Patent Publication Number: US-2023143676-A1

Title: Device for assembling implant systems

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. This application claims the benefit of U.S. Provisional Patent Application No. 62/263,921, filed Nov. 11, 2021, the content of which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Field 
     This disclosure generally relates to assembling multi-component implant systems. More specifically, this disclosure relates to devices and methods for mechanically coupling together two components of an implant system using a hand operated coupling system. 
     Description of the Related Art 
     Hip replacement femoral head implants are used in the medical field to replace part or entire hip structures. In some examples, a portion of a femoral implant is designed to be placed into a patient&#39;s femur. Femoral head implants may include a ball-like “head” coupled to an upper portion (a “taper”) of the femoral implant. The natural socket in the hip joint is replaced with an artificial “cup,” an implant that can include a hemispherical-shaped outer shell and a corresponding hemispherical-shaped inner liner nested inside, and coupled to, the outer shell. The inner head and outer head are separate components. Prior to being coupled to the taper portion, the heads are assembled such that the inner head is positioned in the cavity of the outer head. The inner head fits tightly into the outer head, and coupling them together requires a great deal of force. The shape of the outer and inner head can make it difficult to correctly apply the required force quickly without damaging the components. It would be advantageous to have a fast, easy-to-use coupling device to increase efficiency and minimize potential damage to the inner and outer head. 
     SUMMARY 
     The devices, systems, and methods of the present disclosure have several features, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of embodiments of the invention as expressed by the claims which follow, certain innovations will now be discussed briefly. After considering this discussion, and other sections provided herein, one will understand how the features of embodiments of the implant system assembly device in this disclosure provide several advantages. 
     To address problems with assembling the components of a femoral head implant, the disclosure describes aspects of a device for assembling the components of a head efficiently, easily, and without damaging the plastic outer head. One innovation includes a femoral head implant assembly device for coupling together an inner head and an outer head portion, the assembly device comprising a handle, a rod coupled to the handle, the rod aligned along a longitudinal axis and coupled to the handle, a body comprising a distal end and a proximal end, the body having a base portion, a top portion, and a support portion between the base portion and the top portion, the support portion including a grip for a user to hold while moving the handle. 
     The assembly device can further include an actuator system in the top portion, the actuator system coupled to the rod to move the rod along the longitudinal axis and to allow the rod to be at least partially rotated around the longitudinal axis. The actuator system includes a drive pawl coupled to the handle and configured to engage the rod and drive the rod along the longitudinal axis towards the base portion when the handle is moved from a first position to a second position, and a set pawl configured to engage the rod and hold the rod in place while the handle is moved from the second position to the first position. The assembly system can further include a head support having an inner member coupled to the base portion and positioned between the rod and the base portion, an inner head support extending from the inner member towards the rod and configured to receive an inner head thereon, the inner head support aligned along the longitudinal axis with the rod, and a stage circumferentially positioned around and slidably coupled to the inner member such that the stage can move along an exterior surface of the inner member. 
     Various embodiments of a device for assembling implant systems include various additional features. For example, the assembly device can further include a cupola coupled to the proximal end of the rod such that the cupola is positioned between the rod and the stage. The cupola can include a concave surface that faces the stage, the concave surface configured to fit against the exterior surface of an outer head portion. In some embodiments, the cupola is frustum shaped. 
     The set pawl includes a proximal end, having an edge that includes a first portion and a second portion, the first portion of the edge extending further than the second portion of the edge. The extension of the first portion and the second portion define a setback region. In some embodiments, the first portion of the edge has a curved transition to the second portion of the edge. The set pawl includes a distal end and a proximal end, wherein the distal end is movably coupled to the actuator system. 
     The rod can include teeth on a surface of the rod extending along at least part of the length of the rod, wherein the first portion of the edge of the set pawl is positioned to engage with teeth on the surface of the rod when the teeth are positioned adjacent to the first portion. In some examples, the teeth are aligned perpendicular to the length of the rod. 
     The set pawl is positioned such that the first portion engages with the teeth of the rod and the second portion does not engage with the teeth of the rod when the rod is positioned with the teeth of the rod aligned in parallel with the edge of the set pawl. 
     The stage can include a platform on the distal end of the stage. The platform can be aligned substantially normal to the longitudinal axis of the rod. The stage also includes an aperture longitudinally positioned in the center of the platform and sized such that the inner member fits into the aperture. The stage can further include one or more fingers positioned on the interior surface of the aperture and extending into the aperture. The fingers are configured to contact the inner member to provide a friction fit between the stage and the inner member. The friction fit between the fingers and the inner member allow the stage to be positionable at different heights on the inner member. In some embodiments, the body comprises one or more cavities making the assembly device lighter weight. In some embodiments, the platform comprises indicia to guide placement of the outer head on the platform. In some embodiments, the indicia is etched into the platform. In some embodiments, the indicia includes at least one ring surrounding the aperture. In some embodiments, the indicia includes two or more concentric rings. 
     The stage can include a guard positioned at the proximal end of the stage. The guard is positioned so the user does not get their fingers caught between the stage and the base portion of the device as the stage is lowered. 
     In some embodiments, the assembly device further includes a base support coupled to the base to provide support for the device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the devices and methods described herein will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. These drawings depict only several embodiments in accordance with the disclosure and are not to be considered limiting of its scope. In the drawings, similar reference numbers or symbols typically identify similar components, unless context dictates otherwise. In some instances, the drawings may not be drawn to scale. 
         FIG.  1    illustrates a perspective view of a femoral head implant assembly device in accordance with an illustrative embodiment. 
         FIG.  2    illustrates the right-side view of the femoral head implant assembly device, in accordance with an illustrative embodiment. 
         FIG.  3    illustrates a cross-sectional view of the femoral head implant assembly device, in accordance with an illustrative embodiment. 
         FIG.  4    illustrates a perspective view from the distal end of a femoral head implant assembly device in accordance with an illustrative embodiment. 
         FIG.  5    illustrates a front view of a femoral head implant assembly device in accordance with an illustrative embodiment. 
         FIG.  6    illustrates a top view of a femoral head implant assembly device in accordance with an illustrative embodiment. 
         FIG.  7    illustrates a bottom view of a femoral head implant assembly device in accordance with an illustrative embodiment. 
         FIGS.  8 A- 8 E  illustrate a stage shown in  FIG.  1   , in accordance with an illustrative embodiment, where  FIG.  8 A  depicts a perspective view of the stage in one position,  FIG.  8 B  depicts a perspective view of the stage in a second position,  FIG.  8 C  depicts a front view of the stage,  FIG.  8 D  depicts a top view of the stage, and  FIG.  8 E  depicts a bottom view of the stage. 
         FIGS.  9 A- 9 F  illustrate views of six sides of an example of an inner member of a head support of a femoral head implant assembly system. 
         FIGS.  10 A- 10 C  illustrate a cupola shown in  FIG.  1   , in accordance with an illustrative embodiment, where  FIG.  10 A  depicts a side view of the cupola,  FIG.  10 B  depicts a top view of the cupola, and  FIG.  10 C  depicts a bottom view of the cupola. 
         FIGS.  11 A- 11 D  illustrate a set pawl as shown in  FIG.  3   , in accordance with an illustrative embodiment, where  FIG.  11 A  depicts a perspective view of the set pawl in one position,  FIG.  11 B  depicts a perspective view of the set pawl in a second position,  FIG.  11 C  depicts a left-side view of the set pawl, and  FIG.  11 D  depicts a right-side view of the set pawl. 
         FIGS.  12 A,  12 B,  12 C, and  12 D  depict the set pawl as shown in  FIGS.  3   , and  11 , in accordance with an illustrative embodiment, where  FIG.  12 A  depicts a top view of the set pawl,  FIG.  12 B  depicts a bottom view of the set pawl,  FIG.  12 C  depicts a front view of the set pawl, and  FIG.  12 D  depicts and back view of the set pawl. 
         FIGS.  13 A- 13 D  illustrative an example of a “floating” or “movable” platform, according to some embodiments. 
         FIGS.  14 A- 14 C  further illustrate an example of a set pawl as it is engaged with the teeth on a rod, according to some embodiments. 
         FIGS.  15 A- 15 D  illustrate another example of a set pawl as it is engaged with the teeth on a rod, according to some embodiments. 
         FIGS.  16 A- 16 B  illustrate the set pawl as it is disengages with the teeth on the rod, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN INVENTIVE ASPECTS 
     The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. It should be apparent that the aspects herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative of one or more embodiments of the invention. An aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, a device for assembling implant systems includes, or a method of assembling implant systems maybe practiced, using any number of the aspects set forth herein. In addition, disclosed devices may be implemented, or such a method may be practiced, using other structure, functionality, or structure and functionality in addition to, or other than one or more of the aspects set forth herein. 
     Dual mobility hip replacement femoral head implants are used in the medical field to replace part or entire hip structures. In some examples, a portion of a femoral implant is designed to be placed into a patient&#39;s femur. A ball-like “head” is coupled to an upper portion (a “taper”) of the femoral implant. The natural socket in the hip joint is replaced with an artificial “cup,” an implant that can include a hemispherical-shaped outer shell and a corresponding hemispherical-shaped inner liner nested inside, and coupled to, the outer shell. When the inner liner is nested inside the cup, a concave surface of the inner liner faces away from the cup and is designed to receive the head coupled to the femoral implant. The head includes a hard (rigid) inner head component (“inner head”) and a plastic larger outer head component (“outer head”). The outer head includes an opening and a cavity shaped and sized to receive the inner head. 
     In some examples, the outer head can comprise polyethylene, or other suitable materials. In some embodiments, the outer head comprises HXe+™ polyethylene, a highly-crosslinked material designed for ball and socket kinematics, and which are blended with Vitamin E. The inner head and outer head are separate components, but prior to being coupled to the taper portion, the heads are assembled such that the inner head is positioned in the cavity of the outer head. Once assembled, the inner head must be retained within the outer head for proper function and patient safety. The inner head is retained within the outer head by under-sizing the opening of the outer head, or other feature, such that it takes a large amount of force to assemble the inner head through the opening and into the cavity; and therefore, accidental dissociation also requires a large amount of force. Due to the force required to assemble the inner head and the outer head, and because the plastic outer head is susceptible to damage, it can be difficult and time consuming to properly place the inner head in the cavity of the outer head. 
     Overview of Technology 
     A damaged or arthritic hip joint can cause pain and decreased mobility and may necessitate hip replacement surgery. Hip replacement surgery involves removal of at least part of a hip joint and replacement with a prosthetic implant. In a total hip replacement surgery, both the femoral head and the acetabulum of the damaged hip joint are replaced. A newer implant known as “dual mobility” provides a greater range of motion and has been shown to reduce the risk of instability in younger, more active patients. A typical hip replacement implant is a ball-in-socket mechanism designed to simulate a human hip joint. Dual mobility implants provide an additional bearing surface compared to a traditional implant. With the dual mobility hip, a large polyethylene plastic head fits inside a polished metal or ceramic hip socket component, and an additional smaller metal or ceramic head is fitted within the polyethylene head. 
     Dual mobility systems and used an assembly fixture to press the hard (metal or ceramic) inner head into the large polyethylene head. This action happens in the operating room away from the patient.  FIGS.  13 A- 13 D  illustrate an example of portions of the assembly fixture fitting the inner head  133  into a cavity of the outer head  134 . Some systems use a C-clamp style fixture, where the implant components are pressed together by turning a threaded rod, however, such a system can be slow to use due to having to repeatedly turn the threaded rod, or a piece that is coupled to the threaded rod. Embodiments of the subject assembly fixture is such that the handle is squeezed while the fingers grasp the body of the fixture, level with where the implants are located while being pressed together. The unique orientation provides a compact overall envelope, which is needed for instrument transportation and sterility. The orientation of the handle also permits the user to press downward with body weight, while squeezing, providing additional force if needed. This orientation allows for a very stable setup as the fixture is gripped by the user near the center of mass. The assembly fixture includes a unique ‘floating platform’ feature, which simplifies preparing the implants for being pressed together. In addition, the floating platform provides quick and easily alignment for the implants as they are being pressed together. The platform slides up around the hard inner head and provides a flat/stable surface for the large outer poly head to rest on. Getting the large poly head to be flat and aligned with the hard inner head is a challenge for fixtures that position the poly head above the inner head during pressing. Then, while the poly head is being pressed, the platform is able to slide downward, which maintains the orientation of the poly head. 
     The assembly fixture also includes two toothed cams or pawls, one drives the movement and applies the force during the press (referred to herein as the “drive pawl”), the other (referred to herein as the “set pawl”) prevents the rod from returning upwards while the handle returns upward after a press. That means that when the handle is squeezed, released and squeezed again, the rod will always continue pressing downward. When the user is finished pressing and wants to lift the rod back up, they would spin the rod to disengage the teeth and the rod would be free to move upward. What is unique is the shape of the set pawl, in particular, the edge of the set pawl that engages the teeth on the rod. This design addresses a specific problem condition: when the teeth jam due to the assembly fixture being compressed beyond what is necessary by the user. The jam is caused by that extra compressive force holding the set pawl tooth and rod tooth together. The unique features of the set pawl are twofold. First, the modified tooth allows the set pawl to slip out of this condition without adding additional compressive forces and frees the jam with much less exertion by the user. Without this modified tooth design, rotating the rod (to disengage the teeth and reset the fixture) actually further drives the rod downward, as the pawl rotates and extends in the axis of the rod, which increase the severity of the jam condition. Second, the pawl is not assembled with a true pin-in-hole style assembly, which only allows for a rotational degree of freedom. The pawl can also translate a finite amount in the axis of the rod, to allow the rod to back off the implants it is pressing and reduce the stored stress in the fixture. 
     The assembly system described herein is advantageous at least because it allows a quicker assembly of the inner and outer head, and thus it is a more efficient way of preparing the implants. The femoral head implant assembly device for assembling implant systems, components of such devices, and methods of using implant assembly systems are disclosed herein. In some embodiments, the femoral head implant assembly system can include a body comprising a base portion and a top portion, and a support coupled to the base and the top portion that includes a grip so that a user can hold the assembly system. The femoral head implant assembly system can also include a rod, a handle, and an actuator system coupled to the rod and the handle, and configured to move the rod when the handle is moved. In some embodiments, the actuator system can include a set pawl that engages with structures (e.g., teeth) on the rod. The set pawl can have a two-part edge, one part being setback to allow the set pawl to release from engagement with the teeth when the rod is rotated around its longitudinal axis. The femoral head implant assembly system can also include a movable or “floating” platform movable along an inner vertical member coupled to the base portion that holds a portion of an implant and move along the vertical member during assembly of the implant. The assembly system can include a cupola coupled to a proximal end of the rod, the cupola used to press on the implant. 
     The following is a list of certain annotations and components that are described and enumerated in this disclosure in reference to the above-listed figures. However, any aspect, structure, feature or operational function of the devices illustrated in the figures, whether or not named out separately herein, can form a portion of various embodiments and may provide basis for one or more claim limitation relating to such aspects, with or without additional description. The annotations and enumerated components include: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 100 femoral head  
                 115 outer distal edge  
               
               
                 assembly system 
                 of inner member 
               
               
                 101 body 
                 116 inner head support 
               
               
                 102 handle 
                 117 indent 
               
               
                 103 platform 
                 118 set pawl spring 
               
               
                 104 support 
                 119 guard 
               
               
                 105 grip 
                 120 stage 
               
               
                 106 base 
                 121 structures (fingers) 
               
               
                 107 body cavities 
                 122 inner member 
               
               
                 108 base support 
                 123 distal edge of  
               
               
                 109 aperture 
                 inner head support 
               
               
                 110 top portion 
                 124 lower (proximal)  
               
               
                 111 drive pawl 
                 surface of cupola 
               
               
                 112 rod 
                 125 coupling member 
               
               
                 113 drive pawl spring 
                 126 disengagement knob 
               
               
                 114 cupola 
                 128 locking  
               
               
                 131 head support 
                 movement assembly 
               
               
                 132 actuator system 
                 129 coupling member head 
               
               
                 133 inner head 
                 130a-b target rings (indicia) 
               
               
                 134 outer head 
                 226 distal end of  
               
               
                 135 top or top (distal) surface 
                 inner member 
               
               
                 136 surface of rod 
                 227 teeth of rod 
               
               
                 137 first position 
                 228 proximal end of rod 
               
               
                 138 second position 
                 229 distal end of rod 
               
               
                 139 third position 
                 230 set pawl 
               
               
                 140 (peripheral ) ridge  
                 231 body of set pawl 
               
               
                 on inner member 
                 232 first portion of set pawl 
               
               
                 141 beveled surface 
                 233 second portion (setback  
               
               
                 150 distal end of  
                 region) of set pawl 
               
               
                 assembly system 
                 234 holes of set pawl 
               
               
                 151 proximal end of  
                 235 setback region 
               
               
                 assembly system 
                 236 distal end of set pawl 
               
               
                 202 longitudinal axis 
                 238 proximal end of set pawl 
               
               
                 218 proximal end of stage 
                 239 length of hole  
               
               
                 219 distal end of stage 
                 of set pawl 
               
               
                 220 exterior surface  
                 240 width of  
               
               
                 (on side of stage) 
                 hole of set pawl 
               
               
                 221 side of stage 
                 252 distal end of cupola 
               
               
                 222 proximal end  
                 254 proximal end of cupola 
               
               
                 of inner member 
                 256 edge 
               
               
                   
               
            
           
         
       
     
     Illustrative Examples of Device for Assembling Implant Systems 
     Turning now to the figures,  FIG.  1    illustrates an example of a femoral head implant assembly system (device)  100 , which may be referred to herein as an “assembly system” or simply as a “device” or “system” for ease of reference. The assembly system  100  has a proximal end  151  and a distal end  150 . Components may be described herein with reference to having a distal end or a proximal end, and such references are in correspondence to the distal end  150  and the proximal end  151  of the assembly device  100 , unless otherwise stated or illustrated or as discernable by the drawings or the context of the description. 
     The assembly system  100  includes a body  101  having a base portion (“base”)  106  at the proximal end  151 , a top portion  110  at the distal end  150 , and a support  104  positioned between the base  106  and the top portion  110 . In some embodiments, two or more of the base  106 , the support  101 , and/or the top portion  110  are integrally formed. In other embodiments, one or more of the base  106 , the support  104 , and/or the top portion  110  are separate pieces that are coupled together. In some embodiments, the base  106  includes a base support  108  on the portion of the base  106  near the head support  131 . In some embodiments, the base support  108  is a half-circle and is attached at the front end of the base portion  106 . In some embodiments the base support  108  is made of metal. In an example, the base support  108  can be curved or C-shaped. The support  104  can include a grip  105  which is sized and shaped to allow a user&#39;s hand to grasp the grip  105 , at least partially encircling the grip  105  to stabilize the system  100  during operation and providing a safe place to hold (grip) the assembly system  100  set back from certain movable components (e.g., handle  102 , rod  112 , and stage  120 ) to protect the user&#39;s hand and fingers. For example, a user can stabilize the assembly system  100  by holding the grip  105  when moving the handle  102  from a first position A to a second position B while coupling the outer head and inner head. In this example, first position A is an upper position relative to second position B which is a lower position. When the handle  102  is moved from the first position A to the second position B, the assembly that couples the handle to a rod  112  correspondingly drives the rod  112  from a raised (distal) position to a lower (proximal) position to press an implant outer head onto an inner head, as illustrated in  FIGS.  13 A- 13 D . Movement of the handle from first position A to second position B correspondingly moves the rod  112  a certain distance towards the implant through use of a drive pawl  111 , that engages with teeth on the rod  112  to move the rod. To continue to move the rod  112  towards the implant, the handle  102  may have to be moved back to the first position A, and then to the second position B in a ratchet-like manner (depending on the configuration of the assembly). A set pawl  230  in the assembly also engages with teeth on the rod  112  and holds the rod  112  in place during the ratchet-like process. Due to the pressure being applied on the implant, a significant amount of force can be on the set pawl  230  locking it tightly into the teeth. Embodiments of the set pawl  230  described herein prevent the rod  112  and set pawl  230  to become jammed together such that it is difficult to disengage the teeth  227  from the set pawl  230 . 
     The top portion  110  includes an actuator system  132  with a locking assembly  128  ( FIG.  3   ) for driving a rod  112  along a longitudinal axis  202  ( FIG.  2   ) towards a head support  131 , the head support  131  coupled to the base  106 . Rod  112  has a proximal end  228  and a distal end  229 . In this example, the rod  112  includes a knob  126  coupled to the distal end  229 , which may be used to rotate the rod  112  around its longitudinal axis. In this example, a cupola  114  is coupled to the proximal end  228  of the rod  112 . The cupola  114  includes a lower (proximal) surface  124  facing the base  106  that contacts an exterior surface of the outer head  134  when it presses an outer head  134  onto an inner head  133  (see  FIGS.  13 A- 13 D ). In preferred embodiments, the surface  124  may be partly, or entirely, concave to provide a better fit of the surface  124  against the curved exterior surface (e.g., ball-like) of the outer head  134 . The rod  112  includes a series of teeth  227  ( FIG.  3   ) that are positioned along a surface  136  ( FIG.  3   ) of rod  112 , i.e., along a portion of the length of the rod  112 . In this example, the teeth  227  are aligned perpendicular to a longitudinal axis  202  ( FIG.  2   ) of the rod  112 . The actuator system  132  also includes a drive pawl  111  ( FIG.  3   ) and a set pawl  230  (see e.g.,  FIGS.  3  and  11 A- 11 D ) which are further described hereinbelow. The handle  102  is coupled to the drive pawl  111  such that when the handle is moved from a first position to a second position, the drive pawl  111  engages with the rod&#39;s teeth  227  and moves the rod  112  towards the base  106 . 
     The locking assembly  128  includes a set pawl  230 . While the drive pawl  111  drives the rod  112  downward to apply a force on a surface of the outer head, the set pawl  230  prevents the rod  112  from moving upwards (away from the base  106 ) while the handle  102  is moved to its first position. The set pawl  230  engages with the rod&#39;s teeth  227  each time the rod  112  is moved towards the base  106 , in a ratchet-like manner. As described in more detail reference to  FIGS.  11 A- 11 D , the set pawl  230  includes a specially designed edge  256  that interfaces with the rod&#39;s teeth  227  to alleviate a binding condition that can occur when the user rotates the rod  112  to raise it off of the outer head. 
     The head support  131  provides support for both the inner head and the outer head while they are being coupled together. The head support  131  includes an inner member  122  which is coupled to the base  106 . The inner member  122  includes a raised peripheral ridge  140 , extending from above the surface  135 , around the inner member  122  and adjacent to the bevel  141  which is on an outer surface of the ridge  140 . The ridge  140  retains and aligns an inner head on the inner member  122 . The head support  131  also includes an inner head support  116  extending from a distal surface (top surface)  135  of the inner member  122  towards the cupola  114 . The inner head support  116  is shaped to fit inside a cavity in the inner head  133  to support and retain the inner head  133  in a certain position (upright) while the outer head  134  is pressed onto the inner head  133 . The distal surface  135  of the inner member  122  is designed to support edges of the inner head  133  around its cavity. In some embodiments, the surface  135  includes indicia to help correctly place or center the outer head on the distal surface  135 . In some examples, the distal surface  135  includes a ring  130 . In some examples, the distal surface  135  includes one or more concentric rings  130  (see  FIG.  8 D ). 
     The head support  131  further includes a stage  120 . The stage  120  is structured to surround and move along the inner member  122  (e.g., vertically with respect to the orientation of  FIG.  1   ). In other words, the stage  120  is slidably coupled to the inner member  122 . In the illustrated embodiment the shape of an outer surface of the inner member  122  is cylindrical. In other embodiments, the shape of the outer surface of the inner member  122  may have other shapes (e.g., rectangular, multi-sided, hexagonal, curved, etc.). 
     In this example, the stage  120  includes a platform  103  at the distal end of the head support  131  facing the cupola  114 . The platform  103  is arranged laterally around the inner member  122  and extends outward from the inner member  122 . The platform  103  may be aligned substantially normal to an axis of the rod  112 . The platform  103  has a surface  135 . The stage  120  includes an aperture  109  ( FIGS.  8 C- 8 E ) longitudinally oriented within the stage  120  and sized to fit around the inner member  122 . A set of one or more structures (fingers)  121 , as illustrated in  FIGS.  8 A,  8 B , extend from a portion of the stage  120  in the aperture  109  and contact the inner member  122  such that the fingers  121  have a friction fit onto the inner member  122  allowing the stage  120  to be positioned at different heights on the inner member  122  and remain at there. In some embodiments, the structures  121  can be connected to a portion of the stage  120  at a distal end, and be unconnected at a proximal end such that although they are rigid or semi-rigid, they may move slightly to allow them to grip the inner member  122 . That is, when the structures  121  are placed around the inner member  122  such that a portion of the inner member  122  is inside a portion of the stage  120 , the structures  121  in contact with the inner member and are slightly flexed outward by the inner member  122 . In an assembly operation, the stage  120  slides along the inner member  122  and around the inner femoral head and when the cupola  114  presses a large polyethylene liner  134 , that rests on the stage  120 , the stage  120  slides back to a proximal position (e.g., a lower position relative to the orientation of system  100  when in use). This way, the stage  120  provides a movable and stable support for the outer head  134  (e.g., a polyethylene liner) to rest on as it is pushed onto the inner head  133 . This is further described in reference to  FIGS.  13 A-D . 
       FIG.  2    illustrates the right-side view of the femoral head implant assembly device  100  in  FIG.  1    and the angles between such components. Various embodiments may be configured differently. In some embodiments, angle F between the top portion  110  and the body support member  104  is between about 148 degrees and about 153 degrees. In some embodiments, angle F between the top portion  110  and the body support member  104  is between about 90 degrees and about 180 degrees. In some embodiments, angle G between the body support member  104  and the base portion  106  is between about 68 degrees and about 72 degrees. In some embodiments, angle G between the body support member  104  and the base portion  106  is between about 45 degrees and about 90 degrees. In some embodiments, the grip  105  is made from plastic. In some embodiments, the grip  105  is made from a metal. In some embodiments the body has one or more cavities  107 . 
       FIG.  3    illustrates further a cross-sectional view of the femoral head implant assembly device  100  from  FIG.  1   . In some embodiments, the cupola  114  has a distal end  252  and a proximal end  254  (see  FIG.  10 A ). In some embodiments, the cupola  114  has a concave surface  124  on the proximal end  254  of the cupola  114 . 
       FIG.  4    further illustrates a perspective view from the distal end of the femoral head implant assembly device  100  from  FIG.  1   . 
       FIG.  5    further illustrates a front view of the femoral head implant assembly device  100  from  FIG.  1   . 
       FIG.  6    further illustrates a top view of the femoral head implant assembly device  100  from  FIG.  1   . 
       FIG.  7    further illustrates a bottom view of the assembly device  100  from  FIG.  1   . 
       FIGS.  8 A- 8 E  illustrate views of five sides of an example of the stage  120 . The stage  120  has a proximal end  218  and a distal end  219 .  FIGS.  8 A and  8 B  show perspective views of different angles from the distal end  219  of the stage  120 .  FIG.  8 C  is a perspective view of the side of the stage  120 .  FIG.  8 D  is a top view of the stage  120 .  FIG.  8 E  is a bottom view of the stage  120 . 
     In some embodiments the stage  120  has at least one finger  121 . In some embodiments the fingers  121  are used to create friction between the stage  120  and the inner member  122 . In some embodiments, the stage  120  has a guard  119  that is positioned on the proximal end of the stage  120 , the guard  119  extending laterally from the proximal end  218  of the stage  120  to at least partially shield the fingers  121  and the area where the stage  120  contacts the inner member  122  from contact by a user while providing a surface for the user to grip when actuating the stage  120  along the inner member  122 . In some embodiments, the stage  120  has a flat distal surface  135 , aligned substantially normal to the longitudinal axis  202 . In some embodiments, the stage  120  has target rings  130   a  and  130   b  etched or marked on the distal surface  135 . Target rings  130   a ,  130   b  are on the distal surface  135  and can be formed therein. The target rings  130   a ,  130   b  provide a reference for the user to properly center an outer head when it is placed on the stage  120 . In some embodiments an exterior surface  220  at the distal end  219  of the stage  120  can be curved. In some embodiments the side surface  221  of the stage  120  is curved. In some embodiments, the radius of the top surface  135  is between about 15 and about 38 millimeters. In some embodiments, the radius of the top surface  135  is between about 25 and about 31 millimeters. In some embodiments, the radius of the top surface  135  is between about 26 millimeters and about 28 millimeters. In some embodiments, the first target ring  130   a  has a radius between about 18 mm to about 19 mm. In some embodiments, the first target ring  130   a  has a radius between about 15 mm to about 23 mm. The radius of the second target ring  130   b  is larger than the radius of the first target ring. In some embodiments the second target ring  130   b  has a radius between about 22 mm to about 23 mm. In some embodiments the second target ring  130   b  has a radius between about 20 mm to about 28 mm. 
       FIGS.  9 A- 9 F  illustrate views of six sides of an example of an inner member  122  of a head support  131  of a femoral head implant assembly system  100 .  FIG.  9 A  shows a front view of the inner member  122 .  FIG.  9 B  shows a side view of the inner member  122 .  FIG.  9 C  shows a perspective view of the proximal end  222  of the inner member  122 .  FIG.  9 D  shows a perspective view from the distal end  226  of the inner member  122 .  FIG.  9 E  shows a bottom view of the inner member  122 .  FIG.  9 F  shows a top view of the inner member  122 . 
     Still referring to  FIGS.  9 A- 9 F , the inner member  122  has a proximal end  222  and a distal end  226 . The inner head support  116  extends from the center of the top surface  135  of the inner member  122 . In some embodiments, the inner head support  116  extends from the top surface  135  between about 10 mm to about 13 mm. In some embodiments, the inner head support  116  extends from the top surface  135  between about 5 mm and 20 mm. In some embodiments the inner head support  116  has a radius from about 3 mm to about 7 mm. In some embodiments the inner member  122  has a circumferential indent  117  on an exterior surface. In some embodiments, the inner member  122  includes an indent  117 . The indent  117  can be aligned normal to the longitudinal axis of the inner member  122 . In some embodiments the indent  117  is used as a stop for the fingers  121  to allow the stage  120  to be positioned at a certain height while it moves along the inner member  122  and further prevents the stage  120  from being pulled off the inner member  122 . In some embodiments the inner member  122  has additional features to assist with the coupling of the inner member  122  to the stage  120 . 
     In some embodiments, the distal end  226  of the inner member  122  has a beveled surface  141  along its curved edge  115 . In some embodiments the beveled surface  141  allows for the inner head  133  and outer head  134  to assemble together completely. Once assembled, the outer head  134  may fully contain the inner head  133  (depending on the style of the inner head). During assembly, part or all of the inner member  122  may pass into a portion of the outer head  134  as the inner head  133  and outer head  134  are pressed together (for example, see  FIGS.  13 A- 13 D ). In some embodiments, the inner member  122  is slanted on the proximal end  222 . In some embodiments the inner head support  116  has a slanted, beveled, or curved edge  123  around the inner head support where it meets the inner member  122 . 
     In an example, the depth of the circumferential indent  117  on the inner head support  116  is 0.010 inches. In another example, the depth of the circumferential indent  117  can be between about 0.008 inches and about 0.012 inches (e.g., 0.010 inches plus or minus 20%). In another example, the depth of the circumferential indent  117  can be between about 0.009 inches and about 0.011 inches (e.g., 0.010 inches plus or minus 10%). 
       FIGS.  10 A- 10 C  illustrate views of three sides of an example of a cupola  114  of a femoral head implant assembly system  100 .  FIG.  10 A  shows a side view of the cupola  114 .  FIG.  10 B  shows a top view of the cupola  114 .  FIG.  10 C  shows a bottom view of the cupola  114 . In some embodiments the cupola  114  has a proximal end  252  and a distal end  254 . In some embodiments, at distal end  254  of the cupola surface is concave. In some embodiments the cupola  114  has a frustum shape. 
       FIGS.  11 A- 11 D  illustrate views of four sides of an example of a set pawl  230  of a femoral head implant assembly system  100 .  FIGS.  11 A and  11 B  show perspective views of the set pawl  230  from different angles.  FIG.  11 C  shows a left side view of the set pawl  230 .  FIG.  11 D  shows a right-side view of the set pawl  230 . In some embodiments the set pawl has a proximal end  236  and a distal end  238 . In some embodiments the set pawl is coupled to the top portion  110  of the femoral head implant assembly system  100  through holes  234  on either side of the set pawl. In the example illustrated, the holes  234  are elongated holes or non-symmetrical (e.g., oval-shaped). For example, as shown in  FIG.  11 C , the length  239  of the hole  234  is longer than the width  240  of the hole  234  such that the hole is not circular. In other embodiments, the holes  234  can be circular. Having elongated holes can help prevent jams that can occur when the cupola  114  is pressed tightly against an outer head. In this configuration, the elongated holes  234  provide strain relief and allow the rod  112  to be rotated to disengage the teeth  227  and the set pawl  230 , allowing the set pawl  230  to move slightly longitudinally. In some embodiments the set pawl has a first portion  232  and a second portion  233  at the edge of the distal end of the set pawl  238 . In some embodiments the first portion  232  is configured to engage the teeth of the rod  227 . In some embodiments the second portion  233  of the set pawl  230  is of lesser stature than the first portion  232 , so when the disengagement knob  126  is turned to move the rod  112 , the set pawl  230  does not jam with the rod  112 . In some embodiments, the set pawl  230  may include multiple edges  256  aligned in parallel and configured to engage with multiple teeth  227  of the rod. In such embodiments, each of the multiple edges may have a first portion  232  and a second portion  233 , for example, as illustrated in  FIG.  11 A . In such embodiments, at least one of the multiple edges may have a first portion  232  and a second portion  233 , for example, as illustrated in  FIG.  11 A . 
       FIGS.  12 A- 12 D  further illustrate views four sides of an example of a set pawl  230  of a femoral head implant assembly system  100 .  FIG.  12 A  illustrates a top view of a set pawl  230 .  FIG.  12 B  illustrates a bottom view of a set pawl  230 .  FIG.  12 C  illustrates a front view of a set pawl  230 .  FIG.  12 D  illustrates a back view of a set pawl  230 . 
       FIGS.  13 A- 13 D  illustrate the vertical positioning of the stage  120  relative to the inner member  122  during an assembly operation where the inner head  133  is positioned within the outer head  134 . The stage  120  and the inner member  122  are configured such that the stage  120  can be positioned at various heights on the inner member  122 . In  FIG.  13 A , the stage  120  and the cupola  114  are in a starting position. The stage  120  is positioned low on the inner member  122  such that the stage  120  is adjacent to the base  106 . The inner head  133  is placed on the inner member  122  such that the inner head support  116  extends into the inner head  133 . The platform  103  is at a first position  137 . In  FIG.  13 B , the stage  120  has been moved up on the inner member  122  such that the platform  130  is at a second position  138  at or near the top of the inner head  133 .  FIG.  13 B  also illustrates how, in this position, the inner head  133  is in, or at least partially in, the aperture  109  of the stage  120 . In  FIG.  13 C , the outer head  134  has been placed on the platform  103  above the inner head  133 . Finally, in  FIG.  13 D  the cupola  114  is driven downward and contacts an exterior surface of the outer head  134  to move the outer head  134  over the inner head  133  until the inner head  133  is within the outer head  134 . As the cupola  114  applies force downward on the outer head  134 , the outer head correspondingly applies a downward force on the stage  120  moving it towards the base  106  as the outer head  134  is pushed down over the inner head  133 . Position  139  indicates a position of the platform  103  as the stage  120  is moved down the inner member  122 . The fingers  121  ( FIG.  8 A ) cause friction against the inner member  122  but allow the stage  120  to move, so that the platform  103  provides a movable support structure. Also, as the inner head  133  is at least partially within the aperture  109  of the stage  103 , the interior wall of the aperture can provide lateral support (if necessary) to the inner head  133  to keep it vertically aligned such that it is positioned into the outer head  134  correctly. As the cupola  114  presses the outer head  134  downward, the inner head  133  is properly set into place with the outer head  134  and the assembly is complete. 
     In an example, the stage  120  can move 0.7 inches from the uppermost position to the lowest position. In another example, the stage  120  can move between about 0.56 inches and about 0.84 inches (e.g., 0.7 inches plus or minus 20%). In another example, the stage can move between about 0.63 inches and about 0.77 inches (e.g., 0.7 inches plus or minus 10%). 
     In some embodiments, the amount of force needed for the cupola  114  to press the outer head downward over the inner head  133  may be less for thinner large heads, for example about 2 kN of force. In other embodiments, more force may be needed with the large head is thicker, for example about 3.7 kN of force. 
       FIGS.  14 A- 14 C  further illustrate the set pawl  230  as it is engaged with the set of teeth  227  on the rod  112 .  FIG.  14 A  illustrates that the set pawl  230  includes an edge  256  that engages the teeth  227  of the rod  112 .  FIG.  14 A  illustrates the first portion  232  engaged with the teeth  227  when the rod  112  is in a first position (e.g., the teeth oriented to be aligned with the edge  256 ). The second portion  233  is not engaged with the teeth  227  when the rod  112  is at a first position. The second portion  233  of the edge  256  has a setback region  235  ( FIG.  11 A ) relative to the first portion  232 .  FIG.  14 B  illustrates the set pawl  230  positioned such that when the rod  112  is rotated (around its longitudinal axis) such that the teeth  227  are correspondingly rotated towards the first portion  232 , and at least one of the teeth  227  extends into the setback region  235  ( FIG.  11 A ) facilitating the disengagement of the teeth  227  with the set pawl  230 .  FIG.  14 C  illustrates the rod  112  being further rotated such that the teeth  227  are disengaging with the first portion  232  of the edge  256 . The setback region  235  of the second portion  233  of the edge  256  allows the teeth  227  to more easily be disengaged from the set pawl  230  even when the rod  112  is under tension from having the cupola  114  forcibly pressed against the outer head  134  (e.g., as illustrated in  FIG.  13 D ). Additionally, presence of the setback region  235  allows the pawl  230  to swing ‘up’ without jamming into the rod tooth with which it is engaged. Due to the setback region  235  being present only on one side of the pawl  230  ‘easy’ disengaging of the pawl will only occur when the rod  112  is rotated counter-clockwise. Location of the pawl tooth relative to the space between the rod teeth and the underside of the pawl determine how the pawl is lifted. 
     In some embodiments, the set pawl  230  is made of metal or stainless steel, or some other corrosion resistant material. 
     In an example, the second portion  233  has a setback region distance  235  of 0.053 inches. In another example, the setback region distance  235  can be between about 0.0424 inches and about 0.0636 inches (e.g., 0.053 inches plus or minus 20%). In some embodiments, the setback region distance  235  has a length of any of or between any two of the following dimensions: 0.0424 inches, 0.045 inches, 0.0477 inches, 0.0503 inches, 0.053 inches, 0.0556 inches, 0.0583 inches, 0.0609 inches, and 0.0636 inches. In another example, the setback region distance  235  can be between about 0.0477 inches and about 0.0583 inches (e.g., 0.053 inches plus or minus 10%). 
     In an example, the teeth  227  are 0.031 inches off the rod  112 . In another example, the teeth  227  can be between about 0.0248 inches and about 0.0372 inches (e.g., 0.031 inches plus or minus 20%). In another example, the teeth can be between about 0.0279 inches and about 0.0341 inches (e.g., 0.031 inches plus or minus 10%). 
     In an example, the width of the set pawl  230  is 0.425 inches. In another example, the width of the set pawl  230  can be between about 0.34 inches and about 0.51 inches (e.g., 0.425 inches plus or minus 20%). In another example, the width of the set pawl  230  can be between about 0.3825 inches and about 0.374 inches (e.g., 0.34 inches plus or minus 10%). 
     In an example, the second portion  233  is between about 33% and 53% of the setback region distance  235 . 
       FIGS.  15 A- 15 D  further illustrate the set pawl  230  as it is engaged with the teeth  227  on the rod  112 , according to some embodiments. In particular, these figures show the set pawl  230  in a starting position, then in a position after the rod  112  is turned and the teeth  227  begin to disengage. The first row,  FIGS.  15 A and  15 B  illustrate the set pawl  230  in a starting position where the surface  256  is engaged with the rod teeth  227 . The second row,  FIGS.  15 C and  15 D , illustrate the set pawl disengaged from the teeth  227  in a second position, and the area marked in red indicates the point of contact between the set pawl and the teeth.  FIG.  15 A  is a side view of the starting position, and  FIG.  15 B  is a close-up of the teeth  227  in contact with the set pawl  230 . In some embodiments, the teeth  227  may begin to disengage when the rod is rotated 3 degrees, 4 degrees, or 5 degrees. As the rod teeth  227  rotate ‘up’ with the rotation of the rod  112 , the set pawl  230  is lifted by the teeth making contact on the underside. 
       FIGS.  16 A and  16 B  illustrate the set pawl  230  as it is disengages with the teeth  227  on the rod  112 , according to some embodiments. In some embodiments, the rod  112  is rotated 8 degrees, 9 degrees, or 10 degrees causing the teeth  227  of the set pawl  230  to disengage from the teeth of the rod  112 .  FIG.  16 A  is a side view of the disengaged set pawl  230  and  FIG.  16 B  is a close up, ghost view of the set pawl  230  in contact with the teeth  227  of the rod  112 . 
     Examples of an Assembly System Having the Disclosed Stage 
     Some (but not all) examples of embodiments of an assembly system, and/or components of an assembly system, for coupling together an inner head and an outer head of a femoral head implant are listed below, where the assembly system may include a movable stage, are listed below. 
     Embodiment 1: An assembly system, comprising: a handle; a rod coupled to the handle, the rod aligned along a longitudinal axis and coupled to the handle; a body comprising a distal end and a proximal end, the body having a base portion, a top portion, a support portion between the base portion and the top portion, the support portion including a grip for a user to hold while moving the handle, an actuator system coupled to the rod to move the rod along the longitudinal axis and to allow the rod to be at least partially rotated around the longitudinal axis; an implant support having an inner member coupled to the base portion and positioned between the rod and the base portion, the inner member extending from the base portion towards the top portion and aligned with the longitudinal axis; an inner head support extending from the distal end of the inner member towards the rod and configured to receive an inner head thereon, the inner head support aligned along the longitudinal axis with the rod, and a stage circumferentially positioned around and slidably coupled to the inner member such that the stage can move along an exterior surface of the inner member. 
     Embodiment 2: The assembly system of embodiment 1, further comprising a cupola having a distal end and a proximal end, the distal end of the cupola being coupled to the proximal end of the rod such that the cupola is positioned between the rod and the stage. 
     Embodiment 3: The assembly system of embodiment 2, wherein the cupola comprises a concave distal surface on a portion of the cupola surface that faces the stage for contacting a portion of an exterior surface of an outer head portion positioned on the platform. 
     Embodiment 4: The assembly system of embodiment 2, wherein the cupola is frustum shaped. 
     Embodiment 5: The assembly system of embodiment 1, wherein the stage has a proximal end and a distal end, and the stage comprises a platform on the distal end of the stage. 
     Embodiment 6: The assembly system of embodiment 5, wherein the platform is planar and aligned substantially normal to the longitudinal axis. 
     Embodiment 7: The assembly system of embodiment 5, wherein the stage comprises an aperture longitudinally positioned in the center of the platform sized such that the inner member sized to fit into the aperture. 
     Embodiment 8: The assembly system of embodiment 7, wherein the stage includes one or more structures positioned on the interior surface of the aperture and extending into the aperture, the one or more structures configured to provide contact the inner member and provide a friction between the inner member and the stage. 
     Embodiment 9: The assembly device of embodiment 7, wherein the stage includes a structure that contacts the inner member and provides friction between the stage and the inner member such that the stage can be moved along the inner member and be held in place at a position on the inner member by the friction between the stage and the inner member. 
     Embodiment 10: The assembly system of embodiment 8, wherein the one or more structures comprises a plurality of structures positioned symmetrically on the interior surface of the aperture. 
     Embodiment 11: The assembly system of embodiment 9, wherein the stage is movably positionable at different heights on the inner member. 
     Embodiment 12: The assembly system of embodiment 5, wherein the platform comprises indicia to guide placement of the outer head on the platform. 
     Embodiment 13: The assembly system of embodiment 12, wherein the indicia includes at least one ring surrounding the aperture 
     Embodiment 14: The assembly system of embodiment 13, wherein the indicia includes two or more concentric rings. 
     Embodiment 15: The assembly system of embodiment 1, wherein the stage comprises a guard positioned circumferentially around the proximal end of the stage. 
     Embodiment 16: The assembly system of embodiment 1, further comprising a base support coupled to the base and extends laterally on either side of the base portion. 
     Embodiment 17: The assembly system of embodiment 16, wherein the base support is U-shaped and is coupled to the base portion at the center of the inside of the U-shape such that the base support extends laterally around part of the base portion. 
     Embodiment 18: The assembly system of embodiment 1, wherein the body comprises one or more cavities for reducing weight of the assembly device. 
     Embodiment 19: The assembly system of embodiment 1, wherein the rod comprises a knob coupled to the distal end of the rod for rotating the rod around the longitudinal axis. 
     Embodiment 20: An assembly system for coupling together an inner head and an outer head of a femoral head implant, the assembly device comprising: a body having a top portion and a base portion; a rod having a distal end and a proximal end, the rod coupled to the top portion and aligned along a longitudinal axis; a head support having an inner member coupled to a base portion, the head support positioned between the proximal end of rod and the base portion, the head support having an inner head support extending from the inner member towards the proximal end of the rod and configured to receive an implant inner head thereon, the inner head support aligned along the longitudinal axis, and a stage circumferentially positioned around, and slidably coupled to, the inner member such that the stage can move along an exterior surface of the inner member, the stage being aligned substantially normal to the longitudinal axis and configured to receive an outer implant head thereon. 
     Examples of an Assembly System having the Disclosed Set Pawl 
     Some, but not all, examples of embodiments of an assembly system, and/or components of an assembly system, for coupling together an inner head and an outer head of a femoral head implant are listed below, where the assembly system may include set pawl, are listed below. 
     Embodiment 1: A femoral head implant assembly system for coupling together an inner head and an outer head portion, the assembly device comprising a set pawl configured to engage teeth on a rod and hold the rod in place while a handle that is coupled to the rod is moved from a second position to a first position, the first position being a position where the handle can be moved to move the rod to push an outer head portion of an implant onto an inner head portion of the implant, the set pawl having an edge that includes a first portion and a second portion, the second portion having a setback region such that the first portion of the edge extends farther than the second portion of the edge. 
     Embodiment 2: The femoral head implant assembly system of claim  1 , wherein the distance of the second portion setback region is 0.053″ plus or minus 20%. 
     Embodiment 3: The femoral head implant assembly system of claim  1 , wherein the distance of the second portion setback region is 0.053″ plus or minus 10%. 
     Embodiment 4: The femoral head implant assembly system of claim  1 , wherein the distance of the second portion setback region is 0.053″ plus or minus 5%. 
     Embodiment 5: The femoral head implant assembly system of claim  1 , wherein the length of the second portion is between about 33% and 53% of the length of the first portion. 
     Embodiment 6: The femoral head implant assembly system of claim  1 , wherein the length of the second portion is between about 0.140 inches and 0.225 inches, and the edge of the set pawl is about 0.425 inches in length, plus or minus 20%. 
     Embodiment 7: The femoral head implant assembly system of claim  1 , further comprising: a body comprising a distal end and a proximal end, the body having a base portion, a top portion, and a support portion between the base portion and the top portion, the support portion including a grip for a user to hold while moving the handle; an actuator system coupled to the rod to move the rod along the longitudinal axis and to allow the rod to be at least partially rotated around the longitudinal axis, the actuator system comprising a drive pawl coupled to the handle and configured to engage the rod and drive the rod along the longitudinal axis towards the base portion when the handle is moved from a first position to a second position, and the set pawl; and a support platform for holding an implant, the support platform aligned with the longitudinal axis in a position such that a proximal end of the rod moves towards the support platform when the handle is actuated. 
     Embodiment 8: The assembly device of claim  7 , further comprising a cupola coupled to the proximal end of the rod such that the cupola is positioned between the rod and the stage. 
     Embodiment 9: The assembly device of claim  8 , wherein the cupola comprises a concave surface on a portion of the cupola surface that faces the stage to contact a portion of an exterior surface of an outer head portion positioned on the platform. 
     Embodiment 10: The assembly device of claim  8 , wherein the cupola is frustum shaped. 
     Embodiment 11: The assembly device of claim  7 , wherein the set pawl includes a distal end and a proximal end, wherein the distal end is movably coupled to the actuator system. 
     Embodiment 12: The assembly device of claim  7 , wherein the set pawl further comprises elongated holes that are used to couple the set pawl to the body 
     Embodiment 13: The assembly device of claim  1 , wherein the first portion of the edge has a curved transition to the second portion of the edge. 
     Embodiment 14: The assembly device of claim  1 , wherein the rod comprises teeth on a surface of the rod extending along at least part of the length of the rod, wherein the first portion of the edge of the set pawl is positioned to engage with teeth on the surface of the rod when the teeth are positioned adjacent to the first portion. 
     Embodiment 15: The assembly device of claim  14 , wherein the teeth are aligned perpendicular to the length of the rod. 
     Embodiment 16: The assembly device of claim  15 , wherein the set pawl is positioned such that the first portion engages with the teeth of the rod and the second portion does not engage with teeth of the rod when the rod is positioned with the teeth of the rod aligned in parallel with the edge of the set pawl. 
     Embodiment 17: The assembly device of claim  15 , wherein the set pawl is positioned such that when the rod is rotated, the teeth are rotated towards the first portion, a least one of the teeth extends into the setback region facilitating disengagement of the teeth with the set pawl. 
     Embodiment 18: An assembly device comprising a set pawl having an edge that includes a first portion and a second portion, the second portion having a setback region such that the first portion of the edge extends a distance of about 0.042 inches and about 0.064 inches farther than the second portion of the edge. 
     Embodiment 19: The assembly device of claim  18 , wherein the set pawl is positioned to engage teeth on a rod and hold the rod in place while a handle that is coupled to the rod is moved from a second position to a first position, wherein moving the handle from the first position to the second position moves the rod to push an outer head portion of an implant onto an inner head portion of the implant. 
     Embodiment 20: A femoral head implant assembly system for coupling together an inner head and an outer head portion, the assembly device comprising a set pawl having an edge that includes a first portion and a second portion, the second portion having a setback region such that the first portion of the edge extends farther than the second portion of the edge, and the first portion has a curved transition to the second portion. 
     In some embodiments, an assembly system includes the disclosed movable stage and the disclosed set pawl. For example, the assembly system in  FIG.  1    (and other figures) includes a movable stage and a set pawl, as described in the corresponding description. 
     Implementation Considerations 
     The foregoing description details certain embodiments of the systems, devices, and methods disclosed herein. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the systems, devices, and methods can be practiced in many ways. As is also stated above, it should be noted that the use of particular terminology when describing certain features or aspects should not be taken to imply that the terminology is being re-defined herein to be restricted to including any specific characteristics of the features or aspects of the technology with which that terminology is associated. 
     Conditional language such as, among others, “can,” “could,” “might” or “may,” unless specifically stated otherwise, are otherwise understood within the context as used in general to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment. 
     Headings are included herein for reference and to aid in locating various sections. These headings are not intended to limit the scope of the concepts described with respect thereto. Such concepts may have applicability throughout the entire specification. 
     Disjunctive language such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present. 
     The phrase “based on” does not mean “based only on,” unless expressly specified otherwise. In other words, the phrase “based on” describes both “based only on” and “based at least on.” Unless otherwise explicitly stated, articles such as “a” or “an” should generally be interpreted to include one or more described items. Accordingly, phrases such as “a device configured to” are intended to include one or more recited devices. 
     It will be appreciated by those skilled in the art that various modifications and changes may be made without departing from the scope of the described technology. Such modifications and changes are intended to fall within the scope of the embodiments. It will also be appreciated by those of skill in the art that parts included in one embodiment are interchangeable with other embodiments; one or more parts from a depicted embodiment can be included with other depicted embodiments in any combination. For example, any of the various components described herein and/or depicted in the figures may be combined, interchanged or excluded from other embodiments. 
     The above description discloses several methods and systems of certain embodiments. These embodiments are susceptible to modifications. Such modifications will become apparent to those skilled in the art from a consideration of this disclosure or practice of the embodiments disclosed herein. Consequently, it is not intended that this invention be limited to the specific embodiments disclosed herein, but that it cover all modifications and alternatives coming within the true scope and spirit of the invention as embodied in the attached claims. 
     Applicant reserves the right to submit claims directed to combinations and sub-combinations of the disclosed inventions that are believed to be novel and non-obvious. Inventions embodied in other combinations and sub-combinations of features, functions, elements and/or properties may be claimed through amendment of those claims or presentation of new claims in the present application or in a related application. Such amended or new claims, whether they are directed to the same invention or a different invention and whether they are different, broader, narrower or equal in scope to the original claims, are to be considered within the subject matter of the embodiments of the inventions described herein.