Patent Publication Number: US-2005128867-A1

Title: Bone cement mixing and delivery system

Description:
RELATED APPLICATIONS  
      This application is a continuation-in-part of U.S. patent application Ser. No. 10/843,813, filed May 12, 2004, which claims the benefit of U.S. provisional patent application Ser. No. 60/469,651, filed May 12, 2003 and U.S. provisional patent application Ser. No. 60/520,877, filed Nov. 18, 2003, the advantages and disclosures of which are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION  
      The present invention generally relates to a bone cement mixing and delivery system. More specifically, the present invention relates to a mixing cartridge for receiving liquid and powder components of bone cement to be mixed, a mixing device for mixing the components, and a delivery gun for discharging the bone cement from the mixing cartridge into an anatomical site of a patient.  
     BACKGROUND OF THE INVENTION  
      Bone cement mixing and delivery systems are well known for receiving and mixing liquid and powder components of bone cement and delivering the prepared bone cement to an anatomical site during various surgical procedures. Bone cement is particularly useful in orthopedic procedures in which a prosthetic device is fixed to a bone or joint structure to improve the strength, rigidity, and movement of the structure. In a total hip arthroplasty (THA) procedure, in which a hip joint is replaced with a prosthetic device, bone cement is used to fix the prosthetic device in place in a medullary canal of a femur.  
      Typically, the bone cement is prepared in a mixing cartridge. The mixing cartridge includes a cylinder having proximal and distal ends with a mixing chamber defined between the ends. The mixing cartridge further includes a cap to cover the proximal end of the cylinder and a piston disposed in the distal end of the cylinder such that the mixing chamber is further defined between the cap and the piston. The piston may be releasably secured in a locked position in the cylinder by a cotter pin. The cap supports a mixing device, i.e., a mixing shaft and blade, for mixing the liquid and powder components of the bone cement in the mixing chamber. Typically, a manual mixing handle is connected to the mixing shaft to mix the components of the bone cement.  
      Once the bone cement is mixed, the mixing cartridge is prepared for inserting into a delivery gun to discharge the bone cement. This may include disengaging the mixing shaft and coupling a nozzle to the cap to provide a discharge point for the bone cement. At the same time, the piston is released from the locked position in the distal end of the cylinder by pulling the cotter pin. This allows the piston to be driven by the delivery gun through the mixing chamber to discharge the bone cement from the nozzle.  
      Once the piston is released from the locked position, the mixing cartridge is inserted into the delivery gun. A typical delivery gun includes a ram disk that engages the piston and drives the piston through the mixing chamber to discharge the bone cement from the nozzle. The delivery gun includes a cradle for supporting the mixing cartridge and a casing for supporting a drive rod that engages the ram disk and advances the ram disk to drive the piston. The drive rod includes a plurality of teeth and a pawl member engages the teeth to advance the drive rod. A trigger supports the pawl member and the casing rotatably supports the trigger. Actuation of the trigger relative to the casing urges the pawl member against the teeth to advance the drive rod and discharge the bone cement into the anatomical site.  
     BRIEF SUMMARY OF THE INVENTION  
      A bone cement loading system for receiving liquid and powder components of bone cement to be mixed for medical use is provided. The bone cement loading system includes a cylinder having an open proximal end and a closed distal end with a mixing chamber defined between the ends. A base is releasably coupled to the closed distal end of the cylinder to support the cylinder while loading the liquid and powder components in the mixing chamber. A funnel is releasably coupled to the open proximal end of the cylinder to channel the components of the bone cement into the mixing chamber. Packaging is used to enclose the cylinder, base, and funnel in a ready-to-use state such that the cylinder, base, and funnel can be transported in the ready-to-use state. A method of loading the components of the bone cement in the bone cement loading system is also provided.  
      One advantage of the bone cement loading system and method is the ability to provide end users with a pre-assembled, ready-to-use bone cement loading assembly thereby eliminating the need for the user to assemble the base and funnel to the cylinder prior to loading the components in the mixing chamber.  
      A bone cement mixing system for mixing the liquid and powder components of the bone cement after they are loaded in the mixing chamber is also provided. The bone cement mixing system comprises a cartridge having proximal and distal ends with the mixing chamber defined between the ends. A mixing device is supported by the cartridge to mix the liquid and powder components of the bone cement. A plurality of actuators are capable of being selectively, interchangeably, and operatively connected to the mixing device to actuate the mixing device and mix the liquid and powder components of the bone cement in the mixing chamber. Thus, the bone cement mixing system provides the advantage to the user of selecting the actuator that best meets their particular needs. In one aspect of the bone cement mixing system, the plurality of actuators include a power tool and a manual mixing handle thereby allowing the user to select between power mixing and manual, hand mixing.  
      In another aspect of the bone cement mixing system, a proximal end of the mixing device is adapted for operatively connecting with each of the plurality of actuators to selectively, interchangeably, and operatively connect each of the plurality of actuators to the mixing device.  
      In yet another aspect of the bone cement mixing system, an adapter that is separable from and independent of the power tool is used to operatively connect the power tool to the mixing device.  
      A bone cement mixing system that converts rotational input from a power tool into axial and rotational output is also provided. Here, a converter operatively interconnects the power tool and the mixing device. During use, the converter converts rotational input from the power tool into axial and rotational output. The converter applies the axial and rotational output to the mixing device to completely mix the liquid and powder components of the bone cement in the mixing chamber. A method of mixing the liquid and powder components of the bone cement using the converter is also provided. This configuration allows the user to simply pull a trigger of the power tool to completely mix the components of the bone cement, without having to manually extend and retract the mixing device in the cartridge.  
      A delivery gun for receiving the cartridge containing the bone cement and delivering the bone cement to an anatomical site is also provided. The delivery gun comprises a casing. A drive rod is supported by the casing and includes a plurality of teeth along a length thereof. At least one pawl member engages the plurality of teeth to advance the drive rod. A trigger is pivotally supported by the casing and operatively connected to the at least one pawl member to advance the drive rod during actuation of the trigger. During actuation of the trigger the at least one pawl member exerts a force upon the drive rod having a force vector with an X component that is from 1 to 6 times larger than a Y component of the force vector.  
      In one aspect of the delivery gun, the X component of the force vector is parallel to the drive rod and the Y component is transverse to the drive rod. By applying a force having a substantially larger X component than Y component, transverse forces acting on the drive rod are reduced. This is important in reducing wear and other stresses associated with bushings through which the drive rod slides. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
       FIG. 1  is an exploded perspective view of a mixing cartridge of the present invention in combination with a mixing shaft and blade;  
       FIG. 2  is an assembled perspective view of the mixing cartridge with the mixing shaft and blade supported therein;  
       FIG. 3  is an exploded perspective view of a cap of the mixing cartridge;  
       FIG. 4  is a cross-sectional view of the cap of  FIG. 3  and a partial cross-sectional view of a cylinder of the mixing cartridge to illustrate fitting of the cap to the cylinder;  
       FIG. 5  is an exploded perspective view of the cap and the mixing shaft and blade;  
       FIG. 6  is an assembled perspective view of the cap with the mixing shaft and blade supported therein;  
       FIG. 7  is a perspective view of the blade;  
       FIG. 7A  is a side elevational view of the blade of  FIG. 7 ;  
       FIGS. 8-8A  and  9  are perspective views of alternative blades;  
       FIG. 10  is a an exploded perspective view of the mixing shaft and a latch rod;  
       FIG. 11  is an elevational end view of the mixing shaft and latch rod of  FIG. 10 ;  
       FIG. 12  is a cross-sectional view of the mixing shaft and latch rod of Figs.  10  and  11 ;  
       FIG. 13  is an exploded perspective view of a release latch coupling the mixing shaft and latch rod;  
       FIGS. 14A-14C  illustrate the release of the blade from the mixing shaft;  
       FIG. 15  is an exploded perspective view of a piston of the mixing cartridge;  
       FIG. 16  is a cross-sectional view of the piston of  FIG. 15 ;  
       FIG. 17  is a perspective view of an alternative piston of the mixing cartridge;  
       FIG. 18  is a top view of the alternative piston of  FIG. 17 ;  
       FIG. 19  is an exploded perspective view of the cap and a nozzle;  
       FIG. 20  is an assembled perspective view of the cap and nozzle;  
       FIG. 21  is a blown-up view of a locking mechanism of the cap and nozzle;  
       FIGS. 22-23  are perspective views of the nozzle;  
       FIG. 24  is a perspective view of a delivery gun of the present invention illustrating a linkage system of the delivery gun;  
       FIGS. 24A-24B  illustrate alternative linkage systems of the present invention;  
       FIG. 25  is an elevational view illustrating release of a locking member securing the piston;  
       FIG. 26  is a partial perspective view of an alternative linkage system and drive mechanism of the delivery gun;  
       FIG. 27  is a partial perspective view of the alternative linkage system and drive mechanism of  FIG. 26  employing a striker to prevent freeze-up of the drive mechanism;  
       FIG. 28  is an elevational view of a second alternative embodiment of the linkage system and drive mechanism of the delivery gun in a low-speed position;  
       FIG. 28A  is a blown-up view of the linkage system and drive mechanism of the delivery gun shown in  FIG. 28 ;  
       FIG. 29  is a perspective view of the second alternative embodiment of the linkage system and drive mechanism in the low-speed position;  
       FIG. 30  is an elevational view of the second alternative embodiment of the linkage system and drive mechanism in a high-speed position;  
       FIG. 31  is a perspective view of the second alternative embodiment of the linkage system and drive mechanism in the high-speed position;  
       FIG. 32  is an exploded view of a cylinder of the mixing cartridge and a base and funnel used to fill the cylinder with components of bone cement;  
       FIG. 32A  is an assembled view of the cylinder, base, and funnel of  FIG. 32  enclosed in packaging for transportation;  
       FIGS. 33-42  illustrate various steps associated with the present invention;  
       FIG. 43  is an elevational view illustrating multiple arrangements for connecting an actuator, e.g., a power tool or mixing handle, to the mixing shaft;  
       FIG. 44  is an elevational view of the power tool connected to the mixing shaft using an adapter;  
       FIGS. 45-46  are perspective views of the adapter;  
       FIG. 47  is an elevational view of the rotary power tool connected directly to the mixing shaft;  
       FIG. 48  is an elevational view of the mixing handle connected directly to the mixing shaft;  
       FIG. 49  is an exploded perspective view of a converter used to convert rotational input into axial and rotational output;  
       FIG. 49A  is a cross-sectional view of an input shaft and an output shaft of the converter of  FIG. 49  taken along the line  49 A- 49 A in  FIG. 49 ;  
       FIG. 50  is an assembled view of the converter connected to the mixing cartridge;  
       FIG. 51  is an exploded perspective view of an alternative converter used to convert rotational input into axial and rotational output; and  
       FIG. 52  is an assembled view of the alternative converter connected to the mixing cartridge. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to the Figures, wherein like numerals indicate like or corresponding parts, throughout the several views, a bone cement mixing and delivery system is generally shown. The bone cement mixing and delivery system comprises a mixing cartridge  100  for receiving liquid monomer and powdered copolymer components of bone cement to be mixed, a mixing device (mixing shaft  150  and blade  152 ) for mixing the components, and a delivery device, e.g., a delivery gun  500 , for discharging the bone cement from the mixing cartridge  100  into an anatomical site (not shown). An exemplary use for the bone cement is to secure a prosthetic device used to replace a joint structure such as in a total hip arthroplasty (THA) procedure.  
      Referring to  FIGS. 1 and 2 , the bone cement mixing system comprises the mixing cartridge  100  in combination with the mixing shaft  150  and blade  152  used to mix the components of the bone cement in the mixing cartridge  100 . The mixing cartridge  100  includes a cylinder  102  having proximal  104  and distal  106  ends. A mixing chamber  108  is defined between the ends  104 ,  106 . The cylinder  102  includes a cylinder wall  110  extending between the ends  104 ,  106 , about a longitudinal axis L. A cap  112  is coupled to the cylinder  102  at the proximal end  104  and a piston  114  is disposed in the cylinder  102  at the distal end  106  such that the mixing chamber  108  is further defined between the cap  112  and the piston  114 . The components of the bone cement are placed in the mixing chamber  108  and mixed by the mixing shaft  150  and blade  152 , as will be described further below.  
      In the preferred embodiment, the cylinder  102  has locking strips  116  disposed on the cylinder wall  110  at the proximal end  104  to insert into locking slots  118  on the cap  112 . Each of the locking strips  116  include a straight portion lying perpendicular relative to the longitudinal axis L and an angled portion lying at an angle relative to the straight portion. As should be appreciated, the locking strips  116  and locking slots  118  could be reversed, i.e., the locking strips  116  positioned on the cap  112  and the locking slots  118  defined in the cylinder wall  110 . The locking strips  116  and locking slots  118  are configured to provide quick locking of the cap  112  onto the cylinder  102  with a one-quarter turn of the cap  112 . Those of ordinary skill in the art will appreciate that numerous methods are available for connecting the cap  112  to the cylinder  102 , such as mating threads, snap-fit connections, etc. A groove  120  is formed in the cylinder  102  at the proximal end  104  to seat an o-ring seal  122 . The o-ring seal  122  assists in sealing the cap  112  to the cylinder  102 .  
      Referring to  FIGS. 3-4 , the cap  112  includes radially inwardly protruding ramps  124  that lead into the locking slots  118  to facilitate the fit with the locking strips  116  on the cylinder wall  110 . When first placing the cap  112  on the cylinder  102 , the locking strips  116  are positioned between the ramps  124 . As the cap  112  is rotated, the ramps  124  cam the locking strips  116  proximally to urge the proximal end  104  of the cylinder  102  into a sealed relationship with the cap  112 , as shown in  FIG. 4  (only a portion of the cylinder wall  110  with two locking strips  116  is shown in  FIG. 4  for illustrative purposes). In the preferred embodiment, there are four locking strips  116  and four locking slots  118  to facilitate the sealed relationship between the cap  112  and the cylinder  102 .  
      Referring specifically to  FIG. 4 , an o-ring seal  126  and dynamic seal  128  operate together within an orifice  130  in the cap  112  to movably support and seal to the mixing shaft  150 . The mixing shaft  150  slides through the orifice  130  and the dynamic seal  128  and is movably supported therein. The dynamic seal  128  allows nearly frictionless rotational, as well as axial movement of the mixing shaft  150  within the mixing chamber  108  to mix the liquid and powder components of the bone cement, while maintaining a snug fit within the orifice  130 . A filter  132  and liner  134  are positioned on an interior of the cap  112  to allow a vacuum to be drawn in the mixing chamber  108  by way of a vacuum port  136 . The vacuum port  136  is isolated from the mixing chamber  108  by the filter  132  and liner  134  to prevent fouling of a vacuum pump (not shown). Referring to  FIGS. 5-6 , a vacuum tube  138  is shown attached to the vacuum port  136  to draw the vacuum in the mixing chamber  108  during mixing.  
      Referring to  FIG. 7 , the preferred blade  152  used to mix the bone cement is shown. The blade  152  is integrally formed from plastic in one piece and has an outer ring  154  connected to a center hub  156  by vanes  158 . Ears  160  protrude radially inwardly from the center hub  156  to facilitate a releasable connection to the mixing shaft  150 . The releasable connection is described further below. Referring to  FIG. 7A , the outer ring  154  forms an acute angle α with the longitudinal axis L of the cylinder  102  (which is also a rotational mixing axis of the blade  152 ). The acute angle α is important for efficient mixing of the bone cement. The acute angle α is preferably between twenty and seventy degrees, and more preferably sixty degrees. The blade  152  has an effective height H that is greater than one quarter inch to ensure adequate mixing. Preferably, the effective height H of the blade  152  is approximately one half inch.  
      Referring back to  FIG. 7 , two radially inwardly protruding fingers  157  are attached to the outer ring  154 . One of the fingers  157  protrudes radially inwardly in a first plane and the other finger  157  protrudes radially inwardly in a second plane spaced from and parallel to the first plane. The center hub  156  is positioned between the planes. The fingers  157  are used to scrape proximal and distal regions of the mixing chamber  108  to ensure complete mixing. A protruding node  159  is also attached to the outer ring  154 . The node  159  protrudes radially outwardly to control spacing between the blade  152  and an inner periphery of the cylinder wall  110  by scraping along the inner periphery of the cylinder wall  110  in the mixing chamber  108 .  
       FIGS. 8 and 8 A illustrate alternative blades  252 ,  352  that could also be used to mix the bone cement. Each of the blades  152 ,  252 ,  352  is designed to flatten at the proximal end  104  of the cylinder  102  adjacent to the cap  112  after the blade  152 ,  252 ,  352  is released from the mixing shaft  150  in the mixing chamber  108 . This ensures that the maximum possible amount of bone cement can be discharged from the mixing cartridge  100 . In the case of the preferred blade  152 , the blade  152  is flexible and the outer wall  154  flattens into a plane perpendicular to the longitudinal axis L and occupied by the center hub  156 , as illustrated by hidden lines in  FIG. 7A . Thus, the effective height H is reduced and the acute angle α becomes close to ninety degrees. This is accomplished by twisting at the vanes  158 . Spaces  155 ,  255 ,  355  formed in the center hub  156 ,  256 ,  356  ensure that once the blade  152 ,  252 ,  352  is flattened, the bone cement can pass through the blade  152 ,  252 ,  352  when discharged from the mixing cartridge  100 . To further facilitate the discharge of the bone cement past the blades  152 ,  252 ,  352 , each of the center hubs  156 ,  256 ,  356  are sized to partially fit within the aperture  130  defined in the cap  112 .  
      Another alternative blade  452  is shown in  FIG. 9 . This blade  452  is a relatively thick disk  452  with chamfered ends  453  forming an acute chamfer angle with a sidewall  457 . The chamfer angle is preferably sixty degrees. In the preferred embodiment, the disk is about one half inch thick and about one eighth inch less in diameter than the inner periphery of the cylinder wall  110 . In one embodiment, the inner periphery of the cylinder wall  110  is about two and one quarter inches in diameter. As should be appreciated, the slight distance between the side wall  457  of the disk  452  and the inner periphery of the cylinder wall  110  creates a shear force on the bone cement as the disk  452  is rotated and moved axially in the mixing chamber  108 . The shear force is the force applied to the bone cement to mix the bone cement. This blade  452  also includes a space  455  formed in a center of the disk  452  and ears  460  for releasably attaching to the mixing shaft  150 .  
      Referring to  FIGS. 10-13  the mixing shaft  150  has a release latch  162  for releasing the blade  152  from the mixing shaft  150  once mixing of the bone cement is complete. The release latch  162  moves between a holding position and a releasing position. In the holding position, the blade  152  is secured to the mixing shaft  150  to mix the bone cement in the mixing chamber  108 . In the releasing position, the blade  152  is released from the mixing shaft  150  to remain in the mixing chamber  108  while the mixing shaft  150  is removed from the cap  112  to make way for a nozzle  204 , as will be described further below. The release latch  162  is operatively connected to a latch rod  164 , which latches the blade  152  to the mixing shaft  150  in the holding position. The latch rod  164  defines a split cavity  166  for receiving split legs  168  of the release latch  162  in a snap-fit manner. The latch rod  164  is rotatably supported within the mixing shaft  150 .  
      Referring to  FIGS. 14A-14C , the transition of the release latch  162  between the holding position and the releasing position is illustrated. Referring first to  FIG. 14C , the exposed end  170  of the latch rod  164  is generally “T” shaped. The corresponding end  172  of the mixing shaft  150  has opposed notches  174  that are adapted to receive the ears  160  on the center hub  156  of the blade  152 . Initially, the ears  160  are positioned in the notches  174  and the exposed end  170  is positioned over the ears  160  to hold the blade  152  to the mixing shaft  150 . See  FIG. 14A . To release the blade  152 , the release latch  162  is depressed and rotated. Rotating the release latch  162  rotates the latch rod  164  with respect to the mixing shaft  150  thus rotating the exposed end  170  away from the ears  160  to release the blade  152 . See  FIG. 14B . With the blade  152  released, the mixing shaft  150  is withdrawn from the cap  112  while the blade  152  remains in the mixing chamber  108 .  
      A proximal end  176  of the mixing shaft  150 , which represents a portion of the mixing shaft  150  extending outside of the mixing chamber  108  during mixing, is adapted to engage a rotary power tool  177  (see  FIG. 43 ), such as an electric or pneumatic reamer drill, used to rotate the mixing shaft  150  and blade  152  and mix the bone cement. The proximal end  176  of the mixing shaft  150  is operatively connected to the blade  152  to transfer the rotation of the rotary power tool  177  to the blade  152 . When the blade  152  is released from the mixing shaft  150 , the operative connection is removed. The operative connection is also removed if the portion of the mixing shaft  150  extending outside of the mixing chamber  108  is severed from the rest of the mixing shaft  150  in the mixing chamber  108 , as in alternative embodiments. A manually operated mixing handle  177   a  (see  FIG. 43 ) could engage the mixing shaft  150  at the proximal end  176  to mix the bone cement in other embodiments.  
      Referring to  FIGS. 15-16 , the piston  114  is positioned within the distal end  106  of the cylinder  102  to further seal the mixing chamber  108 . The piston  114  has a skirt  178  extending about the inner periphery of the cylinder wall  110 . The piston  114  also includes a proximal end  180  and a distal end  182  defining a cavity  184 .  
      Referring specifically to  FIG. 16 , the piston  114  is releasably secured in a locked position in the distal end  106  of the cylinder  102  by a locking member  186 . The locking member  186  is disposed in the cavity  184  and includes diametrically opposed locking tabs  188  protruding into diametrically opposed slots  190  defined in the cylinder wall  110  to secure the piston  114  to the cylinder  102 . It should be appreciated that the slots  190  could be in the form of any suitable female portion, e.g., slot, groove, channel, etc., used for interlocking with a corresponding male portion such as the locking tabs  188 . Furthermore, while the embodiment of  FIG. 16  illustrates two-way locking, i.e., the piston  114  being locked from moving proximally and distally, the locking member  186  could also be used for one-way locking, i.e., for preventing only proximal movement of the piston  114 .  
      The locking member  186  is integrally formed from plastic and a resilient portion  192  of the locking member  186  biases the locking tabs  188  radially outwardly from the longitudinal axis L into the slots  190 . The resilient portion  192  is in the form of a thin resilient ribbon  192  acting like a spring and extending is a winding shape between the locking tabs  188 . The locking tabs  188  couple the locking member  186  to the piston  114  by protruding through carrier slots  194  formed in the skirt  178 . In the preferred embodiment, a step  196  protrudes into each of the carrier slots  194  to define a guide for sliding engagement within a channel  198  partially defined in each of the locking tabs  188 . In the locked position, the carrier slots  194  are axially and radially aligned with the slots  190  formed in the cylinder wall  110 .  
      The piston  114  is locked at the distal end  106  of the cylinder  102  while the liquid and powder components are added and mixed in the mixing cartridge  100 . The piston  114  is released from the locked position after mixing of the bone cement is complete. Release buttons  200 , integrally formed with the locking tabs  188 , are used to release the piston  114  from the locked position. The release buttons  200  are disposed on the locking tabs  188  and protrude distally therefrom. Each of the release buttons  200  includes a cam surface  202  forming an acute angle with the longitudinal axis L. The piston  114  is released from the locked position by squeezing the release buttons  200  radially inwardly against the bias of the resilient portion  192  to withdraw the locking tabs  188  from the slots  190 . This action can be performed either manually or mechanically, as will be described further below. After release from the slots  190 , the locking tabs  188  remain coupled to the piston  114  in the carrier slots  194 .  
      Referring to  FIGS. 17-18 , an alternative locking member  386  is shown. The alternative locking member  386  includes locking tabs  388  that are biased radially outwardly from the longitudinal axis L of the cylinder  302  to engage the slots  390  in the cylinder wall  310 . In this embodiment, four slots  390  are defined in the cylinder wall  310  to receive the locking tabs  388 . The resilient portion  392  is further defined as a resilient base  392  resiliently supporting each of the locking tabs  388  on the piston  314  with each of the locking tabs  388  being radially biased outwardly from the skirt  378  of the piston  314  to engage the slots  390  in the cylinder wall  310 . The release buttons  400  are further defined as fingers  400  extending radially inwardly toward the longitudinal axis L of the cylinder  302  with the fingers  400  being engageable to urge the locking tabs  388  radially inwardly and withdraw the locking tabs  388  from the slots  390  in the cylinder wall  310  to release the piston  314  from the locked position.  
      Referring to  FIGS. 19-23 , once the bone cement is mixed, and the mixing shaft  150  is withdrawn from the cap  112 , the nozzle  204  is positioned on the cap  112 . In the disclosed embodiment, the nozzle  204  is set in place by pushing a hollow shaft  205  of the nozzle  204  down into the orifice  130  of the cap  112  and then twisting the nozzle  204  slightly, about one-quarter turn. The o-ring seal  126  and dynamic seal  128  positioned within the orifice  130  in the cap  112 , which are used to movably support and seal to the mixing shaft  150  (refer briefly to  FIG. 4 ), are also used to seal to the hollow shaft  205 . The nozzle  204  is attached to the cap  112  to prepare the mixing cartridge  100  for placement into the delivery gun  500 .  
      The cap  112  has a nipple  206  protruding from an outer surface  208  thereof. The nipple  206  has tabs  210 , which engage detent members  212  in the nozzle  204 . After the nozzle  204  is fully rotated into position, the tabs  210  fully engage the detent members  212  while being positioned proximal to the detent members  212  to secure the nozzle  204  in place. A stop  214  on the cap  112 , best shown in  FIG. 19 , prevents the nozzle  204  from rotating freely in the clockwise direction after the tabs  210  have engaged the detent members  212 . The stop  214  extends downwardly from one of the tabs  210  to abut a side surface  216  of one of the detent members  212  to prevent further clockwise rotation.  
      The nozzle  204  and cap  112  have first  218  and second  220  locking protrusions. The first locking protrusion  218  acts as a detent and slides over the second locking protrusion  220  to a locked position as illustrated in  FIG. 21 . In this position, rear flat surfaces  222 ,  224  of the locking protrusions  218 ,  220  abut one another to prevent the nozzle  204  from being turned in the opposite direction, thereby preventing removal of the nozzle  204  from the cap  112 . The nozzle  204  can be removed by deflecting an outer skirt  226  of the nozzle  204  and rotating the nozzle  204  counterclockwise thereby disengaging the locking protrusions  218 ,  220 . Both the nozzle  204  and cap  112  are formed from plastic, which facilitates the detent-like locking and unlocking of the nozzle  204  to the cap  112 .  
      With the nozzle  204  in place, the mixing cartridge  100  is ready to be placed within the delivery-gun  500 . Referring to  FIG. 24 , the delivery gun  500  of the present invention includes a cradle  502  for supporting the mixing cartridge  100  and a casing  504  fixed to the cradle  502  for supporting a drive mechanism  506 , a linkage system  508 , and corresponding components. The cradle  502  includes an endplate  510 , which has an opening  512  for receipt of the nozzle  204 . The endplate  510  holds the mixing cartridge  100  in position in the cradle  502 . In the preferred embodiment, the casing  504  and the endplate  510  are connected by two connecting bars  514  (one on each side of the mixing cartridge  100 ) to reduce the weight of the delivery gun  500 . A handle  516  is integrally formed with the casing  504  to maneuver the delivery gun  500  during use.  
      To dispense the bone cement from the mixing cartridge  100 , the piston  114  must first be released from the locked position. Referring to  FIG. 25 , this is accomplished using a release mechanism  518  integrated into the delivery gun  500 . Once the mixing cartridge  100  is in place in the cradle  502 , a ram disk  520  protrudes into the cavity  184  in the distal end  182  of the piston  114 . The release mechanism  518  is integrated into the ram disk  520 . The release mechanism  518  includes a bearing surface  522  forming an acute angle with the longitudinal axis L for catching the release buttons  200  to cam the release buttons  200  radially inwardly. More specifically, the cam surfaces  202  of the release buttons  200  slide along the bearing surface  522 , while being cammed radially inwardly. This action pulls the locking tabs  188  radially inwardly to withdraw the locking tabs  188  from the slots  190  in the cylinder wall  110  and release the piston  114  from the locked position (when the alternative piston  314  is used, the ram disk has a flat bearing surface that axially presses the fingers  400  proximally to bend each resilient base  392  inwardly and urge the locking tabs  388  radially inward). A centering pin  800  can be used to center the ram disk  520  in a centering cavity  802  of the piston  114  to facilitate the release of the piston  114  from the locked position.  
      Referring back to  FIG. 24 , once the piston  114  is released, the piston  114  can be driven through the mixing chamber  108  by the drive mechanism  506  to force the bone cement from the nozzle  204 . The drive mechanism  506  includes a drive rod  524  movably supported by bushings  526  in the casing  504 . The ram disk  520  is fixed to the drive rod  524 . The drive mechanism  506  further includes a first gripper plate  528  responsive to movement of the linkage system  508  upon actuation of a trigger  530 . The first gripper plate  528  defines an aperture surrounding the drive rod  524 . The first gripper plate  528  frictionally engages the drive rod  524  to advance the drive rod  524 . The first gripper plate  528  is urged forward while in frictional contact with the drive rod  524  by the linkage system  508  when the trigger  530  is actuated. The first gripper plate  528  thereby advances the drive rod  524  and ram disk  520  relative to the casing  504  to drive the piston  114  and force the bone cement from the mixing cartridge  100 . The trigger  530  is pivotally supported by the casing  504  and operatively connected to the drive mechanism  506  to advance the drive mechanism  506  upon actuation of the trigger  530 .  
      The linkage system  508  includes a first link  532 , which is pivotally mounted to the casing  504  about a pivot axis A adjacent to the first gripper plate  528 . The first link  532  is adapted to engage the first gripper plate  528  when the first link  532  pivots about the pivot axis A. A second link  536  pivotally interconnects the trigger  530  to the first link  532  via support pins  538 ,  540 . The links  532 ,  536  and trigger  530  are interconnected to move in unison upon rotation of the trigger  530  about a second pivot axis B. When the trigger  530  is pulled, the second link  536  rotates the first link  532  about the pivot axis A, which engages the first gripper plate  528  and urges the first gripper plate  528  forward while the first gripper plate  528  is in frictional engagement with the drive rod  524  thereby advancing the drive rod  524 . A return spring  542  returns the links  532 ,  536  and the trigger  530  to an initial position upon release of the trigger  530 . At the same time, a first spring  534  momentarily disengages the first gripper plate  528  from the drive rod  524  to slide the first gripper plate  528  back to an initial position to await the next pull of the trigger  530 . The casing  504  pivotally supports the first link  532  and the trigger  530  about the pivot axes A and B via support pins  544 ,  546 .  
      A speed-changing link  548  is pivotally connected to the second link  536  about a support pin  549 . The speed-changing link  548  selectively pivots into and out from engagement with the first gripper plate  528  by way of a switch  550 . The speed-changing link  548  pivots between a high-speed position and a low-speed position about the support pin  549  (the low-speed position is shown in  FIG. 24 ). The high-speed position corresponds to faster advancement of the drive rod  524  at a lower force. This allows the user to quickly advance the drive rod  524  to drive the piston  114  and dispense high volumes of bone cement at low pressure. The low-speed position corresponds to slower advancement of the drive rod  524  at a higher force, which exerts more force on the piston  114  to pressurize the bone cement.  
      The first gripper plate  528  and the speed-changing link  548  have complementary first and second coupling devices  552 ,  554  used to couple the first gripper plate  528  with the speed-changing link  548  in the high-speed position. More specifically, in the embodiment of  FIG. 24 , the first gripper plate  528  has a shoulder  552  that is received within a channel  554  on the speed-changing link  548 . The speed-changing link  548  engages the shoulder  552  in the high-speed position. In the high-speed position, a user&#39;s gripping force is transmitted through the trigger  530  to the second link  536  and the speed-changing link  548  to engage the first gripper plate  528  and advance the drive rod  524 . The speed-changing link  548  is isolated from the first gripper plate  528  in the low-speed position. The low-speed position corresponds to the speed-changing link  548  being switched or disconnected from the shoulder  552 . In the low-speed position, the user&#39;s gripping force is transmitted through the trigger  530  to both the first  532  and second  536  links to engage the first gripper plate  528  and advance the drive rod  524 . This results in slower advancement of the drive rod  524 , but at a much higher mechanical advantage than the high-speed position. As a result, the user can better pressurize the bone cement during injection.  
      The pivot axes A and B and the links  532 ,  536 ,  548  are positioned above the drive rod  524 , while the trigger  530  extends below the drive rod  524 . A channel  556  defined in the trigger  530  facilitates this configuration. There are several advantages to this configuration. Moving the second pivot axis B away from a user&#39;s hand results in better usage of the stronger index and ring fingers by allowing those fingers more travel distance as the trigger  530  is actuated. This configuration also allows the handle  516  to be closer to the drive rod  524 , which is believed to reduce wrist strain when the user pushes the delivery gun  500  forward during cement pressurization. Another benefit is that it allows for a more streamlined casing design and better weight distribution.  
      In one embodiment, shown in  FIG. 24 , a secondary gripper plate  562  is mounted about the drive rod  524  adjacent to the first gripper plate  528 . The addition of one or more secondary gripper plates  562  to the first gripper plate  528  adds strength to the delivery gun  500  while still permitting proper operation. By using two or more gripper plates  528 ,  562 , increased frictional contact with the drive rod  524  is obtained without adversely affecting performance.  
      A release pin  558  disengages the gripper plates  528 ,  562  to allow a user to freely move the drive rod  524  by hand. The release pin  558  is connected to a retainer plate  560  and is adapted to engage the first gripper plate  528 . When the retainer plate  560  is pushed by the user, the release pin  558  engages the first gripper plate  528  which forces the first gripper plate  528  to tilt back against the bias of the first spring  534  thus releasing the drive rod  524 . Any secondary gripper plates  562  follow. As should be appreciated, pushing the retainer plate  560  also pivots the retainer plate  560  releasing its engagement with the drive rod  524 . With both the retainer plate  560  and the gripper plates  528 ,  562  released, the drive rod  524  is free to move. This allows the user to manually move the drive rod  524  with respect to the casing  504 .  
      The delivery gun  500  is unique among bone cement guns with a friction-plate mechanism in the way that it handles wear and deformation of the gripper plates  528 ,  562 . In the disclosed embodiments, the gripper plates  528 ,  562  are tilted by the first spring  534  into frictional contact with the drive rod  524 . Regardless of the amount of wear or deformation of the gripper plates  528 ,  562  or the drive rod  524 , the gripper plates  528 ,  562  require no further tilting to engage the drive rod  524  upon actuation of the trigger  530 . Thus, advancement of the drive rod  524  is produced over the entire actuation of the trigger  530  and efficiency is maintained throughout the life of the delivery gun  500 .  
      Referring to  FIGS. 24A and 24B , alternatives of the linkage system  508 ′ and  508 ″ are shown. These alternatives are represented with similar numerals to the embodiment of  FIG. 24  to indicate like parts.  FIG. 24A  illustrates a configuration of the linkage system  508 ′ in which the linkage system  508 ′ lies beneath the drive rod  524 ′. Furthermore, the speed-changing link  548 ′ in this embodiment is pivotally connected to the first gripper plate  528 ′ and includes a hook-shaped end to engage the support pin  538 ′ in the high-speed position and disengage the support pin  538 ′ in the low-speed position.  FIG. 24B  illustrates a configuration of the linkage system  508 ″ in which the first gripper plate  528 ″ is pushed by the linkage system  508 ″, as opposed to being pulled by the linkage system  508  and  508 ′ in  FIGS. 24 and 24 A. Here, the speed-changing link  548 ″ is pivotally connected to the first gripper plate  528 ″ to pivot into engagement with a notch  555 ″ defined in the trigger  530 ″ in the high-speed position and out from engagement with the notch  555 ″ in the low-speed position. These alternatives of the linkage system  508 ′ and  508 ″ illustrate the flexibility of design, e.g., the selection of mechanical advantage, provided by the linkage system of the present invention.  
      Referring to  FIGS. 26-27 , an alternative embodiment of the drive mechanism  606  and linkage system  608  is shown (only a portion of the drive mechanism  606  and linkage system  608  is shown for illustrative purposes). In this embodiment, the linkage system  608  comprises the same components as previously described with an improved first link  632  and gripper plates  628 ,  662 . In this embodiment, a plurality of secondary gripper plates  662  are aligned along the drive rod  624  next to the first gripper plate  628 . The first link  632  defines a female recess  664  and the first gripper plate  628  includes a male member  668  for mating engagement with the female recess  664 . The secondary gripper plates  662  are aligned relative to the first gripper plate  628  via mating notches  670  and pegs  672  formed therein. The notches  670  and pegs  672  assume the same shape to mate with one another and maintain alignment. This arrangement minimizes alignment changes that may cause slipping or uneven wear. The arrangement also reduces contact between the gripper plates  628 ,  662  and an interior wall of the casing  504 . The gripper plates  628 ,  662  are shown spaced in  FIG. 26  for illustration only. In practice, the gripper plates  628 ,  662  abut one another, as shown in  FIG. 27 .  
      In this embodiment, each of the gripper plates  628 ,  662  also defines a pair of semi-spherical grooves  674 . In  FIG. 26 , only the first of the pair of grooves  674  are shown in each of the gripper plates  628 ,  662 . The other of the pair of grooves  674  is located in a rear surface of each of the gripper plates  628 ,  662 , cater-cornered from the first of the pair of grooves  674 . These grooves  674  increase the frictional contact with the drive rod  624 . When the gripper plates  628 ,  662  are urged forward while in frictional engagement with the drive rod  624  by the first link  632 , a substantial portion of a rim  676  defined by each of the grooves  674  frictionally contacts the drive rod  624 .  
      Referring to  FIG. 27 , autoclave sterilization of the delivery gun  500  can create a tendency for the gripper plates  628 ,  662  to adhere to the drive rod  624  beyond their initial positions when the trigger  630  is released. In this situation the first spring  634  cannot produce enough force to disengage the gripper plates  628 ,  662  from the drive rod  624 , and the gripper plates  628 ,  662  do not return to their initial positions.  FIG. 27  shows a way to prevent this condition. A striker  678 , in the form of a downwardly protruding portion of the second link  636 , closely follows one of the gripper plates  628 ,  662  during actuation of the trigger  630 . In the event that any of the gripper plates  628 ,  662  do not properly disengage the drive rod  624  upon release of the trigger  630 , the striker  678  will contact the notch  670  in the closest gripper plate  628 ,  662  and dislodge the gripper plate  628 ,  662  from the drive rod  624 . The first spring  634  can then properly return the gripper plates  628 ,  662  to their initial positions.  
      A coating has been added to an exterior of each of the gripper plates  528 ,  562 ,  628 ,  662  in  FIGS. 24 and 26 - 27 . The coating increases lubricity and corrosion resistance. This facilitates sliding between the gripper plates  528 ,  562 ,  628 ,  662  as they engage the drive rod  524 ,  624 . The coating also reduces corrosion due to autoclave sterilization that may cause the gripper plates  528 ,  562 ,  628 ,  662  to adhere to one another and prevent proper engagement with the drive rod  524 ,  624 . The coating used may be Electroless-Nickel with polytetrafluoroethylene (PTFE) or other like coatings possessing the same or similar properties.  
      Referring to  FIGS. 28-31 , another alternative embodiment of the drive mechanism  706  and linkage system  708  is shown. This embodiment also provides selective high-speed and low-speed advancement of the drive rod  724 . This alternative drive mechanism  706  eliminates the gripper plate by providing teeth  780  on the drive rod  724 . A cross-section of the drive rod  724  shows the teeth  780  on a flat upper surface  782 , while a lower surface  784  is smooth and round. The first link  732 , which in previous embodiments urged the first gripper plate  528 ,  628  forward with the drive rod  524 ,  624 , now pivotally supports a first pawl member  786 . The first pawl member  786  is spring-biased into engagement with the teeth  780 .  
      A second pawl member  788  is pivotally supported by the second link  736 . The second pawl member  788  is pivotable between a high-speed position in which the second pawl member  788  is spring-biased into engagement with the teeth  780  to advance the drive rod  724 , and a low-speed position in which the second pawl member  788  is disengaged and isolated from the teeth  780 . In the low-speed position, the first pawl member  786  advances the drive rod  724 . The low-speed position is illustrated in  FIGS. 28-29 . In the high-speed position, with the second pawl member  788  engaging the teeth  780 , the first pawl member  786  remains in engagement with the teeth  780 , but only ratchets along the teeth  780  as the second pawl member  788  advances the drive rod  724 . The high-speed position is illustrated in  FIGS. 30-31 . The principle of increasing mechanical advantage in the low-speed position relative to the high-speed position also applies in this embodiment.  
      The switch  750  is used to pivot the second pawl member  788  out from engagement with the teeth  780  of the drive rod  724  in the low-speed position (see  FIGS. 28-29 ) and into engagement with the teeth  780  in the high-speed position (see  FIGS. 30-31 ). A switch similar to that shown in U.S. Pat. No. 5,431,654 to Nic, herein incorporated by reference, can be used for this purpose. The switch  750  extends through the casing  704  and terminates in a button that is manipulated by a user to move the second pawl member  788  between the high-speed and low-speed positions (see briefly  FIGS. 41-42 ). This also applies to the switch  550  used to move the speed-changing link  548  in previous embodiments.  
      In this embodiment, the retainer plate  560  can be removed. In its place, a spring-biased non-return pawl member  790  retains the drive rod  724  in position upon advancement. The drive rod  724  can be freely moved in the casing  704  by rotating the drive rod  724  one hundred and eighty degrees such that the pawl members  786 ,  788 ,  790  are out of engagement with the teeth  780 . Upon such rotation, the pawl members  786 ,  788 ,  790  ride on the smooth lower surface  784  of the drive rod  724  allowing the user to freely pull the drive rod  724  relative to the casing  704 . This is generally disclosed in the &#39;654 patent to Nic.  
      Each of the pawl members  786 ,  788 ,  790  are pivotally supported by pins. Springs, such as those shown in the &#39;654 patent to Nic, bias the pawl members into engagement with the teeth  780  on the drive rod  724  (except when the switch  750  acts against the bias of the spring in the low-speed position to disengage the second pawl member  788  from the teeth  780 ). Referring to  FIG. 28A , a force vector F is shown to illustrate the force placed on the drive rod  724  by the first pawl member  786  when the second pawl member  788  is in the low-speed position. As shown, the X component of the force vector F (along the drive rod  724 ) is considerably larger than the Y component of the force vector F (transverse to the drive rod  724 ). This configuration is important to reduce the stress placed on the bushings  726  as the drive rod  724  moves through the bushings  726 . Preferably, the X component is from 1 to 6 times larger than the Y component, and more preferably, from 2 to 3 times larger than the Y component. Furthermore, the non-return pawl member  790  is arranged such that a reference line passing through a pivot axis  787  of the non-return pawl member  790  and an engaging end  789  of the non-return pawl member  790  forms an acute angle α with the drive rod  724  that is from 0 to 45 degrees. This minimizes reverse travel of the drive rod  724  after the trigger  730  has been released by reducing the travel and swing arc of the non-return pawl member  790  between the teeth  780 . This configuration also applies to the first pawl member  786 . Additionally, the first pawl member  786  and the non-return pawl member  790  are curved along their lengths from their pivot axes to their engaging ends to better fit between the teeth  780 .  
      Referring to  FIG. 32 , a bone cement loading assembly is shown. The bone cement loading assembly comprises a base  900  supporting the cylinder  102  while loading the liquid and powder components of the bone cement into the mixing chamber  108 . The base includes a cavity for receiving the distal end  106  of the cylinder  102 . Detents  903  are formed in the cavity. A groove  905  is defined in an outer surface of the cylinder  102  to receive the detents  903  and facilitate a snug fit between the base  900  and the cylinder  102 . It should be appreciated that the detents  903  could be formed on the cylinder  102  with the groove  905  defined in the base  900 . The distal end  106  of the cylinder  102  may also be press fit into the base  900 . The base  900  is oblong and oval in shape to fully support the cylinder  102  on a work surface, while the cavity is circular in shape to fit the circular shaped cylinder  102 . A funnel  902  couples to the cylinder  102  to channel the powder into the cylinder  102  during loading. The funnel  902  includes a proximal end  911  having an oblong oval-shaped periphery to facilitate the loading of the powder into the mixing chamber  108  and a distal end  909  having a circular periphery to snugly fit inside the proximal end  104  of the cylinder  102 .  
      In  FIG. 32A , the bone cement loading assembly is shown pre-assembled in packaging  901  in a ready-to-use state. This bone cement loading system provides for transportation of the bone cement loading assembly in the ready-to-use state. The packaging  901  preferably comprises a tray  901   a  with the cylinder  102 , base  900 , and funnel  902  assembled together and lying in the tray  901   a . A cover  901   b  is placed over the tray  901   a  to enclose the cylinder  102 , base  900 , and funnel  902  therein. The tray  901   a  and cover  901   b  could be formed from transparent, flexible, sterilizable materials, or more rigid, opaque, sterilizable materials, or any combination thereof. In the tray  901   a , the base  900  and the funnel  902  are coupled to the cylinder  102  to present the bone cement loading assembly to a user in the pre-assembled, ready-to-use state. Furthermore, the bone cement loading assembly is sterilized and remains sterilized in the packaging  901 .  
       FIGS. 33-42  illustrate ten steps for preparing and injecting the bone cement. The mixing cartridge  100 , delivery gun  500 , and other components are generically shown in each step for illustrative purposes only.  
      In STEP  1 , shown in  FIG. 33 , the bone cement loading assembly, i.e., the pre-assembled cylinder  102 , base  900 , and funnel  902 , is removed from the packaging  901  and the powder is poured into the mixing chamber  108  through the funnel  902 .  
      In STEP  2 , shown in  FIG. 34 , after the powder is poured into the mixing chamber  108 , the funnel  902  is released, and the liquid component, e.g., liquid monomer, of the bone cement is added. In this manner, the present invention avoids wetting of the funnel  902  and the associated clean-up.  
      In STEP  3 , shown in  FIG. 35 , the cap  112  with the mixing shaft  150  and blade  152  supported therein is attached to the cylinder  102 .  
      In STEP  4 , shown in  FIG. 36 , the vacuum line  138  is attached to the vacuum port  136  and a vacuum is drawn in the mixing chamber  108  with the liquid and powder components therein.  
      In STEP  5 , shown in  FIG. 37 , with the vacuum drawn, the power tool (reamer) is then connected to the mixing shaft  150 . In alternative embodiments, the mixing handle  177   a  is connected to the mixing shaft  150 .  
      In STEP  6 , shown in  FIG. 38 , with the vacuum still drawn, the mixing shaft  150  is moved axially and rotationally with respect to the mixing cartridge  100 . As previously discussed, this can be accomplished by using the mixing handle  177   a  or by using the rotary power tool  177 . The blade  152  (not shown in  FIG. 38 ) is moved axially the entire extent of the mixing cartridge  100  while rotating to ensure that the liquid and powder components are fully mixed.  
      In STEP  7 , shown in  FIG. 39 , once mixed, the release latch  162  is moved to release the blade  152  (not shown in  FIG. 39 ). The blade  152  remains in the mixing chamber  108  once released. The mixing shaft  150  is then removed from the mixing cartridge  100 . Mixing is now complete.  
      In STEP  8 , shown in  FIG. 40 , the nozzle  204  is pushed down on the cap  112  and rotated into place.  
      In STEP  9 , shown in  FIG. 41 , the mixing cartridge  100  is positioned in the cradle  502 .  
      In STEP  10 , shown in  FIG. 42 , the piston  114  is released from the distal end  106  of the cylinder  102  and the delivery gun  500  is primed and ready to discharge the bone cement from the mixing cartridge  100 .  
      Referring to  FIG. 43 , the rotary power tool  177  and the mixing handle  177   a  of the bone cement mixing system can be selectively, interchangeably, and operatively connected to the proximal end  176  of the mixing shaft  150  in STEP  5  to mix the liquid and powder components of the bone cement in STEP  6 . This provides the user with the flexibility of selecting the actuator that best suits their particular mixing needs. An adapter  1400  could be used to interconnect the rotary power tool  177  and the proximal end  176  of the mixing shaft  150 .  FIG. 44  shows this configuration. Here, the connection between the adapter  1400  and the rotary power tool  177  is a quick-connect type, which is well known in the power tool arts and will not be described in detail. Other connections, such as Jacob chuck connection or the like could also be used. It should be appreciated that the connection employed prevents relative axial and rotational motion between the adapter  1400  and the rotary power tool  177 .  
      The adapter  1400 , best shown in  FIGS. 45 and 46 , is connected to the proximal end  176  of the mixing shaft  150  via a snap-lock connection. Referring briefly back to  FIG. 43 , the proximal end  176  of the mixing shaft  150  includes a pair of flats  1402  that are received within a bore  1404  of the adapter  1400  along ribs  1406 . The ribs  1406  are disposed in proximity to the flats  1402  to prevent relative rotation between the adapter  1400  and the mixing shaft  150 . The adapter  1400  further includes a pair of snap-locking tabs  1408  that snap-lock to the mixing shaft  150  about an annular flange  1410  of the mixing shaft  150 . This locks the adapter  1400  to the mixing shaft  150  and prevents relative axial motion between the adapter  1400  and the mixing shaft  150 . Once snap-locked in place, a lip  1407  of each snap-locking tab  1408  rests within a groove  1409  defined about the mixing shaft  150  below the annular flange  1410  to axially restrain the adapter  1400 . The ribs  1406  also abut the annular flange  1410  to axially restrain the adapter  1400  in the opposite direction. It should be appreciated that a proximal end of the adapter  1400  has a like configuration to the proximal end  176  of the mixing shaft  150 . In fact, multiple adapters  1400  could be snap-locked together in the same fashion as snap-locking the adapter  1400  to the mixing shaft  150 .  
      In practice, the adapter  1400  is preferably connected to the rotary power tool  177  initially and then snap-locked to the mixing shaft  150 . This simplifies the connection between the rotary power tool  177  and the mixing shaft  150  for the user. In a typical connection between a power tool (such as a reamer drill) and its bit, a collar must be moved axially to lock the power tool and bit. By already having the adapter  1400  locked to the rotary power tool  177 , the user only need make the simple snap-lock connection between the adapter  1400  and the mixing shaft  150  to mix the bone cement.  
      In  FIG. 47 , the connection is a quick-connect type, with the rotary power tool  177  being directly connected to the proximal end  176  of the mixing shaft  150 . As previously discussed, this type of connection for power tools is well known to those skilled in the power tool arts. The connection employed prevents relative axial and rotational motion between the mixing shaft  150  and the rotary power tool  177 . It should be appreciated that the rotary power tool  177  could also be configured in the same manner as the adapter  1400  to lock to the proximal end  176  of the mixing shaft  150 .  
      Lastly, in  FIG. 48 , the mixing handle  177   a  is shown directly connected to the proximal end  176  of the mixing shaft  150 . In this arrangement, the mixing handle  177   a  is locked to the mixing shaft  150  in precisely the same manner as the adapter  1400  is locked to the mixing shaft  150 . In other words, the mixing handle  177   a  includes the same features as the adapter  1400  to snap-lock to the proximal end  176  of the mixing shaft  150 . The mixing handle  177   a  includes a bore (see the bore  1404  of the adapter  1400 ) for receiving the flats  1402  on the proximal end  176  of the mixing shaft  150  along ribs (see the ribs  1406  of the adapter  1400 ) and a pair of snap-locking tabs  1508  that snap-lock to the mixing shaft  150  about the annular flange  1410  of the mixing shaft  150  to lock the mixing handle  177   a  to the mixing shaft  150  and prevent relative axial motion between the mixing handle  177   a  and the mixing shaft  150 . In alternative embodiments, the adapter  1400  could also be used to interconnect the mixing handle  177   a  and the mixing shaft  150 .  
      It should be appreciated that, in other embodiments, the plurality of actuators, i.e., the rotary power tool  177  or the mixing handle  177   a , could also be fixed directly to the mixing shaft  150  by any conventional fastening technique such as using clamps, set screws, press-fits, and the like.  
      Referring to  FIGS. 49, 49A , and  50 , a converter  1300  can be used in combination with the rotary power tool  177  to mechanically convert rotational input provided by the rotary power tool  177  into both axial and rotational output to mix the liquid and powder components of the bone cement during mixing STEP  6  of  FIG. 38 . In previous embodiments, the user provides axial motion in the mixing chamber  108  by physically moving the mixing handle  177   a  or rotary power tool  177  axially. Here, the converter  1300  reduces the energy exerted by the user and subsequent fatigue. The converter  1300  can be integral with the cap  112  of the mixing cartridge  100 , or the converter  1300  can be a separate component that locks onto the cap  112 , as shown in  FIG. 50 .  
      The converter  1300  includes a cam housing  1302  and an input shaft  1308  rotatably supported and journaled in the cam housing  1302 . The rotary power tool  177  is adapted to connect to the input shaft  1308  to rotate the input shaft  1308  relative to the cam housing  1302 . An output shaft  1306  is coupled to the input shaft  1308 . More specifically, the input shaft  1308  and the output shaft  1306  matingly engage one another to rotate together, as shown in  FIG. 49A . The input shaft  1308  drives the output shaft  1306  via torque exerted on the input shaft  1308  by the rotary power tool  177 . A collar  1305  is fixed to the output shaft  1306  and a follower  1304  is rotatably coupled to the collar  1305 . A groove  1303  having helically-shaped crossing paths is formed on an inner surface of the cam housing  1302 . The follower  1304  follows along the groove  1303  as the output shaft  1306  rotates with the input shaft  1308 . This results in axial movement of the output shaft  1306  and collar  1305  relative to the input shaft  1308  and cam housing  1302 . The follower  1304  follows along one helical path of the groove  1303  when moving distally and then transfers over to the other helical path of the groove  1303  to move proximally.  
      In operation, as the input shaft  1308  is driven, the output shaft  1306  rotates therewith while sliding along the input shaft  1308  in response to the follower  1304  following along the groove  1303 . This action converts the rotational motion of the input shaft  1308  into rotational and axial motion of the output shaft  1306 . The mixing shaft  150  is operatively connected to the output shaft  1306  to mix the bone cement. The mixing shaft  150  can be connected to the output shaft  1306  in any conventional manner known to those skilled in the art. In the embodiment shown in  FIGS. 49 and 50 , the output shaft  1306  is snap-locked to the mixing shaft  150  in a similar fashion as the adapter  1400 .  
      Prior to mixing, the converter  1300  would first be snap-fit to the cap  112 , as shown in  FIG. 50 , with the output shaft  1306  telescoping distally to lock to the proximal end  176  of the mixing shaft  150 . Once mixing is complete, the release button  162  would be actuated through a window formed in the cam housing  1302  to release the blade  152 , and the converter  1300  would be removed from the cap  112 . Alternatively, the mixing shaft  150  could be severed with the broken portion of the mixing shaft  150  and blade  152  remaining in the mixing chamber  108  after mixing. In the embodiment  1300 ′ shown in  FIGS. 51 and 52 , the output shaft is the mixing shaft  150 , while the remaining features operate in the same manner as the previous embodiment of  FIGS. 49 and 50 .  
      It will be appreciated that the above description relates to the disclosed embodiments by way of example only. Many apparent variations of the disclosed invention will be known to those of skill in this area and are considered to be within the scope of this invention and are considered to be within the scope of the following claims. Obviously, many modifications and variations of the present invention are possible in light of the above teachings.