Abstract:
A controlled force surgical implant impaction instrument is provided which includes a striking assembly, a retaining pin, and an actuator component. The striking assembly is configured to impact a surgical implant. The retaining pin is moveable between a first position and a second position. In the first position, the retaining pin inhibits distal movement of the striking assembly. In the second position, the retaining pin does not inhibit distal movement of the striking assembly. The actuator component includes a reloading channel. The actuator component is movable between a third position and a fourth position. In the third position, the retaining pin is in the first position and the retaining pin cannot be forced along the reloading channel. In the fourth position, the striking assembly can be used to move the retaining pin along the reloading channel.

Description:
BACKGROUND 
       [0001]    The hip joint includes an acetabulum and a femur which fit together in such a way that enables rotation at the joint. In particular, the head of the femur fits within the acetabulum to form the “ball in socket” joint at the hip. In total hip arthroplasty, both the acetabular side and the femoral side of the hip joint are replaced with prosthetic devices. The prosthetic device used on the acetabular side includes a cup constructed of a ceramic or an alloy including, for example, titanium and/or cobalt-chromium. The prosthetic device used on the acetabular side also includes a cup liner affixed to the concave surface of the cup in a substantially concentric configuration. The liner is provided to reduce friction between the acetabular cup and the head or “ball” of the femoral prosthesis and to improve retention of the head within the cup. 
         [0002]    Liners are constructed from a polymer such as, for example, ultra-high-molecular-weight-polyethylene (UHMWPE) or from a metal or an alloy. Materials are chosen to balance wear resistance and fatigue fracture during use within the patient&#39;s body. In use, liners have inherent potential for failure in a variety of ways. First of all, the pressures and forces applied to the prosthesis within the hip joint can cause a liner to crack or fracture due to the material properties of the liner. Secondly, if a liner is improperly sterilized prior to implantation, the patient&#39;s hip can become infected. Thirdly, a liner can be seated poorly during placement within the implanted cup which can later cause the liner to dislocate or slip out of position during use. Fourthly, a liner can include a manufacturing flaw causing the surface of the liner to be too rough. In this instance, rather than passing smoothly over the surface of the head of the femoral prosthesis, the liner will then adhere to the surface and wear due to the increased adhesive contact. After bearing weight repeatedly on the adhered surface, particles of the liner can break off the liner and be released into the patient&#39;s body causing more surface damage to the liner or causing infection. Finally, once a portion of the liner begins to wear, the liner can become delaminated, exacerbating the wear. 
         [0003]    Once a liner fails, it is removed from the patient to prevent further trauma and is replaced with a functioning liner to restore functionality. Removing and replacing part of a hip prosthesis is called hip revision arthroplasty. For the purposes of surgical procedures, such as a hip revision arthroplasty, positions and directions relative to surgical instruments may be described using anatomical directions with reference to the physician using the instrument. Accordingly, as used herein, proximal refers to the longitudinal direction of the instrument toward the user/physician when the instrument is in use and distal refers to the longitudinal direction of the instrument away from the user/physician when the instrument is in use. Additionally, inward refers to the direction of the instrument toward the longitudinal axis of the instrument and outward refers to the direction of the instrument away from the longitudinal axis of the instrument. 
         [0004]    When performing surgical procedures such as hip revision arthroplasty, physicians generally attempt to damage as little tissue as possible to minimize further trauma to the patient reducing time and effort required for the patient&#39;s recovery. Accordingly, if only the liner of the hip prosthesis requires replacement, it is undesirable to remove the cup as well. To facilitate this goal, surgical procedures and instrumentation have been developed which enable separation and removal of the liner from the acetabular cup during hip revision arthroplasty. 
         [0005]    Some acetabular prostheses include a locking mechanism to retain the liner within the cup. Removing liners from such prostheses requires using company and/or device specific removal instruments to disengage the locking mechanism. Using company and/or device specific removal instruments increases the number of specific parts and instruments required for the procedure, thus increasing instrumentation costs. Additionally, using company and/or device specific removal instruments increases the time and precision necessary for the procedure due to accurate alignment of particular elements and performance of particular methods to disengage particular features. 
         [0006]    In acetabular prostheses that do not include locking mechanisms, liners can be removed by levering out the liners from the acetabular cups with osteotomes. Osteotomes are sharp cutting and chiseling tools used to cut and separate bones. To remove liners using osteotomes, sharp points of the osteotomes are inserted between the cups and the liners. The osteotomes are then levered against the cups to pop the liners out. Using osteotomes to remove liners increases the time and precision necessary for the procedure due to precise placement and manipulation of sharp cutting tools. Additionally, using osteotomes to remove liners employs blunt force and tools which are not necessarily specially adapted to the goal, introducing risks for error. For example, using osteotomes to remove liners potentially results in inadvertent cutting or slicing off parts of the liners which are then loose in the surgical environment. 
         [0007]    Another way to remove liners from acetabular prostheses that do not include locking mechanisms is to drill a hole in the liner with a cortical screw and subsequently insert a cancellous screw having a larger diameter than the cortical screw into the drilled hole. The cancellous screw engages the liner along the sides of the drilled hole and the liner is then pulled apart from the acetabular cup by pulling outwardly on the cancellous screw. Using cortical and cancellous screws to remove liners increases the time and precision necessary for the procedure due to precise placement and manipulation of the screws and the drill. Additionally, using cortical and cancellous screws to remove liners employs and tools which are not necessarily specially adapted to the goal, introducing risks for error. For example, using cortical and cancellous screws to remove liners potentially results in drilling the holes into the liners at unfavorable angles which then requires more time to drill a new hole and/or further damages the prosthesis. 
         [0008]    Given the above discussion, it would be advantageous to provide an improved acetabular cup liner removal tool including features enabling removal of an acetabular liner from an acetabular cup that is implanted in a patient&#39;s acetabulum with greater efficiency and requiring fewer, easier to use tools. 
       SUMMARY 
       [0009]    In accordance with one embodiment of the disclosure, there is provided a controlled force surgical implant impaction instrument including a striking assembly, a retaining pin, and an actuator component. The striking assembly is configured to deliver a controlled force impact to a surgical implant. The retaining pin is moveable between a first position and a second position. In the first position, the retaining pin inhibits distal movement of the striking assembly. In the second position, the retaining pin does not inhibit distal movement of the striking assembly. The actuator component includes a reloading channel. The actuator component is movable between a third position and a fourth position. In the third position, the retaining pin is in the first position and the retaining pin cannot be forced along the reloading channel. In the fourth position, the striking assembly can be used to move the retaining pin along the reloading channel. 
         [0010]    In accordance with another embodiment of the disclosure, there is provided a controlled force surgical implant impaction instrument, including a rotatable actuator component, a retaining pin, and a striking assembly. The rotatable actuator component includes a reloading channel defining a reloading channel axis. The retaining pin is moveable between a first position and a second position. When the retaining pin is in the first position, the retaining pin is offset from the reloading channel axis. When the retaining pin is in the second position, the retaining pin is aligned with the reloading channel axis. The striking assembly is movable between a third position and a fourth position. When the striking assembly is in the third position and the retaining pin is in the second position, the striking assembly can be used to move the retaining pin along the reloading channel axis. 
         [0011]    The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. While it would be desirable to provide a controlled force surgical implant impaction instrument that provides one or more of these or other advantageous features, the teachings disclosed herein extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Features of the controlled force surgical implant impaction instrument are apparent to those skilled in the art from the following detailed description with reference to the following drawings. 
           [0013]      FIG. 1  depicts a side cross-sectional view of a controlled force surgical implant impaction instrument. 
           [0014]      FIG. 2  depicts an exploded schematic view of the striking assembly separate from the controlled force surgical implant impaction instrument of  FIG. 1 . 
           [0015]      FIG. 3  depicts a side schematic view of the actuator assembly separate from the controlled force surgical implant impaction instrument of  FIG. 1 . 
           [0016]      FIG. 4  depicts a side perspective schematic view of the retaining pin of the actuator assembly of  FIG. 3 . 
           [0017]      FIG. 5  depicts a side schematic view of a distal portion of the controlled force surgical implant impaction instrument of  FIG. 1  in use. 
           [0018]      FIG. 6  depicts a cross-sectional view of a portion of the controlled force surgical implant impaction instrument of  FIG. 1  when the instrument is arranged in the resting configuration. 
           [0019]      FIG. 7  depicts a side cross-sectional view of a portion of the controlled force surgical implant impaction instrument of  FIG. 1  arranged in the loaded configuration. 
           [0020]      FIG. 8  depicts a side cross-sectional view of a portion of the controlled force surgical implant impaction instrument of  FIG. 1  arranged in the actuated configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    As shown in  FIG. 1 , the instrument  100  includes a housing assembly  104 , a striking assembly  108  (shown in  FIG. 2 ), and an actuator assembly  112  (shown in  FIG. 3 ). The housing assembly  104  includes a housing body  118 , a housing proximal end portion  120 , and a housing distal end portion  124  opposite the housing proximal end portion  120 . The housing assembly  104  also includes a housing assembly longitudinal opening  128  extending through the housing body  118  from the housing proximal end portion  120  to the housing distal end portion  124 . The housing assembly  104  defines a housing assembly longitudinal axis  132  extending axially through the housing assembly longitudinal opening  128  through the housing proximal end portion  120  and the housing distal end portion  124 . Positions and directions of features of the instrument  100  are referred to relative to the housing assembly longitudinal axis  132 . 
         [0022]    The housing assembly  104  also includes a cap  136  and a tip portion  140 , each of which is aligned axially with the housing assembly longitudinal axis  132 . The cap  136  is located at the housing proximal end portion  120  and is configured to threadably engage the housing body  118  at the housing proximal end portion  120 . The cap  136  acts as a plug to seal the housing assembly longitudinal opening  128  at the housing proximal end portion  120 . In another embodiment, the cap  136  need not threadably engage the housing proximal end portion  120 , but is located at the housing proximal end portion  120  and acts as a plug to seal the housing assembly longitudinal opening  128  at the housing proximal end portion  120 . The cap  136  includes a cap cavity  144  extending proximally into the cap  136  such that the cap cavity  144  extends away from the housing distal end portion  124 . The housing assembly longitudinal opening  128  is adjacent to the cap cavity  144  and is in open communication with the cap cavity  144 . 
         [0023]    The tip portion  140  is located at the housing distal end portion  124  and is configured to threadably engage the housing body  118  at the housing distal end portion  124  to enable assembly/disassembly with the housing body  118  at the housing distal end portion  124 . In another embodiment, the tip portion  140  need not threadably engage the housing distal end portion  124 , but is located at the housing distal end portion  124  and enables assembly/disassembly with the housing body  118  at the housing distal end portion  124 . The tip portion  140  defines a tip portion longitudinal opening  148  extending through the tip portion  140 . The housing assembly longitudinal opening  128  is adjacent to the tip portion longitudinal opening  148  and is in open communication with the tip portion longitudinal opening  148 . 
         [0024]    As shown in  FIG. 2 , the striking assembly  108  includes a hammer biasing component  152 , a hammer component  156 , an intermediate member  160 , and a contact member  162 . The striking assembly  108  defines a striking assembly longitudinal axis  150  extending axially through the intermediate member  160  and the contact member  162 . When the instrument  100  is assembled as shown in  FIG. 1 , the striking assembly  108  (shown in  FIG. 2 ) extends through and is supported by the housing assembly  104  such that the striking assembly longitudinal axis  150  is coincident with the housing assembly longitudinal axis  132 . 
         [0025]    The hammer biasing component  152  in this embodiment is a coil spring which biases the hammer component  156  distally. In another embodiment, the hammer biasing component  152  need not be a coil spring, but is configured to bias the hammer component  156  distally. When the instrument  100  is assembled as shown in  FIG. 1 , the hammer biasing component  152  extends within the cap cavity  144  of the housing assembly  104 . 
         [0026]    The hammer component  156  includes a hammer component proximal end portion  164  and a hammer component distal end portion  168 . The hammer component  156  further includes a hammer component biasing surface  172 , a hammer component protrusion  176 , and a hammer component mallet portion  180 . When the instrument  100  is assembled as shown in  FIG. 1 , the hammer component  156 , located distally relative to the hammer biasing component  152 , extends within the housing assembly longitudinal opening  128  of the housing assembly  104 . 
         [0027]    The hammer component biasing surface  172  is a substantially planar surface that extends outwardly from the striking assembly longitudinal axis  150  and is located at the hammer component proximal end portion  164 . The hammer component  156  is oriented such that the hammer component biasing surface  172  faces proximally and contacts the hammer biasing component  152 . 
         [0028]    The hammer component protrusion  176  also extends outwardly from striking assembly longitudinal axis  150  and is located distally relative to the hammer component biasing surface  172 . The hammer component protrusion  176  includes an angled face  184 , an outward-most point  186 , and a flat face  188 . The angled face  184  of the hammer component protrusion  176  extends outwardly and distally from the hammer component proximal end portion  164  toward the outward-most point  186 . The flat face  188  of the hammer component protrusion  176  extends inwardly from the outward-most point  186 . The flat face  188  is substantially parallel to the hammer component biasing surface  172  but faces in the opposite direction, or distally, toward the hammer component distal end portion  168 . 
         [0029]    The hammer component mallet portion  180  extends outwardly from the striking assembly longitudinal axis  150  such that the hammer component mallet portion  180  has a large size and, accordingly, a large mass. 
         [0030]    The intermediate member  160  includes an intermediate member proximal end portion  192 , an intermediate member distal end portion  196 , and an intermediate member face  216  located at the intermediate member proximal end portion  192 . The intermediate member  160  is substantially cylindrical and the intermediate member proximal end portion  192  is configured such that the intermediate member face  216  faces proximally. 
         [0031]    The contact member  162  includes a contact member proximal end portion  220  and a contact member distal end portion  224 . The contact member  162  is located distally relative to the intermediate member  160 , and the contact member proximal end portion  220  is configured to couple with the intermediate member distal end portion  196  via, for example, complementary threaded portions. 
         [0032]    When the instrument  100  is assembled as shown in  FIG. 1 , the intermediate member  160 , located distally relative to the hammer component  156 , is received within the housing assembly longitudinal opening  128  and the tip portion longitudinal opening  148  of the housing assembly  104 . The intermediate member  160  extends distally of the housing assembly  104  such that the contact member  162 , located distally relative to the intermediate member  160 , is located entirely outside the housing assembly  104 . 
         [0033]    When the instrument  100  is assembled as shown in  FIG. 1 , the striking assembly  108  (shown in  FIG. 2 ) is arranged within the housing assembly  104  such that the intermediate member  160  and the contact member  162  remain fixed relative to the housing assembly  104 , but the hammer component  156  is longitudinally slidable between the housing proximal end portion  120  and the housing distal end portion  124 . 
         [0034]    Turning now to  FIG. 3 , the actuator assembly  112  includes an actuator component  228 , a transfer member  244 , and an actuator handle  246 . The actuator component  228  is bent such that it is substantially L-shaped and includes a load arm  248  and a lever arm  252 . In another embodiment, the actuator component  228  need not be bent such that it is substantially L-shaped, but includes a load arm  248  and a lever arm  252 . The actuator component  228  is rotatably coupled to the housing body  118  at an actuator component rotation point  230  located between the load arm  248  and the lever arm  252  such that the load arm  248  and the lever arm  252  rotate together relative to the housing assembly  104 . 
         [0035]    The load arm  248  defines a reloading channel  256  extending laterally through the load arm  248 . The reloading channel  256  is substantially L-shaped having a reloading portion  260  and a retaining portion  264  in open communication with one another. The reloading portion  260  of the reloading channel  256  defines a reloading channel axis  268 . The reloading channel axis  268  extends through the reloading portion  260  of the reloading channel  256  but does not extend through the retaining portion  264  of the reloading channel  256 . The lever arm  252  is rotatably coupled to the transfer member  244 . 
         [0036]    The actuator assembly  112  further includes a retaining pin  232 , a retaining pin biasing member  236 , and a ramp member  240  all disposed within the reloading channel  256  of the load arm  248  of the actuator component  228 . For clarity, the retaining pin  232  is shown in more detail in  FIG. 4  separated from the rest of the actuator assembly  112 . The retaining pin  232  includes a central portion  233  and post portions  234 A and  234 B arranged on opposite ends of the central portion  233 . The central portion  233  is sized and configured to extend within the reloading channel  256  (shown in  FIG. 3 ) such that when the retaining pin  232  is positioned within the reloading channel  256 , the post portions  234 A and  234 B (shown in  FIG. 4 ) are positioned on either side of the actuator component  228  (shown in  FIG. 3 ). The actuator assembly  112  (shown in  FIG. 3 ) is arranged relative to the housing assembly  104  (shown in  FIG. 1 ) and the striking assembly  108  (shown in  FIG. 2 ) such that the central portion  233  of the retaining pin  232  (shown in  FIG. 4 ) is in contact with the hammer component protrusion  176 . 
         [0037]    Returning to  FIG. 3 , the actuator assembly  112  is configured such that the retaining pin  232  is movable within the reloading channel  256  by sliding between the retaining portion  264  and the reloading portion  260  of the reloading channel  256 . Additionally, the actuator assembly  112  is configured such that the retaining pin  232  is movable relative to the housing assembly  104  because the retaining pin  232  is retained within the actuator component  228  which is rotatably coupled to the housing body  118  at the actuator component rotation point  230 . 
         [0038]    Continuing with  FIG. 3 , the ramp member  240  is positioned within the reloading portion  260  of the reloading channel  256  adjacent to the retaining pin  232 . The ramp member  240  includes a ramp portion  272 , configured to contact the central portion  233  of the retaining pin  232  (shown in  FIG. 4 ), and a cylindrical portion  276 , opposite the ramp portion  272 , configured to contact the retaining pin biasing member  236 . The ramp portion  272  is angled such that the ramp member  240  generally faces toward the retaining portion  264  of the reloading channel  256 . Accordingly, the ramp portion  272  of the ramp member  240  generally biases the retaining pin  232  toward the retaining portion  264  of the reloading channel  256 . 
         [0039]    The retaining pin biasing member  236  is mounted within the reloading portion  260  of the reloading channel  256  and is operably coupled to the ramp member  240 . The retaining pin biasing member  236  is configured to bias the ramp member  240  toward the retaining pin  232  such that the ramp member  240  in turn biases the retaining pin  232  toward the retaining portion  264  of the reloading channel  256 . The retaining pin biasing member  236  is a coil spring oriented along the reloading channel axis  268 . In another embodiment, the retaining pin biasing member  236  need not be a coil spring, but is oriented along the reloading channel axis  268  and biases the ramp member  240  toward the retaining pin  232 . 
         [0040]    The actuator handle  246  includes an actuator handle free end portion  280  (shown in  FIG. 1 ) and an actuator handle coupled end portion  284 . When the instrument  100  is assembled as shown in  FIG. 1 , the actuator handle coupled end portion  284  is coupled to the housing body  118  of the housing assembly  104  and the actuator handle free end portion  280  extends away from the housing assembly  104  such that the actuator handle  246  generally extends along the housing assembly  104 . The actuator handle  246  is elongated and is substantially planar such that it acts as the beam portion of a lever. 
         [0041]    The actuator handle coupled end portion  284  includes an actuator handle rotating portion  288  rotatably coupled to the housing body  118  as shown in  FIG. 1 . The actuator handle coupled end portion  284  further includes an actuator handle actuating portion  292  rotatably coupled to the transfer member  244 . The actuator handle rotating portion  288  extends inwardly from the actuator handle  246  such that the actuator handle  246  acts as the beam portion and the actuator handle rotating portion  288  acts as a fulcrum portion of a lever. 
         [0042]    The actuator handle  246  further includes an actuator handle biasing member  296  configured to bias the actuator handle free end portion  280  away from the housing assembly longitudinal axis  132  (shown in  FIG. 1 ). The actuator handle biasing member  296  is a torsion spring located within the actuator handle rotating portion  288 . In another embodiment, the actuator handle biasing member  296  need not be a torsion spring, but is located within the actuator handle rotating portion  288  and is configured to bias the actuator handle free end portion  280  away from the housing assembly longitudinal axis  132  (shown in  FIG. 1 ). 
         [0043]    In operation, the controlled force surgical implant impaction instrument  100  is operated to deliver a controlled force impact to a surgical implant. In this embodiment, the instrument  100  delivers a controlled force impact to an acetabular cup thereby loosening a liner from the acetabular cup for removal. In alternative embodiments, the instrument  100  is operated to deliver a controlled force impact to other surgical implants during surgical procedures. By way of example, in an alternative embodiment, the instrument  100  is operated to deliver a controlled force impact to an acetabular cup liner to secure the liner within the acetabular cup. In another alternative embodiment, the instrument  100  is operated to deliver a controlled force impact to a femoral head to secure the femoral head on a hip stem with a taper fit. In another alternative embodiment, the instrument  100  is operated to deliver a controlled force impact to a Steinmann pin to secure the pin for skeletal traction. In another alternative embodiment, the instrument  100  is operated to deliver a controlled force impact to a portion of a modular stem to secure the portions of the stem to one another with a taper fit. 
         [0044]    In the resting configuration, shown in  FIG. 1 , wherein no external force is applied to the instrument  100 , the hammer biasing component  152  biases the hammer component  156  distally against the intermediate member  160 , and the actuator handle biasing member  296  (shown in  FIG. 3 ) biases the actuator handle  246  clockwise about the actuator handle rotating portion  288 . 
         [0045]    Due to the lever configuration of the actuator handle  246 , when the actuator handle  246  is biased clockwise, the actuator handle free end portion  280  is positioned away from the housing body  118  and the actuator handle coupled end portion  284 , and specifically the actuator handle actuating portion  292 , is positioned near the housing body  118 . Because the transfer member  244  is rotatably coupled to the actuator handle actuating portion  292 , the transfer member  244  is therefore forced inwardly toward the housing assembly longitudinal axis  132 . Because the transfer member  244  is also rotatably coupled to the lever arm  252  of the actuator component  228 , when the transfer member  244  is forced inwardly, the actuator component  228  is rotated clockwise about the actuator component rotation point  230 . Because the retaining pin  232  is arranged within the load arm  248  of the actuator component  228 , when the actuator component  228  is rotated clockwise, the retaining pin  232  is positioned against the flat face  188  of the hammer component protrusion  176 . 
         [0046]    Because the actuator assembly  112  (shown in  FIG. 3 ) is configured such that the retaining pin  232  is in contact with the hammer component protrusion  176 , the rotational position of the actuator component  228  relative to the housing assembly  104  determines the position of the retaining pin  232  relative to the hammer component protrusion  176  and, thus, also determines the position of the hammer component  156  relative to the housing assembly  104  (shown in  FIG. 1 ). 
         [0047]    More specifically, when the instrument  100  is in the resting configuration, the load arm  248  is angled inwardly and distally and the retaining pin  232  is in the retaining portion  264  of the reloading channel  256  (shown in  FIG. 3 ) and rests on the flat face  188  of the hammer component protrusion  176 . When the retaining pin  232  is in the retaining portion  264  of the reloading channel  256 , the retaining pin  232  is offset from the reloading channel axis  268  (shown in  FIG. 3 ). When the retaining pin  232  rests on the flat face  188  of the hammer component protrusion  176 , the retaining pin biasing member  236  is unconstrained and biases the ramp member  240  (shown in  FIG. 3 ) inwardly. The ramp member  240 , in turn, biases the retaining pin  232  inwardly and distally. Because the retaining pin  232  is biased inwardly and distally, the retaining pin  232  applies no force to the flat face  188  of the hammer component protrusion  176 . Accordingly, the hammer biasing component  152  is unconstrained and biases the hammer component  156  distally within the housing assembly  104 . 
         [0048]    When ready to use the instrument  100 , the physician places the contact member distal end portion  224  in contact with the surgical implant to be impacted. In this embodiment, the physician places the contact member distal end portion  224  in contact with an outer edge  408  of the acetabular cup  404  as shown in  FIG. 5 . For clarity, the acetabular cup  404  and liner  400  are shown in a cross-sectional view in  FIG. 5 . When the physician initially places the controlled force surgical implant impaction instrument  100  in contact with the outer edge  408  of the acetabular cup  404 , the controlled force surgical implant impaction instrument  100  is arranged in the resting configuration, as shown in  FIG. 6 . 
         [0049]    When ready to apply the impact to the surgical implant, the physician grips both the housing assembly  104  and the actuator handle  246  of the instrument  100  as shown in  FIGS. 1 and 6  in one hand and squeezes inwardly toward the striking assembly longitudinal axis  150  to apply force to the actuator handle  246  toward the housing body  118 . When the physician applies initial inward force to squeeze the actuator handle free end portion  280  toward the housing assembly  104 , the controlled force surgical implant impaction instrument  100  moves from the resting configuration (shown in  FIGS. 1 and 6 ) toward the loaded configuration which is shown in  FIG. 7 . 
         [0050]    More specifically, the physician squeezes the actuator handle free end portion  280  with enough force to overcome the force of the actuator handle biasing member  296  in the actuator handle rotating portion  288  and compresses the actuator handle biasing member  296  such that energy is stored in the actuator handle biasing member  296 . 
         [0051]    Pressing the actuator handle free end portion  280  toward the housing body  118 , rotates the actuator handle  246  about the actuator handle rotating portion  288  and moves the actuator handle actuating portion  292  away from the housing body  118 . Moving the actuator handle actuating portion  292  away from the housing body  118  pulls the transfer member  244  of the actuator assembly  112  outwardly. Because the transfer member  244  is rotatably coupled to the lever arm  252  of the actuator component  228 , pulling the transfer member  244  outwardly rotates the actuator component  228  counter-clockwise about the actuator component rotation point  230  such that the load arm  248  also rotates counter-clockwise about the actuator component rotation point  230 . Because the retaining pin  232  is positioned within retaining portion  264  of the reloading channel  256  of the load arm  248 , rotating the load arm  248  of the actuator component  228  counter-clockwise in turn rotates the retaining pin  232  counter-clockwise about the actuator component rotation point  230 . 
         [0052]    Rotating the retaining pin  232  counter-clockwise about the actuator component rotation point  230  causes the retaining pin  232  to apply force to the flat face  188  of the hammer component protrusion  176  which moves the hammer component  156  proximally. The retaining pin  232  thereby inhibits distal movement of the hammer component  156 . 
         [0053]    The physician initially squeezes the actuator handle free end portion  280  with enough force such that the retaining pin  232  overcomes the force of the hammer biasing component  152 . By overcoming the force of the hammer biasing component  152 , the retaining pin  232  moves the hammer component  156  proximally within the housing assembly  104  (shown in  FIG. 1 ). As the hammer component  156  moves proximally, the hammer component  156  becomes spaced apart from the intermediate member  160  which is fixed relative to the housing assembly  104  (shown in  FIG. 1 ). Additionally, as the hammer component  156  moves proximally, the hammer component biasing surface  172  compresses the hammer biasing component  152  within the cap cavity  144  such that energy is stored in the hammer biasing component  152 . 
         [0054]    Squeezing the actuator handle free portion  280  closer toward the housing assembly longitudinal axis  132  causes further counter-clockwise rotation of the actuator handle  246  about the actuator handle rotating portion  288 . Further counter-clockwise rotation of the actuator handle  246  causes the retaining pin  232  to continue to rotate counter-clockwise about the actuator component rotation point  230 . Further counter-clockwise rotation of the retaining pin  232  causes the retaining pin  232  to travel along the flat face  188  of the hammer component protrusion  176  and to further apply force to the flat face  188  in the proximal direction. Once the retaining pin  232  has rotated about the actuator component rotation point  230  such that it is positioned at the outward-most point  186  of the hammer component protrusion  176 , the retaining pin  232  slips past the outward-most point  186  and slips onto the angled face  184  of the hammer component protrusion  176 . 
         [0055]    As noted above, the retaining pin biasing member  236  and ramp member  240  bias the retaining pin  232  inwardly and distally toward the retaining portion  264  of the reloading channel  256 . Additionally, counter-clockwise rotation of the retaining pin  232  about the actuator component rotation point  230  forces the retaining pin  232  against the flat face  188  and the outward-most point  186  of the hammer component protrusion  176 , thereby applying a distal force to the retaining pin  232 . Accordingly, as the retaining pin  232  travels along the flat face  188  and past the outward-most point  186 , the hammer component protrusion  176  cannot force the retaining pin  232  to move from the retaining portion  264  to the reloading portion  260  within the reloading channel  256 . 
         [0056]    As shown in  FIG. 8 , wherein the instrument  100  is arranged in the actuated configuration, the retaining pin  232  is in contact with the angled face  184  of the hammer component protrusion  176 . Once the instrument  100  is in the actuated position, the retaining pin  232  no longer applies proximal force to the hammer component  156 . In other words, the retaining pin  232  no longer inhibits distal movement of the hammer component  156 . The hammer component  156  is free to slide distally and no longer constrains the hammer biasing component  152 . Accordingly, the hammer component  156  slides distally within the housing assembly  104  due to the force applied by the release of the stored energy of the hammer biasing component  152 . 
         [0057]    The hammer component  156  slides distally within the housing assembly  104  (shown in  FIG. 1 ) toward the intermediate member  160  until the hammer component proximal end portion  164  on the hammer component mallet portion  180  contacts intermediate member face  216  on the intermediate member  160 . Accordingly, the striking assembly  108  is configured such that when the hammer component  156  slides distally within the housing assembly longitudinal opening  128 , the relatively large mass of the hammer component mallet portion  180  is able to impart force to the intermediate member face  216  upon contact between the movable hammer component distal end portion  168  and the fixed intermediate member proximal end portion  192 . 
         [0058]    Upon contact of the hammer component mallet portion  180  with the intermediate member  160 , the hammer component  156  transfers the distal force to the intermediate member  160 . The distal force then propagates distally through the intermediate member  160  and into the contact member  162  (shown in  FIG. 1 ). The distal force propagates through the contact member  162  to the contact member distal end portion  224  (shown in  FIG. 1 ) and thereby impacts the surgical implant. In this case, distal force impacts the outer edge  408  of the acetabular cup  404  (shown in  FIG. 5 ). In alternative embodiments, the contact member distal end portion  224  is configured with a tip having a size and shape suited to deliver an impact to a particular surgical implant. By way of example, in one embodiment, the contact member distal end portion  224  is configured with a tip having a size and shape suited to impacting an acetabular cup liner to secure the liner within an acetabular cup. In another embodiment, the contact member distal end portion  224  is configured with a tip having a size and shape suited to impacting a femoral head to secure the femoral head on a hip stem with a taper fit. In another embodiment, the contact member distal end portion  224  is configured with a tip having a size and shape suited to impacting a Steinmann pin to secure the pin for skeletal traction. In another embodiment, the contact member distal end portion  224  is configured with a tip having a size and shape suited to impacting a portion of a modular stem to secure the portions of the stem to one another with a taper fit. 
         [0059]    Because the distal force that propagates through the striking assembly  108  (shown in  FIG. 1 ) to the outer edge  408  of the acetabular cup  404  (shown in  FIG. 5 ) is generated by the hammer biasing component  152 , the amount of distal force applied to the acetabular cup  404  by the contact member distal end portion  224  (shown in  FIG. 5 ) is consistent each time the controlled force surgical implant impaction instrument  100  is operated. 
         [0060]    Once the physician has delivered the distal force to the surgical implant, in this case the outer edge  408  of the acetabular cup  404 , the physician is able to subsequently deliver another distal force to the outer edge  408  of the acetabular cup  404  without removing the controlled force surgical implant impaction instrument  100  from contact with the outer edge  408  of the acetabular cup  404  (shown in  FIG. 5 ). To do so, the physician relaxes the grip on the actuator handle free end portion  280  such that the inward force no longer overcomes the force of the actuator handle biasing member  296 , the hammer biasing component  152 , and the retaining pin biasing member  236 . When no external force is applied to the controlled force surgical implant impaction instrument  100 , the instrument  100  then automatically returns to the resting position shown in  FIGS. 1 and 6 . 
         [0061]    The actuator handle biasing member  296  rotates the actuator handle  246  clockwise about the actuator handle rotating portion  288  due to the force applied by the release of the stored energy of the actuator handle biasing member  296 . Rotating the actuator handle  246  clockwise forces the transfer member  244  inwardly via the actuator handle coupled end portion  284 . When the transfer member  244  is forced inwardly, the actuator component  228  is rotated clockwise about the actuator component rotation point  230 . As the load arm  248  of the actuator component  228  is rotated clockwise, the retaining pin  232  is forced against the angled face  184  of the hammer component protrusion  176 . Because the angled face  184  is oriented in the opposite direction as the ramp member  240  (shown in  FIG. 3 ), the angled face  184  biases the retaining pin  232  proximally within the reloading channel  256 . The force applied by the actuator handle biasing member  296  is strong enough to overcome the force applied by the retaining pin biasing member  236  such that the retaining pin biasing member  236  is compressed within the reloading portion  260  of the reloading channel  256  and energy is stored within the retaining pin biasing member  236 . 
         [0062]    When the retaining pin biasing member  236  is compressed within the reloading portion  260  of the reloading channel  256  and the angled face  184  biases the retaining pin  232  proximally, the retaining pin  232  moves from the retaining portion  264  to the reloading portion  260  of the reloading channel  256 . When the retaining pin  232  is in the reloading portion  260 , the retaining pin  232  is aligned with the reloading channel axis  268  (shown in  FIG. 3 ). Thus, the angled face  184  of the hammer component protrusion  176  of the hammer component  156  forces the retaining pin  232  into alignment with the reloading channel axis  268  (shown in  FIG. 3 ). 
         [0063]    While the retaining pin  232  is positioned within the reloading portion  260  of the reloading channel  256  (shown in  FIG. 3 ), the actuator component  228  continues to rotate clockwise about the actuator component rotation point  230 . Thus, the retaining pin  232  also continues to rotate clockwise about the actuator component rotation point  230  and thereby travels distally along the angled face  184  of the hammer component protrusion  176 . Once the retaining pin  232  slips distally past the outward-most point  186  of the hammer component protrusion  176  and back to the flat face  188  of the hammer component protrusion  176 , the force applied by the release of the stored energy of the retaining pin biasing member  236  forces the retaining pin  232  inwardly. 
         [0064]    Because the ramp portion  272  biases the retaining pin  232  inwardly and distally and the retaining pin biasing member  236  biases the ramp member  240  inwardly, the retaining pin  232  moves within the reloading channel  256  from the reloading portion  260  back to the retaining portion  264  (shown in  FIG. 3 ). When the retaining pin  232  returns to the retaining portion  264  of the reloading channel  256 , the controlled force surgical implant impaction instrument  100  is again arranged in the resting configuration. 
         [0065]    In another embodiment, the amount of distal force applied to the surgical implant, by the contact member distal end portion  224  is varied by replacing the hammer biasing component  152 . The replacement hammer biasing component has a different spring constant and, therefore, applies a different amount of distal force when releasing stored energy. The replacement hammer biasing component is configured to deliver an impact having a force suited for a particular use. By way of example, in one embodiment, the replacement hammer biasing component is configured to deliver an impact having a force suited to securing an acetabular cup liner within an acetabular cup. In another embodiment, the replacement hammer biasing component is configured to deliver an impact having a force suited to securing a femoral head on a hip stem with a taper fit. In another embodiment, the replacement hammer biasing component is configured to deliver an impact having a force suited to securing a Steinmann pin for skeletal traction. In another embodiment, the replacement hammer biasing component is configured to deliver an impact having a force suited to securing portions of a modular stem to one another with a taper fit. 
         [0066]    The hammer biasing component can be replaced easily by disengaging the cap  136  from the housing body  118  at the housing proximal end portion  120 . Because the hammer biasing component extends within the cap cavity  144 , once the cap  136  is removed from the housing body  118 , the replacement hammer biasing component can be installed and the cap  136  can then be reengaged with the housing body  118 . 
         [0067]    The foregoing detailed description of one or more embodiments of the controlled force surgical implant impaction instrument has been presented herein by way of example. It will be recognized that there are advantages to certain individual features and functions described herein that may be obtained without incorporating other features and functions described herein. Moreover, it will be recognized that various alternatives, modifications, variations or improvements of the above-disclosed embodiments and other features and functions, or alternatives thereof, may be desirably combined into many other different embodiments, systems or applications. Presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the appended claims. Therefore, the spirit and scope of any appended claims should not be limited to the description of the embodiments contained herein.