Patent Publication Number: US-2019175329-A1

Title: Method and injection system for bone tissue implant

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATION 
     This patent application claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 62/595,615, filed Dec. 7, 2017 by Paul V. Fenton Jr. et al. for METHOD AND INJECTION SYSTEM FOR BONE TISSUE IMPLANT (Attorney&#39;s Docket No. PINVIVO-1 PROV), which patent application is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method and injection system for embedding an implant in the bone tissue of a patient or other structure, and, more particularly, to a method and injection system to embed a flowable implant material into a porous region to form, shape and create the implant in situ where desired. 
     BACKGROUND OF THE INVENTION 
     At the present, bone anchor implants are used in patients for the attachment of soft tissue to the bone of a patient. Current anchors are generally implants made from prefabricated metallic, polymeric or synthetic materials, and are relatively rigid and manufactured in precise fixed shapes (i.e., fixed volume envelopes and fixed surface topologies). 
     Typically, anchors are screws or interference fit devices which are surgically embedded in the bone, beneath the cortical bone layer, and may have an eyelet for attaching sutures used to encircle soft tissue to affix the soft tissue to the bone. 
     To accommodate individual patient anatomical differences, it would be advantageous to have a polymeric implant, injection system and method to introduce the implant material in situ, allowing the polymeric material to be infused into the surrounding bone material and subsequently becoming solidified, rigid and secured at or proximate to the location where the implant is desired. 
     In addition to the attachment of soft tissue to the bone of a patient, it would also be advantageous if the polymeric material implant could be used to fill a void with relatively arbitrary shape or size in bony structures. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention relates to a polymeric implant material, a method and an injection system to embed the implant material within a structure, such as a bone of a patient. 
     The present invention will be described with respect to a living patient and wherein the implant material is melted in order to fill a void in a bone of a patient, or to create an anchor within the bone of a patient, however, it will be seen that the present invention can also be used with other structures, not involving a living patient. By patient, it is meant that the present invention is applicable to any mammal. 
     A polymeric material that can be used with an exemplary embodiment is a low flowing point material such as polycaprolactone [PCL] with a flowing temperature of about 60 degrees Centigrade. With such material, the implant material can be melted so as to be infused into the desired area, such as the bone of a patient, without necrotic damage to that bone. Necrotic side effects occur in bone when the temperature is in excess of 57 degrees Centigrade for long durations of time and can be mitigated if the duration of temperature exposure in excess of 60 or 70 or 80 degrees Centigrade is shortened by the cooling effect of the heat transfer from the polymeric material to the body. Cooling to below 60 degrees Centigrade solidifies the polymeric material, secures it to the bone in situ, and provides the anchoring function of currently available implants or the filling of a void in bone. 
     The resultant implant is shaped to fit the underlying bone structure whereas the shape of current anchors are predetermined and forces the underlying bone structure to conform to the manufactured shape of current anchors. Other polymeric materials have lower temperature flowing points which would be preferred but are not yet biocompatible but may be in the future. 
     The implant injection system includes a handle with a shaft extending outwardly therefrom, and a means to heat the implant material so as to melt that material and allow it to be infused into the desired area. The actual heating of the material from its normal solid state to its flowable state can take place in situ within the body or other structure, or ex vivo, that is, just outside the body or structure and proximate to the desired location of the implant. The transformation of the material within the body from a solid state into a flowable state such as by heating can be accomplished with an active heating element within the injection system shaft. The ex vivo heating of the material can be accomplished with the shaft body of the injection system being actively heated so as to melt the material followed by a short time duration transfer of the melted material by the injection system to the implantation site for the material to be infused before the material re-solidifies and becomes rigid. 
     Accordingly, in one exemplary embodiment, the distal end of the shaft includes an electrical resistance heater that is used to heat and melt the implant material so as to render that implant material flowable. Alternatively, the heating may be applied to the implant material by means of a heated fluid, such as hot water, heated air or some other external heating system that heats and melts the implant material so as to render it flowable. As such, the distal end of the injection system can be placed into or proximate to the cancellous bone where the implant is desired, whereupon the implant material can be transformed into a flowable state and caused to migrate into the cancellous bone to create a bone anchor or to fill a void. 
     In another exemplary embodiment, there can be a looped suture that passes though the implant material, with the free ends of the looped suture extending outwardly from the implant material. As such, the implant material, when infused into the cancellous bone, anchors the suture loop to the bone and the free ends of the suture can surround the soft tissue and be tied together so as to affix that soft tissue to the bone. 
     In a still further exemplary embodiment, the implant material can be formed of multiple layers, with an inner layer or layers (or region or regions) that has/have a known flowing temperature and with an outer layer or layers (or region or regions) flowing at a higher temperature. With this construction, the heater is designed to reach the flowing temperature of the inner layer or layers (or region or regions) but not reach the flowing temperature of the outer layer or layers (or region or regions) so that only the inner layer or layers (or region or regions) is/are melted and diffused into the cancellous bone. 
     In another exemplary embodiment, another means of producing an anchor or filler that fills a void is to use an epoxy two-part polymer cement like polymethyl methacrylate (PMMA), which is loaded by means of a cement loading syringe into the distal end of an injection system. The implant material is then inserted by the injection system into the desired site. The PMMA material is specifically located at the distal end of the injection system since PMMA is rheopectic and hence difficult to flow down the length of a shaft. 
     More particularly, a material that is rheopectic exhibits a time-dependent increase in viscosity—the longer the fluid undergoes shearing force, the higher its viscosity. Thus PMMA, which is rheopectic, is difficult to flow down the length of a shaft. Accordingly, rather than trying to push the rheopectic PMMA material down the barrel of the implant device, the PMMA material is initially located at the distal end of the syringe, thereby eliminating the need to flow the PMMA material down the length of a shaft. 
     In one preferred form of the invention, there is provided an implant injection system for implanting an implant material into a structure comprised of a latticework having spaces formed therein, the implant injection system containing a quantity of a meltable implant material, and a heater for heating the meltable implant material to form a flowable implant material for introduction into the spaces of the latticework. 
     In another preferred form of the invention, there is provided a method for implanting an implant material into a structure comprising a latticework having spaces formed therein, the method comprising the steps of: 
     providing an implant injection system having a quantity of a meltable implant material located within the implant injection system; 
     heating the meltable implant material to create a flowable implant material; and 
     introducing the flowable implant material into the spaces of the latticework to harden in situ. 
     In another preferred form of the invention, there is provided a method for affixing soft tissue to the bone of a patient, the method comprising the steps of: 
     providing an implant injection system containing a quantity of a meltable implant material with a suture looped through the quantity of the meltable implant material and with free ends of the suture extending outwardly therefrom; 
     heating the quantity of meltable implant material to melt the meltable implant material to form a flowable implant material; 
     flowing the flowable implant material into the bone of a patient; 
     providing a quantity of soft tissue; and 
     tying the free ends of the suture around the soft tissue to affix the soft tissue to the bone of a patient. 
     In another preferred form of the invention, there is provided a method for affixing soft tissue to the cancellous bone of a patient, the method comprising the steps of: 
     providing an implant injection system having a distal end, a heater located proximate to the distal end of the implant injection system, and a quantity of bone implant material located proximate to the distal end of the implant injection system, the quantity of bone implant material comprising multiple regions of bone implant material, with an inner region having a predetermined flowing point temperature and outer regions having a flowing point temperature higher than the flowing point temperature of the inner region; 
     positioning the distal end of the implant injection system within the cancellous bone of a patient; and 
     activating the heater to create a temperature sufficient to melt the bone implant material of the inner region but lower than the flowing temperature of the outer regions to allow the bone implant material of the inner region to flow into the cancellous bone of the patient. 
     In another preferred form of the invention, there is provided an implant injection system for inserting a flowable material into a bone of a patient, the implant injection system comprising: 
     a container having a distal end and an open proximal end, a plunger movable with the container, a heater located proximate to the distal end of the container; and 
     a quantity of meltable material within the container and located proximate to the heater, wherein the material may be melted by the heater and forced from the distal end of the container by movement of the plunger. 
     In another preferred form of the invention, there is provided a method for loading a bone cement material into a delivery tip of an implant injection system, the method comprising the steps of: 
     providing a cement loading syringe having a barrel with an open distal end, a plunger and a quantity of bone cement material located at the open distal end of the barrel; 
     placing the open distal end of the barrel of the cement loading syringe proximate to the delivery tip of the implant injection system; and 
     activating the plunger of the cement loading syringe to force the bone cement material from the cement loading syringe into the delivery tip of the implant injection system. 
     These and other features and advantages of the present invention will become more readily apparent during the following detailed description of the preferred embodiments of the invention, which is to be taken in conjunction with the drawings herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  are schematic views illustrating an implant injection system formed in accordance with the present invention and showing a method for implanting implant material into the cancellous bone tissue of a patient; 
         FIGS. 2A-2E  are further schematic views illustrating the distal end of the implant injection system of  FIGS. 1A-1C  and showing the method of implanting implant material into the cancellous bone tissue of a patient; 
         FIGS. 3A and 3B  are schematic views showing an alternative exemplary embodiment of an implant injection system formed in accordance with the present invention and showing a method of use for implanting an implant material into the cancellous bone tissue of a patient; 
         FIG. 4  is an exploded schematic view of another implant injection system of the present invention that can be used to melt and introduce a polymer into the bone of a patient; 
         FIG. 5  is a perspective view of the assembled implant injection system of  FIG. 4 ; 
         FIG. 6  is a perspective view of the implant injection system of  FIG. 4  and illustrating its use in injecting a flowable melted polymer material into the bone of a patient; 
         FIGS. 7A and 7B  are schematic views of an electrical circuit usable with the embodiment of  FIG. 4 ; 
         FIGS. 8A-8G  are schematic views illustrating a method of loading an applicator tip with a material, such as a bone cement, to ready the applicator for injecting the material into the bone of a patient; and 
         FIG. 8H  is a schematic view showing an additional construction formed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIGS. 1A-1C , there is shown schematic views illustrating an implant injection system  10  formed in accordance with the present invention and showing the steps taken to carry out a method of the present invention. As can be seen in  FIG. 1A , the implant injection system  10  is positioned in close proximity to a bone  12  of a patient, and the implant injection system  10  includes a handle  14  and a shaft  16  extending therefrom. In this exemplary embodiment, a small resistance heater  18  is located at the distal end of the shaft  16 . 
     Bone implant material  20  is positioned at the distal end of the implant injection system  10  and a suture  22  is looped through that bone implant material  20  and the free ends  24  of the suture  22  extend from that bone implant material  20  proximally towards the handle  14 . 
     Moving on to the step shown in  FIG. 1B , the shaft  16  has pierced the cortical bone layer  26  of the bone  12  and the distal end of the shaft  16  is located in the cancellous bone  28 . 
     In the step of  FIG. 1C , the implant injection system  10  has been withdrawn from the bone  12  of the patient and the bone implant material  20  separated therefrom such that the bone implant material  20  remains in the cancellous bone  28 . To reach the step of  FIG. 1C , the bone implant material  20  has been heated by the resistance heater  18  to melt the bone implant material  20  and allow the implant injection system  10  to be pulled clear of the bone implant material  20 . The bone implant material  20  itself has melted and spread through the interstices of the cancellous bone  28  so that the bone implant material  20  is firmly affixed to the cancellous bone  28 , with the free ends  24  of the suture  22  available for use in securing soft tissue to the cortical bone layer  26 . 
     It should be appreciated that in one form of the invention, the bone implant material  20  is secured to the distal end of shaft  16 , adjacent to the resistance heater  18  disposed at the distal end of shaft  16 , so that bone implant material  20  essentially forms, in its pre-heated state, the distal end of shaft  16 ; and so that bone implant material  20  is carried into cancellous bone  28  by shaft  16 , whereupon activation of resistance heater  18  causes bone implant material  20  to flow off the distal end of shaft  16  and into the interstices of cancellous bone  28 . Thus, in one form of the invention, the heated bone implant material  20  is set at the distal end of shaft  16  and, when heated by resistance heater  18 , simply flows off the shaft and into the interstices of the cancellous bone  28 , whereafter it sets when cooled to body temperature. In another form of the invention, the bone implant material  20  may be positioned within a syringe chamber (not shown) disposed at the distal end of shaft  16 , and the heated bone implant material may be ejected, under force, out of the syringe chamber and into the interstices of cancellous bone  28 , whereafter it will set when cooled to body temperature. 
     In the method shown in  FIGS. 1A-1C , the heater  18  has been described in the exemplary embodiment to be an electrical resistance heater, however, it may be seen that other types of heaters can be used instead of a resistance heater in any of the embodiments described herein, including a heater employing a heated fluid, such as heated water or heated air. 
     In addition, in this embodiment and in subsequent applicable embodiments, the meltable implant material is one having a low flowing temperature such as polycaprolactone (PCL) which has a flowing point of about 60 degrees Centigrade so that necrotic damage to the bone is prevented. When that material is thereafter cooled, it hardens within the bone at the desired location and becomes an effective anchor for a suture or fills a void in the bone. 
     Accordingly, as an alternative to the use of a resistance heater, the implant bone material  20 , located in one embodiment at the distal end of an implant instrument, can be placed into a heated chamber or bath so that the implant bone material softens to a moldable state and then can be emplaced into the cancellous bone. 
     Turning now to  FIGS. 2A-2E , there is shown a series of steps further illustrating the use of the present implant injection system  10  in carrying out the present method of emplacing the bone implant material  20 . As can be seen, in the step of  FIG. 2A , a hole  30  has been made in the bone  12  of the patient that passes through the cortical bone layer  26  and extends into the cancellous bone  28 . As with the embodiment of  FIGS. 1A-1C , at the end of the shaft  16 , there is affixed the bone implant material  20  and which has the suture  22  passing through the bone implant material  20 , with the free ends  24  of the suture  22  extending outwardly therefrom. The resistance heater  18  is also located at the distal end of the shaft  16  so that the resistance heater  18  can heat the bone implant material  20  to its melt point to cause it to be flowable. 
     In the step of  FIG. 2B , the distal end of the shaft  16  has been introduced into the hole  30  so that the bone implant material  20  passes through the cortical bone layer  26  and into the cancellous bone  28 . 
     In the step of  FIG. 2C , the resistance heater  18  has been activated and the bone implant material  20  has melted and spread into the cancellous bone  28 , thereby forming a mass having a larger diameter than the diameter of the hole  30 . In the step of  FIG. 2D , the shaft  16  has been retracted, leaving the melted bone implant material  20  to re-solidify at body temperature within the cancellous bone  28 , with the suture  22  passing through the bone implant material  20  so that the suture  22  is anchored within the bone  12 . 
     Finally, in the step of  FIG. 2E , there can be seen the re-hardened bone implant material  20  positioned within the cancellous bone  28 , with the free ends  24  of the suture  22  tied together, encircling soft tissue  32 , so that the soft tissue  32  is affixed to the cortical bone layer  26 . 
     Turning next to  FIGS. 3A and 3B , there is shown steps of an alternative embodiment of an implant injection system  34  of the present invention, wherein the distal end of the shaft  36  is in position proximate to the bone  38  of the patient. In this embodiment, again a hole  40  has been drilled in the bone  38  and passes through the cortical bone layer  42  and enters into the cancellous bone  44 . 
     In this exemplary embodiment, however, at the distal end of the shaft  36  there is a multi-layer bone implant material  46 . As can be seen in  FIGS. 3A and 3B , the bone implant material  46  comprises a distal region  48 , an intermediate region  50  and a proximal region  52 . The distal region  48  and proximal region  52  comprise a high melt temperature polymer while the intermediate region  50  comprises a lower melt temperature polymer. In the exemplary embodiment, the polymer used in the distal region  48  and the proximal region  52  can be the same material. 
     Again, a resistance heater  54  is provided to carry out the melt step of the present invention. The suture  56  passes through the distal region  48  of the bone implant material and has its free ends  58  external of the bone  38  of the patient. 
     As such, turning now to  FIG. 3B , again, as described with respect to  FIGS. 1A-1C and 2A-2E , the resistance heater  54  has heated the bone implant material  46  and has been retracted from the cortical bone layer  42 , leaving the bone implant material  46  in the cancellous bone  44  of the patient. 
     In this embodiment, however, the intermediate region  50 , being formed out of a polymer having a lower melt temperature than the polymers of the distal region  48  and the proximal region  52 , has melted and infused into the cancellous bone  44  of the patient. The polymer or polymers of the distal region  48  and proximal region  52 , being of a higher melt point, have not melted and remain intact in situ within the cancellous bone  44  of the patient. 
     In this form of the invention, proximal region  52  can make a simple friction fit with the distal end of shaft  16 , such that bone implant material  46  can disconnect from the distal end of shaft  16  after bone implant material  46  has been positioned within bone  38 . 
     The suture  56  is firmly anchored to the distal region  48  and has its free ends  58  extending outwardly from the bone  38  of the patient for attachment of an object (such as soft tissue) to the bone  38  of the patient. 
     Alternatively, if desired, proximal region  52  of bone implant material  46  may be omitted and intermediate region  50  may be connected to the distal end of shaft  16 , whereupon bone implant material  46  will detach from the shaft when the bone implant material is heated to a flowable state. 
     Turning now to  FIG. 4 , there is shown an exploded, schematic view of a still further implant injection system  60  of the present invention that can be used to melt and introduce a polymer bone implant material into the bone of a patient. As can be seen in  FIG. 4 , the implant injection system  60  comprises an insulated container  62  having a cylindrical opening  64  extending therethrough, and the implant injection system  60  has a distal end  66  and a proximal end  68 . A heater  70  is provided proximate the distal end  66  of the container  62  and, in the exemplary embodiment, the heater  70  may be an electrical resistor. A nozzle  72  is also located at the distal end  66  of the container  62  (and the implant injection system  60  itself). A flange  74  is provided at the proximal end  68  of the container  62  and the purpose of the flange  74  will be later explained. 
     Within the cylindrical opening  64  of container  62 , there is located a meltable polymer capsule (which may also be referred to as a cartridge or block or plug, etc.)  76 . A plunger  78  interfits into the cylindrical opening  64  and is axially movable within the cylindrical opening  64 . The plunger  78  also has a recessed opening  80  and a closed proximal end flange  82 , and a battery  84  is interfitted into the recessed opening  80  that is used to power the heater  70 . At the distal end  86  of the plunger  78 , there is provided an insulator  88  that closes the distal end  86  of the plunger  78  and can serve to retain and insulate the battery  84  within the recessed opening  80  of the plunger  78 . 
     As is conventional, there is suitable wiring to electrically connect the battery  84  to the heater  70  and a switch, not shown, that can be used to complete the circuit between the battery  84  and the heater  70  to activate the heater  70  at the will of the user. Typical switches that can be used include manual switches or pressure-actuated switches that complete the electrical circuit when the plunger  78  is pushed inwardly toward the distal end  66  of the container  62 . 
     In  FIG. 5 , there is a perspective view of the complete implant injection system  60  assembled from the components of  FIG. 4 . Accordingly, the user can hold the implant injection system  60  by holding the flange  74  and then depressing the plunger  78  inwardly to operate the implant injection system  60 . 
     In  FIG. 6 , taken along with  FIGS. 4 and 5 , it can be seen that the polymer capsule  76  of  FIG. 4  has been melted by the activated heater  70  such that the polymer emerges as a flowable, melted polymer material  90  out of the nozzle  72  that may be used to form an anchor in, and/or to fill a void in, a bony structure. 
     Note that with the construction of  FIGS. 4-6 , the polymer is melted by heater  70  at the distal end of implant injection system  60 , adjacent to exit nozzle  72 . Thus, the melted polymer only needs to travel a short distance to its implant site, whereupon it re-hardens within the bone. 
     Turning next to  FIGS. 7A and 7B , there is shown a schematic view of a typical electrical circuit that can be used with the embodiment of  FIG. 4 . In  FIG. 7A , the circuit is open since the manual switch  92  is in its open position. As such, the battery  84  is not connected to the heater  70  so the polymer capsule  76  remains intact (i.e., in solid form). An arrow F indicates the force exerted on the polymer capsule  76  as the plunger  78  ( FIG. 4 ) is pushed forward by the user. 
     In  FIG. 7B , the circuit has been closed since the manual switch  92  has been moved to its closed position and therefore the electrical energy of the battery  84  passes to the heater  70  that heats the polymer to a temperature exceeding its flowing temperature. The force F can now be exerted on the plunger  78  ( FIG. 4 ) and the flowable, melted polymer 90 emerges from the implant device  60  (for subsequent re-hardening at the implant site). 
     Next, with reference to  FIGS. 8A-8G , there are shown schematic views illustrating a method of filling an implant injection system  94  with polymethyl methacrylate (PMMA) bone cement. As can be seen in  FIG. 8A , a cement loading syringe  96  is shown in position proximate to the delivery tip  98  of the implant injection system  94 . The cement loading syringe  96  contains a predetermined quantity of a bone cement, such as PMMA (not shown), therein and the cement loading syringe  96  has an open, distal end  100  and a movable plunger  102  at the opposite end thereof. 
     In  FIG. 8B , the cement loading syringe  96  is in position proximate to the delivery tip  98  of the implant injection system  94 . In  FIG. 8C , the movable plunger  102  has been depressed to load the PMMA into the delivery tip  98  of the implant injection system  94 . As such, in  FIG. 8D , the cement loading syringe of  FIG. 8C  has been removed and a PMMA bolus  104  is present in the open, delivery tip  98  of the implant injection system  94 , ready for injection into the bone of a patient. 
     The PMMA material is specifically located at the distal end of the syringe  96  since PMMA is rheopectic and is difficult to push down a tube. A rheopectic material has a fluid flow behavior wherein time and stress affect the viscosity—the longer a rheopectic material undergoes a shearing force, the higher its viscosity and the lower its flowability. Accordingly, rather than trying to push the material down the full length of the barrel of the syringe, the PMMA material is positioned at the distal end of the implant injection system  94 , which then requires a short travel to the implant site. 
     Turning next to  FIG. 8E , the implant injection system  94  is shown in position to deliver the PMMA into the bone  106  of a patient. As can be seen in  FIG. 8E , a hole  108  has been drilled into the bone  106  that passes through the cortical bone layer  108  and into the cancellous bone  110 . The implant injection system  94  is shown in  FIGS. 8E-8G  to be a syringe with a plunger  112 . Next, in  FIG. 8F , the delivery tip  98  of the implant injection system  94  is placed into the hole  108  and is positioned proximate to the cancellous bone  110 . 
     Finally, in  FIG. 8G , the plunger  112  has been depressed so as to force the PMMA bolus  104  into the cancellous bone  110 , where it is allowed to expand into the cancellous bone  110  to act as an anchor or reinforcement. 
     A suture could also be added to this embodiment to retain soft tissue to a bone surface. 
     Furthermore, if desired, cooling can be provided to the distal end of implant injection system  94  to retard polymerization of the PMMA cement and allow for improved flowability and increased working time. By way of example but not limitation, implant injection system  94  may be configured to circulate a cooling fluid through the distal end of implant injection system  94  so as to provide cooling to PMMA bolus  104  prior to the injection of the PMMA bolus into cancellous bone  110 . See, for example,  FIG. 8H , which shows passageways  200  for circulating a cooling fluid through the distal end of implant injection system  94  so as to provide cooling to PMMA bolus  104  prior to the injection of the PMMA bolus into cancellous bone  110 . 
     Modifications of the Preferred Embodiments 
     While the present invention has been set forth in terms of a specific embodiment or embodiments, it will be understood that the present implant device and the method of using the same herein disclosed may be modified or altered by those skilled in the art to other configurations. Accordingly, the invention is to be broadly construed and limited only by the scope and spirit of the claims appended hereto.