Patent Publication Number: US-11642189-B2

Title: Surgical instrument with fastener preload lock-out

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 16/508,183, filed on Jul. 10, 2019, now U.S. Pat. No. 11,007,030, which claims the benefit of U.S. Provisional Application No. 62/697,354, filed Jul. 12, 2018 and U.S. Provisional Application No. 62/798,178, filed Jan. 29, 2019. The entire contents of these applications are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     Disclosed embodiments are related to a surgical instrument for deploying fasteners. 
     BACKGROUND 
     A surgical mesh fabric or other prosthetic repair fabric may be used to surgically repair a hernia. The prosthetic repair fabric is typically placed in an open procedure or laparoscopically. To secure the repair fabric in place, one or more fasteners may be deployed through the prosthetic repair fabric and into the underlying tissue. Oftentimes, surgical instruments used during the surgical repair of a hernia, or other appropriate procedure, include magazines, or other structures, that are capable of holding a plurality of fasteners for deployment from the surgical instrument. The inclusion of a plurality of fasteners within the surgical instrument may increase the speed of the procedure and may also reduce the need to remove and re-introduce the surgical instrument into a surgical field to provide additional fasteners. 
     SUMMARY 
     In one embodiment, a surgical instrument comprises a handle, an elongated shaft extending in a distal direction from the handle, at least one fastener located within the elongated shaft, a fastener deployment system configured to deploy the at least one fastener from the elongated shaft in response to actuation thereof, and a lock-out removably attached to the elongated shaft. The fastener deployment system is configured to apply a first load to the at least one fastener prior to actuation thereof. The lock-out is configured and arranged to prevent the fastener deployment system from applying the first load to the at least one fastener while the lock-out is attached to the elongated shaft. 
     In another embodiment, a method is provided of operating a surgical instrument. The method comprises acts of: (a) providing a surgical instrument including a handle, an elongated shaft extending in a distal direction from the handle, at least one fastener located within the elongated shaft, a fastener deployment system configured to deploy the at least one fastener from the elongated shaft in response to actuation thereof, the fastener deployment system configured to apply a first load to the at least one fastener prior to actuation thereof, and a lock-out attached to the elongated shaft to prevent the fastener deployment system from applying the first load to the at least one fastener. The method also comprises acts of (b) detaching the lock-out from the elongated shaft whereby the fastener deployment system applies the first load to the at least one fastener, and (c) following act (b), actuating the fastener deployment system to deploy the at least one fastener from the elongated shaft. 
     In another embodiment, a surgical instrument comprises a handle, an elongated shaft extending in a distal direction from the handle, a stack of fasteners located within the elongated shaft, a fastener deployment system configured to deploy at least one of the fasteners from the elongated shaft in response to actuation thereof, and a lock-out clip removably attached to an exterior surface of the elongated shaft. The elongated shaft includes an internal channel and a hole extending from the external surface to the internal channel. The stack of fasteners is located within the internal channel of the elongated shaft. The fastener deployment system includes a follower which has a pusher configured to engage and apply a first load to the stack of fasteners. The lock-out clip includes a pin extending through the hole in the elongated shaft and into the internal channel of the elongated shaft. The pin is located between the stack of fasteners and the pusher to prevent the pusher from applying the first load to the stack of fasteners while the lock-out is attached to the elongated shaft. 
     In another embodiment, a lock-out is provided for a surgical instrument including an elongated shaft, a stack of fasteners located within the elongated shaft, and a fastener deployment system to deploy a fastener from the elongated shaft. The fastener deployment system is configured to apply a preload to the stack of fasteners. The lock-out comprises a grip handle configured to be grasped and manipulated to attach and detach the lock-out to and from the elongated shaft, the grip handle including first and second sides. The lock-out further comprises a first pair of opposing clip fingers and a second pair of opposing clip fingers. The first and second pairs of clip fingers are configured to receive the elongated shaft therebetween and engage an exterior surface thereof. Each of the first and second pairs of clip fingers includes a first clip finger and a second clip finger, the first clip fingers being located at the first side of the grip handle and the second grip fingers being located at the second side of the grip handle. The first grip fingers are spaced a first distance from each other and the second grip fingers are spaced a second distance from each other, the first and second distances being different from each other. 
     In another embodiment, a lock-out is provided for a surgical instrument including an elongated shaft, a stack of fasteners located within the elongated shaft, and a fastener deployment system to deploy a fastener from the elongated shaft. The fastener deployment system is configured to apply a preload to the stack of fasteners. The lock-out comprises a grip handle and a pin extending from the grip handle. The grip handle is configured to be grasped and manipulated to attach and detach the lock-out to and from the elongated shaft. The pin is configured to cooperate with the fastener deployment system when the lock-out is attached to the elongated shaft. The lock-out further comprises a shroud configured to shield the pin from contact by a user when the lock-out is detached from the elongated shaft, and a pair of opposing clip fingers configured to receive the elongated shaft therebetween and engage an exterior surface thereof to detachably retain the lock-out on the elongated shaft. 
     In another embodiment, a surgical instrument system comprises a tray and a surgical instrument loaded in the tray. The surgical instrument includes a handle, an elongated shaft extending in a distal direction from the handle, a stack of fasteners located within the elongated shaft, and a fastener deployment system configured to deploy at least one of the fasteners from the elongated shaft in a distal direction in response to actuation thereof. The fastener deployment system is configured to engage and apply a first load to the stack of fasteners in the distal direction prior to actuation thereof. The surgical instrument system also comprises a lock-out removably attached to the elongated shaft and a tether coupling the lock-out to the tray so that the lock-out remains attached to the tray when the lock-out is detached from the elongated shaft. The lock-out is configured and arranged to prevent the fastener deployment system from applying the first load to the stack of fasteners while the lock-out is attached to the elongated shaft. 
     It should be appreciated that the foregoing concepts, and additional concepts discussed below, may be arranged in any suitable combination, as the present disclosure is not limited in this respect. The foregoing and other aspects, embodiments, and features of the present teachings can be more fully understood from the following description in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings: 
         FIG.  1    is a schematic representation of a surgical instrument for deploying fasteners and includes a preload lock-out; 
         FIG.  2    is a schematic representation of the interior of the surgical instrument handle of  FIG.  1   ; 
         FIG.  3    is a schematic exploded view of the elongated shaft and the components disposed within the channel of the elongated shaft; 
         FIG.  4    is a schematic representation of a follower; 
         FIG.  5    is a schematic representation of a distal portion of the reciprocating driveshaft; 
         FIG.  6    is a schematic cross-sectional view of the follower located within the driveshaft; 
         FIG.  7 A  is a schematic representation of a stack of fasteners and the follower in an unbiased position; 
         FIG.  7 B  is a schematic representation of the stack of fasteners and the follower of  FIG.  6    with a biasing force applied; 
         FIG.  7 C  is a schematic representation of the stack of fasteners and the follower of  FIG.  6    after the stack of fasteners have been distally displaced; 
         FIG.  8 A  is a schematic representation of a distal portion of the anti-backup mechanism; 
         FIG.  8 B  is a schematic representation of the anti-backup mechanism depicted in  FIG.  8 A  after one actuation cycle; 
         FIG.  9 A  is a schematic front view of a preload lock-out; 
         FIG.  9 B  is a schematic top view of the preload lock-out of  FIG.  9 A ; 
         FIG.  10    is a schematic perspective view of the lock-out attached to the elongated shaft of the surgical instrument of  FIG.  1    illustrating the lock-out preventing the follower from applying a preload to the fasteners; 
         FIGS.  11 A- 11 C  are schematic perspective views of the lock-out with a shroud for shielding the lock-out pin and a tether for attaching the lock-out to a tray; 
         FIG.  12    is a schematic perspective view of the shroud for the lock-out of  FIGS.  11 A- 11 C ; 
         FIG.  13    is a schematic top view of a surgical instrument loaded in a tray with the preload lock-out coupled to the tray with the tether; 
         FIG.  14    is a schematic perspective view of a tether for retracting the follower extending from the proximal end of the handle; 
         FIG.  15    is a schematic perspective view of the rigid straight portion including first and second restraints; 
         FIG.  16    is a schematic end view of the rigid straight portion depicted in  FIG.  15   ; 
         FIG.  17    is a schematic side view of the rigid straight portion depicted in  FIG.  15   ; 
         FIG.  18    is a schematic side view of the rigid straight portion depicted in  FIG.  17    rotated 120°; 
         FIG.  19 A  is a cross-sectional view of the elongated shaft, reciprocating driveshaft, and fasteners in the unactuated position; 
         FIG.  19 B  is a cross-sectional view of the elongated shaft, reciprocating driveshaft, and fasteners depicted in  FIG.  19 A  in the actuated position; 
         FIG.  19 C  is a cross-sectional view of the elongated shaft, reciprocating driveshaft, and fasteners depicted in  FIG.  19 A  after actuation; 
         FIG.  20    is a schematic exploded view of the elongated shaft and the reciprocating driveshaft including a stack of fasteners; 
         FIG.  21    is a schematic top view of a fastener; 
         FIG.  22    is a schematic bottom view of the fastener depicted in  FIG.  21   ; 
         FIG.  23    is a schematic perspective view of the fastener depicted in  FIGS.  21 - 22   ; 
         FIG.  24    is a schematic end view of the reciprocating driveshaft including a stack of fasteners disposed therein; and 
         FIG.  25    is a schematic end view of the elongated shaft with the reciprocating driveshaft and stack of fasteners disposed therein. 
     
    
    
     DETAILED DESCRIPTION 
     The inventors have recognized that the application of force, such as a preload, to a fastener for an extended period of time, such as during shipping and/or storage of a surgical instrument loaded with one or more fasteners, may adversely affect mechanical, structural and/or material properties and/or characteristics of the fasteners. For example, when subjected to a preload for an extended period of time prior to use of the surgical instrument, a stack of fasteners subjected to a preload may undergo deformation during accelerated aging. 
     In view of the foregoing, the inventors have recognized the benefits associated with preventing the application of a force to one or more fasteners, including a stack of fasteners, prior to using the surgical instrument for deploying the fasteners. In some embodiments, this force may be a preload applied to the stack of fasteners for facilitating fastener deployment. The above noted benefit may lead to improved consistency in fastener deployment and surgical instrument operation. 
     In one embodiment, the surgical instrument may include a handle and an elongated shaft extending in a distal direction from the handle. The elongated shaft may include a distally located fastener deployment position from which a fastener may be deployed at a distal end of the elongated shaft. The surgical instrument may also include a fastener deployment system to deploy a fastener from the fastener deployment position out of the distal end of the elongated shaft. The fastener deployment system may be embodied in any number of ways. Further, in some embodiments, the fastener deployment system may include a magazine, or other appropriate structure for containing a plurality of fasteners. Depending upon the particular embodiment, the plurality of fasteners may be arranged as a nested stack of fasteners, although other arrangements are also envisioned. 
     The fastener deployment system may be configured to preload the stack of fasteners with a force which is sufficient to facilitate deployment of the fasteners but yet less than the force required to deploy a fastener. For example, the application of a preload to the stack of fasteners in the distal direction may help maintain a distalmost fastener in the fastener deployment position, while also preventing movement of the stack of fasteners in the proximal direction away from the distal end of the shaft. In one embodiment, the fastener deployment system may include a follower, or other appropriate component, that is associated with the stack of fasteners such that it displaces one or more fasteners towards the fastener deployment position during an actuation cycle of the fastener deployment system. 
     The surgical instrument may be provided with a preloaded stack of fasteners. However, an extended period of time may pass from when the stack of fasteners is loaded into the instrument and actual use of the instrument for fastener deployment. For example, the fasteners may be loaded into the instrument during assembly by a manufacturer. An extended period of time may pass, such as many months or even longer, during which the instrument may reside in inventory, be shipped, and be stored at a user facility, such as a hospital, before the surgical instrument is eventually employed for fastener deployment. During this time, the fasteners may undergo deformation during accelerated aging and/or other physical or property changes when subjected to a constant preload. 
     In one embodiment, the surgical instrument may include a lock-out to reduce, and preferably prevent, the application of the preload on the stack of fasteners until the surgical instrument is to be used for deploying one or more fasteners. The lock-out may be attached to a portion of the elongated shaft suitable for interacting with the fastener deployment system in a manner which prevents the preload from being applied to the stack of fasteners. When it is desired to use the surgical instrument for deploying fasteners, the lock-out may be detached from the shaft to allow the fastener deployment system to apply the preload to the stack of fasteners prior to actuation of the instrument. 
     The lock-out may be configured as a clip which can be snapped on and off the elongated shaft. In one embodiment, the clip may include at least one pair of opposing clip fingers which are attachable to the shaft and an outwardly extending handle configured to be gripped and pulled to detach the clip from the shaft. The clip fingers may be configured to conform to the outer surface of the shaft. For example, in one embodiment, the clip fingers may have opposing curved shapes which correspond to the shape of the shaft. The clip fingers may have sufficient resilience or flexibility which permits the fingers to open and close for attaching and detaching the clip and gripping the elongated shaft therebetween. 
     As indicated above, the clip may be configured to interact with the fastener deployment system to lock-out and prevent a preload from being applied to the stack of fasteners until the instrument is used for fastener deployment. In one embodiment, the clip may include a pin or other suitable component which is associated with the fastener deployment system when the clip is attached to the elongated shaft. The pin may be arranged to extend inwardly from the clip and into an internal channel of the elongated shaft to prevent distal movement of the fastener deployment system toward the stack of fasteners. In one embodiment, the pin may be arranged to retain the follower in a spaced relation away from the stack of fasteners so that the follower does not engage and apply a preload or other force against the fasteners. Detaching the clip from the elongated shaft and removal of the pin from the internal channel allows the follower to move into engagement with and apply a preload force against the fasteners to move, if necessary, and hold the distalmost fastener in the fastener deployment position for subsequent fastener deployment upon actuation of the fastener deployment system. 
     The clip may be formed as a one-piece component although any suitable arrangement may be employed. The pin may be a separate component which is integrated with the clip. For example, in one embodiment, the pin may be insert molded to the clip. Such an arrangement allows the use of a pin fabricated from a relatively stronger material, such as a metal, as compared to the clip, which may be formed of a plastic material. However, the lock-out may be constructed in any suitable manner. 
     In some situations, the lock-out may be considered a sharp object due to the presence of a pin or similar component which could require disposal of the lock-out in accordance with a particular protocol for handling sharps. For example, the lock-out may need to be placed in a sharps container for subsequent disposal. To reduce the incidence of a potential contact by an individual handling the lock-out, it may be desirable to provide a cover or other suitable arrangement to shield the pin or other potential sharp component. 
     In one aspect, the lock-out may include a shroud configured to cover the clip fingers and the pin therein and thereby shield the pin from contact by an individual when the lock-out is detached from the shaft of the surgical instrument. The shroud may be configured to open and close so as to permit attachment and detachment of the lock-out to and from the shaft. When closed, the shroud may have a tubular-like configuration designed to wrap about the clip fingers as well as the elongated shaft when the lock-out is attached to the shaft. 
     For some situations, it may be desirable to avoid a loose component within a particular environment, such as an operating room. For example, a loose component within an operating room could potentially be dropped into a patient or otherwise become misplaced and require time to locate and account for the component. Thus, it may be desirable to avoid having a loose lock-out which potentially could become misplaced when it is detached from the shaft of the surgical instrument. 
     According to one aspect, the lock-out may be coupled to the packaging tray or a blister pack for the surgical instrument. When the lock-out is detached from the instrument to prepare the instrument for use, the lock-out will remain attached to the tray so that it will not become inadvertently misplaced during a surgical procedure. The lock-out may be coupled to the tray with a tether, such as a strap, having one end attached to the tray and its opposing end attached to the lock-out. The tether may be configured with a length which is sufficient to permit removal and manipulation of the instrument while also maintaining the detached lock-out in relatively close proximity to the tray so that the lock-out does not dangle from the tray when it is detached from the instrument. 
     Because the lock-out may be considered a sharp object, it may be desirable to detach the lock-out from the tray to facilitate its proper disposal following surgery. For example, the tether may be cut or detached from either the tray or the lock-out to detach the lock-out from the tray. In one embodiment, the lock-out may be configured to facilitate its detachment from the tether. The lock-out may include a slot or other suitable relief configured to permit removal of the tether, for example, by slipping the tether through the slot and from the lock-out. 
     In addition to deploying the fastener, actuation of the fastener deployment system may also result in the distal displacement of the follower so as to distally displace the stack of fasteners towards the fastener deployment position and position a next distalmost fastener in the fastener deployment position. The fastener deployment system may displace the follower in any appropriate fashion. For example, in one embodiment, the follower may be associated with a driveshaft of the fastener deployment system such that distal displacement of the driveshaft distally displaces the follower. Proximal movement of the follower may also be prevented through the use of an anti-backup element associated with the follower. Regardless of the specific manner in which the follower is displaced, the follower may be arranged and adapted to provide a controlled force to the stack of fasteners during displacement. The force applied to the stack of fasteners may be any appropriate force, and in one embodiment may be less than the actuation force applied to deploy a fastener from the fastener deployment position. 
     In certain embodiments, the follower may be constructed in any appropriate fashion such that it applies similar forces to the stack of fasteners during subsequent actuation cycles of the fastener deployment system. For example, the follower may include a driver which is associated with the fastener deployment system such that actuation of the fastener deployment system distally displaces the driver. The driver may also be associated with a compressible elastic component which is associated with a pusher. The elastic component may be adapted and arranged to provide a controlled force to the pusher upon displacement of the driver. The elastic component may comprise a coil spring, a conical spring, a pneumatic spring, an appropriately shaped component made of a compressible material (e.g. rubber), or any other appropriately shaped and sized compressible component capable of applying a force to the stack of fasteners when it is compressed. In some embodiments, in addition to providing a controllable force to the stack of fasteners, the elastic component may be sufficiently flexible to permit the follower to pass through an articulated portion of the elongated shaft while still applying a force to the stack of fasteners. In such an embodiment, the driver, elastic component, and pusher may also be sized and shaped to pass through the elongated shaft in both the straight and articulated configuration. 
     While the embodiments described herein refer to, and depict, the driver, elastic component, and pusher as separate components that are physically associated with one another, the current disclosure is not limited to the use of separate components. For example, in some embodiments, the driver, elastic component, and pusher may be provided as part of an integral component. 
     In some embodiments, the follower may be adapted to provide similar forces to the stack of fasteners during subsequent actuation cycles. Although this may be accomplished in any number of ways, in one embodiment, the follower may operate in the following manner. Upon actuation of the fastener deployment system, the driver may be distally displaced. The distal displacement of the driver may compress the elastic component from a first length to a compressed second length. Subsequent to compressing the elastic component, the elastic component may expand from the compressed second length to the original first length. As the elastic component expands to the second length, the fasteners may be distally displaced along the elongated shaft towards the fastener deployment position. In some embodiments, the difference between the first length and the second length may correspond to the length of one fastener. When the elastic component is in the expanded state corresponding to the first length, the elastic component may apply a first force to the pusher and the stack of fasteners. Subsequently, when the elastic component is in the compressed state corresponding to the second length, the elastic component may apply a second force to the pusher and the stack of fasteners. As would be expected for a compressed elastic component, the second force is greater than the first force. In some embodiments, the first force may be approximately zero. However, in other embodiments, it may be desirable to provide a distal bias to the stack of fasteners throughout the actuation cycle to prevent backwards or proximal movement of the stack of fasteners. In such an embodiment, the first force may be greater than zero and correspond to an initial compression of the elastic component prior to actuation of the fastener deployment system. 
     In addition to the forces applied to the stack of fasteners by the follower, restraining forces may also be applied to the stack fasteners to prevent distal movement of the fasteners until the force applied by the follower exceeds a preselected threshold force. For example, a first restraining force may be applied to the stack of fasteners prior to, and during, actuation of the fastener deployment system. The first restraining force may be applied to the stack of fasteners to oppose the first force applied to the stack of fasteners by the follower. Consequently, prior to actuation of the fastener deployment system, the stack of fasteners may remain stationary within the elongated shaft. However, during actuation, the elastic component may be compressed to a second compressed length to apply a greater force to the stack of fasteners as noted above. Once the applied force (e.g. the second force) is greater than the first restraining force, the stack of fasteners may be distally displaced by the follower to position the next fastener in the fastener deployment position. A second restraining force may subsequently be applied to restrain the stack of fasteners from additional distal movement during that actuation cycle. 
     Each of the noted restraining force may be provided by one or more restraints. Further, the restraints may be embodied in any number of fashions. For example, the restraints may include: one or more tabs that extend inwards and distally relative to the elongated shaft; detent arrangements; and other appropriate features. Further, the restraints may be integrally formed with the elongated shaft, or the restraints may be formed separately and subsequently assembled with the elongated shaft using any appropriate fashion including, but not limited to, welding, soldering, brazing, adhesives, mechanical couplings, fasteners, and interference fits. 
     In some embodiments, in addition to providing the restraining forces to the stack of fasteners, the restraints may also be used to define the fastener deployment position. For example, a head, or other appropriate feature, of a fastener may be retained between the first and second restraints to define the fastener deployment position. 
     In addition to providing a follower to control the forces applied to the stack of fasteners, as noted above, it may be desirable to provide a mechanism for maintaining the orientation of the fasteners within the elongated shaft as the stack of fasteners is displaced towards the fastener deployment position by the follower. In one embodiment, a guide surface may be sized and shaped to interact with a corresponding surface on at least a portion of the fasteners to maintain the orientation of the fasteners as they move within the elongated shaft. In some instances, the corresponding surface on the fastener may be shaped such that it is complementary both in shape and size to the guide surface. The guide surface may be positioned on any appropriate component of the elongated shaft, or a component that is disposed within the elongated shaft, that interacts with the fasteners as they are moved through the elongated shaft. Further, the guide surface may extend along a distal portion of the component, a portion of the component corresponding to the stack of fasteners, or the entire length of the component as the current disclosure is not limited as to the location and extent of the guide surface. 
     It should be understood that the guide surface and the corresponding surfaces on the fasteners may include any combination of appropriate shapes and/or features that are capable of maintaining the orientation of the fasteners. For example, the guide surface and the corresponding surfaces on the fasteners may include: corresponding flats; a protrusion and corresponding groove; and other complementary arrangements as should be apparent to one of ordinary skill in the art. 
     In one particular embodiment, the fasteners may be disposed within an internal channel of a reciprocating driveshaft that reciprocates in a proximal and distal direction. Further, the guide surface may be incorporated with the interior surface of the channel. In such an embodiment, the guide surface may interact with the corresponding surface of the fasteners to maintain an orientation of the fasteners within the reciprocating driveshaft. During actuation of the fastener deployment system, the driveshaft may be moved in a distal direction to deploy a fastener prior to moving in a proximal direction in preparation for the next actuation cycle. During this reciprocating movement of the driveshaft, the driveshaft may be moved relative to the stack of fasteners. Additionally, during, or subsequent to deployment of the fastener, the stack of fasteners may be displaced towards the distal end of the driveshaft to position the next distalmost fastener in the fastener deployment position using any appropriate biasing element. For example, the stack of fasteners may be displaced using a follower as described herein. As the stack fasteners are displaced towards the fastener deployment position, and as the driveshaft is moved relative to the stack of fasteners disposed therein, the guide surface may maintain the fasteners in a preselected orientation relative to one another and the driveshaft. As previously noted, maintaining the fasteners in a preselected orientation relative to one another and the driveshaft ensures proper alignment of the fasteners and may lower the necessary force to move the fasteners through an articulated portion of the elongated shaft. 
     For the sake of clarity, the currently disclosed embodiments are directed to a laparoscopic device. However, the current disclosure is not limited to laparoscopic devices. Instead, the currently disclosed lock-out, followers, restraints, and guide surfaces could be used in any appropriate device for the deployment of a fastener into tissue. For example, any of the currently disclosed components, or combination of disclosed components, could be incorporated into an endoscopic device, a borescopic device, a catheter, a surgical instrument for use in “open” procedures, or any other appropriate surgical instrument. Additionally, the surgical instrument may be loaded with one or more fasteners prior to being provided to an end user, or it may be constructed to allow the user to load the instrument with one or more fasteners. Further, while the various embodiments depicted herein are described as being used with a specific fastener, any appropriate fastener could be used with the currently disclosed embodiments including a tack, a clip, a staple, a pin, a tissue anchor, a bone anchor, or any other appropriate type of fastener. 
     Turning now to the figures, specific embodiments of the surgical instrument are described. 
       FIG.  1    illustrates one embodiment of a surgical instrument  2  for deploying one or more surgical fasteners. The surgical instrument includes a handle  4  and an elongated shaft  6  extending distally from the handle  4 . In addition to fasteners being deployed from a distal end of the elongated shaft, the elongated shaft  6  may include an articulable portion  8 . A trigger  14  may be provided on the handle to actuate an associated fastener deployment system  15 , as shown in  FIG.  2   , and deploy a fastener into tissue. The surgical instrument may also include a lock-out  150  to prevent the fastener deployment system from applying a force, such as a preload, to fasteners carried by the instrument until fastener deployment is desired using the instrument. 
     As illustrated, and as described in more detail below, the lock-out  150  may be attached to a portion of the elongated shaft associated with the fastener deployment system  15  to prevent a preload from being applied to the fasteners. When it is desired to use the surgical instrument for deploying fasteners, the lock-out  150  may be detached from the shaft to allow a preload to be applied to the fasteners prior to actuation of the instrument. 
     The fastener deployment system  15  may be embodied in any number of different ways. However, in the particular embodiment depicted in  FIG.  2    the fastener deployment system may include a trigger  14 , a rigid linkage  20 , a shuttle  22 , a power assist device  24 , and a reciprocating driveshaft  26  as well as other components that are not depicted. Actuation of the trigger  14  may distally displace the rigid linkage  20  to distally displace the shuttle  22  and store energy in the power assist device  24 . After a preselected amount of actuation, the power assist device  24  may release the stored energy to distally accelerate the driveshaft  26  and deploy a fastener from the distal end of the elongated shaft  6 . 
     While a particular power assist device  24  is depicted, the power assist device  24  may correspond to any appropriate construction capable of aiding in deploying a fastener from the elongated shaft  6  of the surgical instrument. Depending on the particular embodiment, the power assist device  24  may supply all of the power necessary to deploy a fastener in response to actuation of the trigger  14 , or it may only supply a portion of the power necessary to deploy a fastener. In one specific embodiment, the power assist device  24  may correspond to the power assist device disclosed in application Ser. No. 13/804,043, entitled POWER ASSIST DEVICE FOR A SURGICAL INSTRUMENT, filed on Mar. 14, 2013. While a surgical instrument including a power assist device has been depicted, in some embodiments, the surgical instrument  2  may not include a power assist device, in which case actuation of the trigger  14  may displace the driveshaft  26 , either directly or indirectly through the use of an appropriate transmission, to deploy a fastener from a distal end of the elongated shaft  6 . 
       FIG.  3    presents an exploded view of one embodiment of the elongated shaft  6  and the various components disposed within the elongated shaft. In the depicted embodiment, the driveshaft  26  is located within the elongated shaft  6 . As illustrated by  FIGS.  2  and  3   , when disposed within the elongated shaft  6 , the driveshaft  26  extends proximally from the elongated shaft  6  into the handle  4 . The surgical instrument also includes a stack of fasteners  28 , a follower  34 , and an anti-backup element disposed within an internal channel of the driveshaft  26 . The follower and/or the anti-backup element may be associated with or part of the fastener deployment system. The stack of fasteners  28  may include one or more fasteners  30 , and in some instances may be a plurality of fasteners  30 . 
     In addition to the above components, the surgical instrument may also include a fastener guide  32  to help maintain the alignment of the stack of fasteners  28 , the follower  34 , and the anti-backup element  36  within the internal channel of the driveshaft  26 . While any appropriate structure may be used, in the depicted embodiment, the fastener guide  32  is a distally extending wire positioned in approximately the center of the channel of the driveshaft. The fastener guide  32  may be retained within the channel in any appropriate fashion. For example, the fastener guide  32  may be attached to a portion of the anti-backup element  36 , a portion of the handle  4 , or any other appropriate structure. Further, the faster guide  32  may be attached using any appropriate method including, but not limited to, adhesives, mechanical interference, clamping, soldering, brazing, and welding. 
     Upon actuation of the trigger, the fastener deployment system may be actuated resulting in a distal displacement of the driveshaft  26 . As described in more detail below, a distal displacement of the driveshaft  26  deploys a distalmost fastener located in the fastener deployment position. The driveshaft  26  also distally displaces the follower  34  so as to displace the stack of fasteners  28  and position the next distalmost fastener in the fastener deployment position. The follower  34  and anti-backup element  36  may be associated such that a distal displacement of the follower  34  results in the anti-backup element extending in the distal direction to prevent a proximal movement of the follower  34 . After deployment of a fastener, and positioning of the next fastener in the fastener deployment position, the driveshaft  26  may be moved in a proximal direction to prepare the surgical instrument for the next actuation while preventing proximal movement of the stack of fasteners  28 , the follower  34 , and the anti-backup element  36 . 
     The interaction between the follower  34  and the driveshaft  26  is depicted in  FIGS.  4 - 6   . 
     In the depicted embodiment, the follower  34  includes a driver  100 , an elastic component  102 , and a pusher  104 . The driver  100  is adapted to interact with the driveshaft  26  to displace the follower  34  in a distal direction. The driver  100  includes tabs  106  which interact with openings  124  on the driveshaft  26 . The tabs  106  may be flexible and extend outwards and distally from the driver  100 . In addition, the tabs  106  may be sized, shaped, and arranged such that the tabs  106  may be disposed within the openings  124  as the driver  100  is distally moved through driveshaft  26 . The driver  100  may also include a distal portion  108   a  as well as a shoulder  110 . The distal portion  108   a  and the shoulder  110  may be sized and shaped to retain a distal end of the elastic component  102  on the distal portion  108   a . The distal portion  108   a  may also include one or more retention features  116 . As illustrated, the retention features  116  may be protrusions located on the distal portion  108   a  that interfere with the elastic component  102  to retain the elastic component thereon. Alternatively, the elastic component  102  may be retained on the driver  100  using any appropriate method including, but not limited to, mechanical interference, interlocking features, adhesives, welding, soldering, and brazing. The driver  100  may also include a coupling  118  located on a proximal portion  108   b . The coupling  118  may be adapted and arranged to attach the follower  34  to the anti-backup element  36 . 
     In one embodiment, the elastic component  102  is a coil spring that extends between the driver  100  and the pusher  104 . As noted above, while a coil spring has been depicted, other springs and appropriate components could be used in place of a coil spring. Regardless of the specific component used as the elastic component  102 , the elastic component  102  may be sized, shaped, and arranged to be associated with both the driver  100  and the pusher  104 . Further, due to the use of a spring, or other appropriate compressible component, as the driver is moved in a distal direction, the elastic component  102  is compressed to apply a force to the pusher  104 . Larger displacements of the driver  100  prior to movement of the pusher  104  may result in larger compressions of the elastic component  102  and correspondingly larger forces. Depending upon the particular embodiment, the elastic component  102  may exhibit a linear force to displacement relationship, or a nonlinear force to displacement relationship, as the current disclosure is not limited in this fashion. 
     Similar to the driver  100 , the pusher  104  may include a proximal portion  112   b  and a shoulder  114  that are sized and shaped to retain a distal end of the elastic component  102 . The pusher  104  may also include one or more retention features  116  for retaining the elastic component  102  similar to those described above for the driver  100 . The pusher  104  may also include a distal portion  112   a  that is adapted and arranged to apply a force to the most proximally located fastener of the fastener stack. In some embodiments, the distal portion  112   a  may directly contact at least the proximal most fastener in the stack of fasteners, though embodiments in which the distal portion  112   a  indirectly applies a force to the stack of fasteners are also envisioned. 
     As depicted in  FIG.  5   , the driveshaft  26  may include one or more fastener drivers  120  located on the distal end of the driveshaft  26 . In some embodiments, the fastener driver  120  may be one or more flexible tabs that extend inwards and distally from the distal end of the driveshaft  26 . The fastener drivers  120  may be adapted to apply a force to a fastener located in the fastener deployment position to deploy the fastener from the distal end of the elongated shaft. The driveshaft may also include a flexible portion  122  to accommodate movement of the reciprocating driveshaft through the articulable portion of the elongated shaft. In the depicted embodiment, the flexible portion  122  is formed by providing a pattern of slots, or cuts, in the driveshaft  26 . As noted above, the driveshaft  26  may also include openings  124  that are sized and shaped to accommodate the tabs  106  of the driver  100  in an expanded position. One or more sets of openings  124  may be axially spaced along one or more surfaces of the driveshaft  124 . In some embodiments, the axial spacing between the openings  124  may correspond to the length of a single fastener. In the current embodiment, two sets of openings  124  extend along opposite sides of the driveshaft  26  to accommodate both of the tabs  106  of the driver  100 . The openings  124  may extend along the entirety of driveshaft  24 , or as depicted in the figures, the openings  124  may extend along a portion of the driveshaft  24  corresponding to an initial proximal position of the follower  34  and a final distal position of the follower  34  after all of the fasteners have been deployed from the surgical instrument. 
     Having described the corresponding features on the driveshaft  26  and the follower  34 , the interactions of these two components during actuation in one possible embodiment will now be described with reference to  FIG.  6   . Prior to actuation, the tabs  106  of the driver  100  may be located in the expanded state in any one of the corresponding openings  124  of the driveshaft  26 . While the tabs  106  are in the expanded state within a corresponding opening  124 , a proximal portion of the driveshaft  124   a , such as a proximal edge of the opening may be axially aligned with a proximal aspect  106   a  of a tab  106 . Consequently, as the driveshaft  26  is moved in a distal direction during actuation, the proximal driveshaft portion  124   a  applies a distally directed force to the proximal aspect  106   a  of the tabs  106  resulting in a distal displacement of the driver  100 . After the fastener has been deployed, the driveshaft  26  is subsequently moved in a proximal direction. During the proximal movement of the driveshaft  26 , a distal portion of the shaft  124   b , such as a distal edge of the openings  124 , may be drawn over an exterior aspect  106   b , such as an exterior surface, of the tabs. As described in more detail below, the driver  100  may be prevented from moving backwards during the relative movement of the driveshaft  26  and the driver  100 . Further, as noted above, the tabs  106  are flexible. Thus, as the distal driveshaft portion  124   b  is drawn over the exterior aspect  106   b  of the tabs, the tabs  106  may be displaced inwards and out of the openings  124  to permit the relative movement of the driver  100  and the driveshaft  26 . The proximal displacement of the driveshaft  26  may be continued until the tabs  106  are aligned with the next distally located set of openings  124  and the tabs  106  are in the expanded state within the openings  124 . Subsequent actuation cycles may result in the driver  100  progressively moving in a distal direction as the driver  100  engages with the next corresponding set of openings  124  of the driveshaft. In view of the above, the driver  100  of the follower  34  and the driveshaft  26  may be described as forming two separate components of a walking beam assembly that is configured to sequentially displace the follower  34  in a distal direction during each actuation cycle of the fastener deployment system. 
       FIGS.  7 A- 7 B  depict the interaction of the stack of fasteners  28 , the follower  34 , and the anti-backup element  36  during an actuation cycle of the fastener deployment system. As illustrated in the figures, the pusher  104  may be in contact with a proximally located fastener of the fastener stack  28 . The elastic component  102  may also be associated with a proximal portion of the pusher  104  and a distal portion of the driver  100 . The driver  100  may be coupled to a rack arm  126  of the anti-backup element  36  by a coupling  130 . The driver  100  and rack arm  126  may be coupled in such a manner that distal movement of the driver  100  may result in the distal extension of the rack arm  126  relative to a pawl arm  128  of the anti-backup element  36 . Thus, as the follower  34  is distally displaced through the elongated shaft, the anti-backup element  36  correspondingly elongates. Consequently proximal movement of the follower  34  may be prevented by the anti-backup element  36  throughout the actuation cycle. As depicted in the figures, coupling  130  corresponds to a pin connection. However, any appropriate connection may be used including, but not limited to, interlocking mechanical features, a set screw, fasteners, adhesives, welding, brazing, and interference fits. 
     Prior to actuation, as depicted in  FIG.  7 A , the elastic component  102  of the follower  34  is in the expanded state corresponding to the first length and may apply a first distally directed force to the distally located pusher  104  and the stack of fasteners  28 . The follower  34  and the stack of fasteners  28  are prevented from moving in a proximal direction by the anti-backup element  36 . In the depicted embodiment, the anti-backup element  36  includes a rack arm  126  which may be moved in the distal direction, and a pawl arm  128  which remains stationary during actuation of the surgical instrument. 
     Referring to  FIG.  7 B , as the fastener deployment system is actuated, the driveshaft, not depicted, may apply a force F D  to the tabs  106  of the driver  100  which drives the driver  100  in a distal direction as described above. A proximally directed first restraining force F R1  may be applied to the stack of fasteners  28 . Initially, the first restraining force F R1  may be equal to force F D . Thus, during the initial portions of actuation, the stack of fasteners  28  may remain stationary resulting in the compression of elastic component  102  between the pusher  104  and the driver  100 . As actuation continues, the force applied to the driver  100  may continue to increase as the elastic component  102  is further compressed. This continued compression of the elastic component  102  applies an increasing distally directed force to the stack of fasteners  28 . At some point during actuation, the spring may be compressed to a second length corresponding to the elastic component  102  applying a second distally directed force to the pusher  104  and the associated stack of fasteners  28 . This second distally directed force may be greater than the first restraining force F R1  resulting in the expansion of the elastic component  102  and distal displacement of the pusher  104  and associated stack of fasteners  28 , see  FIGS.  7 B- 7 C . 
     As depicted by the figures, the elastic component  102  continues to expand from the second length to the first length as the stack of fasteners  28  is displaced in the distal direction. As the elastic component  102  approaches the expanded first length, a proximally directed second restraining force F R2  may be applied to the stack of fasteners  28  to prevent further distal movement of the stack of fasteners. The second restraining force F R2  may be greater than the first restraining force to oppose both the force applied to the stack of fasteners  28  by the elastic component  102  as well as possible kinetic energy stored in the stack of fasteners  28  and follower  34  as they are being distally displaced. The second restraining force may also be less than the actuation force to deploy a fastener from the elongated shaft. In some embodiments, the second restraining force F R2  may be applied once a distally located fastener of the stack fasteners  20  has been positioned in the fastener appointment position. After the stack of fasteners  28  has been distally displaced and the fastener deployment system has been reset, the surgical instrument may be actuated again resulting in further distal displacement of the follower  34  and the associated stack of fasteners  28 . 
     In addition to displacement of the follower  34  and the associated stack of fasteners  28 , actuation of the fastener deployment system may also result in an extension of the anti-backup element  36  as noted above. More specifically, due to the driver  100  and the rack arm  126  being coupled, distal displacement of the driver  100  may result in a corresponding distal displacement of the rack arm  126  relative to the pawl arm  128 . The distal movement of the rack arm  126  may extend the anti-backup element  36  in a distal direction to prevent backwards movement of the driver  100  after the stack of fasteners  28  has been distally displaced. The interactions of the rack arm  126  and the pawl arm  128  are illustrated in more detail in  FIGS.  8 A and  8 B . Teeth  134  may be spaced along the axial length of the rack arm  126 . A corresponding pawl  132  may be positioned on a distal portion of the pawl arm  128 . The pawl  132  and the corresponding teeth  134  may be adapted and arranged to permit distal movement of the rack arm  126  in response to distal movement of the driver. The pawl  132  and the corresponding teeth  134  may also be adapted and arranged to prevent proximal movement of the rack arm  126 . In one embodiment, the distance between the teeth  134  may be approximately equal to one fastener length. However, embodiments in which the distance between teeth  134  is a fraction of a fastener length, or greater than a fastener length, are also envisioned. In addition to the above, while a rack and pawl system have been depicted for the anti-backup element  36 , any appropriate mechanism capable of preventing backwards movement of the follower and the stack fasteners could be used. 
     As indicated above, the follower is 34 is configured and arranged to apply a distally directed preload to the stack of fasteners to drive the stack of fasteners toward the distal end of the shaft and maintain the distalmost fastener in the fastener deployment position. For some applications, it may be desirable to employ a lock-out prevent the preload from being applied to the fasteners until it is desired to use the instrument for fastener deployment. 
     In one embodiment shown in  FIGS.  9 A- 10   , the lock-out  150  may be configured as a clip which can be mounted on and removed from the elongated shaft. As illustrated, the clip  150  may include two pairs of opposing first clip fingers  152   a  and second clip fingers  152   b  which are attachable to the shaft  6  and an outwardly extending grip handle  154  configured to be grasped and pulled to detach the clip from the shaft. One or more features may be provided to enhance the user&#39;s ability to grasp the grip handle pull the lock-out from the shaft. In one embodiment, one or more raised ribs  156  may extend about at least a portion of the outer periphery of the grip handle. It is to be appreciated that other suitable grip features may be utilized as should be apparent to one of skill in the art. 
     The clip fingers  152   a ,  152   b  may be configured to conform to the outer surface of the shaft  6 . For example, in one embodiment, the clip fingers  152   a ,  152   b  may have opposing curved shapes which correspond to the shape of the shaft. The clip fingers may have sufficient resilience or flexibility which permits the fingers to open and close for attaching and detaching the clip and gripping the elongated shaft therebetween. Although illustrated as having two pairs of opposing clip fingers, it should be understood that the lock-out may include any number of clip fingers, including a single pair, or more than two pairs. Moreover, other suitable arrangements for attaching and detaching the lock-out to the elongated shaft may be employed as should be apparent to one of skill in the art. 
     The grip fingers may be arranged in any suitable configuration to facilitate attachment and detachment of the lock-out relative to the elongated shaft. As shown in  FIGS.  9 A- 9 B , the clip fingers may be arranged with the first fingers  152   a  provided on a first side of the lock-out being spaced apart by a first length L 1  and the second fingers  152   b  provided on a second opposite side of the lock-out being spaced apart by a second length L 2  which is different from the first length L 1 . In one embodiment, the first length L 1  between the first fingers  152   a  is less than the second length L 2  between the second fingers  152   b . As illustrated, the first fingers  152   a  may be located inward of the second fingers  152   b , and the second fingers  152   b  may be located at opposite ends of the lock-out. 
     The lock-out  150  may also include a pin  158  which is configured to cooperate with the fastener deployment system when the clip is attached to the elongated shaft. As illustrated in  FIG.  10   , the pin  158  may be arranged to extend inwardly from the grip handle  154 , through a corresponding hole  160  in the elongated shaft  6 , and into an internal channel  162  of the shaft to prevent distal movement of the fastener deployment system toward the fasteners. In one embodiment shown in  FIG.  10   , the pin  158  may be arranged to maintain the follower  34  in a spaced relation away from the stack of fasteners  28  so that the follower does not engage and apply a preload or other force against the fasteners. More particularly, the clip is positioned so that the pin  158  extends through the shaft and is located between the stack of fasteners  28  and the follower  34  with the pin  158  engaging the shoulder  114  of the distally biased pusher  104 . Detaching the clip  150  from the elongated shaft and removal of the pin  158  from the internal channel allows the pusher  104  to move into engagement with the proximal-most fastener  30  and apply a preload force against the stack of fasteners  28  for subsequent fastener positioning and deployment upon actuation of the fastener deployment system. 
     In one exemplary embodiment, the lock-out may have an overall length L of about 1.25 inches with the first fingers  152   a  spaced apart by a length L 1  of about 0.65 inches and the second fingers being spaced apart by a length L 2  of about 1.09 inches. The clip fingers  152  may be configured with a curvature having an inner diameter of about 0.22 inches with the free ends of the fingers being spaced apart by a width Wi about 0.15 inches. The grip handle  154  may have a length L 3  from the center of the clip fingers of about 1.18 inches. The pin  158  may have a diameter of about 0.03 inches and extend from the surface of the grip handle by a length L 4  of about 0.07 inches. It is to be understood that the lock-out dimensions are exemplary and that the lock-out may employ any suitable shape and/or sizes as should be apparent to one of skill in the art. 
     As indicated above, the lock-out may be considered a sharp object due to the presence of the pin  158  or similar component which could require disposal of the lock-out in accordance with a particular protocol for handling sharp objects. For example, the lock-out may need to be placed in a sharps container for subsequent disposal. To reduce the incidence of a potential contact by an individual handling the lock-out, it may be desirable to provide a cover or other suitable arrangement to shield the pin or other potential sharp component. 
     In one illustrative embodiment shown in  FIGS.  11 A- 11 C , the lock-out  150  may include a shroud  170  configured to cover and shield the pin  158  from contact by an individual when the lock-out is detached from the elongated shaft  6  of the surgical instrument. The shroud may be configured to open and close so as to readily permit attachment and detachment of the lock-out to and from the shaft. When closed as shown in the figures, the shroud  170  may have a tubular-like configuration designed to wrap about and cover the clip fingers  152   a ,  152   b  as well as the elongated shaft  6  when the lock-out is attached to the shaft. 
     The shroud  170  may include a base  172  and a pair of shroud segments  174   a ,  174   b  extending from the base which can be opened relative to the clip fingers for attaching and detaching the lock-out, and closed to encompass the clip fingers and the pin when the lock-out is attached to and detached from the shaft. Each shroud segment  174   a ,  174   b  may have an arcuate shape configured to form approximately 180° of the tube-like structure when the shroud is in the closed configuration. 
     In one embodiment shown in  FIG.  12   , at least a portion of one of the shroud segments  174   a  may extend beyond 180° to form an extension  176 , such as a tongue, which is configured to cover the pin should the shroud segments be collapsed inwardly toward the pin when the lock-out is detached from the elongated shaft. The opposing shroud segment  174   b  may include a recess  181  configured to receive the extension  176  when the shroud segments are closed. As illustrated, the free ends  177   a ,  177   b  of the shroud segments may be positioned in close proximity to each other in the closed position to form a relatively narrow gap  179  therebetween. 
     The shroud  170  may be fabricated as a separate component which can be coupled to the lock-out  150 . In one embodiment illustrated in  FIGS.  11 A- 11 C , the shroud  170  may be configured so that the base  172  is located adjacent the end of the lock-out handle  154  with the shroud segments  174   a ,  174   b  extending from the base and about the clip fingers  152   a ,  152   b . As shown in  FIG.  12   , the base may include a slot  178  or other suitable opening configured to slidably receive the grip handle  154  therethrough to position the shroud on the lock-out. 
     The lock-out may include one or more locking features to maintain the shroud in its desired position. In one embodiment illustrated in  FIGS.  11 A- 11 C , a pair of locks  180  may be provided on opposite sides of the grip handle  154  in proximity to the clip fingers to engage the base  172  when the shroud is positioned on the lock-out. Each lock  180  may include a cam-like configuration which facilitates placement of the shroud into position between the locks and the clip fingers, and thereafter restricts movement of the shroud away from the clip fingers. In one embodiment, each lock  180  may include a ramp-like surface  182  which facilitates sliding the shroud over the locks in a direction toward the clip fingers and into position, and an abutment  184  at the end of the ramp-like surface which is configured to abut the base and act as a stop to restrict movement of the shroud in a direction away from the clip fingers. It is to be appreciated that any suitable lock arrangement may be employed as should be apparent to one of skill in the art. 
     The shroud  170  may be formed to have a flexible configuration which facilitates opening and closing the shroud segments, as well as placement of the shroud on the lock-out. In this manner, the shroud is not required to grasp and hold the elongated shaft of the instrument as done by the clip fingers. However, if desired, the shroud segments could be configured to assist with holding the lock-out on the shaft as should be apparent to one of skill in the art. 
     In one embodiment, the shroud may be formed from a material which is conducive to providing flexible characteristics. For example, and without limitation, the shroud may be molded from a polyurethane or polyethylene material, although other suitable materials may be used as should be apparent to one of skill in the art. 
     For some situations, it may be desirable to avoid having a loose component within a particular environment, such as an operating room. For example, a loose component could potentially become misplaced and require time to locate and account for the component. Thus, it may be desirable to avoid having a lock-out which potentially can become misplaced when it is detached from the shaft of the surgical instrument. 
     In one embodiment, the lock-out may be coupled to a packaging tray or blister pack of the surgical instrument. When the lock-out is detached from the instrument to prepare the instrument for use, the lock-out will remain attached to the tray so that it will not become inadvertently misplaced during a surgical procedure. 
     In one embodiment illustrated in  FIG.  13   , the lock-out  150  may be coupled to the tray  186  using a tether  188  having one end attached to the tray and its opposing end attached to the lock-out. As shown in  FIGS.  11 A- 11 C , the tether  188  may include a strap formed as a loop with the free ends  190  of the strap coupled together with a grommet  192 , or other suitable component, which may be attached to the tray with a fastener  193 , such as a rivet. The looped-end of the strap may be coupled to the grip handle  152  of the lock-out. In one embodiment, the strap  188  may be looped through a hole  194 , such as a slot or other suitable opening, in the grip handle. 
     The tether  188  may be configured with a length which is sufficient to permit removal and manipulation of the instrument while also maintaining a detached lock-out in relatively close proximity to the tray so that the lock-out does not dangle excessively from the tray when it is detached from the instrument. In one embodiment, the tether may have a length of about 1.75 inches, although a tether of any suitable length may be employed as should be apparent to one of skill in the art. 
     Because the lock-out may be considered a sharp object, it may be desirable to detach the lock-out from the tray to facilitate its disposal following a procedure. If desired, the tether may be cut or detached from either the tray or the lock-out to remove the lock-out from the tray. For some applications, the lock-out may be configured to facilitate its separation from the tether. 
     In one embodiment illustrated in  FIGS.  11 A- 11 B , the lock-out  150  may include a slot  196  (shown in phantom in  FIG.  11 A ) or other suitable passage configured to permit removal of the tether, for example, by slipping the tether from the lock-out. As shown, the slot  196  may be configured to extend from the hole  194  in the grip handle, which is used for attaching the tether  188  to the lock-out, through the outer periphery of the grip handle. The slot  196  may be oriented transverse to the hole  194  and have a width sufficient to accommodate the thickness, but not the width, of the tether to permit the tether to be slipped through the slot when the tether and the lock-out are manipulated relative to each other so that the edge of the tether can be slid into and through the slot. In one embodiment, the slot  196  may be oriented perpendicular to the hole  194 . It is to be appreciated that other suitable arrangements may be employed for detachably coupling the lock-out to the tether as should be apparent to one of skill in the art. 
     The lock-out may be attached to the elongated shaft during assembly of the surgical instrument to minimize the period of time that the stack of fasteners would be subjected to a preload. However, it is to be appreciated that the lock-out may be attached to the surgical instrument at any appropriate time as should be apparent to one of skill in the art. 
     In one embodiment, the lock-out may be attached by initially displacing the pusher  104  of the follower  34  in the proximal direction away from the stack of fasteners and against the biasing force of the spring  102 . The pusher  104  may be displaced a distance sufficient to locate the shoulder  114  of the pusher proximal to the hole  160  through the shaft  6 . Thereafter, the lock-out  150  may be attached to the instrument by pushing the clip fingers onto the shaft  6  with the pin  158  extending through the hole  160  and into the internal channel  162  between the fasteners  30  and the pusher shoulder  114 . Once the lock-out is attached, the follower  34  may be released so that the spring  102  drives the pusher in the distal direction until the shoulder  114  engages the pin  158  to prevent further advancement of the pusher toward the stack of fasteners  28 . When engaged by the pin  158 , the pusher  104  is spaced an appropriate distance from the stack of fasteners so that the follower does not apply a preload to the fasteners. 
     In one embodiment, a tether may be attached to the pusher  104  and extend in the proximal direction along the elongated shaft  6  to a location where it is accessible and can be used to retract the follower away from the fasteners to facilitate attachment of the lock-out. The tether may extend through and exit the proximal end of the handle  4  with a sufficient length of the tether available for grasping and pulling the pusher proximally. After the lock-out has been attached to the shaft, the tether may be detached and removed from the instrument. 
     In one embodiment, the tether  164  may be looped through the pusher with two segments of the tether extending from the pusher and exiting the handle  4 , as shown in  FIG.  14   . After the lock-out clip has been attached, one segment  164   a  of the tether may be pulled proximally and to draw the other segment  164   b  of the tether distally through the handle, the shaft, the pusher and eventually proximally back through the shaft and the handle to remove the tether from the instrument. 
     The lock-out  150  may be formed as a one-piece component although any suitable arrangement may be employed. The pin  158  may be a separate component which is integrated with the clip. For example, in one embodiment, the pin  158  may be insert molded to the grip  154 . Such an arrangement allows the use of a pin fabricated from a relatively stronger material, such as a metal, as compared to the clip, which may be formed of a plastic material. 
     In one embodiment, the clip fingers  152  and the grip body  154  may be integrally formed of a polycarbonate resin, such as CALIBRE 2061-15 FC850122 available from Trinseo. The pin  158  may formed of 304 stainless steel, full hard per ASTM F899 and passivated per ASTM A967, and is insert molded with the clip material to provide a connection therebetween having a minimum pull-out force of 5 lbf. However, it is to be understood that the lock-out may be fabricated from any suitable material, using any suitable technique, and/or to provide any suitable pull-out force as should be apparent to one of skill in the art. 
       FIGS.  15 - 18    depict an inner tubular member  200  which is a component of the elongated shaft  6 . The inner tubular member  200  includes the rigid straight portion  12  which forms the distal end of the elongated shaft  6 . The inner tubular member may also include one or more first restraints  202  and one or more second restraints  204  located within the rigid straight portion  12 . As depicted in  FIG.  15   , the two second restraints  204  are distally located relative to a first restraints  202 . The first restraint may be adapted and arranged to provide the first restraining force to the stack of fasteners during actuation. Correspondingly, the second restraints  204  may be adapted and arranged to provide the second restraining force to the stack fasteners during actuation. As noted previously, the first restraining force may be less than the second restraining force. The different restraining forces may be provided in any number of ways as the current disclosure is not limited to the manner in which the restraining forces are applied to the stack of fasteners. In some embodiments the restraints may be integrally formed with elongated shaft, or a component of the elongated shaft. Alternatively, the restraints may be formed separately and assembled with elongated shaft in any appropriate fashion including, but not limited to, welding, soldering, brazing, adhesives, interference fits, and fasteners. 
     The different first and second restraining forces may be provided in any appropriate manner. For example, in one embodiment, different compliances of the first and second restraints may be used to provide the different first and second restraining forces. More specifically, the second restraints may be less compliant than the first restraints. In another embodiment, the different first and second restraining forces may be provided using different numbers of the first and second restraints. In such an embodiment, a greater number of the second restraints may be used as compared to the number of first restraints. While specific methods of providing the different restraining forces have been noted above, other ways of providing the restraining forces are also contemplated. 
     In one possible embodiment, and as depicted in  FIGS.  15 - 18   , the first and second restraints  202  and  204  may correspond to tabs that extend inwards and distally relative to the inner tubular member  200  of the elongated shaft. To provide the desired first and second restraining forces, a single more compliant first restraint  202  and two less compliant second restraints  204  are incorporated into the rigid straight portion  12  of the inner tubular member  200  of the elongated shaft. The tabs corresponding to the second restraints  204  may have reduced lengths and/or increased widths as compared to the tab corresponding to the first restraint  202 . Without wishing to be bound by theory, this results in the second restraints  204  being less compliant than the first restraint  202 . Consequently, due to the use of two less compliant tabs for the second restraints  204  as compared to a single more compliant tab for the first restraint  202 , the depicted embodiment is adapted to provide a second restraining force that is greater than the first restraining force. It should be understood that while a particular arrangement of first and second restraints has been depicted in the figures and described above, other embodiments for providing the first and second restraining forces are also possible. 
     The interaction between the first restraints  202 , the second restraints  204 , the fasteners  30 , and the driveshaft  26  of the fastener deployment system are illustrated by  FIGS.  19 A- 19 C  depicting a series of cross-sections of a distal portion of the elongated shaft  6  during actuation of the fastener deployment system. Prior to actuation, a distally located fastener  30  is positioned in the fastener deployment position  206 . The fastener deployment position  206  may be defined by the relative locations of the first restraints  202  and the second restraints  204 . The first restraints  202  and the second restraints  204  may define the fastener deployment position by retaining the head  30   a  of a fastener  30  between them prior to actuation. Retaining a fastener  30  in the fastener deployment position  206  using the restraints  202  and  204  may beneficially prevent a fastener from inadvertently being displaced out of the elongated shaft  6  as well as providing a consistent position of a fastener for subsequent deployment. Upon actuation of the fastener deployment system, the driveshaft  26  is distally displaced resulting in the fastener drivers  120  applying a force to the fastener  30  located in the fastener deployment position  206 . The applied actuation force is greater than the second restraining force provided by the second restraints  204  resulting in the distal displacement and deployment of the fastener as depicted in  FIG.  19 B . As noted above, the stack of fasteners may have a separate force applied to distally displace the stack of fasteners and position the next fastener in the fastener deployment position  206  for the next actuation cycle. As the driveshaft  26  is withdrawn in a proximal direction to reset the fastener deployment system for the next actuation cycle, the fastener drivers  120  deform around and past the head  30   a  of the fastener  30  located in the fastener deployment position  206 , see  FIG.  19 C . As depicted in the figure, the tabs corresponding to the first and second restraints  202  and  204  may be arranged and adapted to resist proximal movement of a fastener  30  located distally from the restraints  202  and  204 . Consequently, proximal movement of a fastener  30  located in the fastener deployment position  206  may be prevented by the first restraint  202  as the driveshaft is moved in the proximal direction. Once the driveshaft  26  has been fully moved in the proximal direction, the surgical instrument is ready to deploy the next fastener. 
     While the above described embodiments have been directed to a follower that is driven by the reciprocating action of a driveshaft in a proximal and distal direction, other embodiments are possible. For example, in one embodiment, the follower may be associated with a rotating driveshaft such that rotation of the driveshaft may result in a distal displacement of the follower and the associated fasteners disposed within the driveshaft. In another exemplary embodiment, the follower may be associated with another component of the fastener deployment system such that actuation of the fastener deployment system results in a distal movement of the follower. For example, the follower may be associated with the trigger  14 , the rigid linkage  20 , or the shuttle  22 . Further, the follower may be directly, or indirectly, associated with any of the above components. 
     As noted previously, in addition to displacing the stack of fasteners to position the next fastener in the fastener deployment position, in some embodiments, it may be desirable to maintain a particular orientation of the fasteners within the elongated shaft.  FIG.  20    depicts a schematic exploded view of the elongated shaft  6  and the driveshaft  26  which may be disposed within the interior of the elongated shaft  6 . The depicted pattern of slots formed in the exterior of the elongated shaft  6  impart flexibility to the portion of the elongated shaft  6  corresponding to the articulable portion  8 . In the depicted embodiment, the driveshaft includes an internal channel to accommodate one or more fasteners  30  disposed therein. The driveshaft  26  may also include a guide surface  136 . The guide surface  136  may be any appropriate shape, and as depicted in the figure, may correspond to a flat extending along the axial direction of the driveshaft  26 . The guide surface  136  may interact with a corresponding surface on the fasteners  30  to maintain an orientation of the fasteners while they are disposed within the driveshaft  26  and as the driveshaft reciprocates between a distal position and a proximal position during actuation. In addition to the guide surface  136 , the driveshaft  26  may also include a fastener driver  120   a  that interacts with the corresponding surface on the fasteners  30  to maintain the orientation of a fastener  30  as it is positioned in the fastener deployment position. 
     In the depicted embodiment, a flat corresponding to the guide surface  136  is present on an internal surface of the internal channel of the driveshaft  26 . Additionally, the guide surface  136  may optionally be present on an exterior surface of the driveshaft  26  as well. While a particular shape has been depicted for the guide surface  136 , any appropriate shape or combination of features could be present on the driveshaft  26  to maintain an orientation of the fasteners  30  disposed therein. For example, the guide surface  136  may correspond to a protrusion, a groove, or any other appropriate shape. Further, the guide surface  136  may extend along any appropriate portion of the driveshaft  26 . For example, the guide surface  136  may extend along a distal portion of the driveshaft, a flexible portion  122  of the driveshaft, a portion of the driveshaft corresponding to the stack of fasteners located within the driveshaft, or the entire length of the driveshaft as the current disclosure is not limited in this fashion. 
       FIGS.  21 - 23    depict one possible embodiment of a fastener  30  for use with the driveshaft  26 . The depicted embodiment of the fastener  30  includes: a head  30   a ; a shaft  30   b  extending from the head  30   a ; and a barbed end  30   c  located at a distal end of the shaft  30   b . A surface  138  corresponding to the guide surface  136  of the driveshaft may be disposed on the head  30   a . The surface  138  may be sized and shaped to complement the guide surface  136  the driveshaft such that the fastener  30  smoothly interfaces with the internal surfaces of the driveshaft  26 . In the depicted embodiment, the surface  138  corresponds to a flat such that a cross-section of the head  30   a  includes a flat portion and a round portion sized and shaped to complement corresponding flat and round portions of a cross-section of the internal channel of the driveshaft. While the surface  138  corresponding to the guide surface  136  has been depicted as being located on the head  30   a  of the fastener, the surface  138  may be located on any appropriate portion of the fastener  30 . For example, a portion of the shaft  30   b  or barbed end  30   c  could include a corresponding surface, or feature, that is shaped, sized, and arranged to interact with the guide surface  136  of the driveshaft to maintain an orientation of the fastener  30 . 
     In addition to the surface  138  present on the fastener  30  which corresponds to the guide surface  136 , the fastener  30  may also include a through hole  140  extending distally from a proximal surface of the head  30   a  through the shaft  30   b  and the barbed end  30   c . The through hole  140  may be sized and shaped to accommodate the fastener guide, as described above, to maintain the alignment of the fasteners  30  within the elongated shaft. The through hole  140  may be centrally located, radially offset, or arranged in any other appropriate location as the current disclosure is not limited as to where the through hole  140  is located. While it may be desirable to include a through hole  140  to help maintain the alignment of the fasteners  30  within the elongated shaft, it may also be desirable in certain embodiments to provide a pointed tip  142  on the fastener as depicted in the figure. However, embodiments using a blunt tip and an associated piercing needle are also envisioned. To accommodate the through hole  140 , the pointed tip  142  may be radially offset relative to the through hole  140 . 
       FIG.  24    depicts a distally located fastener  30  disposed within the internal channel  140  of the driveshaft  26 . As illustrated by the figure, guide surface  136  and the fastener driver  120   a  of the driveshaft  26  are aligned with the corresponding surface  138  of the fastener  30 . Due to the interaction of the flat portions of the internal channel cross-section and the fastener head (i.e. the guide surface  136  and corresponding surface  138 ), as well as the round portions of the internal channel cross-section and the fastener head, the fastener  30  may be maintained in a preselected orientation throughout the length of the driveshaft  26 . 
       FIG.  25    depicts the fastener  30  and driveshaft  26  of  FIG.  24    disposed within the elongated shaft  6 . As best illustrated by  FIG.  19 B , in some embodiments, the fastener drivers  120  may extend distally relative to the first and second restraints  202  and  204  when the driveshaft  26  is distally displaced to deploy a fastener. Consequently, it may be desirable to arrange the fastener drivers  120  and the first and second restraints  202  and  204  such that they do not interfere with one another during distal displacement of the driveshaft. In the depicted embodiment, the fastener drivers  120  are arranged in a triangular pattern at a distal end of the driveshaft  26  and the first and second restraints  202  and  204  are arranged in another corresponding triangular pattern around the internal surface of the elongated shaft  6  such that the fastener drivers  122  do not interfere with the first and second restraints  202  and  204  during the distal displacement of the driveshaft. It should be understood that while a particular number and arrangement of the fastener drivers and restraints has been depicted in the figures and described herein, the current disclosure is not limited in this manner. Instead, any appropriate number and arrangement of fastener drivers and restraints may be used. Further, other appropriate types of fastener drivers and restraints may also be used. 
     As indicated above, the elongated shaft  6  may include an articulable portion  8 . The articulable portion may be articulated between a first position, such as an unarticulated (i.e. straight) position, and a second position, such as a fully articulated position, using the articulation control  10 . In some embodiments, the articulable portion  8  may be articulated only between the first and second positions. In other embodiments, the articulable portion  8  may be articulated to one or more preselected articulated positions, or any arbitrary (i.e. not preselected) articulated position as the current disclosure is not limited in this fashion. Further, depending upon the embodiment, the articulable portion  8  may only be articulated in one direction, or it may be articulated in two directions. For example, the articulable portion  8  may be articulated between approximately 0° and 90°, 0° and 45°, −90° and 90°, −180° and 180° or any other appropriate range of angles. In addition, in some embodiments the articulable portion  8  may articulate about two different axes (e.g. articulation in the horizontal direction and vertical direction). 
     In some embodiments, it may be desirable to rotate the elongated shaft  6  to facilitate positioning of the distal tip. One such embodiment is depicted in  FIGS.  1  and  18   . The rotation of the elongated shaft  6  may be provided in any appropriate manner. For example, the elongated shaft  6  may simply be adapted to be rotatable to at least a portion of the handle  4 . Alternatively, a portion of the handle  4  including the elongated shaft  6  may be rotatable relative to another portion of the handle  4 , such as the portion including the grip. One such embodiment is depicted in  FIG.  1   . In the depicted embodiment, the surgical instrument  2  includes a first handle portion  16  and a second handle portion  18  including the elongated shaft  6 . The first and second handle portions  16  and  18  may be constructed and arranged in any appropriate fashion to be rotatable relative to one another. It should be understood that while a surgical instrument including a rotatable elongated shaft  6  or handle  4  is depicted in the figures, a surgical instrument including a unitary handle and/or an elongated shaft  6  that is stationary relative to the handle are also possible as the current disclosure is not limited in this manner. 
     In certain applications, it may be advantageous to include a rigid straight portion  12  distally located from the articulable portion  8 . For example, and without wishing to be bound by theory, when a driveshaft applies a force to a fastener as it goes around a curve, the force applied by the driveshaft to a proximal portion of the fastener may not be aligned with the deployment direction of the fastener. This may result in a portion of the applied force being directed against a side of the elongated shaft  6 . In contrast, when a driveshaft applies a force to a fastener along a straight section, the applied force is aligned with the deployment direction of the fastener. Thus, including a rigid straight portion  12  that distally extends from the articulable portion  8  for a given length may enable the driveshaft to apply a reduced actuation force to deploy the fastener since the applied actuation force may be aligned with the deployment direction. Further, applying an actuation force that is aligned with the deployment direction may also improve the consistency of fastener deployment as the surgical instrument is varied between different articulation angles. In addition to the benefits noted above, the rigid straight portion  12  may also incorporate other components or features to aid in the positioning and deployment of a fastener from the surgical instrument. While a surgical instrument  2  including a distal rigid straight portion  12  has been described herein, and depicted in figures, it should be understood that embodiments are also envisioned in which the articulable portion  8  extends all the way to the distal end of the elongated shaft  6  such that the surgical instrument does not include a distal rigid straight portion. 
     While the present teachings have been described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments or examples. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art. Accordingly, the foregoing description and drawings are by way of example only.