Abstract:
A method and apparatus for making armed sutures has a pair of opposed die assemblies that may be driven by actuating surfaces of a swaging machine to hold and swage a needle on a suture. The dies grip and confine the needle in the area of the suture receptacle. A pair of opposed swaging elements with offset stakes insert through passageways in the dies and impinge on the captured needle making a plurality of indentations in the needle barrel and gripping the suture in the suture receptacle. The indentations are offset and aligned generally in alternating peak-to-valley relationship, causing the suture receptacle and the contained suture to assume a serpentine configuration. The stakes and the resulting indentations can be dimensioned to result in a converging suture receptacle, which exhibits increasing shear force being exerted on the suture with increasing depth into the suture receptacle. The apparatus and method permit reliable suture-needle attachment over a larger range of tolerances, such that a single die setup can be used on a plurality of needle and suture materials. The resulting product exhibits a serpentine suture/needle attachment interface with reliable attachment and smooth outer dimensions.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a divisional of U.S. patent application Ser. No. 11/601,077, filed Nov. 17, 2006 now U.S. Pat. No. 7,814,630. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to apparatus and methods for attaching needles to sutures, such as for making armed sutures for surgical application, and more particularly, to methods of attaching surgical needles to sutures using a swaging process. 
     BACKGROUND OF THE INVENTION 
     Various methods for swaging needles to sutures are known. Given a needle of a desired gauge, composition and shape, a hole is formed in one end. The hole extends axially into the needle to constitute a suture receptacle and may be formed by mechanical or laser drilling. The term “needle” as used herein is intended to refer to a surgical needle, such that the term “needle” is intended to be a short form of the term “surgical needle” and is synonymous therewith. Typically, the end of the needle having the suture receptacle could be generally described as being in the form of a hollow cylinder, the diameter of the interior hollow of the cylinder being greater than the outside diameter of the suture to be attached to the needle, providing a clearance for insertion of the suture. To attach the suture, a free end of a suture is slidably, axially inserted into the suture receptacle (hole) in the needle and held in that position while a swage die impinges upon the outer peripheral surface of the needle receptacle (the outer surface of the cylinder), collapsing some or all of the cylinder radialy inwardly, such that the interior dimensions of the suture receptacle are reduced at some portion thereof. The reduced interior dimensions of the needle receptacle grasp the inserted suture end via mechanical interference and by surface contact (friction). Generally, suture material has some degree of deformability/malleability, but there are limits to same, which, when exceeded, lead to suture material failure. Similarly, there are limits (albeit generally less problematic) to the malleability/deformability/elasticity of needle materials. In swaging, it is desirable to preserve a smooth and continuous exterior needle surface in the area of the suture receptacle. Out of round conditions or sharp edges produced by swaging can increase the drag that the needle experiences when passing through the tissue being sutured, injure the tissue and/or unnecessarily enlarge the hole in the tissue made by the needle as it is passes through the tissue during use. Manufacturing artifacts that protrude from the surface of the needle in the swaging area, (such as “fins”) sometimes occur when the swaging is conducted by a pair of dies which abut one another in the compressed position of a swaging operation. Sharp edges transverse to the axial direction are also sometimes produced by swaging processes at the transition from the uncompressed to the compressed/deformed swaged area of the needle. One approach that has been utilized to provide good suture attachment and smooth outer surfaces in the swaged area is multiple hit swaging, wherein a needle is subjected to swaging of controlled depth, but distributed over a larger area, viz., around the circumference of the needle. To achieve this type of swaging, the needle is rotated (repositioned relative to the swaging dies between multiple swaging compressions. In this manner, multiple angularly offset swaging operations (hits) are performed to attach a single needle to a single suture. While this produces good results, the apparatus used is more complex and expensive than single hit swaging apparatus and the process takes longer. Yet another approach is to use confined stake swaging, wherein the suture receptacle end of a needle to be swaged is inserted between a pair of mating holding dies which, when compressed together, define a substantially cylindrical cavity that grips the needle securely, but does not deform the needle, i.e., the holding dies do not swage the needle. After being gripped by the holding dies, a suture is inserted into the suture receptacle in the needle. One or more elongated swaging elements with one or more staking points (stakes or nibs) slidably extend through the holding dies in mating channel(s) provided therein. When the swaging operation is conducted, the stake(s) are driven into the needle and deform the receptacle end of the constrained needle, such that the needle grips the suture. The holding dies insure that the outer periphery of the needle is supported to allow the stakes to deform the needle in a very localized area without otherwise deforming the receptacle end of the needle. Two adjacent stake swages may be employed to produce two adjacent, inwardly extending dimples/indentations that protrude into the needle receptacle area to capture the suture between the dimples and interior surface of the suture receptacle to grip the suture therebetween. The result is a double stake swaged needle with a pair of indentations but no protrusions, out of round areas or sharp ledges formed as a consequence of swaging. 
     While double stake swaging produces good results, the process requires a high degree of precision, in particular when used to swage needles to monofilament sutures and to sutures that are made from materials that are sensitive to being pinched off or clipped by the inwardly converging dimples. For example polypropylene is less deformable/malleable than other suture materials, e.g., nylon and tends to be clipped off when subjected to excessive pinching pressure/shear forces. Precision in the formation of the needle diameter, needle hole (and resultant wall thickness), suture diameter, and depth of penetration of the stake swage dies all must be closely controlled to prevent excessive shear force on the suture, while insuring adequate force to provide secure attachment. The precise setup will typically vary for each type of suture/needle combination, requiring reconfiguration of the swaging apparatus for each different product run. During production, testing is used to insure that adequate needle pull-off strength is achieved. Since insuring effective attachment without compromising suture integrity adds significantly to the cost of armed suture production, it remains an objective to make the process easier, more efficient and effective. 
     SUMMARY OF THE INVENTION 
     The problems and disadvantages associated with conventional armed sutures and the apparatus and techniques utilized to manufacture them are overcome by the present invention, which includes a swaging apparatus driven by a swaging machine with a pair of actuating surfaces that selectively converge to exert pressure and diverge to release pressure on the swaging apparatus for attaching a needle to a suture. The needle has a suture receptacle at one end for receiving the suture, which is retained therein by swaging. The swaging apparatus includes a die assembly with a needle aperture, which slideably accommodates the needle. The die assembly has a plurality of a swage passageways therein communicating with the needle aperture and extending through the die assembly at a plurality of radial orientations relative to the needle aperture. A plurality of swaging elements are insertable into corresponding ones of the plurality of swage passageways, each of the swaging elements having an end with at least one stake. At least one of the stakes on a first swaging element is longitudinally offset relative to the stakes on the remainder of the plurality of swaging elements. 
     A method in accordance with the present invention for attaching a needle having a suture receptacle at one end to a suture, includes inserting the suture receptacle end of the needle into a die which surrounds the needle at the receptacle end and inserting a suture into the suture receptacle. The needle is then indented in the area of the suture receptacle, forming a first indentation at a first longitudinal position and a first radial orientation. The needle is also indented in the area of the suture receptacle to form a second indentation at a second longitudinal position and a second radial orientation. The first and second indentations are longitudinally and radially offset and deform the suture at least some portion of its length to approximate a reverse curve. 
     An armed suture made in accordance with the present invention has a needle with a suture receptacle at one end and a suture retained in the suture receptacle by a plurality of indentations in the needle wall disposed around the suture receptacle. The plurality of indentations include a first indentation in the needle wall and a second indentation in the needle wall longitudinally and radially offset from all other indentations of said plurality of indentations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a pair of opposed swaging dies in accordance with an embodiment of the present invention in three stages of use. 
         FIG. 2  is a cross-sectional view of one of the swaging dies of  FIG. 1  taken along section line II-II and looking in the direction of the arrows. 
         FIG. 3  is a perspective view of an end of one of the swaging dies of  FIGS. 1 and 2 . 
         FIGS. 4 and 5  are perspective views of the swage dies of  FIGS. 1-3  abutted and with the stake swage extended and retracted, respectively. 
         FIG. 6  is a cross-sectional view of an armed suture where the needle is attached to the suture by aligned, opposed stake swaging and by single stake swaging. 
         FIG. 7  is a cross-sectional view of a needle held in the swage die of  FIGS. 1-5 . 
         FIG. 8  is a cross-sectional view of a needle that has been swaged in accordance with the present invention. 
         FIG. 9  is a cross-sectional view of an armed suture where the needle is attached to the suture by offset stake swaging in accordance with the present invention. 
         FIG. 10  is a cross-sectional view of the armed suture of  FIG. 7  taken at an orientation substantially perpendicular to that of  FIG. 7 . 
         FIG. 11  is a side view of a needle that has been staked in accordance with an embodiment of the present invention. 
         FIG. 12  is a cross-sectional view of an armed suture where the needle is attached to the suture by offset stake swaging in accordance with the present invention. 
         FIG. 13-17  are graphs of pull strength performance for five different sets of armed suture samples made in accordance with the present invention, with  FIG. 15  also illustrating comparative results produced by another swaging method. 
         FIGS. 18 and 19  are diagrams illustrating certain dimensions of swaging stakes and the resultant indentations in a needle barrel formed thereby which may be used to quantify and predict suture compression and shear force. 
         FIG. 20  is a perspective view of a swaging die in accordance with an alternative embodiment of the present invention. 
         FIG. 21  is a perspective view of a die holder holding the swage die of  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a needle swaging assembly  10  having first and second swage dies  12   a ,  12   b  in three different states of compression A, B, and C. Each of the swage dies  12   a ,  12   b  have a substantially identical structure, such that only the swage die  12   a  on the left hand side of  FIG. 1  will be described. The reference numbering convention used, viz., reference numbers for identical elements of the two swage dies are the same except for a different subscript letter, indicates this commonality in structure and function. The present invention does not require identical or mirror-image swage dies  12   a ,  12   b , however. Swage die  12   a  has a needle holder  14   a  and a needle stop  16   a , which, when acting is conjunction with the corresponding parts  14   b ,  16   b  of swage die  12   b , retain and support a needle N (a fragment of which is shown in phantom) to be attached to a suture by swaging. Both the needle holder  14   a  and the needle stop  16   a  are carried by a die support  18   a  which is attached to a conventional tool holder assembly of a swaging machine (not shown). Swaging machines conventionally utilize a mechanism, such as a cam or a hydraulic or pneumatic ram/cylinder acting either directly or through a lever arm to urge opposing dies towards one another for the purpose of impinging upon a needle to be swaged. The support  18   a  could therefore be adapted to be held by a tool holder of known swaging apparatus using techniques known to one normally skilled in the art. The swaging machine will have at least one surface that articulates relative to another surface, which may be stationary or articulating to conduct swaging. In the present application, pressure plates  26   a ,  26   b  which represent surfaces of the swaging machine that converge forcefully to actuate the swaging assembly  10 . Swaging die  12   a  has a pair of springs or resilient blocks of elastomeric material  22   a  and  24   a  which urge the needle holder  14   a  and the pressure plate  26   a  apart and allow a swaging element  28   a  to assume a retracted position. The pressure plate  26   a , may overcome the force exerted by the springs  22   a ,  24   a  to act upon stake  28   a  which extends through the interior of the needle guide  14   a  to impinge on the needle N during swaging, as shall be further described below. 
     In  FIG. 1 , the swage dies  12   a ,  12   b  are shown oriented in the horizontal direction, but could equally well be oriented vertically or in any other orientation, as long as they are opposed to one another and their respective movement is approximately along the same axis, such that they converge when compressed and diverge when uncompressed. Each of the needle holders  14   a ,  14   b  has a semi-cylindrical groove  29   a ,  29   b  for holding a needle therebetween when the dies  12   a ,  12   b  are urged together, the grooves  29   a ,  29   b  when conjoined, approximating a cylinder. The needle stop  16   a  has a limited range of freedom of motion along the axis of swage die movement relative to support  18   a , which is delimited by the clearance between a keyway  30   a  in the support  18   a  and a mating key  32   a  projecting downwardly from the needle stop  16   a , which is received in keyway  30   a . The clearance permits the needle stop  16   a  to “float” relative to die support  18   a  allowing the needle holders  14   a ,  14   b  to assume positions: (i) to allow insertion of a needle therebetween, (ii) to support the needle during swaging and (iii) to permit removal of the needle after swaging. As shall be seen below, the needle guide  14   a  is fixedly keyed or otherwise mechanically conjoined, e.g., by threaded fasteners, to the needle stop  16   a  to prevent relative movement therebetween.  FIG. 1  shows three positions A, B and C for the first and second swage dies  12   a ,  12   b . In the first position, swage dies  12   a ,  12   b  are separated and the springs  22   a ,  24   a ,  22   b ,  24   b  are expanded, such that driven ends  40   a ,  40   b  ( FIG. 2 ) of the swaging elements  28   a ,  28   b  extend beyond the rear surfaces of the needle holders  14   a ,  14   b . In the second position B, the swaging machine has exerted an inward compressive force on the swage dies  12   a ,  12   b  (via pressure plates  26   a ,  26   b ) pushing them towards each other, such that the semi-cylindrical needle grooves  29   a ,  29   b  are brought into contact to form a cylinder for grasping a needle N. In position B, the springs, e.g.,  22   a ,  22   b , are still expanded. In position C, the swaging machine has exerted pressure via pressure plates  26   a ,  26   b  to compress the springs  22   a ,  24   a ,  22   b ,  24   b  and to urge the swaging elements  28   a ,  28   b  inwardly towards the needle N held in the semi-cylindrical needle grooves  29   a ,  29   b.    
       FIG. 2  shows a cross-sectional view of swage die  12   a  wherein the swaging element  28   a  is visible in a slot  31   a  formed in the needle holder  14   a . The driven end  40  of the swaging element  28   a  is enlarged and is received in corresponding keyway  41   a , which limits its movement in the forward direction. As described above, the needle stop  16   a  has a key way  34   a  for receiving a key  36   a  extending from the bottom surface of the needle guide  14   a . (The key  36   a  is just visible behind the swaging element  28   a .) Key  32   a  extends from the bottom of the needle stop  16   a . The swaging element  28   a  has a pair of points or stakes  38   a  which are driven into the needle to be swaged. In  FIG. 2 , the swaging element  28   a  is in the retracted position, such that the stakes  38   a  do not extend into the semi-cylindrical needle groove  29   a . When in the extended position, the stakes  38   a  intrude into the groove  29   a . Needle funnel portion  42   a  conjoins with a corresponding needle funnel portion  42   b  to form a conical taper that facilitates the insertion of a needle into conjoined abutting needle grooves  29   a ,  29   b , which form a cylindrical receptacle for the needle N. 
       FIG. 3  shows the end of swage die  12   b  with its semi-cylindrical needle groove  29   b  and needle funnel portion  42   b . The needle stop  16   b  has a V-shaped suture groove  47   b  which guides the suture S into a suture receptacle SR in the needle N. Since the suture groove  47   b  has different dimensions than the semi-cylindrical needle groove  29   b , a ledge  48   b  is formed relative to the needle groove  29   b , against which the end of the needle N abuts, delimiting the position of the needle N when it is held in the dies  12   a ,  12   b . When conjoined, the swage dies  12   a ,  12   b  hold the needle N and the suture S in alignment to permit the insertion of the suture S into the suture receptacle SR of the needle N. 
       FIG. 4  illustrates the abutment of the first and second swage dies  12   a ,  12   b  whereby the semi-cylindrical needle grooves  29   a ,  29   b  of the needle holders  14   a ,  14   b  conjoin to form a substantially cylindrical receptacle  45  for receiving a needle N. The stakes  38   b  of the swaging elements  28   b  are visible through the cylindrical receptacle  45  between the swage dies  12   a ,  12   b . In  FIG. 4 , the stakes  38   b  are extended into the cylindrical receptacle  45 , whereas in  FIG. 5 , the swaging elements  28   b  and the stakes  38   b  are in the retracted position. 
       FIGS. 6   a  and  6   b  illustrate two prior art methods of swaging, namely single-sided, multiple indentation swaging ( FIG. 6   a ) and double-sided, aligned swaging ( FIG. 6   b ), which retain a suture S within a suture receptacle SR of a needle N. In single-sided swaging, the suture S is inserted into the suture receptacle SR of the needle N, and at least one stake point is driven into one side of the needle N in the suture receptacle SR region, deforming the wall W and creating a depression D 1 . The depression D 1  causes the wall W of the needle N to impinge upon the suture S within the needle receptacle, creating a pressure point P 1  between the depression D 1  and the opposing portion for the needle wall W. One or more additional indentations D 2  can be made to create additional pressure points, e.g. P 2 . As an alternative, if two opposed stakes are utilized, the points of which are aligned opposite to one another, two depressions D 3  and D 4  are made in the wall W of the needle N, creating a pressure point P 3  between the two depressions D 3 , D 4 . In either case, the suture is retained in the needle by virtue of the impingement of a small portion of the needle wall W on a correspondingly limited area of the suture S. As a result, the shear force exerted at pressure points P 1 , P 2  or P 3  is focused on a very limited area of the suture S. In order to create sufficient holding force, depressions D 1 , D 2 , D 3 , D 4  must protrude inwardly to an extent that grasps the suture S with sufficient force. The focused pressure at P 1 , P 2 , P 3  creates shear stress which may result in fracturing of the suture, leading to suture detachment. To avoid exceeding the shear stress limits of the suture material, the dimensions of the suture receptacle SR, the thickness and deformability (material dependent) of the wall W, the depression depth of depressions, e.g., D 1 , (all degrees of precision that are difficult and expensive to achieve and maintain), must be carefully controlled. 
       FIG. 7  shows the needle swaging assembly  10  with first and second swage dies  12   a ,  12   b  converging to hold a needle N for swaging. The needle N is gripped between needle holders  14   a ,  14   b  and abuts against needle stops  16   a ,  16   b  with the suture receptacle SR aligned with the suture grooves  47   a ,  47   b . Insertion of the needle N between the needle holders  14   a ,  14   b  is facilitated by needle funnel portions  42   a ,  42   b . The suture funnel  44  aids in threading the suture S through the suture grooves  47   a ,  47   b  and into the suture receptacle SR. Swaging elements  28   a ,  28   b  are slideably received in and articulate in corresponding slots  31   a ,  31   b  such that the stakes  38   a ,  38   b  thereof, respectively, can impinge upon the needle N. In  FIG. 7 , the swaging elements  28   a ,  28   b  both feature a plurality of stakes  38   a ,  38   b . The stakes  38   a  are laterally offset relative to the stakes  38   b  such that when the swaging elements  28   a ,  28   b  are urged together during the swaging operation, the needle N will be swaged to create a serpentine configuration in the suture receptacle SR. A greater or lesser number of stakes  38   a ,  38   b  may be utilized, ranging from one stake  38   a ,  38   b  on each swaging element  28   a ,  28   b , up to any selected number of stakes  38   a ,  38   b . The height, spacing and shape of the stakes  38   a ,  38   b , as well as the relative lateral offset of stakes  38   a ,  38   b  on opposing swaging elements  28   a ,  28   b , may be selected to adjust swaging and suture attachment strength. 
       FIG. 8  shows the generally S-shaped or serpentine configuration of the suture receptacle SR and enclosed suture S resulting from offset swaging conducted in accordance with the present invention. The sheer force experienced by the suture S at any given point X along the suture-needle interface is graphically illustrated. As can be seen by the graph in the lower portion of  FIG. 8 , the shear force increases from left to right starting at X I , to a maximum at X M  and then drops off at the end X E  of the suture S within the suture receptacle SR. This illustrates a recognition of the present invention that the shear force can be affected, distributed and controlled by a number of factors, namely the depth of the indentation made by the stakes, e.g.  28   a , the radius of curvature of the stakes, and the relative spacing of the stakes. For example, indentations  56  and  62  have radii of curvature R 1 , R 2  respectively, which are approximately equal, as are the depth of penetration of the depressions  56 ,  62 , viz., D 1  and D 2 , respectively. (The depth of penetration can be expressed relative to the central axis of the needle and/or the outer peripheral surfaces P 1 , P 2 .) The distance between depressions, N 1 , N 2 , etc. in conjunction with the radius of curvature, depression depth and relative lateral offset are adjustable parameters that may be varied to achieve desired shear and frictional forces. In general, lesser indentation depths, larger radiuses, wider spacing between depressions and peak-to-valley relative lateral offset result in more even distribution of shear forces along the length of the swaged suture-needle interface hence, lower maximum shear force values. Accordingly, greater indentation depths, smaller radiuses, narrower spacing between depressions and peak-to-peak lateral alignment result in greater concentration of shear force at the suture-needle interface. The present invention recognizes that each of these parameters may be varied to control shear force distribution and that such variations along the length of the needle-suture interface and further, gradually increasing shear force with increasing depth into the suture receptacle results in easier, more reliable suture attachment. For example, in  FIG. 8 , R 1  and R 2  are approximately equal, but D 2  is greater than D 1  resulting in an increase in shear force. The distance N 2  is approximately equal to the distance N 1 , however radius R 3  associated with indentation  58  is less than R 1  or R 2  and the depth of penetration D 3  is greater, causing a more severe/focused intrusion into the suture receptacle SR and an increase in shear force. Indentation  64  has an even smaller radius of curvature R 4  and a greater depth of penetration D 4  leading to an even greater shear force. 
     In  FIG. 8 , the indentations  62 ,  64  are laterally offset relative to indentations  56 ,  58 ,  60  such that there is peak-to-valley relative alignment. This is consistent with one of the basic teachings of the present invention, viz., peak-to-valley relative alignment results in greater contact area between needle N and suture S (and hence greater frictional interaction and more even distribution of shear force resulting in greater cumulative force over a greater contact area (suture-needle interface) than peak-to-peak alignment. Moreover, a tortuous, serpentine suture-needle interface requires the entire length of effected suture (in the swaged area) to simultaneously rebend to conform to the serpentine shape under the influence of its frictional interaction with the interior surface of the deformed suture receptacle in order to be pulled from the suture receptacle SR. This contrasts with pulling an otherwise unconstrained suture from a pinch point between two opposed indentation peaks. As can be appreciated, the suture receptacle is deformed by swaging into a converging serpentine space. The present invention recognizes that it is beneficial to gradually increase the shear force area with increasing depth into the suture receptacle SR for two reasons, viz., (1) the increased shear force results in greater surface-to-needle contact and increased frictional interaction between suture and needle; (2) unlike peak-to-peak swaging, the swaged area giving rise to the excessive shear force is not the only area of suture-needle attachment. In the present invention, because the swaged area gradually converges with greater depth into the suture receptacle, the area of greatest sheer force may be exerted deep within the suture receptacle SR such that, even if the maximum sheer force is exceeded at a position far into the suture receptacle, pinching of the suture will not result in suture separation from the needle, in that the swaged areas in shallower regions of the suture receptacle SR are adequate to maintain suture-needle attachment. 
       FIGS. 9-11  illustrate an armed suture made in accordance with the present invention. More particularly,  FIG. 9  shows a needle, N having a plurality of swaged indentations  50 ,  52  and  54  which result in a serpentine suture receptacle SR for grasping the suture S. The indentations were formed by utilizing a first stake with stake points, e.g.,  38   a ,  38   b  that are spaced apart yielding depressions  52 ,  54  that are spaced along the length of the needle in the suture receptacle area. On the opposite side of the needle, a stake with a single stake point was impinged on the needle to create a depression  50  in the wall W of the needle intermediate depressions  52 ,  54 , i.e. in peak-to-valley alignment.  FIG. 10  is a cross section of the needle of  FIG. 9  taken at 90° relative to the view shown in  FIG. 9 . The tops of the indentations  52 ,  54  are visible through the suture S which is translucent, the indentation  50  having been removed in this cross-sectional view.  FIG. 10  shows how a suture S may be deformed by swaging to radially fill the suture receptacle SR in an even manner, whereby the frictional interaction between the suture receptacle SR and the suture S is enhanced.  FIG. 11  shows the exterior of the needle end with the suture S extending therefrom and with the two depressions  52 ,  54  extending into the wall W of the needle N. 
       FIG. 12  shows a suture S retained in suture receptacle SR of needle N. The needle has four alternating indentations  70 ,  72 ,  74 ,  76  made in the wall W of the needle N. The indentations are in peak-to-valley alignment, viz., the peak  75  made by indentation  74  is aligned with the valley  71  between the peaks  77  and  79  associated with depression  70  and  72 , respectively. 
       FIG. 13  shows the process capability of the automated attachment of 3/0 Vicryl suture to laser drilled 26 mil. needles with a suture receptacle having a diameter of 14.5 mils. This diameter was chosen to be in excess of the standard hole size used for producing armed sutures of this type commercially by square swaging methods. More specifically, the established process requires a suture receptacle having a diameter of 12.8 mils to provide adequate pull strength, but has wastage implications due to a significant percentage of failures of the suture to insert into the suture receptacle and “hook-up” or attach after swaging—as determined by pull testing to a limit of 0.9 lbs. Increasing the size of the suture receptacle to 14.5 mils. therefore significantly increases the likelihood of successful suture insertion into the suture receptacle. However, using known swaging methods, such as square swaging, the increase in suture receptacle size would have negative implications on successful needle-suture attachment. A swaging method and apparatus as described above (four stake point, opposed, offset swage staking, e.g., as illustrated in  FIG. 7 ) and in accordance with the present invention was utilized to swage the needles with the oversized suture receptacles and the results graphed in  FIG. 13  were realized. More particularly, given a sample size of 60, a sample mean pull strength of 3.36 lbs. pull strength before separation was achieved, which greatly exceeded the lower spec limit of 0.9 lbs. pull strength. There were no suture attachment failures nor any pull strengths less than the minimum of 0.9 lbs observed. 
     The graph shown in  FIG. 14  illustrates the results obtained with a second sample set of 60 armed sutures, where the swaging (indentation) depth was increased above that utilized in making the sample set of  FIG. 13 . While still below the pinch-off threshold of excessive shear force, the mean pull strength increased to 4.66 with no failures to attach or clip-offs observed and a short term IPQA Cpk of 3.1. 
       FIG. 15  shows two histograms of attachment strength for the same needle/suture combination, viz., 5/0 Prolene suture swaged to a 14 mil. needle with a 6.7 mil. hole but using different swaging techniques. At the top, square swaging results in an overall PPL and Ppk of 1.472. The bottom histogram shows improvement in needle attachment, with a PPL and Ppk of 2.772, indicating an excellent process. 
       FIGS. 16 and 17  show pull strength results for the same needle and off-set swaging process used to generate the results shown in the bottom of  FIG. 14 , but using 6/0 and 7/0 sutures respectively. The use of thinner sutures result in PPL and Ppk values of 2.51 and 1.98, respectively, and mean pull strengths that are far in excess of the lower spec limit. These results illustrate that a swaging apparatus made in accordance with the present invention can be used to swage a range of different sized sutures to a given needle with results exceeding those accomplished by traditional methods. 
       FIGS. 18 and 19 , illustrate various dimensions of the suture, needle, stakes and relative positions thereof that may be used to calculate the spacing between stakes to achieve a specific suture compression ratio and to illustrate generally the relationships between the relevant dimensions and suture compression ratio. More specifically, the following variable names will be used: 
                                           Variable Names                                    Wire (needle) diameter   W d             Suture diameter   S d             Hole diameter   H d             Nib (stake) radius   N R             Initial length, centerline-to-centerline   L I             between neighboring opposed nibs               (before compression)               Wall thickness   W T             Suture compression ratio   C           Suture compression ratio over nib (stake)   C T             Suture compression ratio between opposed,   C b             neighboring nibs (stakes)               Ratio of C b /C T     Ratio           Angle between centerlines of neighboring,    A C             opposed nibs at compression               Angle between centerlines of neighboring,    A I             opposed nibs (before compression)               Lateral (x-direction) spacing between nibs   N S             Length between centerlines of opposed,                adjacent nibs in compressed state   L C                          
The following equations describe certain relationships between the foregoing variables.
 
Relationships
 
               Wall   ⁢           ⁢   Thickness   ⁢           ⁢     W   T       :=         W   d     -     H   d       2           Compression over nib  C   T   :=S   d *(1 −C ) Compression between nibs  C   b :=Ratio· C   T  
 
 N   s :=((2· N   R +2· W   T +Ratio· C   T ) 2 −[2· N   R +2 ·W   T +2·( S   d /2 −S   d   +C   T )] 2 ) 1/2  
 
 A   I   :=a  tan( N   S   /W   d +2 N   R )
 
 L   I   :=[N   s   2 +( W   d +2 N   R ) 2 ] 1/2  
 
 A   C   :=a  tan [ N   S /( W   d +2 N   R −2( H   d   −S   d   +C·S   d ))]
 
 L   C   =[N   S   2 +( W   d +2 N   R −2( H   d   −S   d   +C·S   d )) 2 ] 1/2  
 
 C   b   =L   c −2 N   R −2[( W   d   −H   d )/2]
 
     The following are examples to illustrate the use of the foregoing relationships to calculate selected values. 
     Example 1 
     Given: 
     Wire Dia W d :=0.026 
     Suture Dia S d :=0.01255 
     Hole Dia H d :=0.0157 
     Nib Radius N R :=0.003 
     Suture Compression Ratio C:=10%; then 
     Nib Spacing N s :=0.012″ 
     C b :=0.0098″ 
     C T :=0.0113″ 
     Ratio:=0.8686 
     A c =27.36° 
     Example 2 
     Given: 
     Wire Dia W d :=0.026″ 
     Suture Dia S d :=0.01255″ 
     Hole Dia H d :=0.0157″ 
     Nib Radius N R :=0.003″ 
     Suture Compression Ratio C:=20%; then 
     Nib Spacing N s :=0.012″ 
     C b :=0.0076″ 
     C T :=0.0100″ 
     Ratio:=0.760 
     A c :=30.125° 
     Example 3 
     Wire Dia W d :=0.026 
     Suture Dia S d :=0.01255 
     Hole Dia H d :=0.0157 
     Nib Radius N R :=0.003 
     Suture Compression Ratio C:=26%; then 
     Nib Spacing N s :=0.012″ 
     C b :=0.0063″ 
     C T :=0.0092″ 
     Ratio:=0.6804 
     A c :=32.04° 
       FIG. 20  shows another type of swage die  80  having a needle guide  82  and needle stop  84  similar to that shown in  FIGS. 1-5 , but held in a support  86  by a cap  88  retained to the support  86  by a pair of Allen bolts  89   a ,  89   b  or the like. The needle guide  82  and needle stop  84  are urged away from a ledge  93  of the support  86  by a pair of springs  90 ,  92 , e.g., coil springs. The springs may be inserted into corresponding sockets  94 ,  96  to prevent them from slipping out of position on the ledge  93 . Similar sockets or other spring retaining means (not shown) may be provided on the needle guide  82  and/or the needle stop  84  to retain the springs  90 ,  92 . 
       FIG. 21  shows the swage die  80  of  FIG. 20  held in a needle holder  98 . 
     The present invention, by diminishing the levels of required precision and increasing the tolerances of production, diminishes wastage due to ineffective attachment procedures and increases quality of needle-to-suture attachment. By decreasing the criticality of manufacturing tolerances, it permits use of a common, single hit swaging process and apparatus to attach different types of needles and sutures, e.g., laser, EDM or mechanically drilled needles, fabricated from one or more of a variety of different alloys including ETHALLOY® 4310, 455, and 420 alloys (sold by Ethicon, Inc.), which may be annealed or non-annealed, to various types of sutures, such as braided, twisted, or monofilament sutures made from synthetic or natural materials. By utilizing a die which constrains the needle, ‘bell-mouth’ or ‘fin’ formation defects are eliminated and needle barrel outside diameter remains substantially uniform across the attachment region. The increased tolerances utilized in the set-up and use of the swaging apparatus of the present invention allows operators of every experience level to set-up batches quicker and more consistently when using the same swage die series for all attachment work. The increased tolerance also allow one set of dies to be used on a range of different suture sizes and suture receptacle diameters, eliminating a corresponding multiplicity of more specialized dies.