Abstract:
A cartridge in which bone cement is mixed and from which the cement is discharged. A blade with plural vanes is disposed in the cartridge for mixing the cement. A piston located in one end of the cartridge is actuated to push the mixed cement out of the cartridge. The blade has plural vanes, one for scraping cement off the side of the cartridge, one for scraping cement off the piston and one for scraping cement off the end of the cartridge opposite the end in which the piston is normally located. The blade is collapsible so that when the piston is actuated the blade compresses to allow the cement in the cartridge to be pushed out.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/704,618 filed 12 Feb. 2010 now U.S. Pat. No. ______. application Ser. No. 12/704,618 is a divisional of U.S. patent application Ser. No. 12/138,620, filed 13 Jun. 2008, now U.S. Pat. No. 7,677,418. application Ser. No. 12/138,620 is a divisional of application Ser. No. 11,837,649 filed 13 Aug. 2007, now U.S. Pat. No. 7,393,342. application Ser. No. 11/837,649 is a divisional of application Ser. No. 10,843,813, filed 12 May 2004, now abandoned. application Ser. No. 10/843,813 claims the benefit of U.S. provisional patent application Ser. No. 60/469,651, filed 12 May 2003 and U.S. provisional patent application Ser. No. 60/520,877, filed 18 Nov. 2003. The advantages and disclosures of the above listed priority applications are herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This 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 
       [0003]    Bone cement mixing and delivery systems are well known for 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. 
         [0004]    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 covering 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. 
         [0005]    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. An alternative solution for securing and releasing the piston is shown in U.S. Pat. No. 5,328,262 to Lidgren et al. 
         [0006]    In Lidgren et al., the piston is releasably secured in the locked position in the distal end of the cylinder by a gripping portion in the form of a flange, which extends along only a portion of an inner periphery of the cylinder. The piston in Lidgren et al. has a corresponding gripping portion in the form of an outwardly directed lip that protrudes behind the flange. The lip defines a groove with an outer surface of the piston to receive the flange. To release the piston from the locked position, the flange is rotated through the groove until the flange has been rotated past the lip. Lidgren et al. discloses a base that is used to secure the piston from rotation while a user rotates the cylinder relative to the piston to release the piston from the locked position. This method of releasing the piston from the locked position, much like pulling the cotter pin, requires additional manipulation by a user. 
         [0007]    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. 
         [0008]    An example of such a delivery gun is illustrated in U.S. Pat. No. 5,431,654 to Nic. In the &#39;654 patent to Nic, two pawl members are used to independently advance the drive rod and the ram disk. The pawl members provide high speed/low force and low speed/high force advancement of the drive rod. A switch is used to select between the speeds. When high speed is selected, both pawl members engage the drive rod, while only the high-speed pawl member actually advances the drive rod. When low 1’ speed is selected, the high-speed pawl member is isolated from the teeth such that only the low speed pawl member engages the teeth to advance the drive rod. However, in Nic, the trigger directly supports each of the pawl members which results in a low mechanical advantage to advance the drive rod and ram disk. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    A mixing cartridge for receiving liquid and powder components of bone cement to be mixed for medical use. The mixing cartridge comprises a cylinder having proximal and distal ends with a mixing chamber defined therebetween. The cylinder includes a cylinder wall extending between the ends about a longitudinal axis of the cylinder. A piston is disposed in the cylinder at the distal end such that the mixing chamber is further defined between the proximal end and the piston. A locking member is coupled to the piston to lock the piston in the distal end. The locking member includes a male portion engaging a female portion in the cylinder wall to place the piston in a locked position at the distal end of the cylinder. The locking member includes a resilient portion for biasing the male portion into mating engagement with the female portion. The piston remains in the locked position at the distal end of the cylinder while mixing the liquid and powder components. 
         [0010]    One advantage of the mixing cartridge is the conveniently positioned locking member used to lock the piston in the distal end. By using the resilient portion to bias the male portion into mating engagement with the female portion, a user can easily release the piston from the locked position by either manually or mechanically acting against the bias of the resilient portion to disengage the male and female portions. 
         [0011]    A delivery gun is also provided for discharging the bone cement from the cartridge once the bone cement is prepared. The delivery gun comprises a casing for supporting the cartridge. A drive mechanism is supported by the casing and advanceable relative to the casing to force the bone cement from the cartridge. The casing pivotally supports a trigger operatively connected to the drive mechanism to advance the drive mechanism upon actuation of the trigger to force the bone cement from the cartridge. A linkage system works in conjunction with the trigger to advance the drive mechanism. The linkage system comprises a first link pivotally connected to the casing and a second link interconnecting the first link and the trigger such that actuating the trigger moves the second link and the first link to advance the drive mechanism. 
         [0012]    An advantage of the delivery gun is the use of the linkage system to increase the mechanical advantage needed to successfully advance the drive mechanism and force the bone cement from the cartridge while minimizing fatigue to a user of the delivery gun. 
         [0013]    In one aspect of the delivery gun, the drive mechanism includes a drive rod and gripper plates to advance the drive rod. The gripper plates frictionally engage the drive rod to advance the drive rod when the trigger is actuated. In one embodiment, the gripper plates include mating pegs and notches to align adjacent gripper plates. In another embodiment, the gripper plates are coated to increase lubricity and corrosion resistance thereof. 
         [0014]    In another aspect of the delivery gun, the drive mechanism includes a drive rod and first and second pawl members to advance the drive rod. In one embodiment, the second pawl member is movable into engagement with teeth on the drive rod for high-speed advancement of the drive rod and out from engagement with the teeth for low-speed advancement. During low-speed advancement, only the first pawl member engages the teeth to advance the drive rod. During high-speed advancement, both pawl members engage the teeth, but only the second pawl member works to advance the drive rod. 
         [0015]    A bone cement mixing and delivery system is also provided. The mixing and delivery system includes the cartridge and the delivery gun. In this aspect of the invention, the locking member includes a release button to release the piston from the locked position. At the same time, the delivery gun includes a release mechanism integrated into the drive mechanism to engage the release button. When the cartridge is placed into the cradle of the delivery gun, the drive mechanism is advanced and the release mechanism engages the release button to release the piston from the locked position. This configuration reduces the number of steps typically associated with releasing the piston. By incorporating the release mechanism into the drive mechanism, when the drive mechanism is advanced, the piston is automatically released. 
         [0016]    A bone cement loading system for receiving the liquid and powder components of the bone cement is also provided. The loading system includes the cylinder with the piston locked in the distal end. A base defining a cavity is provided for receiving and securing the distal end of the cylinder. A funnel is provided for coupling to the proximal end of the cylinder to channel the powder component of the bone cement into the mixing chamber. The funnel has a proximal end with an oblong oval-shaped periphery to facilitate loading of the powder component of the bone cement into the mixing chamber and a distal end with a circular periphery for snugly fitting into the proximal end of the cylinder. One particular advantage to this loading system is the use of the oblong oval-shaped funnel. The shape of the funnel reduces any mess typically associated with filling the mixing chamber with powder. 
         [0017]    A bone cement mixing system comprising the mixing cartridge and a mixing shaft and blade is also provided. The blade is coupled to the mixing shaft and disposed in the mixing chamber for rotating with the mixing shaft about the longitudinal axis to mix the liquid and powder components of the bone cement. The blade includes a center hub coupled to the mixing shaft and an outer ring extending from the center hub. The outer ring forms an acute angle with the longitudinal axis of between twenty and seventy degrees to ensure adequate mixing of the bone cement in the mixing chamber. 
         [0018]    A method of mixing the liquid and powder components of the bone cement in the mixing chamber is also provided. The method includes using a rotary power tool connected to a portion of the mixing shaft extending outside of the mixing chamber to mix the liquid and powder components of the bone cement. The blade is disposed in the mixing chamber while being operatively connected to the portion of the mixing shaft extending outside of the mixing chamber. In the method, the rotary power tool is first connected to the portion of the mixing shaft extending outside of the mixing chamber. Then the rotary power tool is actuated to rotate the blade and mix the liquid and powder components of the bone cement. At the same time, the rotary power tool is axially displaced relative to the mixing cartridge to completely mix the liquid and powder components of the bone cement. Once mixing is complete, the operative connection between the blade and the portion of the mixing shaft extending outside of the mixing chamber is removed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    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: 
           [0020]      FIG. 1  is an exploded perspective view of a mixing cartridge of the present invention in combination with a mixing shaft and blade; 
           [0021]      FIG. 2  is an assembled perspective view of the mixing cartridge with the mixing shaft and blade supported therein; 
           [0022]      FIG. 3  is an exploded perspective view of a cap of the mixing cartridge; 
           [0023]      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; 
           [0024]      FIG. 5  is an exploded perspective view of the cap and the mixing shaft and blade; 
           [0025]      FIG. 6  is an assembled perspective view of the cap with the mixing shaft and blade supported therein; 
           [0026]      FIG. 7  is a perspective view of the blade; 
           [0027]      FIG. 7A  is a side elevational view of the blade of  FIG. 7 ; 
           [0028]      FIGS. 8-8A  and  9  are perspective views of alternative blades; 
           [0029]      FIG. 10  is a an exploded perspective view of the mixing shaft and a latch rod; 
           [0030]      FIG. 11  is an elevational end view of the mixing shaft and latch rod of  FIG. 10 ; 
           [0031]      FIG. 12  is a cross-sectional view of the mixing shaft and latch rod of  FIGS. 10 and 11 ; 
           [0032]      FIG. 13  is an exploded perspective view of a release latch coupling the mixing shaft and latch rod; 
           [0033]      FIGS. 14A-14C  illustrate the release of the blade from the mixing shaft; 
           [0034]      FIG. 15  is an exploded perspective view of a piston of the mixing cartridge; 
           [0035]      FIG. 16  is a cross-sectional view of the piston of  FIG. 15 ; 
           [0036]      FIG. 17  is a perspective view of an alternative piston of the mixing cartridge; 
           [0037]      FIG. 18  is a top view of the alternative piston of  FIG. 17 ; 
           [0038]      FIG. 19  is an exploded perspective view of the cap and a nozzle; 
           [0039]      FIG. 20  is an assembled perspective view of the cap and nozzle; 
           [0040]      FIG. 21  is a blown-up view of a locking mechanism of the cap and nozzle; 
           [0041]      FIGS. 22-23  are perspective views of the nozzle; 
           [0042]      FIG. 24  is a perspective view of a delivery gun of the present invention illustrating a linkage system of the delivery gun; 
           [0043]      FIGS. 24A-24B  illustrate alternative linkage systems of the present invention; 
           [0044]      FIG. 25  is an elevational view illustrating release of a locking member securing the piston; 
           [0045]      FIG. 26  is a partial perspective view of an alternative linkage system and drive mechanism of the delivery gun; 
           [0046]      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; 
           [0047]      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; 
           [0048]      FIG. 29  is a perspective view of the second alternative embodiment of the linkage system and drive mechanism in the low-speed position; 
           [0049]      FIG. 30  is an elevational view of the second alternative embodiment of the linkage system and drive mechanism in a high-speed position; 
           [0050]      FIG. 31  is a perspective view of the second alternative embodiment of the linkage system and drive mechanism in the high-speed position; 
           [0051]      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; and 
           [0052]      FIGS. 33-42  illustrate various steps associated with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0053]    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. 
         [0054]    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. 
         [0055]    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 . 
         [0056]    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 . 
         [0057]    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. 
         [0058]    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 a with the longitudinal axis L of the cylinder  102  (which is also a rotational mixing axis of the blade  152 ). The acute angle a is important for efficient mixing of the bone cement. The acute angle a 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. 
         [0059]    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 . 
         [0060]      FIGS. 8 and 8A  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 a 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 . 
         [0061]    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 . 
         [0062]    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 . 
         [0063]    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 . 
         [0064]    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. 37 ), such as a 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 (not shown) could engage the mixing shaft  150  at the proximal end  176  to mix the bone cement in other embodiments. 
         [0065]    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 . 
         [0066]    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 . 
         [0067]    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 . 
         [0068]    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 . 
         [0069]    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. 
         [0070]    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 nozzle  204  is attached to the cap  112  to prepare the mixing cartridge  100  for placement into the delivery gun  500 . 
         [0071]    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. 
         [0072]    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 . 
         [0073]    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. 
         [0074]    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. 
         [0075]    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 . 
         [0076]    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 . 
         [0077]    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. 
         [0078]    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. 
         [0079]    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. 
         [0080]    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. 
         [0081]    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 . 
         [0082]    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 . 
         [0083]    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 24A . 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. 
         [0084]    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 . 
         [0085]    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 . 
         [0086]    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. 
         [0087]    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. 
         [0088]    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 . 
         [0089]    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. 
         [0090]    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. 
         [0091]    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. 
         [0092]    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 ). 
         [0093]    Mixing and delivery of the bone cement will now be described with reference to  FIGS. 32-42 . Referring first to  FIG. 32 , a bone cement loading system is shown. The bone cement loading system 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 . 
         [0094]      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. 
         [0095]    In STEP  1 , shown in  FIG. 33 , the funnel  902  is coupled to the cylinder  102  and the powder is poured into the mixing chamber  108 . 
         [0096]    In STEP  2 , shown in  FIG. 34 , after the powder is poured into the mixing chamber  108 , the funnel  902  is removed, 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. 
         [0097]    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 . 
         [0098]    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. 
         [0099]    In STEP  5 , shown in  FIG. 37 , with the vacuum drawn, the power tool (reamer) is then connected to the mixing shaft  150 . 
         [0100]    In STEP  6 , shown in  FIG. 38 , with the vacuum still drawn, the mixing shaft  150  is moved axially with respect to the mixing cartridge  100  and rotated by the power tool. 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. 
         [0101]    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. 
         [0102]    In STEP  8 , shown in  FIG. 40 , the nozzle  204  is pushed down on the cap  112  and rotated into place. 
         [0103]    In STEP  9 , shown in  FIG. 41 , the mixing cartridge  100  is positioned in the cradle  502 . 
         [0104]    In STEP, 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 . 
         [0105]    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.