Abstract:
In accordance with the present disclosure a cartridge for use with a surgical stapler is disclosed. The cartridge has a plurality of individual directionally biased surgical staples therein and associated pushers for ejecting the staples from the cartridge, each of the staples being supported within the cartridge in spaced relation from adjacent staples and each of the staples comprising a backspan, and a pair of deformable legs depending from the backspan. The legs are configured to come into contact with anvil pockets for formation of the staple. Each of the staples has a substantially uniform cross-section along substantially the entire length of each leg, the cross-section includes a shape that is selected from the group consisting of a trapezoid, a triangle and a semicircle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation of, claims the benefits of and priority to U.S. patent application Ser. No. 10/424,606 filed on Apr. 28, 2003, which is a Continuation of, claims the benefits of and priority to U.S. patent application Ser. No. 09/693,379 filed on Oct. 20, 2000, the entire contents of each of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    This invention relates to formable surgical fasteners and, more particularly, to directionally biased formable staples for use in surgical staplers having anvil pockets for forming the staples. 
         [0004]    2. Background of Related Art 
         [0005]    Surgical stapling instruments have become critical to many life saving surgical procedures. Surgical staples are usually mechanically inserted into tissue with surgical stapling instruments such as those known as anastomosis devices, including gastrointestinal anastomosis devices and transverse anastomosis devices. In such devices, the staples are loaded in one or more elongated rows into a cartridge. A mechanism for pushing, or driving the stapler is actuated to drive the staples through two or more sections of tissue toward a deforming anvil. At the conclusion of the driving operation, the legs of each staple are conventionally clamped or bent, by the anvil, to a closed configuration to complete the suture and join the tissue sections together. Gastrointestinal anastomosis-type devices drive and bend the staples aligned in a row sequentially in rapid sequence, while transverse anastomosis-type devices drive and bend all staples simultaneously. See, e.g. U.S. Pat. Nos. 4,520,817 and 4,383,634. Circular anastomosis-type devices simultaneously apply annular rows of staples to tissue. See, e.g. U.S. Pat. No. 4,304,236. 
         [0006]    One type of conventional staple  20 , shown in  FIGS. 1-3 , used with both gastrointestinal anastomosis and transverse anastomosis-type surgical stapling devices is made of stainless steel or titanium. The undeformed staple  20  ( FIG. 1 ) is generally U-shaped and includes a back span  22  and two legs  24  depending substantially perpendicularly from the back span. Each leg  24  has a sharp chiseled end point  26  for piercing body organs or tissue. The chisel point also creates torque in the staple, allowing it to form. The staple penetrates the tissue from one side to engage an anvil spaced apart and located at an opposing side of the tissue. The staple is bent by having the legs engage and follow an anvil  25  to form a B-shaped closed staple  28  as shown in  FIG. 2 . In this closed configuration tissue is compressed between the legs and backspan of the staple. 
         [0007]    Because of their substantially circular cross-section ( FIG. 3 ), these conventional staples require approximately the same amount of force to form the staple into its final shape as is required to twist or malform it. 
         [0008]    For example, referring back to  FIG. 3 , a conventional round cross section staple has a moment of inertia in the x forming dimension (I x ) given by the equation: 
         [0000]        I   x =1/4 —   r   4    
         [0000]    Its moment of inertia in the y twisting dimension (I y ) is given by the same equation: 
         [0000]        I   y =1/4 —   r   4    
         [0009]    Using a round wire stock of uniform 0.009 in diameter (r=0.0045), 
         [0000]    
       
         
           
             
               
                 
                   
                     I 
                     x 
                   
                   = 
                   
                     
                       I 
                       y 
                     
                     = 
                     
                       
                         1 
                         / 
                         4 
                       
                        
                       _ 
                        
                       
                         
                           ( 
                           .0045 
                           ) 
                         
                         4 
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                   
                     3.22 
                     × 
                     
                       10 
                       
                         - 
                         10 
                       
                     
                      
                     
                         
                     
                      
                     
                       in 
                       4 
                     
                   
                 
               
             
           
         
       
     
         [0010]    The Moment of Inertia Ratio, given by the equation: 
         [0000]      is I y /I x   
         [0000]    
       
         
           
             
               
                 3.22 
                 × 
                 
                   10 
                   
                     - 
                     10 
                   
                 
                  
                 
                     
                 
                  
                 
                   in 
                   4 
                 
               
               
                 3.22 
                 × 
                 
                   10 
                   
                     - 
                     10 
                   
                 
                  
                 
                     
                 
                  
                 
                   in 
                   4 
                 
               
             
             = 
             1 
           
         
       
     
         [0000]    In order to insure accurate and consistent formation of these conventional staples, considerable research and development has been conducted in the areas of forming and driving structures. For example, anvils have been developed with specific coatings and/or structure, see, e.g. U.S. Pat. Nos. 5,173,133 and 5,480,089. Also, staple cartridges have been configured with driver structure to balance forces encountered during staple formation. See, commonly assigned U.S. Pat. No. 4,978,049 to Green. Thus, to control and insure consistent staple formation without twisting or deformation, extremely strict manufacturing tolerances have been implemented. 
         [0011]    Other types of staples for different types of instruments are also found in the prior art. Some have non-circular cross-section.  FIGS. 4 ,  4 A and  4 B illustrate by way of example a staple of this type marketed by United States Surgical of Norwalk, Conn. for use with its MULTIFIRE ENDO HERNIA and ENDO UNIVERSAL 65 staplers. The anvil in these staplers, as shown in  FIGS. 4C and 4D , is adjacent the backspan of the staple as tissue is approached from only one side. Unlike the staples described above which are formed by contact of the staple legs with anvil pockets, these staple legs are bent around an anvil abutting the backspan. This staple has a side portion H with a height dimension greater than the dimension of the base portion B (i.e. 0.020 in vs. 0.015 in.). 
         [0012]    The Moment of Inertia Ratio is given by the equation: 
         [0000]    
       
         
           
             
               Moment 
                
               
                   
               
                
               of 
                
               
                   
               
                
               Inertia 
                
               
                   
               
                
               Ratio 
             
             = 
             
               
                 
                   I 
                   y 
                 
                 
                   I 
                   x 
                 
               
               = 
               
                 
                   Moment 
                    
                   
                       
                   
                    
                   of 
                    
                   
                       
                   
                    
                   Inertia 
                    
                   
                       
                   
                    
                   About 
                    
                   
                       
                   
                    
                   Twisting 
                    
                   
                       
                   
                    
                   Axis 
                 
                 
                   Moment 
                    
                   
                       
                   
                    
                   of 
                    
                   
                       
                   
                    
                   Inertia 
                    
                   
                       
                   
                    
                   About 
                    
                   
                       
                   
                    
                   Forming 
                    
                   
                       
                   
                    
                   Axis 
                 
               
             
           
         
       
     
         [0000]    where 
         [0013]    I x =(1/12) bh 3  and I y =(1/12) hb 3 , with h=0.020 in. and b=0.015 in. 
         [0014]    Thus, I x =(1/12)(0.015)(0.020) 3 =1.0×10 −8  in 4 , and 
         [0015]    I y =(1/12)(0.020)(0.015) 3 =6.0×10 −9  in 4 . 
         [0016]    Accordingly, 
         [0000]      Moment of Inertia Ratio=6.01×10 −9  in 4 =0.60/1=0.60 1.10×10 −8  in 4  
 
         [0017]    This staple is specifically configured to accommodate twisting during staple formation to permit the legs of the staple to cross as shown in  FIG. 4E . Thus, it is engineered so the force to form the staple is slightly greater than the force to malform or twist the staple. The forming is accomplished by bending the staple legs around an anvil positioned adjacent the inner surface  32  of the backspan  34 . 
         [0018]    U.S. Pat. No. 5,366,479 describes a hernia staple with adjacent anvil having a height of 0.38 mm and a thickness of 0.51 mm. This staple is formed the same way as in  FIGS. 4C and 4D . The moment of inertia ratio of this staple in accordance with the foregoing formula is as follows: 
         [0000]    
       
         
           
             
               I 
               x 
             
             = 
             
               
                 
                   ( 
                   
                     1 
                     / 
                     12 
                   
                   ) 
                 
                  
                 
                   ( 
                   .51 
                   ) 
                 
                  
                 
                   
                     ( 
                     .38 
                     ) 
                   
                   3 
                 
               
               = 
               
                 2.33 
                 × 
                 
                   10 
                   
                     - 
                     3 
                   
                 
               
             
           
         
       
       
         
           
             
               I 
               y 
             
             = 
             
               
                 
                   ( 
                   
                     1 
                     / 
                     12 
                   
                   ) 
                 
                  
                 
                   ( 
                   .38 
                   ) 
                 
                  
                 
                   
                     ( 
                     .51 
                     ) 
                   
                   3 
                 
               
               = 
               
                 4.2 
                 × 
                 
                   10 
                   
                     - 
                     3 
                   
                 
               
             
           
         
       
       
         
           
             
               Moment 
                
               
                   
               
                
               of 
                
               
                   
               
                
               Inertia 
                
               
                   
               
                
               Ratio 
             
             = 
             
               
                 
                   4.2 
                   × 
                   
                     10 
                     
                       - 
                       3 
                     
                   
                 
                 
                   2.33 
                   × 
                   
                     10 
                     
                       - 
                       3 
                     
                   
                 
               
               = 
               1.8 
             
           
         
       
     
         [0019]    This staple for use as described would actually result in greater force to produce the desired shape. In fact, the staple legs would likely contact each other before crossing over into their crossed configuration. 
         [0020]    Thus, it is apparent that this type of hernia staple, i.e. where the anvil is adjacent the backspan as the tissue is approached from only one side, is quite different than the staple of the present invention, e.g. the B-shaped staple, wherein the legs penetrate through the tissue to contact anvil pockets. These anvil pockets direct the staple legs to form the staple into a closed configuration. Thus staple configuration and considerations of twisting, bending and staple formation of these hernia staples are inapplicable to these considerations for anvil pocket directed staples, such as the B-shaped staples. 
         [0021]    It would therefore be desirable to provide a staple configuration for a staple designed to penetrate tissue and contact an anvil pocket on the opposing side of tissue, which, in complement with conventional cartridge and anvil technology, enhances correct staple formation while reducing twisting/malformation caused by misalignment or unusual tissue while minimizing reliance on strict manufacturing tolerances. 
       SUMMARY 
       [0022]    In accordance with the present disclosure a cartridge for use with a surgical stapler is disclosed. The cartridge has a plurality of individual directionally biased surgical staples therein and associated pushers for ejecting the staples from the cartridge, each of the staples being supported within the cartridge in spaced relation from adjacent staples and each of the staples comprising a backspan, and a pair of deformable legs depending from the backspan. The legs are configured to come into contact with anvil pockets for formation of the staple. Each of the staples has a substantially uniform cross-section along substantially the entire length of each leg, the cross-section includes a shape that is selected from the group consisting of a trapezoid, a triangle and a semicircle. 
         [0023]    In accordance with the present disclosure, a directionally biased surgical staple for use with a surgical stapler is disclosed. The directionally biased staple comprises a backspan having first and second ends and defining a longitudinal axis, and a pair of deformable legs depending from the first and second ends of the backspan. Each of the legs diverging outwardly from the other leg and forming an angle θ with respect to an axis perpendicular to the longitudinal axis of the backspan. The deformable legs have substantially uniform dimensions over substantially their entire length. Each of the legs includes a substantially uniform cross-section along substantially the entire length. The cross-section includes a shape that is selected from the group consisting of a trapezoid, a triangle and a semicircle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Various preferred embodiments are described herein with reference to the drawings, wherein: 
           [0025]      FIG. 1  is a side view of a conventional staple as known in the art; 
           [0026]      FIG. 2A  is a side view of the staple of  FIG. 1  formed into a “B” configuration; 
           [0027]      FIGS. 2B ,  2 C and  2 D illustrate the staple of  FIG. 2  being formed as the legs, after penetrating tissue, come into contact with the anvil pockets; 
           [0028]      FIG. 3  is a cross-sectional view of the staple of  FIG. 1  taken along line  3 - 3 ; 
           [0029]      FIG. 4  is a perspective view of a conventional rectangular cross-section staple as known in the art which is formed around an anvil contacted by the backspan; 
           [0030]      FIG. 4A  is a side view of the staple of  FIG. 4 . 
           [0031]      FIG. 4B  is a cross-sectional view of the staple of  FIG. 4  taken along line  4 B- 4 B; 
           [0032]      FIGS. 4C ,  4 D and  4 E illustrate the staple of  FIG. 4  being formed as the legs are bent by the pusher and the backspan is held against the anvil; 
           [0033]      FIG. 5  is a side view of a directionally biased staple in accordance with the present disclosure; 
           [0034]      FIG. 6  is a perspective view of the staple of  FIG. 5 ; 
           [0035]      FIG. 7  is a top view of the staple of  FIG. 5 ; 
           [0036]      FIG. 8  is a cross-sectional view of the staple of  FIG. 5  taken along line  8 - 8 ; 
           [0037]      FIG. 9A  is a side view of the staple of  FIG. 5  after it has been deformed to a “B” configuration; 
           [0038]      FIG. 9B  is an end view showing the coplanarity of the AB@ sections of the staple of  FIG. 9A ; 
           [0039]      FIGS. 10A  B  10 F are side views showing staple formation of the staple of  FIG. 5  as the staple penetrates tissue and the legs come into contact with the anvil pockets; 
           [0040]      FIG. 11A  graphically illustrates the comparison of the mean twist (in inches) vs the offset of the conventional staple of  FIG. 1  and the novel staple of  FIG. 5 . 
           [0041]      FIG. 11B  graphically illustrates the comparison of the mean twist (in %) vs the offset of the conventional staple of  FIG. 1  and the novel staple of  FIG. 5 ; 
           [0042]      FIG. 12A  is a cross-sectional view of another embodiment of a directionally biased staple in accordance with the present disclosure; 
           [0043]      FIG. 12B  is a cross-sectional view of another embodiment of a directionally biased staple in accordance with the present disclosure; 
           [0044]      FIG. 12C  is a cross-sectional view of another embodiment of a directionally biased staple in accordance with the present disclosure; 
           [0045]      FIG. 13  is a cross-sectional view of another embodiment of a directionally biased staple in accordance with the present disclosure; 
           [0046]      FIG. 14  is a cross-sectional view of another embodiment of a directionally biased staple in accordance with the present disclosure; 
           [0047]      FIG. 15  is a perspective view of an endoscopic gastrointestinal anastomosis-type device for firing the staple of  FIG. 5 ; 
           [0048]      FIGS. 16-16C  are enlarged views showing the staple formation by the anvil pockets of the instrument of  FIG. 15 ; 
           [0049]      FIG. 17  is a perspective view of a gastrointestinal anastomosis-type device for firing the staple of  FIG. 5 ; 
           [0050]      FIG. 18  is a perspective view of a transverse anastomosis-type device for firing the staple of  FIG. 5 ; 
           [0051]      FIG. 18A  is an enlarged view of the staple forming anvil and a portion of the disposable loading unit of the device of  FIG. 18 ; 
           [0052]      FIGS. 18B and 18C  are enlarged views showing the staple formation by the anvil pockets of the instrument of  FIG. 18A ; 
           [0053]      FIG. 19  is a perspective view of a circular anastomosis-type device for firing the staple of  FIG. 5 ; 
           [0054]      FIG. 19A  is an enlarged view of the staple forming anvil and a portion of the disposable loading unit of the device of  FIG. 19 ; 
           [0055]      FIGS. 19B and 19C  are enlarged views showing the staple formation by the anvil pockets of the instrument of  FIG. 19A ; 
           [0056]      FIG. 20  is a perspective view of another embodiment of a directionally biased staple in accordance with the present disclosure; 
           [0057]      FIG. 21  is a cross-sectional view taken along section lines  21 - 21  of  FIG. 20 ; 
           [0058]      FIG. 22  is a front elevational view of the directionally biased staple shown in  FIG. 20  after the staple has been deformed to the B-shaped configuration; 
           [0059]      FIG. 23  is a side elevational view from the direction of lines  23 - 23  of  FIG. 22 ; 
           [0060]      FIG. 24  is a perspective view of an anvil adapted for attachment to an endoscopic gastrointestinal anastomosis-type device; 
           [0061]      FIG. 25  is an enlarged view of the indicated area of detail shown in  FIG. 24 ; 
           [0062]      FIG. 26  is a top partial cutaway view of the anvil shown in  FIG. 24 ; 
           [0063]      FIG. 27  is a cross-sectional view taken along section lines  27 - 27  of  FIG. 26 ; and 
           [0064]      FIG. 28  is a cross-sectional view taken along section lines  28 - 28  of  FIG. 26 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0065]    Preferred embodiments of the presently disclosed directionally biased staple will now be described in detail with reference to the drawings, in which like reference numerals designate identical or corresponding elements in each of the several views. 
         [0066]    A directionally biased staple  50  in accordance with one embodiment of the present disclosure is illustrated in  FIGS. 5-9 . Referring specifically to  FIGS. 5-7 , staple  50  has a U-shaped configuration and includes a pair of substantially parallel legs  52  connected by a crown portion  54  with a bending region  55  therebetween. The legs are shown perpendicular to the backspan and are substantially straight along their length. Tissue penetrating portions  56  are preferably formed adjacent a distal end of legs  52 . These penetrating portions  56  may be of any known configuration which facilitates entry of the legs  52  into tissue to be stapled. As shown in  FIG. 5 , the tissue penetrating portions  56  are preferably formed in a chisel shape with points  58  adjacent inner facing sides of legs  52 . 
         [0067]    In this embodiment, the cross section is preferably formed in a substantially rectangular configuration as shown in  FIG. 8  with x designating the major base dimension (b) and y designating the minor height dimension (h) of the crown portion of the staple when positioned in an inverted-U configuration as shown in  FIG. 5 . As used herein, the staple is intended to be formed about the x dimension (x axis). Thus, as illustrated in  FIGS. 10A-10F  staple  50  is formed downward relative to the page. 
         [0068]    This cross-sectional configuration may be achieved by any known method including extrusion, rolling, coining, etc. Preferably, this configuration is accomplished by flat rolling round wire stock on opposing sides. In the fabrication process, the stock can be pre-rolled by the wire manufacturer or may be round wire stock which is rolled into the desired cross-sectional configuration by the staple manufacturer. 
         [0069]    I y  of the cross-sectional configuration of the novel staple illustrated in  FIG. 5  is given by the equation: 
         [0000]        I   y =(1/12)( b ) 3 ( h ) 
         [0070]    For a base dimension b=0.010 in and a height dimension h=0.008 in, 
         [0000]        I   y =(1/12)(0.010) 3 (0.008) 
         [0000]        I   y =6.67×10 −10  in 4  
 
         [0071]    I x  is given by the equation: 
         [0000]        I   x =(1/12)( b )( h ) 3    
         [0000]        I   x =(1/12)(0.010)(0.008) 3    
         [0000]        I   x =4.26×10 −10  in 4  
 
         [0072]    The Moment of Inertia ratio (I y /I x ) is thus 
         [0000]    
       
         
           
             
               
                 6.67 
                 × 
                 
                   10 
                   
                     - 
                     10 
                   
                 
                  
                 
                     
                 
                  
                 
                   in 
                   4 
                 
               
               
                 4.26 
                 × 
                 
                   10 
                   
                     - 
                     10 
                   
                 
                  
                 
                     
                 
                  
                 
                   in 
                   4 
                 
               
             
             = 
             1.57 
           
         
       
     
         [0073]    Similarly, for a base dimension b=0.012 in and a height dimension h=0.008 in, I x =1.0×10 −9  in 4  and I y =5.12×10 −10  in 4 , yielding a Moment of Inertia ratio of 1.95. 
         [0074]    Given that I y  defines the dimension corresponding to proper formation of the staple when fired and I x  defines the dimension corresponding to twisting and/or malformation, it is readily apparent that the directionally biased configurations provide a “functionally similar” forming force as a conventional round staple while requiring up to twice as much force to twist or malform when compared to conventional staples. This novel staple provides a substantial improvement over conventional staples. 
         [0075]    Table 1 below sets forth by way of example Moment of Inertia Ratios for a variety of sizes and types of novel directionally biased staples for use in surgical staplers. Clearly staples of other dimensions are contemplated so long as they have the novel moment of inertia ratio described herein. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                   
                   
                 I y /I y   
               
               
                   
                   
                   
                   
                   
                 Moment 
               
               
                 Staple 
                 Height 
                 Base 
                   
                   
                 of Inertia 
               
               
                 Size 
                 (in.) 
                 (in.) 
                 I y   
                 I x   
                 Ratio 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 3.5 mm. 
                 .007 
                 .010 
                 5.83 × 10−10 
                 2.86 × 10−10 
                 _ 2.04/1 
               
               
                 Titanim 
               
               
                 3.5 mm. 
                 .007 
                 .0115 
                 8.87 × 10−10 
                 3.29 × 10−10 
                 _ 2.70/1 
               
               
                 Stainless 
               
               
                 Steel 
               
               
                 3.8 mm. 
                 .007 
                 .010 
                 5.83 × 10−10 
                 2.86 × 10−10 
                 _ 2.04/1 
               
               
                 Stainless 
               
               
                 Steel 
               
               
                 4.8 mm. 
                 .009 
                 .014 
                 2.00 × 10−9  
                 8.51 × 10−10 
                 _ 2.35/1 
               
               
                 Titanim 
               
               
                 4.8 mm. 
                 .007 
                 .0115 
                 8.87 × 10−10 
                 3.29 × 10−10 
                 _ 2.70/1 
               
               
                 Titanim 
               
               
                   
               
             
          
         
       
     
         [0076]    Further, as illustrated below, for comparable size staples, the novel staple configuration provides increased resistance to twist without changing firing forces. 
         [0077]    For example, twisting stress  —b , is defined by the equation: 
         [0000]        —b =Mc       Iy
 
with moment M kept constant at M=1lb$in.
         
         [0079]    For a conventional round 0.009 in. diameter staple: M=1 lbs in; c=0.0045 in; and I x =I y =3.22×10 −10  in 4 , so 
         [0000]    
       
         
           
             _b 
             = 
             
               
                 
                   ( 
                   
                     1.01 
                      
                     b 
                      
                     
                         
                     
                      
                     in 
                   
                   ) 
                 
                  
                 
                   ( 
                   
                     .0045 
                      
                     
                         
                     
                      
                     in 
                   
                   ) 
                 
               
               
                 3.22 
                 × 
                 
                   10 
                   
                     - 
                     10 
                   
                 
                  
                 
                     
                 
                  
                 
                   in 
                   4 
                 
               
             
           
         
       
       
         
           
             _b 
             = 
             
               13 
               , 
               975 
                
               
                   
               
                
               ksi 
             
           
         
       
     
         [0080]    For the directionally biased staple of  FIG. 8  having b=0.010 in and h=0.008 in: M=1.0 lb$in; c=0.005 in; and I y =6.67×10 −10  in 4 . 
         [0000]    
       
         
           
             _b 
             = 
             
               
                 
                   ( 
                   
                     1.01 
                      
                     b 
                      
                     
                         
                     
                      
                     in 
                   
                   ) 
                 
                  
                 
                   ( 
                   
                     .0045 
                      
                     
                         
                     
                      
                     in 
                   
                   ) 
                 
               
               
                 6.67 
                 × 
                 
                   10 
                   
                     - 
                     10 
                   
                 
                  
                 
                     
                 
                  
                 
                   in 
                   4 
                 
               
             
           
         
       
       
         
           
             _b 
             = 
             
               7 
               , 
               496 
                
               
                   
               
                
               ksi 
             
           
         
       
     
         [0081]    Thus, not only is this embodiment of the novel staple more resistant to twisting and/or malformation, e.g.  — 14,000 ksi for the conventional staple vs.  — 7,500 ksi for the novel staple, it also maintains minimal firing forces. The directionally biased staple is effectively desensitized against the effects of misalignment during staple formation while, at the same time maintaining a minimal firing force. This directionally intelligent design can reduce malformations caused by misalignment or twisting as well as reduce the need for very sensitive manufacturing tolerances for anvils and anvil forming cups, cartridges, etc. 
         [0082]    The benefits of the novel staple can also be appreciated by reference to the graphs of  FIGS. 11A and 11B . Since staples are forced through thick tissue and the staple cartridge and anvil can flex as tissue is compressed and can move slightly relative to another, this affects the point of contact between the staple leg points and the anvil. For example, if the anvil moves slightly out of alignment, the staple legs will contact a different point of the anvil which can affect uniform formation of the staple. Additionally, due to manufacturing tolerances, the staple points may not contact the anvil in the exact optimal location. Although such staple formation is clinically satisfactory and effective, the novel staple of the present application provides for more uniform formation of the row of staples and accommodates for manufacturing tolerances as it is more resistant to twisting. That is, the staple will have the tendency to bend in the direction of the thinner dimension which is desired since in this case the thinner dimension defines the desired bending direction. By relaxing manufacturing tolerances, the cost of manufacturing is reduced as well. 
         [0083]    As shown in  FIG. 11A , the prior art round staple, since the height and width are the same, can twist in different directions if there is misalignment between the staple and anvil. Thus the direction of twisting cannot be controlled. In contrast, the Moment of Inertia ratio of the novel staple of the present invention results in reduced twisting. Note that not only is there more twisting initially with the prior art staple, but as the offset increases, the amount of twisting in the current staple is greater at any degree of offset. The percentage of twist is defined as x/d x100% wherein x is the distance between the centerline of the staple and d is the diameter (or width) of the staple. 
         [0084]      FIGS. 12-14  illustrate alternate directionally biased cross-sectional configurations in accordance with the disclosure. These cross-sectional configurations all have aspect ratios in the range of about 1.1 to about 3.0 wherein the x axis designates the major base dimension (b) and the y-axis designates the minor height dimension (h) in each of these cross-sections. 
         [0085]      FIGS. 15-19  disclose by way of example several types of surgical staplers which can utilize the novel directionally biased staples. Other types of surgical staplers are also contemplated. 
         [0086]      FIG. 15  illustrates a known endoscopic sequential stapler  100  including an anvil  110  and a staple cartridge  102  having novel directionally biased staples  50  loaded into the staple cartridge  102  thereof. Referring to  FIGS. 16-16C , with anvil  110  and staple cartridge  102  in an open position ( FIG. 16 ), tissue  120  is positioned between anvil  110  and cartridge  102  ( FIG. 16A ). Anvil  110  is now pivoted in the direction indicated by arrow “A” towards cartridge  102  ( FIG. 16B ) in a known manner to compress tissue  120  between anvil  110  and staple cartridge  102 . Thereafter, staples  50  are ejected from staple cartridge  102  into pockets  122  formed on anvil  110 . Pockets  122  deform staples  50  into a substantially B-shaped configuration ( FIG. 16C ). Anvil  110  can now be pivoted to the open position to permit tissue  120  to be removed from stapler  100 . 
         [0087]      FIG. 17  illustrates a known open type sequential stapler  150  including an anvil  152  and a staple cartridge  154  having novel directionally biased staples loaded therein. Ejection of staples from stapler occurs in a manner similar to that disclosed in  FIGS. 16-16C  and will not be discussed in further detail herein. 
         [0088]      FIG. 18  illustrates a known transverse type surgical stapler  200  including an anvil  210  and a staple cartridge  202  having novel directionally biased staples  50  loaded into the staple cartridge  202 . Referring to  FIGS. 18A-18C , with anvil  210  and staple cartridge  202  in an open position, tissue  220  is positioned therebetween ( FIG. 18A ). Anvil  210  is now moved in the direction indicated by arrow “B” to an approximated position towards cartridge  202  ( FIG. 18B ) in a known manner to compress tissue  220  between anvil  210  and staple cartridge  202 . Thereafter, staples  50  are ejected from staple cartridge  202  into pockets  222  formed on anvil  210 . Pockets  222  deform staples  50  into a substantially B-shaped configuration ( FIG. 18C ). Anvil  210  can now be moved to the open position to permit tissue  220  to be removed from stapler  200 . 
         [0089]      FIG. 19  illustrates a circular stapler  300  including an anvil  310  and a staple cartridge  302  having the novel directionally biased staples  50  loaded in the staple cartridge  302 . Referring to  FIGS. 19A-19C , with anvil  310  and staple cartridge  302  in an open position, tissue  320  is positioned therebetween ( FIG. 19A ). Anvil  310  is now moved towards cartridge  302  in a known manner to compress tissue  320  between anvil  310  and staple cartridge  302  ( FIG. 19B ). Thereafter, staples  50  are ejected from staple cartridge  302  into pockets  322  formed on anvil  310 . Pockets  322  deform staples  50  into a substantially B-shaped configuration ( FIG. 19C ). Anvil  110  can now be moved to the open position to permit tissue  320  to be removed from stapler  300 . 
         [0090]      FIGS. 20-23  illustrate another preferred embodiment of the presently disclosed directionally biased staple shown generally as  400 . Directionally biased staple  400  includes a crown portion  410  and a pair of outwardly angled legs  412  with a bending region  414 . Legs  412  define an angle about 5″ to about 15″ with crown portion  410 . Preferably, legs  412  define an angle of about 9″ with respect to crown portion  410 . Alternately, other angle orientations are envisioned. The angle of legs  412  function to retain the staple within staple receiving slots of a staple cartridge prior to use, i.e., legs  412  frictionally engage the slot walls of a staple cartridge to retain the staple within a cartridge slot. Tissue penetrating portions  416  are formed at the distal end of legs  412  and preferably have a chisel shape with points  418  adjacent inner facing sides of legs  412 . Referring to  FIG. 21 , staple  400  has a cross-section having flat top and bottom surfaces  420  and  422  and semi-circular side surfaces  424  and  426 . Preferably, this cross-section is achieved by rolling top and bottom surfaces of wire stock. Alternately, other methods including extrusion and coining may be used to form staple  400 . Using the appropriate formulas, the Moment of Inertia ratio of staple  400  is approximately 2. Alternately, the dimensions of staple  400  may be varied in a manner to achieve a Moment of Inertia ratio within the preferred range of about 1.1 to about 3. 
         [0091]      FIGS. 22 and 23  illustrate staple  400  in the formed state wherein staple  400  assumes a B-shaped configuration.  FIGS. 24-28  illustrate an anvil  500  which is configured for attachment to a transverse-type surgical stapler such as shown in  FIG. 18 . Anvil  500  includes a plurality of staple pockets  510  formed in the surface of the anvil. Each staple pocket  510  includes first and second staple forming cups  512  and  514  and a channeling surface  516  disposed around each of the staple forming cups. An anvil including such a staple forming pocket has been disclosed in U.S. Pat. No. 5,480,089 filed Aug. 19, 1994, the entirety of which is incorporated herein by reference. Anvil  500 , including staple forming cups  512  and  514  and channeling surface  516  can be adapted for use with any of the surgical stapling devices described in the specification above including endoscopic gastrointestinal anastomosis-type devices ( FIG. 15 ), gastrointestinal anastomosis-type devices ( FIG. 17 ), transverse anastomosis-type devices ( FIG. 18 ) and circular anastomosis-type devices ( FIG. 19 ). 
         [0092]    There are various methods of manufacture of the surgical staple. For example, the method could include the steps of flat rolling the wire stock to form at least one flat surface thereon and cutting a length of round wire stock to a predetermined length corresponding to a desired length of a finished staple or extruding the stock with a flat surface. The stock is bent into a form having a backspan and a pair of legs wherein the staple has an aspect ratio of between about 1.1 to about 3.0. 
         [0093]    Although a specific embodiment of the present disclosure has been described above in detail, it will be understood that this description is merely for purposes of illustration. Various modifications of and equivalent structures corresponding to the disclosed aspects of the preferred embodiment in addition to those described above may be made by those skilled in the art without departing from the spirit of the present disclosure which is defined in the following claims, the scope of which is to be accorded the broadest interpretation so as to encompass such modifications and equivalent structures. For example the anvil shown and described in U.S. Pat. No. 5,480,089, the contents of which are incorporated herein by reference, can also be utilized.