Bone cement mixing and delivery system including a delivery gun and a cartridge having a piston, the delivery gun configured to release the piston Number:7,393,342 from the United States Patent and Trademark Office (PTO) owispatent A bone cement mixing and delivery system is provided. The system includes a mixing cartridge for receiving liquid and powder components of bone cement, a mixing device for mixing the components, and a delivery gun for discharging the bone cement from the mixing cartridge. The mixing cartridge comprises a cylinder having proximal and distal ends with a cylinder wall extending between the ends. A piston is locked at the distal end by a locking member that includes a pair of locking tabs protruding into slots in the cylinder wall. With the piston in the locked position, the mixing device, e.g., a mixing shaft and blade, mixes the components. After mixing, the cartridge is placed in the delivery gun and release buttons on the locking member are engaged by a release mechanism on the delivery gun to release the piston from the locked position.<H configured, cartridge, Bone, cement, mix, 7393342.html, Patent, pto, 7393342

Title: Bone cement mixing and delivery system including a delivery gun and a cartridge having a piston, the delivery gun configured to release the piston

Abstract: A bone cement mixing and delivery system is provided. The system includes a mixing cartridge for receiving liquid and powder components of bone cement, a mixing device for mixing the components, and a delivery gun for discharging the bone cement from the mixing cartridge. The mixing cartridge comprises a cylinder having proximal and distal ends with a cylinder wall extending between the ends. A piston is locked at the distal end by a locking member that includes a pair of locking tabs protruding into slots in the cylinder wall. With the piston in the locked position, the mixing device, e.g., a mixing shaft and blade, mixes the components. After mixing, the cartridge is placed in the delivery gun and release buttons on the locking member are engaged by a release mechanism on the delivery gun to release the piston from the locked position.

Patent Number: 7,393,342 Issued on 07/01/2008 to Henniges, et al.

Inventors: Henniges; Bruce D. (Galesburg, MI), Coffeen; Jared P. (Paw Paw, MI)
Assignee: Stryker Corporation (Kalamazoo, MI)

Appl. No.: 11/837,649

Filed: August 13, 2007

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
10843813	May., 2004
60520877	Nov., 2003
60469651	May., 2003

Current U.S. Class: 604/187 ; 222/327; 366/189

Current International Class: A61M 5/00 (20060101); B01F 15/02 (20060101); G01F 11/32 (20060101)

Field of Search: 366/189,184 222/327,326,325 604/187,181

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Primary Examiner: Soohoo; Tony G
Attorney, Agent or Firm: Howard & Howard Attorneys, P.C.

Parent Case Text

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/843,813, filed May 12, 2004, and 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 each of the aforementioned applications are hereby incorporated by reference.

Claims

What is claimed is:

1. A bone cement mixing and delivery system for mixing components of bone cement to form a bone cement mixture and delivering the bone cement mixture to a target site, said system comprising: a cartridge having proximal and distal ends, said cartridge comprising; a wall extending between said ends, a piston releasably secured to said wall in a locked position near said distal end, and a locking member for releasably securing said piston in said locked position near said distal end, a delivery device adapted to hold said cartridge, said delivery device comprising; a casing, and a drive mechanism supported by said casing and advanceable relative to said casing to discharge the bone cement mixture from said cartridge wherein said drive mechanism includes a release mechanism for engaging said locking member to unlock said piston.

2. A bone cement mixing and delivery system as set forth in claim 1 wherein said wall is disposed about a longitudinal axis and defines at least one slot, said locking member including at least one locking tab protruding into said at least one slot in said locked position.

3. A bone cement mixing and delivery system as set forth in claim 2 wherein said at least one slot is further defined as a plurality of slots and said at least one locking tab is further defined as a plurality of locking tabs protruding into said slots in said locked position.

4. A bone cement mixing and delivery system as set forth in claim 3 wherein said locking member includes a resilient portion biasing said plurality of locking tabs into said slots.

5. A bone cement mixing and delivery system as set forth in claim 4 wherein said plurality of slots include a pair of diametrically opposed slots and said plurality of locking tabs include a pair of diametrically opposed locking tabs protruding radially outwardly into said diametrically opposed slots under the bias of said resilient portion.

6. A bone cement mixing and delivery system as set forth in claim 5 wherein said resilient portion extends between said diametrically opposed locking tabs to bias said diametrically opposed locking tabs radially outwardly into said diametrically opposed slots.

7. A bone cement mixing and delivery system as set forth in claim 6 wherein said resilient portion is integral with said diametrically opposed locking tabs and extends in a thin resilient ribbon portion between said diametrically opposed locking tabs.

8. A bone cement mixing and delivery system as set forth in claim 3 wherein said piston defines a pair of carrier slots for slidably retaining said plurality of locking tabs.

9. A bone cement mixing and delivery system as set forth in claim 3 wherein said locking member includes a plurality of release portions and said release mechanism engages said plurality of release portions to move said plurality of release portions and unlock said piston.

10. A bone cement mixing and delivery system as set forth in claim 9 wherein said plurality of release portions are further defined as a plurality of fingers engageable by said release mechanism to urge said plurality of locking tabs radially inwardly and withdraw said plurality of locking tabs from said plurality of slots in said wall to unlock said piston.

11. A bone cement mixing and delivery system as set forth in claim 2 wherein said locking member includes at least one release portion and said release mechanism engages said at least one release portion to move said at least one release portion and unlock said piston.

12. A bone cement mixing and delivery system as set forth in claim 11 wherein said at least one release portion includes a cam surface engageable by said release mechanism to slide said at least one release portion radially inwardly and withdraw said at least one locking tab from said at least one slot thereby unlocking said piston.

Description

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 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 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.

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.

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.

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.

An example of such a delivery gun is illustrated in U.S. Pat. No. 5,431,654 to Nic. In the '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 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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 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. 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; and

FIGS. 33-42 illustrate various steps associated with the present invention.

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 .alpha. 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 .alpha. 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 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 .alpha. 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. 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.

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 bia