Patent Publication Number: US-11020111-B2

Title: Fasteners and fastener delivery devices for affixing sheet-like materials to bone or tissue

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 13/889,737, filed on May 8, 2013, which is a Continuation of U.S. application Ser. No. 13/717,493 filed on Dec. 17, 2012, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/577,626 filed on Dec. 19, 2011, the disclosures of each incorporated herein by reference. 
     The present disclosure is related to the following commonly assigned applications, the disclosures of which are incorporated herein by reference: U.S. Provisional Application No. 61/577,6121 filed on Dec. 19, 2011; U.S. Provisional Application No. 61/577,632 filed on Dec. 19, 2011; and U.S. Provisional Application No. 61/577,635 filed on Dec. 19, 2011. 
    
    
     INCORPORATION BY REFERENCE 
     All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     FIELD 
     The present invention relates generally to orthopedic medicine and surgery. More particularly, the present invention relates to methods and apparatus for delivery and fixation of sheet-like materials, such as for treating tendons or like tissue of articulating joints such as tendons in the rotator cuff of the shoulder. 
     BACKGROUND 
     The glenohumeral joint of the shoulder is found where the head of the humerus mates with a shallow depression in the scapula. This shallow depression is known as the glenoid fossa. Six muscles extend between the humerus and scapula and actuate the glenohumeral joint. These six muscles include the deltoid, the teres major, and the four rotator cuff muscles. The rotator cuff muscles are a complex of muscles. The muscles of the rotator cuff include the supraspinatus, the infraspinatus, the subscapularis, and the teres minor. The centering and stabilizing roles played by the rotator cuff muscles are critical to the proper function of the shoulder. The rotator cuff muscles provide a wide variety of moments to rotate the humerus and to oppose unwanted components of the deltoid and pectoral muscle forces. 
     The muscles of the rotator cuff arise from the scapula. The distal tendons of the rotator cuff muscles splay out and interdigitate to form a common continuous insertion on the humerus. The supraspinatus muscle arises from the supraspinatus fossa of the posterior scapula, passes beneath the acromion and the acromioclavicular joint, and attaches to the superior aspect of the greater tuberosity. The mechanics of the rotator cuff muscles are complex. The rotator cuff muscles rotate the humerus with respect to the scapula, compress the humeral head into the glenoid fossa providing a critical stabilizing mechanism to the shoulder (known as concavity compression), and provide muscular balance. The supraspinatus and deltoid muscles are equally responsible for producing torque about the shoulder joint in the functional planes of motion. 
     The rotator cuff muscles are critical elements of this shoulder muscle balance equation. The human shoulder has no fixed axis. In a specified position, activation of a muscle creates a unique set of rotational moments. For example, the anterior deltoid can exert moments in forward elevation, internal rotation, and cross-body movement. If forward elevation is to occur without rotation, the cross-body and internal rotation moments of this muscle must be neutralized by other muscles, such as the posterior deltoid and infraspinatus. The timing and magnitude of these balancing muscle effects must be precisely coordinated to avoid unwanted directions of humeral motion. Thus the simplified view of muscles as isolated motors, or as members of force couples must give way to an understanding that all shoulder muscles function together in a precisely coordinated way—opposing muscles canceling out undesired elements leaving only the net torque necessary to produce the desired action. Injury to any of these soft tissues can greatly inhibit ranges and types of motion of the arm. 
     With its complexity, range of motion and extensive use, a common soft tissue injury is damage to the rotator cuff or rotator cuff tendons. Damage to the rotator cuff is a potentially serious medical condition that may occur during hyperextension, from an acute traumatic tear or from overuse of the joint. With its critical role in abduction, rotational strength and torque production, the most common injury associated with the rotator cuff region is a strain or tear involving the supraspinatus tendon. A tear at the insertion site of the tendon with the humerus, may result in the detachment of the tendon from the bone. This detachment may be partial or full, depending upon the severity of the injury or damage. Additionally, the strain or tear can occur within the tendon itself. Injuries to the supraspinatus tendon and current modalities for treatment are defined by the type and degree of tear. The first type of tear is a full thickness tear, which as the term indicates is a tear that extends through the thickness of the supraspinatus tendon regardless of whether it is completely torn laterally. The second type of tear is a partial thickness tear which is further classified based on how much of the thickness is torn, whether it is greater or less than about 50% of the thickness. 
     The accepted treatment for a full thickness tear or a partial thickness tear greater than 50% includes reconnecting the torn tendon via sutures. For the partial thickness tears greater than 50%, the tear is completed to a full thickness tear by cutting the tendon prior to reconnection. In contrast to the treatment of a full thickness tear or a partial thickness tear of greater than 50%, the current standard treatment for a partial thickness tear less than 50% usually involves physical cessation from use of the tendon, i.e., rest. Specific exercises can also be prescribed to strengthen and loosen the shoulder area. In many instances, the shoulder does not heal and the partial thickness tear can be the source of chronic pain and stiffness. Further, the pain and stiffness may cause—restricted use of the limb which tends to result in further degeneration or atrophy in the shoulder. Surgical intervention may be required for a partial thickness tear of less than 50%, however, current treatment interventions do not include repair of the tendon, and rather the surgical procedure is directed to arthroscopic removal of bone to relieve points of impingement or create a larger tunnel between the tendon and bone that is believed to be causing tendon damage. As part of the treatment, degenerated tendon may also be removed using a debridement procedure in which tendon material is ablated. Again, the tendon partial thickness tear is not repaired. Several authors have reported satisfactory early post operative results from these procedures, but over time recurrent symptoms have been noted. In the event of recurrent symptoms, many times a patient will “live with the pain”. This may result in less use of the arm and shoulder which causes further degeneration of the tendon and may lead to more extensive damage. A tendon repair would then need to be done in a later procedure if the prescribed treatment for the partial tear was unsuccessful in relieving pain and stiffness or over time the tear propagated through injury or degeneration to a full thickness tear or a partial thickness tear greater than 50% with attendant pain and debilitation. A subsequent later procedure would include the more drastic procedure of completing the tear to full thickness and suturing the ends of the tendon back together. This procedure requires extensive rehabilitation, has relatively high failure rates and subjects the patient who first presented and was treated with a partial thickness tear less than 50% to a second surgical procedure. 
     As described above, adequate treatments do not currently exist for repairing a partial thickness tear of less than 50% in the supraspinatus tendon. Current procedures attempt to alleviate impingement or make room for movement of the tendon to prevent further damage and relieve discomfort but do not repair or strengthen the tendon. Use of the still damaged tendon can lead to further damage or injury. Prior damage may result in degeneration that requires a second more drastic procedure to repair the tendon. Further, if the prior procedure was only partially successful in relieving pain and discomfort, a response may be to use the shoulder less which leads to degeneration and increased likelihood of further injury along with the need for more drastic surgery. Further, it would be beneficial to be able to treat partial thickness tears greater than 50% without cutting the untorn portion of the tendon to complete the tear before suturing back together. There is a large need for surgical techniques and systems to treat partial thickness tears and prevent future tendon damage by strengthening or repairing the native tendon having the partial thickness tear. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure is generally directed to a fastener or staple that can be used to attach an implant to bone or other tissue. The staple or fastener can be included in a kit or system that also can include a staple delivery device and a pilot hole forming trocar assembly. The trocar assembly is used to create pilot holes and retain instrument position within those pilot holes for staple insertion. The staple delivery device can carry the staple into the pilot holes and release the staple in engagement with bone to retain the implant in position. 
     The staple for insertion and retention in bone can include a bridge portion having arms extending from proximate each end thereof, at least a portion of each arm including tissue retention members, each tissue retention member having at least two barbed projections extending laterally therefrom. Each arm can have a cross sectional area of reduced strength proximate each projection relative to other portions of the tissue retention member such that a portion of the tissue retention member flexes laterally proximate each projection in response to a pullout force applied to the bridge. The tissue retention members can include a trunk of greater cross sectional area than a non-trunk portion of the arms. 
     The fastener or staple can also include, in alternative embodiments, a first arm having a proximal end and a distal end, a second arm having a proximal end and a distal end, and a bridge connecting the first arm and second arm, wherein each of the first and second arms include a trunk portion extending over at least a portion of the length thereof. Each trunk can have a lateral extent larger than a lateral extent of the bridge or non-trunk arm portion adjacent thereto such that the staple includes a first change in lateral stiffness disposed proximate the bridge or non-trunk arm portion abutment with the first trunk and a second change in lateral stiffness disposed proximate the bridge or non-trunk arm portion abutment with the second trunk. The lateral extent of each trunk in at least one direction can be at least about three times the lateral extent of at least a portion of the bridge or non-trunk portion of the arm. 
     Each trunk can further include a first projection and a second projection, the first projection including a first proximal surface extending away from the trunk in a first direction, the first direction being such that the first proximal surface will engage the tissue or bone when the trunk is inserted therein so that a first moment is applied to the trunk in response to a pullout force on the bridge. Likewise, the second projection can include a second proximal surface extending away from the trunk in a second direction, the second direction being such that the second proximal surface will engage the tissue or bone when the trunk is inserted therein so that a second moment is applied to the trunk in response to a pullout force on the bridge. Each of the trunks can further include a localized area of weakness proximate the second projection thereon. For example, a second area of reduced strength can include a slit in the cross section of the tissue retention member or trunk adjacent at least one of the projections therefrom. Further, reduced strength can be created where the trunk meets the non-trunk portion of the arm adjacent thereto or the bridge. 
     In some embodiments, the change in lateral stiffness and the localized area of weakness allow flexing of each arm portion in response to the first and second moment, respectively. 
     The projections can be arranged to extend in first and second directions to achieve increased pullout strength. The first direction can extend proximally and laterally away from each trunk while the second direction can extend proximally and laterally away from each trunk and a lateral component of the second direction is generally opposite a lateral component of the first direction. The forces on the projections create moments about the more flexible portions of the staple where the direction of the first moment is generally opposite the direction of the second moment on each arm. 
     In some embodiments, the fastener first trunk and the second trunk each define a cavity, each cavity being spaced laterally from the respective non-trunk portion or bridge adjacent thereto. Each cavity defined by the first and the second trunk is sized to receive a first stake and a second stake, respectively, of a fastener delivery device. Each cavity defined by the first and the second trunk can extend from the proximal end to the distal end of the trunk. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating an exemplary tissue fastener or staple in accordance with the present disclosure; 
         FIG. 2  is a an alternative perspective view of the tissue fastener or staple of  FIG. 1  illustrating other features in accordance with the present disclosure; 
         FIG. 3  is a top plan view of the tissue fastener or staple of  FIG. 1  illustrating the laterally extending legs having lumens for receiving the stakes of a delivery device for positioning the staple in desired tissue; 
         FIG. 4  is a front plan view of the tissue fastener or staple of  FIG. 1  illustrating in phantom flexing of the barbs and legs of the staple in response to grasping of tissue in one embodiment of the disclosure; 
         FIG. 5  is a stylized anterior view of a shoulder including a humerus and a scapula; 
         FIG. 6  is a stylized of a shoulder depicting the head of the humerus shown mating with the glenoid fossa of the scapula at a glenohumeral joint and a sheet-like material is affixed to the tendon; 
         FIG. 7  is a stylized perspective view showing a portion of the body of a human patient divided into quadrants by planes for descriptive purposes herein; 
         FIG. 8  is a stylized perspective view illustrating an exemplary procedure for arthroscopic treatment of a shoulder of a patient in accordance with one embodiment of the disclosure; 
         FIG. 9  is a stylized perspective view of a shoulder including a supraspinatus having a distal tendon with a sheet-like material affixed thereto; 
         FIG. 10A  is a simplified perspective view of a tissue fastener or staple delivery device in accordance with the present disclosure; 
         FIG. 10B  is a simplified perspective view of a trocar assembly, including a trocar disposed within a guide sheath assembly for creating pilot holes and retaining the sheath within the formed pilot holes for delivery of a tissue fastener or staple by a device such as that depicted in  FIG. 10A . 
         FIG. 11A  is a perspective view of the sheath assembly of  FIG. 10B  with the trocar removed; 
         FIG. 11B  is a perspective view of the trocar of  FIG. 10B  as removed from the sheath assembly; 
         FIG. 11C  is a perspective view of one pilot hole position retention member which is positioned in a distal portion of the sheath assembly in one embodiment of the present disclosure; 
         FIG. 12  is a perspective view depicting the sheath and staple pusher assemblies of a staple delivery device in one embodiment of the disclosure; 
         FIG. 13  is a simplified exploded view of the tissue fastener or staple delivery device of  FIG. 10A  depicting additional features thereof; 
         FIG. 14  depicts further features of the staple pusher assembly of  FIG. 13 ; 
         FIGS. 15A and 15B  illustrate the features of the distal portion of the staple pusher assembly of  FIG. 13  with a staple mounted thereon in accordance with one embodiment of the disclosure; 
         FIGS. 16A and 16B  further illustrate the staple pusher assembly in one embodiment of the disclosure; 
         FIG. 17  is a more detailed perspective view of the distal portion of the staple pusher assembly illustrating stakes that mate with the staple in one embodiment of the disclosure; 
         FIG. 18A  is simplified perspective view of a shoulder having an implant affixed to the tendon and depicting the first step in a method of delivering fasteners to affix the implant to bone of the humeral head in accordance with one method of the disclosure; 
         FIG. 18B  is a simplified plan view of the distal portion of the trocar assembly as position to create pilot holes for affixing the implant to bone in a further step of a method of the disclosure; 
         FIG. 18C  depicts the trocar assembly of  FIG. 18B  as inserted into the bone to form pilot holes in accordance with a method of the disclosure; 
         FIG. 18D  depicts the trocar assembly with the trocar portion removed and the remaining sheath assembly retaining its position in the pilot holes formed; 
         FIG. 18E  is a partial perspective view of the articular side of the supraspinatus tendon illustrating the position relative to the biceps tendon and a marker inserted from the bursal side to identify the location of the biceps tendon which is not visible from the bursal side; 
         FIG. 18F  illustrates a fastener or staple as inserted in accordance with a method of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. 
       FIG. 1  is a perspective view illustrating an exemplary staple  100  in accordance with the present detailed description. With reference to  FIG. 1 , it will be appreciated that staple  100  may assume various orientations without deviating from the spirit and scope of this detailed description. Although the various parts of this exemplary embodiment are depicted in relative proportion to other parts of the staple  100 , other configurations in size and orientation of the various parts are possible. A number of reference directions are illustrated using arrows in  FIG. 1  to assist in understanding the details of the staple  100 . The illustrated directions include: a proximal direction P, a distal direction D, a first laterally outward direction LOA, a second laterally outward direction LOB, a first laterally inward direction LIA, and a second laterally inward direction LIB. 
     Staple  100  comprises a first arm  102 A, a second arm  102 B, and a bridge  104  extending from, abutting or adjacent to the proximal end of first arm  102 A to the proximal end of second arm  102 B. The first arm  102 A includes a first trunk  106 A extending for at a least a portion of the length of the first arm  102 A. As depicted in  FIG. 1 , a proximal portion of the first arm  102 A abuts the proximal end of the first trunk  106 A. The first arm  102 A, in this embodiment includes the trunk portion  106 A and a non-trunk portion  105 A. The length of first trunk  106 A relative to the overall length of the first arm  102 A can vary in different embodiments. The first trunk  106 A can extend for the entire length of the first arm  102 A such that the bridge abuts with or is adjacent to the trunk  106 A. Similarly, the second arm  102 B includes a second trunk  106 B extending for at least a portion of the length of the second arm  102 B. A proximal portion of the second aim  102 B abuts the proximal end of the second trunk  106 B. The second arm  102 B, in this embodiment includes the trunk portion  106 B and a non-trunk portion  105 B. The length of second trunk  106 B relative to the overall length of the second arm  102 B can vary in different embodiments. The second trunk  106 B can extend for the entire length of the second arm  102 B such that the bridge abuts with or is adjacent to the trunk  106 B. In  FIG. 1 , first trunk  106 A and second trunk  106 B are shown extending distally from a proximal portion of first arm  102 A and second arm  102 B, respectively. 
     In the embodiment of  FIG. 1 , first trunk  106 A has a lateral extent, or cross sectional area, that is larger than a lateral extent of the non-trunk portion  105 A of first arm  102 A and bridge  104 . The staple  100  includes a first change in lateral stiffness  108 A disposed where the distal end of non-trunk portion  105 A of first arm  102 A abuts first trunk  106 A. As depicted, the change in stiffness is abrupt, but can be gradual in alternative embodiments. In an embodiment where the first trunk  106 A extends for the full length of the first arm  102 A, the change in stiffness occurs where the first trunk  106 A abuts the bridge  104 . With reference to  FIG. 1 , it will be appreciated that first trunk  106 A is mounted eccentrically to first arm  102 A and second trunk  106 B is mounted eccentrically to second arm  102 B. As with first trunk  106 A, second trunk  106 B has a lateral extent, or cross sectional area that is larger than a lateral extent of second arm  102 B or bridge  104 . The staple  100  includes a second change in lateral stiffness  108 B where the distal end of second arm  102 B abuts second trunk  106 A in the embodiment of  FIG. 1 . If the second trunk  106 B extends for the entire length of second arm  102 B, the change in stiffness occurs at the abutment with the bridge  104 . 
     Each of the first trunk  106 A and second trunk  106 B can include at least a first projection  122 A,  122 C and a second projection  122 B,  122 D, the first projection  122 A,  122 C on each trunk  106 A,  106 B includes a first proximal surface  124 A,  124 C extending away from the trunk in a first direction, the first direction being such that the first proximal surface  124 A,  124 C will engage the tissue or bone after the trunk is inserted therein and a pullout force is applied to the bridge  104 . This force creates a first moment centered on the area of reduced lateral extent adjacent the trunk, tending to rotate the trunk thereabout, further providing a greater holding force in response to the pullout force as the trunk presses against the tissue or bone. The second projection  122 B,  122 D includes a second proximal surface  124 B,  124 D extending away from the trunk in a second direction, different from the first direction, the second direction being such that the second proximal surfaces  124 B,  124 D will engage the tissue or bone after the trunk is inserted therein and a pullout force is applied to the bridge  104 . A slit or area of reduced cross section in the trunk adjacent the second projections provide an area of weakness so that a second moment is applied to the trunk in response to a pullout force on the bridge  104 . This moment causes rotation of the trunk about the area of weakness and increases the holding force with increased pullout force. 
     As specifically illustrated in the embodiment of staple or fastener  100  in  FIG. 1 , first trunk  106 A includes a first projection  122 A disposed at an outer side of trunk  106 A and a second projection  122 B disposed at an inner side of the trunk. First projection  122 A includes a first proximal surface  124 A extending away from first trunk  106 A in a first direction. With reference to  FIG. 1 , it will be appreciated that the first direction has an outward lateral component and a proximal component so that first proximal surface  124 A extends outwardly and proximally away from first trunk  106 A. The first direction is selected such that first proximal surface  124 A will engage tissue or bone proximate the outer side of first trunk  106 A after being inserted therein so that a first moment is applied to the trunk in response to a pullout force on bridge  104 . The moment centers on the arm portion of lesser cross section adjacent the first projection. 
     In the embodiment of  FIG. 1 , first trunk  106 A includes a first localized area of weakness  120 A disposed proximate second projection  122 B. Second projection  122 B includes a second proximal surface  124 B extending away from first trunk  106 A in a second direction. The second direction is selected such that second proximal surface  124 A will engage tissue or bone proximate the inner side of first trunk  106 A when inserted therein so that a second moment is applied to the trunk in response to a pullout force on bridge  104 . The moment centers around the area of weakness  120 A. The second moment has a direction that is generally opposite a direction of the first moment. It will be appreciated that the second direction has an inward lateral component and a proximal component so that second proximal surface  124 B extends inwardly and proximally away from first trunk  106 A. 
     Second trunk  106 B includes a third projection  122 C disposed at an outer side of second trunk  106 B and a fourth projection  122 D disposed at an inner side of the trunk. In the embodiment of  FIG. 1 , third projection  122 C includes a third proximal surface  124 C extending away from second trunk  106 B in a third direction. With reference to  FIG. 1 , it will be appreciated that the third direction has an outward lateral component and a proximal component so that third proximal surface  124 C extends outwardly and proximally away from second trunk  106 B. The third direction is selected such that third proximal surface  124 C will engage tissue or bone proximate the outer side of second trunk  106 B when inserted therein so that a third moment is applied to the trunk in response to a pullout force on bridge  104 . 
     In the embodiment of  FIG. 1 , second trunk  106 B includes a second localized area of weakness  120 B disposed proximate fourth projection  122 D. Fourth projection  122 D includes a fourth proximal surface  124 D extending away from second trunk  106 B in a fourth direction. In the embodiment of  FIG. 1 , the fourth direction is selected such that second proximal surface  124 A will engage tissue or bone proximate the inner side of second trunk  106 B when inserted therein so that a fourth moment is applied to the trunk in response to a pullout force on bridge  104 . The fourth moment has a direction that is generally opposite a direction of the third moment. It will be appreciated that the fourth direction has an inward lateral component and a proximal component so that fourth proximal surface  124 D extends inwardly and proximally away from second trunk  106 . 
     As depicted in  FIG. 1 , the staple  100  includes proximal projections that extend away from or outward from the bridge  104 , while the distal projections extend inward or toward the center of the bridge  104 . This creates generally opposing forces in response to tension on the bridge which, in combination with areas of weakness or reduced lateral extent, substantially increases the holding force of the staple in bone as the different portions of the trunks tend to rotate in opposite directions and apply force to an opposing wall in the hole in bone in which the staple is positioned. It is however, understood that other configurations of the projections are possible. In some embodiments, at least two projections are included and they extend in different directions to cause different force responses as tension is applied to the bridge. It is believed this provides adequate holding force in bone, which can include differing thicknesses of hard and soft tissue along with porous areas. 
     In some useful embodiments, each projection of staple  100  may be clefted to form a plurality of points for greater retention in tissue. In the exemplary embodiment of  FIG. 1 , first projection  122 A of first trunk  106 A defines a first notch  126 A that divides first projection  122 A into a first sub-projection and a second sub-projection. Second projection  122 B of second trunk  106 B defines a second notch  126 B. In the exemplary embodiment of  FIG. 1 , second notch  126 B divides second projection  122 B into a first sub-projection and a second sub-projection. Third projection  122 C of second trunk  106 B defines a third notch  126 C that divides third projection  122 C into a first sub-projection and a second sub-projection. Fourth projection  122 D of second trunk  106 B defines a fourth notch  126 D that divides fourth projection  122 D into a first sub-projection and a second sub-projection. 
     With continued reference to  FIG. 1  and further reference to  FIGS. 2 and 3 , first trunk  106 A defines a first cavity  128 A and second trunk  106 B defines a second cavity  128 B. In the exemplary embodiment of  FIGS. 1, 2 and 3 , first cavity  128 A extends into first trunk  106 A and second cavity  128 B extends into second trunk  106 B. The cavity is sized to cooperate with a staple delivery device for holding and inserting the staple into tissue or bone, as later described in detail herein. In summary, the staple delivery device includes longitudinally extending stakes that fit within the cavities  128 A,  128 B to hold the staple  100  and push it into position in the tissue as the stake abuts a portion of its respective trunk. In some embodiments the cavity may extend through a portion of the length of each trunk, as best depicted in  FIG. 2  which indicates the distal end of the staple  100  is closed. Alternatively, first cavity  128 A and second cavity  128 B may extend through the entire length of each trunk  106 A,  106 B or other portions of staple  100  in some embodiments. As illustrated by the top view of the staple  100  in  FIG. 3 , first cavity  128 A and second cavity  128 B each have a generally rectangular or square cross-sectional shape to cooperate with a similarly shaped cross section on a staple delivery device. However, that first cavity  128 A and second cavity  128 B may have various cross-sectional shapes to cooperate with alternative staple delivery device designs without deviating from the spirit and scope of the present detailed description. 
       FIG. 4  is an alternative perspective view of the embodiment in  FIG. 1  illustrating an exemplary staple  100  in accordance with the present detailed description. In particular,  FIG. 4  illustrates in phantom the flexing and bending of the trunks  106 A and  106 B after implant in response to tension applied to the bridge, as by tissue or an implant affixed at an implant site. Staple  100  comprises a first arm  102 A, a second arm  102 B, and a bridge  104  extending from the proximal end of first arm  102 A to the proximal end of second arm  102 B. The distal end of first arm non-trunk portion  105 A abuts the proximal end of first trunk  106 A. Similarly, the distal end of second aim non-trunk portion  105 B abuts the proximal end of a second trunk  106 B. In  FIG. 4 , first trunk  106 A and second trunk  106 B are shown extending distally from first arm  102 A and second arm  102 B, respectively. 
     In the embodiment of  FIG. 4 , first trunk  106 A has a lateral extent that is larger than the lateral extent of the non-trunk portion  105 A of first arm  102 A. This combination creates a relatively abrupt change in lateral stiffness  108 A disposed where the distal end of the non-trunk portion  108 A of first arm  102 A abuts first trunk  106 A. With reference to  FIG. 4 , first trunk  106 A is mounted eccentrically to first arm  102 A and second trunk  106 B is mounted eccentrically to second arm  102 B, however, other mountings or abutments can be used, such as a non-trunk portion having walls that surround the cavity and include a lumen therethrough to access the cavity with a staple delivery stake. A change in lateral stiffness would still be accomplished where the lateral extend changed. Further, a change in lateral stiffness could be accomplished by using a different material for the non-trunk portion relative to the trunk portion. Second trunk  106 B in combination with the non-trunk portion  105 B of second arm  102 B provides the same change in lateral stiffness  108 B. The first arm  102 A, the second arm  102 B, and the bridge  104  may be integrally formed of a polymeric material, such as polyether ether ketone (PEEK). 
     As earlier described the configuration of the four projections  122 A,  122 B,  122 C and  122 D, contact the tissue or bone and provide a holding force upon implantation. Each projection is positioned to provide a force moment in a desired direction to the trunk in response to the pullout force on the bridge  104 . 
     In the embodiment of  FIG. 4 , first trunk  106 A and second trunk  106 B include first and second localized areas of weakness  120 A,  120 B disposed proximate second projections  122 B,  122 D. This area of weakness is formed by a slit formed proximal of the projection. However, the area of weakness could be formed by other means, such as a change in material, pinching or perforations. 
     The combination of projections, areas of weakness and changes in lateral extent provide desired flexing, bending and rotating of the trunk in response to pull out forces once implanted in a bone, such as in a pilot hole formed in the bone. Together these components act as tissue retention members. An exemplary deflected shape is shown with dashed lines in  FIG. 4 . Staple  100  may be urged to assume the deflected shape shown in  FIG. 4 , for example, by applying a pullout force on the bridge  104  of the staple  100 . Alternatively, distally directed forces can be applied on staple  100  using, for example, the staple delivery system shown later and described herein. In some applications, the staple delivery tool may be used to urge first projection  122 A and third projection  122 C into orientations which lock staple  100  into a target tissue. For example, first projection  122 A and third projection  122 C may be rotated so that these projections engage the target tissue. When this is the case, tension extending through bridge  104  of staple  100  may keep first projection  122 A and third projection  122 C in the rotated position. Also when this is the case, the projections may inhibit staple pullout. Further, rotation of any projection causes a rotational force and within limits defined by the hole in the bone some rotation to an adjacent portion of the trunk which contacts or engages the wall of the hole in the bone. Increased pullout force results in increasing holding force with this design. 
     Next referring to  FIG. 5 , an exemplary use or application of the staples of the present disclosure is described.  FIG. 5  is a stylized anterior view of a patient  20 . For purposes of illustration, a shoulder  22  of patient  20  is shown in cross-section in  FIG. 5 . Shoulder  22  includes a humerus  14  and a scapula  12 . In  FIG. 5 , a head  24  of humerus  14  can be seen mating with a glenoid fossa of scapula  12  at a glenohumeral joint. With reference to  FIG. 5 , it will be appreciated that the glenoid fossa comprises a shallow depression in scapula  12 . The movement of humerus  14  relative to scapula  12  is controlled by a number of muscles including: the deltoid, the supraspinatus, the infraspinatus, the subscapularis, and the teres minor. For purposes of illustration, only the supraspinatus  26  is shown in  FIG. 5 . 
     With reference to  FIG. 5 , a distal tendon  28  of the supraspinatus  26  meets humerus  14  at an insertion point. Scapula  12  of shoulder  22  includes an acromium  32 . In  FIG. 5 , a subacromial bursa  34  is shown extending between acromium  32  of scapula  12  and head  24  of humerus  14 . Subacromial bursa  34  is shown overlaying supraspinatus  26  as well as supraspinatus tendon  28  and a portion of humerus  14 . Subacromial bursa  34  is one of the hundreds of bursae found the human body. Each bursa comprises a fluid filled sac. The presence of these bursae in the body reduces friction between bodily tissues. 
     The exemplary staples or fasteners described herein may be used to affix tendon repair implants to various target tissues. The shoulder depicted in  FIG. 5  is one example where a tendon repair implant may be affixed to one or more bones associated with an articulating joint, such as the glenohumeral joint. Additionally, the tendon repair implant may be affixed to one or more tendons to be treated. The tendons to be treated may be torn, partially torn, have internal micro-tears, be untorn, and/or be thinned due to age, injury or overuse. Applicants believe that the methods and apparatus of the present application and related devices may provide very beneficial therapeutic effect on a patient experiencing joint pain believed to be caused by partial thickness tears and/or internal microtears. By applying a tendon-repair implant early before a full tear or other injury develops, the implant may cause the tendon to thicken and/or at least partially repair itself, thereby avoiding more extensive joint damage, pain, and the need for more extensive joint repair surgery. 
       FIG. 6  is a stylized anterior view of a shoulder  22  including a humerus  14  and a scapula  12 . In  FIG. 6 , a head  24  of humerus  14  is shown mating with a glenoid fossa of scapula  12  at a glenohumeral joint. A supraspinatus  26  is also shown in  FIG. 6 . This muscle, along with others, controls the movement of humerus  14  relative to scapula  12 . A distal tendon  28  of supraspinatus  26  meets humerus  14  at an insertion point  30 . 
     As depicted in  FIG. 6 , distal tendon  28  includes a first damaged portion  36 . A number of loose tendon fibers  40  in first damaged portion  36  are visible in  FIG. 6 . First damaged portion  36  includes a first tear  42  extending partially through distal tendon  28 . First tear  42  may therefore be referred to as a partial thickness tear. With reference to  FIG. 6 , first tear  42  begins on the side of distal tendon  28  facing the subacromial bursa (shown in the previous Figure) and ends midway through distal tendon  28 . Accordingly, first tear  42  may be referred to as a bursal side tear. 
     With reference to  FIG. 6 , distal tendon  28  includes a second damaged portion  38  located near insertion point  30 . As illustrated, second damaged portion  38  of distal tendon  28  has become frayed and a number of loose tendon fibers  40  are visible. Second damaged portion  38  of distal tendon  28  includes second tear  44 . Second tear  44  begins on the side of distal tendon  28  facing the center of the humeral head  24 . Accordingly, second damaged portion  38  may be referred to as an articular side tear. 
       FIG. 6  illustrates a sheet-like implant  50  has been placed over the bursal side of distal tendon  28 . The sheet-like implant  50  is affixed to distal tendon  28  by a plurality of tendon staples  51 . Sheet-like implant  50  is affixed to humerus  14  by a plurality of bone staples  100  in accordance with designs of staples disclosed herein. Sheet-like implant  50  extends over insertion point  30 , first tear  42  and second tear  44 . Some useful methods in accordance with this detailed description may include placing a tendon repair implant on the bursal side of a tendon regardless of whether the tears being treated are on the bursal side, articular side or within the tendon. In some cases the exact location and nature of the tears being treated may be unknown. A tendon repair implant may be applied to the bursal side of a tendon to treat shoulder pain that is most likely caused by one or more partial thickness tears in the tendon. 
       FIG. 7  is a stylized perspective view showing a portion of the body  82  of a human patient  20 . Body  82  includes a shoulder  22 . In the exemplary embodiment of  FIG. 7 , a plurality of cannulas are positioned to access a treatment site within shoulder  22 . In some cases, shoulder  22  may be inflated by pumping a continuous flow of saline through shoulder  22  to create a cavity proximate the treatment site. The cannulas shown in  FIG. 7  include a first cannula  80 A, a second cannula  80 B and a third cannula  80 C. 
     In  FIG. 7 , a sagital plane SP and a frontal plane FP are shown intersecting body  82 . Sagital plane SP and frontal plane FP intersect one another at a medial axis MA of body  82 . With reference to  FIG. 7 , sagital plane SP bisects body  82  into a right side  84  and a left side  86 . Also with reference to  FIG. 7 , frontal plane FP divides body  82  into an anterior portion  92  and a posterior portion  88 . Sagital plane SP and a frontal plane FP are generally perpendicular to one another. These planes and portions are used to describe the procedures used in exemplary embodiments. 
     First cannula  80 A is accessing a treatment site within shoulder  22  using a lateral approach in which first cannula  80 A pierces the outer surface of right side  84  of body  82 . The term lateral approach could also be used to describe situations in which an instrument pierces the outer surface of left side  86  of body  82 . Second cannula  80 B is accessing a treatment site within shoulder  22  using a posterior approach in which second cannula  80 B pierces the outer surface of posterior portion  88  of body  82 . Third cannula  80 C is accessing a treatment site within shoulder  22  using an anterior approach in which third cannula  80 C pierces the outer surface of anterior portion  92  of body  82 . 
       FIG. 8  is a stylized perspective view illustrating an exemplary procedure for treating a shoulder  22  of a patient  20 . The procedure illustrated in  FIG. 8  may include, for example, fixing tendon repair implants to one or more tendons of shoulder  22 . The tendons treated may be torn, partially torn, have internal micro-tears, be untorn, and/or be thinned due to age, injury or overuse. 
     Shoulder  22  of  FIG. 8  has been inflated to create a cavity therein. A fluid supply  52  is pumping a continuous flow of saline into the cavity. This flow of saline exits the cavity via a fluid drain  54 . A camera  56  provides images from inside the cavity. The images provided by camera  56  may be viewed on a display  58 . 
     Camera  56  may be used to visually inspect the tendons of shoulder  22  for damage. A tendon repair implant in accordance with this disclosure may be affixed to a bursal surface of the tendon regardless of whether there are visible signs of tendon damage. Applicants believe that the methods and apparatus of the present application and related devices may provide very beneficial therapeutic effect on a patient experiencing joint pain believed to be caused by internal microtears, but having no clear signs of tendon tears. By applying a tendon repair implant early before a full tear or other injury develops, the implant may cause the tendon to thicken and/or at least partially repair itself, thereby avoiding more extensive joint damage, pain, and the need for more extensive joint repair surgery. 
     An implant delivery system  60  can be seen extending from shoulder  22  in  FIG. 8 . Implant delivery system  60  is extending through a first cannula  80 A. In certain embodiments, first cannula  80 A can access a treatment site within shoulder  22  using a lateral approach in which first cannula  80 A pierces the outer surface of a right side of the patient&#39;s body. In some cases a physician may choose not to use a cannula in conjunction with implant delivery system  60 . When that is the case, the implant delivery system may be advanced through tissue. Implant delivery system  60  comprises a sheath that is affixed to a handle. The sheath defines a lumen and a distal opening fluidly communicating with the lumen. In the embodiment of  FIG. 8 , the distal opening of the sheath has been placed in fluid communication with the cavity created in shoulder  22 . 
     A tendon repair implant is at least partially disposed in the lumen defined by the sheath of implant delivery system  60 . Implant delivery system  60  can be used to place the tendon repair implant inside shoulder  22 . In some embodiments, the tendon repair implant is folded into a compact configuration when inside the lumen of the sheath. When this is the case, implant delivery system  60  may be used to unfold the tendon repair implant into an expanded shape. Additionally, implant delivery system  60  can be used to hold the tendon repair implant against the tendon. 
     The tendon repair implant may be affixed to the tendon while it is held against the tendon by implant delivery system  60 . Various attachment elements may be used to fix the tendon-repair implant to the tendon. Examples of attachment elements that may be suitable in some applications include sutures, tissue anchors, bone anchors, and staples. In the exemplary embodiment of  FIG. 8 , the shaft of a fixation tool  70  is shown extending into shoulder  22 . In one exemplary embodiment, fixation tool  70  is capable of fixing the tendon repair implant to the tendon and bone with one or more staples of the present disclosure while the tendon repair implant may held against the tendon by implant delivery system  60 . 
       FIG. 9  is a stylized perspective view of a shoulder  22  including a supraspinatus  26  having a distal tendon  28 . With reference to  FIG. 9 , a tendon repair implant  50  has been affixed to a surface of distal tendon  28 . Tendon repair implant  50  may comprise, for example, various sheet-like structures without deviating from the spirit and scope of the present detailed description. In some useful embodiments, the sheet-like structure may comprise a plurality of fibers. The fibers may be interlinked with one another. When this is the case, the sheet-like structure may comprise a plurality of apertures comprising the interstitial spaces between fibers. Various processes may be used to interlink the fibers with one another. Examples of processes that may be suitable in some applications including weaving, knitting, and braiding. In some embodiments, the sheet-like structure may comprise a laminate including multiple layers of film with each layer of film defining a plurality of micro-machined or formed holes. The sheet-like structure of the tendon repair implant may also comprise a reconstituted collagen material having a porous structure. Additionally, the sheet-like structure of the tendon repair implant may also comprise a plurality of electro-spun nanofiber filaments forming a composite sheet. Additionally, the sheet-like structure may comprise a synthetic sponge material that defines a plurality of pores. The sheet-like structure may also comprise a reticulated foam material. Reticulated foam materials that may be suitable in some applications are available from Biomerix Corporation of Fremont, Calif. which identifies these materials using the trademark BIOMATERIAL™. The sheet-like structure may be circular, oval, oblong, square, rectangular, or other shape configured to suit the target anatomy. 
     Various attachment elements may be used to fix tendon repair implant  50  to distal tendon  28  without deviating from the spirit and scope of this detailed description. Examples of attachment elements that may be suitable in some applications include sutures, tissue anchors, bone anchors, and staples. In the embodiment of  FIG. 9 , sheet-like implant  50  is affixed to distal tendon  28  by a plurality of tendon staples  51 . Sheet-like implant  50  is affixed to humerus  14  by a plurality of bone staples  100  as described with respect to the exemplary embodiment of  FIG. 1  and detailed throughout this disclosure. 
     In some exemplary methods, a plurality of staples may be applied using a fixation tool. After the staples are applied, the fixation tool may be withdrawn from the body of the patient. Distal tendon  28  meets humerus  14  at an insertion point  30 . With reference to  FIG. 9 , it will be appreciated that sheet-like implant  50  extends over insertion point  30 . Tendon repair implant may be applied to distal tendon  28 , for example, using the procedure illustrated in the previous figures. In various embodiments, staples may straddle the perimeter edge of the sheet-like implant (as shown in  FIG. 9 ), may be applied adjacent to the perimeter, and/or be applied to a central region of the implant. In some embodiments, the staples may be used to attach the implant to soft tissue and/or to bone. 
     Staples or fasteners  100 , as exemplified in  FIG. 1  and described and illustrated herein can be used to attach tissue and implants to bone. In at least some embodiments, the staple is generally flexible and includes areas of relative lateral weakness on the trunks and can further include an increase in flexibility at the transition from the trunk to the non-trunk portion of the arm or the transition from the trunk to the bridge. As described above, these areas of increased flexibility provide improved staple retention as these portions allow flexing and bending in response to increasing pullout forces. With this flexibility, the fasteners cannot be pounded or driven into bone or other tissue as a conventional hard staple would be driven into paper, wood, tissue or bone. Therefore, for application of the staple of the present disclosure to affixing tissue or implants to bone, the staple is generally included in a kit that also includes a staple delivery device  200  and a pilot hole forming trocar assembly  300 , as schematically illustrated in  FIGS. 10A and 10B , respectively. 
     In general, the staple delivery device  200  can include a handle assembly  201  and a barrel assembly  205 . The handle assembly  201  includes a trigger  203  that is operatively coupled to mechanisms in the barrel assembly  205  to deploy a staple of the present disclosure in bone. The staple delivery device  200  can be used in conjunction with the pilot hole forming trocar assembly  300  of  FIG. 10B . 
     The pilot hole forming trocar assembly  300 , illustrated generally in  FIG. 10B  includes a trocar  302  and a position retention sleeve  304 . The trocar  302  is releasably coupled to the position retention sleeve  304  and slides in keyed arrangement within the sleeve  304  when uncoupled. The trocar  302  includes a distal portion having a retractable blade  306  and a pair of pilot hole forming spikes  308  extending distally from the trocar shaft. The retractable blade  306  is useful in inserting the assembly through an incision. The retractable blade  306  can be retracted in this embodiment by activating release button  315  which causes a spring (not shown) to pull the retractable blade  306  into the shaft of the trocar within the position retention sleeve  304 . In this the position, the pilot hole forming spikes remain extended from the shaft. In some embodiments the retractable blade  306  can be omitted if the pilot hole forming trocar assembly is to be inserted into an incision that already has a cannula extending therethrough to provide an instrument path. 
     Referring to  FIGS. 11A-11C , details of the elements of one embodiment of a pilot hole forming trocar assembly  300  are illustrated. The pilot hole forming trocar assembly is used to created pilot holes in a bone for subsequent placement of a staple or fastener, such as staple  100  of  FIG. 1 . Further, the pilot hole forming trocar assembly includes a means for retaining instrument position with respect to the pilot holes when the trocar is removed so that a staple delivery device  200  can be inserted and the staple be in alignment with the already formed pilot holes. This prevents the time and difficulty associated with finding the pilot holes with the staple, which in fact may not be possible for many practitioners. 
     As previously stated, a pilot hole forming trocar assembly  300  can include a trocar  302  and a position retention sleeve  304 . One embodiment of a position retention sleeve  304  is illustrated in  FIG. 11A . The position retention sleeve  304  includes a shaft  311  having a lumen  310  extending therethrough. The lumen  310  is sized to receive the trocar  302  when used to form pilot holes. The lumen  310  is also sized to receive a staple delivery device  200  when used to position a staple in a pilot hole formed in bone. The lumen is shaped or keyed to cooperate with either of these instruments or other instruments so that relative rotational position of the trocar  302  or staple delivery device  200  is fixed when slidably positioned in the position retention sleeve. An opening or window  313  may be included near the distal end of the position retention sleeve to allow viewing of devices inserted therein. 
     Position retention members  314  extend distally from the shaft  311 . As detailed in  FIG. 11C , the position retention members can be included on an insert  312  that is affixed proximate the distal end of the shaft  311 . Alternatively, the position retention members can be integral to the shaft  311 . The position retention members are sized and designed to extend into pilot holes as they are foamed by the trocar  302  described below. When the trocar  302  is removed, the position retention members  314 , along with the sleeve  311  remain in position to provide a guide for the staple delivery device  200  to be inserted into proper position and position a staple  100  in the pilot holes. As depicted, the position retention members  314  can include longitudinally extending semi-cylindrical projections. In the disclosed embodiment, the pilot hole forming spikes  308  of the trocar  302  slide within the partial lumens of the position retention members  314 . This design can provide support for the spikes as they are pounded into bone and can also allow the position retention members to readily slide into pilot holes formed by the spikes  308 . 
     A more detailed depiction of one alternative embodiment of a trocar  302  is included in  FIG. 11B . The trocar includes a shaft  320  having at its proximal end a knob  324  that can be used to pound or push the trocar  302  into bone. The trocar can further include a collar  322  which can be used to releasable engage the position retention sleeve  304  when the two are mated for forming pilot holes. A spring  323  can be included which causes or aids the retraction of the trocar when it is released from the position retention sleeve. 
     As previously disclosed, the distal end of the trocar  302  includes two pilot hole forming spikes  308  extending from shaft  320 . A retractable blade  306  is positioned between the spikes  308 . In use, the blade  306  is retracted prior to the spikes  308  being used to form pilot holes in bone. 
     Now referring to  FIG. 12 , the two main components of one embodiment of the barrel assembly  205  are illustrated. The barrel assembly includes an outer sleeve  250  having a lumen  251  extending therethrough. The outer sleeve  250  is secured to the handle assembly  201  in fixed relationship when the staple delivery device  200  is assembled. A staple delivery assembly  252  is slidably disposed in the lumen  251  and includes a proximal end  254  extending beyond the proximal end of the sleeve  250 . The proximal end  254  of the staple delivery assembly  252  operatively interacts with trigger assembly  203  when the barrel  205  is mounted on the handle assembly  201 . In the embodiment of  FIG. 12 , the outer surface of the sleeve  250  is shaped so as to be rotationally keyed and sized for desired fitting within the position retention sleeve  304 . The sleeve  250  includes a flat surface  257  keyed to fit within a flat surface on the interior of the position retention sleeve  304 . 
     The operation of some embodiments of the staple delivery device  200  is further understood with reference to  FIG. 13 .  FIG. 13  is an exploded view showing the staple delivery device  200  that may be used in conjunction with a staple  100  and the above described pilot hole forming trocar  300 . The handle assembly  201  and barrel assembly  205  are shown with the barrel assembly including both the sleeve  250  and staple delivery assembly  252  included. Staple delivery assembly  252  includes a fork  232 , a shaft  240 , and two staple setting rods  234 . Staple setting rods  234  include a first staple setting rod  234 A and a second staple setting rod  234 B. Both staple setting rods  234  are affixed to a rod coupler  236  of staple delivery assembly  252  in the embodiment of  FIG. 13 . When the barrel  205  is in an assembled state, first staple setting rod  234 A and second staple setting rod  234 B can extend through two grooves defined by shaft  240 . Each groove is dimensioned so that a staple setting rod can be partially disposed therein while the sleeve  250  surrounds the staple setting rods  234  and shaft  240 . 
     When staple delivery device  200  is in an assembled state, staple  100  may be carried by a first stake  238 A and a second stake  238 B of fork  232 . As previously described with respect to  FIG. 1 , staple  100  can include a first aim  102 A, a second arm  102 B, and a bridge  104  extending from the proximal end of first arm  102 A to the proximal end of second arm  102 B. The distal end of the non-trunk portion of first arm  102 A abuts the proximal end of a first trunk  106 A. Similarly, the distal end of the non-trunk portion of second arm  102 B abuts the proximal end of a second trunk  106 B. 
     Now referring to  FIGS. 14-17 , details of some exemplary embodiments and features of the staple delivery assembly  252  and the mounting and delivery of a staple  100  are illustrated. Various aspects of these elements may be included in embodiments of the overall staple delivery device  200  of this disclosure. 
     The components of a staple delivery assembly  252  are illustrated in  FIG. 14 . First stake  238 A and second stake  238 B of fork  232  can be seen extending distally away from a distal end of shaft  240  in  FIG. 14 . The distal direction is indicated with an arrow D. In the embodiment of  FIG. 14 , first stake  238 A includes a distal portion  244 A and a proximal portion  246 A. Second stake  238 B includes a distal portion  244 B and a proximal portion  246 B. In some useful embodiments, each distal portion  244  is dimensioned to extend into a cavity defined by a staple, such as cavity  128 A,  128 B of staple  100  in  FIG. 1 . When this is the case, the staple may be supported by each distal portion  244  that extends into a passage defined by the staple. In this way, fork  232  may be used to carry a staple. Staple  100  is illustrated proximate the distal end of shaft  240  to show the staple features relative to the staple delivery assembly  252  prior to mounting the staple thereon. Staple setting rods  234  are illustrated as attached to rod coupler  236  and it can be seen how these rods can slidably engage the channels running longitudinally on shaft  240 . Spring  242  is also depicted. 
     In  FIGS. 15A and 15B , the staple setting rods  234 , fork  232  and staple  100  are shown as initially assembled in one embodiment, prior to adding shaft  240 . In particular,  FIG. 15B  depicts fork  232  slidably disposed in channels  233 . It further shows the way in which staple settings rods are disposed within cavities in the staple and the distal ends of the staple setting rods  234  extend to abut a proximal surface of the staple, in this embodiment the proximal surface is the proximal end of the trunk. In some useful methods, staple setting rods  234  are moved distally to apply pushing forces to one or more proximal surfaces of staple  100 . These pushing forces may be used, for example, to urge first projection  122 A and third projection  122 C into orientations that lock staple  100  into a target tissue. For example, first projection  122 A and third projection  122 C may be rotated so that these projections engage the target tissue. When this is the case, tension extending through bridge  104  of staple  100  may keep first projection  122 A and third projection  122 C in the rotated position. Also when this is the case, the projections may inhibit staple pullout. 
     In  FIGS. 16A and 16B , the initial assembly of  FIG. 15A  is shown with the shaft  240  in position, along with the staple setting rods affixed to the rod coupler  236  and the spring positioned between the rod coupler  236  and the proximal end of the shaft  240 . The spring  242  of staple delivery assembly  252  may be compressed as staple setting rods  234  are moved distally to urge first projection  122 A and third projection  122 C into orientations that lock staple  100  into a target tissue. After staple  100  has been set, spring  242  may urge staple setting rods  234  proximally toward a starting position. When staple delivery assembly  252  is in an assembled state, a distal end of spring  242  is seated against a proximal end of shaft  240  and a proximal end of spring  242  is seated against the distal end of rod coupler  236 . Spring  242  may deflect as staple setting rods  234  are moved proximally and distally relative to shaft  140 . Distal and proximal directions are indicated with arrows labeled D and P. 
       FIG. 17  is a perspective view further illustrating fork  232  shown more generally in the previous figures. Fork  232  includes a first stake  238 A and a second stake  238 B. First stake  238 A includes a distal portion  244 A and a proximal portion  246 A. Second stake  238 B includes a distal portion  244 B and a proximal portion  246 B. The proximal portion  246  of each stake  238  has generally dovetail-shaped lateral cross-section. In some useful embodiments, each proximal portion  246  is dimensioned to be received in a dovetail-shaped slot defined by a staple setting rod  234 . When this is the case, the staple setting rod and the fork are coupled to each other with a single degree of freedom for relative movement such that the staple setting rod can slide in distal and proximal directions relative to the fork, as previously described. 
     As depicted in the prior drawings, the manner in which a staple  100 , a first staple setting rod  234 A and a second staple setting rod  234 B engage fork  232  allows placement of the staple with active engagement and retention in the tissue or bone. Each staple setting rod  234  is disposed in sliding engagement with fork  232 . A distal end of each staple setting rod  234  is disposed near a staple  100  that is carried by fork  232 . 
     Staple  100  is designed to cooperatively engage the fork and staple setting rods when mounted thereon for placement in bone. As previously described, the staple  100  can include a first arm  102 A, a second arm  102 B, and a bridge  104  extending from the proximal end of first arm  102 A to the proximal end of second arm  102 B. At least the distal portion of first arm  102 A is a trunk that abuts a non-trunk portion of first arm  102 A or the bridge  104 . The same is true of second arm  102 B. First trunk  106 A and second trunk  106 B define a first cavity  128 A and a second cavity  128 B, respectively. 
     Fork  132  includes a first stake  238 A and a second stake  238 B. A distal portion  244 A of first stake  238 A of fork  232  can be seen extending into first cavity  128 A defined by first trunk  106 A of staple  100 . A distal portion  244 B of second stake  238 B of fork  232  extends into second cavity  128 B defined by second trunk  106 B of staple  100 . 
     The proximal portion of each stake  238  has a generally dovetail-shaped lateral cross-section. Proximal portion  246 A of first stake  238 A is slidingly received in a dovetail-shaped slot defined by first staple setting rod  234 A. Similarly, proximal portion  246 B of second stake  238 B is slidingly received in a dovetail-shaped slot defined by second staple setting rod  234 B. Accordingly, each staple setting rod is coupled to fork  232  with a single degree of freedom for relative movement such that the staple setting rod can slide in distal and proximal directions relative to the fork. 
     The staple setting rods  234  may be moved so that the distal end of each staple setting rod abuts a proximal surface of staple  100 . Each staple setting rod may apply pushing forces to one or more proximal surfaces of staple  100 . Forces applied by the staple setting rods may be used to urge first projection  122 A and third projection  122 C into orientations that lock staple  100  into a target tissue. For example, first projection  122 A and third projection  122 C may be rotated so that these projections engage the target tissue. When this is the case, tension extending through bridge  104  of staple  100  may keep first projection  122 A and third projection  122 C in the rotated position in which the projections inhibit staple pullout. 
     As assembled, the distal end of the staple delivery assembly  252  is enclosed by the end of the sheath  250 . Initial movement of the trigger causes the stable delivery assembly to extend beyond the distal end of the sheath  150  which inserts the staple  100  into pilot holes in the bone. Continue movement of the trigger then forces the staple setting rods distally to set the staples in engagement with the bone. 
     The process of forming pilot holes and delivery staples of the present disclosure to bone is described with respect to  FIGS. 18A-18F  which depict the various steps in affixing an implant  50  to bone with staples or fasteners of the present disclosure.  FIG. 18A  schematically depicts a shoulder  22  of a patient  20  having an implant  50  positioned over a supraspinitus tendon  28 . The implant is partially affixed to the tendon  28  with fasteners  51  and extends laterally to and over the insertion point of the tendon to the humeral head  24 . As depicted, the implant  50  is not yet affixed to the humeral head  24 . A distal portion of a pilot hole forming trocar assembly  300 , in particular the position retention sleeve  304 , is disposed over a desired location near the lateral edge of the implant  50  where it overlies the humeral head  24 . It is noted the  FIG. 18A  is a depiction with all overlying tissue removed from the shoulder  22  to clearly show the location of the entire implant  50  on the supraspinitus tendon  28 . This view is not possible during actual arthroscopic procedures in which the fasteners and instruments of the present disclosure can be used, however the depiction provides a clear understanding of the placement of an implant and the use of fasteners disclosed herein. In actual use the surgeon will have a side view from a viewing scope (not shown) of a small space created by inflating the area with fluid and clearing necessary obstructions from the implant area. 
       FIG. 18B  is a schematic illustration of a cross-sectional side view of the partially affixed implant of  FIG. 18A  showing the small portion of the implant  50  that is not yet affixed to the humeral head  24 . As can be seen in the illustration, the humeral head  24  is shown in cross-section which illustrates the composite nature of bone structure. In general, bone includes hard outer portion or cortical layer  375  and a porous softer inner portion or cancellous bone  376 . The pilot hole forming trocar assembly  300  is positioned with the spikes  308  over a selected position on the implant  50 . As previously discussed, the trocar  302  is positioned within the lumen of the position retention sleeve  304  with spikes  308  extending distally. The spikes  308  can be used to manipulate and position the implant as needed. Once in position, the spikes  308  can be driven into the bone. 
     Referring to  FIG. 18C , the illustration of  FIG. 18B  is re-illustrated with the pilot hole forming trocar  300  spikes pounded or otherwise driven into the humeral head  24 , penetrating the cortical layer  375  into the cancellous portion  376 . As illustrated, position retention members  314  also penetrate the bone with the spikes  308 . In  FIG. 18D , it is illustrated that the trocar  302  and its distal spikes  308  are now removed leaving formed pilot holes  309  with the position retention sleeve  304  remaining in position with position retention member  314  extending into pilot holes  309 . The position retention member  304  lumen provides a guide to the pilot holes  309  for a staple delivery device  200 . In  FIG. 18E , a staple  100  is shown extending into the pilot holes  309  as mounted on the distal end of a staple delivery device  200  that has been inserted into the lumen of position retention member  304 . In this position the staple can be delivered and retained in the tissue or bone as previously described in the various embodiments disclosed herein.  FIG. 18F  depicts a staple  100  as delivered into bone with bridge  304  holding the implant in position on the bone and arms of the staple retaining position in the in the bone, such as within the cancellous portion  376 . 
     While exemplary embodiments of the present invention have been shown and described, modifications may be made, and it is therefore intended in the appended claims and subsequently filed claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.