Abstract:
Apparatus for increasing the span length of a bone staple, which includes two prongs connected by a system which provides a mechanical advantage to facilitate bringing the prongs closer together or further apart. One prong includes a staple receptor. The other prong includes a cam-like head such that when the prongs are brought together the staple span length of a staple in the receptor increases. Alternatively, the two prongs are disposed for mounting a staple. When the prongs are pushed apart the staple span length increases. The present invention also relates to a bone staple formed of a shape-memory alloy and an apparatus associated with the staple. The apparatus deforms the staple by increasing its span length and facilitating its insertion into bone tissue. The deformation range of the staple allows the staple to revert to its original shape when the temperature is changed.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to staples for bone fixation, formed of shape-memory-alloys (SMA) and other biocompatible metals and alloys. The present invention relates in particular to SMA staples of adjustable length spans. 
     BACKGROUND OF THE INVENTION 
     Titanium-nickel, shape-memory alloys are biocompatible and resistant to corrosion; therefore, they are suitable for medical applications. These alloys have different phase structures, hence, different mechanical properties, at different temperatures. Information about shape memory alloys may be found, for example, on web site www.nitinol.com, by Nitinol Devices &amp; components, copyright 1998, and in Conference information of “The Third International conference on Shape Memory and Superelastic Technologies Engineering and Biomedical Applications,” held in Pacific Grove, Calif. during Apr. 30-May 4, 2000. 
     FIGS. 1A and 1B, together, schematically illustrate a typical temperature hysteresis, typical elastic stresses, es, in phase transitions, and typical stress-strain curves for a shape-memory alloy in the austenitic and martensitic phases. At a low temperature, the alloy is martensitic, and is soft and plastic, having a low es. At a high temperature, the alloy is austenitic and tough, having a high es. When a martensitic alloy is heated to a temperature A s , the austenitic phase begins to form. Above a temperature A f , the alloy is fully austenitic. Likewise, as an austenitic alloy is cooled to a temperature M s , the martensitic phase begins to form. Below a temperature M f , the alloy is fully martensitic. 
     The temperature-dependent phase structure gives rise to shape memory. At the fully austenitic phase, under proper heat treatment and working conditions, an SMA element can be given a physical shape and “pre-programmed” to memorize that shape and resume it, whenever in the austenitic phase. The “memorized” SMA element may then be cooled to a martensitic phase and plastically deformed in the martensitic phase. But when heated back to the austenitic phase is will resume its memorized shape. The transformation temperature between the phases is noted as TTR. 
     The reason for the shape memory is found in the phase structure of the alloy. Most metals deform by atomic slip. Dislocations and atomic planes slide over one another and assume a new crystal position. In the new position, the crystal has no memory of its order prior to the deformation. With increased deformation, there is generally a work-hardening effect, in which the increased tangle of dislocations makes additional deformation more difficult. This is the case even when the increased deformation is in the direction of restoring the crystal to its original shape. However, for shape memory alloys, both transitions between the austenitic and martensitic phases and deformation in the martensitic phase change lattice angles in the crystal, uniformly for the whole crystal. The original austenitic lattice structure is “remembered” and can be restored. 
     FIG. 1C schematically illustrates typical phase structures of a shape-memory alloy, as functions of temperature and deformation, as follows: 
     in the austenitic phase, the crystal has a cubic structure, and the atoms in the lattice are arranged generally at right angles to each other; 
     when the austenitic crystal is cooled to a martensitic phase, a twinned lattice structure is formed; 
     when the twinned martensitic crystal is deformed by an amount no greater than δ, the twinned structure is “stretched” so that the atoms in the lattice are arranged generally at oblique angles to each other, wherein the oblique angles are determined by the amount of deformation; and 
     when the deformed martensitic crystal is heated, the crystal resumes its cubic structure, wherein, again, the atoms in the lattice are arranged generally at right angles to each other. 
     Another property that can be imparted to SMA elements, under proper heat treatment and working conditions, is super-elasticity, or Stress-Induced Martensite (SIM). With this property, a fully austenitic SMA element, at a temperature above A f , will become martensitic and plastic under high stress, and deform under the stress. When the stress is removed, the SMA element will return to the austenitic phase and to its memorized shape in the austenitic phase. Super-elasticity is also referred to as rubber-band like property, because the SMA element behaves like a rubber band or a spring, deforming under stress and resuming its original shape when the stress is removed. However, this property is present only above the temperature A f , and only when it is specifically imparted to an SMA element, by proper heat treatment and working conditions. 
     FIG. 1D schematically illustrates a typical cyclic transformation of a super elastic alloy, at a constant temperature above the temperature A f . The transformation between the austenitic phase and a stress-induced martensitic phase is brought about by stress and is eliminated when the stress is removed. 
     It should be emphasized that both full shape memory and stress-induced superelasticity occur as long as the deformation is no greater than δ, and with greater deformations the crystal structure will be damaged. 
     Staples and clamps for bone fixation of fractures, formed of shape-memory alloys, are known. They are easily inserted in a martensitic phase, when deformed to an open, straightedge state, and they resume a closed, clamped state in the body, thus forming a closure on the fracture. 
     Basically, there are two approaches to working with SMA elements for bone fixation. In accordance with the first approach, the elements are fully martensitic at room temperature and are deformed and inserted into the bone when at room temperature. After insertion, the elements are locally heated to about 42-45° C., a temperature above A f , and transform to the austenitic shape, resuming their memorized austenitic shape. The staples then cool down to body temperature, which is generally below A f , although still above M s . Thus, in the body, the SMA elements remain austenitic and retain their austenitic shape. The advantage of this approach is that the SMA elements need not be cooled in order to remain in the martensitic phase, prior to insertion. The disadvantages, however, are that the mechanical properties of the SMA elements are not uniquely defined at body temperature, and that the SMA elements are not super-elastic in the body. 
     In accordance with the second approach, A f  is designed below body temperature. The SMA elements are cooled to 0-5° C., or lower, to a temperature below their M f  temperature, for deformation and insertion into the bone. Upon insertion, the elements are naturally heated to body temperature, by contact with the body only. Since body temperature is above A f , the elements transform to the austenitic phase and resume their memorized austenitic shape. The advantages of this approach are that, in the body, the SMA elements are fully austenitic, their mechanical properties are defined, and if properly heat-treated, they are super-elastic. The disadvantage, however, is that plastic deformation in the martensitic phase must be performed after the elements are cooled, and the deformed SMA elements must remain cooled during procedure manipulation and insertion. 
     The publication, “Use of TiNiCo Shape-Memory Clamps in the Surgical Treatment of Mandibular Fractures,” by Drugacz J., et al., American Association of Oral and Maxillofacial Surgeons, 0278-2391/95/5306-0006, describes a study in which clamps made of Ti 50 Ni 48.7 Co 1.3 , memorized to resume their shape at body temperature, were used to fix mandibular fractures. Seventy-seven patients with mandibular single or multiple fractures were treated, using 124 clamps. In 72 of the 75 patients, the treatment progressed satisfactorily, and only in five cases, infections occurred. The study concluded that the application of shape-memory clamps for surgical treatment of mandibular fractures facilitated treatment and ensured stable fixation of the bone fragments. There was no observation of pathologic tissue reaction to the clamps. 
     SMA staples are commercially avialable from MEMOMETAL Industries, of Cedex, France, as well as from Medical Engineering Center, Siberian Physics &amp; Technical Institute, Tomsk, Russia, and from DePuy International Ltd., a Johnson &amp; Johnson company, in Leeds, England, and DePuy France S.A., Cedex, France, as well as from other companies. Generally a range of shapes and sizes are offered by each company. 
     U.S. Pat. No. 4,665,906 to Jervis describes medical devices that incorporate stress-induced martensite alloy elments. Generally, the steps involved in the use of these devices are: 
     deforming a medical device into a deformed shape different from a final shape, by the formation of stress-induced martensite; 
     restraining the deformed shape by the application of a restraining means; 
     positioning the medical device and restraining means within, or in proximity to, the body; 
     removing the restraining means; 
     isothermally transforming the device from the deformed shape into the final shape. 
     Methods and apparatus for adjusting the length spans of bone staples are known. For example, U.S. Pat. No. 4,841,960 to Garner describes a staple whose web, or central portion, can be crimped by a pliers-like crimping device, thus shortening its length. However, this method is inappropriate for SMA elements, since the deformation will not be maintained in the austenitic shape, in the body; rather, the SMA elements will resume their memorized shape. 
     SUMMARY OF THE INVENTION 
     It is an aim of the present invention to provide apparatus and method for adjusting the length spans of SMA staples for bone fixations, prior to their insertion into the bone. 
     There is thus provided, in accordance with the present invention, apparatus for increasing a length span of a staple, which includes: 
     proximal and distal ends with respect to a user, which define a z-axis of an x;y;z coordinate system between them; and 
     first and second prongs, joined by a system which provides a mechanical advantage to selectably bringing said first and second prongs together and pushing them apart, 
     wherein said first prong further includes, at said distal end, a staple receptor, with a channel, for mounting said staple thereon, said channel defining an x-axis of the x;y;z coordinate system, parallel to said staple length span, and perpendicular to the direction of bringing first and second prongs together and pushing them apart, 
     wherein said second prong further includes, at said distal end, a thin, cam-like head, having a width span that increases in the direction of increasing y, operable to increase said staple length span, 
     and wherein, as said first and second prongs are brought together, said thin, cam-like head is arranged to slide between said staple receptor and said staple, mounted thereon, so as to wedge between said staple receptor and said staple and increase the length span of said staple. 
     Further in accordance with the present invention, said apparatus includes a mechanical stopping component, for controlling the amount by which said first and second prongs are brought together, hence, the length-span increase to said staple. 
     Additionally, in accordance with the present invention, said apparatus includes a gauge, for measuring the amount by which said first and second prongs are brought together, hence, the length-span increase to said staple. 
     Further in accordance with the present invention, said system which provides a mechanical advantage to selectably bringing said first and second prongs together and pushing them apart is a swivel pin. 
     Alternatively, said system which provides a mechanical advantage to selectably bringing said first and second prongs together and pushing them apart is a threaded bolt. 
     Alternatively, said system which provides a mechanical advantage to selectably bringing said first and second prongs together and pushing them apart is a pulley. 
     Further in accordance with the present invention, said staple is formed of an SMA alloy. 
     Additionally, in accordance with the present invention, said staple has an initial length span of 6 mm, wherein said apparatus is arranged for increasing said length span to a value between 6 and 10 mm. 
     Alternatively, said staple has an initial length span of 10 mm, wherein said apparatus is arranged for increasing said length span to a value between 10 and 14 mm. 
     Alternatively, said staple has an initial length span of 14 mm, wherein said apparatus is arranged for increasing said length span to a value between 14 and 18 mm. 
     Alternatively, said staple has an initial length span between 3 and 100 mm, wherein said apparatus is arranged for increasing said length span by an amount between 0 and 10 mm. 
     There is thus provided, in accordance with an alternative embodiment of the present invention, apparatus for increasing a length span of a staple, which includes: 
     proximal and distal ends with respect to a user; and 
     first and second prongs, joined by a system which provides a mechanical advantage to selectably bringing said first and second prongs together and pushing them apart, 
     wherein said first and second prongs further include, at said distal end, tips, arranged for mounting said staple thereon, when said prongs are brought together, 
     and wherein, as said first and second prongs are pushed apart, said tips pry said staple, mounted thereon, wider, thus increasing the length span of said staple. 
     There is thus also provided, in accordance with the present invention, a method of increasing a length span of a staple, which includes the steps of: 
     employing prongs which define a z-axis of an x;y;z coordinate system, generally parallel with their longitudinal axis; 
     mounting the staple on a staple receptor, which is arranged on the first prong, and which defines an x-axis of the x;y;z coordinate system, parallel with a length direction of the staple; and 
     sliding a thin cam, arranged on a second prong, and having a width which increases in the direction of increasing y, between the staple receptor and the staple mounted thereon, thus wedging the thin cam between the staple receptor and the staple; and 
     plastically deforming the staple, to increase its length span. 
     Further in accordance with the present invention, said step of sliding a thin cam further includes sliding by a predetermined amount, thus predetermining the length-span increase of the staple. 
     Additionally, in accordance with the present invention, the staple is formed of a shape-memory alloy having a fully martensitic phase within a first temperature range, and having a fully austenitic phase within a second temperature range, which is higher than the first temperature range, wherein said step of plastically deforming the staple includes plastically deforming the staple by reversible martensitic deformation. 
     Further in accordance with the present invention, said step of plastically deforming the staple by reversible martensitic deformation includes plastically deforming the staple at a temperature range of the fully martensitic phase. 
     Alternatively, said step of plastically deforming the staple by reversible martensitic deformation includes plastically deforming the staple in a stress-induced martensitic phase at a temperature range of the fully austenitic phase. 
     There is thus also provided, in accordance with the present invention, a method of bone fixation with an SMA staple, which includes the steps of: 
     drilling at least one pair of bores across a fracture interface of a bone; 
     measuring the distance span between the two bores of the bore pair; 
     selecting an SMA staple having a length span which is smaller than the distance span; 
     plastically deforming the staple, to increase its length span; 
     inserting the staple into the bores; and 
     employing the staple in the plastically deformed state, which resulted from the length-span increase. 
     There is thus also provided, in accordance with the present invention, a method of increasing a length span of a staple, which includes the steps of: 
     mounting the staple on two tips that are arranged for receiving the staple when they are brought together; and 
     plastically deforming the staple by prying the tips apart, to increase the length span of the staple. 
     Additionally, said step of plastically deforming the staple by prying the tips apart further includes prying by a predetermined amount. 
     There is thus also provided, in accordance with the present invention, a staple for bone fixation, formed of a shape-memory alloy having a fully martensitic phase within a first temperature range, and having a fully austenitic phase within a second temperature range, which is higher than the first temperature range, which includes: 
     a web having a first length span and a thickness; 
     two bending points, forming the end points of said web; and 
     two semicircular end sections, beginning from said bending points, having a radius of curvature, an angle of curvature that is greater than 90°, and a thickness which is substantially the same as said web thickness, 
     wherein by plastically deforming said staple, reversibly, in the fully martensitic phase, to decrease said angle of curvature to 90°, said semicircular end sections are straightened, to facilitate insertion into the bone, and said length span may be increased to a desired value, 
     and wherein upon transformation to its austenitic shape, said staple generally resumes its original shape, but with a second length span that is greater than said first length span. 
     There is thus also provided, in accordance with the present invention, a method of bone fixation, which includes the steps of: 
     drilling at least one pair of bores across a fracture interface of a bone; 
     measuring the distance span between the two bores of the bore pair; 
     employing a staple for bone fixation, formed of a shape-memory alloy having a fully martensitic phase within a first temperature range, and having a rally austenitic phase within a second temperature range, which is higher than the first temperature range, which includes: 
     a web having a length span; and 
     two semicircular end sections, having angles of curvature that are greater than 90°; 
     plastically deforming the staple, reversibly, in its martensitic phase, to simultaneously decrease said angle of curvature to 90°, thus straightening the semicircular end sections, to facilitate insertion into the bone, and to increase the length span of the web to a desired value; 
     inserting the staple into the bores; and 
     employing the staple in the plastically deformed state, which resulted from the length-span increase. 
     Additionally, in accordance with the present invention, said step of plastically deforming the staple, reversibly, in its martensitic phase, includes plastically deforming the staple at a temperature range of the fully martensitic phase. 
     Alternatively, said step of plastically deforming the staple, reversibly, in its martensitic phase, includes plastically deforming the staple in a stress-induced martensitic phase at a temperature range of the fully austenitic phase. 
     Further in accordance with the present invention, said method further includes plastically deforming the staple to increase the length span to a value which is substantially the same value as the distance span between the two bores of the bore pair. 
     Additionally, in accordance with the present invention, said step of plastically deforming includes plastically deforming to a strain that is less than 15%. 
     There is thus also provided, in accordance with the present invention, a method of bone fixation, which includes the steps of: 
     drilling at least one pair of bores across a fracture interface of a bone; 
     measuring the distance span between the two bores of the bore pair; 
     employing a staple for bone fixation, formed of a shape-memory alloy having a fully martensitic phase within a first temperature range, and having a fully austenitic phase within a second temperature range, which is higher than the first temperature range, which includes: 
     a web having a length span; and 
     two semicircular end sections, having angles of curvature that are greater than 90°; 
     plastically deforming the staple, reversibly, in its martensitic phase, to simultaneously decrease said angle of curvature to 90°, thus straightening the semicircular end sections, to facilitate insertion into the bone, and to increase the length span of the web to a desired value; 
     inserting the staple into the bores; and 
     employing the staple in a partially plastically deformed state, resulting from the length-span increase. 
     There is thus also provided, in accordance with the present invention, a staple for bone fixation which includes: 
     a web having: 
     a length span; 
     a curvature; and 
     a thickness, 
     wherein said staple may be plastically deformed by straightening its curvature, to increase its length span, and wherein the staple is employed in its plastically deformed state. 
     Additionally, said web includes more than one curvature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the accompanying detailed description and drawings, in which same number designations are maintained throughout the figures for similar elements and in which: 
     FIGS. 1A and 1B schematically illustrate a typical temperature hysteresis and typical elastic stresses, es, in phase transitions, for a shape-memory alloy, in accordance with the prior art; 
     FIG. 1C schematically illustrates typical phase structures of a shape-memory alloy, as functions of temperature and deformation, in accordance with the prior art; 
     FIG. 1D schematically illustrates a typical cyclic transformation of a shape-memory alloy, between an austenitic phase and a stress-induced martensitic phase, in accordance with the prior art; 
     FIGS. 2A-2C schematically illustrate staples for bone fixation, in accordance with the present invention; 
     FIGS. 3A-3F schematically illustrate a method of using SMA staples for bone fixation, in accordance with the present invention; 
     FIGS. 4A-4D schematically illustrate apparatus for increasing a length span of a staple, in accordance with a preferred embodiment of the present invention; 
     FIGS. 5A and 5B schematically illustrate apparatus for increasing a length span of a staple, in accordance with a first alternative embodiment of the present invention; 
     FIGS. 6A-6C schematically illustrate apparatus for increasing a length span of a staple, in accordance with a second alternative embodiment of the present invention; 
     FIG. 7 schematically illustrates apparatus for increasing a length span of a staple, in accordance with a third alternative embodiment of the present invention; 
     FIG. 8 schematically illustrates a staple for bone fixation, in accordance with a preferred embodiment of the present invention; 
     FIGS. 9A-9C illustrate, in a table format, the percentage of plastic deformation that is encountered when the curvature of an element is varied, for the staple of FIG. 8; 
     FIGS. 10A and 10B schematically illustrate a staple for bone fixation, in accordance with an alternative embodiment of the present invention; and 
     FIGS. 11A-11C schematically illustrate apparatus for increasing a length span of the staple of FIGS. 10A and 10B, in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to FIG. 2A, which schematically illustrates a staple  10 , in accordance with an embodiment of the present invention. Staple  10  includes a web  12 , legs  14 , clamping portions  16 , and pointed edges  18 . Preferably, staple  10  is used for bone fixation, for example of the maxillofacial or mandibular jawbones or of the hand, the foot, or the skull. However, staple  10  may be used for bone fixation of other bones as well. Preferably, staple  10  is formed of titanium-nickel, shape-memory alloy and is seen in FIG. 2A in an austenitic phase, depicting its memorized shape. 
     Staple  10  may have a length span L from as low as 4 mm to as high as 80 or 100 mm, depending on its application. In accordance with a preferred embodiment of the present invention, length span L is between 4 and 25 mm, and preferably between 6 and 18 mm. Preferably, legs  14  are formed at right angles to web  12  and clamping portions  16  are formed at right angles to legs  14 , parallel to web  12 . 
     Reference is now made to FIGS. 2B and 2C, which schematically illustrate staple  10 , in accordance with an alternative embodiment of the present invention. In accordance with the present embodiment, in its austenitic phase, staple  10  is formed of web  12  of length L, a thickness t, and two semicircular end sections  19 , having a radius of curvature, R, measured as an inner radius plus half the thickness t. The cross-section of staple  10  may be rectangular, as shown. Alternatively, it may be circular, oval, or of another shape. Bending points  13  are the points at which semicircular end sections  19  begin. Values for R may be, for example, between 1.2 and 1.4 mm, and values for t may be between 0.5 and 1.0 mm, for staples of length spans between 6 and 18 mm. Preferably, for staples of other sizes, similar relationships are maintained between L and R, L and t and R and t. In accordance with an alternative embodiment of the present invention, end sections  19  may be elliptical. Semicircular or elliptical end sections  19  have two advantages over clamping portions  16  (FIG.  2 A): 
     1. since there is no 90° corner that is memorized, length span L of staple  10  may be adjusted in the martensitic phase, for example, by moving bending points  13  along semicircular end sections  19 , so as to increase length span L; and 
     2. pointed edges  18  (FIG. 2B) are arranged to dig into the bone when staple  10  resumes its memorized shape. 
     In accordance with other embodiments of the present invention, staple  10  may be asymmetrical, having, for example, one leg  14  (FIG. 2A) that is shorter than the other, or one end section  19  (FIG. 2B) with a different radius of curvature R than the other. Additionally, staple  10  may have more than two legs, for example, three, four, or six legs. In accordance with still other embodiments of the present invention, one or more of legs  14  and clamping portions  16  (FIG. 2A) may coil around an axis defined by legs  14 . Similarly staple  10  may have more than two semicircular end sections  19 . For example, staple  10  may have 3, 4, 5, or 6 semicircular end sections  19 , so as to resemble a crab. In accordance with the present invention, staple  10  may be manufactured by any known process for bone staples, and in particular, any known process for SMA bone staples. 
     Reference is now made to FIGS. 3A-3F, which together schematically illustrate a method of using at least one SMA staple  10  for bone fixation, in accordance with a preferred embodiment of the present invention. Preferably, the method includes the following steps: 
     1. As seen in FIG. 3A, clamping portions  16  (FIG. 2A) or end sections  19  (FIGS. 2B and 2C) are straightened, to form straightedges  30 , in order to facilitate insertion into the bone. Preferably, the straightening plastic deformation is performed while staple  10  is fully martensitic. In accordance with a first embodiment of the present invention, which is the preferred embodiment, SMA staple  10  is fully austenitic at body temperature and is cooled to below room temperature, for example to 0-5° C., or lower, for the straightening deformation in the martensitic phase. In accordance with a second embodiment of the present invention, SMA staple  10  is fully martensitic at room temperature, and is straightened at room temperature. 
     2. As seen in FIG. 3B, at least one pair of bores  50 , and preferably, several pairs of bores  50  are drilled into a fractured bone  38 , having a first fragment  40 , a second fragment  46 , and a fracture interface  36 . Bone  38  has a hard, cortical exterior tissue  42 , and a soft cancellous interior tissue  44 . Each pair of bores  50  includes one bore in bone fragment  40 , and another bore in bone fragment  46 , across interface  36 . A pair of bores  50  has a distance span d between the two bores that form the pair, wherein d depends on the nature of the fracture and the nature of interface  36 . Preferably, a single value of d is used for all pairs of bores  50 . However, d may have a different value for each pair of bores  50 . 
     3. As seen in FIG. 3C, at least one staple  10  with straightedges  30 , and preferably several staples  10  with straightedges  30 , are inserted into bore pairs  50 . Each staple  10  includes length span L which is substantially the same as distance span d between bores  50  that form a pair. In accordance with the prior art, staples  10  must be supplied with a wide range of length spans, to suit different bone fractures. However, in accordance with the present invention, a method for adjusting length span L of staple  10  is described hereinbelow, in conjunction with FIGS. 4A-11C. The method averts the need to provide staples in a wide range of dimensions and allows a manufacturer to provide staples of only two or three standard dimensions for each type of application, wherein the staples can be further adjusted before insertion into the bone. 
     4. As seen in FIG. 3D, staples  10  are fully inserted into bone  38 . 
     5. As seen in a cross-sectional view of bone  38 , in FIG. 3E, staples  10  are inserted so that legs  14  penetrate cortical bone tissue  42  and straightedges  30  protrude from cortical bone tissue  42  into cancellous bone tissue  44 . 
     6. As seen in FIG. 3F, in accordance with the first embodiment of the present invention, in the body, staples  10  warm up to body temperature and become fully austenitic, resuming their memorized shape of FIG. 2A or  2 B, and clamping bone fragments  40  and  46  together. Preferably, staples  10  have been imparted with super-elasticity, so as to provide dynamic osteosynthesis of the bone fragments. In accordance with the second embodiment of the present invention, staples  10  must be locally heated to a temperature above A f  (FIG.  1 A), which may be for example, 42-45° C., for transforming staples  10  to the fully austenitic phase. When fully austenitic, staples  10  resume their memorized shape and clamp bone fragments  40  and  46  together. The memorized shape is maintained in the body, even when body temperature is below A f  (FIG.  1 A). 
     Reference is now made to FIGS. 4A-4D which together, schematically illustrate scissors-like apparatus  60  for increasing length span L (FIGS. 2A-2C) of staple  10 , in accordance with a preferred embodiment of the present invention. As seen in FIG. 4A, apparatus  60  has a proximal end  58  and a distal end  56  with respect to a user (not shown). Apparatus  60  includes a first prong  62  and a second prong  64 , joined by a swivel pin  66 , at a point somewhere between proximal end  58  and distal end  56 , arranged to slide past each other at distal end  56 . Apparatus  60  further includes finger-gripping components  68 , arranged on first and second prongs  62  and  64 , at proximal end  58 , for opening and closing apparatus  60 , thus facilitating the sliding of first and second prongs past each other. Apparatus  60  defines a z-axis of an x;y;z coordinate system, parallel to its longitudinal axis. 
     As seen in FIG. 4B, which illustrates a side view of distal portion  56  and in FIG. 4C, which illustrates an end view of distal portion  56 , first prong  62  further includes a staple receptor  70 , which has a channel  72 , for mounting staple  10  thereon. Channel  72  defines an x-axis of the x;y;z coordinate system, parallel to length span L of staple  10  and perpendicular to the direction of opening and closing of apparatus  60 . 
     Additionally, second prong  64  further includes a thin, cam-like head  74 , having a width span w that increases in the direction of increasing y. Thin, cam-like head  74  is operable to increase length span L of staple  10 . 
     Preferably, as finger-gripping components  68  are moved towards each other, for closing apparatus  60 , thin, cam-like head  74  is arranged to slide between staple receptor  70  and staple  10  mounted thereon, in the direction of increasing y, for a predetermined y value, thus wedging itself between staple receptor  70  and staple  10 , deforming staple  10  to width w of thin, cam-like head  74  at the predetermined y value. 
     Additionally, as seen in FIG. 4D, apparatus  60  includes a mechanical stopping component  54 , for controlling the amount of closure between first and second prongs  62  and  64 , thus predetermining the value of y, and controlling the amount of length-span increase to staple  10 . Preferably, mechanical stopping component  54  includes a first rod  76  with a hook  80 , arranged on one of the prongs, and a second rod  78  with a plurality of notches  82 , arranged on the other prong, generally near proximal end  58 . Each of plurality of notches  82  is arranged to lock with hook  80 . The distance between notches  82  is calculated to yield length-span increases of desired increments, for example, 1 mm or 0.5 mm. By closing apparatus  60  only to a specific notch  82 , a desired length-span increase of staple  10  mounted in channel  72  is achieved. 
     Reference is now made to FIGS. 5A and 5B, which together, schematically illustrate scissors-like apparatus  90  for increasing length span L (FIGS. 2A-2C) of staple  10 , in accordance with a first alternative embodiment of the present invention. As seen in FIG. 5A, apparatus  90  has proximal end  58  and a distal end  96  with respect to the user. Apparatus  90  includes a first prong  95  and a second prong  93 , joined by a swivel pin  66 , at a point somewhere between proximal end  58  and distal end  96 , arranged for closing and opening at distal end  96 . Apparatus  90  defines a z-axis of an x;y;z coordinate system, parallel to its longitudinal axis. 
     In accordance with the present embodiment, first and second prongs  95  and  93  include, at distal end  96 , tips  98 , which include slits  99 , arranged for receiving staple  10  thereon, when apparatus  90  is closed. Tips  98  define an x-axis of the x;y;z coordinate system between them. Tips  98  and slits  99  may be arranged for receiving staple  10  so that its web  12  is parallel with the x-axis and its legs  14  are parallel with the z-axis. Alternatively, tips  98  and slits  99  may be arranged for receiving staple  10  so that its web  12  is parallel with the x-axis and its legs  14  are parallel with a y-axis. 
     Preferably, as seen in FIG. 5B, staple  10  is positioned in slits  99  when apparatus  90  is closed. By opening apparatus  90 , tips  98  pry staple  10  wider, increasing its length span. 
     Preferably, apparatus  90  further includes, at proximal end  58 , mechanical stopping component  54 , for controlling the amount of opening between first prong  95  and second prong  93 , thus predetermining the extent of prying staple  10 , and the incremental length-span increase to staple  10 . 
     Reference is now made to FIGS. 6A-6C, which together, schematically illustrate apparatus  100  for increasing length span L (FIGS. 2A-2C) of staple  10 , in accordance with a second alternative embodiment of the present invention. As seen in FIG. 6A, apparatus  100  has a proximal end  102  and a distal end  104  with respect to the user. Apparatus  100  includes a first prong  106  and a second prong  108 , joined by a bolt  114 , at a point somewhere between proximal end  102  and distal end  104 , arranged for selectably increasing and decreasing the distance between first prong  106  and second prong  108 . Apparatus  100  defines a z-axis of an x;y;z coordinate system, parallel to its longitudinal axis. 
     As seen in FIG. 6B, which illustrates a side view of distal portion  104  and in FIG. 6C, which illustrates an end view of distal portion  104 , first prong  106  further includes a staple receptor  111 , which has a channel  112 , for mounting staple  10  thereon. Channel  112  defines an x-axis of the x;y;z coordinate system, parallel to length span L of staple  10  and perpendicular to the direction of increasing and decreasing distances between first prong  106  and second prong  108 . 
     Additionally, second prong  108  further includes a thin, cam-like head  110 , having a width span w that increases in the direction of increasing y. Thin, cam-like head  110  is operable to increase length span L of staple  10 . 
     Furthermore, second prong  108  includes a through hole  122  and first prong  106  includes a threaded, preferably through hole  120 . Bolt  114  includes a head  116 , a tip  118 , and a threaded portion  124 . Preferably, head  116  is a relatively large knob  116 , arranged to be rotated by fingers of the user. Preferably, bolt  114  is arranged inside through hole  122  and internally thread hole  120 . 
     Thus, as knob  116  is rotated in the direction of threading portion  124  further into threaded hole  120 , the distance between first prong  106  and second prong  108  is decreased, and cam-like head  110  is wedged between channel  112  and a staple  10  mounted thereon, deforming staple  10  to width w of thin, cam-like head  110 . The amount of deformation is determined by the number of turns of knob  116 . Preferably, a gauge  113 , which preferably protrudes from first prong  106  and is arranged to slide in a slit  101  in second prong  108 , or arranged to slide along second prong  108 , helps the user determine the distance between first and second prongs  106  and  108 , and the amount of length increase that is applied to staple  10 . Alternatively, a hand-held gauge, not physically attached to the prongs, may be used. 
     Reference is now made to FIG. 7, which schematically illustrates apparatus  140  for increasing length span L of staple  10 , in accordance with a third alternative embodiment of the present invention. In accordance with the present embodiment, prongs  106  and  108  are manipulated by a rotating knob  130 , to selectably increase and decrease the distance between them. 
     In accordance with the present invention, the method of using any of apparatus  60  (FIG.  4 A), apparatus  90  (FIG.  5 A), apparatus  100  (FIG.  6 A), or apparatus  140  (FIG. 7) is as follows: 
     1. As seen in FIG. 3A, staple  10 , preferably of standard dimensions, having standard web length span L, and straightedges  30  is provided; 
     2. As seen in FIG. 3B, bore pairs  50  are drilled into fractured bone  38 , across fracture interface  36 , wherein each bore pair  50  is associated with distance d between the bores of the pair, and wherein d is equal to or greater than length span L of staple  10 ; 
     3. Where d&gt;L, the surgeon (not shown) will adjust the length span L of staple  10  by increasing it, using any of the aforementioned apparatus; and 
     4. As seen in FIGS. 3C-3E, staple  10  of adjusted length span L, so that L is equal to d, is inserted into bone  38 . 
     In accordance with a preferred embodiment of the present invention, staple  10  may be employed in a plastically deformed state that results from the length-span increase. In other words, the deformed shape that results from the length-span increase is the final shape, and staple  10  may be used to provide bone fixation, while in a stress-induced martensite state. 
     In accordance with a preferred embodiment of the present invention, staples  10  of length spans between 6 and 18 are provided in three length spans, of 4 mm increments, as follows: 
     1. A staple of 6 mm length span L, arranged for length spans between 6 and 10 mm. 
     2. A staple of 10 mm length span L, arranged for length spans between 10 and 14 mm. 
     3. A staple of 14 mm length span L, arranged for length spans between 14 and 18 mm. 
     Alternatively, staples  10  of length-spans between 5 and 30 are provided in five length spans, of 5 mm increments, as follows:ps 
     1. A staple of 5 mm length span L, arranged for length spans between 5 and 10 mm. 
     2. A staple of 10 mm length span L, arranged for length spans between 10 and 15 mm. 
     3. A staple of 15 mm length span L, arranged for length spans between 15 and 20 mm. 
     4. A staple of 20 mm length span L, arranged for length spans between 20 and 25 mm. 
     5. A staple of 25 mm length span L, arranged for length spans between 25 and 30 mm. 
     Alternatively, staples  10  of length spans between 10 and 100 mm are provided in ten length spans, of 10 mm increments, or in 20 length spans of 5 mm increments. 
     Alternatively, other length spans and other incremental increases are provided. 
     Reference is now made to FIG. 8, which schematically illustrates a staple  150 , in accordance with a preferred embodiment of the present invention. In its austenitic shape, staple  150  is similar to staple  10  of FIGS. 2B and 2C. Staple  150  includes web  12  of a length L1, thickness t and two semicircular end sections  19  of a radius R1, measured as the inner radius plus half thickness t. Bending points  13  are the points at which semicircular end sections  19  begin. Values for R1 may be, for example, between 1.2 and 1.4 mm, and values for t may be, for example, between 0.5 and 1.0 mm, for staples of length spans L1 between 6 and 18 mm. 
     In accordance with the preferred embodiment of the present invention, staple  150  is plastically deformed to simultaneously achieve the following: 
     1. form straightedges  30 , to facilitate insertion into the bone; and 
     2. increase length span L1 to a length span L2. 
     This type of plastic deformation can be achieved, for example, by apparatus  90  (FIGS.  5 A and  5 B). 
     Preferably, each semicircular end section  19  has an angle α associated therewith, measured from point  13 , wherein α is generally greater than 90°. Preferably, staple  150  is plastically deformed so that α becomes 90°. When this happens, a new radius of curvature, R2, is generated, and the length span of web  12  increases from L1 to L2. 
     Preferably, the plastic deformation is performed while staple  150  is fully martensitic. In accordance with a preferred embodiment of the present invention, staple  150  is fully austenitic at body temperature and is cooled to below room temperature, for example to 0-5° C., or lower, for the plastic deformation in the martensitic phase. Alternatively, staple  150  is fully martensitic at room temperature, and is plastically deformed at room temperature. Alternatively, staple  150  posses superelasticity and the plastic deformation is performed while staple  150  is fully austenitic, to form stress-induced martensite. 
     In accordance with a preferred embodiment of the present invention, staple  150  may be employed in its plastically deformed state, which resulted from the length-span increase. In other words, staple  150  may be employed to provide bone fixation, while it is in a stress-induced martensite state. 
     In accordance with the preferred embodiment of the present invention, the plastic deformation is maintained within an allowable range for restoration of the austenitic shape, as described hereinbelow. 
     Reference is now made to FIGS. 9A-9C, which illustrate, in a table format, plastic deformation strains, δ, for different ratios R1/t and different initial angle α and a final angle of 90°, for the staple of FIG.  8 . Generally, complete restoration of the austenitic shape occurs when the plastic deformation strain does not exceed 10.4%. Yet, partial restoration of the austenitic shape occurs when the plastic deformation strain does not exceed 15%, which may be considered the allowable limit for plastic deformation. 
     For example, given an R1 value of 1.4 mm and a t value of 0.7 mm, so that R1/t=2.00, and given an initial angle α of 165°, the plastic deformation strain, associated with changing the angle α to 90°, as read from FIGS. 9A-9C, is 10%, well below the allowable limit of 15%. 
     The darkly shaded portion of FIGS. 9A-9C illustrates the allowable operational range for plastic deformation of staple  150 . The lightly shaded portion of FIGS. 9A-9C illustrates the desired operational range of plastic deformation of staple  150 . A special shading is used for values near 2.00, which are generally preferred. 
     It will be appreciated by persons versed in the art, that a similar analysis may be made for a staple of another geometry. 
     Reference is now made to FIGS. 10A and 10B, which schematically illustrate a staple  200 , in accordance with an alternative embodiment of the present invention. Staple  200  is shown with straightedges  30 , in a manner similar to staple  10  of FIG.  3 A. In its austenitic shape, staple  200  includes a web  202 , which has a length span L, at least one curvature  220 , having a radius R1 and an angle α, and an effective web width V. Additionally, staple  200  may have an additional curvature  230 , also having radius R1 and angle α. However, curvature  220  may have different values of R1 and α from those of curvature  230 . Preferably, length span L of staple  200  may be increased by straightening, or partially straightening at least one curvature  220 , or curvatures  220  and  230 . Preferably, staple  200  is formed of a shape-memory alloy, and preferably, straightening includes straightening by plastically deforming web  202 , while maintaining the values of R1 and α, so that the plastic deformation does not exceed 15%, as seen in FIGS. 9A-9C. 
     Preferably, the plastic deformation is performed while staple  200  is fully martensitic. In accordance with a preferred embodiment of the present invention, staple  200  is fully austenitic at body temperature and is cooled to below room temperature, for example to 0-5° C., or lower, for the plastic deformation in the martensitic phase. Alternatively, staple  200  is fully martensitic at room temperature, and is plastically deformed at room temperature. Alternatively, staple  200  posses superelasticity and the plastic deformation is performed while staple  200  is fully austenitic, to form stress-induced martensite. 
     In accordance with a preferred embodiment of the present invention, staple  200  may be employed in its plastically deformed state, which resulted from the length-span increase. In other words, staple  200  may be employed to provide bone fixation, while it is in a stress-induced martensite state. 
     Reference is now made to FIGS. 11A-11C, which schematically illustrate apparatus  210  for increasing length span L of web  202  of staple  200 . In essence, apparatus  210  is similar in construction and operation to apparatus  60  of FIGS. 4A-4D. However, apparatus  210  has a channel  212  of effective width V, arranged to receive staple  200  of effective web width V. 
     In accordance with a preferred embodiment of the present invention, staples  10 ,  150  and  200  are formed of a shape-memory alloy having a fully martensitic phase within a first temperature range, and having a fully austenitic phase within a second temperature range, which is higher than the first temperature range. Preferably, plastically deforming the staple includes plastically deforming the staple by reversible martensitic deformation. 
     Preferably, plastically deforming the staple by reversible martensitic deformation includes plastically deforming the staple at a temperature range of the fully martensitic phase. 
     Alternatively, plastically deforming the staple by reversible martensitic deformation includes plastically deforming the staple in a stress-induced martensitic phase at a temperature range of the fully austenitic phase. 
     It will be appreciated by persons skilled in the art, that the scope of the present invention is not limited by what has been specifically shown and described hereinabove, merely by way of example. Rather, the scope of the invention is limited solely by the claims, which follow.