Abstract:
Apparatus and methods are disclosed for securely, yet releasably, connecting separate parts. A shaft engages a cooperating socket to form a connection capable of sustaining service loads. The shaft has a protruding pin which slides within a slot in the socket to guide the shaft into locked engagement with the socket. The shaft also has a cantilever body which wedges into a tapered region in the socket to frictionally bind the shaft and socket together.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of U.S. Application No. 61/259,722, which was filed on Nov. 10, 2009, is entitled QUARTER TURN LOCKING MECHANISM FOR SURGICAL INSTRUMENT CONNECTION. The contents of U.S. Application No. 61/259,722 are hereby incorporated by reference as part of this application. 
    
    
     BACKGROUND OF THE INVENTION 
     The present disclosure relates to interconnections for securely yet releasably connecting separate components. In certain embodiments, quarter turn locking mechanisms are disclosed. Specific embodiments are disclosed in the context of a spinal system comprising a trial implant and an inserter tool. 
     SUMMARY OF THE INVENTION 
     The present disclosure sets forth components, systems, kits, and methods for securely yet releasably connecting separate parts. In an embodiment, a spinal trial implant inserter tool and a spinal trial implant are securely, yet releasably, connected. The connection is capable of sustaining intraoperative loads as the spinal trial implant is maneuvered relative to the spine. The connection may be connected and disconnected quickly and easily when desired. The connection relies upon cooperating features on the tool and the trial. The geometry of the cooperating features is relatively insensitive to dimensional variation, therefore relatively larger manufacturing tolerances may be specified without sacrificing acceptable function. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a spinal trial implant and an inserter tool; 
         FIG. 2  is a perspective detail view of a distal end of the inserter tool of  FIG. 1 ; 
         FIG. 3A  is a perspective cephalad-lateral view of the spinal trial implant of  FIG. 1 ;  FIG. 3B  is a perspective caudal-lateral view of the spinal trial implant of  FIG. 1 ; and  FIG. 3C  is an anterior view of the spinal trial implant of  FIG. 1 ; 
         FIG. 4  is a perspective view of the spinal trial implant and inserter tool of  FIG. 1 , with the inserter tool partially inserted into the trial; 
         FIG. 5  is a lateral view of the spinal trial implant and inserter tool of  FIG. 1 , with the inserter tool fully locked to the spinal trial implant; 
         FIG. 6  is a cross-sectional view of the spinal trial implant and inserter tool of  FIG. 5 ; 
         FIG. 7A  is a perspective view of a shaft;  FIG. 7B  is a top view of the shaft of  FIG. 7A ;  FIG. 7C  is an end view of the shaft of  FIG. 7A ; and  FIG. 7D  is a front view of the shaft of  FIG. 7A ; 
         FIG. 8A  is a top perspective view of a socket;  FIG. 8B  is a top view of the socket of  FIG. 8A ;  FIG. 8C  is an end view of the socket of  FIG. 8A ;  FIG. 8D  is a front view of the socket of  FIG. 8A ;  FIG. 8E  is a front perspective view of the socket of  FIG. 8A ; and  FIG. 8F  is a cross sectional view of the socket of  FIG. 8A  taken along the section line indicated in  FIG. 8D ; 
         FIG. 9A  is a perspective view of the shaft of  FIG. 7A  in an unlocked position relative to the socket of  FIG. 8A ;  FIG. 9B  is a front view of the shaft and socket of  FIG. 9A ;  FIG. 9C  is a cross sectional view of the shaft and socket of  FIG. 9A , taken along the section line shown in  FIG. 9B ;  FIG. 9D  is a top view of the shaft and socket of  FIG. 9A ; and  FIG. 9E  is a cross sectional view of the shaft and socket of  FIG. 9A , taken along the section line shown in  FIG. 9D ; 
         FIG. 10A  is a perspective view of the shaft of  FIG. 7A  in an intermediate position relative to the socket of  FIG. 8A ;  FIG. 10B  is a front view of the shaft and socket of  FIG. 10A ;  FIG. 10C  is a cross sectional view of the shaft and socket of  FIG. 10A , taken along the section line shown in  FIG. 10B ;  FIG. 10D  is a top view of the shaft and socket of  FIG. 10A ; and  FIG. 10E  is a cross sectional view of the shaft and socket of  FIG. 10A , taken along the section line shown in  FIG. 10D ; 
         FIG. 11A  is a perspective view of the shaft of  FIG. 7A  in a locked position relative to the socket of  FIG. 8A ;  FIG. 11B  is a front view of the shaft and socket of  FIG. 11A ;  FIG. 11C  is a cross sectional view of the shaft and socket of  FIG. 11A , taken along the section line shown in  FIG. 11B ;  FIG. 11D  is a top view of the shaft and socket of  FIG. 11A ; and  FIG. 11E  is a cross sectional view of the shaft and socket of  FIG. 11A , taken along the section line shown in  FIG. 11D ; 
         FIG. 12A  is a perspective view of another shaft, with two cantilever bodies and one pin;  FIG. 12B  is a perspective view of yet another shaft, with four cantilever bodies and two adjacent pins;  FIG. 12C  is a perspective view of yet another shaft, with four cantilever bodies and two opposite pins;  FIG. 12D  is a perspective view of yet another shaft, with four cantilever bodies and four pins;  FIG. 12E  is a perspective view of yet another shaft, with five cantilever bodies and one pin; and  FIG. 12F  is a perspective view of yet another shaft, with six cantilever bodies and three pins; 
         FIG. 13A  is a perspective view of another socket, with one slot having a starting portion, a helical portion, and a terminal portion;  FIG. 13B  is a perspective view of yet another socket, with three slots like the slot in  FIG. 13A ;  FIG. 13C  is a perspective view of yet another socket, with two slots, each having a starting portion, a helical portion, and a terminal portion;  FIG. 13D  is a perspective view of yet another socket, with two slots, each having a helical portion and a terminal portion;  FIG. 13E  is a perspective view of yet another socket, with two slots, each having a starting portion and a helical portion;  FIG. 13F  is a front view of the socket of  FIG. 13A ;  FIG. 13G  is a front view of the socket of  FIG. 13C ;  FIG. 13H  is a front view of the socket of  FIG. 13D ; and  FIG. 13J  is a front view of the socket of  FIG. 13E ; 
         FIG. 14A  is a perspective view of yet another socket, with two slots, each having a helical portion;  FIG. 14B  is a perspective view of yet another socket, with two slots like the slots in  FIG. 14A  extending partially through a side wall of the socket;  FIG. 14C  is a perspective view of yet another socket, with two slots, each having a starting portion and a terminal portion;  FIG. 14D  is a perspective view of yet another socket, with two slots, each having a starting portion and a terminal portion;  FIG. 14E  is a front view of the socket of  FIG. 14A ;  FIG. 14F  is a front view of the socket of  FIG. 14C ; and  FIG. 14G  is a front view of the socket of  FIG. 14D . 
     
    
    
     DETAILED DESCRIPTION 
     While certain embodiments have been shown and described in detail below, it will be clear to the person skilled in the art upon reading and understanding this disclosure that changes, modifications, and variations may be made and remain within the scope of the components, systems, kits, and methods described herein. Furthermore, while various features are grouped together in the embodiments for the purpose of streamlining the disclosure, it is appreciated that features from different embodiments may be combined in a mix and match fashion. 
     The following description and accompanying drawings are offered by way of illustration only. In particular, while the present disclosure sets forth an embodiment in the context of surgical instruments, one of skill in the art will appreciate that the components, systems, kits, and methods may be applicable outside the realm of surgical instruments or the field of medicine altogether. 
     Not every feature of each embodiment is labeled in every figure in which that embodiment appears, in order to keep the figures clear. Similar reference numbers (e.g., those that are identical except for the first numeral) are used to indicate similar features in different embodiments. 
     Standard medical planes of reference and descriptive terminology are employed in this specification. A sagittal plane divides a body into right and left portions. A mid-sagittal plane divides the body into equal right and left halves. A coronal plane divides a body into anterior and posterior portions. A transverse plane divides a body into superior and inferior portions. Anterior means toward the front of the body. Posterior means toward the back of the body. Superior means toward the head. Inferior means toward the feet. Medial means toward the midline of the body. Lateral means away from the midline of the body. Axial means toward a central axis of the body. Abaxial means away from a central axis of the body. 
     Referring to  FIG. 1 , an embodiment of a locking mechanism is shown in the context of a system for spinal surgery. An inserter tool  10  is shown connected to a trial implant  60  by means of a connection mechanism  8 . The trial  60  includes a mock implant body portion  61  which may be positioned within an intervertebral disc space in order to determine the proper size for a spinal implant (not shown) for permanent implantation. The tool  10  includes a handle  11 . The tool  10  is used to hold and manipulate the trial  60  as the trial  60  is inserted into the intervertebral disc space. The connection mechanism  8  between the trial  60  and the tool  10  may have cooperating features on the trial  60  and the tool  10  which releasably couple the trial  60  and the tool  10 . The connection mechanism  8  may be subjected to service loads which are oriented with respect to one or more of three mutually perpendicular axes. The service loads may act along an axis, such as tensile or compressive loads, or around an axis, such as a torque load. Furthermore, service loads may be a combination of axial and/or torque loads along and/or around any or all of the three mutually perpendicular axes. The three mutually perpendicular axes may be aligned with respect to the structure of the trial  60  and/or the tool  10  or with respect to anatomic planes and/or axes of reference. 
     Referring to  FIG. 2 , the tool  10  may have a shaft  12  with a longitudinal axis  14  centered in the shaft  12 . The axis  14  may be described as an axis of revolution or axis of radial symmetry of the basic shaft  12 . 
     The shaft  12  may have an outer diameter  16 , a tip end  18 , and a first pin  20 . The tip end  18  may also be described as a working end of the shaft  12 , in the sense that tip end  18  may have features to connect the tool  10  to the trial  60 . The first pin  20  may be proximate the tip end  18 . The first pin  20  protrudes outwardly beyond the outer diameter  16  of the shaft  12 . The first pin  20  may protrude normal to the outer diameter  16  and orthogonal to the axis  14 . The first pin  20  may be cylindrical. 
     The tip end  18  may be split into a plurality of cantilever bodies  22 ,  24 . The cantilever bodies  22 ,  24  are so named because they function as cantilever flex beams, as will be described presently in more detail. The cantilever bodies  22 ,  24  may also be described as resilient prongs which extend alongside axis  14 . The tip end  18  may be split into two cantilever bodies  22 ,  24  by slit  26 . Slit  26  may also be described as a slot or notch. 
     Slit  26  is shown extending through the tip end  18  and along a portion of the shaft  12 . Slit  26  may extend completely across the shaft  12  in a direction orthogonal to the first pin  20 . Slit  26  may have a uniform width over most of its length. In other words, slit  26  may provide a uniform separation, or gap, between cantilever bodies  22 ,  24  over most of their length. For a given material, the width of slit  26  may be designed so that cantilever bodies  22 ,  24  provide a desired resistance to pinching the slit  26  closed at the tip end  18 . The width of slit  26  may also step down, or become narrower, proximate the tip end  18 , so as to form opposing raised bosses  28 ,  30  between the cantilever bodies  22 ,  24  at the tip end  18 . The bosses  28 ,  30  may serve to protect the shaft  12  from overload conditions during use. More specifically, for a given material, the width of slit  26  at the tip end  18  between the bosses  28 ,  30  may be selected so that the shaft  12  experiences only elastic deformation, even when slit  26  is squeezed completely closed at the tip end  18  so that the bosses  28 ,  30  touch. In other words, stresses in shaft  12  remain below an elastic limit of the shaft  12  material because bosses  28 ,  30  serve as physical stops to prevent excess deflection of the cantilever bodies  22 ,  24 . 
     The first pin  20  may be situated on a first cantilever body  22 . Shaft  12  may include a second pin  32  like the first pin  20 . The second pin  32  may be in a position that is rotated around the axis  14  relative to the first pin  20 , so that the first pin  20  and the second pin  32  are arranged in a circular array around the axis  14 . In  FIG. 2 , the second pin  32  is in a position that is rotated 180 degrees from the first pin  20 , so that the pins  20 ,  32  are symmetrically arranged around the axis  14  on opposite sides of the shaft  12 . 
     The shaft  12  may have flattened portions  34 ,  36 ,  38 ,  40  along the outer diameter  16  where the slit  26  breaks through the shaft  12 , as illustrated in  FIGS. 2 and 4 . The flattened portions  34 ,  36 ,  38 ,  40  soften, or break, edges along the intersection of slit  26  and outer diameter  16 . The flattened portions  34 ,  36 ,  38 ,  40  also make the cantilever bodies  22 ,  24  narrower. 
     The shaft  12  may have flattened regions  42 ,  44  around the first and second pins  20 ,  32 , as illustrated in  FIGS. 2 and 4 . 
     The tip end  18  of shaft  12  may have a circumferentially bevel  46 . The bevel  46  softens, or breaks, an edge where the outer diameter  16  terminates at the tip end  18 . The bevel  46  also tapers the tip end  18 . 
     The shaft  12  may be fabricated from polymers, metals, ceramics, composites, glass, wood, or other materials according to the requirements of a particular application. The shaft  12  may be fabricated from a combination of materials, so that each feature of the shaft  12  is fabricated from a material suitable to the particular requirements of the individual feature. In the context of surgical instruments, implants, and systems, it is contemplated that the shaft  12  may be fabricated from polymers such as polyetheretherketone (PEEK), acetal, or ultra high molecular weight polyethylene (UHMWPE), or from metals comprising iron, chrome, titanium, nickel, or molybdenum. 
     Referring to  FIGS. 3A-C  and  6 , the trial  60  may have a tube or socket  62  with a longitudinal axis  64  centered in the socket  62 . The axis  64  may be described as an axis of revolution or axis of radial symmetry of the basic socket  62 . 
     The socket  62  may have an inner diameter  66 , an open end  68 , a second end  70 , a tapered region  72 , a side wall  74 , and a first slot  76 . The inner diameter  66  extends between the open end  68  and the tapered region  72 . The second end  70  is opposite the open end  68 , thus in this embodiment, the second end  70  is deep within the socket  62 . The second end  70  may be closed, or blind. The tapered region  72  is inside the socket  62 , between the inner diameter  66  and the second end  70 , and distant from the open end  68 . The tapered region  72  may be oriented to form a tapered constriction, such that the second end  70  is smaller than the inner diameter  66 . 
     The first slot  76  may project through the side wall  74  of the socket  62 . 
     The first slot  76  may have a starting end  78  at the open end  68  and a terminal end  80  spaced apart from the open end  68 . The starting end  78  provides an opening, or mouth, through the open end  68  into the first slot  76 . The terminal end  80  may be a blind end, or terminus. The terminal end  80  has a combined offset from the starting end  78 , with a first component of the offset in a direction parallel to the axis  64 , and a second component of the offset in an angular direction around the axis  64 . In the embodiment of  FIGS. 3A-C , the angular offset is about 90 degrees, although other angular offsets are contemplated. 
     The first slot  76  may have a starting portion  88  that extends parallel to the axis  64  and a terminal portion  90  that extends perpendicular to the axis  64 . The first slot  76  may also have a helical portion  92  between the starting end  78  and the terminal end  80 . The helical portion  92  spirals around the side wall  74  of the socket  62  in a manner similar to a screw thread. 
     The socket  62  may include a second slot  94  like the first slot  76 . The second slot  94  may be in a position that is rotated around the axis  64  relative to the first slot  76 . Thus, the first slot  76  and the second slot  94  may be arranged in a circular array around the axis  64 . In  FIGS. 3A-C , the second slot  94  is in a position that is rotated 180 degrees from the first slot  76 , so that the slots  76 ,  94  are symmetrically arranged around the axis  64  on opposite sides of the socket  62 . 
     With reference to FIGS.  2  and  3 A-C, one may appreciate that the pins  20 ,  32  and the slots  76 ,  94  are advantageously arranged in complementary circular arrays. 
     The socket  62  may be fabricated from polymers, metals, ceramics, composites, glass, wood, or other materials according to the requirements of a particular application. The socket  62  may be fabricated from a combination of materials, so that each feature of the socket  62  is fabricated from a material suitable to the particular requirements of the individual feature. In the context of surgical instruments, implants, and systems, it is contemplated that the socket  62  may be fabricated from polymers such as polyetheretherketone (PEEK), acetal, or ultra high molecular weight polyethylene (UHMWPE), or from metals comprising iron, chrome, titanium, nickel, or molybdenum. 
     An alternate embodiment shaft  112  is shown in  FIGS. 7A-D . Shaft  112  is similar to shaft  12  of tool  10 , but shaft  112  only includes features which cooperate with a socket to form a connection mechanism. Shaft  112  may thus be described as a subcomponent or design element which could be incorporated into the design of a more fully featured component. For example, shaft  112  may be incorporated onto a working end of a shaft of a nut driver for nuts incorporating a cooperating socket (described below). As another example, shaft  112  may be incorporated onto a stem of a tibial trial component for removably attaching modular trial stems incorporating a cooperating socket. 
     Shaft  112  may have an axis  114 , an outer diameter  116 , a tip end  118 , two pins  120 ,  132 , two cantilever bodies  122 ,  124 , a slit  126 , two bosses  128 ,  130 , four flattened portions  134 ,  136 ,  138 ,  140 , two flattened regions  142 ,  144 , and a bevel  146 . All of these features are identical to the corresponding features described for shaft  12 . 
       FIGS. 12A-F  illustrate additional shaft embodiments, each of which shares at least some features in common with shafts  12 ,  112 . The following descriptions disclose distinguishing characteristics of each embodiment. 
     Shaft  212  of  FIG. 12A  may have a longitudinal center axis  214 , two cantilever bodies  222 ,  224 , a slit  226 , and a single pin  220 . Pin  220  is carried by cantilever body  222 , and slit  226  is orthogonal to pin  220 . 
     Shaft  312  of  FIG. 12B  may have a longitudinal center axis  314 , four cantilever bodies  322 ,  323 ,  324 ,  325 , two slits  326 ,  327 , and two pins  320 ,  332 . Pin  320  is carried by cantilever body  322  and pin  332  is carried by cantilever body  323 , so that pins  320 ,  332  are asymmetrically arranged about axis  314 . Slits  326  and  327  are identical, and are oriented at 45 degree angles to pins  320 ,  332 . Shaft  312  lacks a flattened portion, comparable to flattened portion  34 , along any of the cantilever bodies  322 ,  323 ,  324 ,  325 . 
     Shaft  412  of  FIG. 12C  may have a longitudinal center axis  414 , four cantilever bodies  422 ,  423 ,  424 ,  425 , two slits  426 ,  427 , and two pins  420 ,  432 . Slit  426  is similar in design to slit  26 . Slit  427  terminates beside pins  420 ,  432  so that slit  427  is much shorter than slit  426 . Slit  426  is orthogonal to pins  420 ,  432 , while slit  427  is parallel to pins  420 ,  432 . Pin  420  is carried at the juncture of cantilever bodies  422 ,  423  and pin  432  is carried at the juncture of cantilever bodies  424 ,  425 , so that pins  420 ,  432  are symmetrically arranged about axis  414 . Shaft  412  lacks a flattened portion, comparable to flattened portion  34 , along any of the cantilever bodies  422 ,  423 ,  424 ,  425 . 
     Shaft  512  of  FIG. 12D  may have a longitudinal center axis  514 , four cantilever bodies  522 ,  523 ,  524 ,  525 , two slits  526 ,  527 , and four pins  520 ,  521 ,  532 ,  533 . Pin  520  is carried by cantilever body  522 , pin  521  is carried by cantilever body  523 , pin  532  is carried by cantilever body  524 , and pin  533  is carried by cantilever body  525 , so that pins  520 ,  521 ,  532 ,  533  are symmetrically arranged about axis  514 . Slits  526  and  527  are identical, and are oriented at 45 degree angles to pins  520 ,  532 . Shaft  512  lacks a flattened portion, comparable to flattened portion  34 , along any of the cantilever bodies  522 ,  523 ,  524 ,  525 . 
     Shaft  612  of  FIG. 12E  may have a longitudinal center axis  614 , five cantilever bodies  622 ,  623 ,  624 ,  625 ,  629 , five slits  626 ,  627 ,  631 ,  635 ,  637 , and a single pin  620 . Pin  620  is carried by cantilever body  622 . Slits  626 ,  627 ,  631 ,  635 ,  637  are identical, extending only halfway through shaft  612 . Slits  626 ,  627  are oriented at 36 degree angles to pin  620 , and all five slits  626 ,  627 ,  631 ,  635 ,  637  are symmetrically arranged about axis  614 . Shaft  612  lacks a flattened portion, comparable to flattened portion  34 , along any of the cantilever bodies  622 ,  623 ,  624 ,  625 ,  629 . 
     Shaft  712  of  FIG. 12F  may have a longitudinal center axis  714 , six cantilever bodies  722 ,  723 ,  724 ,  725 ,  729 ,  739 , three slits  726 ,  727 ,  731 , and three pins  720 ,  721 ,  732 . Pin  720  is carried by cantilever body  722 , pin  721  is carried by cantilever body  724 , and pin  732  (obscured by remainder of shaft  712 ) is carried by cantilever body  729 , so that pins  720 ,  721 ,  732  are symmetrically arranged about axis  714 . Shaft  712  lacks a flattened portion, comparable to flattened portion  34 , along any of the cantilever bodies  722 ,  723 ,  724 ,  725 ,  729 ,  739 . 
     Any of the pins described herein may alternatively protrude from the corresponding shaft in a direction other than normal to the corresponding outer diameter and/or in a direction other than orthogonal to the corresponding axis. Any of the pins described herein may alternatively have a non-circular cross sectional shape, such as triangle, oval, elliptical, polygonal, teardrop, or lobed. Such cross sectional shapes may cause the pin to resemble a tab, ear, flange, or post instead of a cylinder. 
     The tip end of a shaft may have a single cantilever body, or may be split into two or more cantilever bodies according to the needs of a particular application.  FIGS. 12B-F  show embodiments having different numbers of cantilever bodies. The tip end may have slits that extend partially or entirely across the shaft in order to form the desired number of cantilever bodies.  FIG. 12E  shows an embodiment with slits that extend partially across shaft  612 , while  FIGS. 12A-D  and F show embodiments with slits that extend entirely across the corresponding shaft. 
     Pins may be arranged around a shaft in a symmetric or asymmetric circular array.  FIGS. 12C , D, and F illustrate symmetrical pin arrays, while  FIG. 12B  illustrates an asymmetric pin array. Pins may all be alike, so that a shaft may have a single array of pins. Alternatively, a shaft may have a plurality of arrays, wherein each array is characterized by a different pin configuration. For example, one such embodiment may include two pin configurations which alternate around an outer diameter of a shaft. Each of the pins may be situated on a separate cantilever body, in a manner reminiscent of  FIG. 12D . Alternatively, each cantilever body may carry a plurality of pins. In a further alternative, selected cantilever bodies may lack pins altogether, as illustrated in  FIGS. 12A , B, E, and F. 
     Alternative shaft embodiments may employ edge break configurations that differ from flattened portions  34 ,  36 ,  38 ,  40 . These may include features such as chamfers, bull noses, radii, fillets, or variable edge blends. The edge break may be confined to a zone proximate the tip end of a shaft. Edge break may be unnecessary in certain embodiments, such as those shown in  FIGS. 12B-F . 
     A shaft may optionally include a longitudinal through hole or cannulation. 
     Alternative shaft embodiments may employ edge break configurations that differ from bevel  46 . These may include features such as a chamfer, bull nose, radius, fillet, or variable edge blend. Edge break may be unnecessary in certain embodiments. 
     An alternate embodiment socket  162  is shown in  FIGS. 8A-F . Socket  162  is similar to socket  62  of trial  60 , but socket  162  only includes features which cooperate with a shaft to form a connection mechanism. Socket  162  may thus be described as a subcomponent or design element which could be incorporated into the design of a more fully featured component. By way of non-limiting example, socket  162  may be incorporated on a working end of a shaft for a screwdriver for use with screws incorporating shaft  112 , or socket  162  may be formed into a broach for use with a broaching handle incorporating shaft  112 . 
     Socket  162  may have an inner diameter  166 , an open end  168 , a second end  170 , a tapered region  172 , a side wall  174 , a first slot  176 , a starting end  178 , a terminal end  180 , a starting portion  188 , a terminal portion  190 , a helical portion  192 , and a second slot  194 . All of these features are identical to the corresponding features described for socket  62 . 
       FIGS. 13A-J  illustrate additional socket embodiments, each of which shares at least some features in common with sockets  62 ,  162 . The following descriptions disclose distinguishing characteristics of each embodiment. 
     Socket  262  of  FIGS. 13A and 13F  may have a longitudinal center axis  264  and a single slot  276 . Slot  276  is identical to slot  76 . Slot  276  follows a path  282  between a starting end  278  and a terminal end  280 . The path  282  may extend between a starting point  284  and a terminal point  286 . The starting point  284  may be at the starting end  278  or at a location outside the open end  268 . The terminal point  286  may be at or near the terminal end  280 . The terminal point  286  may be offset from the starting point  284  along the longitudinal axis  264  and around the inner diameter  266 , in order to produce a desired combined offset for the terminal end  280 . The path  282  may describe a tool path followed by a cutter during fabrication of the slot  276 . 
     Socket  362  of  FIG. 13B  may have a longitudinal center axis  364  and three slots  376 ,  394 ,  395 . Each of the slots  376 ,  394 ,  395  is identical to slot  76 . The slots  376 ,  394 ,  395  are symmetrically arranged around axis  364 . 
     Socket  462  of  FIGS. 13C and 13G  may have a longitudinal center axis  464 , an open end  468 , and two identical slots  476 ,  494  symmetrically arranged around axis  464  on opposite sides of socket  462 . Slot  476  extends between a starting end  478  and a terminal end  480 . Slot  476  follows a path  482  between a starting point  484  and a terminal point  486 . The path  482  resembles path  282 , but a portion of the path  482  between the starting point  484  and the terminal point  486  is spaced farther from the open end  468  than is the terminal point  486 , as is best appreciated in  FIG. 13G . As a result, slot  476  extends along the socket  462  past the location of the terminal end  480 , and then turns back to reach the terminal end  480 . 
     Socket  562  of  FIGS. 13D and 13H  may have a longitudinal center axis  564  and two identical slots  576 ,  594  symmetrically arranged around axis  564  on opposite sides of socket  562 . Slot  576  extends between a starting end  578  and a terminal end  580 . Slot  576  may have a terminal portion  590  like terminal portion  90  and a helical portion  592  like helical portion  92 . However, slot  576  lacks a starting portion like starting portion  88 . Instead, helical portion  592  extends all the way to the starting end  578  along path  582 . 
     Socket  662  of  FIGS. 13E and 13J  may have a longitudinal center axis  664  and two identical slots  676 ,  694  symmetrically arranged around axis  664  on opposite sides of socket  662 . Slot  676  extends between a starting end  678  and a terminal end  680 . Slot  676  may have a starting portion  688  like starting portion  88  and a helical portion  692  like helical portion  92 . However, slot  676  lacks a terminal portion like terminal portion  90 . Instead, helical portion  692  extends all the way to the terminal end  680  along path  682 . 
       FIGS. 14A-G  illustrate additional socket embodiments, each of which shares at least some features in common with sockets  62 ,  162 . The following descriptions disclose distinguishing characteristics of each embodiment. 
     Socket  762  of  FIGS. 14A and 14E  may have a longitudinal center axis  764  and two identical slots  776 ,  794  symmetrically arranged around axis  764  on opposite sides of socket  762 . Slot  776  extends between a starting end  778  and a terminal end  780 . Slot  776  may have a helical portion  792  like helical portion  92 . However, slot  776  lacks a starting portion like starting portion  88 . Slot  776  also lacks a terminal portion like terminal portion  90 . Instead, helical portion  792  extends all the way to the terminal end  780  along path  782 . 
     Socket  862  of  FIG. 14B  may have a longitudinal center axis  864  and two identical slots  876 ,  894  symmetrically arranged around axis  864  on opposite sides of socket  862 . Slots  876 ,  894  are identical to slots  776 ,  794 . However, slots  876 ,  894  project only partially through a side wall  874  of socket  862 , so that socket  862  possesses a smooth, continuous outer surface. This embodiment may afford greater strength to slots  876 ,  894  in service, and may be less likely to snag on surrounding objects. 
     Socket  962  of  FIGS. 14C and 14F  may have a longitudinal center axis  964  and two identical slots  976 ,  994  symmetrically arranged around axis  964  on opposite sides of socket  962 . Slot  976  extends between a starting end  978  and a terminal end  980 . Slot  976  may have a starting portion  988  like starting portion  88  and a terminal portion  990  like terminal portion  90 . However, slot  976  lacks a helical portion like helical portion  92 . Instead, starting portion  988  blends directly into terminal portion  990  along path  982 . 
     Socket  1062  of  FIGS. 14D and 14G  may have a longitudinal center axis  1064 , an open end  1068 , and two identical slots  1076 ,  1094  symmetrically arranged around axis  1064  on opposite sides of socket  1062 . Slot  1076  extends between a starting end  1078  and a terminal end  1080 . Slot  1076  resembles slot  976 . However, a portion of slot  1076  lies farther from the open end  1068  than does the terminal end  1080 , as is best seen in  FIG. 14G . 
     In alternative embodiments, a socket may have a hole or cannulation (not shown) extending from a second end of the socket. The hole or cannulation may go partially or completely through the socket. The second end may simply be an intersection, or edge, between a tapered region within the socket and a hole extending farther into the socket. 
     Slots and their corresponding paths may be configured in various ways. A terminal portion of a slot may make an angle of precisely 90 degrees with respect to a corresponding axis.  FIGS. 3A-C ,  8 D,  13 F, and  14 F show examples of this type of terminal portion. Alternatively, it may be advantageous for a terminal portion to make an acute angle with respect to the axis. For example, the terminal portion may hook back toward the open end of the socket, as is shown in  FIGS. 13G and 14G . Starting and terminal portions of a slot may be separated by one or more intervening portions, such as a helical portion ( FIGS. 13A  and F) or a non-helical ramp. Alternatively, the starting portion may transition directly to the terminal portion so that the slot more closely resembles an “L” or a dogleg configuration, as illustrated in  FIGS. 14  C, D, F, and G. It is further contemplated that a starting portion could combine with dual terminal portions to form a “T” configuration. 
     In further embodiments, a slot may be made up of multiple portions or segments so that a shaft and a socket may be locked together with varying degrees of security, or in multiple orientations and positions. 
     In other embodiments, a slot may terminate in a recessed portion into which a pin must be forced against friction. An embodiment with this characteristic may provide additional locking force to couple a shaft and a socket together. 
     In alternate embodiments, a socket may have a plurality of slots arranged in a circular array around a longitudinal center axis of the socket. The plurality of slots may be arranged symmetrically or asymmetrically. The slots may all be alike, so that the socket may have a single array of slots. Alternatively, the socket may have a plurality of arrays, wherein each array is characterized by a different slot configuration. For example, one such embodiment may include two slot configurations which alternate around a side wall of the socket. 
     The number and arrangement of pins on a shaft need not exactly match the number and arrangement of slots on a corresponding socket. Rather, it is sufficient that the number and arrangement of pins on the shaft coordinates with the number and arrangement of slots on the socket to provide the desired number of mating orientations between the shaft and the socket. By way of non-limiting example, a shaft having only one pin may provide two mating orientations with a socket having two slots. A shaft with two pins may provide six mating orientations with a socket having six slots. A shaft having a larger first pin and a smaller second pin may provide one mating orientation with a socket having a larger first slot and a smaller second slot. 
     The embodiment shown in  FIGS. 1-6  is configured for assembly of the shaft  12  to the socket  62 . The inner diameter  66  of the socket  62  is larger than the outer diameter  16  of the shaft  12 , such that the outer diameter  16  fits within the inner diameter  66 . The first and second slots  76 ,  94  are larger than the first and second pins  20 ,  32 , respectively, such that the first and second pins  20 ,  32  fit within the first and second slots  76 ,  94 , respectively. 
     The shaft  12  is selectively movable, relative to the socket  62 , between an unlocked position and a locked position.  FIG. 4  illustrates the unlocked position.  FIGS. 5-6  illustrate the locked position. In the unlocked position, the shaft  12  and the socket  62  are freely separable. In the locked position, the shaft  12  and the socket  62  are secured together sufficiently to resist service loads. One can appreciate that the security of the locked position for a specific application may be directly proportional to the magnitude of service loads in that application. 
     In the unlocked position of  FIG. 4 , the axes  14 ,  64  are substantially aligned, the tip end  18  is positioned in the inner diameter  66 , and the first pin  20  is positioned in the starting end  78 , or mouth, of the first slot  76 . In the embodiment of  FIGS. 1-6 , the second pin  32  is also in a starting end of the second slot  94  in the unlocked position. In alternate embodiments comprising a plurality of pins and slots, one can appreciate that some or all of the pins may be in starting ends of corresponding slots. 
     In the locked position of  FIGS. 5-6 , the axes  14 ,  64  are substantially aligned, the tip end  18  is wedged in the tapered region  72  so as to at least partially pinch the slit  26  closed, and the first pin  20  is in the terminal end  80 , or terminus, of the first slot  76 . Thus, the cantilever bodies  22 ,  24  are at least partially compressed together. The flattened portions  34 ,  36 ,  38 ,  40  provide relief across the incompressible width of the cantilever bodies  22 ,  24  so that there is clearance with the tapered region  72 . The bevel  46 , if present, may be complementary to the tapered region  72 . In the embodiment of  FIGS. 1-6 , the second pin  32  is also in a terminal end of the second slot  94 . In alternate embodiments comprising a plurality of pins and slots, one can appreciate that some or all of the pins may be in terminal ends of corresponding slots. Furthermore, the sort of relief provided by flattened portions  34 ,  36 ,  38 ,  40  may not be necessary in alternative embodiments with narrow cantilever bodies, such as embodiments comprising three or more cantilever bodies. 
     Any material possesses inherent material properties. Material properties may be modified through manufacturing processes such as heat treatment, work hardening, pressure treatments, or aging. By way of non-limiting example, a material may be characterized by an elastic limit. The elastic limit is a stress at which the material begins to experience plastic, or permanent, deformation. At stresses below the elastic limit, the material experiences elastic, or temporary, deformation which spontaneously resolves as soon as applied forces are removed. For example, the shaft  12  may be designed so that stresses in the shaft  12  due to deformation of the cantilever bodies  22 ,  24  are less than the elastic limit when the tip end  18  is wedged in the tapered region  72  so as to pinch the slit  26  completely closed at the tip end  18 . This may be accomplished by designing a specific clearance, or gap, between bosses  28 ,  30 , so that the bosses  28 ,  30  contact each other and thereby prevent further deformation of the cantilever bodies  22 ,  24 . Slit  26  may be advantageously designed in view of the material properties resulting after completion of all applicable manufacturing operations. 
     In the locked position, the shaft  12  and socket  62  are secured together by frictional forces. At least some of the frictional forces may result from elastic deformation of the cantilever bodies  22 ,  24  when the tip end  18  wedges into the tapered region  72 . 
     A first frictional force may exist where the tip end  18  is wedged into the tapered region  72 . The cantilever bodies  22 ,  24  tend to resist being compressed together. Thus, the tip end  18  exerts a force against the tapered region  72 , acting in a direction generally normal to the contacting surfaces. This outward normal force causes the first frictional force, which resists rotation of the tip end  18  against the tapered region  72 . 
     A second frictional force may exist where the first pin  20  rests within the terminal end  80  of the first slot  76 . The second frictional force may be related to the first frictional force. The tip end  18  tends to resist wedging into the tapered region  72 . At least a portion of such resistance may act along the axes  14 ,  64  so as to force the first pin  20  against a side of the first slot  76  opposite the tapered region  72 , i.e., a side closer to the open end  68 . The force between the first pin  20  and the side of the first slot  76  acts in a direction generally normal to the contacting surfaces. This axial normal force causes the second frictional force, which resists sliding of the first pin  20  along the side of the first slot  76 . One can appreciate that a similar frictional force may exist between other pins and slots in alternate embodiments. 
     The second frictional force may alternatively be caused by other interactions between features of the shaft  12  and the socket  62 , such as wedging of the first pin  20  into an undercut, a recessed region, or a tapered constriction proximate the terminal end  80  of the first slot  76 . Furthermore, additional frictional forces may be present in alternative embodiments. 
     With reference to  FIGS. 4-6 , the shaft  12  is selectively movable between the unlocked and locked positions by rotating the shaft  12  within the socket  62  so that the first pin  20  slides along the first slot  76  between the starting and terminal ends  78 ,  80 . In the present embodiment, clockwise rotation of the shaft  12  in the socket  62  moves the shaft  12  from the unlocked position of  FIG. 4  to the locked position of  FIGS. 5-6 . Counterclockwise rotation of the shaft  12  in the socket  62  moves the shaft  12  from the locked position of  FIGS. 5-6  to the unlocked position of  FIG. 4 . In an alternate embodiment, these rotational directions may be reversed. 
     As the shaft  12  moves between the unlocked position and the locked position, the first pin  20  slides along the first slot  76  between the starting and terminal ends  78 ,  80 . Thus, the specific configuration of the first slot  76  dictates the motion of the shaft  12  relative to the socket  62 . By way of non-limiting example, the starting portion  88  of the first slot  76  of  FIGS. 4-6  guides the shaft  12  into the socket  62  in a direction generally parallel to the axes  14 ,  64 . The starting portion  88  prevents rotation of the pin  20  about the axes  14 ,  64 . The helical portion  92  constrains the shaft  12  to rotate clockwise about the axes  14 ,  64  and simultaneously advance within the socket  62  in a direction generally parallel to the axes  14 ,  64 . The terminal portion  90  permits the shaft  12  to rotate clockwise about the axes  14 ,  64 . Axial advancement is prevented. 
     The shaft  12  may be selectively movable, relative to the socket  62 , to an intermediate position in which the tip end  18  makes incipient contact with the tapered region  72 , the slit  26  is uncompressed, the cantilever bodies  22 ,  24  are undeflected, and the first pin  20  is in the first slot  76  between the starting and terminal ends  78 ,  80 . The intermediate position may be described as a transitional position between the loose unlocked position and the secure locked position. 
     As the shaft  12  moves from the intermediate position to the locked position, one or more of the aforementioned frictional forces builds between the shaft  12  and the socket  62  to bind the shaft  12  and socket  62  together. As the shaft  12  moves from the locked position to the intermediate position, the friction diminishes so that the shaft  12  and socket are mutually separable. 
     The embodiment shown in  FIGS. 7-11  is configured so that shaft  112  may be assembled, or connected, to socket  162 . The inner diameter  166  of the socket  162  receives the outer diameter  116  of the shaft  112  with clearance. The slots  176 ,  194  of the socket  162  receive the pins  120 ,  132  of the shaft  112  with clearance. 
     The shaft  112  is selectively movable, relative to the socket  162 , between an unlocked position, illustrated in  FIGS. 9A-E , and a locked position, illustrated in  FIGS. 11A-E . In the unlocked position, the shaft  112  and socket  162  are freely separable. In the locked position, the shaft  112  and socket  162  are secured together sufficiently to resist service loads. The security of the locked position may be proportional to the magnitude of service loads for a particular application. 
     In the unlocked position of  FIGS. 9A-E , the axes  114 ,  164  are substantially aligned, the tip end  118  is positioned in the inner diameter  166 , and the first pin  120  is positioned in the starting end  178 , or mouth, of the first slot  176 . In the embodiment of  FIGS. 9-11 , the second pin  132  is also in a starting end of the second slot  194  in the unlocked position.  FIGS. 9C and 9E  show mutually perpendicular cross sections through the shaft  112  and socket  162  in the unlocked position. It can be appreciated that outer diameter  116  of shaft  112  is a clearance fit with inner diameter  166  of socket  162 , and that flattened portions  134 ,  136 ,  138 ,  140  provide additional clearance across the width of cantilever bodies  122 ,  124 . 
     In the locked position of  FIGS. 11A-E , the axes  114 ,  164  are substantially aligned, the tip end  118  is wedged in the tapered region  172  so as to at least partially pinch the slit  126  closed, and the first pin  120  is in the terminal end  180 , or terminus, of the first slot  176 . Thus, the cantilever bodies  122 ,  124  are at least partially compressed together. The flattened portions  134 ,  136 ,  138 ,  140  provide relief across the incompressible width of the cantilever bodies  122 ,  124  so that there is clearance with the tapered region  172 . In the embodiment of  FIGS. 9-11 , the second pin  132  is also in a terminal end of the second slot  194 .  FIGS. 11C and 11E  show mutually perpendicular cross sections through the shaft  112  and socket  162  in the locked position. It can be appreciated that tip end  118  of shaft  112  is wedged within tapered region  172  of socket  162 , slit  126  is pinched at least partially closed, and flattened portions  134 ,  136 ,  138 ,  140  provide clearance across the width of cantilever bodies  122 ,  124 . 
     The shaft  112  is selectively movable between the unlocked and locked positions by rotating the shaft  112  within the socket  162 . Clockwise rotation of the shaft  112  in the socket  162  moves the shaft  112  from the unlocked position of  FIGS. 9A-E  to the locked position of FIGS.  11 A-E. Counterclockwise rotation of the shaft  112  in the socket  162  moves the shaft  112  from the locked position of  FIGS. 11A-E  to the unlocked position of  FIGS. 9A-E . 
     The shaft  112  may be selectively movable, relative to the socket  162 , to an intermediate position, illustrated in  FIGS. 10A-E , in which the tip end  118  makes incipient contact with the tapered region  172 , the slit  126  is uncompressed, the cantilever bodies  122 ,  124  are undeflected, and the first pin  120  is in the first slot  176  between the starting and terminal ends  178 ,  180 . In the embodiment of  FIGS. 9-11 , the second pin  132  is also in a similar location in the second slot  194 .  FIGS. 10C and 10E  show mutually perpendicular cross sections through the shaft  112  and socket  162  in the intermediate position. It can be appreciated that tip end  118  of shaft  112  has made incipient contact with tapered region  172  of socket  162 . 
     While the present disclosure has been made in the context of a spinal system comprising a trial implant and an inserter tool, the corresponding connection features described herein have a broad range of applications. By way of non-limiting example, the connection features may be applied to surgical trials, rasps, handles, pilot cutters, awls, and mallets, and further applications may be contemplated outside the medical field. 
     It should be understood that the present components, systems, kits, apparatuses, and methods are not intended to be limited to the particular forms disclosed. Rather, they are intended to include all modifications, equivalents, and alternatives falling within the scope of the claims. They are further intended to include embodiments which may be formed by combining features from the disclosed embodiments. 
     The claims are not to be interpreted as including means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively. 
     The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically. 
     The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more” or “at least one.” The term “about” means, in general, the stated value plus or minus 5%. The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternative are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” 
     The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements, possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features, possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.