Abstract:
The invention pertains to a method and apparatus for delivering an article formed of a shape memory alloy to a surgical implantation site.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to provisional patent Application No. 61/161,604, filed Mar. 19, 2009, the disclosure of which is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Shape memory articles (SMAs), comprised, for instance, substantially of NiTinol alloy, are used in many surgical applications, including use as staples for re-attaching tissue or bone. Usually, external heat is applied to the shape memory article in order to transition it from a first shape in a martensitic, softer, morphology to a second shape in an austentitic, stiffer, morphology. 
         [0003]    When a patient suffers an injury in which tissue or bone must be reapproximated, reattached, or fused, the injury often must be repaired by surgically securing the tissue or bone together with internal fixation devices such as plates, screws, pins, or staples. These devices are often rigid and have geometric features that enable them to reapproximate, reattach, or fuse tissues. Examples of these features include threads, grooves, overall shape of the device, and other features that provide attachment or support. Any undesired deformation of these devices could lead to increased amounts of strain and ultimate failure of the device. 
         [0004]    Since the late 1980&#39;s, NiTinol, a Nickel-Titanium alloy, has been increasingly utilized in a variety of medical devices and, in some cases, has become one of the materials of choice for many designers and engineers. From surgical devices to endoluminal stents and other prostheses, the thermo-mechanical characteristics of the material and its biocompatibility have allowed its use across many medical and surgical specialties both for diagnostic and therapeutic applications. 
         [0005]    The shape memory effect results from a reversible crystalline phase change known as martensitic transformation. Shape memory alloys can display various types of shape memory. The type of shape memory that has probably found the most use in commercial applications is commonly referred to as one-way shape memory. In one-way shape memory, an article formed of a shape memory alloy in an original shape can be substantially plastically deformed into a shape while it is in the soft, martensitic phase and it will remain in that shape, (hereinafter the deformed shape). Then, upon heating above a first temperature, the material returns to its original (prior to deformation) shape while transitioning from the soft, martensitic phase to a much stiffer austentitic phase. It should be noted that, while the article is much stiffer in the austentitic phase, it usually is still somewhat deformable, but primarily elastically, as opposed to plastically, deformable. Upon cooling below a second temperature that is below the first temperature, the material transitions back to the softer, martensitic phase, but maintains the shape it took during the transformation to the austentitic phase (i.e., its original shape) until it is acted upon by an external force or stress. Because the material is less stiff (i.e., more pliable) in its martensitic phase, it is much easier to bend (back to the deformed shape or any other shape) and it will maintain that new shape up to and until it is heated once more above its transformation temperature. 
         [0006]    The strength and transition temperatures of SMAs can be greatly varied by changing the exact composition of the alloy and/or the thermal history of the article. 
         [0007]    The use of shape memory staples in surgical skeletal repair enables a staple to be installed in bone or tissue in one shape while in its martensitic phase and then be heated to cause it to transition to the much stiffer austentitic phase while shifting to another shape that, for instance, draws the tissue or bone closer together. Many medical applications use SMAs having a transition temperature for complete martensitic to austentitic transformation of about 55° C. However, other medical applications utilize alloys having a complete transition temperature at about human body temperature of 37° C. 
         [0008]    While metallic staples have long been used for static fixation, the use of shape memory alloys (SMAs) in staples and their attendant ability to apply dynamic continuous compression is a major advancement in tissue and bone uniting that potentially improves the healing process in connection with the repair, fusing, and remodeling of damaged tissue. These SMA staples are smaller and less bulky than other fixation devices, such as plates, screws, and nails. They permit smaller incisions, which cause less trauma and scarring and lead to faster post-operative recovery. Also, since fewer holes need to be drilled and no screws are needed, more rapid surgical procedures are possible. 
         [0009]    The shape memory properties described hereinabove are sometimes referred to as superelasticity, particularly when the transition from martensitic phase to austentitic phase occurs at lower temperatures, such as room temperature or below. The terminology is not consistent in the art. In this specification, we shall simply use the term shape memory generically as encompassing superelasticity. 
         [0010]      FIG. 1  is a graph showing a dynamic scanning calorimetry (DSC) for one particular NiTinol composition. DSC is useful for determining the temperatures at which various substances undergo phase changes. In the case of NiTinol or other SMA articles, DSC is utilized to understand the temperatures required for transitioning from the martensitic phase to the austentitic phase and back again. DSC measures the heat flow necessary to maintain the article at a certain temperature. The bottom portion of the scan represents the state of the article at −50° C. as it is subjected to increasing temperature over time. This graph shows a stable structure (martensitic morphology) during temperatures up to an austentitic start temperature (A s ) of approximately 29° C., where phase transformation to the austentitic phase theoretically begins. As demonstrated by this scan and the change in heat flow, the metal is fully transformed into its stiff, austentitic phase at the austentitic finish temperature (A f ) of approximately 50° C. The top portion of this scan represents cooling of the austentitic NiTinol article starting at 100° C. Note that the martensitic phase recovery theoretically begins at the martensitic start temperature (Ms) of approximately 19° C. and is complete at the martensitic finish temperature of approximately 0° C. This is only an example of one form of NiTinol shape memory alloy. Other transition temperatures are achievable with different chemical compositions and thermo-mechanical treatments. 
         [0011]    Using the exemplary material above, one can see that the device is geometrically stable in its martensitic phase up to room temperature, can be transformed to an austentitic phase via heating it to around 55° C. and that it stays in a stable austentitic phase down to temperatures well below body temperature. This is very advantageous in surgical applications as devices, such as orthopaedic staples, can be programmed during manufacture with a clinical utility shape in the austentitic phase (the shape that it will take after heating during a surgical procedure) and then be deformed during manufacturing to an operable configuration in its martensitic phase (the shape in which it will be delivered to the surgeon for insertion into the body prior to heating). 
         [0012]    Orthopaedic NiTinol staples have been available clinically in the US for approximately ten years. The manufacturers of these devices are using various instruments and power sources for heating the staples in order to effect the transformation to the austentitic phase in vivo. Tissue cautery and coagulation devices typically are available in an operating theater and are commonly used to provide heat to shape memory articles. 
         [0013]    Shape memory materials typically have a temperature range of about 20° C. over which they make the transformation from the martensitic phase to the austentitic phase. Thus, for instance, a shape memory article designed to complete its transformation to the austentitic phase at body temperature, i.e., about 37° C., will begin transitioning at temperatures as low as 17° C., or at approximately room temperature. 
         [0014]    Thus, shape memory articles, particularly ones designed for body temperature activation often are exposed to temperatures higher than the temperature at which they start the phase change from martensitic to austentitic phase prior to surgery, such as during transportation. Accordingly, shape memory articles often are packaged in the manufacturing plant in a constraining device that prevents them from changing shape until released from the constraining device. 
         [0015]    Once a shape memory article has transformed to its austentitic phase, it can be transformed back to martensitic by exposing the shape memory article to a much lower temperature. In the example above, such a transition temperature back to the martensitic phase would occur at or below (minus) 15° C. thus, immediately prior to surgery, shape memory articles commonly are frozen to return them as fully as possible to their original martensitic phase and delivered to the operating room in a frozen or other cold state, such as in a cooler filled with ice. 
         [0016]    Using a shape memory surgical staple as an example, a surgeon typically might remove the staple from its packaging and constraining device while in its martensitic phase essentially at the time it is needed for implantation. A surgeon typically might grasp the backspan of the staple with a clamp and pull it out of the constraining device. The surgeon might have an extremely small window of time in which to implant the staple into the patient, e.g., into pre-bored holes in a bone, because the staple may start its transformation from the martensitic phase to the austentitic phase almost immediately upon removal from the constraining device. Particularly, operating rooms are commonly maintained at about the austentitic phase transition starting temperature for body temperature activated shape memory articles. 
         [0017]    Even if the operating room is colder than the activation temperature, the surgeon may have to expose the staple to body temperature for a period of time before while he is locating the holes within which the legs of the staple must be inserted, which also could cause the staple to start deforming before it is in the implantation position. 
         [0018]    This can be a significant problem during surgery insofar as, once the staple or other shape memory article begins deforming, then its legs may not match up with the pre-bored holes into which they are to be inserted. In such situations, typically, the surgeon would have to discard the staple and start over with a new staple and move much more quickly. 
       SUMMARY OF THE INVENTION 
       [0019]    The invention pertains to an apparatus for removing a shape memory article, such as a shape memory surgical staple, from its constraining device and delivering it directly to the surgical implantation site while still constraining the shape memory device from deforming until the shape memory device is implanted. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a graphical representation of a dynamic scanning calorimetry for one particular NiTinol composition 
           [0021]      FIG. 2  is a perspective view of a shape memory surgical staple disposed in a constraining device pre-surgically. 
           [0022]      FIG. 3  is a perspective view of a transfer apparatus in accordance with the principles of the present invention. 
           [0023]      FIGS. 4A-4F  illustrate the transfer apparatus of  FIG. 3  in various stages of use. 
           [0024]      FIG. 5  is a perspective view of a transfer apparatus in accordance with another embodiment with a staple partially released therefrom. 
           [0025]      FIG. 6  is a perspective view of a shape memory surgical staple packaged pre-surgically in accordance with another embodiment of the present invention. 
           [0026]      FIG. 7A  is a top perspective view of an alternative embodiment of a transfer apparatus in accordance with the principles of the present invention in a closed condition. 
           [0027]      FIG. 7B  is a top perspective view of the transfer apparatus of  FIG. 7A  in an open condition. 
           [0028]      FIG. 7C  is a bottom perspective view of the transfer apparatus of  FIGS. 7A and 7B . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    As noted above, shape memory staples and other shape memory articles often are packaged in a constraining device so that they do not deform should they be exposed to temperatures higher than the phase transition starting temperature. Nevertheless, shape memory articles must spend some period of time between being removed from their constraining packaging and being fully implanted into bone, tissue, or any other anatomical feature, during which time the article may deform prematurely, which may make it difficult or impossible to implant correctly. 
         [0030]      FIG. 2  shows a shape memory staple  500  comprising a backspan  504  with legs  505   a ,  505   b  extending substantially orthogonally from the opposite ends of the backspan. The staple is disposed with its legs  505   a ,  505   b  extending into passages such as holes  501  and  502  in a constraining device  503  and with its backspan without (i.e., outside of) the constraining device  503 . As long as the staple is disposed with its legs in the holes  501 ,  502  of the constraining device  503 , it essentially cannot deform to any significant extent. 
         [0031]    In order to further prevent or minimize the possibility of the shape memory staple  500  (or other shape memory article) from deforming prematurely after it is removed from the constraining device  503 , but before it is fully implanted, a transfer device is provided such as the exemplary transfer device  506  shown in  FIG. 3 . In accordance with this embodiment, the transfer device  506  includes a wedge formation  510  that provides a ramp running from a minimal height at its front end  510   a  and terminating at a maximum height, H, at its rear end  510   b , as shown in  FIG. 3 . The transfer device  506  further comprises a passage such as groove  521  in a major surface  506   a  of the transfer device  506  having a first portion  521   a  that conforms to the size and shape of the backspan  504  of the staple  500  (at least in terms of the length, L, and the diameter, D, of the backspan  504 ) and second and third portions  521   b ,  521   c  that each conforms to a proximal portion of the legs of the staple. The ends of the second and third portions  521   b ,  521   c  of the groove are open to a second surface of the transfer device so that the distal portions of the legs of the staple may extend from the transfer device from those ends. 
         [0032]    As will be described in detail below, the staple will be secured in the groove  521  from a time prior to removing the staple  500  from the constraining device  503  up until the staple  500  is implanted. Particularly, with reference to  FIG. 4A , when a surgeon is ready to deliver the shape memory staple  500  to the implantation site, the ramp  510  of the transfer apparatus is used to partially pull the legs of the staple out of the holes in the constraining device. Particularly, as shown in  FIG. 4A , the surgeon pushes the ramp  510  of the transfer apparatus  506  in the direction of arrow A between the backspan  504  of the staple  500  and the surface  503   a  of the constraining device  503  against which the staple backspan is abutted so as to force the backspan  504  away from the surface  503   a  up to the height H of the ramp. This terminal height H of the ramp may be equal to or slightly greater than the length of the leg portions of the groove  521  in the transfer apparatus. 
         [0033]    The transfer apparatus is then pulled back out in the direction opposite of arrow A to disengage it from the staple  500  and the constraining device  503 . At this point, after the ramp has been removed, the shape memory staple still essentially cannot deform from its constrained state since the ends of the legs  505   a ,  505   b  are still constrained within the holes  501 ,  502  of the constraining device  503 . Next, the surgeon grasps the transfer apparatus  506  by the ramp portion  510  and forces the groove  521  over the backspan  504  and proximal portions of the legs  505   a ,  505   b  of the staple  500  as shown in  FIG. 4B  to lodge the staple  500  in the groove  521 . 
         [0034]    With reference to  FIG. 3 , in one embodiment of the invention, the groove  521  may have one or more detents  522  to assure that the staple  500  does not inadvertently fall out of the groove after it has been pushed into it. The detents may, for instance, be narrowed portions of the groove formed by one or more protrusions in the groove that make that portion of the groove narrower than the diameter D of the wire from which the staple is formed, which protrusions the staple must be snapped past to become seated within the groove  521 . 
         [0035]    Next, with reference to  FIGS. 4B and 4C , the surgeon can pull the transfer device  506  away from the constraining device  503  in the direction of arrow C (see  FIG. 4B ) to pull the distal ends of the staple legs  505   a ,  505   b  out and completely free of the constraining device  503  ( FIG. 4C ). At this point, even though the distal ends of the legs  505   a ,  505   b  of the shape memory staple  500  are free, the transfer apparatus  506  is constraining the proximal ends of the legs (as well as the backspan  504 ) of the staples, thus still substantially preventing the staple  500  from deforming. 
         [0036]    The transfer apparatus  506  can then be used to hold the staple and deliver the staple to the implantation site. Only after the distal ends of the legs  505   a ,  505   b  have been inserted into the pre-bored holes at the implantation site is the staple  500  released from the transfer apparatus  506 . 
         [0037]    For instance, once the distal ends of the legs are reasonably firmly implanted in the holes, the staples should be relatively stable such that the transfer apparatus can release the staple without inadvertently removing the staple from the holes. If the staple is not sufficiently stable in the implantation holes, the part of the exposed portion of one of the legs of the staple  500  that is extending from the hole but not within the groove  521  of the transfer apparatus  506  can be grasped with a clamp to help stabilize it while the transfer apparatus  506  is snapped off of the staple  500 . The staple can be removed from the transfer apparatus  506  by twisting it about an axis substantially perpendicular to the axes of the legs of the staple. For instance, the transfer apparatus  506  may first be twisted about the axis of one of the legs, e.g., leg  505   a , of the staple (to snap the other leg  505   b  past the detent  522  and out of the transfer apparatus) as illustrated in  FIG. 4D  (with arrow  1201  showing the direction of twisting and axis  1200  showing the axis of twisting. Then, referring to  FIG. 4E , the transfer apparatus  506  may be twisted in the opposite direction (see arrow  1205  showing the direction of twisting) about another axis  1203  substantially parallel to, but not collinear with, the axis  1202  of the first leg  505   a  to snap the first leg  505   a  past the detent  522  and out of the transfer apparatus to completely remove the staple from the transfer apparatus. At this point, the staple  500  can then be pushed fully into the holes, as needed. 
         [0038]    Alternately, with reference to  FIG. 4F , the transfer apparatus may be twisted about an axis  1207  generally defined by the backspan  504  of the staple as illustrated by arrow  1206  to snap both legs  505   a ,  505   b  out of the transfer apparatus simultaneously. Then, the backspan (assuming no detent adjacent the backspan) will simply fall out of the transfer apparatus. It should be noted however, that because the backspan of surgical shape memory staples typically have a zigzag in them as seen in the Figures (to allow the backspan to also achieve some compression during the transition from martensitic state to austentitic state), if the portion  521   a  of the channel in the transfer apparatus that accommodates the backspan is formed as a straight groove and with a width reasonably close to the diameter of the staple, there may not be enough clearance in that channel portion to permit releasing of the staple from the transfer apparatus by twisting about the backspan. Specifically, the zigzag in the backspan  504  may hit the wall of the channel portion  521   a  and prevent further twisting before the staple can be twisted enough to cause the legs  505   a ,  505   b  to clear the detents  522 . Since a reasonably tight fit of the backspan  504  in the channel portion  521   a  of the transfer apparatus  500  is desirable in order to keep the staple  500  from sliding in the transfer apparatus in the direction parallel to the legs  505   a ,  505   b  of the staple  500  when seated in the transfer apparatus  506 , channel portion  521   a  may be shaped eccentrically to accommodate the zigzag and to permit twisting of the staple about its backspan.  FIG. 5  illustrates such an embodiment. As can be seen, the portion of the channel  521   a ′ in the transfer apparatus  506 ′ that accepts the backspan  504  of the staple has two portions  1301  and  1302  that cause that channel portion  521   a ′ to correspond generally to the zigzag shape of the backspan of the staple. As shown, the channel portion  521   a ′ can accommodate the backspan  504  of the staple even when the staple is twisted a full 90° out of the transfer apparatus, as shown. 
         [0039]      FIG. 5  also illustrates another alternative feature of the transfer apparatus. Particularly, in order to enhance the ability of the transfer apparatus  500 ′ to deform to allow the legs  505   a ,  505   b  of the staple  500  to snap past the detents  522  as previously described, grooves  1306 ,  1307  are cut into the material of the transfer apparatus  506 ′ parallel to the channel portions  521   b ,  521   c  bearing the detents. This will allow more flex in the material portions  1308 ,  1309  adjacent these channel portions  521   b ,  521   c . This feature may be particularly desirable in connection with transfer apparatus for larger size staples, which transfer apparatus may be larger in size, and therefore inherently more rigid. 
         [0040]    The transfer apparatus also may be used to remove the staple from the surgical site in cases where that is necessary. Again, the wedge formation  510  may be inserted between the backspan of the staple (or other proximal portion of a shape memory article) and the bone (or other anatomical feature) to which the backspan is adjacent in order to force the backspan away from the bone essentially as described above in connection with the use of the wedge portion to pull the backspan away from the constraining device  503 . Once the wedge is inserted so as to push the backspan sufficiently away from the surface, the surgeon can simply pull the transfer apparatus  506  perpendicularly away from the surface of the bone. If more force is necessary than can reasonably be applied via the transfer apparatus, then the surgeon may instead remove the transfer apparatus and grasp the staple with a grasping tool to pull it out. 
         [0041]    The transfer apparatus comes in contact with the anatomy at the surgical site. Accordingly, it should be made of a biocompatible material, preferably a plastic biocompatible material. The transfer apparatus can be designed as a re-usable device or as a single use device. If it is to be reused, it should be fabricated from a material that can withstand repeated autoclaving processes. Many such materials are well known in the medical arts. 
         [0042]      FIG. 6  illustrates an alternative embodiment of the invention. In this embodiment, the shape memory article  500  is packaged at the factory embedded within both a constraining device  555  and a transfer apparatus  560  as shown in  FIG. 6 . In this embodiment, there is no ramp on the transfer apparatus insofar as the staple backspan and the proximal portion of the legs are already embedded in the groove of the transfer apparatus. 
         [0043]    In another embodiment, the constraining device may be completely eliminated. For instance, depending primarily on the size, shape, and shape memory properties of the shape memory device as well as the size and shape of the passage in the transfer apparatus relative to the shape memory device, the transfer apparatus may sufficiently restrain the shape memory article so as to completely eliminate the need for a separate constraining device to hold the distal end of the shape memory article pre-surgically. Accordingly, the shape memory article may simply be packaged without a constraining device essentially as shown in  FIG. 4C , i.e., with the proximal end embedded in the transfer apparatus and the distal end free. 
         [0044]      FIGS. 7A-7C  illustrate another embodiment of the invention. This embodiment is substantially similar to the embodiment described above in connection with  FIGS. 2-3  insofar as the transfer apparatus includes a wedge formation  910  and a groove  921  that conforms to the size and shape of the backspan of the shape memory staple and the proximal portions of the legs of the staple. However, rather than having one or more detents in the groove to assure that the staple does not inadvertently fall out of the groove, this transfer apparatus includes a cover portion  950  that is slidable between an open position, in which it does not cover the opening of the groove  921  in the major surface  951  of the transfer apparatus (the position shown in  FIG. 7A ) and a closed position, in which it does at least partially cover the groove  921  (the position shown in  FIG. 7B ). The cover  950  may be shaped, as shown, to provide a convenient thumb rest for the surgeon when holding the transfer device with a staple in it. 
         [0045]    In this embodiment, the transfer apparatus is delivered to the surgeon with the cover  950  in the closed position, as shown in  FIG. 7A . The cover would remain in this closed position throughout the entire surgical procedure until the time when the transfer apparatus is to be detached from the staple (e.g., after the distal portions of the legs of the staple have been inserted into the holes in the anatomical feature in which it will be implanted). Then, the surgeon can slide the cover  950  back with his thumb and simply translate the transfer apparatus in the direction represented by arrow B in  FIG. 7B , i.e., parallel to the major surface  951 , to disengage the transfer apparatus from the staple. An advantage of this embodiment is that the detents may be eliminated so that the entire groove  921  is sized slightly larger than the diameter of the staple so that no force need be applied to the staple when removing the transfer apparatus from the staple after partial implantation. 
         [0046]    The slidable cover  950  may be attached to the main body of the transfer apparatus by any reasonable mechanism that would allow it to slide. For instance, in one embodiment illustrated in  FIG. 7C , a slot  955  is provided in the aforementioned major surface  951  and completely through to the opposing major surface  922  of the transfer apparatus  906  and a corresponding pin  957  is provided on the underside of the cover  950  to mate with the slot  955  and slide in the slot. The distal-most portion of the pin  957  may be enlarged to form a button, ball, T shaped extension or other form of flange  958  with a diameter larger than the width of the slot so that the flange  957  is trapped in the slot  955  to hold the cover  950  to the main portion of the transfer apparatus, but allow it to slide in the slot  955 . 
         [0047]    In the embodiment illustrated in  FIGS. 7A-7C , the cover  950  covers only the backspan portion of the groove  921 . However, in other embodiments, it can cover the entire groove, including the portions that hold the proximal portions of the legs of the shape memory staple. This might provide more support for the staple and, particularly, prevent it from rocking about an axis parallel to the legs of the staple during implantation. 
         [0048]    In another embodiment, the features of the embodiment of  FIG. 5  allowing easier removal of the staple by providing grooves  1306 ,  1307  parallel and adjacent the channel portions  521   b ,  521   c  that allow the material portions  1308 ,  1309  that bear the detents  522  to flex more easily (see  FIG. 5 ) may be combined with the cover feature of the embodiment of  FIGS. 7A-7C . In fact, in yet another embodiment, the grooves  1306 ,  1307  may be reduced to nominal size such that there is a very small gap or no actual gap between material portions  1308 ,  1309  and middle material portion  1311 . Instead, material portion  1311  (or at least a substantial portion of it extending up to the front surface) may be integral with or attached to the cover so that it slides back with the cover. Thus, when the cover is in the closed position covering backspan channel portion  521   a , the staple is held securely in the channel by detents  522  because material portions  1308 ,  1209  bearing the detents cannot move because they are blocked by material portion  1311 . However, when the cover is slid open to reveal the backspan channel  521   a , the material portion  1311  also slides back so that it no longer blocks material portions  1308 ,  1309 . Material portions  1308 ,  1309  may be slidable medially once material portion  1311  is moved away. Alternately, they may be flexible as described in connection with the embodiment of  FIG. 5 . Of course, in such an embodiment, material portion  1311  would need to be specially shaped and attached to the cover to provide clearance to slide back without being blocked by the backspan of the staple held in the channel portion  521   a . For instance, material portion  1311  could be attached to the cover via the flange  958  adjacent the back surface  922  (as illustrated in the embodiment of  FIG. 7C ) and material portion could be shallower in depth so as not to extend all the way to front surface  951  so as not to interfere with the staple. Furthermore, another channel would need to be provided in the transfer apparatus into which material portion  1311  would slide when the cover is opened. 
         [0049]    Having thus described a few particular embodiments of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements as are made obvious by this disclosure are intended to be part of this description though not expressly stated herein, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only, and not limiting. The invention is limited only as defined in the following claims and equivalents thereto.