Abstract:
Apparatus and method to dispense PMMA bone cement including a temperature controller, a disposable cement cartridge and a means for extracting cement from the cement cartridge so that the temperature of the extracted cement is first cooled to discourage polymerization and to prolong working time, then warmed so as to control viscosity of the cement flowing into the desired bone repair location. A first embodiment includes a spiral cement cartridge along with a means for extracting cement therefrom. A second embodiment includes a linear disposable cement cartridge along with a means for extracting cement therefrom. A color matching mechanism identifies cement temperature and viscosity during dispensation. A manual cement dispensing method includes a calibrated hand crank mechanism for causing calibrated delivery of cement. An automatic cement dispensing method uses a stepper motor and computer programmed means for causing calibrated flow of cement.

Description:
[0001]    This application claims priority to U.S. provisional patent application No. 60/967,698 filed on Sep. 5, 2007. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention relates to the controlled delivery of PMMA cement and more specifically to a cement dispenser device for the controlled delivery of bone cement in orthopedic surgical operations. 
       BACKGROUND OF THE INVENTION 
       [0003]    Poly-methyl-methacrylate (PMMA) bone cement has been in use since about 1960 for hip replacement surgery and not long thereafter came into use for percutaneous vertebroplasty, the latter being a palliative procedure requiring the injection of bone cement into the vertebral body at the cervical, thoracic or lumbar locations. The indications for percutaneous vertebroplasty are severe osteoporosis with vertebral compression fractures and vertebral haemangiomas and possibly patients with vertebral tumors. PMMA cement is manually injected into the vertebral body, the cement usually containing a high concentration of zirconium dioxide to allow for X-ray fluoroscopy. The cement permeates the vertebral body hardening and stabilizing the bony structure, the surgical procedure intending to stabilize the affected site and provide relief from significant pain. 
         [0004]    PMMA is dough-like cement that gradually hardens into a solid material with good biocompatibility. The preparation of PMMA bone cement requires the combination of two components: a solid powder and a liquid monomer. The cement becomes progressively viscous as polymerization to poly-methyl-methacrylate proceeds at a rate governed by the Arrhenius equation. Specific clinical applications such as vertebral fracture augmentation (e.g. kyphoplasty, vertebroplasty, arcuplasty) demand an optimal range of viscosity. Upon mixing the two components, the latency to achieve usable viscosity is dependent on the ambient temperature. In clinical use it is often difficult to accurately anticipate the appropriate time for mixing of the PMMA. Consequently, it is frequent to wait for adequate polymerization before proceeding. Conversely, occasionally the PMMA will be too viscous to apply and will need to be discarded. A need exists in the art to adequately control the polymerization process and the viscosity of delivered PMMA in clinical orthopedic applications. 
         [0005]    The present invention incorporates a solid-state Peltier junction with a PMMA reservoir on the cold side to prevent premature polymerization. As the PMMA is needed it is passed over the heated (opposite) side to provide adequate activation energy to ensure adequate polymerization as the PMMA exits the apparatus. A roller pump is integrated into the device. 
         [0006]    Arrhenius equation may be utilized to predict cement activation and viscosity. As known in the art, Arrhenius equation is an expression that shows the dependence of the rate constant k of chemical reactions on the temperature T (in Kelvin) and activation energy Ea, according to: 
         [0000]        k=Ae   −E     α     /RT . 
         [0000]    where A is the pre-exponential factor or simply the prefactor and R is the gas constant. The units of the pre-exponential factor are identical to those of the rate constant and will vary depending on the order of the reaction. If the reaction is first order it has the units s −1 , and for that reason it is often called the frequency factor or attempt frequency of the reaction. When the activation energy is given in molecular units, instead of molar units, e.g. joules per molecule instead of joules per mol, the Boltzmann constant is used instead of the gas constant. It can be seen that either increasing the temperature or decreasing the activation energy (for example through the use of catalysts) will result in an increase in rate of reaction. 
         [0007]    Given the small temperature range in which kinetic studies are carried, it is reasonable to approximate the activation energy as being independent of temperature. Similarly, under a wide range of practical conditions, the weak temperature dependence of the pre-exponential factor is negligible compared to the temperature dependence of the exponential factor, exp(−E α /RT); except in the case of “barrierless” diffusion-limited reactions, in which case the pre-exponential factor is dominant and is directly observable. 
         [0008]    When a reaction has a rate constant which obeys the Arrhenius equation, a plot of ln(k) versus 1/T gives a straight line, whose slope and intercept can be used to determine E α  and A. This procedure has become so common in the art of chemical kinetics that practitioners often use it to define the activation energy for a reaction. That is the activation energy is defined to be (−R) times the slope of a plot of ln(k) vs. (1/T) at constant pressure P: 
         [0000]    
       
         
           
             
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         [0009]    Once the activation energy Ea is determined for a given reaction involving PMMA cement, the viscosity may be predicted as a function of temperature and reaction time as known in the art. Furthermore, PMMA cement may be mixed with a chemical additive which predictably changes color with temperature as shown by D. C. Smith and M. E. D Bains, J. D. Res, Vol 35, No. 1, p 16-24. A bone cement dispensing device that controls PMMA cement temperature and uses a color based temperature indicator would be useful for delivering PMMA cement at a desired viscosity, temperature and polymerization rate to the desired bone location for proper setup. It is the objective of the present invention to provide such a bone cement dispensing device. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is an apparatus and method conceived for delivering PMMA bone cement in a procedure to attach bone or fill a bone cavity. A first embodiment bone cement dispenser utilizes a spiral shaped cement cartridge and a spiral shaped cement extractor. A second embodiment bone cement dispenser utilizes a rectangular shaped cement cartridge and a rectangular shaped cement extractor. These embodiments have the common inventive feature of cooling the cement in the cement cartridge and heating the cement as it is dispensed. 
         [0011]    A first embodiment bone cement dispenser is comprised of a housing with a bone cement dispensing mechanism contained therein and a crank attached to the bone cement dispensing mechanism to effect the delivery of bone cement. Bone cement is dispensed through Luer-lock ports to cement hoses which are placed in proximity to the bone or vertebra to be cemented. A handle is attached to the housing for holding the dispenser while turning the crank. An output selector is included on the bone cement dispenser to select one of four output cement hoses. A viewing port indicates the color of cooled cement which may be compared to a color chart placed on the housing, the color chart associating cement color to a temperature and viscosity of cement. 
         [0012]    Dispensing mechanism of first embodiment bone cement dispenser is comprised of a cement extractor placed above a cement temperature controller, the cement cartridge being inserted. The cement extractor includes a cement extraction plate, an extractor disc placed inside the cement extraction plate and made to rotate about an axle shaft inserted through the extraction plate. The cement extraction plate has a spiral ball guide attached for controlling the movement of ball along a spiral path, the ball being held in a radial ball slot in the extractor disc. The crank is in contact with an extractor disc so as to effect rotational motion of the extractor disc. The cement extraction plate, extractor disc, extractor ball, crank and spiral ball guide are assembled to form a cement extractor. 
         [0013]    The cement temperature controller is comprised of a cold plate, a Peltier plate and a hot plate, the Peltier plate being in thermal contact with the cold plate and hot plate and further being configured to transfer heat from the cold plate to the hot plate when a voltage is applied thereto. Cavities are made in the cold plate and in the hot plate to transfer cement from the cement cartridge to a selectable output hose. The output selector is positioned in the Peltier plate and allows connection between cold plate cavities and hot plate cavities. 
         [0014]    The cement extractor is attached by a hinge mechanism to the cement temperature controller, the two being opened and closed to effect the placement of a spiral shaped cement cartridge there between. The cement cartridge and cement contained therein is cooled by the cold plate in operation. 
         [0015]    In use the crank is rotated, causing the ball within the cement extractor to press on the cement cartridge and extract cement therefrom. Extracted cement flows from the upper surface of the cold plate to a cavity on the lower surface of the cold plate. Cement continues to flow through the output selector and then through a cavity inside the hot plate where the cement is warmed to a temperature consistent with the desired viscosity and setup time for the procedure. Cement exits the hot plate and is dispensed through output cement hoses. 
         [0016]    A second embodiment bone cement dispenser is comprised of a housing with a bone cement dispensing mechanism contained therein and a crank attached to the bone cement dispensing mechanism to effect the delivery of bone cement. Bone cement is dispensed through Luer-lock ports to cement hoses which are placed in proximity to the bone or vertebra to be cemented. A handle is attached to the housing for holding the dispenser while turning the crank. 
         [0017]    An output selector is included on the bone cement dispenser to select one of four output cement hoses. A viewing port indicates the color of cooled cement which may be compared to a color chart placed on the housing, the color chart associating cement color to a temperature and viscosity of cement. 
         [0018]    The dispensing mechanism of a second embodiment bone cement dispenser is comprised of a cement extractor placed above a cement temperature controller, the cement cartridge being inserted there between. The cement extractor includes a cement extraction press attached to a linear slide which translates according to the motion of the crank. The cement extraction press has a cylindrical protrusion for pressing cement out of a rectangular shaped cement cartridge. The cement extraction plate, extractor press, cylindrical protrusion, and crank are assembled to form a cement extractor. 
         [0019]    The cement temperature controller is comprised of a cold plate, a Peltier plate and a hot plate, the Peltier plate being in thermal contact with the cold plate and hot plate and further being configured to transfer heat from the cold plate to the hot plate when a voltage is applied thereto. Cavities are made in the cold plate and in the hot plate to transfer cement from the cement cartridge to a selectable output hose. The output selector is positioned in the Peltier plate and allows connection between cold plate cavities and hot plate cavities. 
         [0020]    The cement extractor is attached by a hinge mechanism to the cement temperature controller, the two being opened and closed to effect the placement of a rectangular shaped cement cartridge there between. The cement cartridge and cement contained therein is cooled by the cold plate in operation. 
         [0021]    In use the crank is rotated, causing the cylindrical protrusion within the cement extractor press to press on the cement cartridge and extract cement therefrom. Extracted cement flows from the upper surface of the cold plate to a cavity on the lower surface of the cold plate. Cement continues to flow through the output selector and then through a cavity inside the hot plate where the cement is warmed to a temperature consistent with the desired viscosity and setup time for the procedure. Cement exits the hot plate and is dispensed through output cement hoses. 
         [0022]    The present invention is not limited to be a handheld device or manual device, embodiments conceived to automate the bone cement dispensing process. In an embodiment disclosed herein, the bone cement dispenser is attached to a table with a motor utilized as a rotational drive in place of the previously described crank. The motor may be controlled by manual settings or by programmable means to effect the dispensing of bone cement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    For a more complete understanding of the exemplary embodiments herein, and for further details and advantages thereof, reference is now made to the following Detailed Description taken in conjunction with the accompanying drawings, in which: 
           [0024]      FIG. 1A  is a front view isometric drawing of a first exemplary embodiment of a handheld bone cement dispenser. 
           [0025]      FIG. 1B  is a rear view of the first exemplary embodiment of a handheld bone cement dispenser. 
           [0026]      FIG. 2  is an exploded cross-sectional view of the first exemplary embodiment of the cement dispensing mechanism. 
           [0027]      FIGS. 3A ,  3 B and  3 C are top and side view drawings of the cement extractor plate of the first exemplary embodiment. 
           [0028]      FIGS. 4A ,  4 B and  4 C are top and side view drawings of the extractor disc of the first exemplary embodiment. 
           [0029]      FIGS. 5A and 5B  are top and side view drawings of the spiral shaped ball guide of the first exemplary embodiment. 
           [0030]      FIGS. 6A and 6B  are top and side view drawings of the disposable cement cartridge of the first exemplary embodiment. 
           [0031]      FIGS. 7A ,  7 B and  7 C are top, side and bottom view drawings, respectively, of the cold plate of the first exemplary embodiment. 
           [0032]      FIGS. 8A ,  8 B,  8 C and  8 D are top and side view drawings of the Peltier plate and output selector disc of the first exemplary embodiment. 
           [0033]      FIGS. 9A ,  9 B and  9 C are top, side and bottom view drawings, respectively, of the hot plate of the first exemplary embodiment. 
           [0034]      FIG. 10  is a rear view exploded isometric drawing of the first exemplary embodiment of a bone cement dispenser. 
           [0035]      FIG. 11  is a side view drawing of the extractor and cement cartridge interface of the first exemplary embodiment. 
           [0036]      FIG. 12A  is a front view isometric drawing of a second exemplary embodiment of a handheld bone cement dispenser. 
           [0037]      FIG. 12B  is a rear view of the second exemplary embodiment of a handheld bone cement dispenser. 
           [0038]      FIGS. 13A ,  13 B and  13 C are side, top and bottom views, respectively, of the cement dispensing mechanism of the second exemplary embodiment. 
           [0039]      FIG. 14  is an exploded isometric drawing of the cement dispensing mechanism of the second exemplary embodiment. 
           [0040]      FIGS. 15A ,  15 B and  15 C are top, cross-section and bottom views, respectively, of the cold plate of the second exemplary embodiment. 
           [0041]      FIGS. 16A ,  16 B and  16 C are top, cross-section and bottom views, respectively, of the hot plate of the second exemplary embodiment. 
           [0042]      FIGS. 17A ,  17 B and  17 C are top, side and end views, respectively, of the extractor press of the second exemplary embodiment. 
           [0043]      FIG. 17D  is an end view of an alternative embodiment of an extractor press. 
           [0044]      FIG. 18  is an end view of the cement extractor of the second exemplary embodiment. 
           [0045]      FIG. 19  is a side view of the crank mechanism of the second exemplary embodiment. 
           [0046]      FIG. 20  is an end view of the bone cement dispenser of the second exemplary embodiment. 
           [0047]      FIGS. 21A ,  21 B and  21 C are top and side views of the disposable cement cartridge of the second exemplary embodiment. 
           [0048]      FIG. 22  is a perspective drawing of an exemplary embodiment of the present invention wherein the bone cement dispenser is mounted on a table top. 
           [0049]      FIG. 23  is a perspective drawing of a bone cement extractor of an alternate embodiment of the present invention. 
           [0050]      FIG. 24  is a perspective drawing of an array of independently controlled Peltier junction devices of an alternate embodiment of the present invention. 
           [0051]      FIG. 25  is a perspective drawing of a cement temperature controller of an alternate embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0052]    The present invention is described in the context of a preferred embodiment and other exemplary embodiments. The following description of the preferred embodiment is not intended to limit the application of the inventive concepts but merely provide a concrete example of the inventive concept especially related to the application of bone cement in orthopedic surgery. Other situations may be conceived wherein a temperature controlled and prescribed flow of PMMA cement is applicable and useful to the art. 
         [0053]    Referring to  FIG. 1A , a first exemplary embodiment of a bone cement dispenser  300  commensurate with the present invention is shown. Bone cement dispenser  300  has an upper housing cover  302  rotatably attached to a lower housing cover  303  which is further attached to a lower housing base  304 . A handle  306  is attached to lower housing base  304  so that bone cement dispenser  300  may be held firmly by hand while in operation. Furthermore, a set of four Luer-lock ports  308  are fixed to upper housing cover  302  to which a set of outlet hoses  307  are attached. Outlet hoses  307  provide a path for cement to flow from bone cement dispenser  300  to the point of operation, for example, a human vertebra. Outlet hoses  307  are made of clear plastic in the first exemplary embodiment. Bone cement is stored in a disposable cement cartridge located within bone cement dispenser  300 . 
         [0054]    A crank  311  is rotatably attached through upper housing cover  302  to a temperature controlled cement dispensing mechanism contained inside bone cement dispenser  300 . An indicator  312  with a marked set of graticules  313  appears on the top side of housing cover  302 , preferably with a transparent surface showing a marker on the temperature controlled cement dispensing mechanism and useful for indicating a quantity of cement dispensed. Color chart  315  is placed on the top surface of housing cover  302  for indicating cement viscosity by color comparison with dispensed cement. Electrical cable  316  is attached through handle  306  to the temperature controlled cement dispensing mechanism. The cement cartridge and temperature controlled cement dispenser mechanism will be explained further below. 
         [0055]    A shown in  FIG. 1B  bone cement dispenser  300  has a rotatable output selector  318  which is a round disc rotating between selectable positions  322  and having indicator  321  indicating the current selector position. Cement dispenser  300  may have viewing port  319  for viewing the color of the cement as it is dispensed. 
         [0056]      FIG. 2  is a cross-sectional drawing of bone cement dispenser  300  showing the temperature controlled cement dispensing mechanism which comprises a cement extractor assembly  330  and a cement temperature controller  335 . The top of bone cement dispenser  300  is near the top of the drawing, the bottom being near the bottom of the drawing so that upper surfaces face the top and lower surfaces face the bottom. Housing base  304  is attached to the bottom of cement temperature controller  335 , lower housing cover  303  (shown in  FIG. 1 ) being attached thereto and upper housing cover  302  covering cement extractor assembly  330 . 
         [0057]    Cement extractor assembly  330  comprises cement extractor plate  350 , extractor disc  370 , extractor ball  371 , spiral ball guide  378 , and crank  311 . Crank  311  has threaded shaft  355  with smoothed ends, end shaft  347  and shoulder  345 , and crank arm  342  attached to threaded shaft  355  and to handle  341 . Referring to  FIGS. 2 ,  3   a ,  3   b  and  3   c , cement extractor plate  350  is a solid plate having a cylindrical cavity  361  with cavity walls  356  and a guide surface  362  with guide wall  358  and threaded holes  357  in guide surface  362 . A central hole  353  is drilled through cylindrical cavity  361  to the upper surface of cement extractor plate  350 . Cylindrical cavity  361  adjoins a rectangular cavity  359  having hole  354  on one end and hole  351  on the other end. Crank  311  is inserted through hole  354  in cement extractor plate  350  so that end shaft  347  is fixed in end hole  351  but with sufficient clearance to allow rotation. A collar  346  is secured on shoulder  345  to hold crank  311  in place while allowing free rotation of crank  311 . 
         [0058]    Extractor disc  370  has a diameter similar to that of cylindrical cavity  361  and is positioned inside cylindrical cavity  361 .  FIGS. 4   a ,  4   b  and  4   c  show a more detailed view of extractor disc  370  which is comprised of a cylindrical solid having a bearing assembly  365  inserted through its center axis allowing for rotation about the center axis. Extractor disc  370  has a linear ball slide  369  along one radius. Extractor ball  371  rolls along the radius with approximately 30% of the ball&#39;s surface protruding from ball slide  369 . Threads on the outer edge surface  367  are in contact with threaded shaft  355 . 
         [0059]    Spiral ball guide  378  is explained with the aid of  FIGS. 2 ,  5   a  and  5   b . Spiral ball guide  378  is attached to guide surface  362  with a set of screws  373  positioned through a set of holes  377  and into threaded holes  357 . Axle screw  374  is inserted through center hole  375  into an upper axle shaft  352  which itself is inserted through the upper surface of cement extractor plate  350 . Upper axle shaft  352  further extends through bearing assembly  365  so that spiral ball guide  378  and extractor disc  370  are attached to cement extractor plate  350  to form a single unit with extractor disc  370  rotating on axle shaft  352  with the aid of bearing assembly  365 . 
         [0060]    Spiral ball guide  378  has a spiral shaped guide  379  extending from the outer radius to near the central point at center hole  375 . Extractor ball  371  is positioned inside spiral guide  379  protruding through the lower surface of spiral ball guide  378 . 
         [0061]    Cement temperature controller  335  is comprised of a cold plate  380 , Peltier junction plate  385 , hot plate  390  and housing base  304  connected together by a set of assembly screws  399 . Cement temperature controller  335  further comprising an output selector  318  held in place between cold plate  380  and hot plate  390  by a threaded selector shaft  392 . 
         [0062]    Cold plate  380  is further explained using  FIG. 2  in conjunction with  FIGS. 7A and 7B  wherein cold plate  380  is a rectangular solid with a cartridge receiving area  381  formed as a shallow cylindrical hollow in its upper surface defined by cylindrical wall  384  and having approximate depth of 2 mm. A set of standoff pins  382  is attached on the upper surface inside cartridge receiving area  381  protruding upward from said upper surface. Near the center of cartridge receiving area  381  a hole forming a cement receiver  383  extends from the upper surface to the lower surface. A cavity forming an upper cement channel  388  having a semicircular channel shape on one end and a linear channel shape to the opposite end is made into the lower surface of cold plate  380  so that cement receiver  383  extends into upper cement channel  388 . Cold plate  380  has a hole  393   d  drilled through from the upper to the lower surface and a set of threaded holes  398   d  near each corner tapped approximately halfway up from the lower surface. 
         [0063]    Peltier junction plate  385  is a thermoelectric device typically made of a stacked series of semiconductor thermocouple elements. Each thermocouple element is made of N-type and P-type semiconductor pieces bonded together. A voltage applied across each element in series causes heat to be transferred from one surface to the other, thereby forming a heat pump which transfers heat from the upper surface in thermal contact with cold plate  380  to the lower surface in thermal contact with hot plate  390 . A thermally conductive paste is used to thermally bond the surfaces together. 
         [0064]      FIG. 8  shows detail of Peltier plate  385  wherein a semicircular notch  420  is cut through plate  385  on one end so that when assembled between the cold and hot plates, a cavity is formed there between to receive output selector  318 . A set of holes  398   c  are drilled through Peltier plate  385  near its corners. Output selector  318  has an axis hole  393   b  at its center and a transit hole  417  off center, both holes being drilled through from upper to lower surfaces. 
         [0065]    Hot plate  390  is described with the aid of  FIGS. 9A and 9B  in conjunction with  FIG. 2 , the upper surface of hot plate  390  being shown in  FIG. 9A  and cross section being shown in  FIG. 9B  with relations to other components shown in  FIG. 2 . A set of cement channel input holes  422   a ,  422   b ,  422   c  and  422   d  are clear holes from the upper surface to the lower surface and adjoin a set of lower cement channels  423   a ,  423   b ,  423   c  and  423   d , respectively. The lower cement channels are formed by rectangular grooves in the lower surface starting from the cement channel input holes and ending at cement channel output holes  425   a ,  425   b ,  425   c  and  425   d  corresponding to lower cement channels  423   a ,  423   b ,  423   c  and  423   d , respectively. Hole  393   b  is a clear hole from the upper surface to the lower surface of hot plate  390 . Additionally, a set of four holes  398   b  are clear holes from the upper surface to the lower surface near the corners of hot plate  390 . 
         [0066]    Housing base  304  is a flat plate having hole  393   a  and set of holes  398   a  drilled through from its upper to lower surface. A set of assembly screws  399  are inserted through holes  398   a ,  398   b , and  398   c  and threaded into threaded hole  398   d  to hold the cement temperature controller  335  together as one piece. Additionally, selector shaft  392  with threads near the upper end is inserted into holes  393   a ,  393   b ,  393   d  in output selector  318  and threaded into threaded hole  393   d  to hold output selector  318  in place so that transit hole  417  may align by rotation of output selector  318  with one of the set of cement channel input holes  422   a ,  422   b ,  422   c  and  422   d  to create an opening from cement receiver  383  to upper cement channel  388  through transit hole  417  and into the lower cement channel associated to the aligned cement channel input hole. 
         [0067]    Luer-lock ports  308  are a fastened to the cement channel output holes  425   a ,  425   b ,  425   c  and  425   d  so that output hoses  307  may be suitably attached. 
         [0068]    Cement cartridge  400  is shown in detail in  FIGS. 6 and 6   b  wherein a foil bottom layer  412  is adjoined to a foil upper layer  411  to form cement cartridge  400 . A spiral cement pocket  402  forms a bubble on the top surface of cement cartridge  400 , spiraling from the outer radius at position  408  to an inner radius at position  409  and into an output nozzle  405  formed on the lower surface of cement cartridge  400 . Spiral cement pocket  402  is pressure filled with PMMA cement  410 , an exemplary PMMA cement being KyphX® HV-R™ bone cement from Kyphon Corporation. A set of guide holes  404  perforate the foil at various locations outside of the spiral cement pocket  402 , the pattern and sizes of the set of guide holes  404  matching the pattern and sizes of the set of standoff pins  382  in cold plate  380 . 
         [0069]    Referring to  FIG. 10 , upper housing cover  302  is securely attached with screws to cement extractor assembly  330  and lower housing cover  303  is securely attached to housing base  304  of temperature controller  335 . Upper housing cover  302  is attached to lower housing cover  303  with a set of hinges  430   a  and  430   b  and a set of latches  431   a  and  431   b , upper housing cover  302  forming a lid which opens to the top surface of cold plate  380 . 
         [0070]    In operation, output hoses  307  are attached to Luer-lock ports  308  of cement dispenser  300  with their output ends suitably placed in desired bone locations. Upper housing cover  302  is rotated away from lower housing cover  303  and cement cartridge  400  is positioned over standoff pins  382  atop the surface of cylindrical hollow  381  of cold plate  380 . Prior to the positioning of cement cartridge  400  the end of output nozzle  405  is punctured to create a path for cement  410  to exit from spiral cement pocket  402 . Once the upper housing cover  302  is closed and latched, cement cartridge  400  is adjacent to and covered by spiral ball guide  378  according to  FIG. 11 . Extractor ball  371  is pressed into spiral ball guide  378  by extractor disc  370  so that extractor ball  371  is in contact with and depresses spiral cement pocket  402  at the point of contact. Crank  311  is rotated causing extractor disc  370  to rotate via contact with threaded shaft  355 . As extractor disc  370  rotates, extractor ball  371  moves along spiral guide  378  depressing spiral cement pocket  402  and ultimately forcing cement  410  through output nozzle  405  and into cement receiver  383 . 
         [0071]    Peltier junction plate  385  has a voltage, V, applied via electrical cable  316  so that heat is being pumped from cold plate  380  to hot plate  390  subsequently creating a stable temperature difference, ΔT, between the cold and hot plates, wherein ΔT is proportional to V. Cement  410  is cooled since cement cartridge  400  is in contact with cold plate  390 . As cement  410  flows from cement receiver  383  into upper cement channel  388 , cement  410  remains cooled which retards cement polymerization. 
         [0072]    Output selector  318  is rotated to a desired position allowing for the flow of cooled cement  410  into one of the set of lower cement channels and ultimately out of a chosen output port so that cement is dispensed to a desired bone location associated with the output port and output hose. While cement  410  flows through the lower cement channels it is warmed to a temperature ΔT above that of the cooled cement in the cement cartridge. As cement  410  is warmed, its polymerization rate is increased according to the Arrhenius equation so that cement  410  is dispensed to the desired bone location with a desired cement viscosity so that the cement sets up to a desired strength in a desired timeframe. To better enable the desired set up time and viscosity, cement  410  is mixed with potassium permanganate to create a polymerization dependent color, and hence viscosity dependent color. As cement  410  exits through output hoses  307 , its color may be matched to a viscosity with the aid of color indicator  315 . The correlation between color, temperature and desired characteristics of cement set up may be determined empirically or by other methods known in the art. In another embodiment, a transparent window to the upper cement channel in cold plate  380  may be used to observe cement color in the cooled state. 
         [0073]    Once a desired bone location has received enough cement  410 , a second desired bone location may be selected by rotating output selector  318  and repeating the given process. Cement dispenser  300  may be cleaned by inserting a cleaning cartridge. The cleaning cartridge is filled with acetone or some other suitable solvent. More aggressive cleaning may be accomplished by removing housing base  304  from the cement temperature controller assembly  335  to access the lower cement channels. Alternatively, some or all of the pieces of the device may be made disposable. 
         [0074]    Referring now to  FIG. 12A , a second exemplary embodiment of a bone cement dispenser  100  commensurate with the present invention is shown in perspective drawing. Bone cement dispenser  100  has housing  101  comprised of upper housing cover  102 , a lower housing plate  103  and handle  105  attached to lower housing plate  103  so that bone cement dispenser  100  may be held firmly by hand while in operation. Furthermore, a set of four Luer-lock ports  109  are fixed to housing  101  to which a set of outlet hoses  108  are attached, outlet hoses  108  providing a path for cement to flow from bone cement dispenser  100  to the point of operation, for example, a human vertebra. The set of outlet hoses  108  are made of clear plastic. Bone cement is stored in a disposable cement cartridge held firmly inside dispenser  100 , the disposable cement cartridge being described further below in relation to  FIGS. 21A ,  21 B and  21 C. 
         [0075]    Crank  111  is rotatably attached through housing  101  to a cement dispensing mechanism contained therein for causing cement to be dispensed from the disposable cement cartridge into the set of outlet hoses  108 . An indicator  112  protruding through one side of housing  101  is provided in combination with a set of calibrated graticules  113  marked on the same side of housing  101 , the combination being useful for indicating a quantity of cement dispensed. Color chart  115  is placed on the outside of housing  101  for indicating cement viscosity. Furthermore, a set of clear windows  114  allow for viewing of cement as it is dispensed. A temperature controller device, explained in connection with  FIG. 14 , is contained in housing  101  and powered through electrical cable  106 . Viscosity of cement is controlled by cooling stored cement in the disposable cement cartridge and then heating dispensed cement as it moves from the cartridge to the Luer-lock ports  109 . 
         [0076]      FIG. 12B  shows a rear perspective view of bone cement dispenser  100 . Outlet selector  118  is a rotatable selector wheel which selects between positions  119 , each position correspondingly allowing cement to dispense through one of the four respective Luer-lock outlet ports  109 . 
         [0077]    Detailed views of the cement dispensing mechanism contained within bone cement dispenser  100  are shown in  FIGS. 13A ,  13 B and  13 C.  FIG. 13A  shows a side view of cement dispensing mechanism  130  which is attached to lower housing plate  103 , upper housing cover  102  normally covering cement dispensing mechanism  130 . Cement dispensing mechanism  130  comprises cement extractor  150  adjacent to the top of cold plate  180 , cement extractor  150  having crank  111  attached thereto and having an indicator slot  151  for indicator  112 . Cold plate  180  and hot plate  190  are affixed to Peltier junction block  185 , cold plate  180  being affixed to the cold side of Peltier junction block  185  and hot plate  190  being affixed to the hot side of Peltier junction block  185 . Output selector  118  is positioned between cold plate  180  and hot plate  190 . Luer-lock ports  109  are fastened to lower housing plate  103  and are connected to cement channels  133  inside hot plate  190 . 
         [0078]    Lower housing plate  103  is attached to the bottom side of hot plate  190 . The drawing of  FIG. 13B  shows that lower housing plate  103  contains mounting holes  197  and a hole  198  for placing electrical wires to power the Peltier cooling block. When a DC voltage V is applied to Peltier cooling block  185 , heat is transferred from cold plate  180  to hot plate  190 , causing cold plate  180  to attain a temperature lower than ambient temperature and hot plate  190  to attain a temperature higher than ambient temperature, the temperature difference ΔT between cold plate  180  and hot plate  190  being proportional to V. 
         [0079]    The heating and cooling elements comprising cement dispensing mechanism  130  are further explained with the aid of  FIGS. 14 through 16 . Beginning with  FIG. 14 , Peltier plate  185  is sandwiched between cold plate  180  and hot plate  190 , the assembly being fastened together by screws  198  inserted through lower housing plate  103  through sets of holes  199   a ,  199   b  and  199   c  into threaded holes  199   d  machined into cold plate  180 . A thermally conductive paste may be applied to the top and bottom surfaces of Peltier plate  185  to effect an efficient thermal path to the cold and hot plates, respectively. Output selector  118  having a central hole  191   b  and a cement transit hole  195  is inserted into selector slot  177  which is a semicircular cutout in Peltier plate  185 . Pin  181  is placed through hole  191   a  of cold plate  180 , through the central hole  191   b  of output selector  118  and into hole  191   c  of hot plate  190  so that output selector  118  may rotate to preferably align cement output hole  195  with a given cement channel hole of the set of cement channel holes  192  in hot plate  190 . A set of index bumps  178  are machined into selector slot  177  to aid in positioning output selector  118  to effect alignment of the given cement channel hole to the cement transit hole  195 . 
         [0080]    Cold plate  180  has a cartridge receiver area  182  for holding disposable cement cartridges containing PMMA cement. PMMA cement is received through cement receiver  183  which is a slot through which PMMA cement may flow from the top surface of cold plate  180  through cement transit hole  195  to one of the set of cement channel holes  192  aligned thereto. Cement channels (not shown) in hot plate  190  allow cement to flow through hot plate  190  to cement output ports  194 . 
         [0081]    Detail of cold plate  180  is shown in  FIGS. 15A ,  15 B and  15 C. Cartridge receiver area  182  is a rectangular pan structure of approximately 3 mm depth into which a disposable cement cartridge is placed. Cement receiver slot  183  is machined into the top surface of cold plate  180  at one end having at least the width of the disposable cement cartridge. Hole  191   a  is a clear hole for holding pin  181 . A cross sectional view of cold plate  180  in  FIG. 15B  shows that cement receiver  183  has a curved wall  188  in connection with through-slot  184 . A semicircular cement distribution slot  189  is cut into the bottom surface of cold plate  180 , the wall  187  of distribution slot  189  being in contact with through-slot  184 . 
         [0082]    Detail of hot plate  190  is shown in  FIGS. 16A ,  16 B and  16 C. The top surface of hot plate  190  has four holes  192   a ,  192   b ,  192   c  and  192   d  drilled through to cement channels  193   a ,  193   b ,  193   c  and  193   d , respectively. Cement channels  193   a ,  193   b ,  193   c  and  193   d  are rectangular channels cut approximately 3 mm deep into the bottom surface of hot plate  190 , running along the length of hot plate  190  and connecting to the outside through cement output ports  194  which have Luer-lock connectors  109  attached thereto. 
         [0083]    Returning now to  FIG. 13C , a drawing showing the top view of cement extractor  150  is shown with upper housing cover  102  removed. Cement extractor  150  has right rail  155  and left rail  154 , both rails attached to end plate  152  and further attached to end plate  153 , the rails and end plates forming a fixed frame. Rails  154  and  155  are machined to accept a moveable extractor press  170  which slides along rails  154  and  155 , the extractor press having indicator  112  attached thereto. Crank  111  is attached to a threaded shaft  175  which is held in a freely rotatable position between end plate  152  and end plate  153 . Threaded shaft  175  is threaded through a hole in extractor press  170  so that upon rotating crank  111 , threaded shaft  175  causes extractor press  170  to linearly move in a direction parallel to rails  154  and  155 . Underneath extractor press  170  is a disposable cement cartridge  160  having a set of cement packets  161  running the length of disposable cement cartridge  160  in a direction parallel to rails  154  and  155  and protruding upward, disposable cement cartridge  160  being placed in cartridge receiving area  182  of cold plate  180 . 
         [0084]      FIGS. 17A ,  17 B and  17 C show more detail of extractor press  170  in a top, side and end view, respectively. Extractor press  170  has indicator  112  attached to its top surface  171 . Extractor press  170  also has a pair of slots  171   a  and  171   b  on either side into which rails  154  and  155  are inserted. A cylindrical protrusion  172  extends to form a bottom surface. Hole  173  is threaded through extractor press  170  through which threaded shaft  175  is run. 
         [0085]      FIG. 17D  shows an end view of another exemplary embodiment of extractor press  170  wherein a cylindrical roller  181  rotates on axis  182 . 
         [0086]      FIG. 18  shows cement extractor  150  frame as viewed towards end plate  153 . End plate  153  has clear hole  174  for mounting threaded shaft  175 . Left rail  154  has lip  177   a  and right rail  155  has lip  177   b  which are inserted into slots  171   a  and  171   b , respectively. Indicator  112  protrudes from the side of cement extractor  150  nearest left rail  155 . 
         [0087]    In  FIG. 19 , a drawing of crank  111  is shown, crank  111  comprising threaded shaft  175  to which arm  142  is attached with screws  143   a  and  143   b  and a handle  141  attached to arm  142  with rivet  140 . Collar  146  is fastened to collar end shaft  148  near shoulder  145 , collar end shaft  148  being inserted into clear hole  174  of end plate  153  with collar  146  fastened just inside end plate  153  and shoulder  145  placed just outside end plate  153  to hold threaded shaft  175  rotatably in the fixed frame of cement extractor  150 . Smooth end shaft  147  is placed into hole  152   a  (shown in  FIG. 13   c ) drilled into end plate  152  and opposite clear hole  174 . 
         [0088]    Alternative embodiments are conceived wherein other rotational means may cause rotation of threaded shaft  175 . Handle  141  and arm  142  may be replaced with other suitable coupling means between threaded shaft  175  and the rotational means. For example, a stepper motor may be coupled to threaded shaft  175  to effect rotation. Also, simple improvements may be conceived wherein rotational bearings may be inserted into end plate  153  for holding shoulder  145  and inserted into end plate  152  for holding shaft  147 . Linear bearing devices may be used in place of the lip and slot rail system to increase durability and accuracy of the extractor press movement. 
         [0089]      FIG. 23  is a perspective drawing of an alternate cement extractor  500  which is comprised of guide bars  554  and  555  each fastened to end plate  552  and to end plate  553  to form a rigid structure. Extractor press  570  has guide holes  564  and  565  into which guide bars  554  and  555  are inserted so that extractor press  570  can be moved linearly along the guide bars. Holes  557  and  558  in the end plates allow the placement of threaded shaft  559  through threaded hole  566  to effect linear movement of extractor press  570 . A spanner connection  561  is provided for attachment of a handle or motor drive (not shown). Retaining collars  571  and  581  retain the threaded rod in end plates  552  and  553  respectively. A roller rod  540  having dispensing roller  542  placed thereon, is fastened to the lower side of extractor press  570 . Dispensing roller  542  may slide laterally along roller rod  540 . Reservoir selector  544  surrounds dispensing roller  542  and is guided by roller rod  540 , and may be used to preferably position dispensing roller  542  over a cement packet to extract cement therefrom. A pin  544   a  extends through slot  544   b  in end plate  553  to align reservoir selector  544 . 
         [0090]      FIG. 24  is a perspective drawing of another embodiment of the present invention, showing an array of independently controllable Peltier junction devices  610 , each member of the array having cold side  602 , hot side  604  and having independent power connections. Each member device of array  610  is thermally insulated from the adjacent member devices of the array by insulating material  606 .  FIG. 25  shows array  610  in cement temperature controller  600  which is comprised of an array of cold plates  612  and an array of hot plates  614 , between which is placed array  610  of Peltier junction devices, cold side  602  of each Peltier junction device being in thermal contact with one of cold plates  612  and hot side  604  being in contact with one of hot plates  614 . A set of metallized PMMA cement packets  620  are placed on top of the array of cold plates  612 , the set of cement packets  620  having a corresponding set of Luer-lock ports  622  for dispensing the cement into connectable hoses. A depression  618  is fashioned in the top of the cold plates  612  in which the dispensing roller  542  of cement extractor  500  is translated. Cement temperature controller  600  is fixed between end plates  552  and  553  of cement extractor  500  to form an alternate embodiment cement dispenser. 
         [0091]      FIG. 20  shows a side view of bone cement dispenser  100  of  FIG. 12B , illustrating the mechanism by which disposable cement cartridges  160  are inserted and removed from bone cement dispenser  100 . Upper housing cover  102  is rotationally attached to lower housing plate  103  by hinge  120  so that cement receiving area  183  may be accessed. A set of latches  122  are made to fit into a set of latch receivers  123  to hold upper housing cover  102  firmly to the lower housing plate  103 . Once closed, cylindrical protrusion  172  on extractor press  170  applies pressure to cement packets  161 . 
         [0092]    Disposable cement cartridges are a novel and useful means for inertly holding PMMA until ready for dispensing.  FIGS. 21A ,  21 B and  21 C show three perspective views of a second exemplary embodiment disposable cement cartridge  160 . A foil bottom layer  162  is sealed to foil top layer  163  forming cement packets  161  which are filled with PMMA cement  164  and run the length of cement cartridge  160 . At one end of cement cartridge  160  a set of small outlet slits  166  are cut into foil bottom layer  162  during manufacturing. Foil bottom layer  162  is in contact with cold plate  180  when the device is in operation. In an alternate embodiment, foil top layer  163  may be integrated with a transparent material such as plastic to allow for visual inspection of cement  164  while still inside cement packets  161 . 
         [0093]    Refer to  FIGS. 12A through 15  and  FIG. 20  for an explanation of the operation of the cement dispenser  100 . In operation, output hoses  108  are attached to Luer-lock ports  109  of cement dispenser  100  with their output ends suitably placed in desired bone locations. To begin the operation, PMMA monomer is mixed with PMMA powder to form PMMA cement  164  which is caused to flow into disposable cement cartridge  160  and out of outlet slits  166  just enough to expunge any trapped air in the cartridge. Upper housing cover  102  is rotated away from lower housing base  103  and disposable cement cartridge  160  is positioned on the upper surface of cartridge receiver  182  of cold plate  180 . Once the upper housing cover  102  is closed and latched, disposable cement cartridge  160  is adjacent to and covered by cement extractor  150  while cylindrical protrusion  172  is in contact with and depresses cement packet  161  at the point of contact. Crank  111  is rotated causing extractor press  170  to move linearly towards end plate  152 , wherein extractor press  170  compresses cement packets  161  causing cement to flow towards end plate  152 , out of cement cartridge  160  and into cement receiver  183  of cold plate  180 . 
         [0094]    Peltier junction plate  185  then has a voltage V applied via electrical cable  106  so that heat is pumped from cold plate  180  to hot plate  190  subsequently creating a stable temperature difference ΔT between the cold and hot plates, wherein ΔT is proportional to V. Cement  410  is typically cooled since cement cartridge  160  is in contact with cold plate  190 . As cement  164  flows from cement receiver  182  into distribution slot  189 , cement  164  is further cooled which decreases the cement temperature discouraging cement polymerization. 
         [0095]    Output selector  118  is rotated to a desired position allowing for the flow of cooled cement  164  into one of the set of lower cement channels and ultimately out of a chosen output port so that cement is dispensed to a desired bone location associated to the output port and output hose. While cement  164  flows through the lower cement channels it is warmed to a temperature ΔT above that of the cooled cement in the cement cartridge. As cement  164  is warmed, its polymerization rate is increased according to the Arrhenius equation so that cement  164  is dispensed to the desired bone location with a desired cement viscosity so that the cement sets up to a desired strength in a desired timeframe similar to the first exemplary embodiment. As cement  164  exits through output hoses  108 , its color may be matched to a temperature with the aid of color indicator  115 . Clear window  114  may be used to observe the color of PMMA cement prior to being dispensed, wherein cement packets  161  are transparent on the top surface. 
         [0096]    Once a desired bone location has received enough cement  164 , a second desired bone location may be selected by rotating output selector  118  and repeating the given process. Cement dispenser  100  may be cleaned by inserting a cleaning cartridge. More aggressive cleaning may be accomplished by removing housing base  104  from hot plate  190 . 
         [0097]      FIG. 22  is a diagram of an alternative embodiment of the present invention wherein a bone cement dispenser is mounted on a table instead of being held by hand. Furthermore, the alternative embodiment has automatic means for dispensing cement. Bone cement dispenser  200  is mounted onto table  201  by mounting plates  205  attached thereto. Output cement hoses  208  are connected to Luer-lock connectors on the outside of cement dispenser  200  and are appropriately placed in the receiving patient according to required surgical process. Bone cement dispenser  200  has cold and hot plates driven by a Peltier cooling block, the Peltier cooling block requiring DC power supply  213 , the electrical input cable  212  to DC power supply  213  being connected to premises AC power and the output DC cable  214  being connected to the Peltier cooling block. 
         [0098]    Stepper motor  210  is coupled to bone cement dispenser  200  to actuate a cement dispensing mechanism contained therein, stepper motor  210  having an electrical cable  211  connected to electrical power and electrical control cable  215  connected to motor controller  220 . Motor controller  220  may selectably operate with a programmable step size to inject a given amount of cement. Alternatively, motor controller  220  may operate to deliver a continuous programmable flow of cement by continuous stepping to match a curing time and temperature. Motor controller  220  has step button  224  to operate a programmable injection of cement and control means  222  for selecting forward motion to continuously inject cement, for selecting reverse motion to reset cement dispenser  200 , and step modes to programmably inject a fixed amount of cement. Motor controller has a step size and velocity selector control  223 . Alternatively, motor controller  220  may be interfaced to a computer for more detailed control by computer interface  225 . 
         [0099]    In another embodiment, electronics integrated into the bone cement dispenser may include a timer, an ambient temperature sensor, temperature sensors on the hot and cold junction surfaces, and a rotary position sensor. A computer may be interfaced to evaluate Arrhenius equation to predict the remaining set up time available, provide visual feedback on the optimal flow rate, calculate the infused volume, and control the Peltier junction temperature. 
         [0100]    Another embodiment is conceived to switch the current direction through the Peltier junction plates so as to cool the cement just prior to dispensation, thus decreasing the polymerization prior to dispensation. 
         [0101]    In yet another embodiment combining the integrated electronics and the stepper motor and motor controller with computer interface, the computer may further control the dispensation of cement according to optimal flow rate computations and calculated infused volumes. 
         [0102]    While these exemplary embodiments have been described along with other illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the exemplary and illustrative embodiments, as well as other embodiments, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.