Abstract:
The present invention is related to methods and apparatus that can enhance the security of a suture knot by annealing a portion of the suture knot. Such a suture knot is less likely to fail by slippage. Advantageously, the methods and apparatus can operate in a liquid environment, such as the inside of a body. Conventional knots made from monofilament sutures exhibit an unfortunate tendency to slip or untie. A surgeon can tie a conventional monofilament suture using standard knot tying techniques and anneal the suture. The annealing can fuse the tails of the suture together, thereby preventing failure by slippage. In one embodiment, the annealing textures the surface of the monofilament tails, thereby increasing friction and resistance to slippage. In another embodiment, the annealing is applied to the last throw in the knot.

Description:
RELATED APPLICATION 
     This application claims the benefit priority under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/143,532, filed Jul. 13, 1999, the entirety of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is generally related to surgery. In particular, the present invention relates to suturing with synthetic suture material. 
     2. Description of the Related Art 
     For many years, surgeons have reconnected tissue using suturing and other methods. Suturing is a surgical technique involving the connection of tissue by stitching the tissue together with a strand of appropriate suturing material. Synthetic or polymer sutures are among the class of appropriate suturing material. 
     Typically, a suture is prepared by piercing the suture through tissue on both sides of a wound, by pulling the ends of the suture to bring the sides of the wound together, and tying the suture into a knot. The knot preserves the tension on the suture to maintain the sides of the wound in approximation and allow the tissue to heal. 
     Generally, it is undesirable for the suture to slip and become untied. An improperly tied knot can slip and untie at a tension far lower than the tension required to break the suture. When the suture is internal to the body, replacement of the failed suture can require another surgery. 
     Synthetic sutures are available as monofilament (single strand) or polyfilament (multiple strands). Polyfilament sutures can exhibit less shape memory and more friction than monofilament sutures, thus rendering a conventional knot made from polyfilament suture relatively more resistant to slippage than a conventional knot made from monofilament suture. 
     However, monofilament sutures (sutures made from one strand) are preferred in many applications. One such application is arthroscopy, where a surgeon accesses the surgical area through a hollow tube known as a cannula. In arthroscopy, the surgeon passes a suture through the cannula to the tissue. Conventional arthroscopy tools do not permit the direct passage of a polyfilament suture, as the polyfilament suture is too flexible. Thus, to use a polyfilament suture, the surgeon must first pass a monofilament suture (“feeder line”) first, and then pull the polyfilament suture through the tissue using the monofilament suture. Cumulatively, the extra steps of first passing monofilament sutures can undesirably add a significant amount of time to a surgical procedure and can increase the trauma and anesthesia risk endured by a patient. Surgeons also prefer monofilament sutures in situations where a wound site may be contaminated. In those situations, monofilament sutures can lessen the risk of infection. 
     One drawback to monofilament sutures is that knots tied with monofilament sutures can slip and become untied more readily than polyfilament suture. Monofilament suture has a smoother exterior surface than polyfilament suture and thus exhibits less friction to prevent a knot from slipping. Monofilament suture also tends to exhibit more “memory,” i.e., monofilament suture has a greater tendency to return to a previous form, such as an untied form. 
     Prior techniques to improve the security of a knot made from a monofilament suture have proven inadequate. One prior technique includes tying a knot with extra throws to reduce the tendency of the knot to slip. Extra throws, however, disadvantageously increase the bulk of a suture, consume extra time to process, and require extra space, which is not always available. 
     Additionally, proper knot tying techniques are not always followed. For example, through inadvertence or inexperience, the disfavored and easily loosened “Granny knot” can be accidentally tied instead of a “Square knot,” which is a relatively more secure knot. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention advantageously improve the security of knots. Surgical knots tied in accordance with an embodiment of the present invention can be tied with fewer throws, in less time, with more security, and with more resistance to incorrectly tied throws. According to one embodiment, a monofilament knot in arthroscopy can advantageously combine the resistance to slippage of a polyfilament suture and yet retain the advantage of not requiring the extra step of passing a feeder line. 
     One embodiment of the present invention places the ends of a knot in contact with each other and fuses the ends together with heat. The extraneous end portions of the suture are then cut, leaving the fused portion behind to prevent the knot from slipping. Preferably, the fused portion is about 3 millimeters (mm) long. The heat can be advantageously applied in a liquid environment, such as inside a human body. 
     Another embodiment of the present invention applies heat to the limbs of the knot such that the limbs deform. The deformation renders the knot more resistant to slippage. Again, the heat can be applied within the liquid environment of a human body. 
     Another embodiment of the present invention applies heat to the last throw of the knot. The last throw of the knot already has strands in contact with each other. The applied heat fuses the strands together and inhibits the tendency for the knot to loosen through slippage. The heat can again be applied within a liquid environment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the invention will now be described with reference to the drawings summarized below. These drawings and the associated description are provided to illustrate preferred embodiments of the invention, and not to limit the scope of the invention. 
     FIG. 1 illustrates a conventional Square knot. 
     FIG. 2 illustrates a Granny knot. 
     FIG. 3 illustrates 4 half-hitches with reversed throws. 
     FIG. 4 illustrates 4 half-hitches with no alteration between throws. 
     FIG. 5 illustrates a 3-throw Square knot. 
     FIG. 6 illustrates a 5-throw Square knot. 
     FIG. 7 illustrates the conventional Square knot with tails placed in contact. 
     FIG. 8 illustrates the conventional Square knot with tails fused. 
     FIG. 9 illustrates the conventional Square knot with tails trimmed. 
     FIG. 10 illustrates an embodiment of the invention that can anneal the tails of a suture knot. 
     FIG. 11A illustrates a tip of an annealing element. 
     FIG. 11B illustrates another tip of the annealing element. 
     FIG. 12 illustrates an embodiment of the invention that can anneal the last throw of a suture knot. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Although this invention will be described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art, including embodiments which do not provide all of the benefits and features set forth herein, are also within the scope of this invention. Accordingly, the scope of the present invention is defined only by reference to the appended claims. 
     The following definitions and explanations provide background information pertaining to the technical field of the present invention. Additional definitions are provided throughout the detailed description. 
     Glossary of terms: 
     limb: The ends of a suture are known as limbs. One limb is a post, and the other limb is a loop. 
     post: The end (limb) of the suture that the knot is tied around. 
     loop: The end (limb) of the suture that forms the knot by looping around the post. 
     ears or tails: The ends of the suture after the knot is complete and the limbs are cut. 
     throw: An at least 360-degree wrapping or weaving of two limbs. A throw is also known as a half-hitch. A knot is a combination of at least two throws. 
     suture: In the art, the term “suture” may refer to either the tissue-sewing material or the “stitch” formed by that material. 
     A surgical suture or stitch is created by forming a tight loop around the tissue with suture material and tying a knot. The knot maintains the tension on the suture so that the suture loop can hold the tissue together. There are an almost endless variety of knot configurations. Generally, the variety of knots can be split into two categories: non-sliding knots and sliding knots. 
     FIG. 1 illustrates an example of a suture tied with a conventional non-sliding knot known as a Square knot  100 . The Square knot  100  includes a first throw  102  and a second throw  104 . Both the first throw  102  and the second throw  104  shown are made by looping the limbs of the suture 360 degrees. To make the knot “square,” the second throw  104  is wrapped in the opposite rotational direction to the first throw  102 . The Square knot  100  includes a first tail  106  and a second tail  108 . If and when the Square knot  100  slips, the first and the second tails  106 ,  108  are drawn into the knot. Slippage itself is an undesirable trait and when severe enough, the knot fails by becoming untied. Well-known variations of the Square knot  100  include knots such as the friction or the surgeon&#39;s knot, where the first throw  102  makes a 720-degree wrap. 
     FIG. 2 illustrates an example of a suture tied with a disfavored non-sliding knot known as a Granny knot  200 . The Granny knot  200  is disfavored because it is notorious for slippage. The Granny knot  200  slips and becomes untied at a lower tension than the Square knot  100 . The Granny knot  200  is constructed by rotating a first throw  202  and a second throw  204  in the same rotational direction. The Granny knot  200  is usually not an intended configuration, but rather, the result of an error. 
     FIGS. 3 and 4 are examples of conventional sliding knots. A sliding type of knot can be used when access to the environment is limited, such as in arthroscopy. A surgeon can pass the suture through a cannula and into tissue, then tie a sliding knot with the suture external to the body, then slide the knot down to the tissue, and then trim off the excess suture. FIG. 3 illustrates a four half-hitch knot  300 , where the throws (the half-hitches) alternate directions between throws. FIG. 4 illustrates a four half-hitch knot  400 , where the throws share a common direction. The four half-hitch knots  300 ,  400  are formed by throwing a half-hitch loop  302 ,  402  around a post  304 ,  404  four times to form the knot. After the knot is completed, the knot is pushed or pulled down the post  304 ,  404  to the tissue. 
     One conventional technique used to improve the resistance to slippage of a knot is to use extra throws. FIGS. 5 and 6 illustrate knots with extra throws. FIG. 5 illustrates a Square knot formed with 3 throws  500 . FIG. 6 illustrates a Square knot formed with 5 throws  600 . Although additional throws can increase the resistance of a knot to slippage, the additional throws disadvantageously increase the bulk of the suture and require extra time. Furthermore, the extra space required to accommodate the extra throws is not always available. 
     A method according to one embodiment of the present invention can simply, quickly, and efficiently reduce the tendency for knots to slip without increasing the bulk of the suture. After a knot has been tied, portions of the ends of the knot are brought into contact with each other and fused together with heat. 
     The Square knot  100 , described in connection with FIG. 1, will be used to illustrate the principles of the method described. It will be understood by one of ordinary skill in the art that the method can apply to all types of knots. A non-exhaustive list of types of knots includes: Square knots, Granny knots, Revo Knots, Half-Hitch knots, Duncan knots, Roeder knots, Lieurance Modified Roeder knots, and Tennessee Slider knots. 
     FIG. 7 illustrates the Square knot  100  with the first and the second tails  106 ,  108  brought into contact with each other in a first region  702 . Preferably, the first region  702  is close to the knot  100 . Following an application of heat to the first region  702 , the first and second tails  106 ,  108  fuse together in the first region  702  and form a fused portion  802 , as shown in FIG.  8 . After the fusing operation is complete, the surgeon trims off the excess suture material in the remainder of the first and the second tails  106 ,  108  distal to the fused portion  802 , as shown in FIG.  9 . Of course, part of the trimmed material can include part of the fused portion  802 . In one embodiment, a length of the fused portion  802  is approximately 3 millimeters (mm). 
     In one embodiment, the method is performed on the suture while the suture is submerged in a liquid environment, such as underwater. Such liquid environments exist, for example, within a human body. An added concern for the performance of the method in liquid is the relative increase in heat capacity and heat conductivity of a liquid, such as water, as compared to the heat capacity and heat conductivity of air. If adequate care is not taken to protect the surrounding tissue from the heat, tissue damage may result. 
     Of course, the temperature used to fuse the suture can vary with material, thickness, duration of application of heat, etc. In one embodiment, the temperature of an annealing (heating) device is set to about 99 degrees Centigrade (C) during the fusing procedure for a 0 PDS-II Polydiosanone suture material from Ethicon, Inc. 
     Applicants have verified the efficacy of the method by experiment. Four different knot configurations were tested, two of which were prepared in a conventional manner and the other two prepared in accordance with an embodiment of the invention. Each group consisted of twenty identically prepared sutures, each of which was tied from the same fresh batch of the 0 PDS-II Polydiosanone suture material (a synthetic monofilament) referenced above. For added consistency, each suture was tied around a caliper and presented a circumference of approximately 128.81 mm prior to test. 
     In the two groups where the tails of the sutures were annealed and fused, the sutures were placed in one-liter of Lactate Ringer solution at room temperature. The tails of the sutures were clamped and then annealed and fused. An Orotec ORA-50 Electrothermal Generator and a TAC-C Electrothermal probe, set at a temperature of 99 degrees C. and a power setting of 40, provided the heat for the annealing and fusion operation. The TAC-C Electrothermal probe was applied to the clamped tails while the clamped tails were immersed in the solution to anneal and fuse the tails. 
     The sutures were tested to failure with an Instron Model 8521 materials testing machine configured to measure ultimate tensile strength. The failure load data provided in Table 1, below, is in Newtons (N). Table 1 summarizes test results of the groups of knots. 
     
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Annealing 
                 Failure 
                   
                   
               
               
                   
                   
                 and 
                 Load 
                 Standard 
                 Failure 
               
               
                 Group 
                 Knot Type 
                 fusion? 
                 (N) 
                 Error (N) 
                 Mechanism 
               
               
                   
               
             
             
               
                 1 
                 4 half-hitches 
                 yes 
                 77.505 
                 1.775 
                 breakage 
               
               
                 2 
                 5 Square knots 
                 no 
                 88.965 
                 1.687 
                 breakage 
               
               
                 3 
                 3-throw 
                 no 
                 34.115 
                 2.976 
                 slippage 
               
               
                   
                 Square knots 
               
               
                 4 
                 3-throw 
                 yes 
                 78.210 
                 1.723 
                 breakage 
               
               
                   
                 Square knots 
               
               
                   
               
             
          
         
       
     
     Clearly, the suture knots in Groups  1 ,  2 , and  4  exhibit relatively more strength than the suture knots in Group  3 . Group  2  suture knots, which conform to the 5-throw suture knot described in connection with FIG. 6, are examples of conventional suture knots that use extra throws for enhanced security. Suture knots from Group  2  break, rather than slip. 
     Suture knots from Group  1 , which conform to the four half-hitch knot  300  described in connection with FIG. 3 with the addition of the annealing and fusing of tails, also resisted slippage. The half-hitch knots used in Group  1  are typically resistant to slippage even without the annealing and fusion of the tails. The test results for Group  1  indicate that a secure conventional suture knot, such as that formed with a 4 half-hitch knot, is not weakened by the annealing and fusion of the tails. 
     The suture knots in Groups  3  and  4  conform to the 3-throw Square knot  500  described in connection with FIG.  5 . The tails for the suture knots from Group  4  were additionally annealed and fused in accordance with an embodiment of the invention. The conventional 3-throw Square knot used in Group  3  failed due to slippage at a relatively insecure average of 34.115 Newtons (N). By contrast, the 3-throw Square knots, with annealing and fusion of the tails used in Group  4 , did not fail until the sutures broke at a relatively secure average of 78.210 N. Significantly, the Group  4  knots would slip until held by the annealed and fused tails, at which point the knots tightened up until the sutures broke. 
     In another embodiment of the present invention, the tails of a knot, such as the first and the second tails  106 ,  108  of the Square knot  100 , are annealed without fusing. The heat applied from the annealing textures the surface of the suture tails. As a result, the friction coefficient of a monofilament suture can increase and the security of a knot is enhanced. 
     Another embodiment advantageously anneals and fuses the top-most throw (the last throw made) of a knot. The strands of a suture knot are already in contact with each other in the knot, thus avoiding the need to bring two strands into contact with each other to fuse the strands into one strand. 
     FIG. 10 illustrates one embodiment of the invention. An annealing element  1002  performs annealing and fusing to the tails of the suture and a cutter  1040  trims the excess lengths of the tails after annealing and fusion. The annealing element  1002  and the cutter  1040  shown in FIG. 10 are long and thin instruments suitable for passage through a hollow tube such as a cannula used in arthroscopy. The cutter  1040  contains a hollow cavity  1042  such that the annealing element  1002  can pass through the cutter  1040 . 
     The annealing element  1002  includes a tip  1004  located at a distal end of the annealing element  1002 . The tip  1004  of the annealing element  1002  heats and fuses the tails of the suture without excessive heating of the liquid environment. FIG. 11A illustrates the tip  1004  of the annealing element  1002  in greater detail. The tip  1004  includes a channel  1010  with a distal opening  1012  and a proximal opening  1014 . The channel  1010  is a hollow tubular structure with a cross sectional area adapted to receive both tails of the suture. A cross section of the channel  1010  can be circular, elliptical, rectangular, or a variety of other shapes. In one embodiment, a path length of the channel  1010 , as measured from the distal opening  1012  to the proximal opening  1014  is 3 mm. 
     FIG. 11B illustrates an alternative embodiment of an annealing tip  1100 . The annealing tip  1100  couples to the annealing element  1002  and the annealing tip  1100  includes a channel  1102  with a first opening  1104 . The suture tails are fed through the first opening  1104 , through the channel  1102  of the annealing tip  1100 , out through a second opening  1110 , and through a chamber  1108  in the annealing element  1002 . The channels  1010 ,  1102  can take the form of tunnels, grooves or cutouts. 
     When the surgeon has positioned the first opening  1104  near to the suture knot, the surgeon can activate a heat source to anneal the portion of the suture tails in the channel  1102 . A cutting tip  1106 , preferably about 3 mm from the first opening  1104 , cuts the excess length of the suture tails. The cutting tip  1106  can be located in the channel  1102 , the chamber  1108 , or in-between. In one embodiment, the surgeon rotates the cutter  1106  such that a sharp edge of the cutter slices the excess length of the suture tails. It will be understood that the cutter  1106  includes other forms of cutters that are well known in the art. 
     The channel  1010  is preferably formed within a material with a relatively high amount of thermal conductivity. In one embodiment, the channel  1010  is formed from stainless steel. The channel  1010  is thermally coupled to a heat source. One example of a heat source is a coil of Nichrome resistance wire, which heats in response to an application of electrical current. The coil of Nichrome wire can be wrapped around the channel  1010  to provide uniform heating. Conventional wires can electrically couple a power source for the Nichrome wire from a connector located at the proximal end  1006  of the annealing element  1006 . 
     The power source can be a Direct Current (DC) source or an Alternating Current (AC) source and is preferably configurable to activate for a selectable momentary duration and a selectable power level. In one embodiment, the power level is controlled by adjusting a DC current limit of a current limit circuit within the power source. The current can be switched on and off by, for example, a MOSFET or bipolar transistor. The power source can be powered off of standard AC wiring or by batteries. 
     The tip may further include a heat sensor, such as a negative or positive temperature coefficient resistor, to provide the power source with a feedback of the annealing temperature. In one embodiment, the electrical components of the tip are electrically insulated from exterior surfaces of the annealing element  1002  such that a patient does not encounter a shock hazard. For example, a ceramic insulator such as alumina disposed between the channel  1010  and the heat source can provide electrical isolation and yet allow the heat source to transfer heat to the channel  1010 . To further enhance electrical safety, the exterior surfaces of the annealing element  1010  (including the interior surface of the channel) can be tied to an electrical ground. One embodiment of the annealing element  1002  is substantially watertight so as to permit the submersion of at least a portion of the annealing element  1002  in liquid. 
     The remainder of the tip  1004  is preferably formed from a material that is relatively resistant to temperature and has a relatively low amount of thermal conductivity. A relatively low amount of thermal conductivity is preferred to limit the amount of heat transferred to the liquid environment. In one embodiment, the remainder of the tip  1004  is constructed from Teflon®, which is a trade name for polytetrafluoroethylene (PTFE). In another embodiment, only an exterior surface of the tip  1004  is insulated by the material resistant to temperature with a low thermal conductivity. 
     Typically, the tails of a knot in arthroscopy are quite long such that the surgeon can tie the knot outside the body and slide the knot down to the tissue. After the suture has been tied by the surgeon, the surgeon inserts the tails of the knot into the distal opening  1012  and out of the proximal opening  1014 . The surgeon then slides the annealing element  1002  and the cutter  1040  down the cannula to the suture knot. The surgeon can manipulate the annealing element  1002  through the cutter  1040  or by grasping a proximal end  1006  of the annealing element  1002 . Of course, a proximal end  1046  of the cutter  1040  or the proximal end  1006  of the annealing element  1002  can include grips and handles to facilitate handling. 
     Upon reaching the suture knot, the surgeon activates the heat source within the tip  1010 , which anneals and fuses the tails. The surgeon then slides the cutter  1040  such that a sharp edge  1044 , mounted at a distal end of the cutter  1040 , cuts the excess length of the tails. The surgeon then withdraws the excess length of the tails, the annealing element  1002 , and the cutter  1040 . 
     In one embodiment, the application of heat from the channel  1010  to the suture tails is set low enough such that fusion of the suture tails does not occur. However, the heat provided is high enough to impart a surface texturing for the suture tails. The surface texturing of a monofilament suture can advantageously increase the friction coefficient of the suture tails such that the security of the knot is enhanced. 
     FIG. 12 illustrates another embodiment of the invention. The annealer  1200  again includes a long thin structure to allow the annealer  1200  to pass through a cannula to tissue. A proximal end  1202  of the annealer  1200  connects through conventional wires  1204  to an electrical power source  1206 . The wires pass through an interior cavity of the annealer  1200  to a heating element  1208 . The heating element  1208  can be a Nichrome wire. The heating element  1208  is located in a tip  1210  of the annealer  1200 . In one embodiment, the tip  1210  is integrated with the structure of the annealer  1200 . The bulk of the tip  1210  can be insulated with Teflon® to limit inadvertent heating of the liquid environment. 
     A heating surface  1212  of the tip is thermally coupled to the heating element  1208  and applies heat to the top-most (last tied) throw of a suture knot. Preferably, the heating surface is constructed from a material with a relatively high amount of thermal conductivity, such as stainless steel. The heating surface  1212  can include a small portion of the area of the end of the tip, or the heating surface  1212  can include the entire area of the end of the tip. The heating surface  1212  can also feature a flat, concave, or convex shape to adapt to various shapes of knots. 
     Various embodiments of the present invention have been described above. Although this invention has been described with reference to these specific embodiments, the descriptions are intended to be illustrative of the invention and are not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.