell) and Dyneema® (DSM), braided with at least one other fiber, natural or synthetic, to form lengths of suture material. The preferred FiberWire® suture includes a core within a hollow braided construct, the core being a twisted yarn of UHMWPE. The suture may optionally include filaments of various colors. 
         [0014]    The suture chains  99  ( FIG. 2 ) incorporating advanced, high strength materials, such as FiberWire® suture, can be used in demanding orthopedic applications such as shoulder repairs. The suture chains used in the present invention offer surgeons practical means for creating suture constructs of adjustable size without having to tie a knot in situ. The suture chains can be used in a variety of surgical procedures, and most preferably are used to approximate tissue, for example, to approximate torn tendons to bone. Examples of bone anchors used to secure one or more suture chains to bone are threaded anchors, forked suture anchors, swivel anchors (such as an Arthrex SwiveLock™) or press-in anchors (such as the Arthrex Push-Lock™ anchor described in U.S. Patent Application Publication No. 2004/0093031, the disclosure of which is incorporated by reference herein), among many others. 
         [0015]    Techniques for knotless fixation of anatomical tissue during surgical applications by employing a chain of suture loops (the FiberChain® technique) have been detailed, for example, in U.S. Appl. Publication No. 2007/0135843 (the disclosure of which is incorporated by reference herein in its entirety), which describes a double-row knotless fixation technique using a chain of suture loops. As detailed in U.S. Appl. Publication No. 2007/0135843, a method for tendon to bone fixation includes, for example, the steps of: (i) providing a first medial row constructed with a first plurality of fixation devices, at least one of the first plurality of fixation devices being an anchor; (ii) providing a second lateral row constructed with a second plurality of fixation devices, at least one of the second plurality of fixation devices being a knotless fixation device; (iii) providing a suture loop construct that includes at least two loops formed of and connected by suture; and (iv) fixating the suture loop construct so that it extends over the soft tissue and is secured in place by at least one of the fixation device of the anchors. 
         [0016]    A construct  100  formed by the double-row knotless fixation technique described above, using a chain of suture loops (FiberChain®), is illustrated in  FIG. 2 . Construct  100  is formed by two lateral rows of FiberChain® 99 that secure a first tissue  20  (for example, rotator cuff  20 ) to a second tissue  10  (for example, humerus  10 ). Two fixation devices  21 ,  23  (for example, a SwiveLock™ anchor  21  and a Biocorkscrew™ anchor  23 ) fixate the suture loops to the humerus  10 . 
         [0017]    The mechanism of the present invention which characterizes construct  100  has the following effects: 
         [0000]    (i) Elastic deformation of the tendon resulting in a compressive restoring force (normal force relative to the bone surface) which increases the frictional force that is opposing the tensile failure force. The compressive restoring force also creates a “grasping” configuration of tendon indentation to resist slippage.
 
(ii) Wedge effect of the suture (FiberChain®) against the tendon as the tensile failure force increases.
 
(iii) Larger surface area of FiberChain® relative to suture to enhance the effects of (i) and (ii).
 
       The Constructs 
       [0018]      FIG. 1  illustrates a standard double-row repair with medical mattress sutures  15  and lateral simple sutures  15  with Biocorkscrew™ suture anchors  11 ,  13 . 
         [0019]      FIG. 2  illustrates a FiberChain®/SwiveLock™ double-row repair  100 . 
       Modeling the Self-Reinforcing Mechanisms 
       [0020]      FIG. 3  is a schematic view of a construct A (before loading the tendon), i.e., construct  100  before loading the tendon  20 . 
         [0021]      FIG. 4  is a schematic view of a construct B (after loading the tendon), i.e., construct  100   a  which is the construct  100  after loading the tendon  20 . 
         [0022]    Comparing Schematics A and B: 
         [0023]    l 1 =l 2  (since the point where suture passes through tendon remains the same); 
         [0024]    a=h 1  (since the total length of suture between the anchors remains the same); and 
         [0025]    h 2 &lt;h 1  (tendon becomes compressed as construct fails). 
         [0000]    Consequences of Loading Construct B ( 110   a ) (Fiber Chain®/SwiveLock™) 
         [0026]    1) Tendon  20  becomes elastically compressed under the suture, increasing the distributed normal force N that is perpendicular to bone  10  ( FIG. 5(   a )). 
         [0000]    As the tensile load T increases, the normal force N increases, thereby increasing the frictional resistance to failure, since: 
         [0027]    F=μN, where
       f=frictional force;   μ=coefficient of friction; and   N=normal force       
 
         [0031]    2) Wedge effect of tendon  20  under suture  99 —suture wedges tendon more tightly underneath it as load increases and angle α decreases ( FIGS. 5(   b )-( d )). 
         [0032]    3) Larger surface area of FiberChain® 99 (compared to suture) augments the effects of 1) and 2) above. 
       Tests Conducted 
       [0033]    Biomechanical tests were conducted wherein failure modes and parameters for double-row FiberChain®/SwiveLock™ rotator cuff repair were compared to the same parameters in standard double-row rotator cuff repair. The repairs were cyclically loaded from 10 to 100N at 1 Hz for 500 cycles and the elongation (gapping) at the repair site was measured. A single-cycle pull to failure was then conducted to measure yield load and ultimate load. The elongation (gapping) was 3.2 mm. for SwiveLock™ and 2.1 mm. for standard double-row (slightly greater gapping for SwiveLock™, though not statistically significant). However, the ultimate load to failure for the SwiveLock™ system was greater (539N) than that of the standard double-row (511N). This implies an inherent quality in the FiberChain®/SwiveLock™ construct that “detects” its early failure and self-reinforces to achieve a higher ultimate load to failure. 
       Additional Applications 
       [0034]    1) By the same mechanisms (1 and 2), the Suture Bridge™ technique (with FiberWire® and PushLock™ and Biocorkscrew™ anchors), which is described in U.S. Application Publication No. 2007/0191849, and the SpeedBridge™ technique (with FiberTape™ and SwiveLock C™ anchors), which is described in U.S. application Ser. No. 12/043,008, filed on Mar. 5, 2008 (the entire disclosures of these two applications being herein incorporated by reference) should operate under the same self-reinforcing mechanisms.  FIGS. 6(   a ) and  6 ( b ) show these techniques, wherein the hole in bone is identified by reference number  60 , the anchors are indicated by reference number  62 , the suture or tape is indicated by reference number  82 , and the construct is represented generally by reference number  100 . 
         [0035]    2) Running side-to-side suture would have a similar self-reinforcing mechanisms, especially when the terminal free end is anchored to bone (as in the FiberChain® technique). 
         [0036]    3) These mechanisms apply to all fixation of soft tissue to bone in all joints. 
       Comparison to Standard Double-Row Repair 
       [0037]    The standard double-row construct has suture loops that are maximally tightened when the knots are tied so there are no additional degrees of freedom (i.e., no slack). Accordingly, it has no capacity to develop further compression of tendon as load is applied and therefore cannot be self-reinforcing. 
         [0038]    The above description and drawings illustrate preferred embodiments which achieve the objects, features and advantages of the present invention. It is not intended that the present invention be limited to the illustrated embodiments. Any modification of the present invention which comes within the spirit and scope of the following claims should be considered part of the present invention.