Patent Document

FIELD OF THE TECHNOLOGY 
     This application relates generally to an apparatus and method for the delivery of highly viscous materials to a surgical site, and more particularly, to a syringe-like device for the in vivo application of bone cement. 
     BACKGROUND 
     Age, injury, trauma, and disease can cause degenerative changes in both the joints and bones of the body. At some point, these degenerative changes can become so advanced and/or debilitating that it becomes necessary to replace a damaged joint with a prosthetic device. In such cases, bone cement is often used to secure the prosthetic device to the natural bone. For those suffering from severer osteoporosis, procedures such as vertebroplasty and kyphoplasty use bone cement to stabilize and/or build up the vertebral bodies that have been weakened by compression fractures. These procedures can help prevent further fracturing of the vertebral bodies as well as relieve the pain caused by existing fractures. 
     When referring to bone cement it should be understood that bone cement includes any type of surgical cement used in any type of surgical procedure including: resorbable cement, bone graft material, bone substitute, bone filler or any other biologically compatible mixture that is highly viscous. 
     Bone cement is primarily a two component material, the first component being a powder and the other being a liquid. The cement may also include additional ingredients such as stabilizers, one or more antibiotics, contrast agent(s), and/or colorants. Typically, the powdered component is comprised of polymethylmethacrylate (PMMA) which copolymerizes with the liquid component, methylmethacrylate (MMA), upon mixing. The polymerization process can be divided into four different phases: mixing, waiting, working, and setting. 
     The mixing phase starts the moment the powder and liquid components come into contact with each other. During this phase the cement is thoroughly mixed to reduce the porosity of the cement and increase its mechanical strength. The mixing phase is also characterized by changes in cement viscosity. At the beginning of mixing, the cement viscosity increases slowly. As the polymerization reaction progresses, however, the cement rapidly becomes increasingly viscous. 
     In the waiting phase, the cement will achieve a suitable viscosity for delivery to the surgical site. At the beginning of the waiting phase, the cement has a sticky dough-like consistency. However, the optimal consistency for delivering the cement in vivo is attained when the cement loses this sticky quality. Loss of stickiness marks the beginning of the working phase. 
     In the working phase, the cement is no longer sticky and has a viscosity that is high enough to allow penetration into cancellous bone without leaking into the surrounding tissues. The duration of the working phase is relatively short-lived and, in part, depends upon the type of bone cement being used. For example, low viscosity cements have a relatively short working phase while high viscosity cements have a longer working phase. Cements with a longer working phase typically allow a surgeon more time to apply the cement before the cement enters the setting phase and begins to harden. Regardless of the type of cement used, the finite duration of the working phase necessitates an efficient and precise means for its delivery and application. 
     In the setting phase, the cement hardens completely and attains its full mechanical strength. Hardening is generally a temperature sensitive process and can be influenced by body temperature, the temperature of the operating room, and the temperature of the bone cement material itself. High viscosity cements are sometimes pre-chilled before mixing, which prolongs the working phase as well as the setting phase. Humidity can also affect the working and setting phases of bone cement. 
     Considering the time dependent relationship between the optimal viscosity for delivery of the cement to the surgical site and the onset of cement hardening, an efficient, effective and convenient means for delivering bone cement is highly desirable. 
     SUMMARY 
     An apparatus and a method are configured for the efficient delivery of a viscous material to a surgical site. To more efficiently deliver a viscous material such as bone cement to a surgical site, the present apparatus and method employs a syringe-type assembly where vibrational forces are applied to the central barrel portion during the time that the viscous material is being delivered and/or applied in vivo. The vibration to the central barrel portion increases the tendency of the viscous material to flow, in this case, towards the outlet of the syringe needle. 
     In one embodiment, the apparatus comprises a housing member with a central portion that is capable of receiving a standard syringe barrel. A large gauge needle is removably connected to the standard syringe barrel. A cut-out window in the central portion of housing member allows for viewing though a transparent syringe barrel to ascertain the position of the plunger. The apparatus may include at least one switch to actuate vibrating motors and at least one power supply. 
     In a preferred embodiment, an apparatus for the delivery of a viscous material includes a plurality of vibrating motors disposed on either side of the central barrel portion. 
     In another preferred embodiment, an apparatus will have several switches that will separately actuate at least one of the plurality of vibrating motors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of the apparatus; 
         FIG. 2  is a perspective view, portions removed, of the apparatus of  FIG. 1  in disassembled form; 
         FIG. 3  is a perspective view, partly broken away and partly in section, of the apparatus of  FIG. 1 ; and 
         FIG. 4  is a perspective view of the syringe portion of the apparatus of  FIG. 3  in disassembled form. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawings, wherein like numerals represent like elements throughout the various views, an apparatus for the delivery of viscous materials is generally designated by the numeral  10 . The delivery apparatus  10  generally employs a large gauge syringe  12  which includes a large bore needle  14 , a barrel  16  and a plunger rod assembly  18  which is specially adapted for more effective and efficient in vivo delivery of viscous materials, such as bone cement, to a surgical site. It should be understood, however, that the delivery apparatus is not limited to the delivery of bone cements but rather its use also extends to, inter alia, biocompatible adhesives and medicines. 
     As illustrated in  FIG. 4 , the syringe  12  includes a large bore needle  14  having a proximal end  14   a  and a distal tip end  14   b . In one preferred embodiment, needle  14  is a 7 gauge needle. The proximal end of the needle  14   a  is removably connected to a luer connector  15  of a standard syringe barrel  16  (20 ml barrel). The connector  15  may be of any conventional design used in standard medical practice, such as a hub having a luer lock or a thread lock for the attachment of syringes or other medical devices that require the attachment of a needle. 
     The delivery apparatus  10  includes a contoured housing  20  which generally mounts the principal components such as barrel  16 . 
     The housing  20  has a central barrel-like receiver  22  with an outlet  23 . The central receiver  22  is designed to efficiently receive and hold a standard plastic or glass syringe barrel, such as barrel  16 . If more adhesive is required during a procedure, the surgeon can simply remove the needle  14  from the standard syringe barrel  16 , and then remove the standard syringe barrel and plunger from the main vibration housing  20 . Next, the surgeon would reload the main vibration housing with a full syringe barrel and plunger assembly, and reattach the needle. Upon loading of the syringe  12 , the receiver  22  is coaxial to the needle  14  which extends axially from the housing and plunger rod assembly  18 . The barrel  16  is adapted to receive a predetermined volume of material. Material within the barrel portion  16  is advanced through the needle  14  by the actuation of the plunger rod assembly  18 . 
     In one embodiment, the central portion of receiver  22  of the housing  20  features a viewing window  24 . Preferably, the viewing window  24  is a cut-out portion of the receiver. Alternatively, the window  24  may be made from a clear plastic material, which allows the user to observe the contents of the syringe barrel  16  which is also transparent. In a preferred embodiment, the housing is about 3.7 inches in length and about 2.2 inches in width with the central barrel portion having an approximate volume of 20.0 milliliters (ml). 
     A finger flange  26  to facilitate injection of the syringe may integrally project from the housing  20 . In another preferred embodiment the central barrel portion may have two finger flanges  26 , each protruding from opposite sides of the housing. 
     As best illustrated in  FIG. 3 , the plunger rod assembly  18  is comprised of a rod  17  and a substantially cylindrical plug  19  disposed within the barrel  16 . The cylindrical plug  19  is axially movable along the interior surface of the barrel portion. The cylindrical plug  19  may have a plurality of O-rings or similar means to achieve a sealing fit between the plug and the interior surface of the barrel  16  as the plunger rod is axially displaced. Preferably, the plunger rod assembly is hand operated. Alternatively, the plunger rod assembly may be adapted for use with a mechanical actuator, such as a pneumatic actuator, to assist the user in axially moving the plug  19  within the central barrel to inject viscous material through the needle. 
     Two side tubular compartments  30  and  32  within the housing may flank the central receiver  22  and extend in generally parallel relationship. Each compartment may have a removable cap  34 . 
     Preferably, each compartment  30 ,  32  is configured to accommodate a power source  36 , a switch  38 , and a vibrating motor  40 . In another preferred embodiment, the apparatus employs a single vibrating motor. In a preferred embodiment, each power source  36  is a DC battery and each switch  38  is a tactile switch. One exemplary switch is a double-sealed type, B3WN tactile switch manufactured by OMRON Electronics. The switch may be configured or connect with an auxiliary controller to provide a selectively variable speed for the motor. 
     It should be understood that the placement of the vibrating motor(s)  40  is intended to focus and supply vibration mostly on the front of the internal syringe barrel  16  and where the larger I.D. of the syringe barrel reduces to a smaller I.D. in the vicinity of the connector  18 . It is in this area that the cement has a tendency to dam up and block the flow. 
     A rubber dampener  50  may be placed on the exterior surface of the needle hub to start to reduce vibrations down the length of the needle. In addition, another dampener  52  may be added to the needle shaft, and is capable of sliding along its length. The dampeners  50 ,  52  include respectively transversely projecting flexible wings  54 ,  56  or flaps to absorb vibration. Dampener  50  may be axially retained between flanges  60 ,  62 . 
     Preferably, the vibrating motor  40  is a micro vibration motor that operates at a predetermined speed in the range of between about 5,500 to 11,000 rpm (rotations per minute). It is also preferable that the vibrating motor has an overall length of between about 11 to 25 mm. One exemplary vibrating motor  40  is a coreless cylindrical permanent magnetic micro vibration motor manufactured by JinLong Machinery (part no. 7AL-09WA). 
     In a preferred embodiment, a vibrating motor operating at a predetermined fixed speed or at a variable speed of, for example, 7,000±1500 rpm increases the tendency of viscous material (not illustrated) within the central syringe barrel to flow, which thereby increases the overall efficiency of the in vivo delivery of the material. In addition, applying vibration to the barrel increases the effectiveness and efficiency of the plunger rod assembly  18  in advancing the material within the barrel portion towards the needle. Also, by applying vibration to the internal syringe barrel loaded with highly viscous material, the resistance pressure to the manual squeezing force between the hand and plunger will be considerably reduced, giving the doctor more control of the delivery of the material. 
     The delivery apparatus preferably has a plurality of vibrating motors which are each powered by a corresponding power source disposed within the housing  20 . A single power source typically energizes a single vibrating motor. Alternatively, a single power source may power the plurality of vibrating motors. 
       FIG. 3  illustrates one exemplary embodiment of a connection between a power source  36 , a switch  38 , and a vibrating motor  40 . In one embodiment the power source  36  is a AAA battery. Preferably, in an embodiment having a plurality of vibrating motors, each motor may be activated and/or deactivated individually via a dedicated switch. Alternatively, a single switch may actuate a plurality of motors and selectively impose a variable speed for the motors. 
     The delivery apparatus and particularly the housing  20  is manufactured from durable materials capable of withstanding repeated sterilization. 
     The vibrating housing receiver is dimensioned to hold standard plastic and glass prefilled/premixed syringes. Naturally, housing receiver  22  may be designed to hold a custom volume premixed/prefilled syringe assembly. The delivery assembly maintains the loaded premixed syringe in a mixed state before and during delivery of the bone cement and facilitates replacement of the syringe during a procedure. 
     Exemplary embodiments illustrating the apparatus and the method of increasing the efficiency of delivering viscous materials to a surgical site are described for purposes of explanation and are not intended as limitations of the invention herein. Alternative designs and additional modifications may occur to one skilled in the art without departing from the spirit and the scope of the present invention.

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